Abstract:
A conveying apparatus capable for conveying a magnetic workpiece at high speed with low vibration and low noise, superior in durability, and capable of achieving a reduction in driving force. The conveying apparatus includes a non-magnetic rail having a guide surface for slidably guiding a first surface of a workpiece, a non-magnetic belt having a conveying surface in contact with a second surface of the workpiece and movable along the rail, driving means for running the non-magnetic belt in circulation, and a rotatable roller whose peripheral surface is in contact with the surface of the non-magnetic belt opposite to the feeding surface. Provided in the roller is a magnet adapted to generate a magnetic force having a component force for causing the second surface of the workpiece to be attracted to the roller through the intermediation of the non-magnetic belt and a component force for bringing the first surface of the workpiece into contact with the rail.

Description:
Priority is claimed under 35 U.S.C. § 119 to Japanese Patent Application No. 10-252271 filed in Japan on Sep. 7, 1998, the entire content of which is hereby incorporated by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a conveying apparatus and, in particular, to a conveying apparatus suitable for conveying magnetic workpieces such as lead frames. 
     2. Description of the Related Art 
     As a conventional example of a lead frame conveying apparatus, a guiding apparatus has been proposed in Japanese Utility Model Publication No. 7-35388, in which a lead frame is guided along the upper surface of a non-magnetic guide rail and in which a non-magnetic guide member is provided at one side edge of the upper surface of the guide rail. The apparatus also has magnets embedded in the guide member at appropriate intervals. In this apparatus, the side edge of the lead frame is attracted by the magnetic force and kept in contact with the guide member, so that a high level of positional accuracy can be achieved. Further, there is no need to provide a device for preventing the lead frame from going backward or a device for imparting tension. 
     In the above-described apparatus, however, it is necessary to employ transfer means such as a transfer lug for transferring the lead frame, and it is difficult to perform high-speed conveying with low vibration and low noise. Further, since the lead frame is in close contact with the guide member, there is frictional resistance between the lead frame and the guide member. When the transfer lug is engaged with the lead frame to transfer the lead frame, a large load is partially applied to the lead frame, and there is a danger of the lead frame being expanded or deformed. 
     To solve the above problem, U.S. Pat. No. 5,816,385 proposes a conveying apparatus capable of conveying a magnetic workpiece at high speed with low vibration and low noise and allowing high-accuracy positioning to be effected. This conveying apparatus serves to convey a magnetic workpiece having two adjacent surfaces. The apparatus comprises a non-magnetic rail having a guide surface for slidably guiding a first surface of the workpiece. The conveying apparatus also comprises a non-magnetic belt having a conveying surface in contact with a second surface of the workpiece and movable along the rail and driving means for running the belt. The conveying apparatus further comprises a magnet which is arranged at a position opposed to the rail through the intermediation of the belt and which generates a magnetic force including a component force for bringing the second surface of the workpiece into close contact with the belt and a component force for bringing the first surface of the workpiece into contact with the rail. 
     In the above conveying apparatus, the magnetic workpiece is conveyed in a state in which it is attracted to a magnet (yoke) through the intermediation of the non-magnetic belt. When conveying a workpiece requiring a large magnetic force, the friction between the non-magnetic belt and the magnet (yoke) increases. This friction leads to wear of the non-magnetic belt and the magnet (yoke) which results in a deterioration in durability and a degeneration in conveying position accuracy of the apparatus. Furthermore, a large driving force is required to drive the belt. 
     The wear on the non-magnetic belt and the magnet (yoke) may be avoided to some extent by performing low-friction surface treatment on the sliding surface of the non-magnetic belt or the yoke, or applying oil for lubrication. These solutions, however, are not permanent measures to solve the problem. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is an object of the present invention to provide a conveying apparatus capable of conveying magnetic workpieces at high speed with low vibration and low noise, superior in durability, and contributing to a reduction in driving force. 
     To achieve the above-described object, according to a first aspect of the present invention, there is provided an apparatus for conveying a magnetic workpiece having two adjacent surfaces, comprising a non-magnetic rail having a guide surface slidably guiding a first surface of the workpiece, a non-magnetic conveying member having a conveying surface in contact with a second surface of the workpiece and movable along the rail, driving means for running the non-magnetic conveying member, a rotatable roller whose peripheral surface is in rolling contact with a surface opposed to the conveying surface of the magnetic conveying member, and a magnet incorporated in the roller and adapted to generate a magnetic force having a component force for causing the second surface of the workpiece to be attracted to the roller through the intermediation of the non-magnetic conveying member and a component force for bringing the first surface of the workpiece into contact with the rail. 
