JP2012032295A - Photoelectric encoder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately find the position of a detector relative to a scale while expanding an operation temperature range even when a lens array provided to the detector is different in coefficient of linear expansion from one of a light reception part of the detector and the scale.SOLUTION: A first lens array 114 and a second lens array 122 have a different coefficient of linear expansion from the scale 102 and light reception part 124, and the first lens array 114, second lens array 122, and light reception part 124 are fixed in one body at one specific place Xst of the first lens array 114 and second lens array 122. Phase signals φi found from a period signal Fi are each corrected so as to eliminate a phase difference due to a different coefficient α, and further corrected phase signals Cφi having been corrected are averaged to find an average phase signal φav, thereby finding the position of the detector 110 relative to the scale 102.

Description

  The present invention relates to a photoelectric encoder comprising a scale in which optical gratings are formed at equal intervals in the length measurement direction, and a detector that is relatively displaced with respect to the scale, and in particular, a lens array provided in the detector. The present invention relates to a photoelectric encoder that can accurately determine the position of a detector with respect to a scale even if the linear expansion coefficient differs from any one of a light receiving unit and a scale of the detector and the operating temperature varies greatly.

  Photoelectric encoder comprising a scale in which optical gratings are formed at equal intervals in the length measuring direction, a detector that is displaced relative to the scale, and a lens array that forms an image of the scale on the light receiving portion of the detector Has been proposed (for example, Patent Documents 1 and 2). FIG. 18 and FIG. 19 (A) show the relationship between the scales 2 and 52, the lens arrays 14 and 64, and the scale image Img on the light receiving unit in Patent Documents 1 and 2, respectively. In Patent Documents 1 and 2, by using the lens arrays 14 and 64, the detection range of the scales 2 and 52 can be expanded without increasing the size of the detector.

JP 2004-264295 A JP 2005-522682 A

  However, in order to reduce the cost of the encoder, for example, when the lens array is changed from glass to plastic, since the conventional scale is glass, at least the linear expansion coefficient between the lens array and the scale is greatly different. For this reason, even if the precision of the scale and the detector is adjusted in the initial state, if the operating temperature Tp of the photoelectric encoder changes from the temperature Ta at the time of precision adjustment, each lens portion of the lens array is configured. The center of the optical axis of the optical system of the detector will move. That is, an error may occur in the detection position by the detector.

  In particular, the encoder of Patent Document 2 will be described with reference to FIG. 19B. When the optical axis center O1 of the lens portion 64A of the lens array 64 is used as a reference, the operating temperature Tp changes from the temperature Ta during accuracy adjustment. As a result, the optical axis center O2 of the lens portion 64B changes from the position at the time of accuracy adjustment to the outside of the distance dx. Therefore, considering the scale image Img1 by the lens unit 64A as a reference, the scale image Img2 by the lens unit 64B is shifted in the length measurement direction (X direction). That is, in Patent Document 2, if the lens array 64 has a linear expansion coefficient different from that of the scale 52, the image Img1 of the scale 52 by the lens unit 64A and the image Img2 of the scale 52 by the lens unit 64B are particularly affected when the operating temperature Tp varies. As a result, the continuity cannot be maintained and a large position detection error may occur.

  The present invention has been made to solve the above problems, and the operating temperature range is expanded even if the linear expansion coefficient of the lens array provided in the detector is different from either the light receiving unit or the scale of the detector. However, it is an object of the present invention to provide a photoelectric encoder that can accurately determine the position of the detector with respect to the scale.

The invention according to claim 1 of the present application includes a scale in which optical gratings are formed at equal intervals in the length measurement direction, and a detector that is relatively displaced with respect to the scale, and the detector has a number n (n ≧ 2) in the length measuring direction, a lens array for forming an image of the scale, and a number n of light receiving elements for receiving the image of the scale formed for each lens unit. And a light receiving unit that outputs a periodic signal Fi (i = 1,..., N) according to the period of the optical grating for each light receiving element, wherein the lens array includes at least the scale and the light receiving unit. A linear expansion coefficient α _LA different from any one of the first and second portions, and the lens array and the light receiving portion are integrally fixed at a specific position of the lens array in the length measuring direction, and the light receiving element Every The phase signal φi obtained from the periodic signal Fi uses the operating temperature Tp of the scale and the detector and the distance Li from the specific one place to the center of the optical axis of each lens unit, respectively. Correction is made so as to eliminate the phase shift caused by the different linear expansion coefficient α _LA , and the corrected correction phase signal Cφi obtained for each light receiving element is averaged to obtain an average phase signal φav. Since the position of the detector with respect to the scale is obtained by the phase signal φav, the problem is solved.

