JP4582955B2 - Encoder - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an encoder used for detecting the position of an object to be detected such as a motor or a movable part used in industrial robots, NC machine tools, etc., and more particularly to offset correction thereof.
[0002]
[Prior art]
In order to increase the resolution, the encoder detects two signals of the A phase signal and the B phase signal that are out of phase from the signal recording body that rotates or moves together with the detected object, and each of the two phase signals is detected. An analog / digital converter (hereinafter referred to as “A / D converter”) converts the signal into a digital signal, and detects the angle and position of the detected object based on the converted digital signal.
[0003]
FIG. 4 shows an example of a conventional encoder. In FIG. 4 , an angle data storage drum 1 is a signal recording body that is connected to a detection body such as an output shaft of a motor and rotates together with the detection body. The angle data storage drum 1 constitutes means for storing a rotation angle by forming magnetic poles at regular intervals around the drum. Two pairs of magnetoresistive elements 2 and 3 are arranged to face the peripheral surface of the angle data storage drum 1. The magnetoresistive elements 2 and 3 form a sensor for detecting the magnetic pole of the angle data storage drum 1 and output an A phase analog signal and a B phase analog signal having a phase difference of 90 degrees.
[0004]
The output signals of the magnetoresistive elements 2 and 3 are respectively inputted to the comparators 4 and 5 as waveform shaping means and binarized. That is, the comparators 4 and 5 function as A / D converters. The A-phase and B-phase binarized signals are input to the quadruple circuit 6, converted to a digital signal having a frequency four times, and input to the up / down counter 7. The up / down counter 7 also receives an up signal or a down signal from the quadrature circuit 6 based on the phase difference between the A phase signal and the B phase signal. The up / down counter 7 up-counts or down-counts the pulses from the quadruple circuit 6 according to the up signal or down signal, and outputs the count value. This count value is a value indicating the rotational position of the angle data storage drum 1 which is a signal recording body.
[0005]
In the encoder as described above, it is necessary to adjust the offset to zero. For example, in the example of FIG. 4 , if the reference value of the comparators 4 and 5 as the A / D converter is zero level, the duty ratio of the binarized A phase and B phase signals is 50%. The reference values of the comparators 4 and 5 may deviate from the zero level. This is called an offset in the encoder. If there is an offset, the duty ratio of the A-phase and B-phase digital signals deviates from 50%, the counter value deviates back and forth, and the rotational position of the angle data storage drum 1 as the signal recording body matches the counter value. Therefore, a detection position error occurs.
[0006]
[Problems to be solved by the invention]
Therefore, various offset correction devices in the encoder have been proposed. The invention described in Japanese Patent No. 3026949 is one of them.
However, the offset correction in the conventional encoder has various problems as described below.
a. When calculating the offset, abnormal detection is not performed, so even if an offset value greatly different from the true offset value is calculated due to noise in the calculated data, it is not detected as an abnormal value, and angle interpolation is performed with an incorrect value. Will go.
b. Since the calculated offset value is not compared with the offset value stored in the initial stage, even if the offset value fluctuates fatally due to a secular change or the like, this is not detected as an abnormal value.
c. Since the calculated data is not stored, the calculated offset value is deleted when the power is turned off. Therefore, when the power is turned on again, the angle cannot be interpolated with an optimum value. For this reason, the position accuracy at the time of power-on becomes very poor.
[0007]
The present invention has been made to solve the problems of the prior art as described above. When an abnormal offset value is detected by always estimating the offset value and subjecting it to offset correction, the present invention is used. An object of the present invention is to provide an encoder that can be determined as an abnormal value.
The present invention also makes it possible to detect when an offset value fluctuates fatally, and to perform offset correction using an inconvenient offset value instead of the fatally fluctuating offset value. The purpose is to provide.
It is another object of the present invention to provide an encoder that maintains a calculated offset value even when the power is turned off, and allows angle interpolation with an appropriate value when the power is turned on again. Objective.
[0008]
[Means for Solving the Problems]
The invention according to claim 1 is a signal recording body in which signals are recorded at regular intervals, a pair of sensors for detecting signals recorded on the signal recording body as the signal recording body moves, and the pair of sensors An encoder having an offset correction unit and an amplitude ratio correction unit for correcting an offset and an amplitude ratio of a signal obtained from a sensor, and an electric division unit for calculating an interpolation angle from the signal subjected to the offset correction and the amplitude ratio correction An estimation unit that estimates an offset value and an amplitude value and uses the offset value and an amplitude ratio correction, and a storage unit that stores the estimated offset value and the amplitude value, and the storage unit stores the estimation A plurality of offset values and amplitude values estimated by the unit are stored in chronological order .