     The second surface of the workpiece is attracted to the conveying surface of the workpiece by the magnet, so that, when the non-magnetic conveying member is moved along the rail by the driving means, the workpiece moves integrally with the non-magnetic conveying member. At this time, the first surface of the workpiece is slidably guided by the guide surface of the rail, so that the workpiece is conveyed while maintaining a stable attitude. The back surface of the non-magnetic conveying member, that is, the surface opposed to the conveying surface, is supported by the roller so that it can roll, so that the conveying member does not slide on the magnet (yoke). Since the conveying member does not slide on the magnet (yoke), wear of the conveying member and the magnet can be prevented. Further, since there is substantially no friction between the conveying member and the roller, it is possible to reduce the driving force for driving the belt. During conveying, the workpiece moves in contact with the non-magnetic member, so that concentration of load on a part of the workpiece does not occur. Thus, it is possible to convey the workpiece at high speed without applying excessive load to it, whereby deformation and deflection of the workpiece can be prevented. 
     When the non-magnetic conveying member is stopped abruptly, there is a danger of the workpiece undergoing positional deviation due to inertial force. In the present invention, however, the second surface of the workpiece is in close contact with the non-magnetic conveying member due to the magnetic force, so that, if the conveying member is stopped abruptly, the workpiece can be stopped without resulting in any positional deviation. Further, since there is no need to provide a device for preventing the workpiece from going backward or a device for imparting tension, the size of the apparatus can be reduced. 
     When the non-magnetic conveying member of the present invention is run no return operation is required. Since no return operation is required high-speed conveying is possible, and no violent vibration or noise is involved if the speed is increased. 
     According to another aspect of the present invention, there is provided a conveying apparatus for conveying a magnetic workpiece having two adjacent surfaces, comprising, a non-magnetic rail having a guide surface for slidably guiding a first surface of the workpiece, a plurality of rollers having peripheral surfaces in rolling contact with a second surface of the workpiece, driving means for causing the rollers to rotate in synchronism in the same direction, and magnets incorporated in the rollers and adapted to generate a magnetic force having a component force for causing the second surface of the workpiece to be attracted to the rollers and a component force for bringing the first surface of the workpiece into contact with the rail. 
     In the apparatus described above, the magnetic workpiece is directly attracted by the rollers, and the workpiece is conveyed in one direction by rotating the rollers. In this case also, as in the case of the first aspect of the present invention, the workpiece can be conveyed at high speed with low vibration and low noise. Further, positioning can be effected with high accuracy. In addition, the workpiece and the rollers are only in rolling contact with each other, and there is no sliding movement between them, so that wear of the workpiece and the rollers can be prevented. 
     According to yet another aspect of the present invention, it is desirable that the magnet incorporated in the roller be an axially magnetized permanent magnet, and that a yoke be mounted to at least one pole of this magnet, the guide surface of the rail being positioned near the border portion between one pole of the magnet and the yoke. According to this aspect of the present invention, it is possible to effectively generate a magnetic force having a component force for causing the second surface of the workpiece to be attracted to the roller and a component force for bringing the surface of the workpiece into contact with the rail. 
     In the present invention, it is desirable that the non-magnetic conveying member be formed of a material which is thin and which has low magnetic permeability so that the magnetic force of the magnet may be efficiently applied to the workpiece through the conveying member. 
     The magnetic force of the magnet has a component force for bringing the second surface of the workpiece into close contact with the conveying member and a component force for bringing the first surface of the workpiece into contact with the rail. In order to enlarge the force with which the workpiece is held in close contact with the conveying member and to make the sliding friction between the workpiece and the rail as small as possible, it is desirable to determine the position of the magnet such that the component force for bringing the second surface of the workpiece into close contact with the conveying member is larger than the component force for bringing the first surface of the workpiece into contact with the rail. 
