Patent Publication Number: US-6213369-B1

Title: Material feeding apparatus

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a material feeding apparatus, and particularly to an apparatus which intermittently feeds a material such as a sheet material, a wire material and the like to a working machine such as a press machine and the like at every fixed amounts. 
     2. Description of the Related Art 
     As an apparatus which feeds a material such as a sheet material, a wire material and the like to a working machine such as a press machine and the like, for example, Japanese Utility Model Examined Publication 60-27549 has been conventionally known. The apparatus is provided with a first gripper apparatus structured such as to perform a material clamping (gripping) operation and a material unclamping (releasing) operation between a first stationary gripper and a first movable gripper, and a second gripper apparatus disposed on a sliding block capable of oscillating along a transfer path of the material and structured such as to perform material clamping and unclamping operations between a second stationary gripper and a second movable gripper, and performs the material clamping and unclamping operation and the sliding block sliding operation by means of the first and second gripper apparatuses at a predetermined timing with using a cam apparatus, a swinging arm and the like. 
     In this case, since the apparatus is structured such as to control both of the first gripper and the second gripper by the single swinging arm which is swung by the single cam so as to perform the material clamping and unclamping operation by the first gripper apparatus and the second gripper apparatus, there has been a problem that it is hard to suitably set a timing of the operation of the first gripper apparatus and the second gripper apparatus. Particularly, it is impossible to design such that both of the first and second gripper apparatuses temporarily clamp the material at a starting time and a finishing time of each one of the material intermittent feedings, whereby the material is prevented from becoming a free state, so that it is hard to improve a feeding accuracy and make the feeding high-speed. 
     Then, in order to solve the problem, the applicant of the present application proposed Japanese Patent Unexamined Publication No. 63-82271. This apparatus respectively drives the first and second gripper apparatuses and the sliding block by independent cams so as to prevent a free state in which the material is not fully clamped from being generated during all the period of the material feeding operation, thereby making a high-speed and high-accuracy material feeding possible. 
     However, even the apparatus proposed by the applicant can not always satisfy a requirement with respect to the feeding accuracy and the feeding speed which have been required for this kind of feeding apparatus in recent days. 
     That is, in recent years, electronic information devices such as a portable telephone, a personal computer and the like are significantly spread, however, while these devices become compact and inexpensive, in a production field, in order to correspond to making parts compact and high-density, a feeding (a positioning of the material) at significantly higher accuracy than the conventional one is going to be desired. Further, in order to satisfy the requirement for improving a productivity, reducing a cost, mass production and the like, it is desired to provide an apparatus which can be operated at higher speed. 
     For example, in a press working industry, a requirement with respect to a high-speed operation has been increased year by year, and there is provided a press machine which can operate at two or three times higher speed than that of the conventional apparatus proposed by the applicant. However, in a current status, a feeding apparatus for supplying a material to the press machines does not always correspond to the operation speed of the press machine. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a feeding apparatus which can transfer and supply a material at higher speed and higher accuracy. 
     In order to achieve the object mentioned above and solve the problem, in accordance with a first aspect of the present invention, there is provided a material feeding apparatus comprising: 
     a first gripper apparatus which performs material clamping and unclamping operations by a first stationary gripper and a first movable gripper; 
     a second gripper apparatus which performs material clamping and unclamping operations by a second stationary gripper and a second movable gripper; 
     a sliding block which supports the first gripper apparatus and can oscillate in a material transfer direction; 
     a cam apparatus having a first cam which is fixed to an input shaft continuously rotated in one direction and has a predetermined cam surface shape for converting a rotating motion of the input shaft into a linear motion of the sliding block, a second cam which is fixed to the input shaft and moves the first movable gripper between a clamping position at which the first movable gripper is moved near the first: stationary gripper and an unclamping position at which the first movable gripper is moved apart from the first stationary gripper and a third cam which is fixed to the input shaft and moves the second movable gripper between a clamping position at which the second movable gripper is moved near the second stationary gripper and an unclamping position at which the second movable gripper is moved apart from the second stationary gripper; 
     a first gripper sliding apparatus having a swinging arm which swings in correspondence to a rotation of the first cam, and connecting means which operatively connects the swinging arm to the sliding block so as to convert a swing motion of the swinging arm into a linear motion of the sliding block; 
     a first gripper operating apparatus which operatively connects the second cam to the first movable gripper; 
     a second gripper operating apparatus which operatively connects the third cam to the second movable gripper; and 
     first urging means which always urges so that the sliding block, the connecting means and the swinging arm are closely connected to each other along a transfer path of a force from the first cam to the sliding block. 
