GRIPPER FOR SHEET HANDLING EQUIPMENT

Abstract: A gripper mechanism for printing press folding machines or other sheet handling equipment comprises a rigid holder (24) mounted on a pivot shaft (22) and a resilient gripper finger (26), fixed to the holder (24), which pivots into engagement with a clamping surface (32). The tip (34) of the gripper finger (26) and the point (36) where the finger is attached to the holder (24) lie generally along a common radius (38) through the pivot axis (22), to produce non-sliding engagement of a sheet of paper positioned over the clamping surface (32) and said tip (34).

Description: GRIPPER FOR SHEET HANDLING EQUIPMENT The present invention relates to grippers used in printing press folding machines and in other sheet handling equipment, and more particularly to a gripper which clamps one or more sheets of paper in a non-sliding engagement. In a web-fed printing press, multiple cosies of matter are printed simultaneously on a continuous web of sheet material. The web is slit into ribbons, which are in turn cut into sheets of the printed product. The cut sheets are delivered to the collect cylinder of a folding machine, which grips the sheets and transports them to a jaw cylinder. The folding machine subsequently folds the products at an appropriate point prior to the binding operation. One aspect of the assembly of the final product from the printed web involves the ability of the collect cylinder to deliver successive intermediate products to the jaw cylinder directly, which is referred to as "straight delivery" or to collect two or more intermediate products and deliver the collected products to the jaw cylinder, which is referred to as "two collect" or "three collect". The collect cylinder should be capable of handling products of various sizes, both as to sheet size and the number of sheets that make up the end product. The collect cylinder of the folding machine generally includes grippers positioned-axially upon its surface. The grippers clamp the sheets of paper to the surface of the cylinder prior to the folding operation. Each gripper is pivotally mounted within the collect cylinder, and is actuated by a cam in a pre-dete#ined, timed relationship. My co-pending U.S. application Serial No. 271,407 filed June 8, 1981, discloses a rotary folding machine for a printing press, having a novel collect cylinder that can easily and quickly be adjusted to handle products of various sizes and to change the mode of product delivery. As disclosedin the specification of U.S. application Serial No. 271, 07 which is incorporated herein by reference, a collect cylinder typically has multiple spaced pairs of grippers around the outside circumference of the collect cylinder. It is important that the gripper used in the collect cylinder of a folding machine clamp the sheets of paper securely to the surface of the cylinder. When the position of the product on the collect cylinder is altered, the product can be folded -at an incorrect point, thus ruining the final result. In addition, if the product slides along the surface of the collect cylinder, the sheets will not register1 also producing an undesirable final result. Three types of grippers have been developed for use in folding machines. In a spring type gripper, a resilient gripper, which is fixed to a pivot shaft, rotates into engagement with a fixed clamping surface on the cylinder, and the gripper acts as a spring to clamp the product to the cylinder. In a rigid gripper, a non resilient gripper is rigidly fixed to a pivot shaft and pivots into engagement with a clamping surface which is spring loaded on the cylinder. Such existing gripper constructions tend to be high wear items requiring frequent maintenance. In such constructions, the gripper is prone to slide on the surface being gripped, as the resilient clamping force is increased, changing the position of the product and resulting in poor fold or sheet register. Each time a different thickness of printed matter is to be collected, many of such known grippers must be readjusted. In the third type of gripper mechanism, a rigid gripper, which engages a rigid surface of the cylinder, is rotatably mounted, rather than fixedly mounted, on the pivot shaft. The gripper is spring biased on the pivot shaft, such that when the shaft is pivoted and the gripper engages the fixed clamping surface, the pivot shaft continues to rotate against the force of the spring mechanism, loading the spring. The increasing spring force is transmitted through the rigid gripper to the rigid clamping surface. While this arrangement, which is illustrated in U.S. patent No. 1,600,790 to Blaine, can produce non-sliding engagement, it is more complicated in construction than the aforedescribed arrangements, and by design tends to wear. SUMMARY OF THE INVENTION The present invention is a new and improved gripper mechanism for use in a printing press folding machine or in other sheet handling equipment, which may be used to clamp variable numbers of sheets of papers to the collect cylinder, and which, due to its structural geometry, produces non-slip engagement of the sheets by the gripper. More particularly, the present invention is a gripper mechanism which may be mounted on the collect cylinder of a folding machine. A holder is mounted on a pivot shaft, which is mounted to the collect cylinder for pivoting rotation in an axis parallel to the rotational axis of the collect cylinder. A resilient gripper