Pneumatic artificial muscle is a new type of actuator with large power-to-weight ratio, good flexibility and easy to manufacture and use. It has been successfully applied in many foreign robot research. Pneumatic muscle structure such as the cabinet. The inside is a rubber tube with good elasticity, and the outside is made of high-strength fiber. When a gas is allowed, the pneumatic muscle expands while causing it to contract in the longitudinal direction. , its end is connected to the load. It is possible to drive the load by the force generated by the contraction.
At present, the most commonly used formula for aerodynamic muscle static model is that the formula is carried out during the derivation process. The shape of the aerodynamic muscle expansion is ideal. The cylinder 2 does not consider the elasticity of the rubber; 3 between the Tingwei mesh and the rubber ridge. Without friction, there is a big gap between the ideal and actual characteristics of pneumatic muscles due to the neglect of the effects of actual factors. This paper analyzes the effects of some real factors on the aerodynamic muscle model.
In order to have a deeper understanding of the actual characteristics of pneumatic muscles.
2 An improved model considering the influence of the shape of the end of aerodynamic muscles. When deriving the traditional model formula, the assumption that the aerodynamic muscle is expanded is the ideal cylinder. But in fact, after the aerodynamic muscle is inflated, at the two ends, there is a transition from the largest diameter to the end. When the aerodynamic muscle has a small aspect ratio, the assumption of the part is ignored when deducing the formula and the ideal cylinder is assumed. Possible Fo pneumatic muscle contraction force; F gas supply pressure; 0 fiber between the network line and the longitudinal direction of the pneumatic muscle; 1 fiber line length; a large error. To this end, model derivation is carried out taking into account the effects of end transitions.
When the aerodynamic muscle is the ideal cylinder, the length of the diameter of the braided wire has a long geometric relationship of 2, considering that the aerodynamic muscle does not have the shape of an ideal cylinder.
Suppose that the transition curve of the section of the pneumatic muscle from the cylinder with the intermediate diameter of 0 to the end of the diameter is the length of the braided line on the ideal cylinder. Due to the transition zone at the end, the actual fiber The length of the braided wire and the ideal length are not. The length of the lower row of the braided wire and the length of the twisted wire are the length of the braided wire at the end transition zone, which is the length of the braided wire at the end of the ideal cylinder, and the middle cylinder The length of the braided wire is the total length of the braided wire on the ideal cylinder, and the total length of the braided wire on the actual pneumatic muscle is the length of the transitional arc in the cross section. The length of the arc is approximately the same as the relationship between the initial position and the initial position. It is considered that the diameter of the rubber tube and the diameter of the end are equal, so the relationship is established. Therefore, the above-mentioned various types are available, and the bamboo is set in a certain balance state. The internal pressure of the pneumatic muscle is the corpse, and the external force is a virtual force for the pneumatic muscle. The displacement causes the change of the volume of the aerodynamic muscle. The principle of the virtual work is considered. When considering the end effect, the volume after the expansion of the aerodynamic muscle is not an ideal cylinder, and the volume is the actual body. When the knitting angle is smaller, the closer it is, the more the number of windings of the braided wire is. Also loaded close to 1.
The size of the moxibustion 2 and the aspect ratio and diameter of the aerodynamic muscle are the first when the pneumatic muscle diameter after the inflation bearing is closer to the end diameter, the closer the moxibustion 2 is to the end effect.
It can be seen from the above analysis that when considering the influence of the end of the pneumatic muscle, the actual contraction force can be obtained by multiplying the ideal contraction force model formula by a factor.
3 Considering the influence of rubber tube elasticity, the pneumatic muscle model of the rubber tube will be inflated after being deformed due to its elasticity. After the transverse diameter becomes larger, part of the elastic energy can be stored in the rubber, which offsets the force of part of the air pressure. At the same time, when the rubber tube is stretched by the external force, the contraction force due to the elasticity of the rubber itself is also applied in the longitudinal direction. . The following is an analysis of the effects of these two forces on the ideal model.
