JP2661714B2 - Stepping motor drive circuit - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a circuit for driving a stepping motor at a constant current by a chopper method, and more particularly to a stepping motor for improving instability caused by a floating capacity of a winding of a stepping motor. It relates to a drive circuit.

[Prior Art] In order to maintain good torque characteristics of a stepping motor in a high-speed rotation region, it is necessary to shorten a rise time of a current flowing through a winding of the stepping motor. There is a drive circuit.

FIG. 2 shows a part of a conventional four-phase stepping motor driving circuit using a chopper type constant current driving circuit. The stepping motor is driven together with another set of circuits having the same configuration (not shown).

In the figure, a motor driving power supply E1 is supplied to a common terminal of windings L1 and L2 of a stepping motor via an emitter and a collector of a switching transistor TR1. Winding
The other terminals of L1 and L2 are each a current detection resistor.
The transistors TR3 and TR4 are connected to the collectors of the phase excitation transistors TR3 and TR4 commonly connected to Rf, and are selectively driven by the phase excitation signals from the input terminals 1 and 2, respectively. The current flowing through the winding L1 or L2 by this drive is
It flows into the current detection resistor Rf via the transistor TR3 or TR4. The emitter common connection point of the transistors TR3 and TR4 connected to the resistor Rf is connected to the negative input terminal of the comparator COMP1, and the voltage generated at the resistor Rf is input to the negative input terminal of the comparator COMP1 as the feedback voltage Vf. The positive input terminal of the comparator COMP1 is connected to the input terminal 3 to which the reference input voltage Vi is input via an input resistor R1 and connected to the output terminal of the comparator COMP1 via a feedback resistor R2. In the comparator COMP1, the reference input voltage Vi is input from the input terminal 3 to the positive input terminal via the resistor R1, and as will be described later, a reference voltage Vs having two threshold voltages depending on the output state of the comparator COMP1, The feedback voltage Vf input from the resistor Rf to the negative input terminal is compared, and the comparison result is output to the transistor TR2 via the buffer BUF1. When the comparator COMP1 has an open collector output, the power supply E2 is connected to the resistor R3 and the buffer BUF1.
Is a power supply for driving the transistor TR2 via the. The transistor TR2 amplifies the output signal of the buffer BUF1 and adjusts the output signal polarity, that is, is provided to invert the output signal polarity.
1 is connected via a resistor R4 and the transistor TR1
For switching control. Therefore, the power supply to the windings L1 and L2 is chopper-controlled by the output signal of the comparator COMP1. Note that the diode D1 is a feedback rectifier diode connected between the ground and the collector of the switching transistor TR1 in order to flow back electromotive current of the windings L1 and L2, which are inductive loads.

The switching circuit 5 is constituted by the buffer BUF1, the transistor TR2, the resistor 4, and the switching transistor TR1.

The operation of the above-described stepping motor drive circuit when the winding L1 of the winding L1 or L2 is driven at a constant current with a predetermined current will be described. The same applies to the winding L2.

When the phase excitation signal is input to the input terminal 1, the transistor TR3 turns on. At this time, the feedback voltage Vf is still small and the output of the comparator COMP1 is in the high voltage state, and the buffer BUF
Since the transistor TR2 is turned on via the switching transistor TR1, the switching transistor TR1 is turned on, and power is supplied from the power supply E1 to the winding L1 via the transistor TR1.
Current flows through 1. Accordingly, a feedback voltage Vf proportional to the winding current is generated between the terminals of the current detection resistor Rf via the transistor TR3, and the feedback voltage Vf is input to the negative input terminal of the comparator COMP1, and the value is applied to the winding. It increases with increasing current. Here, assuming that the input current of the buffer BUF1 can be ignored, assuming that the higher value of the reference voltage of the comparator COMP1 in the output off state (high voltage state) is Vsu, the threshold value Vsu is expressed by the following equation. .

Vsu = (R2 + R3) Vi / (R1 + R2 + R3) + R1E2 / (R1 + R2 + R3) (1) When the feedback voltage Vf increases and exceeds the threshold Vsu level,
Since the output of the comparator COMP1 turns on, the buffer BUF1
Turns off the transistor TR2. Therefore, although the switching transistor TR1 is turned off, the transistor TR1
Before and after turning off, the magnetic flux of the winding L1, which is an inductive load, cannot change suddenly. Decrease. At this time, the output of the comparator COMP1 is in the on state, and the comparator in this output on state is in the on state.
If the lower value of the reference voltage of COMP1 is Vsl, this threshold
VsL is represented by the following equation.

