EP0453472A1

EP0453472A1 - Process for controlling the operation of a printing head.

Info

Publication number: EP0453472A1
Application number: EP90901786A
Authority: EP
Inventors: Ralph Baeuerle; Dietmar Kottwitz; Michael Mantwill; Joachim Schwarzkopf
Original assignee: Wincor Nixdorf International GmbH
Current assignee: Wincor Nixdorf International GmbH
Priority date: 1989-01-12
Filing date: 1990-01-10
Publication date: 1991-10-30
Anticipated expiration: 2010-01-10
Also published as: DD291512A5; KR910700151A; JPH03505712A; DE3900765C2; DE3900765A1; WO1990008039A1; DE59002754D1; EP0453472B1; KR950010444B1; JP2573422B2; ES2043357T3; US5219233A

Abstract

Un procédé de commande du fonctionnement d'une tête d'impression permet de reconnaître des perturbations dans le transport de la tête d'impression le long d'une ligne d'impression et le cas échéant de les éliminer. Une unité de commande (24) commande une source de courant (16) qui alimente en courant un moteur (12) de déplacement d'une tête d'impression (10). Les éléments d'impression (14) de la tête d'impression (10) sont alimentés en un courant pulsé d'attaque (ID) par un module d'attaque (18). Un capteur de position (20) détecte le chemin parcouru par la tête d'impression (10) le long d'une ligne d'impression. Le temps de transport entre deux positions d'impression est contrôlé, et lorsqu'une valeur limite (G) est dépassée, l'entraînement de la tête d'impression (10) est interrompu et le cas échéant la tête d'impression est déplacée en sens opposé et/ou au moins un élément d'impression (14, 15) fonctionne alors avec une énergie réduite par rapport à l'énergie requise pour l'impression. Ces mesures permettent de reconnaître et d'éliminer automatiquement une perturbation provoquée par l'adhérence d'un élément d'impression (14) au ruban encreur.A method of controlling the operation of a print head makes it possible to recognize disturbances in the transport of the print head along a print line and if necessary to eliminate them. A control unit (24) controls a current source (16) which supplies current to a motor (12) for moving a print head (10). The printing elements (14) of the printing head (10) are supplied with a pulsating driving current (ID) by a driving module (18). A position sensor (20) detects the path traveled by the print head (10) along a print line. The transport time between two printing positions is checked, and when a limit value (G) is exceeded, the drive of the print head (10) is interrupted and if necessary the print head is moved in the opposite direction and / or at least one printing element (14, 15) then operates with reduced energy compared to the energy required for printing. These measurements make it possible to automatically recognize and eliminate a disturbance caused by the adhesion of a printing element (14) to the ink ribbon.

Description

Method for controlling the operation of a printhead

The invention relates to a method for controlling the operation of a printhead, which is moved from the printing position in a predetermined direction and within a predetermined transport time to a further position after the printing of a drawing element or a character in each case by actuating at least one printing element, wherein the transport time is monitored for exceeding a limit value and the drive of the print head is interrupted when the limit value is exceeded.

Methods of this type are used in printers for printing text, data or image information. They serve to bring a printhead into a predetermined printing position and then to produce an impression on a carrier, for example paper, by actuating at least one printing element. For this purpose, an ink ribbon is arranged between the print head and the carrier, which comes into contact with the carrier when the printing element is actuated. With a large number of printers, the information to be printed is printed character by character, i.e. the printhead is shifted in the line direction and carries out the printing process.

After a line has been printed, the print carrier is moved one line spacing, for example by a roller, and a new cell-shaped printing process takes place. During printing, the current position of the printhead is recorded in one line and can be reported by a position signal to a controller which actuates a printing element to print a character when a specific position is reached. This principle can be used both in interval-controlled operation, in which the movement of the print head is interrupted and the printing element is then actuated, and in so-called "flying" printing. at the latter is the printhead for printing one

Character not silent, but the printing element is operated without interrupting the movement of the print head along the line.

