Abstract:
A photoelectric encoder is provided which has an optical system including a first lens array inserted between a main scale and a light receiving element. An image divided or reversed by the first lens array can be electrically or optically re-reversed. This can achieve the reduction of the entire size as well as increase in the scale field of view, while maintaining the image shape and/or pattern.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
   The disclosure of Japanese Patent Application No. 2005-69579 filed on Mar. 11, 2005 including specifications, drawings and claims is incorporated herein by reference in its entirety. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a photoelectric encoder. In particular, the invention relates to improvements in a photoelectric encoder that has a telecentric optical system wherein a lens and an aperture are inserted between a main scale and a light receiving element. 
   2. Description of the Related Art 
   As described in Japanese Patent Laid-Open Publication No. 2004-264295 and as shown in  FIG. 1 , a photoelectric encoder is designed in which a lens optical system (telecentric optical system)  40 , comprising a lens  42  and an aperture  44  that functions as a telecentric optical diaphragm, is inserted between a main scale  20  and a light receiving element array  34  constituting a light receiving unit  30 , for example, and as shown in  FIG. 2  this lens optical system can set the magnification by adjusting the distances a and b between the lens  42  and the scale  21  of the main scale  20  and between the lens  42  and the light receiving element  35  on the light receiving element array  34 , respectively. In  FIG. 1 , the reference numeral  10  denotes a light source and the reference symbol f denotes a focal length of the lens  42 . 
   In the photoelectric encoder that uses this telecentric optical system  40 , an image on the main scale  20  is made pass through the lens optical system ( 42 ,  44 ) and is projected onto the light receiving element array  34 . Here, by positioning the aperture  44  at the focal position of the lens  42 , even when the distance (gap) between the main scale  20  and the lens  42  changes, fluctuations in the magnification of the image formed on the light receiving element array  34  can be controlled if the positional relationship between the lens  42 , the aperture  44 , and the light receiving element array  34  does not change. 
   In particular, when the lens array  46  is used as the lens  42  as shown in  FIG. 3  (light path view) and  FIG. 4  (perspective view), the entire size can be made smaller and the scale field of view (FOV) can be increased. 
   As shown in  FIG. 3  and  FIG. 5 , however, when a photoelectric encoder employs the lens array  46 , there was a problem in which the image was divided and reversed in each single lens optical system. 
   This is a problem with not only image patterns but is an especially serious problem with absolute types which are required to reproduce accurate shapes. 
   SUMMARY OF THE INVENTION 
   In view of the foregoing problems, various embodiments of this invention provide an incremental type photoelectric encoder that can maintain image patterns (a first object). 
   Furthermore, various embodiments of this invention also provide a photoelectric encoder that can maintain not only image patterns but also shapes (a second object). 
   The present invention achieves the first object by providing an incremental type photoelectric encoder that has a first lens array inserted between a main scale and a light receiving element, and wherein pitches of the respective lenses are brought into agreement with a period of the main scale or natural number multiple thereof. 
   The present invention achieves the second object by providing a photoelectric encoder that has a first lens array inserted between a main scale and a light receiving element, and wherein a second lens array with a set pitch of lenses identical to the first lens array, and a third lens array that optically re-reverses the light emitted from the second lens array are provided. 
   The focal position of each lens of the third lens array is smaller than the focal position of each lens of the first and second lens array to shorten the entire optical length. 
   The present invention also achieves the second object by providing a photoelectric encoder that has a first lens array inserted between a main scale and a light receiving element, and wherein connection of outputs of a light receiving element array is changed to electrically re-reverse an image that has been divided and reversed by the first lens array. 
   The present invention achieves the second object by providing a photoelectric encoder that has a first lens array inserted between a main scale and a light receiving element, and wherein a second lens array with a set pitch of lenses identical to the first lens array, and a plurality of small mirrors with a set pitch identical to that of respective lenses of the first lens array are provided to optically re-reverse an image that has been divided and reversed by the first lens array, by the small mirrors. 
   The present invention achieves the second object by providing a photoelectric encoder that has a first lens array inserted between a main scale and a light receiving element, and wherein a second lens array with a set pitch of lenses identical to the first lens array, a mirror for making light emitted from the second lens array again be incident on the second lens array, and a half mirror for extracting the light passing through the first and second lens arrays towards a direction of the light receiving element are provided to optically re-reverse an image that has been divided and reversed by the first lens array, by the mirror. 
   The lens array may be a two-dimensional lens array to perform two-dimensional measurements. 
   Further, aperture may be provided at focal position of each lens to cut light from neighbor lens. 
   According to the present invention, image patterns in an incremental type photoelectric encoder can be maintained by bringing the set pitches of respective lenses of a lens array into agreement with the period of the main scale or natural number multiple thereof. 
   Image shapes can also be maintained by electrically or optically re-reversing the image reversed by a lens array. The photoelectric encoder can be applied not only to incremental types but also to absolute types. 
