JPS5833999A - Drive circuit for step motor - Google Patents

Abstract

PURPOSE:To drive a two-phase step motor so that exciting currents of two phases may not flow simultaneously by providing timing setting means when the step motor is connected in bipolar manner and is driven in switched manner, thereby making the timing phase of each phase in staggered manner. CONSTITUTION:Exciting coils 21A, 21B are connected to transistors 22A-25A, 22B-25B in bipolar manner. An input signal 45 is applied to timer ICs 46A, 46B, thereby generating triangular waves of different phase angles of 180 deg. at signal lines 43A, 43B. Thus, the reference voltage VRef is varied, is compared by comparators 38A, 37B with the values of current detectors 28a, 28B, thereby operating the drive circuits 31, 33 of the respective transistors. Accordingly, since both reference voltages VRef are different in phase of 180 deg. from each other, the exciting periods of the coils 21A, 21B can be displaced in staggered manner so as not to superpose each other, and even when two phases are simultaneously excited, the current may be similar to the case of one phase excitation, thtereby reducing the capacity of the power source.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a drive circuit for a step motor that rotates in response to a pulse signal.

Step motors are widely used as elements of high-precision servomechanisms because they have good responsiveness to signals and can relatively easily control rotational speed, etc.

FIG. 1 shows a drive circuit conventionally used for such a step motor. In this circuit, one end of the four-phase excitation coils 1 to 4 is commonly connected to one end of a power supply 9 via the collector/emitter of the corresponding switching transistors 5 to 8, and the other end is is a resistor 11.12 that is grouped into two phases and has a relatively high resistance value.
It is connected to the other end of the front distribution power source 9 via. When a control signal is supplied to the base of each transistor 5 to 8 of this circuit, each excitation coil 1 to 4 is
Due to the zero resistance 11゜12 through which the exciting current selectively flows, i
``Since the instantaneous time constant due to the inductance of the excitation coil is reduced, a rapid rise of the excitation current is ensured at this time. However, in this conventional step motor drive circuit, the electric power is The problem is that the waste is not wasted, but that the heat generated has an adverse effect on surrounding circuit elements.

FIG. 2 shows a step motor drive circuit using a switching method, which has been proposed to solve these problems. In this circuit, one end of each excitation coil 1 to 4 is commonly connected to one end of a power supply 14 via the emitter-collector of a transistor 13 that controls on/off the supply of excitation current, and the other end is connected to each excitation coil. Coil 1~4f,
Via a current detection resistor 15 with a relatively low resistance value for detecting the sum of the excitation currents of the collector-emitters of the individually excited transistors 5 to 8 and the excitation current of each excitation coil 1 to 4,
It is connected to the other end of the power supply 14. In this circuit, as shown in FIG. 3A, a voltage peak that appears at one end of the current detection resistor 15 in proportion to the magnitude of the excitation current is used as a reference voltage that repeats a frequency of several KH to several tens of KH. A comparison is made between VR and the comparator 16. As shown in FIG. 3B, the output voltage of the comparator 16 is changed in a rectangular shape according to the comparison result, and the Hennis current of the transistor 13 for supplying the excitation current is controlled by the transistor 19. .

In this proposed circuit, each of the excitation coils 1 to 4 is applied with a relatively high voltage by the power supply 14 in the initial state of being excited, and while ensuring a rapid rise of the excitation current, After the current increases to a certain extent, the value is appropriately controlled by the comparator 16. That is, when a control signal for controlling the drive of the step motor is supplied to the base of each transistor 5 to 8, an excitation current flows selectively to each excitation coil 1 to 4, and the sum of these excitation currents is calculated by a comparator 16. Constant current control is performed.

However, in the conventionally proposed circuit using this switching method, the excitation current is intermittent during the excitation period of each phase, and when both phases are excited, the excitation current flows through the two excitation coils at the same time. Ta. At this time, the instantaneous value of the excitation current was larger than that in the circuit shown in FIG. Therefore, there was a problem in that the current capacity of the power supply 14 had to be increased accordingly. In addition, since such a large current is switched at a high speed, high frequency noise is generated from the line connecting the power supply, the step motor drive circuit, and the step motor, and noise is mixed into other electronic circuits. There were also problems such as malfunction of these devices.

The present invention was developed in view of the above-mentioned circumstances, and an object of the present invention is to provide a step motor drive circuit that makes the peak value of excitation current during two-phase simultaneous excitation the same as that during one-phase excitation.゛Target.

In the present invention, in a step motor drive circuit that connects two-phase step motors in a bipolar manner and performs constant current drive using a switching method, the switching timing of each phase is shifted by a timing setting means so that, in principle, the excitation current does not flow simultaneously in two phases. The above objective is achieved by driving the driver circuit.

