三坐標數(shù)控雕刻機的設計含11張CAD圖

三坐標數(shù)控雕刻機的設計含11張CAD圖,坐標,數(shù)控,雕刻,設計,11,十一,cad 英文原文Research on a Novel Parallel Engraving Machine and its Key TechnologiesAbstract: In order to compensate the disadvantages of conventional engraving machine and exert the advantages of parallel mechanism, a novel parallel engraving machine is presented and some key technologies are studied in this paper. Mechanism performances are analyzed in terms of the first and the second order influence coefficient matrix firstly. So the sizes of mechanism, which are better for all the performance indices of both kinematics and dynamics, can be confirmed and the restriction due to considering only the first order influence coefficient matrix in the past is broken through. Therefore, the theory basis for designing the mechanism size of novel engraving machine with better performances is provided. In addition, method for tool path planning and control technology for engraving force is also studied in the paper. The proposed algorithm for tool path planning on curved surface can be applied to arbitrary spacial curved surface in theory, control technology for engraving force based on fuzzy neural network (FNN) has well adaptability to the changing environment. Research on teleoperation for parallel engraving machine based on B / S architecture resolves the key problems such as control mode, sharing mechanism for multiuser, real-time control for engraving job and real-time transmission for video information. Simulation results further show the feasibility and validity of the proposed methods. Keywords: parallel mechanism, engraving machine, influence coefficient, performance indices, tool path planning, force control, fuzzy neural network, teleoperation1 IntroductionConventional computer engraving machine has played an important role in industries such as machinery machining, printing and dyeing and entertainment, but it has the inherent disadvantages such as cutting tool can be fed only along the fixed guideway, lower degree-of-freedom (DOF) of cutting tool, lower flexibility and mobility for machining etc. Parallel mechanism has the merits such as high mechanical stiffness, high load capacity, high precision, good dynamic performance etc (Zhen, H.; Ling-fu, K. & Yue-fa, F., 1997). According to the characteristics of parallel mechanism, it has been a hot research topic to apply parallel mechanism to the domain of future machining. By applying parallel mechanism to engraving domain, its inherent advantages can be fully exerted and the disadvantages of conventional engraving machine can be overcome or compensated. But as the special structure of parallel mechanism, the related theory and technology during its engraving is very different from that of conventional engraving machine, and it is a undeveloped research topic by now. In addition, with the development of computer network technology, the new concept and method such as network machining and manufacturing has become hot research topic (GQ, Huang & K.L, Mak., 2001; Taylor, K. & Dalton, B., 2000; Ying-xue, Y. & Yong, L., 1999). A novel parallel engraving machine with six-axis linkage is proposed in this paper, which uses the 6-PUS parallel mechanism with 6-DOF as the prototype, and some key technologies such as size design, tool path planning, engraving force control and teleoperation are studied on this basis.2. Confirming of mechanism type and engraving machines size2.1 Selection of mechanism and coordinate systemThe selection of mechanism type is the first step for designing novel engraving machine, the following reasons make us select the 6-PUS parallel mechanism for designing our engraving machine. Comparing with traditional mechanism, 6-PUS parallel mechanism uses base platform, three uprights layout and high rigidity framework structure and has the merits such as high modularization, high accuracy and low cost. Itsmodel is shown in Fig.1.Fig. 1. The model of 6-PUS parallel mechanismAs shown in Fig.1, 6-PUS parallel mechanism consists of base platform, dynamic platform and 6 branch chains with same structure, every branch joins with base platform through prismatic pairs (P), slider of prismatic pairs joins with up end of the fixed length link through universal joint (U), down end of the fixed length link joins with dynamic platform through sphere hinge (S), so it is called 6-PUS parallel mechanism. The coordinate system of 6-PUS parallel engraving mechanism is shown in Fig. 2. In Fig.2, the geometry centers of base platform and dynamic platform plane are supposed as OB and op respectively. In every branch, the centers of prismatic pairs, universal joint and sphere hinge are marked with Ai, Bi, and Ci (i = 1,2, ., 6) respectively. Coordinate system OB-XBYBZB is fixed on base platform, taking