   These and other novel features and advantages of the present invention will become apparent from the following detailed description of preferred embodiments. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The preferred embodiments will be described with reference to the drawings, wherein like elements have been denoted throughout the figures with like reference numerals, and wherein; 
       FIG. 1  is a perspective view showing the essential components of a photoelectric encoder that uses a telecentric optical system; 
       FIG. 2  is a plan view of the same photoelectric encoder; 
       FIG. 3  is a light path view showing conventional problems; 
       FIG. 4  is a perspective view of  FIG. 3 ; 
       FIG. 5  is a plan view of  FIG. 3 ; 
       FIG. 6  is a light path view showing essential components of a first embodiment of the present invention; 
       FIG. 7  shows the principle of the present invention; 
       FIG. 8  is a modification of the first embodiment; 
       FIG. 9  is a light path view showing essential components of a second embodiment of the present invention; 
       FIG. 10  is a perspective view of  FIG. 9 ; 
       FIG. 11  is a modification of the second embodiment. 
       FIG. 12  is a perspective view of  FIG. 11 ; 
       FIG. 13  is a light path view showing essential components of a third embodiment of the present invention; 
       FIG. 14  is a modification of the third embodiment; 
       FIG. 15  is a light path view showing essential components of a fourth embodiment of the present invention; 
       FIG. 16  is a modification of the fourth embodiment; 
       FIG. 17  is a light path view showing essential components of a fifth embodiment of the present invention; 
       FIG. 18  is a modification of the fifth embodiment; 
       FIG. 19  is a light path view showing essential components of a sixth embodiment of the present invention; 
       FIG. 20  is a modification of the sixth embodiment; 
       FIG. 21  is a light path view showing essential components of a seventh embodiment of the present invention; 
       FIG. 22  is a light path view showing essential components of a eighth embodiment of the present invention; 
       FIG. 23  is a light path view showing essential components of a ninth embodiment of the present invention; 
       FIG. 24  is a modification of the ninth embodiment; 
       FIG. 25  is a light path view showing essential components of a tenth embodiment of the present invention; and 
       FIG. 26  is a modification of the tenth embodiment. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   In the following, embodiments of the present invention will be described in detail with reference to the drawings. 
   As shown in  FIG. 6 , according to a first embodiment of the present invention, an incremental type photoelectric encoder has a lens array  46 . The lens array  46  is composed of a plurality of lenses with a set pitch P 1  (referred to as “lens pitch”) which is brought into agreement with a period Ps of a main scale  20  or natural number multiple thereof. 
   As shown in  FIG. 7 , in the present embodiment since the pattern is ensured even if the image is divided and reversed in each separate lens, there is no problem as long as it is used as an incremental type. 
   Further, as shown in  FIG. 8 , aperture  44  can be provided at focal point of each lens of the lens allay  46  so as to form a telecentric optical system  40 . 
   Next, a second embodiment of the present invention will be described with reference to  FIG. 9  (light path view) and  FIG. 10  (perspective view). 
   In the present embodiment, a second lens array  48  identical to the lens array  46  (first lens array) is provided in the reverse direction so as to make the focal points thereof be positioned at the positions where the focal points of the first lens array  46  are located, thereby forming an optical system  50 . 
   In the present embodiment, the lens array  48  is the same as the lens array  46 . Because of this, aberrations occurring on the first lens array  46  provided on the input side can be almost completely inversely corrected by the second lens array  48  provided on the output side. Therefore, even if a low-cost lens array with large aberrations is used, the aberrations can be almost completely cancelled and the signal detection efficiency can be greatly improved. 
   Further, as shown in  FIGS. 11 and 12 , aperture  44  can be provided at focal point of each lens of the lens allays  46  and  48  so as to form a bilateral telecentric optical system  51 . 
   Next, a third embodiment of the present invention will be described with reference to  FIG. 13 . 
   The present embodiment relates to an absolute type photoelectric encoder that has a lens array  46 . In this photoelectric encoder, an image is electrically re-reversed by changing the output connection of a light receiving element array  34  by the pixels. 
   Further, as shown in  FIG. 14 , aperture  44  can be provided at focal point of each lens of the lens allay  46  so as to form a telecentric optical system  40 . 
   Next, a fourth embodiment of the present invention will be described with reference to  FIG. 15 . 
   The present embodiment relates to an absolute type photoelectric encoder that has an optical system  50  composed of lens arrays  46  and  48 . In this photoelectric encoder, an image is electrically re-reversed by changing the output connection of a light receiving element array  34  by the pixels. 
   An absolute type encoder can be realized according to the third and fourth embodiments without forming a complicated optical system. 
   Further, as shown in  FIG. 16 , the optical system  50  can be made as a bilateral telecentric optical system  51  which has aperture  44  disposed at focal point of each lens of the lens allays  46  and  48 . 
   Next, a fifth embodiment of the present invention will be described with reference to  FIG. 17 . 
   The present embodiment relates to an absolute type photoelectric encoder that has an optical system  50  composed of lens arrays  46  and  48 . This photoelectric encoder is further provided with a third lens array  52  identical to the first and second lens arrays  46  and  48  on the output side of the optical system  50 , thereby optically re-reversing an image. 
