GB2042481A

GB2042481A - Paper feeder for printing machines

Info

Publication number: GB2042481A
Application number: GB8004879A
Authority: GB
Original assignee: Rotaprint GmbH
Current assignee: Rotaprint GmbH
Priority date: 1979-02-20
Filing date: 1980-02-13
Publication date: 1980-09-24
Also published as: FR2449627B3; DE2906482A1; DE2906482C3; FR2449627A1; JPS5856351B2; JPS55146759A; IT8019428A0; IT1129782B; DE2906482B2; GB2042481B

Abstract

A paper feeder for a printing machine has pivotable grippers 6 mounted parallel to the axis of an impression cylinder 4 of the machine and associated gripper pads 5 on the periphery of the impression cylinder. The adjacent surfaces of the grippers and gripper pads are curved in the direction of motion of the sheet so as to provide an elastic deformation of the leading edge of the gripped sheet. in this manner the noise level of the running printing machine is greatly reduced. <IMAGE>

Description

SPECIFICATION Paper feeding for printing machines The present invention relates to a paper feeder for printing machines, particularly office printing and offset printing machines or other paper-using machines.

In a known relatively simple paper feeder, the grippers are mounted on an axis which runs parallel to the periphery of the paper feed roller, the grippers being controlled by a control cam so that they clamp the arriving leading edge of the printing sheet in between a gripper pad, provided on the periphery of the paper feed roller, and the gripper and feed the sheet to the actual printing unit. The surface of the grippers or gripper pads which contacts the printing sheets is normally plane or substantially plane. In such a feeder since the paper feed roller rotates continuously and the grippers are rigidly joined to the paper feed roller, the grippers must strike the printing sheet at a considerable speed in order to be able to grip the latter properly.

Because of the high speed of impact of the grippers on the printing sheet, a loud impulselike report occurs, in particular with better grades of paper, and this is quite distinct above the remaining noise level of the printing machine. At relatively high printing speeds, this impulse-like report can have a highly disturbing effect and frequently it has the result that the noise level of the printing machine is above the limiting values permitted by the relevant authorities.

In an effort to damp the noise level of a machine of the initially mentioned type and, in particular, the-impulse-like report on impact of the grippers, many attempts have been made by the Applicant, but none of these had led to any substantial damping. Thus, attempts were made inter alia to provide the grippers and gripper pads with a damping rubber layer or the like or to line the whole of the machine with a sound-absorbing material or the like.

None of these measures has led to a substantial lowering of the noise level and it is accordingly, an object of the present invention to damp the noise level of a printing machine, working with such a gripper system, and particularly the impulse-like report on impact of the grippers on the printing sheet.

According to this invention there is provided a paper feeder for printing machine comprising a plurality of pivotable grippers mounted parallel to the axis of an impression cylinder and associated gripper pads on the periphery of the impression cylinder, the grippers and grippers pads being arranged in operation to grip and transport a sheet to be printed, the adjacent surfaces of the grippers and gripper pads being curved in the direction of motion of the sheet whereby the curved surfaces impart an elastic deformation to the gripped leading edge of the sheet.

Although it is not possible to give a precise explanation of the reason, it has been observed that the noise level is lowered by 15-20 dB by employing the present invention.

The invention will now be described by way of example with reference to the drawings in which: Figure 1 shows a side view of an office machine of conventional design, Fgure 2 shows the known sheet feed table with the paper feed roller or the impression cylinder, on an enlarged scale, Figure 3 shows the paper feed roller of the present invention, and Figure 4 shows a detail bounded by the broken line A of Fig. 3 of the grippers and of the gripper pads on an enlarged scale.

