JPH07239247A - Signal processor for magnetic encoder - Google Patents

Abstract

PURPOSE:To enhance resolution by applying an AC voltage to magnetic sensors for A and B phases and subjecting the output from an encoder to amplitude modulation and then determining the displacement from the amplitude ratio of signals detected synchronously through AC coupling thereby eliminating the influence of fluctuation or offset of the encoder output while sustaining high response performance. CONSTITUTION:Magnetic sensors 10, 11 for phases A and B having phase difference of 90 deg. are connected in parallel and an AC voltage (sine wave signal) is applied from an oscillator 1 in order to amplitude modulate the encoder output. The outputs are subjected to AC coupling through AC couplings 12, 13 thus removing the offset component. The AC signal is subjected to synchronous detection with a (carrier) signal from a transmitter 1 by means of synchronous detectors 14, 15 to produce sine wave signals Va, Vb, which are then subjected to division 16 and a displacement is operated 17 based on the ratio Va/Vb. Since the magnetic sensors 10, 11 are disposed closely each other, fluctuation in the vibration of the rotary drum of encoder due to vibration of shaft has equal effect on the sensors 10, 11 and thereby has no effect on the detection of displacement.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a signal processing device of a magnetic encoder for detecting position and angle.

[0002]

2. Description of the Related Art FIG. 4 is a diagram showing a conventional example of a sensor section. 18 is a DC voltage source, 2 to 5 are MR elements for A phase detection,
6 to 9 are MR elements for detecting B phase, 10 is an A phase magnetic sensor,
Reference numeral 11 represents a B-phase magnetic sensor. FIG. 5 is a diagram showing a conventional example of a signal processing device. 19 is a two-phase oscillator, 20, 21
Is a multiplier, 22 is an adder, and 23 is a displacement amount calculation circuit. FIG. 6A shows an output waveform of the magnetic sensor in FIG.
FIG. 6B is a diagram showing two input waveforms of the displacement amount calculation circuit in FIG. In the conventional magnetic encoder, as shown in FIG.
As shown in FIG.
Is applied, and as shown in FIG. 5, the A-phase signal Vaout ′ =
sin θ, B-phase signal Vbout ′ = cos θ are multiplied by a sine wave signal and a cosine wave signal (hereinafter referred to as carriers), respectively, and one of the signal obtained by adding them and the carrier, for example, a cosine wave signal The phase difference is measured by a counter circuit using a clock or the like, and the displacement amount θ is detected. At this time, the amplitude fluctuations and offsets of the incremental phases (A phase, B phase) due to axial deviation of the encoder rotating drum, unbalance of resistance values of the MR elements constituting the magnetic sensor, etc., limit high resolution. In addition, since the encoder output is a DC output in the related art, the CPU is used to compensate for the amplitude variation and offset.

[0003]

However, the conventional method has a problem in that the peripheral circuit configuration such as the A / D converter is complicated because the CPU is used, and the response frequency is limited due to the long processing time. . It is therefore an object of the present invention to provide a signal processing device that realizes high resolution without being affected by amplitude fluctuations, offsets, etc. of encoder output signals while maintaining high-speed response with a simple circuit configuration.

[0004]

In order to solve the above problems, the present invention uses an incremental phase (A phase, B phase) detection magnetic sensor to which a DC voltage is conventionally applied as shown in FIG. By applying an AC voltage from the encoder, the encoder output signal is amplitude-modulated, the AC coupling is performed to remove the offset component, and the position and the angle are calculated from the amplitude ratio of the signal amplitudes Va and Vb synchronously detected by the frequency of the AC voltage. The displacement amount θ is obtained by the equation (1). θ = tan ⁻¹ (Va / Vb) (1)

[0005]

