DE29623079U1 - Retroreflective scanning module for electro-optical readers - Google Patents

Description

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Retroreflecting scanning module for electro-optical readers

The invention relates to electro-optical readers or scanning systems such as bar code or bar code symbology scanners or scanners and in particular the invention relates to retroreflective reader scanning modules for use in applications requiring particularly compact scanners or scanners.

Electro-optical readers, such as bar or bar code symbol readers, are common today. A typical bar code symbol comprises one or more rows of light and dark regions, typically in the form of rectangles. The widths of the dark regions, i.e. the bars or dashes, and/or the widths of the light regions, i.e. the spaces between the dashes, indicate the encoded information to be read.

0 A bar code symbol reader illuminates the symbol and senses the light reflected from the coded regions to detect the widths and spacing of the coded regions or zones and to derive the coded information. Bar code reader type data entry systems improve the efficiency and accuracy of data entry - ■··■ for a wide variety of applications. The ease of data entry in such systems facilitates more frequent and detailed data entry, for example, to provide more efficient inventory management, to track work in progress, etc. However, to obtain these benefits, users or employees must be willing to use the readers consistently. The readers must therefore be easy and convenient to use.

A wide variety of scanning systems are known. A particularly advantageous type of reader is an optical

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scanner that scans or directs a beam of light, such as a laser beam, across the symbols. Laser scanning systems and components of this type are described in U.S. Patents 4,387,297 and 4,760,248, and they are generally designed to read indicia or characters having portions of different light reflectivity, i.e., bar code or bar code symbols, particularly the Universal Product Code (UPC), within a specific working range or reading distance from a hand-held or stationary scanner.

Fig. 1a illustrates an example of a prior art bar code symbol reader 10 implemented as a pistol-like device with a pistol-grip handle 53. A lightweight plastic housing 55 contains a light source 46, a detector 58, optics 57, a signal processing circuit 63, a programmed microprocessor 40 and a power source or battery 62. A translucent window 56 at the front end of the housing 55 allows an outgoing light beam 51 to exit and an incoming reflected light beam 52 to enter. A user aims the reader 10 at a bar code symbol 70 from a position where the reader is spaced from the symbol, i.e., not touching or moving over the symbol.

As further shown in Fig. 1a, the optics means may include a suitable lens 57 (or multiple lens system) to focus the scanned beam to a scanning point at a suitable reference plane. The light source 46, such as a semiconductor laser diode, directs a beam of light into an optical axis of the lens 57 and the beam passes through a partially silver coated mirror 47 and other lenses or beam shaping structures as required. The

Beam is reflected by an oscillating mirror 59 which is coupled to a scan drive motor 60 which is energized when a trigger 54 is manually pulled. The oscillation or vibration of the mirror 59 causes the emerging beam 51 to scan backwards and forwards in a desired pattern.

Different mirrors and motor configurations can be used to move the beam in a desired scan pattern. For example, U.S. Patent No. 4,251,798 discloses a rotating polygon with a planar mirror on one side, each mirror scanning a line across the symbol. U.S. Patent Nos. 4,387,297 and 4,409,470 both use a planar mirror that is repeatedly driven back and forth in alternate circumferential directions about a drive shaft on which the mirror is mounted. U.S. Patent No. 4,816,660 illustrates a multiple mirror structure consisting of a generally concave mirror portion and a generally planar mirror portion. The multiple mirror structure is repeatedly moved back and forth in alternate circumferential directions about a drive shaft on which the multiple mirror structure is mounted.

Light reflected back by symbol 70 travels back through window 56 for transmission to detector 58. In the exemplary reader 10 of Fig. 1a, the reflected light is reflected by mirror 59 and partially silver coated mirror 47 and impinges on light sensitive detector 58. Detector 58 produces an analog signal proportional to the intensity of reflected light 52.

The signal processing circuit includes a digitizer 63 mounted on a printed circuit board 61. The digitizer processes the analog signal from the detector 58 to produce a pulse signal.

where the widths and spacing between the pulses correspond to the widths of the bars and spacing between the bars. The digitizer serves as an edge detector or waveform circuit and a threshold set by the digitizer determines which points of the analog signal represent bar edges. The pulse signal from the digitizer 63 is applied to a decoder typically built into the programmed microprocessor 40 which also has an associated program memory and data RAM. The microprocessor decoder 40 first determines the pulse widths and spacing of the signal from the digitizer. The decoder then analyzes the widths and spacing to find and decode a genuine (legitimate) bar code message. This includes analysis to recognize genuine (legitimate) characters and sequences as defined by the appropriate code standard. This may also include an initial recognition of the particular standard or norm to which 0 the scanned symbol conforms. This recognition of the norm is typically referred to as "autodiscrimination" or self-discrimination or recognition.

To scan the symbol 70, the user aims the bar code reader 10 and actuates the movable trigger switch 54 to activate the light source 46, the scanning motor 60 and the signal processing circuitry. When the scanning beam 51 is visible, the user can see a scanning pattern on the surface on which the symbol appears and adjust the aiming of the reader 10 accordingly. The light beam 51 produced by the source 46, which is only slightly visible, can be provided as an aiming light. If the aiming light is required, it produces a point of visible light which can be fixed or scanned as the laser beam 51. The user uses this visible

Light to guide the reader to the symbol before pulling the shutter button.

The reader 10 may also serve as a portable data collection terminal. If so, the reader 10 would include a keyboard 48 and a display 49 as described in the previously mentioned U.S. Patent 4,409,470.

In electro-optical scanners of the type described above, the scanning engine ¹¹ may include the laser source, the optics means, the mirror structure, the drive for oscillating the mirror structure, the photodetector and the associated signal processing and decoding circuitry all increase the size and weight of the scanner or scanner. In applications where prolonged use is required, a large, heavy hand-held scanner may cause user fatigue. If the use of the scanner causes fatigue or appears in any way uncomfortable, the user will be reluctant to operate the scanner. Any reluctance to use the scanner continuously is counter to the data collection purposes for which these bar code systems are intended. Furthermore, there is a need to provide compact scanners so that they can fit into small, compact devices such as notebook computers.

It is therefore a constant goal of bar code reader development to miniaturize the reader as much as possible and there is also a need to reduce the size and weight of the scanning machine and to provide a particularly user-friendly scanner. The mass of the moving components should be as small as possible in order to minimize the power required to generate the scanning movement.

It is also useful to modularize the scanning machine so that a specific module can be used with a wide variety of different scanners. However, there is a need to develop a particularly compact, lightweight module that contains all the necessary scanning components.

Smaller size scanning components tend to operate at higher frequencies. However, in a typical bar code scanning application, the scanning frequency of the moving beam spot should be relatively low, typically 20 Hz or less. As the frequency increases, so does the speed of the spot as it passes over the symbol. The signals generated by the detector also increase in frequency and, as a result, the bandwidth of the processing circuitry analyzing the detector signals must be increased. Also, operation at higher scanning frequencies generally produces detector signals that contain higher levels of noise, making accurate decoding difficult.

Summary of the invention
Objectives of the invention

The object of the present invention is to develop a completely self-contained electro-optical retroreflective scanning module, including all components necessary to generate the light beam, scan the beam in a pattern across a symbol, detect light reflected back from the symbol, and process processing signals representative of the reflected light.

In this respect, the retroreflective module should be small, lightweight and easy to install in a wide variety of electro-optical scanning systems.

Another object of the invention is to minimize the size and weight of the components used to generate the scanning motion of the light beam and to collect the reflected light. 5

Another related objective is to develop an electro-optical scanning system that is smaller and lighter in weight when received by a user and that is easier to manipulate to scan coded indicia, as compared to known systems.

