EP0919391B1 - Method for adjusting and maintaining the distance between a printing surface and a printhead and printing device for carrying out the method - Google Patents

Description

The invention relates to a method for setting and Maintaining the distance between the printable Surface of a pressure medium attached to a pressure abutment abuts, and a movable parallel to this Printhead with one for abutting the print abutment or the sensing element surface certain sensing element connected is.

In computer printers and especially receipt printers, the papers different thicknesses such as Single receipts, Process multi-layer copying receipts or passbooks must be the touching as a printing principle DOT matrix printing process used. One for all Ensure print media consistently good typeface To be able to, the distance between the print carrier surface and keep the printhead constant. This is e.g. thereby achieved that on the printhead or attached to the carrier holding him a feeler roller is that with a certain force against the print medium is pressed. Position the printhead in one fixed spatial relation to the touch roller, so it is also the distance of the print head to the print carrier surface fixed.

Strikes along as the print head travels the thrust roller on a spur edge (Paper margin, fold area of passbooks and the like), this leads briefly to one of the amount of Interfering edge and dependent on the travel speed Increase the distance of the print head from the print carrier surface. Since the carrier with the printhead, the Tracer roller and the pressure spring an oscillating system form, by driving over interfering edges in this system excited vibrations that are in the printed image find it visibly.

From the English abstract of JP-A-7 117 277 is a printing device according to the preamble of the claim 5 known. The control of the printhead drive takes place in this printing device such that the Printhead feed speed if there is one Change in thickness of the recording medium over the entire Print line is kept low and in the absence a change in thickness is greater.

In the English language abstract of JP-A-5 169 761 described a printing device in which the print head before the actual printing process over the printing area performed and thereby a thickness profile of the record carrier is created. This is saved and the distance of the printhead to the platen at a subsequent one Printing process according to the thickness profile controlled.

The invention has for its object a method of the type mentioned at the beginning, in which is independent on the type of print medium with high printing performance results in a trouble-free printed image.

This object is achieved in that parallel during an empty pass of the printhead to the pressure abutment over the inserted pressure carrier Changes in the distance of the print carrier surface from the pressure abutment according to its location within the Travel of the print head and determined by their size and that the positioning speed of the printhead for a print run depending on location and The size of the distance changes determined is controlled in this way will that with a substantially trouble-free print image a maximum positioning speed is reached.

With the method according to the invention thus become interfering edges detected. By lowering the speed in this Area can be reached that the printhead is not by bumping against the interference edge of the pressure abutment is thrown away, but in contact with the print carrier surface remains. Between the interfering edges the Printhead but moving at full speed so that even with a good printed image a high one Print performance results. At the same time, the power with the printhead is pressed against the abutment, can be reduced so that the tracer roller leaves no traces leaves the print carrier. The printing device must not manually adjusted to the different print media become. The position of an interfering edge changes over the length of the paper, this can also be recorded.

In a preferred embodiment of the invention the required as a result of a detected change in distance Change the current printhead speed on hand a predetermined functional relationship between the size and possibly the gradient of a change in distance on the one hand and the print head speed on the other determined. That determined after the empty passage Speed profile of the print head over the travel can be saved so that it can be printed for everyone Line is available.

The distance of the print carrier surface is preferred from the pressure abutment by a non-contact one Sensor arrangement determined. The distance detection can through capacitive, inductive, optical or magnetic Sensors.

The invention further relates to a printing device a print abutment and a print head, which by means of a printhead drive in parallel along an actuating path adjustable to the pressure abutment and with a feeler element is firmly connected to the system on the pressure abutment or the surface of a print carrier adjacent to it is determined, the printhead and / or the Pressure abutment in the direction of the other part is biased. To carry out the above The method comprises such a printing device according to the invention a sensor arrangement for detecting the distance the print carrier surface from the pressure abutment along the travel of the printhead and a control device to control the print head drive such that the printhead speed depending on the location and Size of changes in distance without significant interference maximum of the printed image.

To determine the optimal printhead speed in Dependence of the position and size of interfering edges and from them resulting control changes a computing device taking into account a predetermined functional relationship between the size and possibly the gradient of a change in distance on the one hand and the print head speed on the other and depending on the size and location of changes in distance along the travel of the printhead Speed profile for the printhead movement determined. The predetermined functional relationship is preferably between the distance change and the printhead speed in a memory of the control device saved. The location of the printhead is everyone Time known.