finger is fixed to the holder and extends outwardly from a point on the holder. The tip of the gripper finger is arranged to engage a clamping surface, which may be part of the gripper mechanism proper or a portion of the surface of the collect cylinder. When the product. is to be gripped or "taken" by the gripper assembly, the holder shaft pivots to move the gripper tip to open and reclose the gripper. This opening and closing motion is then repeated at the point where the product is released to a jaw cylinder. The clamping surface preferably angled, or beveled, toward the gripper tip such that the tip approaches the clamping surface at an obtuse angle. In accordance with the present invention, the gripper tip and the point where the resilient finger is attached to the holder lie generally along a common radius of the rotational arc, i.e., passing through the pivotal axis of the holder. Accordingly, when the gripper finger rotates into engagement with the surface, the geometry of the mechanism is such that further rotation of the holder about its axis, to increase the resilient holding force of the finger against the surface, does not impart any substantial radial component of motion to the gripper tip, and the tip remains substantially stationary on the surface as the gripping force is increased. Preferably, the gripper finger is at least partially curved, to permit elongation of the finger in the longitudinal direction to compensate for the rotational movement of the holder. In one form, the gripper finger is substantially Zshaped, and the oppositely oriented curved portions (that define the Z) lie on opposite sides of the tip radius. The upper and lower finger portions of the Z are oriented at other than 900 to the radius to cause the curved portions, upon engagement of the tip and clamping surface, to flex or bow. Accordingly, an advantageous bending is produced to provide the compensating elongation of the gripper finger. Since, as described above, the further rotation of the holder, after the tip engages the clamping surface, imparts only a small or zero component of radial motion to the tip, the tip need only compensate for the small elongation required by the movement of the pivot point away from the gripper tip. In other words, by flexing, the pivot point pulls away slightly from the tip, but the flexing force per se does not impart motion to the tip. Accordingly, non-sliding engagement results. Preferably, the clamping surface is beveleO#W3955 extend below the cylindrical surface of the collect cylinder. Accordingly, when the gripper tip moves into engagement with the beveled surface, it engages the surface and thereby the paper at an obtuse or at substantially a right angle. Moreover, once clamped the leading edge of the sheet is disposed below the cylinder surface and removed from the air stream, i.e. tucked into a cavity. Beveling of the clamping surface below the outside cylinder surface also promotes better friction between the paper and the cylinder due to-the fact that the leading edge of the paper is wrapped around the beveled edge. For a better understanding of the invention, reference is made to the following detailed description of a preferred embodiment, taken in conjunction with the drawings accompanying the application. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a partial sectional view of a collect cylinder, taken along-a plane perpendicular to the axis of the cylinder, and illustrating a gripper mechanism in accordance with the present invention; Fig. 2 is a plan view of a portion of the gripper mechanism shown in Fig. 1; Figs. 3a-3c are diagramatic representations comparing the movement imparted by a gripper in accordance with the present invention with alternate arrangements; and Figs. 4a-4c are schematic representations, corresponding to Figs. 3a-3c, comparing the geometric construction of a gripper in accordance with the present invention with alternate constructions DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT Fig. 1 illustrates a portion of a collect cylinder 10 of a folding machine. The collect cylinder rotates#about an axis in a direction indicated by arrow 12. As described in greater detail in my co-pending appiication Serial No. 271,407, after the printed web leaves the printing press it is slit into "ribbons", and cut into an intermediate product, i.e. a stack of sheets cut from the ribbons. Each intermediate product is delivered separately to the collect cylinder 10. Shortly after the intermediate products contact and run with the collect cylinder, a gripper mechanism 14 that is then in position under the leading edge of the intermediate product opens and then recloses to grip the leading edge of the product. After the product is "taken" by the gripper assembly 14, it is carried around on the collect cylinder to a jaw cylinder (not shown) to which it may be transferred by a tucker mechanism (not shown). Each gripper mechanism 1 includes a housing 16 that may be fastened to a spider 18 of the collect cylinder 10. A pair of end plates 20 (one shown) carries a transverse gripper shaft 22 that in turn carries a series of holders 24, each in the form of a bracket that may be clamped by screws 25 to the pivot shaft 22 and arranged to support a gripper finger 26. The gripper finger 26 is resilient, and is attached to the holder 24 by a plate 29 held by bolts 28. The shaft 22 of the gripper mechanism extends out through bearings in the outboard end plates 20 