Features of the invention

With these objects in view, a feature of the invention is embodied in a self-contained electro-optical retroreflective scanning module for reading optically encoded indicia or characters having portions of differing non-reflectivity. The module comprises: a base; a light source on the base for emitting a light beam along an outgoing or departing path toward and reflecting the characters; a light detector on the base for detecting light reflected from the characters along an incoming or returning path across a field of view and for producing electrical signals corresponding to the character portions of differing light reflectivity; a movable reflector mounted in the paths of the light beam and the reflected light and movable; and a drive on the base for moving the movable reflector for the purpose of sweeping the light beam over the characters and simultaneously sweeping or panning the field of view.

According to the invention, the light source is housed in a housing and a stationary collecting mirror is fixed

attached to the housing and a stationary scanning mirror is firmly attached to the collecting mirror. Advantageously, the collecting mirror is concavely curved and the scanning mirror is flat or planar. Furthermore, a bracket also holds the mirrors at a distance from the housing.

Another advantageous aspect of the invention is embodied in the fixed mounting of the housing and the mirrors at one of two end regions of the base and further in the mounting of the movable reflector for movement at the other end region of the base. The light detector is mounted in a central area or region on the base facing the collecting mirror and is further located at the center of curvature thereof.

The drive comprises an elongated beam having opposite end portions. The reflector is mounted on one of the end portions of the beam. The drive comprises a permanent magnet mounted on the other end portion of the beam and an electromagnetic coil mounted near the permanent magnet and operable when an alternating drive signal is applied to the coil to produce an alternating magnetic field acting on the permanent magnet to cause the magnet to vibrate or oscillate and in turn the beam and the reflector mounted thereon about an axis located approximately centrally between the reflector and the permanent magnet.

The resulting compact design allows the retroreflective module to be arranged within different system configurations, especially miniature configurations.

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The novel features which are considered characteristic of the invention are set forth with particularity in the appended claims. The invention itself, both the structure and the method of operation, together with further objects and advantages, will become apparent from the following

Description of specific embodiments together with the drawing. Further features of the invention are set out in the appended independent and dependent claims.
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Short description of the drawings

Fig. 1a is a schematic view of a known hand-held laser scanning and data collection terminal;

Fig.Ib is a schematic view of a hand-held pistol or revolver type scanning device according to the invention;

Fig. 2 is a perspective view of an embodiment of a scanning module according to the invention, with parts broken away for clarity;
Fig. 3 is a plan view of the module of Fig. 2, again with parts removed to show the interior of the module;

— Fig. 4 is a left side view of the module of Fig.

2;
Fig. 5 is a right side view of the module of Fig.

2;

0 Fig. 6 is a view of a drive component of the module of Fig. 2;
Fig.7a is a perspective view of another

Embodiment of a scanning module according to the invention;

Fig.7b is a plan view of another embodiment of a scanning module according to the invention;

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Fig. 8 shows a scanning module according to another aspect

the invention;

Fig. 9 shows a scanning module according to a further embodiment of the invention; Fig. 10 shows an alternative embodiment of the

scanning module of Fig. 9;
Fig.11 shows a nominal bar code symbol and a

reading beam point;

Fig.12 shows a laser focusing aperture and a beam waist;

Fig.13a shows an improved opening shape; Fig.13b shows an alternative opening shape to that of the

Fig. 13a;

Fig.13c shows an alternative opening shape to that of Fig.13a;

Fig.14 shows a nominal MTF curve based on

an opening shape for a 6000th inch density

Dode;

Fig.15 shows an MTF curve for an aperture shape for 0 a 7.5th density code;

Fig.16 shows an MTF curve for a 20-th

inch density barcode;
Figl.17 shows an MTF curve for a 55-thousandth inch density bar code;
Fig.18 shows a schematic connection between a

scanning module and a decoding module; Fig.19 shows a conventional two-photodiode detector

gate system from above;

Fig.20 shows the system of Fig. 19 from one side; Fig.21 shows the system of Fig. 19 from the front; Fig.22 shows an improved detector system according to the

invention from above;

Fig.23 shows the system of Fig.22 from a side; Fig.24 shows the system of Fig.22 from the front; Fig.25 shows a part of a conventional scanning module; Fig.26 shows a decoding module according to another aspect of the invention; and

Fig.27 shows a "back-to-back" dual laser arrangement according to another aspect of the invention.

Detailed description of the preferred Examples of implementation

As used in the application and claims, the term "indicia" or "character" broadly encompasses not only symbol patterns made up of alternating bars and spaces of varying widths, each referred to as a bar code symbol, but also other one- or two-dimensional graphic patterns, including alphanumeric characters. In general, the term "indicia" or "character" can refer to any type of pattern or information that can be recognized or identified by a scanning light beam by detecting the reflected or scattered light as a representation of changes or variations in the light reflectivity at different points of the pattern or information. A bar code symbol is an example of an "indicia" or "character" that the present invention can scan.

Fig. 2 to 6 show the structure of a small, self-contained retroreflective scanning module

400. The module 400 is substantially rectangular and in no example has been manufactured to a size of only 1.35" x 0.95" x 0.69". A perspective view of the module 400 with certain parts removed is shown in Fig. 2.

Although the scanning module is discussed below with reference to a pistol- or revolver-shaped scanner, it should be noted that the module is also suitable for installation in any system, such as a scanning terminal, or finally a

scanning part and a keypad and/or a display screen.

The module includes a generally planar elongated metal base 410, typically formed of aluminum. The base 410 has an end region or portion 402 and an opposite end region or portion 404 and an intermediate or central region or portion 406. A semi-cylindrical housing 412 contains a laser diode and a focusing module similar to that shown in U.S. Patent 5,367,151.

As shown, the housing 412 is bolted or screwed to the base 410 at stud 408, although the housing could also be integrally formed as a portion of the base. The housing 412 and the housing 410 serve as a heat trap or heat sink to dissipate heat generated by the laser diode during scanning operations.

The module 400 includes two circuit boards arranged at right angles to each other. A first circuit board 416, arranged orthogonally or perpendicular to the base 410 at one end thereof, carries a portion of the circuitry used by the scanner. Typically, the first circuit board 416 carries the circuitry for generating the current to drive the laser diode.

A second circuit board 418 is arranged orthogonally to the first circuit board and parallel to base 410. Assuming that the flat major surface of base 410 is the bottom of module 400, second circuit board 418 would form the top of module 400. An electrical cable (not shown) connects the circuitry on the first and second circuit boards together. Second circuit board 418

carries the remainder of the necessary circuitry. It should be noted in particular that this board 418 carries an application specific integrated circuit 419 which comprises analog signal processing circuitry, the digitizer and may also include the microprocessor based decoder.

Fig. 3 is a top view of the module 400 as if the second circuit board 418 were removed to provide a view of the interior of the module. As shown, a support structure 300 provides the flexible support or support for a reflector 359 such that it can perform a reciprocating movement. The flexible support structure is described below in connection with Fig. 6.

The interior of the module also includes a stationary mirror structure 200 (mirrored structure 200) attached to the housing 412 by a bracket 202 at the end region 402 of the base. The mirror structure 200 includes a concavely curved collecting mirror 204 having a center of curvature at which a photodetector 206 is located. The photodetector 205 is mounted in the center region 406 of the base 410 within a housing 208. A filter 210 is located upstream of the photodetector 206 within the housing 208.

A louvre of known design may be provided in front of the photodetector 2 06, although this is not shown in the drawing.