[0009]
According to a second aspect of the invention, in the invention according to the first aspect, memorize means, characterized in that it consists of a volatile memory backed up by non-volatile memory or a backup power supply.
[0011]
According to a third aspect of the invention, in the first aspect of the invention, in addition to the storage means, an initial offset storage unit that stores an estimated offset value before factory shipment and an initial gain storage that stores an estimated amplitude value before factory shipment. Output an abnormal value signal when the latest offset value or amplitude value stored in the storage means and the initial offset value or amplitude value stored in the initial offset storage unit or the initial gain storage unit are significantly different from each other. It has a pass / fail judgment unit.
[0012]
According to a fourth aspect of the present invention, in the third aspect of the present invention, when an abnormal value signal is output, the previous estimated offset value or estimated amplitude value in which no abnormal value is detected is read from the storage means, and this is offset-corrected. Alternatively, it is used for amplitude correction.
The invention described in claim 5 is stored in the initial offset storage unit and the initial gain storage unit when the estimated offset value or the estimated amplitude value stored in the storage unit is lost in the invention described in claim 3 . The initial offset value or the initial amplitude value is used for offset correction or amplitude correction.
[0013]
According to a sixth aspect of the present invention, in the third aspect of the invention, when all of the estimated offset value or the estimated amplitude value stored in the storage means are abnormal values, the initial offset storage unit and the initial gain storage unit store them. The initial offset value or the initial amplitude value that has been set is used for offset correction or amplitude correction.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of an encoder according to the present invention will be described with reference to the drawings.
In FIG. 1, an angle data storage drum 11 is connected to a detection object such as an output shaft of a motor and rotates together with the detection object, similarly to the angle data storage drum in the conventional example. The angle data storage drum 11 is formed with magnetic poles at regular intervals around it, so that different waveform information corresponding to the amount of movement, that is, the amount of rotation in the illustrated example, is recorded, and a signal recording for storing the rotation angle Make up body. Two magnetoresistive elements 12 and 13 are arranged facing the peripheral surface of the angle data storage drum 11. The magnetoresistive elements 12 and 13 form a sensor that detects the magnetic pole of the angle data storage drum 11 and converts it into an electric signal. The magnetoresistive elements 12 and 13 receive an A-phase analog signal and a B-phase analog signal having a phase difference of 90 degrees. Output.
[0015]
The A-phase analog signal and the B-phase analog signal are amplified by amplifiers 14 and 15, respectively, and then converted into digital signals ADa and ADb by an A / D converter 16. The digital signals ADa and ADb are input to an offset subtraction unit 17 serving as an offset correction unit. The offset subtracting unit 17 subtracts the offset values a1 and b1 from the digital signals ADa and ADb. That is,
a_phs ′ = ADa−a1
b_phs = ADb−b1
And outputs the result.
[0016]
The amplitude ratio a0 (described later) of b_phs with respect to the calculated a_phs ′ is integrated by an amplitude ratio integration unit 18 as an amplitude correction unit, and the amplitudes of a_phs and b_phs are made uniform. That is, a_phs = a0 * a_phs ′. a_phs and b_phs are input to the electrical divider 19, which performs electrical interpolation, that is, θ = atan (a_phs, b_phs)
To calculate the electrical interpolation angle θ.
[0017]
The a_phs and b_phs are also input to the offset estimation unit 20, and the electrical interpolation angle θ is also input to the offset estimation unit 20. The offset estimation unit 20 calculates the offset estimated values ^ a1, ^ b1 and the amplitude ratio estimated value ^ a0. As these calculation methods, for example, the same method as the conventional method described in Japanese Patent No. 3026949 is used.
[0018]
The offset estimated values ^ a1, ^ b1 and the amplitude ratio estimated value ^ a0 calculated by the offset estimating unit 20 are stored in a storage device 21 as storage means. The storage device 21 may be a volatile memory or a non-volatile memory. In the case of a volatile memory, backup is performed by a backup power source 23 in addition to the main power source 22. As the backup power source 23, a primary battery, a secondary battery, a large-capacitance capacitor called a super capacitor, or the like can be used. The circuit is configured to automatically switch to the backup power source 23 when the main power source is cut off. Regardless of the nonvolatile or volatile memory, the stored value is retained even when the main power supply 22 is shut off, and the stored values a1, b1, and a0 are used as initial values when the operation is resumed.
