A method and arrangement for monitoring the modus operandi of matrix printers

Abstract

 A matrix printer includes a printing head which incorpo­rates a plurality of printing needles (11), each of which can be maneuvered individually with the aid of a respec­tive electromagnetic maneuvering device (10), by means of which the printing needle (11), carried by a spring-bias­sed, movable armature (12), can be caused to carry out a working cycle, upon activation of the maneuvering device, this working cycle including a working stroke, during which the needle (11) is moved in a direction towards a printing anvil (20) for the purpose of printing a puncti­form sign on a record carrier (21) located in front of the printing anvil, and a subsequent return stroke, during which the printing needle (11) is returned to a withdrawn rest position. For the purpose of enabling simple inexpen­sive, but nevertheless reliable monitoring of the manner of working of the printer, it is proposed that the move­ment of at least one printing needle (11) during at least a part of a needle working cycle is monitored by detecting changes in the magnetic flux in the magnetic circuit (12, 14) of an associated maneuvering device (10) caused by movement of the needle (11).

Description

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

[0002] More specifically, but not exclusively, the invention relates to a method for monitoring the manner 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record carrier located in front of the anvil, and a subsequent return stroke, during which the needle is returned to a withdrawn rest position.

[0003] Such printers already operate at very high speeds, and could readily be caused to operate at still greater speeds, if it could be assured that an increase in their operational working speeds would not carry with it an increased danger of malfunctioning. For this reason stre­nuous efforts have been made in enabling reliable monitor­ing of the manner of operation of matrix printers of this kind while the printer is in operation. However, no such monitoring method which can be accepted in practice has been proposed hitherto.

[0004] Consequently, an object of the present invention is to provide a method for monitoring the manner of operation of a matrix printer of the aforesaid kind which can be carried out with the aid of simple and inexpensive means while nevertheless ensuring extremely reliable monitoring of the working function of said printer.

[0005] The method proposed in accordance with the invention for the purpose of achieving this object is characterized pri­marily by monitoring the movement of at least one printing needle or pin during at least a part of a needle working cycle, by detecting changes in the magnetic flux in the magnetic circuit of an associated maneuvering device caused by movement of the needle.

[0006] The invention eliminates those drawbacks encumbered by earlier proposed methods intended for monitoring the operational functioning of a matrix printer and based on an endeavour to detect needle movement with the aid of an optical sensor or by mechanical influence of the needle on a transducer intended herefor.

[0007] The inventive method enables the transition time at which the needle passes from a working stroke to a return stroke during a working cycle to be established with a high degree of accuracy, i.e. the time point at which the needle strikes against the record carrier, since the time derivative of the magneti flux in the magnetic circuit resulting from this reversal in the direction of movement of the armature carrying the needle changes sign at said time point.

[0008] Furthermore, the inventive method will also enable the time point at which the needle arrives at its rest posi­tion at the end of a working cycle to be readily establi­shed, since the time derivative of the magnetic flux at this time point will assume the value zero or, if the armature rebounds, the sign will change and thus pass the value zero.

[0009] The aforedescribed monitoring method can be utilized advantageously to control automatically the manner of ope­ration of the printer in dependence on the result thereof. Furthermore, the method can also be utilized to stop the printer or to indicate a fault, should the printer operate in an unsatisfactory fashion.

[0010] Examples of the different operating parameters which can be controlled or regulated in dependence on the aforesaid monitoring of needle movement include the time point at which the working cycle of a particular needle is initia­ted, the impact force of the needle against the record carrier and the distance betwen the printing head and anvil surface.

[0011] It will be understood that the invention is not restricted to the monitoring of one single printing needle, but that the proposed monitoring of needle movement can, instead, be applied to advantage on all needles of the printer.

[0012] The invention also relates to an arrangement for monitor­ing the manner of operation of a matrix printer of the aforesaid kind. This arrangement is characterized primari­ly in that it is intended to monitor the movement of at least one printing needle during at least one needle work­ing cycle, by detecting changes in the magnetic flux in the magnetic circuit of an associated maneuvering device caused by movement of the needle.

[0013] The arrangement may be equipped with any suitable kind of sensor for detecting said changes in the magnetic flux. For instance, the sensor may comprise a Hall effect ele­ ment exposed to said magnetic flux. The sensor, however, will preferably have the form of a winding arranged on a stationary part of the magnetic circuit. The advantage gained using such a winding as the required sensor is that the electric signal produced by the sensor will be propor­tional to the time derivative of the magnetic flux.

