Pneumatic height adjustment column for a chair

A pneumatic height adjustment column is provided for a chair. The column includes a support tube, a carrier tube, a pneumatic cartridge, a hub fastener, and a shaft fastener. The support tube has a top end which is generally open, and a bottom portion which is adapted to be mounted to a chair base. The bottom portion has an opening with a smaller diameter than that of the support tube. The carrier tube has a top portion adapted to be mounted to a support housing for a chair seat. The top portion has an opening with a smaller diameter than that of the carrier tube. The carrier tube also has a generally open bottom end which telescopically engages the top end of the support tube. The pneumatic cartridge has a cylinder positioned within the carrier tube, a shaft, and a hub. The cylinder has a diameter greater than that of the opening in the carrier tube. The shaft extends downwardly from the cylinder and has a bottom end which passes through the opening in the bottom of the support tube. The hub is disposed on a top portion of the cylinder and passes through the opening in the top of the carrier tube. The hub fastener releasably engages the hub and maintains the position of the hub through the opening in the top of the carrier tube. The shaft fastener is attached to the shaft and maintains the position of the bottom end of the shaft through the opening in the bottom of the support tube.

BACKGROUND OF INVENTION 
The present invention relates generally to support columns for chairs, and 
more particularly, to pneumatic height adjustment columns. 
In general, a chair's seating surface, or seat, is maintained at an 
elevated level to provide a user with support while in a sitting position. 
Typically, the seat is elevated by interposing a support structure between 
the seat and the surface above which it is positioned. Support structures 
come in a variety of forms. For example, a plurality of legs can support 
the seat. In another form, the support structure consists of a single 
support column, which eliminates the need for multiple load bearing 
members and improves the aesthetics of the chair. Support columns have 
also been made height adjustable to accommodate both a variety of users 
and a variety of uses for the chair. For example, a height adjustable 
chair can be raised or lowered to accommodate users of different heights. 
Similarly, the height adjustable chair can be raised or lowered to provide 
a fixed seating surface at a plurality of elevated work stations. 
Therefore, a single user may use the chair at different heights, 
regardless of their height characteristics. To accommodate a wide range of 
users and uses, it is therefore important to maximize the stroke of the 
support column, i.e., the difference between the lowest elevation and the 
greatest elevation of the chair. 
Height adjustable chairs typically include a pneumatic height adjustment 
column for supporting the chair. A pneumatic height adjustment column 
generally includes a pneumatic cartridge disposed in a telescopically 
movable carrier tube that engages a support tube. Generally, the pneumatic 
cartridge includes a cylinder and a shaft, and is retained in the tube by 
securing a bottom of the cylinder to the carrier tube using a securing 
element such as a nut or clip. Other securing elements can secure the top 
of the cartridge to the carrier tube, but are typically positioned inside 
the tube. The securing element prevents the cartridge from falling out of 
the tube during installation and prevents the cartridge from becoming 
disengaged from the carrier tube when the chair is lifted upwardly. The 
securing element can also maintain the relationship of the pneumatic 
cartridge within the tube such that an unintentional slackening of the 
column is reliably avoided when the chair is raised upwardly by the tube 
structure. 
Securing the pneumatic cartridge inside the tube structure has several 
disadvantages, however. For example, when the securing element attaches to 
the bottom of the cartridge cylinder, the height of the support column at 
a fully compressed position necessarily includes the height of the 
compressed pneumatic cartridge cylinder and the height of the securing 
element. Therefore, the overall stroke of the support column is reduced by 
the amount of internal space occupied by the nut or other securing element 
inside the tube structure. This is also true of securing elements, 
interconnecting the top of the pneumatic cartridge and the carrier tube, 
that are positioned inside the carrier tube. 
