JPH0434684B2 - - Google Patents

Description

[Detailed description of the invention] The present invention relates to magnetic encoders.

Conventionally, in a magnetic encoder, as shown in FIG. 1, an information recording medium 3 made of a magnetic material is provided on the circumferential surface of a rotating body 2 such as a motor that is coaxially coupled to a shaft 1. 3 in advance
Information signals are magnetically recorded by alternately magnetizing a large number of poles and S poles. The magnetoresistive element 4 is arranged close to and facing the circumferential surface of the information recording medium 3, and is driven by a DC power source 5. This magnetoresistive element 4 senses the magnetic flux from the information recording medium 3 and detects the information signal with a phase difference of 90 degrees.
A set of elements are installed internally, and the output signals of these elements are output from output terminals A and B as shown in Figure 2.
Obtained as sinθ and cosθ. This output signal is information regarding the rotation speed and rotation angle of the rotating body 2,
For example, the rotating body 2 is controlled based on this information.

In the case of this magnetic encoder, if it is an ideal one with no variations in assembly accuracy or magnetization strength, each output signal of the two sets of elements constituting the magnetoresistive element 4 will be As shown in Figure 2, envelope 3 is a straight line with a certain constant value.
This results in a waveform 36 surrounded by 3 and 34. However, in actual magnetic encoders, due to variations in assembly accuracy and magnetization strength, the magnetoresistive element 4
As shown in FIG. 6, the envelopes 27, 28, 29, and 30 of the output signals of the two sets of elements constituting the circuit are no longer straight lines with a certain constant value, but become wavy, resulting in level fluctuations.

In order to explain this point in an easy-to-understand manner, let us assume that this magnetic encoder is the encoder 21 as shown in FIG. In this encoder 21,
The rotating body 2 and the information recording medium 3 have their outer peripheral surfaces
For example, it is composed of a rotor magnet 22 magnetized with 12 poles and is integrally attached to the rotating shaft 1,
The two sets of elements constituting the magnetoresistive element 4 are composed of two sets of magnetic sensors α and β arranged with a phase shift of 90 degrees. It is now assumed that the rotating shaft 1 is eccentrically attached to the rotor magnet 22 as shown in FIG.

The rotor magnet 22 rotates in the direction of the arrow around the eccentrically attached rotating shaft 1.

FIG. 6 shows changes in the output signals of the magnetic sensors α and β. While the rotor magnet 22 rotates once from the position shown in FIG. 5, the magnetic sensor α shows the output value of the waveform 24 from phase A to phase D. Further, the magnetic sensor β shows an output value of waveform 25 from phase A to phase D.

Since the rotor magnet 22 is eccentric due to variations in assembly accuracy, the magnetic sensors α and β
The output signal is largest at the position shown in Fig. 5 (position A in Fig. 6), and the positional relationship is such that the rotor magnet 22 is rotated 180 degrees from the position shown in Fig. 5 (position C in Fig. 6). The output is the smallest.

The magnetic sensors α and β draw sine curves as waveforms 24 and 25 because the magnetic poles N and S alternately pass in front of them as the rotor magnet 22 rotates. Since the magnetic sensor α and the magnetic sensor β are arranged at an electrical angle of 90 degrees (half the angle of one magnetic pole of the rotor magnet 22), their respective output signal waveforms are also shown in FIG. As shown, waveform 24 and waveform 25 have output signal waveforms shifted by 90 degrees.

If the rotating shaft 1 of the rotor magnet 22 is not eccentric (in an ideal state), the output signal waveform of the magnetic sensor α is as shown in the output signal waveform 26 in FIG.
Although the output signal is constant (envelopes 33 and 34 are in a straight line state), if it is eccentric as shown in FIG. 5, the output signal waveform 24 is surrounded by drum-shaped envelopes 27 and 28 as shown in FIG. It will change over time.

The output signal waveform 25 of the magnetic sensor β also changes between the drum-shaped envelopes 29 and 30.

Therefore, for example, the output value of the magnetic sensor α in the ideal state at phase B in FIG. 6 is a little smaller than the output value 31.

In addition, the output value of magnetic sensor β in the ideal state is
It will be a little larger than the output value of 32.

In this way, the envelopes 33 and 34 surrounding the output signal waveforms of the magnetic sensors α and β do not maintain a constant value due to variations in assembly precision and magnetization strength, etc., and wave, causing the output signal levels of the magnetic sensors α and β to vary. Fluctuations occur.

The present invention improves the above-mentioned drawbacks by compensating the envelope surrounding the output signal waveform so that it maintains a constant linear shape without undulating due to variations in assembly accuracy or magnetization strength of the information recording medium. An object of the present invention is to provide a magnetic encoder that can prevent variations in output signal level.

The present invention will be described below by way of examples with reference to the drawings.

FIG. 3 shows an embodiment of the invention.

This embodiment compensates for the undulation of the envelope surrounding the output signal waveform in the above-mentioned magnetic encoder, so that the envelope surrounding the output signal waveform obtains an output signal that shows a straight line with a certain constant value, as shown in Figure 2. This eliminates level fluctuations in the output signal. In this embodiment, output signal voltages (sin θ, cos θ) having a phase difference of 90° obtained from output terminals A and B are squared by square operators 6 and 7, respectively, and are then squared by an adder 8.
is added by The output voltage of the adder 8 is compared with a reference voltage E of a reference voltage source 11 by an error detector consisting of an amplifier 10 equipped with a feedback resistor 9, and the magnetoresistive element 4 is driven by the error. Therefore, the output voltage of adder 8 (sin ² θ+
The sensitivity of the magnetoresistive element 4 is controlled so that cos ² θ) is equal to the reference voltage E, and level fluctuations in the output signal are eliminated.

