Development of a structurally compact magnetorheological prosthetic knee joint with obstacle-crossing function

Abstract To address the difficulty of simultaneously achieving motion bionics, active driving capability, and structural compactness in prosthetic knee joints, a structurally compact magnetorheological prosthetic knee joint (SCMRPK) with obstacle-crossing function is proposed in this paper. The SCMRPK combines a four-bar linkage mechanism and a linear magnetorheological actuator (LMRA). By integrating a micro linear motor into the piston rod of an MR damper, the LMRA combines the active and semi-active modes, enabling it to output driving force in the active mode and controllable damping force in the semi-active mode. The four-bar linkage mechanism is used to mimic the variation of the instantaneous center of rotation of the human knee. The structure and working principle of the SCMRPK are presented. A key dimensional design method for the LMRA magnetic circuit is proposed, and simulation and experimental tests are conducted to verify the effectiveness of the designed magnetic circuit. A control method for the SCMRPK is developed, and a prototype is fabricated. Under a locking current of 1.5 A, the LMRA prototype achieves stable displacement tracking in active mode. At a walking speed of 1.2 m/s, the semi-active mode of the SCMRPK prototype yields a root mean square error of 1.54° between the measured and ideal knee angles. In active mode, the SCMRPK-based lower-limb prosthesis successfully crosses an obstacle 0.3 m high. These results demonstrate that the proposed SCMRPK is compact and capable of achieving a relatively natural gait and obstacle crossing.