     Further, in accordance with a second aspect of the present invention, there is provided a material feeding apparatus in the first aspect of the present invention, wherein the first gripper sliding apparatus is provided with a turret which swingably supports the swinging arm, and a cam follower which is rotatably placed in the turret and rotates a cam surface of the first cam, 
     the connecting means includes a sliding barrel which is placed in the swinging arm in such a manner as to change a distance from a center of rotation of the swinging arm, and a connecting member which is rotatably and slidably brought into contact with the sliding barrel so as to connect the swinging arm to the sliding block via the sliding barrel, 
     the first gripper operating apparatus is provided with a first movable gripper supporting rod which is placed in the sliding block in such a manner as to move between the clamping position and the unclamping position, and a first lift arm which swings together with the rotation of the second cam so as to move the first movable gripper supporting rod forward and rearward, 
     the first movable gripper supporting rod is provided with second urging means which urges the rod toward an engaging surface of the first lift arm, and a rolling element which is brought into rolling contact with the engaging surface of the first lift arm in such a manner as to move together with the sliding block, in one end portion thereof, 
     the second gripper operating apparatus is provided with a second movable gripper supporting rod which is placed in an apparatus housing in such a manner as to move between the clamping position and the unclamping position, and a second lift arm which swings together with a rotation of the third cam so as to move the second movable gripper supporting rod forward and rearward, 
     the first and second lift arms have cam followers which are respectively brought into rolling contact with the second and third cams, and third urging means which respectively urge these cam followers toward the second and third cams, and 
     the first urging means includes a spring which urges the sliding block in any one of a feeding direction and a returning direction of the material. 
     The applicant of the present application has considered the conventional apparatus including the proposed apparatus (Japanese Patent Unexamined Publication No. 63-82271) mentioned above, in order to further improve the material feeding accuracy and increase the feeding speed. As a result, the applicant found that the conventional apparatus had problems which prevent a further improvement of an accuracy and realization of a high speed, in view that many sliding mechanisms are used for the clamping and unclamping operation and the feeding operation of the gripper and the feeding at a desired accuracy is performed by completely holding the motion of the gripper in accordance with a shape of the elements. In order to perform the oscillating operation by means of this kind of hold type apparatus construction, a slight gap (play/backlash) is necessarily required between the parts, and this play generates a slight error in feeding. Accordingly, the applicant eagerly endeavors for developing a operating mechanism in place of the hold type apparatus construction, and as a result, provides the present invention. 
     A material feeding apparatus in accordance with the present invention supplies (feeds) a material basically by repeating a series of operations that material holding members (a stationary gripper and a movable gripper) called grippers grip (clamp) the material, for example, in a vertical direction, move in a feeding direction, release (unclamp) the material there and thereafter return to an original position. 
     However, in the apparatus in accordance with the present invention, only one of the forwarding and returning operations is performed by a hold type driving system by means of cams, and another operation (returning or forwarding) is performed by using an elastic force of urging means (for example, a spring). 
     That is, the apparatus in accordance with the present invention is provided with the first gripper apparatus and the second gripper apparatus which clamp and unclamp the material, and each of the gripper apparatuses has the stationary gripper and the movable gripper which moves forward and rearward with respect to the stationary gripper so as to clamp the material. The first gripper apparatus is arranged on the sliding block which can oscillate in the transfer direction of the material, and accordingly, the first gripper apparatus performs an oscillating motion together with the sliding block in addition to the clamping and unclamping operation of the material, thereby feeding the material. The first and second gripper apparatuses and the sliding block are driven by three cams (the first cam, the second cam and the third cam) which are fixed to the input shaft continuously rotated in one direction. 