That is, in this embodiment, if the magnetic encoder shown in FIG. 1 is the magnetic encoder shown in FIG.
By correcting the output signal waveforms 24 and 25 by adding or subtracting a slightly larger value, the output signal waveforms are corrected and controlled to follow linear envelopes 33 and 34 as shown in FIG. . The output signal waveforms 24 and 25 of the magnetic sensors α and β are set so that the output values are a little closer to 0 at the positions of phases A and D (in the case of FIG. 6, the waveforms are a little more contracted), and At the position of phase C, the output value is controlled so as to move a little further away from 0 (in FIG. 6, the waveform swells up and down a little more).

For example, output signal waveform 2 of magnetic sensors α and β
4 and 25 at the position of phase B, it is found that when the rotary shaft 1 is eccentrically attached to the rotor magnet 22, the waveform becomes vertically contracted compared to the ideal state. , the absolute values of the output values of the magnetic sensors α and β are smaller than the ideal state as waveforms 31 and 32.

Therefore, since the value of the output voltage (sin ² + cos ² ) of the adder 8 also becomes smaller, the input signal to the amplifier 10 constituting the error detector becomes smaller. , the output signals of the magnetic sensors α and β are increased by controlling the input voltages of the magnetic sensors α and β to be large. As a result, the output signals of the magnetic sensors α and β approach the output values in the ideal state.

However, if the input value to the amplifier 10 is not the sum of the square values of the output signals 24 and 25 of the magnetic sensors α and β, but for example a voltage (sin+cos) is input to the amplifier 10, the input value of the amplifier 10 is the sum of the square values of the output signals 24 and 25 of the magnetic sensors α and β, but does not become a constant value, but changes to the amplifier 10 from time to time as the rotor magnet 22 rotates. Since the input values change, proper control (control that brings the envelopes 27, 28, 29, and 30 from the drum-shaped state shown in FIG. 6 to the linear state shown in FIG. 2, which approaches the ideal state) cannot be performed.

Due to this action, the rotor magnet 22
The output signal waveforms of magnetic sensors α and β are compensated so that the envelopes surrounding the output signal waveforms of magnetic sensors α and β do not wave due to variations in the gap caused by the eccentricity of Fluctuations in the output signal level can be prevented. The output signal is outputted to the outside from terminals 12 and 13 derived from the output terminals A and B of the magnetoresistive element 4, but the output signals of the square calculators 6 and 7 may be outputted to the outside.

FIG. 4 shows another embodiment of the medium.

In this embodiment, Hall elements 41 and 42, which are other magnetic sensing elements, are used in place of the magnetoresistive element 4 in which two sets of elements are installed in the above embodiment. The Hall elements 41 and 42 are arranged at positions having a phase difference of 90 degrees in electrical angle, and are driven by the output current of the amplifier 10.

Note that although the above embodiment is of a rotary type, it may be of a linear type or the like. In this case, the information recording medium 3 is replaced by a moving body that moves linearly and information signals are recorded in the direction of the movement. When two magnetic sensing elements are used (two magnetic resistance elements 4 are used), they are generally arranged at positions where the phase difference is an odd multiple of 90 degrees in electrical angle, but when n (≧3) magnetic sensing elements are used, Sensing elements may be used and arranged at positions shifted by a phase difference of 360°/n in electrical angle. In this case, the sum S of the n-phase sine waves raised to the x power is S= _o 〓 ^K=1 sin ^x {θ−360°(k−1)/n}, so the The output voltages may each be raised to the power of x using a power calculator, added together using an adder, and then input to the amplifier 10. In this case, as in the above embodiment, the sensitivity of the magnetic sensing element is controlled so that the added voltage from the adder to the amplifier 10 becomes a constant value, and variations in the gap due to eccentricity of the rotor magnet 22, uneven magnetization, etc. Accordingly, it is possible to compensate so that the envelope surrounding the output signal waveform does not wave and maintain a straight line of a constant value, thereby preventing fluctuations in the output signal level. However, x is limited to an even number because it needs to be set so that the output voltage of the adder is a constant value other than zero. In addition, in the above embodiment, two magnetically sensitive elements are arranged with a phase difference of 120 degrees in electrical angle, and the sum and inversion of the output signals of these two magnetically sensitive elements and the output signal of the two magnetically sensitive elements are By outputting the output signal of the element to the outside, three-phase signals can be output using two magnetically sensitive elements.

As described above, in the magnetic encoder according to the present invention, the envelope surrounding the output signal waveform does not wave due to variations in assembly accuracy or variations in the magnetization strength of the information recording medium, and maintains a constant value in a straight line. It is possible to compensate for this and prevent fluctuations in the output signal level.

[Brief explanation of drawings]

FIG. 1 is a perspective view showing a conventional magnetic encoder, FIG. 2 is a waveform diagram showing an example of an ideal output signal waveform of the magnetic encoder, and FIGS. 3 and 4 are configurations of each embodiment of the present invention. FIG. 5 is a plan view showing an example of a conventional magnetic encoder, and FIG. 6 is a waveform diagram showing an output signal waveform of the magnetic encoder. 6, 7...square calculator, 8...adder, 10...
...Error detection amplifier, 11...Reference voltage source.

Claims (1)

[Claims] 1 A magnetically sensitive element is placed close to and facing an information recording medium on which an information signal is recorded by magnetization, and the information signal is obtained from the magnetically sensitive element by relative movement between the magnetically sensitive element and the information recording medium. In the equation encoder, n (≧2) magnetically sensitive elements are arranged with a predetermined phase difference, and each output signal of the n magnetically sensitive elements is raised to a power by n power calculators and summed. A magnetic encoder comprising: a control means for controlling the magnetically sensitive element so that the added sum voltage becomes a constant value.