Abstract:
A method for manufacturing teeth of a stator or rotor of a linear stepping motor includes a step of placing a mask above an object and the mask having apertures, and a step of hitting the object at high speed via the apertures by the particles so as to from teeth on the object.

Description:
[0001]     This application is a Continuation-in-Part of U.S. patent application Ser. No. 10/439,687, filed May. 16, 2003, to which application priority is claimed. 
     
    
     FIELD OF THE INVENTION  
       [0002]     The present invention relates to a method for making teeth of rotor or stator of linear stepping motors. The teeth are made by way of sand spreading which is easily to proceed and involves less pollution.  
       BACKGROUND OF THE INVENTION  
       [0003]     Linear stepping motors are used in a wide range of industry such as the picking machine for transferring chips or high speed chip examining machine. The linear stepping motors are functioned by the magnetic mutual affection between the stator and the rotor. In order to provide delicate feeding, tiny grooves are carved in the stator or the rotor so as to make teeth at the abutment portion between the stator and the rotor.  
         [0004]      FIG. 6  shows a conventional linear stepping motor and includes a core  82  and a coil  81  wrapped around the core  82 . Teeth  821  are defined in the core  82  and a stator  83  is located beneath the core  82 . The stator  83  has teeth  831  which are engaged with the teeth  821  of the core  82 . The core  82  and the coil  81  are moved relative to the stator  83  so that they are called stator in a motor. The shape of the teeth  821  and  831  is rectangular so that even only a tiny gap is moved between the stator and the rotor, a huge change is resulted in the magnetic lines and the change of the motor becomes too much severe.  
         [0005]     Generally, the way of the method for making teeth of the linear stepping motor is itching carving or milling. Either of the two methods has inherent shortcomings. For the milling, the milling tool has to be made to be able to make delicate teeth so that the tool is expensive. The gaps between teeth are so tiny so that it takes a lot of manufacturing time. Besides, the milling tool can only be move in linear direction so that it is difficult to make special shape of teeth. Because of the wearing on the milling tool, it is hard to maintain a desired precision of the teeth.  
         [0006]     For the itching carving, it involves too many steps and has a high manufacturing cost. Besides, the chemical used in the itching process includes pollutants.  
         [0007]     U.S. Pat. No. 6,155,245 (Zanzuri) discloses a method of producing detailed and precise cuts by using high pressure stream of fluid with an abrasive additive. However, this method is unable to produce complicated 3-dimensional shaped teeth, and the precision of the teeth is very difficult to be controlled. Moreover, this is wet processing, the related components must be dried, otherwise rust may appear and damage the motor. Consequently, the processing cost and the maintenance fee are relatively high.  
         [0008]     U.S. Pat. No. 6,368,195 (Oshio et al.) discloses a method for sandblast processing plasma display panel substrate by using a sandblasting-resistant photosensitive resin composition layer to keep abrasive particles from removing metal in the wrong locations. However, since the sandblasting-resistant photosensitive resin composition layer is formed on the object to be operated without any space left therebetween, the abrasive particles are unable to flow effectively. In this case, it will be very difficult to produce a very small pitch tooth, for example, the tooth pitch is 320 um in width and 100 um in width.  
         [0009]     The present invention intends to provide a method for making the teeth in a linear stepping motor and the method is less expensive and environmentally friendly.  
       SUMMARY OF THE INVENTION  
       [0010]     In accordance with one aspect of the present invention, there is provided a method for manufacturing teeth of linear stepping motors and the method is sand spreading. The particles of hard material such as alumina or silicon carbide, hit the surface of the stator or rotor at high speed so as to form the desired shape of teeth. The method does not involve pollutants as involved in the itching carving and the area of the stator or rotor that is not to be hit by the particles is masked by a mask so that the mask can be made to produce plural layers of teeth for the rotor or stator. The directions that the particles are sent or the molds from which the particles eject can be adjusted, and the times of spreading can also be increased so as to obtain smooth teeth and to reduce the change of the speed of the linear stepping motor.  
         [0011]     The present invention will become more obvious from the following description when taken in connection with the accompanying drawings which show, for purposes of illustration only, a preferred embodiment in accordance with the present invention. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]      FIG. 1  shows the method for manufacturing teeth of linear stepping motors of the present invention;  
         [0013]      FIG. 2  shows the linear stepping motor which is made by the method of the present invention;  
         [0014]      FIG. 3  shows one of the processes of the method the method of the present invention;  
         [0015]      FIG. 4  shows another one of the processes of the method the method of the present invention;  
         [0016]      FIG. 5  shows a chart of the comparison of cogging forces of different linear stepping motors;  
         [0017]      FIG. 6  shows a conventional linear stepping motor;  
         [0018]      FIG. 7  shows 3D shaped teeth produced according to the method of the present invention.  
