JPH0317593Y2 - - Google Patents

Description

[Detailed description of the invention] (Field of industrial application) The present invention relates to a stepping motor drive circuit.
In particular, the present invention relates to a stepping motor drive circuit that drives a stepping motor with electromagnetic coupling between windings at a constant current using a chopper method.

(Prior Art) In order to maintain good torque characteristics of a stepping motor in a high-speed region, it is necessary to shorten the rise time of the winding current, and a chopper type constant current drive circuit is known as this type of circuit.

Figure 2 shows part of an example of a four-phase PM type stepping motor drive circuit using a conventional chopper type constant current drive.The stepping motor is driven in conjunction with another set of circuits with the same configuration (not shown). .
In the same figure, the stepping motor drive circuit is
It is composed of a switching circuit 4, windings 51 and 52, a feedback voltage generating circuit 6, an integrating circuit 7, and a comparing circuit 8. Switching circuit 4 is transistor 4
1 and 42, resistors 43 and 44, and a diode 45. The motor drive power supply +E1 is input to the emitter of the switching transistor 41, and is supplied from the collector of the transistor 41 to a common terminal of windings 51 and 52 of a stepping motor, which will be described later. The transistor 42 is provided to amplify the output signal from the comparison circuit 8 via a resistor 43 and to adjust the output signal polarity, and is connected from its collector to the base of the transistor 41 via a resistor 44. Diode 45 connects winding 5, which is an inductive load.
It is connected between the emitter and collector of the transistor 41 to flow a back electromotive current of 1.52.

The windings 51 and 52 are wound in the same direction around one core and have a common terminal at the center. Other terminals of the windings 51 and 52 are connected to phase excitation transistors 6, which will be described later.
1,62 collectors.

The feedback voltage generation circuit 6 is a phase excitation transistor 6
1, 62, a resistor 63, and diodes 64, 65. Transistors 61 and 62 are input terminal 1,
It is selectively driven by a phase excitation signal from 2. The emitters of the transistors 61 and 62 are connected to a current detection resistor 63, and the voltage generated across the resistor 63 is output to the integrating circuit 7 as a feedback voltage. Diodes 64 and 65 are connected between the collectors of transistors 61 and 62 and ground, respectively, in order to flow back electromotive currents generated in windings 51 and 52.

Integrating circuit 7 includes a resistor 71 and a capacitor 72, and delays the feedback voltage input from feedback voltage generating circuit 6 and outputs the delayed feedback voltage to comparison circuit 8.

Comparison circuit 8 consists of a single comparator 81. The comparator 81 compares the reference voltage input from the input terminal 3 to the non-inverting terminal with the feedback voltage input from the integrating circuit 7 to the inverting terminal, and outputs the comparison result to the switching circuit 4. In addition, power supply +E2 is comparator 8
1 is an open collector output, it is provided to drive the transistor 42 of the switching circuit 4 via the resistor 9 and the resistor 43.

Next, the operation will be explained. A phase excitation signal is input to input terminal 1, transistor 61 is turned on, and winding 5 is turned on.
When a current flows through the resistor 63, a feedback voltage proportional to the current is generated between the terminals of the resistor 63 via the transistor 61.
V _f is generated and input to the comparator 81 via the resistor 71 and capacitor 72 of the integrating circuit 7 . When this feedback voltage V _f increases and becomes higher than the reference voltage, the output voltage of the comparator 81 becomes a low voltage, and the transistor 42 is turned off. Therefore, transistor 4
1 is turned off, but since the magnetic flux of the winding 51, which is an inductive load, cannot suddenly change before and after the transistor 41 is turned off, the diode 65, the winding 52, the winding 51,
A back electromotive current flows through the loop of the transistor 61 and the resistor 63. Since the windings 51 and 52 are wound in the same direction around one iron core and are closely electromagnetically coupled, the current flowing through the windings 51 and 52 at the moment the switching transistor 41 is turned off is the same as when the transistor 41 is turned off. If the current that was flowing through the winding 51 until just before becomes I _P , it suddenly changes to 1/2 I _P.

As a result, the feedback voltage V _f across the resistor 63 also changes suddenly. This feedback voltage V _f is delayed by the integrating circuit 7 and input to the comparator 81 . When this input voltage falls below the reference voltage, the output voltage of the comparator 81 is inverted and becomes a high voltage, so the transistor 42 and the transistor 41 are turned on and the current flowing through the winding 51 increases again. The above process is repeated, and the current flowing through the winding is driven at a constant current. FIG. 3 is a diagram showing the feedback voltage V _f in the above circuit operation. In the figure, point A is the timing when the switching transistor 41 is turned on from off, and point B is the timing when the transistor 41 is turned off from on.

(Problems to be Solved by the Invention) However, the stepping motor drive circuit having the above configuration has the following problems.

