JPH03175319A - Correcting method for error of linear encoder - Google Patents

Abstract

PURPOSE:To improve the detecting accuracy of position by measuring the pattern of an error of a measuring signal of a linear scale within the defined section, and obtaining and storing the pattern of an average error within the section from the pattern of the error. CONSTITUTION:A linear interferometer 7 is fixed at a predetermined position. An interference signal is outputted from an optical reflecting mirror 6 mounted to a measuring head 3, so that the distance S between the meter 7 and reflecting mirror 6 is measured by a laser head 8. This measuring signal is supplied to an interface 10 of a data collecting computer 11 via a laser controller 9 and stored in the computer 11. The data of the positional error is divided in sections corresponding to every width of slits 2, and the pattern of an average error in each section is obtained. When the counting value of a counter 5 indicates the position of each section, the pattern of the average interpolation error in the section is read out from the computer 11. If the pattern of the average interpolation error is removed from the measuring signal of a measuring amplifier 4, it is possible to obtain a signal having the interpolation error corrected.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a technique that can improve the accuracy of position detection of a linear encoder used, for example, in an X-Y table of semiconductor manufacturing equipment.

(Prior Art) A linear encoder is an i+q constant means that can output position data as an electric signal, and is widely used for various position detection applications.

FIG. 5 shows a configuration diagram of a general optical linear encoder.

In the figure, when the measuring head 3 scans the scale 1 in which the slit 2 is carved, the measuring head 3 scans the scale 1 in which the slit 2 is carved.
Two sine wave signals 40, 41 having a phase shift of 90' relative to each other as shown in a) are generated.

In order to obtain the required resolution, this signal 40.degree. 41 is divided by the measurement amplifier 4 and shaped into rectangular wave pulses 42 and 43 as shown in FIG. 6(b).

In the above optical linear encoder, the measurement amplifier 4
The relative position of the measurement head 3 with respect to the scale l can be detected by counting the rectangular wave pulses, which are the output signals of the scale l, using a counter.

(Problems to be Solved by the Invention) However, for example, linear encoders used in XY child tables of semiconductor manufacturing equipment are required to detect positions with extremely high precision.

In such applications, if the slits 2 carved on the scale l of the linear encoder are created at a deviation from the predetermined interval,
This is an error that directly affects the output of the measurement amplifier 4.

Furthermore, although the method described above by dividing the waveform within the measurement amplifier 4 to increase the resolution can be easily realized using electronic circuits, it is impossible to divide the waveform strictly evenly, and in this case, there is a certain tendency. An interpolation error occurs when an error pattern with .

That is, as shown in FIG. 6(b), the pulse width of the actual rectangular wave pulse from the measurement amplifier 4 is not constant, but deviates from the ideal division, and patterns that tend to have this deviation are completed and repeated.

As a result, in the linear scale of the linear encoder with the configuration shown in Figure 5, the above two errors, the shift error and the interpolation error, occur simultaneously, so even if the resolution is high, the error will be several times to several tens of times higher. There was a problem in that only positional accuracy was guaranteed.

SUMMARY OF THE INVENTION In view of the problems of the prior art described above, an object of the present invention is to provide a linear encoder error correction method that can improve the position detection accuracy of a linear encoder to the original resolution of a linear scale with a relatively simple configuration. .

(Means for Achieving the Object) A linear encoder error correction method according to claim 1 of the present invention divides the entire linear scale of a linear encoder into a plurality of regions, and divides the entire linear scale of the linear encoder into a plurality of regions. Measure the error pattern of the measurement signal of the linear scale in each area, calculate the average error pattern in the block from these measured error patterns, store the average error pattern as the error pattern in the block, and store the average error pattern in the block. The method is characterized in that the error within the block is corrected using the average error pattern.

Furthermore, a linear encoder error correction method according to a second aspect of the present invention is characterized in that the error is an interpolation error of a measurement amplifier of the linear encoder.

Further, in the linear encoder error correction method according to claim 3 of the present invention, the entire linear scale of the linear encoder is divided into a plurality of regions, and the position error of the linear scale measurement signal in each region with respect to the origin on the linear scale is provided. , calculate the average value of the shift error of the entire region from these measured position errors, store the average shift error value as the shift error within the region, and use the stored average shift error value to calculate the shift error of the entire region. It is characterized by correcting shift errors within the region.

(Function) According to claims 1 and 2, the divided areas of the linear scale of the linear encoder are collectively addressed to a plurality of areas in which the error pattern (interpolation error pattern) forms the shape of -. The error pattern of the linear scale measurement signal in each area is measured, and the average error pattern in each block is determined and stored from these error patterns, and the error (interpolation error) in the block is calculated. Used for correction.

According to claim 3, the position error of the measurement signal of the linear scale is measured in each divided area of the linear scale of the linear encoder, and the average value of the shift error of the entire area is determined from these position errors. is stored and used to correct shift errors within the region.

According to claim 4, both the interpolation error correction of claim 1.2 and the shift error correction of claim 3 are performed simultaneously.

