JP2011220864A - Optical reference position detection type encoder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To allow a reference position such as an original point to be detected in a resting state just by supply of power without moving a scale and a detector relative to each other.SOLUTION: An optical reference position detection type encoder includes a detector and a scale 12 that can be moved relative to each other, a light-emitting element 11, an optical element 13, and a photodetector 14 for reference position detection provided on the detector side, and predetermined position reference patterns 33, 33', and 33" provided on the scale side. The photodetector has an array form extending in a measuring direction and the output of the array-form photodetector (a position reference photodiode array 43) is electrically swept to correlate with a design value, so that the reference position can be detected in a resting state without moving the scale and the detector relative to each other.

Description

  The present invention relates to an optical reference position detection type encoder, and in particular, it is possible to detect a reference position such as an origin in a stationary state without turning the scale and detector relative to each other simply by turning on the power. The present invention relates to an optical reference position detection type encoder.

  Conventionally, an optical encoder is provided with a light emitting element, an optical system, and a light receiving element for detecting an origin on the detector side, and a predetermined value on the scale side, as illustrated in Patent Document 1, for detecting the origin. The origin pattern is arranged. According to this configuration, when the scale and the detector are relatively moved, when the origin pattern on the scale crosses the detection unit, for example, a delta function like that illustrated in FIG. 5 or FIG. The peak signal is generated, and the origin can be detected by setting an appropriate threshold value in advance.

  Further, as described in Patent Documents 2 and 3, a plurality of reference marks are arranged on the scale, and the arrangement pitch is characteristically shifted as unequal, thereby performing pseudo absolute position (ABS) detection. Optical encoders have also been put into practical use.

  In addition to the incremental (INC) pattern formed by the arrangement pitch Pi of light and dark equal intervals and the absolute (ABS) pattern in which the absolute position is expressed by a pseudo-random pattern in Patent Documents 4 and 5, the applicant has disclosed an absolute. Proposing a three-track optical absolute position measurement encoder with a position reference pattern that has a predetermined phase relationship with the pattern and is formed with a light and dark equidistant arrangement pitch Pr (> Pi) Yes.

JP-A-7-318371 (FIGS. 5 and 13) Japanese Patent Laid-Open No. 60-120216 (FIG. 1) JP 62-291507 A (FIGS. 2 and 3) JP 2008-261701 A JP 2009-2702 A

  However, in any case, in order to detect the reference position such as the origin and the arrangement pitch, it is necessary to move the scale and the detector relative to each other. It could not be detected.

  In addition, in the optical absolute position length measurement type encoder based on the three tracks (ABS, position reference, INC) proposed in Patent Documents 4 and 5, when position information is extracted from the imaged position reference pattern, pattern matching A technique using image correlation is used for detection. This method generates a single correlation peak on the correlation function obtained by calculating the "difference" or "product" between the reference pattern stored in itself and the detection pattern obtained from imaging. It is a method of letting.

  Theoretically, since a necessary and sufficient condition can be satisfied by using a single line as a position reference pattern when performing this image correlation, conventionally, a single pattern has been used as the position reference pattern. However, since there are only two edges in one pattern, it is not only difficult to improve the accuracy, but there is a problem that the accuracy of the correlation peak is degraded due to the influence of noise and the accuracy is deteriorated due to the embedding. there were.

  The present invention has been made to solve the above-described conventional problems, and it is possible to detect a reference position such as an origin in a stationary state by simply turning on the power without moving the scale and the detector relative to each other. This is the first problem.

  The second object of the present invention is to improve detection accuracy and make it less susceptible to noise caused by dust on the scale.

  The present invention includes a detector and a scale that can move relative to each other, a light emitting element for detecting a reference position, an optical system, and a light receiving element are arranged on the detector side, and a predetermined position reference pattern is arranged on the scale side. In the reference position detection type encoder, the light receiving element is formed in an array extending in the length measuring direction, and the output of the arrayed light receiving element is electrically swept to correlate with the design value. The first problem can be solved by making it possible to detect the reference position in a stationary state without relative movement.

  Here, the second problem can be solved by configuring the position reference pattern with a plurality of lines arranged in the length measuring direction according to a predetermined relationship.

  The lines constituting the position reference pattern can be arranged according to a Barker sequence code, an M sequence code, a Gold sequence code, or a random code sequence.

  Further, the position reference pattern arranged according to the random code sequence can be divided randomly or at equal intervals.