     The first cam has a predetermined cam surface shape for converting the rotating motion of the input shaft into the linear motion of the sliding block, the second cam and the third cam has a predetermined cam surface shape for moving the movable gripper (the first movable gripper and the second movable gripper) of the respective gripper apparatuses between the clamping position at which the movable grippers (the first and second movable grippers) are moved near the stationary grippers (the first stationary gripper and the second stationary gripper) of the respective gripper apparatuses and the unclamping position at which the movable grippers are moved apart from the stationary grippers. 
     The first cam and the sliding block are connected to each other by the first gripper sliding apparatus provided with the swinging arm which swings together with the rotation of the first cam and the connecting means which converts the swinging motion of the arm into the linear motion of the sliding block, whereby the sliding block slides at a predetermined timing due to the rotation of the input shaft, so that the first gripper apparatus performs the material forwarding and returning operations. 
     The swinging arm is, preferably as the second aspect in accordance with the present invention, rotatably supported by a suitable rotary shaft and fixed on the turret provided with the cam follower for rolling the cam surface of the first cam. Further, in the swinging arm fixed on the turret in the manner mentioned above, the sliding barrel arranged in such a manner as to change the distance from the rotary shaft (the center of rotation of the swinging arm) is provided and the swinging arm and the sliding block are connected by the connecting member rotatably and slidably brought into contact with the sliding barrel in one end portion, whereby the connecting means stated in the first aspect in accordance with the present invention can be constructed. 
     The arranging position of the sliding barrel is set to be changeable because the operation stroke of the sliding block can be easily adjusted by enabling the connecting point between the swinging arm and the sliding block (the connecting member) to shift. For example, when shifting the sliding barrel in a direction of the front end of the swinging arm so as to move apart from the center of rotation of the swinging arm, it is possible to increase the moving distance of the sliding block so as to increase the feeding amount of the material. On the contrary, when moving the sliding barrel near the center of rotation of the swinging arm, it is possible to reduce the moving distance of the sliding block so as to reduce the feeding amount of the material. 
     In the apparatus in accordance with the present invention, there is provided with first urging means which urges so that the respective connections among the sliding block, the connecting means and the swinging arm become close with each other along the force transfer path from the first cam to the sliding block. By providing this urging means so as to always closely attach the members disposed from the first cam to the sliding block to each other during the operation, it is possible to apply an accurate feeding displacement given by a cam curve of the first cam to the first gripper apparatus. For example, since the members are always closely attached to each other by the urging means during a series of forwarding and returning operations even when any play exist between the first cam and the connecting means or between the members contained in the connecting means, the apparatus is not influenced by the play, so that a feeding at a high accuracy can be performed. 
     In this case, “the respective connections become close with each other” means that the members are always under a tensional state (a state of not generating a shift) in the force transmitting direction, and does not always mean only pressing the members to each other. Because it is possible to cancel the feeding error caused by the play between both the members as far as the members are always under the tensioned relation during a series of forwarding and returning operations even when urging the members in a tensioning direction. 
     In the second aspect in accordance with the present invention, the structure is made such that the first urging means is constituted by a spring and the sliding block is urged by the spring in any one of the forwarding direction and the returning direction. In this case, since a larger force is required in the forwarding operation in comparison with the returning operation, as an embodiment mentioned below, it is preferable to urge the sliding block in the returning direction so as to perform the forwarding operation by the rotational torque of the first cam and perform the returning operation by an elastic force of the spring. 
     On the contrary, the first and second gripper apparatus which perform the clamping and unclamping operations of the material, and the second and third cams driving them are respectively connected by the first gripper operating apparatus and the second gripper operating apparatus. These operating apparatuses transmit the predetermined motions on the basis of the respective cam surface shapes of the second cam and the third cam to the movable gripper of the first gripper apparatus and the movable gripper of the second gripper apparatus. 
