This three-axis servo-controlled bandsaw from Warsaw Machinery, Warsaw, Ind., cuts blocks or panels into any size, shape, or number of component parts. Here it uses synchronization to shape the bodies of guitars.

Suppose, in this example, that one of the motion system design goals is to maintain a 3:1 angular ratio between the nip rolls and cutting wheel on the web line where the plastic casing is formed. Naturally, the controller must be able to handle round-off error in order to generate digital commands that comply with the required ratio and, more importantly, keep the two axes turning in precise synchronization. This calls for a digital processor with floating-point math and automatic rollover a bit handling function that knows what to do when a register value reaches its limit. Otherwise, cumulative errors will make it impossible to maintain the desired relationship, causing all sorts of manufacturing problems.

There are other complicating factors, however. Extruded materials in a web-handling system must be processed at whatever speed they come off the roll or extruder; all timed operations must be consistent and in synch regardless of unexpected variations in speed. One of the challenges in maintaining this angular ratio between the nip rolls and cutting wheel is that the nips continually change speed in order to exert constant pressure on the hot extruded plastic.

Tool wear and other age-related issues also pose a problem. The variations caused by these mechanisms introduce a sort of phase shift in the angular relationship between the product and cam profile.

One solution is to maintain a cam with different data densities for different stages of a process. A cam can be pointed to a high-density array for dynamic operations — when knives are slicing through product, for example. Then in more static or coarse-movement situations, as when knives hover above product or when they return to a home position, the cam can be pointed to a low-density array.

What's more, manipulating the data arrays to advance or retard phase can extend blade life by ensuring that each engagement begins at the optimal starting point.

For more information, visit parkermotion.com or search for synchronization at motionsystemdesign.com.