(Example) Hereinafter, an error correction method for a linear encoder according to the present invention will be described in detail with reference to the drawings.

FIG. 1 is a schematic block diagram of a linear encoder to which the error correction method of the present invention is applied.

In FIG. 1, 1 is, for example, a linear scale attached to a fixed body. The scale 1 is provided with a slit 2 that utilizes optical effects such as transmission. The measurement head 3 is provided with photoelectric conversion means for detecting light from a light emitting means (not shown), and is provided so as to be movable along the linear scale 1 and facing the slit 2 . Note that the light emitting means is provided on the opposite side of the measurement head 3 with the slit 2 in between. The measuring amplifier 4 is connected to the output side of the measuring head 3, and receives the measuring signals from the measuring head 3 at 90° to each other.
``Two out-of-phase sine wave signals (Figure 6(a)),
In order to improve the resolution, the signal is divided and shaped into a rectangular wave (FIG. 6(b)).

The output side of the measurement amplifier 4 is a data collection computer 11.
The counter 5 is connected to the measuring amplifier 4.
Count the square wave pulses from.

On the other hand, an optical reflector, 6
, a linear interferometer 7, a laser head 8, and a laser controller 9. The linear interferometer 7 is fixed at a predetermined position and outputs an optical interference signal from the optical reflector 6 attached to the measurement head 3. Based on this output, a laser head 8 with a built-in receiver
and the optical reflector 6, and the measurement signal is supplied via the laser controller 9 to the interface 10 of the data acquisition computer 11 and stored therein.

Next, a method for correcting errors in the linear encoder configured as described above will be explained.

When the measurement head 3 scans the fixed linear scale 1, the measurement signal is divided and waveform-shaped by the measurement amplifier 4, and the rectangular wave pulse from the measurement amplifier 4 is sent to the counter 5.
counts, and the count value is read into the data collection computer 11.

On the other hand, the laser length measuring devices 6 to 9 measure the distance S, and the distance S is read as a signal P from the laser controller 9 into the computer 11 through the interface IQ.

In such a configuration, when the measurement head 3 is moved and the count value of the counter 5 indicates a position to be corrected on the linear scale, the computer 11 outputs the count value and the read position output signal of the laser length measuring device. By comparing P with P, the position error (interpolation error plus shift error) at the count position is measured. If this measurement is performed over the entire linear scale l, then the scale l
can be completely corrected. However, if left as is, the amount of correction data would be enormous, so in the method according to the present invention, the position error data is compressed as described below to reduce the amount of correction data.

FIG. 2 is a diagram showing the position error measured as described above.

In the figure, the horizontal axis indicates the position of the linear scale, and the vertical axis indicates the position error (interpolation error + shift error).

Further, FIG. 3 shows the interpolation error, and FIG. 4 shows the shift error.

As shown in FIG. 3, a pattern of interpolation errors with a certain tendency is repeated at a period a corresponding to the slit width of the linear scale. On the other hand, as shown in FIG. 4, when a predetermined position on the linear scale is set as the origin, the shift error can be determined as the amount of deviation from the origin. 2nd L
Figure (a) shows the above two errors (interpolation error g, shift error e) superimposed.

According to the present invention, as shown in FIG. 2(a), position error data is divided into regions corresponding to the slit width unit a, and each of the thus divided regions is collected in a predetermined number. Divide into multiple blocks.

Since each adjacent region has substantially the same error pattern, even if a predetermined number of a plurality of patterns are grouped together, the accuracy of the data is hardly affected. The size of this block corresponds to the compression degree of the data, and the larger the number of areas in one block, the higher the data compression rate.

This compression ratio may be determined based on the required accuracy, cost, etc.

Next, the average error pattern of the error patterns gl-gn within each block set in this manner is determined.

For example, the waveform C in FIG. 2(b) shows the average error pattern of the error patterns in block l.

Next, since the average error pattern C also includes the average value of the shift error, in order to remove the shift error, this shift error is subtracted to obtain the average error pattern d1.

That is, in this embodiment, as will be described later, the shift error e
In order to calculate the average value for each area without averaging for each block, the average error pattern d (interpolation error correction amount) and shift error correction amount are separated. The average error pattern d1 obtained in this manner is stored in a storage means such as a RAM as an average interpolation error pattern representative of the interpolation error of block l. The blocks 2 and subsequent blocks shown in FIG. 2(a) are processed in the same way, and the average interpolation error pattern d2. d3.・
...and compress all data across scale.

Next, in order to correct the interpolation error, when the count value of the counter 5 indicates the position of each block, the average interpolation error pattern of the block is read out from the storage means, and the average interpolation error pattern of the block is read out from the measurement signal from the measurement amplifier 4. Its average interpolation error pattern d
By calculating and removing , it is possible to obtain a signal with the interpolation error corrected.

Next, a shift error correction method according to the present invention will be explained.

