Abstract:
A magnetic type digital-analogic position-sensing device utilizes plural magnetic strips and plural digital sensing readers to perform position-sensing operation. One of the magnetic strips is provided with an analogic sensing reader. After being finely divided, the signal outputted from the analogic sensing reader can cooperate with the signals outputted from the digital sensing readers to obtain the displacement of the sensor. By such arrangements, the position-sensing device can both have high environment adaptability and high resolution.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a program control system for a magnetic recording media, and more particularly to a magnetic type digital-analogic position-sensing device. 
         [0003]    2. Description of the Prior Art 
         [0004]    The existing sensing devices for measuring a displacement of a rotary or linear displacement deice for a motor or a linear motor can be divided into two types: magnetic type and optical type. The optical type sensing devices are better than the magnetic type sensing devices in precision, so the industries which seek high precision will adopt the optical type sensing devices. A conventional optical sensing device, as shown in  FIG. 1 , consists of an optical scale A and a sensor B. The optical scale A includes four parallel-arranged elongated scale elements A 1 , A 2 , A 3 , A 4 , and each of the scale elements A 1 , A 2 , A 3 , A 4  includes plural through holes A 11 , A 21 , A 31 , A 41 . The length of the through holes A 11 , A 21 , A 31 , A 41  of the respective scale elements A 1 , A 2 , A 3 , A 4  is the same and identical to the distance between each pair of neighboring through holes A 11 , A 21 , A 31 , A 41  of the respective scale elements A 1 , A 2 , A 3 , A 4 . Further as shown in  FIG. 2 , the length of the through holes A 11  of the first scale element A 1  is two times as long as that of the through holes A 21  of the second scale element A 2 , the length of the through holes A 21  of the second scale element A 2  is two times as long as that of the through holes A 31  of the third scale element A 3 , and the length of the through holes A 31  of the third scale element A 3  is two times as long as that of the through holes A 41  of the fourth scale element A 4 . The sensor B is provided with four digital sensing readers B 1 , B 2 , B 3 , B 4  opposite the respective four scale elements A 1 , A 2 , A 3 , A 4 . The respective sensing readers B 1 , B 2 , B 3 , B 4  will output a high or low signal depending on if there are the through holes of the respective scale elements A 1 , A 2 , A 3 , A 4  or not. The signals outputted from the four sensing readers B 1 , B 2 , B 3 , B 4  are integrated as shown in  FIG. 3 , so that the relative distance between the sensing device B and the optical scale A can be known from the signals of that time. 
         [0005]    Since the length of the through holes A 11 , A 21 , A 31 , A 41  of the respective scale elements A 1 , A 2 , A 3 , A 4  and the distance between each pair of neighboring through holes A 11 , A 21 , A 41  of the respective scale elements A 1 , A 2 , A 3 , A 4  determine the resolution of the sensing device B (the resolution is the minimum value to measure the displacement of the sensor B). The length of through holes A 11 , A 21 , A 31 , A 41  and the distance between each pair of neighboring through holes A 11 , A 21 , A 31 , A 41  of the respective scale elements A 1 , A 2 , A 3 , A 4  of the optical scale A in the optical type sensing device can be finely formed by adopting the nano technology, so that the precision is relatively high. On the contrary, the magnetic sensing device uses the magnetic scale in which N poles and S poles are alternately arranged to make the sensing reader to output a high or low signal. Since the distance between the N pole and S pole of the magnetic type sensing device cannot achieve the normal precision of the optical type sensing device, the high precision industries will select the optical type sensing devices. 
         [0006]    However, the more precise the optical type sensing device is, the better the working environment is needed (if the working environment is not good enough, the dust or particles are likely to obstruct the through holes of the scale elements to greatly lower the precision). Since the general industries cannot provide the location with better working environment satisfying the requirements of the optical type sensing device, they can only adopt the magnetic type sensing devices which cannot be affected by the environment condition, consequently, the corresponding precision is greatly reduced. 
         [0007]    The present invention has arisen to mitigate and/or obviate the afore-described disadvantages. 
       SUMMARY OF THE INVENTION 
       [0008]    The primary objective of the present invention is to provide a magnetic type digital-analogic position-sensing device, which has both high environment adaptability and high resolution. 