VsL = R2Vi / (R1 + R2) + R1VoL / (R1 + R2) (2) where VoL is the ON voltage of the comparator COMP1 (≒ ov) When the feedback voltage Vf decreases and becomes lower than the threshold VsL level, Output becomes high voltage and buffer B
The transistor TR2 is turned on via UF1. Therefore, the switching transistor TR1 turns on, a current flows again through the winding L1, and the current increases.

The above process is repeated, and the winding L1 is driven at a constant current.

FIG. 3 is a waveform diagram showing the state of the feedback voltage Vf and the output signal of the comparator COMP1 in the circuit operation described above. In FIG. 3, point A is the timing when the switching transistor TR1 switches from on to off, and point B is the timing when the transistor TR1 switches from off to on. While a constant current drive, and the winding current fall time t _f from the threshold Vsu to VsL, stepping motor chopping period of total time of the winding current rise time T _r from the threshold VsL to Vsu driven .

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

In the case of a stepping motor in which the two-phase windings L1 and L2 are bifilar wound, since the windings L1 and L2 are wound in pairs on the same stator, as shown by the broken lines in FIG. L2
The floating capacitances C1 to C3 exist between the respective terminals. When the switching transistor TR1 is turned on from off, the charging current to the floating capacitances C1 to C3 flows through the current detection resistor Rf, and particularly the winding capacitance is large, and therefore the floating capacitance is large in a stepping motor having a large number of windings. Since C1 to C3 are also large, the feedback voltage as a noise component generated in proportion to the charging current also becomes large. As a result, before the winding current of the winding L1 or L2 reaches the predetermined value, the charging voltage causes the feedback voltage to exceed the threshold voltage Vsu of the comparator COMP1 to turn on the comparator COMP1, so that the switching transistor TR1 is turned on. Since the winding current is turned off and the winding current is reduced, there has been a problem that constant current driving cannot be performed stably.

As a countermeasure, a method was considered in which an RC filter was inserted between the current detection resistor Rf and the negative input terminal of the comparator COMP1 to remove the floating capacitance charging current component of the feedback voltage. As a result, the winding current component is also delayed, and the chopping frequency is reduced to an audible frequency, so that there is a disadvantage that an oscillating sound is generated.

SUMMARY OF THE INVENTION An object of the present invention is to provide a stepping motor drive circuit that eliminates the above-mentioned problems and can stably drive at a constant current irrespective of the floating capacity of the stepping motor winding.

Means for Solving the Problems A stepping motor drive circuit according to the present invention adds a feedback voltage generated in proportion to a current flowing through a winding of a stepping motor to a comparison circuit, and provides a feedback voltage higher than a reference voltage set in the comparison circuit. When the voltage is low, the switching transistor of the switching circuit is turned on to supply power to the winding, and when the feedback voltage is higher than the reference voltage, the switching transistor is turned off to release the energy stored in the winding. Thus, in the stepping motor drive circuit for driving the winding at a constant current, a signal generation circuit for turning on the switching transistor for a predetermined period is provided between the comparison circuit and the switching circuit.

This signal generation circuit is turned on by a comparison circuit output generated when the feedback voltage generated in proportion to the charging current flowing to charge the floating capacitance of the winding becomes larger than the reference voltage when the switching transistor is turned on from off. A signal is generated and has a function of outputting the ON signal to the switching circuit at least continuously during a period until the feedback voltage by the charging current becomes smaller than the reference voltage. Power.

[Operation] When the switching transistor changes from off to on, the current flowing through the winding via the switching transistor is initially used as a charging current for charging the floating capacitance of the winding. Since the charging current flows instantaneously,
Its value is large, so that the feedback voltage, which occurs in proportion to the current, quickly becomes larger than the reference voltage.

Then, if only the comparison circuit output is used, the switching transistor of the switching circuit is turned off before the winding current reaches a predetermined value, so that power is supplied to the winding only for a short time. . However, in the present invention, since the signal generation circuit is provided between the comparison circuit and the switching circuit, the ON signal is output from the signal generation circuit to the switching circuit when the feedback voltage due to the charging current exceeds the reference voltage. .

Therefore, the power supply to the winding is continued without interruption in order to keep the switching transistor that is about to be turned off in the on state.

As a result, even when charging the floating capacity of the winding, the current flowing through the winding does not decrease.

[Embodiment] An embodiment of the present invention will be described below with reference to FIG. 1 and FIGS.

FIG. 1 shows a part of an example of a stepping motor driving circuit according to the present invention using a chopper type constant current circuit. The stepping motor is driven together with another set of circuits having the same configuration (not shown).