  Further, the position of the edge of the position reference pattern arranged according to the random code sequence can be shifted in the length measuring direction within a range of ± 1/2 of the pattern line width.

  Further, a plurality of the position reference patterns can be arranged at different intervals in the length measurement direction, and at least two position reference patterns can be detected simultaneously by the arrayed light receiving element.

  Alternatively, a plurality of the position reference patterns can be arranged at the same interval in the length measurement direction.

  Further, the correlation can be a correlation by multiplication with a design value.

  Alternatively, the correlation can be a correlation by subtraction with a design value.

  According to the present invention, it is possible to detect a reference position such as an origin in a stationary state without turning the scale and the detector relative to each other by simply turning on the power.

  In addition, the position reference pattern is composed of a plurality of lines arranged in the length measurement direction according to a predetermined relationship, so that a sharp correlation peak is generated in detecting a pattern match by image correlation. It is possible to improve the detection accuracy and make it less susceptible to noise caused by dust on the scale.

Schematic which shows the whole structure of 1st Embodiment of this invention. The top view which shows the structure of the scale of 1st Embodiment. The top view which similarly shows the composition of a position reference pattern Similarly, a plan view showing the configuration of the photodiode array Similarly, a circuit diagram showing a detailed configuration of the position reference photodiode array. The figure which similarly shows the example of the multiplication correlation function in a correlation calculation circuit The figure which shows the example of the subtraction correlation function in a correlation calculation circuit similarly Schematic which shows the whole structure of 2nd Embodiment of this invention. The top view which shows the structure of the scale of 2nd Embodiment. Similarly, a plan view showing the configuration of the photodiode array The figure explaining operation | movement of 2nd Embodiment. Schematic which shows the whole structure of 3rd Embodiment of this invention. The top view which shows the structure of the scale of 3rd Embodiment. Similarly, a plan view of the scale configuration without hatching Similarly, a plan view showing the configuration of the photodiode array The conceptual diagram which shows the 1st structural example of the ABS / position reference integrated scale in a scale similarly The conceptual diagram which shows the 2nd structural example of the ABS / position reference integrated scale in the same scale The top view which shows the structure of the scale of 4th Embodiment of this invention. The top view which shows the structure of the scale of 5th Embodiment of this invention. Plan view showing an example of a position reference track A diagram for explaining an example of a conventional position reference pattern and its problems The figure explaining one of the effect | actions of this invention Plan view showing another example of position reference track Plan view of an example scale including the position reference track of FIG. A plan view showing an example of a scale including another example of a position reference track Plan view showing an example of a scale including yet another example of the position reference track (A) Plan view showing an example in which a random code sequence is arranged on a scale, and (b) an example in which the position of an edge is randomly shifted Diagram showing definition of edge position Diagram showing how to shift the edge position Schematic showing a modification of the embodiment

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[First embodiment]
FIG. 1 is a schematic diagram showing the overall configuration of the optical encoder according to the first embodiment of the present invention. The optical encoder of this embodiment includes a light emitting element 11, a scale 12, a lens 13, a photodiode array 14, and a signal processing circuit 20.

  The light emitting element 11 is a light source that emits coherent light, for example, a laser diode.

  As shown in FIG. 2, the scale 12 has an incremental track 301 composed of an incremental pattern 31 formed on a transparent glass substrate with an arrangement pitch Pi (for example, 40 μm) at equal intervals of light and dark at different intervals in the length measurement direction. A position reference track 303 in which a plurality of position reference patterns 33 are arranged is formed.

  As illustrated in FIG. 3, the position reference pattern 33 can be (A) a single line pattern, (B) a predetermined pattern, or (C) an M-sequence code pattern.

  The light emitting element 11 irradiates the scale 12, and the irradiation light transmitted through the scale 12 is projected onto the photodiode array 14 via the lens 13.

  As shown in FIG. 4, the photodiode array 14 composed of, for example, a CMOS includes an INC photodiode array 41 and a position reference photodiode array 43 corresponding to the incremental track 301 and the position reference track 303. A length WPDr in the length measurement direction of the position reference photodiode array 43 is set to a length capable of simultaneously detecting at least two position reference patterns 33.

  The INC photodiode array 41 has, for example, four sets of photodiode arrays having different phases by 90 degrees, detects a light / dark signal based on the incremental pattern 31, and outputs a four-phase sine wave signal having a phase difference of 90 degrees. The position reference photodiode array 43 is dimensioned in the length measuring direction so that at least two position reference patterns 33 can be detected. As shown in FIG. The obtained signals are output by sweeping the 43 light receiving elements 1 to N.

