CA2118110C - Apparatus for detecting relative movement - Google Patents
Apparatus for detecting relative movement Download PDFInfo
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- CA2118110C CA2118110C CA002118110A CA2118110A CA2118110C CA 2118110 C CA2118110 C CA 2118110C CA 002118110 A CA002118110 A CA 002118110A CA 2118110 A CA2118110 A CA 2118110A CA 2118110 C CA2118110 C CA 2118110C
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- 230000000737 periodic effect Effects 0.000 claims abstract description 7
- 239000012141 concentrate Substances 0.000 claims abstract description 6
- 239000004065 semiconductor Substances 0.000 claims description 5
- HGMDNMBBCKDWTQ-UHFFFAOYSA-N 1,4-diguanidinobutane Chemical compound NC(=N)NCCCCNC(N)=N HGMDNMBBCKDWTQ-UHFFFAOYSA-N 0.000 abstract 2
- 238000000926 separation method Methods 0.000 description 7
- 238000006073 displacement reaction Methods 0.000 description 6
- 230000003287 optical effect Effects 0.000 description 3
- 238000010276 construction Methods 0.000 description 2
- 238000005286 illumination Methods 0.000 description 2
- 238000000034 method Methods 0.000 description 2
- 241000518994 Conta Species 0.000 description 1
- 238000003491 array Methods 0.000 description 1
- 230000005540 biological transmission Effects 0.000 description 1
- 230000015556 catabolic process Effects 0.000 description 1
- 238000006731 degradation reaction Methods 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 230000003993 interaction Effects 0.000 description 1
- 238000005259 measurement Methods 0.000 description 1
- 238000007493 shaping process Methods 0.000 description 1
Classifications
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01D—MEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR
- G01D5/00—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable
- G01D5/26—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light
- G01D5/32—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light
- G01D5/34—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells
- G01D5/36—Forming the light into pulses
- G01D5/38—Forming the light into pulses by diffraction gratings
Abstract
The apparatus disclosed herein employs a grating or scale (13) which concentrates light at a preselected wavelength into the positive (33) and negative (35) first orders while minimizing the zeroth order (31). The scale (13) is illuminated with monoch-romatic light of the selected wavelength and a poly-phase periodic detector (25) has its sensing plane spaced from the scale a dis-tance less than W: 2 tan .THETA. where .THETA. = arcain [.lambda.: P], where W
is the width of the illuminated region of the scale. The period of the poly-phase detector is equal to P/2 so that each detector element (51) or phase responds principally to interference between the positive and negative first orders without requiring magnification or redirection of the diffracted light. Preferably, the distance of the sensing plane from the scale (13) is greater than W: 2 tan .PSI. where .PSI. = arcsin [3.lambda.: P], so that the detector response does not include substantial components from diffraction orders higher than the first.
is the width of the illuminated region of the scale. The period of the poly-phase detector is equal to P/2 so that each detector element (51) or phase responds principally to interference between the positive and negative first orders without requiring magnification or redirection of the diffracted light. Preferably, the distance of the sensing plane from the scale (13) is greater than W: 2 tan .PSI. where .PSI. = arcsin [3.lambda.: P], so that the detector response does not include substantial components from diffraction orders higher than the first.
Description
'~V~O 93/22615 ~ PCfI US93104260 APPARATUS FOR DETECTING RELATIVE MOVEMENT
Backetround of the Invention The present invention relates to an optical instrument for measuring displacement and more .5 particularly to such an instrument which utilizes diffraction of monochromatic light from a scale or grating which is movable relative to a light source or sensing head.
A number of systems have been proposed heretofore for measuring relative displacement utilizing diffraction of light from an optical grating. Examples of such prior art systems may be seen in the Pettigrew patent 4,776,701; the I~anayama et al. patent 4,S15,S50; and the Taniguchi et al.
patent 4,676,645. A commercially ava~.lable system of this type is sold by Optra, Inc. of Beverly, MA under its trademark "Nanoscale°'. Each of these prior art systems, however, involves magnification. or separation of the different diffraction orders obtained back from the diffraction grating which are then brought back together and interfered.
