Drives and Controls Magazine
Algorithm boosts servo performance in precision applications
Published:  29 January, 2014

The Israeli motion control specialist ACS has developed an algorithm that, it claims, will improve the performance of high-accuracy servo applications – reducing moving and settling times, eliminating cogging, and improving their ability to handle significant changes in load. This, in turn, will leads to higher accuracies and throughput. ACS reports that field trials of the ServoBoost algorithm have achieved performance improvements several times better than those of competing products.

The algorithm adapts automatically to large load changes and compensates in real-time for resonances, interacting axes, cogging and other disturbances. It not only identifies a disturbance in real time, but also analyses it root causes, compensates for it, and reduces its impact.

The algorithm is aimed at high-accuracy applications such as electronic assembly, semiconductor inspection and bio-medical analysis equipment. It is said to deliver standstill jitter in the sub-nanometer region. The algorithm combines smooth and constant velocity with stability and robustness, to provide a high level of control.

In one early application, on a three-axis machine designed to manufacture and test ultra-precision optical components, ServoBoost is said to have achieved a residual standstill jitter of about 250pm when performing steps down to 2nm using an air bearing stage.

Because these stages show inherently low damping, it is more challenging to achieve such results with them than with hydrostatic or roller-type bearings. According to Dr-Ing Giora Baum, who was involved in the testing the application at the Fraunhofer Institute in Germany, the ACS algorithm overcomes this drawback, because it provides digitally controlled damping.

The algorithm is available as a plug-in function for new ACS motion control products, or as an upgrade for existing installations.