The sensor characteristics can vary from sensor to sensor and moreover during the lifetime of the sensor itself to change. In order to be able to calibrate the sensor arrangement if necessary, is according to the invention outside of the system for Pressure medium of certain area on the pressure abutment at least one calibration threshold in the sensing path of the sensing element provided for calibrating the sensor arrangement. The calibration threshold causes a defined change in distance, the be compared with the measurement result of the sensor arrangement can, so that the sensor arrangement is calibrated in this way can be. A linear sensor characteristic is sufficient a single calibration threshold. With a non-linear course there must be several calibration thresholds.

Figur 1

eine schematische Seitenansicht der erfindungsgemäßen Druckvorrichtung parallel zur Bewegungsrichtung des Druckkopfes entlang dem Druckwiderlager,

Figur 2

eine schematische Ansicht der in Figur 1 dargestellten Druckvorrichtung in Richtung des Pfeiles A in Figur 1.

Further features and advantages of the invention will become apparent from the following description, which explains the invention with reference to an exemplary embodiment in conjunction with the accompanying drawings. Show it:

Figure 1

2 shows a schematic side view of the printing device according to the invention parallel to the direction of movement of the print head along the print abutment,

Figure 2

2 shows a schematic view of the printing device shown in FIG. 1 in the direction of arrow A in FIG. 1.

In FIGS. 1 and 2, one can generally see 10 designated pressure abutment with a contact surface 12 for a print carrier 14, which is shown in FIG. 2 as a savings book is shown.

A support arm 16 which is pivotally mounted about an axis 18 is, carries a guide rod 20 on which a print head carrier 22 in Figure 1 perpendicular to the plane and in Figure 2 in the direction of the double arrow B. is stored. On the print head carrier 22 is a needle print head 24 held. It is also on the print head carrier 22 a feeler roller 26 rotatably mounted about an axis 28. The feeler roller is in contact with the bearing surface 12 of the Pressure abutment 10 or the surface of the printing medium 14 determined to the mouthpiece 30 of the printhead 40 in the optimum distance from the print carrier surface for printing 14 hold. The feeler roller 26 is a on the holding arm 16 engaging spring 32 against the bearing surface 12 of the pressure abutment 10 excited. Of course the guide rod 20 could also be arranged stationary be and the pressure abutment 10 towards the feeler roller 26 be biased.

In Figures 1 and 2, the feeler roller 26 is immediately on the bearing surface 12 of the pressure abutment 10. In this position is the distance between the print head carrier 22, or the print head rigidly connected to it 24 and the bearing surface 12 of the pressure abutment 10 minimal. This distance is, for example, by the distance a between the planes X and Denotes Y.

If the print head 24 is used with the help of its only in FIG schematically indicated drive 34 in Figure 2 moved to the left, the feeler roller 26 moves over the edge 36 of the print carrier, i.e. of the passbook 14 on the one to be printed Page up. The print head carrier 22 and the Printhead 24 are raised accordingly, so that the distance a increases. If this happens at high speed, so the print head 24 jumps over the edge 36, i.e. it moves further away from the pressure abutment 10 than is absolutely necessary. Because the print head carrier 22 by means of the spring 32 in the direction of the pressure abutment 10 is biased, the system vibrates a few more Paint back and forth until printhead 30 is the optimal one again Distance from the surface of the print carrier to be printed 14 has. These vibrations could reach up to one avoided to some extent by reinforcing the spring 32 be, which has other disadvantages. The same thing Problem also occurs on the fold 38 of the passbook 14.

According to the invention, the change in distance is now using a sensor 40 arranged on the print head carrier 22 detected. The distance determined by the sensor 40 becomes one Control device 42 fed to a computer 44th Has. With a known sensor characteristic curve, the Output signal of the sensor 40, the height of the interference edge 36 be determined. The position of the printhead 24 along its travel path is always known. So the location the interference edge 36 can be detected.

The computing device 44 calculates depending on the interference edge height and possibly the rise of the interfering edge 36, i.e. of the gradient the maximum travel speed, for who do not yet see any impairment of the typeface is. This functional relationship between the Störkantenhöhe and their gradient on the one hand and the The maximum possible travel speed can theoretically and / or determined experimentally and in one Memory 46 of the control device 42 can be stored.

