Abstract:
An optical encoder is disclosed, in particular, which has a light sensing element with light-sensing cells arranged in a matrix. The light sensing element repeatedly detects the same reflective light beam by different rows of light-sensing cells to increase the precision of feedback control. Furthermore, since the light sensing element synchronously and repeatedly receives the reflective light beam, the reliability of detected signals is increased.

Description:
BACKGROUND  
       [0001]     1. Field of Invention  
         [0002]     The invention relates to an optical encoder and, in particular, to one having a light sensing element with light-sensing cells arranged in a matrix, thereby increasing its precision and reliability.  
         [0003]     2. Related Art  
         [0004]     When detecting the location of a rotating device (e.g. a motor or a machine axis) or a high-speed moving device, one usually generates a binary identification code in response to each location of the detected device by the on and off of a detecting element in an optical or magnetic ways. For example, several typical optical encoders taught in the U.S. Pat. Nos. 4,451,731, 4,691,101, 4,952,799, and 5,317,149.  
         [0005]     These encoders mainly include: a light source for emitting light, a code strip for modulating the light in response to the operation of the rotating device, such as a code wheel, an optical grating disk, or an optical scale, and a photo detector for receiving and detecting the modulated light beam. In generally, some code strips have opaque and transparent regions which are staggered. In this case, the light source and the photo detector are located on opposite sides of a measure element, i.e. the code strip. In other case, the code strips have some reflective regions, and the light source and the photo detector are located on the same side of a measure element.  
         [0006]     Refer to  FIG. 1 , showing the structure of a conventional optical encoder. It is mainly comprised of a main optical grating disk  110 , an auxiliary optical grating disk  120 , an LED illuminator  130 , a photo receiver  140 , and a main axis  150 . The main optical grating disk  110  is sited on the main axis  150  and driven by the main axis  150  in response to a rotating device. The main optical grating disk  110  has transparent regions  112  and opaque regions  114  which are staggered, as shown in  FIG. 2 . The light emitted by the LED illuminator  130  illuminates the main optical grating disk  110 . Part of the light penetrates through the transparent regions  112  and reaches the photo receiver  140  via the auxiliary optical grating disk  120 , while the other part of the light is blocked by the opaque regions  114 . Therefore, the transparent regions  112  and opaque regions  114  which are staggered on the main optical grating disk  110  provide a basis for the photo receiver  140  to generate the binary identification code, thereby determining the location of the rotating device. However, since the light source and the photo receiver of the optical encoder are on opposite sides of the grating respectively, only one side can be used to generate codes. The resolution is thus limited and the device cannot be made too thin.  
         [0007]     The structure of another conventional optical encoder is shown in  FIG. 3 . It includes: a code wheel  210 , an LED illuminator  220 , and a photo receiver  230 . The code wheel  210  is driven by a wheel (not shown) in response to a rotating device. Moreover, the code wheel  210  has reflective regions  212  and non-reflective regions  214  which are staggered. The LED illuminator  220  illuminates the reflective regions  212  on the code wheel  210 , and then the photo receiver  230  disposed on the same side as the LED illuminator  220  receives the modulated light beam directly reflected from the reflective regions  212  to obtain a binary identification code indicating the location of the code wheel  210 . The location of the rotating device is thus determined for subsequent controls of the speed and stroke of the rotating device.  
         [0008]     In the conventional optical encoder, better control precision is usually achieved by increasing its resolution. The increase of the resolution is often achieved by changing the number of transparent and opaque regions on the code strip (or the number of reflective and non-reflective regions) or by adopting several code strips and several photo detectors. However, this is likely to increase the thickness of the optical encoder, contrary to the trend of miniaturization. Moreover, errors occur when the code wheel is dirty. Therefore, the existing optical encoders need to be improved.  
       SUMMARY  
       [0009]     In view of the foregoing, the present invention is to provide an optical encoder to substantially solve the problems in the prior art.  
         [0010]     According to the invention, the precision of feedback control of the disclosed optical encoder is increased using the reflection difference between different rows of light-sensing cells.  
         [0011]     According to the invention, multiple detections are made simultaneously to increase the reliability of detected signals of the disclosed optical encoder.  
         [0012]     According to the invention, the errors, which are caused by the dirt on the code strip, e.g. a code wheel or optical scale, of the disclosed optical encoder are reduced.  
         [0013]     The disclosed optical encoder comprises: a light source, a code strip, a first lens set, and a light sensing element.  
         [0014]     The light source emits light to the code strip having reflective and non-reflective regions which are staggered. The reflective regions reflect light from the light source. The first lens set sited on the same side of the code strip as the light source converges and emits the reflected light. The light sensing element includes several light-sensing cells arranged in a matrix and opposite to the code strip on another side of the first lens set. The light-sensing cells are used to receive the light beam converged by the first lens set and convert it into an electrical signal, thereby producing a binary identification code.  
         [0015]     The disclosed optical encoder further comprises a second lens set, which is installed between the light source and the code strip for magnifying the light from the light source to converge on the code strip.  