  As an example, the signal processing device 20 shown in FIG. 1 includes a noise filter / amplifier circuit 21, an A / D converter 22, a relative position detection circuit 23, a preamplifier 27, a correlation calculation circuit 28, a reference position detection circuit 29, and a position correction circuit. 30.

  The noise filter / amplifier circuit 21 removes noise from the analog output signal (90-degree phase difference 4-phase signal) from the INC photodiode array 41 and then amplifies and outputs the signal.

  The A / D converter 22 converts the analog output signal output from the noise filter / amplifier circuit 21 into a digital signal. The relative position detection circuit 23 performs an arctan calculation of the amplitude of the obtained digital signal (90-degree phase difference signal), thereby outputting a relative position signal D1 indicating the relative movement amount / movement direction of the scale 12.

  The preamplifier 27 amplifies and outputs the output of the switching element 45. The correlation calculation circuit 28 performs correlation calculation with the design value, and the reference position detection circuit 29 detects the position reference pattern position based on the calculation result of the correlation calculation circuit 28.

  In the correlation calculation circuit 28, for example, as shown in FIG. 6 (A), the multiplication correlation calculation with the design value is performed, and further, the peak position as shown in FIG. 6 (B) is enlarged in the length measuring direction. Thus, for example, a quadratic curve is fitted, and the peak position is interpolated from three peaks to obtain the reference position. According to this multiplication correlation, although the number of digits is increased and the calculation time is long, the peak contrast is high, and the origin position can be detected with high accuracy of about 1 μm, for example.

  Alternatively, as shown in FIG. 7 (A), a subtractive correlation with the design value is obtained, and a quadratic curve, for example, is applied to the peak position as shown in FIG. The peak position is interpolated from the three peaks to obtain the reference position. According to this subtraction correlation, the number of digits is small and calculation is easy, and distinction from ambient light is also possible.

  Note that the interpolation method is not limited to the method shown in FIG. 6B or 7B.

  The position correction circuit 30 corrects and outputs the relative position D1 obtained by the relative position detection circuit 23 with the reference position detected by the reference position detection circuit 29.

  In the present embodiment, a plurality of position reference patterns 33 are arranged at different intervals in the measurement direction, and at least two position reference patterns can be detected simultaneously by the arrayed light receiving element (43). Based on this, it is possible to identify each pattern.

[Second Embodiment]
Next, a second embodiment of the present invention applied to the absolute position measurement encoder proposed by the applicant in Patent Document 3 will be described in detail.

  FIG. 8 is a schematic diagram showing the overall configuration of an optical absolute position measurement encoder according to the second embodiment of the present invention. The same components as those in the first embodiment are denoted by the same reference numerals, and detailed description thereof will be omitted below.

  FIG. 8 is a schematic diagram showing the overall configuration of the second embodiment, and FIG. 9 shows the planar configuration of the scale 12. In the present embodiment, as shown in FIG. 9, the scale 12 is a general absolute pattern 32 in which the absolute position is expressed by an incremental track 301 similar to that of the first embodiment and a pseudo random pattern (here, an M-sequence code). A position reference pattern 33 having a predetermined phase relationship with respect to the absolute track 302 and the absolute pattern 32 and having a width Wr in the length measurement direction formed at a bright and dark equidistant arrangement pitch Pr (<Pi). And a position reference track 303 ′ composed of ′. That is, the absolute pattern 32 represents the absolute position of the equally spaced pattern of the position reference pattern 33. For example, the arrangement pitch Pi of the incremental pattern 31 is set to 1 / integer of the arrangement pitch Pr of the position reference pattern 33. In the present embodiment, Pi = 4Pr is assumed as an example. As an example, when Pi = 40 μm, Pr = 160 μm is set.

  Since both the incremental pattern 31 and the position reference pattern 33 'are formed at an equally spaced arrangement pitch (Pi, Pr) over the entire length of the encoder, it is relatively easy to accurately form the entire length of the encoder. Here, as in the prior art, an encoder is assumed in which there is no position reference pattern 33 ′ and only the incremental pattern 31 and the absolute pattern 32 exist. In such an encoder, for example, when the arrangement pitch of the incremental patterns 31 is 40 μm, the accuracy of the absolute pattern 32 must be less than ± 20 μm, which is less than half of the entire length of the scale 12.