When a printhead is in operation, it can happen that it adheres to the printing medium, that is to the ink ribbon or to the carrier, after actuation of a printing element. For example, in the case of a needle printhead, the printing elements of which are needles, a needle actuated for printing can pierce the ribbon and hook into it, i.e. it does not return to its resting position. When the print head moves to the next print position, the needle is bent or broken by the relative movement between it and the ink ribbon. Both mean destruction of the entire print head. This risk is increased in newer dot matrix printers by the fact that the number of needles per print head is high and thin needles are used which can pierce the ribbon more easily. Even in the case of printing processes which do not use an ink ribbon but instead use so-called active paper as a support, it can happen that a printing element penetrates into the support and adheres to it by hooking it.

With other printing methods it can also happen that the printhead and the ribbon stick together. For example, in the thermal printing process, in which the printing elements are electrical heating resistors which transmit characters to the printing medium with the aid of a melting ink ribbon, the risk of printing elements of the printing head sticking to the melting material adhering to the ink ribbon. The ribbon made of plastic film can also adhere to the printing elements due to overheating or surface defects and thus cause a malfunction of the printhead operation.

Furthermore, malfunctions during the transport of the printing caused by incorrectly inserted print media, paper jam or malfunctions in the drive. In all of these cases it would be desirable to identify these faults at an early stage in order to prevent damage to sensitive components.

It is therefore an object of the invention to provide a method for controlling the operation of a print head, in which transport malfunctions are recognized and, if necessary, eliminated.

This object is achieved for a method of the type mentioned above in that, in order to release adhesion between the printing element and a printing medium, the print head moves in the opposite direction to the predetermined direction when the limit value is exceeded and / or at least one printing element with that used for printing Energy reduced energy is operated.

The invention makes use of the knowledge that the forward movement of the printhead by the ink ribbon or the recording medium is prevented by the printhead and printing medium, that is to say the ink ribbon or recording medium, and that the next printing position is reached only with delay or not at all becomes. By monitoring the transport time, it is possible to detect a fault in the transport of the print head and to interrupt the drive of the print head. This prevents damage to the print head and measures can be taken to remedy the transport disruption. The position signal of the printer known per se is advantageously used as a criterion for reaching predetermined printing positions.

The invention now provides that the print head when the limit value is exceeded in to the predetermined opposite direction is moved. This simple measure alone can loosen the adhesion of the print head and print medium. For example, if a needle pierces the ribbon with a needle printhead and the ribbon tensions due to the further movement of the printhead, the backward movement of the printhead reduces the elastic tension between the needle and the ribbon to such an extent that the needle restoring force pushes the needle into a rest position in the printhead is sufficient to detach it from the ribbon.

Another possibility of eliminating the sticking of the print head and the ink ribbon is to actuate one or more printing elements, the energy applied for this being reduced compared to the energy used for printing a character. By actuating the printing element it is achieved that at the location where the ink ribbon and the printhead adhere to each other, energy is supplied which causes the two parts to be released from one another. For example, in the case of a thermal printer, when thermal energy is supplied, the adhesive connection between the print head and the melt ribbon can be softened and thus released. In the case of a dot matrix printer, mechanical energy is activated at the point at which the needle is hooked into the ink ribbon by actuating one or more printing elements. The tensile and compressive forces that occur at the point of adhesion, together with the restoring force of the needle, cause the needle to be released from the ink ribbon and return to its rest position.

A combination of the measures mentioned can preferably also be used. This can be done in such a way that the pressure elements during or after the backward movement of the. Printhead are operated. The two work together in such a way that the sticking together of the print head and the ribbon is released with high reliability. In a method according to the invention, the limit value, to which the time between the printing of a character and the occurrence of the position signal is monitored, is preferably set as a function of the type of printhead or of printing parameters. Such printing parameters are, for example, the speed at which the print head is moved, the type of ink ribbon or the energy to be used to actuate the printing element. Through these measures, it is possible the principle of the invention for a large number of printing 10 ^'köpfarten and for different printers with multiple operating modes to use.

In a practical development of the invention, the amount required to actuate the pressure element is reduced

15. Measure the energy so that no characters are printed yet. It is thereby achieved that the measures for eliminating the fault by the ink ribbon and print head adhering to one another leave no traces on the print carrier. The quality of the printing experience is therefore determined by these

20 were not affected.

