The Implementation Of The Control Theory Of Virtual Tool Position Of Robot's Compliant Grinding Free-Form Surface

1.IntroductionIn the research of robot control technology, it has a core conflict.Namely when robot contact special operation environment, between requireproduce the complaisance of random force and require robot towardposition precision and structure firm. It is called complaisance thatrobot can compliant the contact environment, and the research of thisproblem is called the research of compliant control. The technology ofrobot compliant control, is the forward of cross subject between theoryof modern control and the technology of automated manufacturing, it isalways one of the difficulty of the area of automation, and the textestablish the foundation in order to further research the theory ofcompliant control. The text take the control of grinding force as theobject, integrate a series of advance technology of the application ofrobot technology, compliant control technology, modern control theory,modern mathematics, NC technology. Take the research of the controltheory of virtual tool position of robot's compliant grinding free-formsurface, resolve the problem of implantation of standard NC of robot'scompliant control in free-form surface.2.Robot Flexibility Grinding ToolThe text develop a flexibility grinding tool using by robot, it canself-determination fit the the outline of big scale free-form surfaceto be machined, supply the rotate motion in process of grinding by motor,it can separate the normal pressure, tangent displacement, tangent angle inthe process of grinding, correct tangent angle yaw the by itself, and thetop of grinding tool has the specialty of no velocity dead-center. The sketchfigure of flexibility grinding tool and the practicality image are shownas figure 1,figure 2.Figure1. the sketch of flexibility grinding tool Figure2. practicality imageAs figure 1 shown the flexibility grinding tool mainly composed by1.upper fixation connection board, 2. flexibility adaptable body,3.Electrical Motor, 4. lower fixation connection board, 5.ring grindingtool and other correlation connection parts.The process of grinding sketch is shown as follow.Figure 3. the process of grinding sketchAs figure 3 shown, the grinding tool fixed on robot,via PC to controlthe position and gesture of robot, make tool axis vector of grinding tooland normal of the surface of workpiece to be machined superposition, andmake the grinding tool contact the surface of workpiece to be machinedwith definite pressure, the grinding tool adjust the ring top to adaptthe outline of the surface of workpiece to be machined by its flexibilityadaptable body, in the process of machining, via PC control robot adjustthe position and gesture of the bottom of robot, to ensure the pressurebetween grinding tool and workpiece invariableness, and the electricalmotor drive the ring top circumrotate at the meantime to make themachining of the workpiece surface.3.Ascertain The Position and Gesture of The Grinding Tool and The VirtualTool Position(1)Ascertain the gesture matrix of grinding tool in workpiececoordinateAssume the Matrix of grinding tool coordinate in workpiececoordinate is:F=?????? nnn0 xzy ooo0xzyaaa0xzyPPP1xzy?????? (1)Because we use the flexibility grinding tool,under the grindingpressure, the grinding tool will take place flexibility distortion inthe process of grinding, assume the distortion value of grinding toolis L, the position of grinding tool will change, as well as the positionof the bottom part of robot need to be changed, should reduce thedistortion value of grinding tool from the position Matrix, gained theposition Matrix is:????? PPP xzy ???????????LLL aaaxyz?????= ????? PPPyxz ??? LLLaaazxy????? (2)Finally gained the position and gesture Matrix of grinding toolcoordinate in workpiece coordinate is:IXF=?????????????????????0001(1)(1)(1)(1)(1)(1)zzzzzyyyyyxxxxxnoaPLanoaPLanoaPLa(3)(2)Ascertain the final position and gesture in robot coordinateThe final position and gesture of grinding tool in robot coordinateis the final position and gesture of grinding tool coordinate. The finalposition and gesture of grinding tool coordinate will gain via theposition and gesture Matrix of grinding tool in workpiece coordinatemultiply the transformation Matrix in the left side.U F = TU×F= ??????1 000 ?0001?0001CCC1 xyz???????????? nnn0 xyz ((( ???1 1 10)))oooxyz(((???1110)))aaaxyzPPPyxz???1LLLaaaxzy??????????????????????????+?=0001(1)()(1)()(1)(1)()zzzzzzyyyyyyxxxxxxnoaCPLanoaCPLanoaCPLa(4)(3)Ascertain the virtual tool positionThe virtual tool position is the tool position that use CAM softwaresystem to compute the data by a series of transformation which gainedfrom NC simulate machining and applied in practical machining. In theprocess of modeling the workpiece, due to the grinding tool exist theflexibility distortion, a new group generatrix data gained by reducingthe flexibility distortion of the grinding tool form the practicalworkpiece along its generatrix normal direction. The virtual workpiecemodel is the new workpiece model found by this new group generatrix data.The virtual tool position is the tool position applied in practicalmachining process solving on the basis of this virtual tool model.X4.The transformation from NC code to robot commandNC code and robot command have many common ground, they are all usespecial symbol which descript the machining motion to express the spacetrack path in the process of machining and the gesture of tool inmachining space, and they all express themotion preface need to be done,so the convertion from NC code to robot command can absolutely come true.(1)The convertion of rapid point orientation code, the NC code G00is similar to MOVL and MOVJ in robot motion command, so we use one ofboth to convert the code G00.(2)The conversion of line interpolation code, among robot command,the MOVL is correspond to code G01, and the definition of them is resemble,so we use MOVL as the conversion of code G01.(3)The conversion of arc interpolation code, among robot command,only MOVC can displace the code G02 and G03, but the definition of themhas great difference, here we don't consider the difference betweentheir definition, via the NC code to determine the conversion of G02,G03 and MOVC in foundation of correlation geometry figure information.In the meantime of their conversion, also need to consider thegrinding position and gesture of grinding tool in every point correspondto every robot command. In the process of grinding, the grinding toolneed to hold definite position and gesture to machining the workpiece.Because the grinding tool can adapt the outline of the surface of theworkpiece, for every robot command, in order to convenient for request,we hold the position and gesture of grinding tool fixedness in the processof machining, and using the mid point of start point and end point tocompute the position and gesture of the grinding tool.5.The experiment of the control theory of virtual tool position ofrobot's compliant grinding free-form surfaceAfter complete the data traffic transmission between PC and robot,the process of machining is shown as figure 4.This experiment mainly validate the feasibility of the controltheory of virtual tool position in process of machining of robot'scompliant grinding the free-form kind workpiece, in the process of theexperiment, robot execute the robot command produced by the controltheory of virtual tool position correctly, validate the validity and thefeasibility of the control theory of virtual tool position of robot'scompliant grinding free-form surface put forward by this text.Figure 4. process of robot machining6.ConclusionThis text develop a robot flexibility grinding tool system.Ascertain the position and gesture of grinding tool in process ofmachining, present the forward and backward resolution of robotkinematics, deduct the normal vector of the workpiece surface, thegesture matrix of grinding tool in workpiece coordinate, the finalposition and gesture in robot coordinate and the transformation Matrixbetween workpiece coordinate and robot coordinate, establish thefoundation of implementation of the control theory of virtual toolposition of robot's compliant grinding free-form surface. Research theconversion method between NC code and robot command, deeply expatiatethe communication protocol of robot, develop the communication softwaresystem between PC and robot. Firstly bring forward the control theoryof virtual tool position of robot's compliant grinding free-form surface,bring forward a series of expression which the implementation of thetheory of the virtual tool position need, and have the experimentresearch aim at its feasibility. The experiment research indicate thatthe control theory of virtual tool position of robot's compliant grindingfree-form surface is validate and feasible.