If a print carrier 14 is inserted into the printer, it moves the print head carrier 22 once without printing, i.e. in one Full width empty passage over the inserted document, around the interfering edges in terms of their height and position to investigate. With reference to the stored functional relationship between interfering edge height and maximum Travel speed becomes a speed profile determined for the respective print lines. In the following Printing then becomes the printhead drive 34 from the control device 42 according to this speed profile controlled.

A document can then be printed dynamically be checked whether the interference edge parameters (Height and position) have changed. If necessary the speed profile are updated.

For the initialization and the adjustment of the system in the ongoing operation, i.e. for the calibration of the sensor 40 is in a non-printable area of the platen, i.e. in Figure 2 on the right edge of the same a calibration threshold 48 arranged. This forms a defined increase, over which the feeler roller 26 can run. Thereby the print head carrier 22 by a defined distance raised so that the sensor signal is defined with this Distance change can be compared to the sensor if necessary. The number of such calibration thresholds 48 depends on the required accuracy and the mathematical function with which the sensor characteristic can be described. With a linear sensor characteristic e.g. a single threshold is sufficient.

Reference list

10th

Pressure abutment

12th

Contact surface

14

Print carrier

16

Beam

18th

axis

20th

Guide rod

22

Printhead carrier

24th

Printhead

26

Tracer roller

28

axis

30th

Mouthpiece

32

feather

34

drive

36

Edge

38

Fold

40

sensor

42

Control device

44

Computing device

46

Storage

48

Calibration threshold

Claims (8)

1. Method of setting and maintaining the distance between the surface to be printed of a printing medium (14), which is resting on a print backing support (10), and a print head (24) which can be moved parallel to the said print backing support (10) and which is connected to a sensing element (26) which is intended to rest on the print backing support (10) or the printing medium surface, characterized in that during an empty pass of the print head (24) parallel to the print backing support (10) over the inserted printing medium (14), changes in the distance (a) between the printing medium surface and the print backing support (10) are determined according to their position within the actuating path of the print head (24) and in accordance with their magnitude, and in that the actuating speed of the print head (24) for a print pass is controlled as a function of the position and magnitude of the distance changes determined in such a way that, with a substantially fault-free printed image, a maximum actuating speed is achieved.
2. Method according to Claim 1, characterized in that the change in the current print head speed, required as a result of a detected distance change, is determined by using a predetermined functional relationship between the magnitude of a distance change, on the one hand, and the print head speed, on the other hand.
3. Method according to Claim 1 or 2, characterized in that the speed profile, determined after the empty pass, of the print head (24) over the actuating path is stored.
4. Method according to one of Claims 1 to 3, characterized in that the distance between the printing medium surface and the print backing support (10) is determined by a sensor arrangement (40) that operates without contact.
5. Printing device having a print backing support (10) and a print head (24), which can be displaced by means of a print head drive (34) along an actuating path parallel to the print backing support (10) and is firmly connected to a sensing element (26), which is intended to rest on the print backing support (10) or the surface of a printing medium (14) resting on the said print backing support (10), the print head (24) and/or the print backing support (10) being prestressed in the direction of the respective other part, characterized by a sensor arrangement (40) for detecting the distance between the printing medium surface and the print backing support (10) along the actuating path of the print head (24), and by a control device (42) for controlling the print head drive (34) in such a way that the print head speed becomes a maximum as a function of the position and magnitude of distance changes, without significant faults in the printed image.
6. Printing device according to Claim 5, characterized in that the control device (42) has a computing device (11) which, taking into account a predefined functional relationship between the magnitude of a distance change, on the one hand, and the print head speed, on the other hand, and as a function of the magnitude and position of distance changes along the actuating path of the print head (24), determines a speed profile for the print head movement.
7. Printing device according to Claim 6, characterized in that the control device (42) has a memory (46) for storing the predefined functional relationship between the distance change and the print head speed.
8. Printing device according to one of Claims 5 to 7, characterized in that, outside the area (12) on the print backing support (10) intended for the printing medium (14) to rest on, at least one calibration threshold, (48) for calibrating the sensor arrangement (40) is arranged in the sensing path of the sensing element (26).

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