Asynchronous Control of a Prototype Inchworm Actuator: Control Design and Test Results

Abstract

Inchworm actuators are innovative mechanisms that offer nanometer-level positioning coupled with extreme dynamic range. Because of this, they have found applications in optical instruments of various types including interferometers, segmented reflectors, and coronagraphs. In this paper, we present two prototypes of flight-qualifiable inchworm actuators developed at the Jet Propulsion Laboratory. These actuators have two sets of brake piezoceramic (PZT) stacks and an extension PZT stack used for mobility. By proper phasing of the signals to these PZTs, a walking gait can be achieved that moves a runner attached via a flexure to the optic to be moved. A model of these devices, based on first principles, is developed as well as an estimation and control scheme for precise positioning. The estimator estimates physical parameters of the device as well as a self-induced motion disturbance caused by the brakes. Simulations and test data are presented that demonstrate nanometer-level positioning precision as well as the cause of variations in the brake-induced disturbance.

The Frequency-Variable Rotor-Blade-Based Two-Degree-of-Freedom Actuation Principle for Linear and Rotary Motion

“…They have a wide range of applications in many aspects, such as biomedicine [5][6][7], ultra-precision machining [8,9], precision optics [10,11], micro-and nano-positioners [12,13], triboelectricity [14], and microscopes [15][16][17], etc. The current mainstream research on piezoelectric precision drives focuses on stepper-type piezoelectric actuation [18][19][20], ultrasonic-type piezoelectric actuation [21,22], and inertial impact piezoelectric actuation [23,24]. Inertial impact piezoelectric actuation has received much attention, due to the distinctive actuation method of the inertial force changing the drive force and positive pressure for fast motion, a high resolution, a large stroke, and a simple structure [25,26].…”

Parameter identification of Duhem model based on antlion-fish swarm hybrid algorithm and robust backstepping sliding mode control for rate-dependent hysteresis of piezoelectric actuators

“…The flight inchworm actuators (FIA) which is composed of PEA stacks is used to position various optical elements in highly sensitive optical instruments. 3 PEA also is used as the actuator of micro-robots 4 and cell piercing 5 in life science and technology.…”

Modeling of Piezoceramic Actuators for Control

“…Three main issues, however, compromise the utility of these devices. The first is that the stroke of these devices is limited to about 40 μm, which for some applications, necessitates the use of dual stage actuation [2,3] or inchworm actuators [4] which combine brake PZTs with actuation PZTs to extend the dynamic range of these devices. In addition, PZTs suffer from significant amounts of hysteresis (15 percent of full stroke) and creep which causes drift of the device over time.…”