JPS58170393A - Rotating speed controller - Google Patents

Abstract

PURPOSE:To control the rotating speed of a motor to be controlled by displacing the mechanical resonance point of the motor by supplying a control signal of rotating speed to signal converter and controlling the rotating speed with the output of the converter. CONSTITUTION:When a setter 1 is operated to input a control signal of the prescribed value to a signal converter 2, a speed set signal corresponding to the signal is generated from the converter, compared by a comparator 3 with the speed signal, and the control voltage is supplied to an inverter 4. Thus, the inverter 4 supplies the drive power of the voltage and frequency in response to the control voltage to an induction motor 6, thereby rotating the motor 6. The converter 2 has stepped discontinuous characteristic at part of the output signal characteristic for the input signal so tht the rotating speed of the motor 6 may not be permanently held in mechanical resonance.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a rotational speed control device that uses an inverter or the like to arbitrarily set the rotational speed of an electric motor using a control signal.

Among various types of electric motors, induction motors (hereinafter referred to as
) have the advantages of simple structure, low cost, long life, and easy maintenance, so they are widely used for small to large capacity stones. Since there was no method for efficient control, the applications were limited, and even in applications where speed control would be preferable, they were used without speed control in order to take advantage of the above advantages.

However, in recent years, 91 different semiconductor devices have been provided, and static inverters have appeared that can easily obtain an output of any frequency regardless of the frequency of the commercial power supply, and supply it to IM. By changing the power supply frequency and voltage, extremely efficient speed control is possible.
With the growing interest in energy saving, IMs that perform speed control have come to be widely used in various fields.

By the way, in a conventional rotational speed control device using such an inverter, as shown in FIG. 1, the rotational speed of the IM is continuously controlled substantially in proportion to a control signal.

As a result, in conventional rotational speed control devices, when the rotational speed was controlled by changing the control signal, the noise and vibration of the IM increased significantly at a specific control signal level. .

This is due to the following reason. That is, an electric motor such as an IM generally has a unique mechanical resonance point, and mechanical resonance occurs at a specific rotation speed. Therefore, if a point that causes such resonance, the so-called mechanical resonance point A, exists within the rotation control range as shown in Figure 1, when the control signal is set at this point A, the IM The rotational speed causes mechanical resonance and the rotational speed causes noise and vibration.

An object of the present invention is to eliminate the above-mentioned drawbacks of the prior art, and eliminate the problem of increasing the noise and vibration of electric motors such as IMs that are pointed at the controlled object even when the control signal is set at any point within the adjustable range. The purpose of the present invention is to provide a rotation speed control device that never fails.

In order to achieve this object, the present invention supplies a control signal input for rotational speed control to a signal conversion circuit, and controls the rotational speed using the output of the signal conversion circuit, thereby rotating the electric motor to be controlled. It is characterized in that the speed is controlled outside the mechanical resonance point of the motor.

Embodiments of the rotational speed control device according to the present invention will be described below with reference to the drawings.

FIG. 2 shows an embodiment of the present invention, in which 1 is a rotation speed setting device;
2 is a signal conversion circuit, 3 is a comparator, 4 is an inverter, 5 is an AC power supply, 6 is an IM, and 7 is a speed detector.

The setting device 1 has the function of generating a control signal Vi for setting the rotation speed of 1M6. For example, it is made up of a variable resistor such as a potentiometer.

The signal conversion circuit 2 converts the input control signal Vi into a third signal.
It functions to generate a speed setting signal Vs that changes according to the characteristic indicated by B in the figure.

The comparator 3 compares the speed setting signal v8 and the speed signal Vd from the speed detector 7, and functions to generate an inverter control voltage V such that Va=Vd is achieved.

The inverter 4 functions to generate driving power P with a frequency and voltage corresponding to the control voltage V and supply it to 1M6.

The speed detector 7 is called a tachometer dynamo or the like, and is rotationally driven by the 1M6, and functions to generate a speed signal Vd representing the rotational speed.

Next, the operation of this embodiment will be explained.

When the setting device 1 is operated and a predetermined value of the control signal Vt is input to the signal conversion circuit 2, the corresponding speed setting signal Vt is inputted to the signal conversion circuit 2.
a is generated, which is compared with the speed signal Vd by the comparator 3, and the control voltage V is supplied to the inverter 4.

Thereby, the inverter 4 supplies the driving power P of the voltage and frequency according to the control voltage V to the 1M6, generates torque in the 1M6, and drives the 1M6 to rotate. As a result, since the speed signal Vd representing the rotational speed of 1M6 is supplied from the speed detector 7 to the comparator 3, these signals Va
When the control voltage V is supplied to the inverter 4 such that Vd and Vd are equal to each other, the operation becomes stable and the
The rotation speed of No. 6 is always automatically controlled relative to the rotation speed set by the speed setting signal v8! +, 1M6
If the rotational speed of is V, then a state of v=Vs will be obtained.