Typically, fairly large numbers of optical components are required and the several components must be accurately spaced and aligned in order for the instruments to perform in accordance with their respective designs.
Among the seueral objects of the, present invention may be noted the provision of apparatus for detecting relative displacement which employs a ' 30 minimum of components; the provision of such a system in which tolerance of spacing and alignment of system ~ components is relatively great; the provision of such an apparatus which is easily manufactured; the provision of such apparatus in which sensing components can be implemented using integrated ._,,l WO 93/22615 PCT/US93/04260 a a2-circuit techniques; the provision of such apparatus which can provide measurement with high accuracy; the provision of such apparatus which is highly reliable and which is of relatively simple and inexpensive construction. Other objects and features are in part apparent and in part pointed out hereinafter.
Summary of the Invention The apparatus of the present invention utilises a scale or grating {hereafter collectively referred to as ''scale'°) which, for a preselected wavelength, concentrates diffracted light into the positive and negative first orders. The scale is relatively movable with respect to a source providing .
m~noch~omatic light of the selected wavelength and which illuminates a region of the scale having a width W along the length of the scale. A poly-phase periodic detector is spaced close to the scale so that each detector phase or element responds principally to interference between the positive and negative first orders diffracted from the scale without intermediate reflection or magnification.
~r~ef Description of the Drawings Fig. 1 is a top diagrammatic view of displacement sensing apparatus in accordance with the present invention;
Fig. 2 .is. a d=iagram illustrating, where different orders interfere in regions close to a diffraction scale employed in the apparatus of Fig. 1;
Fig. 3 is a diagrammatic illustration, with exaggerated scale spacing and diffraction angles, illustrating the operation of a periodic mufti-phase detector employed in the apparatus of Fig. 1 in relation to light diffracted from a scale or grating;
and -v .~ PC:T/US93104260 WO 93/22b~5 f ~ ;. ~ ~. ~. to _3_ Fig. 4 is a diagram of the front of the detector of Fig . 3 .
Corresponding reference characters indicate corresponding parts throughout the several views of the drawings.
Description of the Preferred Embodiment For convenience in description, Fig. 1 is described as being a top view although, as will be apparent to those skilled in the art, the apparatus can be opera~:ed in any orientation. As indicated previously, the apparatus of the present invention operates to detect or sense relative movement or displacement between a sensing head, designated generally by reference character 11, and a scale or grating 13. The sensing head 11 incorporates a monochromatic light source, preferably a semiconductor laser as indicated by reference character 15. Semiconductor laser 15 provides essentially monochromatic light having a wavelength designated a. Again, for convenience in description only, the direction of relative movement is designated the X-axis, this being along the length of the scale, while distance from the face of the scale is considered to be measured along the Y-axis.
Correspondingly, the Z-axis is considered to be vertical or orthogonal to the plane of the drawing.
The, scale 13 is ruled parallel to the Z-axis.
As will be apparent from the description following, the scale 13 employed in the embodiment illustrated operates in reflection and is tailored to concentrate light diffracted at a selected wavelength into the positive and negative first orders and to minimize the wroth order. As is understood by those skilled in the art, such a characteristic is obtained principally by employing a depth which is ~/4, i.e. a WU 93/22615 PCT/US93/Oa260 quarter wavelength, as well as by shaping the surface as is shown in Fig. 3. It should be understood that an essentially equivalent scale can be designed to operate in transmission.
Light from the semiconductor laser 15 is essentially collimated by a lens 17 and directed by a mirror 19 approxima°~ely orthogonally toward the face of the scale 13 illuminating a region 20 having a width W along the length of the scale. Light diffracted back from the scale 13 is detected by a poly-phase periodic detector 25. The period of the detector along the X-axis corresponds to the period of the interference pattern generated by interference of the positive and negative first orders diffracted from the scale 13 and is thus equal to P/2. The width of the active area of the detector 25 is preferably substantially smaller than the width of the illuminated region on the scale 13. While the detector 25 is shown as though being in the path of the light beam proceeding from the mirror 15 to the scale 13, it can in fact be located above or below the beam since exact orthogonality of the beam to the scale surface in the Z direction is not required.
