外文翻譯-可重構(gòu)和靈活的裝置方面

1、 外文資料翻譯資料來源：文章名：Aspects of reconfigurable and flexible fixtures作 者：Marie Jonsson.Gilbert Ossbahr出版社：German Institute of production engineering文 章 譯 名： 可重構(gòu)和靈活的裝置方面 Aspects of reconfigurable and flexible fixturesMarie Jonsson Gilbert OssbahrReceived: 31 January 2010 / Accepted: 9 June 2010 / Published

2、 online: 1 July 2010 German Academic Society for Production Engineering (WGP) 2010Abstract The design and manufacture of fixtures and other dedicated tooling for positioning of workpieces are among the major cost drivers in product industrialization. This has spurred research and commercial interest

3、 towardsother fixturing solutions like reconfigurable fixtures, with the ability to be changed, or reconfigured, to suit dif- ferent parts and products. When reconfiguring, the product interface not only has to be moved but moved to a desired position and orientation. Several different approaches ha

4、ve been used to move and position these devices, all with their own advantages and disadvantages. This article presents different methods used to position and reconfigure flexible fixture devices using a parallel kinematic device as a case. Discussing the different ways to reconfigure a flexible dev

5、ice, the article aims to arrange the techniques according to their key features.Keywords Tooling Jigs Fixtures Assembly ReconfigurableIntroductionThe increase in global competition and more rapid changes in customer demands have resulted in a trend toward higher product variety and innovation, short

6、er product lifecycles, demand for lower unit cost and thus shorter lead time. This has spurred companies to adapt new flexible approaches to manufacturing and automation, such as FMS (Flexible Manufacturing Systems) and RMS (ReconfigurableM. Jonsson (&) G. OssbahrDepartment of Management and Enginee

7、ring, Linkoping University, 581 83 Linkoping, Sweden e-mail: HYPERLINK mailto:marie.jonssonliu.se h marie.jonssonliu.seManufacturing Systems) HYPERLINK l _bookmark9 1, HYPERLINK l _bookmark10 4, HYPERLINK l _bookmark11 10. During the course of manufacturing processes, such as machining, assembly, or

8、 inspection, it is necessary to immobilize, support, and locate the workpiece or product. This is referred to as workholding or fixturing. Today, fixtures are mostly dedicated, i.e. they are manufactured for a specific part and a specific purpose. This single-purpose approach is costly due to the lo

9、ng lead time and effort required for design and manufacture, but also often due to manual set-up or mod- ifications when a manufacturing process is completed or parts and operations are modified. Cost is also induced by the need to store and retrieve dedicated fixtures. For a manufacturing system to

10、 be truly flexible, all of its com- ponents have to be flexible, including the fixtures. In the manufacturing industry, the design and manufacture of fixtures and other dedicated tooling for locating and posi- tioning workpieces or products are among the major cost drivers in product industrializati

11、on. The design and man- ufacture of dedicated fixtures typically amount to 1020% of total manufacturing cost HYPERLINK l _bookmark12 5. For the automotive indus- try, the cost of redesigning, manufacturing and installing fixtures is on the order of $100 million/plant/year HYPERLINK l _bookmark9 3. T

12、his high cost is paired with the need to shorten lead time too allow rapid response to market change and customer needs HYPERLINK l _bookmark13 9.1.1 Flexible fixturingThe research on the area regarding the process of designing fixtures and of different, flexible fixture solutions is vast. Some revi

13、ew articles on this area include: HYPERLINK l _bookmark9 2, HYPERLINK l _bookmark14 6, HYPERLINK l _bookmark15 13. The reference HYPERLINK l _bookmark15 13 presents a comprehensive schematic of dif- ferent approaches to flexible fixturing which include sen- sory based assembly, modular and reconfigu

14、rable fixtures, programmable clamps, adaptable clamps and phase-changeFig. 1 Left A typical modular fixturing kit for machining HYPERLINK l _bookmark12 5. Right A modular kit for assembly (courtesy of VolvoCars)Fig. 2 Example of a reconfigurable fixture for sheet metal (source: MTorres)fixtures. Bi

