[机械模具数控自动化专业毕业设计外文文献及翻译]【期刊】可重构机床的一体化及控制设计-外文文献

Integrated Machine and Control Designfor Reconflgurable Machine ToolsD. M. Tilbury and S. KotaEngineering Research Center for Reconflgurable Machining SystemsDepartment of Mechanical Engineering and Applied MechanicsThe University of MichiganAnn Arbor, MI 48109-2125ftilbury,Abstract| In this paper, we describe a systematic designprocedure for reconflgurable machine tools and their asso-ciated control systems. The starting point for the design isa set of operations that must be performed on a given partor part family. These operations are decomposed into a setof functions that the machine must perform, and the func-tions are mapped to machine modules, each of which hasan associated machine control module. Once the machineis constructed from a set of modules, the machine controlmodules are connected. An operation sequence control mod-ule, user interface control module, and mode-switching logiccomplete the control design. The integration of the machineand control design and the reconflgurability of the resultingmachine tool are described in detail.I. IntroductionIn todays competitive markets, manufacturing systemsmust quickly respond to changing customer demands anddiminishing product life cycles. Traditional transfer linesare designed for high volume production, operate in a flxedautomation paradigm, and therefore cannot readily accom-modate changes in the product design. On the other hand,conventional CNC-based exible manufacturing systemofier generalized exibility but are generally slow and ex-pensive since they are not optimized for any particularproduct or a family of products.An efiort at the University of Michigan aims to developthe theory and enabling technology for reconflgurable ma-chining systems 3, 4. Instead of building a machiningsystem from scratch each time a new part is needed, an ex-isting system can be reconflgured to produce the new part.In this paper, we describe how an integrated machine andcontrol design strategy can result in machine tools whichcan be quickly and easily conflgured and reconflgured.In order to provide exactly the functionality and capac-ity needed to process a family of parts, RMTs are designedaround a given family of parts. Given a set of operationsto be performed, RMTs can be conflgured by assemblingappropriate machine modules. Each active module in thelibrary has a control module associated with it. As the me-chanical modules are assembled, the control modules willbe connected and the machine will be ready to operate.Extensive and time-consuming specialized control systemdesign will not be required. Section II describes how themachine is designed from a set of basic machine modules,This research was supported in part by the NSF-ERC under grantnumber EEC95-92125.connected in a well-deflned fashion, and Section III de-scribes how the control is similarly assembled from a li-brary of control modules. This modular construction ofthe machine and control allows for many levels of reconflg-urability as described in Section IV. The paper concludeswith a description of future work in Section V.II. Machine DesignOngoing work on manufacturing system conflguration atthe University of Michigan addresses the problem of start-ing from a part (or part family) description and extractingthe machining operations necessary to produce the part(s)7. The operations are grouped according to tolerance, or-der of execution, and desired cycle time of the system, withthe intention that each operation cluster can be producedon a single machine tool. The operation cluster consideredhere is to drill a set of holes for the cam tower caps on V6and V8 cylinder heads shown in Figure 1. The input to thereconflgurable machine tool design procedure is the cutterlocation data generated by a process planner for this oper-ation cluster. Figure 2 shows sample data which includespositioning and drilling information.The RMT design procedure consists of three main stages:task clariflcation, module selection, and evaluation 14.After a brief literature review, these three stages will beoutlined in this section.A. Related researchSince reconflgurability is a relatively new concept in ma-chining systems, there is little, if any, published literatureon the design of reconflgurable machine tools. However,modular machine tools have been on the market for sev-eral years, and some of the published articles on modularrobots, modular machines and