In the invention according to claim 2 of the present application, the distance Li from the specific location to the center of the optical axis of each lens unit, and the linear expansion coefficients α _LA and α _{S of the} lens array, the scale, and the light receiving unit , Α _D , and the temperature difference δT between the operating temperature Tp and the temperature Ta around the scale and the detector when the accuracy of the detector is adjusted with respect to the scale, the above-mentioned on the detection unit in each lens unit The moving amount dxi of the scale image is obtained by the equation (1), the moving phase δφi is obtained by the equation (2) from the period P of the periodic signal Fi with respect to the moving amount dxi, according to the position of the respective optical axis of each lens unit, the by adding or subtracting the mobile phase δφi the phase signal .phi.i, the phase signal .phi.i of each of the light receiving element, respectively, to the different linear expansion coefficient alpha _LA The correction is made so as to eliminate the phase shift caused.
dxi = (2α _LA −α _S −α _D ) * Li * δT (1)
δφi = 2πdxi / P (2)

  In the invention according to claim 3 of the present application, the one specific position is made to coincide with the optical axis center of any one of the lens portions in the length measuring direction.

  The invention according to claim 4 of the present application is such that the specific location is set to the center position of the lens array in the length measurement direction.

  The invention according to claim 5 of the present application is such that the number n of the lens portions of the lens array is three.

  The invention according to claim 6 of the present application is such that the material of the scale is glass, the material of the lens array is plastic, and the material of the light receiving part is silicon.

  In the invention according to claim 7 of the present application, the detector is provided with a one-side telecentric optical system including an aperture plate aperture at a focal position of the lens array.

  In the invention according to claim 8 of the present application, the detector includes a two-side telecentric optical system including two lens arrays in series in the optical axis direction and a diaphragm plate aperture at a focal position between the lens arrays. It is provided.

  According to the present invention, even if the linear expansion coefficient of the lens array provided in the detector is different from any one of the light receiving unit and the scale of the detector, the position of the detector with respect to the scale is increased while the operating temperature range is expanded. It can be obtained accurately.

The perspective view which shows the outline of an example of the photoelectric encoder which concerns on 1st Embodiment of this invention. Similarly, a schematic diagram including the signal processing unit of the photoelectric encoder Similarly, a schematic diagram of the scale part Similarly, a schematic diagram showing changes in the position of the scale image by each lens unit. Similarly, a schematic diagram showing changes in the position of the scale image by each lens unit. Similarly, a schematic diagram showing changes in the position of the scale image by each lens unit. The schematic diagram which shows the position change of the image of the scale by each lens part of the photoelectric encoder which concerns on 2nd Embodiment of this invention. Similarly, a schematic diagram showing changes in the position of the scale image by each lens unit. Similarly, a schematic diagram showing changes in the position of the scale image by each lens unit. The schematic diagram which shows the position change of the image of the scale by each lens part of the photoelectric encoder which concerns on 3rd Embodiment of this invention. Similarly, a schematic diagram showing changes in the position of the scale image by each lens unit. Similarly, a schematic diagram showing changes in the position of the scale image by each lens unit. The schematic diagram which shows the position change of the image of the scale by each lens part of the photoelectric encoder which concerns on 4th Embodiment of this invention. Similarly, a schematic diagram showing changes in the position of the scale image by each lens unit. Similarly, a schematic diagram showing changes in the position of the scale image by each lens unit. Schematic including the signal processing unit of the photoelectric encoder according to the fifth embodiment of the present invention. Schematic of a photoelectric encoder according to a sixth embodiment of the present invention Schematic diagram of a conventional photoelectric encoder Schematic diagram of a conventional photoelectric encoder

  Hereinafter, an example of an embodiment of the present invention will be described in detail with reference to the accompanying drawings.

  First, the configuration of the photoelectric encoder according to the first embodiment of the present invention will be described below with reference to FIGS.

  As shown in FIGS. 1 and 2, the photoelectric encoder 100 of the present embodiment includes a scale 102 and a detector 110 that is displaced relative to the scale 102. Note that a signal processing unit 126 is connected to the detector 110.

