Powered exoskeletons can facilitate after-stroke rehabilitation of patients with shoulder disabilities. Designs using serial mechanisms usually result in complicated and bulky exoskeletons. This paper presents a new parallel actuated shoulder exoskeleton that consists of two spherical mechanisms, two slider crank mechanisms, and a gravity balancing mechanism. The actuators are grounded and placed side-by-side. Thus, better inertia properties can be achieved while lightweight and compactness are maintained. An adaptive mechanism with only passive joints is introduced to compensate for the exoskeleton-limb misalignment and size variation among different subjects. Linear series elastic actuators (SEAs) are proposed to obtain accurate force and impedance control at the exoskeleton-limb interface. The total number of force sensors and actuators is minimized using the adaptive mechanism and SEAs. An exoskeleton prototype is shown to provide bidirectional actuation between the exoskeleton and upper limb, which is required for various rehabilitation processes. We expect this design can provide a means of shoulder rehabilitation.
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