With the above-mentioned means, while the high-speed response is maintained with a simple circuit structure, the shaft runout of the encoder rotary drum and the MR
High resolution can be achieved without being affected by amplitude fluctuations, offsets, etc. due to unbalanced resistance values of the elements.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a specific embodiment of the sensor section of the present invention, and FIG. 2 shows a specific embodiment of the signal processing apparatus of the present invention.
In FIG. 1, 1 is an oscillator. Also in FIG.
Reference numerals 12 and 13 are AC coupling devices, 14 and 15 are synchronous detectors, 16 is a divider, and 17 is a displacement amount calculation circuit.
Assuming that the output signal of the oscillator 1 is Vc · sin (ωt), the A-phase and B-phase output signals Vaout and Vbout are Vaout = Vc · sin (ωt) · k · sin θ (2) Vbout = Vc · sin ( ωt) · k · cos θ (3), which are amplitude-modulated signals as shown in FIG. Even if there is an offset component in each signal, the offset component can be removed by AC coupling as shown in FIG. By synchronously detecting this AC signal with the oscillator (carrier) signal, 90 degrees in electrical angle with respect to each other as shown in FIG.
It is possible to obtain the sine wave signals Va and Vb having different degrees of phase. The displacement amount is detected by the displacement amount calculation circuit 17 shown in FIG. 2 according to the equation (1). The detection of the displacement amount, that is, the phase detection can be obtained by calculating the amplitude ratio of two signals whose phases differ by 90 degrees in electrical angle. Therefore, even if there is an amplitude variation due to shaft deviation of the encoder rotating drum, the amplitude variation at this time occurs at the same ratio because the A-phase magnetic sensor and the B-phase magnetic sensor are sufficiently close to each other, and the amplitude ratio is calculated. The method does not affect the detection of the displacement amount.

[0007]

As described above, according to the present invention, a simple operation is not affected by fluctuations in the amplitude of an encoder output signal or offsets caused by shaft runout of an encoder rotary drum, imbalance of resistance values of MR elements, and the like. The circuit configuration has the effect of achieving high electrical resolution. The present invention is applicable to both rotary magnetic encoders and linear magnetic encoders. That is, an angle can be detected in the case of a rotary magnetic encoder, and a position can be detected in the case of a linear magnetic encoder.

[Brief description of drawings]

FIG. 1 is a diagram illustrating an embodiment of a sensor unit according to the present invention.

FIG. 2 is a diagram illustrating an embodiment of a signal processing device of the present invention.

FIG. 3 is a diagram illustrating a signal waveform of each part of FIG.

FIG. 4 is a diagram illustrating a conventional example of a sensor unit.

FIG. 5 is a diagram illustrating a conventional example of a signal processing device.

FIG. 6 is a diagram for explaining signal waveforms of respective parts of FIG.

[Explanation of symbols]

 1 Oscillator 2-5 A phase detection MR element 6-9 B phase detection MR element 10 A phase magnetic sensor 11 B phase magnetic sensor 12, 13 AC coupling device 14, 15 Synchronous detector 16 Divider 17 Displacement amount calculation Circuit 18 DC voltage source 19 Two-phase oscillator 20, 21 Multiplier 22 Adder 23 Displacement amount calculation circuit

Claims (1)

[Claims] 1. A signal processing device of a magnetic encoder, comprising a magnetic medium magnetized by alternately repeating N poles and S poles at the same pitch and a magnetic sensor for detecting a magnetic field in the vicinity of the surface of the magnetic medium, in an electrical angle of 90. Two magnetic sensors each consisting of a magnetoresistive element for detecting two signals having different degrees of phase are connected in parallel, and an oscillator generating a sine wave signal of a constant frequency is connected in parallel to the two magnetic sensors, Two AC coupling devices that respectively take out only an AC component from each output signal of the magnetic sensor, and two synchronous detectors that detect the output signals of the two AC coupling devices in synchronization with the oscillation frequencies of the oscillators, It is characterized by comprising a divider for obtaining an amplitude ratio of output signals from two synchronous detectors, and a displacement amount calculation circuit for calculating a displacement amount from the output of the divider. The signal processing apparatus of the magnetic encoder.