         [0016]     In particular, the light sensing element has the light-sensing cells in a N 1 ×N 2  matrix, where N 1  and N 2  are positive integers. In this case, the light-sensing cells detects N 1  channels and synchronously receive the light beam converged by the first lens set for N 2  times. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]     The invention will become more fully understood from the detailed description given herein below illustration only, and thus are not limitative of the present invention, wherein:  
         [0018]      FIG. 1  is a schematic structural diagram of a conventional optical encoder;  
         [0019]      FIG. 2  is a structural diagram of the main optical grating disk in  FIG. 1 ;  
         [0020]      FIG. 3  is a schematic structural diagram of another conventional optical encoder;  
         [0021]      FIG. 4  is a schematic structural diagram of the optical encoder according to an embodiment of the invention;  
         [0022]      FIG. 5A  is a schematic view of a first embodiment of the arrangement of the light-sensing cells in the light sensing element in  FIG. 4 ;  
         [0023]      FIG. 5B  is a binary identification code obtained in one cycle of the electrical signal of the light sensing element in  FIG. 5A ;  
         [0024]      FIG. 6A  is a schematic view of a second embodiment of the arrangement of the light-sensing cells in the light sensing element in  FIG. 4 ;  
         [0025]      FIG. 6B  is a binary identification code obtained in one cycle of the electrical signal of the light sensing element in  FIG. 6A ;  
         [0026]      FIG. 7A  is a schematic view of a third embodiment of the arrangement of the light-sensing cells in the light sensing element in  FIG. 4 ;  
         [0027]      FIG. 7B  is a binary identification code obtained in one cycle of the electrical signal of the light sensing element in  FIG. 7A ;  
         [0028]      FIG. 8A  is a schematic view of a fourth embodiment of the arrangement of the light-sensing cells in the light sensing element in  FIG. 4 ;  
         [0029]      FIG. 8B  is a schematic view of the code strip in the light sensing element of  FIG. 8A ; and  
         [0030]      FIG. 9  is a schematic structural diagram of the optical encoder according to another embodiment of the invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0031]     With reference to  FIG. 4 , an embodiment of the optical detector comprises: a code strip  310 , a light source  320 , a light sensing element  330 , and a first lens set  340 .  
         [0032]     The code strip  310  is driven by a wheel (not shown) in response to the rotating device. It has reflective regions  312  and non-reflective regions  314  which are staggered. The code strip  310  is such as a code wheel or an optical scale.  
         [0033]     The light source  320  emits light to illuminate the reflective regions  312  on the code strip  310 . The light source  320  is such as an LED illuminator.  
         [0034]     The light sensing element  330  disposed on the same side of the code strip  310  as the light source  320  receives the modulated light beam reflected by the reflective regions  312  and converts it into an electrical signal, thereby producing a binary identification code to determine the location of the rotating device for controlling the speed and stroke of the rotating device.  
         [0035]     The light detecting element  330  has several light-sensing cells  3301  arranged in a matrix. The vertical lines of the light-sensing cells are used to distinguish the channels of different code strips  310 . That is, the light-sensing cells on each vertical line detect the signal of the previous channel on the code strip  310 . Therefore, the same feedback control is achieved by a low-resolution code strip  310  (e.g. a paper optical scale). Moreover, the reliability is increased by comparing the light-sensing cells on the horizontal lines, thereby preventing errors caused by a dirty code strip  310 . The width of the reflective and non-reflective regions is smaller or roughly equal to the width of which the image is read by the light sensing element each time. That is, it is that the width of the light sensing element multiplied by the number of rows.  
         [0036]     The first lens set  340  is installed between the code strip  310  and the light sensing element  330  to converge the modulated light beam reflected by the reflective regions  312  to transmit to the light sensing element  330 .  
         [0037]     In the following, the relation between the composition of the light sensing element and the code strip precision is described, with reference to appropriate drawings.  
         [0038]      FIG. 5A  shows the arrangement of the light-sensing cells in the light sensing element according to an embodiment of the invention. In this case, the light-sensing cells are disposed in a 2×2 matrix. In terms of vertical lines, vertical line A and vertical line B detect the modulated light beam in different channels to obtain a two-digit binary identification code. When a code strip of an appropriate length is used, the four binary identification code S 1 ˜S 4  is obtained in one cycle of its electrical signal, as shown in  FIG. 5B . In terms of horizontal lines, horizontal line  1  and horizontal line  2  are used to detect repeatedly the same channel to increase the reliability of signals.  
         [0039]     Suppose the light-sensing cells in the light sensing element are disposed in a 3×3 matrix, as shown in  6 A. In terms of vertical lines, vertical lines A, B, and C detect the modulated light beam in different channels to obtain a three-digit binary identification code. With a code strip of an appropriate length, the six binary identification code S 1 ˜S 6  is obtained in one cycle of its electrical signal, as shown in  FIG. 6B . In terms of horizontal lines, horizontal lines  1 ,  2 , and  3  are used for repeated detections.  
         [0040]     Likewise, suppose the light-sensing cells in the light sensing element are disposed in a 4×4 matrix, as shown in  7 A. In terms of vertical lines, vertical lines A, B, C, and D detect the modulated light beam in different channels to obtain a four-digit binary identification code. With a code strip of an appropriate length, the eight binary identification code S 1 ˜S 8  is obtained in one cycle of its electrical signal, as shown in  FIG. 7B . In terms of horizontal lines, horizontal lines  1 ,  2 ,  3 , and  4  are used for repeated detections.  
         [0041]     In summary, the light-sensing cells in the light sensing element is disposed in an N 1 ×N 2  matrix, as shown in  8 A, where N 1  and N 2  are positive integers. Suppose the resolution of the code strip is 1/X DPI and the light sensing element has the configuration of an N 1 ×X matrix, as shown in  FIG. 8B . Therefore, the detection precision is N 1 ×X, and the number of times for a synchronization detector is N 2 . A preferred embodiment of the light sensing element is a charge coupled device (CCD), a complementary metal oxide semiconductor (CMOS) image sensor, or a contact image sensor (CIS). Here, X represents the number of reflective and non-reflective regions in one unit.  
         [0042]     Further, a second lens set  342  is installed between the code strip  310  and the light source  320  to magnify the light from the light source  320 , and converge the magnified light beam on the code strip  310 , as shown in  FIG. 9 .  
         [0043]     Certain variations would be apparent to those skilled in the art, which variations are considered within the spirit and scope of the claimed invention.