JPS6323757B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a pulse motor driving method suitable for controlling a printer, and particularly to a method in which one operation of the pulse motor is performed using a plurality of consecutive pulses. This invention relates to a phase excitation current drive system that is less affected by power supply voltage fluctuations and that enables stable stop control.

[Technology background]

When one operation of a pulse motor is performed in several steps, various damper circuits such as a reverse phase control circuit and a DLSED circuit are conventionally used in order to stop the motor smoothly without causing vibration. Also, 1
In order to perform high-speed and high-precision positioning through motion,
A linear acceleration/deceleration control method in which an acceleration period and a deceleration period are continued as shown in FIG. 1 is widely used.

In general serial printers, the pulse motor drive circuit that selectively controls the rotational position of the type wheel uses the technology described above to operate at high speed and with high stability.However, during operation, power supply voltage fluctuations and It is easily affected by load fluctuations, and as shown in FIG. 2, a vibration component appears in the linear acceleration/deceleration characteristics, making it difficult to stop stably.

[Prior art and problems]

In conventional pulse motor drive circuits, switching-type constant current drive control is performed on each phase excitation current in order to improve starting characteristics and continuous operation characteristics in the high frequency range.

In other words, a pulse motor works as a generator when the motor rotates due to the influence of the time constant of the coils in each phase, and because the rotor is made up of magnets and the stator is made up of coils. A back electromotive force is generated. The direction of this back electromotive force acts in the opposite direction to the applied voltage, so
Unless a voltage is supplied to overcome this back electromotive force, high frequency characteristics will not improve. As one means of solving this problem, a constant current drive circuit is used in which a high voltage is applied to the pulse motor to overcome this back electromotive force, thereby extending the operating characteristics to a high frequency range.

FIG. 3 shows a conventional example of such a constant current drive circuit. In the figure, 1A, 1B, 1C,
1D is a stator excitation coil for each A, B, C, and D phase of the four-phase pulse motor. Also, 2 is the power supply, 3
and 4 are main switching transistors,
Current is supplied to coils 1A, 1C and 1B, 1D, respectively. 5A, 5B, 5C, 5D are coil drive transistors, 6 and 7 are current detection resistors, 8
and 9 is a comparator with hysteresis, 1
0 and 11 are control transistors, and 12 and 13 are commutating diodes.

To briefly explain the operation, for example, coil 1A
When the coil drive transistor 5A is turned on by the A-phase clock pulse applied to its base, an excitation current is supplied via the main switching transistor 3 in a self-excited switching manner. The magnitude of the excitation current is detected by the voltage generated in the current detection resistor, and compared with the reference voltage Vr by the comparator 8.

When the detected voltage is greater than Vr, the comparator 8 controls the main switching transistor 3 to turn off via the control transistor 10. When the transistor 3 is turned off, the current continues to flow through the commutation diode 12 while being attenuated due to the flywheel effect of the energy stored in the coil 1A.

Here, the comparison operation level of the comparator 8 varies due to its hysteresis characteristic. Therefore, when the current flowing through the coil 1A falls to a certain level, it responds again to the detected voltage from the resistor 6 and starts the main switching. Transistor 3 is turned on and current flows through coil 1A. Thereafter, similar operations are repeated in a self-exciting manner.

FIG. 4 shows the state of the excitation current flowing through the coil 1A in this manner. In the figure, Vr ₁
and Vr ₂ represent two reference levels at which the comparator 8 operates in hysteresis, and I ₀ represents a constant average current.

The circuit shown in Figure 3 performs the above-mentioned constant current drive for the coils 1A, 1B, 1C, and 1D of each phase of the pulse motor, but this circuit has the disadvantage that its high frequency characteristics are easily affected by fluctuations in the power supply voltage and load. There is,
Even if the design is designed to achieve a stable stop through linear acceleration/deceleration for a given power supply voltage, for example, the high frequency characteristics may change due to fluctuations in the power supply voltage, and the constant current characteristics may change depending on the speed of the pulse motor. Since the effect of the electromotive force is canceled out, there is no feedback on the speed, and as shown in FIG. 2, the problem is that stable stopping is not possible.

[Object and structure of the invention]

The purpose of the present invention is to solve the problems of the conventional method described above, and to provide a means that can feed back the amount of speed change of a pulse motor based on constant current drive, and also to prevent the influence of power supply voltage fluctuations or load fluctuations. This allows for stable stopping by absorbing the

To this end, the configuration of the present invention includes a switching type constant current control circuit connected in series to the phase excitation coil of the pulse motor, and a commutation circuit connected in parallel to the phase excitation coil. The control circuit includes a switching transistor that switches and controls the excitation current flowing through the phase excitation coil, and a switching transistor that periodically switches and drives the switching transistor according to the timing of phase excitation, and alternately conducts a conductive period and a non-conductive period. During the conduction period of the clock signal means to be set and the switching transistor, the level of the excitation current flowing through the switching transistor is detected and compared with a predetermined reference level, and when they match, the switching is performed by the clock signal means. circuit means for blocking switching control of the transistor and controlling the switching transistor to be non-conductive for a predetermined period that is extremely shorter than the conduction period based on the clock signal means; When controlled to be non-conductive for the predetermined period of time, the excitation current flowing through the phase excitation coil is commutated to the commutation circuit, using the fact that the rotational speed of the pulse motor appears as a change in the excitation current. This is characterized by applying feedback to the excitation current.

[Embodiments of the invention]

The details of the present invention will be explained below with reference to Examples.

