JP2009276325A - Rotation angle detector - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a rotation angle detector that determines the maximum value and minimum value of a detection signal, without an accident where the maximum value and the minimum value obtained from the detection signal are affected by the phase difference between an excitation signal and the detection signal or distortion component of the excitation signal, and that accurately determine the rotation angle, based on the maximum value and the minimum value. <P>SOLUTION: This rotation angle detector 10 includes a resolver 11 for outputting a two-phase detection signal, having 90° phase different due to input of the excitation signal according to the rotation angle of a body to be detected; a peak-and-hold circuit 17 for holding the maximum value of each detection signal output from the resolver 11, a bottom hold circuit 18 for holding the minimum value of each detected signal output from the resolver 11; an A/D conversion section 19 for A/D-converting the maximum value and minimum value of each detection signal held by the peak hold circuit 17 and bottom hold circuit 18, respectively; and an angle arithmetic section 21 for determining the rotation angle of the body to be detected, based on the maximum value and minimum value of each detection signal A/D-converted by the A/D conversion section 19. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a rotation angle detection device that detects a rotation angle of an output shaft or the like of a motor.

For example, in an electric power steering apparatus, a brushless motor is used as a generation source of a steering assist force to be applied to a vehicle steering mechanism. This brassless motor needs to appropriately control the current flowing through the motor in accordance with the rotation angle of the rotor in order to prevent torque ripple and the like due to uneven rotation of the rotor. Therefore, the motor control device that controls the brushless motor is provided with a resolver for detecting the rotation angle of the rotor, and the value of the current flowing through the motor is appropriately set based on the rotation angle detected by the resolver. .
Further, the value of the current flowing through the motor is set in consideration of the steering torque, and some torque detection devices for detecting the steering torque include a resolver for detecting the twist angle of the steering shaft.

  Generally, an excitation signal consisting of a sine wave is input to the resolver, and a two-phase detection signal (sin signal, cos signal) having a 90 ° phase difference is output according to the rotation angle of the detected object. The The two-phase detection signals are sampled a plurality of times (for example, four times) for each period and A / D converted by the A / D converter. Then, based on a plurality of sampling values converted by the A / D converter, the amplitude (maximum value, minimum value) of the detection signal is calculated by a microcomputer using a method such as a least square method, From the amplitude, the rotation angle of the rotor or the like is obtained by calculation.

In addition, as a resolver for detecting the rotation angle of a to-be-detected body, what was described, for example in patent document 1 is well-known.
JP-A-6-241834

The two-phase detection signal output from the resolver is sampled a plurality of times at a timing corresponding to the oscillation timing of the excitation signal. However, there may be a phase difference between the excitation signal and the detection signal due to variations in the characteristics of components related to the resolver, temperature characteristics, etc. If a phase difference occurs between the excitation signal and the detection signal, There is also a deviation in sampling timing.
On the other hand, since the excitation signal includes a distortion component instead of an ideal sine wave, the deviation of the sampling timing is affected by the distortion component of the excitation signal, and the amplitude of the detection signal calculated based on the sampling value There is a problem that an error occurs in the rotation angle calculated based on this amplitude. When a resolver is used for the rotor rotation angle detection device of a brushless motor, an error in the rotation angle causes an increase in torque ripple and generation of control noise. When a resolver is used for the steering torque detection device, the twist angle of the steering shaft This error is caused by a decrease in torque detection accuracy.
In addition, since the conventional resolver samples the detection signal a plurality of times per cycle and obtains the amplitude of the detection signal by calculation from the sampled value, there is also a problem that the calculation load of the microcomputer increases.

  The present invention has been made in view of such circumstances, and the maximum value and the minimum value of the detection signal are less affected by the phase difference between the excitation signal and the detection signal and the distortion component of the excitation signal. An object of the present invention is to provide a rotation angle detection device capable of reducing an angle error.

  The rotation angle detection device of the present invention includes a resolver that outputs a two-phase detection signal having a phase difference of 90 ° according to the input of an excitation signal in accordance with the rotation angle of the detection target, and the maximum value of each detection signal output from the resolver. A peak hold circuit for holding the signal, a bottom hold circuit for holding the minimum value of each detection signal output from the resolver, and a maximum value and a minimum value of each detection signal held by the peak hold circuit and the bottom hold circuit, respectively. An A / D conversion unit that performs D / D conversion, and an angle calculation unit that obtains the rotation angle of the detected object from the maximum value and the minimum value of each detection signal A / D converted by the A / D conversion unit. It is characterized by being.

