Abstract:
A reflection type encoder includes a reflection scale  20  having an origin pattern formed thereon, a light source  42  for irradiating light to the origin pattern, and a light receiving element  50  for detecting reflection light from the origin pattern, in which the origin pattern on the reflection scale  20  is detected by the reflection light, and further includes an incoming side origin pattern  26  and an outgoing side origin pattern  28 , which are formed on the reflection scale  20 , a reflection slit  46  disposed at the same side as the light source  42  and the light receiving element  50  with respect to the reflection scale  20 , an incoming side lens  44  that composes an incoming side telecentric optical system in which the incoming side origin pattern  26  is made to be the object plane, and an outgoing side lens  48  that composes the outgoing side telecentric optical system in which the outgoing side origin pattern  28  is made to be the image forming plane, wherein a telecentric optical system is composed of the incoming side telecentric optical system and the outgoing side telecentric optical system at both sides of the reflection slit  46 . Thereby, highly accurate origin detection is carried out with a simplified configuration without lowering utilization efficiency of light using a beam splitter and without using complicated optical components such as a trapezoidal prism, etc.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    The disclosure of Japanese Patent Application No. 2007-139109 filed on May 25, 2007 including specifications, drawings and claims is incorporated herein by reference in its entirety. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a reflection type encoder including a reflection scale having an origin pattern formed thereon, a light source for irradiating light onto the origin pattern, and a light receiving element for detecting reflection light from the origin pattern, wherein an origin pattern on the reflection scale is detected by reflection light, and in particular to a reflection type encoder that is preferably used for detecting an origin by means of a reflection type incremental encoder and is capable of detecting the origin at high accuracy without use of complicated optical components. 
         [0004]    2. Description of the Related Art 
         [0005]    In an incremental encoder, an origin pattern is provided, and a detection position is corrected by forcibly causing the corresponding origin pattern to pass through immediately after the power is turned on. 
         [0006]    There exist a transmission type encoder and a reflection type encoder. In the reflection type encoder, a method shown in  FIG. 1  that corresponds to FIG. 11 of, for example, Japanese Translation of International Application (Kohyo) No. 2004-520591 (Patent Document 1) has been proposed as a method for detecting the origin pattern (or a reference pattern) on a reflection scale by reflection light. 
         [0007]    In this method, light L from a light source  53  is reflected by an origin pattern rm on a reflection scale  57 , and produces origin pattern images a, b and c on the plane on which light receiving elements  59  of a detection portion are placed. And the light receiving elements  59  output origin signals. Herein, if the width of the origin pattern rm on the reflection scale  57  in the detection axis x direction is narrowed, the width of the origin signals can be narrowed, wherein the detection accuracy of the origin can be improved. 
         [0008]    Or, as shown in  FIG. 2  that corresponds to FIG. 4 of Japanese Published Unexamined Patent Application No. 2005-17023 (Patent Document 2), a method for detecting an origin pattern on the reflection scale by means of an image-forming lens  410  and a detection element  440  has been proposed. In  FIG. 2 , reference numeral  2  denotes an optical reader,  101  denotes a shaft,  102  denotes its bearing,  310  denotes a light projecting LED,  330  denotes a light projecting circuit,  410  denotes a pin hole,  420  denotes a half mirror,  430  denotes a light shielding plate,  440  denotes a photo IC,  450  denotes a light receiving circuit,  451  denotes a signal processing portion, and  452  denotes an output circuit. 
         [0009]    Or, as shown in  FIG. 3  corresponding to FIG. 2 of Japanese Published Unexamined Patent Application No. Hei-8-184465 (Patent Document 3), such a method has been proposed, in which light receiving and emitting elements (light source  2  and light receiving element  3 ) and a turn-down optical system (trapezoidal prism  8 ) are disposed with a transmission scale (moving plate  1 ) placed therebetween, a slit image at the light source  2  side is once transformed to an intermediate image on a focusing plane  11  in the optical component  8 , and the intermediate image is projected onto slits  5  at the light receiving side and is detected. In  FIG. 3 , reference numeral  4  denotes projecting means,  6  denotes an object lens,  7  denotes an image forming lens,  9  denotes a slit object image,  10  denotes the first entire reflection surface of the trapezoidal prism  8 ,  12  denotes the second entire reflection surface as well,  13  denotes a slit real image, and  14  denotes an optical axis. 
