A method and an arrangement for controlling the method of operation of a matrix printer

Abstract

 A matrix printer comprises a printing head which includes a plurality of printing needles (11) each having a respective electromagnetic maneuvering device (10) by means of which the needle, carried by a spring-biassed, movable armature (12), can be caused to carry out a working cycle, which includes a working stroke and a subsequent return stroke. The maneuvering device (10) is activated by temporarily lowering the magnetomotive force in the magnetic circuit (12,14) of the device from a previous, constant value. The previously attracted armature (12) will herewith commence to move in a direction away from the stationary part (14) of the magnetic circuit as a result of the spring force acting on the armature. The magnetomotive force is then caused to return to its previous value. For the purpose of reducing the noise and wear generated by the armature (12) and to reduce the tendency of the armature to rebound, the armature is slowed down during the final stage of its return stroke, by again lowering the magnetomotive force temporarily for a limited part of the time taken to effect the return stroke.

Description

[0001] The present invention relates to a method for controlling the method of operation of a matrix printer.

[0002] More specifically, although not exclusively, the invention relates to a method for controlling the method of operation of a matrix printer of the kind which includes a printing head which is located in front of a printing anvil and is reciprocatingly movable in a direction substantially paral­lel with the anvil and which incorporates a plurality of printing needles each of which is capable of being maneuve­red individually with the aid of a respective electromagne­tic maneuvering device by means of which, when said device is activated, the needle, carried by a spring-biassed, movable armature, can be caused to carry out a working cycle which includes a working stroke, during which the needle is moved in a direction towards the anvil such as to print a punctiform symbol or some other graphic symbol on a record carrier located in front of the anvil, and a subse­quent return stroke, during which the needle is returned to a withdrawn rest position, wherewith activation of the maneuvering device is effected by temporary pronounced lowering of the magnetomotive force in the magnetic circuit of the maneuvering device, this magnetomotive force being maintained at a substantially predetermined constant value prior to this activation, such as to permit the armature previously located in a magnetically attracted position to begin to move away from the stationary part of the magnetic circuit under the action of the spring bias on said arma­ture while forming an increasing air gap between the sta­tionary part and the armature, whereafter the magnetomotive force is restored to its predetermined value so as to give rise to an attractive force which strives to return the armature to its starting position.

[0003] One troublesome drawback with printers of this kind is that when the armature approaches its starting position as it completes a working cycle, the armature is moving at a very high speed. This results in a great deal of noise and wear. Furthermore, the armature is probe to rebound at relatively large rebound amplitudes.

[0004] Despite strenuous efforts, no acceptable solution to this problem has previously been found.

[0005] Consequently, it is the object of this invention to provide an improved method for controlling a matrix printer of the kind disclosed in the introduction which avoids the draw­backs associated with the solutions earlier proposed.

[0006] The inventive method proposed to this end is characterized primarily by braking the armature during the final stage of its return movement, by further lowering the magnetomotive force temporarily in said magnetic circuit.

[0007] This temporary lowering of the magnetomotive force enables the speed reached by the armature as it approaches its starting position to be greatly reduced without needing to extend the total time taken to effect this return movement of the armature to more than a very limited extent.

[0008] The further temporary lowering of the magnetomotive force can be controlled, for instance, in dependence on the result obtained when monitoring or observing the method of operation of the armature during a printing operation. Furthermore, said further temporary lowering of the magne­tomotive force can be controlled suitably with respect to the time at which it is commenced and/or the extent of its duration.

[0009] The invention also relates to an arrangement for control­ling the method of operation of a matrix printer of the kind disclosed in the introduction. The characterizing fea­tures of this arrangement are set forth in Claims 5-8.

[0010] The invention will now be described in more detail with reference to the accompanying drawings, in which

Figure 1 is a simple outline diagram which illustrates the principle construction of a matrix printer of the aforesaid kind, by showing a printing needle included in the printing head of the printer and an electro-magnetic device for maneuvering the needle, whereas

Figure 2 is a circuit diagram which includes a combined operating and monitoring circuit by means of which printer working operations can be monitored, by monitoring the movement of the needle shown in Figure 1; and

Figure 3 is a time diagram which shows a number of curves illustrative of needle movement during a needle working cycle and also illustrating various electric signals occur­rent in the circuit of Figure 2.

[0011] In Figure 1 the reference numeral 10 identifies generally an electro-magnetic device for maneuvering a printing needle or pin 11 of a matrix printer of the kind disclosed in the introduction. The needle 11 is rigidly mounted on one end of an arm 12, the other end of which is pivotally mounted on a pivot shaft 13. In practice, however, the requisite pivotal movement of the arm 12 can be obtained by means of an arm which comprises a springy, flexible element which is firmly attached at one end thereof and which exhi­ bits along the major part of its length a stiffening 12′ consisting of magnetic material.

[0012] The arm 12 forms a movable armature on the device 10, the magnetic circuit of which also includes a stationary, U-shaped part 14 made of magnetic material and having two windings 15 and 16 arranged thereon.

