JP2001033206A - Position detecting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a highly accurate position detecting device having a reduced position detection error periodically caused by a change in offset value with the passage of time, including in output signals of a position sensor outputting a plurality of signals having different phases and periodically changing corresponding to measurement displacement. SOLUTION: Signals DS and DC, which are digitized from output signals AS and AC through AD converters 4 and 5, are made to pass through digital low pass filters 12 and 13, thereby converting into signals SDC and CDC. A velocity transducer 14 differentiates a position signal POS to convert it to a velocity signal VEL. An offset setting means 15 sets the signals SDC and CDC as offset signals SOF and COF in a offset memory units 16 and 17 according to the value of the velocity signal VEL. Subtracters 9 and 10 eliminate the values SOF and COF, which have been set in the offset memory units, from the signals DS and DC to output signals S and C. An interpolation means carries out an arc tangent operation of the two inputs, the signals S and C, so as to convert them into the position signal POS.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention automatically detects a temporal change of an offset value included in a signal from a position sensor which outputs a plurality of signals having phases different from each other and which periodically changes in accordance with a measured displacement. The present invention relates to a highly accurate position detection device that can be removed.

[0002]

2. Description of the Related Art FIG. 4 is a block diagram showing an example of a conventional position detecting device. In FIG. 1, a position sensor 1 is a one-phase excitation, two-phase output type resolver having a shaft multiple angle of 100 ×. As a result, the signals AS and AC amplified are output. In the example of FIG. 4, the frequency of the excitation signal is 50 KHz, and the position sensor 1
Let θ be the rotation angle of the input shaft and G be the amplitude of the output signal.
The signals AS and AC can be expressed by the following equations (1) and (2).

AS = G · SIN (100θ) SIN (2 · π
・ 50,000 ・ t)

## EQU2 ## AC = G · COS (100θ) SIN (2.π
.50000.t) These signals AS and AC are supplied to the timing controller 8
Are sampled and digitized by the AD converters 4 and 5 at the timing when SIN (100000πt) = 1 by the pulse signal TIM having a period of 20 μS output in synchronization with the excitation signal from
It is converted to S, DC. Therefore, the signals DS and DC can be expressed by the following equations (3) and (4), respectively, and the position sensor 1 outputs two signals having phases different from each other by 90 degrees, which periodically change in correspondence with the measured displacement θ. Can be considered.

## EQU3 ## DS = G · SIN (100θ)

## EQU4 ## DC = G · COS (100θ)

Since the digitized signals DS and DC actually include the product variation of the position sensor and the offset voltage due to the signal amplifier or the like,
Strictly speaking, the following Expressions 5 and 6 are obtained.

## EQU5 ## DS = G · SIN (100θ) + SOF

DC = G · COS (100θ) + COF The offset value SO included in these signals DS and DC
F and COF are measured in advance when the position detecting device is manufactured,
These are set in the memories 6 and 7, respectively. Subtractor 9,1
At 0, the offset values SOF and COF stored in the storages 6 and 7 are removed from the signals DS and DC, respectively.
C. The signals S and C from which the offset values have been removed are subjected to an arc tangent operation using two variables as input by the interpolation means 11 to obtain a position signal POS indicating the rotation amount within 1/100 rotation of the input shaft of the position sensor 1. Is converted. Thereafter, although not shown in the drawing because there is no necessity in the description of the present invention, in an actual position detecting device, at least one of the input shafts of the position detecting sensor 1 is obtained by an incremental process or the like based on a change in the position signal POS. Position data equal to or greater than the rotation is required.

[0004]

In general, when moving a movable portion of a machine tool, not only position control is performed based on position information detected by a position detecting device, but also based on speed information obtained from a difference between position information. The speed feedback control of the electric motor is performed. In particular, recently, there is a tendency to increase the loop gain of the speed feedback in order to improve the response performance of the machine. In the above-described conventional position detection device, the offset value included in the output signal of the position detection sensor immediately after the manufacture can be removed, but the position detection error caused by the change in the offset value caused by the aging after the manufacture cannot be removed. . That is, even after the manufacture, the offset value is slightly changed due to a change in the ambient temperature or a change in a member constituting the position sensor, but the offset value cannot be removed due to such a change with time. Usually, the influence of the change over time of the offset value on the processing accuracy of a machine tool or the like is so small that it can be almost ignored. However, the position detection error caused by the change over time of the offset value is the same cycle as the change of the output signal of the position detection sensor (FIG. 4).
In this example, the error has 100 cycles per rotation). Therefore, depending on the moving speed of the movable part, the frequency of the speed ripple generated by the error matches the mechanical resonance frequency, and abnormal noise is generated from the resonance part. There was a problem. In particular, since the abnormal noise increases in proportion to the magnitude of the loop gain of the speed feedback, the abnormal noise cannot increase the loop gain and is one of the causes of lowering the mechanical performance. This problem is not limited to the resolver described in the conventional example, but also in optical encoders and magnetic encoders, as long as the position is obtained by interpolation from a plurality of signals having different phases that periodically change according to the measured displacement, There was a similar problem.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a position for outputting a plurality of signals each having a different phase that changes periodically in accordance with a measured displacement. An object of the present invention is to provide a high-accuracy position detection device in which a periodic position detection error caused by a temporal change of an offset value included in an output signal of a sensor is reduced, and to improve responsiveness of a movable portion of a machine tool or the like. .