         [0010]    However, with the method according to Patent Document 1, when the width of the origin pattern rm is narrow, a pattern image detected by the light-receiving element  59  does not become clear due to diffusion of light or a diffraction phenomenon, and the width of the origin signal is widened. In particular, when the reflection scale  57  and the detection portion are apart from each other, there is a problem that it is difficult to obtain a sharply clear origin pattern image. 
         [0011]    In addition, with the method according to Patent Document 2, since there is a beam splitter (half mirror  420 ) provided between the light projecting LED  310  and the image forming lens  410 , light will attenuate in terms of light projecting (L 11 ) and light receiving (L 12 ), wherein there is another problem that efficient utilization of light is worse. 
         [0012]    Also, with the method according to Patent Document 3, although efficient utilization of light is satisfactory since no beam splitter is provided, it becomes necessary to provide complicated optical components such as a trapezoidal prism, etc., and there is still another problem that it is not utilized for detection of the reflection scale. 
       SUMMARY OF THE INVENTION 
       [0013]    The present invention was developed to solve the conventional problems, and it is therefore an object of the present invention to improve the detection accuracy of origin with a simple configuration without lowering the utilization efficiency of light using a beam splitter and without using any complicated optical components such as a trapezoidal prism, etc. 
         [0014]    A first aspect of the present invention is a reflection type encoder including a reflection scale having an origin pattern formed thereon, a light source for irradiating light to the origin pattern, and a light receiving element for detecting reflection light from the origin pattern, wherein the origin pattern on the reflection scale is detected by the reflection light, and further including an incoming side origin pattern and an outgoing side origin pattern, which are formed on the reflection scale, a reflection slit disposed at the same side as the light source and the light receiving element with respect to the reflection scale, an incoming side lens that composes an incoming side telecentric optical system in which the incoming side origin pattern is made to be the object plane, and an outgoing side lens that composes the outgoing side telecentric optical system in which the outgoing side origin pattern is made to be the image forming plane, wherein a telecentric optical system is composed of the incoming side telecentric optical system and the outgoing side telecentric optical system at both sides of the reflection slit, thereby solving the problems. 
         [0015]    Also, a second aspect of the present invention has a further simplified configuration by disposing the light source, the incoming side lens, the outgoing side lens and the light-receiving element on the same substrate. 
         [0016]    In addition, a third aspect of the present invention is such that both the incoming side lens and the outgoing side lens are made to be a cylindrical lens disposed to form an image in the measurement axis direction. 
         [0017]    Further, a fourth aspect of the present invention is such that the incoming side lens and the outgoing side lens have the same focal distance. 
         [0018]    Still further, a fifth aspect of the present invention has a further simplified configuration in which the incoming side lens and the outgoing side lens are integrated with each other. 
         [0019]    Also, a sixth aspect of the present invention is such that at least either one of the incoming side lens or the outgoing side lens is made to be a Fresnel lens, and the origin detection unit is made small-sized. 
         [0020]    In addition, a seventh aspect of the present invention is such that the origin pattern is composed of a plurality of patterns and the detection accuracy of the origin is improved. 
         [0021]    Also, an eighth aspect of the present invention is such that a plurality of patterns are disposed to be asymmetrical with respect to the pattern center with unequal pitches. 
         [0022]    Further, a ninth aspect of the present invention is such that a plurality of patterns are disposed to be symmetrical with respect to the pattern center. 
         [0023]    Still further, a tenth aspect of the present invention is such that the incoming side origin pattern and the outgoing side origin pattern are integrated with each other, wherein the tolerance of the origin detection unit in the lengthwise direction of the origin pattern is widened, and the origin pattern can be disposed at high accuracy. 
         [0024]    In addition, an eleventh aspect of the present invention is such that an incremental track is disposed between the incoming side origin pattern and the outgoing side origin pattern to be prevented from being subjected to influences due to moiré fluctuations. 
         [0025]    Further, a twelfth aspect of the present invention is such that the reflection slit is made wide to increase the detection light quantity, wherein the SN ratio is improved, or a light source drive current is attempted to be decreased and a light source service life is attempted to be improved. 
         [0026]    According to the present invention, it is possible to improve the detection accuracy of an origin with a simple configuration without lowering utilization efficiency of light using a beam splitter and without using any complicated optical components such as a trapezoidal prism, etc. 
         [0027]    That is, since no beam splitter is provided in an optical path from the light source to the detection element, the detection light quantity is large. Also, since a both-sided telecentric system is composed, the tolerance in distance fluctuation between the origin detection unit and the reflection scale is wide. Furthermore, the width of the origin signal is narrow, and the origin detection can be carried out at high accuracy. 
