D2.1 Requirements and Specification - CORBYS

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D2.1 Requirements and Specification The HapticWalker is based on the same concept of permanent foot-machine contact Figure 45: End-effector type devices: (from left to right) HapticWalker®, G-EO®, ARTHuR (Schmidt et al., 2005a). This concept is also typically found in parallel type rehabilitation robots with a platform for rehabilitation of the ankle/foot and for balance training as for instance in Saglia et al. (2010); Yoon and Ryu (2005). ARTHuR is a unilateral 2 DOF device using a back driveable two-coil linear motor and a pair of lightweight linkages to drive a footplate (Emken et al., 2006). It has been used primarily to study motor learning principles and to evaluate a teach-and-replay procedure with impedance adaptation (Emken et al., 2008). 16.2.2 Exoskeleton type devices Most gait rehabilitation robots are exoskeleton based and prototype development in this type of device is often supported and stimulated by advancements in related applications: assistive exoskeletons, human performance augmenting exoskeletons and powered prosthetics (Figure 46). Rehabilitation exoskeletons, assistive exoskeletons and human performance augmenting exoskeletons are the three main types of powered exoskeletons for humans and the past decade has seen a multitude of research prototypes and devices of this sort. As their common rationale is the assistance of human gait, these exoskeletons are not easily categorised and sometimes assistive exoskeletons and human performance augmenting exoskeletons find their way to a rehabilitation setting. Also, from an engineering viewpoint, these applications have common requirements with respect to the performance of the actuators, the weight and compactness of the structure and the wearability of the design. There remains however a clear distinction of basic functionality. Rehabilitation exoskeletons are aimed at recovery of impaired function, whereas assistive exoskeletons assist impaired function and human performance augmenting exoskeletons augment sound function. Powered prosthetics replace lost function. Although acting in series with the human body instead of in parallel, powered lower limb prostheses also inspire the development of gait rehabilitation exoskeletons, as they require high performance actuators, gait phase detection and user-oriented control. An overview of the state-of-the-art in powered lower limb prosthetics can be found in Martin et al., 2010; Versluys et al., 2009. 16.2.2.1 Commercially available devices To date there are two commercially available exoskeleton-based gait rehabilitation robots: the AutoAmbulator (Healthsouth, US) and the Lokomat (Hocoma, Switzerland). Both devices consist of a treadmill, an overhead suspension system with a harness and a robotic orthosis attached to the patient's lower limbs, assisting the hip and the knee bilaterally. The Lokomat, in particular, has undergone substantial testing with patients and, as opposed to AutoAmbulator, is extensively reported in literature. Lokomat, originally purely position 166
D2.1 Requirements and Specification controlled, uses ball screw actuators and joint-space impedance control to achieve naturalistic joint trajectories at the hip and knee. Various patient-cooperative control strategies have been investigated (Jezernik et al., 2004; Duschau-Wicke et al., 2008) as well as a hardware extension of the system with additional actuated DOF (ab/adduction of the hip and lateral and vertical pelvic displacement, see Bernhardt et al., 2005a), but most functionalities were not transferred to the device that is currently on the market and in use in rehabilitation centres. The KineAssist (Kinea Design, US), having no lower body structure, is primarily intended for adaptable body weight support and walking balance training of stroke patients. 16.2.2.2 Research prototypes Figure 46: Commercially available exoskeleton type devices: (from left to right) Lokomat®, AutoAmbulator®, KineAssist® Several research groups recognised the need for assistance-as-needed control strategies and for more physiological gait movements, both considered essential to increase the effectiveness of robot-assisted gait training. Most research efforts are focused on introducing adaptable compliance (or variable impedance) into the hardware and/or the control of the system and on extending the number of DOF of the exoskeleton, i. e. active DOF (actuated) and/or passive DOF (passive elements or none). Bilateral prototypes In LOPES, besides flexion/extension of the knee and hip, lateral and forward/ backward displacement of the pelvis and abduction/adduction of the hip are assisted (Veneman et al., 2007). Bowdencable based series elastic actuators are used to power the exoskeleton's joints for reasons of inherent safety and force tracking performance (Veneman et al., 2005). The device is intended for use in stroke patients and focus is on task-specificity of assistance by means of virtual model control (Ekkelenkamp et al., 2007). PAM and POGO use pneumatic cylinders to compliantly assist five out of six DOF of the pelvis and flexion/extension of the knee and hip. Zero-force control and impedance control are used consecutively in a teach-and-replay procedure (Aoyagi et al., 2007). Both LOPES and PAM/POGO are treadmill based devices. The WalkTrainer (Stauffer et al., 2009) is a mobile overground walking device, that consists of a mobile base with an active body weight supporting harness, a pelvic orthosis (6 actuated DOF) and two leg orthoses (3 actuated DOF each) (Allemand et al., 2009). It combines task-space impedance control of the orthoses with closedloop functional electrical stimulation (FES) of the paraplegic patient's leg muscles. Unilateral and single-joint prototypes in addition to bilateral prototypes, several unilateral rehabilitation exoskeletons, comprising one or more powered joints, have been developed. ALEX is a leg exoskeleton of which the hip and knee joint are actuated by linear drives (Banala et al., 2009). A force field controller is implemented in task-space that displays a position dependent force field acting on the foot. In Sawicki et al. (2005) ankle-foot and kneeankle-foot orthoses powered by McKibben type pneumatic muscles are investigated for task-specific 167
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D2.1 Requirements and Specification
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D2.1 Requirements and Specification - CORBYS

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