and receives a lever 27 carrying a cam follower 27A. In a preferred arrangement shown and described inmy co-pending application Serial No. 271,407, the rotation of the pivot shaft 22 is controlled by a pair of cam followers, rather than a single cam follower. The two cam followers are controlled by a pair of cams, rotating masking cam 30 having a cam surface 30A and a stationary-gripper cam (not shown). As shown in Fig. 1, movement of the cam follower 27A inwardly causes corresponding pivoting movement of the holder 24 and thereby of the gripper finger 26 away from a beveled edge, or clamping surface 32 of the gripper mechanism 14. Correspondingly, movement of the follower mechanism -27A outwardly causes the tip 34 of the gripper finger 26 to pivot about an are into engagement with the clamping surface 32. As shown in Fig. 1, the gripper finger 26 extends from the rigid holder 24 at a point 36, which forms a flex point for the resilient gripper finger 26. The bending point 36 and the gripper tip 34 lie on the same radius 38, through rotational axis 40 of the shaft 22 and the holder 24. As discussed below, due to this structural geometry there is no substantial component of radial motion imparted to the tip 34 upon engagement of the tip 34 and clamping surface 32. This zacilitates the gripping of the leading edge of the paper product by the tip 34, which is preferably beveled, without a resultant sliding between the tip 34 and the surface 32. Also, as described below, the extending portion of the gripper finger 26 is essentially Z-shaped, such that the resilient member 26, in gripping the product, compensates for the enlargement of the distance between point 36 and tip 34 such that the tip 34 remains stationary. As shown, the clamping edge 32 is beveled, that is, is angled toward the gripper tip 34. As a result, as the gripper tip 34 rotates toward the gripper surface 32, from a position spaced from the surface 32, the tip 34 approaches surface 32 from close to a perpendicular angle. However, the clamping surface 32 need not lie on radius 38, i.e., perpendicular to the direction of approach of the gripper tip 34, but can lie at an obtuse angle, as shown. It may also, if desired, co-extend with the surface of the cylinder 10 Also, rather than providing the clamping surface 32 as part of the gripper mechanism 14, the surface could be formed as part of the cylinder 10 per se. Figs. 3a-3c and Figs. 4a-4c represent schematically the geometry of the present invention, as compared with alternative constructions, at the instant of engagement of the clamping surface 32 to illustrate the motion produced thereafter upon further pivotal movement of the holder 24. Fig. 4a illustrates schematically a gripper mechanism having a resilient gripper finger 26 in accordance with the invention. Upon rotational engagement of the fixed surface 32, the rigid holder 24 and flexible finger 26 act, as shown in Fig. 3a, as a slidable linkage in which the links are fully extended and co-linear. Upon counterclockwise rotation of the holder 24, the tip 34 of the gripper finger 26 strikes fixed surface 32. Since the tip and point 36 are aligned radially through the axis of rotation 40, at the instant of engagement of surface 32, further rotation of the holder 24, to increase the resilient force of the finger 26 against the clamping surface 32 to grip the product, imparts no component of radial motion to tip 34 either toward or away from point 40, as shown in Fig. 3a. In contrast, Figs. 4b and 4c illustrate gripper mechanisms in which the flex points 36b and 36c do not lie on the same radius as gripper tip 34b or 34c. At the instant of engagement of fixed surface 32b or 32c, the holder and fingers 26b and 26c react as shown in the corresponding crank mechanisms illustrated in Figs. 3b and 3c. In the arrangement shown in Fig. 4b, further rotation of the cranking arm about point 40b imparts a radial component of motion to tip 34b toward the center of rotation 40b Correspondingly, as illustrated in Fig. 3c, engagement of the finger 26c and the fixed surface 32c imparts a component of radial motion to tip 34c outwardly away from pivot point 40c. As illustrated in Figs. 3 and 4, the rotational geometry of the present invention is such that at the instant of engagement of gripper tip 34 and surface 32, the flexing force per se imparts no radial component of motion to tip 34. Accordingly, as opposed to the gripper configuration shown in Figs. 4b-4c, in the present invention engagement of the tip with surface 32 and the further rotation of the holder to impart a resilient holding force against surface 32, does not produce sliding movement of the gripper tip 34. As described above, the gripper finger 26 is preferably resilient, for-example made of spring steel. Upon engagement of surface 32, further rotational foreulio Ugo parted to the holder by cam follower 28 causes the gripper tip 34 to bear against surface 32 (with the paper sheets interposed) to impart a resilient holding force to the product being gripped. The force imparted at point 36 causes the resilient finger 26 to flex such that point 36 continues to rotate slightly The rotation of the point 36 thus increases slightly the distance between print 36 and the tip 34. In other words, while the rotational force does not impart motion to the tip 34, the continued rotation of the holder 24, in applying the resilient force, itself has the secondary effect of pulling the pivot point 36 slightly away