JPH10337097A - Image reader - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image maker which can set the drive torque optimally, according to the scan mode, without changing the number of divided steps of microsteps. SOLUTION: An excitation signal producing circuit 202 issues an excitation signal which becomes the basis geared to the setting speed, and outputs it to each AND circuit 204, and also, a microstep producing circuit 203 gets the data on the number of divided steps of microsteps, the maximum drive current, and the percentage to the maximum drive current at each step being set for every scan mode from a current/ PWM control circuit 205, and decides the number of times of generation of the chopping signals in each divided step cycle, and outputs it to an AND circuit 204, and performs microstep drive. In this case, the waveform of the microstep is changed, according to the scan mode, so the stepping motor 36 is driven with the drive torque geared to each scan mode.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image reading apparatus used in a document reading section such as a copying machine.

[0002]

2. Description of the Related Art For example, in a mirror scan type copying machine, an original is placed on a platen glass of an original reading section, and a scanner provided below the platen glass is caused to travel in parallel with the original surface. Thus, the image of the document is optically read.

At this time, the traveling speed of the scanner (scanning speed)
If the read start timing is unstable, the reproduced image is disturbed, and high-quality image formation cannot be expected. Therefore,
A stepping motor is used as a drive source of a traveling mechanism of the scanner, and the scanning speed and the reading position of the scanner are accurately controlled by pulse control. Such a stepping motor excites a group of a plurality of stator coils (generally called “phase”) arranged around the rotor by applying a rectangular constant-current drive pulse (full-step pulse) to excite the same. The phase to be excited is changed one after another to rotate the motor. The excitation method is a one-phase excitation method in which only one phase is always excited, and a driving method in which two phases are always excited. There are a two-phase excitation method and a 1-2 phase excitation method in which these excitation methods are mutually performed.

However, in drive control of a stepping motor using such a full-step pulse (hereinafter referred to as "rectangular wave drive"), the drive current rises sharply every time the phase to be excited changes, so that the magnetic flux inside the motor is increased. The distribution changes abruptly, causing a change in the driving torque (torque ripple), which causes a lack of smooth rotation of the rotor and causes noise and vibration.

[0005] In particular, when vibration occurs, the vibration is transmitted to the scanner via the power transmission mechanism and adversely affects image reading accuracy, resulting in image blurring.
To avoid such a problem, for example, Japanese Patent Laid-Open No.
Japanese Patent Application Publication No. 198 discloses a method of controlling the rotation of a stepping motor by dividing a rectangular drive pulse to be sequentially applied to each phase into a number of steps to approximate a sinusoidal curve. This driving method is generally called a micro-step driving method, in which the rise and fall of the drive current are smooth and the change in magnetic flux distribution is small, so that torque ripple hardly occurs and the rotation of the rotor becomes smooth. There is an advantage. As a result, vibration and noise during driving of the stepping motor can be reduced, and image reading accuracy can be improved.

[0006]

However, with the spread of automatic document feeders that can continuously feed a large number of documents to an image reading unit, the efficiency of reading a document by a copying machine, and consequently the number of copies per unit time ( Hereinafter, "CPM" (Co
py Per Minute). ) Is widely desired. For this purpose, it is necessary to return the scanner to the scanning start position as soon as possible after reading the original with the scanner.

For this purpose, in the above-described drive control by the micro-step drive, the number of divided steps of the micro-step is increased or decreased according to the operation mode of the scanner at the time of scanning of the original or at the time of return, so that the drive torque at the time of return is increased. However, in this case, it is necessary to switch the number of division steps when the stator and the rotor match a specific phase, and it is necessary to perform the synchronization processing at high speed. As a result, the cost of the CPU to be used for the control increases.

In view of the above problems, the present invention provides an image forming apparatus capable of setting a driving torque according to an operation mode of a scanner (scanning means) without changing the number of microstep division steps. The purpose is to:

[0009]

In order to achieve the above-mentioned object, an image reading apparatus according to the present invention comprises a scanning device which travels relative to a document to read an image of the document optically. In the reading device, a driving unit that uses a stepping motor as a driving source, causes the scanning unit to travel at a predetermined scanning speed from a scanning start position along a document surface, and divides a driving pulse to be applied to the stepping motor into a plurality of steps, Control means for performing step drive and changing the drive current value in each of the divided steps according to the scan mode, thereby performing control to change the microstep waveform.