As shown in part in FIG. 3, the scale 102 has an incremental track in which optical gratings 106 are formed at equal intervals (period Pr) in the length measurement direction (X direction). The scale 102 is a transmissive scale and uses glass as a base material 104. Here, when soda lime glass (also called blue plate glass) is used as the base material 104, the linear expansion coefficient α _S of the scale 102 is about 8 * 10 ⁻⁶ / ° C. A light shielding metal film is formed on the surface of the scale 102, and only the portion of the optical grating 106 is transparent. The scale 102 is provided with an origin mark (not shown) that can be detected by the detector 110 outside the length measurement range of the incremental track.

  As shown in FIGS. 1 and 2, the detector 110 includes a light source 112, a first lens array 114, a diaphragm plate 116, a second lens array 122, and a light receiving unit 124.

  As shown in FIG. 2, the light source 112 is disposed on the back surface of the scale 102 so that light transmitted through the scale 102 enters the light receiving unit 124. The light source 112 is, for example, an LED, and includes the same number (n = 3) of LEDs 112A to 112C as the number n of lens portions 114A to 114C and 122A to 122C described later of the first lens array 114 and the second lens array 122. ing. For this reason, the part in which the light source 112 of the detector 110 is accommodated can be made thin.

  As shown in FIG. 2, the first lens array 114 is arranged at a focal distance f away from the scale 102 in the Y direction. The first lens array 114 includes several n (n = 3) lens portions 114A to 114C at equal intervals L0 in the length measuring direction (X direction).

  As shown in FIG. 2, the diaphragm plate 116 is disposed at a focal distance f away from the first lens array 114 in the Y direction. The aperture plate 116 is made of a highly light-shielding material, and openings 120A to 120C are provided at equal intervals L0 at portions corresponding to the optical axis centers O1 to O3 of the lens portions 114A to 114C of the first lens array 114. is there.

As shown in FIG. 2, the second lens array 122 is arranged at a focal distance f away from the diaphragm plate 116 in the Y direction. Similarly to the first lens array 114, the second lens array 122 includes several n (n = 3) lens portions 122A to 122C at equal intervals L0 in the length measurement direction (X direction). In the present embodiment, the focal lengths f of the lens portions 114A to 114C and the lens portions 122A to 122C are the same. The first lens array 114 and the second lens array 122 are made of polycarbonate (plastic) and have a linear expansion coefficient α _LA of about 70 * 10 ⁻⁶ / ° C.

As shown in FIG. 2, the light receiving unit 124 is disposed at a focal distance f away from the second lens array 122 in the Y direction. The light receiving unit 124 is provided with three light receiving element arrays 124A to 124C (light receiving elements). The light sources 112A to 112C, the lens portions 114A to 114C, the openings 120A to 120C, the lens portions 122A to 122C, and the light receiving element arrays 124A to 124C are disposed on the optical axis centers O1 to O3, respectively. That is, the three light receiving element arrays 124A to 124C receive the images of the scale 102 formed by the lens portions 114A to 114C of the first lens array 114 and the lens portions 122A to 122C of the second lens array 122, respectively. . Each of the light receiving element arrays 124A to 124C outputs a periodic signal Fi (i = 1, 2, 3) according to the period Pr of the optical grating 106. Specifically, each of the periodic signals Fi is a two-phase analog signal of a sine wave and a cosine wave. As described above, the detector 110 includes the first lens array 114 and the second lens array 122 in series in the optical axis directions O1 to O3, and the focal position f between the first lens array 114 and the second lens array 122. A double-sided telecentric optical system having openings 120A to 120C of the diaphragm plate 116 is provided. Note that the light receiving unit 124 is made of silicon, and has a linear expansion coefficient α _D of about 2.6 * 10 ⁻⁶ / ° C.

  The detector 110 is integrated with a casing (not shown). At this time, the first lens array 114, the second lens array 122, and the light receiving unit 124 are integrally fixed at the position of the optical axis center O2 in the length measurement direction (X direction) (FIG. 2). That is, a specific point Xst of the first lens array 114 and the second lens array 122 is coincident with the optical axis center O2 of the lens portions 114B and 122B in the length measurement direction (X direction). At the same time, the optical axis center O2 is also the center position of the first lens array 114 and the second lens array 122 in the length measurement direction (X direction). That is, one specific position Xst of the first lens array 114 and the second lens array 122 is the center position of the first lens array 114 and the second lens array 122 in the length measurement direction (X direction). In addition, as the method of fixing integrally, it can implement | achieve by screwing, an epoxy-type adhesive agent, or welding. Except for the fixed position, the first lens array 114, the second lens array 122, and the light receiving unit 124 can expand and contract with respect to each other about a specific point Xst by changing the operating temperature Tp. It is affixed with an elastic adhesive or the like. Note that the position variation due to the increase in the operating temperature Tp of the apertures 120A to 120C of the aperture plate 116 does not greatly affect the positions of the images ImgA to ImgC of the scale 102, so that the detector 110 is not limited to a specific one place Xst. Fixed to.