     The present invention is suitable for the conveying of, among other things, a thin plate-like hoop material like a lead frame. In the case of a hoop material, deflection and deformation are apt to be generated when a large load is locally applied. However, in a system in which, as in the case of the present invention, the workpiece is conveyed while being attracted by magnetic force, it is possible to effect high speed conveying without locally applying excessive load to the hoop material. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a conveying apparatus according to a first embodiment of the present invention; 
     FIG. 2 is a sectional view taken along the line II—II of FIG. 1; 
     FIG. 3 is a perspective view of a conveying apparatus according to a second embodiment of the present invention; and 
     FIG. 4 is a sectional view taken along the line IV—IV of FIG.  3 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIGS. 1 and 2 illustrate a conveying apparatus according to the first embodiment of the present invention. This conveying apparatus is used to horizontally convey a lead frame W, which is an example of the workpiece. The lead frame W of this embodiment is stamped from a thin, strip-like magnetic metal plate (hoop material), and has on one longitudinal side a tie bar a having conveying holes and on the other side a plurality of terminal portions b formed integrally and protruding from the tie bar a substantially at right angles. 
     This conveying apparatus is equipped with a rail  1  slidably supporting the lower surface (first surface) of the tie bar a of the lead frame W. The rail  1  is formed of a non-magnetic material such as stainless steel, aluminum or resin, and the upper surface (guide surface)  2  of rail  1  can be provided with fluororesin coating or the like in order to reduce the frictional resistance between it and the lead frame W. The rail  1  is fastened to a side surface of a rail base  3 , which is formed of a non-magnetic material, by means of screws or the like. On the rail base  3 , a plurality of rollers  4  are longitudinally arranged at equal intervals. 
     As illustrated in FIG. 2, each roller  4  is equipped with a rotation shaft  5 , which is rotatably mounted to the rail base  3  through the intermediation of a bearing  6 . It is desirable to form the rotation shaft  5  of a non-magnetic material. Attached to the upper end portion of the rotation shaft  5  are an axially magnetized cylindrical permanent magnet  7  and yokes  8  and  9 . Yokes  8  and  9  are arranged at the poles of this permanent magnet  7 . The upper yoke  8  has a larger diameter than the lower yoke  9 , and its peripheral surface is in contact with the back surface of a non-magnetic belt  18  described below. The guide surface  2  of the rail  1  is positioned near the upper surface portion of the upper yoke  8 . While in this embodiment the yokes  8  and  9  are attached to the two poles of the permanent magnet  7 , it is possible to omit the yoke  9  which is on the side where the workpiece W is not attracted. 
     Referring again to FIG. 1, the longitudinal end portions of the rail base  3  are horizontally supported by support bases  10  and  11 . Secured to one support base  10  is a driving motor  12  consisting of a servo motor, pulse motor or the like. The rotation shaft  13  of the motor  12  is connected through a coupling  14  to a driving pulley  15  arranged on the upper surface of one end portion of the rail base  3 . On the upper surface of the other end portion of the rail base  3 , a rotatable driven pulley  16  is arranged, the rotation axis of this driven pulley  16  being guided so as to be movable in the longitudinal direction of the rail base  3  by a support mechanism (not shown). The rotation shaft of the driven pulley  16  is biased by a tension spring  17  in a direction opposite to the driving pulley  15 , imparting a predetermined tension to the non-magnetic belt  18  described below. 
     The belt  18  consists of a non-magnetic material. The non-magnetic belt  18  runs with tension between the driving pulley  15  and the driven pulley  16  and is driven horizontally. The non-magnetic belt  18  may be a resin belt or a metal belt such as a stainless steel belt. The non-magnetic belt  18  is formed thin, and its conveying surface (outer peripheral surface)  18   a  is horizontally movable through the gap between the upper yoke  8  and the rail  1 . The back surface of the non-magnetic belt  18  is supported by the peripheral surfaces of the rollers  4  (the peripheral surfaces of the yokes  8 ). The conveying surface  18   a  of the non-magnetic belt  18  is substantially perpendicular to the guide surface  2  of the rail  1 . The end surface of the tie bar a (the second surface) of the lead frame W is in close contact with the conveying surface  18   a . The speed at which the lead frame W is conveyed by the non-magnetic belt  18  can be varied through drive control of the motor  12 . In addition to continuous conveying, the apparatus can also operate using tact conveying and switching between forward and rearward conveying. 
     The operation of this conveying apparatus will now be described. 
     Since the yoke  8  and  9  are arranged at the upper and lower poles of the permanent magnet  7 , lines of magnetic force are concentrated in the border portions between the permanent magnet  7  and the yokes  8  and  9 , as illustrated in FIG.  2 . Since the guide surface  2  of the rail  1  is positioned in the vicinity of the border portion between the upper yoke  8  and the permanent magnet  7 , the tie bar a of the lead frame W sliding on the guide surface  2  is arranged at a position where lines of magnetic forces are concentrated, whereby it is most effectively influenced by the magnetic force. 
