Static Force Balancing of a 2R1T Parallel Manipulator with Remote Center of Motion

Abstract

Assistive robots in surgical applications should be gravity balanced due to safety considerations. This study presents a gravity balancing solution for a 3-degree-of-freedom parallel manipulator to be used as an endoscope navigation robot for transnasal minimal invasive surgery applications. The manipulator has a rather simple structure that allows individual balancing of the three legs in their respective planes of motion. First, sole counter-mass balancing is investigated, but it is seen that the extra mass amount is too much. Sole spring balancing is not considered as an option due to constructional complexity. A hybrid solution as a combination of counter-mass and spring balancing is devised. In the proposed solution, the masses on the distal links of a leg are balanced with counter-masses so that all masses are lumped to the link connected to the base of the manipulator. Hence the problem is simplified into the balancing of a pendulum. The necessary formulations are derived and numerical calculations demonstrate that the hybrid balancing yields a feasible solution.

Partial gravity compensation of a surgical robot

“…Recently, a study was conducted using only countermass based and a combination of counter-mass and spring in a previous study for our surgical system. 4 The increase in the total moving mass was investigated when only counter-masses are used. To reduce the total moving mass, the use of springs was proposed for the links that are connected to the base platform.…”

“…The system is designed to handle and direct an endoscope in a minimally invasive surgery procedure called a pituitary tumor surgery. 3 The system is called NeuRobo-Scope 4 and its first functional prototype is shown in Figure 1.…”

“…13 In fact, these two techniques can be used simultaneously. 4 A design tool was proposed by Martini et al 14 to determine a feasible gravity compensation solution by selecting appropriate mixtures of counter-masses and springs. Martini et al 14 evaluated the performance of unbalanced/balanced mechanism in terms of energy efficiency, peak motor loads, and joint reactions to assess the most convenient balancing solution.…”

Gravity compensation of a 2R1T mechanism with remote center of motion for minimally invasive transnasal surgery applications

“…Van Dorsser et al [7] developed a system to adjust a spring and a linkage-based balancer by changing the active coils of the spring which effects its spring stiffness and allows the system to stay in balance when the payload changes in an energy-conserving way. Yaşir et al [8] and Maaroof et al [9] have introduced two different partial gravity compensation solutions with springs for a 2URRR-URR parallel manipulator. Maaroof et al [9] achieved partial gravity compensation by using torsional springs on actuator shafts.…”

“…In this work, the balancing solution of ref. [8] is slightly modified and formulated in detail. The balancing solution is implemented in parallel with the constructional design of the balancing components.…”