WIRE DOT IMPACT PRINTER

Abstract: A device for controlling the driving of a printing wire of a wire dot impact printer which effects the printing by impinging the printing wire upon a printing medium, and the amount of displacement is detected when the printing wire is moved or the printing timing is detected. Print recurring period of the printing wire, operation characteristics of the printing wire, or timing for driving the printing wire, is ajusted based on the amount of displacement of the printing wire or the printing timing that is detected. Therefore, there is provided the wire dot impact printer which performs the printing operation in an optimum manner and which effects the printing of high quality at all times.

Description: The present invention relates to a wire-dot impact printer capable of printing by striking a printing wire provided at a wire-dot printing head onto a printing medium, especially to a wire-dot impact printer adapted for high quality printing. GB-A-2 143 970 discloses a bidirectional drive printer actuator with feedback control and methods of operation to optimize the performance of impact type printing actuators. By monitoring the forward velocity of the print wire, a forward input power pulse can be varied as to magnitude and duration to maintain a desired predetermined velocity of the print wire up until the time of impact with minimum energy. Further, by monitoring position feedback signals generated as the print wire returns to a rest position, a reverse input power pulse and forward input power pulse can be modulated for magnitude and duration to maintain a desired rearward velocity of the print wire, and bring the print wire to a rest position in a minimum time, yet with a minimum of rebound off the back stop. There is illustrated in Fig. 1 a construction of a type of wire-dot impact printer adopted conventionally. In the same figure, designated at 100 is a centro I/F, 101 is a CPU, 102 is I/O LSI as an interface, 103 is a timer, 104 is a head driver, 105 is a wire-dot head, 106 is an operation switch, 107 is a line feed motor, 108 is a spacing motor. In the apparatus, the CPU 101 receives a printing date via the centro I/F 100 and supplies a control signal issued on the basis of the printing data to the timer 103, the head driver 104, the line feed motor 107 and the spacing motor 108 via the I/O LSI 102. The head driver 104 receives a control signal from the CPU 101 and a drive timing signal from the timer 103 for driving the wire-dot printing head 105 to effect printing. As the wire-dot printing head 105, there is an arrangement as illustrated in Fig. 2. In the same figure, designated at 110 are a plurality of printing wires (two printing wires are illustrated in the same figure) provided in the wire-dot printing head 105, 111 is a guide frame having a guide groove 111a, 112 is an armature for supporting the printing wires 110, and 113 is a plate spring for supporting the armature 112. Hereupon, designated at 114 is a base plate, 115 is an electromagnet composed of a core 115a and a coil 115b wound around the core 115a, 116 is a permanent magnet, 117 is a rack, 118 is a spacer, 119 is a yoke, and 120 is a clamp. The clamp 120 presses and holds the base plate 114, the permanent magnet 116, the rack 117, the spacer 118, the plate spring 113, the yoke 119, the front cover 111 in the manner that each of these members are laid one over another in turn and integrated. The armature 112 is supported at the side of a free end 113a of the plate spring 113 while a base end 110a of one of the printing wires 100 is fixedly mounted on a distal end 112a of the armature 112. A distal end 110b of the printing wire 110 is guided by the guide groove 111a of the guide frame 111 so as to strike a predetermined position of the printing paper (not shown). With the arrangement as set forth above, when the coil 115b of the electromagnet 115 is deenergized, the armature 112 is attracted to the side of the base plate 114 (downward direction in the figure) by the attraction force of the permanent magnet 116 against the resilience force of the plate spring 113. When the coil 115b is energized, a magnet flux of the permanent magnet 116 is cancelled by the magnet flux of the electromagnet 115 to release the armature 112 from the attraction force of the permanent magnet 116 to move the armature 112 toward the side of the guide frame 111 (upward direction in the same figure) by the resilience force of the place spring 113. At the same instant, the printing wire 110 provided at the armature 112 moves toward the side of the guide frame 111 and the distal end 110b thereof projects over the guide slit 111a and strikes the printing paper to effect printing. Fig. 3 is a circuit diagram of the timer 103 and Fig. 4 is a waveform of operation of the timer circuit 103. The timer 103 is a portion to adjust an optimum time for energizing the coil 115b on the basis of the voltage to be applied to the coil 115b. In the same figure, designated at 120 is an open-collector type NOT circuit, 121, 122, 123 are resistors, 124 is a diode, 125 is a capacitor, and 126 is a comparator. The timer circuit 103 operates as follows. Firstly, a signal t1 received from the I/O LSI 102 is applied to the NOT circuit 120 on the basis of the instruction from the CPU 101. The signal t1 becomes high level (5V) during the period of T1 as illustrated in Fig. 4. At the time when the signal t1 is in high level, an output of the NOT circuit 120 becomes low level (0V) whereby the electric charge of the capacitor 125 is sharply discharged. After the lapse of the time T1 and the signal t1 is returned to low level so that the capacitor 125 is re-charged by a drive power supply voltage Vh which is applied to the wire-dot printing head via the resistor 121 and the output voltage of the NOT circuit 120 increases. The comparator 126 compares a reference voltage Vr which is decided by the resistance values R122, R123 of the resistors 122, 123 and a power supply Vcc supplied to the logic circuit, which is expressed as R123/(R122 + R123) Vcc and the output voltage of the NOT circuit 120. An output signal t2 of the comparator 126 becomes high level during the output voltage of the NOT circuit 120 is lower than the reference voltage Vr while it returned to low level at the time when the output voltage of the NOT circuit 120 reaches the reference compare voltage Vr (after the lapse of time T2). Accordingly, in the case where the drive