GB2191467A - Compliant link - Google Patents

Description

GB2191467A 1 SPECIFICATION We have discovered that a compliant link age

having three degrees of freedom in a sin Compliant ink gle plane can be provided by a pair of plates which are free to slide relative to each other The invention relates to a compliant linkage 70 but which are provided with means to cause device which provides three degrees of freethe plates to be attracted to each other in a dom, e.g., one used in registering workpieces. particular orientation so as to resiliently resist In manufacturing processes involving gener- relative lateral and rotational displacements of ally flat plate-like workpieces, it is a standard the plates.

practice to secure the workpiece in a defined 75 In preferred embodiments magnetism is location on a flat work surface such as a va- used to cause the plates to attract each other cuum chuck by registering two orthogonal in the desired orientation; the plates are made edges of the workpiece against three registra- of nonferrous material, and there are discrete tion points defining a corner. This is the com- magnets at corresponding locations on oppos- mon practice, for example, in the hybrid circu- 80 ing surfaces of the upper and lower plates; its manufacturing process, wherein ceramic and the relative sliding between the two plates are used as substrates upon which cir- plates is provided by an air cushion between cuitry is created by the silkscreening of con- them created by compressed air admitted into ductive and resistive pastes. Subsequently, re- the interface of the plates through one or sistors within the circuitry are modified, usu- 85 more orifices.

ally by automatic laser trimming, to adjust The preferred use for the compliant linkage their resistance to within a specified tolerance is in apparatus for mechanically registering a of the desired value. In addition, adtive elec- flat workpiece on a flat work surface in a tronic components are often incorporated registration corner. A displacement mechanism within the circuit; the loading of these compo- 90 providing displacement in a direction generally nents is also generally done by automatic toward the corner is connected to the upper equipment. Repeatable registration of the plate, and a workpiece holder is connected to workpiece relative to the workholders of the the lower plate. The displacement mechanism various machines in the production line is escauses displacement of the upper plate, lower sential if expensive and time consuming 95 plate, workpiece holder and workpiece toward alignment procedures for each workpiece are the registration corner, and the plates are free to be avoided. to slide relative to each other in three degrees Registration of the workpieces may be done of freedom, against the forces of attraction, manually or mechanically. Manual registration after the workpiece makes initial contact with is extremely simple in concept: the operator 100 the registration corner, permitting registration places the workpiece on the work surface with the registration corner.

(e.g., vacuum chuck) and slides it into contact Preferably the displacement mechanism in with the three registration points (usually tool- cludes a parallelogram linkage connected to ing pins); the human hand has no difficulty the upper plate so that downward motion, ap ascertaining that the workpiece has made con- 105 plied for example by a loader arm, of the up tact with all three registration points and that per member of the linkage toward the work no more force or motion is required. Mechani- surface is converted into horizontal motion cal registration is necessary when the work- along the work surface toward the registration pieces are to be loaded by automatic ma- corner. Thus, after the workpiece has been chines (e.g.,---pickand place- robots) without 110 placed on the work surface, the continued operator intervention. When such a machine downward motion of the loader arm causes places a workpiece on the work surface, the collapsing of the linkage, and drives the work workpiece will in general need to be translated piece toward the registration corner automati in two axes (e.g., X and Y) and rotated cally.

through some angle (Theta) in order to make 115 Other features and advantages of the inven contact with the registration points. Mechanition will be apparent from the following de cal registration has generally been accom- scription of the preferred embodiment thereof, plished by incorporating in the workholder of and from the drawings in which:

each process machine some form of gripping Fig. 1 is a diagrammatic perspective view of mechanism, typically including a pair of springworkpiece registration apparatus according to loaded arms which push the workpiece into the invention in one position; the registration corner from the variable posi- Fig. 2 is a diagrammatic perspective view of tion at which it was deposited by the loader. the Fig. 1 apparatus showing the workpiece in Such mechanisms work well when configured a registered position; and for a particular size and shape of workpiece, 125 Fig. 3 is an exploded perspective view but their reliability can suffer when a variety of showing the compliant linkage and workpiece workpiece sizes must be accommodated; and holding components of the Fig. 1 apparatus.

