JP2547320Y2 - Independently driven constant current chopper drive circuit of inductive load - Google Patents

Description

[Detailed description of the invention] <Industrial application field> This invention is based on an inductive load with self-inductance,
For example, unlike the separately-excited type of stepping motor used in dot-wire printers, that is, the self-excited type in which a chopper signal is processed by processing the phase current itself, a method of obtaining a chopper signal for driving the chopper by a separately provided oscillation circuit is required. The present invention relates to a current chopper drive circuit.

<Prior Art> FIG. 4 shows an example of a conventional inductive load circuit of a separately excited constant current chopper type, that is, a drive circuit of a stepping motor for driving a carriage mounted on a dot wire printer or the like. This circuit includes a drive current variable control circuit 1 and a drive circuit 2, and drives the coils L1 (one phase) and L3 (three phases) of the stepping motor 3. Incidentally, 4
In the case of controlling a phase stepping motor, another drive circuit unit 2 and a coil L2 (two phases) of a motor (not shown),
L4 (4 phase) is required, but is omitted here.

In this drive circuit, in order to variably control the speed of the stepping motor 3 from a stop position to start acceleration, constant speed, deceleration stop, etc., the drive current value is switched in several stages by setting the corresponding voltage. Has been done. This switching is specifically described as follows.

First, in the drive current variable control circuit unit 1 of FIG.
DC component voltage from the oscillation circuit 4 (hereinafter referred to as DC component)
A triangular wave signal, which is a separately excited chopper signal having an AC component voltage (hereinafter, referred to as an AC component), is generated. The DC component is cut by the capacitor C1, and an AC component for a reference voltage is formed. Here, as the oscillation circuit 4, for example, a Miller integration circuit can be used. Such an oscillation circuit always has a DC component in addition to the AC component, and the amount of the DC component is undefined. Therefore, in order to obtain the AC component for the reference voltage, it is necessary to remove the DC component from the chopper signal of the oscillation circuit with a capacitor.

Also, the resistor R2 and the resistor
A voltage of (R1 · V2) / (R1 + R2) volts is formed as a basic DC component according to the voltage dividing ratio with R1. Then, any one or a combination of resistors R11, R12, and R13 selected based on the basic DC component and the current setting signals (A, B, and C) is inserted in parallel with R1. Is superimposed with the voltage obtained by the above, a DC component for reference voltage is formed.

Then, by superimposing the DC component for reference voltage and the AC component for reference voltage, a reference voltage, that is, a drive current value necessary for variably driving the stepping motor 3 as described above is set. Is formed, and this reference voltage is connected and input to the drive circuit unit 2.

<Problem to be Solved by the Invention> FIG. 5 shows the current of the coil L1 of the stepping motor 3 driven by the drive current variable control circuit unit 1 and the drive circuit unit 2 in the conventional circuit configured as described above. 7 shows an example of a waveform.

Here, the fact that a current waveform as shown in FIG. 5 is obtained by the reference voltage created in FIG. 4 will be briefly described with reference to both figures. As described above, I _A in FIG. 5, when the flow I _B, the current setting signal A, B, to the non-inverting input terminal of the comparator by the selection of the C (+), an average value in correspondence to the I _A
V _A, 20 KHz of corresponding to the I _B average value V _B (kilohertz) to 3
A voltage on which a triangular wave signal having a frequency of 0 KHz is superimposed appears.
By the way, when the phase designating signal PH1 is designated (PH3 is not designated at the same time), TR2 is turned on. In this state, when IC1 supplies the base current of TR1 based on the output of comparator 7 and TR1 is turned on, current I flows through the coil of L1. As a result, the voltage of the product I · R9 resistor and I R9 the inverting input terminal of the comparator 7 (-) appear in, for example, for I _B
In the case where V _B is set, comparison of V _B and the voltage I _B · R9 is made. And since the AC component is a triangular wave signal,
Magnitude of V _B and the voltage I _B · R9 is always cut instead, the comparator 7
Output is on, off repeatedly, thereby also on TR1, repeat off constant current I _B is maintained, so-called separately excited constant current chopper driving is performed. This is I _A
But the same is true.

