Improvement of human–machine compatibility of upper-limb rehabilitation exoskeleton using passive joints

Abstract

The upper-limb rehabilitation exoskeleton is a critical piece of equipment for stroke patients to compensate for deficiencies of manual rehabilitation and reduce physical therapists’ workloads. In this paper, configuration synthesis of an exoskeleton is completed using advanced mechanism theory. To adapt glenohumeral (GH) movements and improve exoskeletal compatibility, six passive joints were introduced into the connecting interfaces based on optimal configuration principles. The optimal configuration of the passive joints can effectively reduce the gravitational influences of the exoskeleton device and the upper extremities. A compatible exoskeleton (Co-Exos) with 11 degrees of freedom was developed while retaining a compact volume. A new approach is presented to compensate vertical GH movements. The theoretical displacements of translational joints were calculated by the kinematic model of the shoulder loop Θs. A comparison of the theoretical and measured results confirms that the passive joints exhibited good human–machine compatibility for GH movements. The hysteresis phenomenon of translational joints appeared in all experiments due to the elasticoplasticity of the upper arm and GH. In comparable experiments, the effective torque of the second active joint was reduced by an average of 41.3% when passive joints were released. The wearable comfort of Co-Exos was thus improved significantly.