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Posted on: August 23, 2012
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Powered transfemoral prostheses can give above-knee amputees more flexibility than passive devices, for example allowing them to ascend and descend stairs more easily, or allowing a more natural and symmetrical gait pattern. To achieve the high torques required, most devices employ an electric motor with a ball-screw transmission, as is done in this work. The geometry of such a design determines how the peak torque is modulated as a function of joint angle. Therefore, it is important that this geometry is optimized to fulfill the requirements of the application. In this paper, we optimize this geometry to approximate a physiological peak torque versus joint angle versus joint velocity profile. Other powered knee prostheses commonly employ a single-axis joint. We investigate four different joint types: a single-axis joint, a biomimetic polycentric joint, a polycentric joint used in conventional passive prostheses, and an optimized polycentric joint. Our simulations suggest that employing an optimized polycentric joint can generate a uniform torque profile over the whole range of motion. An optimized geometry using a single-axis joint, however, can be used to obtain a peak torque versus angle profile that is similar to a physiological profile, and should, hence, be suitable for our application.
Posted on: August 23, 2012
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We describe a simple and intuitive policy gradient method for improving parametrized quadrocopter multi-flips by combining iterative experiments with information from a first-principles model. We start by formulating an N-flip maneuver as a five-step primitive with five adjustable parameters. Optimization using a low-order first-principles 2D vertical plane model of the quadrocopter yields an initial set of parameters and a corrective matrix. The maneuver is then repeatedly performed with the vehicle. At each iteration the state error at the end of the primitive is used to update the maneuver parameters via a gradient adjustment. The method is demonstrated at the ETH Zurich Flying Machine Arena testbed on quadrotor helicopters performing and improving on flips, double flips and triple flips.
Posted on: August 23, 2012
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We describe a process for enabling quadrocopters to perform and improve upon aerobatic maneuvers. We describe such maneuvers as a set of desired keyframes and a parametrized input trajectory. The full state trajectory of the vehicle is left unspecified – only predefined partial-state keyframes are used to measure errors and to refine the primitive. A first-principles model is used to find nominal trajectory parameter values and a first-order correction matrix. We apply this method to extending previous work on vertical-plane 2D adaptive flips to a fully 3D adaptive maneuver. We also show how this method can be applied to finding trajectories for flips with matching non-zero initial and final velocities. Preliminary results are presented from simulation and from quadrocopters in the ETH Flying Machine Arena.
Posted on: August 23, 2012
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Swimming microrobots have the potential to be used in medical applications such as targeted drug delivery. The challenges for navigating microrobots in the human body lie not only in the viscosity of body fluids but also in the existence of different types of fibers and cells such as blood cells or protein strands. This paper investigates artificial bacterial flagella (ABFs), which are helical microrobots actuated by an external magnetic field, in methyl cellulose solutions of different concentrations. It can be shown that the microrobots can be propelled in these gel-like heterogeneous solutions and successful swimming was demonstrated in solutions with a viscosity of more than 20 times that of water. Furthermore, results indicate that the existence of fibers can help ABFs swim more effectively, which agrees with previous experimental results reported for natural bacteria.
Posted on: August 23, 2012
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We present a conceptually and computationally lightweight method for the design and iterative learning of fast maneuvers for quadrocopters. We use first-principles, reduced-order models and we do not require nor make an attempt to follow a specific state trajectory-only the initial and the final states of the vehicle are taken into account. We evaluate the adaptation scheme through experiments on quadrocopters in the ETH Flying Machine Arena that perform multi-flips and other high-performance maneuvers.
Posted on: August 23, 2012
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During natural locomotion, the stiffness of the human knee is modulated continuously and subconsciously according to the demands of activity and terrain. Given modern actuator technology, powered transfemoral prostheses could theoretically provide a similar degree of sophistication and function. However, experimentally quantifying knee stiffness modulation during natural gait is challenging. Alternatively, joint stiffness could be estimated in a less disruptive manner using electromyography (EMG) combined with kinetic and kinematic measurements to estimate muscle force, together with models that relate muscle force to stiffness. Here we present the first step in that process, where we develop such an approach and evaluate it in isometric conditions, where experimental measurements are more feasible. Our EMG-guided modeling approach allows us to consider conditions with antagonistic muscle activation, a phenomenon commonly observed in physiological gait. Our validation shows that model-based estimates of knee joint stiffness coincide well with experimental data obtained using conventional perturbation techniques. We conclude that knee stiffness can be accurately estimated in isometric conditions without applying perturbations, which presents an important step toward our ultimate goal of quantifying knee stiffness during gait.
Posted on: August 23, 2012
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A simple and general fabrication method for helical swimming micromachines by direct laser writing and e-beam evaporation is demonstrated. The magnetic helical devices exhibit varying magnetic shape anisotropy, yet always generate corkscrew motion using a rotating magnetic field. They also exhibit good swimming performance and are capable of pick-and-place micromanipulation in 3D. Cytotoxicity of the devices was investigated using mouse myoblasts. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Posted on: August 23, 2012
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In this paper we propose a method to modulate the level of assistance provided by a shared controller, not only given the environmental context, but also according to the context of the user’s current behaviour. We show that the enhanced situational context can be adequately captured by using online performance metrics (such as those more usually found in the evaluation of shared control systems). The resultant controller not only allows the user to perform better in the primary task (like many shared control systems), but has also has increased the level of user acceptance, due to the personalised dynamics of the control policy.
Posted on: August 15, 2012
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In this literature review we explain anthropomorphism and its role in the design of socially interactive robots and human-robot interaction. We illus-trate the social phenomenon of anthropomorphism which describes people’s tendency to attribute lifelike qualities to objects and other non lifelike artifacts. We present theoretical backgrounds from social sciences, and integrate related work from robotics research, including results from experiments with social ro-bots. We present different approaches for anthropomorphic and humanlike form in a robot’s design related to its physical shape, its behavior, and its interaction with humans. This review provides a comprehensive understanding of anthro-pomorphism in robotics, collects and reports relevant references, and gives an outlook on anthropomorphic human-robot interaction.
Posted on: August 14, 2012
