Patent Publication Number: US-6701840-B2

Title: Hopper gripper drum

Description:
This application is a divisional of U.S. patent application Ser. No. 09/506,625 filed on Feb. 18, 2000 now U.S. Pat. No. 6,308,625. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to printing presses and more particularly to a device and method for transporting printed products. 
     2. Background Information 
     U.S. Pat. No. 5,447,302 purports to disclose an apparatus for removing paper products from a stack on a hopper. The apparatus has a rotatably mounted gripper drum which rotates about a central axis at a constant angular velocity. A stationary cam is rigidly mounted adjacent the gripper drum. A cam follower follows the outer side of the cam, and is attached at one end to a link, which also rotates with the gripper drum. The rotating link is pivotable about a pin, so that a variation in the cam radius can cause the link to pivot, so that an other end of the link compresses or stretches a spring. This other end of the link connects to a further link which can retract a toggle arm on which a gripper and a gripper seat are supported. If the toggle arm is pulled so that the gripper and the gripper seat accelerate in the same direction as the movement of the gripper drum, the gripper is opened. If the gripper and the gripper seat are slowed down relative to the gripper drum, the gripper is closed. 
     The device of the &#39;302 patent has the disadvantage that the link structure is complicated, especially in that a spring is required to force the cam to follow the cam follower. The repeated compression and expansion of the spring can lead to a weakening of the spring over many rotations and can cause the entire apparatus to malfunction. At high speeds, high spring forces must be maintained to keep the cam follower on the cam and the gripper from engaging properly. Departure of the follower from the cam can cause gripper malfunction or damage. 
     Moreover, the gripper force remains relatively constant regardless of toggle arm displacement. A large gripping force thus is necessary for thick products, which can then damage thin products if they are used on the same machine. 
     BRIEF SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a rotating gripper drum which is durable and which has improved high speed operating characteristics. An additional or alternate objective is to provide a reliable rotating gripper gripper drum. Another additional or alternate objective is to provide a method and device for gripping with increased gripping force as product thickness increases. 
     The present invention provides a gripper drum device comprising a drum body rotatable about a central axis, an actuating shaft rotatable within the drum body, a box cam follower connected to the actuating shaft for moving the actuating shaft, a gripper seat connected to the actuating shaft, a gripper connected to the actuating shaft, and a box cam, the box cam follower being located within the box cam for following the box cam. 
     The box cam of the present invention controls and limits the movement of the cam follower, and eliminates the need for a spring to force the cam follower. 
     Advantageously, a gripper seat may be moved about a first axis by a first link to the cam follower, and the first axis being different from an axis of the actuating shaft. The actuating shaft preferably is connected to the gripper by a second link. 
     By separating the link between the actuating shaft and the gripper seat from that between the cam follower and the gripper, gripping movement can be better controlled, so that, for example, a smoother pick-up of printed products can be obtained. 
     Advantageously, the second link connects directly to the cam follower and drives a rack of a rack-and-pinion mechanism, the pinion being connected to the gripper. The gripper seat preferably is connected directly on the first link, which is driven by a support link connected directly between the first link and the cam follower. 
     The gripper preferably is spring-loaded, in that a spring is located directly between the spring and a spring support attached to the rotating drum. Because the spring in the present embodiment acts only against the gripper, it may be compact and not suffer acceleration distortions which had been present in the prior art. Moreover, because the spring acts solely on the gripper, the gripping force advantageously may be increased as the gripped product becomes thicker. This permits a small initial load to be applied for thin products, and results in less damage to these products. Less wear of components and less required torque for the entire system thus is also results. 
     The present invention also provides a gripper drum comprising a drum body rotatable about a central axis, a gripper movable at an outer circumference of the drum body, a gripper seat for interacting with the gripper, and a cam follower connected to the gripper seat by a first link and connected to the gripper by a second link different from the first link. 
     The present invention also provides a method for gripping printed products including the steps of rotating a drum about a central axis, moving a cam follower within a box cam, and gripping a printed product with a gripper attached to the cam follower. 
     The term “box cam” as used herein is defined as a cam having a groove or slot in which a cam follower rides and which constrains the cam in both a radially outward and radially inward direction. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A preferred embodiment of the present invention is described below by reference to the following drawings, in which: 
     FIG. 1 shows a perspective view of the inside of a gripper drum of the present invention; 
     FIG. 2 shows the gripper drum of FIG. 1 gripping a printed product from a hopper; 
     FIG. 3 shows the cam follower which is attached to the side of the gripper drum not shown in FIG. 1; and 
     FIG. 4 shows a box cam of the gripper drum device of the present invention. 
    
