Development of a hot gas actuator for self-powered robots

IEEE/ASME Transactions on Mechatronics, 2006

This paper describes the design and energetic characterization of an actuator designed to provide enhanced system energy and power density for self-powered robots. The proposed actuator is similar to a typical compressible gas fluid-powered actuator, but pressurizes the respective cylinder chambers via a pair of proportional injector valves, which control the flow of a liquid monopropellant through a pair of catalyst packs and into the respective sides of the double-acting cylinder. This paper describes the design of the proportional injection valves and describes the structure of a force controller for the actuator. Finally, an energetic characterization of the actuator shows improvement relative to prior configurations and marked improvement relative to stateof-the-art batteries and motors.

Vanderbilt Undergraduate Research Journal, 2013

This paper presents the design and control of a free-liquid-piston engine compressor (FLPEC). The FLPEC produces low temperature, high-pressure air for use as a high energy density power supply for untethered, compact robots. Internal combustion with a propane-air mixture in the engine combustion chamber drives a high inertance, low mass liquid piston, which compresses air into an onboard reservoir. A real time logical controller is implemented in Matlab to regulate the timings of the air and fuel injection, spark, and exhaust valve and to compensate for misfires. Experimental pressure data is overlaid with the logical state of the injectors, spark plug, and exhaust valve to demonstrate the efficacy of the controller to account for cycle-to-cycle pressure variations in the combustion chamber.

Proceedings of the 2005 IEEE International Conference on Robotics and Automation, 2005

The design of a free piston compressor (FPC) intended as a pneumatic power supply for pneumatically actuated autonomous robots is presented in this paper. The FPC is a proposed device that utilizes combustion to compress air into a high-pressure supply tank by using the kinetic energy of a free piston. The device is configured such that the transduction from thermal energy to stored energy, in the form of compressed gas, is efficient relative to other small-scale portable power supply systems. This efficiency is achieved by matching the dynamic load of the compressor to the ideal adiabatic expansion of the hot gas combustion products. The device proposed exploits this fact by first converting thermal energy into kinetic energy of the free piston, and then compressing air during a separate compression phase. The proposed technology is intended to provide a compact pneumatic power supply source appropriate for human-scale robots. The design and implementation of the FPC is shown, and preliminary experimental results are presented and discussed with regard to efficiency and energetic characteristics of the device. Most significantly, the device is shown to operate nearly adiabatically. 0-7803-8914-X/05/$20.00 ©2005 IEEE.

International Journal of Fluid Power, 2007

The design and dynamic characterization of a free piston compressor (FPC) is presented in this paper. The FPC is a proposed device that utilizes combustion of a hydrocarbon fuel to compress air into a high-pressure supply tank, thus serving as a portable pneumatic power supply for mobile untethered robotic systems. The device is configured such that the transduction from thermal energy to stored energy, in the form of compressed gas, is efficient relative to other small-scale portable power supply systems. This efficiency is achieved by matching the dynamic load of the compressor to the ideal adiabatic expansion of the hot gas combustion products. It is shown that a load that is dominantly inertial provides a nearly ideally matched load for achieving high thermodynamic efficiency in a heat engine. The device proposed exploits this fact by converting thermal energy first into kinetic energy of the free piston, and then compressing air during a separate compressor phase. The proposed technology is intended to provide a compact pneumatic power supply source appropriate for human-scale robots. An analytical model of the proposed device is developed, and an FPC prototype is designed and built and its yielded experimental results are compared with theoretical.

2006 International Conference of the IEEE Engineering in Medicine and Biology Society, 2006

This paper describes the design of a 21 degree-offreedom, nine degree-of-actuation, gas-actuated arm prosthesis for transhumeral amputees. The arm incorporates a directdrive elbow and three degree-of-freedom wrist, in addition to a 17 degree-of-freedom underactuated hand effected by five actuators. The anthropomorphic device includes full position and force sensing capability for each actuated degree of freedom and integrates a monopropellant-powered gas generator to provide on-board power for untethered operation. Design considerations addressed in this paper include the sizing of pneumatic actuators based on the requisite output energy at each joint; the development of small low-power servovalves for use with hot/cold gases; the design of compact joints with integrated position sensing; and the packaging of the actuators, on-board power, and skeletal structure within the volumetric envelope of a normal human forearm and elbow. The resulting arm prototype approaches the dexterous manipulation capabilities of its anatomical counterpart while delivering approximately 50% of the force and power output of an average human arm.