  On the other hand, if the position reference pattern 33 ′ having an arrangement pitch Pr larger than the arrangement pitch Pi of the incremental pattern 31 is formed as in the present embodiment, the position accuracy of the absolute pattern 32 can be improved. It is sufficient to match the arrangement pitch Pr. Therefore, the tolerance of the position error of the absolute pattern 32 can be increased. For example, if the arrangement pitch Pr of the position reference pattern 33 ′ is 160 μm which is four times Pi, the position error of the absolute pattern 32 can be allowed to be ± 80 μm over the entire length of the scale 12. Therefore, the arrangement pitch Pi of the incremental pattern 31 can be determined without considering the accuracy of the absolute pattern 32, and the pitch of the incremental pattern 31 can be reduced to increase the accuracy of the encoder.

  As shown in FIG. 10, the photodiode array 14 includes an INC photodiode array 41, an ABS photodiode array 42, and a position reference photodiode array corresponding to the incremental track 301, the absolute track 302, and the position reference track 303 ', respectively. 43. Each of the photodiode arrays 41 to 43 is configured by arranging photodiodes at an arrangement pitch corresponding to the pitch of the corresponding patterns 31 to 33.

  Similar to the first embodiment, the INC photodiode array 41 includes four sets of photodiode arrays having phases different from each other by 90 degrees, detects a light / dark signal based on the incremental pattern 31, and has a four-phase sine having a phase difference of 90 degrees. Output a wave signal. The ABS photodiode array 42 outputs a signal obtained by sweeping a light / dark signal based on the absolute pattern 32 in the length measuring direction. Further, the position reference photodiode array 43 has a dimension WPDr in the length measuring direction so that at least one position reference pattern 33 ′ can be detected (WPr> Pr + Wr), and a light / dark signal based on the position reference pattern 33 ′. A signal obtained by sweeping in the length measurement direction is output.

  For example, the signal processing circuit 20 includes a noise filter / amplifier circuit 21, an A / D converter 22, a relative position detection circuit 23, a noise filter / amplifier circuit 24, an A / D converter 25, an absolute position detection circuit 26, and a preamplifier. 27, a correlation calculation circuit 28, a reference position detection circuit 29, and an absolute position synthesis circuit 30 '.

  The noise filter / amplifier circuit 24 amplifies this signal after removing the noise of the analog output signal (absolute position signal) from the ABS photodiode array 42. The A / D converter 25 converts the analog signal output from the noise filter / amplifier circuit 24 into a digital signal. The converted digital signal includes M-sequence code data expressed in the absolute pattern 32 in this case.

  The absolute position detection circuit 26 has a table (not shown) indicating the relationship between the M-sequence code and the absolute position expressed by the M-sequence. With reference to this table, the absolute position of the scale 12 is determined. The absolute position signal D2 indicating is output.

  The preamplifier 27, the correlation calculation circuit 28, and the reference position detection circuit 29 output a position reference signal D3 indicating the reference position of the position reference pattern 33 ′, as in the first embodiment.

  The absolute position synthesis circuit 30 ′ calculates the fine absolute position of the scale 12 based on the absolute position signal D2, the relative position signal D1, and the position reference signal D3. The operation of the absolute position synthesis circuit 30 'will be described with reference to FIG. The absolute position signal D2 has information on the absolute position of the scale 12. Since the absolute pattern 32 is formed with predetermined information with respect to the position reference pattern 33 ′, the absolute position is obtained from the absolute position signal D2, so that the scale 12 is positioned at what period Pr of the position reference pattern 33 ′. It can be specified whether it is located ((1) in FIG. 11).

  When the cycle Pr of the position reference pattern 33 ′ is specified, the signal amount of the position reference signal D3 is detected thereafter, and the scale 12 is positioned in the cycle of the incremental pattern 31. Can be specified ((2) in FIG. 11). Since the incremental pattern 31 and the position reference pattern 33 'are both formed by equally spaced light and dark patterns, it is easy to maintain high positional accuracy between the two even when the ratio between the arrangement pitches Pr and Pi is large. For this reason, the cycle of the position reference pattern 33 ′ is determined, and the signal amount of the position reference signal D3 is further detected, thereby specifying the cycle of the incremental pattern 31 to which the scale 12 is positioned. Can do. Thereafter, the absolute position of the scale 12 can be calculated and output by calculating the brightness of the relative position signal D1 obtained from the incremental pattern 31.

