An investigation of a realization method for High Load Capacity and Compact Mechanical Gravity Canceller with tension transmission function via two rotational axes

Abstract

This study aims at realization of Mechanical Gravity Canceller with tension transmission function via two rotational axes, which achieves a good balance between suitability for M-DOF and high load capacity. Providing high power of conventional manipulators causes a problem of increase in their size and weight. To solve this problem, it has been expected to use Mechanical Gravity Canceller (MGC), a device which can compensate torques by the manipulator’s weight and load with tension spring. While MGC succeeded in compensating the weight of M-DOF manipulator completely, there remains a risk of fatigue fracture of wire ropes in its actual use. This is caused by their large curvature bending. CT-MGC (Compression Type-MGC), a type of MGC consisting of compression spring and block slider crank mechanism, was developed to ensure the rigidity and safety of MGC. However, CT-MGC occupies a large space and so is not appropriate for an installment in M-DOF manipulator. To solve these problems of conventional MGC series, HLCC-MGC (High Load Capacity and Compact MGC) is developed. HLCC-MGC can avoid bending of wire rope in large curvature by transmitting tension via two rotational axes. This feature consists of two elements: arrangement of pulleys considering both a range of movement and a configuration of DOF, and use of parallel link rotator, newly developed rotational mechanism. The testing machine with two HLCC-MGCs can compensate gravity force of tip load imitating an end effector whose weight is 5.06 kg, while the weight itself is 5.88 kg.