assembly do have some rel-evance to the design of reconflgurable machine tools. Forexample, Shinno and Ito 17, 18, 19, 20 proposed amethodology for generating the structural conflguration ofmachine tools. They decomposed the machine tool struc-tures into simple geometric forms: e.g. boxes, cylinders,etc. Yan and Chen 21, 1 extended this work to the ma-chining center structural design. Ouyang et al. 12 adaptedItos method for modular machine tool synthesis and de-veloped a method for enumerating machine tool modules.Paradis and Khosla 15 determined the modular assemblyconflguration which is optimally suited to perform a speciflc(a) V6 cylinder head (b) V8 cylinder headFig. 1. Two sample parts. The operation to be performed is to drillthe positioning holes for the cam tower caps. On the V8 engine,there are two such positioning holes located in a line. On the V6engine, there are eight holes in an array.PARTNO/DOHC25M2 UNITS/MMPPRINT/OPERATION CATEGORY & TYPE: Hole Making Ream PPRINT/OPERATION NUMBER & NAME: Operation-1 PPRINT/TOOL IDENTIFIER: Drill6mm PPRINT/POST TOOL ID: 0 PPRINT/TOOL DESCRIPTION: PPRINT/TOOL STATION NUMBER: 1 MODE/MILLMULTAX/OFFLOADTL/0, IN, 1, LENGTH, 0.000000, OSETNO, 0CUTTER/6, 0.79375LINTOL/0.050000SPINDL/1910.000, RPM, CLWFEDRAT/0.127000, MMPRCOOLNT/FLOODCYCLE/DRILL, 20.500000, MMPR, 0.127000, 3.020144, RAPTO, 2.020144, DWELLGOTO/0.000000, 0.000000, 0.000000CYCLE/OFFCOOLNT/OFFPPRINT/OPERATION CATEGORY & TYPE: Hole Making Ream PPRINT/OPERATION NUMBER & NAME : Operation-2 PPRINT/TOOL IDENTIFIER: Drill6mm PPRINT/POST TOOL ID: 0 PPRINT/TOOL DESCRIPTION: PPRINT/TOOL STATION NUMBER: 1 MODE/MILLMULTAX/OFFLINTOL/0.050000SPINDL/1910.000, RPM, CLWCOOLNT/FLOODCYCLE/DRILL, 20.500000, MMPR, 0.127000, 3.020144, RAPTO, 2.020144, DWELLGOTO/0.000000, -43.000000, 0.000000Set-upToolPositionFig. 2. Sample sequence of operations (cutter location) data fordrilling holes in the parts shown in Figure 1. The CL flle isgenerated from a CAD package (such as IDEAS) and includesthe locations of the holes to be drilled along with the spindlespeed, feedrate, and coolant information.task. Chen 2 addressed the problem of flnding an optimalassembly conflguration for specifled tasks; his procedurewas based on the assembly incidence matrix and employeda genetic algorithm to solve the optimization problem. Onthe systems front, Rogers and Bottaci 16 discussed thesigniflcance of reconflgurable manufacturing systems, andOwen et al. 13 developed a modular reconflgurable man-ufacturing system synthesis program for educational pur-poses.In our work, traditional methods of motion representa-tion and topology (i.e. screw theory, graph theory, etc.) areemployed to capture the characteristics of RMTs. Thesemathematical schemes are used for topological synthesis,function-decomposition, and mapping procedures; detailscan be found in 9.B. Task clariflcationThe design of an RMT begins with task clariflcation,which entails analyzing the cutter location data to deter-mine the set of functions which are necessary to accom-plish the desired kinematic motions. There are three steps.First, graphs are generated which abstractly representationPosition Feed Spindle Coolantt1t2t3t4t5t6t7t8Fig. 3. High-level operation sequence, showing causal dependenciesand concurrencies. This abstract representation of the sequenceof operations is derived from the CL data shown in Figure 2, andwill be used to design the sequencing control.the motions. These graphs are then decomposed into func-tions, and flnally the functions are mapped onto machinemodules which exist in the library.A graph representation of the machine tool structureallows for systematic enumeration of alternate conflgura-tions and also provides a method of identiflcation of non-isomorphic graphs. The graph representation is also usedfor bookkeeping to assign machine modules to the graphelements. A graph consists of a set of vertices connectedtogether by edges. In using a graph as an abstract represen-tation of a machine tool structure, we deflne two difierenttypes of vertices: type 0 and type 1. A vertex representsa physical object with two ports; each port represents thelocation on the object where it can be attached to a neigh-boring object. A type 0 vertex has input and output portsthat are in-line with respect to each other, whereas a type 1vertex has input and output ports that are perpendicularto each other. Machining tasks are also classifled as type 0or type 