JPS6315835B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a final stage power amplifier for driving a servo motor.

As is well known, an error signal indicating the difference between a command speed signal (or position signal) and an actual speed signal is amplified to drive a servo motor, and a movable object connected to the servo motor is smoothly started and stopped. In a positioning control device, the quality of the final stage amplifier, that is, the DC servo amplifier, which serves as the drive circuit for the servo motor, influences the function of the entire control device. This type of DC servo amplifier uses an applied voltage method to
There are two types: a dropper type that applies voltage continuously and a chopper type that applies voltage intermittently. Depending on the configuration of the switching element, there is a T type that uses two switching elements and an H type that uses four switching elements.
It is roughly divided into types. Each of these systems has its advantages and disadvantages, but when driving a motor at low power and high speed, an H-type chopper amplifier is mainly used. However, in conventional chopper amplifiers, the chopper frequency changes depending on the current value, and especially in the static region, the chopper frequency decreases and an audible oscillation sound is generated. We had no choice but to adopt a method of cutting off the excitation. This is because in a normal motor that has clicks, if the excitation is cut off in the stationary region in order to stop the oscillation noise, the stationary position will move, making precise position control impossible.

The present invention has been made to solve the above-mentioned conventional problems, and in order to drive a motor at low power and high speed, a combination of a T-type dropper amplifier and a T-type chopper amplifier is operated with two power supplies, and it also operates in a stationary region. Even with a minute current, the chopper operates at a frequency above the audible range to eliminate motor oscillation noise when the motor is stationary without cutting off excitation. Hereinafter, the contents of the present invention will be explained in detail with reference to the drawings.

FIG. 1 shows a schematic block diagram of a servo motor driving amplifier according to the present invention. The servo motor drive targeted by the present invention uses a constant current drive method. Therefore, the error signal voltage is kept below certain values with upper and lower limits, and current feedback is performed to the non-inverting Schmitt circuit to maximize the positive and negative motor current. The basic operation is to keep the value constant.
This facilitates servo control and protects the motor itself from excessive heat generation.

In FIG. 1, an appropriately amplified error signal is input to a voltage limiter circuit 1, and its upper and lower limits are limited to below certain values. The error signal passed through the voltage limiter circuit 1 is sent to a non-inverting amplifier 2.
and is applied to a non-inverting Schmitt circuit 6, and the output of the non-inverting Schmitt circuit 6 is applied to a Miller integrator 8, which drives a servo amplifier 3 and a servo amplifier 7, respectively. Here, the non-inverting Schmitt circuit 6
Assuming that there is no current feedback to the mirror integrator 8, since the Miller integrator 8 is of an inverting type, the output of the servo amplifier 3 and the output of the servo amplifier 7 are always in a relationship of opposite polarity. However, by detecting the motor current by a resistor in the motor 4 and current detector 5 connected in series between both servo amplifiers 3 and 7, and feeding it back to the non-inverting Schmitt circuit 6, normally The output of the non-inverting Schmitt circuit 6 oscillates as a rectangular wave having positive and negative polarities depending on the state of the sum of the error signal and the current value detection signal, which have opposite polarities to each other. When this rectangular wave is mirror-integrated by the mirror integrator 8 and the sawtooth wave is inputted to the servo amplifier 7, the servo amplifier 7 starts a chopper operation. That is, the servo amplifier 3 controls the voltage applied to the motor 4 and the current direction, and the servo amplifier 7 controls the magnitude of the motor current and the chopper frequency.

In conventional H-type chopper amplifiers, the chopper frequency in the stationary region drops to the audible range.To prevent this, we use a special motor with less clicks that prevents the motor from rotating even when the motor is turned off. The method used was to turn off the electricity. In contrast, in the present invention, by lowering the gain of the servo amplifier 3 and configuring an oscillation circuit with a non-inverting Schmitt circuit 6 and a Miller integrator 8, even in the case of a minute current at rest, a frequency higher than the audible range can be achieved. It is designed to perform chopping motion.