In FIG. 1, the same components as those in the conventional example shown in FIG. 2 are denoted by the same reference numerals, and description thereof will be omitted.

The difference between the drive circuit of the present invention and the conventional example shown in FIG. 2 is as follows.

That is, a pulse generation circuit 4 as a signal generation circuit configured as follows is provided between the comparator COMP1 and the buffer BUF1 at the input stage of the switching circuit 5, and the output voltage of the comparator COMP1 becomes high. The switching transistor TR of the switching circuit 5 that is to be turned off for a certain time after
The point is that 1 is turned on. Pulse generation circuit 4
Starts at the time when the output signal of the OR gate OR1 changes from "0" to "1" at a time when the output signal of the OR gate OR1 is added between the comparator COMP1 and the buffer BUF1 of the switching circuit 5, and a predetermined time width t A monostable multivibrator circuit (hereinafter simply referred to as a monomulti circuit) MS that generates a pulse of _w
Consists of one. The output signal of the comparator COMP1 is input to one input terminal of the OR gate OR1, and the output signal of the comparator COMP1 is input to the other input terminal of the OR gate OR1 while the signal of the positive output signal of the monomulti circuit MS1 is “1”. In order to turn on the switching transistor TR1 ignoring the change, the positive output signal of the mono-multi circuit MS1 is input.

Next, the operation of the drive circuit having the above configuration when the switching transistor TR1 is repeatedly turned on and off and the winding L1 is driven at a constant current with a predetermined current will be described with reference to FIG.

The phase excitation signal is input to the input terminal 1 and the transistor TR
When the current of the winding L1 reaches a predetermined current while the switch 3 is on and the feedback voltage Vf generated in the feedback resistor Rf exceeds the level of the threshold Vsu of the comparator COMP1, the comparator which has been turned off until then. When COMP1 is turned on, the output of the OR gate OR1 becomes "0", the transistor TR2 and the switching transistor TR1 are turned off via the buffer BUF1, and the current in the winding L1 decreases. Thus, when the feedback voltage Vf decreases and becomes lower than the level of the threshold value VsL of the comparator COMP1, the output of the comparator COMP1 becomes a high voltage, and the output of the OR gate OR1 changes to "1". The OR gate outputs of OR1 "0" from the change point to "1" to start the mono-multi circuit MS1, positive output signal of the multivibrator circuit MS1 becomes "1" for a predetermined time t _w.

By the way, since the output of the OR gate OR1 becomes “1”, the transistor TR2 and the switching transistor TR1 turn on via the buffer BUF1, and the current of the winding L1 increases.
Immediately after the switching of the switching transistor TR1 from off to on, a charging current for charging the floating capacitances C1, C2, and C3 of the winding flows. The feedback voltage Vf increases in a pulsed manner by this charging current, exceeds the level of the threshold Vsu of the comparator COMP1, turns on the comparator COMP1 (FIG. 4A), and tries to turn off the switching transistor TR1. But,
Floating the output pulse width t _w of the mono-multi circuit MS1 capacity C1~C3
If it is set longer than the charging time t _c, the other terminal of the OR gate OR1 is “1” during this time, so the output of the OR gate OR1 holds “1” and the transistor TR2 is switched via the buffer BUF1 and the transistor TR2 is switched. The transistor TR1 keeps on. When the charging current to the floating capacitances C1, C2, and C3 of the windings disappears, the pulse voltage generated in the feedback resistor Rf also disappears, and becomes lower than the threshold level VsL of the comparator COMP1.
The output of 1 becomes a high voltage (FIG. 4 (b)). Thus, because it can turn on the switching transistor TR1 by the comparator COMP1 output signal from the previous predetermined time t _w has elapsed, even if the positive output signal is "0" of the mono-multi circuit MS1, turn the monostable multivibrator circuit MS1 Instead, the comparator COMP1 takes over the turning on of the switching transistor TR1. Thereafter, when the current of the winding L1 supplied with power reaches a predetermined current, the feedback voltage Vf exceeds the threshold level Vsu of the comparator COMP1, and the comparator COMP1 is turned on again (fourth).
(C).

The above process is repeated, and the current flowing through the winding L1 is driven by a constant current.

Note that the feedback voltage Vf in the circuit operation and the comparator COMP1
In FIG. 4 showing the relationship between the output signal and the output pulse of the mono-multi circuit MS1, point A is the timing when the switching transistor TR1 is turned off from on and B is
The point is the timing when the transistor TR1 is turned on from off. Chopping cycle time that the constant current drive is the total time of the conventional example in floating the absence of capacity as well as winding current fall time t _f and the winding current rise time t _r (t _r>
If you have a t _w).

