Processes may take various forms in automated production. They may be continuous as with the mixing of chemicals, synchronous where operations are performed in unison or asynchronous where operations are performed independently. Manual and automated tasks may be mixed to utilize the decision making and dexterity advantages of human labor.
Chemical, food and beverage production often operates in a continuous fashion. Chemicals or ingredients are mixed together continuously to produce a “batch” of product. Plastics are often extruded continuously and then segmented into individual pieces for further operations.
Processes are said to be asynchronous when they do not rely on a master timing signal. An example of this might be an operation which takes place when a product arrives at an operator station from a previous process on a conveyor. The component may then be operated on when its arrival has been detected by a sensor rather than at the index completion signal from the conveyor.
Synchronous processes rely on a master clock or timing signal. This may be an electrically or mechanically based system; cam driven devices on a line shaft are examples of a synchronous process. Assembly line operations may be synchronous, asynchronous or a combination of both depending on the source of the initiating trigger.
The picture above is an illustration of a device used in both synchronous and asynchronous processes and is commonly used to rotate a dial table. If the driving motor is run continuously the indexer will rotate a fixed number of degrees (typically 45, 60 or 90 for 8, 6 and 4 stations respectively) and then enter a dwell for a fixed period of time based on motor speed. This is an example of using the indexer synchronously. If the indexer is actuated periodically the rotation will occur at the motor speed but then can be stopped by using a clutch or stopping the motor during the dwell period. This “cycle on demand” method would be an example of using the indexer asynchronously.
An important note to remember when using these types of indexers. Ideally you should never stop the motor or during the rotation period of the cam. This puts strain on the engaged mechanism and at high speeds can actually damage the indexer. Because of this a “breakaway mechanism” is often used to disengage the table from the drive if the table is stopped by a physical obstruction.
Well known manufacturers of cam-based indexers include Camco, Stelron and Weiss.