Hydro Muscles are linear actuators resembling ordinary biological muscles in terms of active dynamic output, passive material properties and appearance. The passive and dynamic characteristics of the latex based Hydro Muscle are addressed. The control tests of modular muscles are presented together with a muscle model relating sensed quantities with net force. Hydro Muscles are discussed in the context of conventional actuators. The hypothesis that Hydro Muscles have greater efficiency than McKibben Muscles is experimentally verified. Hydro Muscle peak efficiency with (without) back flow consideration was 88% (27%). Possible uses of Hydro Muscles are illustrated by relevant robotics projects at WPI. It is proposed that Hydro Muscles can also be an excellent educational tool for moderate-budget robotics classrooms and labs; the muscles are inexpensive (in the order of standard latex tubes of comparable size), made of off-the-shelf elements in less than 10 minutes, easily customizable, lightweight, biologically inspired, efficient, compliant soft linear actuators that are adept for power-augmentation. Moreover, a single source can actuate many muscles by utilizing control of flow and/or pressure. Still further, these muscles can utilize ordinary tap water and successfully operate within a safe range of pressures not overly exceeding standard water household pressure of about 0.59 MPa (85 psi).

Stroke is the leading cause of long-term disability in the United States, affecting over 795,000 people annually. In order to regain motor function of the upper body, patients are usually treated by regular sessions with a dedicated physical therapist. A cost-effective wearable upper body orthotics system that can be used at home to empower both the patients and physical therapists is described. The system is composed of a thin, compliant, lightweight, cost-effective soft orthotic device with an integrated cable actuation system that is worn over the upper body, an embedded limb position sensing system, an electric actuator package and controller. The proposed device is robust to misalignments that may occur during actuation of the compliant brace or when putting on the system. Through simulations and experimental evaluation, it was demonstrated i) that the soft orthotic cable-driven shoulder brace can be successfully actuated without the production of off-axis torques in the presence of misalignments and ii) that the proposed model can identify linear and angular misalignments online.

Recent humanoid control investigations have emphasized the importance of controlling whole-body angular momentum throughout a movement task. For typical movement tasks, such as normal walking, such controllers minimize fluctuations in angular momentum about the center of mass (CM). This minimization is consistent with observed behavior of humans for such tasks. However, there are cases where such minimization is not desirable. In this study, we investigate movement tasks where bipedal balance control requires a relaxation of the goal of minimizing whole-body angular moment. We construct a humanoid model having a human-like mass distribution, and a Moment-Exploiting Control algorithm that modulates whole-body angular momentum to enhance CM control. The model only requires reference trajectories for CM position and torso orientation. Joint reference trajectories are not required. While balancing on one leg, we show that the controller is capable of correcting errors in CM state by sacrificing angular postural goals for the swing leg, trunk and head. This prioritization capability provides robustness to significant disturbances, without the need to plan new reference trajectories. We compare the dynamic behavior of our humanoid model to that of human test participants. While standing on one leg, the model, like the human, is shown to reposition its CM just above the stance foot from an initial body state where CM velocity is zero, and the ground CM projection falls outside the foot envelope.

Advanced humanoid robots capable of operating in complex 3D environments likely utilize an online optimization strategy where joint accelerations are varied to achieve whole-body postural balance. To this end, we propose one such strategy that optimizes global body parameters such as spin angular momentum and body principal angles, or the angles between the inertia tensor principal axes and the lab frame axes. This optimization strategy is easily combined with other optimization objectives (e.g. maximal efficiency) subject to physical constraints such as requiring that the ZMP operates within the support base. To deal with Bellman's "curse of dimensionality" we suggest, in parallel, two computational simplifications that may make the optimization problem tractable and easily implemented on today's humanoid robots. Finally, we address the problem of support base planning during ground and aerial locomotory phases. We propose novel online strategies for robust coordination of interacting limbs compatible with the proposed optimization strategy.

Motivated by biomechanical studies on human walking, we present a control strategy for biologically realistic walking based on the principle of spin angular momentum regulation. Using a morphologically realistic human model and kinematic gait data, we compute the total spin angular momentum at a self-selected walking speed for one human test subject. We find that dimensionless spin angular momentum remains small (S/sub 1//(mass height velocity) < 0.02) throughout the gait cycle, and maximum whole body angular excursions within sagittal (<1/spl deg/), coronal (<0.2/spl deg/), and transverse (<2/spl deg/) planes are negligible. These data support the hypothesis that spin angular momentum in human walking is highly regulated by the central nervous system, and that there exists a nonlinear coupling between ground reaction force, F~, center of mass position, r~/sub CM/ , and center of pressure location, r~/sub CP/, or F~ = (FZ/sub ///Z/sub CM/)(r~/sub CM/ -r~/sub CP/). We employ this relationship to rapidly generate biologically realistic CP and CM reference trajectories. Using an open loop optimization strategy, we show that biologically realistic leg joint kinematics emerge through the minimization of spin angular momentum and the total sum of joint torque squared, suggesting that both angular momentum and energetic factors are important considerations for biomimetic controllers.

We present an algorithm that provides enhanced flexibility and robustness in the control of single-leg humanoid standing through the coordination of stance leg ankle torques and stabilizing movements of non-contact limbs. Current control approaches generally assume the presence of explicitly specified joint reference trajectories or desired virtual force calculations that ignore system dynamics. Here we describe a practical controller that 1) simplifies control of abstract variables such as the center of mass location using a two-stage model-based plant linearization; 2) determines motion of non-contact limbs useful for achieving control targets while satisfying dynamic balance constraints; and 3) provides robustness to modeling error using a sliding controller. The controller is tested with a morphologically realistic, 3-dimensional, 18 degree-of-freedom humanoid model serving as the plant. It is demonstrated that the controller can use less detailed control targets, and reject stronger disturbances, than previously implemented controllers that employ desired virtual forces and static body calculations.