The scanning mode includes an image reading mode in which the scanning means reads an image at a constant speed, and a return mode to a scanning start position after the image is read.
In the image reading mode, the rise and fall of the microstep waveform are made gentler than in the return mode. Further, the scanning mode includes a plurality of reading modes having different scanning speeds when the scanning unit reads an image at a constant speed. As the scanning speed is lower, the rising and falling of the microstep waveform is made gentler. It is characterized by the following.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of an optical system driving apparatus according to the present invention will be described below in a case where it is applied to an analog copying machine. First, the overall configuration of the analog copying machine (hereinafter, simply referred to as "copying machine") will be described with reference to FIG.

As shown in FIG. 1, the copying machine includes an automatic document feeder 10, a document reading section 30, a printer section 50,
And a paper feeding unit 70. The automatic document feeder 10 includes:
A known device that automatically sends a plurality of documents one by one onto the platen glass 22 of the document reading unit 30, reads a document image by the document reading unit 30, and then discharges the document onto the document discharge tray 19. is there.

The original reading section 30 includes a first slider unit (scanner) 31 that travels below the platen glass 22 in the direction of the arrow in FIG. 2 by driving a pulse motor 36 (see FIG. 2). The first slider unit reciprocates a predetermined distance according to the size of the document conveyed to the document reading position with the start position of the movement (scanning start position) as a left end and the start position as a reference position. The document reading unit 30
The surface of the photosensitive drum 51 is exposed while changing the optical path of the reflected light from the document by the irradiation of the exposure lamp 311 via a predetermined mirror.

Around the photosensitive drum 51, a charging charger 53, a developing unit 54, a transfer charger 55, a separation charger 56, and a cleaning unit 52 are arranged in this order in the rotation direction of the drum. The toner image of the document is transferred onto the copy paper fed from the paper supply unit 70. The copy paper onto which the toner image has been transferred is conveyed to a fixing unit 60 by a conveyance belt 57, and is fixed by a heat-pressing action of a fixing roller 61 having a heater therein. The copy paper after the fixing is discharged onto a discharge tray 63 by discharge rollers 62.

An operation panel 90 (broken line in FIG. 1) is provided at a position on the front of the copying machine where it can be easily operated.
The operation panel includes various input keys such as a copy start key for instructing the start of copying and a numeric keypad for setting the number of copies, and a display unit for displaying the set contents. FIG. 2 is a perspective view showing a structure of a driving portion of the document reading section 30. This document reading unit 30
A first slider unit 31, a second slider unit 32, and a third slider unit 33 are provided. Each of the slider units has a rail (not shown) provided at both ends in a sub-scanning direction (the direction of arrow A). ) So as to be slidable.

The first slider unit 31 functions as a scanner, and includes an exposure lamp 311 and a first slider unit 31.
Mirror 312 and first slider 3 holding these
13 and the second slider unit 32
The mirror 321 includes a mirror 321, a third mirror 322, and a second slider 323 that holds these mirrors in a state where their mirror surfaces are at 90 degrees. Similarly, the third slider unit 33 also includes a fourth mirror 331, a fifth mirror 332, and a third slider 333 that holds these mirrors with their mirror surfaces at 90 degrees, and these mirrors 312, 321 1, 322, 331, and 332 are as shown in FIG. 1, and together with the sixth mirror 34, the reflected light from the document surface of the exposure lamp 311 is guided to the surface of the photosensitive drum 51. Will be arranged.

Next, the first slider unit 31,
A drive mechanism for reciprocating the second slider unit 32 will be described. A pulse motor 36 is used as the driving source. The pulse motor 36 rotationally drives a shaft 37 rotatably held by a bearing (not shown) via a pinion 361 and a spur gear 371. Pulleys 372 are provided at both ends of the shaft 37.
A pulley 372 'is coaxially fixed to the shaft 3
It rotates with the rotation of 7. These pulleys 372, 37
Pulleys 39 and 3 provided on the opposite side of 2 ′ and the sub-scanning direction
Wires 38, 38 ′ are respectively laid between 9 ′, and an end of the first slider unit 31 is fixed in the middle of each wire 38, 38 ′.