[0006]

SUMMARY OF THE INVENTION The present invention relates to a position detecting device for converting a signal from a position sensor which outputs a plurality of signals having phases different from each other, which periodically change in accordance with a measured displacement, into position information. The object of the present invention is to provide an offset storage device that stores an offset value of the plurality of signals, an offset removal unit that removes the offset value that the offset storage device stores from an output signal of the position sensor, Interpolation means for converting the plurality of sensor output signals after removing the offset value into position signals, speed conversion means for converting the position signals into speed signals, and a low-pass filter having the output signals of the position sensors as inputs And offset setting means for setting an output value of the low-pass filter in the offset storage according to a value of the speed signal. It is achieved by.

In the position detecting device of the present invention, the offset value included in the output signal of the position sensor is detected at the speed at which the low-pass filter works effectively, and the detected offset value is set in the offset storage, and the output of the position sensor is output. It is possible to automatically remove the offset included in the signal.

[0008]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of a position detecting device according to the present invention in correspondence with FIG. 4, and components having the same functions as those in FIG. FIG. 2 is a block diagram showing an example of the internal structure of the offset setting means 15 of FIG.

In the position detecting device shown in FIG. 1, digital signals DS and DC are output from the position detecting sensor 1.
Are input to tertiary digital low-pass filters 12 and 13 each having a cutoff frequency of 10 Hz. The speed converter 14 performs a difference process on the position signal POS obtained by the interpolation means 11 and converts the position signal POS into an absolute value speed signal VEL. The speed signal VEL output from the speed converter 14 is set in the offset setting means 15 so that the change frequency of the signals DS and DC preset in the storage unit 19 is the same as the cutoff frequency of the digital low-pass filter. 6min-1 (60 * 10
/ 100) and a speed VLO = 60 min-1;
The speed 15000 m when the frequency of the signals DS and DC preset in the memory 18 becomes 1/2 of the sampling frequency 50 kHz of the digital low-pass filters 12 and 13.
The speed VHI = 10000 min-1 smaller than in-1 (60 * 50000/2/100) is compared with the comparator 21 and the comparator 20 respectively, and further, the OR circuit 22
By taking the sum of the outputs of the comparators 21 and 20, the speed signal VEL becomes equal to the speed VLO (60 min-
1) Below or above speed VHI (10000 min-
1) At the time of the above, a signal CL for stopping the setting operation is output. The timer 23 is cleared by the input of the signal CL, outputs the setting signal SET until the signal CL is input after counting the pulse signal TIM after clearing 50,000 times. That is, when there is no input of the setting operation stop signal CL, the setting signal SET is output from the timer 23. When there is an input of the signal CL, the output of the setting signal SET from the timer 23 is stopped, and the signal CL is output. The output of the setting signal SET is restarted after a certain period of time has elapsed after the input has disappeared. Memory devices 16 and 17
In FIG. 4, the offset values of the signals DS and DC measured in advance when the position detecting device is manufactured are set as the initial data as in FIG.
When ET is input, digital low-pass filter 1
Output values 2 and 13 of SDC and CDC are set respectively. The set values are output to the subtracters 9 and 10 as offset signals SOF and COF, and are removed from the signals DS and DC as offset values.

By the above operation, when the input shaft of the position detecting sensor 1 is 60 min-1 or more, the signals DS and DC are output.
Is changed to 100 Hz or more, and the change due to the signals DS and DC after passing through the third-order digital low-pass filters 12 and 13 having the cutoff frequency of 10 Hz is attenuated to about 1/1000. Therefore, the signals SDC and CDC after passing through the digital low-pass filter become the signal D
The DC components of S and DC, that is, the offset values are almost equal to each other. Conversely, when the input shaft is rotating at a low speed, the change frequency of the signals DS and DC changes at a frequency close to or lower than the cutoff frequency of the digital low-pass filters 12 and 13, so that the signals SDC and DC The signal change of the signals DS and DC is output to the CDC without being attenuated much. In such a case, since the offset setting means 15 stops the setting operation to the storage units 16 and 17, it is possible to prevent values other than the offset of the signals DS and DC from being set to the storage units 16 and 17. I have. Further, the input shaft rotates at a high speed, and the signals DS and DC become 1/1 of the sampling frequency of the digital low-pass filters 12 and 13.
When the frequency is changed at two or more frequencies, the output signals SDC and CDC of the digital low-pass filters 12 and 13 are output with a determinate value by the sampling theorem. Even in such a case, since the offset setting means 15 stops the setting operation to the storage units 16 and 17, values other than the offset of the signals DS and DC are stored in the storage unit 1.
It is prevented from being set to 6, 17. Further, the low-pass filters 12 and 13 cancel the speed condition for stopping the setting operation determined by the storage units 18 and 19, the comparators 20 and 21 and the OR circuit 22 by the relatively large acceleration / deceleration of the input shaft. Immediately after that, the past rambling value is still the signal SD
C and CDC may remain without being attenuated. Even in such a case, the offset setting means 15 uses the timer 2
By the operation of 3, the setting operation to the storage units 16 and 17 is stopped for a certain period of time, so that values other than the offset of the signals DS and DC are prevented from being set to the storage units 16 and 17. When the maximum rotation speed of the input shaft of the position detection sensor 1 is sufficiently low, or when the low-pass filters 12 and 13 are realized by analog circuits, the setting operation stop condition at the time of high-speed rotation is unnecessary. When the input shaft of the position detection sensor 1 has only a gradual operation of acceleration / deceleration, the offset storages 16 and 17 for a fixed time by the timer 23 and the like.
There is no need for a function to halt the setting operation for.