[0013] The reference numeral 17 identifies a thrust or pressure spring which is arranged between a rigid spring abutment 18 and the armature 12 and which strives to swing the armature 12 away from the stationary part 14 of the magnetic cir­cuit. In practice, however, this spring can be replaced with a spring bias which is found incorporated intrinsi­cally in a resilient or spring part of the armature and which endeavours to hold the armature at a distance from the stationary part 14.

[0014] A constant current I₀ is fed continuously through the winding 15 while the printer is in operation. This current is sufficiently high to hold the armature 12 in the illustrated, attracted position of abutment with a stop member 19, in spite of the spring bias acting on said armature.

[0015] The illustrated printing needle 11 and maneuvering device 10 are included, together with a plurality of further need­les and associated maneuvering devices, in a printing head of the printer, said head being movable reciprocatingly along a printing anvil or like counterforce surface 20 in a direction at least substantially parallel with the anvil. All printing needles can be maneuvered individually, so as to provide a punctiform print or the print of some other graphic symbol on a record carrier 21 located in front of the anvil 20. The record carrier 21 will consist normally of paper web on which a needle is able to print a symbol with the aid of a carbon ribbon or some like aid.

[0016] When the illustrated needle 11 is to print a symbol on the carrier 21, the maneuvering device 10 is activated, by sending a short current pulse i₁ through the winding 16. This current pulse produces a brief but pronounced lowering of the resulting magnetomotive force in the magnetic cir­cuit formed by the armature 12 and the stationary part 14. In response to the spring bias acting thereon, the armature will commence to move therewith in a direction away from the part 14 and towards the printing anvil 20 while forming a progressively increasing air gap between the armature and said part. When the current pulse i₁ ceases, the arma­ture, as a result of the kinetic energy obtained thereby during the duration of the current pulse, will continue to move in said direction towards the carrier 21 until the needle 11 carried by the armature strikes said carrier. The direction of armature movement is therewith changed and the armature is restored to its starting position by the attraction force exerted thereon from the stationary part 14 as a result of the magnetomotive force generated in the winding 15 by the current I₀.

[0017] The aforesaid current pulse i₁ in the winding 16 can be generated with the aid of the combined drive and monitoring circuit illustrated in Figure 2. As shown in this Figure, one end of the winding 16 is connected to the connection point between a switch 23 connected to conductor 22 on which a positive potential is applied and diode 25 which is connected to a conductor 24 of earth potential and which is provided with a resistor 26 which is coupled in parallel across the diode. The other end of the winding 16 is con­nected to the connection point between a diode 27 connected to the conductor 22 with a switch 28 connected to the con­ ductor 24. Each of the switches 23 and 28 consists of a steerable electronic switch, e.g. an MOS-transistor.

[0018] With the aid of the aforesaid circuit components, it is possible to impart to the current pulse i₁ in a known manner an appearance of the kind illustrated in Figure 3 such that the current pulse will comprise three mutually sequential parts i₁₁, i₁₂ and i₁₃. The two switches 23 and 28 are closed over the duration of the pulse part i₁₁, whereas only the switch 28 is closed over the dura­tion of the pulse part i₁₂. Both switches are open over the duration of the pulse part i₁₃.

[0019] The movement carried out by the needle 13 during a working cycle has been illustrated in Figure 3 with the aid of a curve, which shows the position s of the needle as a func­tion of time.

[0020] In addition to producing the aforedescribed drive pulse i₁, the circuit illustrated in Figure 2 also functions to enable movement of the needle 11 to be monitored during a working cycle, this working cycle comprising a working stroke and a return stroke of the needle. This monitoring process is achieved by detecting those changes in the mag­netic flux in the magnetic circuit formed by the stationary part 14 and the armature 12 during the common movement of said needle and armature which take place as a result of the consequentially occurring change in the length of the air gap between the part 14 and the armature 12.

[0021] In the case of the circuit illustrated in Figure 2, the winding 16 which serves to produce the drive pulse i₁, is utilized as the sensor means for sensing the aforesaid flux changes. The flux changes engendered in the winding 16 by movement of the armature will give rise to an electromotive force which is direclty proportional to the time derivative of the magnetic flux in the magnetic circuit.

[0022] The electromotive force generated in the winding is well suited for use in determining both the time point t₁ of the needle 11 and the transition of the armature 12 from a working stroke to a return stroke and also the time point t₂ at which the armature arrives back at its starting position at the end of a working cycle. This determination of said two time points is effected with the aid of a detector which is connected to the winding 16 and which comprises a transistor 29 and two resistors 30 and 31. Obtained on the output 32 of the detector is a voltage u_d which has the configuration shown in Figure 3 and from which both time points t₁ and t₂ can be read.