On the other hand, on both side surfaces of the second slider 313, two pulley pairs 40, 41 and 40 ', 41' are pivotally supported, and these pulleys 40, 41, 40 ',
The wires 38, 38 'are wound around 41' in a state as shown in the figure. One end of each of the wires 38, 38 ′ is fixed to the main body of the original reading unit 30 by fixing pins 42, 42 ′, and the other end is a torsion coil spring 4.
3 and 43 'are fixed at a time, and the wires 38 and 38' are fixed.
To give an appropriate tension to the

In such a configuration, the pulse motor 3
6, the wires 38, 38 'move via the pulleys 372, 372', and the first wires follow the wires 38, 38 '.
The slider unit 31 and the second slider unit 32 move. At this time, pulleys 40, 41, 4
Since 0 ′ and 41 ′ function as a moving pulley, the second slider unit 32 moves in the same direction at half the speed of the first slider unit 31.

As a result, the first slider unit 31
Is moved for scanning the original, the first mirror 312
The optical path length from the zoom lens 35 to the zoom lens 35 is kept constant, and the image forming position of the zoom lens 35 is
Can be maintained on the surface. When the scanning of the original by the first slider unit 31 is completed, the pulse motor 36 is rotated in the reverse direction to return to the original scanning start position. At this time, the second slider unit 32 also follows and returns to the original position.

Reference numeral 44 in the drawing denotes a drive motor for moving the zoom lens 35 and the third slider unit 33 to change the magnification. This drive motor 44
Of the pulley 45 via a power transmission mechanism (not shown).
Is transmitted to the zooming cam 46, and each of them is driven to rotate at a predetermined rotation speed. A wire 451 is connected to the pulley 45 and another pulley (not shown) provided along the sub-scanning direction.
And a lens mount 351 on which the zoom lens 35 is mounted is fixed in the middle of the wire 451. The lens mount 351 can be moved in the sub-scanning direction by a slide mechanism (not shown), and moves together with the wire 451 as the pulley 45 rotates, whereby the first mirror 312 (actually, the document surface) is moved. The optical path length between the zoom lens and the zoom lens 35 is changed to change the magnification of the reproduced image.

An arm member 334 extending in the sub-scanning direction is provided on the inner side surface of the third slider 333. The outer peripheral surface of the zoom cam 46 is provided at the tip of the arm member 334. Is fixed. On the other hand, since the tension spring 336 urges the arm member 334 in the direction of arrow B, the contact member 335 always comes into contact with the outer periphery of the zoom cam 46, and the rotation of the zoom cam 46 is Accordingly, the arm member 334 and the third slider 333 shift by a predetermined amount.

As a result, the third slider unit 33 shifts by a required amount in synchronization with the movement of the zoom lens 35, and the optical path length from the zoom lens 35 to the photosensitive drum 51 is appropriately adjusted. Thus, the original image is always formed on the surface of the photosensitive drum 51, and the magnification can be easily changed. FIG. 3 shows a control unit 1 installed inside the copying machine.
FIG. 5 illustrates five CPUs 101 to 10
5, and each of the CPUs 101 to 105 has an RO storing programs necessary for the respective control.
M111 to 115 and RAMs 121 to 125 serving as work areas for executing programs are provided.

Each of the CPUs 101 to 105 has a data bus 1
50 and 152 and the serial I / O 151, and data and commands can be mutually exchanged by interrupt control. Also, each CPU 101
When power is applied to the apparatus main body, the initialization programs stored in the respective ROMs are read out.
The internal registers and the RAM are initialized and initialized, and the internal timer is started to measure time so that the time of each routine is monitored within a predetermined time.

Since the configuration and operation of each section of the control section 100 are already known and have been disclosed by the present applicant in previous applications, only the sections relevant to the present invention will be described here. When a document is sent to the document reading position, the CPU 102 that performs document conveyance control communicates the fact to the CPU 105 that performs timing control, and the CPU 105 for timing control causes the CPU 105 for timing control to read
A scan request is sent to the PU 103.

In response to the scan request, the CPU 103 controls the original reading scan in the original reading section 30. That is, a program necessary for the above control is read out from the ROM 113, various control signals are issued while taking timing based on the read out program, the exposure lamp 311 is turned on, and a scanner driving circuit 200 described later is connected via the I / O port 133. To the pulse motor 3
6 by controlling the rotation of the first slider unit 31
Is moved at a predetermined scanning speed to scan the original. Then, after reading the original, the first slider unit 31 is immediately returned to the scanning start position.

