This study validates the effectiveness of a recently developed parallel-actuated shoulder exoskeleton robot for the purpose of characterizing the neuromuscular properties of the human shoulder joint. In particular, shoulder mechanical impedance was quantified, which can be represented by a 2ndorder system consisting of spring, damper and inertia. The shoulder exoskeleton robot, which utilizes a new type of 4-bar spherical parallel manipulator (4B-SPM), has inherently low inertia and as a result can provide fast perturbations that are often essential for characterizing neuromuscular properties. The robot was first evaluated by using a physical shoulder mockup with adjustable and known spring and mass properties. The results of the mockup test confirmed the reliability of the robot for the characterization of the mockup properties. Stiffness of the tested springs was accurately quantified with an error of less than 1.6 Nm/rad in any of the tested conditions. A pilot study with 5 human subjects further confirmed that the robot could be successfully used to quantify multi-dimensional human shoulder impedance in both pitch and yaw directions with high reliability (R2> 0.97). The average human shoulder stiffness and damping at around the neutral arm posture under low muscle activation (< 5% maximum voluntary contraction) were 30.9 Nm/rad and 3.0 Nms/rad, respectively.

The purpose of this work is to introduce a newly developed exoskeleton robot designed to characterize the neuromuscular properties of the shoulder, including intrinsic and reflexive mechanisms, during static posture and dynamic movement in a 3-dimensional space. Quantitative characterization of these properties requires fast perturbation (>100°/s) to separate their contribution from that of voluntary mechanism. Understanding these properties of the shoulder control could assist in the rehabilitation or enhancement of upper limb performance during physical human-robot interaction. The device can be described as a new type of spherical parallel manipulator (SPM) that utilizes three 4-bar (4B) substructures to decouple and control roll, pitch and yaw of the shoulder. By utilizing a parallel architecture, the 4BSPM exoskeleton has the advantage of high acceleration, fast enough to satisfy the speed requirement for the characterization of distinct neuromuscular properties of the shoulder. In this work, the prototype is presented, along with an evaluation of its position accuracy and step response. The development and preliminary testing of the 4B-SPM exoskeleton presented in this work demonstrates its potential to be a useful tool for studying the neuromuscular mechanisms of the shoulder joint.

The purpose of this work is to optimize the stiffness of a novel parallel-actuated robotic exoskeleton designed to offer a large workspace. This is done in an effort to help provide a solution to the issue wearable parallel actuated robots face regarding a tradeoff between stiffness and workspace. Presented in the form of a shoulder exoskeleton, the device demonstrates a new parallel architecture that can be used for wearable hip, ankle and wrist robots as well. The stiffness of the architecture is dependent on the placement of its actuated substructures. Therefore, it is desirable to place these substructures effectively so as to maximize dynamic performance for any application. In this work, an analytical stiffness model of the device is created and validated experimentally. The model is then used, along with a method of bounded nonlinear multi-objective optimization to configure the parallel actuators so as to maximize stiffness for the entire workspace. Furthermore, it is shown how to use the same technique to optimize the device for a particular task, such as lifting in the sagittal plane.