An advantageous further development of the invention is also possible in that one or more pressure elements are actuated several times in succession with reduced energy. If this measure is used, for example, in dot matrix printers, this leads to a shaking movement between the needle and the ribbon. This type of movement supports the detachment of a needle hooked into the ribbon.

Another advantageous development of the invention can also be such that the print elements of the print head are operated simultaneously with reduced energy. For a needle print head, this means that all needles are deflected at the same time and press against the ink ribbon. There-

35 by the ribbon is moved in the direction of the print carrier ben and stripped from the hook hooked into it. In the case of a needle print head, the energy required to actuate the printing element is advantageously measured such that the needle stroke is reduced by approximately half. In practice, it has been found that with this stroke movement of the needle or a plurality of needles, an optimal result is achieved on the one hand when the needle adhering to the ink ribbon is loosened and, on the other hand, no character is printed on the print carrier with a high degree of certainty.

Another development of the invention is characterized in that, when the limit value is exceeded, a transport motor provided for moving the print head is short-circuited or driven with a counter current. As a result of this measure, the motor is braked electrically and the movement of the print head comes to a standstill after a very short distance. The ink ribbon and the print element of the print head are not stressed beyond their elastic limit, i.e. not damaged. In addition, this training shortens the total time required to eliminate the fault »

The method according to the invention can also be carried out in such a way that a transport motor provided for moving the print head is actuated with a predetermined number of current pulses for the movement in the opposite direction. These cause a jerky step movement of the printhead, which causes jerky tensile and compressive forces at the junction between the printhead and the ribbon. These help to loosen the adhesive connection between the print head and the ink ribbon. The number of current pulses is set depending on the type of transport motor, the printer, the ribbon and other print-specific parameters.

A further practical embodiment of the invention provides that the print head is positioned at the print position after a predetermined time which it had before the printout was exceeded Limit value, and that printing is continued at this position. The predetermined time is set depending on the type of the print head, the transport motor and other parameters of the printer. This further training guarantees an almost uninterrupted operation of the printer. However, if such faults repeat within a certain time, an error message can be generated in a further embodiment of the invention if a predetermined number of limit value violations is exceeded. This makes it possible to indicate a malfunction, which cannot be remedied by the method according to the invention, in order to initiate further measures, for example repair or replacement of the print head.

In a further expedient embodiment of the invention, such a measure can also consist in the fact that the operation of the print head is switched off within a predetermined time if the limit value is exceeded several times.

The method according to the invention is advantageously further developed in that after the drive interruption, when the limit value is exceeded, the direction of movement of the printing head is determined, and that if the direction is not reversed, a further error message is generated. This measure ensures that errors which are manifested in the fact that the limit value is exceeded and which cannot be attributed to the adherence of a printing element can be reliably detected. When a printing element adheres to the ink ribbon or to the print carrier, an elastic tension occurs, which results in a restoring force and thus causes a reversal of the direction of the print head. For example, after a printing needle is hooked into the ink ribbon, a needle printhead stretches it by a certain amount as a result of its kinetic energy, so that the restoring force that arises causes the print head to swing back. The reversal can be recognized, for example, on the basis of the position signal. If this reversal of direction does not occur, there is a malfunction, which was caused, for example, by a mechanical jamming of the print head or a paper jam. As a result, an error message can be generated or the print head can be interrupted.

An embodiment of the invention is explained below with reference to the drawing. In it shows

Fig. 1 shows the basic structure of a controller in

Block diagram for the operation of a printhead,

2 signal curves of the driver current for actuating a pressure element and of the position signal over time,

Fig. 3 is a logical flow chart of process steps and

Fig. 4 states and waveforms during normal operation and when a fault occurs.

