A variable recruitment bundle is a configuration of fluidic artificial muscles (FAM) in parallel that allows a subset of the bundle, referred to as a motor unit, to be activated separately to adaptively respond to varying load requirements. This control strategy originates from how the motor units in a biological muscle are sequentially recruited to provide fine control and minimize muscle fatigue by increasing efficiency during varying load needs. Extensive research has already been done and is on-going on the modelling and fabrication of variable recruitment bundle itself. However, there is limited research on the hydraulic system that provide the power and control of bundles such as the valves. This paper addresses the design and implementation of a valve system to control a promising concept.

The conventional configuration of a variable recruitment FAM bundle requires a valve for each motor unit, which is referred to as a multi-valve system (MVS). As each motor unit is selectively recruited and controlled separately, this configuration is more adaptable and flexible in performance. However as the number of motor units increase, the valve setup can become complex and heavy in its design. To address the increase in complexity and weight, a concept of orderly recruitment valve (ORV) has been proposed and analyzed. The ORV allows multiple motor units to be controlled using one valve by prescribing a sequence at which the motor units are recruited. The ORV resembles a spool valve with multiple outlet ports with a motor unit connected to each port. A single actuator controls the position of the spool allowing fluid flow into each port in succession. Naturally, de-recruitment happens in reverse order. Despite artifacts of its design such as cross flow in between motor units and the dead band between ports that lower the efficiency, the ORV still performs comparable to a MVS with the advantage of greatly decreased complexity and bulk which is crucial especially when considering its potential applications to mobile or wearable systems. The objective of the ORV is to strike a balance between performance and compactness of design. The purpose of this paper is to experimentally validate the ORV concept. A hydraulic ORV system is fabricated and used to actuate a variable recruitment bundle in free contraction, isometric contraction and block force condition. A comparable MVS is fabricated and tested in identical conditions. The dynamic response of both systems are evaluated to support the results from prior analyses.


Development and Demonstration of an Orderly Recruitment Valve for Fluidic Artificial Muscles

Division / Sponsors: 
Aerospace Division

Paper Proceedings: https://asmedigitalcollection.asme.org/SMASIS/SMASIS2020/volume/84027

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