In addition, the typical support column secured at the bottom of the 
cylinder can experience premature failure at the seal interfacing the 
cylinder and shaft of the pneumatic cartridge. This failure is experienced 
when the cylinder is forced to take up bending stresses. For example, when 
a user sits off center in the chair, a bending moment is applied to the 
support column. This moment must be carried by the support column to the 
base. By securing the pneumatic cartridge to the tube at both ends of the 
cylinder, the pneumatic cartridge is forced to absorb some of the bending 
moment and resultant bending stresses imposed on the tube. 
Because pneumatic cartridges can be damaged or worn out, it is important 
for the cartridge to be easily removed from the cylinder. Accordingly, the 
securing element must releasably engage either the cartridge or the 
carrier tube, such that the cartridge can be disengaged from the tube. For 
example, a spring clip can be mounted inside the carrier tube and can be 
adapted to releasably engage the pneumatic cartridge. Alternatively, many 
of the current securing devices accomplish releasable engagement by 
engaging threads disposed on the carrier tube. For example, U.S. Pat. No. 
4,940,202 entitled Steplessly Adjustable Vertical Movement Device and 
issued to Hosan et al., discloses a pneumatic catridge having a securing 
element attached to the top of it. The pneumatic cartridge is removed by 
turning the pneumatic catridge and the attached securing element through 
an internal threading in the top of the carrier tube. However, if the 
threads are damaged, the carrier tube may have to be discarded. Similarly, 
if a spring clip is located inside the carrier tube, the entire tube may 
have to be discarded if the clip is damaged. 
Finally, most securing elements, whether positioned inside or outside the 
carrier tube, interconnect only the pneumatic cartridge and carrier tube, 
and do not additionally interconnect the carrier tube and the seat. For 
example, the securing element disclosed in the Hosan et al. patent does 
not secure the carrier tube to the seat. Indeed, when located inside the 
carrier tube, the securing element is incapable of making this attachment. 
Thus, most securing elements do not provide a secondary retention device 
for preventing the seat from becoming disengaged from the support column. 
SUMMARY OF THE INVENTION 
Briefly stated, the invention is directed to a pneumatic height adjustment 
column for a chair. The support column includes a support tube, a carrier 
tube, a pneumatic cartridge, a hub fastener and a shaft fastener. The 
support tube has a top end which is generally open, and a bottom portion 
adapted to be mounted to a chair base. The bottom portion includes an 
opening with a smaller diameter than that of the support tube. The carrier 
tube has a top portion adapted to be mounted to a chair seat, which 
includes an opening with a smaller diameter than that of the carrier tube. 
The carrier tube also has a generally open bottom end which telescopically 
engages the top end of the support tube. The pneumatic cartridge includes 
a cylinder which is positioned within the carrier tube, and has a diameter 
greater than that of the opening in the top portion of the carrier tube. 
The cartridge also has a shaft extending downward from the cylinder. The 
shaft has a bottom end which passes through the opening in the bottom of 
the support tube. The pneumatic cartridge also includes a hub disposed on 
a top portion of the cylinder. The hub passes through the opening in the 
top of the carrier tube. The hub fastener releasably engages the hub and 
maintains the position of the hub through the opening in the top of the 
carrier tube. The shaft fastener is attached to the shaft and maintains 
the position of the bottom end of the shaft through the opening in the 
bottom of the support tube. 
One object of the present invention is to provide a pneumatic height 
adjustment column whereby the stroke of the column is maximized. By 
providing a hub and externally securing the pneumatic cartridge to the 
carrier tube at the top of the carrier tube, the hub fastener does not 
increase the internal height of the support column when fully compressed, 
regardless of the fastener's thickness. Similarly, the fastener does not 
interfere with the maximum extension of the support column. Thus, the 
present invention provides a significant advantage over other support 
columns. 
Another object of the invention is to provide a support column whereby the 
portion of the bending moment carried by the pneumatic cartridge is 
greatly reduced, thereby increasing the life of the cartridge. By 
attaching the top of the pneumatic cartridge to the top of the carrier 
tube, rather than fixing it to the carrier tube at the lower portion of 
the cylinder, the cartridge is precluded from carrying the bending moment 
and the resultant bending stresses. 
