JPS61124298A - Drive circuit of stepping motor - Google Patents

Abstract

PURPOSE:To prevent a coil from wastefully generating heat by controlling an exciting current by the period of a drive command signal, and reducing an exciting current at stopping and low speed time. CONSTITUTION:A drive command signal (a) and a rotating direction command signal (b) are inputted to a distributor 3 to drive transistors Tr1-Tr4 to drive a stepping motor. The signal (a) is inputted also to a retriggerable monostable multivibrator 4, and when the period of a drive command signal (a) becomes the prescribed value or higher, a NOR gate is opened, and the output from a pulse oscillator 5 is inputted to a transistor Tr5. Thus, the ON drive transistor is switched by switching the transistor Tr5 to decrease an exciting current.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a drive circuit for a step motor used for position control that often involves incremental drive.

[Background of the invention]

Generally, the torque of a step motor is proportional to the magnitude of the excitation current flowing through each phase coil of the step motor unless magnetically saturated. However, if the frequency of the drive command signal pulse is increased in order to increase the rotation speed of the step motor, the impedance increases due to the inductance of each phase coil, υ, and the excitation current flowing through each phase coil decreases, resulting in a decrease in torque. . This situation is shown in FIG. Now, the coil specifications of the step motor are set so as to have the characteristics shown by the dotted line in FIG. 5, and the torque when the frequency is fl is T. If this value is insufficient, the coil specifications of the step motor must be changed to achieve the characteristics shown by the solid line in FIG. 5 in order to improve this. That is, if the excitation current when the step motor is driven at the frequency f1 of the drive command signal pulse is changed from T to I, the torque will change from T1 to T! to amplify. However, if the step motor is used for many incremental drives such as position control, the time for stopping the step motor increases. Then, the excitation current at this stop has a large value when the pulse frequency is 00 in Figure 5. This results in an abnormal temperature rise in the coil section, which may lead to coil burnout. In order to deal with such problems, that is, to increase the responsiveness and torque of the step motor, various measures have been taken to increase the excitation current during driving and reduce the excitation current when stopped. For example, in the device disclosed in JP-A-58-175997, a control circuit is provided to turn the excitation current on and off, and when the drive command signal pulse is not applied even after the period, it is determined that the drive is stopped, and the control circuit Although the excitation current is turned off, the detection of whether the motor is rotating or stopped is performed for one predetermined rotation speed, so it is only effective when driving at a constant speed, and the drive speed is variable. That is, when the frequency of the drive command signal is variable, there is a drawback that it becomes difficult to detect a stopped state. Moreover, since the step motor is started with a delay of one cycle of on/off of the excitation current when restarting from a stop, the starting responsiveness also deteriorates.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to eliminate the above-mentioned drawbacks, and to provide a step motor drive circuit that reduces excitation current at low speeds or when stopped even when the frequency of a drive command signal is variable, and has good starting characteristics. There is a particular thing.

[Summary of the invention]

A feature of the present invention is that a drive command signal is applied to a retriggerable monostable multivibrator, and when the drive command signal is applied with a cycle larger than the pulse width of the monostable multivibrator or when the monostable multivibrator is stopped, the monostable multivibrator is activated. Since there are times when the output is off, the excitation current of the step motor is turned on and off during that time to reduce its average magnitude.

[Embodiments of the invention]

The present invention will be explained below with reference to the embodiment shown in FIG.

In FIG. 1, four coils φ1. φ
2. φ3. φ4 is 1. Each drive transistor Tri
, Tr2. Tr3. When Tr4 is turned on, excitation current is supplied from the power supply +v. A Zener diode ZDI is connected in parallel between the collector and emitter of each drive transistor.

Zn2. Zn2. Zn2 protects the drive transistor by absorbing energy generated in the coil when the drive transistor is off. A distribution circuit 3, which receives as input a drive command signal 3 for advancing the step motor by one step angle and a rotation direction command signal, is connected to the pace terminal of each drive transistor through a resistor, and is connected to the pace terminal of each drive transistor through a resistor. It performs on/off control and outputs phase excitation signals A, A, B, and B that instruct the excitation of each coil. This distribution circuit 3 is composed of a combination of two D type slip-flops and two exclusive OR gates.