   Further, as shown in  FIG. 18 , the optical system  50  can be made as a bilateral telecentric optical system  51  which has aperture  44  disposed at focal point of each lens of the lens allays  46  and  48 . Further, aperture  54  may be disposed at focal point of each lens of the lens allay  52 . 
   Next, a sixth embodiment of the present invention will be described with reference to  FIG. 19 . 
   The present embodiment relates to an absolute type photoelectric encoder that has an optical system  50  composed of lens arrays  46  and  48 . This photoelectric encoder is further provided with an optical system  60  on the output side of the optical system  50 , thereby optically re-reversing an image. The optical system  60  has the same composition as the optical system  50  and contains a third lens array  52  and a fourth lens array  56 . 
   Because the same optical systems are used on the input side and the output side in this embodiment, the components can be shared. 
   Further, as shown in  FIG. 20 , the optical system  50  can be made as a bilateral telecentric optical system  51  which has aperture  44  disposed at focal point of each lens of the lens allays  46  and  48  and the optical system  60  can be made as a bilateral telecntric optical system  61  which has aperture  54  disposed at focal point of each lens of the lens allays  52  and  56 . 
   Next, a seventh embodiment of the present invention will be described with reference to  FIG. 21 . 
   The present embodiment employs the same photoelectric encoder as that in the fifth embodiment shown in  FIG. 18 . In this embodiment, the focal length f′ of the third lens array  52  is made smaller than the focal length f of the first and second lens arrays  46  and  48 , thereby shortening the entire optical length. While ensuring the air gap between the main scale  20  and the input side lens array  46 , the size of the photoelectric encoder can be reduced. 
   In other words, if the distance (equivalent to air gap) between the main scale  20  and the input side lens array  46  is equal to the focal length f of the input side lens array  46 , the entire optical length in the seventh embodiment will be L′=4f+4f′&lt;8f and the entire optical length can be shortened in this embodiment. This is in contrast to the entire optical length L nearly equal to 8f when the first to third lens arrays are composed of the same lenses as in the fifth embodiment. 
   Next, an eighth embodiment of the present invention will be described with reference to  FIG. 22 . 
   The present embodiment employs the same photoelectric encoder as that in the sixth embodiment shown in  FIG. 20 . In this embodiment, the focal length f′ of the third and fourth lens arrays  52  and  56  is made smaller than the focal length f of the first and second lens arrays  46  and  48 , thereby shortening the entire optical length. While ensuring the air gap between the main scale  20  and the input side lens array  46 , the size of the photoelectric encoder can be reduced. 
   In other words, if the distance (equivalent to air gap) between the main scale  20  and the input side lens array  46  is equal to the focal length f of the input side lens array  46 , the entire optical length in the eighth embodiment will be L′=4f+4f′&lt;8f and the entire optical length can be shortened in this embodiment. This is in contrast to the entire optical length L nearly equal to 8f when the first to fourth lens arrays are composed of the same lenses as in the sixth embodiment. 
   Next, a ninth embodiment of the present invention will be described with reference to  FIG. 23 . 
   The present embodiment relates to an absolute type photoelectric encoder that has an optical system  50  composed of lens arrays  46  and  48 . This photoelectric encoder is further provided with a plurality of small mirrors  70 , thereby optically re-reversing an image. The small mirrors  70  are arranged with a set pitch identical to each lens of the lens arrays  46  and  48 . 
   Further, as shown in  FIG. 24 , the optical system  50  can be made as a bilateral telecntric optical system  51  which has aperture  44  provided at focal point of each lens of the lens allays  46  and  48 . 
   Next, a tenth embodiment of the present invention will be described with reference to  FIG. 25 . 
   The present embodiment relates to an absolute type photoelectric encoder that has an optical system  50  composed of lens arrays  46  and  48 . This photoelectric encoder is further provided with a mirror  80  and a half mirror  82 , thereby optically re-reversing an image. The mirror  80  functions to reflect light emitted from the output side of the lens array  48  towards the optical system  50  for re-entering. The half mirror  82  functions to extract light that has passed through the optical system  50  two times towards a light receiving array  34 . 
   Further, as shown in  FIG. 26 , the optical system  50  can be made as a bilateral telecentric optical system  51  which has aperture  44  provided at focal point of each lens of the lens allays  46  and  48 . 
   Not only can the third to tenth embodiments be applied to an absolute type but also to an incremental type. 
   The present invention can be applied to a photoelectric encoder with separately formed index grid and light receiving element as well as to a photoelectric encoder that has a light receiving element integrally formed with these. Furthermore, not only can the present invention be applied to a transmission type encoder but also to a reflecting type encoder. 
   It should be apparent to those skilled in the art that the above-described embodiments are merely illustrative which represent the application of the principles of the present invention. Numerous and varied other arrangements can be readily devised by those skilled in the art without departing from the spirit and the scope of the invention.