FIG. 2 shows a specific example of the circuit configuration of FIG. 1. In FIG. 2, the same blocks as in FIG. 1 are labeled with the same numbers. The error signal is input to the voltage limiter circuit 1, where it is suppressed to below a constant positive and negative value by a positive constant voltage source and a negative constant voltage source through diodes D17 and D18. The error signal passed through this voltage limiter circuit 1 is given to a non-inverting amplifier 2, and the output of the non-inverting amplifier 2 becomes an input to a servo amplifier 3 composed of multi-stage transistors. By driving either one of Q2, motor 4
Controls the direction of current flow. As previously mentioned,
Since the error signal is limited to a certain value or less by the voltage limiter circuit 1, the current value flowing through the motor 4 is naturally kept below a certain value. The gains of the servo amplifier 3 and the non-inverting amplifier 2 are kept low, as mentioned above, in order to maintain the chopper frequency at a high frequency when the motor is stationary. Q
The slew rate at the connection point of the diodes D1 and D2 connected in series with the transistor Q2 is reduced, and the transistor Q
The purpose is to prevent short circuit current in Q1 and Q2.
In order to reduce the gain, the emitters of the first-stage transistors Q5 and Q6 of the servo amplifier 3 are grounded through a resistor R6 connected in series with a group of diodes D5 to D8 connected in parallel in the opposite direction, and further connected to the diode D6. The gain is lowered by connecting a resistor R5 from the connection point with the resistor R6 to the connection point between the diodes D1 and D2. At the same time, in order to keep the gain of the servo amplifier 3 constant, the potential at the connection point between the diodes D1 and D2 of the servo amplifier 3 is negatively fed back to the non-inverting amplifier 2. Furthermore, in order to prevent short circuits between the transistors Q1 and Q2, it is effective to provide a dead zone in the front stage of the servo amplifier 3.
~D8 and the base-emitter voltages of transistors Q5 and Q6 form this dead zone. Therefore,
The delay time of transistors Q1 and Q2 is determined by the voltage of this dead zone and the slew rate of the emitter of transistor Q5.

Conventional drive circuits return the back electromotive voltage generated when the motor's current direction is switched to the power supply, but this has the problem of causing the power supply voltage to fluctuate. Therefore, in this embodiment, the back electromotive voltage is suppressed inside the servo amplifier 3 to stabilize the power supply voltage. In FIG. 2, diodes D1 and D2 act to suppress this back electromotive force. However, since there is a limit to the withstand voltage of the diode, a back electromotive voltage exceeding a certain level is detected by the Zener diode D3 or D4 and the transistor Q
1. I try to consume it in Q2. in this case,
Short-circuit diodes D1 and D2 to create a negative power supply (-V)
is a diode anode, the cathode is connected to the base of transistor Q1, and similarly, the positive power supply (+
It is also possible to make V) a diode cathode and connect the anode to the base of the transistor Q2, but in this case, the heat generation of the transistors Q1 and Q2 increases. However, in this case, transistor Q2
A PNP transistor is used for the transistor Q
The emitter of Q8 is connected to -V, and the emitter of transistor Q8
The collector of Q2 must be connected to the base of transistor Q2.

