JPH0235308A - Position detecting method - Google Patents

Abstract

PURPOSE:To detect an absolute position characterized by high resolution and high accuracy by using a pair of detected signals having the 90-degree phase difference for each of binary coded patterns in a plurality of degrees, and sequentially limiting detected regions with said detected signals. CONSTITUTION:Higher third-order gray binary coded patterns (a)-(c) and lower third-order binary coded patterns (d)-(f) are formed on a code plate 4. Binary coded patterns a'-c' and d'-f' whose phases are different by 90 degrees with respect to the phases of above described patterns are formed, respectively. For example, when the position of a point P is to be detected, a pair of the detected signals having the 90-degree phase difference is obtained based on the highest patterns (a) and (a'). A detected region A' is limited under the state which includes an error E based on the detected signals. The detected regions are sequentially limited as B, B', C, C'... based on the detected signals obtained by (b) and b, (c) and (c')... by the same way. Finally, it is judged that the detected region is present in a region F'.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a position detection method for detecting an absolute position.

2. Description of the Related Art A conventional absolute encoder for detecting absolute position includes a light source, a code plate on which a binary code pattern is formed on a plurality of tracks along the movement direction, and a plurality of photodetectors arranged in correspondence with the tracks. A typical device is equipped with a photodetector and detects the output signal of the photodetector to determine the position of the corner plate. In addition, the binary code pattern includes a pure binary code pattern from which binary position data can be obtained, and a binary code pattern for each order.
There is a gray binary code pattern in which the boundary positions of the binary code patterns of each degree are different from each other so that the position data is not significantly disturbed due to minute formation errors between the binary code patterns.

In addition, in order to perform high-resolution position detection, the position detection method using the binary code pattern described above and the incremental method of position detection are combined, and the rough absolute position is detected with a fixed detection width using the binary code pattern. An absolute encoder is also known in which the detailed position within the detection width is detected by an incremental method from a reference position set within the detection width.

Problems to be Solved by the Invention By the way, position detection methods that use binary code patterns can detect absolute positions digitally, so they are less susceptible to vibration and noise, and can perform highly accurate position detection. In order to perform high-resolution position detection, it is necessary to form the binary code patterns of each order with extremely high precision, and also to form the relative positions between the binary code patterns of each order with extremely high precision. need to be positioned. In the case of the pure binary code pattern described above, the relative positions of the binary code patterns of each order must match completely, and the gray 2
Even in the case of hexagonal code patterns, the binary code patterns of all orders must match with an accuracy of 1/4 of the bit of the binary code pattern of the lowest order. Therefore, it is necessary to have extremely high precision in forming patterns and patterns.
High-resolution position detection of 15 to 220 degrees requires enormous cost, is impossible due to manufacturing technology except in special cases, and signal detection accuracy for all orders cannot be achieved. In order to maintain a high level, signal processing becomes complicated, resulting in problems such as high cost and difficulty in high-speed response.

In addition, in a combination of a position detection method using a binary code pattern and an incremental method, the number of patterns and photodetectors is relatively small, and high-resolution position detection can be performed at low cost. After detecting the approximate position using the binary code pattern, the reference position set within the detection width is detected by searching for the reference signal pattern, and the amount of displacement from the reference position to the position to be detected is detected incrementally. The problem is that the response speed is slow because the operation is complicated.

In view of the above-mentioned conventional problems, the present invention is capable of high-resolution and highly accurate absolute position detection, and position detection that does not cause detection errors even when the relative position accuracy between binary code patterns of each order is relatively low. The purpose is to provide a method.

Means for Solving the Problems In order to achieve the above object, the present invention obtains a pair of detection signals having a phase difference of 90' for each of the binary code patterns of multiple orders, and detects signals from the highest order to the lowest order. The method is characterized in that the detection area is sequentially limited based on a pair of detection signals of each order, including errors, and the range of the absolute position to be detected is specified.

The above pair of detection signals can also be obtained by arranging detectors with a phase shift of 90° from each other for the binary code Bakun of each order. It is also possible to form binary code Bakuns having a phase difference of 90°.

Furthermore, the position detection operation may be carried out by sequentially limiting the area from the highest order to the lowest order, but it is possible to form a table that sets the correspondence between the detection position and the detection signal, and to Position detection can also be performed based on a table.