15、and Zhang HYPERLINK l _bookmark9 2, on the other, hand classifies fixtures according to their structure, and separates between modular structure systems (which include different modu- lar kits and reconfigurable fixtures) and single structure systems (which include phase change fixtures and adaptive

16、 clamps). The most researched and used in industry are modular fixtures and reconfigurable fixtures.Modular fixture kits for machining, assembly and inspection operations have received the most research and commercial attention, and several solutions are available in the retail market (see Fig. HYPE

17、RLINK l _bookmark0 1). Machining solutions often consist of elements such as V-blocks, rectangular blocks and clamps bolted on a T-slotted plate or on a base plate with plain or tapped holes. Both research and commercial interest has focused on rather simple 2D or 3D geometries. The modular elements

18、 are manufactured with narrow tol- erances, and a full kit is an expensive investment. Modular tooling kits for assembly and control operations are often made up of grinded steel parts or aluminum profiles with different add-on parts. Successful fixture builds for eithermachining or assembly require

19、 skilled personnel and, due to several iterative steps between building, measuring and correcting the fixture, the process also consumes a large amount of time.Reconfigurable fixtures that can be repositioned within a working envelope to conform to a wider variety of products have also been addresse

20、d by research. While a modular fixture has to be rebuilt to fit a specific part, a reconfigu- rable fixture is, as the name implies, able to be reconfigured in-between parts in the same family. Rebuilding means to physically detach or reattach fixture components while reconfiguring implies that some

21、 parts are adjustable, although the line between modular and reconfigurable is not clear-cut and several hybrid solutions exist. A reconfigurable fixture may be limited in the amount of dif- ferent geometries it can conform to, but reconfiguration can be done faster. Figure HYPERLINK l _bookmark1 2

22、shows an example of a reconfig- urable fixture which consists of a bed of servo driven pogo sticks for fixturing sheet metal within the aircraft industry.The Affordable Reconfigurable Tooling conceptAffordable Reconfigurable Tooling, here called ART, is a concept for reconfigurable fixturing in whic

23、h the product interface points are set to correct positions by the use of external measuring devices. This is in contrast to dedicated and modular fixtures, which are often made up of welded or machined components, and where the accuracy is made up by a chain of added tolerances as illustrated in Fi

24、g. HYPERLINK l _bookmark2 3. If only the position for level 0 is known, this results in a long chain of added tolerances and a need for high accuracy in all fixture parts. Ideally, one would like to position key features of the product to be constrained (level 3 in Fig. HYPERLINK l _bookmark2 3, lef

25、t) and build the fixture top down instead of bottom up. This would eliminate the need for accuracy in the fixture parts, but the need for stability and robustness would remain. This may be possible in some cases, but cannot be considered as a general approach. Another solution is to measure key feat

26、ures on the fixture body (level 1) or where the fixture interfaces with the product, called the pick up Fig. 3 Left Tolerance chain and levels of measure for dedicated fixtures. Right Description of the ART conceptFig. 4 The Flexapod 6points (level 2). This lessens the need for costly accuracy. This

27、 is the key reasoning behind ART, or Affordable Reconfigurable Tooling (see Fig. HYPERLINK l _bookmark2 3, right): namely to measure as close to the product as possible or even on the product itself. This concept for flexible, reconfigurable fixturing was developed for the aircraft industry in colla

28、boration with SAAB Aerostructures, Sweden HYPERLINK l _bookmark16 8. This type of rea- soning is not unique to the ART concept, however; dedi- cated fixtures may also be built in this manner, often by using shimming to achieve desired position, a process which is often iterative, time-consuming and

29、requires skilled personnel. The ART concept fuses modularity with by combining a relatively cheap but robust modular framework with reconfigurable units, referred to hereafter as flexapods. Figure HYPERLINK l _bookmark3 4 shows one example of a flexapod in detail, a six-legged Stewart mechanism call

