1. Field of the Invention
This invention relates to sheet feeding separators having a pneumatic bottom feed and more particularly to blank feeding machines having an adjustable backstop means for maintaining a portion of the weight of the stack off the bottom sheet and providing a means for automatically positioning the backstop means along the support table for accommodating different size stacks on the support table.
2. Description of the Prior Art
Blank feeders for feeding the bottom blank a stack of paperboard blanks are well known in the art and are used for feeding the blanks into adjacent processing machinery.
There are basically two types of blank feeders used in industry today. One type of feeder utilizes a kicker bar which reciprocates back and forth along the feed table picking up the bottom blank on its rearward position and then pushing the bottom blank through an opening in a gate and into the adjacent processing apparatus. The use of a reciprocating feed bar by itself has inherent disadvantages. In a typical blank feeding machine there is a gate that is spaced above the feed table approximately the same as the thickness of the bottom blank to be fed. The stack of blanks are placed upon the feed table so that the stack of blanks is resting against a front stop which forms the gate. The bottom blank is then fed through the opening by the reciprocating feed bar. This type of feeder works well when all the blanks of the stack are flat. However, the blanks that are processed in the corrugating paperboard industry are not always flat but are warped. When a warped blank becomes the bottommost blank of the stack it is unable to be fed through the opening in the gate by the reciprocating feed bar. This then necessitates a shut down of the machinery until the warped blank can be removed from the machinery.
To pull the leading edge of the warped bottom blank flat against the feed table so the kicker bar can feed the warped blank through the opening in the gate the corrugating industry developed suction feeders. One type of suction feeder utilizes a stationery suction chamber such as shown in Ward et al U.S. Pat. No. 3,588,095 and Thayer U.S. Pat. No. 3,754,752. Such suction feeders are designed to hold the bottom blank against the support table. The reciprocating feed bar then engages the trailing edge of the bottom blank and moves it through the opening in the gate and into the processing apparatus. These suction feeders utilize the reciprocating feed bar to move the bottom blank through the gate mechanism and as previously explained were developed to eliminate the problem of feeding warped blanks which prevent them from passing through the opening in the gate mechanism. These suction feeders generally do their job very well. The suction chamber pulls the warped botttom blank against the support table and the suction pressure is strong enough to flatten the warped blank and allow the feeder bar to engage the trailing edge of the blank and move it through the gap in the gate mechanism.
Although the reciprocating feed bar type suction feeder has the above mentioned advantage, it does have a number of disadvantages. First, the suction pressure in the suction chamber must be continuously applied so that the warped blank will stay flat during movement through the opening in the gate mechanism. This continuous suction pressure creates friction between the blank and support table which the feeder bar must overcome to advance the blank. The feeder bar pushes against the trailing edge of the blank and tends to bend or deform the trailing edge thus damaging the product.
Another disadvantage of the reciprocating feed bar type feeder whether used singularly or in combination with the stationery suction chamber is that the feeder bar reciprocates rapidly in the area where the machine operator stands at the rear of the stack. As he loads the stack onto the support table, his hands are in close proximity to the feeder bar. Should the operator be careless or make a mistake, his hands may contact the moving feeder bar and injure his hands.
A second type of suction feeder is shown in E. L. Bishop U.S. Pat. No. 2,331,533 and T. D. Bishop U.S. Pat. No. 3,226,108, which is an improvement over the E. L. Bishop patent. In this type of suction feeder the suction box itself reciprocates along the plane of the feed table eliminating the need for a feeder bar and consequently the disadvantages associated with the feeder bar. Suction in the box draws the bottom blanks downward into flat contact with the top of the suction box. The suction box moves the blanks forward until its leading edges are gripped by a pair of pull rollers beyond the gate which pull the blank into the processing machinery. When the pull rolls grip the blank the vacuum in the suction box is released to atmosphere which releases the blank from the suction box and allows easy pulling of the blank by the pull rolls. The suction box then moves rearward until it is below the next bottom blank at which time the vacuum is reapplied to the suction box to feed the next blank.
On all three of the above mentioned type feeders, the operator places a stack of box blanks on the support table so that the leading edges of the box blank are in contact with the gate mechanism. In addition, it is customary to have a backstop means which is movable along the support table and which rests against the trailing edge of the box blanks. Thus, when the backstop is in contact with the trailing edge of the blanks in the stack of blanks, it will maintain the leading edge of the box blanks in contact with the gate mechanism. This is to insure that the box blanks that are placed upon the support table are not cocked sideways and thus when fed through the opening in the gate mechanism would not enter the processing machinery at the correct angle and thus cause the processing machinery to stop or produce a box blank which is not processed correctly.
A disadvantage of the above type feeders is that a stack of blanks are placed upon the support table by the operator and this stack of blanks places a lot of weight upon the bottom blank. In those type feeders that utilize a reciprocating feeder bar the feeder bar contacts the trailing edge of the bottom blank and moves the bottom blank through the opening in the gate mechanism. When the weight of the stack is on the bottom blank, there is a great amount of friction between the bottom blank and the blank above it and between the bottom blank and the support table. Thus, the reciprocating feed bar must overcome the weight of the stack above it and the various frictional forces before moving the bottom blank through the opening. In many instances, the feed bar is unable to overcome the weight of the stack above it, and consequently it damages the trailing edge of the bottommost blank.
The above disadvantage is also inherent in the suction type feeders that utilize both the stationery suction chamber and the reciprocating feeder bar. In fact, the disadvantages are even greater in this type of feeder because in addition to the weight of the stack of blanks on the bottommost blank the stationery suction chambers also cause additional friction on the bottommost blank. The above disadvantage also presents problems for the reciprocating suction chamber in that the reciprocating suction chamber must create a sufficient amount of suction to overcome the weight of the stack on the bottommost blank and thus the friction between the bottom blank and the blank just above it. This necessitates large machinery to create the great amount of suction pressure that is needed to move the bottommost blank through the opening in the gate.
Another disadvantage of the above type blank feeders is that different width blanks are stacked on the support table and thus the backstop must be movable along the support table to accommodate the different size blanks that form the stacks on the support table. Conventionally, the backstop is moved manually by the machine operator each time different size blanks are to be run. When a different size blank is to be run, the operator manually unlocks the backstop from the support table and moves the backstop forward or rearward to accommodate the proper size blanks. The operator then relocks the backstop in place on the support table and places a new stack of blanks thereon.
Hottendorf U.S. Pat. No. 3,804,402 has overcome the disadvantage of manually moving the backstop when associated with a kicker bar type feeder. Hottendorf utilizes a pair of rotatable shafts each connected to the backstop and the kicker bar respectively. The pair of rotating shafts are interconnected by gearing which is connected to a conventional motor for rotating the two rotatable shafts simultaneously. When it is desired to adjust the backstop and the kicker bar, the operator energizes the motor which simultaneously turns the pair of shafts moving the backstop and kicker bar forward and backward along the support table until the desired position is reached that will accommodate the desired size of blanks. However, Hottendorf still has the disadvantage of having to overcome the entire weight of the stack upon the support table when the kicker bar tries to move the bottom blank through the opening in the gate mechanism. Thus the disadvantage of the kicker bar is still inherent in Hottendorf. In addition, the backstop cannot be moved independently of the kicker bar.