JPS61266083A - Servo circuit - Google Patents

Abstract

PURPOSE:To readily regulate the rotating speed of a motor by comparing an output from a tachometer generator with the preinput signal to alter the limiting value of a voltage limiter. CONSTITUTION:A voltage limiter 8 inputs a command signal in response to an input signal 1 to a motor driver 4. A tachometer generator 6 outputs the rotating speed of a motor 5 through a trimmer 3 for regulating the feedback amount to the driver 4. The difference of the both signals is amplified to rotate the motor 5. A comparator 7 inputs the maximum speed of the motor in advance and a signal corresponding to the prescribed speed, compares it with a signal from the generator 6, and a voltage limiter 8 resultantly outputs the resulted value.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a servo circuit, and particularly to a servo circuit that uses a tacho generator to control the rotational speed of a motor.

(Prior Art) Conventionally, a circuit shown in FIG. 1, for example, has been widely used as a servo circuit that uses a tacho generator to control the rotational speed of a motor.

In the figure, 1 is an input signal, and 2 is a voltage limiting circuit, which outputs only a signal below a predetermined voltage even if the human input signal 1 changes variously. Reference numeral 4 denotes a motor drive amplifier which amplifies the difference between the signal from the voltage limiting circuit 2, that is, the command signal, and the signal whose feedback amount is adjusted from the tacho generator 6 by the trimmer 3, and drives the motor 5 so that both signals are equal. It's rotating. As a result, the number of revolutions of the motor proportional to the command signal from the voltage limiting circuit 2 is obtained.

FIG. 2 is an explanatory diagram showing the relationship between the human power voltage V corresponding to the command signal at this time and the rotation speed of the motor 5.

In the figure, straight line A shows the case where the feedback amount of the tachogenerator is small, and straight line B shows the case where the feedback amount of the tachogenerator is also large. Here, the voltage limit value VL is a limit value of the maximum voltage output from the voltage limit circuit 2.

Even if the input voltage V exceeds the voltage limit value VL, the output value from the voltage limit circuit 2 is prevented from exceeding VL. Therefore, the rotation speed of the motor 5 has the maximum rotation speed corresponding to the feedback amount when the voltage limit value VL is reached, and the rotation speed of the motor does not increase thereafter.

In this way, conventionally, the maximum rotation speed of the motor 5 has been controlled by changing the feedback amount of the tachogenerator 6 using the trimmer 3 to shift the maximum rotation speed of the motor 5 in parallel. For this reason, the torque of the mechanism that acts as the load on the motor changes depending on the usage conditions, and when the optimal response to this is controlled by the amount of feedback from the tachogenerator, the motor rotation speed is set at a low speed, and the time However, it has disadvantages such as poor efficiency in terms of energy and cases where the motor is used at a speed exceeding the maximum rating, that is, the maximum rotational speed of the motor.

(Objective of the present invention) The present invention is capable of controlling the maximum rotation speed of the motor by fixing it at a value close to the rated value or at an arbitrary value even when the feedback amount from the tachogenerator is varied and the response is set to an optimal value. Particularly, the present invention is characterized by providing a servo circuit that controls the rotational speed of a motor using a tachogenerator that prevents deterioration of the motor due to overrating and increases operating efficiency. purpose.

(Main features of the present invention) The present invention has a motor drive circuit that drives the motor, a tacho generator that detects the rotation speed of the motor, and an adjustment circuit that uses an output signal from the tacho generator as a feedback amount to control the rotation speed of the motor. In the servo circuit, the output from the tachogenerator is compared with a predetermined signal voltage, and the output signal from the comparison circuit is The motor drive circuit has a voltage limiting circuit that changes the voltage limiting amount, and after limiting the input voltage using the same circuit, the limited input voltage is input to the motor drive circuit.

Other features of the invention are described in the examples.

(Embodiment) FIG. 3 is a block diagram of an embodiment of the present invention. In the figure, 1 is an input signal, and 8 is a voltage limiting circuit, which inputs a command signal corresponding to the input signal 1 to the motor drive circuit 4.

6 is a tacho generator which detects the rotation speed of the motor 5. The output from the tacho generator 6 is also input to the motor drive circuit 4 through a trimmer 3 for adjusting the amount of feedback, which is an adjusting means. The difference between the two signals is then amplified to rotate the motor 5. 7
is a comparison circuit to which a signal corresponding to the maximum rotational speed or a predetermined rotational speed of the motor is input in advance, and is compared with the signal from the tacho generator 6 and the result is sent to the voltage limiting circuit 8.
outputs. A specific circuit diagram of the comparator circuit 7 and voltage limiting circuit 8 at this time is shown in FIG.