30、ed the Flexapod 6. This device will be used as an example in this paper, but the reasoning is applicable to other kinds of reconfigurable devices. The six legs of the Flexapod 6 are connected in parallel between the top andthe bottom plate, thus resembling a parallel kinematic machine but without th

31、e actuators and encoders. The links can be locked in position by a hub-shaft connection mechanism, and the resulting device has 6 degrees of freedom. At the top of Flexapod 6 a mechanical interface, in this example a Coromant Capto, is attached. The inter- face serves as the docking point for a posi

32、tioning robot, for a metrology probe and for the pick up interface that will hold the part. The Capto system has a repetitive accuracy of 2 lm and was originally designed to hold cutting tools in CNC machines; hence, they are mass-produced and relatively cheap.Figure HYPERLINK l _bookmark4 5 shows a

33、n overview of an assembly fixture according to the ART concept - in this case equipped with flexapods of Flexapod 6 type, and the modular framework made of standard hollow steel beams with a detachable fastener system called BoxJoint. A robot docks to the top of a Flexapod 6, and opens the clutches

34、on the legs of the device. The robot then moves the top of the Flexapod 6 to a new position and orientation. The clutches are again locked, resulting in a firm pose. To achieve better accuracy, the final position of the robot is adaptively guided with the aid of a laser tracker. The combination of a

35、 modular framework and reconfigurable units makes it possible for the system to conform to a large variety of different geometries, since the fixture can both be rebuilt and reconfigured.Methods for reconfigurationTo reposition a reconfigurable device, a force to achieve movement is needed along wit

36、h a measuring system to achieve the desired position. This is also true for modular fixtures, where research has been done on building these using for example NC machines to position fixture parts on a base plate HYPERLINK l _bookmark17 12 or using a robot as in HYPERLINK l _bookmark9 1. Automated b

37、uildup of modular fixtures, however, will not be covered in this paper. Several different approaches have been testedFig. 5 An overview of the ART conceptto position reconfigurable devices. One approach is to use robots to set up and configure fixtures for assembly. In HYPERLINK l _bookmark18 14 a r

38、obot is used to place reconfigurable, modular fixture parts on an electromagnetic base plate. The robot is also used to adjust the height of the modules by unlocking and sliding a mechanism. Here, the robot is used as both actuator and measuring system. Manual repositioning was tried in HYPERLINK l

39、_bookmark19 11 where modular, reconfigurable components were placed on a T-slotted plate and positioned using scales on both the plate and on the fixture parts. Built-in drives have been used in research to reposition a fixture, as suggested for example in HYPERLINK l _bookmark20 15 where 1 DoF pneu

40、matic cylinders form a supporting fixture bed and a force-feed- back controlled robot is planned to be used for loading the fixture. Commercial solutions are available mostly for drilling large sheet metal parts in the aircraft industry. These solutions utilize built-in servos to form a bed-like str

41、ucture to support the part/product. Robotic Fixtureless Assembly (RFA) is a method where the robot, equipped with flexible gripper, is used as a fixture. This is described for example in HYPERLINK l _bookmark9 3 where a vision system guides the robot. The robots own internal measuring system may als

42、o be used if parts are positioned accurately prior to grasping. At Linkoping University, repositioning of the previously described Flexapod 6 has been done both manually and using a robot (ses Fig. HYPERLINK l _bookmark5 6). The latter is described in HYPERLINK l _bookmark21 7 where a robot is used

43、to dock to the Flexapod 6 and move it to a desired position and orientation. The legs of the device are then locked by hydraulic clutches. In this case, an external on line measuring system (a laser tracker) was used to enhance accuracy. Time for repositioning is dependant, on the start position of

44、the robot and the desired final pose. Due to the system setup and the communication with the robot controller, a few iterations were necessary between the laser tracker and the controller in order to achieve desired accuracy. This resulted in some 1015 s added time for calculations and a final absol

