An adjustable length strut having a unique locking device. An annular spring within a housing surrounds an actuator rod. An actuator member engages one end of the annular spring axially compressing it and causing radial bulging resulting in locking the rod in position relative to the housing. Numerous embodiments are disclosed which may replace gas springs in such applications as seat height adjusters, chair arm adjusters and seatback adjusters. An embodiment is disclosed employing a switch to activate and deactivate the actuator member.

BACKGROUND AND SUMMARY OF THE INVENTION 
The present invention is directed to improved strut designs. More 
particularly, this invention involves a plurality of embodiments of struts 
and other devices which can be adjusted over a range of positions and 
locked in the position desired. The present application is related to 
application Ser. No. entitled "Locking and Positioning Device" filed 
contemporaneously herewith. 
The present invention involves a number of applications of surface effect 
locking devices, the surface effect principles having been disclosed in 
conjunction with dampers in commonly assigned U.S. Pat. Nos. 5,183,137 and 
5,257,680 which are incorporated by reference. One particular application 
involves seat height adjustment devices. A second such application is in 
the area of seat back adjustment. A third utilization is in chair arm 
height adjustment. Currently, a variety of gas springs and hydraulic 
cylinders are being utilized to provide the desired adjustments. 
These devices have a number of difficulties. First, most such devices lack 
any damping in either the extending or retracting direction. Stopping of 
movement, then, is typically abrupt, with a hard stop providing stroke 
limits. High pressure sealing requirements necessitate strict 
manufacturing tolerances, typically accelerate wear of the seals resulting 
in leakage and the possibility of catastrophic failure. For certain 
applications, the ratio of stroke length to device length proves to be too 
small for many of these devices (i.e., inherent inefficiencies and lack of 
flexibility result in these mechanisms providing limited stroke length in 
a lengthy package). Recent legislation relating to the ergonomics of 
office furniture have made existing adjustment mechanisms inadequate to 
meet the legislative requirements. 
The present invention provides an adjustable, lockable strut which 
overcomes these difficulties. The strut typically includes an outer 
cylindrical member; an inner cylindrical member; locking means including a 
first annular spring member surrounding at least a portion of an outer 
periphery of said inner cylindrical member and engaging at least a portion 
of an inner periphery of said outer cylindrical member; an element for 
causing said annular spring member to undergo bulging normal to the 
locking surfaces and in direct contact with a portion of said annular 
spring member to cause said radial bulging thereby increasing a resistance 
force exerted by said annular spring member to movement between said inner 
and said outer cylindrical members; an actuator moving said element for 
causing said annular spring member to undergo radial bulging, from a first 
bulge-producing position to a second inoperative position where said 
resistance force is significantly reduced; whereby said inner cylindrical 
member can be locked in a first axial position with respect to said outer 
cylindrical member by said spring member, unlocked by said actuator and 
moved to a second alternate axial position and relocked in said second 
alternate axial position. 
In one preferred embodiment, the first spring comprises an elastomeric 
spring comprised of an annular ring positioned on a piston member within a 
cylinder. The elastomer is caused to bulge outwardly into engagement with 
the inner wall of the cylinder producing the surface effect locking force 
which inhibits axial movement. The elastomeric spring can be made to bulge 
by axially compressing the ring or by camming a plurality of movable 
elements into engagement with one of its axially extending surfaces. In 
the case of the axial compression, a second spring is used to bias a 
compression member into engagement with an end portion of the first 
spring. As another feature, a second elastomeric ring rides upon a tapered 
surface to provide a directionally increasing/decreasing baseline 
resistance to motion of the second cylindrical member with respect to the 
first cylindrical member. This second damping ring helps provide a smooth 
feel to the relative movement of the elements. A third, or return, spring 
can be used to bias the piston member to an extended position within the 
cylinder. Such a feature is useful in position adjustment devices such as 
seat-height, arm-height and seat-back adjustment devices and other 
applications currently utilizing gas springs. 
In a second embodiment, the locking spring is formed as a coil spring which 
engages an elastomeric sleeve to produce the desired locking. Axial 
compression of the coil spring causes radial bulging as with the 
elastomeric spring. In an alternate embodiment, the locking spring takes 
the form of a fluid filling a portion of the cylinder and a reservoir of 
fluid which may take the form of an auxiliary chamber atop the cylinder or 
a secondary cylinder surrounding the first cylinder. A valve permits fluid 
to flow from the cylinder to the auxiliary chamber so that the relative 
positions of the inner and outer cylinders can be adjusted. 