supply power voltage Vh is high the output voltage of the NOT circuit 120 reaches the reference voltage Vr quickly so that the time T2 when the output of the comparator 126 keeps high level is shortened. In the case where the drive supply power voltage Vh of the wire-dot printing head is low, the time when the output voltage of the NOT circuit 120 reaches the reference voltage Vr in a long period of time, hence the time T2 becomes long. Fig. 5 illustrates a circuit diagram of the head driver 104 and Fig. 6 is a waveform of operation of the head driver 104. In the same figures, denoted at 130 is a buffer gate, 131 is an AND gate, 132, 133, 134 are transistors, 135, 136 are resistors, 137, 138 are diodes, and 115b is the head coil as shown in Fig. 2. The head driver 104 operates as follows. Firstly, the buffer gate 130 receives the signal t2 (over drive signal) shown in Fig. 6 from the timer circuit 103 and applies the drive power supply voltage Vh to the head coil 115b. Since the AND circuit 131 receives an enable signal t3 from the timer circuit 103 and a print signal t4 from the I/O LSI 102, the signals t3 and t4 are ANDed at the AND circuit to issue an AND signal to the base of the transistor 134 via a resistor 136. The print signal t4 is a selection signal of the print wire corresponding to the characters to be printed. Accordingly, in the case where all the signals t2, t3 and t4 are high levels, both the transistors 133, 134 will be ON so that the drive power supply voltage Vh is applied to the head coil 115b. Then, the current Ih flows in the direction of the arrow H1 as shown in one dot one dash line in Fig 5, and the current value thereof is increased gradually as shown within a range F1 of Fig. 6. In the case where output of the signal t2 becomes low level after the lapse of time T2, the transistor 133 is OFF so that on the basis of a reverse electromotive force of the head coil 115b a circuit current flows in the direction of the arrow H2 as shown in two dotted and one dash line whereby the current value of the current Ih is gradually decreased as shown within a range F2. In the case where the output of the signal t3 becomes low level, the transistor 134 is OFF so that the current Ih flows in the direction of the arrow H3 as shown in three dotted and one dash line and the current value of the current Ih is sharply decreased as shown within a range F3. In the prior art as described above, in the case where the drive power supply voltage Vh of the wire-dot printing head is high the time T2 when the signal t2 becomes high level is shortened to thereby shorten the range F1 of the current Ih while in the case where the drive power supply voltage Vh is low the time T2 is lengthened to thereby lengthen the range F1 of the current Ih. That is, the current Ih is controlled corresponding to the variation of the power supply voltage VH to be applied to the head coil 115b in order to fix the time of the drive time required from the drive timing for instructing the printing wire 110 to start printing (timing where the signal t1 becomes from the low level to the high level) to the print timing where the printing wire 110 actually strikes the printing paper. Meanwhile, the drive time from the drive timing to the print timing are differentiated for each print wire by the variation of the interval between the printing wire 110 and the printing medium and magnetic interference of the head coil 115b in the wire-dot printing head 105. However, in the prior art as described above although the correction of the variation of the drive power supply volatage Vh of the head coil 115b is made with respect to the drive time of the wire-dot printing head 105, the drive timing for each printing wire 110 is same and not individually set for each printing wire 110. Therefore, there generates a timing divergence lag between each printing wire 110 for thereby producing a displacement of the printing position which results in deterioration of the printing quality. Furthermore, there was no means for correcting the variation of characteristics of each wire-dot printing head 105 and each printing wire 110 whereby the driving time of the printing wire 110 is not set to optimum for the wire-dot printing head 105 used at that time. In the case where the driving time is less than the optimum value, the energy required for operating the printing wire 110 is small to thereby weaken the striking force of the printing wire 110 againt the printing medium to deteriorate the printing quality. To solve the problem, in considering the variation of characteristic each for the wire-dot printing head 105 and the printing wire 110, the driving time is set to be somewhat longer to provide a margin to some extent for the driving time. However, there was such problems that adoption of the step has required much energy for operating the printing wire 110 to thereby firstly generate much heat in the head coil 115b, secondly, sometimes a thermal alarm function is operated for preventing the printing head from being highly heated for suspending the operation of the apparatus whereby a throughput is decreased. Furthermore, a minimum value of the print repetitive cycle due to driving of the wire-dot printing head 105 in the printing process is fixed. That is, a printing speed F (number/sec) (number of printing character per unit time) in the one line printing operation is gradually increased from the print starting position as illustrated in Fig. 7 and kept the same speed when it reaches a nominal printing speed Fn, and thereafter decreases gradually at the time close to the print ending position. Accordingly, the print repetitive cycle is gradually decreased at the print starting position and minimum at the constant printing mode and is gradually increased at the print ending position. An optimum value variable in various conditions exists in a minimum value in the printing operation during a prescribed cycle among the print repetitive cycles. For example, in case that the printing medium is one piece of paper, the time taken for actuation operation of the printing wire 110, striking of the printing medium by the distal end 110b thereof, and returning to the original position of the same (hereafter referred to as a flight time) is relatively a short period. This is caused because the energy when the printing wire 110 struck onto the printing paper is not fully absorbed in the printing paper in case that the printing medium is one piece