The present invention will be described in detail below with reference to Examples.

FIG. 4 shows the main part of a drive circuit for a four-phase step motor having two excitation coils. In this circuit, one end of the first excitation coil 21A is connected to the first to fourth transistors 22A-, - provided for switching.
25A (switching means) is connected to the emitter of the first transistor 22A and the collector of the second transistor 23A, and the other end is connected to the emitter of the third transistor 24A and the collector of the fourth transistor 25A. First and third transistors 22A, 24A
The collectors of the transistors are commonly connected to a power supply terminal 27 for driving the motor, and the emitters of each of the second and third transistors 23A and 25A are connected to a current having a relatively low resistance value with one end grounded. It is connected to the other end of the detection resistor 28A. first and fourth transistors 2
2A, 25A base is the first excitation coil 21A
It is connected to the corresponding output end of a human phase driver circuit 31A for performing phase excitation (hereinafter referred to as human phase excitation) by flowing current in the direction of the arrow 29A. Further, the bases of the second and third transistors 23A and 24A are connected to the first excitation coil 2.
1A in the opposite direction (direction of arrow 32A) to the corresponding output terminal of an A-phase driver circuit 33A for performing phase excitation (hereinafter referred to as A-phase excitation).

The A-phase driver circuit 31A has two input terminals,
One of them is connected to the A phase excitation signal input terminal 34A,
It is designed to receive a phase excitation signal 35A. The other one is a comparator 3 that outputs a comparison signal 36A for determining switching timing and performing constant current control.
Connected to the 7A output terminal. A phase driver circuit 31
A is configured to operate for A-phase excitation when the A-phase excitation signal 35A and comparison signal 36A are input simultaneously.
One of them is connected to the A-phase excitation signal input terminal 39A, and
It is designed to receive a phase excitation signal 41A. The other one is commonly connected to the output terminal of the comparator 37A described above. The input phase driver circuit 33A is
When the phase excitation signal 41A and the comparison signal 36A are applied manually at the same time, the 0 comparator 37A, which operates for X-phase excitation, detects the 4 quasi voltage vRef,A and the voltage appearing at one end of the current detection resistor 28A. V? A comparison signal 36A is output by comparing the signals. Reference voltage vR
e7. A is a signal ?A to a predetermined constant voltage input from the constant voltage input terminal 42? This is a superimposed triangular wave supplied from IIj43A. The triangular wave appearing on the signal line 43A is the timer IC 4 which operates in response to the switching pulse input signal 45 supplied from the switching pulse input terminal 44.
6A and a charging/discharging circuit 47A connected to its output terminal. The timer IC 46A and the charging/discharging circuit 47A are connected to a power supply terminal 48 for power supply.

The second excitation coil 21 of the drive circuit in this step;
The circuit portion for exciting B to B phase or π phase is basically the same as the case of the first excitation coil 21A described above. For this reason, the letter A at the end of the reference numeral used to represent each part will be replaced with the letter B. However, it should be noted that the switching pulse input signal 49 supplied to the timer IC 45A associated with the second excitation coil 21B is a signal obtained by inverting the logic of the switching pulse input signal 45 using the inverter 51. be.

Now, regarding this step motor drive circuit, the operation of driving the step motor using the 1-2 phase excitation method will be described next.

When the power is turned on, a switching pulse input signal 45 with a duty of 50% read from a ROM (read-only memory), not shown, is supplied to the switching pulse input terminal 44. This switching pulse input signal 45 is input to one timer IC 46A with its phase unchanged.

The other timer IC 46B is inputted as a switching pulse input signal 49 with a phase shift of 180°.

When each of the timer ICs 46A and 46B receives a switching pulse input signal 45.49 having six inverted phases, its output terminals are grounded at a predetermined period synchronized with the switching pulse input signal 45.49. When the output end is grounded, the charging/discharging circuit 46A, 4
When the corresponding capacitor 6B is discharged and the output terminal is opened, the capacitor is charged through the resistors of the charging/discharging circuits 46A and 46B. As a result, two sets of signal lines 4
Triangular waves having a phase difference of 180 degrees are generated at 3A and 43B.

These triangular waves are superimposed on a predetermined constant voltage applied to the constant voltage input terminal 42. As a result, comparator 37A
The reference voltage V ゛ supplied to Ref@A shows a voltage change as shown in Figure 5A, and the comparator 37
The reference voltage vRof supplied to B, B is 180
The voltage changes as shown in FIG. 5C with a phase shift of degrees are shown.