In a preferred embodiment, the hub disposed on top of the pneumatic 
cartridge cylinder has a circumferential groove. The hub fastener is 
Y-shaped, having two resilient members and an enlarged portion. The 
resilient members form an opening between them. When installed, the 
resilient members are disposed in the groove and engage the hub, thereby 
preventing the cylinder from falling into the carrier tube when the 
support column is raised upwardly by the carrier tube. Moreover, the hub 
fastener is curved such that it biases the cartridge upwardly against the 
carrier tube, thereby eliminating any unintentional slackening or chatter 
when the chair is lifted upwardly. In addition, the hub fastener engages 
the seat, thereby preventing the seat from becoming disengaged from the 
carrier tube. 
The present invention also provides for a method of assembling the 
pneumatic height adjustment column. The method includes inserting the 
pneumatic cartridge in the carrier tube such that the hub passes through 
the opening in the top portion of the carrier tube. The pneumatic 
cartridge is then secured in the carrier tube by attaching the hub 
fastener to the hub. The carrier tube and pneumatic cartridge are then 
inserted into the support tube. When inserting the carrier tube and 
pneumatic cartridge in the support tube, the bottom end of the shaft is 
passed through the opening in the bottom portion of the support tube and 
the bottom end is secured with a shaft fastener. When using the preferred 
embodiment, the hub fastener can also be removed without destroying it, 
thereby allowing for repeated use of the fastener over the life of the 
chair. 
The present invention, together with further objects and advantages, will 
be best understood by reference to the following detailed description 
taken in conjunction with the accompanying drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring to the drawings, FIGS. 2 and 5 show a pneumatic height adjustment 
column 1 including a support tube 7, a carrier tube 13, a pneumatic 
cartridge 17, a hub fastener 35 and a shaft fastener 51. As shown in FIGS. 
2 and 3, the carrier tube 13 has a top portion 14 which is adapted to be 
mounted to a chair seat 5. The chair seat 5 includes a support housing 6 
which has a tapered bore 4 adapted to receive the top portion 14 of the 
carrier tube 13, which is also tapered, as shown in FIGS. 2 and 3. The 
carrier tube 13 is mounted to the support housing 6 by press fitting the 
tapered top portion 14 of the carrier tube 13 within the tapered bore 4. 
Because the weight of the user is transferred from the seat 5 to the 
carrier tube 13 at the tapered interface, the corresponding tapers of the 
top portion 14 of the carrier tube 13 and the bore 4 in the support 
housing prevent the carrier tube 13 from passing through the bore 4 when a 
user occupies the seat 5. 
As shown in FIG. 2, a base 3 also has a tapered bore 77 adapted to receive 
a tapered bottom ,portion 9 of the support tube 7. The support tube 7 is 
press fitted into the tapered bore 77 of the base 3, thereby providing for 
a proper load transfer between the support tube 7 and the base 3. 
As shown in FIGS. 2 and 5, the carrier tube 13 includes a bottom end 16 
which is generally open. The bottom end 16 of the carrier tube 13 is 
telescopically received in a generally open top end 8 of the support tube 
7. As the pneumatic height adjustment column moves between a fully 
extended position, as shown in FIG. 2, to a fully compressed position, as 
shown in FIG. 5, the carrier tube 13 slidably engages the support tube 7. 
At a fully extended position, a portion of the carrier tube 13 must remain 
engaged with a portion of the support tube 7 in order to provide a 
sufficient contact surface for reacting against the bending moment 
produced by a user sitting off-center in the seat. In a preferred 
embodiment, about two inches of the carrier tube 13 remains engaged with 
the support tube 7 at a fully extended position, as shown in FIG. 2. 
As shown in FIGS. 2 and 5, a pneumatic cartridge 17 is coaxially disposed 
in the carrier tube 13. The pneumatic catridge 17, carrier tube 13 and 
support tube 7 each have a longitudinal axis 100 as shown in FIGS 2-6. The 
pneumatic cartridge 17 includes a cylinder 19, a shaft 23, and a hub 30. 