According to the present invention, for each order of binary code pattern, 9
By using a pair of detection signals with a phase difference of 0°, the detection area can be successively connected to lower orders while limiting the detection area including errors, and the area can be expanded from the highest order to the lowest order. By sequentially limiting the values, the position can be detected with a predetermined resolution without causing a detection error.

Furthermore, in order to obtain a pair of detection signals for each order of binary code patterns, if the detectors are arranged in pairs with a 90° phase shift, the number of patterns can be reduced; By forming binary code patterns with different phases, the space for installing a detector can be reduced, and when the pattern is scanned, it can be detected by a single detector, and errors due to differences in detector characteristics do not occur.

Further, if the detection positions specified by the detection signal group of each order are made into a table and the position is detected based on the detection signals, the position can be detected with high-speed responsiveness.

EXAMPLE Hereinafter, an example of the present invention will be described based on FIGS. 1 to 3.

In FIG. 2, 1 is a semiconductor laser as a light source, 2 is a polygon mirror that scans light, 3 is a lens that makes scanning light approximately parallel, and 4 is a code plate attached to a moving body (not shown) along the direction of movement thereof. , 5 is a fixed mask, 6 is a lens 7 for condensing the scanning light, is a photodetector, and 8 is a photodetector element for generating a synchronizing signal for optical scanning.

A large number of fine slits 11 are regularly formed in the center of the code plate 4 in the width direction so as to be parallel to each other in the moving direction, and the mask 5 has slits 11 that are inclined so as to produce moire fringes between the slits 11 and the slits 11. 12 are formed. In this example, there is one slit between both ends to produce three moiré stripes.
It is formed with an inclination of 3 pitches.

On the code plate 4, six tracks 13 of a binary code pattern are formed on each of the upper and lower sides of the slit 11. The upper six tracks 13 contain upper tertiary gray binary code patterns a to C and 90° to these patterns.
Binary code patterns a° to C'' with different phases are formed, and the lower tertiary gray binary code patterns df and 90' phase binary code patterns are formed in the lower six tracks 13. Different binary code patterns d° to f' are formed. The position detection width of these binary code patterns af and a to f'' corresponds to one pitch of the slit 11. Moreover, between the upper six tracks 13 and the slits 11,
A trigger generation bag 14 is formed.

Next, the operation will be described. First, the light emitted from the semiconductor laser 1 scans the code plate 4 via the polygon mirror 2 and the lens 3 in a direction substantially perpendicular to its moving direction. As a result, the binary code patterns a to c, , a - c )
The trigger generation pattern 14, the slit 11, and the binary code patterns df, d'' to f'' are sequentially scanned, and the transmitted light enters the photodetector 7 via the mask 5 and the condensing lens 6.

Then, for each scan of the scanning light, a synchronizing signal is output from the photodetector element 8, and a detection signal as shown in FIG. 3 is output from the photodetector 7. This detection signal includes code plate 4
The binary code patterns a-c, a' ~ formed on the top of
A binary code obtained by scanning C°, a trigger signal based on the 1-trigger generation pattern 14, a code plate 4 and a mask 5
A moire fringe transmitted light quantity waveform obtained by scanning the moire fringes formed by the slits 11 and 12 and a binary code pattern df, d to f formed at the bottom of the code plate 4. Contains a binary code.

These detection signals are input to a position detection circuit (not shown),
Each signal is discriminated based on the synchronization signal, and position detection is performed. The binary code is subjected to signal processing as described later, and the rough position of the code plate 4 is detected. On the other hand, based on the moiré fringe transmitted light amount waveform, the detection signal determines the time T from when the trigger signal is output until the scanning light reaches a predetermined position approximately at the center of the slit 11. After passing through, the R interval T until it crosses the predetermined threshold pole FL/HEL downward is measured, and then T-T is calculated, and the scanning time T corresponding to the cycle width of the moiré fringe is calculated. By dividing by, the phase difference of the detection signal with respect to the reference position shown by the broken line in FIG. 3 is detected, and by multiplying this by the slit pitch, the minute position with respect to the reference position within each slit pitch is detected.