A generally planar scanning mirror 212 is fixedly attached to the collecting mirror 204, preferably

integrally formed and as a part therewith, preferably »

manufactured by injection molding. The scanning mirror 212 is &igr;

inclined and points both at the laser diode within the housing 412 and at the reflector 359. The front sides of the mirrors 204, 212 are provided with a light-reflecting coating.
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As shown in Fig. 6, the support structure 300 comprises a U-shaped member 303 having a first arm 305 to which the reflector 359 is attached. A second arm 307 of the member 303 carries a permanent magnet 3. A straight portion 311 extends between and connects the first and second arms together to form the U-shaped member 303.

A pair of flexible strips 321, 323 connect to one of the arms of the U-shaped member 303 and serve as a planar spring. These spring strips comprise a flat portion or flat surface made of a flexible plastic material such as Mylar (trademark) or Kapton (trademark) film.

0 Or other flexible elements such as a flat strip of magnetic metal such as a beryllium-copper alloy. In the rest position shown, the strips 321, 323 remain in a relatively unbent state and extend in a direction substantially parallel to the straight portion 311 in the space between the first arm 303 and the second arm 307. One set of ends of the strips 321, 323 connect to the first arm 305 and opposite set of ends of the strips 321, 323 are secured.

In particular, the ends of the Mylar or Kapton material sheet elements forming the flexible strips 321, 323 are secured by suitable fasteners 325 and thereby clamped between a plate 327 and a frame member 326 extending from the rear surface or back of the first arm 305.

and a portion of the underside or lower surface of the straight portion 311. The opposite ends of the strips 321, 323 are secured to a fixed support by suitable fasteners 329 which clamp the strips between a plate 331 and an extended or enlarged portion of a stationary arm 337 which extends outwardly from a support post 335 (Fig. 2). The support post 335 is secured to the flat portion of the metal base 410 at the end region 404.

The components of the support structure 300, the reflector 359 and the magnet 309 are dimensioned such that the weight of the magnet approximately balances the weight of the reflector with respect to a pivot axis A halfway between the reflector and the magnet. As a result, the strips 321, 323 act as planar leaf spring elements and flex about this pivot axis. The pivot axis A extends perpendicular to the flat lower portion of the base 410 (or vertically in Fig. 6).

An electromagnetic coil 333 is attached to the bottom (lower surface) of the second circuit board 418 by a bracket 334 (Fig. 5). Mounting the second circuit board 418 on top or on the top of the module 400 positions the attached coil 333 in close proximity to the permanent magnet 309, as seen in Fig. 3. The axis between the north and south poles of the permanent magnet 309 is aligned in the plane of the drawing of Fig. 3, i.e. parallel to the flat lower part of the base 410. When an alternating current is passed through the coil of the electromagnet 333, the interaction between the magnetic fields of the coil and the permanent magnet 3 09 produces an oscillatory motion of the permanent magnet 309 and a torsional vibration or torsional oscillation of the attached member 3 03 against the restoring forces

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generated by the flat planar spring strips 321, 323. The flexible strips 321, 323 twist backward and forward about the axis A and cause the member 303 to vibrate or oscillate and the mirror 359 to move back and forth in both circumferential directions over an arc about the axis A.

When the laser diode emits a beam of light, the beam of light travels along path portion 100 and strikes scanning mirror 212, and is in turn reflected along path portion 102 to reflector 359, which in turn reflects the beam of light along path portion 104 toward a target surface on which a character appears. The beam exits through an aperture formed in one side of the module. The back-and-forth oscillation or vibration of reflector 359 during emission of the beam from the laser diode causes the beam to scan a line across the characters.

If module 400 is mounted horizontally in a scanner, the resulting scan line would be horizontal and would scan a character having vertical bars or stripes. Conversely, if module 400 is mounted vertically in a scanner, the resulting or resulting scan line would be vertical and would scan a character having horizontal bars.

The light reflected back by the character or characters travels back along path portion 104, whereupon it is reflected along path portion 102 for collection by concave collecting mirror 204. Collecting mirror 204 in turn reflects the returning light along path portion 106 through ambient light blocking optical filter 210 for impingement on the detector. The filter blocks most wavelengths of light, but passes light of a wavelength

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which corresponds to the wavelength of the light beam emitted by the laser diode. An aperture can also be arranged in front of the detector.

The detector 206 generates an analog signal proportional to the intensity of the reflected light, which can be processed, digitized and decoded by the application of specific integrated circuits 419. Electrical conductors are used to conduct signals from the detector to the application specific integrated circuit 419, but are not shown for clarity.

The small size of the flexible support structure 300 in the scanning module does not prevent operation at low scanning frequencies. Again, the location of the reflector and magnet at opposite ends of the member 303 positions the weight thereof relatively far from the pivot axis, thereby providing a high moment of inertia. Also, the mass of the moving components is quite large; and the preferred materials of the springs 321, 323 tend to be quite flexible. The high mass, high inertia, and spring flexibility cause the flexible support structure to have a relatively low characteristic vibration or oscillation frequency (natural frequency). In this way, the small self-contained scanning module operates at the low scanning frequencies preferred for bar code scanning, such as 20 Hz or less. The Moldul 400 also provides for balancing the weight of the reflector and the weight of the permanent magnet, which reduces or eliminates unwanted oscillations or vibrations that could disrupt the scanning motion, and thereby minimizes the amount of power that must be applied to initiate the movement of the scanning component, making the scanner more efficient.

Although the embodiment discussed above has been described with reference to a single laser arrangement, it should be understood that more than one laser may be provided in the module as required (for example, a total dual range scan may be provided as described in detail below). The lasers used may be of any known type, such as conventional lasers, laser diodes, or a combination thereof. Such an arrangement is shown in Figure 7b in addition to the scanning arrangement shown generally at 300 in that figure, with a far laser for scanning more distant objects shown at 310a and a near laser for scanning closer objects shown at 310b. The far laser beam is directed by a folding mirror 310c to the common mirror 359 with the near laser beam.

Figures 2 to 6 or 7, discussed in detail below, show one possible embodiment of the scanning module 400 of Figure 1b. It will be seen that the module 400 is simply located and positioned within a pistol-shaped reader 10. Where possible, the same reference numerals have been used throughout the description. The module 400 may be mounted by any suitable means and is oriented such that the outgoing beam 104 exits in the scanning direction through the scanning window 56. One or other of the circuit boards 416, 418 may alternatively be housed within the pistol-grip handle or, as shown, an additional printed circuit board may be separately located within the handle. The ease of fabricating such an arrangement is obvious since the self-contained scanning module is simply positioned and suitably mounted within the pistol-grip scanner 10. When the additional printed circuit board 61 is installed,

then it can also be easily mounted in the handle 53 and connected to the module 400 in the usual way, the resulting device has the advantages of the pistol-type scanning device together with the reduced size and low weight achieved by the module according to the invention.

The flexible support structure could be modified to provide beam spot scanning in two directions that are substantially orthogonal to each other. A number of different scanning applications require scanning in two different directions. Such scanning provides a scanning pattern that moves across the character or characters of a bar code type to find positions thereof that are sufficiently intact to allow accurate reading of the code. Bi-directional scanning applications refer to the scanning of characters encoded in two different dimensions.

A two-dimensional bar code comprises a series of rows or lines of optically-encoded information. Each row or line is oriented in the X (horizontal) direction and a plurality of rows are arranged one above the other in the Y (vertical) direction. Each row or line of information comprises a series or series of coded symbols and each symbol consists of a series of light and dark zones or regions, typically of rectangles. The widths of the dark regions, the bars, and/or the widths of the light spaces between the bars indicate the encoded information in each row or line. Two-dimensional bar codes can contain considerably more encoded information than the usual one-dimensional codes.