The operation in the case where the current flowing through the winding L1 is driven by the constant current has been described above. However, the operation is similarly performed with respect to the current flowing through the winding L2 when the phase excitation signal is input to the input terminal 2.

FIG. 5 shows another embodiment of the pulse generation circuit according to the present invention, in which the output signal of the pulse generation circuit is compared with a comparator COMP.
Unlike the pulse generation circuit 4 of FIG. 1 in which the output signal of the output signal 1 and the positive output signal of the monomulti circuit MS1 are ORed, the output signal of the pulse generation circuit is only the positive output signal of the monomulti circuit MS1. is there. In the stepping motor drive circuit of FIG. 1 in which this pulse generation circuit is adopted,
When the winding L1 or L2 is driven with a constant current, the chopping cycle is the output pulse width t _w of the mono-multi circuit MS1.
The only point determined by the total time of the winding current fall time t _f from the threshold voltage Vsu until VsL differs from the Figure 1 embodiment, the same function at all with respect to the floating capacitance charging current.

As described above, according to the present embodiment, the current supply to the winding L1 or L2 is temporarily stopped by the feedback voltage Vf caused by the floating capacitance charging current generated when the switching transistor TR1 changes from off to on. To prevent dripping, a pulse generating circuit 4 for generating a pulse having a predetermined time width at the time of charging is provided, and regardless of the feedback voltage Vf, the switching transistor TR1 of the switching circuit 5 is turned on during that time, and the winding L1 or Since the current supply to L2 is continued, even if the winding L1 or L2 is bifilar wound and a floating capacitance is present, the winding current will be reduced when power is supplied to the winding L1 or winding L2. The constant current drive does not become unstable due to the decrease.

Further, since the pulse generation circuit 4 does not delay the signal but forms a pulse signal for power supply compensation, an RC filter is inserted between the current detection resistor Rf and the comparator COMP1. Unlike the one that removes the floating capacitance charging component of the feedback voltage, the chopping frequency does not drop to the audible frequency, and no oscillation sound occurs.

Note that the pulse generation circuit is not limited to the one in the above embodiment, and any pulse generation circuit having a function of turning on a switching transistor of a switching circuit that is to be turned off at least when charging the floating capacitance of the winding is used. good.

According to the present invention, a signal generation circuit that outputs an ON signal to the switching circuit for a predetermined time when the floating capacitance of the winding is charged is provided between the comparison circuit and the switching circuit, and at least the ON signal is generated. During this period, the power supply to the winding is continued, so that it is possible to effectively avoid a decrease in the winding current due to the charging current immediately after the power supply flowing through the floating capacity of the winding, and Regardless of the presence or absence of the floating capacity, the stepping motor can be stably driven at a constant current.

[Brief description of the drawings]

1 is a stepping motor drive circuit diagram showing an embodiment of the present invention, FIG. 2 is a conventional stepping motor drive circuit diagram, and FIG. 3 is a waveform diagram showing a state of a feedback voltage in the circuit operation of FIG. FIG. 4 is a waveform diagram showing the feedback voltage, the output pulse of the mono-multi circuit, and the state of the switching transistor in the circuit operation of FIG. 1, and FIG. 5 is a circuit showing another embodiment of the pulse generating circuit in FIG. FIG. 4 ... Pulse generation circuit, 5 ... Switching circuit, Vs ...
... Reference voltage, Vf ... Feedback voltage, TR1 ... Switching transistor, L1, L2 ... Stepping motor winding, C
1, C2, C3 ... The floating capacity of the winding.

Claims (1)

(57) [Claims] 1. A stepping motor drive circuit having a comparison circuit for comparing a reference voltage with a feedback voltage generated in proportion to a current flowing through a winding of a stepping motor, wherein a switching transistor of the switching circuit is turned on from an off state. After the power is supplied to the winding, the switching transistor is turned off by the comparison circuit detecting that the feedback voltage has become larger than the reference voltage, and the energy stored in the winding is released. In the stepping motor drive circuit for driving the winding at a constant current, between the comparison circuit and the switching circuit, after the switching transistor is turned on from the off state, at least to charge the floating capacity of the winding. The feedback voltage generated in proportion to the flowing charging current has become larger than the reference voltage A stepping motor drive characterized in that a signal generating circuit for generating a control signal for continuously maintaining the switching transistor in an on state until the voltage is reduced again is provided, and power is supplied to the windings during the period. circuit.