  As shown in FIG. 2, the signal processing unit 126 includes amplification circuits 128A to 128C, interpolation circuits 130A to 130C, a temperature sensor 132, various storage units 134 to 140, an arithmetic circuit 142, and a phase arithmetic circuit 144. And a phase averaging circuit 146.

  As shown in FIG. 2, the amplifier circuits 128A to 128C perform filtering and amplification of the periodic signal Fi (two-phase analog signal) output from the light receiving element arrays 124A to 124C according to the period Pr of the optical grating 106. The interpolation circuits 130A to 130C perform an arc tangent calculation (arctan calculation) from the amplified two-phase analog signals to obtain phase signals φ1 to φ3 smaller than the period P of the periodic signal Fi.

On the other hand, the detector 110 is provided with a temperature sensor 132 as shown in FIG. 2, and the scale 102 and the ambient temperature Ta of the detector 110 when the accuracy of the detector 110 with respect to the scale 102 is adjusted are The temperature difference δT when the detector 110 changes to the operating temperature Tp is output. In the various storage units 134 to 140, the α _S storage unit 134 stores the linear expansion length coefficient α _S (8 * 10 ⁻⁶ / ° C.) of the scale 102, and the α _LA storage unit 136 includes the first lens array 114 and the second lens array. The linear expansion coefficient α _{LA of} 122 (70 * 10 ⁻⁶ / ° C.), the α _D storage unit 138, the linear expansion coefficient α _D of the light receiving unit 124 (2.6 * 10 ⁻⁶ / ° C.), and the Li storage unit Reference numeral 140 stores distances Li (i = 1, 2, 3) from the specific one point Xst to the optical axis centers O1 to O3 of the lens portions 114A to 114C (122A to 122C), respectively. Since the specific one place Xst is the same as the optical axis center O2, the distance L1 from the specific one place Xst to the optical axis center O1 and the distance L3 from the specific one place Xst to the optical axis center O3. Are equal to each other by the distance L0 between the optical axis centers.

The arithmetic circuit 142 calculates the amount of movement dxi of the image Img of the scale 102 on the light receiving unit 124 in each lens unit 114A to 114C (122A to 122C) from the output of the temperature sensor 132 and the outputs of the various storage units 134 to 140. (1) (dx2 is zero).
dxi = (2α _LA −α _S −α _D ) * Li * δT (1)

Here, the movement of the image Img of the scale 102 due to the difference in the linear expansion coefficients of the scale 102, the first lens array 114, the second lens array 122, and the light receiving unit 124 will be described in detail with reference to FIGS. . In FIGS. 4 to 6, only changes due to the first lens array 114 and the second lens array 122, which have greatly different linear expansion coefficients α _LA from the scale 102 and the light receiving unit 124, are represented.

  The first lens array 114, the second lens array 122, and the light receiving unit 124 are integrally fixed at one position of the optical axis center O2 in the length measurement direction (X direction) (specific to the optical axis center O2). One place Xst matches). When the photoelectric encoder 100 is configured, the accuracy adjustment of the detector 110 with respect to the scale 102 is performed as described above. That is, the positions of the images ImgA to ImgC of the scale 102 by the lens portions 114A to 114C and 122A to 122C at the temperature Ta around the scale 102 and the detector 110 at this time are the reference on the light receiving unit 124. At this time, as shown in the Lissajous figure LSJ of FIG. 4A, the phase shift of the images ImgA to ImgC of the scale 102 hardly occurs.