  As described above, according to the present embodiment, the absolute position of the scale 12 is detected in relation to the position reference pattern 33 ′ based on the absolute position detection signal D2 obtained by the absolute pattern 32, and then the position is detected. A precise absolute position signal of the scale 12 can be obtained by the position reference signal D3 based on the reference pattern 33 ′ and the relative position signal D1 based on the incremental pattern 31. The absolute pattern 32 is not required to have positional accuracy with respect to the finely formed incremental pattern 31, and it is sufficient if the absolute pattern 32 is formed with a predetermined positional accuracy with respect to the position reference pattern 33 'having a larger arrangement pitch. Therefore, according to the present embodiment, the pitch of the incremental pattern 31 can be reduced, and thus the encoder can be highly accurate.

[Third embodiment]
Next, an optical absolute position measurement encoder according to a third embodiment of the present invention will be described. The same components as those of the second embodiment are denoted by the same reference numerals, and detailed description thereof is omitted below.

  FIG. 12 is a schematic diagram showing the overall configuration of the third embodiment, and FIG. 13 shows the planar configuration of the scale 12. As shown in FIG. 13, in this embodiment, instead of the absolute pattern 32 and the position reference pattern 33 ', an ABS / position reference integrated track comprising an ABS / position reference integrated pattern 34 in which these two types of patterns are integrated into one track. It differs from 2nd Embodiment by the point provided with 304. FIG. As shown in FIG. 13, the ABS / position reference integrated track 304 has an absolute pitch 32 ′ representing a pseudo-random pattern and an arrangement pitch Pr larger than the arrangement pitch Pi of the incremental pattern 31 in the gap between the absolute pattern 32 ′. The position reference pattern 33 ″ is arranged in one track. In FIG. 13, the position reference pattern 33 ″ is hatched. 32 ′ and the position reference pattern 33 ″ are added for easy understanding. In an actual scale, as shown in FIG. 14, the absolute pattern 32 ′ and the position reference pattern 33 ″ are on the scale 12. Are made of the same material and differ only in the shape of the pattern. There. In this embodiment, since the scale 12 has only two tracks as described above, the size can be reduced as compared with the second embodiment including three tracks.

  In addition, the photodiode array 14 corresponds to each of the incremental track 301 and the ABS / position reference integrated track 304 as shown in FIG. 15 in correspondence with the scale 12 configured as described above. , The INC photodiode array 41 and the ABS / position reference photodiode array 44 having the same configuration as the position reference photodiode array 43 of the first and second embodiments.

  As shown in FIG. 12, in the signal processing circuit 20 of the present embodiment, the configuration (21 to 23) for signal processing based on the incremental pattern 31 is the same as that of the second embodiment. On the other hand, a signal based on the above-described ABS / position reference integrated pattern 34 is different from the second embodiment in that it is input to the separation circuit 201 via the preamplifier 27. The separation circuit 201 has a function of separating the signal from the position reference pattern 33 ″ in the ABS / position reference integrated pattern 34 and the signal from the absolute pattern 32 ′ described above. This can be executed by performing a correlation calculation between the signal based on the ABS / position reference integrated pattern 34 and the design value of the position reference pattern 33 ″. That is, a signal based on the position reference pattern 33 "can be obtained as a result of the correlation calculation. Either a multiplication type or a subtraction type can be used for the correlation calculation. The separated position reference pattern 33 is used. The signal from “is input to the reference position detection circuit 29, and the reference position detection circuit 29 outputs a position reference signal D3.

  Contrary to the above, the correlation between the signal based on the ABS / position reference integrated pattern 34 and the design value of the absolute pattern 32 'is calculated, and a signal based on the absolute pattern 32' is obtained as a result of the calculation. Is possible. In this case, as indicated by a broken line in FIG. 12, a correlation calculation circuit 28 similar to that in the first and second embodiments is inserted between the separation circuit 201 and the reference position detection circuit 29.

  A configuration example of the ABS / position reference integration pattern 34 of the present embodiment will be described with reference to FIGS. 16 and 17. FIG. 16 shows a first configuration example. In the first configuration example, an absolute pattern 32 ′ and a position reference pattern 33 ″ as shown in FIG. 6A are integrated into one track, and the configuration shown in FIG. When this integration is performed, the absolute pattern 32 ′ and the position reference pattern 33 ″ partially overlap (position indicated by the arrow A). In this first configuration example, the absolute pattern 32 ′ is omitted in this overlapping portion, and instead, a position reference pattern 33 ″ is formed at that position (arrow A). Even if the pattern 32 ′ is omitted (erased), if the absolute position detection circuit 26 knows the design value (including the position above the position of the arrow A) of the position reference pattern 33 ″, it is not omitted. Similarly, the absolute position can be detected.

