JPH01207628A - Encoder - Google Patents

Abstract

PURPOSE:To reduce the error of a commutation control signal due to the eccentricity of a code disk by equalizing the quantity difference between light transmission slits in an inside and an outside array to the number of teeth of a brushless motor. CONSTITUTION:The code plate 1 which has light transmission slits 2 and 3 is fitted to the rotor of the brushless motor 20, light emitting means 34-37 and photodiode arrays (PHD) 30-33 are arranged opposite each other across the slits 2 and 3, and the rotating speed of the code disk 1 is detected according to photodetected light beams passed through the slits 2 and 3. Then two arrays of the slits 2 and 3 are formed and the quantity difference between the inside slits 3 and outside slits 2 is equalized to the number of the teeth of the motor 20. Then, pairs of light emitting means 34 and 35, and 36 and 37, and PHDs 30 and 31, and 32 and 33 are arranged for the slits 2 and 3 at 180 deg. shift positions of the code disk 1. The detection signals of the PHD 30 and 31 corresponding to the slits 2 are summed up by an adder 42 and the detection signals of the PHDs 32 and 33 corresponding to the slits 3 are summed up by an adder 43; and a control part 17 generates the commutation control signal for the motor 20 according to the phase difference between those adders.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an improvement of an optical rotary encoder used for detecting rotation of a motor.

[Prior Art] Conventionally, such an encoder is described, for example, in the specification of Japanese Patent Application No. 61-249363 filed by the present applicant.

This encoder will be explained below.

The configuration of the encoder described above is shown in FIG.

In the figure, 1 is a disc-shaped code plate that rotates together with the output shaft M of the motor, and two rows of light-transmitting slit rows are formed at a constant pitch in the circumferential direction. The outer slit row is provided with n1 translucent slits 2, and the inner slit row is provided with n1 translucent slits 2.
Two transparent slits 3 are provided. Difference in the number of transparent slits n.

-n2 is the same number as the number of teeth of the motor to which the code plate 1 is fixed.

4.5 is a light emitting means, for example an LED; 6.7 is a light emitting means 4.
This lens converts the light beam from 5 into a parallel beam. Light passing through lenses 6 and 7 is projected onto slits 2 and 3, respectively.

Reference numerals 8 and 9 designate image sensors as light receiving means for receiving light (slit image) that have passed through the transparent slits 2 and 3, respectively, and these include, for example, eight photodiodes 8. ~
8B and 9. This is a photodiode array with ~98 photodiodes arranged.

Photodiodes 8 and 9 are arranged with their code plates shifted by 180 degrees.

Photodiodes 81-8B and 9. The width of ~98 corresponds to one pitch of slits 2 and 3.

10 is a signal processing unit that calculates the positional relationship between the rotor and stator teeth of the motor based on the detection signals of photodiodes 81-8 and 91-9. A specific configuration of the signal processing section 10 is shown in FIG.

In FIG. 6, SWI to SW8 are photodiodes 8, to 8.
Day and 9. This is a switch that scans the signals from ~96 at a constant timing.

11.12 is an OP amplifier, and each switch SWI~S
Amplify the signal applied via W8. OP Anne 71
The outputs of 1 and 12 have a stepped waveform, and the height of the waveform corresponds to the number of photodiodes that have detected light.

13.14 is a low pass filter (hereinafter referred to as LPF)
and extracts signal components in the low frequency range of the OP amplifiers 11 and 12. The output of the OP amplifier becomes a sinusoidal waveform by passing through these LPFs.

15.16 is a comparator that shapes the waveform of the sine wave signal from the LPF 13.14.

17 is the signal fl (t) passed through LPF13.14
This is a control unit that controls the commutation of the motor 20 based on the phase difference between and f2 (t) and the torque command signal. The operation of this encoder will be explained.

Signals f1 (t) and f2 (t) are expressed by the following equations.

f+ (t)=A1 5in (ω+n, θ)
■f2 (t)=A2 s i n (ωt+n2θ)
■A,,A2: Constant, θ: Rotation angle of code plate ω=2
πfs.

fs: Scanning frequency of the photodiode array Here, the phase difference φ between both signals is φ=(n+n2)θ2.

Here, the relationship between the phase difference φ and the rotation angle θ of the code plate will be explained.

For example, a case will be described in which the number of outer slits n1 is eight and the number of inner slits n2 is six.

In this case, the number m of teeth of the motor is set from 8-6 to 2.

In this case, the relationship between the detection signals of the photodiode arrays 8 and 9 and the rotation angle of the motor is as shown in FIGS. 7(a) and 7(b).