Next, position detection using a binary code will be explained with reference to FIG. When detecting the position of, for example, P on the code plate 4, the detection signal from the detector 7 is rl from the binary code pattern a toward the binary code pattern f°.
A signal llololoollJ is obtained. Here, since the signal based on the binary code pattern a is "1", the detection position includes the formation error of the binary code pattern a (for example, the allowable error at both end positions is ±1/16 of the total length). This means that it is also located within area A. Next, since the signal based on the binary code Bakun a'' is "1", the detection position is located within the area A' which is further limited within the area A. Similarly, the binary code patterns b, b"・
...By limiting the area where the detected position exists, including the error, using the signals from f and i', it is finally determined that the detected position exists within area F, and this Position detection can be performed using the size of the area F' as the resolution. Position detection using the above algorithm is performed by signal processing in the position detection circuit.

By combining the coarse detection position based on the binary code pattern obtained in this way and the minute detection position based on the moiré fringes, position detection can be performed over a wide range with high resolution.

In the above embodiment, in the position detection circuit, the detection area is sequentially limited by the detection signal based on the binary code pattern "a-f". If the correspondence between the signals and the detected positions obtained by the above algorithm is made into a table in advance and stored in the ROM, and the position can be detected by accessing a predetermined location in the ROM based on the detected signal, the response will be speed increases.

In addition, in the embodiment 1, a single photodetector is arranged and two
Although an example in which a binary code pattern is scanned has been shown, a photodetector may be arranged for each binary code pattern. Also, 2 of each order
We have shown an example in which binary code patterns with a 90° phase difference are formed to obtain detection signals with a 90° phase difference for each binary code pattern. At the same time, each pair of photodetectors is set at 90°.
They may be arranged with different phases.

Furthermore, position detection using a binary code pattern
Some, for example, provide a single gray binary code pattern for each order and perform position detection using a normal binary code Bakun.
The method of the present invention may be applied only to some parts. Further, in the above embodiment, a phase division method using moiré fringes was applied to detect minute positions, but positions may be detected entirely using binary code patterns, and in that case, the method of the present invention may be applied to some or all of the positions. It can be used.

Effects of the Invention According to the position detection method of the present invention, as is clear from the above explanation, since position detection is performed using a binary code pattern, it is difficult to be affected by vibrations and noise, and highly accurate position detection can be achieved. and 90 for each order of binary code pattern.
By using a pair of detection signals with a phase difference of °, it is possible to sequentially connect the detection area to the lower orders while limiting the detection area including errors, and to expand the area from the highest order to the lowest order. By sequentially limiting
．． Even if the formation accuracy of the binary code pattern is low, the position can be detected with a predetermined resolution without causing a detection error, and the resolution can also be easily increased.

In addition, in order to obtain a pair of detection signals for each order of binary code patterns, if the detectors are arranged in pairs with a 90° phase shift, the number of patterns can be reduced, -90 for each order. By forming binary code patterns with different phases, the space for installing a detector can be reduced, and when the pattern is scanned, it can be detected with a single detector, and errors due to differences in detector characteristics do not occur.

Furthermore, if the detection positions specified by the detection signal group of each order are made into a table and the position is detected based on the detection signals, a great effect is achieved in that the position can be detected with high-speed responsiveness.

[Brief explanation of the drawing]

1 to 3 show one embodiment of the present invention, FIG. 1 is an explanatory diagram of the algorithm of the method of the present invention, FIG. 2 is a perspective view showing the schematic configuration of a position detection device, and FIG. 3 is a detection It is a waveform diagram of a signal. 4... Code plate, 7... Photodetector, 1
3...Track of binary code pattern, a - f.
...Binary code pattern, a゛~f''...
Binary code pattern with 90° phase difference. Represented by Shigetaka Awano, a patent attorney, and one other person

Claims (4)

[Claims] (1) 90 for each binary code pattern of multiple orders
A pair of detection signals with a phase difference of ° is obtained, and the detection area is sequentially limited from the highest order to the lowest order, including errors based on the pair of detection signals of each order. A position detection method characterized by specifying a range of absolute positions to be detected. (2) At each order, the binary code pattern and this and 9
2. The position detection method according to claim 1, wherein a pair of detection signals is obtained from binary code patterns having a phase difference of 0°. (3) The position detection method according to claim 1, wherein a pair of detection signals is obtained by arranging detectors with a phase shift of 90 degrees from each other for each order of binary code pattern. (4) A position detection method according to claim 1, characterized in that a table is formed in which a correspondence relationship between detection positions and detection signals is set, and the position is detected from the detection signals based on the table.