If the operator has designated the magnification from the operation panel 90 in advance, the I
A control signal is supplied to the magnification drive circuit via the / O port 143, thereby driving the drive motor 44 to shift the zoom lens 35 and the third slider unit 33 so as to obtain a predetermined magnification. . The image of the document obtained by such a scanning operation is transmitted to the document reading unit 30 described above.
Forms an electrostatic latent image on the surface of the photosensitive drum 51 rotating at a predetermined peripheral speed by the optical system of
The electrophotographic process is executed under the print control of the above, and an image is formed on the copy paper.

FIG. 4 shows that the stepping motor 36 is driven and controlled based on the control signal from the CPU 103 described above.
A scanner drive circuit 20 for moving the first slider unit 31 and the second slider unit 32 as intended.
0 is a block diagram of FIG. As shown in the figure, the scanner drive circuit 200 includes an up / down (U / D) counter 201, an excitation signal generation circuit 202, a micro step generation circuit 203, an AND circuit 204, a current / PWM control circuit 205, a buffer amplifier 206, transistor 20
7, a current detection circuit 208 for detecting a current value supplied to each phase of the stepping motor 36, a diode 209 for protecting the transistor 207, and each bias resistor RS
1, RS2.

The stepping motor 36 is of a two-phase type, and its stator coils are composed of A phase, B phase and A '.
Phase, B 'phase. The speed setting signal output from the CPU 103 is given by a clock signal to instruct a rotation operation such as acceleration → constant speed → deceleration → return of the stepping motor 36. The clock cycle becomes shorter as time goes on. The rotation direction setting signal is given as “H” and “L” level signals. For example, when the signal is at “L” level, clockwise rotation (C
W), counterclockwise rotation at "H" level (CCW)
Is controlled as Microstep division number setting signal s
ig3 and sig4 are control signals for instructing the number of division steps in one cycle of the excitation phase switching pulse signal described later, and are given as "H" and "L" level signals,
By this combination, as shown in FIG. 5, one of the four types of division step numbers is specified.

When the above-described speed setting signal and rotation direction setting signal (for example, CW signal) are input to the U / D counter 201, the U / D counter 201 divides the speed setting signal to obtain a frequency. 6, the excitation phase switching pulse signal as shown in the uppermost stage of FIG. 6 is generated, and the excitation phase switching signal is supplied to the excitation signal generation circuit 202 at the subsequent stage at each rising edge of the pulse (that is, for each period of the excitation phase switching pulse signal). And sends a rotation direction setting signal. Further, the U / D counter 201 divides the speed setting signal to realize micro-step driving with the number of divisions corresponding to the micro-step division number setting signal input from the CPU 103.
For example, a speed setting pulse signal as shown in the upper part of FIG. 7 is generated and output to the micro-step generation circuit 203. FIG.
The example shown in FIG. 7 is a microstep division number setting signal sig3
= L and sig4 = H are input from the CPU 103, that is, a speed setting pulse signal generated when the number of microstep divisions is designated as 8 (FIG. 5). Therefore, the cycle of the speed pulse setting signal is 1/8 cycle of the excitation phase switching pulse signal.

The excitation signal generation circuit 202 generates a basic excitation signal for two-phase excitation as shown in FIG. 6 so as to rotate the stepping motor 36 clockwise each time the excitation phase switching signal is received. And each AND circuit 20
4 is output. When the CCW signal is received, the rotation direction is changed at the rising edge of the excitation phase switching pulse signal immediately after the CCW signal, and an excitation signal for phase switching in the reverse order is generated, and the stepping motor 36 is turned off. Control to rotate clockwise.

As described above, the excitation signal generation circuit 202
Generates a basic excitation signal for two-phase excitation,
These periods are shorter as the period of the excitation phase switching pulse signal is shorter (that is, as the required rotation speed is higher). The micro-step generation circuit 203 is a circuit that generates a signal to be input to each AND circuit 204 together with the basic excitation signal, and micro-step driving is realized by the content of the signal.

The current / PWM control circuit 205 refers to a later-described micro-step control table stored in its internal memory to determine the maximum drive current of the drive pulse in the micro-step drive and the maximum drive current in each step. The percentage with respect to the drive current is sent to the microstep generation circuit 203. Hereinafter, the micro step generation circuit 203 and the current / PWM control circuit 20
The overall control operation will be described focusing on the operation in FIG.

