Abstract
This paper proposes a novel underwater dexterous hand structure whose fingertip is equipped with underwater tactile force sensor (UTFS) array to realize the grasping sample location determination and force perception. The measurement structure, theoretical analysis, prototype development and experimental verification of the UTFS are purposefully studied in order to achieve accurate measurement under huge water pressure influence. The UTFS is designed as capsule shape type with differential pressure structure, and the external water pressure signal is separately transmitted to the silicon cup bottom which is considered to be an elastomer with four strain elements distribution through the upper and lower flexible contacts and the silicone oil filled in the upper and lower cavities of UTFS. The external tactile force information can be obtained by the vector superposition between the upper and lower of silicon cup bottom to counteract the water pressure influence. The analytical solution of deformation and stress of the bottom of the square silicon cup bottom is analyzed with the use of elasticity and shell theory, and compared with the Finite Element Analysis results, which provides theoretical support for the distribution design of four strain elements at the bottom of the silicon cup. At last, the UTFS zero drift experiment without force applying under different water depths, the output of the standard force applying under different water depth and the test of the standard force applying under conditions of different 0 C–30 C temperature with 0.1 m water depth are carried out to verify the performance of the sensor. The experiments show that the UTFS has a high linearity and sensitivity, and which has a regular zero drift and temperature drift which can be eliminated by calibration algorithm.
Highlights
The underwater manipulator is an indispensable part of the underwater vehicle, performing the tasks such as biological samples collection, underwater salvage and so on [1,2,3]
The tactile sensor array is distributed on the surface of the finger, and the position determination and tactile force measurement of the grasping target are realized, so that the tactile force sensor is the core of the measurement
The differential pressure capsule-shaped underwater tactile force sensor (UTFS) transforms the external tactile force into the pressure of silicone oil inside the sensor, and the silicone oil pressure is uniformly loaded on the silicon cup bottom elastomer containing four strain elements to deform, so that the four strained elements constituting the full bridge are realized to the tactile force measurement
Summary
The underwater manipulator is an indispensable part of the underwater vehicle, performing the tasks such as biological samples collection, underwater salvage and so on [1,2,3]. D.J.O.Brien and D.M.Lane designed and employed a dexterous hand named AMADEUS [35,36], and force and slip information were gained with strain gauge force sensor and PVDF (Polyvinylidene Fluoride) piezoelectric film-based vibration sensor, while the whole structure couldn’t judge the slip directions in the single fingertip and ignored the temperature influence Much work such as structure design, temperature compensation, zero-point compensation and calibration equipment design can be done in order to realize the accuracy and stability output of underwater tactile force measurement under water pressure disturbance. To accurately determine the grasping position and the force feedback value measurement of the underwater manipulator sample collection process under the influence of water static pressure, we propose a structure of an underwater dexterous hand with an array of UTFSs for each fingertip.
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