We describe the design of a modular system for untethered real-time kinematic motion capture using sensors with inertial measuring units (IMU). Our system is comprised of a set of small and lightweight sensors. Each sensor provides its own global orientation (3 degrees of freedom) and is physically and computationally independent, requiring only external communication. Orientation information from sensors is communicated via wireless to host computer for processing. We present results of the real-time usage of our untethered motion capture system for teleoperating the NASA Robonaut. We also discuss potential applications for untethered motion capture with respect to humanoid robotics.

Motion Capture from Inertial Sensing for UntetheredHumanoid Teleoperation

Dielectric elastomer transducers are often subject to large tensile stretches and are susceptible to rupture. Here we carry out an experimental study of the rupture behavior of membranes of an acrylic dielectric elastomer. Pure-shear test specimens are used to measure force-displacement curves, using samples with and without pre-cracks. We find that introducing a pre-crack into a membrane drastically reduces the stretch at rupture. Furthermore, we measure the stretch at rupture and fracture energy using samples of different heights at various stretch-rates. The stretch at rupture is found to decrease with sample height, and the fracture energy is found to increase with stretch-rate.

https://absimage.aps.org/image/MAR12/MWS_MAR12-2011-004460.pdf

Rupture of a highly stretchable acrylic dielectric elastomer

Stimulus-responsive soft structures, with biological organs like intrinsic sensing, are needed to enable controlled movements and hence bring the transformative advances in soft robotics. Herein, bioinspired inchworm- and earthworm-like soft structures with intrinsic strain sensing achieved by seamless embedding of a graphite-paste-based sensor material are presented. The developed strain sensor exhibits a record stretchability (900%) and sensitivity (of 103 up to ≈200 and of the order of 105 at around 700% linear strain). With tiny permanent magnets incorporated at the ends of these soft structures, the sensory-feedback-based controlled movements of magnetically driven inchworm- and earthworm-like soft robots are also demonstrated. The presented results potentially boost the prospects of self-sensing in soft robots and advance the field toward cognitive soft robotics.

Bioinspired Inchworm- and Earthworm-like Soft Robots with Intrinsic Strain Sensing

Enhancement of electromechanical properties of natural rubber by adding barium titanate filler: An electro‐mechanical study

Robot teleoperation via motion mapping has been demonstrated to be an efficient and intuitive approach for controlling and teaching the whole-body motion coordination of humanoid robots. However, the physical fatigue in the usage of such robot teleoperation interfaces may prevent this approach to be widely used in large scale by diverse workforce populations. As a result, this paper conducts a user study to investigate the physical fatigue of teleoperators in the whole-body motion mapping teleoperation of a mobile humanoid assistive robot. Through a Vicon motion capture system, participants teleoperated the robot to perform general purpose assistive tasks that involve reaching-to-grasp, bimanual manipulation, loco-manipulation and human-robot interaction. We assess the physical fatigue based on surface electromyography (sEMG) measurement, and compare it between different tasks and muscles. Our analysis results indicate that: (1) Fatigue happens more in the tasks that involve more precise manipulation and steady posture maintenance; (2) Deltoids, Biceps and Trapezius are used more for such tasks and thus have more fatigue than others. These findings imply that automating the fatigue-causing task components may reduce the physical fatigue in motion mapping teleoperation.

Physical Fatigue Analysis of Assistive Robot Teleoperation via Whole-body Motion Mapping

Fracture toughness, hysteresis and stretchability of dielectric elastomers under equibiaxial and biaxial loading

In recent years significant attention has been made towards teleoperation of a humanoid robot using haptic devices. Methodologies developed are either cost prohibitive or they are not very effective. The lack of an effective, economical and a simple technique for teleoperation of humanoids is a barrier in exploring their full potential. In this paper we have reported a novel method for teleoperation of a humanoid robot using an exoskeleton for lower limb and upper limb. Experiments were performed to test the effectiveness of the exoskeleton in capturing human motion by analyzing different walking patterns like slow walking, fast walking and jogging. The motion data captured using exoskeleton can be directly applied to the servo motors of the humanoid for teleoperation. The joint angles of the human subject and the humanoid were also compared using image processing to see the overall effectiveness of the proposed method for teleoperation. The results indicate that the method is effective and affordable for teleoperation of the humanoid robots.