of paper whereby the printing wire 110 is forcibly bounced due to the resilience force of the platen and the like for supporting the rear of the printing paper. Accordingly, in this case the flight time can be shortened to thereby shorten the print repetitive cycle and increase the printing speed. However, if the minimum value of the print repetitive cycle is determined in accordance with the flight time of the single paper in the case where coping papers as a printing medium composed of a couple of carbon papers, etc. lay one on another, the coping papers absorb the energy at the time of striking of the printing wire 110 greater than the case of single paper to thereby weaken the elastic bouncing force caused by the platen and the like so that the printing wire returns slowly to its original position. In such case, the flight time is longer, occasionally, than the print repetitive cycle so that the printing wire 110 can not return to its original position before next printing. As a result, it generated such a problem that the striking energy of the printing wire in next printing is insufficient for thereby considerably deteriorating the printing quality. There was proposed a method for controlling to decide the minimum value of the print repetitive cycle in view of the maximum time of the flight time which varies depending on the kind of the printing medium. This method requires that the wire-dot printing head can be used in the large print repetitive cycle which generates such a problem that the printing speed may be reduced than that to be effected by the inherent capacity of the wire-dot printing head. As another step, a method for controlling to switch the minimum value of the print repetitive cycle in several stages in accordance with the head gap is not a means to solve fully the problem since the flight time is controlled not only by the thickness of the printing medium but the material of the printing medium and also affected by the variation of the characteristic of the wire-dot printing head or variation of the power supply voltage. Accordingly, it is an object of the present invention to provide a wire dot impact printer to solve the aforementioned problems of the prior art in the manner of preventing the printing position from being got out by striking simultaneously a plurality of printing wires onto the printing medium, or correcting the variable of the characteristic for each printing wire, or setting the optimum print repetitive cycle whereby the high quality printing can be carried out. This object is solved by the invention claimed in claim 1 or in claim 2. With the above arrangement and the control method, it is possible to obtain the wire-dot impact printer eliminating the reduction of the printing speed, the deviation of the characteristic, or the getting out of the printing position for thereby carrying out the printing with high quality. Fig. 1 is a block diagram of a prior art; FIG. 2 is a longitudinal cross sectional view of a wire-dot printing head of Fig. 3; Fig. 3 is a circuit diagram of a timer circuit of Fig. 1; Fig. 4 is a waveform of operation of Fig. 3; Fig. 5 is a circuit diagram of a head driver of Fig. 1; Fig. 6 is a waveform of operation of head driver of Fig. 5; Fig. 7 is a graph showing variations of printing speed in the printing interval of one line in the prior art; Fig. 8 is a block diagram of a wire dot impact printer not forming an embodiment of the present invention but necessary for explaining it; Fig. 9 is a longitudinal cross sectional view of a wire-dot printing head according to an embodiment of the present invention; Fig. 10 is a plan view of a printing substrate; Fig. 11 is a perspective view showing a main portion of the printing substrate; Fig. 12 is a circuit diagram of an electrostatic capacitor sensor circuit of the printer of Fig. 8; Fig. 13 is a view explaining a principle of operation of Fig. 12; Fig. 14 is a waveform of operation of Fig. 13; Fig. 15 is a graph showing variations of output of the electrostatic capacitor sensor circuit relative to a displacement of a printing wire; Fig. 16 is a block diagram of a wire-dot impact printer according to an embodiment of the present invention; Fig. 17 is a block diagram of a characteristic extraction circuit; Fig. 18 is a waveform of operation of Fig. 17; Figs. 19(a), 19(b), 19(c), 19(d) are views showing respectively concrete examples of correction values stored in ROM; Fig. 20 is a block diagram of a wire dot impact printer according to another embodiment of the present invention; Fig. 21 is a block diagram of a drive time detection circuit; Fig. 22 is a waveform of operation of Fig. 21; and Fig. 23 is a view showing a concrete correction value Co in the case where a plurality of printing wires are simultaneously operated. In Fig. 8, designated at 1 is a centro I/F adopted as an interface for receiving the printing data, 2 is a CPU as a controller for controlling the operation of the whole apparatus, 3 is an I/O LSI as an interface, 4 is a timer circuit, 6a is a head drive, 6b is a head coil, 6 is a drive means for driving a printing wire having the head driver 6a and the head coil 6b, 7 is a wire-dot printing head having the printing wire, 8a is a sensor electrode, 8b is an electrostatic capacitor sensor circuit (hereafter referred to as sensor circuit), 8 is a variation detection means composed of a sensor electrode 8a and the sensor circuit 8b, 9 is a flight time detection circuit for detecting the flight time counting from actuation of the wire-dot printing head 7 to return of same to its original position, 10 is an operation switch 11 is a line feed motor for feeding a printing paper as a printing medium to the longitudinal direction, and 12 is a spacing motor for moving the wire-dot printing head 7 toward the width direction of the printing paper. The CPU 2 receives a printing data via the centro I/F 1 and supplies a signal issued from this printing data to the head drive 6a, the line feed motor 11 and the spacing motor 12 via the I/O LSI 3. The head driver 6a drives the wire-dot printing head 7 and carries out a printing operation on the basis of a signal received from the CPU 2 and a signal received from the timer circuit 4. The present embodiment having the arrangement as set forth above is different from the prior art shown in Fig. 1 in that the present embodiment has the variation detection means 8 and the flight time detection circuit 9, and in respect of the content