Therefore, now, as shown in FIG. 3, the mechanical resonance point A of 1M6 is at a rotational speed V of V. In this respect, characteristic B of the signal conversion circuit 2 is set as shown in the figure. That is, in the period from 0 to Vis and in the portion where the control signal v1 exceeds kis, a setting signal v8 that is approximately proportional to the control signal Vt is provided, but when the control signal Vt becomes V
When it is between il and Viz, a constant setting signal 8□ is applied regardless of changes in the control signal Vt.

The setting signal ■8□ corresponding to the control signal Vi1 at this time is the rotational speed V at the resonance point A. The setting signal V82 corresponding to the control signal Via is set to a value corresponding to the rotational speed v0, which is lower by, for example, 20 (RPM) than the rotational speed v0.
) is set to a value corresponding to a higher rotational speed v2.

As a result, in order to increase the rotation speed of IM6, the setting device 1
When the control signal Vi is increased from O by operating -
until it reaches v1□, the rotational speed V of IM6 increases according to that value, but after the control signal v1 reaches Vh, even if the control signal Vt is increased, the setting signal Vs does not increase more than Vat, and the rotation speed of IM6 V4”
It remains at Vl. And the control signal Vi
When V is further increased to Viz, at this point the setting signal VsFiV8□ changes stepwise to VB2, and the rotational speed V of 1M6 also rapidly increases from vo to v2. After that, the setting signal ■8 increases almost in proportion to the increase in the control signal Vi, so ■M60
The rotation speed increases in accordance with the rotation speed signal vl.

On the other hand, the same is true when the rotational speed V of IM6 is lowered from a point larger than v2, and when the control signal Vt drops to Vig, the setting signal Vs changes from ■8□ to v
At this point, the rotational speed V of the machine M6 decreases in a stepwise manner from v2 to V in a short time. Then, the setting signal Vs remains at v8□ until the control signal v1 drops to Vix, t, 9. The rotational speed V of IM6 also remains at V□.

Therefore, according to this embodiment, no matter what value the control signal (1) has, the rotational speed V of the IM6 will not remain at vo for a long time, and no matter what operating position the setting device 1 is at, the rotational speed V of the IM6 This eliminates the risk of significant noise and vibration.

FIG. 4 shows an embodiment of the signal conversion circuit 2, in which 10 is a first non-linear circuit whose input/output characteristics are approximately linear until they reach a predetermined first level, and are saturated beyond that point; is linear when the input/output characteristics are above a predetermined second level,
Below that, the non-linear circuit has a stepwise gain of 0, and 12 is an analog OR gate.

Therefore, by setting the first level of the first non-linear circuit 10 to Vil in FIG. 3 and the second level of the second non-linear circuit 11 to Vig in FIG. 3, signal conversion is possible. Circuit 2 can be obtained.

Note that in the above embodiment, a device that uses an inverter to control the rotational speed of the IM has been described, but the present invention
There is no need to say that the present invention can be applied not only as a rotational speed control device for any electric motor.

It goes without saying that it is also possible to use a chopper circuit or a cycloconverter in place of the inverter 4, and it is also possible to use an open-loop type control device that does not use the speed detector 7 or the comparator 3. It is possible to implement.

As explained above, according to the present invention, it is possible to control the rotational speed under what conditions to control the rotational speed to prevent the rotational speed of the motor such as the controlled object IM from being kept at the mechanical resonance point for a long time. Therefore, it is possible to provide a rotational speed control device that eliminates the drawbacks of the prior art and can always perform speed control in a low-noise, low-vibration state.

[Brief explanation of the drawing]

Fig. 1 is a characteristic diagram explaining the operation of a conventional rotation speed control device, Fig. 2 is a block diagram showing an embodiment of the present invention, and Fig. 3 is a characteristic diagram illustrating the operation of a conventional rotation speed control device.
The figure is a characteristic diagram for explaining its operation, and FIG. 4 is a block diagram showing one embodiment of the signal conversion circuit. 1... Rotation speed setting device, 2... Signal conversion circuit, 3... Comparator, 4... Inverter, 5... AC Power supply, 6...Induction motor (IM), 7...Speed detector 0 Agent Patent attorney Kenji Takeshi Department Fig. 1 VIW No. 2M Fig. 3 Fig. 4

Claims (1)

[Scope of Claims] 1. A rotational speed control device that includes a control circuit that changes at least one of the output frequency or output voltage of a drive power source for the electric motor, and controls the rotational speed of the electric motor according to a control signal, A signal conversion circuit having a step-like discontinuous characteristic is provided in a part of the output signal characteristic with respect to the input signal, and the control signal is supplied to the control circuit via the signal conversion circuit. Rotation speed control device. 2. In claim 1, the signal conversion circuit comprises a first non-linear circuit having an input/output level characteristic whose output level is saturated at a predetermined first input level or higher, and the first input level a second non-linear circuit with input/output level characteristics in which the output level rises from zero to a predetermined level corresponding to the input level at a larger second input level; and outputs of these first and second non-linear circuits. A rotation speed control device characterized in that it is configured with an analog OR gate that receives as input.