The first lens array 114, the linear expansion coefficient alpha _LA of the second lens array 122, the linear expansion coefficient of the scale 102 alpha _S, large unlike the linear expansion coefficient alpha _D of the light receiving portion 124. For this reason, the operating temperature Tp of the scale 102 and the detector 110 after accuracy adjustment rises from the temperature Ta. Then, the first lens array 114 and the second lens array 122 extend greatly in the length measurement direction (X direction) as compared with the scale 102 and the light receiving unit 124. Here, since the optical axis center O2 is fixed, the optical axis center O1 moves from the optical axis center O2 because the lens portions 114A and 122A are larger than the expansion of the scale 102 and the light receiving portion 124. Similarly, the optical axis center O3 moves from the optical axis center O2 because the lens portions 114C and 122C are larger than the expansion of the scale 102 and the light receiving unit 124.

That is, as shown in FIG. 4B, when the operating temperature Tp rises above the temperature Ta, the images ImgA to ImgC of the scale 102 move away from each other. For this reason, in the Lissajous figure based on the image ImgB, the phases of the image ImgA and the image ImgC are shifted (occurrence of phase shift) as compared with the accuracy adjustment. The expansion of the first lens array 114, the second lens array 122, the scale 102, and the light receiving unit 124 is proportional to the temperature difference δT when the temperature difference δT between the temperature Ta and the operating temperature Tp during accuracy adjustment increases. growing. For this reason, in FIGS. 5A and 5B showing a state where the temperature difference δT is large, as shown in the Lissajous figure LSJ, the phases of the image ImgB and the image ImgA and the image ImgC are greatly shifted (phase shift). Expansion). Here, the linear expansion coefficients α _S and α _D of the scale 102 and the light receiving unit 124 are smaller than the linear expansion coefficients α _LA of the first lens array 114 and the second lens array 122. Therefore, as a result, as shown in FIG. 6, the images ImgA and ImgC of the scale 102 move approximately twice (2 dL) dL as much as the optical axis centers O1 and O3 move relative to the scale 102. It becomes. That is, the moving amount dxi of the image Img on the scale 102 can be accurately obtained by the equation (1).

Then, the movement phase δφi is obtained from the period P of the periodic signal Fi with respect to the movement amount dxi by the equation (2). The obtained moving phase δφi is output from the arithmetic circuit 142. The period P can also be said to be a period (Lissajous period) when a Lissajous figure is composed of two-phase analog signals.
δφi = 2πdxi / P (2)

  Here, in FIG. 2, the lens portions 114A to 114C and the lens portions 122A to 122C are the same, and the distance relationship is all the focal length f. For this reason, the period Pr of the optical grating 106 on the scale 102 and the period of the image of the scale 102, that is, the period P of the periodic signal Fi are the same.

  The movement phase δφ1 output from the arithmetic circuit 142 is added to the phase signal φ1 by the phase addition circuit 144A in the phase arithmetic circuit 144, whereby the phase signal φ1 is corrected and the phase shift is eliminated. This is because the expansion of the lens portions 114A and 122A of the first lens array 114 and the second lens array 122 increases as the operating temperature Tp rises, and the position of the image of the scale 102 moves from a specific one place Xst to the left side of the drawing. This is to leave (FIG. 6). Conversely, the moving phase δφ3 (= δφ1) output from the arithmetic circuit 142 is subtracted from the phase signal φ3 by the phase subtracting circuit 144B in the phase arithmetic circuit 144, so that the phase signal φ3 is corrected and the phase shift occurs. Is resolved. This is because the expansion of the lens portions 114C and 122C of the first lens array 114 and the second lens array 122 increases with the increase of the operating temperature Tp, and the position of the image of the scale 102 moves from the specific one place Xst to the right side of the drawing. This is to leave (FIG. 6).

That is, the light receiving element is obtained by adding or subtracting the moving phase δφi to the phase signal φi according to the positions of the optical axis centers O1 to O3 of the lens portions 114A to 114C (122A to 122C) with respect to a specific one place Xst. The phase signal φi for each of the arrays 124A to 124C is corrected so that the phase shift caused by the different linear expansion coefficient α _LA is eliminated. In other words, the phase signal φi obtained from the periodic signal Fi for each of the light receiving element arrays 124A to 124C is obtained from the lens 102A to 114C (122A to 122A to 122C) from the operating temperature Tp of the scale 102 and the detector 110 and the specific one point Xst. by using the distance Li to the respective optical axis O1~O3 of 122C), it is corrected so that the phase shift caused by the different linear expansion coefficient alpha _LA is eliminated. Note that the specific one point Xst is the same as the optical axis center O2, and therefore it is not necessary to correct the phase signal φ2.