As can be seen from FIG. 5, in the conventional circuit, when the current of the coil is changed, this current does not switch linearly or digitally but switches at a transient interval. That is, when switching the current value I _B or vice versa from the I _A, delay occurs that the time to reach the set value T. This corresponds to the reference voltage setting portion (X) of the drive current variable control circuit portion 1 connected / input to the drive circuit portion 2 in FIG.
Part) causes a delay. That is, since the AC component for reference voltage and the DC component for reference voltage are coupled immediately after the capacitor C1 in the portion of X, any one of the resistors R11, R12, and R13 or a combination thereof is used for setting the reference voltage. Is selected, the DC component transiently flows into or out of the capacitor C1 due to a change in the impedance on the DC component side. As a result, a delay of time T occurs in the setting of the reference voltage, and this delay is necessary. This is because there is a delay until the current value is reached.

By the way, if a time delay occurs to reach the required current value, it is not preferable in that the driving time is increased and the speed of the device is increased. In addition, the delay at the time of switching the current value is likely to cause the stepping motor to lose synchronism. To prevent the loss of synchronism and the delay time, the current flows more than necessary, so that the heat generated by the driving element and the stepping motor itself increases. And various problems such as the need to increase the power supply capacity. Furthermore, this leads to the necessity of using an expensive stepping motor of one rank higher to take a margin in consideration of a load.

Further, in this conventional circuit, the current setting signal must be increased in order to obtain a large number of variations of the set driving current value of the stepping motor, that is, three signals A, B, and C shown in FIG. To A, B, C,
There is also a problem that it has to be increased, such as D, E ...

<Means for Solving the Problems> In order to solve the above-mentioned technical problems, the present invention provides a drive circuit section for variably driving an inductive load, and a reference voltage for setting a variable drive current value of the inductive load. And a drive current variable control circuit section for setting and connecting to and inputting to the drive circuit section, the drive current variable control circuit section includes an oscillation circuit for generating a chopper signal having a DC component and an AC component,
A reference voltage AC component forming circuit having a capacitor for removing a DC component from a chopper signal from the oscillation circuit to form a reference voltage AC component; a voltage dividing circuit having a pair of resistors; and the voltage dividing circuit A reference voltage direct current component forming circuit having a plurality of reference voltage setting resistors for connecting one end thereof to a connection point of the two resistors, and forming a reference voltage direct current component by selecting the reference voltage setting resistor The reference voltage AC component from the reference voltage AC component forming circuit and the reference voltage DC component from the reference voltage DC component forming circuit are superimposed and coupled to be supplied to the drive circuit unit. In a separately excited constant current chopper drive circuit of an inductive load, a superposition coupling of a reference voltage DC component and a reference voltage DC component is performed by an operational amplifier.
The influence of the change in impedance accompanying the selection of the reference voltage setting resistor is prevented from affecting the capacitor in the reference voltage AC component forming circuit.

Further, in order to obtain a large number of variations in the set drive current value of the stepping motor without increasing the number of signal lines, the reference voltage is set via a decoder circuit.

<Operation> With the above circuit configuration, the influence on the AC component forming circuit for reference voltage due to the impedance change in the DC component forming circuit for reference voltage as in the coupling immediately after the conventional capacitor described above is avoided. Thus, there is no delay in setting the reference voltage, and the drive current of the stepping motor can be switched linearly and digitally. Further, by interposing the decoder circuit, a large number of variations of the set driving current value of the stepping motor can be obtained without increasing the current setting signal.

<Embodiment> Hereinafter, the present invention will be described in detail with reference to an embodiment shown in the drawings.

FIG. 1 shows a separately excited constant current chopper drive circuit of a stepping motor according to an embodiment of the present invention. This circuit comprises a drive current variable control circuit section 1 and a drive circuit section 2, and coils L1 (one phase) and L3 (3
Phase). In the case of driving a four-phase stepping motor, another set of the drive circuit unit 2 and coils L2 (two phases) and L4 (4
Phase) is required, but the description is omitted.