of the control by the CPU 2. Accompanied by the arrangement, the arrangement of the wire-dot printing head 7 is different from that of Fig. 2. Although the timer circuit 4 is same as the prior art timer circuit, the timer circuit of the prior art is arranged in the manner that the timer circuit may be standardized for setting the drive timing of all the printing wires with a single timer circuit while the timer circuit of the present embodiment may not be standardized but provided in individual print wire. Since the other arrangement of the present embodiment is same as that of the prior art, the explanation thereof is omitted but the arrangement different from that of the prior art will be described hereinafter. An arrangement of the wire-dot printing head 7 will be described first. Fig. 9 is a longitudinal cross sectional view of the wire-dot printing head 7. In the same figure, designated at 20 is a plurality of printing wires provided in the wire-dot printing head 7 (two print wires are illustrated in the same figure), 21 is a guide frame having a guide groove 21a for guiding the printing wires, 20, 22 are armatures each composed of a magnetic material, 23 are plate springs for supporting the armatures 22, 24 is a base plate, 25 is an electromagnet having a core 25a and a head coil 6b wound around the core 25a, 26 is a printed circuit board having printed circuit for supplying a power supply to the electromagnet 25 and a connector terminal, 27 is a permanent magnet, 28 is a rack, 29 is a spacer, 30 is a yoke, 31 is a printed circuit board, and 32 is a clamp. The clamp 32 presses and holds the base plate 24, the permanent magnet 27, the rack 28, the spacer 29, the plate spring 23, the yoke 30, the printed circuit board 31, the guide frame 21 in the manner that these members are laid one on another in turn and integrated. The armature 22 is supported at the side of a free end 23a of the plate spring 23 while a base end 20a of one of the printing wires 20 is fixedly mounted on a distal end 22a of the armature 22. A distal end 20b of the printing wire 20 is guided by the frame groove 21a of the guide frame 21 so as to strike a predetermined position of the printing paper (not shown). Fig. 10 is a plan view of the printed circuit board 31, and Fig. 11 is a perspective of the main portion of the printed circuit board 31. As illustrated in the same figures, the printed circuit board 31 of the present embodiment has sensor electrodes 8a made of a copper foil and positioned in confronted relation with the armature 22 which sensor electrodes 8a are connected to connecter terminals 31a provided at the end of the printed circuit board 31 in accordance with the printed circuit. The printed circuit board 31 is coated by an insulating film for keeping insulation from the yoke 30. Accordingly, there generates an electrostatic capacitance between the sensor electrode 8a and the armature 22 and the capacitance value becomes smaller when the interval between the sensor electrode 8a and the armature 22 is larger while the capacitance value becomes greater when the interval between the sensor 8a and the armature 22 is smaller. With the wire-dot printing head 7 having the arrangement as set forth above, when the head coil 6b is deenergized, the armature 22 is attracted to the side of the base plate 24 (downward direction in the figure) by the attraction force of the permanent magnet 27 against the resilience force of the plate spring 23. When the head coil 6b is energized, a magnet flux of the permanent magnet 27 is cancelled by the magnet flux of the electromagnet 25 to release the armature 22 from the attraction force of the permanent magnet 27 to move the armature 22 toward the side of the guide frame 21 (upward direction in the same figure) by the resilience force of the plate spring 23. Hereupon, the yoke 30 constitutes a part of the magnetic circuit prepared by the electromagnet 25 and functions to stop the mutual interference of the sensor electrodes 8a. The displacement detection means 8 for detecting the displacement of the printing wire 20 will be described next. Fig. 12 is a circuit diagram of the sensor circuit 8b, Fig. 13 is a view of explaining a principle of Fig. 12, Fig. 14 is a waveform of operation of Fig. 13. In Fig. 13, designated at 40 is a digital IC (MSM74HCU04 made of Oki Electric Industry Co., Ltd.), 40a, 40b are MOSFET of internal equivalent circuits (field effect transistor). Designated at 41 is an oscillator, 42 is a resistor, 43 is an integrator, and 44 is an ac amplifier. With the circuit set forth above, the sensor electrode 8a is connected to an output terminal of the digital IC 40 while a square shaped signal S OSC shown in Fig. 13 from the oscillator is applied to the input terminal of the digital IC 40 for thereby permitting a current I C to flow at the output terminal of the digital IC 40. The current I C is a charging/discharging current to be supplied to the sensor electrode 8a so that the FETs 40a, 40b are alternately turned on or off on the reception of the signal S OSC . The discharging current I S flows to ground via the FET 40b, the resistor 42. A value of the integration of the discharging current I S for one periodic cycle corresponds to quantity Q of an electric charge to be substantially charged in the sensor electrode 8a. Assuming that an electrocapacitance of the sensor electrode 8a is C X , an oscillation frequency of the oscillator 41 is f, a resistance value of the resistor 42 is R S , an amplification factor of the amplifier 44 is a times, the mean value of the current I S will be f·Q = f·C X · V DD while the output voltage of the amplifier will be V Q = C X · R S ·a·f·V DD whereby the desired voltage V Q proportional to the electrocapacitance C X is produced. However, actually the amplifier 44 is composed of an ac amplifier so that the offset (dc) such as the distribution capacitance etc. existing other than the sensor electrode 8a is cut off and only the displacement of the printing wire 20 is produced. Accordingly, the relationship between the displacement of the printing wire 20 and the output voltage V Q of the sensor circuit 8b is illustrated in a graph of Fig. 15 since the electrostatic capacitance of the sensor electrode 8a is approximately inverse proportional to the distance between the sensor electrode 8a and the armature 22. Fig. 16 is a block diagram of a wire dot impact printer of a first embodiment of the present invention. In the same