The actuators consist of fibers woven in a specific pattern which achieves a large amount of displacement amplification with very small losses. In the present prototype twelve fibers are run in parallel resulting in a 16 mm diameter package weighing 6 grams and capable of pulling 4 N. In the present configuration, the strain is about 20% and the rise time shorter than 100 ms for an antagonist set-up in ambiant air. Two variable structure controllers were investigated. The first involves a switching control input creating a sliding mode in conjunction with a linear proportional activated within a boundary layer in the vicinity of the set point. The second involves a multi-stage switching control with a constant amplitude feedback that simplifies amplifier construction. Experimental performance results in the time domain demonstrate that this control can achieve very fast rise time, high rejection of disturbance, small tracking as well as steady state error despite their numerous non-linear properties. Patent pending.
D. Grant, V. Hayward
A single NiTi actuator package, 16 mm accross.