It is an additional feature of this invention that the locking mechanism 
may be actuated remotely using an electromagnetic coil to provide an 
actively variable damper whose damping characteristics can be switched 
between two damping levels. 
Various other features, advantages and characteristics of the present 
invention will become apparent after reading the following detailed 
description and the addended claims.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
A first embodiment of the adjustable, lockable strut of the present 
invention is depicted in FIG. 1 generally at 10. FIG. 1A depicts an office 
chair 11 with a seat portion 13, seat back 15, a pedestal 17 and castered 
leg portion 19. A first position for the adjustable strut 10 of the 
present invention is position A within the pedestal 17 to make the height 
of seat portion 13 adjustable. A downsized version of any of the 
embodiments of the strut 10 of the present invention can be used in 
position B shown in FIG. 1A to adjust the position of seat back 15 
relative to seat portion 13. Still a third use of a midsized strut 10 is 
shown in FIG. 1B at position C. In this application, strut 10 can be used 
to adjust the arm height of the office chair. Actuator lever 21 can be 
manually pulled downward to release the locking mechanism 20 which will be 
described in greater detail infra. The sister application noted supra, 
describes and claims various multiple degrees of freedom adjustment 
devices for use in chair arm adjustment applications. It will be 
appreciated that the adjustable, lockable strut 10 of the present 
invention can be utilized in many other potential applications including 
many of the current uses of gas springs. 
Returning to FIG. 1, adjustable, lockable strut 10 a first outer 
cylindrical member 12 which is closed at a first end by element 14 which 
has attachment groove 16 which permits securement to a first component 
such as a chair base, or the like, by a circlip, not shown. The second 
opposite end is closed by element 18. The locking mechanism 20 includes an 
inner cylindrical member 23 with a first end 22 with means 24 attachable 
to a second component such as a chair seat, or the like. Inner cylindrical 
member 23 includes an inner generally cylindrical piston member or pilot 
26 and an actuator 36. Piston member 26 has a first forward, generally 
cylindrical portion 28 and a second trailing portion 30 which tapers 
outwardly toward first end 22 by an amount which may vary between 
1.degree. and 5.degree.. The amount of taper is selected to produce a 
lateral compression of between 5 and 20% of sleeve 34. Elastomeric members 
32, 34 are preferably coated with either powdered silicon resin or 
powdered organic rosin. This coating increases frictional resistance to 
sliding by the elastomeric members 32, 34 relative to outer cylindrical 
member 12 when the elastomeric member is bulging and decreases frictional 
resistance when the elastomeric member is not bulging. 
First cylindrical portion 28 is encircled by a spring 32 which in this 
embodiment takes the form of an elastomeric ring, and second tapering 
portion has an elastomeric element 34 girding it. An end stop 35 is spaced 
from intermediate stop 33 by a distance greater than the length of ring 
34. Accordingly, ring 34 can move axially on tapered section 30 as can be 
seen by noting the difference in position thereof between FIGS. 1 and 2. 
As ring 34 rides up the taper, the level of resistance to motion will 
increase. Ring 34 provides an initial resistance to motion when actuator 
36 is unlocked, a resistance which increases for motion of the piston 26 
in a contracting direction and which decreases for motion in an expanding 
direction. 
Return spring 38 biases piston 26 toward the second end of outer cylinder 
12 as shown in FIG. 2. Hence, when the locking mechanism 20 is released, 
return spring 38 moves piston 26 toward the right in FIG. 1. In the chair 
height adjustment application, when the actuator 36 is engaged and the 
seat unweighted, the return spring will raise the chair to its maximum 
height (FIG. 2). With the actuator still engaged, the seat operator can 
sit in the chair and lower it to the height desired and release the 
actuator 36 to lock the chair at the desired height. Ring 34 will move to 
its lowermost position (leftmost in FIG. 1) to exert a minimum level of 
resistance to movement as the spring forces the chair upwardly (to the 
right in FIG. 1). The ring 34 will climb the taper of section 30 
increasing the pressure exerted on inner surface of outer cylinder 12 to 
slow the rate of downward movement against the upward bias of spring 38 to 
facilitate the desired adjustment. 
The actuator mechanism includes actuator rod 40 extending through the 
center of outer sleeve 42 and piston 26 of locking mechanism 20. The end 
of rod 40 is secured to actuator plate or element 44 so element 44 moves 
with rod 40. Actuator element 44 has a protruding annular rim 45 which may 
be integral or formed by a separate washer-like member. The opposite end 
of rod 40 is biased by spring 46 to an extended position (to the right in 
FIG. 1). This spring biasing causes element 44 to axially compress 
elastomeric ring 32 to cause radial expansion of locking mechanism 20 in 
position to space the first and second components relatively, as desired. 
