US3536321A - Device for clamping sheet material - Google Patents

Description

Oct. 27, 1970 P. STRAUBE 3,536,321

I DEVICE FOR CLAMPING SHEET MATERIAL 2 Sheets-Sheet 1 Filed June 13. 1968 FLGJ,

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United States Patent Office 3,536,321 Patented Oct. 27, 1970 3,536,321 DEVICE FOR CLAMPING SHEET MATERIAL Peter Straube, Radebeul, Germany, assignor to VEB ruckmaschinenwerir Planeta, Radeheul, Germany Filed June 13, 1968, Ser. No. 736,683 Int. Cl. B6511 /14; B41f 1/30 U.S. Cl. 27153 5 Claims ABSTRACT OF THE DISCLOSURE A gripping finger is first moved to a position above and substantially parallel with a stationary support surface upon which the sheet material is lying, and subsequently lowered in perpendicular direction to clamp the sheet material against this support surface.

BACKGROUND OF THE INVENTION The present invention relates to a device for clamping a sheet material between a stationary support and a movable gripping means.

In particular, the present invention relates to sheet processing machines, such as printing machines for example, Where an extremely accurate positioning of sheets is necessary to insure the required accuracy of printing. The devices for clamping of sheets must maintain exactly the same position of the sheet during the printing process as that which has been originally set on the feeding devices. It is necessary to apply considerable holding forces against the sheet and, consequently, great forces in bearings of the clamping mechanism will result.

To reduce these bearing forces there have been known devices where the gripping finger is spring-supported upon a gripper body which, is moved on a circular path. One of the disadvantages of such known devices resides in the fact that due to the circular movement of the resilient gripping finger the latter is tangentially displaced when contacting the sheet support surface and, therefore, an exact fixation of the sheet is impossible.

It has already been proposed to avoid, at least in part, this latter disadvantage of circular movements by arranging the trunnion for the resiliently supported gripping finger, the center point of the gripper shaft and the contact point between the closed gripping finger and the support surface of the impression cylinder, to lie substantially in a straight line. The result of this measure is that the final phase of the clamping movement is approximately in the region of 90 at which the sinus function and, consequently, the displacement of the resilient gripping finger are substantially reduced.

However, even such a small displacement is disadvantageous when an exact fixation is required for the sheet passing through a number of sites of transfer.

SUMMARY OF THE INVENTION It is accordingly a primary object of the present invention to provide exact fixation of the position of a sheet.

In particular, it is an object of the present invention to provide a device which makes it possible to avoid relative traverse motions between the clamping means.

In accordance with a primary feature of this invention, a control shaft is disposed for pivoting about an axis parallel to the front edge of a support surface upon which the sheet material is positioned. The shaft is provided with with a radial pushing arm and a radial carrier arm. Upon the shaft, a slide collar is pivotably arranged. The slide collar is integral with a radial stop arm, a carrier pin and a traverse bracket. Between the radial stop arm and a fixed point, a pulling spring is provided for pivoting the slide collar and thereby the traverse bracket in the direction towards said support surface. A fixed stop screw is located in the path of movement of the radial stop arm to abut the latter in an adjusted position of the slide collar. The carrier pin is adapted for engagement with the carrier arm when the drive shaft rotates in direction away from said support surface. The gripping means consists of a gripping finger attached to a support block. The support block is afiixed to a slide rod which is perpendicular to the traverse bracket and passes through a guide sleeve mounted on this bracket. The support block is further coupled to a number of leaf springs which are arranged in parallel relationship to the traverse bracket and keep the support block with the gripping finger in the proper position with respect to the sheet support surface. A second spring is secured between the traverse bracket and the lower portion of the slide rod and pushes the latter downwardly so that in an unactuated position the support block is adjacent to the traverse bracket. The pushing arm is adapted to thrust the slide rod when the drive shaft rotates in the direction away from the support surface. The position of the carrier arm is adjusted so that it starts moving the slide collar after the slide rod and thereby the gripping finger has been lifted. For a proper operation of the device it is necessary that the first spring be stronger than said second spring.

BRIEF DESCRIPTION OF THE DRAWINGS The invention is illustrated by way of example in the accompanying drawings, in which:

FIG. 1 is a schematic illustration of the device according to the present invention having gripping means in an open position;

FIG. 2 is the device of FIG. 1 at the end of the first phase of the clamping movement;

FIG. 3 is the device of FIG. 2 with gripping means in a closed position; and

FIG. 4 is the device according to this invention mounted on an impression cylinder of a printing machine.