The storage device 21 stores a plurality of offset values and amplitude values estimated by the estimation unit 20 in time series.
[0019]
Reference numeral 25 denotes an initial offset storage unit, and 26 denotes an initial amplitude ratio storage unit. The initial offset storage unit 25 and the initial amplitude ratio storage unit 26 are both ROM (read only memory). The initial offset storage unit 25 stores ^ a1, ^ b1 before factory shipment, and the initial amplitude ratio storage unit 26 stores ^ a0 = ^ a10, ^ b10, ^ a00 before factory shipment.
[0020]
The stored values of the initial offset storage unit 25 and the initial amplitude ratio storage unit 26 are the latest offset estimated values ^ a1 and ^ b1 and the amplitude ratio estimated value ^ a0 stored in the storage device 21 in the pass / fail determination unit 27. And the offset estimated values ^ a1, ^ b1 and the amplitude ratio estimated value ^ a0 are used for pass / fail judgment as to whether they are normal or abnormal. When the offset estimated values ^ a1, ^ b1 and the amplitude ratio estimated value ^ a0 are extremely different from the stored values of the initial offset storage unit 25 and the initial amplitude ratio storage unit 26, they are detected as abnormal values. Specifically, initial values ^ a10, ^ stored in the initial offset storage unit 25 and the initial amplitude ratio storage unit 26 of the latest estimated values ^ a1, ^ b1, ^ a0 stored in the storage device 21. When the fluctuation with respect to b10, ^ a00 is larger than the prescribed ratio, it is regarded as an abnormal value.
[0021]
Reference numeral 24 denotes a switch that switches between the estimated value from the storage device 21 and the stored values of the initial offset storage unit 25 and the initial amplitude ratio storage unit 26. The switch 24 selects either the estimated value or the stored value, inputs it to the offset subtractor 17 as offset values a1 and b1, and inputs it to the amplitude ratio integrator 18 as an amplitude ratio a0. When both the main power source 22 and the backup power source 23 are shut off, or when the value stored in the storage device 21 is destroyed for some reason, the switch 24 switches the initial offset storage unit 25 and the initial amplitude ratio storage unit 26. Connected to the offset subtracting unit 17 and the amplitude ratio integrating unit 18, the stored values of the initial offset storing unit 25 and the initial amplitude ratio storing unit 26 are given as initial values.
[0022]
Next, the operation of the above embodiment will be described. A Lissajous circle can be obtained by using the A-phase and B-phase analog outputs of the magnetoresistive elements 12 and 13 and the amplifiers 14 and 15 as the coordinate axes. The digital signals ADa and ADb converted by the A / D converter 16 are digital values of the Lissajous circle.
[0023]
It is expressed by the above analog value and digital value due to the gap variation between the surface of the angle data storage drum 11 as the detection target and the magnetoresistive elements 12 and 13 as sensors, the influence of external magnetic force, change with time, and other factors. The center of the Lissajous circle deviates from the center of the coordinate axis. This is the offset. The offset subtracting unit 17 subtracts the offset values a1 and b1 from the digital signals ADa and ADb to correct the deviation of the center of the Lissajous circle. The offset values a1 and b1 are values estimated as described above and stored in the storage device 21, or offset values stored in the initial offset storage unit 25.
[0024]
The Lissajous circle is not only shifted from the center due to the above factors, but may not be a perfect circle due to the difference in amplitude between the A phase and the B phase, and may be deformed into an elliptical shape. Therefore, the amplitude ratio integrating unit 18 integrates the amplitude ratio a0 of the B layer digital signal b_phs with respect to the A layer digital signal a_phs ′ corrected by the offset subtracting unit 17 to make the Lissajous circle almost a perfect circle.