they represent a certain level of complexity Referring to Fig. 1, there is shown appara since they contain in general several moving tus 10 for registering flat workpiece 12 (for parts. 130 example a PCB or ceramic substrate) into a 2 GB2191467A 2 position 14 of a registration corner defined by lower and upper plates 22, 24 begin to slide three registration points 16 on flat work sur- relative to each other, because upper plate 24 face 18. Device 10 includes vacuum engage- continues to translate along the longitudinal ment members 20 connected to vacuum plate axes of bars 38, 42 while lower plate 22 has 21, lower and upper plates 22, 24 (separated 70 stopped moving in one axis. Because the from each other slightly by pressurized air magnetic force tending to align the plates is supplied between them and attracted to and generally at 45 degrees toward the registra resiliently aligned with one another by mag- tion corner, workpiece 12 slides relative to nets 26, Fig. 3) and parallelogram linkage 28. the engaged registration pin 16 toward the Referring to Fig. 3, it is seen that lower 75 corner until the second and third pins are en plate 21 has vacuum hose 33 connected to it countered. In general, downward motion of for selectively applying vacuum to engagement upper block 44 continues beyond this point:

members 20 to engage and disengage work- that is, enough lateral motion has been pro piece 12. Magnets 26 are secured in recesses vided by linkage 28 so that some of it must 30 of lower plate 24 via epoxy adhesive. 80 be lost in further relative displacement be Magnets 26 are similarly secured in similar tween the plates. If this were not the case, aligned recesses (not shown) in the lower sur- registration might not be achieved, because face of upper plate 24 and secured therein via motion of workpiece 12 might have stopped epoxy adhesive. Four bolts 32 (only one short of engagement with the third pin.

shown) secure vacuum plate 21 to lower plate 85 An advantage of the invention is the ability, 22. Four bolts 34 (only one shown) secure with essentially no wearing parts, to register the lower horizontal bars 38 of parallelogram various sizes of workpieces onto virtually any linkage 28 to upper plate 24. The'north poles flat work surface, eliminating the need for spe of magnets 26 on plate 22 face the south cial mechanisms in the workholders of the poles of magnets 26 on plate 24. Upper plate 90 various hybrid circuit production machines.

24 has pressurized air hose 36 connected to Other embodiments are feasible. For it and passages within plate 24 leading to a example, as an alternative permanent magnets plurality of orifices in the lower surface of 26, electromagnets can be used, and other plate 24 to provide an air cushion between means can be used to provide sliding in three the plates. 95 degrees between the plates (for example, ball Parallelogram linkage 28 includes a pair of bearings). Also, in place of the magnets and arms 40 pivotally mounted at their bottom the air cushion, springs can be used to pro ends to bars 38 and at their upper ends to vide both the resilience in three degrees and bars 42 secured to upper block 44, which is the attraction of the two plates toward each secured to the loader arm of a loading ma- 100 other in a particular orientation. Also, instead chine (e.g., a pick and place or other robot) of having all north poles on one plate face providing downward motion of upper block 44 one direction and be opposed by all south perpendicular to and toward work surface 18. poles of magnets on the other plate, two of The longitudinal axes of bars 38, 42 of paral- the magnets on one plate could have their lelogram linkage 28 are at 45' angles with the 105 north poles facing the other plate, and two edges of corner position 14 so that move- could have their south poles facing the other ment of plates 21, 22, 24 and workpiece 12 plate, to adjust the stiffness of the resilient is in this direction after workpiece 12 contacts attraction. Also, by incorporating ferromag work surface 18. Magnets 26 are sufficiently netic materials (e.g., soft iron) in the flux path, strong to maintain attraction between plates 110 one can adjust the relative stiffness in each of 22, 24 even after there has been substantial the three axes, as well as the ratio of total (for example, about 1 cm) relative lateral mo- vertical attraction force to resilience in the tion in any direction between them. horizontal plane. Other flat workpieces such as When the loader arm (not shown) on which printed circuit boards, glass, or sheet metal upper block 44 of linkage 28 is attached de- 115 can be registered with the apparatus. Also, scends, a point is reached in the motion when the compliant linkage could be used in other workpiece 12 first makes contact with work apparatus besides a flat workpiece registration surface 18. At this point linkage 28 is still in device; it can be used, for example, to load the open (i.e., arms 40 nearly vertical) posi- integrated circuits onto a board, the pins of tion; lower and upper plates 22, 24 are 120 the integrated circuit chips being directed to aligned with each other, and workpiece 12 is holes having guidance surfaces leading to at some position removed from registration them.