A known offset printing machine is shown in Fig. 1 where the machine has a sheet pile 1 which is located on a table 10 having a transport mechanism 11 and feeder device 1 2. The sheets are transported by a suction feeder 2 and feed rollers 3 via a pull-type lay 13, a knee joint 14 and a front guide 8 between an impression cylinder 4 and an offset cylinder 1 5. An inking unit 16, receiving ink from a reservoir (not shown) which is pumped by a pump 1 7 driven by a motor 18, provides ink via rollers to a plate cylinder 1 9 which contacts the offset cylinder 1 5. A hydro-colour unit 20 is also provided. Printed sheets from the impression cylinder 4 are transported to a delivery station 21.

Referring to Fig. 2, the impression cylinder 4 is provided on the periphery thereof with gripper pads 5 and with grippers 6 which cooperate with the gripper pads 5 and are mounted on an axis 7 which is provided parallel to the axis of rotation in the vicinity of the periphery of the impression cylinder. The opening and closing of the grippers is controlled by a cam control system the detail of which is not shown. When the leading edge of a sheet to be printed is fed in, this leading edge is initially delivered against the normally stationary front guide 8 which ensures proper alignment of the printing sheet but which guide can be pivoted.Due to the continuous rotation of the impression cylinder, the gripper pads 5 provided on the periphery are moved under the edge of the printing sheet, located at the front guide 8, the grippers 6 being caused by the cam control system to pivo towards the gripper pad 5 in such a way that the printing sheet can be clamped between the gripper pad the gripper and can be fed to the printing machine for the actual printing process. Before delivering the printing sheet clamped between the grippers and gripper pads, the front guide must of course be pivoted away, as shown, in Fig. 2.

Since the printing machine and hence also the impression cylinder are operated at a constant peripheral speed, the gripper must strike the gripper pad at a considerable speed so that it can properly grip the sheet and pass it on. As can readily be seen from the drawing, the pivoting step of the grippers must take place against the direction of rotation of the impression cylinder and, in particular, the pivoting motion must be opposite to and faster than the peripheral speed of the impression cylinder.

As previously stated, the necessary fast gripping by the grippers results in a considerable impulse-like report, when they strike the printing sheet. This impulse-like report depends to a high degree on the quality of sheet, that is to say as a rule a more intense report results in the case of better qualities of sheet (stronger paper). This impulse-like noise could have very disturbing effects at higher printing speeds and with better grades of paper. Hitherto, all attempts decisively to damp this impulse-like report have been in vain.

The present invention provides as is shown more clearly in Fig. 4, gripper pads 5 and grippers 6 with rounded surfaces in the direction of paper motion. By such an expedient way the paper in the region of the leading edge is provided with an elastically formed bend across the width of the sheet. A reduction in noise of at least 1 5 dB has been found with the use of such curved surfaces and it appears that the paper is stiffened by the elastic deformation of the paper, so that it cannot be caused to vibrate to the extent previously known.

In an illustrative embodiment, the radius of curvature R1 or R2, shown in Fig. 4, was about 5mm. However, the radius of curvature R2 of the pad 5 can be made larger than that R1.

As a result of the invention, the noise level of a running printing machine with a printing speed of up to 7,000 sheets per hour is reduced to less than 80 dB.

Claims

1. A paper feeder for printing machine comprising a plurality of pivotable grippers mounted parallel to the axis of an impression cylinder and associated gripper pads on the periphery of the impression cylinder, the grippers and gripper pads being arranged in operation to grip and transport a sheet to be pivoted, the adjacent surfaces of the grippers and gripper pads being curved in the dirdction of motion of the sheet whereby the curved surfaces impart an elastic deformation to the gripped leading edge of the sheet.

2. A paper feeder according to Claim 1, wherein the radii of curvature of the curved surfaces of the grippers and pads are equal.

3. A paper feeder according to Claim 1, wherein the radius of curvature of said surface of the gripper pads is greater than that of the grippers.

4. A paper feeder according to Claim 1, 2 or 3, wherein the order of magnitude of the curved surfaces is radius of curvature of 5mm.

5. A printing machine having a paper feeder according to any preceding claim.

6. A paper feeder substantially as herein described with reference to and as shown in the accompanying drawings.

7. A printing machine substantially as herein described with reference to and as shown in the accompanying drawings.