1, depending on whether the tool is parallel or per-pendicular to the workpiece.Figure 4 shows a graph for a type 0 task. Four type 1vertices are combined with several type 0 vertices to createa machine structure in the form of a C. Because type 0vertices dont change the orientation, they can be used asspacers in various combinations. The root vertex repre-sents the base or bed of the machine tool. The choice ofthe root vertex is not unique; difierent choices will resultin distinct machine tool designs. Structural functions areassigned to the vertices of the graph; kinematic functions(where needed) are assigned to the edges. For instance,Figure 4 shows one example of how translational motions inthe X;Y and Z directions can be assigned to graph edges,representing relative motion between the physical objectsrepresented by the two vertices of the edge.The basic functionality of a machine tool is described bythe kinematic motion between the tool and the workpiece.These kinematic functions will be represented by a homoge-neous transformation matrix 11; the desired functionalityof the machine tool will be encoded in the matrix T.Themotions necessary to carry out a given machining task arederived from the sequence of operations. The process flleshown in Figure 2 contains tool positions and motions in aCartesian coordinate system. For example, the flrst motion10101 0 100Type 0TZTaskTYTX0BEDFig. 4. An graph representing a machine tool structure. Transla-tional motions (TX;TY;TZ) are assigned to edges of the graph;the vertices have structural functionality.Milling & Drilling Spindle Feeding Positioning Tool Rotation Translation XTranslation YTranslation Z Translation Z Merge Motor Lead Screw Motor Lead Screw Motor Lead Screw Motor Power Train Fig. 5. Function decomposition template.can be extracted as:P1=2664100 0010100001250000 13775F1=2664100 0010100001200000 13775where P1represents the position and orientation of the toolfor the positioning task, and F1represents the feed motion.From the transformation between any two adjacent posi-tions, the motion description can be extracted:M1= P11F1=2664100 0010 000150000 13775The other motion descriptions are extracted similarly.Corresponding to each type of machining operation, atemplate is retrieved as a starting point in identifying vari-ous kinematic functions necessary to carry out the machin-ing task. For instance, the template for milling and drillingoperations show that kinematic functions are necessary forspindle revolution, tool feeding and tool positioning. Byusing this template, together with the exact feeding andthe positioning information given in the process plan, wecan derive the exact set of kinematic functions that are nec-essary such as tool rotation, translations X;Y,andZforfeeding and translation Z for tool positioning as depictedin Figure 5.Each of the kinematic functions identifled in the functiondecomposition stage is mapped to an edge of the graph asdescribed above. Assigning the functions to difierent edgesFig. 6. The structural graph of Figure 4 can be realized by manydifierent choices of modules.2664100 0010 1001100000 13775Fig. 7. Representation of a machine module. The CAD model ofa slide for a modular machine tool is shown on the left, and itstransformation matrix is shown on the right.can generate multiple solutions. Because purely transla-tional motions are commutative, their order in the graphcan be interchanged. In function mapping, the importantinformation is the topology of screw motions (includingpure rotational motions) and the topology of the bed.C. Module selectionCommercially available modules are selected from themodule library for each of the functions (structural as wellas kinematic) that were mapped to the graph in the taskclariflcation stage. The data stored for each module inthe library includes the homogenous transformation matrixrepresenting its kinematic or structural function, the twistvector supplemented by range of motion information, acompliance matrix representing the module stifiness, mod-ule connectivity information, and power requirements (foractive modules such as spindles and slides).The flrst step in module selection is to compare the ho-mogeneous transformation matrices of the modules withthe task requirement matrix such that when appropriatemodules are selected to meet the task requirements, theproduct of all module matrices should be equal to the de-sired task matrix: T = T1T2Tn. Again, there