JPH0445848B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a constant pressure control device using an electric motor, and particularly to a pressure (or torque) applied to a load by a pressure sensor attached to a transmission mechanism of the motor output to the load. The present invention relates to a device that controls the pressure applied to a load by the motor output to a constant level in accordance with a pressure command while detecting the pressure.

[Prior Art] A constant pressure control device is conventionally known, which applies a predetermined pressure to a load by driving and controlling an electric motor to a predetermined torque in response to a pressure (or torque) command given from the outside. For example, it is applied to machine tools, injection molding machines, etc.

FIG. 4 shows an example of a conventional closed-loop constant pressure control device that can always perform highly accurate constant pressure control. In the figure, a low-rigidity transmission mechanism 2 is attached to the output shaft of an electric motor 1, and the driving force of the electric motor 1 is transmitted to a load 3 such as a workpiece through this transmission mechanism 2, and the load 3 is kept constant. It will be pressed by pressure. A pressure sensor 4 is installed between the transmission mechanism 2 and the load 3, and the pressure detection signal output from the pressure sensor 4 is converted by a conversion circuit 5 into a pressure detection signal e _p consisting of a voltage signal. and is supplied to the summing point 6. Further, at the addition point 6, a pressure command signal consisting of a voltage level corresponding to the pressure command is sent from the pressure command circuit 7.
e _pi is supplied. As a result, from addition point 6, e _pi
An error signal -e _p =Δe _p is output, and the error signal is amplified by the pressure control amplifier 8 and supplied to the addition point 9 as the speed command signal Δe _pp .

Further, a speed generator 10 is directly connected to the electric motor 1 as a speed sensor, and the speed detection signal detected by the speed generator 10 is converted by a conversion circuit 11 into a speed detection signal e _o consisting of a voltage signal and added. It is fed to point 9. As a result, an error signal Δe _pp −e _o =Δe _o is output from the summing point 9, and the error signal Δe _o is amplified by the speed control amplifier 12 and supplied to the summing point 13 as a current command signal Δe _op . .

Further, the output torque of the electric motor 1 is detected by an input current detector 14, and the current detection signal from the current detector 14 is converted by a conversion circuit 15 into a current detection signal e i consisting of a voltage signal, and the current detection signal e _i is sent to an addition point 13.
is supplied to As a result, from addition point 13, Δe _op
An error signal of −e _i =Δe _i is output, and the error signal Δe _i is amplified to Δe _ip by the current control amplifier 16 and then supplied to the power converter 17 .

The power converter 17 is constituted by an ignition control circuit using a thyristor or a pulse width control circuit using a transistor, and is configured to supply a predetermined current to the motor 1 based on the signal Δe _ip to drive the motor 1. It is configured.

[Problems to be Solved by the Invention] However, in such a conventional constant pressure control device, regardless of the pressure command value, the speed control amplifier 1
Since the amplification degree of 2 was fixed, the following problem occurred. Now, as shown in Figure 5A,
If a pressure designation signal e _pi having a step-like voltage waveform is output from the pressure command circuit 7 at time T ₀ , then in the transition period until the pressure applied to the load 3 reaches the pressure responsive to the pressure command signal, , the pressure on the load 3 fluctuates by becoming stronger or weaker than the pressure on the load 3. Therefore, the pressure detection signal e _p changes in a damped oscillatory manner as shown.

In this case, if the amplification degree of the speed limit control amplifier 12 is constant, when the pressure command value is large, the current command signal Δe _op becomes too large, resulting in a pressure command signal
If the error signal Δe _p between e _pi and the pressure detection signal e _p is positive, the transmission mechanism 2 presses the load 3 with more force than necessary (3 to 5 times the rated torque of the motor 1), and the error signal If Δe _p is negative, the transmission mechanism 2 will be pushed back by the load 3. As a result, the sliding table of the transmission mechanism 2, which has low rigidity, repeatedly moves back and forth,
The pressure that presses the load 3 gradually reaches the pressure command value while repeating large vibrations.

The above-described overshoot amount β and settling time t of the pressure detection signal e _p are determined by the magnitude of the output signal of the speed control amplifier 12, and the rising angle α of the pressure detection signal e _p is determined by the amplification degree of the pressure control amplifier 8. However, in a conventional device in which the amplification degree of the speed control amplifier 12 is fixed regardless of the specified pressure value, if the pressure command value is large, the output of the amplifier 12 becomes too large. The time it takes for the pressure applied to the load to respond to the pressure command value becomes longer;
This has the drawback that the life of the gear system of the transmission mechanism 2 is shortened due to extra force being applied to the transmission mechanism 2 and large vibrations occurring in the transmission mechanism 2.

An object of the present invention is to provide a constant pressure control device using an electric motor that can quickly cause the pressure applied to a load to reach a pressure command value.

[Means for Solving the Problems] In order to solve the above problems, the present invention detects the difference between a pressure detection signal obtained by detecting the pressure on the load due to the output of the electric motor with a pressure sensor and a pressure command signal. The signal is operationally amplified to obtain a speed command signal, and the difference signal between the speed detection signal obtained by detecting the rotational speed of the electric motor with a speed sensor and the setting command signal is operationally amplified to be a current command signal, By driving the motor based on a signal obtained by operationally amplifying the difference signal between the current detection signal obtained by detecting the input current of the motor with a current detector and the current command signal, the load due to the output of the motor is driven. In a constant pressure control device using an electric motor that controls pressure to a constant value, a current command signal limiting circuit that is controlled by the pressure command signal and limits an upper limit of the current command signal according to the magnitude of the pressure command signal. It is characterized by having the following.

