JPH0469079A - Apparatus for sensing motor speed - Google Patents

Abstract

PURPOSE:To sense a motor speed with a high accuracy, by providing the memory storing the correction value for correcting the dispersion around a true period, which is exhibited by the periods of the respective pulse signals obtained from an encoder, and by reading out the correction value from the memory every the pulse signal when measuring the period of the pulse signal obtained from the encoder, and further, by correcting the period of the pulse signal with the correction value. CONSTITUTION:In a part 21 for sensing an encoder pulse signal, the encoder pulse signal is specified, and the value corresponding to the specified pulse signal is read out from a ROM 22. Then, the value is inputted to a speed sensing part 11, and the error of the period of the specified pulse signal is compensated. In the speed sensing part 11, a counting value of the period is converted to a pulse number NT corresponding to it. In the pulse number NT, the compensation of the dispersion in the periods of the encoder pulse signal is completed, and the pulse number NT is an accurate speed value. Thereby, since the dispersion of the respective measured periods of the encoder pulse signal is corrected, an accurate speed measurement can be performed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a motor speed detection device, and more particularly to a motor speed detection device that detects the speed of a motor based on pulse signals from an encoder.

[Prior Art] Conventionally, when performing position control or speed control, the speed of a motor is accurately measured and the speed of the motor is controlled to a speed command value. Motor speed control devices are used for this purpose. In such a motor speed control device, the motor speed is controlled according to the deviation between the motor speed signal obtained from the encoder installed coaxially with the motor and the target value expressed by the motor speed command signal, so the control accuracy is improved. In order to increase speed, the motor speed must be detected accurately. Conventional speed detection methods include a pulse counting method in which the number of encoder pulses obtained within a certain period of time is counted, and a period counting method in which the period of the encoder pulses is measured.

The pulse counting method counts the number of encoder pulses that come within a certain period of time, and as shown in P2 of Figure 5 (A), the count value N increases as the motor rotation FIR increases. , Ql in Figure 5(B)
As shown in , the speed accuracy (1/N) improves as the rotation speed R increases.

On the other hand, in the period counting method, the period of the encoder pulse is counted to the right of FIG. 5(A).

As shown by Pl, when the motor rotation speed R is small and the period is large, a large count value N is obtained.
The measurement accuracy is good when is small.

[Problems to be Solved by the Invention] Therefore, when the motor is rotating at a low speed, the accuracy is better if the period counting method is used, so the period counting method is used when the motor rotates at a predetermined number of rotations or less. However, the phase accuracy of commercially available encoders is due to manufacturing tolerances, encoder installation accuracy, and errors in the processing system of the electric circuit that processes signals from the encoder. It is not constant and there are variations. That is, as shown in FIG. 6, the B phase of the encoder pulse does not always have a predetermined phase difference t=(1/4)T with respect to the A phase, where the pulse period is T. The above-mentioned error causes an error of approximately plus or minus (1/8) T, and as a result, the pulse period over the encoder rotation generates an error of approximately -10% to 10%, resulting in a speed detection error. appears.

Therefore, the present invention has been made to solve such problems, and it is possible to accurately detect the motor speed measured by measuring the cycle of encoder pulses regardless of variations in the cycle of the encoder. The task is to submit a motor speed detection device.

[Means for Solving the Problems] In order to solve the above problems, the present invention utilizes a motor speed detection device that detects the speed of a motor based on pulse signals from an encoder. A means for measuring the period, and a memory storing a correction value for correcting variations in the period of each pulse signal from the encoder with respect to the true period. The pulse period is corrected using a correction value read from the memory, and the motor speed is detected based on the corrected pulse period.

[Function] In such a configuration, a means for measuring the period of the pulse signal from the encoder is provided, and the motor speed is detected from the periodic signal by this means. The pulse period is not constant for each signal and has variations due to errors or errors in the signal processing system. Therefore, in the present invention, a correction value for correcting variations in the period of each pulse signal from the encoder with respect to the true period is stored in the memory in advance. When measuring the period of the pulse signal from the encoder, the pulse period is corrected for each pulse using a correction value read from the memory, and the motor speed is detected based on the corrected pulse period. Therefore, each period of the encoder pulse to be measured has its variations corrected, and it is possible to accurately measure the period, that is, to determine the accurate speed 7Il++.

According to a preferred embodiment, a counter is provided to count the number of pulses from the encoder. When this count value is smaller than a predetermined value, the motor speed is detected according to the corrected pulse period (i.e., the period counting method is used), and when it is larger than the predetermined value, the motor speed is detected according to the count value (i.e., the period counting method is used). (using pulse counting method).

[Embodiments] Next, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 shows a basic configuration of a motor speed detection device according to an embodiment of the present invention as a block diagram, and in the figure, the reference numeral 1 indicates a motor to be controlled. The speed of this motor 1 is determined by an encoder 2 installed coaxially with the motor. Pulse signals (φA, φB) from the encoder 2 are input to a U/D (uptown) counter 3 as an actual value signal indicating the current position of the motor. This U/D counter 3 receives a command pulse (CW, CCW) as a position target value from a device (not shown).
) is input, and the U/D counter 3 outputs the speed command generator 4 according to the deviation between this command pulse and the encoder pulse signal.
The speed command value is outputted to the comparison stage 5 via. A measured value of speed is input to this comparison stage as will be described later. After the deviation between the speed command value and its measured value is compensated proportionally (P) and integrally (1) by the compensation circuit 6, the D/A converter 7
After being converted into an analog signal, it is amplified by an amplifier 8 and manually applied to the motor 1 to control the motor 1 to a command speed and to a position corresponding to the command pulse input to the U/D counter 3.

