Research On Condition Cognition And Compliant Control Of Robot In Free-Form Surfacs Polishing

With the development of automobile industry, electric industry, aeronautics and astronautics industry and some new high-tech industries, higher and higher requirements are made for quality and efficiency in machining die and mould with free-form surfaces. These required surfaces are usually shaped by milling on NC machine tools, by tracing, by electrical discharge machining (EDM) or by electrochemical machining (ECM), and then, the required accuracy can be obtained by abrasive polishing to remove the superficial layer along with the machining traces and the residual stress and to obtain the proper surface accuracy. However, at present, these subsequent processes of precision machining still depend mainly on the handwork of skilled mechanists, which becomes a weak line for the die and mould manufacturing with low cost, short production cycle and high quality, and also becomes an adverse factor for the right trends of modern manufacturing to automation ultimately, and advanced die and mould manufacturing to automation, flexibility, integration and intelligence. Therefore, it is inevitable to study the theory and technology of automatic precision machining for free-form surfaces. The machining quality of free-form surfaces is mainly marked by the consistency of both the degree of roughness and the depth of material removal, which can be obtained only by controlling the movement and position of polishing tool and the force in polishing zone. Research work shows that, the industrial robot will play a very important role in the agile manufacturing of the reconfigurable machining units programming, since robot's structure and performance have all the advantages of automatic apparatus, and it has the intelligence, adaptability and accuracy under all work conditions. By now, much work is being carried out to replace the manual task by an automatic robotic polishing system, which has more reliable and versatile controls providing better accuracy, but very few researches have been carried into the technologies of robotic polishing system. There is lots of research work on the compliant control technology and its related ones carry out to make an automatic robotic polishing system of high efficiency and high robustness. Based on a large number of references, data and documents, a comprehensive comment is made on the present situation and the development of the technology of precision machining on free-form surfaces by robot, and the background and necessity of this theme in production are given in this dissertation. Ultrasonic wave, which vibrates and travels along the polishing tool, is a line of oblique incident P-wave and will reflect and refract on the dielectric-dispersed boundary layer where stiff abrasive particles serve as rigid contact boundary and air interstice as free contact boundary for the tool. Essentially, the ultrasonic polishing is the process of reflection and refraction of elastic wave. On the basis of the theories of reflection of elastic waves and dynamic stress concentration, this paper studies the stress and its changing in the polishing zone, finds the phenomenon that ultrasonic contact is not continuous between elastic polishing tool and work-piece and brings forward the cutting mechanism of oblique ultrasonic polishing and ultrasonic EDM polishing. The experimental results show that,these are two kinds of mechanical actions, the machining operation process and the shot-blasting process, make up of the oblique ultrasonic polishing jointly, polishing force Fn and machining angleλcan influence the polishing process directly; and in the ultrasonic EDM polishing, the phenomenon that ultrasonic contact is not continuous between elastic polishing tool and work-piece gives birth to electric spark and robot makes it work well, in which, polishing force Fn is the most important variable for polishing. During the process of polishing, the depth of material removal on different points of free-form surfaces is different because the contact pressure and the polishing condition change with the curvature radius of work-piece of free-form surfaces. The author studies the machining process and cutting mechanism of oblique ultrasonic polishing with free abrasive and ultrasonic EDM polishing without solid abrasive, describes the regularities how the technological factors influence polishing results and the role that robot has to play in polishing free-form surfaces, and gets the theoretical and experimental buttress for the model of work condition of automatic polishing free-form surfaces by robot. By analyzing the movement and controlling of a robot in polishing, it is thought that, the polishing robot must proffer acceptable feed speed Vf, polishing force Fn and machining angleλ. Feed speed Vf determinesthe machining time in polishing zone, polishing force Fn results in the stress and its changing in the polishing zone and machining angleλinfluences the machining velocity and movement intervention. The number of robot's degrees of freedom is analyzed to be no more than 6. Based on the movement and control of polishing robot, this paper studies the movement programming method for polishing tool, introduces the principle and characteristics of both transverse movement programming method and longitudinal movement programming method systematically, demonstrates that, transverse movement programming makes polishing tool move in a 3-D space of two line movements and a writhe movement, longitudinal movement programming makes polishing tool move in a 2-D space of one line movements and a writhe movement, so longitudinal movement programming needs less number of degree of freedom and is much easier to avoid movement intervention and mechanic singularity, and then, reaches the conclusion that the performance of longitudinal movement programming method is better than that of transverse movement programming method in polishing free-form surfaces by robot. With the longitudinal movement programming method, the displacement functions and velocity functions of the polishing robot's joints are deduced, the related technologies on movement of polishing robot, such as interference checkout, degree of freedom redundancy and movement singularity, are resolved by polishing process simulation. Under the structure restrict and movement restrict, this paper constructs track programmer, movement calculator, quadrature solver and movement coupling solver, constitutes and optimizes the robotic polishing system for free-form surfaces, in which the movement of polishing tool can be programmed by controlling the movement of polishing robot's joints. From the movement simulation of the robot polishing system, the work track tracker, the feed speed tracker and the machining angle tracker work in good condition of high accuracy and rapidness. By analyzing the structure and rigidity of polishing robot system, the elastic distortion of this robot polishing system is thought to concentrate on the elastic polishing tool, and the passive distortion structure is constructed for force control in the robot polishing system. With the appropriate rigidity matrix of the robot polishing system, this paper studies the relationship between polishing force and position warp, constitutes the polishing robot force control system with the passive distortion structure by improving the position accuracy under the restrict condition on the force sign feedback, completes a new robot force control method on the basis of the passive...