Referring now to Fig. 2, a region of width W
along the length of the scale 13 is illuminated by the beam from the laser light source. The zeroth order is reflected essentially directly back, this beam being ~.nc~ica~ed by reference character 31. The, positive first order is illustrated as being diffracted at an angle 8 to the right, this beam being indicated by reference character 33 while the negative first order, designated by reference character 35, is diffracted to the left by the same angle. As is understood by those skilled in the art, the angle ~ is equal to arcsin (a/P) where P is the period of the scale along the X-axis.
W~ 93/22615 ~ ~ ~ ~ ~ ~ ~f PLT/US93/04260 As may be seen, there exists a triangular region, designated by reference character 37, where the positive and negative first orders will interfere directly without any intermediate reflection or magnification. This region extends to a distance from the scale equal to W/(2 tan ~) and may be considered a region of near field interference. To avoid confusion with the term "near field interference" in the Fresnel interference sense, the region of interference utilized in the present invention is more accurately described as a "pre-separation" interference, i.e. interference before the plus and minus orders diverge. In this region, the plus and minus orders interfere directly. In accordance with the present invention, the detector is located within this region.
While the characteristics can be tailored to substantially eliminate the zeroth and even orders of diffraction from the scale 13, some appreciable 20 energy will typically remain in the odd orders. With reference to Fig. 2, the positive and negative third order beams are designated by reference characters 41 and 43, respectively. As is understood by those skilled in the art, the angle from normal at which 25 each of these beams depart is cp where rp = arcsin (3~/P). There correspondingly exists a triangular region of pre-separation interference, this region being designated by reference character 47. This region extends from the scale for a distance of W
Backetround of the Invention The present invention relates to an optical instrument for measuring displacement and more .5 particularly to such an instrument which utilizes diffraction of monochromatic light from a scale or grating which is movable relative to a light source or sensing head.
A number of systems have been proposed heretofore for measuring relative displacement utilizing diffraction of light from an optical grating. Examples of such prior art systems may be seen in the Pettigrew patent 4,776,701; the I~anayama et al. patent 4,S15,S50; and the Taniguchi et al.
patent 4,676,645. A commercially ava~.lable system of this type is sold by Optra, Inc. of Beverly, MA under its trademark "Nanoscale°'. Each of these prior art systems, however, involves magnification. or separation of the different diffraction orders obtained back from the diffraction grating which are then brought back together and interfered.
Typically, fairly large numbers of optical components are required and the several components must be accurately spaced and aligned in order for the instruments to perform in accordance with their respective designs.
Among the seueral objects of the, present invention may be noted the provision of apparatus for detecting relative displacement which employs a ' 30 minimum of components; the provision of such a system in which tolerance of spacing and alignment of system ~ components is relatively great; the provision of such an apparatus which is easily manufactured; the provision of such apparatus in which sensing components can be implemented using integrated ._,,l WO 93/22615 PCT/US93/04260 a a2-circuit techniques; the provision of such apparatus which can provide measurement with high accuracy; the provision of such apparatus which is highly reliable and which is of relatively simple and inexpensive construction. Other objects and features are in part apparent and in part pointed out hereinafter.
Summary of the Invention The apparatus of the present invention utilises a scale or grating {hereafter collectively referred to as ''scale'°) which, for a preselected wavelength, concentrates diffracted light into the positive and negative first orders. The scale is relatively movable with respect to a source providing .
m~noch~omatic light of the selected wavelength and which illuminates a region of the scale having a width W along the length of the scale. A poly-phase periodic detector is spaced close to the scale so that each detector phase or element responds principally to interference between the positive and negative first orders diffracted from the scale without intermediate reflection or magnification.
