Abstract:
A cooling apparatus for a linear motor is disclosed which effectively cools heat generated when the motor is driven and provides an accurately maintained motor characteristics. The cooling apparatus for the linear motor include a blower provided outside the linear motor, at least one or more supply pipes, the supply pipes being provided to predetermined locations of the stator, air guide holes coupled to the supply pipes, respectively, for guiding flow of an introduced air, and control valves provided to predetermined locations of the supply pipes, for controlling an amount of an introduced air.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a cooling apparatus for a linear motor, and more particularly to a cooling apparatus for a linear motor effectively cooling heat generated when the motor is driven and providing an accurately maintained motor characteristics. 
     2. Description of the Conventional Art 
     Linear motors having cold plates mounted on one edge of an armature are known in the art. Also, known are armatures having cooling coils or channel therein. These armatures are comprised of laminates of magnetic materials. 
     For example, a conventional linear motor, shown in FIGS. 1 and 2, is comprised of a “U”-shaped stator back plate  50  having inner surfaces thereof on which opposing permanent magnets  51 , each having N- and S-poles, are sequentially disposed with alternate N- and S-poles arrangements; and a rotor  55  having a frame  54  to which a plurality of coil units  53  are provided, with a gap C between the coil units and the stator  52 . 
     On a lower portion of the frame  54  are provided the coil units  53  having core, not shown, made of magnetic material or non-magnetic material around which plural coils are wound. 
     With the stator  52  and the rotor  55  being spaced apart from each other by a predetermined gap C, a thrust generated by the permanent magnets  51  and the coil units  53  makes it possible the movement of the rotor  55 . 
     As described above, the operation of the linear motor is made by applying electric current to the coil units by a controller (not shown). When current is supplied to the coil constituting the coil units  53 , magnetic field is generated from the coil and core. A thrust is then generated between magnetic field thus generated and permanent magnets  51  provided inside stator back plate  50 , causing a linear motion of the rotor  55  provided to a lower portion of the frame  54 . A moving speed of the rotor  55  linearly traveling along the inner side of the stator  52  and the thrust associated therewith and so forth may be controlled by the controller. 
     The repeated linear motion of the rotor  55  inside the stator  52  permits the production of eddy currents, currents and so forth induced in the permanent magnet  51 . This generates relatively higher temperature heat between the coil units  53  and the permanent magnets  51 . Heat generated between the coil units  53  and the permanent magnets  51  varies depending upon the rated currents determined by the coil diameter. 
     High temperature heat generated between the rotor and the stator causes magnetic characteristics of the rotor or the stator to be varied, which makes it difficult to perform a precise linear motor control. In other words, since the permanent magnet and coil units are generally made of material of lower thermal resistance, characteristics thereof are apt to vary due to heat generated between the rotor and the stator, thus resulting in different characteristics of the linear motor itself. 
     SUMMARY OF THE INVENTION 
     Therefore, it is an object of the present invention to solve the above-mentioned problems, by providing a cooling apparatus for a linear motor which effectively cools heat generated when the motor is driven and provides an accurately maintained motor characteristics. 
     Anther object of the present invention is to provide the cooling apparatus for the linear motor being capable of selectively cooling the motor by detecting a position of the moving linear motor to supply an air into air supply holes through a supply pipe installed at a bottom portion of a stator back plate, or to introduce an air into an air gap through supply pipes installed at both sides of the stator back plate. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a linear motor conventionally used. 
     FIG. 2 is a vertical sectional view of FIG.  1 . 
     FIG. 3 is a sectional view of a cooling apparatus for a linear motor in accordance with a first embodiment of the present invention. 
     FIG. 4 is a horizontal sectional view of FIG.  3 . 
     FIG. 5 is a sectional view of a cooling apparatus for a line motor in accordance with a second embodiment of the present invention. 
     FIG. 6 is a sectional view of a cooling apparatus for a linear motor in accordance with a third embodiment of the present invention. 
     FIG. 7 is a horizontal sectional view of FIG.  6 . 
     FIG. 8 is a sectional view of a cooling apparatus for a linear motor in accordance with a fourth embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     A cooling apparatus for a linear motor according to the present invention will be described in detail, with reference to the accompanying drawings. 
     Referring to FIGS. 3 and 4, a linear motor to which the present invention is applied is shown to include: a stator  52  having a plurality of permanent magnets  51  provided on inner side of a stator back plate  50 ; and a rotor  55  provided to one side of a frame  54  and configured to be moved in a specified moving direction along an inner side of the stator  52 . A blower  1  is further provided at a suitable location spaced apart from the linear motor. 