         [0009]    In order to achieve the above objective, the magnetic type position-sensing device in accordance with the present invention comprises a magnetic scale and a sensor. The magnetic scale includes plural magnetic strips, and each of the magnetic strips includes plural magnetic zones. Each of the magnetic zones equally includes an S pole and an N pole. The plural magnetic zones on the same magnetic strip have the same length, and the magnetic zones on any two of the magnetic strips have the different lengths. The sensor is located on the magnetic scale and provided with plural digital sensing readers opposite the magnetic strips of the magnetic scale. The sensor is further provided with an analogic sensing reader opposite one of the magnetic strips. The sensing readers are used to sense the magnetic polarity of the opposite magnetic strips. 
         [0010]    When the sensor moves along the magnetic scale, the digital sensing readers will sense the magnetic polarity of the magnetic zones of the magnetic strips to output high or low signals, in addition, the analogic sensing reader will sense the magnetic polarity of the opposite magnetic strip to output a sinusoidal signal. After being finely divided, the signal outputted from the analogic sensing reader will be used to obtain the relative position of the sensor and the magnetic scale or the displacement of the sensor by integrating the signals outputted from the digital sensing readers. By such arrangements, the magnetic type position-sensing device in accordance with the present invention can have the high environment adaptability of the magnetic-type sensing device and the high resolution achieved by using the analogic sensing reader. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]      FIG. 1  is a perspective view of a conventional optical type sensing device; 
           [0012]      FIG. 2  is a plane view of an optical scale for the conventional optical type sensing device; 
           [0013]      FIG. 3  is a schematic view of signals outputted from the conventional optical type sensing device; 
           [0014]      FIG. 4  is a perspective view of a magnetic type digital-analogic position-sensing device in accordance with the present invention; 
           [0015]      FIG. 5  is a plane view of the magnetic type digital-analogic position-sensing device in accordance with the present invention; and 
           [0016]      FIG. 6  is a schematic view of signals outputted from the magnetic type position-sensing device in accordance with the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0017]    The present invention will be clearer from the following description when viewed together with the accompanying drawings, which show, for purpose of illustrations only, the preferred embodiment in accordance with the present invention. 
         [0018]    Referring to  FIGS. 4-5 , a magnetic type position-sensing device in accordance with a preferred embodiment of the present invention comprises a magnetic scale  10  and a sensor  20 . 
         [0019]    The magnetic scale  10  includes four magnetic strips  11 ,  12 ,  13 ,  14 . The respective magnetic strips  11 ,  12 ,  13 ,  14  include plural magnetic zones  111 ,  121 ,  131 ,  141 . The respective magnetic zones  111 ,  121 ,  131 ,  141  are equally divided into two parts that are N pole and S pole. The magnetic zones  111 ,  121 ,  131 ,  141  on the respective magnetic strips  11 ,  12 ,  13 ,  14  have the same length. The length of the magnetic zones  111  of the first magnetic strip  11  is two times as long as that of the magnetic zones  121  of the second magnetic strip  12 , the length of the magnetic zones  121  of the second magnetic strip  12  is two times as long as that of the magnetic zones  131  of the third magnetic strip  13 , and the length of the magnetic zones  131  of the third magnetic strip  13  is two times as long as that of the magnetic zones  141  of the fourth magnetic strip  14 , in other words, the magnetic zones of any two of the magnetic strips  11 ,  12 ,  13 ,  14  have different lengths, and the length of the magnetic zones of one of every two neighboring magnetic strips is twice as long as that of the other one. 
         [0020]    The sensor  20  is located on the magnetic scale  10  and includes four digital sensing readers  21 ,  22 ,  23 ,  24  that are located opposite the magnetic strips  11 ,  12 ,  13 ,  14  of the magnetic scale  10 , respectively, namely the first digital sensing reader  21  is opposite the first magnetic strip  11 , the second digital sensing reader  22  is opposite the second magnetic strip  12 , the third sensing reader  23  is opposite the third magnetic strip  13 , and the fourth sensing reader  24  is opposite the fourth magnetic strip  14 . The digital sensing readers  21 ,  22 ,  23 ,  24  are used to sense the magnetic polarity of the respective magnetic strips  11 ,  12 ,  13 ,  14 . The sensor  20  is further provided with an analogic sensing reader  25  opposite the fourth magnetic strip  14  to sense the magnetic polarity of the fourth magnetic strip  14 . The analogic sensing reader  25  and the fourth digital sensing reader  24  are located on the same magnetic poles of the neighboring magnetic zones  141 , for example, the analogic sensing reader  25  is located on an N pole of one of the magnetic zones  141  of the fourth magnetic strip  14 , and the fourth digital sensing reader  24  is located on an N pole of a magnetic zone  141  neighboring the one of the magnetic zones  141  of the fourth magnetic strip  14 . 