To read two-dimensional characters, it is desirable to position the characters using a grid or a similar type of

scanning patterns. In such a scanning pattern, a fairly large number of substantially horizontal and substantially parallel scan lines or rows traverse the characters from an upper horizontal scan line, progressing downward with a plurality of intermediate horizontal scan lines or rows to a lower horizontal scan line or row to uniformly cover a desired scanning area comprising the characters. To obtain such a raster-like scanning pattern, the scanning component must be supported or mounted for reciprocating motion in two different directions. Also, the frequency of oscillation in the first direction producing the X-direction spot scanning motion is typically considerably greater than the frequency of oscillation in a second direction producing the Y-direction spot scanning motion.

Fig. 7a shows another embodiment of a module and is analogous to the embodiment of Fig. 2 except for the following two things. First, the radio frequency transmitter 450 is mounted on the printed circuit board 418 and coupled to an antenna 452 to wirelessly transmit electrical signals to a remote host processing device. The signals can either be digitized or the decoded signals generated by scanners. The resulting "wireless scanning module" can be used in countless applications.

Fig. 7a also shows a second housing 412' housing another laser diode for emitting another beam of light along a path portion 108 through an opening in the scanning mirror 212 to impinge on the reflector 359. This "dual laser ^11" module is useful for multiple line scanning applications.

Although the present invention has been described with respect to reading one- or two-dimensional bar codes, it is not limited to such embodiments, but can be used in more complex character scanning applications. It is possible that the method according to the invention can also be used in various machine vision applications or optical character recognition applications, where information is derived from other types of characters, such as letters, characters or the like, or from characteristics on the surface of objects to be scanned.

In all of the various embodiments, the elements of the scanning device can be assembled in a very compact structure or package. Such a module can be used interchangeably as the scanning engine or scanning motor for a variety of different types of data acquisition systems. For example, one or more modules can be used alternatively in a hand-held scanner, a table-top scanner attached to a flexible arm or bracket extending across the surface of the table or attached to the underside of the table top, or attached as a subcomponent or subassembly of a more complex data acquisition system.

An individual module may have special scanning or decorating characteristics, i.e., ability to operate for a certain working distance or ability to operate for specific symbols or print density. The characteristics or properties may also be defined by manually setting control switches associated with the module. The user can therefore adapt the data acquisition system to detect different types of articles or objects

to scan or the system can be made suitable for different applications by changing the modules on the data acquisition system by using the simple electrical connector. 5

The scanning module described above can also be implemented within a self-contained data acquisition system, including one or more of the following components: keyboard, display.

display, printer, data storage, application software and databases. Such a system may also include a communications interface to enable the data acquisition system to communicate with other components of a local network or with a telephone system, either through a modem or ISDN interface or through infrared transmission or low power radio transmission from the portable terminal or connector to a stationary receiver.

Fig. 8 shows an alternative variation of a scanning module generally designated 500. The module includes a laser 510 for generating a scanning beam 511 which passes through a lens system generally designated 512. As in the previous embodiments, the scanning beam 511 impinges on a mirror 520 which is arranged to oscillate about a pivot point 521 to scan the beam as generally indicated by arrows 513 and 514. The assembly is mounted on a circuit board 501 which has a connection or interconnection for a wall-forming circuit board 502 (as discussed with reference to the previous embodiments). As discussed above, a further circuit board (not shown) is mounted parallel to the base circuit board 501. The means for attaching the Modulds 500 siond

at 503 and 504. A receiving photodiode and suitable information processing means such as a filter or aperture are provided at 516, 517, respectively. These components receive and process the returning light beam in a manner that is generally known and has been discussed, typically in terms of the size of the base plate 501, where the respective dimensions A and B1 could be the following: A = 0.7" (17.8 mm) and B = 0.75" (19.1 mm). The typical height could be in the range of 0.42" (10.67 mm).

The arrangement shown in Fig. 8 is particularly suitable for miniature scanning elements having, for example, the dimensions described above. In previous modules it has been found that pointing errors occur in such miniature modules due to the difficulty of maintaining mass balance, which gives rise to the problem of attenuation. This is particularly a problem when it is desired to achieve the low scanning frequency discussed above. The invention overcomes the difficulties by using the special mirror configuration as shown. Looking at the configuration in detail, it can be seen that the mirror 520 is mounted or is mounted on a common body with a permanent magnet 521. The mirror system comprising the mirror 520 and the permanent magnet 521 pivots relative to a fixed point 523 on the base plate 501 via a pivot shaft 522. The mirror system extends from one side of a pivot shaft 522 perpendicular to the pivot axis and the mirror 520 and permanent magnet 521 point in opposite directions relative to a nominal line extending perpendicular to the pivot shaft 522. The mirror system is driven for scanning movement by a coil 524 which generates an alternating magnetic field in a

The mirror 520 is generated in a manner as described with reference to the embodiments of Figs. 2 to 6. The alternating magnetic field drives the permanent magnet 521 back and forth and causes the scanning movement. This configuration differs slightly from the configuration described with reference to Figs. 2 to 6 in that the mirror 520 and the permanent magnet 521 are both arranged on the same side of the pivot shaft 522 and not on opposite sides thereof.

In view of the miniaturization of the system, it is difficult to provide sufficient mass on the mirror system to increase the moment of inertia and thus reduce the oscillation frequency by a sufficient amount. Even the mass introduced or added tends to disappear and the addition of any further mass would increase this problem. This is overcome in the embodiment shown in Fig. 8 by introducing an additional magnetic element 530 positioned on the base plate 501 near the permanent magnet 521. The element 530 can be, for example, an iron rod protruding from the base plate 501. Due to the magnetic interaction between the iron rod 53 0 and the permanent magnet 521, the permanent magnet 521 and thus the mirror system as a whole are biased into alignment with the iron rod. An effective increase in the mass of the mirror system is thus achieved and pointing errors/decreases are reduced accordingly. The iron rod can of course be replaced by any other suitable magnetic element 53 0.

According to a further aspect of the invention, a scanning module system is provided which is suitable for overcoming the difficulties associated with interference in

draw caused by ambient light in the vicinity of the scanning device.

This problem is particularly encountered in non-retrocollective bar code scanning systems where the detector collects not only the reading beam produced by the scanner but also ambient light. This results in poorer performance, especially in moderate to high ambient light conditions. It will be appreciated that the problem can be solved by providing appropriate filters for the reflected light to filter out the noise due to ambient light conditions or states. Spatial filtering of the noise is dictated by the scanning pattern produced by the light received from the reflected bar code. Temporal filtering of the noise is dictated by the waveform produced by the light received from the reflected bar code. Typically, spectral filtering is determined by the following factors;

a) Wavelength variation due to manufacturing variability of visible laser diodes (VLD);

b) Length change due to ageing of the VLD; —c) Wave change with temperature for a

given VLD;
d) Dependence of the optical transmission on the angle of the received light;
e) Multiple mode laser effect of the VLD.

To accommodate all of the above factors, filters typically have a bandwidth of approximately 70 nm. This is orders of magnitude wider than the spectral width of a single VLD mode and as a result, a large proportion of unnecessary noise caused by the ambient light conditions is retained or maintained.

Furthermore, the filter parameters cannot be changed without affecting the scanner performance.

Fig. 9 shows a solution according to the invention. The arrangement has a fixed filter and a VLD with tunable wavelength, the tuning parameter being the temperature of the VLD.