~r~ef Description of the Drawings Fig. 1 is a top diagrammatic view of displacement sensing apparatus in accordance with the present invention;
Fig. 2 .is. a d=iagram illustrating, where different orders interfere in regions close to a diffraction scale employed in the apparatus of Fig. 1;
Fig. 3 is a diagrammatic illustration, with exaggerated scale spacing and diffraction angles, illustrating the operation of a periodic mufti-phase detector employed in the apparatus of Fig. 1 in relation to light diffracted from a scale or grating;
and -v .~ PC:T/US93104260 WO 93/22b~5 f ~ ;. ~ ~. ~. to _3_ Fig. 4 is a diagram of the front of the detector of Fig . 3 .
Corresponding reference characters indicate corresponding parts throughout the several views of the drawings.
Description of the Preferred Embodiment For convenience in description, Fig. 1 is described as being a top view although, as will be apparent to those skilled in the art, the apparatus can be opera~:ed in any orientation. As indicated previously, the apparatus of the present invention operates to detect or sense relative movement or displacement between a sensing head, designated generally by reference character 11, and a scale or grating 13. The sensing head 11 incorporates a monochromatic light source, preferably a semiconductor laser as indicated by reference character 15. Semiconductor laser 15 provides essentially monochromatic light having a wavelength designated a. Again, for convenience in description only, the direction of relative movement is designated the X-axis, this being along the length of the scale, while distance from the face of the scale is considered to be measured along the Y-axis.
Correspondingly, the Z-axis is considered to be vertical or orthogonal to the plane of the drawing.
The, scale 13 is ruled parallel to the Z-axis.
As will be apparent from the description following, the scale 13 employed in the embodiment illustrated operates in reflection and is tailored to concentrate light diffracted at a selected wavelength into the positive and negative first orders and to minimize the wroth order. As is understood by those skilled in the art, such a characteristic is obtained principally by employing a depth which is ~/4, i.e. a WU 93/22615 PCT/US93/Oa260 quarter wavelength, as well as by shaping the surface as is shown in Fig. 3. It should be understood that an essentially equivalent scale can be designed to operate in transmission.
Light from the semiconductor laser 15 is essentially collimated by a lens 17 and directed by a mirror 19 approxima°~ely orthogonally toward the face of the scale 13 illuminating a region 20 having a width W along the length of the scale. Light diffracted back from the scale 13 is detected by a poly-phase periodic detector 25. The period of the detector along the X-axis corresponds to the period of the interference pattern generated by interference of the positive and negative first orders diffracted from the scale 13 and is thus equal to P/2. The width of the active area of the detector 25 is preferably substantially smaller than the width of the illuminated region on the scale 13. While the detector 25 is shown as though being in the path of the light beam proceeding from the mirror 15 to the scale 13, it can in fact be located above or below the beam since exact orthogonality of the beam to the scale surface in the Z direction is not required.
Referring now to Fig. 2, a region of width W
along the length of the scale 13 is illuminated by the beam from the laser light source. The zeroth order is reflected essentially directly back, this beam being ~.nc~ica~ed by reference character 31. The, positive first order is illustrated as being diffracted at an angle 8 to the right, this beam being indicated by reference character 33 while the negative first order, designated by reference character 35, is diffracted to the left by the same angle. As is understood by those skilled in the art, the angle ~ is equal to arcsin (a/P) where P is the period of the scale along the X-axis.
W~ 93/22615 ~ ~ ~ ~ ~ ~ ~f PLT/US93/04260 As may be seen, there exists a triangular region, designated by reference character 37, where the positive and negative first orders will interfere directly without any intermediate reflection or magnification. This region extends to a distance from the scale equal to W/(2 tan ~) and may be considered a region of near field interference. To avoid confusion with the term "near field interference" in the Fresnel interference sense, the region of interference utilized in the present invention is more accurately described as a "pre-separation" interference, i.e. interference before the plus and minus orders diverge. In this region, the plus and minus orders interfere directly. In accordance with the present invention, the detector is located within this region.
