Design And Experimental Research Of Variable Stiffness Continuous Manipulator Based On Air Spring

With the progress of science and technology,manipulator arm plays an important role in many fields,in the field of industrial manufacturing,replace manual painting,grinding,cutting,handling and so on.In the military field,it can perform tasks with high risk factors,such as explosion-proof and mine sweeping.In addition,it is also widely employed in aerospace,medical devices,agriculture and other fields.The traditional rigid manipulator as a mature technology,has strong load capacity.However,it has the disadvantages of poor human-computer interaction security and low degree of freedom,which cause it difficult to meet the requirements of unstructured environment.Therefore,flexible continuous manipulator arm with good flexibility and man-machine safety came into being.Flexible manipulator arm can realize flexible grasping,human-computer interaction and buffering,but it exists shortages,such as low bearing capacity and difficult high-precision control.In recent year,the occurrence of variable stiffness continuous manipulator arm can effectively solve the above mentioned problem.Therefore,this paper creatively applies the air spring to the body structure of manipulator arm.A variable stiffness continuous manipulator arm with adjustable stiffness is realized by varying the internal air pressure of air spring,and it can adjust the appropriate stiffness according to working conditions,so as to complete the grasping.The manipulator arm has bearing capacity,excellent compliance and human-computer interaction safety performance.The main contents of this paper are as follows:(1)A design method of variable stiffness continuous manipulator arm based on air spring is proposed.The analysis of the type,size,stiffness characteristics,bearing capacity and compliance of the air spring shows that the air spring has good variable stiffness characteristics and compliance,and the air pressure regulation is convenient.The mechanical arm comprises a base,a mechanical arm body,a driving rope,a motor and a pneumatic device.The manipulator arm is composed of six air springs in series,air springs are connected and fixed by flange.Two adjacent air springs are one joint segment,the manipulator arm body include three joint segments.The driving rope passes through the flange and is controlled by the motor to realize the movement of the joint segment,each joint segment is driven by three ropes.The pneumatic device consists of a solenoid valve,an air pipe and an air pump.The air pipe is connected with the air port of the air spring.Each solenoid valve regulates the air pressure of a joint segment.According to different working requirements,the solenoid valve adjusts the air pressure and the motor drives the rope to realize the movement of the manipulator arm,so as to complete the grasping task.(2)Based on the constant curvature method and coordinate transformation method,the kinematics modeling and analysis of the designed manipulator arm are carried out.Firstly,the forward kinematics model and inverse kinematics model of the single joint segment for the continuous manipulator arm are derived by the constant curvature method.Then,combining with the coordinate transformation method,the kinematics model of the whole continuous manipulator arm is obtained.Secondly,the natural length of air spring under different air pressure is obtained through the simulation and experiment analysis.The analysis results are coupled to the kinematic model,so as to obtain the kinematic model under different air pressure.Finally,based on Monte Carlo method,the reachable workspace of the end point for the continuous manipulator arm under different air pressure is analyzed.The simulation results indicate that the larger air pressure is,the wider reachable workspace is.(3)The fabrication and experimental researches of variable stiffness continuous manipulator arm are carried out.Firstly,the parts of the mechanical arm are made through 3D printing,CNC and other processing methods.In order to meet the design requirements of the stiffness and bearing capacity for the mechanical arm,the materials with low density and high hardness are selected for parts.Secondly,in the process of experiment,the variable stiffness of manipulator arm is verified by adjusting the internal air pressure of air spring.Finally,the reachable workspace of the end point for manipulator arm is measured and compared with the simulation results.The results show that the larger air pressure is,the wider reachable workspace is.