A scanning module is shown generally at 540. It will be appreciated that the components discussed below could be present on a single module of the type discussed with reference to the above embodiments or in any other suitable form. The module 540 includes a laser 541 which emits a reading beam 542. The beam 542 is directed back by a reflector 543 to a scanning system 544 represented in the figure by a single reflector which is removable for scanning the beam 542 by reciprocating movement in a direction shown by arrow A. The resulting scanning beam is figuratively represented by the main beam 555 with the scanning boundaries shown by dashed lines 556, 556'. To tune the wavelength of laser 541 using temperature as the tuning parameter, laser 541, mounted on a submount or chip of any known type, is mounted on a thermoelectric cooler/heater unit 560. Cooler/heater unit 560 may be of any known type, for example the type where the temperature can be changed by changing the magnitude and direction of the current flowing therethrough. As a result, the wavelength of laser 541 can be kept within the passband of the filter for the detector (not shown) and a narrower passband can thus be used.

The temperature can be controlled in a variety of ways, generally relying on a feedback signal. For example, reflector 543 can be partially silvered or mirrored so as to reflect most of the reading beam 542, but to transmit a portion of the reading beam as shown at 561. The transmitted beam 561 is received by an auxiliary detector 562. The auxiliary detector 562 can be provided on module 540, or located in the scanner housing as needed. The auxiliary detector 562 monitors the wavelength of the transmitted portion of the reading beam 561 and provides a control signal to the cooler/heater unit 561 such that the desired temperature is achieved to keep the wavelength of the reading beam 542 within the passband of the filter. The control signals are conducted via a control line 563. One way to control temperature in this manner is to tune the auxiliary detector 562 to provide maximum response at a desired wavelength within the passband. The temperature of the cooler/heater unit 560 is controlled to maximize the output of the auxiliary detector 562.

This arrangement allows the wavelength of the read beam 562 to be maintained within a desired band. As a result, the filter can have a greatly reduced bandwidth since the wavelength shift or drift can be precisely controlled. Accordingly, the majority of the external noise caused by the ambient light conditions can be filtered out, resulting in an improved signal to noise ratio and thus increasing performance.

The embodiment shown in Fig. 9 is particularly well suited to counteract the wavelength change or variation that occurs due to the above-mentioned factors

a) b\s c) occurs, namely the manufacturing variability, the aging and the temperature, which results from the following. It can be seen that the embodiment thus shows an improved performance. 5

The performance can be further improved by using the embodiment of Fig. 10 which takes into account the wavelength variation due to the dependence of the optical transmission on the angle of the received light. This is achieved by relocating the auxiliary detector so that it is downstream of the scanning system 544. The redirection or re-direction reflector 543 can thus be completely silvered or mirrored. Instead, another partially silvered or mirrored mirror 565 is placed in the path of the beam reflected by the scanning system 544, covering the entire scanning area such that a portion of the beams within the boundaries represented by reference numerals 556 and 556· are reflected and redirected or deflected by reflector 565. A detector 566 then detects the redirected or redirected portion of the reading beam. The detector 566 both detects the wavelength of the read beam (in a manner analogous to detector 562 discussed with reference to Figure 9) and also provides instantaneous information regarding the scan angle. This information is input to a controller 567 (which may be any suitable processor) and the temperature of the cooler/heater unit 560 is controlled accordingly. It will be appreciated that the controller 567 may be integral with the detector 566 or form part of the controller for the module 562 as a whole. The wavelength of the laser 541 may be controlled accordingly to control changes or variations in the optical transmittance depending on the angle of the received light.

It will be appreciated that the cooler/heater 560 and laser temperature must be varied at a rate high enough or fast enough to follow the changes in scan angle for this embodiment to work. Of course, this can only be achieved for sufficiently slow scan rates or speeds, and faster scan rates can be achieved by minimizing the thermal mass of the entire cooler/heater and laser 541 system.

The system can be further improved by taking into account the changes resulting from factor e), i.e. the fact that some VLDs lase in several spectral modes, by selecting a suitable VLD that lases in a single longitudinal mode. Several VLDs are known that would meet this requirement, for example most index-guided VLDs. It will be appreciated that even if the VLD lases in a few modes, improvements are noticeable, although not significant.

In an alternative approach, a fixed wavelength VLD may be incorporated and a tunable filter may be used instead. In this case, the control signals received from the auxiliary detector 562 or from the combined wavelength and scan angle detector 556 would be fed into the filter such that the filter follows changes in the wavelength of the laser. Suitable tunable filters are known, for example from the following reference: Optical Engineering Volume 20, No. 6 (November/December 1981) pages 805 to 845, which is a collection of several articles relating to electronically tunable optical spectral filters. It will be seen that the remaining features of the system are similar to those

as described with reference to Figs. 9 and 10.

In accordance with another aspect of the invention, it is desirable to improve the reading of poor quality one-dimensional bar code symbols. It is known to improve the accuracy of reading one-dimensional bar code symbols by using a reading beam having an elliptical cross-section with the long axis parallel to the bar or eye direction as shown in Figure 11. The reading beam spot is exaggerated at 570 and scans along a bar code symbol 571 as shown by arrow B. The reading beam spot 570 is elliptical and its long axis is parallel to the bar direction and perpendicular to the scan direction. As a result, averaging of the code errors in the vertical direction is provided.

It is desirable to increase the working range of a given scanner to make the scanner more versatile. To increase the working range of the high density bar code scanner (6 to 10 thousandths of an inch), the far end of the working range can be increased by increasing the laser focusing aperture size in the scanning direction, while the near end of the working range can be reduced by bringing the beam waist closer to the aperture or opening. This is illustrated in Fig. 12. A laser 575 emits a beam 576 through a circular focusing aperture or opening 577. The beam 576 has a waist shown exaggeratedly at W. By increasing the aperture size in the scanning direction (again shown by arrow B), the working range increases but the beam waist decreases. As a result, when a poorly printed bar code symbol is scanned near the laser beam part, the

Reading beam spot is increased to a size, resulting in less averaging of the bar code symbol errors in the scan direction, resulting in noise in the read signal that cannot be filtered out by using an elliptical spot elongated perpendicular to the scan line. It is desirable to eliminate or reduce this performance degradation as it has a detrimental effect on the working range.

The present invention overcomes the difficulties in known arrangements by identifying one parameter of the system which can be varied to improve conditions, namely the laser focusing aperture shape. Particularly preferred shapes are described below. It has been found that if the focusing aperture shape is optimized, the laser beam waist can be increased and a correspondingly improved signal to noise ratio for poor quality bar code symbols can be obtained without penalty in scanner operating range.

Conventional aperture shapes are generally circular or rectangular, and consequently the only parameters available for increasing the scanning working area are the aperture size and the beam waist position; this causes the beam waist to be reduced and the working area to be increased as discussed above. Various alternative aperture shapes are shown in Figs. 13a to 13c. Fig. 13a shows an optimized aperture with a stepped shape. The aperture can be viewed as being formed by a series of rectangles Al, A2, A3, Al', A2', A3', these rectangles being symmetrically arranged as shown. The right angles of each pair of Al, Al ¹ and sw have sides of un-

of different lengths in the scanning direction (indicated by arrow B). The widest rectangles or right angles are found at the center, the narrowest at the top and bottom.
5

To facilitate the manufacturing process and to reduce light scattering at sharp corners, various alternative smooth shapes can be selected that approximate the shape shown in Fig. 13a. For example, a diamond shape with rounded corners could be used as shown in Fig. 13b, or a circular shape with upper and lower rounded lobes extending therefrom as shown in Fig. 13c.

