Hand-Held Device for Force Estimation during Tool-Tissue Interaction

When manipulating tissue during medical interventions, high-accuracy movements are important to avoid injuries. However, feedback is limited and it is hard to establish control loops to ensure correct movements. We propose the use of a novel highly compact 6-axis force / torque sensor (Ø 10.5 mm x 11.0 mm) within a hand piece to determine low forces and torques during various small-scale procedures including gentle tool-tissue interaction. For a first validation of the system, different venepuncture cannulas were connected to the sensor top and driven into skinned fruits (toma-toes and grapes) as well as into a silicone block. During insertion of the needle tips, maximum forces of 74 – 158 mN (tomato) and 51 - 161 mN (grape) were recorded, and steadily increasing forces in the range of 0 – 250 mN when inserting needles 7.5 mm into silicone. For a 0.99 g screw nut (9.73 mN), the measured gravitational force was 10.6 ± 1.5 mN during ten measurement sets. During the insertion, needle torques of up to 9.5 mNm were observed. Different cutting phases were seen similar to the phases during needle penetration testing. We conclude that the compact measurement setup used is suitable to measure the low forces and torques occurring when cutting soft, aqueous human tissues with or without skin-like layers.