FIG. 3 is a block diagram showing another example of the internal structure of the offset setting means 15 of the position detecting device of FIG. 1 corresponding to FIG. In the figure, those having the same functions as those in FIG. 2 are denoted by the same reference numerals, and the description thereof is omitted.

In FIG. 3, the acceleration converter 24 performs difference processing on the speed signal VEL from the speed converter 14 and further converts it into an absolute value acceleration signal AC. Acceleration signal AC
A constant AH is set in advance by a value AHI previously set in a storage 25, a comparator 26 and an OR circuit 27, together with the speed condition of the offset setting means in FIG.
The setting operation to the storage units 16 and 17 is also stopped when the value exceeds I.

The low-pass filter may output a value other than the offset of the signals DS and DC at the time of rapid repetition of acceleration and deceleration of the input shaft. In such a case, the offset setting means of FIG. 3 also stops the setting operation to the storage units 16 and 17, so that values other than the offset of the signals DS and DC are set to the storage units 16 and 17. Is prevented.

[0014]

As described above, according to the position detecting device of the present invention, the periodic position detecting error caused by the temporal change of the offset value of the position detecting sensor output signal, which has been a problem in the past, is automatically corrected. And it can reduce reliably. In particular, under the condition of moving at a constant speed at which mechanical resonance becomes a problem, the change with time of the offset value can be effectively removed, so that the responsiveness of a movable portion such as a machine tool can be improved.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating an embodiment of a position detection device according to the present invention.

FIG. 2 is a block diagram showing details of an offset setting unit 15 of FIG. 1;

FIG. 3 is a block diagram showing another detailed example of the offset setting means 15 of FIG.

FIG. 4 is a block diagram showing a conventional position detecting device for detecting positions.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Position detection sensor 2, 3 Amplifier 4, 5 A / D converter 6, 7, 16, 17, 18, 19, 25 Memory 8 Timing controller 9, 10 Subtractor 11 Interpolation means 12, 13, Digital low-pass filter 14 Speed converter 15 offset setting means 20, 21, 26 comparator 22, 27 logical sum circuit 23 timer 24 acceleration converter

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G05D 3/12 306 G05D 3/12 306S

Claims (5)

[Claims] 1. A position detecting device for converting a signal from a position sensor, which outputs a plurality of signals each having a different phase that varies periodically in response to a measured displacement, into position information,
An offset storage device that stores offset values of the plurality of signals; an offset removal unit that removes an offset value stored by the offset storage device from an output signal of the position sensor; and a plurality of sensor output signals after the offset value removal. Interpolation means for converting the position signal into a speed signal, speed conversion means for converting the position signal into a speed signal, a low-pass filter that receives the output signal of the position sensor as an input, and the speed signal according to a value of the speed signal. An offset setting means for setting an output value of a low-pass filter in the offset storage device. 2. When the speed at which the frequency of the output signal of the position sensor is higher than the cut-off frequency of the low-pass filter is VLO, the offset setting means determines the speed of the speed signal from the speed conversion means. 2. The position detecting device according to claim 1, wherein when the value is equal to or less than the VLO, the setting operation to the offset storage is stopped. 3. The digital filter according to claim 1, wherein the low-pass filter performs a filter process in a fixed cycle.
The frequency of the sensor output signal is の of the cycle
When the speed at which the frequency becomes lower than VHI is VHI, the offset setting means stops the setting operation to the offset storage when the value of the speed signal from the speed conversion means is equal to or higher than the VHI. The position detecting device according to claim 1. 4. The offset setting means includes acceleration conversion means for converting a value of a speed signal from the speed conversion means into an absolute value of acceleration, and when the absolute value of the acceleration exceeds a certain acceleration. 2. The position detecting device according to claim 1, wherein the setting operation to the offset storage is stopped. 5. The offset setting means stops the setting operation to the offset storage for a fixed time immediately after the speed condition for stopping the setting operation is canceled. Or the position detection device according to 4.