Static Characteristics Study And Strength Analysis Of Water Hydraulic Artificial Muscle

As a new type of actuator,the pneumatic artificial muscle has been widely investigated and applied in medical and automation fields.Compared with water hydraulic artificial muscles(WHAMs),pneumatic artificial muscles have the disadvantages of low work efficiency,slow response speed,high noise and incompatibility with deep water environment.The oil hydraulic artificial muscles have fast response and high efficiency,but it is easy to pollute the environment and deteriorate the inner rubber tube.WHAMs have the advantages of high force/weight ratio,good bionics,and compatibility with deep water environment.The WHAM is suitable to be used in underwater manipulator.The traditional actuators commonly used in underwater robots are hydraulic cylinders and motors,but they have the disadvantages of their extension rods being susceptible to corrosion by seawater,complex underwater oil pressure systems,and high cost.In this paper,the static physical factor models of WHAMs were established.The static characteristics tests of the relationship between contraction force and pressure at different contractions and the stiffness at different pressures were carried out to verify the accuracy of the models.The influence of process parameters on the static characteristics and the strength of WHAMs were studied.Based on the material properties and geometric structure of WHAMs,the main physical influencing factors were determined in order to improve the static model,and the complex modified physical model was established.The muscles of different wall thicknesses and fiber materials were manufactured,and the static characteristics tests at different contractions were carried out.The influence of the main physical factor model at different working pressures was analyzed,and it was verified that the modified physical model was more accurate than the ideal model.Hysteresis in the static characteristics of the stiffness at different working pressures were observed.The key factor affecting the hysteresis is the friction among the braided fiber strands.The hysteresis model was established and verified by experiments.Simultaneously,the stiffness of the muscle was analyzed.The static model of the high-strength,tightly fiber-braided and thick-walled WHAM provides a theoretical basis for high-precision position control.According to the geometric parameters and material properties of the muscle,the main process parameters affecting the static characteristics were selected.8 sets of static characteristics tests on the relationship between contraction force and pressure at different contractions were carried out.The results of variance analysis show that the initial braid angle A has the greatest influence on the static characteristics.In the variance analysis of contraction force,the larger working pressure,the larger the influence of the fiber material B and A×B produce,and the smaller the influence of the wall thickness C is.The results present a certain theoretical guiding significance for the rational selection of muscle samples.According to the failure forms of the WHAM,the main process parameters affecting the strength are the initial braid angle,the fiber material,the wall thickness of rubber tube,and the end buckle amount.Due to the problems of a very small buckle amount,slippage of the buckle ring and uneven end crimping in the test process,the end structure design was carried out to determine the optimal conditions of the end.On these basis,16 sets of orthogonal scheme of the strength were designed and the high-pressure failure test of the original initial state was performed.The variance analysis of the contraction force indicates that the initial braid angle has the greatest influence.The muscles with the small initial braid angle can withstand large contraction forces.The variance analysis of working pressure describes that the initial braid angle A and the fiber material B have the greatest influence.The WHAM with a large initial braid angle or thick-wall can withstand a large contraction force.Based on the strength analysis of WHAMs,it is beneficial to choose a reasonable geometry in combination with actual working conditions.