B as briefly. The origin of B lies on geometry center of base platforms up plane, axis ZB is vertical with base platform and directs to up, axis YB directs to angle bisector of the first and second branch lead screw center line, and axis XB can be determined with right-hand rule. Supposing the coordinate system set on dynamic platform is op-xpypzp, taking P as briefly, its origin lies on geometry center of dynamic platform, the initial state of dynamic platform system is consistent with that of base platform system completely. Supposing the coordinate of op is (0,0, Z) in B, this configuration without relative rotation to every axis is the initial configuration of this mechanism, and Z changing with mechanisms size. On the basis of coordinate system mentioned, we use influence coefficient theory and the actual parameters of this mechanism to calculate the first and the second order influence coefficient matrix of every branch under different configuration. Then, we can get the first and the second order integrated influence coefficient matrix H of the whole mechanism. 和The significance and detailed solution process for influence coefficient matrix is omitted here, for more information please refer (Zhen, H.; Ling-fu, K. & Yue-fa, F., 1997).Fig. 2. Coordinate system of 6-PUS parallel engraving mechanism2.2 Mechanism performance analysis based on influence coefficient matrix The performance of engraving machine will change with its size. To find out the better size for all the performance indices of both kinematics and dynamics, we obtain a group of mechanisms by changing its parameters. These mechanisms length of fixed length links (L) range between 45cm and 55cm (step is 1cm), radius of dynamic platform (R) range between 10cm and 20cm (Step is 1cm). Other parameters of the mechanism is unchanging, so we get 121 mechanisms totally. Taking these mechanisms as research object, we confirm the sample point for every mechanism in its workspace with algorithm PerformanceAnalysis, then calculate the first and the second order influence coefficient matrix in every point. Furthermore, calculate all the performance indices in every sample point and draw all the global performance atlas of 121 mechanisms ultimately. To describe conveniently, we abbreviate the first and the second order integrated influence coefficient matrix Hq to G and H, and use G, H and G, H as the angular velocity submatrix and linear velocity submatrix of the first and the second order integrated influence coefficient matrix respectively, namely, We can change mechanisms parameters and adjust variables step in the algorithm PerformanceAnalysis to meet actual analysis. The algorithm is programmed with MATLAB and the global performance atlas of 6-PUS mechanism are drawn (see Fig. 3 to Fig. 8), then the mechanisms performance is analyzed using the atlas. Table 1 shows the results of sample point number (abbr. to SPN) for 121 mechanisms respectively, the fixed link length of mechanism with sequence number (abbr. to SN) 1 is 45cm, its radius of dynamic platform is 10cm, the fixed link length of mechanism with SN 121 is 55cm, its radium of dynamic platform is 20cm, the rest may be deduced by analogy. In addition, table 2 gives the performance indices of some mechanism only, where the mean of SN is same as in table 1.Description for algorithm PerformanceAnalysis:PerformanceAnalysis BeginFor L = 45 To 55 / / scope of fixed length linkFor R = 10 To 20 / / scope of radius of dynamic platformSamplePointNumber = 0; / / initialization sample point number is zero for every mechanismFor x =-Maximum To + Maximum moving along Axis X Step 4cmFor y =-Maximum To + Maximum moving along Axis Y Step 4cmFor z =-Maximum To + Maximum moving along Axis Z Step 4cmFor =-Maximum To + Maximum rotating around Axis X Step 12 For =-Maximum To + Maximum rotating around Axis Y Step 12 For =-Maximum To + Maximum rotating around Axis Z Step 12 If sample point (x, y, z, , , )? Reachable point of mechanismsworkspaceCalculating the first order influence coefficient matrix andits Frobenius norm at current point;If The first order influence coefficient matrix is notsingularSamplePointNumber = SamplePointNumber +1;Calculating the second order influencecoefficient matrix and its Frobenius normcalculating condition number at this point withformula and accumulating sum of performanceindices;/ / detailed formula is given in the followingof this sectionEndifEndifEndforEndforEndforEndforEndforEndforCalculating all the performance indices of the mechanism at current size and append the results to corresponding data files for different performance index;/ / performance index of the mechanism =(accumulating sum of performance indices at all sample points) / SamplePointNumber/ / There are