The current / PWM control circuit 2 from the CPU 103
05 is supplied with rotation vector setting signals sig1, sig2 and microstep division number setting signals sig3, sig4. Note that the microstep division number setting signal si
g3 and sig4 are signals similar to those described above input to the U / D counter 210. The rotation vector setting signals sig1 and sig2 are control signals for setting the driving waveform of the micro-step driving, and include “H”,
It is provided by an "L" level signal.

On the other hand, the internal memory of the current / PWM control circuit 205 has a table for micro-step control as shown in FIGS. 8A and 8B and a set current (not shown) of a drive pulse (not shown). , Which is the maximum drive current in each drive pulse, hereinafter, referred to as “maximum drive current”. FIG. 8A shows the rotation vector setting signals sig1 and si input from the CPU 103.
FIG. 8B is a table for setting the scanning mode by g2. FIG. 8B shows the number of division steps of the A-phase and the B-phase in the half cycle of the phase switching signal for each of the set scanning modes. 9 is a table showing the magnitude of the current in a step as a percentage of the maximum drive current. The table shown in FIG. 8B is a table corresponding to the number of micro-step divisions of 8, and the internal memory additionally has tables corresponding to the number of micro-step divisions of 2, 4, and 16. Are stored, but their illustration and description are omitted.

The policy for setting the values in each scanning mode of the table shown in FIG. 8B will be described with reference to FIG. FIG. 9 shows the ratio (percentage) of the current flowing in the A-phase to the maximum driving current on the vertical axis, and the ratio (percentage) of the current flowing in the B-phase to the maximum driving current on the horizontal axis. The percentage change for each step is represented as a vector locus. FIGS. 9A to 9D show cases of the standard mode, the constant speed mode, the acceleration / deceleration mode, and the return mode, respectively.

The values in the standard mode in FIG. 8B are set so that the trajectory of the vector draws an arc as shown in FIG. 9A, and the values in the constant speed mode are as shown in FIG. As shown in (b), the trajectory of the vector is set to a value inside the vector trajectory (arc) in the standard mode. Also, as shown in FIG. 9C, the values in the acceleration / deceleration mode are set so that the trajectory of the vector swells slightly outward from the vector trajectory (arc) in the standard mode. Are set so that the trajectory of the vector bulges further outward than in the acceleration / deceleration mode.

The current / PWM control circuit 205 determines the scanning mode by referring to the table in FIG. 6 based on the combination of "H" and "L" of the rotation vector setting signals sig1 and sig2, and sets the microstep division number setting signal. sig
3. The table to be used is specified by the combination of “H” and “L” of sig4. And, for example, sig3 =
If L and sig4 = H, the percentage of the current in each step with respect to the maximum drive current is sent to the microstep generation circuit 203 as table data with reference to the table of FIG.

The microstep generation circuit 203 calculates the drive current in each step according to the table data of the maximum drive current, and at each rising edge of the speed setting pulse signal from the U / D counter 201 (ie, the speed setting pulse). A chopping signal corresponding to each step is output to the AND circuit 204 (for each cycle of the signal) to generate a microstep waveform.

The procedure for forming such a microstep waveform will be described, for example, in the case of the constant speed mode. The diagram shown in the lower part of FIG. 7 is a model of a microstep waveform in one drive pulse formed in this case. The micro-step generation circuit 203 calculates the current / PW
The value of the maximum drive current from the M control circuit 205 and the percentage of each step (100%, 93%, 86
%, 77%, 65%, 51%, 36%, 20%, 0%)
A drive current required for each step is calculated from (see FIG. 8B), and control is performed so that the current flows. That is, the current flowing through the motor is obtained from the current detection circuit 208, and the chopping signal is output from the microstep generation circuit 203 to the AND circuit 204 so that the required current flows through the motor.

Now, from the current of 100% of the maximum drive current, 93%, 86%, 77%, 65%, 51%, 36%,
20% and 0% currents are obtained by changing the percentage of the maximum drive current at the rising (or falling) edge of the speed setting pulse signal (FIG. 7). Since the chopping signal from the microstep generation circuit 203 is input to each AND circuit 204 in synchronization with the excitation signal from the excitation signal generation circuit 202, the chopping signal during each phase excitation switching period shown in FIG. Is generated, the corresponding AND circuit 204 generates an ON signal.