1 shows various functional units of a control in a printer for operating a wire dot print head 10. This is moved back and forth along a printing line by a transport motor 12. The transport motor 12 is supplied with a motor current IM from a current source 16. The needle print head 10 has, as printing elements, needles 14 which are arranged in columns or in the form of columns in the print head 10 and the number of which, depending on the type of print head, is 7, 9, 12 or more. A needle 15 is shown separately, which will be discussed later in the description of a fault. When printing, the needles 14 are actuated by electromagnetic actuators, and from them 1 rest position in the print head 10 deflected and pressed against an ink ribbon that transfers a character to a print carrier. The electro-mechanical actuators (not shown in FIG. 1) are made up of a driver module 18

5 pulse-shaped driver current ID supplied, wherein the supplied electrical energy can be varied by varying the duration and the level of the current pulses.

The 10 path covered by the print head 10 along a print line is detected by a position sensor 20. This can be a commercially available distance encoder which generates two signals which are phase-shifted by 90 ° at predetermined intervals. On the basis of this, the distance traveled by the print head 10 and the direction of movement of the signals by comparing 15 the phase position of the signals can be determined by counting coding pulses. The position transmitter 20 therefore outputs a position report signal PMS to the control unit 24, which has both information about the current position of the print head 10 and about its current direction of movement. 20th

To carry out the printing process, the control unit 24 receives further control information via a data line 26, such as the character to be printed, the printing speed, start and end of a printing process. From the total

^{• ** ■■ •>} ness of this information, the control unit 24 Steu¬ ersignale they berbaustein to the power source 16 and to the write Trei¬ 18, whereby the movement of Transport¬ motors 12 and placing of characters is controlled. The control unit 24 contains various for executing them

30 functions a microcomputer, which is equipped with program and data storage and a timer unit. This type of control of a wire dot print head is known per se and is therefore not explained in detail. 5 To carry out the method according to the invention, the control unit 24 has access to further control modules 30 to 36, which are contained as software programs in a read memory 22 (ROM). These control modules include a monitoring module 30, which monitors the time between the actuation of a pressure element 14 by a driver current pulse ID and the arrival of a position signal PMS for a limit value G. The control module 32 serves to control the direction of rotation of the transport motor 12 in the event of a fault. The control module 34 is provided to generate a predetermined number m of motor current pulses which are emitted to the transport motor 12, which the latter converts into step movements. Finally, the control module 36 generates a predetermined number n of pulses which indirectly actuate the pressure elements 14 via the driver module 18. A fault indicator 28 is also connected to the control unit 24, which is triggered in the event of a fault and reports an operating error.

2 shows waveforms of the position signal PMS via the driver current ID. The signal states are designated with logic 1 and logic 0 and indicate a current flow or an idle state. The signal profiles differ in normal operation A and in the event of a fault B. In normal operation A, the print head 10 is moved along a line and one or more needles 14 are actuated in the so-called "flying" print. Printing processes are described below with the aid of the needle 15, which is shown separately in FIG. 1. With the type of printer described here, the ink ribbon is stretched along a line and is not moved back and forth with the print head. With a rising edge 40 of the driver current ID, the needle 15 is deflected in the direction of the ink ribbon with a slight delay, which is caused by the inertia of the electromechanical actuator. Which is made of a fabric-like material standing ribbon is pressed against the print carrier by the tip of the needle 15, whereby it forms a punctiform symbol on it. If several needles are actuated in this way, a column-shaped or mosaic-shaped print character is created on the carrier. After the needle 15 has been actuated, it is normally retracted into its rest position in the needle print head 10 by its restoring force.

With a falling driver current edge 42, the monitoring module 30 becomes active, which monitors the time T until the arrival of the next position signal PMS for exceeding the predetermined limit value G. This limit value is set as a function of print-specific parameters, such as the type of print head or the print speed. In normal operation A, the time T is less than the limit value G, which means that the printing process is proceeding properly.