six data files for performance indices totally: angular velocity, linear velocity,angular acceleration, linear acceleration, force and moment, inertia forceEndforEndforDrawing all the global performance atlas of 6-PUS mechanism by all the index data files(Every data file includes the information of 121 mechanisms);/ / There are six performances atlas totally: angular velocity, linear velocity, angular acceleration, linear acceleration, force and moment, inertia forceEndTable 1. The SPN of 121 mechanisms in experiment SN SPN 六個性能指標 角速度 線速度 角加速度線加速度 力和力矩 慣性力 1309620.172760.174420.062360.113150.015210.37454 2280740.182480.181710.080750.132760.014560.40421 3258480.191280.188360.099320.151840.013960.43136 4232520.200870.195450.118970.172250.013480.46030 . . . . . . . . 59423900.211050.189950.100500.013040.013040.40233 60374100.219150.195370.113080.173550.012570.42606 61324460.227170.200410.123120.19230 0.01216 0.44929 . . . . . . . . 119289420.257790.206800.122650.225960.010640.47030 120239980.267860.211850.121160.241390.010410.49500 121198280.277140.216100.113990.255270.010170.51745Table 2. Six performance indices of some mechanisms2.2.1 Analysis of kinematics performance indices2.2.1.1 Global performance indices of angular velocity and linear velocity As the influence coefficient G of engraving mechanism is not a constant matrix, it makes the measuring index for parallel mechanism based on G not to be a constant matrix also, so we cant utilize one value to measure the good or bad of the dexterity, isotropy and controlling accuracy (Xi-juan, G., 2002). Here, we define parallel mechanism global performance indices of angular velocity and linear velocity as following respectively Where W is the reachable workspace of mechanism,anddenote the condition numbers for angular velocity and linear velocity respectively (Where | | | | denotes Frobenius norm of matrix, superscript + denotes generalized inverse matrix, the same mean as following). We can get the performance indices value of the angular velocity and linear velocity according to the condition numbers of every mechanisms sample points. Replacing the underlined part in algorithm PerformanceAnalysis with two formulas in (1) respectively, we can draw the performance atlas for angular velocity and linear velocity as shown in Fig.3 and fig.4 based on 121 mechanisms indices values of angular velocity and linear velocity. According to the rule that the bigger J (J G, Gv), the higher dexterity and controlling accuracy of the mechanism, from Fig.3 we can see that the mechanism performance index of angular velocity is not changing with the link length when the changing range of R is not big, but it has the trend that the bigger R, the betterFig. 3. Atlas of angular velocity global performanceFig. 4. Atlas of linear velocity global performanceperformance index of angular velocity, furthermore, the index of mechanism angular velocity is better when L = 46.5cm 49.5cm and R = 19.5cm, namely, the output error of angular velocity is smaller. Similarly, from Fig.4 we know that the mechanism index of linear velocity is better when L = 45cm 48cm and R = 19cm, that is to say,the output error of linear velocity is smaller.2.2.1.2 Global performance indices of angular acceleration and linear acceleration.Considering the influences on acceleration of both the first and the second order influence coefficient matrix, the condition numbers of angular acceleration and linear acceleration for 6-DOF parallel mechanism are (Xi-juan, G., 2002; Xi-juan, G. & Zhen, H., 2002) Where, a and b is error coefficient.So the global performance indices of angularacceleration and linear acceleration for parallelengraving mechanism can be defined as Where Supposed the mechanism error is smaller than 2% (that is, a = b = 0.02), replacing the underlined part in algorithm .PerformanceAnalysis with formula (4), we can draw the performance atlas for angular acceleration and linear acceleration as shown in Fig.5 and Fig.6. As same as the evaluating method for velocity performance index, from Fig. 5 we can see that the angle acceleration performance of mechanism is better when nearly L = 45cm 47cm and R = 16cm 20cm, output error is smaller accordingly. Among the 121 mechanism we studied, its maximum is 0.16399.Fig.5. Atlas of angular acceleration global performanceBy observing Fig.6 carefully, we know that performanceof linear acceleration is better when nearly L=45cm48cm and R=19.5cm, accordingly, output error should be smaller. From above analysis, we know that mechanism size with good indices for linear velocity and linear acceleration is coincidence in some degree among the 121 mechanisms we studied, but performance index of angular velocity and angular acceleration may not the best in the same size, so it