A second embodiment of the adjustable lockable strut is depicted in FIG. 
1B. This intermediate length strut 10 is shown in a chair arm adjustment 
application. Locking mechanism 20a comprises an elastomeric spring 32a 
encircling inner member 23a and abutting intermediate stop 33a. Biasing 
spring 46a biases actuator element 44a into the leading end of elastomeric 
spring 32a axially compressing the elastomer causing radial expansion 
which locks inner cylindrical member 23a in place relative to outer 
cylindrical member 12a. Actuator rod 40a has a plunger 48a formed on one 
end thereof which engages the top of spring-biased element 50a which is 
attached to actuator rod extension 52a. Rod extension 52a projects through 
end cap 14a and is secured to actuator element 44a. When actuator lever 
21a is moved downwardly by pulling on knob 25a, actuator rod 40a overcomes 
the biasing force of spring 46a allowing elastomeric spring 32a to expand 
axially thereby contracting radially. The chair arm 27 can then be moved 
up and down (as well as rotationally about the axis of inner member 23a) 
to adjust the height thereof as desired. A support spring (not shown) can 
be added to raise the arm to its uppermost position when unlocked, if 
desired. 
FIGS. 3 and 4 depict two fluid embodiments of adjustable lockable struts 
10b and 10c. Inner cylindrical members 23b and 23c are equipped with a 
plurality of protrusions 54b and 54c, respectively, which serve to indent 
elastomeric sleeve 56b and 56c which are secured within outer cylindrical 
members 12b and 12c. Protrusions 54b and 54c interact with elastomeric 
sleeves 56b and 56c to serve as a fluid seal and to cause surface effect 
(a combination of hysteresis and friction) damping in the manner described 
in U.S. Pat. No. 5,257,680 which is hereby incorporated by reference. 
These embodiments have been designed for utilization in the 
seat-height-adjustment application where the weight of the chair seat will 
be countered by the force of the return springs 38b and 38c and the 
pressures of fluids 58b and 58c. 
The fluid may be either compressible (pneumatic) or incompressible 
(hydraulic) with the resultant systems having very different 
characteristics. If the fluid 58b or 58c is compressible, the fluid volume 
will behave as a second spring acting in parallel to spring 38b and 38c. 
If the fluid is incompressible, the system will lock in place and perform 
very stiffly. Some of the stiffness can be designed out of the system by 
the configuration of the valves 60b and 60c which control flow between 
high pressure cylinder 12b, 12c and accumulator 62b, 62c. In addition, a 
portion of closed cell foam can be employed in the upper portion of 
elastomeric sleeves 56b, 56c to provide added compliance to the system. 
In the FIG. 3 embodiment, diaphragm 64b biases actuator 36b to an up, or 
closed, position in which valve 60b is closed preventing fluid from 
flowing between accumulator 62b and cylinder 12b. By depressing actuator 
36b against the bias of diaphragm 64b, valve 60b is opened permitting 
fluid to flow. If the seat 13 is unweighted, spring 38b will extend inner 
cylindrical member 23b to its fully extended position. If the chair 
operator is occupying the seat 13 when actuator 36b is depressed, the seat 
13 will lower until the desired height is reached and the actuator 36b is 
released. By sizing spring 38b to engage the interior walls of elastomeric 
sleeve 56b, additional damping can be designed into the system to provide 
the desired feel and operational characteristics. 
In the FIG. 4 embodiment, accumulator 62c takes the form of a twin tube 66c 
surrounding outer cylindrical member 12c. Valve actuator 36c is biased to 
its upper (closed) position by a spring member (not shown) within valve 
60c. Siphon tube 68c is provided connecting the valve 66c to fluid 58c in 
twin tube 66c. This embodiment can only be utilized in an upright position 
whereas the embodiment of FIG. 3 need not be maintained vertically. 
FIGS. 5, 6 and 7 depict three related embodiments originally designed for 
use as seat height adjustment devices for use in position A (FIG. 1A). 
However, smaller versions could be implemented in the seat back adjustment 
application (position B) and the arm height adjustment application 
(position C). In the FIG. 5 embodiment, strut 10d includes an inner 
cylindrical member 23d with annular protrusions 54d for indenting 
elastomeric sleeve 56d. Biasing spring 46d forces actuator rod 40d to an 
extended position causing actuator element 44d to engage and axially 
compress ring 32d. When biasing spring 46d is collapsed releasing 
compression of ring 32d, return spring 38d, in the absence of any 
resisting force, will return piston 26d to the fully extended position. 