An effective and affordable technique for human motion capturing and teleoperation of a humanoid robot using an exoskeleton

This paper proposes a comparative study of harvesting circuits which were used as energy harvesting circuits for dielectric elastomer generator. The comparison of three different harvesting circuits has been made in terms of output voltage, output power, frequency response and conversion efficiency. The simulations are carried out using PSPICE software to convert low as well as high frequency generator outputs to a steady low DC voltage for storing energy into a Li-ion battery. Simulation results for output voltage are shown to swing between 3.5 V to 4.2 V. The study boosts in understanding the nature of frequency response and effectiveness of different approaches of forward path circuits to store electrical energy produced by dielectric elastomer generator using ambient kinetic energy input sources.

Comparison of circuits for dielectric elastomer based energy harvesting

Dielectric elastomer (DE) generator (DEG) employs a soft capacitive transducer. This transducer is mainly used to convert ambient mechanical motion into electricity. The amplitude of the converted electrical signal is analogous to the magnitude of the mechanical motion. However, the inherently unpredictable nature of ambient mechanical motion causes instability in the energy conversion process. This article aims to develop a controlled conditioning unit, which is to be interfaced with DEG to eliminate this instability. This article generalizes a previously reported conditioning circuit with the help of a proportional and integral (PI) controller under the DEG domain to make the energy conversion process stable. Indeed, the overall analysis is carried out in two different stages. At first, an electromechanical prototype for DEG is designed, which is responsible for converting mechanical motion into a corresponding electrical signal. Second, the generated electrical signal is processed through a conditioning circuit, which constitutes a regulator followed by a switching mode converter. Intuitive analysis of stability is presented for different magnitudes of mechanical motion and for different dynamic resistive loads. As the output voltage is found to vary with the DEG dynamics and resistive load, the inclusion of a controller to the conditioning interface unit is essential for constant voltage application. The experimental investigation shows that the DEG, along with the controlled conditioning unit, could maintain different desired quasi-constant output voltages in spite of variation at mechanical source and electrical load.

A Controlled Conditioning Interface Unit for Dielectric Elastomer Generator

The complement of standalone auxiliary sources with energy harvesters is essential in connection to mobile electronic devices and low power medical appliances due to some shortcomings like recharging of auxiliary cells and operation at low power. This paper deals with a motion based energy harvester which can harvest electrical energy in synchronous to human knee motion using dielectric elastomer (DE). Dielectric elastomer generator (DEG) adopts electrostatic energy conversion principle, by virtue of which the ambient mechanical motion converts into an analog electrical signal. It employs a biaxial stretched soft elastomer with compliant electrodes. At first, an electromechanical prototype is developed to be attached at the knee joints. The prototype constitutes of a DEG, a standalone power supply so as to prime the DEG and an electrical load. The periodical displacement of the knee leads to a synchronous change in capacitance associated with the DEG transducer. In consequence, a relatively high voltage generates across the load. With respect to different knee joint rotation angles, the harvested electrical voltage and current values are measured. Corresponding output electrical signals are measured and presented with respect to time with relevant variations with pre-stretch, coating, and deflection on DE. Parameters like peak power, specific energy and energy conversion efficiency are calculated at different conditions to determine the best condition for optimum electrical energy harvesting from the human knee motion.

Sujit Kumar Sahu

Papers

Fracture toughness, hysteresis and stretchability of dielectric elastomers under equibiaxial and biaxial loading

An effective and affordable technique for human motion capturing and teleoperation of a humanoid robot using an exoskeleton

Comparison of circuits for dielectric elastomer based energy harvesting

A Controlled Conditioning Interface Unit for Dielectric Elastomer Generator

Energy Harvesting from Knee Motion Using Dielectric Elastomer Generator