The transistor 207 is turned on for each of the chopping signals, and a predetermined amount of current flows through the coil of the corresponding phase. The amount of flowing current increases, and as a result, the average current value in the step cycle increases. Since the magnitude of the driving torque generated in the stepping motor 36 depends on the amount of current applied to each phase per unit time, by controlling the number of times the chopping signal is generated as shown in the lower part of FIG. Microstep control equivalent to a change in the current value like this can be performed.

At this time, the cycle of generating the chopping signal is set to be sufficiently short, and there is no possibility that torque ripple will occur in the stepping motor 36 because of this cycle. FIG. 10 is a diagram showing a microstep waveform, which is a change in drive current to each phase when two-phase excitation is performed by the microstep control when the constant speed mode is set.

Similar microstep control is performed based on the table data in FIGS. 8A and 8B in the acceleration / deceleration mode, return mode, and standard mode, as shown in FIGS. 11 to 13, respectively. A drive current having such a microstep waveform is applied to each phase. In the present embodiment, the standard mode is not used.

As can be seen from FIG. 10, when the moving speed of the scanner is slow and the load torque is small when scanning the original,
The micro step waveform is slightly narrowed compared to the waveform in the standard mode shown in FIG. 13, and the driving torque is reduced to prevent imbalance between the load torque and the driving torque. The first slider unit 31 and the second slider unit 32 can be moved at a high speed, and highly accurate document scanning can be realized. On the other hand, as shown in FIG. 11, when it is necessary to quickly shift from the stop state to the scanning speed rather than low vibration at the time of starting scanning, and when it is necessary to rapidly decelerate from the scanning speed at the time of scanning falling, Since the waveform of the standard mode shown in FIG. 13 is slightly closer to a rectangular waveform, a relatively large torque can be obtained. Further, when the scanner is returned to the scanning start position after the scanning is lowered, the document scanning is not performed. Irrespective of this, since the return in a short time is given the highest priority over the low-vibration property, as can be seen from FIG. 12, the waveform in the standard mode shown in FIG. Torque is obtained.

In FIG. 4, the current detection circuit 208
Is for detecting a current value supplied to the coils of each phase when an ON signal is output from the AND circuit 204. If the current value is not within a predetermined range, the current / PWM control is performed. Since the control of the drive current as shown in the table in the circuit 205 cannot be achieved, the microstep generation circuit 203 changes and outputs the number of times of generation of the chopping signal based on the current detection value. Specifically, if the detected value is lower than a preset reference current value, the number of occurrences of the chopping signal is increased accordingly, and if it is higher, the number of occurrences of the chopping signal is reduced accordingly. The amount of increase / decrease is, for example, a table showing the relationship between the difference between the reference current value and the detected current value and the amount of increase / decrease in the number of times of generation of the chopping signal is created in advance and stored in the internal memory of the microstep generation circuit 203 or the like. Can be easily determined by referring to this.

Finally, the scanner driving circuit 2 as described above
The rotation operation of the stepping motor 36 controlled by 00 will be described with reference to the timing chart of FIG. 3A shows the speed pattern of the stepping motor 36, FIG. 3B shows the change in the load torque, and FIG. 3C shows the switching timing of the rotation vector setting signal. d) shows how the drive current of the stepping motor 36 changes.

As shown in FIG. 14A, the stepping motor 36 accelerates the original slider speed from the stopped state to the original scanning speed (scanning start), maintains the scanning speed (original scanning), and scans. After the end, decelerate and stop (scan fall), and then return to the scan start position,
Control is performed such that the moving direction is reversed to accelerate (return and rise), return at high speed (return), and reduce the speed and stop (return and fall) near the original reading position.

Such an operation control pattern is stored in the ROM 1
13 (FIG. 3), and the CPU 103
When there is a scan request from 104, the program is read and control is executed. That is, the U / D counter 201
, A speed setting signal and a rotation direction setting signal CW whose cycle is gradually shortened, and the current / PWM control circuit 20
5, the rotation vector setting signal sig1 = L, sig2 = H
Send. As a result, the stepping motor 36
, And is accelerated with a relatively high torque in the clockwise direction to start scanning.