Protrusions 54d provide an initial level of damping (i.e., resistance to 
axial movement). 
FIGS. 6 and 7 demonstrate two embodiments of strut 10e and 10f in which 
inner cylindrical members 23e and 23f have no separate protrusions. Hence 
all initial or floor value for damping are the result of precompression of 
the outer sleeve 56e,f by spring 32e,f. Note, by also properly 
dimensioning return springs 38e and 38f, an increased amount of floor 
level damping can be provided, if desired. For those applications where 
not only is such a floor level not desired, but locking mechanism 20e,f, 
is not to function as an actual lock but merely as an adjustment between a 
high damping level and a low damping level, then spring members 32e and 
32f can be coated with a low coefficient of friction material such as 
Teflon.RTM. polymer, and the surface of sleeves 56e and 56f treated with 
an appropriate lubricant. Some gas spring substitutionary applications 
(e.g., automobile hatchback extenders) require such capabilities. For such 
an application, the return spring 38f will be positioned on the other side 
of piston 26f and return it toward the collapsed (as opposed to the 
extended) position. 
FIGS. 8-13 depict six embodiments of a downsized adjustable lockable strut 
10g-l which can be used in the seat back adjustment position B (FIG. 1A). 
In FIG. 8, piston 26g has a first cylindrical portion 28g and a second 
trailing portion 30g which may have a 1.degree.-5.degree. taper, as had 
the FIG. 1 embodiment. As with the FIG. 1 embodiment, the length of second 
portion 30g between intermediate stop 33g and end stop 35g exceeds the 
length of second ring 34g. First ring 32g is collapsed axially by rim 45g 
of actuator element 44g to provide the radial bulging which results in 
locking. Return spring 38g biases piston 26g toward its extended position. 
In this embodiment, biasing spring 46g is received within outer sleeve 42g 
and acts between intermediate sleeve 41g and head 39g on actuator rod 40g 
to bias rod 40g to an extended position. 
FIGS. 9 and 10 depict two additional embodiments of the smaller version of 
adjustable, lockable strut 10h and 10i. In the FIG. 9 embodiment, actuator 
rod 40h extend through an outer sleeve member 42h and has a U-bracket 70h 
which engages a crossbar 72h which forms a part of the actuator element 
44h which in this embodiment may comprise a washer-like member of 
Delrin.RTM. polymer. Biasing spring 46h is positioned between actuator 
element 44h and a cup element 68h. Return spring 38h engages the underside 
of cup element 68h. A pair of stiff O-rings 74h and 76h confine 
elastomeric spring 32h, with O-ring 74h performing the same function as 
rim 45g in the previous embodiment. 
In the FIG. 10 embodiment, actuator rod 40i engages the topside of inverted 
cup element 68i with biasing spring 46i acting between the inner bottom of 
cup 68i and a flange 78i on threaded washer 80i. Threaded washer 80i 
permits the compression of elastomeric spring 32i to be adjusted by 
varying the position of washer 80i on externally threaded outer sleeve 
42i. Collar 82i is also threaded on the exterior of outer sleeve 42i for 
ease of assembly. The bore 43i through outer sleeve 42i is stepped and 
actuator rod 40i has a bulge 84i which prevents rod 40i from falling out. 
FIG. 11 depicts another embodiment of strut 10j in which an outer 
elastomeric ring 32j is interconnected to an inner ring 86j by a radially 
oriented, intermediate transition section 88j. Plug 90j is threaded into 
sleeve 92j and provides a reaction surface for biasing spring 46j which 
forces cup 68j axially into inner ring 86j. The pressure applied to inner 
ring 86j is transferred to outer ring 32j by transition section 88j. The 
elastomer in these three elements (32j, 86j and 88j) acts as a solid fluid 
in locking piston 26j in place relative to outer cylindrical member 12j. 
An axial force of biasing spring 46j in the amount of between 10 and 20 
pounds is hydraulically magnified by the ratio of the external surface 
area of ring 32j to the surface area of inner ring 86j in contact with cap 
68j, to produce a locking force of 200 pounds. The other embodiments 
described herein are capable of producing similar levels of locking 
forces. As with previous embodiments, axial force applied to actuator rod 
40j counter to the force exerted by biasing spring 46j unloads the inner 
ring 86j permitting the transition section to flow inwardly unloading 
outer ring 88j such that piston 26j can be moved within housing 12j to an 
alternate position against the bias of return spring 38j. 