  The corrected correction phase signal Cφi obtained for each of the light receiving element arrays 124A to 124C is input to the phase averaging circuit 146 as shown in FIG. The phase averaging circuit 146 averages the corrected phase signals Cφ1 and Cφ3 and the phase signal φ2, and obtains and outputs an average phase signal φav. The signal processing unit 126 includes a circuit that outputs a two-phase digital signal (not shown) as a two-phase square wave signal and a counter circuit that counts the two-phase square wave signal. For this reason, the square wave signal is counted from the origin mark on the scale 102, and the position information of the average phase signal φav is added to the square wave signal, thereby obtaining the accurate and detailed position of the detector 110 with respect to the scale 102.

  Thus, in this embodiment, even if the operating temperature Tp rises and the first lens array 114 and the second lens array 122 expand, the phase shift can be eliminated by correcting the obtained phase signal φi, and detection Accuracy can be maintained.

  Since the first lens array 114 and the second lens array 122 are made of plastic (polycarbonate) having a large linear expansion coefficient, the first lens array 114 and the second lens array 122 are detected more than glass. The cost of the device 110 can be reduced.

  In addition, since the first lens array 114, the second lens array 122, and the light receiving unit 124 are integrally fixed at one specific place Xst, calculation of phase correction by the temperature difference δT is easy. At the same time, the expansion of the first lens array 114, the second lens array 122, and the light receiving unit 124 due to thermal expansion is not forcibly suppressed. For this reason, since a large distortion is not given to the first lens array 114, the second lens array 122, and the light receiving unit 124, long-term quality of the encoder can be maintained.

  Moreover, since the correction of the phase signal φi is performed for each of the light receiving element arrays 124A to 124C, the correction can be easily performed. At that time, the specific one point Xst coincides with the optical axis center O2. Therefore, the distances L1 and L3 to the optical axis centers O1 and O3 are the same as the distance L0, and the phase signal φi can be corrected more easily.

  In addition, since the optical axis center O2 is also the center position of the first lens array 114 and the second lens array 122 in the length measuring direction (X direction), the amount of movement of the image Img of the scale 102 is equal to the left and right. The amount of movement due to temperature can be accurately determined. At the same time, even if warpage or the like occurs in the first and second lens arrays due to temperature rise, it can be made smaller than the warpage that occurs when restrained at one end, thereby reducing the influence of warpage or the like. Can do. Further, in terms of configuration, the first lens array 114, the second lens array 122, and the light receiving unit 124 can be fixed to each other and fixed to the casing accurately and easily.

  In this embodiment, since the detector 110 has a double-sided telecentric optical system, high detection is possible even if both the position of the scale 102 and the position of the light receiving unit 124 are slightly shifted in the optical axis direction (Y direction). It is possible to maintain accuracy.

That is, according to the present embodiment, the linear expansion coefficient α _{LA of} the first lens array 114 and the second lens array 122 provided in the detector 110 is different from any one of the light receiving unit 124 and the scale 102 of the detector 110. However, it is possible to accurately obtain the position of the detector 110 with respect to the scale 102 while expanding the operating temperature range.

  Although the present invention has been described with reference to the first embodiment, the present invention is not limited to the first embodiment. That is, it goes without saying that improvements and design changes can be made without departing from the scope of the present invention.

  In the first embodiment, the diaphragm plate 116 is disposed between the first lens array 114 and the second lens array 122, but the present invention is not limited to this. For example, the second embodiment shown in FIG. 7A without a diaphragm may be used. In that case, the number of parts can be reduced by the absence of the diaphragm plate, and the cost of the encoder can be reduced. FIGS. 7 to 9 show how the images ImgA to ImgC of the scale 202 move when the operating temperature Tp rises compared to the temperature Ta.

  Moreover, in the said embodiment, although two, 1st lens array and 2nd lens array, were provided in the detector, this invention is not limited to this. For example, only the first lens array 314 may be used as in the third embodiment shown in FIG. In that case, the number of parts can be further reduced, and the cost of the encoder can be reduced. 10 to 12 show how the images ImgA to ImgC on the scale 302 move when the operating temperature Tp rises compared to the temperature Ta.

