Sheet feeding or delivering – Feeding – With means to align sheet
Reexamination Certificate
2000-03-15
2002-04-30
Ellis, Christopher P. (Department: 3651)
Sheet feeding or delivering
Feeding
With means to align sheet
C271S239000, C271S230000
Reexamination Certificate
active
06378862
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a method of and a system for positioning sheet elements in the introduction station of a machine for processing sheet material, and more particularly a system for positioning a sheet of paper, cardboard or similar material very accurately in the introduction station of the machine, just before the leading edge of said sheet is gripped by a transport system comprising a series of grippers mounted on a transverse bar connected to side chains subsequently feeding said sheet to the different subsequent processing stations of the machine, such as the printing, cutting or other stations.
BACKGROUND OF THE INVENTION
In the positioning systems currently in use, the sheet is jogged on the feed table against front and lateral stops by means of feed members such as rollers or bands of elastic material descending from above on to the table, or a pair of rollers arranged above and below the table.
In the case of untreated sheets, the front and side stops used are disposed exactly with respect to the references of the subsequent stations. The sheet is then rapidly pushed against the stops by the feed members and then gripped by the gripper bar. The stops are then retracted and the gripper bar can pull the sheet to the following processing station and position it exactly with respect to the tools of the platen of that station.
Positioning is slightly more complicated when the sheet has previously undergone one or more processing operations, for example printing or scoring of fold lines, and the subsequent processing operations have to be carried out very accurately with reference to the results of the previous processing operations. The patent CH 676695 discloses a positioning system in which the stops are motor-driven so as to be able to control a variation in their position and wherein a printing mark or other distinctive sign of the previous processing operation can be logged by opto-electronic reading means in order to adjust the position of the stops, and hence of the sheet, directly in dependence on the mark or sign.
However, these stop type positioning systems mean that the advance of each sheet must be practically stopped for the entire duration of its jogging and adjustment operation, and this substantially limits the possible speed of movement of the sheets in the machine.
Also, the fact that a sheet is applied against a stop may result in the formation of an unsightly mark on the corresponding edge. The swelling of this mark may also interfere with the introduction of the sheet in critical circumstances.
The object of this invention is to provide a method of and a system for positioning sheet elements, such as sheets of paper, cardboard or similar material, in the introduction station of a processing machine, such method and systems being faster so as to allow the machine cycle to be increased while remaining very accurate, particularly in the case of sheets which have received a previous treatment. Preferably, the system should leave no mark on the sheet element. Nevertheless, the design of this system must remain relatively simple in order to increase its reliability, simplify maintenance, and reduce the production costs as far as possible.
SUMMARY OF THE INVENTION
These objectives are achieved by a method of positioning sheet elements in the introduction station of a processing machine comprising, starting from a shelf in a rear starting position, engaging means for fixing a sheet element on the shelf, then controlling actuators to advance the shelf forward and if necessary sideways and/or askew depending on the readings of opto-electronic means, said readings being effected at the start of the advance of the shelf so as to feed and finally stop the leading edge of the sheet element in the grippers of a drive bar in a predetermined position, releasing the fixing means, and then returning the shelf to the rear starting position.
Thus after the reading of the effective position of the sheet element with respect to the shelf by the opto-electronic means during a first phase of the shelf advance, the subsequent advance phase can be utilized to advantage to effect adjustments of the movement of the shelf with respect to its basic travel in order very dynamically to correct any longitudinal, lateral or skew errors of the sheet element. If the sheet element is untreated, the corrections can be advantageously carried out on the basis of logging its edges; if the sheet has previously been processed, the corrections are advantageously carried out on the basis of a reference mark of, or distinctive signs corresponding to, said treatment. The corrections thus made during sheet movement mean that it is no longer necessary to stop the sheet element uselessly, so that the possible rate of operation of the machine can be substantially increased.
The method of controlling the positioning system therefore comprises, starting from the rear starting position of the shelf, controlling the actuators to advance the shelf forward until the leading edge of the sheet element has been detected by the opto-electronic means, then controlling the corresponding actuator in order to move the shelf transversely until the side edge of the sheet element has been detected by the opto-electronic means.
Preferably, the control method comprises, starting from the shelf in the rear starting position, controlling the actuators to advance the shelf forward at a constant speed until the machine gripper bar arrives at the standby position for receiving a sheet element, then controlling the actuators to effect adjustments of the movement of the shelf with respect to its basic travel in order to correct any longitudinal, lateral or skew errors of the sheet element as determined by the readings of the opto-electronic means and finally to stop the leading edge of the sheet element in position in the grippers of the drive bar.
Thus by postponing the shelf correction movements to the end of its travel only when the gripper bar has arrived in the standby position, this obviates any adverse collision risk between the two elements which might be caused by unpredictable acceleration of the shelf.
The system for positioning sheet elements in the introduction station of a processing machine comprising a transport system made up of one or more gripper bars for driving the sheet element to the subsequent stations comprises:
a shelf provided with means for temporarily fixing the sheet element, having a notched leading edge complementary to the grippers of the drive bar driven by actuators on the one hand in reciprocating longitudinal translation from a rear starting position to a forward position at the level of a gripper bar in standby to receive a sheet element, and on the other hand in complementary longitudinal translation and/or in transverse translation and/or in rotation about a vertical axis,
opto-electronic means reading the front and/or side edge and/or a distinctive sign of a previous treatment of the sheet element disposed slightly forwardly of the starting position of the shelf,
electronic control means for controlling the actuators of the shelf in dependence on the machine cycle and the results of the readings of the opto-electronic means.
The pneumatic temporary fixing means for the sheet element on the shelf may comprise a network of apertures formed on the top surface of the shelf communicating with an internal chamber connected by an electromagnetic shut-off/opening valve to a negative pressure supply. However, pneumatic means of this kind prove to be relatively slow and complex to use.
According to a preferred embodiment, the temporary fixing means comprise a comb mounted pivotably above, near and parallel to the front notched edge of the shelf, the teeth of the comb being oriented forward so that each of them forms with each projection of the shelf separating a notch a gripper for gripping the leading edge of the sheet element, and means for controlling the angular position of the comb.
Advantageously, the means for controlling the angular position of the comb compri
Bobst SA
Ellis Christopher P.
Mackey Patrick
Ostrolenk Faber Gerb & Soffen, LLP
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