peter bailey, alexander slocum, scott ziegenhagen teradyne...

Peter Bailey, Alexander Slocum, Scott Ziegenhagen Teradyne case # 1412 4/6/2001

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KINEMATIC SPRING WASHERS AND COUPLING SYSTEM

The present invention relates to a wavy spring washer with integral bumps and

grooves to enable the washers to locate with respect to each other deterministically to

provide more accurate centering and to be less likely to slip off of each other when

stacked. In addition, the integral bumps and grooves enable the spring washers to mate

with corresponding bumps or grooves on other components to deterministically, that is

kinematically, locate them, and to also enable torques and forces to be transmitted

between components, so the washers act as a spring coupling between components.

BACKGROUND

Wavy spring washers are a well-known type of spring element that is widely used

in many applications in place of a cold spring, because they enable the same spring rate to

be achieved in a much smaller space. Belleville washers are another type of spring washer

that provides even greater spring force in a small place. However, spring washers, like

any other washer, do not have centering features, so they can become non-concentric,

which can cause loads to be borne unevenly. In addition, they provide only a spring force

function in a single direction. They cannot provide any locational capability.

If a kinematic coupling system could be incorporated into a wavy spring washer,

then it would be possible for the washer to achieve its spring function, and also to locate

itself with respect to other washers in a stack, or to other components such as those for

which it is providing spring function. Precision three-groove kinematic couplings, such

as described by coapplicant Slocum (A. Slocum Precision Machine Design, Prentice Hall,


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1991, Section 7.7), achieve stability, and good overall stiffness if the normals to the plane

of the contact force vectors bisect the angles of the triangle formed by the hemispheres

(e.g., balls) that lie in the grooves. To accomplish this effect in a spring washer requires

the creation of formed grooves and ball-like elements.

It should be noted that a kinematic coupling has been located on top of a spring

mount, as shown in US Patent #5,678, 944 by co-applicant Slocum et-al. What is desired

in this case is kinematic coupling that itself is spring compliant. US Patent #5,769,554 by

co-applicant Slocum shows a method for coupling sand cores where a kinematic coupling

ball indents itself in vees in sand cores. In addition, pending US Patents serial number

(XXXXXX) by co-applicant et-al. shows two components effectively kinematically

coupled with three balls in one component elastic/plastically deforming three

corresponding grooves in a second component to which it is being mated, thereby

allowing the components to be kinematically coupled and then bolted together to have a

tight interface such as would be required for the assembly of engine components. What is

still needed, however, is a simple springy kinematic element that can be stamped from

spring steel to kinematically locate itself or other components with respect to each other,

while providing significant compliance.

OBJECTS OF THE INVENTION

An object of the present invention, accordingly, is to provide a spring washer with

kinematically effective sets of three grooves and three bumps.

A further object is to size the bumps and grooves such that stacks of washers can

be nested where the top of a groove and mate with the bottom side of a groove, and the


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top of a bump can mate with the bottom side of a bump to achieve an increase in the

spring rate while maintaining alignment of the washers with respect to each other.

A further object is to size the bumps and grooves such that stacks of washers can

be nested where the top of a groove and mate with the bottom side of a bump to achieve a

decrease in the spring rate while maintaining alignment of the washers with respect to

each other.

Another object of the invention is to enable the washers to be deterministically, that is

kinematically, located with respect to a component to which they are providing spring

support to, by having bumps or grooves on the washers engaging bumps or grooves on

the component.

Still a further object of the invention is for the bumps to have a larger radius at the

inside diameter of the washer than at the outside diameter to minimize stresses in the

washer.

Still a further objective of the invention is for the washers to function as a

coupling element between two components, such that the kinematic location capability in

combination with the spring washer effect creates a compliant coupling between the two

components.

Still a further objective of the invention is to function as a slip clutch, whereby the

bumps and grooves that engage corresponding elements do so at an angle, and thus if a

drive torque is exceeded, they can slide to disengage, and the motion can be

accommodated by compression of the spring washer.