  In the third embodiment, the optical system of the detector is configured by only the first lens array 314. However, the present invention is not limited to this. For example, as in the fourth embodiment shown in FIG. 13A, the detector may be provided with a one-side telecentric optical system having an aperture of the diaphragm plate 416 at the focal position of the first lens array 414. In that case, the number of parts can be reduced compared to the first and second embodiments while improving the placement tolerance of the position of the scale 402 in the optical axis direction (Y direction) compared to the third embodiment, and the encoder can be reduced. It can be a cost. Note that FIGS. 13 to 15 show how the images ImgA to ImgC of the scale 402 move when the operating temperature Tp rises compared to the temperature Ta.

  Moreover, in the said embodiment, although the lens part and the light receiving element array were both three, this invention is not limited to this, What is necessary is just two or more. For example, it may be as in the fifth embodiment shown in FIG. 16 in which the lens portion and the light receiving element array are each increased by one compared to the first embodiment.

  In the fifth embodiment, the center position of the first lens array 514 and the second lens array 522 is a specific one place Xst. However, since there are four lens portions 514A to 514D (522A to 522D), the specific one place Xst is set at an intermediate position between the lens portions 514B and 514C (522B and 522C). For this reason, in any of the optical axis centers O1 to O4, the movement of the images ImgA to ImgD of the scale 502 occurs due to the change in the operating temperature Tp. Therefore, the optical phase centers O2 and O3 having a short distance from the specific one place Xst are obtained with the movement phase δφ2 using the distance 0.5L0 stored in the Li storage unit 540B. Further, for the optical axis centers O1 and O4 that are far from the specific one place Xst, the moving phase δφ1 is obtained using the distance 1.5L0 stored in the Li storage unit 540A.

  Thus, the present invention is not limited to the number of lens portions, and in the present invention, the phase shift can be eliminated by correcting the phase signal φi, and the position of the detector with respect to the scale can be obtained stably and accurately.

  In the above embodiment, the transmissive photoelectric encoder is used, but the present invention is not limited to this. For example, a reflective photoelectric encoder 600 may be configured as in the sixth embodiment shown in FIG. In FIG. 17, the depth direction in the drawing is the length measurement direction, and a plurality of lens units are provided in that direction. In FIG. 17, the detector has a double-sided telecentric optical system. However, the present invention is not limited to the telecentric optical system as long as a lens array is used.

Moreover, in the said embodiment, although phase signal (phi) i was each corrected using Formula (1) and Formula (2) and the phase shift was eliminated, this invention is not limited to this. The present invention is not limited to the equations (1) and (2), and the phase signal φi obtained from the periodic signal Fi for each light receiving element array is calculated from the operating temperature Tp of the scale and the detector and a specific one point Xst. What is necessary is just to correct | amend so that the phase shift resulting from different linear expansion coefficient (alpha) _LA may be canceled using distance Li to each optical-axis center of each lens part.

  In the above embodiment, the specific one point Xst is the center position of the lens array in the length measurement direction (X direction) and coincides with the intermediate position of the lens portion and the lens portion or the optical axis center. However, the present invention is not limited to this. For example, the lens array and the light receiving unit may be integrally fixed to the casing of the detector with the end of the lens array as a specific place Xst.

In the above embodiment, the material of the scale is glass, the material of the lens array is plastic, and the material of the light receiving part is silicon, and the respective linear expansion coefficients α _LA , α _S , α _D are respectively Although different, the present invention is not limited to this. For example, the lens array only needs to have a linear expansion coefficient α _LA different from at least one of the scale and the light receiving unit. That is, it is possible to freely select materials for the scale, the lens array, and the light receiving unit regardless of the linear expansion coefficient for the convenience of design and cost reduction of the lens array.

  In the above embodiment, the operation temperature Tp has been described as being higher than the temperature Ta, but the present invention is not limited to this. For example, the operating temperature Tp may be lower than the temperature Ta. In that case, the lens array contracts, and therefore, the sign of the temperature difference may be reversed in the above description.

  Moreover, in the said embodiment, although the temperature sensor was provided in the detector, this invention is not limited to this. For example, the temperature may be detected outside the encoder and used. Alternatively, for example, an output of a temperature sensor for a high temperature alarm provided in the encoder may be used, or a temperature sensor may be provided separately.

  Moreover, in the said embodiment, although the light receiving element array was used as a light receiving element, this invention is not limited to this. For example, the light receiving element may be configured by a combination of an index scale and a light receiving sensor that does not form an array.

  The optoelectronic encoder of the present invention extends the operating temperature range of the encoder while maintaining the accuracy of position detection even if the linear expansion coefficient of the lens array is made different from the linear expansion coefficient of the light receiving unit or the scale for cost reduction. Therefore, it can be applied to various fields where position detection is required.

