In this paper, we developed a novel artificial muscle using shape memory alloy (SMA) spring bundles. We arranged the SMA springs in honeycomb architecture to increase the utilization of the designed space. This artificial muscle has small size and small weight and can be repeated easily for various biologically inspired applications such as an exoskeleton and exo-suit, where small size and small weight of the actuator are momentous. This muscle consists of two sets of SMA springs: six SMA springs (Set A) and six antagonistic SMA springs (Set B) arranged in hexagon vertexes for forward and reverse motion respectively. This modular muscle can be reduplicated in parallel to increase the output force or in series to increase the stroke length in order to fit the desire dactuation application.
We used an inertial measurement unit (IMU) sensor to
feedback the angle and two sets of temperature sensors were
applied to monitor the SMA temperature. The system is
modeled and experimentally verified in open-loop and closed-
loop control. We used a proportional-integral-derivative (PID)
controller to track the desired trajectories. The experimental
results show that the system is capable of tracking the desired
trajectory with delay time 1.2 sec., rise time 2.5 sec. (per 30
o ), and overshoot 2.3%.