Patent Application
20160023420
The present invention relates to improvements in feeding sheets, and more specifically to novel methods and apparatus for feeding sheets in the art of box making.
In the art of box making sheets of corrugated board are individually conveyed in a timed manner at high speed along a path to several stations where each board for example is slit and/or slotted and/or creased, and printed. The boards are individually fed to the processing conveyor from a stack of boards by a feeder for example disclosed in U.S. Pat. No. 6,824,130 Bland 7,635,124 B2 whose disclosures are hereby incorporated by reference into the subject application as part hereof.
A new concept has recently emerged in the box making industry which is the use of a plastic sheet rather than corrugated board to form the box. However, one of the most difficult applications for high speed sheet feeding is plastic. The weight and static friction that is associated with this medium causes difficulty in separating the sheets to allow them to feed individually. Tests of this new concept in box making apparatus have shown that the weight of the plastic sheet stack and the static friction between the sheets causes difficulty in separating the sheets to allow them to be fed individually especially when the width of the sheets is much smaller than the length. The result can cause jamming of the sheets and disruption of production keeping in mind that the sheets are required to move at a high speed and in timed manner.
It is well known in the art of paper copiers to use air flow such as “air knifes” to separate sheets from a stack for conveying the sheets such as disclosed for example in U.S. Pat. Nos. 4,163,277, 5,048,813, and 5,275,393. However, in the art of box making from corrugated boards, separation of the corrugated boards in typical operations has not posed a problem due to the lighter nature, air permeable, and lower friction material of the corrugated boards. To overcome the above noted problem, when plastic sheets are processed in box making machines, the present invention uniquely adapts an air knife as will be described below.
The method and apparatus of the present invention include a feeder conveyor for individually feeding the lowermost sheet along a horizontal path from a stack of plastic sheets to the inlet of a box making machine. The sheet stack rests on a support which is termed a “metering bar”. The latter is positioned above the conveyor path but below the rear end portion of the stack. Once the conveyor moves the lowermost sheet off the metering bar, the rear end portion of the lowermost sheet drops by gravity creating a space between it and the above sheet into which space air flow is injected from an air knife at the rear end of the stack to overcome the frictional forces and allow separation of the lowermost sheet by the conveyor. The sheets are made from any suitable plastic, for example, urethane, and the air pressure can range from 15 to 80 psi depending on the sheet size and the height of the sheet stack.
The present invention will become more apparent from the detailed description below taken in conjunction with the accompanying drawings in which;
Referring to the drawings in detail there is shown for illustrative purposes only box making apparatus embodying the present invention for processing plastic sheets from a stack 1, whose underlying sheets 6 are individually fed by a timed feeder conveyor 2 below a gate 3 to pull rolls 4 which in turn feed the sheet to a processing conveyor 10. The latter moves the sheet along a horizontal path to one or more downstream processing stations where the sheet may be, for example, slotted, creased, scored, or printed. One such station is shown at 5.
Referring to
Extending transversely of the path of the conveyance and positioned below the metering bar 7 is an elongated air knife 9 for directing jets of air into the space between the lowermost sheet 6 in the stack and its overlying sheet 6, once the conveyor 2 moves the lowermost sheet 6 forwardly off the metering bar 7. Air under pressure is introduced from hoses 30 into ports 25 in the opposite ends of the air knife 9 which has outlet ports or nozzles on its front face for directing the air jets between the sheets as described above. Adjustment of the angle and position of the air flow is accomplished by the mounting brackets 20 and 23 which have vertical and horizontal slots for moving the air knife along these slots into desired vertical and horizontal positions.
Summarizing operation of the apparatus, the lowermost sheet 6 moves forward to the pull rolls 4 by the normal action of the feeder 2. This action “meters” the sheet allowing one sheet to drop from bar 7 by the force of gravity. The dropped sheet then provides a space or a gap where air is injected to reduce the frictional forces between the sheets. This reduction of forces allows the sheet 6 to be fed without jams. The air injection in the space at the rear of the sheet in accordance with the present invention, reduces the force through two phenomena:
The sheet is also supported by the top of the back stop 16. The metering bar 7 allows a single sheet to drop by the force of gravity when pulled slightly forward by the feeder 2. Fine adjustment of the metering bar position is accomplished by rotating the support arm 8 with the use of the hand wheel 26.
The air pressure required to allow jam-free feeding of sheets will vary between 15-80 psi. depending upon the size of the sheet and the weight of the sheet stack. The sheets have high frictional forces and are significantly heavier than common corrugated board sheets. This combined with the fact that the plastic medium is not air permeable can make initial separation of the sheets quite difficult but for the present invention. The height of the stack in the feeder adds to the difficulty by increasing the overall downward force on the sheets. It should be understood that although the air knife itself is a conventional product available on the market, its particular use and positioning together with a metering bar in box making apparatus as shown and described herein, is believed to be unique especially when processing plastic sheets to be made into boxes.
Although preferred forms of the method and apparatus of the present invention have been disclosed in this application, other forms of the invention will become apparent to those skilled in the art but without departing from the invention as defined in the appended claims.
