Novel Monolithic Shape Memory Alloy (SMA) Actuator with an Embedded Strain Gauge Sensor

Until now, sensor-less position estimation of SMA actuators under dynamic unknown applied stresses has been impossible due to the complexity of the systems and the number of unknown parameters. The current work describes a novel self-sensing NiTi Shape Memory Alloy (SMA) actuator was designed and fabricated by using two distinct material compositions in a monolithic wire. Each compositional section exhibited distinctly different properties at room temperature, including shape memory effect (SME) for actuation and pseudo-elasticty (PE) to enable sensing capability. Fabrication of the wire included Multiple Memory Material (MMM) laser processing followed by post processing procedures. This included a training step to stabilize thermo-mechanical properties using iso-stress thermal cycling. Additionally, a model-based sensor-less position estimation algorithm was developed to estimate the position of the actuator under varying applied stresses with an approximate accuracy of 96% only using two resistance measurements across the two different material compositions. The current work overcomes existing sensing limitations and can enable SMA applications in robotics, wearables, automotive, and other applications where the mechanical load is not known in advance.