DESCRIPTION OF THE PREFERRED EMBODIMENT As shown in FIGS. 1 to 4, the clamping device of this invention consists of a gripper control shaft 1 which is mounted for rotation about its axis 19 in a recess 18a of an impression cylinder 18. The control shaft supports a slide collar 2 and is terminated at one end thereof with an adjustable clamp ring 11. The slide collar 2 is integral with a traverse bracket 2a which at a certain angular position of the collar is parallel to a sheet support surface 1817 on the impression cylinder. The collar 2 is further provided with an axially protruding carrier pin 16 and with a radial stop arm 9. The traverse bracket 2a carries gripping means which are guided for a slidable movement perpendicular to the traverse bracket. The gripping means consist of a gripping finger 4 attached to a gripper block 6 which is afiixed to a slide rod 6a. The slide rod passes through a guide sleeve 13 and is provided with a push spring 12 which pushes the entire gripping means downwardly. The traverse bracket also supports a number of leaf springs 5 which are mounted in parallel spaced relationship one to another in a leaf spring block 3 and coupled to the gripper block 6 to insure the exact orientation of the gripping finger 4 with respect to the sheet.

A pull spring 8 is connected between a fixed point 14 on the cylinder 18 and the radial stop arm 9 to pull the latter as far as to an adjustable stop screw 10 which defines the parallel position of the traverse bracket 2a and thereby of the gripping finger 4 with respect to the support surface 181:.

The clamp ring 11 is provided with a radial carrier arm 11a which engages the carrier pin 16, and with a radial pressure arm 11b which actuates the slide rod 6a by engaging a foot 6b fixed on the rod 6a.

All movements of the gripping finger 4 (as designated by arrows in FIGS. 1 to 3) are derived from pivotable movements of the control shaft 1. To release the gripping means, the control shaft rotates counterclockwise as far as to an end position shown in FIG. 1. At the first phase of this counterclockwise movement (see FIG. 3), the pressure arm 11b first abuts the slide rod 6a. Since the tension of the spring 12 is lower than that of the spring 8, the pressure arm 11b pushes the slide rod upwardly while the slide collar 2 remains stationary. As a result, the gripping finger 4 releases the sheet 17 in exactly perpendicular direction so that no tangential displacement thereof can occur.

As soon as the gripping finger is in the elevated position above the support surface as shown in FIG. 2, the carrier arm 11a will engage the carrier pin 16 and initiate a second phase of the movement by pivoting the traverse bracket about the axis 19 until the end position of FIG. 1 is attained.

The closing operation is carried out in opposite order by driving the control shaft in clockwise direction. The perpendicular travel of the gripping means which in practice equals approximately a double thickness of the clamped sheet material, may be adjusted by setting screw 20. On the other hand, the clamping force of the gripping finger against the sheet 17 is adjustable by means of the stop screw which permits the pull spring 8 to execute the so-called over-pressure phase of the clamping motion.

What is claimed is:

1. A device for clamping a sheet material between a stationary support surface and a movable gripping means, comprising a drive member mounted for pivoting about an axis parallel to the plane of the support surface from a first position in which the sheet material is clamped between the gripping means and the support surface to a second position in which the gripping means is displaced further from the support surface along a line perpendicular to the support surface and finally to a third position in which the gripping means is displaced furthest from the support surface and outside said line, a slide member freely mounted on the drive member for pivoting about the axis, two leaf springs arranged mutually parallel, parallel to the support surface and in a plane transverse to the axis, means rigidly fixing one end of each of the leaf springs to each other and to the slide member, connecting means rigidly fixing the other end of each of the leaf springs to each other, said gripping means being connected to the connecting means, means for drivingly connecting the drive member with the slide member continuously between the second position and the third position so that the drive member pivots the slide member with the drive member and disconnecting the drive member from the slide member continuously between the first position and the second position and means for drivingly'connecting the drive member with the gripping means continuously between the first position and the second position.

2. A device according to claim 1, in which the means for drivingly connecting the drive member with the slide member comprises a pin on the slide member and an arm on the drive member, said arm being displaced from said pin when the drive member is between the first position and the second position and being in engagement with said pin when the drive member is between the second position and the third position.

3. A device according to claim 2, in which the means for drivingly connecting the drive member with the gripping means comprises a second arm on the driving member, an elongated member, one end of the elongated member being fixed to the means connecting the other end of each of the leaf springs to each other and the other end of the elongated member being in driven engagement with the second arm continuously between the first position and the second position.

4. A device according to claim 3, further comprising spring means one end of which is fixed to supporting structure which is stationary relative to the support surface and the other end of which is fixed to the slidable member so that the spring means is stressed as the slidable member is driven from the second position to the third position.

5. A device according to claim 4, further comprising a bearing arm fixed to the slidable member, said bearing arm being transverse to and slidably supporting said elongated member, and second spring means, one end of said second spring means being fixed to said other end of the elongated member and the other end of said second spring means being fixed to said bearing arm so that the second spring means is stressed as the slidable member is driven during the pivoting of the driven member from the first position to the second position.

References Cited UNITED STATES PATENTS 549,282 11/1895 Wenot 101-409 2,699,941 1/1955 Huck et a1 27153 2,865,289 12/1958 Fowlie et al. 101-409 3,172,353 3/1965 Helms 10193 WILLIAM B. PENN, Primary Examiner E. M. COVEN, Assistant Examiner US. Cl. X.R. 101-409

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