         [0028]    In particular, where the incoming side lens and the outgoing side lens are made to be cylindrical lenses and are integrated with each other, the number of optical components can be decreased. 
         [0029]    Also, where a Fresnel cylindrical lens is disposed instead of the cylindrical lens, since it is a plain optical component, downsizing can be achieved. 
         [0030]    In addition, where the origin pattern is composed of a plurality of patterns, the detection accuracy of the origin signal can be improved. 
         [0031]    Further, where the reflection slit is widened, the detection light quantity can be increased, wherein the light source drive current is decreased, and the service life of the light source can be improved. 
         [0032]    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 
         [0033]    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; 
           [0034]      FIG. 1  is a view showing a detection method of origin pattern, which has been proposed in Patent Document 1; 
           [0035]      FIG. 2  is a view showing a detection method by an image-forming lens, which has been proposed in Patent Document 2; 
           [0036]      FIG. 3  is a view showing a detection method by a turn-down optical system, which has been proposed in Patent Document 3; 
           [0037]      FIG. 4  is a perspective view showing the entire configuration of embodiment 1 according to the present invention; 
           [0038]      FIG. 5  is a configurational view showing Embodiment 1 when being observed from the YZ plane; 
           [0039]      FIG. 6  is a configurational view showing Embodiment 1 when being observed from the XZ plane; 
           [0040]      FIG. 7  is a developed view showing an optical path with the reflection slit replaced by a transmission slit in Embodiment 1; 
           [0041]      FIG. 8  is a developed view showing a state where the origin pattern is apart by X 1 (         −W) from the center of the optical axis, in order to describe operations of Embodiment 1; 
           [0042]      FIG. 9  is a developed view showing a state where the origin pattern is apart by X 2 (&lt;−W) from the center of the optical axis, in order to describe operations of Embodiment 1; 
           [0043]      FIG. 10  is a developed view showing a state where the origin pattern is apart by X 3  (=−W/2) from the center of the optical axis, in order to describe operations of Embodiment 1; 
           [0044]      FIG. 11  is a developed view showing a state where the origin pattern is apart by X 4  (=−W/4) from the center of the optical axis, in order to describe operations of Embodiment 1; 
           [0045]      FIG. 12  is a developed view showing a state where the origin pattern is made coincident with the center (X=0) of the optical axis, in order to describe operations of Embodiment 1; 
           [0046]      FIG. 13  is a developed view showing a state where the origin pattern is apart by X 5 (=+W/4) from the center of the optical axis, in order to describe operations of Embodiment 1; 
           [0047]      FIG. 14  is a developed view showing a state where the origin pattern is apart by X 6  (=+W/2) from the center of the optical axis, in order to describe operations of Embodiment 1; 
           [0048]      FIG. 15  is a developed view showing a state where the origin pattern is apart by X 7  from the center of the optical axis, in order to describe operations of Embodiment 1; 
           [0049]      FIG. 16  is a perspective view showing a configuration of Embodiment 2 of the present invention; 
           [0050]      FIG. 17  is a perspective view showing a configuration of Embodiment 3 of the present invention; 
           [0051]      FIG. 18  is a perspective view showing a configuration of Embodiment 4 of the present invention; 
           [0052]      FIG. 19  is a developed view showing an optical path according to Embodiment 4; 
           [0053]      FIG. 20  is a developed view showing an optical path according to Embodiment 5 of the present invention; 
           [0054]      FIG. 21  is a perspective view showing an optical path according to Embodiment 6 of the present invention; 
           [0055]      FIG. 22  is a perspective view showing an optical path according to Embodiment 7 of the present invention; 
           [0056]      FIG. 23  is a perspective view showing an optical path according to Embodiment 8 of the present invention; and 
           [0057]      FIG. 24  is a perspective view showing an optical path according to Embodiment 9 of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0058]    With reference to the following drawings, a detailed description is given of embodiments according to the present invention. 
         [0059]    Embodiment 1 according to the present invention includes, as shown in  FIG. 4 , a reflection scale  20  on which an origin track  24  consisting of an incremental (INC) track  22 , an incoming side origin pattern  26  and an outgoing side origin pattern  28  is formed, an INC detection unit  30  disposed opposite to the INC track  22 , and an origin detection unit  40  disposed opposite to the origin track  24 . 
         [0060]    An INC detection light source  32  for irradiating light to the INC track  22  and an INC detection element  34  for detecting reflection light from the INC track  22  are mounted in the INC detection unit  30 . 