Other and further objects will be explained hereinafter and are more fully

delineated in the appended claims.


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SUMMARY

In summary, the invention includes a wavy spring washer with bumps on each of

the peaks and each of the valleys of a wavy spring washer, such that the tops of a bump

can act in effect like protrubances, and the bottoms of a bump can act in effect like

grooves, such that the washers can be stacked upon each other in phase where

protuberances mate with the grooves to enable a stack of such washers to act in parallel as

springs to increase the stiffness of a stack of washers, or if rotated with respect to each

other and stacked up each other where protuberances mate with the grooves to enable a

stack of such washers to act in series as springs to decrease the stiffness of a stack of

washers and increase the amount of spring travel, where the mating of protrubances and

grooves acts to keep the washers located in a deterministic manner. When the washers

are used to support components that have similar effective grooves and protrubances, the

washers can deterministically couple to the components thereby establish defined six

degree of freedom location between the components and the washers, but allowing

motion according to the spring rate of the washers; and in this manner, the washers can

act as a flexible coupling between components such that when two sets of washers are

utilized at two different coupling lengths of two nominally concentric shafts, one shaft

can be deterministically be located with respect to the other, with only desired axial

compliance between the two shafts. The axial compliance provided between the two

shafts enables the mating protrubances and grooves, which nominally contact at six points

at each interface to the components, enables the washers to act as slip clutches, thereby

enabling one shaft to transfer torque to another shaft, yet the axial compression capability

of the spring washer allows a bump to ride out of a groove and slide along until it mates

with the next groove should a desirable torque level be exceeded.


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Preferred and best mode designs and techniques are hereinafter detailed.

DRAWINGS

The invention will now be described with reference to the accompanying drawing

in which:

Fig. 1 is a side view of the prior art;

Fig. 2 is an isometric view of the prior art;

Fig. 3 is a side view of the current invention showing it t be a kinematic wavy

spring washer;

Fig. 4. is an isometric view of a stack of washers of the present invention acting as

springs physically in parallel;

Fig. 5 is an isometric view of a single washer of the present invention;

Fig. 6. is an isometric view of a stack of washers of the present invention acting as

springs physically in series;

Fig. 7 is an isometric view of an inner shaft;

Fig. 8 is an isometric view of an outer shaft;

Fig. 9 is an isometric exploded view of the two shafts and two kinematic wavy

spring washers;

Fig. 10 is an isometric view of the coupled shafts shown in Fig. 9;

Fig. 11 is a side cutaway view of the coupled shafts shown in Fig. 10;

Fig. 12 is an isometric of a rectangular kinematic wavy spring washer;

Fig. 13 is an isometric view of a lower block of an assembly;

Fig. 14 is an isometric of an upper block of an assembly;


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Fig. 15 is an isometric assembly of an upper and lower block kinematically

coupled with a kinematic wavy spring washer;

Fig. 16 is an end view of an upper and lower block kinematically coupled with a

kinematic wavy spring washer.

PREFERRED EMBODIMENT(S) OF THE INVENTION

Fig. 1 is a side view of the prior art, which shows a wavy spring washer 5 that is

commonly used to replace a traditional coiled spring. Fig. 2 is an isometric view of the

prior art 5 that shows the peaks 2a, 2b, and 2c and the valleys 3a, 3b, and 3c that

effectively form essentially a three dimensional sine wave. Nominally a stack of such

washers can be assembled where the tops of the peaks mate with the bottoms of peaks to

form a springs-in-parallel stack that has a stiffness about equal to the product of the

number of washers and the spring stiffness of a washer. Such a stack will be accurately

located with respect to each other; however, if the peaks of a washer contact the bottoms

of the valleys of a washer to form in effect a springs-in-series stack of washers, there are

no features to prevent the washers from displacing with respect to each other and thus

lose their concentricity. In the latter case, a shaft that runs down their center must

concentrically locate the washers, or the stack must be placed in a bore. Either way, the

prior art washers can function only as simple spring elements.