  FIG. 17 shows a second configuration example. In this example, when a portion where the absolute pattern 32 ′ and the position reference pattern 33 ″ overlap is generated as shown in FIG. 10A, instead of omitting the overlapping portion as shown in FIG. The absolute pattern 32 'is reduced and formed so as not to cause an overlapping portion, and the overlapping portion is eliminated.

[Fourth Embodiment]
FIG. 18 shows the configuration of an absolute position detecting encoder according to the fourth embodiment of the present invention. Since the overall configuration is substantially the same as that of the second embodiment (FIG. 8), illustration is omitted.

  This embodiment is different from the second embodiment in that two types of position reference tracks 303A and 303B are provided on both sides of the incremental track 301 (not shown, but the position of the photodiode array 14 is omitted). Two reference photodiode arrays 43 are also provided correspondingly). According to such a configuration, even when the scale 12 is tilted (yawed), an error based on this is canceled by taking an average of the signals based on the two position reference patterns 33A and 33B. Is possible.

[Fifth Embodiment]
FIG. 19 shows the configuration of an absolute position detection type encoder according to the fifth embodiment of the present invention. Since the overall configuration is substantially the same as that of the second embodiment (FIG. 8), description thereof is omitted.

  This embodiment is different from the second embodiment in that ABS / position reference integrated tracks 304A and 304B similar to those of the fourth embodiment are formed so as to sandwich the incremental track 301 therebetween. According to such a configuration, even when inclination (yawing) occurs in the scale 12, an error based on this is obtained by taking an average of signals based on the two systems of ABS / position reference integrated patterns 34A and 34B. It becomes possible to cancel.

  Next, the position reference pattern will be examined in detail.

  FIG. 20 shows an example of the position reference track 303 in which the single line pattern shown in FIG. 3A is arranged at the arrangement pitch P as the position reference pattern. In the example as shown in FIG. 20, the position reference track 303 can be easily formed. However, since the number of edges is small, it is difficult to improve accuracy and it is also susceptible to noise.

  On the other hand, as illustrated in FIGS. 3B and 3C, when the position reference pattern is configured by a predetermined pattern of a plurality of lines, the number of edges increases, so that the detection accuracy of the position reference pattern is improved. As well as improving, it is possible to reduce the influence of noise caused by dust on the scale.

  That is, when detecting the coincidence of the position reference pattern by image correlation, as shown in FIG. 21 and FIG. 22, the position reference pattern is divided to increase the edge position, and the edge position is shifted as necessary. In addition to generating a sharp correlation peak, it is possible to improve the detection accuracy of the position reference pattern, and as shown in FIG.

  An 11-bit Barker sequence code is used for the position reference track, and “1” in the pattern code string indicated by the code length 11 in Table 1 is replaced with black and “0” is replaced with white, and the position reference pattern is arranged at the pitch P. An example of this is shown in FIG. In this case, pattern widths corresponding to “1” and “0” are determined so that the pattern length is equal to or shorter than the pitch P of the position reference pattern.

Here, when the code length is longer, the number of edges increases and it becomes difficult to be affected by dust or the like. However, since the line width becomes narrower and difficult to make, the code length is 4 (except for the lower stage that forms a single line pattern). ˜13 are preferable, and code lengths 11 and 13 are particularly preferable. In the upper stage of the code length 4 and the pattern of the code length 5, the pattern length L _B needs to be shorter than the arrangement pitch P in order to distinguish from the adjacent pattern.

11-bit Barker sequence code 11100010010 on the position reference track
An example of the scale 12 when using is shown in FIG.

In addition, an M-sequence code generated with a characteristic polynomial: f (x) = x ⁴ + x + 1 on the position reference track 100010011010111
An example of the scale 12 when using is shown in FIG.

In addition, the position reference track
Characteristic polynomial: M sequence code generated by f (x) = x ⁶ + x ⁵ + x ² +1,
Characteristic polynomial: Gold sequence code generated using an M sequence code generated by f (x) = x ⁶ + x ³ + x + 1 10000010001100101011111000010001
An example of the scale 12 when using is shown in FIG.

