One simple form of motion synchronization, still widely used, is an external signal trigger that causes a synchronized change in the profile for one or more axes. Modern motion controllers allow a range of automatic trigger conditions (sometimes called breakpoints) so that axes can be started, stopped, or otherwise altered by an external signal change, and so that the triggering condition can be nearly any combination of signal conditions.

One simple form of motion synchronization, still in widespread use, is an external signal trigger that causes a synchronized change in the profile for one or more axes.

In a typical application, the host controller preloads a new set of target profile parameters and sets a breakpoint event to occur when the external signal condition goal is reached. When the signal arrives at the target state, the motion controller automatically initiates the new motion profile.

For most applications, because moves are short, or because it is okay for axes to arrive at slightly different times, this is acceptable. However, a number of applications exist for which this approach won't work — including situations requiring continual synchronization between axes, and not just at the start of motion.

Why would two or more axes get out of synch during a motion? Motion controllers run their clocks from an internal oscillator. Each oscillator provides a slightly different frequency, so drift can slowly accumulate between multiple axes.

Where it is problematic, one solution is to explicitly synchronize the servo loop rates of each controller. Explicit synchronization is done by designating one motion controller to serve as the “master” and generate a synch or strobe signal — in turn, sent to one or more slave controllers.

Alternatively, the same benefit of explicit axis synchronization occurs automatically using a multi-axis controller rather than a chain of single-axis controllers. This is because multi-axis controllers use one master internal clock, so their servo loops are explicitly synchronized.

For most applications, moves are short, or axes can arrive at slightly different times without issue. Elsewhere, explicity synchronizing controller servo loop rates is indespensible. As show here one of the motion controllers serves as the master by generating a synch or strobe signal, which is then accepted by one or more slave controllers.

Get your gear on

What if synchronization is more than a matter of keeping an axis coordinated with itself? Consider the application of a robot arm that must track the speed of an external conveyor. In this application, the conveyor speed may not be exactly known; therefore, the robot arm must somehow be synchronized by a signal that changes constantly.

Enter electronic gearing, and its more sophisticated cousin, electronic camming: Electronic gearing utilizes an external position data stream, nearly always quadrature encoder signals, to provide the master drumbeat by which all motions occur.