In Fig. 4, the output voltage V from the tacho generator 6
TG is added to the amplification integrated circuit Ul. integrated circuit U
1, the diode D1 becomes conductive when the input signal is small and the motor 5 rotates slower than a predetermined rotation speed, that is, when VTG≦VO. Here VR is motor 5
The rotational speed of the motor 5 is controlled so that the output voltage from the tacho generator 6 obtained when the motor reaches a desired rotational speed is VOξVR. The voltage limit value VL at this time is the diode D2. ．． D3. From resistors R3 and R4, VL = (VO-VF)XR3/(R3+R4)
becomes. However, VF is the unidirectional voltage of the diode.

Also, when the input signal becomes large at a certain moment and the motor reaches a rotation speed higher than the maximum rotation speed due to a transient phenomenon, that is, V
TG> VR, VO=VR-(VTG-VR
) R2/R1, and the amplification factor β of the integrated circuit Ul = R2/
If R1 takes a sufficiently large value, the signal voltage 0 can be made zero even if (VTG-VR) is a very small value. From this, the voltage limit value VL can also be set to zero, and for the portion exceeding the specified circuit of the motor, the specified rotation speed TL
can be limited to.

FIG. 5 is an explanatory diagram showing the state at this time.

In the figure, even if the input voltage V is varied by changing the feedback amount of the tachogenerator, the rotation speed of the motor is limited to around the rotation speed TL corresponding to the voltage limit value VL. Straight lines C, D, and E are graphs illustrating the relationship between the human power signal V and the motor rotation speed when the feedback amount is changed.

In this way, in this embodiment, the amount of feedback is adjusted to the trimmer 3.
The servo circuit is controlled so that the maximum rotational speed of the motor does not exceed a certain level even when the motor is operated. Note that the value of the rotation speed TL of the motor has a slight slope depending on the human input signal, but this is due to the amplification factor β = R2 of the integrated circuit U1.
/R1, and R2 is determined by this value.
If /R1>0, the rotational speed TL can be kept almost constant.

In this embodiment, a case of analog calculation is shown, but it can also be applied to a case of performing digital processing using a microcomputer or the like. Also, although a control circuit that rotates the motor in one direction is shown, it is also possible to control the motor in both directions. In this case, a negative comparison circuit and a voltage control circuit may be added.

(Effects of the present invention) According to the present invention, the output from the tacho generator is manually input to the comparison circuit, compared with a previously input signal, and the output signal is used to vary the limit value of the voltage limit circuit. Since the upper limit of the motor rotation speed can be set without depending on the adjustment amount of feedback from the tacho generator, a servo circuit that can easily adjust the motor rotation speed can be achieved. Also, an effective servo circuit can be achieved when manually or automatically adjusting the response due to load fluctuations.

[Brief explanation of the drawing]

Figure 1 is a block diagram of an example of a servo circuit that uses a conventional tacho generator to control the rotation speed of a motor, Figure 2 is a characteristic diagram of the servo circuit of Figure 1, and Figure 3 is a diagram of the servo circuit of the present invention. FIG. 4 is a block diagram of one embodiment, FIG. 4 is a circuit diagram of a part of FIG. 3, and FIG. 5 is a characteristic diagram of the servo circuit of FIG. 3. In the figure, 1 is an input signal, 2.8 is a voltage limiting circuit, 3 is a trimmer, 4 is a motor drive circuit, 5 is a motor, 6 is a tacho generator, 7 is a comparison circuit, and Ul to U3 are integrated circuits for operational amplification. be.

Claims (1)

[Claims] A servo that controls the rotation speed of the motor, comprising a motor drive circuit that drives a motor, a tacho generator that detects the rotation speed of the motor, and an adjustment circuit that uses an output signal from the tacho generator as a feedback amount. In the circuit, the output from the tachogenerator is compared with a predetermined signal voltage set in advance, and the output signal from the comparison circuit is 1. A servo circuit comprising a voltage limiting circuit that changes a voltage limiting amount, and after limiting an input voltage with the circuit, the limited input voltage is input to the motor drive circuit.