Fig. 3 is a side view of the current invention 9 showing it to be a kinematic wavy

spring washer. Fig. 4. is an isometric view of a stack of washers 9a and 9b of the present

invention acting as springs physically in parallel where the regions 16a, 17a, and 18a

represent regions where the tops of peaks of washer 9b mate with the bottoms of peaks of

washer 9a to in effect deterministically located one washer with respect to the other while


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enabling them to act as springs-in-series having a spring constant about equal to the

product of the number of washers and the spring constant of a single washer. Notes that

there are three other such regions occurring in the valleys of the washers, so the total

number of contact regions between the washers is six, but given the spring nature of the

material and since they would all be stamped from the same die, in this case the

overconstraint is not detrimental and any errors will average elastically thereby still

effectively guaranteeing a deterministic location between the washers.

Fig. 5 is an isometric view of a single kinematic wavy spring washer 9 showing in

detail each of the three peak and valley regions. There are three peaks 10b, 11b and 12b,

and three valleys 13b, 14b, and 15b. transition between peaks and valleys occurs via the

use of section pairs 10c and 13a, and 13c and 11a, and 11c and 14a, and 14c and 12a, and

12c and 15a, and 15c and 10a. These sections are all tangent to each other and to their

respective peaks and valleys. The effect is to create a sum of phase-shifted sinusoids that

enable the washer 9 to act as a spring washer and also as a quasi-kinematic coupling.

Fig. 6. is an isometric view of a stack of kinematic spring washers 9a and 9b of

the present invention acting as springs physically in series. Note the regions 16b, 17b,

and 18b where the peaks and valleys of the washers mate to form a quasi-kinematic

coupling. This keeps the washers concentric, while still allowing them to axial deflect as

spring elements. There is no danger that the washers could shift and lose concentricity.

This greater increases the reliability of a stack of such washers.

The bumps 10b, 11b, and 12b on the peaks of the washer are shown as a section of a very

small angle cone, or nearly a cylinder. This shape can have other forms including a

spherical “bump” or a canoe-like ball, as described in US Patent 5,711,647. In addition,


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the shape can be a larger angle cone, which can help to reduce stresses along the inner

diameter of the washer.

In a conventional wavy washer the amplitude of the wave is largely similar

between the outside and inside diameters (OD to ID). A consequence is that with a

smaller circumference, the metal at the ID has to flex through a larger angle and about a

smaller radius than that of the OD. It is thus being worked more aggressively, and will

become the weak link at the point of failure. This negative effect can be mitigated both

by increasing the effective length of the ID circumference and thinning the metal at this

zone. To increase the length (without increasing the overall amplitude or ID) a secondary

wave can be overlaid such that it appears as a section of a cone extending from maximum

amplitude at the ID to minimum at the OD. When this conical section is pressed in from a

blank it also thins the metal (as it is spread over a larger surface area). This has a

cooperating helpful effect in further reducing bending stresses. The conical section need

not be too extreme to compensate for the varying stresses between OD and ID. A washer

given this treatment will have no weak link and will thus make better use of its material.

This conical section can be combined with the desirable locating features, which

are another object of this invention. The locating peaks and troughs can increase in

amplitude between OD and ID such that in one extreme they have zero amplitude at the

OD and extend uniformly towards their maximum amplitude at the ID.

While the invention has been described with reference to circular washers with

three waves, other shapes and styles are possible and may indeed be desirable for some

applications. For example, if the washer has only two waves it can have greater

amplitude for the same metal stress when flattened. This enables a bigger compression

ratio. It does not however locate kinematically and can only be stacked as a pair before


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the stack becomes unstable. However, to locate a two-wave washer one could use a

socket and dimple style, as it locates about 2 axes rather than just one. Of course this style

would not be universally useful as it is over-constrained and hence less kinematic. If the

washer has four or more waves it's compression ratio will decrease and it's quasi -

kinematic location becomes over-constrained; however they may be benefits for washers

with large diameters compared to their thickness and/or width in generating a greater

number of contact zones.