The drive command signal a is also input to a monostable multivibrator 4 that can be retriggered. Pulse oscillation circuit 5
The output of C and the output C of monostable multivibrator 4 are NOR.
The output d of the NOR gate 6 is input to the gate of the excitation current control transistor Tr5 via a resistor. The emitter of this control transistor Tr5 is grounded, and the collector is connected to backflow prevention diodes DI, D2, . D3. It is connected to the full power node of D4. Therefore, while the output of the pulse oscillation circuit 5 passes through the NOR gate, the excitation current control transistor T
r5 is switched, and when the excitation current control transistor Tr5 is on, the pace current of each drive transistor becomes the collector current of Tr5 via the reverse current prevention diode, and the drive transistor that was on turns off, resulting in excitation. By switching the current control transistor Tr5, the turned-on drive transistor is also switched, thereby reducing the excitation current. The pulse width T of the output C of the retriggerable monostable multivibrator 4 is determined by the values of the resistor RX and the capacitor C1, and if this is now set to '1' = 40m9ec, it is possible to detect whether the signal period is greater than or less than 4Qm9eO. become.

In other words, if the next signal does not enter even after 40 m (8) have elapsed, the signal C becomes O, and the output of the pulse oscillator 5 passes through the NOR gate 6, turning on and off the transistor Tr5, so the excitation current is reduced. .

FIG. 2 is a time chart showing the waveforms of each part of the circuit in FIG. 1. First, phase excitation signals A and B generated by the distribution circuit 3
etc. are as follows. When one drive command a is input, for example, the signal person becomes one. When the next signal a enters, signal B also l
Then, at the next signal a, only the signal person returns to O, and furthermore, at the next signal 1, signal B also returns to O. Similarly, signal a
The level of the signal person or B as described above is switched every time one pulse of . The phase excitation signal AI is an inversion of the H&A, B.If the drive command signal a is input as shown in Figure 2, as mentioned above, if the interval is greater than T, the monostable multi Vibrator 4 output C
becomes O, and during this time c=0, a pulse from the pulse oscillator 5 appears at the NOR gate output d. Therefore, as described above, the phase excitation signals that are on are turned on and off by this pulse, so the excitation currents im, IB, etc. flowing through each of the coils φ1 to φ4 are reduced as shown in FIG.

The degree of reduction at that time is the duty ratio of the pulse of the pulse oscillation circuit 5 output, that is, the excitation current control transistor Tr.
It is determined by the on/off duty ratio of 5. Monostable multivibrator 4 that can be retriggered in this way
For example, if t is less than the driving frequency f, then if you want to increase efficiency by reducing the excitation current, set T = 1/ r t to give the desired reduction effect. Furthermore, as is clear from this example, immediately after the start of excitation, at least T time is always C=1.
Since the excitation current is not reduced by turning on and off, it has a current waveform that rises quickly, and the rotor follows the external rotating magnetic field created by the stator coil of the step motor with good responsiveness, resulting in high responsiveness of the step motor. For this reason, in order to improve responsiveness, a costly two-power supply system,
There is no need to use the chopper method. The excitation current control transistor Tr5 can be a low power transistor, and is small and inexpensive, since the base current of each drive transistor becomes a converter current. Further, as the retriggerable monostable multivibrator 4, an IC such as Motorola's Mo 145280P may be used, or a circuit as shown in FIG. 3 may be constructed, and this may also be a simple circuit. The circuit shown in Figure 3 differentiates the input pulse with a capacitor C and a resistor, and outputs the output from the inverter INV, .
INV.

This is used to shape the pulse into a pulse shape.

〔Effect of the invention〕

As described above, according to the present invention, in a drive method such as incremental drive where the drive frequency ranges over a wide range, the excitation current is controlled by the cycle of the drive command signal, and the excitation current is reduced when stopped and at low speeds. This is an efficient step motor that prevents unnecessary heat generation in the coil, and improves torque and response by supplying sufficient excitation current at high speeds. can be provided.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing a step motor drive circuit according to an embodiment of the present invention, Fig. 2 is a time chart of signal waveforms of each part in Fig. 1, and Fig. 3 is a retriggerable monostable as shown in Fig. 1. FIG. 4 is a diagram showing the circuit of the multivibrator 4, and FIG. 4 is a diagram showing the characteristics of the step motor. 3... Distribution circuit, 4... Retriggerable monostable multivibrator, 5... Pulse oscillation circuit, 6... NO
R gate, φ1. φ2. φ3. φ4...Step motor coil A/, Tri, Tr2. Tr3. Tr4--drive transistor, Tr5--excitation current control transistor.

Claims (2)

[Claims] 1. In a step motor drive circuit that generates a phase excitation signal that excites each phase coil from a drive command signal and causes an excitation current to flow through each phase coil, a drive command signal is input at a certain point and then a predetermined When the next drive command signal is input after a period of time, the detection circuit turns on the gate for the period of time that exceeds that period, and turns on and off the excitation current of each phase coil while the gate is on. A step motor drive circuit comprising switching means for reducing the average value. 2. 2. A step motor drive circuit according to claim 1, wherein said detection circuit is constituted by a retriggerable monostable multivibrator.