Abstract
Minimally invasive surgery (MIS) presents many constraints on the design of robotic devices that can assist medical staff with a procedure. The limitations of conventional, rigid robotic devices have sparked interest in soft robotic devices for medical applications. However, problems still remain with the force exertion and positioning capabilities of soft robotic actuators, in conjunction with size restrictions necessary for MIS. In this article we present hydraulically actuated soft actuators that demonstrate highly repeatable open loop positioning and the ability to exert significant forces in the context of MIS. Open loop position control is achieved by changing the actuator volume, which causes contraction. In one degree of freedom (DOF) configurations, root mean square error (RMSE) values of 0.471 mm, 1.506 mm, and 0.350 mm were recorded for a single actuator against gravity, a single actuator with a pulley, and a horizontal antagonistic configuration, respectively. Hysteresis values of 0.711 mm, 0.958 mm, and 0.515 mm were reported in these experiments. In addition, different numbers of soft actuators were used in configurations two and three DOFs to demonstrate position control. When deactivated, the soft actuators are low-profile and flexible as they are constructed from thin films. As such, a robot with a deployable structure and three soft actuators was constructed. The robot is therefore able to reversibly transition from low to high volume and stiffness, which has potential applications in MIS. A user successfully controlled the deployable robot in a circle tracing task.
Highlights
As part of our work to use soft robotic methods with the Cyclops robot, we have developed a soft hydraulic actuator inspired by the pneumatically actuated ‘Pouch Motors’
Our soft hydraulic actuators are a good choice for Minimally invasive surgery (MIS) and other potential applications because the actuators have a low-profile form factor, they avoid the friction effects of Bowden tubes, and open loop length control can be achieved with a simple method
The paths filled a large portion of the workspace and included two circular patterns, a helix aligned with the X axis, an Archimedean spiral projected on a cone, and another Archimedean spiral projected onto a cylindrical surface
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. The robot consists of a support structure connected to the endoscope tip that can deploy (increase in volume) to provide space for two surgical instruments to manoeuvre One disadvantage of this system is friction between the long force transmission cables that are used to actuate the surgical instruments and the Bowden tubes containing them. Our soft hydraulic actuators are a good choice for MIS and other potential applications because the actuators have a low-profile form factor, they avoid the friction effects of Bowden tubes, and open loop length control can be achieved with a simple method. We have developed soft actuators with the aim of approaching these disadvantages and of building on the work in [9] to produce an entirely deployable cable-driven robot. This has been shown by using the actuators in a variety of configurations: from simple one degree of freedom (DOF) tests to planar parallel mechanisms, a three DOF hybrid parallel mechanism, and a proof-of-concept deployable hybrid parallel robot with inflatable structure
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