Experimental investigations of the large deflection capabilities of a compliant parallelmechanism actuated by shape memory alloy wires

Abstract

This experimental study investigates the coupled effect of the force developed by the shapememory alloy (SMA) actuators and the force required for the large deflection of an elasticamember in a compliant parallel mechanism. The compliant mechanism developed in houseconsists of a moving platform mounted on a superelastic pillar and three SMA wireactuators to manipulate the platform. A three-axis MEMS accelerometer has been mountedon the moving platform to measure its tilt angle. Three miniature force sensors have beendesigned and fabricated out of cantilever beams, each mounted with a pair of strain gauges,to measure the force developed by the respective actuators. The force sensors are highlysensitive and cost effective compared to commercially available miniature forcesensors. Calibration of the force sensors has been accomplished with known weights,and for the three-axis MEMS accelerometer a rotary base has been consideredwhich is usually used in optical applications. The calibration curves obtained, withR-squared values between 0.9997 and 1.0, show that both the tilt and force sensorsconsidered are most appropriate for the respective applications. The mechanism fixed withthe sensors and the drivers for the SMA actuators is integrated with a NationalInstrument’s data acquisition system. The experimental results have been compared withthe analytical results and it was found that the relative error is less than 2%. This is apreliminary study in the development of a mechanism for eye prosthesis and similarapplications.