The feedback voltage V _f generated across the resistor 61 is converted to a voltage with little fluctuation through the integrating circuit 7 and then compared with the reference voltage in the comparator 81, so that a voltage different from the actual current detection voltage may be different from the reference voltage. There is a drawback that accurate constant current driving according to the reference voltage cannot be performed. Furthermore, if the time constant of the integrating circuit is made small in order to achieve constant current drive with less error, there is a drawback that the chopping frequency becomes higher or becomes unstable, increasing the switching loss of the switching transistor 41.

The present invention solves the above problems and allows the feedback voltage, which is the actual current detection voltage, to be passed through an integrating circuit.
The present invention provides a stepping motor drive circuit that has a simple circuit configuration, performs accurate constant current drive in comparison with a reference voltage, and enables stable circuit operation.

(Means for Solving the Problems) In order to solve the above-mentioned problems, the present invention provides a stepping motor drive circuit that uses a chopper method to drive the current flowing through the windings of a stepping motor that are electromagnetically coupled to each other at a constant current. a feedback voltage generation circuit that generates a feedback voltage proportional to the current flowing through the winding; a comparator that compares the feedback voltage from the feedback voltage generation circuit with a reference voltage; and a switching circuit that switches the current flowing through the winding, and the comparator feeds back the output voltage of the comparator to a terminal to which the reference input voltage is input via a resistor, thereby adjusting the output voltage to the reference voltage. The reference voltage has a maximum value V _SU and a minimum value V _SL , and the distance between the maximum value V _SU and the minimum value V _SL is KV _SU > V _SL (K is 1 > K >0 and satisfies the relationship (a constant determined by the degree of electromagnetic coupling between the windings).

(Function) According to the present invention, since the stepping motor driving circuit is configured as described above, the technical means functions as follows. The feedback voltage generation circuit operates to directly input a feedback voltage proportional to the current flowing through the selected winding by inputting the phase excitation signal to the comparator, and the comparator generates a signal as the input feedback voltage increases. When the maximum value of the reference voltage obtained by the hysteresis characteristic exceeds the level of _VSU , it turns on and works to turn off the switching circuit. The switching circuit operates to turn off and not supply power to the winding, and the feedback voltage generation circuit operates to directly input a feedback voltage proportional to the back electromotive current flowing from the winding to the comparator. The comparator reduces the input feedback voltage to the minimum value of the reference voltage obtained with hysteresis characteristics.
When it reaches the V _SL level, it turns off and works to turn on the switching circuit. Therefore, the switching circuit turns on and works to supply power to the winding, and the feedback voltage generating circuit again works to output a feedback voltage proportional to the current flowing through the winding. The above operation is repeated to drive the current flowing through the winding at a constant current. Therefore, the problems of the prior art described above can be solved.

(Embodiment) FIG. 1 is a circuit diagram showing an embodiment of a stepping motor drive circuit according to the present invention. The same reference numerals as in FIG. 2 indicate identical components. The difference with Fig. 2 is that the integrating circuit 7 has been removed and the resistor 6 has been removed.
The second reason is that the feedback voltage V _f generated in the third embodiment is directly input to the comparator circuit 8a, and the second thing is that the comparator circuit 8a is configured as follows to give the comparator 81a a hysteresis characteristic.

The comparison circuit 8a includes a comparator 81a and resistors 82, 8
Consists of 3. The non-inverting terminal of the comparator 81a is connected to the input terminal 3 via a resistor 82 having a resistance value R1.
A resistor 8 having a resistance value R2 and connected to
3 to the output of the comparator 81a. The comparator 81a receives the reference input voltage V _i from the input terminal 3 via the resistor 82 to the non-inverting terminal, and as described later, the reference voltage V _S has two threshold voltages depending on the input state of the feedback voltage V _f . The switching circuit 4 compares the feedback voltage V _f input from the feedback voltage generation circuit 6 to the inverting terminal and outputs a signal indicating the comparison result.
Output to. The output of the comparator 81 is a high voltage when the comparator 81a is off, and a low voltage (approximately
0V).

Next, the operation of the stepping motor drive circuit according to the present invention will be explained. When a phase excitation signal is input to input terminal 1, transistor 61 is turned on. At this time, since the comparator 81a is turned off and the transistor 42 is turned on, the switching transistor 41 is turned on, and power is supplied from the power supply +E1 to the winding 51 through the transistor 41, and a current flows through the winding 51. flows. Therefore, the resistance 63
A feedback voltage V _f proportional to this winding current is generated between the terminals of the transistor 61 via the transistor 61 . This feedback voltage V _f is directly input to the inverting terminal of the comparator 81a and increases. Here, if the resistance values of the resistors 9 and 41 are R3 and R4, respectively, there is a relationship of R3<<R4. Further, assuming that the base current of the transistor 41 can be ignored, and the value of the reference voltage V _S of the comparator 81a at this time is V _SU , the threshold value V _SU is expressed by the following equation.

