Hydraulic transformers implemented in a common pressure rail architecture have been suggested as a means to efficiently distribute hydraulic power to a system of actuators. This thesis explores the role that the configuration of the system plays in the operating region and efficiency performance of the power distribution system. The primary tool used in this thesis is a dynamic loss model of a hydraulic transformer. Full mathematical documentation and experimental parameter tuning are described. Six configurations for distributing power with a hydraulic transformer are presented, and it is shown that each configuration has a unique operating region and efficiency trend. The hydraulic circuit is given for a port switching transformer that utilizes valves to switch between configurations during operation, and experimental tests demonstrate successful switching on a prototype machine. The maximum displacements of the two rotating groups within a set of hydraulic transformers distributing power to linear actuators driving the hip, knee, and ankle joints of a humanoid robot are optimized to maximize efficiency over a walking gait duty cycle. The resulting size ratios of the groups vary from a 1:1 ratio to a 1:2.4 ratio for the three duty cycles investigated. A comparison of the hydraulic transformer architecture against a throttling valve architecture for the humanoid robot indicates that the transformer system can achieve a distribution efficiency of 47.6%, which is a 31.9% increase over the throttling architecture distribution efficiency of 16.0%. The transformer system consumes 142 J to drive a single step of the walking gait, which is a decrease of 281 J from the 422 J required by the throttling architecture. This thesis thoroughly captures the efficiency performance and operating region of hydraulic transformers, and demonstrates how system configurations can improve the performance of the system beyond what has been generally considered in previous literature. These factors can then be weighed along with complexity, size, control performance, production cost, and other such metrics to enable a decision as to whether transformers are an appropriate power distribution architecture for a given application.
University of Minnesota M.S. thesis.September 2016. Major: Mechanical Engineering. Advisor: Perry Li. 1 computer file (PDF); viii, 150 pages.
Configuration and Performance of Hydraulic Transformer Power Distribution Systems.
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