Engineering Incipient Slip Into Surgical Graspers to Enhance Grasp Performance

Abstract

The surgical community has long reported the need for improved control of surgical graspers when handling delicate soft tissues, both to avoid the over application of force which leads to trauma, and to avoid tissue slip. The majority of research has sought to mitigate these issues through the integration of force feedback into the graspers. In this work we investigate an alternative strategy in which the grasper design is engineered to create preferential localised slip, also known as incipient slip, on the premise that this can be detected before the onset of macro slip, allowing graspers to use the minimum force required to maintain stable control. We demonstrate the ability to encourage incipient slip in a predictable and repeatable manner through the design of the grasper face profile and pattern. This provides an important foundation for development of sensing systems capable of detecting these slips during surgery to improve operative outcomes.

Utilising Incipient Slip for Grasping Automation in Robot Assisted Surgery

“…We approached this using a concept which employs a curved grasping surface that is segmented into independently mobile sections. The curved surface causes higher frictional forces to occur in the middle of the grasper in comparison to the edges, thus encouraging slip to occur in the outer sections of the grasper prior to the middle [17] as illustrated in (Fig. 1).…”

“…To evaluate this sensor concept, a scaled prototype was developed and realised. Based on preliminary work [17], a curved grasper face with a radius of 100.25 mm was separated into a 5×3 grid of islands as shown in Figure 2, providing islands spanning the width and length of the grasper face. Islands were separated along the length of the grasper to isolate them from the effect of slip propagation between the front and back of the grasper caused by the elastic properties of the tissue [17].…”

“…Based on preliminary work [17], a curved grasper face with a radius of 100.25 mm was separated into a 5×3 grid of islands as shown in Figure 2, providing islands spanning the width and length of the grasper face. Islands were separated along the length of the grasper to isolate them from the effect of slip propagation between the front and back of the grasper caused by the elastic properties of the tissue [17]. Each island comprises a 3D printed upper rigid face (Rigid 4000 Resin, Formlabs) to provide the gripping surface, and a 1 mm thick silicone elastomer base (Ecoflex 00-30, Smoothon) to allow independent movement of the rigid face.…”

“…The islands were then attached to a PET film on a rigid base. The grasper faces featured a regular hexagonal pattern (0.75 mm width, height and separation) to provide an isometric gripping surface suited to soft deformable materials [17], [19].…”

“…Biomimicry of the human finger has been used by many as inspiration; typically employing a curved finger-like surface to create a normal force distribution, and thus corresponding variation of frictional force, across the contact surface [14], [15], [16]. This approach has been demonstrated as a viable method for encouraging the incipient slip of lubricated and deformable materials similar to soft biological tissues [17]. Khamis et al [18] investigated an alternative to using a continuous curved surface to control friction forces, instead using an array of stepped pillars to create discrete variations in height and thus normal force.…”