Comparative Performance of the VPGTM System
The VPGTM Stacker System Delivers Unprecedented Performance
A single operator is all that is needed for the GBI stacker. With our system layout, both the lumber infeed and sticker infeed are easily serviced by one operator. The sticker infeed is totally open throughout the sticker travel area. All stickers stop between cycles in an area close to the operator. He can quickly and easily decide if a sticker does not meet the mill's specifications. Replacement with an acceptable strip is done in seconds.
Neither the overhead magazine type system nor the USNR Lunden system offers the convenient sticker inspection available from the GBI design.
For feeding stickers, GBI uses a rotary tong style feeder built under license from PLC. Inc., Quebec, Canada. Besides handling poor quality stickers, the tong feeder can also handle varying widths from 1-1/2" to 3-1/2" wide.
Sticker Feed Comparison
As the timing charts below show, there is no speed advantage gained by picking the stickers up while the forks are extended. In fact there is a distinct disadvantage to having the sticker cycle 180E out of phase with the fork cycle. In the Lunden method, a misloaded sticker can proceed from the feeder directly into the pick up area without stopping. This puts considerably more pressure on the operator to continuously watch the sticker feeder.
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The natural tendency of the operator is to wait until the stickers stop before pushing the stacker cycle button. This is especially true if he is dealing with poorer quality stickers with higher misfeed rates. How can you straighten a misfed sticker on a moving chain? As the operator delays the start of the next cycle until the stickers stop, the overall cycle rate of the Lunden stacker is significantly reduced.
When the operator does cycle with the sticker chain moving and part way through its cycle, he is never sure he has the correct sticker pattern on the lugs. The Lunden patterns are complicated as we shall see in item #2.
*To achieve the same cycle speed as the GBI stacker, the operator of the Lunden must always initiate the next cycle while the sticker chain is moving. In other words, the sticker inspection delay time must always be zero. We know this cannot happen because anytime there is a cycle with a sticker misfeed, the delay time will be required while the operator lets the chain come to a stop and corrects the problem.
Sticker Advance Comparison
The length of travel of the sticker distribution chain is important in considering the overall speed and longevity of the sticker system.
This chart shows the sticker distribution chain plans for both Gillingham-Best and Lunden/USNR for a 20' stacker with stickers on 2' centers. Each chain section represents the advance for one stacker cycle.
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Gillingham-Best uses a plan that changes the advance for each length of lumber. The advance is the minimum amount required to do the job. This is compared to Lunden/USNR which uses a constant advance no matter what length is being stacked.
Let's compare an 8' pattern. With Lunden the advance is always 11 lugs even though only 5 stickers are required. The feed pattern is shown with an "x" under each sticker. Imagine the operator trying to keep track of this pattern and inspect stickers on the fly! (See x above.)
For Gillingham-Best the pattern is just feed 5 stickers and stop.
With Gillingham-Best the operator is looking for a full sticker chain. This greatly reduces the complexity of the sticker inspection process. Plus for Gillingham-Best the stickers are stopped during the inspection. Ref: Item #1.
Stacker Cycle Time Comparison
For any manufacturer's stacker, the distance the forks travel (stroke) and the amount the forks lift help determine the overall speed. The following diagrams compare the path the fork tip follows while placing a layer on the package.
As you can see, the GBI has a distinct advantage because both the lift and stroke are less than the competition's. In the example for a 54" sticker, the GBI travel is 28% less than Lunden.
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The lift at the tip of the forks also determines the amount of vertical travel required for the overhead rake-off. The overhead rake-off is the unit that drops behind the lumber and stickers as the forks retract. The USNR rake-off needs to travel 5-1/2" farther than GBI to maintain the same clearance to lumber on the forks as the forks lift and move forward with the course of lumber.
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