Kinematic stacking washers need to have at least 3 upper and 3 lower contact

zones with two-each contact points or lines (for a total of six contact points or lines). This

can be accommodated with shapes other than round. One other style that particularly

lends itself to this objective is a hexagonal washer. In this embodiment the waves would

be principally carried in the side length defined by the inner boundary hexagon, while the

extensions afforded by the longer sides of the outer boundary hexagon can be deformed

into the stacking location features.

Fig. 7 is an isometric view of an inner shaft 30 with a base 38 and surfaces 32 and

34 which each have peaks 31c, 31b, 31a and 33c, 33b (and not showable because of the

isometric view, but would otherwise be 33a) respectively. Threaded hole 35 in the top

plate 32 will allow for the axial preloading of an outer shaft. Fig. 8 is an isometric view

of an outer shaft 40 with surfaces 42 and 44 which each have peaks 41c, 41b, 41a and

43c, 43b (and not showable because of the isometric view, but would otherwise be 43a)

respectively. Hole 45 in the top plate 42 will allow for the axial preloading to an inner

shaft.

Fig. 9 is an isometric exploded view of the two shafts 40 and 30 and two

kinematic wavy spring washers 19a and 19b. The kinematic wavy spring washer 19a can


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be seen coupling to one end of the shaft 30 with the bottoms of its bumps in its valleys

engaging the tops of bumps 33c and 33b (and 33a not shown) to form a quasi kinematic

coupling between the washer and the plate 34. At the other end of the shaft 30, kinematic

wavy spring washer 19b, of a smaller diameter than washer 19a, has the bottoms of its

bumps in its valleys engaging the tops of bumps 31c 31b and 31a to form a quasi-

kinematic coupling between the washer and the plate 32. Bumps 10b’ and 10c’ on

washer 19a will engage the bottoms of bumps 43c and 43b on shaft 40 respectively (once

again, the third bump pair cannot be seen in this view). Similarly, bumps 10b’’ and 10c’’

on washer 19b will engage the bottoms of bumps 41c and 41b on shaft 40 respectively

(once again, the third bump pair cannot be seen in this view, only bump 41a)

Fig. 10 is an isometric view of the coupled shafts shown in Fig. 9 where shaft 40

is fitted over shaft 30 and the kinematic coupling regions 43b and 43c (43a cannot be

seen in this view) couples the washer 19a kinematically to plate 44 attached to shaft 40,

and the kinematic coupling regions 33c (33a and 33b cannot be seen in this view) also

kinematically couples washer 19a to plate 34 attached to shaft 30. Plate 42 on top of

shaft 40 has bumps 41a, 41b, and 41c, the undersides of which are kinematicaly coupled

to a washer 19b not shown in this view, but shown in cross section in Fig. 11. Bolt 50

preloads shaft 40 to shaft 30 and prevents them from separating, while allowing axial

compliance to occur.

Fig. 11 is a side cutaway view of the coupled shafts shown in Fig. 10 where the

bolt 50 passes through plate 42 to engage threaded portion 35 in plate 32 attached to inner

shaft 30. The upper portion of the figure shows kinematic coupling regions 41a and 41b

(41c is not shown) to kinematically couple washer 19b to the outer shaft 40, and

kinematic coupling regions 31a and 31c (31b is not shown) to kinematically couple


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washer 19b to the inner shaft 30. At the bottom of the figure, kinematic coupling regions

43c (43a and 43b are not shown) kinematically couple washer 19a to shaft 40, and

kinematic coupling regions 33c (33a and 33b are not shown) kinematicaly couples washer

19a to inner shaft 30. Two distinct regions of kinematic coupling between the tops and

bottoms of the shafts are possible because of the spring nature of the washers 19a and

19b; however, as a pair, they will rigidly couple the two shafts together, while allowing

some axial compliance. This greatly eases the assembly of the two shafts, and increases

the accuracy and ease with which they can be concentrically assembled. Inner shaft 30

may then have torque transmitted to it by surface 38 which may actually have an integral

motor attached to it. There are many such applications of this type of coupling, most

notably to replace expensive splines in many types of machines. A single such coupling

interface (one washer only) can also form an effective motor coupling between a motor

shaft and a load.