[0023] The information thus obtained in respect of the time points t₁,and t₂ is utilized to slow down the armature during the final stage of the return movement of the arma- ture to its starting position with the aid of control means included in the printer, such that the armature will have a much slower speed when it reaches its starting position. This braking of the armature is achieved by generating a further pulse i₂ in the winding 16 during a selected part of the time taken for the armature to return to its start­ing position, as illustrated in chain lines in Figure 3. This further current pulse results in a temporary lowering of the magnetomotive force in the magnetic circuit of the maneuvering device 10 and therewith damping or braking of armature movement.

[0024] The current pulse which functions as an armature movement damping pulse is preferably not generated until the print­ing needle, during a first working cycle, has performed an undampened movement with subsequent rebound, in accordance with the unbroken line s in Figure 3. The two time points t₁ and t₂ of this working cycle are then established and are subsequently utilized in controlling the generation of the damping pulse i₂ during subsequent working cycles. During these working cycles, the needle can be caused to move along the curve s′ shown in chain lines in Figure 3.

[0025] The invention is not limited to the aforedescribed and illustrated embodiment. Many alternative embodiments are conceivable within the scope of the invention. For example, the damping pulse i₂ need not be supplied through the same winding as the drive pulse i₁, but may instead con­ceivably be supplied through another winding disposed on the stationary part 14.

Claims

1. A method for controlling the working operation of a matrix printer of the kind which includes a printing head which is located in front of a printing anvil and is reci­procatingly movable in a direction substantially parallel with said anvil and which incorporates a plurality of print­ing needles each of which is capable of being maneuvered individually with the aid of a respective electromagnetic maneuvering device by means of which, when said device is actuated, a spring-biassed, movable armature carrying said needle can be caused to carry out a working cycle which includes a working stroke during which the needle is moved in a direction towards the anvil such as to print a puncti­form symbol or some other graphic symbol on a record carrier located in front of the anvil, and a subsequent return stroke during which the needle is returned to a withdrawn rest position, wherewith activation of the maneuvering device is effected by temporary pronounced lowering of the magnetomotive force in the magnetic circuit of said device, this magnetomotive force being maintained at a substantially predetermined constant value prior to said activation, such as to permit the armature previously located in a magnetically attracted position to begin to move away from the stationary part of the magnetic circuit under the action of a spring bias on said armature while forming an increasing air gap between the stationary part and the armature, whereafter the magnetomotive force is restored to its predetermined value so as to give rise to an attractive force which strives to return the armature to its starting position, characterized by braking movement of the armature during the final stage of its return movement, by further lowering the magnetomotive force in said magnetic circuit temporarily during a given part of said movement.

2. A method according to Claim 1, characterized by control­ling said further temporary lowering of the magnetomotive force in dependence on the result of a monitoring process carried out on the working method of the printer during its operation.

3. A method according to Claim 2, characterized by control­ling said futher temporary lowering of the magnetomotive force with respect to the time point of its commencement.

4. A method according to Claim 2 or Claim 3, characterized by controlling said further temporary lowering of the mag­netomotive force with respect to the length of its duration.

5. An arrangement for controlling the method of operation of a matrix printer of the kind which includes a printing head which is located in front of a printing anvil and is reciprocatingly movable in a direction substantially paral­lel with said anvil and which incorporates a plurality of printing needles each of which is capable of being maneou­vered individually with the aid of a respective electro­magnetic maneuvering device by means of which, when said device is activated, a spring-biassed, movable armature carrying said needle can be caused to carry out a working cycle which includes a working stroke, during which the needle is moved in a direction towards the anvil such as to print a punctiform symbol or some other graphic symbol on a record carrier located in front of the anvil, and a subse­quent return stroke, during which the needle is returned to a withdrawn rest position, wherewith said device is inten­ded to cause activation of the maneuvering device by tempo­rary pronounced lowering of the magnetomotive force in the magnetic circuit of said device, this magnetomotive force being maintained at a substantially predetermined constant value prior to such activation, so as to permit the arma­ture previously located in a magnetically attracted posi­ tion to begin to move away from the stationary part of the magnetic circuit under the action of a spring bias on said armature while forming an increasing air gap between the stationary part and the armature, whereafter the magneto­motive force is restored to its predetermined value so as to give rise to an attractive force which strives to return the armature to its starting position, characterized in that the arrangement is constructed in a manner such that movement of the armature is braked during the final stage of the return movement of the armature to its starting position, by causing a further, temporary lowering of the magnetomotive force in said magnetic circuit during a limi­ted part of the time taken to carry out this movement.

6. An arrangement according to Claim 5, characterized in that that arrangement is intended to control said further, temporary lowering of the magnetomotive force in dependence on the result of a monitoring process carried out on the working method of the printer during its operation.

7. An arrangement according to Claim 6, characterized in that the arrangement is intended to control said further, temporary lowering of the magnetomotive force with respect to the time point of its commencement.

8. An arrangement according to Claim 6 or Claim 7, charac­terized in that the arrangement is intended to control said further, temporary lowering of the magnetomotive force with respect to the extent of its duration.

Drawing