     In the second aspect in accordance with the present invention, each of the first and second gripper operating apparatuses is provided with the movable gripper supporting rod and the lift arm. These movable gripper supporting rods are arranged in the sliding block or the apparatus housing so as to be movable between the clamping position and the unclamping position, and urged toward the engaging surface of the lift arm by the second urging means. On the contrary, the lift arm is provided with the cam follower which is brought into rolling contact with the second cam or the third cam, and provided with the third urging means which presses the cam follower to the second cam or the third cam, thereby swinging together with the rotation of the cam. Accordingly, the first movable gripper and the second movable gripper moves forward and rearward with respect to the first and second stationary grippers at a predetermined timing on the basis of the cam surface shapes of the second cam and the third cam, so as to perform each of the clamping and unclamping operations of the material. 
     Further, the first gripper apparatus is oscillated in the transfer direction of the material together with the sliding block as mentioned above, however, in order to enable the operation, the first movable gripper supporting rod is provided with the rolling element which is brought into rolling contact with the engaging surface of the first lift arm at one end portion thereof. It is possible to easily move the first gripper apparatus in the forwarding direction and the returning direction while maintaining the clamping or unclamping state by means of the gripper by bringing the first movable gripper supporting rod into rolling contact with the first lift arm. In this case, it is preferable that the contact system between the first movable gripper supporting rod and the lift arm mentioned above is performed by the rolling contact in the manner stated in claim  2  in view of reducing the operation resistance of the sliding block, however, the structure can be made such that a suitable sliding member is provided in place of the rolling element so as to be brought into sliding contact therewith. 
     Further, the second and third urging means mentioned above can be constituted by, for example, a spring (a coil spring, a plate spring and the like) in the same manner as the first urging means mentioned above. 
     As mentioned above, in accordance with the material feeding apparatus of the present invention, in comparison with the conventional apparatus, it is possible to feed and supply the material at a higher speed and at a higher accuracy. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematically perspective view which shows an outer appearance of a material feeding apparatus in accordance with an embodiment of the present invention; 
     FIG. 2 is a perspective view which schematically shows a part of an inner structure of the feeding apparatus in accordance with the embodiment; 
     FIG. 3 is a horizontal cross sectional view which shows an inner structure of the feeding apparatus in accordance with the embodiment; 
     FIG. 4A is a cross sectional view along a line  4 A— 4 A in FIG. 3; 
     FIG. 4B is a cross sectional view along a line  4 B— 4 B in FIG. 3; 
     FIG. 5 is a vertical cross sectional view which shows an inner structure of the feeding apparatus in accordance with the embodiment; 
     FIG. 6A is a notional view which shows an operation of the feeding apparatus in accordance with the embodiment (at a time of starting a forwarding operation); 
     FIG. 6B is a notional view which shows an operation of the feeding apparatus in accordance with the embodiment (at a time of finishing a forwarding operation); 
     FIG. 6C is a notional view which shows an operation of the feeding apparatus in accordance with the embodiment (at a time of starting a returning operation); 
     FIG. 6D is a notional view which shows an operation of the feeding apparatus in accordance with the embodiment (at a time of finishing a returning operation); 
     FIG. 7A is a plan view which shows a forwarding operation (a state before forwarding) in the feeding apparatus in accordance with the embodiment; 
     FIG. 7B is a plan view which shows a forwarding operation (a state after forwarding) in the feeding apparatus in accordance with the embodiment; 
     FIG. 8A is a vertical cross sectional view which shows an inner structure of the feeding apparatus in accordance with the embodiment as seen from an  8 A direction in FIG. 2; 
     FIG. 8B is a vertical cross sectional view which shows an inner structure of the feeding apparatus in accordance with the embodiment as seen from a  8 B direction in FIG. 2; 
     FIG. 9A is a front elevational view which shows a slide mechanism of a sliding barrel provided in the feeding apparatus in accordance with the embodiment; 
     FIG. 9B is a plan view which shows a slide mechanism of a sliding barrel provided in the feeding apparatus in accordance with the embodiment; 
     FIG. 10A is a plan view which shows an embodiment that a moving stroke of a sliding block is changed by the sliding mechanism (a case of increasing the stroke); and 
     Fig  10 B is a plan view which shows an embodiment that a moving stroke of a sliding block is changed by the sliding mechanism (a case of reducing the stroke). 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     An embodiment in accordance with the present invention will be described below with reference to the accompanying drawings. FIGS. 1 to  5  and FIGS. 6A to  8 B respectively show a structure and an operation of a feeding apparatus in accordance with an embodiment of the present invention. 