     The attracting force of the magnet  7  contained in the roller  4  can generate a component force X for bringing the end surface (second surface) of the tie bar a of the lead frame W into close contact with the non-magnetic belt  18 . The attracting force of the magnet  7  can also generate a component force Y for bringing the side surface (first surface) of the tie bar a of the lead frame W into close contact with the rail  1 . To bring the lead frame W into close contact with the non-magnetic belt  18  and to make the sliding friction between the lead frame W and the rail  1  as small as possible, the component force X is set so that it is larger than the component force Y. Due to the above attracting force of the magnet  7 , the end surface (second surface) of the lead frame W is held in close contact with the roller  4  through the intermediation of the non-magnetic belt  18 , and the side surface (first surface) of the lead frame W is held in contact with the guide surface  2  of the rail  1 . When the non-magnetic belt  18  is driven, the lead frame W is conveyed integrally with the non-magnetic belt  18 , wherein the lead frame W is in sliding contact with the rail  1 . Thus, it is possible to maintain a stable attitude if it is conveyed at high speed. Further, since the lead frame W is in contact with the non-magnetic belt  18  substantially over its entire length, it is possible to ensure the contact state over a long distance, so that no large load is locally applied to the lead frame W. Thus, even if the lead frame W is formed of a thin material, it is possible to prevent deformation, warpage, deflection, etc. of the lead frame W. Furthermore, since the non-magnetic belt  18  serving as the conveying member is driven in circulation, it is possible to restrain the generation of vibration or noise as in the case of conventional apparatuses using reciprocating conveying lugs or the like. 
     Further, since the back surface of the non-magnetic belt  18  is held in rolling contact with the roller  4 , it is possible to prevent deflection of the non-magnetic belt  18 . Further, since there is no sliding between the non-magnetic belt  18  and the roller  4  (yoke  8 ), it is possible to prevent them from being worn. Thus, it is possible to improve the durability of the non-magnetic belt  18  and the roller  4 , and to always secure a stable conveying position accuracy. Further, since there is substantially no friction between the non-magnetic belt  18  and the roller  4 , it is possible to diminish the driving force of the motor  12  for driving the non-magnetic belt  18 . Thus, it is possible to realize a small and inexpensive conveying apparatus. 
     When the non-magnetic belt  18  is stopped, the lead frame W is maintained in the stop position by the magnetic force of the magnet  7 , so that, if vibration or impact is applied to it in this condition, the position of the lead frame W does not get out of order, and a high level of positioning accuracy can be achieved. Thus, when this conveying apparatus is used in an electronic components assembly process or characteristic measurement process, there is little variation in the position of the electronic component. Further, since there is no need to provide a device for preventing the lead frame W from going backward or a device for imparting tension, the apparatus can be reduced in size and simplified. 
     When starting the non-magnetic belt  18  which has been at rest, a predetermined starting torque is necessary due to the friction between the non-magnetic belt  18  and the roller  4 . However, since the roller  4  is rotatable, the friction is small, so that the requisite starting torque for the motor  12  is small. Thus, even when the non-magnetic belt  18  is tact-conveyed or when switching between forward and rearward drive is effected, it is possible to drive with a small motor, thereby reducing the starting delay. 
     FIGS. 3 and 4 illustrate the second embodiment of the present invention. 
     A rail  20  consisting of a non-magnetic material and having a guide surface  21  is secured to a side surface of a rail base  22  which is formed of a non-magnetic material. On the rail base  22 , a plurality of driving rollers  23  are arranged in the longitudinal direction of the rail base  22  at equal intervals. As illustrated in FIG. 4, each roller  23  is equipped with a rotation shaft  25  rotatably mounted to the rail base  22  through the intermediation of a bearing  24 . Attached to the upper end portion of the rotation shaft  25  are an axially magnetized cylindrical permanent magnet  26  and yokes  27  and  28  attached to the poles of this permanent magnet  26 . It is desirable to form the rotation shaft  25  of a non-magnetic material. The upper yoke  27  has a larger diameter than the lower yoke  28 , and its peripheral surface is in contact with the end surface (second surface) of the lead frame W. The guide surface  21  of the rail  20  is positioned in the vicinity of the upper surface portion of the upper yoke  27 . A pulley  29  is mounted to the lower end portion of the rotation shaft  25 . 