While the characteristics can be tailored to substantially eliminate the zeroth and even orders of diffraction from the scale 13, some appreciable 20 energy will typically remain in the odd orders. With reference to Fig. 2, the positive and negative third order beams are designated by reference characters 41 and 43, respectively. As is understood by those skilled in the art, the angle from normal at which 25 each of these beams depart is cp where rp = arcsin (3~/P). There correspondingly exists a triangular region of pre-separation interference, this region being designated by reference character 47. This region extends from the scale for a distance of W
2 tan ~p Preferably, the detector 25 is located further from the scale than the region of pre-separation interference from the positive and negative third i%VO 93/22615 PCT/US93/04260 orders so that the signals obtained correspond most closely with the sine wave characteristic of the pure first order interference pattern. Preferably, the detector 25 is located just outside of the apex of the region 47 so as to allow maximum detectar width.
As will be apparent, the whole active area of the detector should be within the region of the desired interference .
In view of this explanation, it can be seen that it is desirable that the designed width of the illuminated region 20 correspond to the designed spacing of the sensing plane from the diffraction scale. lHowever, it should be understood that illumination beyond the designed width does not prevent the desired interference but, rather, only allows some contribution from higher diffraction orders since portions of a broadened region of illumination may allow light leaving at a larger diffraction angle to reach the detector. Thus, the problem of mismatching of illuminated region width to _ detector spacing is more in the nature of a gradual degradation rather than a failure to function as intended. Thus, it is a feature of the design of the present invention that spacing is not highly critical.
As indicated previously, the width of the active area of the detector 25 is smaller than the width of the illuminated region on the scale. Thus, as illustrated in Fig. 3, positive (first older diffraction from a region on the left hand side of the region 20 can meet and interfere with negative first order diffracted light from a zone on the right hand side of the region 20 and the meeting light components can interfere at the sensing plane of the detector 25.
WO 93!22615 ~ ~ ~' ~ '9 ~ Ptr't'f'/U593/0426ti _7_ As indicated, the dimensions and angles are exaggerated in Figures 2 and 3 for the purpose of explanation. Dimensions and angles for a practical design may, far example be as follows. The light source is a semiconductor laser providing light at a wavelength of 780 nanometers. The scale 13 is ruled at 424 lines per inch (16.64 lines per millimeter) so that the period P is 60 microns. Accordingly, the angle of first order diffraction a is 1.7 degrees, 20 and the angle of third order diffraction cp is 2.2 degrees. Assuming that the width of the illuminated region is 1.0 millimeter, the pre-separation .first order region of interference extends 38.5 millimeters from the scale while the pre-separation third order region of interference extends 12.8 millimeters from the scale.
As is understood by those skilled in the art, the pattern of light intensity produced by interference of the positive and negative first order diffraction components will have a periodicity which is twice that of the scale itself. The detector 25 is constructed to have a matching periodicity, i.e.
P/2 so that the contributions from the several elements in each phase of the detector combine additively. Preferably, the detector 25 is constructed as an integrated circuit comprising an array of narrow elongate photodiodes. Such an array of photodiades,is illustrated in Fig.,4. The individual photodiodes are indicated by reference character 51. As indicated previously, the array should be poly-phased. For example, two arrays providing Quadrature signals could define the relative displacement. An arrangement simpler to~
fabricate can be implemented by offsetting the two phases in the Z-axis direction so as to simplify the interconnection of the various photodetector WO 9312261 S ' P(.'T/ US93/0426U ~ ' _$_ elements. Another alternative is to employ relatively large area photodetectors, each of which is provided with a respective mask for admitting light of the appropriate phase. Again, while this construction is simpler to implement, it is less efficient in the utilization of the available light energy.
A still further alternative is to provide a lenticular screen at the sensing plane which disperses the different phases at different angles after interference at the sensing plane so that spaced apart detectors can be utilized. The .
lenticular screen will thus have a periodicity of P/2 along the X-axis. Tn this case, the photo--electric Z5 detectors themselves need not be placed within the so-called region of pre-separation interference 37 but, rather, the sensing plane and the point of interference is at the lenticular screen which is within the region.