In fact, the optimized aperture shape shown in Fig. 13a can be achieved by MTF analysis, where MTF is the convolution integral for the aperture function. Let us now turn to the mathematical treatment of the aperture shape using MTF analysis.

Assume that the scanner is to read the 6, 7.5, 20 and mil (mil = 1000 inch) code. Typically, after optimizing the scanner working ranges, MTF for the highest code density (6 mil in this example) will vary with target distance as shown by the cross-shaped curve in Fig. 14. Assume that a digitizer can provide a reading at MTF>15%. In the example shown, a scanner with a rectangular aperture 0.027" (0.686 mm) wide would provide the working range of 2.5" (63.5 mm) to 9" (228.6 mm) for the 6 mil bar code.

The MTF curve for the 6 mil code reaches a maximum value at approximately 45% of the beam waist position or location at 5" (13 0 mm) from the scanner. The scanner performance

The accuracy is not improved in any way by setting the maximum MTF significantly higher than the 15% threshold. Instead, the scanner resolves higher spatial frequencies representing printing defects and a noise level enlarges the beam around the beam waist location. Ideally, a flat MTf curve just above the threshold level is desired. In other words, the beam waist can be increased until the flat MTF curve is achieved.

Accordingly, the additional degree of freedom is used to control the shape of the MTF curve, namely the aperture shape when reading one-dimensional bar codes. For the aperture shown in Fig. 13a, which consists of three rectangular regions with different sides along the scanning direction x1, x2, and x3, and taking into account the fact that MTF is the convolution integral for the aperture function, one can calculate the MTF of the aperture shown by the following formula:

MTF=(MTFl.S1+MTF2.S2+MTF3.S3+...)/(Pl+P2+P3...),

where MTFi is the MTF of the i-th zone of the aperture, Pl is the laser beam power within the i-th zone. Therefore, there is additional freedom of design by shaping the opening or aperture. In Fig. 13 is an example of the aperture that provides the flat MTF for the 6 mil code. Calculated MTFs for the 7.5 mils, 20 mils and 55 mil codes are shown by the solid lines in Figs. 15 to 17, respectively. One can expect that all print defects or printing errors smaller than 6 mils will be filtered out.

Another way to optimize the aperture shape is to increase the working areas for the low-density barcodes or barcodes (40, 55 mil) when

the width ranges are maintained for high density
Barcodes, as can be seen in Fig. 16 and 17.

Referring to Fig. 14, the nominal MTF curve function
for the "Diament" aperture and a 6 mil (6 thousandths of an inch) code given by:

MTFl (wb, Z, &khgr;, Ox, Ax) = MTP(wb, 2/X, ex, Ax+0 . Oil) +NTTF(Wb. Z,x, &thetas;·&khgr;. Ax) *MTF< wb. Z, x, ex, Ax-Q . Oil )

Where wb is the code density, Z is the distance from the
Aperture (mm), &khgr; is the distance between the laser and

the lens focal plane (/im), θ is the laser divergence angle and Ax is the aperture size of the relevant part of the opening (inches). The given numerical values correspond to the embodiment of Fig. 13a.
15

The distance WR is the working area, as defined above,
and the MTF curves are for a rectangular
opening (curve marked with crosses) and an optimized opening (solid line). The threshold
of MTF = 15% is shown with a dashed line, which defines the working range WR.

Fig. 15 to 17 use the same convention, but for codes of 6.4 mil, 20 mil and 55 mil respectively. The improvement
the working area is represented by ÄWR

- As far as Fig. 17 is concerned, a threshold value of 20% is selected, which, as explained above, is
low density bar codes can be achieved.

0 According to another aspect of the invention, the problem of deadband response for small sensing modules is addressed.

Fig. 19 is a conventional design for improving the performance of small non-retrocollective (one-dimensional and two-dimensional) sampling modules,
shown from above. A pair of Lin-

sen 600, 601 is associated with the corresponding detectors (e.g. photodiodes) 602, 603 in a scanning module 605 of any type, for example the module type as described above with reference to other embodiments of the invention.

Other components of the scanning module 605, such as a laser, etc. are not shown. The lenses serve to reduce the field of view and thus remove some of the background noise and ambient light.

The lenses 600, 601 also increase the signal collection area of the respective detectors 602, 603, thereby increasing the signal to noise ratio. The signals from both detectors 602, 603 are summed in summing means of conventional design (not shown).

Where the field of view of each detector is shown as a corresponding opposing dashed region or zone 604 and 605, respectively, it will be appreciated that there is an area or region of non-overlap referred to as the "dead zone" and represented by the distance L^ re-0. It will be appreciated that within this region a non-uniform signal will result if one attempts to scan a printed character within this zone. In particular, the center or middle of the summed signal will be either zero or twice the amplitude of its ends. The dead zone defines a non-encoding zone or region, as a result of which decoding near the "nose" or output window of the physical or physical scanning module is not available. It will be appreciated that such decoding is often desirable but moves the photodiodes back

If the field of view is extended to cover the "dead zone", the working area is lost. A side view and a front view of the arrangement in Fig. 19 are shown in Fig. 20 and 21 respectively.
35

The solution proposed according to the invention is shown in plan view in Fig. 22. In addition to the two

Detectors 602, 603, a third photodiode detector 606 is arranged centrally in module 604. The field of view of the third detector 606 is shown by dashed lines and is represented by reference numeral 607. It can be seen that the third detector 606 will detect signals within the dead zone, providing additional working range without sacrificing the working range of the main detectors 602, 603. Since the signal closer to the scanning module 605 is of relatively good quality and much larger than further out, a small photodiode detector is sufficient. A smaller photodiode detector need not decode below the distance Lfj, since the two larger detectors adequately cover this area. The smaller detector 606 is of particular assistance in decoding nearby characters on the axis. In order to make the pattern appear sufficiently large, the laser path can be folded using a suitable mirror system. This may mean that the two main detectors 602, 603 have to be moved further away from each other, again improving the

third detector 605 the situation by covering the dead zone. A side view and a front view of the arrangement according to the present invention are shown in Figs. 23 and 24 respectively.
25

According to a further aspect of the invention, it is desirable to provide multi-bit capability with minimal or no modification of existing components. Various non-multi-bit sampling modules are known. This component is incorporated into a sampling module or machine of the type discussed above with reference to Figures 1 to 7 and in particular comprises a sampling signal input, a sampling signal digitizer and a digitized signal output together with an analog signal differentiator and output. Heretofore, it has not been considered desirable to provide a multi-bit version of such components.

unless an application specific integrated circuit (ASIC) was introduced, since there would be no space available on the small circuit boards provided in conventional scanning modules for the additional multi-bit circuitry. Moreover, even if multi-bit scanning modules were achievable, they would not be compatible with decoders in any existing portable terminals.

The present invention overcomes these problems by retaining the current sampling modules, but using the existing components in such modules to interface with a multi-bit decoder in an improved manner.

An example of the invention is shown in Figure 25. A sampling module of the type described with reference to Figure 2 (although any other module could be used) is shown at 620. Only the components relating to this signal processing are shown. The module 620 has a signal input 621 and a digitizer 622 which serves to convert the analog input signal into a digital output signal or output 632. The digital output is held at interface pin 624. This allows the sampling module to be used in true modular form to work with a suitable decoding module (in the manner of an interface). In addition to a digitizer 622, an analog signal differentiator 625 is also provided. The output differentiated signal 626 is held at a second interface pin 627. Conventional non-multi-bit systems do not use a second interface pin.

Fig. 26 shows a decoding module 630. For non-multi-bit decoding, the digitized signal 623 from the inter-

facepin 624 and decoded in decoder 631. The differential signal 626 interface pin 627 is not used; the decoder uses the standard digitizer bar pattern signal, supplied by digitizer 622 to scanning plate 620.