         [0019]      FIG. 8  is a comparative view for showing the cogging forces which are caused by sandblast processing method and other processing methods. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0020]      FIG. 1  shows the method for manufacturing teeth of linear stepping motors. A mask  2  is placed above an object  1  to be manufactured and apertures  21  are defined through the mask  2  so that particles  5  pass through the apertures  21 . A pressurizing machine  4  provides energy for the particles  5  so that the particles  5  hit the surface of the object  1 . Only the area which is not covered by the mask  2  is hit by the particles  5  passing through the apertures  21 . The particles  5  make recesses  11  on the surface of the object  1  so that the area that is not covered forms the desired shape of teeth. The method is convenient to proceed and will not pollute the environment.  
         [0021]      FIG. 2  shows the linear stepping motor made by the method of the present invention, the linear stepping motor  8  includes a core  82  and a coil  81  which is wrapped around the core  82 . Teeth  822  are defined in the core  82  and a stator  83  is located beneath the core  82 . The stator  83  has teeth  832  which are engaged with the teeth  822  of the core  82 . The teeth  832  and  822  can be made by multiple times of spreading of particles  5  so that the teeth  832  can be made to be stepped teeth which improve the severe change of speed of the linear stepping motor.  
         [0022]      FIG. 3  shows the method for manufacturing the teeth  832  as shown in  FIG. 2 , wherein the mask  2   a  and  2   b  are respectively placed above the object. On the left side of  FIG. 3  shows the high speed particles  5  travel downward so as to form desired shape of teeth  12   a . On the right side of  FIG. 3  shows that the teeth  12   a  is covered by the mask  2   b  and the particles  5  hit the object so as to form stepped teeth  12   b.    
         [0023]     As shown in  FIG. 4 , masks  2   c,    2   d  and  2   e  are respectively placed above the object. The left of  FIG. 4  shows that the mask  2   c  covers the object and particles  5  hit downward the object so as to from teeth  12   c.  The middle and the right of  FIG. 4  show the apertures of the masks  2   d  and  2   e  has inclined inner periphery so that when the particles  5  pass through the apertures, the teeth  12   c  are formed to be teeth  12   d  and  12   e  having rounded teeth.  
         [0024]      FIG. 5  shows the cogging forces between three different linear stepping motors. One of the three linear stepping motors is a conventional linear stepping motor which has the teeth as shown in  FIG. 6  made by milling and is represented by circles in  FIG. 5 . The other two linear stepping motors in  FIG. 5  are stepped teeth as shown in  FIG. 3  and represented by rectangles, and rounded teeth as shown in  FIG. 4  and represented by triangles. A width of each tooth of a linear stepping motor is separated into  30  sections which are calculated the magnetic force by magnetic analysis software. The result shows that the change of the magnetic force of the linear stepping motors having stepped teeth and rounded teeth is less than the linear stepping motor having teeth made by conventional method. Accordingly, the speed change can be improved.  
         [0025]     The method of the present invention has better efficient and is friendly to the environment. The manufacturing cost is lower than conventional methods. The rounded and stepped teeth improve the change of speed of the linear stepping motors.  
         [0026]     On the hand, the method of the present invention is a dry processing method, the maintenance fee for the manufacturing cost is relatively low. And the mask is placed a distance above the object to-be-operated for allowing flow of the particles, thus, the method of the present invention can be used to manufacture the teeth whose teeth depth is over 300 um.  
         [0027]     In addition, the method of the present invention is able to produce complicated 3-dimensional shaped teeth as shown in  FIG. 7 .  
         [0028]      FIG. 8  is a comparative view for showing the cogging forces which are caused by sandblast processing method and other processing methods. When a linear stepping motor in use, strength disturbance (so-called cogging force) will be caused due to the flux interaction between the rotor and the stator, and the cogging force has a bad effect on the performance of the stepping motor. 3 dimensional teeth can be used to reduce the occurrence of the cogging force, so that not only the velocity ripple, the force ripple and the noise of the stepping motor can be reduced, but also the close loop control problem will be fixed.  
         [0029]     While we have shown and described the embodiment in accordance with the present invention, it should be clear to those skilled in the art that further embodiments may be made without departing from the scope of the present invention.