Abstract
This paper proposes a sampled-data polydyne as a feedforward input for a high-speed and high-precision positioning control system that does not excite specified mechanical resonant modes. The polydyne curve is an optimal cam profile that does not generate residual vibrations due to the follower's resonant mode. Research papers have reported applications of polydyne curve to feedforward control, and they have been formulated in continuous-time domain. However, when the frequency of vibration to be suppressed is high and the sampling frequency is relatively low, the reference trajectory for feedforward control should be generated in discrete-time domain. Thus, we derived the sampled-data polydyne which is a formulation of the polydyne curve in discrete-time domain. For suppressing one resonant mode, the order of polynomial must be seventh or higher, and eleventh or higher-order is necessary for suppressing two modes. Simulations of seek control in a hard drive was performed with the proposed feedforward input using sampled-data polydyne. It was confirmed that the sampled-data polydyne input suppressed the residual vibrations substantially and improved the tracking error after seek motion. Furthermore, it was shown that the apparent damping ratio in the residual vibration should be used for generating the polydyne feedforward input instead of the true modal damping ratio of the control object.