  According to this configuration, the maximum value and the minimum value of the detection signal output from the resolver are held by the peak hold circuit and the bottom hold circuit, and the maximum value and the minimum value are A / D converted by the A / D converter. Then, the rotation angle of the detected object is obtained by the angle calculation unit based on the maximum value and the minimum value subjected to A / D conversion. Therefore, there is no need to sample the detection signal multiple times at the timing according to the oscillation timing of the excitation signal as in the past, and the maximum and minimum values of the detection signal are the phase difference between the excitation signal and the detection signal and the distortion of the excitation signal. It becomes difficult to be influenced by the components, and the error of the rotation angle can be reduced. Further, since it is not necessary to calculate the maximum value and the minimum value from the plurality of sampling values of the detection signal as in the prior art, it is possible to reduce the calculation load by the microcomputer.

  According to the present invention, the maximum value and the minimum value acquired from the detection signal are hardly affected by the phase difference between the excitation signal and the detection signal and the distortion component of the excitation signal, and the rotation angle error can be reduced. it can.

FIG. 1 is a block diagram showing a rotation angle detection device according to an embodiment of the present invention. Hereinafter, an outline of the rotation angle detection device 10 will be described.
The rotation angle detection device 10 includes a resolver 11. The resolver 11 is, as is well known, a two-phase different 90 ° phase from a rotor that is attached coaxially to a rotor such as a brushless motor and includes an excitation coil. And a stator having a detection coil, and configured to output from each detection coil a two-phase detection signal corresponding to the rotation angle of the rotor based on the excitation signal input to the excitation coil.

The rotation angle detection apparatus 10 includes a control unit 13 including a microcomputer including a CPU, a ROM, a RAM, and the like. The control unit 13 includes a PWM signal oscillation unit 14, an A / D conversion unit 19, an angle calculation. Part 21 and the like. The PWM signal oscillating unit 14 outputs a PWM signal. The PWM signal is filtered by the filter 15 and input to the drive circuit 16 as a sine wave signal, and further input from the drive circuit 16 to the resolver 11 as an excitation signal.
The two-phase detection signals output from the resolver 11, that is, the sine signal and the cosine signal are input to the peak hold circuit 17 and the bottom hold circuit 18, respectively, and the maximum value and minimum value of the detection signal are sampled. Then, the sampled maximum value and minimum value signals are input to the A / D converter 19 of the control means 13.

The A / D converter 19 converts the signals output from the peak hold circuit 17 and the bottom hold circuit 18 into sample signals as digital signals. The sample signal digitally converted by the A / D conversion unit 19 is input to the angle calculation unit 21, and the rotation angle of the rotor is obtained by calculation based on this sample signal.
In addition to the above, the control means 13 includes an A / D conversion start instruction unit 22 that provides a conversion start signal to the A / D conversion unit 19, a reset unit 23 that provides a reset signal to the peak hold circuit 17 and the bottom hold circuit 18. Is provided.

The peak hold circuit 17 and the bottom hold circuit 18 have a known configuration including an operational amplifier, a hold capacitor, a reset switch, and the like. The peak hold circuit 17 and the bottom hold circuit 18 hold the maximum value or the minimum value of the input signal (voltage) with the hold capacitor. It is configured to output to the D converter 19.
FIG. 2 is a time chart showing the time course of the operation of the rotation angle detection device 10. The peak hold circuit 17 monitors a detection signal having a higher potential than the reference potential among the input detection signals (sin signal, cos signal) after the detection start time t0. Then, the peak hold circuit 17 sequentially updates the maximum value of the detection signal and holds the maximum value H at the time point t1 when the detection signal turns from increasing to decreasing.

  On the other hand, the A / D conversion start instructing unit 22 of the control unit 13 sends a conversion start signal to the A / D conversion unit 19 at a predetermined time t2 (time after t1) based on the oscillation timing of the PWM signal in the oscillating unit 14. give. The A / D converter 19 generates a sample signal by A / D converting the maximum value H of the detection signal output from the peak hold circuit 17 based on the conversion start signal, and sends the sample signal to the angle calculator 21. Output.