When the first slider unit 31 reaches a predetermined scanning speed, the CPU 103 sends a rotation vector setting signal sig1 = H, sig2 to the current / PWM control circuit 205.
= L, and the stepping motor 36 is driven with the microstep waveform shown in FIG. 10 to achieve low vibration.
When the document scanning is completed, the CPU 103 sets the current / PWM
The control circuit 205 supplies a rotation vector setting signal sig1 = L,
Send sig2 = H, decelerate the scanner with relatively high torque, and perform scanning fall.
103, the CCW rotation direction setting signal is supplied to the U / D counter 201 and the current / PWM control circuit 20
5 includes rotation vector setting signals sig1 = L, sig2 =
H is sent, the micro step waveform (FIG. 12), which obtains the highest torque during a series of operations, starts up at a steep acceleration, moves at the highest return speed, and then falls down rapidly to a predetermined reading start position. To stop.

As described above, the original reading speed per unit time and, consequently, the copy efficiency (CPM) are improved by using the high-torque stepping motor and performing the high-speed return movement without changing the number of microstep division steps. And at the same time, achieve low-vibration during scanning of the original to achieve high-precision image reading. As described above, the present invention has been described based on the embodiment. However, the content of the present invention is not limited to the embodiment, and for example, the following modifications can be considered. (1) In the above embodiment, only the microstep waveform is changed according to each scanning mode. However, the maximum drive current may be changed together. this is,
8 is stored in the internal memory of the current / PWM control circuit 205.
A table similar to the table shown in (a) is prepared, and the maximum drive current is stored in correspondence with each rotation vector setting signal. The current / PWM control circuit 205
3 can be realized by sending the maximum drive current value corresponding to the rotation vector setting signal input from the micro step generation circuit 203. (2) In the above embodiment, one scanning cycle of the scanner is divided into three scanning modes of low speed, acceleration / deceleration, and return, and the microstep waveform is changed corresponding to each scanning mode. That is, the microstep waveform may be changed according to the reading mode corresponding to the scanning speed when the scanner reads an image at a constant speed. For example,
As shown in FIG. 15, in the case of the high-speed reading mode with a magnification of 0.500 to 0.816, the microstep waveform in the acceleration / deceleration mode of the above embodiment is 0.817 to 1.2.
In the case of the medium speed reading mode of 24, the stepping motor is driven by the micro step waveform of the standard mode, and in the case of the low speed reading mode of 1.225 to 2.000, the stepping motor is driven by the micro step waveform of the constant speed mode. .

By doing so, as the enlargement magnification increases, that is, as the scanning speed decreases and the load torque decreases, the rise and fall of the microstep waveform become gentler, and the drive torque decreases. And the driving torque is hardly unbalanced, and highly accurate original scanning can be realized. (3) In the above embodiment, the number of division steps is set to 8 throughout each scanning mode. However, the number of division steps may be changed according to the scanning mode. For example, both the torque of the motor and the vibration generated by the motor tend to decrease as the number of divisions increases, so when reading an image, increase the number of divisions to reduce the vibration, and otherwise reduce the number of divisions. To secure the torque. FIG. 16 shows an example of the speed setting pulse signal and the microstep waveform when the number of divisions is four. (4) In the above embodiment, the case where a two-phase stepping motor is controlled has been described, but a three-phase stepping motor may be used. In this case, the number of excitation signals output from the excitation signal generation circuit 202 (FIG. 4) and the number of AND circuits 204, transistors 207, etc. are also increased, but the basic control method is almost the same as described above. It is.

Since the two-phase stepping motor has a difference in magnetic flux of each phase due to its structure, the micro-step drive has a drawback that the movement amount of one step tends to vary. On the other hand, in the case of the three-phase stepping motor, since there is no difference in the magnetic flux of each phase due to the structure, when the micro-step drive is performed, one step is taken.
The moving amount of the step is easily uniform, and the rotation accuracy is more excellent. Therefore, if such a three-phase stepping motor is used as the stepping motor 36, it is possible to provide an image reading apparatus with further excellent scanning accuracy. (5) In the above-described embodiment, the number of generations of the chopping signal in each step cycle of the microstep is controlled by the microstep generation circuit 203 to obtain the drive current for each step. Similar results can be obtained by controlling the ON time of the signal to control the energization time of each step of the transistor 207.

In the above-described embodiment, the micro-step waveform is formed by digital control. However, the micro-step waveform is formed in the same manner even when the analog switch is switched for each step to give a different current value. be able to. (6) In the above embodiment, an example in which the image reading apparatus according to the present invention is applied to an analog copying machine has been described. However, in other words, a scanner such as a digital copying machine or an image scanner for a computer may be used. It is applicable to all devices that need to be moved and scan images.