figure, designated at 120 is a CPU as a controller for controlling the operation of the whole of the present apparatus and has inside thereof a RAM 2a and ROM 2b (read only memory) as a memory. Designated at 140 is a timer circuit and has a plurality of registers 4b and comparators 4c. Designated at 190 is a characteristic extraction circuit (characteristic extraction means) for detecting the time counting from when the head driver 6a received an printing actuation instruction until the printing wire can operate and the maximum displacement of the printing wire. The other arrangements are same as those explained in Fig. 8. According to this embodiment, the CPU 120 receives the print data via the centro I/F 1 and supplies the signal issued from the print data to the timer circuit 140, the head driver 6, the line feed motor 11, and the spacing motor 12 via the I/O LSI 3. The head driver 6a drives the wire-dot printing head 7 to effect printing operation on the basis of the signals received from the CPU 120 and the timer circuit 140. This embodiment having the arrangement set forth above is different from the prior art as illustrated in Fig. 1 in that this embodiment has the timer circuit 140 and the characteristic extraction circuit 190 and in respect of different content of control to be made by the CPU 120 provided with ROM26. Accompanied by these differences, the arrangement of the wire-dot printing head 7 is different from that of Fig. 2. Other arrangements are fundamentally same as those of the prior art or those of Fig. 8. Hence, the explanation thereof is omitted and the different arrangements will be described. The characteristic extraction circuit 190 will be described first. Fig. 17 is a block diagram of the characteristic extraction circuit 190 and Fig. 21 is a waveform of operation of the characteristic extraction circuit 190. In the same figures, designated at 150 is a differentiator, 151 is a comparator, 152 is a clamping circuit, 153 is an analog switch, 154 is a hold capacitor, 155 is a 4-bits A/D converter, 156 is D flip-flop circuit, 157 is an AND circuit, 158 is a 8-bits binary counter, 159 is a 8-bits D latch, 160 is a 4-bits D latch, 161, 162 are one-shot multivibrators (hereafter referred to as multivibrator), and 163 is a variable resistor. With the arrangement set forth above, the differentiator 150 receives a signal A from the sensor circuit 8b. The signal A is differentiated by the differentiator 150 and produced as a signal B while the comparator 151 compared a comparator voltage M produced by the variable resistor 163 with a voltage of the signal B to produce a signal C. The signal C will be 5V at high level and 0V at low level. The signal C is supplied to an input Reset of the D flip-flop circuit 156 and to an input Gate of the analog switch 153. Hereupon, a drive start signal D showing a drive actuation is applied to the inverse time 1 µs multivibrator 161 from the I/O LSI 3. The multivibrator 161 starts to operate after detecting the leading edge of the signal D and issues a signal E which is inversed 1 µs later. The signal E is applied to an input Clock of the D latch 159, an input Clock of the inverse time 1 µs multivibrator 162 and to an input convert actuation timing of the A/D Converter 155. The multivibrator 162 receives the signal E as a trigger signal and starts to operate after detecting the trailing edge of the signal E to thereby issue a signal F which is inversed after 1 µs later and supplied to an input Clock of the D flip-flop circuit 156, an input Reset of the counter 158 and input Clock of the D latch 160. Accordingly, at the time when the drive start signal D goes to high level, the multivibrator 161 is inverted to thereby permit the D latch 159 to latch the value of the counter 158. The multivibrator 162 is inverted, just after latching of the D latch 159, to reset the counter 158 and set the D flip-flop circuit 156 at the same time. The AND circuit 157 receives a signal G issued from an output Q of the D flip-flop circuit 156 and a clock of 500 kHz which are applied to the AND circuit and are ANDed to produce an AND signal H which is applied to an input Clock of the counter 158. Hence, the D flip-flop circuit 156 is set and the counter 158 counts the signal H at the time when the signal G keeps high level. Hereupon, the D flip-flop circuit 156 is reset and the signal G is inverted to the low level when the output signal C of the comparator 151 rises up to high level. The rising and the dropping of the signal C corresponds to an operation position of the printing wire 20. That is, the time when the signal C rises accords with the time when the printing wire 20 starts to operate while the time when the signal C drops accords with the time when the printing wire 20 strikes onto the printing paper. Accordingly, the output signal G of the D flip-flop circuit 156 keeps high level during the period from the application of the drive start signal D until the actuation of the printing wire 20, and the counter 158 counts the period. The counted value is latched by the D latch 159 just after the application of the drive start signal D, and the value of the counter 158 is cleared after latching. The value latched by the D latch 159 is supplied to the I/O LSI 3 as a 8-bits signal I and read by the CPU 120. A time resolution of the count value is 2 µs. The signal A is applied also to the clamping circuit 152 and dc of the output J of the clamping circuit 152 is regenerated as illustrated in Fig. 18 and the lower end of the waveform is clamped to 0V. The output J is applied to the analog switch 153 which is open or closed by the output C of the comparator 151 while the output K of the analog switch 153 is applied to an input terminal of the A/D converter 155 connected to the hold capacitor 54. The analog switch 153 is turned on when the signal C is in high level during which time the hold capacitor 154 is charged. At the time when the signal C is returned to low level, the analog switch 153 is turned off so that the voltage of the signal K is stored by the hold capacitor 154. Since the time when the analog switch 153 is turned off accords with the time when the displacement of the printing wire 20 is maximized, an up-to-date maximum value (latest head gap data) is at all times stored in the signal K. The multivibrators 161, 162 are successively inverted by the next drive start signal D for thereby issuing the convert starting signal to the A/D converter 155 