Overview:

 

Precision Tracking Control of SMA Actuactors
Abstract:
In many other cases, such as active rotorcraft blade control or active shape control, precise actuation of SMA is required. The lack of a precision control strategy is one the factors hinders further application of SMAs. In this research, a new approach is proposed to compensate hysteresis in SMA actuators by using a neural network controller and a sliding-mode based robust controller to achieve precision tracking control. The feed forward neural network controller is used to cancel the hysteresis and the sliding-mode based robust controller compensates uncertainties such as the error in hysteresis cancellation and ensures system's stability. A single wire SMA actuator is used as the controlled object in this research. The experiment results demonstrate that the proposed method of hysteresis compensation using neural network and sliding-mode based controller is very effective.
               
Position Control of SMA Actutators without a Position Sensor
Abstract:
Tracking control of shape memory alloy (SMA) actuators is essential in many applications such as vibration controls. Due to the hysteresis, open-loop control design has proven inadequate for tracking control of SMA actuators. Aimed at eliminating the position sensor to reduce cost of an SMA actuator system, in this research, a neural network open loop controller was proposed and tested for tracking control of an SMA actuator. A test stand, including a titanium-nickel (TiNi, or Nitinol) SMA wire actuator, a position sensor, bias springs, and a programmable current amplifier, was used to generate training data and to verify the neural networks open loop controller. Based on the training data, two neural networks were used to respectively model the forward and inverse hysteretic relations between the applied voltage and the displacement of the SMA wire actuator. To control the SMA actuator without using a position sensor, the neural network inverse model is used as a feedforward controller. Experiments were conducted and successfully demonstrated that shape memory alloy actuators with the proposed control design can track a sinusoidal reference command with reasonable accuracy without using a position sensor.
                 
Design and Control of a Shape Memory Alloy Rotary Servo
Abstract:
The objective of this project is to design a SMA-driven rotary servo actuator and to implement robust control for the actuator. First, A rotary servo device using NiTi type of SMA wire have been designed and fabricated for this research. This rotary servo is equipped with an RVIT sensor for angular position measurements. Then, to actively control the servo, a sliding-mode based robust control approach is used. The control strategy is implemented using a dSPACE real-time control system. Experimental results show that the rotary servo can be precisely controlled using the sliding-mode based robust control approach. The rotary servo can achieve a rotation of 100 degree at a steady state error of 0.2 degree. This validates the design of this SMA rotary servo. Experimental results also demonstrate the advantages of the robust control over PD control.
                    
Presion Control of an Underwate Shape Memory Alloy Actuators
One major drawback associated with a shape memory alloy actuator operated in the air is its low bandwidth due to the slow cooling process. Obviously, the heat transfer condition for underwater SMAs eliminates this drawback. Recent years have seen an increasing amount of attention paid to the potential applications of underwater SMA actuators such as actuation of robotic fish and tab assisted control of active surfaces for marine vehicles. However, SMA exhibits severe hysteresis, a type of non-linearity, which adversely affects its precision positioning. This project studied active position control of underwater SMA wire actuators using the sliding-mode based robust approach. In this research, the sliding-mode based robust approach is employed to ensure the stability and high control accuracy of this underwater SMA actuator in the presence of the hysteresis. To enable experimental study, a dual-purpose (in air and in water) SMA wire test stand was fabricated. Experimental results show that the SMA actuator in water can be precisely controlled using the proposed control approach with a much faster response.
      
Reduce SMA Acutaor Energy Consumption Using Modulation Techniques
Shape memory alloy (SMA)s, in particular the nickel-titanium alloy (or Nitinol), have been used as actuators in some astronautic, aeronautic and industrial applications. Future will see more SMA application if less energy is required for actuation. This research aimed to reduce the energy consumption of the SMA actuator the by using PWPF and PWM modulation techniques. Based on the open-loop testing results of the SMA actuator and parameter analysis of the modulators, Pulse Width Pulse Frequency (PWPF) and Pulse Width Modulation (PWM) modulators were designed and incorporated in a Proportional plus Derivative (PD) control system for the SMA wire actuator separately. Experiments demonstrate that control of the SMA actuator using PWPF and PWM modulation techniques effectively save actuation energy whiling maintaining same control accuracy as compared to continuous PD control.