     As shown in these drawings, a feeding apparatus  11  is provided with a first gripper apparatus  21  and a second gripper apparatus  41  which respectively have stationary grippers  22  and  42  and movable gripper  23  and  43  and perform a clamping (gripping) operation and an unclamping (releasing) operation of a material  14 , and is structured such as to supply the material  14  to a working machine, for example, a press apparatus  91  in accordance with an intermittent feeding operation. A particular structure of each of portions of the apparatus will be described later, however, a basic operation of the feeding apparatus  11  will be at first described with reference to FIG.  6 . 
     The feeding apparatus  11  is operated as shown in FIG. 6A such that at first (1) the first gripper apparatus  21  clamps the material, and (2) the second gripper apparatus  41  unclamps the material  14 . Next, as shown in FIG. 6B, (3) the first gripper apparatus  21  moves in a forwarding direction of the material  14  (in a rightward direction in the drawing), whereby the material  14  clamped by the first grippers  22  and  23  is forwarded to the press apparatus  91 . Next, (4) as shown in FIG. 6C, the second gripper apparatus  41  clamps the material  14  and thereafter, (5) the first gripper apparatus  21  unclamps the material  14 . (6) As shown in FIG. 6D, the first gripper apparatus  21  moves in a returning direction (in a leftward direction in the drawing) and returns to an original position. 
     It is possible to supply the material  14  to the press  91  (a metal mold  92 ) by repeating these series of operations (1) to (6). In this case, the first gripper apparatus  21  is placed on a sliding block  61  (not illustrated in FIGS. 6A to  6 D) arranged in such a manner as to oscillate in a transfer direction of the material  14 , an oscillating operation (forwarding and returning operations) of the first gripper apparatus  21  is performed by moving the sliding block  61 . 
     Next, a description will be given of a particular structure and an operation of each of portions in the apparatus mainly with reference to FIGS. 1 to  5 ,  7 A,  7 B,  8 A and  8 B. The apparatus  11  is provided with a cam apparatus having three cams (a first cam  16 , a second cam  17  and a third cam  18 ) subsequently fixed to an input shaft  12  as shown in FIG. 3, so as to make the first gripper apparatus  21 , the second gripper apparatus  41  and the sliding block  61  to perform the predetermined operation mentioned above. The input shaft  12  is fixed to an apparatus housing  13  via bearings  19  and  19   a,  a rotation is transmitted from a crank shaft of the press machine via a timing belt, a pulley  10  and the like at a predetermined timing, and the present apparatus  11  is simultaneously operated with the press machine by being continuously rotated in one direction. 
     On the contrary, the first cam  16  forms a taper-like rib on a peripheral surface for converting a rotating motion of the input shaft  12  into a linear motion of the sliding block  61 , and constitutes a roller gear cam having both side surfaces of the taper rib as a cam surface. The second cam  17  and the third cam  18  are respectively constituted as plate cams setting peripheral surfaces to cam surfaces formed in a predetermined shape for moving the movable grippers  23  and  43  between a clamping position at which the movable gripper  23  and  43  are moved near the stationary grippers  22  and  42  and an unclamping position at which the movable grippers  23  and  43  are moved apart from the stationary grippers  22  and  42 . 
     In this case, the structure is made such that the operations (the oscillating operation of the first gripper apparatus  21 , the clamping and unclamping operation of the first gripper apparatus  21  and the clamping and unclamping operation of the second gripper apparatus  41 ) necessary for feeding the material  14  are performed by three independent cams  16  to  18  as mentioned above, because a timing design of each of the portions (each of the operations) can be easily performed. 
