| Parallel mechanisms have been used in many applications since it was proposed.However,in practical applications,their performances are limited due to its singularity,joint error and other factors.In addition,in some cases,not every freedom are required.Therefore,redundant parallel mechanism and less degree parallel mechanisms are getting more and more attention.In this paper,a pneumatic artificial muscle-driven parallel mechanism with elastic components is proposed.A new type of redundant parallel mechanism is designed based on tension network.The mechanism can restrict three translational degrees of freedom and only have three rotational degrees of freedom.Compared with the original structure,it is not affected by the non-linearity of elastic supporting elements in the process of rotational motion.In addition,it can be made into a series as a joint.In this paper,an improved scheme is proposed for this type of redundant parallel mechanism.Under the premise of the wire rope as the isometric constraint,the relationship between the tension network motion and the relative size and relative height of the two indexing circles of the network is analyzed,it is concluded that the wire rope can be equivalent to fixed-point rotation when the stiffness of the wire rope is large.Based on the single-degree-of-freedom motion range,a redundant parallel mechanism driven by eight pneumatic artificial muscles is designed based on the tension network,and the structural design is completed.Pneumatic artificial muscle is used as the driving component,but due to the structural constraints,the displacement sensor is installed to control the position of the pneumatic artificial muscle.Therefore,two attitude control schemes,such as table interpolation and angle sensor,are proposed.In the aspect of pneumatic artificial muscle,the experimental platform for static characteristic test was designed.On the basis of completing the isobaric and isometric experiments,a work table for table interpolation was established.By setting up the working characteristic table,the pneumatic artificial muscle was applied to the experimental platform.In consideration of the influence,the platform proposed in the design process can be approximated as the rotation around the fixed point when rotating in a small range under the constraint of a large tension network,and the measurement method of monocular vision is used to calculate the pose.Finally,on the basis of completing the processing and assembly of the experimental bench,the single-layer redundant parallel mechanism is tested.The maximum motion range,step response and tracking of the sinusoidal signal of the system in three rotational degrees of freedom are obtained through experiments.Through the frequency sweep experiment,the bandwidth of three rotational degrees of freedom is obtained.By changing the inflation pressure of the pneumatic artificial muscle,the variation and trend of the resonant frequency of the redundant parallel mechanism with different internal forces are obtained.Finally,the single design of the subject is tried.The layer redundant parallel mechanism is in the form of a series-parallel mechanism as a joint. |