In case B, the printing operation is disturbed, ie the print head 10 does not reach the next position signaled by a rectangular pulse of the position signal PMS after the driver current ID has dropped in the prescribed time. There can be several reasons for this. For example, a paper jam or incorrectly inserted paper can hinder the forward movement of the print head 10. Such a fault can generally only be remedied by an operator. Another frequently occurring disturbance arises from the fact that one of the needles 14, for example the needle 15, punctures the tissue of the ink ribbon during its lifting movement and adheres to the ink ribbon. The fixed ink ribbon now inhibits the movement of the print head 10, so that the time T to reach the next position exceeds the limit value G. Such a disturbance is therefore reliably detected by time monitoring. This disturbance is automatically remedied by the method steps of the invention, as will be explained in the following. The control functions of the control unit 24 which take place during normal operation and in the event of a fault are shown in FIG. 3 in the form of a flow chart. In a first step 50, as already described, the print head 10 is moved along the line by the transport motor 12 and its current position is determined on the basis of the position signal PMS by counting pulse edges. To print a character at a predetermined position (step 52), the needles forming the character are selected from the printing elements 14 and the corresponding electromechanical actuators are also selected

Driver current ID controlled. With the falling edge of the driver current ID, a time monitor becomes active in the next step 54, which determines whether the pulse edge of the position signal PMS arrives within the limit value time G (step 56). The time monitoring is implemented with the aid of a counter, which is loaded with an initial count that is proportional to the limit value G. When the time monitoring is started, the count is decremented in time with a clock signal derived from the timer unit of the microcomputer. If a position reporting signal PMS occurs before the count 0 is reached, then the printing process is correct and the program branches to step 50 in order to continue the printing process. If so much time elapses until the position signal PMS arrives that the count o is reached, the process branches to the next step 58, in which a query for flour malfunction is carried out, the meaning of which will be explained later. If there is no multiple fault, the transport motor 12 is braked in the next step 59 in order to interrupt the movement of the print head 10. This is done by short-circuiting the motor winding of the transport motor 12, a high delay resulting from the eddy current effect. It would also be conceivable to control the motor winding with a current of opposite polarity, which would further increase the delay. A high deceleration is therefore desirable in order to head 10 as completely as possible by the transport motor 12, thereby reducing the risk of tearing the ribbon or bending the needle 15.

In the following step 60, braking is terminated. The ink ribbon, which is stretched elastically by hooking the printing needle into the ink ribbon, can now relax and takes the print head with it in the relaxation direction, which is signaled by the position sensor 20 when the direction of movement is reversed. In step 61, the reversal of direction is evaluated. If the direction reversal does not occur, there is a malfunction such as a break in the drive connection between the motor and the printhead or a paper jam. It then branches directly to step 70, in which an error avoidance is generated. If the direction is reversed, the direction of motor rotation is reversed in step 62, ie the direction of movement of the print head 10 is now opposite to that before the fault. The motor winding is then actuated with a predetermined number m of current pulses IM (step 64), as a result of which the print head 10 executes jerky step movements which bring about or support the release of the needle 15 from the ink ribbon. The number m of current impulses IM as well as their height and pulse width is dimensioned such that the print head 10 returns approximately to the position it was in before the fault. As a next measure 66, all needles 14 of the print head 10 are actuated. For this purpose, n current pulses of defined width from driver module 18 are output as driver current ID to the electro-mechanical actuators of the needles 14. The energy supplied to the actuators is adjusted by changing the pulse width in such a way that the needles 14 execute about half a stroke. During this movement, the needles 14 are pressed against the ink ribbon and strip it off the needle 15 adhering to it. The reduced stroke movement avoids the printing of a character on the print carrier. Still arises by the multiple actuation of the needles 14, a shaking movement which supports the detachment of the needle 15 from the ink ribbon. The actuation of the needles 14 can already be carried out before or during the braking of the transport motor 12 and during the jerky backward movement of the print head 10. If the pressure elements 14 are actuated only after the backward movement of the print head 10, this has the advantage that the ink ribbon is relaxed, so that no transverse forces are exerted on the hooked needle 15.

In the subsequent step 68, the direction of rotation of the transport motor 12 is reversed again, so that the direction of movement of the print head 10 coincides with that prior to the fault.

