JPS5945209B2 - Magnet drive circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a magnet drive circuit such as a print wire drive magnet in an impact type dot printer or a print hammer drive magnet in a fly fender type printer.

In the above-mentioned impact type dot printers and fly shims type printers, printing wires and printing hammers are required to operate at high speed, and therefore, a problem arises in which the excitation current for the magnets used to drive them runs out. FIG. 1 shows an example of a conventional magnet drive circuit proposed to improve disconnection of magnet drive current.

In the figure, 1 is a magnet coil, one end of which is connected to the emitter of transistor 2, and the other end connected to the collector of transistor 3. The base of the transistor 1 is connected to the output of an AND gate 4, and one input of the AND gate 4 receives a magnet drive signal, and the other input receives the output of a comparator 5.
A reference voltage is applied to the (width side input) of the comparator 5, and this reference voltage is compared with the detection voltage of the magnet current applied to the H side input.The above drive signal is also applied to the transistor 3 via the resistor R1. given to the base.
A magnet current detection resistor R2 is connected to the emitter of the transistor 3, and the detection voltage of the magnet current is taken out. Diodes D1 and D2 are connected between the power supply +Vcc and one end of the magnet coil 1, and between the ground and the other end of the magnet coil 1, respectively. In such a circuit, when the drive signal shown in FIG. 3a is input, the transistor 3 becomes conductive. At this time, the detection voltage of the magnet current is o, so the output of the comparator 5 is at a low level, and the output of the AND gate 4 is "o". Therefore, the transistor 2 is also in a conductive state, so the coil 1 and resistor R2. This current increases the detection voltage of the magnet current input to comparator 5, and when this exceeds the reference voltage, the output of comparator 5 becomes high level and the output of AND gate 4 increases.゛01''
becomes. As a result, transistor 2 becomes non-conductive, and the current flowing through coil 1 and resistor R2 gradually decreases. When the magnet current detection voltage falls below the reference voltage, the output of comparator 5 becomes low level again, and AND gate 4
The output of the transistor becomes "0" and the transistor 2 becomes conductive again. This repetition of conduction and non-conduction of the transistor 2 continues as long as the drive signal is applied, and the current waveform of the coil 1 is as shown in Fig. 3b.
It becomes as shown in . Next, when the drive signal disappears, the transistor 3 returns to the non-conducting state. At this time, the energy stored in coil 1 is transferred to diode D1 and diode D.
2 in the direction of the power supply +Vcc, the current flowing through the coil 1 rapidly decreases as shown in FIG. In this way, in the circuit described above, by connecting the diodes Dl and D2 between the power source and the coil 1 as described above, the magnet current can be cut off easily. If the magnet current is cut more quickly, the armature will return to normal quickly, which is convenient for high-speed operation of the printing wire and printing hammer. However, if the armature returns too quickly, the printing wire or printing hammer that collides with the medium and bounces back hits the returned armature at high speed, causing vibration. Therefore, the present invention attempts to reduce the vibration of the printing wire and printing hammer by appropriately slowing the return of the armature so that the printing wire and printing hammer return to their original positions while coming into contact with the armature. - Provides a magnet drive circuit that allows the armature to act as a buffer when the printing wire or printing hammer collides with each other.

In order to achieve this object, the present invention, in the magnet drive circuit described above, repeats conduction and non-conduction of the transistor 3 after driving the magnet to intermittently return the energy stored in the coil 1 during the drive period to the power supply. It is characterized by adjusting the fall of the magnet current waveform. A detailed explanation will be given below with reference to the drawings.

First, in the circuit shown in FIG. 1, if only transistor 3 is kept conductive from the end of the drive signal, the magnetic current waveform falls as shown by c in FIG. 3, and the magnetic current gradually decreases.

Therefore, when the transistor 3 is made to conduct intermittently from the end of the drive signal, the energy stored in the coil 1 is transferred to the resistor R.
2 side and the power supply +Vcc side via diodes Dl and D2, and the falling edge of the magnet current waveform is
It can be adjusted so that it is slower than Figure b and faster than Figure c. FIG. 2 shows an example of a magnet drive circuit that adjusts the fall of the magnet current waveform in this manner.

In FIG. 2, the same components as in FIG. 1 are given the same numbers.

In the figure, the base of transistor 3 is connected to the output of OR gate 6. A drive signal is applied to one input of the OR gate 6, and an adjustment pulse shown in FIG. 4c is applied to the other input. The adjustment pulse is applied after the end of the drive signal as shown in FIG. 4, and its period and application time are determined depending on the return speed of the printing wire or printing hammer. In this magnet drive circuit,
The operation while the drive signal is applied is the same as that of the circuit shown in FIG. 1 above.

When the supply of the drive signal ends, an adjustment pulse is input to the OR gate 6. The transistor 3, which once became non-conductive due to the termination of the drive signal, repeats the conductive and non-conductive states due to this adjustment pulse, and the current in the coil 1 intermittently flows to the resistor R2 side or the power supply +Vcc side.
Therefore, the waveform of the current flowing through the coil 1 becomes as shown in FIG. 4b, and its falling waveform is adjusted in accordance with the speed of the printing wire or printing machine. As explained above, according to the magnet drive circuit of the present invention, the return of the armature can be adjusted in accordance with the return speed of the printing wire and printing hammer, and the effect of reducing vibration when the printing wire and printing hammer return is achieved. be.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing a conventional magnet drive circuit, Fig. 2 is a diagram showing a magnet drive circuit of the present invention, Fig. 3 is a diagram showing current waveforms in the conventional magnet drive circuit, and Fig. 4 is a diagram showing a magnet drive circuit of the present invention. FIG. 3 is a diagram showing a current waveform in a magnet drive circuit. 1... Coil, 2, 3... Transistor, 4... AND gate, 5... Comparator, 6... OR gate.

Claims (1)

[Claims] 1 The output of a comparator with the reference voltage as one input and the detection voltage of the magnet current as the other input, and the magnet drive signal as inputs of one AND gate, and the output of this AND gate as one of the magnet drive transistors. A magnet equipped with a circuit that inputs a drive signal to the other magnet drive transistor connected to this transistor via the magnet, and returns the energy stored in the magnet coil to the power supply during the magnet drive period. A magnet drive circuit characterized in that the drive circuit is provided with an OR gate that inputs the drive signal and the adjustment pulse and outputs it to the other transistor.