     The first gripper apparatus  21  is fixed on the sliding block  61 . The sliding block  61  is placed in the apparatus housing  13  in such a manner as to oscillate in a transfer direction of the material  14 , and accordingly the first gripper apparatus  21  performs an oscillating operation together with the sliding block  61 . 
     Then, as means (the first gripper sliding apparatus) for operatively connecting the first cam  16  to the first gripper apparatus  21 , the apparatus  11  in accordance with the present embodiment has a swinging arm  64  which swings together with a rotation of the first cam  16 , and a connecting rod  66  which connects the swinging arm  64  to the sliding block  61 . The swinging arm  64  is mounted to a turret  63  rotatably placed to the apparatus housing  13  via a flange  81  and a bearing  82  shown in FIG. 5, and the turret  63  has cam followers  62  and  62   a  which is engaged with the cam surface of the first cam  16 . These cam followers  62  and  62   a  rolls the cam surface of the cam together with the rotation of the first cam  16 , rotate the turret  63  as shown in FIGS. 7A and 7B, and swings the arm  64  fixed thereto. 
     The connecting rod  66  connects one end thereof to the sliding block  61  and brings the other end into contact with a semi-spherical sliding barrel  65  provided on the swinging arm  64  in a rotatable and slidable manner, so that it is possible to maintain a connecting state of both the elements  61  and  64  even when an angle formed by the arm  64  and the sliding block  61  changed in correspondence to the swinging motion of the arm  64 . 
     Further, the sliding barrel  65  can be slid in a longitudinal direction of the swinging arm  64  by a suitable slide mechanism, and the structure is made such as to change a distance from a center  64   a  of rotation of the arm  64 . Because it is possible to change a moving amount of the sliding block  61  so as to adjust a feeding amount of the material  14  by changing a position of the sliding barrel  65 . 
     For example, as shown in FIG. 10A, when shifting the sliding barrel  65  in a direction of a front end of the sliding arm  64  so as to move apart from the center  64   a  of rotation of the swinging arm  64 , it is possible to increase a moving distance ×1 of the sliding block  61  so as to increase the feeding amount of the material  14 . On the contrary, as shown in FIG. 10B, when moving the sliding barrel  65  near the center  64   a  of rotation of the swinging arm  64 , it is possible to reduce a moving distance ×2 of the sliding block  61  so as to reduce a feeding amount of the material  14 . 
     A sliding mechanism of the barrel  65  can be constituted, for example, by meshing a base  67  which holds the sliding barrel  65  and the connecting rod  66  with a male screw portion  87  of a feeding amount adjusting handle  86  fixed to the apparatus handle  13  via a bearing  85  as shown in FIGS. 9A and 9B. When rotating the handle  86 , the base  67  moves in a longitudinal direction of the swinging arm  64  so as to shift the sliding barrel  65 . In this case, the structure is made such that a connecting point between the connecting rod  66  and the sliding block  61  can be shifted in correspondence to the sliding operation of the barrel  65 . 
     Further, in this feeding apparatus  11 , as shown in FIGS. 7A and 7B, there is provided coil springs  70  and  70   a  which urges the sliding block  61  in a returning direction (a direction opposite to a direction of forwarding the material; a leftward direction in FIGS. 6A to  6 D and  7 A to  7 B). These springs  70  and  70   a  serves a function of returning the sliding block  61  and the first gripper apparatus  21  to an original position (FIGS. 7A,  6 A and  6 D) prior to the forwarding, and performs an operation of always pressing the sliding block  61  to the swinging arm  64  during the operation of the apparatus  11 , so that the respective members which realize the forwarding of the material from the first cam  16  to the sliding block  61  due to the urging force of the springs  70  and  70   a,  that is, the respective members comprising the first cam  16 , the cam follower  62  (the turret  63 ), the swinging arm  64 , the sliding barrel  65 , the connecting rod  66  and the sliding block  61  are always closely attached to each other, whereby it is possible to prevent the feeding error of the material from generating due to the gap (play) which may exist between the respective members. 