     The end portions of the rail base  22  are horizontally supported on a table (not shown) by support bases  30  and  31 . On the table, a main shaft  33  whose end portions are rotatably supported by bearings  32  is arranged parallel to the rail base  22 . A motor  34  is connected to one end portion of the main shaft  33 , and rotates the main shaft  33  in the direction of the arrow A. Pulleys  35 , which are equal in number to the number of the driving rollers  23 , are attached to the main shaft  33  at equal intervals. Belts  36 , such as round belts, run between the pulleys  35  and the pulleys  29  which are mounted to the rotation shafts  25  of the rollers  23 . Thus, when the main shaft  33  is driven in the direction of the arrow A, all the driving rollers  23  rotate in synchronism in the direction of the arrow B. 
     In the conveying apparatus constructed as described above, the lead frame W is arranged in the border portion between the yoke  27  and the permanent magnet  26 , where, as shown in FIG. 4, lines of magnetic force are concentrated. By such an arrangement the lead frame W is most effectively influenced by the magnetic force. As in the first embodiment, the attracting force due to the magnetic force acting on the lead frame W can be divided into a component force X for bringing the end surface of the lead frame W into close contact with the rollers  23  (yokes  27 ) and a component force Y for bringing the side surface of the lead frame W into close contact with the rail  20 . 
     When the rollers  23  are driven, the lead frame W is held in sliding contact with the rail  20  and conveyed in the direction of the arrow, while being held in rolling contact with the rollers  23  by the attracting forces X and Y. Thus, even when it is conveyed at high speed, the lead frame can maintain a stable attitude. Further, since the rollers  23  are in close contact with the lead frame W at a plurality of positions, no great load is locally applied to the lead frame W. Thus, even if the lead frame W is formed of a thin material, it is possible to prevent deformation and deflection of the lead frame W. Further, since the lead frame W is in rolling contact with the rollers  23 , it is possible to prevent wear by friction between the lead frame W and the rollers  23  (yokes  27 ). Thus, it is possible to prevent a deterioration in the durability of the rollers  23 , and it is possible to ensure a stable conveying position accuracy. 
     While in the second embodiment the pulleys  29  and  35  and the belts  36  are used to drive the rollers  23  in synchronism, it is also possible, for example, to mount gears to the main shaft  33  and to mount gears in mesh with these gears to the shafts  25  of the rollers  23 . 
     Further, in the second embodiment, it is not necessary for all the rollers to be driving rollers. Some of the rollers may be idle (rotatable) rollers. 
     While the above embodiments have been described with reference to a single unit, when a plurality of units of FIG. 1 are connected in series, the conveying route is elongated, and it is possible to convey workpieces between a number of processes. In this case, by controlling the motors of the units, the belts of the units can be driven in synchronism. In this way, the addition or deletion of units can be easily effected according to the equipment specifications, whereby the degree of freedom in design can be enhanced. 
     While in the above embodiments the guide surface slidably guiding the first surface of the workpiece is a horizontal surface and the conveying surface in contact with the second surface of the workpiece is a vertical surface, it is also possible for the conveying surface to be a horizontal surface and for the guide surface to be a vertical surface. Further, there is no need for the guide surface and the conveying surface to be perpendicular to each other. They may make an angle different from the right angle, that is, they may be oblique to each other. Further, one of the two surfaces may be a curved surface. 
     While in the above embodiments yokes are attached to the two poles of the permanent magnet, it is also possible for the workpiece to be attracted to the guide surface and the conveying surface without using yokes. However, by using yokes, the magnetic force density is enhanced, whereby the workpiece can be attracted more effectively. 
     The magnet used in the present invention is not restricted to a permanent magnet. It is also possible to use an electromagnet. According to this aspect, the electromagnet can be demagnetized when extracting the workpiece from the conveying apparatus in order to facilitate the extraction of the workpiece. 
     The workpiece that can be conveyed in the present invention is not restricted to a lead frame having a tie bar on one side as in the embodiments. It is also possible to convey, for example, a pallet as shown in FIG. 9 of Japanese Unexamined Patent Publication No. 9-199516 or a lead frame having a liner portion on either side as shown in FIG. 11 of the same. 
     Since the non-magnetic conveying member and the driving rollers of the present invention are driven in fixed directions, so that there is no need to perform return operation as in the case of conveying lugs used in conventional apparatuses, whereby it is possible to convey the workpiece at high speed with low vibration and low noise. 
     Many different embodiments of the present invention may be constructed without departing from the spirit and scope of the present invention. It should be understood that the present invention is not limited to the specific embodiment described in this specification. To the contrary, the present invention is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the invention as hereafter claimed. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications, equivalent structures and functions.