1 Regardless of the influence between the transverse and longitudinal strains and stresses in the rubber crucible, it is considered that they are independent; it is considered that there is a line between the deformation and the stress of the rubber ridge, and the following is the derivation of the aerodynamic muscle in consideration of rubber elasticity. The force can be obtained from the above various formulas. In the above process of derivation, it is considered that the magicality is unchanged. The final course is the ideal model of the aerodynamic muscle contraction force and the experimental comparison of the ideal model experimental curve.
Improved model and experimental comparison improved model experimental curve 3 ideal model and experimental contrast ideal model experimental curve, improved model and experimental comparison improved model experimental curve 7 isometric characteristic curve rubber due to the elastic force generated by elongation, the force and length are considered The linear relationship is the elastic modulus of the rubber, 1 is the wall thickness of the rubber tube, and 1 is the length of the rubber tube when the air is not loaded, which is the total force of the fiber line in the lateral direction, which is the fiber line. The total number of roots is the transverse force of a single fiber line, and the force relationship in the longitudinal section. The force balance equation is the elastic force generated by the rubber è‡ in the longitudinal flashing, and the stress and strain are considered to be consistent. The linear relationship is the total force received by the fiber line in the longitudinal direction. The longitudinal force component of the single fiber line and the transverse and longitudinal component forces of the fiber line have the following relationship, and the above formula can be considered. The contraction force of aerodynamic muscles can be seen when the elastic force is considered, the actual contraction force of the aerodynamic muscle is 1 圮 in the ideal model, the contraction force formula plus and minus the consideration of elasticity. The friction between the rubber tube and the braided wire affects the static friction between the rubber tube and the woven mesh. It plays an important role in the impact between the actual æ¡¢ and the ideal model. The static friction is not only related to the weaving density of the rubber type fiber web, but also related to the supply pressure and the rubber diameter.
It can be seen from the force between the fiber web and the rubber tube that no matter the force reduction process or the force, the addition process, there is always a rubber tube between the rubber tube surface and the fiber to be expanded and the fiber web restricts its expansion. trend. There is no case where the rubber tube contracts and the fiber web limits the friction caused by its contraction. Therefore, it can be considered that there is always a direction in which the rubber tube expansion force between the rubber tube and the fiber web is always in the direction of the resultant force at both ends of the pneumatic muscle, that is, opposite to the direction of the external force. Therefore, due to the influence of the static friction force, the actual contraction force of the pneumatic muscle is smaller than that under the ideal condition. The magnitude and the friction of the product friction are more than 茗, and the number of the rest can only be obtained or indirectly through experiments. Here, only the size is considered to be related to the material characteristics of the gas supply pressure and the diameter of the rubber, that is, comprehensive analysis. We present an improved model for the effects of end effect æ“ rubber elasticity and friction force. 5 Improved models and experimental comparisons of pneumatic muscles used in the UK 3, the company's production. The generation parameters are as follows: initial initial length 20 initial length 15, fiber winding circle number 15.
Since the theory of static friction is difficult to formulate, empirical formulas can only be obtained from experiments. The empirical relationship given is the sum given as a function based on experience.
We tested the characteristics of contraction force and length relationship of pneumatic muscles and the relationship between contractile force and pressure in equal lengths, such as escape factories. Comparison of theoretical results and experimental results 67.
6 Conclusion The characteristics of pneumatic artificial muscles are nonlinear, and it is very difficult to obtain a very accurate model. This paper analyzes the factors affecting the gap between the ideal model and the real model, and gives an improved model. Experiments show that the model is closer to reality than the ideal model. However, the aerodynamic muscle characteristics also have a large hysteresis characteristic, which has a great relationship with the characteristics of the rubber. Therefore, there is a large error in the control of the open-loop position of the pneumatic muscle, and it is necessary to adopt a suitable position for obtaining a good positional accuracy. Closed loop control method.
Liu Rong, Zong Guanghua, research on artificial muscle drive characteristics, high-tech communication, author Yan Liming male blog ± graduate student. Harbin Institute of Technology pneumatic technology received date 2001
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