Precision force and position control of an ionic polymer metal composite

Abstract

In this paper, model-based precision force and position control of an ionic polymer metal composite (IPMC) is presented. A 23.8 mm × 3.4 mm × 0.16 mm IPMC strip was used as an actuator in a cantilever configuration. Open-loop force and position responses of an IPMC are not repeatable, and hence closed-loop precision control is of critical importance to ensure proper functioning, repeat-ability and reliability. After feedback controllers were designed and implemented with empirically obtained fourth-order plant transfer functions, the overshoot decreased from 460 to 2.8 per cent and the settling time was reduced from 37.5 to 3.22 s in force control. In position control the overshoot decreased from 333 to 20.3 per cent and the settling time was reduced from 21.5 to 2.56 s. Microscale precision force and position control capabilities of the IPMC actuator were also demonstrated experimentally. An 8 μN force resolution was achieved with a force noise of 0.5μN r.m.s., and the position resolution was 6 μm with a position noise of 2.5 μm r.m.s. The maximum force and tip displacement achieved with the IPMC actuator under closed-loop control were 2 mN and 5 mm respectively. The IPMC actuator could follow various commanded force and position trajectories such as sinusoidal and trapezoidal position profiles, and a velocity profile with a 3 mm/s maximum velocity. A novel hybrid force and position control strategy demonstrated its utility in practical micromanipulalion applications where the actuator force must be limited to prevent damaging micro-objects. High-precision control of the IPMC at low force level proved its potential for micromanufacturing and micromanipulation applications such as robotic and biomedical microgrippers.

Noise characterization in millimeter sized micromanipulation systems

“…Typical dimensions of such systems are (40mm × 10mm × 0.2mm) [8], (15mm × 2mm × 0.3mm) [25] and (23.8mm × 3.4mm × 0.16mm) [26]. The stiffness of micromanipulation systems can vary from tens to hundreds N/m, such as the one studied in a previous work [28].…”

“…The control part is not treated although it is the main perspective of the work. We have then focused our study on kind of micromanipulation systems using cantilevers as end effectors with lengths in the order of several tens of millimeters, such as those designed in [8] [25] [26]. Such systems are often characterized by low resonance frequencies (below 1KHz) and are particularly sensitive to the environmental noise leading to significant vibrations around the resonance.…”

Operator based Robust Nonlinear Control Design to an Ionic Polymer Metal Composite with Uncertainties and Input Constraints

“…The white-box models, on the other hand, attempt to model physical processes taking place within the actuator, which are usually nonlinear models. For linear models, linear quadratic regulator (LQR), proportional integral and derivative (PID), adaptive fuzzy algorithm and impedance control scheme have been designed in precise position control [4]. Moreover, the IPMC shows mainly nonlinear behaviors in characteristics of large strain and stress, and a practical mathematical model and an effective control method are desirable in precise position control.…”

Particle swarm optimization identification of IPMC actuator using fuzzy NARX model

“…An empirical controlled model by Kanno et al was developed and optimized with curve-fit routines based on open-loop step responses with three stages, i.e., electrical, stress generation, and mechanical stages [6][7][8]. Feedback compensators were designed using a similar model in a cantilever configuration to study its open-loop and closedloop behaviors [9][10]. Other IPMC modeling methods presented in [11][12].…”