points 16. As the loader arm (and upper block Also, plural workpieces could be registered 44 of linkage 28) continue to descend, linkage simultaneously with plural registration corners 28 begins to collapse (as shown in Fig. 1), 125 by providing plural lower plates and workpiece resulting in translation of upper plate 24 to- holders sliding relative to and attracted to dif ward the registration corner. Lower plate 22 ferent portions of a single upper plate.

follows this motion, and so does workpiece

Claims (10)

12, of course, until workpiece 12 makes con- CLAIMS tact with the first

registration point 16. Here 130 1. Compliant linkage apparatus for providing, 3 GB2191467A 3 in a single stage, three degrees of freedom in said attracting means comprises plural discrete a single plane, said apparatus comprising: magnets at corresponding locations on oppos an upper plate; ing surfaces of said upper and lower plates.

a lower plate under the upper plate; 11. The apparatus of Claim 10, wherein sliding means for allowing said upper and 70 there are four pairs of said magnets.

lower plates to slide relative to each other in 12. The apparatus of Claims 9 or 10 X, Y, and theta; and wherein said magnets are permanent magnets.

orientation means for causing said plates to 13. The apparatus of Claims 9 or 10 attract each other in a particular orientation to wherein said magnets are electromagnets.

resiliently resist relative lateral and rotational 75 14. The apparatus of any of Claims 8 to displacements of said plates. 13, wherein said workpiece holder employs

2. The apparatus of claim 1, wherein said vacuum engagement.

orientation means employs magnetism to 15. The apparatus of any of Claims 8 to cause said plates to attract each other. 14, wherein said displacement means includes

3. The apparatus of claim 2, wherein said 80 means for converting motion in a direction plates are made of nonferrous material, and transverse to said work surface to said direc said attracting means comprises plural discrete tion toward said corner.

magnets at corresponding locations on oppos- 16. The apparatus of Claim 15, wherein ing surfaces of said upper and lower plates. said displacement means includes a parallelo

4. The apparatus of claim 3, wherein there 85 gram linkage.

are four pairs of said magnets. 17. The apparatus of any of Claims 8 to

5. The apparatus of claims 3 or 4, wherein 16, Wherein said work surface carries a plu said magnets are permanent magriets. rality of means defining registration corners,

6. The apparatus of Claims 3 or 4, wherein and further comprising multiple lower plates said magnets are electromagnets. 90 and one large upper plate, each lower plate

7. The apparatus of any preceding claim, being equipped with a workpiece holder to wherein said sliding means comprises means carry a single workpiece independent of the to supply compressed air into the interface of others, so that multiple workpieces may be said plates through one or more orifices. registered simultaneously.

8. Apparatus for the mechanical registration 95 18. The apparatus of any preceding claim, of a flat workpiece on a flat work surface wherein said sliding means included ball bear carrying means defining a registration corner ings.

for receiving a corresponding corner of said 19. The apparatus of Claims 1 or 8, workpiece, said apparatus comprising: wherein said orientation means is provided by displacement means supported above said 100 resilient springs connected between said work surface for providing displacement in a plates.

direction toward said corner; 20. Compliant linkage apparatus substantially an upper plate connected to said displace- as hereinbefore described with reference to ment means; and as shown in the accompanying drawings.

a lower plate under the upper plate; 105 21. For the mechanical registration of a flat sliding means for allowing said upper and workpiece on a flat work surface, the appara lower plates to slide relative to each other in tus being substantially as hereinbefore de X, Y, and theta; scribed with reference to and as shown in the orientation means for causing said plates to accompanying drawings.

attract each other in a particular orientation to Printed for Her Majesty's Stationery Office resiliently resist relative lateral and rotational by Burgess & Son (Abingdon) Ltd, Dd 8991685, 1987.

displacements of said plates; Published at The Patent Office, 25 Southampton Buildings, and a workpiece holder connected to said London, WC2A 'I AY, from which copies may be obtained.

lower plate for engaging said workpiece under said lower plate and above said work surface:

said displacement means operatively causing displacement of said upper plate, lower plate, workpiece holder and workpiece toward said corner; and said sliding means and orientation means permitting three degrees of freedom of resilient movement of said workpiece with respect to said displacement means after initial contact of said workpiece with said means defining a registration corner, permitting regis- tration with said registration corner.

9. The apparatus of Claim 8, wherein said orientation means employs magnetism to cause said plates to attract each other.

10. The apparatus of Claim 9, wherein said plates are made of nonferrous material, and