The objective of our research at Berkeley is to deter-mine the fundamentals for the design and control of computer-controlled assist devices that are operated directly by auto-assembly and warehouse workers. These assist devices are like virtual reality machines that can simulate forces on the worker’s arms and trunk, forces which are different from and usually much less than the forces needed to maneuver a load.

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A device is described for simulating pedestrian movement in virtual reality. The device is based on the concept of “sufficient motion,” in which the simulator affords just enough movement in the real world to create a sense of reality in the virtual world. The paper describes the concept, and discusses some preliminary results obtained with a proof-of-concept device. A section on requirements lists and discusses seven features of a walking simulator. We conclude with a description of our future work.

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Impedance control of a hydraulic servoactuator joint system is discussed in this paper. Impedance control imparts a desired behavior to a system, rather than it controls position or force individually. Due to nonlinear properties of hydraulic actuators, impedance control is difficult. The control strategy presented here involves a combined feedforward and feedback control. An impedance filter modifies a desired trajectory according to a specified behavior. The modified trajectory is fed to a reduced-order model of the servoactuator hydraulic joint in order to reduce the effects of the nonlinear hydraulic dynamics. Position, velocity and pressure feedback loops compensate for the unmodeled dynamics. Simulation results show the strategy to be promising in providing impedance control to the joint. Special attention is given to the careful choice of impedance and control parameters to ensure smooth transition between contact and non-contact regimes, and to avoid actuator saturation. The developed controller is useful in achieving a desired behavior of hydraulic manipulators in contact tasks. It will provide the basis for a robust impedance control of the SARCOS high-performancehydraulic manipulator.

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The aim of this study was to quantify the energy cost and the cardiorespiratory response while walking at free speed with an Advanced Reciprocating Gait Orthosis (ARGO). The study was conducted on a group of six male paraplegic patients, age range 16 ± 31 years (median =22.50), with complete traumatic injuries ranging from T3 to T12 and a median time lapse from
the trauma of 21 months. The data was recorded 6 ± 8 weeks after the patients were fitted and trained to use the orthosis. Maintaining a standing position produced a significant increase of both the heart rate (HR) and the respiratory rate (RR), whilst the increase of energy consumption was not significant. The data for median speed, energy consumption and energy cost observed during free walking was similar to that of the Reciprocating Gait Orthosis (RGO) in thoracic level paraplegic individuals. This study indicates that in the utilisation of the ARGO the workload is not excessive when it is limited to maintaining a standing position. In contrast, walking results in early anaerobic conditions and unsustainable fatigue after short distances. The great energy cost recorded is considered to be a main reason for the frequent
abandonment or the low utilisation of the orthosis at follow-up.

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