[0025]
As described above, the electric dividing unit 19 performs an electric interpolation operation to calculate the electric interpolation angle θ. As described above, according to the illustrated embodiment, since the electric interpolation angle θ is calculated from the Lissajous circle obtained continuously by the detection signals of the A phase and the B phase and changing continuously, the rotational angle variation or the Position fluctuation can be detected. On the other hand, in the conventional encoder as shown in FIG. 4 , the rotation angle fluctuation or position fluctuation of the detected object is detected using the binarized A-phase signal and B-phase signal. However, although a multiplier circuit is used, there is a limit to increasing the resolution.
[0026]
Further, according to the illustrated embodiment, a plurality of offset values and amplitude ratios estimated by the offset estimation unit 20 are stored in time series in the storage device 21, and the storage device 21 is nonvolatile or volatile. Since the backup power source 23 is used for backup, even if the main power source 22 is shut off or other troubles occur, the offset value and amplitude ratio stored in the storage device 21 are used to correct the center deviation of the Lissajous circle. And distortion correction can be performed.
[0027]
Furthermore, in the pass / fail determination unit 27, the latest offset value and amplitude ratio stored in the storage device 21, the initial offset value and initial amplitude ratio stored in the initial offset storage unit 25 and the initial amplitude ratio storage unit 26, and When the offset value and the amplitude ratio stored in the storage device 21 are significantly different from the initial offset value and the initial amplitude ratio, a signal indicating an abnormal value is output. At the same time as outputting a signal indicating an abnormal value, the previous offset value and amplitude ratio are read from the latest one of the plurality of offset values and amplitude ratios stored in the storage device 21, and this is read out. Is used as an offset correction value in the offset subtraction unit 17 and is used as an amplitude correction value in the amplitude integration unit 18. Thus, if the offset value and the amplitude ratio are changed to be determined as an abnormal value, the offset correction and the amplitude ratio correction are automatically performed using the previous offset value and the amplitude ratio without any inconvenience. The encoder can be operated and the reliability of the encoder can be improved.
[0028]
Furthermore, according to the illustrated embodiment, since the initial offset storage unit 25 and the initial amplitude ratio storage unit 26 are provided, the stored value of the storage device 21 is erased or cannot be used due to some trouble. However, it can be operated using the initial offset value and the initial amplitude ratio stored in the initial offset storage unit 25 and the initial amplitude ratio storage unit 26 before factory shipment.
In addition, when it is determined that all offset values or amplitude ratios stored in the storage device 21 are abnormal values, the initial offset values stored in the initial offset storage unit 25 and the initial amplitude ratio storage unit 26 are It is good to operate using the amplitude ratio.
[0029]
The detected body may be a rotating body as shown in the illustrated example, or may be one that moves linearly.
As a sensor for detecting the position or rotational position of the detected object, a magnetic head, Hall element or other magnetic sensor may be used instead of the magnetoresistive element as shown in the figure, or a light emitting element and a light receiving element are used. An optical sensor may be used. In the case of using an optical sensor, a light reflection part and a transmission part or a light reflection part and an absorption part formed at regular intervals are used as the detection target.
Although not shown in FIG. 1, the rotational direction or the moving direction of the detected object is detected from the anteroposterior relationship of the A-phase signal and the B-phase signal, and the interpolation angle θ is added or subtracted depending on this direction. Good.
[0030]
In the illustrated example, the angle data storage drum 11 as a data recording body that rotates integrally with the detection target body records waveform information for one channel, and a pair of two sensors facing the waveform information for one channel. The magnetoresistive elements 12 and 13 are arranged and position detection is performed by signals for one channel. However, if waveform information is recorded for a plurality of channels and a sensor is arranged corresponding to each channel. A higher resolution encoder can be obtained.
[0031]
In the embodiment shown in FIG. 1, the distances r with respect to the prescribed values ^ a10 and ^ b10 of ^ a1 and ^ b1 calculated by the offset estimation unit 20 are:
r = sqrt {(^ a1- ^ a10) ^ 2 (^ b1- ^ b10) ^ 2}
When the calculated value exceeds the specified value: r ₀ , it may be detected as an abnormal value.
[0032]
【The invention's effect】
According to claim 1, 2 SL placing of the invention, by subjecting it to estimate the constant offset value in the offset correction, when the abnormal offset value is detected may determine this as outliers.
[0033]
According to the invention described in claim 3, the storage means for storing the estimated offset value and the amplitude value, the initial offset storage unit for storing the estimated offset value before factory shipment, and the estimated amplitude value before factory shipment are stored. Abnormal when the latest offset value or amplitude value stored in the initial gain storage unit and the storage means differs greatly from the initial offset value or initial amplitude value stored in the initial offset storage unit or initial gain storage unit Since it has a pass / fail judgment unit that outputs a value signal, it is possible to constantly monitor whether the latest offset value or amplitude value is an abnormal value.