  As the predetermined pattern, in addition to the above, a pattern generated by a pseudo-random code used in the communication field can be used.

Further, as shown in FIG. 27A, when a pattern is arranged on a scale according to a random code sequence, if the line width of the pattern corresponding to one code of the random code sequence is W _bits , the random pattern arranged on the scale The pattern edge of the code sequence appears only at the position of W _bit × n (n is a positive integer).

Due to this feature, when performing the correlation calculation, the edge positions coincide with each W _bit , so that an error peak is likely to occur due to contamination, and there is a high possibility of erroneous detection.

Therefore, as illustrated in FIG. 27B, when the correlation calculation is performed by shifting the position of the scale pattern edge in the range of −W _bit / 2 to W _bit / 2, the edges match at positions other than the incorrect position. As a result, it is possible to suppress the occurrence of error peaks.

As shown in FIG. 28, the edge shift method is such that the pattern edge shift is Δp _i (i = 1, 2, 3... N), and the range of Δp _i is −W _bit / 2 <Δp _i <W _bit. As shown in FIG. 29 (a), it is randomly shifted, as shown in FIG. 29 (b), according to a normal distribution, as shown in FIG. 29 (c), according to a triangular wave, As shown in (d), it can be shifted according to a sine wave.

  In the above-described embodiments, the transmission type optical encoder has been described as an example. However, as in the modification shown in FIG. 30, the light emitting element 11 is used as a reflective optical system from the light emitting element 11. 13 and the light receiving element array 14 may be disposed on the same side.

DESCRIPTION OF SYMBOLS 11 ... Light emitting element 12 ... Scale 13 ... Lens 14 ... Photodiode array 20 ... Signal processing circuit 21, 24 ... Noise filter and amplification circuit 22, 25 ... A / D converter 23 ... Relative position detection circuit 26 ... Absolute position detection circuit 27 ... Preamplifier 28 ... Correlation operation circuit 29 ... Reference position detection circuit 30 ... Position correction circuit 30 '... Absolute position synthesis circuit 31 ... Incremental pattern 32, 32' ... Absolute pattern 33, 33 ', 33 ", 33A, 33B ... Position Reference pattern 34, 34A, 34B ... ABS / position reference integrated pattern 41 ... INC photodiode array 42 ... ABS photodiode array 43 ... position reference photodiode array 44 ... ABS / position reference photodiode array 45 ... switching element 301 ... incremental INC) Track 302 ... absolute (ABS) track 303,303' ... position reference track 304,304A, 304B ... ABS / position reference integration track

Claims (9)

With a relatively movable detector and scale,
On the detector side, a light emitting element for detecting the reference position, an optical system and a light receiving element are arranged,
In the optical reference position detection type encoder in which a predetermined position reference pattern is arranged on the scale side,
The light receiving element is in an array extending in the length measuring direction,
By electrically sweeping the output of the arrayed light receiving element and taking a correlation with the design value,
An optical reference position detection type encoder capable of detecting a reference position in a stationary state without causing relative movement between a scale and a detector.   2. The optical reference position detection type encoder according to claim 1, wherein the position reference pattern is composed of a plurality of lines arranged in a length measuring direction according to a predetermined relationship.   The optical reference position detecting encoder according to claim 2, wherein the lines constituting the position reference pattern are arranged according to a Barker sequence code, an M sequence code, a Gold sequence code, or a random code sequence.   4. The optical reference position detection encoder according to claim 3, wherein the position reference pattern arranged according to the random code sequence is divided randomly or at equal intervals.   4. The optical reference position detection according to claim 3, wherein the position of the edge of the position reference pattern arranged according to the random code sequence is shifted in the length measuring direction within a range of ± 1/2 of the pattern line width. Type encoder. A plurality of the position reference patterns are arranged at different intervals in the length measurement direction,
2. The optical reference position detection type encoder according to claim 1, wherein at least two position reference patterns can be simultaneously detected by the arrayed light receiving element.   2. The optical reference position detection type encoder according to claim 1, wherein a plurality of the position reference patterns are arranged at the same interval in the length measuring direction.   The optical reference position detection encoder according to claim 1, wherein the correlation is a correlation obtained by multiplication with a design value.   The optical reference position detection encoder according to claim 1, wherein the correlation is a correlation obtained by subtraction with a design value.

Images