         [0021]    When the sensor  20  moves along the magnetic scale  10 , the respective digital sensing readers  21 ,  22 ,  23 ,  24  and analogic sensing reader  25  will move along the opposite magnetic strips  11 ,  12 ,  13 ,  14 , and thus the digital sensing readers  21 ,  22 ,  23 ,  24  and analogic sensing reader  25  will sense the magnetic zones  11 ,  121 ,  131 ,  141  of the respective magnetic strips  11 ,  12 ,  13 ,  14  one by one. The magnetic polarity sensed by the respective digital sensing readers  21 ,  22 ,  23 ,  24  and the analogic reader  25  also changes from N pole to S pole alternately, for example, when the first sensing reader  21  moves along the first magnetic strip  11 , the first sensing reader  21  faces the N pole of one of the magnetic zones  111  of the first magnetic strip  11 , after a first displacement, the first sensing reader  21  will face the S pole of the one of the magnetic zones  111  of the first magnetic strip  11 , after a second displacement, the first sensing reader  21  will face the N pole of another of the magnetic zones  111 . As a result, it can be found that the magnetic polarity sensed by the respective sensing readers  21 ,  22 ,  23 ,  24  and the analogic sensing reader  25  will change from N pole to S pole alternately. The respective digital sensing readers  21 ,  22 ,  23 ,  24  will cooperate with the sensed N poles and S poles to output high and low signals, and the analogic sensing reader  25  will cooperate the sensed N poles or N poles to output a sinusoidal signal. The signals outputted from the respective digital sensing readers  21 ,  22 ,  23 ,  24  and the analogic sensing reader  25  are integrated as shown in  FIG. 6 . 
         [0022]    Hence, the relative position of the sensor  10  and the magnetic scale  20  and the displacement of the sensor  10  can be roughly known from the signals outputted from the respective sensing readers  21 ,  22 ,  23 ,  24 . The analogic sensing reader  25  outputs the sinusoidal signal, and every sinusoidal wave represents 360 degrees, so that the sinusoidal wave can be divided into many parts as desired, the minimum value of every parts can be 1 degree, 0.1 degrees or 0.01 degrees. The rough positions of the digital sensing readers  21 ,  22 ,  23 ,  24  cooperating with the position of the corresponding sinusoidal wave of the analogic sensing reader  25  can precisely determine the relative position of the sensor  10  and the magnetic scale  20  and the displacement of the sensor  10 , for example, in the outputted signals, the signal of the first digital sensing reader  21  is high, the signal of the second digital sensing reader  22  is lower, the signal of the third digital signal  23  is low, and the signal of the fourth sensing reader  24  is low, therefore, it can be found that the position is located within the sixth pair of sinusoidal waves of the analogic sensing reader  25  (one pair of sinusoidal waves of the analogic sensing reader  25  includes two sinusoidal waves that have a 90 degree phrase angle difference therebetween). In addition to the abovementioned, as long as the degree of the signal of the analogic sensing reader  25  is known, as shown in  FIG. 6 , the relative position a of the sensor  10  and the magnetic scale  20  and the displacement of the sensor  10  can be precisely obtained. 
         [0023]    Therefore, it can be found that besides high environment adaptability, the magnetic type position-sensing device also has high resolution due to the analogic sensing reader  25 . The number of the magnetic strips and the number of digital sensing readers in accordance with the present invention are not limited to that described in the preferred embodiment. 
         [0024]    While we have shown and described various embodiments in accordance with the present invention, it is clear to those skilled in the art that further embodiments may be made without departing from the scope of the present invention.