Research Of Direct Cardiac Assist Devices Based On Artificial Muscles

Artificial muscle as a new-style smart actuator attracts a great deal of interests in the last years. One important reason is that artificial muscle has the ability of contraction and relaxation like human muscles under external stimulation. More and more researchers devote themselves to develop a delicate, adaptive and robust controller actuator using artificial muscles especially in the biological engineering.We used the BioMetal Helix (BMX) series of Toki Corporation as the artificial muscles, which were coil springs formed by NiTi shape memory alloys. In this article, we analyze the frequency displacement response and the energy conversion efficiency of shape memory alloy (SMA) coil under the controls of square wave and pulse width modulated (PWM) wave. The purpose focuses on this material which can be application for the design of a cardiac assist device. In our experiment, the frequency displacement response of SMA coil with the changing of signal frequency and duty cycle was observed by the 3D optical location tracking system (NDI Polaris) with a sampling frequency of 10 Hz.The experimental results reveal less temperature difference can decrease the necessary heat for phase transformation of materials and the SMA actuator controlled by PWM wave can effectively improve the energy conversion efficiency through reducing the heat release. To minimize the energy consumption, a control strategy of pulse width modulated (PWM) wave with less working duty cycle, less pulse duty cycle and greater electric current under appropriate temperature are proposed.The experimental results also present that the controller employing PWM signal to actuate SMA coil can progress the energy efficiency than using square wave signal, mainly because a large current can promote the phase transformation of SMA and reduce the waste of heat. Finally, efficient cardiac assist devices was designed with the results of our experiments. Maybe this paper could provide some references for others and make them have an intuitive understanding of the characteristics of BMX.