45、ute accuracy of 0.05 mm.Fig. 6 Flexapod 6 reconfigured using an industrial robotManual repositioning of a reconfigurable device is described in HYPERLINK l _bookmark21 7. The Flexapod 6 is repositioned in two steps, first by just dragging the device into a position and orientation close to the desir

46、ed one, and then finely adjusted by using attached screws on the legs of the Flexapod 6. A Leica tracker was used for measuring, and the operator was given feedback on his or her progress via a computer screen interface (Fig. HYPERLINK l _bookmark6 7). The absolute accuracy achieved was 0.07 mm, whi

47、ch is linked to the Leica trackers limits.For a more automated solution, it is possible to use motor-driven actuators instead of screws to lengthen the legs of the flexapod as shown in Fig. HYPERLINK l _bookmark7 8. This is currently under development at Linkoping University. To ensure that this sti

48、ll is an affordable solution, an outer measuring system will be used for positioning. The actuators will be off the shelf products, and a PC will be used as the control computer. The interface between the leg and the actuators is designed so that the actuator is easy to attach/ detach and therefore

49、can be moved between flexapods. Preliminary testing has been done in driving the Flexapod 6 to position in this manner, but integration with a measuring system is under development.3.1 ApplicabilityAlthough flexible fixtures and reconfigurable devices have been of research and commercial interest fo

50、r some time, the development of new technical innovations and princi- ples open the door for interesting new approaches. The possibility to use components developed and mass-pro- duced for other purposes also enables economical and capable solutions in reconfigurable equipment, such as in the case o

51、f the previously mentioned tool holder coupling Cormant Capto.Fig. 7 Manual reconfiguration of a Flexapod 6 by first dragging the Flexapod close to the final position and then do the final adjustment using detachable screwsFig. 8 Flexapod with motor driven actuator attached to the legs. An outer mea

52、suring system ensures accuracyBased on the current technical standpoint, an outline of technical realization for moving and adjusting reconfigu- rable devices can be identified (see Fig. HYPERLINK l _bookmark8 9). The Flexapod 6 is used as a case, but the reasoning applies to other types of reconfig

53、urable devices.Manual external actuators by means of screws and scales. The device may typically be mobile, and therefore able to serve all flexapods of a fixture.Manual permanent internal mechanisms in the legs of the flexapod. Guidance from a remote metrology system (as pictured) or scales.Manual,

54、 detachable actuators which are successively used to position the flexapods of a fixture.Robot, gantry robot, PKM robot or NC machine that uses its own servo drives and metrology system to guide the flexapods into position automatically.Motor drives integrated in the legs of the flexapod working und

55、er guidance of a metrology system.Detachable motor drives guided by an external metrol- ogy system. The drives are able to be moved from one flexapod to the next during the changeover procedureManually setting a reconfigurable device by pushing, tapping or pulling the device to an accurate position

56、suffers from the weakness and compliance of the human body. High accuracy using such a method is therefore not feasi- ble, and in order to reach better accuracy by manual actuation a mechanical reduction by means of screws or other mechanisms is often necessary.Manual reconfiguring, whether with int

57、ernal or external actuators like screws or by dragging the device, takes time.Fig. 9 Structure of current technical realizations. Of these b, c, d and f have been tested or are under development at Linkoping UniversityRepositioning of a Flexapod 6 using manual pre-setting followed by fine adjusting

58、using screws takes approxi- mately 15 min for an experienced operator. Hence, this method is best applied when fixture changes are few, and consequently may take a longer time. This is beneficial, for example, in manufacturing prototypes or one-off products with long cycle times. In these cases, a d

59、edicated fixture is a big investment which may outweigh the setup time. Setup can be sped up by using motor-driven actuators instead of screws as shown in Fig. HYPERLINK l _bookmark8 9f, resulting in an automatic solution with exchangeable external actuators. There is still need to attach and detach

60、 the actuators in-between flexa- pods, which makes this approach useful for intermediate changeover frequency. A device called the Mini Flexapod, with internal manual actuators such as screws, has been developed at Linkoping University. This device is not based on the Stewart platform as the Flexapo