Mechanism And Design Theory Research Of Braided Type Pneumatic Artificial Muscle

Braided type pneumatic artificial muscle is the basic and core of pneumatic artificial muscle. The basic characteristic is simple structure and perfect performance. But the braided type pneumatic artificial muscle is under the influences of elastic deformation, friction and cover radial constraint in the work process of the pneumatic artificial muscle, the precise modeling is very difficult, the theory study remains to be perfect. There are two modeling methods for braided type pneumatic artificial muscle:the energy conservation law under ideal condition and the force balance law under ideal condition. The two laws are all assuming that braided type pneumatic artificial muscle always remaining in the ideal cylindrical state. In fact, there are constraints on both ends of pneumatic artificial muscle, the geometry in the process of the working is not the ideal column, the turning curved surfaces occur at the two ends. Therefore, the improvement of the geometry expression accuracy of braided type pneumatic artificial muscle is the key to establish the more precision mathematical model. This paper will study on the working mechanism, theory modeling and design research of braided pneumatic artificial muscle as the object.The working mechanism research is from two aspects including the function realization and the material characteristics of the key components. On one hand, pneumatic artificial muscle can realize its functions, its basic principle is the deformable closed chamber, under the compressed function, the air closed chamber change, causing the displacement effect; the displacement change ranges are restricted by the pneumatic artificial muscle structure, the output force is related to the pressure of compressed air and the structure of pneumatic artificial muscle.On the other hand, base on laminated theory, composite materials mechanics and thin shell theory, starting with the flexible characteristics mechanism of braided type pneumatic artificial muscle, the flexible material properties of braided type pneumatic artificial muscle has been analyzed. The weaving network has played a decisive role on the deformation of flexible pieces, the plane stiffness of flexible pieces is zero, it will produce "institution type" deformation in the balanced external force. At the same time, weaving network will be in the forces balance state under each stable state of braided type pneumatic artificial muscle. The theoretical expression of the mechanism of pneumatic artificial muscle has been got.Based on the work principle of braided type pneumatic artificial muscle, using winding theory, composite material mechanics, thin shell theory and differential geometry as theoretical basis, the theoretical modeling of the ends of braided type pneumatic artificial muscle has been studied. Braided fibers at the end of braided type pneumatic artificial muscle should be geodesics winding, because of the directional changes of the curvature will happen in theory, so the established mathematical model at the end of braided type pneumatic artificial muscle consists of two parts:one part is from the biggest diameter to the change point of the curvature direction (inflection point), the model of this part can be got by the theoretical analysis; The other part is from the inflexion point to the end cover, this part can be substituted for the spherical surface. Although the built model is not the completely theory solution in this paper, but the end shape is more close to the exact solution, at the same time, the constraints effect on the geometry deformation of braided type pneumatic artificial muscle can be proved.The design calculation formula of structural parameters of braided type pneumatic artificial muscle and the relationship between the various geometric parameters have been provided from the design view. The important parameter-the braiding angle which can influence the work scope of braided type pneumatic artificial muscle, has been focused on. The braiding angle calculation formula has been provided, the extreme value has been determined. The influence formula of rubber elasticity and thickness on the work characteristics of braided type pneumatic artificial muscle have been given; the friction influence between the fibers on the work characteristics of braided type pneumatic artificial muscle has been studied, and the calculation method of friction force has been provided.The geometry modeling of braided type pneumatic artificial muscle has been made from the structure of braided type pneumatic artificial muscle with ABAQUS. By analyzing and calculating, the relationship of output force, inflation pressure and length of braided type pneumatic artificial muscle has been obtained. At the same time, the contour dimension, braided angles and volume of braided type pneumatic artificial muscle in the working state also have been drawn. By using this model, the work characteristics influence of constraints on braided type pneumatic artificial muscle can be simulated.The test bench of braided type pneumatic artificial muscle has been designed and manufactured, and the experimental research has been done. Through the comparisons of the static working characteristics experimental results of braided style pneumatic artificial muscle, the ideal cylindrical model and the finite element analysis, the results of finite element analysis are more close to the experimental results, this is because rubber characteristics and end constraints have been considered in the process of finite element analysis of braided type pneumatic artificial muscle. At the same time, the constraint influence research of the output characteristic of braided style pneumatic artificial muscle has been developed. From two aspects of the finite element simulation and experiments, the conclusion that constraints can reduce the output characteristic of braided style pneumatic artificial muscle has been proved.