As shown in the figure, the deviation (electrical angle) of these detection signals is proportional to the rotation angle θ (mechanical angle).

It increases as φ2...

The deviation φ between both detection signals when the code plate rotates by θ
From formula (■), it becomes as follows.

φ=(8-6)θ On the other hand, when the code plate rotates by θ, the rotor of the motor also rotates by θ. Since the number of teeth of the motor is two, the teeth of the rotor and stator of the motor are angularly shifted by 2θ in electrical angle. That is, the phase difference detected by the code plate corresponds to the electrical angle difference between the teeth of the motor's rotor and stator. Based on this, the positional relationship (mechanical angle) between the teeth of the motor's rotor and stator is detected, and the commutation of the motor is controlled based on this positional relationship.

[Problem to be solved by the invention] However, in this encoder, the position of the code plate 1 is
Since commutation is controlled based on the difference in the detection signals of the outer and inner photodiode arrays 8 and 9, which are arranged in a staggered manner, if the code plate 1 is eccentric, the eccentricity causes the photodiode arrays 8 and 9 to The phase of the error occurring in the detection signal is superimposed on the phase difference signal.

For example, in FIG. 6, when the rotation center 0' of the code plate 1 is eccentric from the true rotation center O by e, if a phase error occurs in the leading direction in the detection signal of the photodiode array 8, the photo A phase error occurs in the detection signal of the diode array 9 in the delay direction. Therefore, two phase errors are added to the commutation control signal obtained by taking the phase difference between the two photodiode arrays. Therefore, there is a problem in that the error in the commutation control signal becomes large and the torque fluctuation of the motor increases.

The present invention was made to solve these problems.

The purpose of this invention is to realize an encoder that can reduce errors in commutation control signals due to code plate eccentricity.

[Means for Solving the Problems] The present invention includes: attaching a code plate in which transparent slits are formed at a constant pitch to a rotor of a brushless motor, and arranging a light emitting means and a light receiving means to face each other with the transparent slits in between; In the encoder that detects the rotation of the code plate based on the light passing through the light-transmitting slits detected by the light receiving means, the light-transmitting slits are formed in two rows, and the light-transmitting slits in the inner and outer rows are arranged in two rows. The difference in number is the same as the number of teeth of the brushless motor, and each translucent slit row has
Two sets of light emitting means and light receiving means are arranged with the positions of the code plates shifted by 180 degrees, and a first adder adds the detection signals of the two light receiving means in the outer translucent slit row. , a second adder that adds the detection signals of the two light-receiving means in the first translucent slit row; The encarder is equipped with a control section that generates a motor commutation control signal.

[Example] The present invention will be explained below using the drawings.

FIG. 1 is a block diagram of an embodiment of an encoder according to the present invention. Components in FIG. 1 that are the same as those in FIGS. 5 and 6 are given the same reference numerals.

In FIG. 1, 30 and 31 are photodiode 4 arrays for detecting light passing through the transparent slit 2, and these are arranged with the position of the code plate 1 shifted by 180 degrees. 32.3
3 is a photodiode for detecting light passing through the transparent slit 3;
This is a door array, and these are also arranged with the position of the code plate 1 shifted by 180°.

34 to 37 are photodiode arrays 30 to 3, respectively.
3, the light emitting means 38 to 41 are light emitting means 30 to 3;
This is a lens that converts the light from No. 3 into parallel light.

42 is an adder that adds the detection signals of the photodiodes in the photodiode arrays 30 and 31 that correspond to each other in the order of arrangement, and 43 the detection signals of the photodiodes that correspond to each other in the order of arrangement of the photodiodes in the photodiode arrays 32 and 33. This is an adder that adds .

44 and 45 are sine wave signals f+ from the addition signal of the adder 42.
(t), f2 Ct). The signal generation circuit 44 includes SW1 to SW8. The signal generation circuit 45 consists of an OP amplifier 11, an LPF 13, and a comparator 15.
It consists of P F 14 and comparator 16.

In such an encoder, if the center 0' of the code plate 1 is eccentric from the true center O by e, and a phase error in the forward direction occurs in the detection signals of the photodiode arrays 30 and 32, the signal on the opposite side by 180° A phase error in the delay direction occurs in the detection signals of the photodiode arrays 31 and 33 located in the photodiode arrays 31 and 33. Adders 42 and 43 connect the inner and outer photodiode arrays 180° apart, ie 3
The detection signals of 0, 31, 32, and 33 are added to cancel the phase error. The signals from which the face center error has been removed in this manner are sent to signal generation circuits 44 and 45, where commutation control is performed in the same manner as in the encoder of FIG. 6.