     The cooling apparatus for the linear motor according to a first embodiment of the present invention has the blower  1  placed at a predetermined location outside the linear motor, as shown in FIGS. 3 and 4. Air produced from the blower  1  is supplied through air supply pipes  3  each installed at a predetermined location of the stator  52  to predetermined areas of the stator  52  and the rotor  55 . Referring to FIG. 3, the air supply pipes  3  may be preferably provided on both side surfaces and a bottom surface of the stator back plate  50  of the stator  52 , but may be, alternatively, provided on one side surface and the bottom surface of the stator back plate  50 . The air supply pipe  3  has a central portion thereof for forming a through hole  2 , the through hole  2  communicating with air guide holes  4  for guiding the air introduced through the air supply pipe  3  into an air gap C in which the permanent magnets  51  are located. 
     The cooling apparatus for the linear motor according to the first embodiment can selectively supply the air from the blower  1  into a central area and lower area of the air gap C by way of the through hole  2  of the air supply pipe  3  and the air guide holes  4 . In other words, since the air introduced through the through hole  2  of the air supply pipe  3  and the air guide holes  4  is supplied to the central area of the air gap C, an effective cooling of heat generated from the permanent magnet  51  and coil units  53  can be accomplished. 
     Only a natural air circulation may be, alternatively, employed without a direct connection of the blower  1  to the through hole  2 , but with somewhat less cooling effect. 
     Next, as shown in FIG. 5, a cooling apparatus for a linear motor according to a second embodiment of the present invention has a configuration similar to that of the first embodiment, except that the air supply pipe  3  having a plurality of through holes  2  therein is provided at a bottom surface of the stator back plate  50 , the through holes  2  communicating with the air supply holes  5   a,  respectively. The air supply holes  5   a  longitudinally extend along the permanent magnet  51 . 
     The cooling apparatus for a linear motor according to a second embodiment thus constructed offers an advantage of further improvement in effectively cooling the permanent magnets by circulating an air passing through both sides of the permanent magnet, as well as in cooling the coil units  51 . The circulation of the introduced air, as indicated by arrow in FIG. 5, provides an effective cooling operation. 
     Next, a cooling apparatus for a linear motor according to a third embodiment of the present invention is shown in FIGS. 6 and 7. In the third embodiment, a control valve  5  is installed on predetermined location of the air supply pipe  3 . The control valve  5  is selectively opened or closed to supply an air into a central area or lower area of the air gap C, when the position of the rotor  55  is detected by a position detecting means (not shown). 
     Between the air supply pipe  3  and the stator back plate  50  are installed plural control valves  5  for controllably providing an intermittent air flow of the air guide hole  4 . For this, a control unit (not shown) is used for allowing only the control valve  5  located corresponding to the moving rotor  55  to become ON, and the remaining control valves  5  to remain OFF, thus resulting in minimal use of air required in a cooling operation without the air being wasted. 
     It is noted that the means for detecting position of the rotor  55  may be embodied in a conventional manner, e.g., by a hole sensor provided to the stator  52  and a magnet (not shown) for sensing the hole sensor and thus detecting a position, attached to a bottom surface of the rotor  55 . 
     The operation of the third embodiment according to the present invention will be described below. 
     The principal operation of the third embodiment is similar to that of the first embodiment, therefore the detailed description thereof will be omitted, except for differences therebetween. 
     With the use of the linear motor during a predetermined time period, high temperature heat is generated from the coil unit  53  and the permanent magnet  51 . The cooling of the generated heat is not dependent upon the simple supply of an air through the air gap C. The cooling is made by a concentrated cooling of only a heating area, which is made possible by, after detecting the position of the rotor  55  by the position detecting unit, only the control valve  5  located corresponding to the position of the moving rotor  55  being ON by the controller. Namely, the remaining valves  5  not facing with the moving rotor  55  remain OFF, so that an air is not supplied into the air gap C. The air supply by only the turned-ON control valve located corresponding to the position of the moving rotor  55  prevents undesirable loss of the air supplied to the air gap C. An air by a saved amount can also be directly supplied to the over-heated area of the rotor  55 , and therefore the relative amount of air further increases which can be used for cooling the rotor  55 . Thus, the cooling efficiency is further enhanced. 
     An embossing may be applied to a surface of the permanent magnet  51  or the coil unit  53 , the surface being contact with an air, within limits that the motor characteristics are maintained. This further increases in an air contact area, so that a better cooling efficiency is provided. 
     FIG. 8 shows a forth embodiment of the present invention where control valves  6  are, respectively, installed on predetermined locations of the air supply pipe  3 . The general operation of the fourth embodiment is similar to that of the above-described third embodiment, therefore the detailed description thereof will be omitted. 
     According to the foregoing, the linear motor of the present invention provides a minimal loss of a supplied air by supplying an air into the air gap C formed between the permanent magnet and the coil unit, and the characteristics fluctuation of the linear motor which may be caused by heat generated during the control of the linear motor can be minimized. Further, with an embossing applied to an air contact surface of the permanent magnet  51  or the coil unit  53  within limits that the motor characteristics are maintained, an increase in an air contact area and a thus better cooling efficiency can be provided.