Similarly, while it is preferable that pure first order~interference be achieved so as to provide the purest possible sinewave out of each of the detector phases, some interference by other orders will not be overly objectionable in some applications and, by use of matching pattern tables, sufficiently accurate interpolations may be provided.
While the embodiment disclosed by way of example provides for sensing along a single axis, it should be understood that the technique of the present invention can be applied to a combined two-axis sensing device by utilizing a scale ruled in orthogonal directions, together with a respective detector for each direction. A single light source can serve both axes. Due to the orthogonality, there will be minimal interaction between movement along WO 93/22615 ,~ ,~ ~, V ~ ~ ~ PC ('/LJS93/04260 _g_ one axis with the sensing signals generated by movement along the other axis.
If the detectors and gratings are properly shaped to provide matching curvatures for the diffracted signal, or sufficiently narrow gratings were used, this invention can be effectively applied to a rotary encoder.
In view of the foregoing it may be seen that several objects of the present invention are achieved and other advantageous results have been atta9~ned.
As various changes could be made in the above constructians without departing from the scope of the invention, it should be understood that all mcitter conta~.ned in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.
As will be apparent, the whole active area of the detector should be within the region of the desired interference .
In view of this explanation, it can be seen that it is desirable that the designed width of the illuminated region 20 correspond to the designed spacing of the sensing plane from the diffraction scale. lHowever, it should be understood that illumination beyond the designed width does not prevent the desired interference but, rather, only allows some contribution from higher diffraction orders since portions of a broadened region of illumination may allow light leaving at a larger diffraction angle to reach the detector. Thus, the problem of mismatching of illuminated region width to _ detector spacing is more in the nature of a gradual degradation rather than a failure to function as intended. Thus, it is a feature of the design of the present invention that spacing is not highly critical.
As indicated previously, the width of the active area of the detector 25 is smaller than the width of the illuminated region on the scale. Thus, as illustrated in Fig. 3, positive (first older diffraction from a region on the left hand side of the region 20 can meet and interfere with negative first order diffracted light from a zone on the right hand side of the region 20 and the meeting light components can interfere at the sensing plane of the detector 25.
WO 93!22615 ~ ~ ~' ~ '9 ~ Ptr't'f'/U593/0426ti _7_ As indicated, the dimensions and angles are exaggerated in Figures 2 and 3 for the purpose of explanation. Dimensions and angles for a practical design may, far example be as follows. The light source is a semiconductor laser providing light at a wavelength of 780 nanometers. The scale 13 is ruled at 424 lines per inch (16.64 lines per millimeter) so that the period P is 60 microns. Accordingly, the angle of first order diffraction a is 1.7 degrees, 20 and the angle of third order diffraction cp is 2.2 degrees. Assuming that the width of the illuminated region is 1.0 millimeter, the pre-separation .first order region of interference extends 38.5 millimeters from the scale while the pre-separation third order region of interference extends 12.8 millimeters from the scale.
As is understood by those skilled in the art, the pattern of light intensity produced by interference of the positive and negative first order diffraction components will have a periodicity which is twice that of the scale itself. The detector 25 is constructed to have a matching periodicity, i.e.
P/2 so that the contributions from the several elements in each phase of the detector combine additively. Preferably, the detector 25 is constructed as an integrated circuit comprising an array of narrow elongate photodiodes. Such an array of photodiades,is illustrated in Fig.,4. The individual photodiodes are indicated by reference character 51. As indicated previously, the array should be poly-phased. For example, two arrays providing Quadrature signals could define the relative displacement. An arrangement simpler to~
fabricate can be implemented by offsetting the two phases in the Z-axis direction so as to simplify the interconnection of the various photodetector WO 9312261 S ' P(.'T/ US93/0426U ~ ' _$_ elements. Another alternative is to employ relatively large area photodetectors, each of which is provided with a respective mask for admitting light of the appropriate phase. Again, while this construction is simpler to implement, it is less efficient in the utilization of the available light energy.