         [0061]    The origin detection unit  40  includes an origin detection light source  42  for irradiating light to the incoming side origin pattern  26 , an incoming side cylindrical lens  44  that composes an incoming side telecentric optical system in which the incoming side origin pattern  26  is made to be an object plane, a reflection slit  46  for reflecting light converged by the incoming side cylindrical lens  44 , an outgoing side cylindrical lens  48  that composes an outgoing side telecentric optical system in which the outgoing side origin pattern  28  is made to be an image forming plane, and an origin detection element  50  for detecting reflection light from the outgoing side origin pattern  28 . 
         [0062]    A view of an optical configuration of the origin detection unit  40 , which is observed from the YZ plane, is shown in  FIG. 5 , and a view thereof, which is observed from the XZ plane, is shown in  FIG. 6 . 
         [0063]    The origin patterns  26  and  28  are formed of chrome film formed on the reflection scale  20  consisting of, for example, glass scale. Therefore, light that reaches the origin patterns  26  and  28  is reflected. 
         [0064]    The incoming side and outgoing side cylindrical lenses  44  and  48  are lenses having the same focal distance F and are juxtaposed in the Y-axis direction. 
         [0065]    Herein, light emitting from the origin detection light source  42  is reflected by the incoming side origin pattern  26  on the reflection scale  20 , and is reflected after reaching the reflection slit  46  through the incoming side cylindrical lens  44 . And the light is reflected after reaching the outgoing side origin pattern  28  on the reflection scale  20  through the outgoing side cylindrical lens  48 , and further reaches the origin detection element  50 . And, the origin detection element  50  detects the reached light as the origin signal. 
         [0066]    Also, when the reflection scale  20  moves in the direction of measurement axis (X axis), and the origin pattern does not exist immediately below the origin detection light source  42  and the origin detection element  50 , since any origin pattern to be reflected is not provided, light from the light source  42  is made incident into the glass scale ( 20 ), wherein an optical path to the origin detection element  50  is not formed. 
         [0067]    As shown in  FIG. 6 , the incoming side and outgoing side cylindrical lenses  44  and  48  are disposed so that the distance from the main plane of the cylindrical lens  44  or  48  to the plane of the origin pattern  26  or  28  on the reflection scale  20  is the same as the focal distance F of the cylindrical lens, and the distance between the main plane of the cylindrical lens  44  or  48  and the reflection slit  46  becomes the same focal distance F. 
         [0068]    In order to make clear the configuration of the optical path, if the optical path is developed under the assumption that the transmission slit  46 ′ that has the same width as that of the reflection slit  46  is disposed, the developed view becomes as shown in  FIG. 7 . 
         [0069]    As has been made clear in  FIG. 7 , since each of the distance from the plane where the incoming side origin pattern  26  is provided to the main plane of the incoming side cylindrical lens  44 , the distance from the main plane of the incoming side cylindrical lens  44  to the transmission slit  46 ′ that replaced the reflection slit  46 , the distance from the transmission slit  46 ′ to the main plane of the outgoing side cylindrical lens  48 , and the distance from the main plane of the outgoing side cylindrical lens  48  to the plane where the outgoing side origin pattern  28  is provided is composed of the focal distance F of the cylindrical lens  44  or  48 , a both-sided telecentric optical system, the optical magnification of which is 1 time, in which the plane where the incoming side origin pattern  26  is provided is made to be the object plane and the plane where the outgoing side origin pattern  28  is provided is made to be an image-forming plane is composed. 
         [0070]    The number of aperture NA (Numerical Aperture) of the both-sided telecentric optical system is obtained by the following expression using the focal distance F of the cylindrical lens and the slit width Ws. 
         [0000]        NA=Ws /(2 F )  (1) 
         [0071]    Therefore, the depth of focus DOF of the both-sided telecentric optical system is obtained by the following expression where it is assumed that the wavelength of light from the light source  42  is λ. 
         [0000]        DOF=λ/{ 2 NA}   2 }=2 λF   2   /Ws   2   (2) 
         [0072]    Herein, where it is assumed that λ is 660 nm, F is 10 mm, and Ws is 0.2 mm, the DOF becomes 3.3 mm. 
         [0073]    This means that such a wide range of fluctuations in position with respect to the Z-axis direction of the reflection scale  20  where the object plane and the image-forming plane of the both-sided telecentric optical system are provided is permissible, wherein it becomes easy to assemble the reflection scale  20  and the detection portion ( 40 ). 
