Position control of a shape memory alloy actuator using a four-term bilinear PID controller

Abstract

This is a postprint version of the following published document: Villoslada, A.; Escudero, N.; Martín, F.; Flores, A.; Rivera, C.; Collado, M.; Moreno, L. (2015). Position control of a shape memory alloy actuator using a four-term bilinear PID controller. Sensors and Actuators AbstractShape memory alloy (SMA) actuators have a number of appealing features, such as their low weight or their high force-to-weight ratio, that make them a potential alternative to traditional actuation tech-nologies in fields such as space applications, surgical devices or wearable robotics. In this paper, a type of bilinear controller consisting of a conventional PID controller cascaded with a bilinear compensator, known as BPID, is proposed. Bilinear controllers are a subset of nonlinear controllers, which is why the BPID may be a promising alternative to control the position of a SMA actuator. Nonlinear control tech-niques are commonly applied to control SMA actuators, because of their nonlinear behavior caused by thermal hysteresis. The BPID controller is simpler and easier to implement than other nonlinear control strategies, which makes it a very appealing candidate to control SMA actuators. The performance of the BPID controller has been compared with other two controllers, a conventional PID and a commuted feed-forward PIPD, controlling a real SMA actuator. To this end, a set of five tests has been defined, in which the controlled actuator must follow a series of position references. From these tests, the position and error of the actuator have been plotted, and a series of metrics has been computed to have quantitative mea-surements of the performance of the three controllers. It is shown that, in most of the experiments, the BPID has a better performance than the other two tested controllers, especially tracking step references. However, the power consumption is slightly higher when the actuator is controlled with this strategy, although the difference is minimal. Also, the BPID imposes greater energy variations to the SMA actuator, which might affect its service life. Overall, the BPID controller has proved to be a viable alternative to control SMA actuators.

Design and Development of Robot Gripper: Shape Memory Alloy Approach

“…They are small and lightweight, which allows for a reduction in size, weight and complexity of the devices where they are used. The force-to March 2017 weight ratio is very high [12,13]. Combined with a torsional spring, it gives same movement characteristics that of gear, gear assembly and a motor.…”

Flexible shape memory alloy actuators for soft robotics: Modelling and control

“…The reason for this non-linear operation is that the temperatures at which the transformation from martensite to austenite takes place are different from the ones of the austenite to martensite transformation, giving rise to thermal hysteresis. 6 For technical applications, the hysteresis SMA property is very important and must be carefully taken into account for control objectives. In general, for robotic applications, small hysteresis is required.…”

“…It uses the play operator as the basis for modelling any hysteresis, although through some modification, it can describe complex features such as saturation or frequency dependence. The play operator is represented by equation (6) max xðtÞ À r; min xðtÞ þ r; yðt À T Þ f g f g ð6Þ…”

Flexible Shape-Memory Alloy-Based Actuator: Mechanical Design Optimization According to Application

“…This introduces in the system non-linear behaviors, which makes it difficult to develop control algorithms for this type of actuator. In [20], a four-term Bilinear PID (BPID) control strategy was successfully applied to control a single SMA wire. Based on this work, a BPID controller with a bilinear compensator is proposed to control SMA actuators.…”