Figs. 3-11 have shown a kinematic wavy spring washer and assembly where the

washer has bumps on each of its peaks and valleys such that the top of a bump can mate

with the bottom of a bump to enable the washers to deterministically locate, as a three

groove-three bump quasi kinematic coupling, with respect to each other to form either an

effectively series or parallel series of washers. The washers can be used to

deterministically locate with axial compliance two components, with similar mating

bumps on them, with respect to each other and because they are compliant and the

coupling is quasi kinematic, two or more sets of washers can be located along the lengths

of the components to enable one component to be rigidly deterministically located with

respect to the other component with the exception of allowing a degree of axial

compliance offered by the washers, and thus also being protected against overtorquing by


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the ability of the bumps to slide out of the bottom sides, grooves, of the mating bumps’

undersides and to slip in rotation until the next set of bumps is engaged.

The location features have also thus far been described as extending out in a

common direction such that for example plugs face upwards and sockets face downwards,

thereby enabling a continuous series stack. When employed as a coupling, it may be

advantageous to have the same locating features extending both up and down so that any

mounting hubs against which the wavy washers might bare could also be identical. Such a

washer can stack with any number of the previously described stackable washers, but

must be at the appropriate end of the stack. It cannot stack with it's own kind.

One embodiment of a coupling working on this principle would feature identical

mounting hubs suitably clamped to both motor and load shafts such that one or more

washers can be trapped in between. If a single washer is used the coupling can support

three degrees of freedom. If two or more are used it can support all five. The assembly is

preloaded on installation as determined by the axial offset of the two mounting hubs.

The hubs can include features to assist in retaining the washer(s) during installation and

preventing them from becoming irrevocably displaced. Such a feature could be a

cylindrical wall loosely surrounding the washer, but such as not to interfere during use

when the washer(s) locates kinematically against each hub.

The kinematic wavy spring washer also need not be round as shown in Fig. 12

where washer 200 is rectangular with three downward facing crowned cone protrusions

202a, 202b, and 202c on flexing arms 204a, 204b, and 204c. Three upward facing

crowned cone protrusions 201a, 201b, and 201c on flexing arms 203a, 203b, and 203c.

Wavy kinematic spring 200 would fit on lower black 300 shown in Fig. 13, which has

vee-grooves 301, 302, and 303 into which crowned cones 202a, 202b, and 202c would


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make contact at 2 points each for a total of six points of kinematic contact. Lower block

300 also has a riser 305 onto which another part’s vertical position would be established

as the kinematic wave washer 200 flexes. The upper block 400 to be kinematically

coupled to the lower block 300 is shown in Fig. 14 which has vee-grooves 401, 402, and

403 into which crowned cones 201a, 201b, and 201c would make contact at 2 points each

for a total of six points of kinematic contact.

The kinematic assembly of upper block 400 to lower block 300 by the action of

kinematic wavy spring washer 200 is shown in Figs. 15 and 16. Note that of the blocks

were to be compressed, the underside of upper block 400 would contact the top of riser

305 to limit its vertical travel, or actually provide a rigid interface should the two blocks

be rigidly coupled. In this manner, the kinematic wavy spring washer works like a two-

sided version of the flexural kinematic coupling described by US Patent #5,678, 944. An

example of applications requiring this configuration is the easy or automatic location and

changing of electrical contacts or other tooling.