and then issuing a clock signal to the D latch 160. An output value of the D latch can be read out by the CPU 120 via the I/O LSI 3. According to this embodiment, each printing wire is provided with the circuit of Fig. 17 and the maximum data about the displacement for each printing wire is obtained during the period between the actuation of driving and the actuation of printing. The timer circuit 140 will be described with reference to Fig. 16. The timer circuit 140 comprises, as shown in the same figure, a counter 4a, a group of registers 4b and a group of comparators 4c wherein the counters are counted up one by one in a prescribed period (2 µsec) counting from 0 by the counter 4a, while the registers 4b set the timer value individually for each printing wire 20. The timer values written in the registers 4b are compared with the value of the counter 4a by the comparators 4c which detect the timing when the value of the counter 4a exceeds over the values of the registers 4b and supply a drive timing to the head driver 6. A process for determining an optimum correction value by the CPU 120 will be described. There are an overdrive signal and an enable signal for each printing wire 20 as the value to be determined by the timer circuit 140. The determination of the overdrive signal is first described hereinafter. A table showing a timer correction value in Fig. 19 is stored in the ROM 2b of the CPU 120 and comprises four tables, namely, a correction number C1 for the number of printing wires effecting simultaneous printing as shown in the same figure (a), a correction number C2 for a past record (number of printing wires effecting previous printing) as shown in the same figure (b), a correction number C3 for a head gap as shown in the same figure (c), and a correction number C4 for a variation of the printing wire as shown in the same figure (d). The correction numbers set forth above may be stored in the RAM 2a but according to the present embodiment they are supplied from a host unit (not shown). The correction number C1 for the number of printing wires effecting simultaneous printing corrects a power supply voltage drop and a magnetic interference with in the wire-dot printing head while the correction number C2 for the past record corrects an affection of the past printing record. The correction number C3 for the head gap corrects the variation of the head gap while the correction number C4 for the variation of the printing wire corrects the variation of period lasting from issuance of the drive instruction until actual actuation of the operation of the printing wire. Inasmuch as the number of printing wires for effecting printing and the data of the past record of the previous printing during the period between the present printing operation and the next printing operation are known from the printing data obtained via the centro I/F, the correction number C1 for the number of printing wires effecting simultaneous printing and the correction number C2 of the past record can be selected from the table stored in the ROM 2b. It is possible to know the head gap data for each printing wire and operation time-current characteristic of the period lasting from actuation of driving until the actuation of the operation of the printing wire by reading out the values of the latch 159 and the latch 160 of the characteristic extraction circuit 190 whereby the correction number C3 for the head gap and the correction number C4 for the variation of the print wire can be selected by the table stored in the ROM 2b. Inasmuch as the characteristic extraction circuit 190 according to the present embodiment have 8-bits counter 159 and a 4-bits A/D converter, and a clock pulse of 500 kHz applied to the counter with a resolution of 2 µs, the timer correction table is prepared in view of this. The correction number C3 can be selected from the values 0 to 15 which are obtained by 4-bits resolution of head gap data stored in the D latch 160. The time data resolution stored in the D latch 159 is 2 µs and this value (standard value) is 100 (equivalent to 200 µs) since the present embodiment adopts the standard wire-dot printing head, the correction number C4 for variation of the printing wire is selected from the value obtained by reduction of 100 from the D latch. Since no printing operation is carried out before determining the correction numbers, the values in the D latches 159, 160 are void so that 0 is selected as the correction number. According to the present embodiment provided with a standard wire-dot printing head, the value (equivalent to standard value) was 150 (equivalent to 300 µs), the timer value to be written in timer circuit becomes the value of the sum of C1 + C2 + C3 + C4 plus 150. As described above, the characteristic extraction circuit 190 according to the present embodiment extracts, on the basis of the displacement data of the printing wire 20 issued by the sensor circuit 8b, the operation time-current characteristic for each printing wire 20 such as a time data for the period lasting from application of drive actuation signal to the head driver until the actual actuation of operation of the printing wire 20 or time data for the period lasting from actuation of operation of the print wire 20 until striking the printing paper by the print printing wire. Since the ROM 2b stores preliminarily the correction table about the operation time-current characteristic in the manner of enabling to be read out, the CPU 2 reads out the appropriate correction number from the ROM 2b on the basis of the operation time-current charactieristic extracted by the character extraction circuit 190 so that the CPU 120 can correct the operation time-current characteristic on the basis of the correction numbers and effects next printing operation. Accordingly, inasmuch as all the printing wires operate dependent upon their own appropriate corrected operation time-current characteristics such problem of an inconvenience that the energy is insufficient for printing operation and an excessive energy more than required is supplied to the head coil 6b are solved. According to this embodiment, the correction number is read out from the ROM on the basis of the resultant detection by the characteristic extraction circuit and the operation time-current characteristic is controlled based on the correction number but the operation time-current characteristic can be controlled by an arithmetic operation. Fig. 20 is a block