For a simple solution to an application requiring one stop to a specific position to line up with another machine or tooling, a limit switch can be added. Mechanical limit switches offer high contact reliability – once the lift comes in contact with the device it causes a break in the electrical connection completely stopping the lift at the set location within 0.25”.
A Non-PLC solution which utilizes photo-eye sensors which shoot across the product being either placed on or taken off the lift. These sensors send a signal to either the motor starter (when indexing UP in an INFEED application), or the dump valve (when indexing DOWN in an OUTFEED application) until the photo-eye path is cleared. This straightforward approach allows an unlimited range of product thicknesses to be run without alerting or modifying the control logic in any way. When standard lift speeds are specified (1 to 2 inches per second), repeatability and accuracies of 0.05” to 0.10” are not uncommon.
For lifting applications requiring no more than 2 to 3 stops, a low-cost PLC can be added to the motor control panel and an operator pushbutton station with multiple control buttons. Each control button is pre-programmed to have the lift sent to a particular stop location; the PLC decides best way to get there and skips any stops in between.
A solution which utilizes PLC logic and a transducer/encoder attached to the lift table. Operator inputs vary in complexity and/or technology, but the idea being that the operator selects a program for the desired task or series of tasks, and initiates movement either manually or automatically. The transducer communicates the vertical position of the lift to the PLC, the PLC in turn either initiates motor start or dump valve – depending on programmed task. A different program would have to be selected whenever different product thicknesses are run, and when standard lift speeds are specified (1 to 2 inches per second), repeatability and accuracies of 0.05” to 0.10” are not uncommon.