cant get coincidence. Thus, our analysis will be helpful for designing and choosing mechanism by actual needs. Similarly, analyzing method of kinematics performance indices is the same when other parameters of the mechanism are changed.Fig. 6 . Atlas of linear acceleration global performance2.2.2 Analysis of dynamics performance indices2.2.2.1 Analysis of power and moment performanceIndex. The condition number of power and moment performance index based on the first order influence coefficient matrix of power GF for 6-DOF parallel mechanism can be defined as(Xi-juan,G.,2002) Similarly, we define global performance index of power and moment for 6-DOF parallel mechanism as We suppose that power and moment of parallel mechanism is isotropy when J=1. With formula (5) as condition number, replacing the underlined part in algorithm with formula (6), we can draw the performance atlas for power and moment as shown in Fig.7. From Fig. 7 we can see in the size range of our experiment the performance index for power and moment would have little change with the link length when the radius of dynamic platform is less then 14cm. The performanc index for mechanisms power and moment will be bigger when L=45cm46cm and radius of dynamic platform R=10cm,here, performance of power and moment will be better.Fig. 7. Atlas of global performance of force and moment2.2.2.2 Analysis of inertia force performance indexConsidering both the first and the second order influence coefficient matrix, the condition number of inertia force for 6-DOF parallel mechanism is defined as(Xi-juan,G.,2002)Where G i is the ith column of matrixG , i=1,2,3.Then global performance index of engravingmechanisms inertia force can be defined as Obviously, the bigger value of G+H , the smaller inertia force of mechanism and the higher controlling accuracy. Replacing the underlined part in algorithm PerformanceAnalysis with formula(8), we can draw the performance atlas for inertia force as shown in Fig.8. According to the rule that the bigger value of G+H , the smaller inertia force of mechanism and the higher controlling accuracy, by observing Fig. 8 carefully, we can see that the inertia force performance index of mechanism is getting better when the link length is getting longer and radius of dynamic platform is getting bigger. Furthermore, the inertia force performance index of mechanism will be the best when nearly L=45cm48cm and R=19.5cm, that is to say, the inertia force performance of mechanism is the best, inertia force is the smallest, sensitivity is the best and dexterity is the highest. According to discusses above, we draw a conclusion that mechanism size with good performance index for power and moment and inertia force is coincidence not in all the time. This result indicates thatthe traditional designing and choosing mechanism method based on only the first order influence coefficient exists some restriction, we have to choose mechanism size on the basis of our analysis and actual demands.Fig. 8. Atlas of global performance of inertia force2.3 The results of size design and summarySummarizing previous analysis, we know that 6-PUS robot mechanisms all performance indices are better except force and moment when L=45cm47cm and R=19cm, the actual size of mechanism with this type owned by laboratory is at the above-mentioned scope. We also find that its performances are same with the results of theory analysis by running the mechanism in deed, so prove the correctness of our theory. To validate our theory analysis further, we also do lots of simulations for this mechanism with other sizes. The results are same with those of theory analysis, so we can draw the conclusion that, in a generally way, there is not a mechanism whose all indices are better at the same time for both the kinematics and dynamics. In fact, we can only select the mechanism with relative better performance for all the indices to meet our need. On the basis for considering all the performance indices, the final sizes of novel parallel engraving machine that we designed are following: The length of fixed link L is 46cm, the radius of dynamic platform R is 19cm,the radius of base platform is 38cm38cm,P1,P2,P3,P4,P5,P6=45,135,165,255,285,15,B1,B2,B3,B4,B5,B6 =82,97,202,217,322,337, C=30,A=15. Where Pi (i=1，2，6)is the angle between tieline from dynamic platforms center op to Ci and the axis xps positive direction of dynamic platforms coordinate system, Bi (i=1，2，6)is the angle between tieline from base platforms center OB to Ai and the axis XBs positive direction of base platforms coordinate system. C and A is the smaller central angle of hexagon made by Ci and Ai(i=1，2，6) respectively.3. Research on path planning of engravingA series of engraving paths can be obtained after the im