In the drive current variable control circuit section 1, a triangular wave signal which is a separately excited chopper signal having a DC component and an AC component from the oscillation circuit 4 passes through the input protection resistor R32 while the DC component is cut by the capacitor C2. It is input to the + input terminal of the operational amplifier 6 as a reference voltage AC component.

On the other hand, the DC component for the reference voltage is a current setting signal (A,
B, C), a resistor R2
If a predetermined voltage, for example, R21 is selected by one of the resistors selected from 1, 22,... R28 and the resistor R20, the stepping motor driving power supply voltage V2 is approximately [0.
7+ ｛R21 (V2-0.7) / (R21 + R20)] volts and is input to the negative input terminal of the operational amplifier 6 through the input protection resistor R33. Here, the numeral 0.7 is a voltage consumed by the decoder circuit 5.

The operational amplifier 6 superimposes the newly formed DC component and AC component to generate a reference voltage for variable current setting. Then, this reference voltage is connected and input to the drive circuit unit 2.

Here, the DC and AC components for the reference voltage are independently input to the + and-input terminals of the operational amplifier 6, respectively, and are superposed and coupled by a circuit inside the operational amplifier.
Even if the DC component caused by the selection of R21, 22,... R28 causes an impedance change, the reference voltage AC component side is not affected by the impedance change, and the delay in setting the reference voltage as in the above-described conventional example is eliminated. Will not occur. Therefore,
The reference voltage is output in a stable state.

Next, this reference voltage is connected and input to the drive circuit unit 2 through the resistor R3 and the + input terminal of the comparator 7.
On the other hand, the negative input terminal of the comparator 7 is a voltage generated by a resistor R9 that converts a current flowing in the phase (L1, L3) of the stepping motor 3 into a voltage, that is, the voltage is actually flowing to the stepping motor 3. Assuming that the current flowing through the coil is I at the actual voltage corresponding to the current, a voltage of I · R9 volts is input through the input protection resistor R10. And
The comparator 7 compares these two inputs to determine the magnitude of the two inputs, and controls ON / OFF of the transistor TR1 for controlling the drive voltage V1 to the stepping motor 3. At this time, one of the phase designation signals (PH1, PH3) of the stepping motor 3 is always at the logical H level, and both signals are at the same time at the H level.
It will never be a level. In this embodiment, it is assumed that PH1 is at H level and PH3 is at L level. That is, when TR1 turns on and TR2 turns on, a set current flows through one phase (L1) of the coil of the stepping motor 3.

FIG. 2 shows an example of a current waveform of the coil L1 of the stepping motor 3 according to the present embodiment.

Here, the fact that a current waveform as shown in FIG. 2 is obtained by the reference voltage generated in FIG. 1 will be briefly described with reference to both figures. I _A in FIG. 2, when the flow I _B, the current setting signal A, B, to the non-inverting input terminal of the comparator by the selection of the C (+), the average value V _A each corresponding to I _A, I _B voltage 20 kHz (kilohertz) to the triangular wave signal having a frequency of 30KHz is superimposed the average value V _B corresponds to appear. By the way, when the phase designation signal PH1 is designated, TR2 is turned on. In this state, when IC1 supplies the base current of TR1 based on the output of comparator 7 and TR1 is turned on, current I flows through the coil of L1. As a result, the voltage of the product I · R9 resistor and I R9 the inverting input terminal of the comparator 7 (-) appear in, for example, for I _B
In the case where V _B is set, comparison of V _B and the voltage I _B · R9 is made. And since the AC component is a triangular wave signal,
Magnitude of V _B and the voltage I _B · R9 is always cut instead, the comparator 7
Output is on, off repeatedly, thereby also on TR1, repeat off constant current I _B is maintained, so-called separately excited constant current chopper driving is performed. This is I _A
But the same is true.

According to Figure 2, a delay time such as T in FIG. 5 described above is not observed, it switched from I _A current value of the I _B or linear-digital not be current transient in the opposite Has been switched to.

Further, the variable current control circuit section 1 employs the decoder circuit 5 for selecting the reference voltage setting resistors R21, 22,... R28, so that the current setting signals (A, B,
Without increasing C), a large number of variations of the set driving current value of the stepping motor 3 can be obtained, and fine current setting according to the load state applied to the stepping motor 3 can be performed.