A still further alternative is to provide a lenticular screen at the sensing plane which disperses the different phases at different angles after interference at the sensing plane so that spaced apart detectors can be utilized. The .
lenticular screen will thus have a periodicity of P/2 along the X-axis. Tn this case, the photo--electric Z5 detectors themselves need not be placed within the so-called region of pre-separation interference 37 but, rather, the sensing plane and the point of interference is at the lenticular screen which is within the region.
Similarly, while it is preferable that pure first order~interference be achieved so as to provide the purest possible sinewave out of each of the detector phases, some interference by other orders will not be overly objectionable in some applications and, by use of matching pattern tables, sufficiently accurate interpolations may be provided.
While the embodiment disclosed by way of example provides for sensing along a single axis, it should be understood that the technique of the present invention can be applied to a combined two-axis sensing device by utilizing a scale ruled in orthogonal directions, together with a respective detector for each direction. A single light source can serve both axes. Due to the orthogonality, there will be minimal interaction between movement along WO 93/22615 ,~ ,~ ~, V ~ ~ ~ PC ('/LJS93/04260 _g_ one axis with the sensing signals generated by movement along the other axis.
If the detectors and gratings are properly shaped to provide matching curvatures for the diffracted signal, or sufficiently narrow gratings were used, this invention can be effectively applied to a rotary encoder.
In view of the foregoing it may be seen that several objects of the present invention are achieved and other advantageous results have been atta9~ned.
As various changes could be made in the above constructians without departing from the scope of the invention, it should be understood that all mcitter conta~.ned in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.
Claims (6)
1. Apparatus for detecting relative movement comprising a diffraction scale relatively movable with respect to a source of light and having a period P and a characteristic which concentrates light diffracted at a preselected wavelength .lambda. into the positive and negative first orders;
means for illuminating with light of wavelength .lambda. a region of said scale having a width W along the length of the scale;
a periodic detector having a sensing plane spaced from said scale a distance less than where .theta. = arcsin (.lambda./P) the period of said detector being equal to P/2 whereby said detector responds principally to interference at said sensing plane between the positive and negative first orders diffracted from said scale.
means for illuminating with light of wavelength .lambda. a region of said scale having a width W along the length of the scale;
a periodic detector having a sensing plane spaced from said scale a distance less than where .theta. = arcsin (.lambda./P) the period of said detector being equal to P/2 whereby said detector responds principally to interference at said sensing plane between the positive and negative first orders diffracted from said scale.
2. Apparatus as set forth in claim 1 wherein said sensing plane is spaced from said scale a distance greater than where .PSI. = arcsin (3.lambda./P)
3. Apparatus for detecting relative movement comprising;
a source of monochromatic light of wavelength .lambda.;
a reflection diffraction scale relatively movable with respect to said source and having a period P and a characteristic which concentrates light diffracted at said wavelength .lambda. into the positive and negative first orders and which minimizes the zeroth order;
means for directing light from said source onto a region of said scale having a width W along the length of the scale;
a poly-phase periodic detector having a sensing plane spaced from said scale a distance less than where .theta. = arcsin the period of said detector being equal to P/2 whereby said detector responds principally to interference at said sensing plane between the positive and negative first orders diffracted from said scale.
a source of monochromatic light of wavelength .lambda.;
a reflection diffraction scale relatively movable with respect to said source and having a period P and a characteristic which concentrates light diffracted at said wavelength .lambda. into the positive and negative first orders and which minimizes the zeroth order;
means for directing light from said source onto a region of said scale having a width W along the length of the scale;
a poly-phase periodic detector having a sensing plane spaced from said scale a distance less than where .theta. = arcsin the period of said detector being equal to P/2 whereby said detector responds principally to interference at said sensing plane between the positive and negative first orders diffracted from said scale.