FIG. 2 is a block diagram of another embodiment of the encoder according to the present invention.

In FIG. 2, 50 and 51 are F/V converters that convert the outputs of the comparators 15 and 16 into speed signals, and 52 is an adder that adds the speed signals of the F/V converters 50 and 51.

When an encoder is used to detect the rotation of a joint drive motor of a robot, the code plate may vibrate due to mechanical resonance or the like occurring in the joint tatg.

When the vibration direction is the moving direction of the slit, such as the a-a' direction, the photodiode array detects the speed even if the code plate is not rotating.

This detected speed becomes an error and is superimposed on the speed signal of the F/V converter.

Since the photodiode array 30.32 and the photodiode array 31.33 are located at positions shifted by 180 degrees on the code plate 1, the error signals generated in these two sets of photodiode arrays are out of phase by 1806 degrees. That is, the speed signal V of the F/V converter 50 changes over time as shown in graph g in FIG. 3, and the speed signal V2 of the F/V converter 51 changes over time as shown in graph g2 in the same figure. do.

Therefore, by adding the signals V and V2 using the adder 52, the detection errors of both signals are canceled.

The signal will be as shown in FIG.

Further, there is no need to provide sensitivity for speed detection with respect to movement in a direction perpendicular to the a-a' direction.

Note that, as the image sensor, something other than a photodiode array, such as a COD, etc., may be used.

[effect] According to the present invention, the following effects can be obtained.

■In the encoder shown in Figure 1, the signals f+ (t) and f2
(t) has the error due to the eccentricity of the code plate removed, so when taking the phase difference between the signals f+ (t) and f2 (t), the positive phase error and negative phase error are subtracted, resulting in a phase error. can be prevented from increasing. This reduces the error in the commutation signal, thereby reducing motor torque fluctuations. Further, it becomes unnecessary to adjust the eccentricity error of the code plate.

■In the encoder shown in Figure 3, the positive and negative errors that occur in the two speed signals due to the vibration of the code plate in the direction of movement of the slit are added together and canceled by the adder, thereby eliminating the influence of mechanical resonance. It becomes difficult to receive.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of one embodiment of the encoder according to the present invention, FIG. 2 is a block diagram of another embodiment of the encoder according to the present invention, and FIGS. 3 and 4 are operation of the encoder of FIG. 2. The explanatory diagrams, FIGS. 5 and 6, are diagrams showing an example of the configuration of a conventional encoder, and FIG. 7 is an explanatory diagram of the operation of the encoder shown in FIGS. 5 and 6. It is. DESCRIPTION OF SYMBOLS 1... Code plate, 2.3... Translucent slit, 4,5 degrees 34~37... Light emitting means, 8,9.30~33...
Photodiode array, 10... signal processing section, 11
゜12...OP amplifier, 13.14...L P F
, 15° 16... comparator, 17... control section,
20...Motor, 42...First adder, 43...
・Second adder, 50.5'l...speed converter, 52
...Adder. Figure 1 Figure 3 Face +', r1 t - Figure 4 Haruma 1-th s['''I

Claims (2)

[Claims] (1) A code plate on which transparent slits are formed at a constant pitch is attached to the rotor of a brushless motor, a light emitting means and a light receiving means are arranged facing each other with the transparent slits in between, and the light transmitting slits detected by the light receiving means are In the encoder that detects the rotation of the code plate based on passing light, the light-transmitting slits are formed in two rows, and the difference in the number of light-transmitting slits between the inner and outer rows is the same as the number of teeth of the brushless motor. In each light-transmitting slit row, two sets of light-emitting means and light-receiving means are arranged with the position of the code plate shifted by 180 degrees, and the two light-receiving means in the outer light-transmitting slit row a first adder that adds the detection signals of the means; a second adder that adds the detection signals of the two light-receiving means in the inner light-transmitting slit array; An encoder comprising: a control section that generates a commutation control signal for the brushless motor from a phase difference between added signals of an adder. (2) A code plate on which transparent slits are formed at a constant pitch is attached to the rotor of a brushless motor, and a light emitting means and a light receiving means are arranged facing each other with the transparent slits in between, and the light transmitting slits detected by the light receiving means are In the encoder that detects the rotation of the code plate based on the passing light, two pairs of light emitting means and light receiving means are arranged in each translucent slit row with the position of the code plate shifted by 180 degrees, First and second speed converters that convert the detection signals of these two light receiving means into speed signals, respectively, and a speed signal that corrects a detection error due to eccentricity of the code plate by adding the speed signals of these speed converters. An encoder equipped with an adder that outputs .