FIG. 3 shows a case where a plurality of current values are set and a current setting signal (A,
FIG. 6B is a diagram illustrating an example of a current waveform of a coil of the stepping motor 3 when switching is performed by the decoder circuit according to B and C). In FIG. 3, there is no time delay in any case of the current value switching, and the current is switched linearly and digitally.

In the present embodiment, the variable control of the drive current of the stepping motor 3 has been described. However, it is needless to say that the variable control of the drive current of another magnet such as an inductive load can be performed.

<Effect of the Invention> As described above, in the separately-excited constant current chopper drive circuit of the inductive load according to the present invention, the coupling between the reference voltage AC component and the reference voltage DC component is superimposed by the operational amplifier. The output voltage from the superimposed-coupled operational amplifier is connected / input to the drive circuit as a reference voltage for setting the drive current variable of the stepping motor, so that the stepping motor is variably driven. The current for switching is switched linearly and digitally without causing a time delay at the time of the switching. As a result, the stepping motor can be controlled at a higher speed, and the step-out that occurs when the stepping motor is started or stopped can be suppressed. Also, as before,
Since it is not necessary to use a stepping motor having a capacity larger than the load required for driving the dot wire or the like, the selection of the driving circuit element and the design of the capacity of the driving power supply can be made more efficient.

Further, since the selection of the resistor used for setting the reference voltage is performed by the decoder circuit, a large number of variations of the set driving current value of the stepping motor can be obtained without increasing the current setting signal, and the load can be increased. , The stepping motor can be controlled finely and efficiently.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing one embodiment of the present invention, FIG. 2 is an example of a current waveform of a coil L1 of a stepping motor driven by the circuit of FIG. 1, and FIG. FIG. 4 is a diagram showing an example of a current waveform of a coil of a stepping motor when a current is switched a plurality of times by a decoder circuit with a signal, FIG. 4 is a circuit diagram of a conventional stepping motor and a separately excited constant current chopper driving circuit, and FIG. FIG. 5 is a diagram illustrating an example of a current waveform of a coil of a stepping motor driven by the circuit of FIG. 4. DESCRIPTION OF SYMBOLS 1 ... Driving current variable control circuit part 2 ... Drive circuit part 3 ... Part of the coil of a stepping motor 4 ... Oscillation circuit 5 ... Decoder circuit 6 ... Operational amplifier 7 ... Comparator C ... Capacitor D ... Diode R ... Resistor TR ... Transistor IC ... Non-inverting circuit of open collector V1 ... Power supply voltage for driving stepping motor V2 ... Power supply voltage for control circuit L1, L3 ... Coil of stepping motor

Claims (2)

(57) [Scope of request for utility model registration] 1. A drive circuit for variably driving an inductive load, a drive current variable control circuit for setting a reference voltage for setting a variable drive current value of the inductive load, and connecting / inputting the drive current to the drive circuit. The drive current variable control circuit section includes an oscillation circuit that generates a chopper signal having a DC component and an AC component, and removes the DC component from the chopper signal from the oscillation circuit to generate a reference voltage AC component. A reference voltage AC component forming circuit having a capacitor to be formed; a voltage dividing circuit having a pair of resistors; and a plurality of reference voltage setting resistors each having one end connected to a connection point of both resistors in the voltage dividing circuit. A reference voltage DC component forming circuit for forming a reference voltage DC component by selecting a reference voltage setting resistor, and a reference voltage from a reference voltage AC component forming circuit. In a separately excited constant current chopper drive circuit of an inductive load adapted to superimpose and couple the current component and the reference voltage DC component from the reference voltage DC component forming circuit to the drive circuit section, The operational amplifier performs the superposition coupling of the AC component for reference and the DC component for reference voltage, so that the influence of the impedance change due to the selection of the reference voltage setting resistor affects the capacitor in the reference voltage AC component forming circuit. A separately excited constant current chopper drive circuit for an inductive load, characterized in that it is prevented. 2. A separately excited constant current chopper drive circuit according to claim 1, wherein a decoder circuit is provided, and said decoder circuit selects a reference voltage setting resistor.