     Means for connecting the second cam  17  to the first movable gripper  23  (a first gripper operating apparatus) and means for connecting the third cam  18  to the second movable gripper  43  (a second gripper operating apparatus) are provided with movable gripper supporting rods (a first movable gripper supporting rod  24  and a second movable gripper supporting rod  44 ) which are provided in such a manner as to be movable between the clamping position and the unclamping position, and lift arms (a first lift arm  31  and a second lift arm  51 ) which swing together with a rotation of the second cam  17  or the third cam  18  so as to vertically move the movable gripper supporting rods  24  and  44 , as shown in FIGS. 4A,  4 B,  8 A and  8 B. 
     The respective movable gripper supporting rods  24  and  44  are respectively constituted by two rods  24  and  24   a,  and  44  and  44   a,  and the first movable gripper supporting rods  24  and  24   a  are placed in the sliding block  61  and the second movable gripper supporting rods  44  and  44   a  are placed in the apparatus housing  13 , respectively in such a manner as to move in a vertical direction. The first movable gripper  23  and the second movable gripper  43  are respectively mounted at the upper ends of these rods  24 ,  24   a,    44  and  44   a,  and contact elements  26  and  46  which are brought into contact with the upper surfaces of the respective lift arms  31  and  51  are provided at the lower ends thereof. Further, in order to always keep contact between the lift arms  31  and  51  so as to securely perform the clamping and unclamping operation of the material, the rods  24 ,  24   a,    44  and  44   a  are respectively urged downward by the springs  25 ,  25   a,    45  and  25   a.  Further, in particular, the contact element  26  of the first movable gripper supporting rod is structured such as to rotate the upper surface  35  of the first lift arm  31  together with the sliding operation of the sliding block  61 . 
     On the contrary, the lift arms  31  and  51  are provided in such a manner as to freely swing around a common supporting shaft  20  placed in the housing  13  as shown in FIG. 3, are respectively provided with cam followers  32  and  52  which are respectively brought into rolling contact with the second cam  17  and the third cam  18 , at the front ends thereof, and have coil springs  33  and  53  which respectively urge the cam followers  32  and  52  toward the second and third cams  17  and  18 . Further, in particular, the first lift arm  31  operating the first movable gripper  23  forms an upper surface  35  thereof wider with respect to a moving direction (a lateral direction in the drawing) of the sliding block  61  as is understood from FIG. 8A, and is structured such that the contact element  26  of the first movable gripper supporting rod can roll on the upper surface  35 . 
     Accordingly, the first gripper apparatus  21  (the first stationary gripper  22 , the first movable gripper  23  and the supporting rod  24 ) can move in the transfer direction of the material (in a lateral direction in FIG.  8 A) together with the sliding block  61  while maintaining its state without relation to the swinging state of the first lift arm  31 , that is, whether the first gripper apparatus  21  is in a clamping state or in an unclamping state. 
     In accordance with the apparatus  11  of the present invention, since it is possible to always press the sliding block  61  to the swinging arm  64  during the forwarding operation of the material  14  and the returning operation of the gripper  21  so as to improve a close attachment between the members between the first cam  16  and the sliding block  61  which oscillate the first gripper apparatus  21 , it is possible to cancel a feeding error due to the gap (play) existing between the members and realize a feeding operation at a significantly higher accurate in comparison with the conventional feeding apparatus which is driven by mechanically restricting both of the forwarding and returning operations. Further, since the operating members are always driven in a close attached state, there is a little possibility of generating a vibration and a sound, so that a high speed operation can be performed. Further, since a connecting structure between the cam apparatus and each of the gripper apparatuses is relatively simple, it is possible to reduce a manufacture cost for the apparatus, troubles are reduced, and a maintenance can be easily performed, so that it is advantageous in view of a running cost. 
     A kind and a shape of the material to be subjected by the present invention are not limited. It is possible to construct an apparatus for transferring, for example, a linear material (wire material) in addition to the plate-like material on the basis of the present invention. In this case, in order to correspond to the material shape of such a linear material, it is possible to suitably change the shape of the grippers (the stationary grippers  22  and  42  and the movable grippers  23  and  43 ).