This paper presents an improved design, complete analysis, and prototype development of high torque-to-mass ratio Magneto-Rheological (MR) clutches. The proposed MR clutches are intended as the main actuation mechanism of a robotic manipulator with five degrees of freedom. Multiple steps to increase the toque-to-mass ratio of the clutch are evaluated and implemented in one design. First, we focus on the Hall sensors’ configuration. Our proposed MR clutches feature embedded Hall sensors for the indirect torque measurement. A new arrangement of the sensors with no effect on the magnetic reluctance of the clutch is presented. Second, we improve the magnetization of the MR clutch. We utilize a new hybrid design that features a combination of an electromagnetic coil and a permanent magnet for improved torque-to-mass ratio. Third, the gap size reduction in the hybrid MR clutch is introduced and the effect of such reduction on maximum torque and the dynamic range of MR clutch is investigated. Finally, the design for a pair of MR clutches with a shared magnetic core for antagonistic actuation of the robot joint is presented and experimentally validated. The details of each approach are discussed and the results of the finite element analysis are used to highlight the required engineering steps and to demonstrate the improvements achieved. Using the proposed design, several prototypes of the MR clutch with various torque capacities ranging from 15 to 200 N·m are developed, assembled, and tested. The experimental results demonstrate the performance of the proposed design and validate the accuracy of the analysis used for the development.

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This paper presents a novel architecture for the actuation and transmission system of a compliant 5-DOF robotic manipulator. The compliant behavior of the robot is achieved using inherently compliant Magneto-Rheological (MR) clutches introduced in antagonistic pairs in every joint of the manipulator. All five antagonistic pairs of MR clutches are driven using a single brushless DC motor in the base of the robot. The MR clutch pairs are coupled to the motor through a system of shafts, belts, and gears. Several possible architectures for realizing the manipulator's drive train are presented, and the advantages and disadvantages of each concept are analyzed. The most efficient architecture for the drive train is selected to complete the design of the manipulator. The kinematics of the designed manipulator and the analyses of its workspace are presented. To the best of our knowledge, this is the first 5-DOF, fully-actuated, compliant robotic manipulator that uses a single DC motor to achieve 5 independent axes of rotations.

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This paper presents the mechanical design and mathematical modeling for the first joint of a five degrees of freedom collaborative manipulator. The robot is actuated using Magneto-Rheological (MR) clutches in order to ensure full backdrivability and intrinsic torque control for safe human-friendly operation. One of the unique features of this design is the usage of a single motor for powering all five joints of the robot simultaneously and independently. After a brief description of the MR clutch principles, the details of the mechanical design and a state-space representation of the first joint are discussed. The paper will conclude with some preliminary simulation results.