[Operation of the invention] In the present invention, since the current command signal limiting circuit limits the upper limit of the current command value according to the magnitude of the pressure command value, when the pressure command value is large, speed control is more effective than in conventional devices. The magnitude of the current command signal at is limited to a low value. Therefore, the speed command signal can be increased by increasing the amplification degree of the pressure control amplifier, and constant pressure control can be performed such that the pressure applied to the load quickly reaches the pressure command value [Example] Embodiments of the present invention will be described in detail below based on the drawings.

FIG. 1 shows an embodiment of the present invention, and in this figure, the same parts as those of the above-mentioned conventional device are given the same reference numerals and explanations will be omitted.

A feature of the present invention is that a current command signal limiting circuit 18 is added to the speed control amplifier 12 to limit the upper limit of the current command value according to the magnitude of the pressure command value. This current command signal limiting circuit 18 has an amplifier 19 and an output limiting circuit 20, as shown in the concrete configuration in FIG.
e _pi is amplified by an amplifier 19 at a predetermined amplification degree determined in consideration of the stiffness and viscosity of the load 3,
It is output as a pressure command signal e _pi '. The output limiting circuit 20 receives the current command signal Δe _op ' from the speed control amplifier 12 and the pressure command signal e _pi ' from the amplifier 19, and limits the upper limit of the current command value according to the magnitude of the pressure command value. That is, when the pressure command value is small, the current command signal Δe ol ' is limited by the large upper limit value, and when the pressure command value is large, the current command signal Δe _ol ' is limited by the small upper limit value. In addition, the pressure command signal
Since the polarity of e _pi ' differs depending on the rotational direction of the electric motor 1, the output limiting circuit 20 outputs an output limiting signal according to the absolute value of the pressure command signal e _pi '.

FIG. 3 is a characteristic curve diagram showing the relationship between the input signal Δe _op ' and the output signal Δe _ol ' of the current command signal limiting circuit 18 using the magnitude of the pressure command signal e _pi as a parameter. As seen in the figure, as the pressure command signal e _pi increases, the magnitude of the output signal is limited by the low value of the input signal. The saturation value e _z of the output signal in this case is a value determined by the Zener voltage of the Zener diode 20d in the output limiting circuit 20 of FIG.

In this way, in this embodiment, the current command value is limited according to the magnitude of the pressure command value, so when the pressure command value is large, the magnitude of the current command signal in speed control is greater than that in the device shown in FIG. is limited to a low value. Therefore, the speed command signal Δe _pp ' can be increased by increasing the amplification degree of the pressure control amplifier 8, and as a result, the pressure response characteristic to the load with respect to the pressure command is as shown in FIG. 5B compared to FIG. 5A. This is improved as shown in . That is, as can be seen by comparing the characteristics of both figures, the pressure detection signal curve shown in the pressure response and the rising angle are α'>α, and the settling time is t'<t
becomes. Therefore, constant pressure control can be performed so that the pressure applied to the load quickly reaches the pressure command value.

[Effects of the Invention] As explained above, according to the present invention, since the upper limit of the current command value is limited according to the magnitude of the pressure command value, the amplification degree of the pressure control amplifier is increased to increase the speed. It is possible to increase the command signal and perform constant pressure control such that the pressure applied to the load quickly reaches the pressure command value.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a circuit diagram showing a specific example of the configuration of the current command limiting circuit in FIG. 1, and FIG. 3 is a characteristic example of the current command signal limiting circuit. FIG. 4 is a block diagram showing an example of a conventional constant pressure control device, and FIG.
Figure A is a characteristic curve diagram showing the response characteristic of the pressure applied to the load to the pressure command in the conventional device of Figure 4, and Figure 5B is a characteristic curve diagram showing the response characteristic of the pressure applied to the load to the pressure command in the above embodiment. It is a diagram. 1...Electric motor, 2...Transmission configuration, 3...Load,
4...Pressure sensor, 7...Pressure command circuit, 8...
Pressure control amplifier, 10...Speed generator as speed sensor, 12...Speed control amplifier, 14...Current detector, 16...Current control amplifier, 17...Power converter, 18...Current command signal limit circuit.

Claims (1)

[Claims] 1 The pressure on the load due to the output of the electric motor is detected by a pressure sensor, and a difference signal between a pressure detection signal and a pressure command signal is operationally amplified to obtain a speed command signal, and the rotational speed of the electric motor is detected by a speed sensor. The difference signal between the speed detection signal obtained by the above-mentioned speed command signal and the speed command signal is operationally amplified to obtain a current command signal, and the current detection signal obtained by detecting the input current of the motor with a current detector and the above-mentioned current command signal are By driving the electric motor based on a signal obtained by operationally amplifying the difference signal,
In a constant pressure control device using an electric motor that controls the pressure applied to the load by the output of the electric motor to be constant,
A constant pressure control device using an electric motor, comprising a current command signal limiting circuit that is controlled by the pressure command signal and limits the upper limit of the current command signal according to the magnitude of the pressure command signal.