         [0074]    Next, with reference to  FIG. 8  through  FIG. 15 , a detailed description is given of actions when the reflection scale  20  having the origin patterns  26  and  28  mounted thereon is moved in the direction of measurement axis. 
         [0075]    First, as shown in  FIG. 8 , in a state (X=X 1 &lt;&lt;−W) where the origin patterns  26  and  28  are located at this side apart by a sufficient distance X 1  from the center of the optical axis in comparison with the width W thereof, an image of the incoming side origin pattern  26  is formed at an area where no outgoing side origin pattern  28  exists. Therefore, in this state, the origin detection element  50  does not detect any light from the incoming side origin pattern  26 . 
         [0076]    Herein, the area where the incoming side origin pattern  26  or the outgoing side origin pattern  28  does not exist is an area where light is made incident into the interior of a glass scale in the case of glass scale as in the present embodiment, and an area where, in the case of a metal scale, the surface is rough and light is irregularly reflected. In any case, no optical path to the origin detection element  50  is formed, wherein the origin detection element  50  does not detect any light. 
         [0077]    Next, as shown in  FIG. 9 , in a state (X=X 2 &lt;−W) where the origin patterns  26  and  28  are approached to the distance X 2  from the center of the optical axis, which is greater than the width W, an image of the incoming side origin pattern  26  is formed at an area where the outgoing side origin pattern  28  does not exist as in  FIG. 8 . Therefore, in this state, the origin detection element  50  does not detect any light from the incoming side origin pattern  26 . 
         [0078]    Next, as shown in  FIG. 10 , as the origin patterns  26  and  28  are approached to the distance X 3  that is one-half the width W thereof (that is, X=X 3 =−W/2), an image of the incoming side origin pattern  26  is formed aside of the outgoing side origin pattern  28 . However, in this state, the origin detection element  50  does not detect light from the incoming side origin pattern  26  yet. 
         [0079]    Next, as shown in  FIG. 11 , as the centerlines of the origin patterns  26  and  28  are approached to the center of the optical axis before the distance X 4 , which is one-fourth the width W of the origin pattern (that is, X=X 4 =−W/4), an image of the incoming side origin pattern  26  is formed so as to cover half the outgoing side origin pattern  28 , wherein half the image of the incoming side origin pattern  26  is reflected by the outgoing side origin pattern  28  and is detected by the origin detection element  50 . 
         [0080]    Next, as shown in  FIG. 12 , as the origin patterns  26  and  28  are further approached to the center of optical axis and the centerlines of the origin patterns  26  and  28  are made coincident with the center of the optical axis (X=0), the entire image of the incoming side origin pattern  26  is formed at the outside origin pattern  28 , and the entire image of the incoming side origin pattern  26  is reflected by the outgoing side origin pattern  28  and are detected by the origin detection element  50 . At this time, the origin detection element  50  is entered into its maximum output. 
         [0081]    Next, as shown in  FIG. 13 , as the centerlines of the origin patterns  26  and  28  overrun by the distance X 5 , which is one-fourth the width W of the origin patterns, beyond the center of optical axis (that is, X=X 5 =+W/4), an image of the incoming side origin pattern  26  is formed so as to cover half the outgoing side origin pattern  28 , and half of the image of the incoming side origin pattern  26  is reflected by the outgoing side origin pattern  28  and is detected by the origin detection element  50 . 
         [0082]    As the reflection scale  20  further advances, and, as shown in  FIG. 14 , the centerlines of the origin patterns  26  and  28  overrun by the distance X 6 , which is half the width W of the origin patterns, from the center of optical axis (that is, X=X 6 =+W/2), an image of the incoming side origin pattern  26  is formed aside of the outgoing side origin pattern  28 . Therefore, in this state, the origin detection element  50  will not detect light from the incoming side origin pattern  26 . 
         [0083]    As the reflection scale  20  still further advances, and, as shown in  FIG. 15 , an image of the incoming side origin pattern  26  will be formed at an area where the outgoing side origin pattern  28  does not exist as in  FIG. 6 . Therefore, in this state, the origin detection element  50  does not detect any light from the incoming side origin pattern  26 . 
         [0084]    By the above-described actions, the origin detection element  50  outputs the maximum signal when the origin patterns  26  and  28  are coincident with the optical axis. Where it is assumed that the maximum output when coincident is Vpp and the half level thereof is Vth, it is possible to obtain an origin signal of half the width W/2 of the origin pattern from the output of the origin detection element  50 . 
         [0085]    This is advantageous in view of detecting the origin at high accuracy because the origin width of the origin signal based on detection by the image-forming lens shown in  FIG. 2  is ½ in regard to the origin pattern width being W since the width at one side does not change. 
