JPH05312839A - Current sensor - Google Patents

Abstract

PURPOSE:To make it possible to eliminate effects of hysteresis characteristics of magnetic substance and control signals of each phase of a servo motor accurately in a current sensor which is used in a servo system. CONSTITUTION:A current sensor is provided with a dither current generation circuit 30 for adding component of dither current to output voltage taken out of a hall element 21 and a low pass filter 26 for removing dither component included in output voltage.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a current sensor used in a servo system, and more particularly to a current sensor for detecting a current of a servo motor.

[0002]

2. Description of the Related Art Conventionally, in a general servo system, current is detected by a current sensor for servo motor control. As these current sensors, for example, a method using a hall element or a method using a shunt resistor is used. Among them, the method using the hall element is widely used because of its small number of parts and small size.

FIG. 5 schematically shows the basic structure of a current sensor using a Hall element. In the figure, two pairs of electrodes are provided around the Hall element 1, of which a current i from a DC power supply 3 is applied to the electrode 2 and an amplifier 5 is connected to the other electrode 4. On the other hand, an electric wire 7 is wound around the magnetic body 6, and a magnetic field e is applied to the Hall element 1 when a current is passed through the electric wire 7. Here, when the magnetic field e is applied in a direction perpendicular to the current i, electromotive force is generated at both ends of the electrode 4 due to the Lorentz force. This electromotive force is called Hall electromotive force, and its voltage is proportional to the strength of the current i and the magnetic field e from the outside.

In the current sensor using the Hall element, a part of the current applied to the servomotor is applied as an input current to the magnetic body 6, and an output voltage proportional to the input current is taken out from the electrode 4. This output voltage is amplified by the amplifier 5 and then fed back to the input side as an output signal.

[0005]

However, since the magnetic body of the current sensor described above has a hysteresis characteristic, there is a bad influence that the sensor output is affected by the hysteresis characteristic. FIG. 6 is a magnetization curve showing a change in magnetic flux density when a magnetic field is applied to a magnetic material, and it is possible that the same path is not followed when H is increased and when H is decreased. It is shown. On the other hand, since the Hall element has a characteristic that the resistance value changes according to the magnitude of the magnetic field, the output voltage is affected by the above-mentioned hysteresis characteristic. The relationship between the input current and the output voltage when affected by the hysteresis characteristic is as shown in FIG. As shown in the figure, the output voltage at the input current A is A0 on the ideal line indicated by the broken line, but in reality, the output voltage is A1 or A2 because it is affected by the above-mentioned hysteresis characteristic. .. When the hysteresis characteristic appears in the output of the current sensor in this way, the signals of the respective phases of the servomotor cannot be controlled accurately, which causes disturbance.

The influence of the hysteresis can be reduced depending on the material of the magnetic material, but the hysteresis cannot actually be made zero.

It is an object of the present invention to provide a current sensor which can eliminate the influence of the hysteresis characteristic of a magnetic material and accurately control the signals of each layer of the servomotor.

[0008]

In order to solve the above problems, a current sensor according to the present invention includes a dither current generating means for adding a dither current component to an output voltage taken out from a Hall element, and an output voltage. It is characterized in that it comprises a removing means such as a low-pass filter for removing the dither component.

[0009]

When the dither current is applied by the dither current generating means, the output voltage has a signal waveform corresponding to the frequency component of the dither current. When the output to which the frequency component of this dither current is added is passed through a low-pass filter, the frequency component is removed, and the signal waveform becomes A0 in FIG. 7, and the influence of the hysteresis characteristic can be eliminated. Therefore, the signals of the respective phases of the servo motor can be accurately controlled, and the occurrence of disturbance can be prevented.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a current sensor according to the present invention will be described below with reference to the accompanying drawings.

