In their Tollcross factory outside Glasgow, United Biscuits have a line dedicated to the production of biscuits called "54321s". One of the first processes is the production of sheets of wafer measuring about 300mm square. These are known as "Books" in the trade. Further along the line these "Books" are coated with chocolate. The production of the books is basically a baking process and so is quite slow. Conversely the chocolate coating process is quite rapid. This mis-match in speeds is overcome by having two baking lines feeding into one coating line.
Initially the merging operation consisted of one conveyor positioned above the other dropping books onto the lower conveyor. However this caused problems with collisions and had to be overseen by an operator 24 hours per day. Pan Controls designed and supplied a solution to this problem using intelligent servo-control of one conveyor to avoid collisions. The general layout of the solution is shown in the following diagram:
The system works as follows. Books from one of the upstream conveyor lines pass unhindered through the junction. Two photocells detect the arrival of books on both conveyors. If the intelligent controller calculates that a collision might occur it either speeds up or slows down a short section of the second conveyor so that the two books will miss one another. Occasionally there are insufficient gaps for either solution and the controller opens a flap to reject a book.