On the other hand, a current detector 5, a non-inverting Schmitt circuit 6, a Miller integrator 8, and a servo amplifier 7 control the current value of the motor 4 and its chopper frequency. The output of the voltage limiter circuit 1 is input to the non-inverting amplifier 2, and is also input to the operational amplifier OP3 of the non-inverting Schmitt circuit 6 through a resistor R27. Further, the motor current detected by the current detector 5 is also input to the operational amplifier OP3 through resistors R25 and R26. Normally, the voltage difference between the two is very small, so the operational amplifier OP
Reversing 3 is not easy. This is aided by capacitor C2 and resistor R29, which constitute a positive feedback circuit for operational amplifier OP3, and capacitor C4, which feeds back the output of Miller integrator 8 to the bias point of operational amplifier OP3. In other words, capacitor C2 and resistor R help the rise of the input signal when it changes.
29, and once the output of the operational amplifier OP3 rises, the capacitor C4 holds the output of the operational amplifier OP3 against changes in the bias point. In other words, the output of the operational amplifier OP2 that constitutes the Miller integrator 8 is a sawtooth wave whose slope is always constant, so the connection point between the resistors R28 and R31, which is the bias point of the operational amplifier OP3, is always positive or negative. is maintained at a constant bias voltage of Another purpose of making the output of the operational amplifier OP2, ie, the input of the servo amplifier 7, a sawtooth wave is to protect the final stage transistors Q3 and Q4 of the servo amplifier 7 from short-circuit current. Although the servo amplifier 7 does not have anything equivalent to the resistor R5 of the servo amplifier 3, this is to increase the gain of the servo amplifier 7, and the dead zone described above still exists. The reason why the gain is set high is to reduce the possibility that the transient heat loss of the transistors Q3 and Q4 will increase due to the high frequency of the servo amplifier 7 and the sawtooth wave input. Diodes D9 and D10 connected in parallel between the collector and emitter of transistors Q3 and Q4 of servo amplifier 7 are called flywheel diodes, and when discharging the current charged in the inductance component of motor 4, these diodes becomes conductive.

Next, the operation of each circuit with respect to positive and negative error signals will be comprehensively explained. First, when the error signal becomes a sufficiently positive voltage from zero, the OP1 output of the non-inverting amplifier 2 becomes positive, and the transistor Q of the servo amplifier 3
5, Q7, and Q1 are turned ON. That is, the connection point between the diodes D1 and D2, which is the output of the servo amplifier 3, becomes a positive voltage. Since the motor current cannot rise instantaneously due to a time constant, the current flowing through resistor R27 is greater than the current flowing through resistor R26. Therefore, the OP3 output of the non-inverting Schmitt circuit 6 becomes positive, and the OP2 output of the Miller integrator 8 becomes negative. As a result, transistors Q12 and Q of the servo amplifier 7
10 and Q4 are turned on, and the connection point between transistors Q3 and Q4, which is the output of the servo amplifier 7, becomes a negative voltage. At this time, the current path of motor 4 is positive power supply (+V) → transistor Q1 → diode D1
→ Motor 4 → Current detection resistor R12 → Transistor Q4 → Negative power supply (-V). Thereafter, when the motor current gradually increases and the current flowing through resistor R26 exceeds the current flowing through resistor R27, the OP3 output of the non-inverting Schmitt circuit 6 becomes negative, and the OP2 output of the Miller integrator 8 becomes positive. To increase.
When the OP2 output exceeds a certain negative voltage, the transistors Q12, Q10, and Q4 of the servo amplifier 7
is in a cut-off state. At this time, the current path of the motor 4 circulates as follows: positive power supply (+V) → transistor Q1 → diode D1 → motor 4 → current detection resistor R12 → diode 9 → positive power supply (+V), and energy is supplied from the power supply. The energy charged in the inductance component of the motor 4 is sequentially discharged. Then, when the balance of the currents in the resistors R26 and R27 is lost, the transistors Q12 and Q1
0 and Q4 turn on again and receive energy from the power supply, and the current increases. Thereafter, similar operations will be repeated. The case where the error signal is a negative voltage is similarly explained.

FIG. 3 is a waveform diagram for explaining the operation of the non-inverting Schmitt circuit 6 and the Miller integrator 8, and shows the case where the error signal is positive. If the error signal is negative, each signal in FIG. 3 is inverted.
In FIG. 3, a is the output voltage waveform of the voltage limiter circuit 1 corresponding to the error signal, and b is the current detector 5.
This is the output current waveform (output of operational amplifier 4).
c is a waveform obtained by adding a and b, and this becomes the input to OP3 of the non-inverting Schmitt circuit 6. In response to the input waveform c, OP3 outputs the signal shown in d.
That is, while a>b, the output of OP3 is positive, but
When a<b, the output of OP3 is inverted to negative.
Upon receiving this d signal, OP2 of Miller integrator 8
is a slope determined by the time constant of resistor R30 and capacitor C3, and outputs a signal that changes from positive to negative or from negative to positive as shown in e. The capacitor C2 and resistor R29 of the non-inverting Schmitt circuit 6 increase the reversal speed of the Schmitt operation of OP3 by applying positive feedback, and the capacitor C4 of the Miller integrator 8 expands the input voltage difference of OP3, increasing the gain of OP3. It works to increase the