diagram of a wire dot impact printer according to another embodiment of the present invention. In the same figure, designated at 240 is a timer circuit, 250 is a delay circuit, and the timer circuit 240 and the delay circuit 250 function as a drive timing setting means. Designated at 280a is a sensor electrode, 280b is an electrostatic capacitor sensor circuit (hereafter referred to as sensor circuit), 280 is a print timing detector means composed of the sensor electrode 280a and the sensor circuit 280b, and 290 is a drive time detector circuit as the driving time detector means for detecting the drive time from application of the print starting instruction to the head driver 6a until the striking of the printing wire on the printing paper to effect printing. Other arrangements are same as those of Fig. 8. According to this embodiment, the CPU 2 receives the printing data via the centro I/F 1 and supplies the signal issued from the printing data to the delay circuit 250, the head driver 6a, the line feed motor 11, and the spacing motor 12 via the I/O LSI 3. The head driver 6a drives the printing wire of the wire-dot head 7 to effect printing operation on the basis of the signals received from the CPU 2 and the timer circuit 240. This embodiment having the arrangement set forth above is different from the prior art as illustrated in Fig. 1 in that this embodiment has the delay circuit 250, the print timing detector means 280 and drive time detector circuit 290 and in respect of different content of control to be made by the CPU 120. Accompanied by these differences, the arrangement of the wire-dot printing head 7 is different from that of Fig. 2. Although the timer circuit 240 is same as the prior art timer circuit, the timer circuit of the prior art is arranged in the manner that the timer circuit may be standardized for setting the drive timing of all the printing wires with a single timer circuit while the timer circuit of the present invention may not be standardized but a timer circuit 240a is provided in each individual printing wire. Other arrangements are fundamentally same as those of the prior art or those of Fig. 8. Hence, the explanation thereof is omitted and the different arrangements will be described. The drive timing detector circuit 290 will be described first. Fig. 21 is a block diagram of the drive timing detector circuit 290, and Fig. 22 is a waveform of an operation of the drive timing detector circuit 290. In the same figures, designated at 250 is a differentiator, 251 is a comparator, 252 is a D flip-flop circuit, 253 is a 8-bits binary counter, 254 is a D latch, 255 is an AND circuit, 256, 257 are one-shot multivibrators (hereafter referred to as multivibrator), and 259 is a variable resistor. With the arrangement set forth above, the differentiator 250 receives a signal A from the sensor circuit 280b. The signal A is differentiated by the differentiator 250 and is changed to a signal B while the comparator 251 compares a reference voltage J produced by the variable resistor 259 with a voltage of the signal B to produce a signal C. The signal C will be 5V at high level and while 0V at low level and supplied to an input CK of the D flip-flop circuit 252. Hereupon, an overdrive signal from the timer circuit 240 as a drive start signal D (drive timing signal) is applied to the inverse time 1 µs multivibrator256. The multivibrator 256 detects the leading edge of the signal D (namely, the drive actuation time) and rises and issues a signal E which is inversed 1 µs later to the multivibrator 257 having inverse time 1 µs and an input Clock of the D latch 254. The multivibrator 257 receives the signal E as a trigger signal and drops after detecting the trailing edge of the signal E to thereby issue a signal F which is inversed after 1 s later and supplied to an input Clock of the D flip-flop circuit 252. Accordingly, at the time when the drive start signal D goes to high level, the multivibrator 256 is inverted to thereby permit the D latch 254 to latch the value of the counter 253. The multivibrator 257 is inverted, just after latching of the D latch, to reset the counter 253 and reset the D flip-flop circuit 252 at the same time. The AND circuit 255 receives a signal G issued from an output NQ of the D flip-flop circuit 252 and a clock of 500 kHz which are ANDed to produce an AND signal H which is applied to an input Clock of the counter 253. Hence, the D flip-flop circuit 252 is reset and the counter 253 counts the signal H at the time when the signal G keeps high level. Hereupon, the D flip-flop circuit 252 is set and the signal G of the output NQ is inverted to the low level when the output signal C of the comparator 251 rises, then drops. The leading edge and the trailing edge of the signal C correspond to an operation timing of the printing wire 20. That is, the time when the signal C rises accords with the time when the printing wire 20 actuates the operation and the time when the signal C drops accords with the time when the printing wire 20 strikes onto the printing paper. Accordingly, the signal G of the output NQ of the D flip-flop circuit 252 keeps high level during the period from the application of the drive start signal D until the actuation of operation and striking the printing paper by the printing wire 20, and the counter 253 counts that period. The counted value is latched by the D latch 254 just after the application of the drive start signal D, the value of the counter 253 is cleared after latching. The value latched by the D latch 254 is supplied to the I/O LSI 3 as a 8-bits signal I and read by the CPU 2. A time resolution of the count value is 2 µs. A deriving process of a delay signal to be applied to the timer circuit 240 will be described next. First, the delay circuit 250 will be described with reference to Fig. 23. As illustrated in the same figure, the timer delay circuit 250 comprises, as a counter 5a, a group of registers 5b and a group of comparators 5c wherein the counter 5a starts to count on the basis of instruction from the CPU 2 and stop counting on the basis of an instruction from the CPU 2 after lapse of prescribed period of time so that the counter 5a is reset. The registers 5b set the delay values independently for each printing wire 20. The delay values written in the registers 5b are compared with the value of the counter 5a by the comparators 5c which detects the timing when the value of the counter 5a exceeds over the values of