Effect of Mechanical Loading and Increased Gap on the Dynamic Response of Multiple Degree of Freedom Electrostatic Actuator

Electrostatic inchworm motor based on gap-closing variable capacitor provides potential solution for larger force actuation compared to area overlapping one. Unlike the constant electrostatic force in area overlapping variable capacitor, the generated electrostatic force in gap-closing variable capacitor increases as the displacement is increased.

However, due to the pull-in phenomena the system stability and controllability is critical design challenges. Various designs of complex electrostatic actuators based on gap-closing variable capacitor were developed as linear inchworm motor [1-2]. However, the force actuation capability is still in mN range.

In this paper, a novel monolithic structural design of electrostatic actuator with multiple degree of freedom is presented as an approach for a system that is capable of performing large electrostatic force and scalable stroke. The actuator is a kind of mechanical oscillator can be driven in xy-directions by three voltage electrodes. One voltage electrode is used to apply vertical displacement in order to release or clutch the comb-like structure side with interdigitated shaft, while other voltage electrodes are used to perform displacement in the lateral direction. Multiple actuators can be used to increase
the overall applied electrostatic force on the shaft.

In this work, an electromechanical system model based on Simulink software was developed for a proposed design of electrostatic actuator. The dynamic response of the actuator was simulated and the mechanical bouncing response due to effect of realizing extra mechanical stoppers or passivation layer was investigated. Also, the mechanical bouncing as well as steady state response of the actuator was investigated under various mechanical loading values. The switching time increased as the mechanical load was increased. Bouncing amplitude increased as the impact force was increased. Both switching time and bouncing amplitudes are important factors for the oscillation stability of the actuated shaft, knowing that the final system contains multiple actuator units.

Literature
[1] S.-H. Kim, Il-H. Hwang, K.-W. Jo, E.-S. Yoon, J.-H. Lee; High resolution inchworm linear motor based on electrostatic twisting microactuators, Journal of Micromechanics and Microengineering 2005, 15, pp. 1674-1682; 2005.
[2] M. A. Erismis, H. P. Neves, R. Puers, C. V. Hoof; A low voltage large displacement large force inchworm actuator; Journal of Microelectromechanical Systems 2008; 17, 6, pp. 1294-1301; 2008.
[3] I. Penskiy, S. Bergbreiter; Optimized electrostatic inchworm motors using a flexible driving arm; Journal of Micromechanics and Microengineering 2013, 23, 015018; 2013.
[4] K. Saito, D. S. Contreras, Y. Takeshiro, Y. Okamoto, S. Hirao, Y. Nakata, T. Tanaka, S. Kawamura, M. Kaneko, F. Uchikoba, Y. Mita, K. S. J. Pister; Study on electrostatic inchworm motor device for a heterogeneous integrated microrobot system; Transactions of The Japan Institute of Electronics Packaging 2019, 12; 2019.