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Bilateral, Misalignment-Compensating, Full-DOF Hip Exoskeleton: Design and Kinematic Validation 时间:2017-07-18 23:44   来源:未知   作者:admin   点击: 次 Abstract:A shared design goal for most robotic lower limb exoskeletons is to reduce the metabolic cost of locomotion for the user. Despite this, only a limited amount of devices was able to actually reduce user metabolic consumption. Preservation of the natural motion kinematics was defined as an important requirement for a device to be metabolically beneficial. This requires the inclusion of all human degrees of freedom (DOF) in a design, as well as perfect alignment of the rotation axes. As perfect alignment is impossible, compensation for misalignment effects should be provided. A misalignment compensation mechanism for a 3-DOF system is presented in this paper. It is validated by the implementation in a bilateral hip exoskeleton, resulting in a compact and lightweight device that can be donned fast and autonomously, with a minimum of required adaptations. Extensive testing of the prototype has shown that hip range of motion of the user is maintained while wearing the device and this for all three hip DOFs. This allowed the users to maintain their natural motion patterns when they are walking with the novel hip exoskeleton.
1. Introduction
  Exoskeletons are usually divided in three classes depending on their aimed use: performance augmentation, rehabilitation, and assistance [1, 2]. A shared design goal for most robotic lower limb exoskeletons is to reduce the metabolic cost of locomotion for the user [3, 4]. Despite this common goal, only a limited amount of devices was able to reduce the metabolic consumption of the user during powered walking [5]. Most of these are tethered and because the weight of the device has a significant impact on the energy consumption of its wearer [6–8], they usually do not span the entire lower limbs [9–11]. When exoskeletons are meant for assistance of activities of daily life, for example, assisting the elderly or allowing paraplegics to walk, being tethered is unacceptable, while the reduction of user energy consumption remains vital [12]. Only recently were researchers capable of reducing user effort with autonomous, untethered exoskeletons [13, 14]. The devices used in these two studies are meant to assist the ankle joint of the wearer during the push-off phase in walking.
  Asbeck et al. [12] stated that for an assistive device to be metabolically beneficial, it should apply the right amount of assistance at the right time to the body, as well as maintain the normal biomechanics of motion and minimize additional mass carried by the wearer, particularly on the distal portion of the leg. Taking these three requirements into account, the use of a full-DOF (degree of freedom), misalignment-compensating hip exoskeleton appears to be a suitable tool to achieve this. Although actuating the ankle joint is a reasonable strategy, the hip joint is also seen as a significant contributor of positive work [9, 15] and it is less dependent on passive mechanisms, thus powering it may be metabolically more efficient [3, 16]. Additionally, it is less susceptible to the addition of mass than the ankle [7, 17, 18] and maintaining unrestricted hip motion is considered important for the energy efficiency of gait [19, 20]. Because the “right” assistance is highly dependent on the physical build of the user and his/her affliction, this paper will focus on the preservation of natural biomechanics by not restricting motion of the hips.