In the FIG. 12 embodiment, elastomeric spring 32k is compressed between end 
stop 32k formed on outer sleeve 42k and cup 68k which has an extension 94k 
received within biasing spring 46k. Elastomeric spring 32k expands 
radially as before locking piston 26k within sleeve 92k. Sleeve 92k may be 
of a self-lubricating material such as Teflon.RTM. polymer and is free to 
move within housing 12k. Return spring 38k biases sleeve 92k and piston 
26k locked therewith, to the fully extended position. This embodiment 
permits relative movement between the two elements which are 
interconnected by strut 10k, influenced by the force of spring 38k. If 
additional damping is desired, a sleeve similar to 34 in the FIG. 1 
embodiment can be provided about the exterior of sleeve 92k. The piston 
26k may be positioned within sleeve 92k as before by depressing actuator 
40k to a level sufficient to offset the preload provided by biasing spring 
46k. In the seatback adjustment application, strut 10k will permit angular 
or axial adjustment of the seatback (depending on the nature of the 
mechanism with which it is used) and still provide the springiness 
afforded by most seatbacks about an adjusted position. 
FIG. 13 depicts an embodiment of strut 101 in which spring 381 performs 
both the return function and the preload of elastomeric spring 321. A 
counter-balance spring 941 is provided which surrounds actuator rod 401. 
Hard elastomeric rings 741 and 761 are positioned at each end of spring 
321 to take the wear and tear. Return spring 381 engages the lower side of 
cup 681 which is biased against ring 741. As with earlier embodiments, the 
upper region 471 of outer sleeve 421 is threaded for attachment to one 
element while first end closure 141 has an hour glass shaped opening 
(double frustoconical tapers meeting in the middle at a minimum diameter) 
161 for attachment to a second element by means of a clevis, or the like. 
Also, as with previous embodiments, actuator rod 401 may be engaged (in 
conjunction with counter-balance spring 941) to overcome the bias of 
spring 381, unloading elastomeric spring 321 to release the locking due to 
bulging, permitting adjustment of the position of piston 261 within 
housing 121. 
FIG. 14 depicts a modified version of strut 10m. In this embodiment, 
elastomeric spring 32m is biased outwardly by a cam member 96m forcing a 
plurality of balls (preferably a minimum of four, two being shown) 98m 
outwardly into the elastomer. This produces a similar bulging of 
elastomeric spring 32m outwardly into locking engagement with outer 
cylindrical member 12m. By depressing actuator rod 40m, cam surface 95m 
will be displaced permitting balls 98m to move into recesses 97m. This 
will relieve the force created by the bulging and permit the position of 
piston 26m to be adjusted as desired. Biasing spring 46m encourages cam 
surface 95m into the ball-biasing position shown in FIG. 14. As is 
generally the case, return spring 38m encourages piston 26m to the fully 
extended position, the force of which must be manually overcome to permit 
adjustment to alternate positions. 
FIG. 15 depicts the use of the locking concept of the present invention 
shown in a different context. Strut 10n includes an actuator rod 40n 
attached to a first relatively movable member (not shown) and an outer 
cylindrical member 12n attached to a second relatively movable member (not 
shown). Snubber damper 102n is threaded onto one end of rod 40n and biased 
to a centered neutral position by upper and lower centering springs 146n. 
Under normal operations, low amplitude relative motions will be resisted 
only by centering springs 146n and therefore no vibration will be 
transmitted between the first and second relatively movable members. 
Larger amplitude vibrations will cause elastomer 104n of snubber damper 
102n to engage the ends 106n or 108n of outer cylindrical member 12n. 
Should it be desired that the first and second relatively movable members 
be locked together for movement, electromagnetic coil 110n can be 
energized attracting actuator element 44n into engagement with the end of 
elastomeric spring 32n causing it to bulge outwardly into engagement with 
the recess 120n in housing 12n, locking rod 40n to housing 12n. The 
strength of the magnetic field can be varied to adjust the level of 
clamping force, if desired. A shoulder 112n can be provided on actuator 
rod 40n as a platform for the element 44n to rest upon when the coil 110n 
is de-energized. Such a shoulder 112n can be formed by cold rolling 
techniques or, alternatively, an O-ring could be utilized to provide an 
adjustably positioned shoulder 112n. Obviously, the switch means of the 
present embodiment could be implemented in any of the previous 
embodiments, if desired. 
Various changes, alternatives and modifications will become apparent after 
a reading of the foregoing detailed description and appended claims. It is 
intended that all such changes, alternatives and modifications as fall 
within the scope of those appended claims be considered to be part of the 
present invention.