  After completion of the A / D conversion, the reset unit 23 gives a reset signal to the peak hold circuit 17 at a predetermined time t3 (for example, a time when the detection signal or the excitation signal becomes the reference potential) based on the oscillation timing of the PWM signal. The peak hold circuit 17 resets the maximum value H held based on the reset signal to the reference potential.

  Similarly, after the detection start time t0, the bottom hold circuit 18 monitors a detection signal having a potential lower than the reference potential among the input detection signals and sequentially updates the minimum value, so that the detection signal shifts from decreasing to increasing. The minimum value L at time t4 is held. The A / D conversion start instruction unit 22 provides a conversion start signal to the A / D conversion unit 19 at a predetermined time t5 (time after t4) based on the oscillation timing of the PWM signal.

  The A / D converter 19 generates a sample signal by A / D converting the minimum value L of the detection signal output from the bottom hold circuit 18 based on the conversion start signal, and sends the sample signal to the angle calculator 21. Output. After the A / D conversion, the reset unit 23 gives a reset signal to the bottom hold circuit 18 at a predetermined time point t6 based on the oscillation timing of the PWM signal. The bottom hold circuit 18 resets the minimum value L held based on the reset signal to the reference potential.

  A memory such as a ROM of the control unit 13 stores the relationship between the sample signal of the sin signal and the cos signal and the rotation angle of the rotor of the resolver 11 in a table, and the angle calculation unit 21 stores the table. The rotation angle is obtained from the sample signal by referring to it.

In the above configuration, the rotation angle detection device 10 of the present embodiment obtains the maximum value H and the minimum value L of the detection signal output from the resolver 11 by the peak hold circuit 17 and the bottom hold circuit 18, so that Compared to the case where the detection signal of the resolver 11 is sampled a plurality of times during one period based on the oscillation timing of the excitation signal, and the amplitude (maximum value and minimum value) of the detection signal is obtained from the sampled value by calculation. Thus, it becomes difficult to be influenced by the phase difference between the excitation signal and the detection signal and the distortion component of the excitation signal, and the error of the rotation angle obtained by the angle calculation unit 21 becomes small. Therefore, when the rotation angle detection device 10 is used for a brushless motor, generation of torque ripple and control sound can be suppressed, and when used for a torque sensor, torque detection accuracy can be improved.
In particular, in the rotation angle detection device 10 of the present embodiment, the maximum value is between the time t1 and t4 when the maximum value H or the minimum value L of the detection signal is held and the time t3 and t6 when the reset signal is output. Since A / D conversion may be performed by sampling H and the minimum value L, strict sampling timing is not required, and there is almost no influence from the phase difference between the excitation signal and the detection signal.

  Further, since it is sufficient to sample the detection signal twice per cycle by the peak hold circuit 17 and the bottom hold circuit 18, when the detection signal is sampled four times per cycle as in the prior art, and the amplitude is obtained by calculation. In comparison, the load on the microcomputer can be reduced.

  The present invention is not limited to the embodiment described above, and can be appropriately changed in design. For example, the rotation angle detection device 10 of the present invention is not limited to a brushless motor or a torque detection device of an electric steering device, and can be used for other applications.

It is a block diagram of the rotation angle detection apparatus which concerns on embodiment of this invention. It is a time chart which shows the time course of operation | movement of the rotation angle detection apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Rotation angle detection apparatus 11 Resolver 13 Control means 14 Oscillation part 17 Peak hold circuit 18 Bottom hold circuit 19 A / D conversion part 21 Angle calculation part

Claims (1)

A resolver that outputs a two-phase detection signal having a phase difference of 90 ° according to the input of an excitation signal in accordance with the rotation angle of the detected object;
A peak hold circuit that holds the maximum value of each detection signal output from the resolver;
A bottom hold circuit that holds the minimum value of each detection signal output from the resolver;
An A / D converter for A / D converting the maximum value and the minimum value of each detection signal held by the peak hold circuit and the bottom hold circuit;
And a rotation angle detector that obtains a rotation angle of the detected object from a maximum value and a minimum value of each detection signal A / D converted by the A / D converter.

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