The field of biorobotics has developed and flourished as a multidiscip-linary interface between biologists and engineers (Ritzmann et al., 2000; Webb & Consi, 2001; Ayers et al., 2002). Collaborative work in the field initially arose from the recognition that studies of animal locomotion could provide insights in solving complex problems in the design and control of mobile machines (Beer et al., 1998). For example, some animals are remarkably successful at efficiently traversing irregu-lar and non-horizontal terrains with great agility. Understanding the principles of leg and foot structure and the neural mechanisms of control of limb movements provides insights that can be emulated in the construction and regulation of legged robots to similar advantage. These insights have been successfully applied both to legged machines that resemble animals in their design and to robots that incorporate these principles more abstractly (Quinn et al., 2003).

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Frequent and repetitive functional training of the upper limb is a key aspect of regaining independence after stroke. Traditionally, this is achieved through manual one-on-one therapy, but patients are often unable to get sufficient treatment due to budget and scheduling cons-traints. An ideal solution may be robotic therapy, which is becoming an increasingly viable tool. Unfortunately, current rehabilitation robots ignore shoulder girdle motion, even though it plays a critical role in stabilizing and orienting the upper limb during everyday movements. To address this issue, a new adjustable robotic exoskeleton is proposed that provides independent control of six degrees of freedom of the upper limb: two at the sternoclavicular joint, three at the glenohumeral joint and one at the elbow. Its joint axes are optimally arranged to mimic natural upper-limb range of motion without reaching singular configurations and while maximizing manipulability across the workspace. This joint configuration also permits reduction to planar shoulder/elbow motion in any plane by locking all but the last two joints. Electric motors actuate the mechanisms using cable and belt transmissions designed to maximize the load capabilities of the robot while maintaining backdriveability and minimizing inertia. The device will be able to operate both as an assessment tool and as a therapy tool by monitoring and assisting movements. It will also be able to provide any level of gravity compensation. Controlling the entire shoulder complex facilitates training with more natural movements, with the added benefit of gaining the ability to observe and prevent compensatory motion.

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This chapter discusses the advantages and feasibility of using compliant actuators in exoskeletons. We designed compliant actuation for use in a gait rehabilitation robot. In such a gait rehabilitation robot large forces are required to support the patient. In case of poststroke patients only the affected leg has to be supported while the movement of the unaffected leg should not be hindered. Not hindering the motions of one of the legs means that mechanical impedance of the robot should be minimal. The combination of large support forces and minimal impedances can be realised by impedance or admittance control. We chose for impedance control. The consequence of this choice is that the mass of the exoskeleton including its actuation should be minimized and sufficient high force bandwidth of the actuation is required. Compliant actuation has advantages compared to non compliant actuation in case both high forces and a high force tracking bandwidth are required. Series elastic actua-tion and pneumatics are well known examples of compliant actuators. Both types of compliant actuators are described with a general model of compliant actuation. They are compared in terms of this general model and also experimentally. Series elastic actuation appears to perform slightly better than pneumatic actu-ation and is much simpler to control. In an alternative design the motors were removed from the exoske-leton to further minimize the mass of the exoskeleton. These motors drove an elastic joint using flexible Bowden cables. The force bandwidth and the minimal impedance of this distributed series elastic joint ac-tuation were within the requirements for a gait rehabilitation robot.

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Today, commercially available ankle-foot prostheses are completely passive, and consequently, their mechanical properties remain fixed with walking speed and terrain. Conversely, normal human ankle stiffness varies within each gait cycle and also with walking speed. Furthermore, some studies have indicated that one of the main functions of the human ankle is to provide adequate energy for forward progression of the body. Thus, an ideal ankle-foot prosthesis should be able to actively control joint impedance, motive power, and joint position. Understanding the dynamic inter-action between an amputee and an active prosthesis is critical to developing truly functional leg pros-theses. For this reason, we have developed a novel robotic ankle-foot emulator. The emulator is capable of changing mechanical impedance and providing sufficient mechanical energy for forward propulsion. In this paper, we present pilot data on the actual interaction between an amputee and the ankle emulator during walking. These data support the hypothesis that actively controlling ankle joint impedance may provide a more natural gait than a conventional passive prosthesis. Furthermore, adding additional mechanical energy beyond that a passive spring ankle can provide during powered plantar flexion can dramatically increase the self-selected walking speed of an amputee.

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In this study, we developed a fuzzy-logic-controlled PGO (Power Gait Othosis) that controls the flexion and extension of each PGO joint using bio-signals and an FSR sensor. The PGO driving system works to couple the right and left sides of the orthosis by spe-cially-designed hip joints and pelvic section. This driving system consists of the orthosis, sensor, and control system. An air supply system for muscle action is composed of an air compressor, 2-way sole-noid valve (MAC, USA), accumulator and pressure sensor. The role of this system is to provide constant “air muscle” with compressed air at the hip joint. With the output signal of the EMG and foot sensors, air muscles assist the flexion of the hip joint during the PGO gait.

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