Energy Storage for Construction Robots

In the construction and nuclear industries the typical robotic tasks, such as tearing, shearing and pushing are repetitive and require intermittently applied high strengths. Control of machine activity is often by machine operator via thin wire umbilical or telemetry link. In these cases, robot autonomy depends on powerful actuators and an independent power source rather than external sensing and ‘on-board’ intelligence. Compressed gas has the potential to provide a controllable energy source with a high power to weight ratio. This form of energy storage is therefore well suited to mobile robots having large intermittent load requirements. In certain types of construction equipment it may be useful to have the extra weight due to a maximum power plant sized for maximum load. However, for any machine that is required to walk, climb or crawl through tunnels, a high power to weight ratio is essential. A power source for hydraulic actuators and motivation is presented which incorporates the essential features of low weight, high efficiency and large energy store. A proof-of-principle device has been constructed which is being used as a basis for more refined design. The prototype will eventually provide power for a small independent construction robot. Test results indicate that a reasonable gaol is for 0.2 m3 of compressed gas at 200 Bar and 200○K to provide 3 kW power output for hourly intervals between recharging. On-board recharging using a small heat engine should extend this operating time indefinitely. The prototype design is purposely simple, just elaborate enough to expand the compressed gas efficiently, while providing control of variable intermittent loads. The processes used are not new, but firmly based on classical thermodynamic principles. The practical use of isothermal expansion may appear novel because this is only because high rotational speeds of conventional power plant do not allow sufficient time for isothermal processes. Preliminary results are provided from tests conducted to determine likely power output and conversion efficiency.