FIG. 5 is a circuit diagram of one embodiment of the present invention. In the figure, 1A, 1B, 1C, and 1D are stator excitation coils of A, B, C, and D phases of the pulse motor, respectively. Further, 14A to 14D are switching transistors for constant current drive, 15 and 16 are current detection resistors, 17 and 18 are comparators without hysteresis, 19 and 20 are monostable multivibrators, 21A to 21D are AND gates,
22A to 22D are control transistors, 23A to 23D are commutation transistors, and 24 is a power input line.

For convenience of explanation, the A-phase driving portion in the circuit will be explained as an example. The other parts perform exactly the same circuit operation. In addition, Fig. 6 is a circuit waveform diagram.
, represents the signal waveform of the same display portion in FIG.

The coil 1A is driven with a constant current in a switching manner by turning on the constant current driving switching transistor 14A. Transistor 14A
When OFF, due to the flywheel effect of the energy within the coil 1A, the current is attenuated and fed back to the circuit including the commutating transistor 23A. Commutation transistor 23A is ON while the A phase clock is applied to control transistor 22A.
state, allowing commutation whenever transistor 14A turns OFF.

First, at time _t0 in FIG. 6, when the A-phase clock is applied and the transistor 14A is turned on, a current flows through the coil 1A as shown in the figure and is taken out from the voltage detection resistor 15. At time _t1 when the detected voltage becomes equal to the reference voltage Vr, the comparator 17 outputs the coincidence signal shown in FIG.
Activate the monostable multivibrator 19.

The monostable multivibrator 19 outputs a signal that is OFF for a certain period r shown in FIG.
Transistor 14A via AND gate 21A
Turn off. As a result, a commutation occurs from the coil 1A through the transistor 23A mentioned above, and as a result, an excitation current as shown in FIG. 6 flows through the coil 1A. At time _t2 after a certain period of time r has elapsed, the transistor 14A is turned on again and the process returns to the beginning. These operations are repeated while the A phase clock is applied.

The peak value of each exciting current waveform is the reference voltage.
It is held at a constant value based on Vr. However, the bottom value differs depending on the amount of energy stored in the coil 1A or the back electromotive force, and is generally related to the rotation speed of the pulse motor.

FIG. 7 is an explanatory diagram of this, and as shown in FIG. 7a, the faster the speed, the lower the bottom value, and the slower the speed, the higher the bottom value. Furthermore, depending on the distance between the rotor and stator in the pulse motor, if they are close together, the influence of speed will be large as shown in b, and if they are far apart, the influence of speed will be small as shown in c.

FIG. 8 shows an example in which such a speed change of the pulse motor causes a variation in the average current I ₀ of the excitation current.

Therefore, according to this embodiment, as the speed increases, the excitation current decreases, and as the speed decreases, the excitation current increases. As a result, fluctuations in the power supply voltage and load can be fed back to the magnitude of the excitation current so as to suppress speed changes, so that the linear acceleration/deceleration characteristics are stabilized as shown in FIG. 9. Also, for a certain period of time
The voltage drop level during the OFF period, that is, the voltage drop caused by the attenuation of the flyback current flowing in the commutation circuit, is detected, and depending on the level,
By changing the length of the OFF period (amplifying this amount of feedback), the linear acceleration/deceleration characteristics can be further stabilized.

〔Effect of the invention〕

As described below, according to the present invention, the speed of the pulse motor can be fed back to the phase excitation current based on constant current drive, so it is possible to suppress the occurrence of vibration due to fluctuations in the power supply voltage or load. , can enable stable stopping.

[Brief explanation of drawings]

Figure 1 is an explanatory diagram of linear acceleration/deceleration control characteristics, Figure 2
The figure is an explanatory diagram of characteristic changes due to power supply voltage fluctuations.
The figure is a circuit diagram of an example of a conventional constant current drive circuit.
5 is a circuit diagram of one embodiment of the present invention, FIG. 6 is an operating waveform diagram, and FIG. 7a,
b and c are waveform diagrams showing the relationship between the speed change of the pulse motor and the exciting current, FIG. 8 is a diagram showing an example of the exciting current change, and FIG. 9 is an explanation of the control characteristics of linear acceleration/deceleration according to this embodiment. It is a diagram. In the figure, 1A to 1D are stator excitation coils, 1
4A to 14D are switching transistors for constant current drive, 15 and 16 are current detection resistors, 17
and 18 are comparators, 19 and 20 are monostable multivibrators, and 21A to 21D are
AND gates, 23A to 23D are commutation transistors, and Vr represents a reference voltage.

Claims (1)

[Scope of Claims] 1. A switching type constant current control circuit, comprising: a switching type constant current control circuit connected in series to a phase excitation coil of a pulse motor; and a commutation circuit connected in parallel to the phase excitation coil; The control circuit includes a switching transistor that switches and controls the excitation current flowing through the phase excitation coil, and a switching transistor that periodically switches and drives the switching transistor according to the timing of phase excitation to alternately conduct a conduction period and a non-conduction period. A clock signal means to be set, and a level of an excitation current flowing through the switching transistor during the conduction period of the switching transistor is detected and compared with a predetermined reference level, and when they match, switching is performed by the clock signal means. circuit means for blocking switching control of the transistor and controlling the switching transistor to be non-conductive for a predetermined period that is extremely shorter than the conduction period based on the clock signal means; When controlled to be non-conductive for the predetermined period of time, the excitation current flowing through the phase excitation coil is commutated to the commutation circuit, using the fact that the rotational speed of the pulse motor appears as a change in the excitation current. A pulse motor drive system characterized by applying feedback to the excitation current. 2. In the pulse motor drive method according to claim 1, the switching type constant current control circuit is configured such that the flyback current flowing through the commutation circuit is attenuated during a predetermined period in which the switching transistor is rendered non-conductive. 1. A pulse motor drive system, characterized in that the voltage drop level caused by this is detected, and the length of the predetermined period of the switching transistor is controlled according to the detected level.