Effect of sampling jitter and control jitter on positioning error in motion control systems

In a digital motion control system, there exist timing variations in feedback sampling and control updating, often referred to as sampling jitter and control jitter. Although jitter has been studied in prior art, no equations or quantitative experimental results have been reported which relate jitter to positioning error in a motion control system. To investigate the effect of jitter on positioning error, this paper presents a simplified discrete model that captures sampling and control jitter's interaction with other system inputs as disturbances to the control system. Based on this model, analyses are carried out for the scenarios of position regulation and command tracking, each resulting in an equation to predict jitter's effect on positioning error using measured or analytical frequency responses of the system. Further, an easily implementable add-on jitter compensator is proposed to mitigate the regulation error due to jitter without affecting the existing controller. Through experiments performed on a fast-tool servo machine tool, the model and analyses are validated and the positioning degradation due to jitter is clearly demonstrated.

► We modeled, analyzed, and experimentally demonstrated jitter effects on positioning error.
► Sampling jitter has negligible effect on regulation error.
► 8% control jitter can result in regulation error twice as much as the sensor noise.
► Jitter effect on regulation can be greatly attenuated by adding Nyquist zeros into controller.
► Sampling jitter and control jitter can contribute significant error in high frequency tracking.