The pulse signal from encoder 2 is input to a timer IO to further measure the speed of the motor. This timer 10 uses φA or ψB of the encoder pulse signal.
The period of the signal is counted by pulses of a predetermined frequency. This count value corresponds to the speed of the motor 1, is input to the speed detection section 11, and is converted into a speed value.

The pulse signal from the encoder 2 is sent to the Ll/D counter 2.
0 is also input. As the encoder pulse signal, a φ2 signal is generated every rotation to identify one rotation of the encoder, and the U/D counter 20 is cleared by this φ2 to count the encoder pulses. This count value is input to the encoder pulse detection section 21, and the encoder pulse is φ
The number of the pulse from 2 is detected. Encoder pulse detection section 21 is connected to ROM22.

As shown in FIG. 2, the ROM 22 stores the correction value of the period of the encoder pulse at the address corresponding to the pulse number according to the pulse number of the encoder pulse. Therefore, the correction value is outputted to the speed detection section 11 to compensate for speed errors due to pulse period variations when speed is measured by pulse period measurement.

The correction value stored in this ROM 22 is determined as follows. First, as shown in FIG. 3, the encoder 2 to be measured is attached to a shaft 30 to which a reference encoder 31 of higher resolution is attached. At the rotation origin of encoder 2, a φZ times signal is generated as shown in the middle part of Figure 4, so number the pulse signal from encoder 2 in synchronization with this ψ2 signal (see the upper part of Figure 4).Next Encoder pulse period TO1T1. T
2, T3, T4,...- for each number using the reference encoder 3.
Measure using the reference pulse from 1. Next, count value TO of the pulse period of each number.

T1. The average value of T2, T3, T4, . . . is determined, and the ratio β to the average value is determined for each pulse. If the true period is T' and the measurement period is T, then T=T' *β, therefore T'
= T/β, so the value of l/β is calculated in advance for each pulse number, and it is stored in the address of the ROM 22 corresponding to each pulse number. A ROM 22 stored in this manner is illustrated in FIG.

Note that each of the devices 4 to 6 and 11.21 above can be realized by functions within the CPU.

Next, the operation of the device configured as described above will be explained.

The pulse signal (φA) from encoder 2 is the timer IO
, and its period is counted by, for example, a clock fO. In addition, pulse signals from encoder 2 (φA, φ
B) is input to the U/D counter 20, and the number of pulses is counted up and down by a factor of 4. The cycle count value counted by the timer 10 and the count value counted by the U/D counter 20 are input to the speed detection section 11.

Furthermore, the encoder pulse detection unit 21 identifies from the encoder pulse signal what pulse number the pulse is from φ2. In this case, the count number is set to 1/4 in the detection section. The 1/β value stored in correspondence with the detected pulse number is read out from the ROM 22, and the value is manually input to the speed detection unit 11 to compensate for the error in the pulse period.The speed detection unit 11 calculates the cycle count. The value is converted into the number of pulses N correspondingly. In this conversion, ST is the sampling period, tO is the period of the period measurement clock fO, tn is the period count value obtained by the timer IO, and β
If is the correction value of the encoder pulse period mentioned above, then NT= (ST/1el) ・ (1/ln ・I/
β).

This number of pulses NT compensates for variations in the period of the encoder pulses and is an accurate speed value. However, as mentioned above, the period counting method achieves this accuracy when the motor rotates at low speed, so the speed detection unit 11, the pulse count value Nn obtained from the U/D counter 20 is set to a predetermined value N.
When Nn is larger than NO, it is assumed that the motor is rotating at high speed, and the data according to the pulse counting method, that is, Nn, is taken as the speed data value, and Nn is NO.
When it is smaller, the data according to the period counting method,
That is, let NT be the speed data value.

[Effects of the Invention] As explained above, according to the present invention, there is provided a means for measuring the period of a pulse signal from an encoder, and a correction method for correcting variations in the period of each pulse signal from the encoder with respect to the true period. When measuring the period of the pulse signal from the encoder, the pulse period is corrected with the correction value read from the memory for each pulse, and the motor speed is determined based on the corrected pulse period. Since the encoder pulses are detected, variations in each period of the encoder pulse to be measured are corrected, and accurate period measurement, that is, accurate speed measurement is possible.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of the device of the present invention, and FIG.
The figure is an explanatory diagram showing period correction data stored in the memory, FIG. 3 is a perspective view of a device for obtaining period variation correction data, and FIG. 4 is a method for obtaining period variation correction data. FIGS. 5A and 5B are explanatory diagrams illustrating the principle of a conventional speed detection method, and FIG. 6 is an explanatory diagram illustrating variations in the cycle of encoder pulses. 1--Motor 2--Encoder 3.20
---U/D counter 10--Timer 11...Speed detection section 22
...ROM Figure 2

Claims (1)

[Claims] 1) A motor speed detection device that detects the speed of a motor based on pulse signals from an encoder, comprising: means for measuring the period of the pulse signals from the encoder; and a period of each pulse signal from the encoder. and a memory storing correction values for correcting variations in the true period of the encoder, and when measuring the period of the pulse signal from the encoder, the pulse period is corrected with the correction value read from the memory for each pulse, and the pulse period is A motor speed detection device that detects a motor speed based on a corrected pulse period.