Design of a continuously variable transmission for efficiently actuating walking robotic sensors

Naves, M. (2015) Design of a continuously variable transmission for efficiently actuating walking robotic sensors.

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Abstract:Dike inspection is currently done by a labour intensive network of trained people. To inspect dikes in a more efficient manner, dike inspection could be done by a group of autonomous walking dike inspection robots. Arising problem of those walking dike inspection robots is the low energy efficiency of the walking mechanisms. This low energy efficiency comes from the repeated acceleration and deceleration of the walking mechanism for consecutive steps, where kinetic energy of the mechanical system gets lost. To improve the energy efficiency, actuation of walking robots could be done by a continuously variable transmission driven by a spring. The amount of spring force which is exerted on the payload can then be controlled by the variable transmission. By reversing the transmission ratio, the force exerted on the payload can be reversed and deceleration of the mechanical system can be used to store energy in the spring. This stored energy can then be used to actuate the system for consecutive steps. The continuously variable transmission which has to be developed for this purpose has to be able to create a positive and negative transmission ratio to reverse the actuation force. Besides negative and positive transmission ratios, a transmission ratio of 0 should be possible. Furthermore high efficiency of the continuously variable transmission is of high importance, as the goal of the system is to obtain a more efficient actuation. This also holds an high efficiency for alternating the transmission ratio, as the transmission ratio has to be continuously adjusted for the considered use-case. First of all translational concepts are considered which are based on a lever with adjustable pivot. Those translational concepts appeared to have fundamental issues regarding an uncontrollable pivot position or high actuation forces for reconfiguring the transmission ratio. Because translation concepts appeared to be unsuited for this purpose, focus is set at rotational variable transmissions. Already existing concepts for rotational continuously variable transmissions appeared to require high actuation forces for reconfiguring the transmission ratio or a lacking of high running efficiency. A new concept for a rotational variable transmission is conceived which is based on friction wheels where the contact angle between both friction wheels can be alternated. This concept has high running efficiency and requires only low actuation forces for reconfiguring the transmission ratio. The problem which arises for this concept is the lack of ability to achieve a negative transmission ratio. This problem is overcome by using a planetary gearbox, which functions as a differential. This makes it possible to achieve both negative as positive transmission ratio's. This combination resulted in a continuously variable transmission which is able to achieve a transmission ratio from -3.5 to 3.5, including a transmission ratio of 0. This variable transmission is then driven by a clock spring which makes it possible to store a relatively large amount of energy in the spring. By using this system, a walking mechanism could be driven with high efficiency by a spring, where energy which is released by deceleration of the mechanical system can be stored temporarily. The stored energy can then be used for actuating the walking mechanism in consecutive steps. When driving a walking robot with such a mechanisms, only an small actuator is needed to reconfigure the transmission ratio and an small actuator for rewinding the spring to compensate for energy losses.
Item Type:Internship Report (Master)
Demcon Advanced Mechatronics B.V., the Netherlands
Faculty:ET: Engineering Technology
Subject:52 mechanical engineering
Programme:Mechanical Engineering MSc (60439)
Keywords:Continuously variable transmission, efficient robotic actuation, temporarily storage of mechanical energy, internship Demcon
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