FIG. 2 is a block diagram showing the basic configuration of a servo system using the current sensor according to the present invention. This system includes a speed detection loop including a servo motor (M) 11, a position sensor 12, a differentiating circuit 13, and a current command circuit 14, and a current detecting loop including a current sensor (IS) 15 and a current amplification unit (PWM) 16. It is composed of loops. This servo system supplies a current based on a speed command from a processor unit (not shown) to the servo motor 11 through a current command circuit 14, detects the rotational position of the motor with a position sensor 12, and through a differentiating circuit 13. It is configured to feed back to the current command circuit 14. Further, the servo motor is controlled by using the current sensor 15 to output signals of two phases u and v supplied to the motor.
And the w phase is generated based on the two phase signals of u and v. This utilizes that the sum of u, v, and w phases is always zero. Therefore,
When the u-phase and v-phase signals detected by the current sensor are affected by the hysteresis characteristic, the w-phase signals become inaccurate, and as a result, the u-, v-, and w-phase signals are all accurate. It becomes out of control.

FIG. 1 schematically shows the basic structure of the current sensor 15. In the figure, two pairs of electrodes are provided around the Hall element 21, of which a current i from a DC power supply 23 is applied to the electrode 22, and the other electrode 24 is provided with an amplifier 25 and a low-pass filter 2.
6 is connected. On the other hand, an electric wire 28 is wound around the magnetic body 27, and by applying an input current to the electric wire 28, a magnetic field e is applied to the Hall element 21. Furthermore, an electric wire 29 is wound around the magnetic body 27,
A dither current is generated by the dither current generation circuit 30.

Next, the operation of the dither current generating circuit 30 and the low pass filter 26 will be described with reference to FIGS.
FIG. 3 shows the relationship between the input current and the output voltage in the above-mentioned current sensor, and FIG. 4 shows the frequency components of the input current and the dither current and the waveform of the output voltage. In FIG. 3, when the dither current is not added when the input current is A,
As described above, the output voltage is A1 or A2.
Here, when a dither current is applied by the dither current generating circuit 30, the output voltage has a signal waveform having a maximum value A1 and a minimum value A2 in the frequency component of B as shown in FIG. Further, when the output to which the frequency component of the dither current is added is input to the low pass filter 26, the frequency component is removed. Thus, the output that has passed through the low-pass filter 26 has no hysteresis characteristic, and its value becomes A0, which is the most ideal value. Therefore, the signals of the u, v, and w phases can be accurately controlled, and the occurrence of disturbance can be prevented.

As the frequency of the dither current applied to the output voltage, a high frequency (for example, about 20 KHz) that does not pose a control problem is selected. Further, the dither current can obtain the intended effect at several mA by increasing the number of turns around the magnetic body, so that it does not require a large amount of electric power and can be easily applied to an existing current sensor.

[0015]

As described above, in the current sensor according to the present invention, the frequency component of the dither current is added to the output voltage extracted from the Hall element, and the dither current is included in the output voltage by the component means such as a low pass filter. Since the frequency component is removed, the influence of the hysteresis characteristic of the magnetic substance can be eliminated. Therefore, the signals of the respective phases of the servo motor can be accurately controlled, and the occurrence of disturbance can be prevented.

[Brief description of drawings]

FIG. 1 is a diagram schematically showing a basic configuration of a current sensor according to the present invention.

FIG. 2 is a block diagram showing a basic configuration of a servo system using a current sensor according to the present invention.

FIG. 3 is a diagram showing a relationship between an input current and an output voltage in a current sensor.

FIG. 4 is a diagram showing waveforms of an input current, frequency components of a dither current, and an output voltage.

FIG. 5 is a diagram schematically showing a basic configuration of a current sensor using a Hall element.

FIG. 6 is a diagram showing a hysteresis curve of a magnetic material.

FIG. 7 is a diagram showing a relationship between an input current and an output voltage of a current sensor.

[Explanation of symbols]

 1, 21 ... Hall element 2, 4, 22, 24 ... Electrode 3, 23 ... DC power supply 5, 25 ... Amplifier 6, 27 ... Magnetic material 11 ... Servo motor 12 ... Position sensor 13 ... Differentiation circuit 14 ... Electrical command circuit 15 Current sensor (IS) 16 Current amplifier (PWM) 26 Low pass filter 30 Dither current generation circuit

Claims (1)

[Claims] 1. A dither current generating means for adding a dither current component to an output voltage taken out from a hall element in a current sensor for detecting an output voltage according to an input current by a hall element, and a dither component included in the output voltage. A current sensor, characterized in that it comprises a removing means for removing.