4. Apparatus as set forth in claim 3 wherein said detector comprises an array of parallel elongate photodiodes.
5. Apparatus as set forth in claim 3 wherein said sensing plane is spaced from said scale a distance greater than where .PHI. = arcsin
6. Apparatus for detecting relative movement comprising:
a semiconductor laser providing monochromatic light of wavelength .lambda.;
an elongate reflective diffraction scale longitudinally relatively movable with respect to said laser, said scale being ruled transversely to its length with a period P and a characteristic which concentrates light diffracted at said wavelength .lambda.
into the positive and negative first orders and which minimizes the zeroth order;
means for directing light from said laser onto a region of said scale having a width W along the length of the scale;
a plurality of elongate photoelectric detectors arranged in a planer parallel array spaced from said scale a distance less than where .THETA. = arcsin said detectors being interconnected in a periodic multiphase array with the period being equal to P/2 whereby said detector responds principally to interference at said sensing plane between the positive and negative first orders diffracted from said scale.
a semiconductor laser providing monochromatic light of wavelength .lambda.;
an elongate reflective diffraction scale longitudinally relatively movable with respect to said laser, said scale being ruled transversely to its length with a period P and a characteristic which concentrates light diffracted at said wavelength .lambda.
into the positive and negative first orders and which minimizes the zeroth order;
means for directing light from said laser onto a region of said scale having a width W along the length of the scale;
a plurality of elongate photoelectric detectors arranged in a planer parallel array spaced from said scale a distance less than where .THETA. = arcsin said detectors being interconnected in a periodic multiphase array with the period being equal to P/2 whereby said detector responds principally to interference at said sensing plane between the positive and negative first orders diffracted from said scale.
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US87849492A | 1992-05-05 | 1992-05-05 | |
| US07/878,494 | 1992-05-05 | ||
| PCT/US1993/004260 WO1993022615A1 (en) | 1992-05-05 | 1993-05-04 | Apparatus for detecting relative movement |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2118110A1 CA2118110A1 (en) | 1993-11-11 |
| CA2118110C true CA2118110C (en) | 2002-08-13 |
Family
ID=25372143
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002118110A Expired - Fee Related CA2118110C (en) | 1992-05-05 | 1993-05-04 | Apparatus for detecting relative movement |
Country Status (7)
| Country | Link |
|---|---|
| US (1) | US5559600A (en) |
| EP (1) | EP0639259B1 (en) |
| JP (1) | JP3390440B2 (en) |
| AT (1) | ATE182677T1 (en) |
| CA (1) | CA2118110C (en) |
| DE (1) | DE69325799T2 (en) |
| WO (1) | WO1993022615A1 (en) |
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-
1993
- 1993-05-04 DE DE69325799T patent/DE69325799T2/en not_active Expired - Lifetime
- 1993-05-04 CA CA002118110A patent/CA2118110C/en not_active Expired - Fee Related
- 1993-05-04 JP JP51961993A patent/JP3390440B2/en not_active Expired - Fee Related
- 1993-05-04 EP EP93911085A patent/EP0639259B1/en not_active Expired - Lifetime
- 1993-05-04 AT AT93911085T patent/ATE182677T1/en not_active IP Right Cessation
- 1993-05-04 WO PCT/US1993/004260 patent/WO1993022615A1/en active IP Right Grant
-
1995
- 1995-02-01 US US08/383,700 patent/US5559600A/en not_active Expired - Lifetime
Also Published As
| Publication number | Publication date |
|---|---|
| EP0639259B1 (en) | 1999-07-28 |
| DE69325799D1 (en) | 1999-09-02 |
| WO1993022615A1 (en) | 1993-11-11 |
| DE69325799T2 (en) | 2000-04-13 |
| EP0639259A4 (en) | 1997-11-05 |
| EP0639259A1 (en) | 1995-02-22 |
| JP3390440B2 (en) | 2003-03-24 |
| US5559600A (en) | 1996-09-24 |
| ATE182677T1 (en) | 1999-08-15 |
| JPH07506669A (en) | 1995-07-20 |
| CA2118110A1 (en) | 1993-11-11 |
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| Date | Code | Title | Description |
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| EEER | Examination request | ||
| MKLA | Lapsed |