the registers 5b and supplies a drive timing to the timer circuit 240. Let us describe a process of calculation of delay time in the case of nine printing wires 20. The calculation of the delay time is fundamentally effected to conform timings of the other printing wires to the print timing which has the longest drive time among the nine printing wires. When the printing operation is actuated, a period data from the drive start to the impact, namely, the driving time is applied to the CPU 2. Assuming that the driving times corresponding to the printing wires 20 are I t1 , I t2 , ... , I t9 , and the delay values to be written in the registers 4b ... are D t1 , D t2 , ... , D t9 . The CPU 2 searches the maximum value of the drive time from Ith (n is an integer which is above 1 but below 9) to determined the maximum value Imax. The delay values D t1 , D t2 , ... , D t9 are set as following expression for conforming the print timing to the print wire having the longest drive time. wherein Co is a correction value in view of an influence of the number of printing wires 20 to be simultaneously driven on the print timing and is stored in the ROM of the CPU 2. According to the present embodiment, the more the number of printing wires 20 to be driven simultaneously increases,the longer is the drive time and the slower the print timing so that the correction value Co as shown in the table in Fig. 23 is adopted. Since the delay value D th is set as set forth above each printing wire strikes the printing paper after lapse of (I th + D th ) from the drive timing. That is, if the above expression is given by the time (I th + D th ), the values are expressed as (Imax + Co) for all the print wires, which means that the print timing is standardized to identify for all the printing wires. According to the present embodiment having the arrangement set forth above, the timer circuit 240 sets the drive timings when the plurality of printing wires 20 actuate driving individually to thereby issue the drive timing signal to the head driver 6a and the drive time detector circuit 290. In addition to that, the sensor circuit 280b detects the electrostatic capacitance of the sensor electrode 280a for thereby detecting the print timing when the printing wire 20 strikes the printing paper, the print timing signal is supplied to the drive time detector circuit 290. The drive time detector circuit 290 detects the drive time for each printing wire 20 on the reception of the drive timing signal and the print timing signal and supplies the drive time data for the plurality of printing wires 20 to the CPU 2. The CPU 2 issues the delay value to the delay circuit 250 on the basis of the aforemention drive time data so that the print timing for each printing wire is same at the next printing operation. The delay circuit 250 delays the drive timing of some printing wire among the printing wires to an appropriate time on the basis of the delay value so that the plurality of printing wires 20 can strike the printing paper simultaneously. Accordingly, a displacement of the print timing, when the printing wire strikes onto the printing paper, for each print wire 20 can be eliminated. As mentioned above, the wire-dot impact printer according to the present invention enables the printing wire to strike onto the printing medium with a sufficient strength for obtaining a clear printed letter and is capable of eliminating the displacement of each print wire. Accordingly, it makes possible to provide the wire-dot impact printer capable of printing at all time with high quality, thereby assuring very high industrial applicability.

Claims: A wire-dot impact printer comprising: a wire-dot printing head (7) disposed with a predetermined interval relative to the printing medium (14); a plurality of printing wires (20) provided at the wire-dot printing head (7) and having distal ends (20b) thereof capable of striking the printing medium when the printing wires (20) are driven; a drive means (6) for independently driving each printing wire (20) of the plurality of printing wires (20) for a given time period within a printing cycle; the plurality of printing wires (20) being selectively driven on the basis of the printing signal applied to the drive means to effect printing; displacement detecting means (8) for detecting a displacement of the printing wire (20) when said printing wire (20) is operated and for outputting a corresponding displacement detecting signal; characterized by a characteristics extraction means (190) extracting an operation time current characteristic of each printing wire (20) on the basis of the displacement detecting signal, and control means (120) for controlling the correction of the operation time current characteristic of each printing wire (20) on the basis of the extracted operation characteristic, whereby said time period for driving each of said printing wires (20) is corrected by a timer circuit means (140) in accordance with said displacement detecting signal obtained in a previous printing cycle. A wire-dot impact printer comprising: a wire-dot printing head (7) disposed with a predetermined interval relative to the printing medium (14); a plurality of printing wires (20) provided at the wire-dot printing head (7), each of said printing wires being displaced in response to a drive signal and having a distal end (20b) capable of striking the printing medium when the printing wires (20) are driven; drive means (6) for independently outputting said drive signal to each printing wire (20) of the plurality of printing wires (20) for a given time period within a printing cycle; and displacement detecting means (280) for detecting print timing of each of said plurality of printing wires (20) and for outputting a corresponding displacement detecting signal (A); characterized by control means (240, 250, 290) for controlling the print timing of each printing wire (20) in accordance with said displacement detecting signal (A) obtained in a previous printing cycle, said control means including delay means (250) for selectively delaying the drive signal of each printing wire such that the print timing for all printing wires is the same.

Inventors: ISHIMIZU HIDEAKI, KIKUCHI HIROSHI, KOMORI CHIHIRO, TANUMA JIRO, ISHIMIZU, HIDEAKI, KIKUCHI, HIROSHI, KOMORI, CHIHIRO, TANUMA, JIRO
Applicants: OKI ELECTRIC IND CO LTD, OKI ELECTRIC INDUSTRY COMPANY, LIMITED
Application year: 1988
Main classification: B41J2
IPC codes: B41J2