A deflectable video camera system for laparoscopic surgery based on shape memory alloy actuators

Laparoscopic instruments are usually not deflectable and therefore have significant usability limitations in minimally invasive surgery. Flexible-tip devices have been introduced, but they are still controlled by manual Bowden cables or conventional motors and are heavy and expensive. An interesting alternative are shape memory alloy (SMA) actuators, because they are lightweight, cost-efficient and offer the potential for a universal actuator platform for laparoscopic and other endoscopic instruments. This paper presents a laparoscopic video camera with electronic deflection control via thumb joystick. Its actuator unit consists of four SMA wires, whose special tensioning mechanism ensures both optimal preload and length compensation. The camera is tiltable in two degrees of freedom, enabled by a laser-cut Nitinol joint. Based on three assembled units and an automated measurement system, the functionality of the camera system was characterised. Deflection angles of more than 178° per degree of freedom were achieved. At operating frequencies of up to 0.5 Hz, the units showed suitable deflection behaviour. Each remained operational for more than 1200 actuation cycles or 4.4 h of continuous operation. Furthermore, the influence of continuous temperature stimulation on characteristic device parameters was investigated. This work contributes to demonstrating the feasibility of SMA actuators for the electrical control of flexible-tip laparoscopic instruments. Temperature control in particular is a challenge for future work.