[0034]
According to the fourth aspect of the present invention, when an abnormal value signal is output, the previous estimated offset value or estimated amplitude value from which no abnormal value is detected is read from the storage means and used for offset correction or amplitude correction. As a result, the encoder can be operated with a practically inconvenient accuracy and the reliability of the encoder can be improved.
[0035]
According to the fifth aspect of the present invention, even if the estimated offset value or the estimated amplitude value stored in the storage means disappears, the initial offset value or the initial amplitude stored in the initial offset storage unit or the initial gain storage unit. Since the value can be used for offset correction or amplitude correction, the encoder can be operated with an accuracy that is not practically inconvenient and the reliability of the encoder can be improved.
[0036]
According to the sixth aspect of the invention, even if the estimated offset value or the estimated amplitude value stored in the storage means is all abnormal values, the initial offset stored in the initial offset storage unit and the initial gain storage unit Since the value or the initial amplitude value can be used for the offset correction or the amplitude correction, the encoder can be operated with an accuracy that is not practically inconvenient and the reliability of the encoder can be improved.
[Brief description of the drawings]
FIG. 1 is a block diagram showing an embodiment of an encoder according to the present invention.
2A and 2B are explanatory diagrams of an electrical interpolation angle θ, where FIG. 2A is a graph showing a relationship between an A-phase signal and a B-phase signal and the electrical interpolation angle θ, and FIG. 2B is a calculation unit for the electrical interpolation angle θ; FIG.
FIG. 3 is a graph showing a Lissajous circle drawn with an A phase signal and a B phase signal and an offset state;
FIG. 4 is a block diagram illustrating an example of a conventional encoder.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 11 Angular data storage drum as a signal recording body 12 Magnetoresistance element 13 as a sensor 13 Magnetoresistance element 17 as a sensor Offset subtraction unit 18 as an offset correction unit Amplitude ratio integration unit 19 as an amplitude ratio correction unit 19 Electric division unit 20 Offset Estimator 21 Storage means 22 Main power supply 23 Backup power supply 25 Initial offset storage section 26 Initial amplitude ratio storage section 27 Pass / fail judgment section

Claims (6)

A signal recording body in which signals are recorded at regular intervals, a pair of sensors that detect signals recorded on the signal recording body as the signal recording body moves, an offset of signals obtained from the pair of sensors, and An encoder having an offset correction unit and an amplitude ratio correction unit that correct an amplitude ratio, and an electric division unit that calculates an interpolation angle from a signal that has been subjected to offset correction and amplitude ratio correction,
An estimation unit that estimates an offset value and an amplitude value, and supplies the offset value and the amplitude ratio to the offset correction and the amplitude ratio correction ;
Storage means for storing the estimated offset value and amplitude value,
The encoder according to claim 1, wherein the storage means stores a plurality of offset values and amplitude values estimated by the estimation unit in time series . Storage means, nonvolatile memory or encoder according to claim 1, wherein the volatile Ru memory Tona backed up by backup power source. In addition to the storage means, an initial offset storage section that stores an estimated offset value before factory shipment, an initial gain storage section that stores an estimated amplitude value before factory shipment, and the latest offset value or amplitude stored in the storage means value initial offset storage unit, an encoder according to claim 1, further comprising an adequacy determining unit outputs an abnormal value signal if the initial offset value or initial amplitude value greatly different from that stored in the initial gain storage unit. If an abnormal value signal is output from the storage means, reads out the estimated offset value or an estimated amplitude value of the previous outliers is not detected, according to claim 3, wherein the Ru with this offset correction or the amplitude correction encoder. When the estimated offset value or an estimated amplitude value stored in the storage unit is lost, Ru using the initial offset storage unit, an initial offset value or initial amplitude value stored in the initial gain storage unit to the offset correction or the amplitude correction The encoder according to claim 3 . When the estimated offset value or the estimated amplitude value stored in the storage unit is all abnormal values, the initial offset value or the initial amplitude value stored in the initial offset storage unit or the initial gain storage unit is offset or amplitude corrected. the encoder according to claim 3, wherein the Ru used.

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