         [0086]    In the present embodiment, since the origin detection light source  32 , the incoming side cylindrical lens  44 , the outgoing side cylindrical lens  48 , and the origin detection element  50  are disposed on the same substrate, assembling and adjustment thereof are facilitated. 
         [0087]    Also, in the present embodiment, although the incoming side cylindrical lens  44  and the outgoing side cylindrical lens  48  are separately provided, both may be integrated with each other as in Embodiment 2 shown in  FIG. 16  (illustration of the INC track and INC detection unit is omitted). 
         [0088]    According to Embodiment 2, since the number of optical components can be decreased, assembling thereof can be facilitated. 
         [0089]    In addition, as in Embodiment 3 shown in  FIG. 17 , it is possible that the incoming side origin pattern  26  and the outgoing side origin pattern  28  are coupled together and integrated with each other. In this case, it is possible to widen a permissible range of the deposing position of the origin detection unit  40  in the Y-axis direction. Furthermore, it becomes hard for the incoming side origin pattern  26  and the outgoing side origin pattern  28  to deviate in regard to their position, wherein the origin patterns can be disposed at high accuracy. 
         [0090]    In any one of Embodiments 1 through 3, although the origin patterns are made by a single pattern line, a group of origin patterns  27  and  29  each consisting of a plurality of pattern lines may be provided instead of a single origin pattern as in Embodiment 4 shown in  FIG. 18 . 
         [0091]    Here, where a plurality of pattern lines are disposed left-right asymmetrically at unequal pitches, it is necessary to reverse the direction of the measurement axis of the incoming side origin pattern group  27  and the outgoing side origin pattern group  29  as shown in detail in a developed view of  FIG. 19 . 
         [0092]    In the present embodiment, since the origin pattern group composed of a plurality of pattern lines is detected, the accuracy of detecting the origin can be improved. 
         [0093]    On the other hand, where the pattern lines of the incoming side origin pattern group  27  and the outgoing side origin pattern group  29  are disposed left-right symmetrically with respect to the center of the pattern as in Embodiment 5 the developed view of which is shown in  FIG. 20 , the incoming side origin pattern group  27  and the outgoing side origin pattern group  29  are made into the same pattern in the direction of measurement axis, and, as in Embodiment 6 shown in  FIG. 21 , the respective pattern lines of the incoming side origin pattern group  27  and the outgoing side origin pattern group  29  coupled together and integrated with each other. 
         [0094]    Also, although, in any one of the above embodiments, normal cylindrical lenses are used, Fresnel cylindrical lenses  45  and  49  may be disposed instead of the cylindrical lenses, as in Embodiment 7 shown in  FIG. 22 . 
         [0095]    According to this embodiment, since planar optical elements may be disposed on the origin detection unit  40 , downsizing and ease in assembling can be achieved. 
         [0096]    In addition, although, in any one of the above embodiments, the width Ws of the reflection slit  46  is narrowed to increase the DOF calculated by the expression (2), a wide reflection slit  47  the slit width Ws of which is widened may be used as in Embodiment 8 shown in  FIG. 23  where a small DOF is sufficient with a large DOF not required. 
         [0097]    According to the embodiments, since the light quantity detected by the origin detection element  50  can be increased, the SN ratio can be improved, or the light source drive current may be decreased, and the service life of the light source can be lengthened. 
         [0098]    Further, although, in any one of the above embodiments, the origin track  24  is disposed at one side of the INC track  22 , the origin track  24  may be separated to the incoming side origin track  24 A composed of the incoming side origin pattern  26  and to the outgoing side origin track  24 B composed of the outgoing side origin pattern  28  on the reflection scale  20  as in Embodiment 9 shown in  FIG. 24 , and is disposed at both sides of the INC track  22 . In line therewith, the origin detection light source  42  and the incoming side cylindrical lens  44 , and the outgoing side cylindrical lens  48  and the origin detection element  50  are disposed on the integrated INC/origin detection unit  36  in a state where the INC detection light source  32  and the INC detection element  34  are placed therebetween. 
         [0099]    According to the embodiments, the origin does not deviate even if moiré is subjected to fluctuation, and the origin signal is not lowered. 
         [0100]    It should be apparent to those skilled in the art that the above-described exemplary embodiments are merely illustrative which represent the application of the principles of the present invention. Numerous and various other arrangements can be readily devised by those skilled in the art without departing from the spirit and the scope of the present invention.