V _SU = R2 + R3 / R1 + R2 + R3V _i + R1 / R1 + R2 + R3E2... (1) When the feedback voltage V _f increases and exceeds the level of the threshold V _SU , the comparator 81a turns on and the transistor 4
1 and 42 are turned off. Therefore, no power is supplied to the winding 51 from the power supply +E1, and the current flowing through the winding 51 until the switching transistor 41 is turned off flows through the diode 65 as explained in the conventional example of FIG. It flows around the loop that it passes through. At this time, the comparator 81a is in an on state, and if the value of the reference voltage V _S of the comparator 81a is V _SL , this threshold value V _SL is expressed by the following equation.

V _SL =R2/R1+R2V _i (2) When the feedback voltage V _f decreases and becomes smaller than the threshold value V _SL , the comparator 81a is turned off and the transistor 42 is turned on. Therefore, the switching transistor 41 is turned on, and the current flowing through the winding 51 increases again. The above process is repeated,
The current flowing through the winding 51 is driven by constant current.

Here, the resistance value of each resistor is set so that the threshold value V _SU expressed by equation (1) and the threshold value V _SL expressed by equation (2) have the following relationship.

V _SL = 1/2V _SU -1/2ΔV (3) Therefore, the reference voltage when the comparator 81a is off
V _S becomes the threshold value V _SU , and the reference voltage V _S when it is on becomes the threshold value V _SL , so the winding current flowing through the winding 51 is V _SU /R _f , where the resistance value of the resistor 63 is R _f .
It will change between V _SL /R _f . As mentioned above, the moment the comparator 81a is turned on and the transistors 42 and 41 are turned off, the winding 51 is disconnected from the power supply +E1, but due to the electromagnetic coupling between the windings 51 and 52, the winding current is line 51
The current value suddenly decreases to 1/2 of the value that was flowing through it, that is, 1/2 V _SU /R _f . As a result, the feedback voltage V _f which is the winding current detection voltage also rapidly decreases to 1/2 V _SU . However, the comparator 81a does not turn off even if the current suddenly decreases to 1/2V _SU , and the comparator 81a does not turn off from on until the current further decreases by an amount corresponding to 1/2ΔV and reaches the threshold V _SL level. Change. Also, at the moment when the comparator 81a is turned off and the transistors 42 and 41 are turned on, the winding current is twice the current flowing through the windings 51 and 52, that is, (V _SU −ΔV)/ rapidly increases to R _f . As a result,
The feedback voltage V _f which is the winding current detection voltage is also V _SU −ΔV
However, the current further increases by an amount corresponding to ΔV, and the comparator 81a changes from off to on only when it reaches the level of the threshold value _VSU . The relationship between the hysteresis voltage due to ΔV and the winding current detection voltage V _f is shown in FIG. In the figure, point A is the timing at which the switching transistor 41 turns from off to on, and point B is the timing at which the transistor 41 turns from on to off. Note that the coefficient 1/2 in equation (3) above generally changes due to the electromagnetic coupling between the windings 51 and 52, and is generally determined by the constant K (0<K<1), which is determined by the degree of electromagnetic coupling between the windings. Become. Therefore, the relationship KV _SU >V _SL holds between the threshold values V _SU and V _SL .

The operation when driving the current flowing through the winding 51 at a constant current has been described above, but when a phase excitation signal is input to the input terminal 2, the same operation is performed for the current flowing through the winding 52. .

In the above embodiment, a case has been described in which the electromagnetic coupling between the windings is dense and the sudden change in current is 1/2, but it is clear that the present invention is not limited to this.

(Effects of the invention) As explained above in detail, according to the invention,
Since the feedback voltage, which is the detection voltage of the current flowing through the winding, is directly input to the comparator without going through an integrating circuit, accurate constant current drive is possible, and the hysteresis effect ensures stable circuit operation with a simple circuit configuration. This has the advantage of being possible.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an embodiment of the stepping motor drive circuit according to the present invention, FIG. 2 is a diagram showing a conventional stepping motor drive circuit, and FIG. 3 is an explanatory diagram of the circuit operation of FIG. FIG. 4 is an explanatory diagram of the circuit operation of FIG. 1. 4...Switching circuit, 51, 52...Winding, 6...Feedback voltage generation circuit, 8a...Comparison circuit, 81a...Comparator, 82, 83...Resistor.

Claims (1)

[Claims for Utility Model Registration] In a stepping motor drive circuit that uses a chopper method to drive the current flowing through the windings of a stepping motor that are electromagnetically coupled to each other at a constant current, a feedback voltage proportional to the current flowing through the windings is provided. a comparator that compares the generated feedback voltage generation circuit with the feedback voltage from the feedback voltage generation circuit; and a switching circuit that switches the current flowing through the winding based on the output signal of the comparator. The comparator connects the output voltage of the comparator to a second terminal to which the reference input voltage is input via the first resistor.
By feeding back the resistor, the reference voltage has a hysteresis characteristic, and the reference voltage has thresholds of a maximum value V _SU and a minimum value V _{SL ,}
and the minimum value V _SL, KV _SU > V _SL (K is 1>K>
0, a constant determined by the degree of electromagnetic coupling between the windings).