On the other hand, the A-phase excitation signal input terminal 34A has R
Based on the information read from the OM, the A-phase excitation signal 35A is supplied at a predetermined timing. In this initial state, no excitation current is flowing through the first excitation coil 21A. Therefore, in this state, the current detection resistor 2
The voltage η appearing at one end of 8A is equal to the ground potential, and a ratio signal 36A is output from the comparator 37A.

In this state, the A-phase driver circuit 31A is supplied with the A-phase excitation signal 35A and the comparison signal 36A, and the first and fourth transistors 22A are activated.

25A is made conductive. As a result, the first excitation coil 21
An excitation current flows through A in the direction of arrow 29A, and human phase excitation is performed.

When A-phase excitation is performed, the resulting excitation current causes a voltage drop across the current detection resistor 28A.

When the voltage value generated as a result becomes higher than the reference voltage vR6 (@A), the comparison signal 36A output from the comparator 37A is disconnected at this point.

As a result, the human-phase driver circuit 31A becomes inactive, and A-phase excitation is interrupted. As mentioned above, the reference voltage “Re”
Since f-A is a voltage with a superimposed triangular wave, when the A-phase excitation reaches a steady state, the relationship between the reference voltage vR13j-A and the voltage input is 5th. As shown in Figure A, comparison signal 36A
shows a regular rectangular voltage change as shown in FIG. 5B. Step movement is being performed in this state.

Now, this step motor drive circuit simultaneously excites two phases A and B at a predetermined timing. At this time, the A-phase excitation signal 35A is supplied to the A-phase excitation signal input terminal 34A,
The B-phase excitation signal input terminal 34B receives the B-phase excitation signal 35. based on the information read from the ROM described above. B is supplied at the same time.

The comparator 37B compares the voltage v8 outputted from the current detection resistor 28B with the reference voltage vRef,B, and outputs a comparison signal 36B as shown in the fifth diagram to control the 1B phase excitation at a constant current. Side reference voltage vR8f, A.

Since VRej and B have a 180 degree phase difference,
The excitation periods of the first and second excitation coils 21A, 21B controlled by both comparison signals 36A, 36B are shifted by k so as not to overlap with each other. Therefore, even if the two phases A and B are excited simultaneously, the current for the two phases will not flow simultaneously in the steady state. Such a relationship is exactly the same when the A phase and the 100 phase, the λ phase and the B phase, and the X phase and the ``phase'' are excited at the same time.

As described above, according to the present invention, the current supplied from the power supply when exciting two phases simultaneously is the same as when exciting one phase, so it is possible to reduce the capacity of the power supply, and the circuit device can be made smaller. can be achieved.

In the embodiment, the waveform to be superimposed on the reference voltage input to the comparator is a triangular wave, but it goes without saying that it may be a rectangular wave or other regularly changing waveform.

[Brief explanation of the drawing]

Figure 1 is a circuit diagram showing the main parts of a conventional step motor drive circuit, Figure 2 is a circuit diagram showing the main parts of a previously proposed step motor drive circuit that performs constant current control, and Figure 3 is a circuit diagram showing the main parts of a conventional step motor drive circuit. The waveform diagrams shown in FIGS. 4 and 5 showing temporal changes in the input and output voltages of the comparator in the circuit shown in the figure are for explaining one embodiment of the present invention. Circuit diagram showing the main parts of the motor drive circuit, Figure 5A
is a waveform diagram of the reference voltage input to the comparator for controlling the first excitation coil, B is a waveform diagram of the comparison signal output from this comparator, and C is a waveform diagram for controlling the second excitation coil. This is a waveform diagram of the reference voltage input to the comparator for performing the comparison, and the same figure is a waveform diagram of the comparison signal output from the comparator in C of the same figure. . 21A...First excitation coil 21B...Second excitation coil 22A, 22B...First transistor 23A
, 23B...second transistors 24A, 24
B...Third transistors 25A, 25B...
...Fourth transistor 28A, 28B...
- Current detection resistor 31A...A phase driver circuit 31B...B phase driver circuit 33A...A phase driver circuit 33B...π phase driver circuit 37A, 37B... Comparator 42...
...Reference voltage input terminal 51...Inverter

Claims (1)

[Claims] ' A switching means for individually switching the current flowing through the excitation coil of each phase of a bipolar-connected two-phase step motor, a current detection means for detecting the current flowing through the excitation coil of each phase, and the switching means Timing setting means for alternately setting the timing at which current can flow through the excitation coil of each phase so that the currents do not overlap each other when the current flowing in each phase exceeds a predetermined value; and timing setting means. and a driver for controlling the switching means on and off within a range in which the current detection means does not exceed a specified current flow value greater than or equal to the predetermined value at each time set by the means. A step motor drive circuit 0 characterized by