[0014] In accordance with one preferred embodiment of the inven­tion, the sensor winding comprises a winding used for generating a magnetic flux in the magnetic circuit. In this case, the sensor function is obtained without needing to supply the control and monitoring equipment with a separate sensor.

[0015] The invention will now be described in more detail with reference to the accompanying drawing, in which

Figure 1 is a simplified outline diagram which illustrates the construction of a matrix printer of the aforesaid kind, by showing a printing needle incorporated in the printing head and an electromagnetic needle maneuvering device, whereas

Figure 2 illustrates a combined drive and monitoring cir­cuit by means of which the manner of operation of the printer can be monitored, by monitoring the movement of the needle shown in Figure 1, and

Figure 3 is a time diagram which includes a plurality of curves illustrating needle movement during a needle work­ing cycle and also the occurrence of various electric sig­nals in the circuit according to Figure 2.

[0016] 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 exhibits along the major part of its length a stif­fening 12′ consisting of magnetic material.

[0017] 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.

[0018] 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 springy part of the arma­ture and which endeavours to hold the armature at a dis­tance from the stationary part 14.

[0019] 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.

[0020] 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.

[0021] 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 magneto-­motive force generated in the winding 15 by the current I₀.

[0022] 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 conductor 24. Each of the switches 23 and 28 con­sists of a steerable electronic switch, e.g. an MOS-tran­sistor.

[0023] 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.

[0024] 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.

[0025] 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.

[0026] 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 directly proportional to the time derivative of the magnetic flux in the magnetic circuit.

[0027] 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.

[0028] The information obtained with respect to the time points t₁ and t₂ can be utilized for controlling or regula­ting automatically the manner of operation of the printer with the aid of control equipment incorporated in the printer. Furthermore, this information can also be utili­zed to stop the printer automatically and/or to instigate the indication of a fault should the value of either one or both of the time points imply that the manner of opera­tion of the printer is unacceptable.

[0029] 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 sensor used to detect changes in the magnetic flux of the magnetic circuit of the needle maneuvering device need not consist of a winding, but may instead be in the form of a Hall effect element.

Claims

1. A method for monitoring 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 incoporates 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, characterized by monitoring the movement of at least one printing needle during at least a part of a needle working cycle, by detecting changes in the magnetic flux in the magnetic circuit of an associated maneuvering device caused by movement of the needle.

2. A method according to Claim 1, characterized by esta­blishing through said monitoring process the transition time point at which a printing needle passes from a working stroke to a return stroke during a working cycle of said needle.

3. A method according to Claim 1 or Claim 2, characterized by establishing through said monitoring process the time point at which a printing needle arrives at its rest posi­tion upon termination of a working cycle.

4. A method according to any of the preceding claims, cha­racterized by utilizing said monitoring of movement of a printing needle tor control or regulating automatically the manner of operation of the printer in dependence on the result of said monitoring process.

5. A method according to any of the preceding claims, cha­racterized by utilizing said monitoring process for stopp­ing the printer and/or instigating a fault indication should the printer operate in an unacceptable fashion.

6. An arrangement for monitoring the manner 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, characterized in that the arrangement is intended for monitoring the move­ment of at least one printing needle during at least a part of a needle working cycle, by detecting changes in the magnetic flux in the magnetix circuit of an associated maneuvering device caused by movement of the needle. 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, characterized in that the arrangement is intended for monitoring the move­ment of at least one printing needle during at least a part of a needle working cycle, by detecting changes in the magnetic flux in the magnetix circuit of an associated maneuvering device caused by movement of the needle.

7. An arrangement according to Claim 6, characterized in that it includes a sensor in the form of a winding arran­ged on a stationary part of the magnetic circuit.

8. An arrangement according to Claim 7, characterized in that the winding which functions as said sensor is formed by a winding used for generating a magnetic flux in the magnetic circuit.

9. An arrangement according to any of Claims 6-8, charac­terized in that the arrangement is intended for detecting a transition from a working stroke to a return stroke occurring during a needle working cycle.

l0. An arrangement according to any of Claims 6-9, charac­terized in that the arrangement is intended for detecting the arrival of a needle at its working position upon com­pletion of a working cycle.

Drawing