Soft robotics, 2014

Many pneumatic energy sources are available for use in autonomous and wearable soft robotics, but it is often not obvious which options are most desirable or even how to compare them. To address this, we compare pneumatic energy sources and review their relative merits. We evaluate commercially available battery-based microcompressors (singly, in parallel, and in series) and cylinders of high-pressure fluid (air and carbon dioxide). We identify energy density (joules/gram) and flow capacity (liters/gram) normalized by the mass of the entire fuel system (versus net fuel mass) as key metrics for soft robotic power systems. We also review research projects using combustion (methane and butane) and monopropellant decomposition (hydrogen peroxide), citing theoretical and experimental values. Comparison factors including heat, effective energy density, and working pressure/flow rate are covered. We conclude by comparing the key metrics behind each technology. Battery-powered microcompressors provide relatively high capacity, but maximum pressure and flow rates are low. Cylinders of compressed fluid provide high pressures and flow rates, but their limited capacity leads to short operating times. While methane and butane possess the highest net fuel energy densities, they typically react at speeds and pressures too high for many soft robots and require extensive system-level development. Hydrogen peroxide decomposition requires not only few additional parts (no pump or ignition system) but also considerable system-level development. We anticipate that this study will provide a framework for configuring fuel systems in soft robotics.

Sensors, and Command, Control, Communications, and Intelligence (C3I) Technologies for Homeland Security and Homeland Defense V, 2006

We present the design and initial results of a power-autonomous planar monopedal robot. The robot is a gasoline powered, two degree of freedom robot that runs in a circle, constrained by a boom. The robot uses hydraulic Series Elastic Actuators, force-controllable actuators which provide high force fidelity, moderate bandwidth, and low impedance. The actuators are mounted in the body of the robot, with cable drives transmitting power to the hip and knee joints of the leg. A two-stroke, gasoline engine drives a constant displacement pump which pressurizes an accumulator. Absolute position and spring deflection of each of the Series Elastic Actuators are measured using linear encoders. The spring deflection is translated into force output and compared to desired force in a closed loop force-control algorithm implemented in software. The output signal of each force controller drives high performance servo valves which control flow to each of the pistons of the actuators. In designing the robot, we used a simulation-based iterative design approach. Preliminary estimates of the robot's physical parameters were based on past experience and used to create a physically realistic simulation model of the robot. Next, a control algorithm was implemented in simulation to produce planar hopping. Using the joint power requirements and range of motions from simulation, we worked backward specifying pulley diameter, piston diameter and stroke, hydraulic pressure and flow, servo valve flow and bandwidth, gear pump flow, and engine power requirements. Components that meet or exceed these specifications were chosen and integrated into the robot design. Using CAD software, we calculated the physical parameters of the robot design, replaced the original estimates with the CAD estimates, and produced new joint power requirements. We iterated on this process, resulting in a design which was prototyped and tested. The Monopod currently runs at approximately 1.2 m/s with the weight of all the power generating components, but powered from an off-board pump. On a test stand, the eventual on-board power system generates enough pressure and flow to meet the requirements of these runs and we are currently integrating the power system into the real robot. When operated from an off-board system without carrying the weight of the power generating components, the robot currently runs at approximately 2.25 m/s. Ongoing work is focused on integrating the power system into the robot, improving the control algorithm, and investigating methods for improving efficiency.

Angewandte Chemie International Edition, 2013

Soft robots have emerged as a new set of machines capable of manipulation and locomotion. [6] Pneumatic expansion of a network of microchannels (pneu-nets) fabricated in organic elastomers, using low-pressure air (< 10 psi; 0.7 atm; 71 kPa), provides a simple method of achieving complex movements: grasping and walking. Despite their advantages (simplicity of fabrication, actuation, and control; low cost; light weight), pneu-nets have the disadvantage that actuation using them is slow, in part because the viscosity of air limits the rate at which the gas can be delivered through tubes to fill and expand the microchannels. Herein, we demonstrate the rapid actuation of pneu-nets using a chemical reaction (the combustion of methane) to generate explosive bursts of pressure.

ASME 2009 Dynamic Systems and Control Conference, Volume 2, 2009

This paper is concerned with the application of fluid power in autonomous robotics where high power density and energy efficiency are key requirements. A hydraulic drive for a bioinspired quadruped robot leg is studied. The performance of a classical valve-controlled (“resistive-type”) and of an energy saving (“switching-control mode”) hydraulic actuation system are compared. After describing the bio-inspired leg design and prototyping, models for both drives are developed and energy efficiency assessments are carried out. It is shown through simulation that the switching-control mode hydraulic actuation can meet the challenge of legged robotic locomotion in terms of energy efficiency with respect to improving robot power-autonomy. An energy saving of about 75% is achieved. Limitations of the current system are identified and suggestions for improvements are outlined.

2000

One of the research goals in robotics is the development of home-help robots. The development of a control approach for a novel lightweight and multifunc- tional shape memory alloy (SMA) actuator scalable in force and length for robots is presented in this paper. The SMA actuator is based on lightweight bundles of thin wires of prestrainend shape memory alloy that