Multi-bit processing can be accomplished with a suitable decoder using the differential or differentiator signal 626 in conjunction with the digitized bar pattern signal from digitizer 622. An analog-to-digital converter 632 is used as a part of the decoding module 630. When decoder 631 detects a transition of the digitizer output from the scanning engine, it applies a signal line 633 to a controller 634, causing analog-to-digital converter 632 to sample the differentiated signal. Analog-to-digital converter 632 therefore supplies edge strength information to decoder 631 via lines 635. The scanning module digitizer 622 provides edge location and polarity information. The main principles of multi-bit signal processing are well known and will not be discussed in detail here, but it will be appreciated that the parameters of interest can be monitored in this way.

The analog-to-digital converter 632 may either be a separate integrated circuit on a decoder board (as shown in Figure 26) or may be incorporated into the decoder microprocessor chip itself. A suitable microprocessor chip is manufactured by Toshiba.

In cases where there are two positive or negative edges in a row in the input signal 621, the conventional digitizer is very sensitive such that even for a very small negative peak between two positive

peaks or vice versa, the digitizer 622 will detect all edges and the weaker ones will be rejected using the strength data in the usual way. It has been found that this does not lead to any significant degradation in the signal processing.

Fig. 18 shows schematically the connection between the sampling module 620 and the decoding module 630.

Msn recognizes that the improved multi-bit modular array can be incorporated into the construction discussed in Figures 1-7, allowing for further improvement in the interchangeability and modularity of the array, and yet another area of application for the basic retroreflective scanning module described therein.

According to a further aspect of the invention, it is desirable to provide or incorporate dual or multiple lasers and in particular the dual diode power sensing functionality, in increasingly small applications and to achieve the desired size and ergonomic requirements.

According to the invention, see an embodiment example according to Fig. 27, the dual diode (ED) arrangement is designed to have a first laser 700 focused for long or wide range scanning and a second laser 702 focused for short range scanning. To obtain the required small sizes, the long range laser 70 is arranged in a "back to back" configuration behind the short range laser 702. The long range laser beam 704 is folded around the short range laser 702 by mirrors 706 and 708. The short range laser beam 710 is folded by mirror 712. According to one embodiment, the two

Beams are recombined at 714 via a "special mirror" 716. The special mirror may be partially silvered (mirrored) or slotted to reflect the short-range beam 710 but allow the long-range beam 704 to pass through. Alternatively, the special mirror 716 could be offset from the long-range beam path 704 to allow the long-range beam 704 to pass through to the special mirror 716.

In addition to allowing for the reduced size, it will be appreciated that this implementation can be constructed using existing modules, with only the additional components provided in the available space. When a modular arrangement of the type discussed here is used, the possibility of adding further lasers and components can be easily accomplished, allowing for greater adaptability and reuse of existing components. It is certainly envisaged that the arrangement of Figure 27 could be incorporated or merged with the modular arrangement described with reference to Figures 1-6.

It should be noted that any of the features described above, or two or more together, may find useful application —other types of scanning devices and also other barcode readers of a different design than those described above.

The invention has been described with reference to a retroreflective scanning module for electro-optical readers, but is not intended to be limited thereto or to the various modifications described.

Claims (53)