The above is a case where the error signal is large, but if the error signal is close to zero, such as when the motor is stationary, the output waveforms of OP3 and OP2 will be at 50% duty due to the free-running oscillator configuration of operational amplifiers OP3 and OP2. Repeat positive and negative. That is, if the error signal is positive, OP3,
The output of OP2 is biased positively as shown in Figure 3 d and e, and when the error signal is negative, the positive/negative relationship in Figure 3 d and e is reversed and biased negative, but the error signal If it is almost zero, the duty will be approximately 50%. In response to the output of OP2 repeating positive and negative,
Transistors Q3 and Q4 of servo amplifier 7 are
Turns on and off. Turn on transistors Q3 and Q4,
Resistor R24 in non-inverting amplifier 2 by OFF
The potential of changes (that is, the input of OP1 changes),
This is amplified by the operational amplifier OP1, and the transistors Q1 and Q2 of the servo amplifier 3 are also turned on and off. As a result, the motor 4 operates as if there were an error signal input, positive and negative currents are forced to alternately flow through the motor 4, and the motor 4 is locked at the target position without any oscillation noise.

FIG. 4 shows the current waveforms of each part of the above embodiment, where a is the output voltage waveform of the voltage limiter circuit 1 with respect to the error signal, and b is the motor current waveform with respect to this. Also, c and d are current waveforms in the static region due to the gain level of the servo amplifier 3,
c is a case where the gain is high, and d is a case where the gain is small.

As explained above, according to the servo motor drive amplifier of the present invention, even when the servo motor is stationary and the error voltage is almost zero, the free-running oscillator configuration allows chopper operation at frequencies above the audible range. Therefore, there is no need to stop the oscillating sound by cutting off the motor's excitation in the stationary area, and there is also no need to use a special motor that does not move the stationary position even when the excitation is turned off. motors can be used.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the overall configuration of an embodiment of a servo motor drive amplifier according to the present invention, and FIG.
The figure shows the specific circuit configuration of each part in Figure 1, Figure 3 is a diagram to explain the operation of the non-inverting Schmitt circuit and Miller integrator in Figure 2, and Figure 4 is a diagram showing the operation of the non-inverting Schmitt circuit and Miller integrator in Figure 2. FIG. 2 is a waveform diagram for explaining the operation of FIG. 2; 1... Voltage limiter circuit, 2... Non-inverting amplifier, 3... Servo amplifier, 4... Motor, 5...
Current detector, 6... Non-inverting Schmitt circuit, 7...
...Servo amplifier, 8...Miller integrator.

Claims (1)

[Claims] 1. Consisting of a non-inverting amplifier that amplifies an error signal to a predetermined level, and a multi-stage transistor whose input is the output of the non-inverting amplifier, one end of the final stage pair of transistors is connected to a positive power supply. , the other end is connected to a negative power supply, the connection point of the pair of transistors is connected to one end of the motor winding, and the first servo further negative feedbacks the voltage at the connection point of the pair of transistors to the non-inverting amplifier. An oscillation device that generates a sawtooth wave by comprising an amplifier, a non-inverting Schmitt circuit that receives the error signal or a signal whose amplitude is limited to a certain value or less, and a Miller integrator that receives the output of the non-inverting Schmitt circuit as input. and a multistage transistor that receives the output of the oscillation circuit as an input, one end of the final stage pair of transistors is connected to a positive power supply, the other end is connected to a negative power supply, and the connection point of the pair of transistors is A second servo amplifier connected to the other end of the motor winding; and a current detection circuit that detects the current of the motor winding and returns it to the input side of the non-inverting Schmitt circuit. Amplifier for driving servo motors.