1、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 thi
2、s 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
3、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
4、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 para
5、llel 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 metho
6、ds. 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, printin
7、g 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, h
8、igh 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 engrav
9、ing 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 engr
10、aving 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,
11、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 t
12、his 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
13、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 mechanism
14、As 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 e
15、nd 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 an
16、d 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 p
17、lane, 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
18、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 thi
19、s 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,
20、 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. Coordina
21、te 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 me
22、chanisms 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
23、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
24、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
25、 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 draw
26、n (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 1
27、0cm, 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
28、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 + Maxi
29、mum 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, , , )? Reac
30、hable 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 Fr
31、obenius 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
32、 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 a
33、cceleration, 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 velo
34、city, angular acceleration, linear acceleration, force and moment, inertia forceEndTable 1. The SPN of 121 mechanisms in experiment SN SPN 六个性能指标 角速度 线速度 角加速度线加速度 力和力矩 惯性力 1309620.172760.174420.062360.113150.015210.37454 2280740.182480.181710.080750.132760.014560.40421 3258480.191280.188360.099320.1
35、51840.013960.43136 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 . . . . . . . . 119289420.257790.206800.122650.225960.010640.470
36、30 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 coeff
37、icient 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
38、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, super
39、script + 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
40、 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 controllin
41、g 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. Atla
42、s 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 linea
43、r 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 coefficie
44、nt 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 parallelengravi
45、ng 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
46、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.
47、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,
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