may bemany possible choices of modules for a given structuralconflguration. Figure 6 shows how difierent slides, spin-dles, and structural elements can be assembled accordingto the graph of Figure 4.A slide module, with its CAD model and transforma-tion matrix, is shown in Figure 7. It is capable of onedirection of linear motion, indicated by the 1variable inits transformation matrix. Its database entry, shown in Ta-ble I, stores not only its transformation matrix but also themanufacturer name, model number, initial position, powerlevel, and motion data. The twist vector is augmented byinformation on the minimum, initial, and maximum dis-placement of the module.TABLE IDatabase information and documentation for the machinemodule shown in Figure 7.Manufacturer SUHNERModel Name UA 35-ACInitial Position2664100 0010 0001100000 13775Twist vector000010TRange of motion155 0 155Max. force 5500NCompliance matrix,Etc. Power requirements,Connectivity information, . . .(a) V6 machine (b) V8 machineFig. 8. Reconflgurable machine tool designs for the two difierentparts.D. EvaluationOnce a set of kinematically-feasible modules have beenselected, the resulting machine design must be evaluated.The criteria for evaluation of the reconflgurable machinetools synthesized by the above systematic procedure in-clude the work envelope, the number of degrees of freedom,the number of modules used, and the dynamic stifiness.The number of kinematic degrees of freedom of the ma-chine tool must be kept to a minimum required to meetthe requirements, both to reduce the actuation power andminimize the chain of errors. Each active Examples showthat the designs generated by this methodology have ex-actly the number of degrees of freedom necessary to per-form the required machining operations on the given part10. Machine tool designs which are generated using thismethodology for the example parts of Figure 1 are shownin Figure 8.The resulting designs must be evaluated with respect tothe expected accuracy. The stifiness of the entire machinetool, one of the most important factors in performance, isestimated based on the module compliance matrices andthe connection method.III. Control DesignAs the machine is built from modular elements, so isthe control. In this work, we focus on the logic controlX - AxisOperationSequenceUserInterfaceManualModeModeSwitcherAutoModeConflictCheckerSpindleY - AxisFig. 9. The overall structure of the modular control system.for sequencing and coordination of the machine modules;a discrete-event system formalism is used 6. There is onecontrol module associated with each active machine mod-ule; we refer to these as machine control modules. In themachine design, there are passive elements which connectthe active elements together. In the control design, theremust also be glue modules which connect the machinecontrol modules. The overall architecture of the controlsystem for an RMT is shown in Figure 9. The structure issimilar for either of the two machines shown in Figure 8;for the V8 machine, there is no Y-axis control module.As shown, the machine control modules are at the lowestlevel; these interact directly with the mechanical system.The user interface control module is at the highest level, in-teracting with the user through pushbuttons and a display.The operation sequence control module is deflned based onthe high-level operation sequnce for the part as shown inFigure 3. Three modules handle the mode switching logic.In this section, we brie y describe each of these types ofcontrol modules as well as their interaction and coordina-tion.A. Machine control modulesEach machine control module has a well-deflned interfacespeciflcation: it accepts discrete-event commands from agiven set, and returns discrete-event responses from a givenset. Within the control module will be all of the continuous-variable control, such as servo control for axes. This con-tinuous control is designed using standard PID algorithmsand the axis parameters such as inertia, power, lead screwpitch, which come from the machine module deflnition. Inaddition, each machine control module will contain con-trols for any machine services associated with the machinemodule, such as lubrication or coolant. Thus, each ma-chine control module is a self-contained controller for themachine module it accompanies, and can be designed andtested independently of the rest of the machine.The design of a machine control module must be don