An example of the use of this type of arrangement is an electrical contactor as

used in Automated Test Equipment (ATE), and a Handler Interface Board (HIB) on a

handling machine that presents parts to be tested to the ATE. In this application, the

contactors frequently become clogged with solder as they contact the solder leads of

devices under test (DUTs), and they need to be rapidly changed.

Another example of the use of this type of arrangement would be the coupling of a

washing machine drum to the post that extends from the transmission. It is needed to

blindly couple the two with high backlash-free torque capacity to minimize noise.

Another application is the use of a single or double kinematic wavy spring

arrangement to couple the shaft of an electric motor to another shaft, such as a ballscrew


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shaft. In the even of overtorquing, the washer can compress by the action of the bumps

sliding out of their mating grooves, yet then they re-engage with the next set of grooves as

the torque level drops.

Further modifications of the invention will also occur to persons skilled in the art,

and all such are deemed to fall within the spirit and scope of the invention as defined by

the appended claims.


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What is claimed is:

1. A wavy spring washer with integral bumps and grooves superimposed on the tops

and bottoms of the waves respectively to enable the washers to locate with respect

to each other deterministically to provide more accurate centering and to be less

likely to slip off of each other when stacked, and such that the integral bumps and

grooves enable the spring washers to mate with corresponding bumps or grooves

on other components to deterministically, that is kinematically, locate them, and

to also enable torques and forces to be transmitted between components, so the

washers act as a spring coupling between components.

2. The system as claimed in claim 1 where two components are to be kinematically

located with respect to each other with compliance between them.

3. The system as claimed in claim 1 where two components are to be kinematically

located with respect to each other with space between them, and then squeezed

together, thereby compressing the kinematic wavy spring washer, so as to achieve

surface contact between the components.

4. A wavy spring washer as claimed in claim 1 with a secondary wave superimposed

on its inner diameter region to reduce circumferential stresses when the washer is

compressed.

5. A system as claimed in claim 1 where one component is a shaft, and the other

component is a motor shaft so as to flexibly kinematically couple the motor shaft

to the shaft with a high degree of torsional stiffness.

6. The system as claimed in claim 5 where the flexibility of the kinematic wavy

spring washer enables the bumps and grooves to slide out from each other in the


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event of overtorquing, and then mate back together again as the shafts spin

relative to each other.

7. A system to couple two components with large aspect ratios where the bases of

the objects have flanges with bumps and grooves that mate correspondingly with

grooves and bumps on a wavy spring washer, and the tops of the objects have

surfaces with bumps and grooves that mate correspondingly with grooves and

bumps on a second wavy spring washer, such that the top and bottoms of the

components are kinematically located with respect to each other and yet are not

over constrained due to the flexing action of the wavy spring washer, thereby

allowing the long objects to be kinematically flexibly coupled.

8. The systems as claimed in claim 7 where the components are the drum of a

washing machine and the transmission post of a washing machine.

9. The system as claimed in claim 7 where the components are an electrical

contactor as used in Automated Test Equipment, and a Handler Interface Board.


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Abstract

A kinematic wavy spring washer and assembly where the washer has bumps on

each of its peaks and valleys such that the top of a bump can mate with the bottom of a

bump to enable the washers to deterministically locate, as a three groove-three bump

quasi kinematic coupling, with respect to each other to form either an effectively series or

parallel series of washers. The washers can be used to deterministically locate with axial

compliance two components, with similar mating bumps on them, with respect to each

other and because they are compliant and the coupling is quasi kinematic, two or more

sets of washers can be located along the lengths of the components to enable one

component to be rigidly deterministically located with respect to the other component

with the exception of allowing a degree of axial compliance offered by the washers, and

thus also being protected against overtorquing by the ability of the bumps to slide out of

the bottom sides, grooves, of the mating bumps’ undersides and to slip in rotation until

the next set of bumps is engaged.

peter bailey, alexander slocum, scott ziegenhagen teradyne...

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