from the tip 34. Preferably, the flexible finger should have a curved portion to permit elongation in the radial direction to compensate for the slight movement of the point 36. Since the finger needs only to compensate for the relatively small displacement of point 36, and since as described above the geometry of the gripper is such that rotation about point 40 imparts little, if any, radial motion to the tip 34 (i.e., does not pull or push on the tip), the tip engages the product without sliding as the resilient holding force is applied. As shown in Figs. 1 and 2, the gripper finger 26 has a pair of oppositely oriented curved portions 42 and 44 that lie on opposite sides of radius 38. The curved portions connect upper and lower finger portions, 46 and 48 respectively, with a connecting portion 50 to define a Z-shaped finger ¯extension. The upper and lower finger portions 46 and 48 are oriented at other than 900 to the radius, such that when the tip 34 engages the clamping surface 32, the curved portions bow, as does the portion 50. In the configuration shown, curved portion 44 bows inwardly, and curved portion 46 bows outwardly. While a particular shape of finger has been shown and described, other shapes of resilient members may be utilized, to conform to the particular gripping requirements. However, it is preferable that the resilient finger should be able to accommodate the slight radial elongation produced by the further rotation of the holder 24 after engagement of the tip 34 and clamping surface 32, unless the finger is sufficiently stiff so that such rotation will be negligible. The beveled edge of the surface 32 also facilitates better gripping. As shown, where the clamping surface 32. is beveled relative to the collect cylinder surface 10, the printed sheet will be wrapped around the beveled edge 32 to increase frictional contact and remove the leading edge of the sheet from the air stream. Also, the gripper tip 34 approaches at an obtuse angle, close to a right angle, as compared with a corresponding engagement of the cylindrical surface of the collect cylinder 10, so that rotational force is substantially aligned with the direction of resilient gripping force. The clamping surface 32 may be at right angles to the direction of approach of the tip 34, but as shown in Fig. 1 need not be since the gripper does not produce a component of radial movement. Thus, the angle of the surface 32 to the direction of movement of the tip may be substantially less than 900, which may in some instances also be desirable to prevent creasing the product. If desired, the clamping surface may co-extend with, or be, the surface of the cylinder 10. The foregoing represents the description of a preferred embodiment of the invention. Variations and modifications of the invention will be apparent to persons skilled in the art without departing from the inventive concepts disclosed herein. All such modifications and variations are intended to be within the scope of the invention as defined in the following claims.

Claims: Claims 1. A gripper mechanism for sheet handling equipment particularly in a collect cylinder (10). for a folding machine for handling sheets of paper comprising a clamping surface (32) on which sheets of paper an#dth#e.like may be positioned; gripper means 114) comprising a holder (24) supported relative to said surface and a resilient gripper finger (26) fixed to said holder (24) and extending outwardly from a point (36) on said holder (24), wherein said gripper finger (26) terminates in a tip (34); and means (27A) for rotating said holder (24) about an axis for rotating said tip (34) in an arc into engagement with said surface; characterized in that said tip {34) and said point (36) lie generally along a common radius 138) of said arc for producing non-sliding engagement of a sheet of paper positioned over said clamping surface and said tip. 2. The mechanism -as defined in claim 1,- characterized in that said clamping surface (32) is- angled toward said tip (34). 3. The mechanism as defined in claim 2, characterized in that said tip (34) is beveled for cooperative engagement of said clamping surface (32). 4. The mechanism as defined in claim 2, characterized in that said finger (26) includes a curved portion to permit limited elongation in the radial direction. 5. The mechanism as defined in claim 4, characterized in that said finger has a pair of oppositely oriented curved portions (42,44) that lie on opposite sides of said radius. 6. The mechanism as defined in claim 5, characterized in that said curved portions (42,44) connect upper and lower finger portions (46,48) with a connecting portion 150), to define a Z-shaped finger, and wherein said upper and lower finger portions (46,48) are oriented at other than 900 to said radius to cause said curved portions 142,44), upon engagement of said tip (34) and clamping surface (32), to bow. 7. Apparatus as defined in claim 2, wherein said collect cylinder has an outside surface, and said clamping surface is disposed below the outside surface of said cylinder. 8. Apparatus as defined in claim 7, wherein said clamping surface and gripper means comprise a gripper mechanism mounted to said collect cylinder. 9. Apparatus as defined in claim 7, wherein said clamping surface is formed on said collect cylinder.

Inventors: LOEBACH, MICHAEL H.
Applicants: MOTTER PRINTING PRESS CO.
Application year: 1982
Main classification: B41F21
IPC codes: B65H29, B41F21, B65H45