100, 500, 600 ... photoelectric encoder 2, 52, 102, 202, 302, 402, 502, 602 ... scale 14, 64, 114, 214, 314, 414, 514, 614 ... first lens array 16, 116, 416, 516, 616 ... Diaphragm plate 24, 124, 224, 324, 424, 524, 624 ... Light receiving part 104, 118, 518 ... Base material 106 ... Optical grating 110, 510 ... Detector 112, 512 ... Light source
64A, 64B, 114A to 114C, 122A to 122C, 514A to 514D, 522A to 522D ... Lens part
120A to 120C, 520A to 520D ... Apertures 122, 222, 522, 622 ... Second lens array 124A to 124C, 524A to 524D ... Light receiving element array 126,526 ... Signal processing units 128A to 128C, 528A to 528D ... Amplifier circuit 130A ˜130C, 530A to 530D, interpolator 132, 532, temperature sensor 134, 534, α _S storage unit 136, 536, α _LA storage unit 138, 538, α _D storage unit 140, 540A, 540B, Li storage unit 142 , 542A, 542B ... arithmetic circuit 144 ... phase arithmetic circuit 144A, 544A, 544B ... phase addition circuit 144B, 544C, 544D ... phase subtraction circuit 146, 546 ... phase averaging circuit

Claims (8)

A scale in which optical gratings are formed at equal intervals in the length measuring direction, and a detector that is relatively displaced with respect to the scale,
The detector includes a lens array of several n (n ≧ 2) in the length measuring direction and forms an image of the scale, and an image of the scale formed for each lens unit. In a photoelectric encoder having a number n of light receiving elements for receiving light and a light receiving unit that outputs a periodic signal Fi (i = 1,..., N) according to the period of the optical grating for each light receiving element.
The lens array includes a linear expansion coefficient α _LA different from at least one of the scale and the light receiving unit,
The lens array and the light receiving unit are integrally fixed at a specific position of the lens array in the length measuring direction,
The phase signal φi obtained from the periodic signal Fi for each of the light receiving elements is respectively the operating temperature Tp of the scale and detector, the distance Li from the specific location to the center of the optical axis of each lens unit, and Is corrected so as to eliminate the phase shift caused by the different linear expansion coefficient α _LA ,
The corrected correction phase signal Cφi obtained for each light receiving element is averaged to obtain an average phase signal φav, and the average phase signal φav is used to determine the position of the detector with respect to the scale. Encoder. The distance Li from the specific location to the center of the optical axis of each lens unit, the linear expansion coefficients α _LA , α _S , α _{D of the} lens array, scale, and light receiving unit, and the operating temperature Tp From the temperature difference δT between the scale and the ambient temperature Ta of the detector when the accuracy of the detector with respect to the scale is adjusted, the moving amount dxi of the scale image on the detection unit in each lens unit is expressed by the equation ( 1),
The movement phase δφi is obtained from the period P of the periodic signal Fi with respect to the movement amount dxi by the equation (2),
Further, the phase signal φi for each light receiving element is obtained by adding or subtracting the moving phase δφi to or from the phase signal φi according to the position of the optical axis center of each lens unit with respect to the specific location. The photoelectric encoder according to claim 1, wherein each of the photoelectric encoders is corrected so as to eliminate a phase shift caused by the different linear expansion coefficient α _LA .
dxi = (2α _LA −α _S −α _D ) * Li * δT (1)
δφi = 2πdxi / P (2)   3. The photoelectric encoder according to claim 1, wherein the specific portion is coincident with an optical axis center of any one of the lens portions in the length measurement direction.   4. The photoelectric encoder according to claim 1, wherein the specific location is a center position of the lens array in the length measurement direction. 5.   5. The photoelectric encoder according to claim 1, wherein the number n of the lens portions of the lens array is three.   6. The photoelectric encoder according to claim 1, wherein a material of the scale is glass, a material of the lens array is plastic, and a material of the light receiving unit is silicon. .   The photoelectric encoder according to claim 1, wherein the detector is provided with a one-side telecentric optical system having an aperture of a diaphragm plate at a focal position of the lens array.   The detector is provided with a double-sided telecentric optical system including two lens arrays in series in the optical axis direction and a diaphragm plate aperture at a focal position between the lens arrays. The photoelectric encoder according to claim 1.