    
     DETAILED DESCRIPTION 
     FIG. 1 shows a gripper drum  10  which has a drum body  12  which rotates about a central axis  14  in the direction of an arrow  16 . Gripper drum  10  preferably is driven at a constant velocity by a drive mechanism having a drive axle which rotates about central axis  14  and fits into the center of drum body  14 . Gripper drum  10  also includes a pin  20  which is attached at one end of a support link  22 . Connected rotatably to the other end of support link  22  through a pin  23  is a gripper seat link  24 , which is rotatable about an axis  26 . 
     A gripper seat  28  is attached to one end of gripper seat link  24 . Gripper seat  28  preferably is made of a high friction material, such as rubber. 
     A cam follower  120  (FIG.  2 ), on the side of the drum which is not shown, connects to a shaft  32 , which, on the side shown in FIG. 1, supports a follower link  30  attached by a pin  20  to a support link  22 . Follower link  30  is clamped fixedly to a shaft  32 . Shaft  32  also rotates a rack  34  geared to a pinion  36  of a rack and pinion mechanism. Pinion  36  is connected to a shaft  38 , on which is a gripper  40  having a gripper end  42 . 
     Gripper end  42  is spring-loaded to a closed position by a spring  46  attached to a spring support  44  connected to drum body  12 . 
     Gripper  40  and gripper seat  28  are movable relative to the drum body  12  within a slot  49  at the outer circumference of drum body  12 . 
     A second gripper mechanism  6  similar to that described above is located 180 degrees about drum body  12 . 
     The device is generally symmetrical to support a gripper  7  on the other side of drum  10 . However, on the opposite side of the drum, a gripper seat link is moved by virtue of axis or axle  26 , thereby eliminating the need for a support link similar to support link  22  on that side of the drum. 
     As shown in FIG. 3, on the opposite side of the gripper drum, which is not shown in FIG. 1, a support  130  is attached to the other end of shaft  32 . A cam follower  120  is attached to support  130 , and runs in a box cam  50  as shown in FIG.  4 . As stated, on the cam side of the drum  10  no similar link to link  22  is present, since the gripper seat link on the cam side is moved by the axle  26 , which extends through the gripper drum. 
     Gripper drum  10  operates as follows. As the gripper drum body  14  rotates, cam follower  120  follows a groove  52  in box cam  50 , as shown in FIG.  4 . Box cam  50  is located at the side of drum body  12  to receive cam follower  120 . In a section of groove  52  having an inner radius  54 , the gripper  40  is open and gripper  40  and gripper seat  28  are moved forward in groove  49  at the outer circumference of drum body  12 . 
     When cam follower  20  reaches a portion of groove  52  having a bigger radius  56 , cam follower  120  moves radially outward, which rotates axle  32  counterclockwise as shown in FIG.  1 . Link  22  then pulls an end of gripper seat link  24  so as to rotate axle  26  clockwise as shown in FIG. 1 by an arrow. Gripper seat  28  thus moves backward with respect to rotating drum body  12  (and opposite arrow  16  in FIG.  1 ). On the opposite side of the drum  10 , axle  26  activates a gripper seat link to likewise move a gripper seat of gripper  7  backwards. 
     At the same time, since cam follower  120  moves shaft  32  counterclockwise, rack  34  attached on shaft  32  is caused to rotate counterclockwise as shown in FIG.  1 . Pinion  36  thus rotates clockwise, as does shaft  38 , which causes gripper  40  to rotate. Gripper edge  42  thus moves backward (opposite the direction of arrow  16 ) in groove  49  and eventually closes on gripper seat  28 , thereby gripping a printed product on a hopper stack. The opposite side of drum  10  may have a similar rack attached on shaft  32  for activating a similar pinion mechanism. 
     Spring  44  and the positioning of gripper edge  42  with respect to the gripper seat  28  can control the strength of the grip in the closed position. The spring  44  provides gripping force for thicker products. 
     FIG. 2 shows the movement of gripper edge  42  and gripper seat  28  (FIG. 1) when gripping a product  60 . When cam follower  120  is in position  20 A, gripper seat  28  is in position  28 A and is apart from gripper edge  42  at position  42 A. As the cam follower  120  moves to position  20 B, gripper seat  28  moves forward to position  28 B and gripper edge to position  42 B. As the cam follower moves to position  20 C, gripper seat  28  is moving back in slot  49  (FIG. 1) opposite direction  16 . The motion of drum  10  in direction  16  is slightly faster than this backwards movement, so that gripper seat  28  still is moving in direction  16 , but slower than drum  10 . At the same time, gripper edge  42  has moved to position  42 C. 
     As the cam follower  120  moves outwardly to position  20 D, gripper seat  28  at position  28 D and gripper edge  42  at position  42 D grip product  60  from a hopper stack. As the cam follower moves on to position  20 E, the gripped product is moved forward, so that gripper edge  42  and gripper seat  28  are in position  42 E and  28 E, respectively. 
     Referring to FIG. 4, when the cam returns to inner radius  54 , the cam follower moves inwardly and releases the product  60 , for example, to a conveyor belt. 
     U.S. Pat. No. 5,447,302 is hereby incorporated by reference herein. 
     Advantageously, the rotational axis of the gripper seat link  24  and the rotational axis of drum  10  are different, which can permit better gripping characteristics.