No abstract

PurposeThe purpose of this paper is to review the challenges present in the development of hand exoskeletons powered by pneumatic artificial muscles. This paper also presents the development of a novel strain sensor and its application in a five‐fingered hand exoskeleton.Design/methodology/approachThe issues of current hand exoskeletons powered by pneumatic artificial muscles are examined by studying the artificial muscles and the human hand anatomy. Traditional sensors are no longer suitable for applications in hand exoskeletons. A novel strain sensor was developed by depositing a conducting polymer called polypyrrole onto a natural rubber substrate through vapor phase polymerization and is used in the authors' five‐fingered hand exoskeleton.FindingsThe error of measurements from the polypyrrole strain sensor in controlling the actuation of pneumatic artificial muscles is within 1.5 mm. The small physical size and weight of the novel polypyrrole strain sensor also helped to keep the exoskeleton's profile (less than 20 mm) and total weight low (<1 kg).Originality/valueThe novel strain sensor allows the realization of hand exoskeletons that are lightweight, portable and low profile. This improves the comfort and practicality of hand exoskeletons to allow their usage outside the research environment.

No abstract

No abstract

A novel flexible strain sensor was developed using a conducting polymer coated on rubber for large strain measurements. A coating of the conducting polymer, polypyrrole, was deposited on a strip of natural rubber through the process of vapour phase polymerisation while the rubber is in a stretched state. This process involves depositing a layer of oxidant on the rubber surface, followed by exposure to pyrrole monomer vapours that polymerize on the oxidantcoated rubber to produce polypyrrole.The change in electrical resistance of the strain sensor was recorded while cyclic strain from 0% to 20% was exerted on it. The gauge factor of the strain sensor was calculated to be 1.86. From repeated electrical resistance-strain measurements, the repeatability of the strain sensor was studied. A hysteresis was observed in a single extensionretraction strain cycle. Further study showed that the observed hysteresis is dependent on the strain rate where lower strain rate resulted in higher hysteresis and vice versa for a higher strain rate. There is also an electrical resistance drift between consecutive extension-retraction cycles.Owing to the flexibility of the rubber, the strain sensor can be used in complex configurations. The strain sensor can also be mounted or attached directly on surfaces to provide low-profile installation where space constraint is an issue. These characteristics offer advantages over traditional strain sensors to be used in applications that were not previously possible.Polypyrrole, Strain Sensor, Natural Rubber, Vapour Phase Polymerisation INTRODUCTIONIntrinsically conducting polymers (ICPs) are a type of smart materials where polymers have the capability to conduct electricity. The discovery of ICPs can be found in literatures dated back to 1862 [1] and as of today numerous types of polymers have been identified as ICPs. ICPs are one of the most sought after smart materials due to its excellent properties where the mechanical properties of polymers are combined with the ability to conduct electricity. Furthermore, the polymers can be tailored to suit a particular role or application by modifying the functional branches of the polymer [2]. Polypyrrole (PPy) is one of the ICPs that have been extensively studied as both actuators and sensors due to its high conductivity, good stability and ease of synthesis using either chemical or electrochemical polymerisation. PPy has been used for various applications that include artificial muscle [3], novel drug delivery system [4],[5], heat generation [6], EMI shielding [7], gas sensor [8][9] and strain sensor [10],[11].