[0055]

As described above, according to the image reading apparatus of the present invention, at the time of scanning a document, a driving pulse applied to a stepping motor as a driving source for driving a scanning unit is divided into a plurality of steps. In addition to micro-step driving, the micro-step waveform is changed by changing the drive current value in each of the divided steps according to the scanning mode. Thus, the driving torque can be set optimally.

Also, the rise and fall of the microstep waveform are slower in the case of the image reading mode than in the case of the return mode.
At the time of image reading, smooth rotation with little torque ripple can be obtained, and at the time of restoration, high-speed restoration can be performed with high torque.
It is possible to increase the value.

Further, the rising and falling of the microstep waveform becomes gentler in the reading mode in which the scanning speed at the time of reading an image is lower, so that a smooth rotation with less torque ripple can be obtained. Thus, the scanning means can be reliably driven at a high speed with a high torque.

[Brief description of the drawings]

FIG. 1 is a diagram showing an overall configuration of an analog copying machine to which a document device according to the present invention is applied.

FIG. 2 is a perspective view showing a configuration of a driving portion of an image reading section of the copying machine.

FIG. 3 is a block diagram of a control unit installed inside the copying machine.

FIG. 4 is a block diagram of a scanner driving circuit in the control unit.

FIG. 5 shows control signals sig3 and sig from CPU 103.
It is a figure which shows the relationship between 4 and the microstep division number set.

FIG. 6 is a diagram illustrating a relationship among an excitation phase switching pulse signal, a rotation direction setting signal, and an excitation signal.

FIG. 7 is a diagram showing a model of a speed setting pulse signal and a microstep waveform.

FIG. 8A shows a control signal sig from a CPU 103;
FIG. 3 is a diagram showing a relationship between 1, sig2 and a mode to be set. (B) is a diagram showing the current in each step in micro-step driving as a percentage of the maximum driving current.

FIG. 9 is a diagram in which the vertical axis represents the ratio (percentage) of the current flowing in the A phase and the horizontal axis to the B phase with respect to the maximum drive current, and the change in the percentage is represented as a vector locus.

FIG. 10 is a diagram showing a change in a drive pulse applied to each phase when a constant speed mode is set during micro-step driving.

FIG. 11 is a diagram showing a change in a drive pulse applied to each phase when the acceleration / deceleration mode is set during micro-step driving.

FIG. 12 is a diagram showing a change in a drive pulse applied to each phase when a return mode is set during micro-step driving.

FIG. 13 is a diagram illustrating a change in a drive pulse applied to each phase when the standard mode is set during micro-step driving.

FIG. 14 is a diagram for explaining the rotation operation of the stepping motor from the start of scanning to the return fall.

FIG. 15 is a diagram showing a relationship between control signals sig1 and sig2 from CPU 103 and a copy magnification in another embodiment.

FIG. 16 is a diagram showing a model of a speed setting pulse signal and a microstep waveform.

[Explanation of symbols]

 Reference Signs List 10 automatic document feeder 30 image reading unit 31 first slider unit 32 second slider unit 33 third slider unit 36 stepping motor 50 printer unit 100 control unit 200 scanner drive circuit 201 U / D counter 202 excitation signal generation circuit 203 microstep Generation circuit 204 AND circuit 205 Current / PWM control circuit 206 Buffer amplifier 207 Transistor 208 Current detection circuit

Claims (3)

[Claims] 1. An image reading apparatus for optically reading an image of a document by causing a scanning means to travel relative to the document, wherein the stepping motor is used as a drive source, and the scanning means is moved from a scanning start position to a document surface. Traveling means for traveling at a predetermined scanning speed along, a driving pulse applied to the stepping motor is divided into a plurality of steps to perform micro-step driving, and a driving current value in each of the divided steps is determined according to a scanning mode. An image reading apparatus, comprising: control means for performing control to change a microstep waveform by changing. 2. The scanning mode includes an image reading mode in which the scanning unit reads an image at a constant speed and a return mode to a scanning start position after image reading. 2. The image reading apparatus according to claim 1, wherein the rise and fall of the microstep waveform are made gentler in the reading mode. 3. The scanning mode includes a plurality of reading modes having different scanning speeds when the scanning unit reads an image at a constant speed. The lower the scanning speed, the more the rising and falling of the microstep waveform. 2. The image reading device according to claim 1, wherein the image reading device makes the image reading speed gradual.