As shown in FIG. 2, for the shift error e, the average value of the shift error with respect to a predetermined scale origin b (FIG. 4) is determined for each area a. This average value is calculated for each area on the scale, and the shift error average value el-
Find en. The shift error average value obtained in this manner is stored in the storage means.

Next, in order to correct the shift error, when the count value of the counter 5 indicates the position of each area a, the average shift error value of the area is read out from the storage means and calculated from the measurement signal from the measurement amplifier 4. By removing this, a signal with the shift error corrected can be obtained.

In the present invention, the above-described interpolation error correction and shift error correction may be performed in combination, and in this case, the average interpolation error pattern d and the shift error average value are determined from the measurement signal from the measurement amplifier 4. By removing both of e, it is possible to obtain a signal in which interpolation errors and shift errors are corrected at the same time.

The measurement using the laser length measuring device to detect the above-mentioned error only needs to be performed once when the linear scale is installed to create correction data, and from then on, it is stored in the computer 11 when the linear encoder is used. The error is corrected using the corrected data and the measurement signal of the linear encoder.

In the above embodiment, the average value of the shift error was calculated for each area a, but if necessary, it may be calculated for each block.
In this case, it is not necessary to separate the shift error correction data and the interpolation error correction data as described above, and the average interpolation error pattern d shown in FIG. 2(c) is not needed as the interpolation error correction data. It is only necessary to find the average error pattern C in (b).

According to the above-described embodiment, the computer required a memory capacity of 1.6 Mbytes for the correction data in the past, but according to the apparatus of the present invention, this can be reduced to about 32 Kbytes. Furthermore, when the slit width of scale l is 10 μm, the conventional method requires ±1.0 μm.
Although it was only possible to achieve an accuracy of approximately ±0.1 μm, the present invention has made it possible to achieve an accuracy of approximately ±0.1 μm.

The present invention is not limited to the embodiments described above, and various embodiments are possible.

For example, the slit of the measurement head of the linear scale is not limited to an optical detection method, and electrical, magnetic, etc. methods can be adopted.

In addition, although we have described an example in which a laser length measuring device is used as a reference length measuring device for error detection, the configuration of the 4° laser length measuring device is not limited to the configuration shown in Figure 1, and is essentially a linear scale. Any configuration that can correct the distance error may be used.

Further, the linear scale to which the error correction method of the present invention is applied can be used in a wide range of applications such as position measurement in measuring instruments and feedback control in digital servos.

(Effects of the Invention) As explained above, according to the linear encoder error correction method of the present invention, by efficiently compressing correction data, a computer can perform correction with a small storage capacity and simple correction calculations. Moreover, it is possible to improve the position detection accuracy of the linear encoder to the original resolution of the scale.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing a configuration example of a linear encoder to which the error correction method of the present invention is applied, FIG. 2 is a diagram for explaining the error correction method of a linear encoder according to the present invention, and FIG. Figure 4 is a diagram showing signals of interpolation error and slit increment error (shift error), Figure 5 is a configuration diagram of a conventional optical linear encoder, and Figures 6 (a) and (b).
) are diagrams showing output waveforms from the measurement head and measurement amplifier of the linear encoder, respectively. scale, 2...slit, 3...measuring head,
4...Measurement amplifier, 5...Counter, 6...Optical reflector, 7...Linear interferometer, 8...
・Laser head, 9... Laser controller, 10...
- Interface, 11... Computer for data collection.

Claims (1)

[Claims] 1. Divide the entire linear scale of the linear encoder into a plurality of regions, measure the error pattern of the measurement signal of the linear scale in each region within a block consisting of a predetermined number of regions, and Determine an average error pattern within the block from the error pattern measured by , and store the average error pattern as an error pattern within the block;
A method for correcting errors in a linear encoder, comprising correcting errors within the block using the stored average error pattern. 2. The linear encoder error correction method according to claim 1, wherein the error is an interpolation error of a measurement amplifier of the linear encoder. 3. Divide the entire linear scale of the linear encoder into multiple regions, measure the position error of the measurement signal of the linear scale in each region with respect to the origin on the linear scale, and calculate the entire region from these measured position errors. A linear encoder that calculates an average value of shift errors, stores the average shift error value as a shift error within the area, and corrects the shift error within the area using the stored average shift error value. error correction method. 4. Divide the entire linear scale of the linear encoder into multiple regions, measure the interpolation error pattern of the linear scale measurement signal in each region within a block consisting of a predetermined number of regions, and calculate the interpolation error pattern of the linear scale measurement signal in each region. Find the average interpolation error pattern within the block from the interpolation error pattern,
While storing the average interpolation error pattern as an interpolation error pattern within the block, the position error of the measurement signal of the linear scale in each region with respect to the origin on the linear scale is measured, and from these measured position errors, The average value of the shift error of the entire area is calculated, the average value of the shift error is stored as the shift error within the area, and the average interpolation error pattern and the average value of the shift error are used to calculate the average value of each block and the area. A linear encoder error correction method characterized by correcting errors in each region.