As already mentioned, a query for multiple faults is carried out in step 58. This serves to detect a multiple occurrence of an interruption or a delay in the movement of the print head. Such successive faults can be caused, for example, by a paper jam, a defective ink ribbon or a needle hooked very firmly into the ink ribbon. If such faults occur several times within a predetermined time, then after a predeterminable number of attempts at exemption, a branch is made to step 70, where an error message is generated and displayed. The operator of the printer can then arrange for maintenance or repair of the device. Of course, such an error message can already be generated when a single fault occurs, it then being possible to statistically analyze the errors that occur. After displaying the multiple trouble, the operation of the print head is interrupted in the present example (step 72 4 shows various states during the operation of the print head 10 over the time t. Shown are the temporal courses of the directions of movement of the print head 10 (DK right, DK left), the position signal PMS, the driver current ID for actuating the print elements 1 and the fault status S. At time t = 0, the print head 10 becomes in the line direction from the left moved to the right. Its path is signaled by the position signal PMS in the form of rectangular pulses. A driver flow ID flows, which means that the printing element 15 is being actuated and a character is being printed. With falling edge 80 of driver current ID, the time monitoring is activated and the time T until the arrival of the rising pulse edge of the position signal PMS is measured. If this is less than the limit value G, there is no fault S, whereupon the time monitoring is reset to an initial state and restarted with the next falling edge 82 of the driver current ID. This time the time T reaches the limit value G, which is the condition for the existence of a fault S. Now the measures for releasing a needle possibly sticking in the ink ribbon are initiated, ie the transport motor 12 is braked and gradually moved to the left in the opposite direction. Then all needles 14 are driven with a fixed number of driver current pulses ID, the

Pulse width b compared to which is reduced with normal actuation of a pressure element. After the printing elements 14 have been actuated several times, the fault S is generally eliminated, and the printing head 10 is moved again in its original direction and continues printing.

Claims

1 patent claims

1. Method for controlling the operation of a print head, which after each by pressing

5 at least one printing element is printed, a drawing element or a character is moved from the printing position in a predetermined direction and within a predetermined transport time to a further position, the

10 transport time is monitored for the exceeding of a limit value and the drive of the print head is interrupted when the limit value is exceeded, characterized in that for releasing adhesion between the printing element and a

15 print medium, the print head (10) is moved in the direction opposite to the predetermined opposite direction when the limit value (G) is exceeded and / or at least one printing element (1 _r 15) is actuated with energy 20 which is reduced compared to the energy used for printing.

2. The method according to claim 1, characterized in that the limit value (G) depending on the type of print head (10) or printing parameters ein¬

25 poses.

3. The method according to claim 1 or 2, characterized gekenn¬ characterized in that the reduced energy is dimensioned such that when actuating the pressure element (14,

30 15) no character is printed.

4. The method according to any one of claims 1 to 3, da¬ characterized in that the pressure element (14, 15) with reduced energy several times in succession -, _£ - is actuated.

5. The method according to any one of claims 1 to 4, da¬ characterized in that the printing elements (14, 15) of the print head (10) are operated simultaneously with reduced energy.

6. The method according to any one of claims 1 to 5, da¬ characterized in that the reduced energy for actuating the as in a needle print head (10)

Needle (14, 15) trained pressure element is dimensioned so that the needle stroke is reduced by about half.

7. The method according to any one of the preceding claims, characterized in that when the limit value (G) is exceeded, a transport motor (12) provided for moving the print head (10) is braked, preferably in that it is short-circuited or driven with a countercurrent.

⁸ - Method according to one of claims 1 to 7, characterized in that for the movement in the opposite direction a transport motor (12) provided for moving the print head (10) with a predetermined number (m) of current pulses ( IM) is activated if necessary after braking.

9. The method according to any one of the preceding claims, characterized in that the print head (10) is positio¬ ned at a predetermined time after exceeding the limit value (G) on the print position that it was in before the limit value (G) was exceeded, and that printing continues from that position.

10. The method according to any one of the preceding claims, characterized in that an error message is generated at a predetermined number of limit violations.

11. The method according to any one of the preceding claims, characterized in that the operation of the print head (10) is switched off within a predetermined time when the limit value is exceeded several times.

12. The method according to claim 1, characterized in that after the drive interruption, the direction of movement of the print head (10) is determined, and that in the absence of a reversal of direction another

Error message is generated.

13. The method according to claim 12, characterized gekennzeich¬ net that the operation of the print head (10) is interrupted in the absence of direction reversal.