nclaims 1. A self-contained electro-optical retroreflective scanning module for reading optically encoded characters having parts of different light reflectivity, comprising: a) a base, b) means on the base for emitting a beam of light along an outward path to the indicia for reflection therefrom; c) means on the base for detecting light reflected from the characters along an incident path across a field of view and for generating electrical signals corresponding to the character portions of differing light reflectivity; (d) a movable reflector mounted in the paths of the light beam and the reflected light; and e) drive means on the base for moving the movable reflector to sweep the light beam over the characters and to simultaneously sweep the field of view. 2. The module of claim 1, wherein the emitting means comprises a housing mounted on the base and further a light source mounted within the housing. 3. The module of claim 2, further comprising a stationary collecting mirror fixedly attached to the housing and a stationary scanning mirror fixedly attached to the collecting mirror. 4. The module of claim 3, wherein the collecting mirror is concavely curved and wherein the scanning mirror is flat and wherein a bracket is further provided for holding the mirrors at a distance from the housing. 5. The module of claim 4, wherein the base has a generally planar elongated configuration and has opposing end zones or regions, and wherein the housing and the mirrors are fixedly mounted at one end of the regions of the base and wherein the movable reflector is mounted for movement at the other end of the regions of the base. 6. The module of claim 3, wherein the detection means comprises a housing mounted on the base and a light detector mounted within the housing and facing the collecting mirror. 7. A module according to claim 1, wherein the drive means comprises an elongate support or carrier means, with opposite end portions, the reflector being attached to one of the end portions of the support, and wherein the drive means comprises a permanent magnet attached to the other of the end portions of the support, and wherein an electromagnetic coil is attached near the permanent magnet, which generates an alternating magnetic field when an alternating drive signal is applied to the coil, the alternating magnetic field acting on the permanent magnet to set it in an oscillating or vibrating motion and consequently to rotate the support and the reflector arranged thereon about an axis arranged approximately centrally between the reflector and the permanent magnet. 8. A self-contained electro-optical retroreflective scanning module for reading optically encoded indicia having parts of different light reflectivity, comprising: (a) an elongated base with opposite end regions or zones; b) a concave curved collecting mirror fixedly attached to an end region of the base; c) a generally planar plane scanning mirror fixedly attached to the collecting mirror; d) a movable reflector mounted for movement at the other of the end regions of the base; e) a light source on the base for emitting a light beam to the scanning mirror for reflection to the reflector for reflection to the indicia for reflection therefrom; f) a light detector on the base for Detecting light reflected from the characters across a field of view to the reflector for reflection to the collecting mirror for reflection to the light detector and generating electrical signals accordingly the character parts of different light reflectivity; and g) drive means for moving the reflector to sweep the light beam reflected therefrom over the characters and for simultaneously Scanning the field of vision. 9. The module of claim 8, wherein the collecting mirror has a center of curvature and wherein the light detector comprises a photodetector provided at the center of curvature of a central zone or region of the base between opposite end regions thereof. 10. Module according to claim 8, wherein the collecting mirror and the scanning mirror are integrally formed as a one-piece mirrored structure, and wherein the mirrored structure is attached to one end of the bracket, the opposite end of which is connected to the light source. 11. A self-contained electro-optical scanning module for reading optically coded characters having parts of different light reflectivity, comprising:
a) a base;
(b) Funds based on issuing a beam of light along an outward path towards and reflecting off the signs; c) means on the base for detecting light reflected from the characters along a incoming path across a field of view, and for generating electrical signals corresponding to the character parts of different light reflectivity; d) a movable reflector attached to at least one of the paths of the light beam and the reflected light; e) drive means on the base for moving the movable reflector to cover at least the field of view and/or the Ray of light over the signs; and f) Means for transmitting the electrical signals to a remote receiving device (host device) by means of electromagnetic waves (radio frequency). 12. The module of claim 11, wherein the transmission means comprises an antenna. 13. Self-contained electro-optical scanning module for reading optically coded characters with parts different light reflectivity, whereby the following is provided; a) a base; (b) Funds based on the issuance of a A multitude of light rays to the characters to reflection of these; (c) means on the basis of detecting light reflected from the characters across a field of view and generating electrical signals corresponding to the Character parts with different light reflectivity; (d) a movable reflector; and e) drive means on the base for moving the movable reflector to sweep at least one of the light rays over the characters. 14. A reflector assembly for scanning or sweeping a reading beam in an optical reader, the assembly comprising a support and a reflector and a counterweight mounted on the support and spaced apart from one another, the support being arranged to be movable relative to a support point located between the reflector and the counterweight. 15. A reflector assembly according to claim 14, wherein the mount is configured to be driven for movement at a point remote from the reflector. 16. The reflector assembly of claim 14, wherein the counterweight includes a permanent magnet that is driven by a changing magnetic field to move the mount. 17. A reflector assembly according to claim 14, wherein the support comprises a main body and elastic connecting means connecting the main body and the support point. 18. A reflector assembly according to claim 14, wherein the support comprises an elongate body with the reflector and the counterweight attached at opposite ends and with resilient connecting means connected to the elongate body substantially at one end and to the support point. 19. Scanning module for an optical reader, wherein the Module comprising: reading beam generating means and a movably driven scanning system including a reflector and a first magnetic element for cooperating with drive means for scanning or sweeping the reading beam, the module further comprising a second magnetic element arranged proximate the scanning system for magnetic interaction with the first magnetic element for biasing the scanning system to a predetermined position. 20. The scanning module of claim 19, wherein the second magnetic element comprises a member consisting entirely or substantially of iron. 21. The scanning module of claim 19, wherein the scanning system comprises a pivoting arm arranged for reciprocal movement, with the reflector pointing in one direction of movement and the first magnetic element pointing in the other direction of movement. 22. A scanning module according to claim 19, wherein the drive means comprises an alternating magnetic field generator, provided in the vicinity of the scanning system. 23. A reading module for an optical reader comprising: reading beam generating means and a detector for receiving a reading beam reflected from an element to be read, a filter having a wavelength passband associated with the detector, and the module further comprising means for monitoring the reading beam and for controlling parameters of either the reading beam generating means and/or the detector to maintain the reading beam wavelength within the passband. 24. A reading module according to claim 23, wherein a portion of the reading beam is received by the monitoring means and parameters of the reading beam generating means 0 are controlled to maintain the reading beam wavelength within the passband. 25. A reading module according to claim 24, wherein the reading beam generating means comprises a laser diode and the control parameters are the temperature of the laser diode. 26. Reading module according to claim 25, wherein the laser diode is mounted on a thermo-electric cooling/heating unit controlled by the monitoring means. 27. Reading module according to claim 23, wherein a portion of the reading beam is received by the monitoring means, wherein the filter has a tunable passband and finally, where the monitoring means controls the parameters of the filter in order to passband in such a way that the reading beam wavelength is also included. 28. The reading module of claim 23, further comprising a scanning system for scanning the reading beam while the monitoring means receives a portion of the scanned reading beam to monitor the scanning angle. 29. The reading module of claim 28, wherein the reading beam generating means comprises a laser diode and the monitoring means controls the parameters of the laser diode to maintain the reading beam wavelength within the passband based on the scan angle. 30. A reading module according to claim 29, wherein the parameter of the laser diode controlled by the monitoring means is the temperature. 31. A reader module according to claim 30, wherein the laser diode is provided on a thermo-electric cooler/heater unit to control the temperature of the laser diode. 32. Reading module according to claim 31, wherein the system of laser diode and thermo-electric cooler/heater unit has a low thermal mass. 33. A reading module according to claim 23, wherein the module comprises a scanning system for scanning the reading beam and wherein a portion of the scanned reading beam is received by the monitoring means to monitor the scan angle, wherein the filter has a tunable passband and the monitoring means tunes the passband based on the scan angle to adjust the passband such that to be adjusted so that the reading beam wavelength is included. 34. A reading beam generating system for an optical reader, comprising: a laser and a laser focusing aperture, the system being arranged to read printed characters oriented in a predetermined direction, the aperture being elongated in a direction perpendicular to the orientation direction and having a central portion having a first relatively large diameter and outer portions having relatively small dimensions. 35. The system of claim 34, wherein the opening is a substantially rectangular central opening with stepped outer portions. 36. The system of claim 34, wherein the opening is substantially diamond-shaped. 37. The system of claim 34, wherein the central portion is substantially circular and the outer portions have lobes. 38. The system of claim 36, wherein the corners of the opening are rounded. 39. The system of claim 37, wherein the corners of the opening are rounded. 40. Detector system for an optical reader, comprising first and second spaced-apart detectors and having first and second partially overlapping fields of view and a third detector having a field of view which is at least partially &bull;J covers the near-field non-overlap region of the first and second visual fields. 41. The system of claim 40, wherein the first and second detectors have respective first and second lenses. 42. The detector system of claim 40, wherein the third detector has a smaller dimension than the first and second detectors. 43. A detector system according to claim 40, wherein one or more of the detectors comprise a photodiode. 44. A detector system according to claim 40, further comprising read beam generating means and a scanning arrangement for scanning the read beam, the path of the read beam being folded within the system to increase the scan pattern size. 45. Scanning and decoding system for an optical reader, comprising:
a scanning module which has the following: Reading beam generating means;
Reading beam scanning means, a detector for detecting a reading beam reflected from an element and outputting an analog signal representative of the reflected beam, a digitizer for receiving the analog signal and outputting a digitized signal, a differentiator for receiving the analog signal and outputting or outputting a derived signal, wherein the digitized signal and the derived signal are held at respective first interface or boundary points, and further the system comprises: a decoding module including a multi-bit decoder and second interface points for receiving the digitized signal and the derived signal from the corresponding first interface points, wherein the multi-bit decoder performs decoding based on the digitized signal and the derived signal received at the second interface points.
10 46. A system according to claim 45, wherein the multi-bit decoder comprises a decoding element and an analog-to-digital conversion element, wherein the decoding element receives the digitized signal and decodes said signal for non-multi-bit decoding, and wherein the arrangement is such that a transition in the digitized signal to multi-bit format is detected and the analog-to-digital conversion element is enabled to sample the derived signal and provide the sampled signal to the decoding element for multi-bit decoding. 47. A decoding module for an optical reader comprising: a multi-bit decoder and an interface having an interface point for mating or matching with a digitized signal interface point on a scanning module and further having an interface point for mating or matching with a derived signal interface point on a scanning module. 48. The module of claim 47, wherein the multi-bit decoder comprises a decoding element and an analog-to-digital converter element that receives a digitized signal and decodes the signal for non-multi-bit decoders, and wherein the arrangement nition is such that a transition in the digitized signal to the multi-bit format is detected and the analog-to-digital converter element is enabled to sample a derived signal corresponding to the digitized signal and further to deliver the sampled signal to the decoding element for multi-bit decoding. 49. An optical reader comprising: first and second read beam generating means for generating first and second read beams, respectively, the second read beam generating means being arranged in the direct path of the first read beam, and the first read beam being folded around the second read beam generating means by beam redirection means, the first and second read beams being recombined substantially downstream of the second read beam generating means. 50. An optical reader according to claim 49, wherein the first and second read beams are substantially recombined via a reflector assembly arranged to transmit the first beam and reflect the second beam. 51. An optical reader according to claim 49, wherein the beams are substantially recombined by a mirror assembly including an aperture, the mirror assembly reflecting the second beam and the first beam passing through the aperture. 52. Optical reader according to claim 49, wherein the reading beams are substantially recombined by a mirror offset from the path of the first reading beam and arranged to reflect the t ···· ·&diams; *· »· _# &bull;&bull;&bull;J second ray is essentially collinear with the path of the first ray. 53. An optical reader according to claim 49, wherein the first read beam generating means comprises long range read beam generating means and the second read beam generating means comprises short range read beam generating means.