The cylinder 19 has a top surface 55 and a bottom surface 53. The bottom 
surface 53 of the cylinder 19 has a hole 57 adapted to receive a shaft 23, 
which extends downwardly from the cylinder 19 as shown in FIGS. 8 and 9. 
The shaft 23 slidably engages the cylinder 19 and is connected to a piston 
disposed within the cylinder 19. When the pneumatic height adjustment 
column 1 is in a fully extended position, a substantial portion of the 
shaft 23 extends downwardly from the cylinder 19 as shown in FIG. 2. When 
in a fully compressed position, a substantial portion of the shaft 23 is 
disposed within the cylinder 19 as shown in FIG. 5. A seal 34 is 
interposed between the shaft 23 and the cylinder 19 at the bottom surface 
53 of the cylinder 19 as shown in FIG. 9. 
As shown in FIGS. 2 and 3, the hub 30 of the pneumatic cartridge is 
disposed on the top surface 55 of the cylinder 19. When the pneumatic 
cartridge 17 is disposed in the carrier tube 19, the hub 30 passes through 
an opening 15 in the top portion 14 of the carrier tube 13. The diameter 
of the opening 15 in the carrier tube 13 is smaller than the outer 
diameter of the cylinder 19 such that the top 55 surface of the cylinder 
engages a shoulder 59 of the carrier tube 19 as shown in FIG. 3, thereby 
preventing the cylinder 19 from passing through the opening and providing 
a load path to transfer a downward vertical load from the carrier tube 19 
to the pneumatic cartridge 17. As shown in FIGS. 2 and 3, an actuating 
button 33 extends through the hub 30 and slidably engages the cylinder 19. 
When depressed, the actuating button 33 actuates a gas spring contained in 
the cylinder 19, thereby permitting the column to be raised or lowered. 
As shown in FIGS. 2 and 3, a hub fastener 35 releasably engages the hub 30 
as it protrudes through the opening 15 in the carrier tube 19. The hub 
fastener 35 maintains the position of the pneumatic cartridge 17 in the 
carrier tube 13 when the chair is lifted upwardly. When the chair is 
lifted upwardly, the support housing 6 transfers an upward force to the 
carrier tube 13. If the pneumatic cartridge 17 were not secured to the 
carrier tube 19, the carrier tube 13 would slide upwards in the support 
tube 7 until the carrier tube 13 and support tube 7 were disengaged. The 
hub fastener 35 is necessary to maintain the position of the pneumatic 
cartridge 17 in the carrier tube 13 and thereby ensure that the carrier 
tube 13 remains slidably engaged with the support tube 7. This is 
accomplished by securing the carrier tube 13 to the pneumatic cartridge 17 
using the hub fastener 35 and by securing the support tube 7 to the 
pneumatic cartridge 17 using the shaft fastener 51. 
The hub fastener 35 also functions as a secondary retention device that 
secures the support housing 6 to the carrier tube 13. As shown in FIG. 3, 
the hub fastener 35 is larger than the top opening of the tapered bore 4 
in the support housing 6. Accordingly, the hub fastener 35 engages a top 
surface 75 of the support housing 6. Therefore, if the tapered portion 14 
of the carrier tube 13 were to come loose from or not fit properly within 
the tapered bore 4 in the support housing 6, the hub fastener 35 ensures 
that the support housing 6 cannot be disengaged from the top portion 14 of 
the carrier tube 13. Thus, the hub fastener 35 functions as a secondary 
retention device between the column 1 and the support housing 6. 
As shown in the preferred embodiment of FIGS. 7A and 7B, the hub fastener 
35 has a pair of resilient members 37 and an enlarged portion 39. The 
resilient members have beveled ends 38 to facilitate the installation of 
the hub fastener 35. The resilient members 37 define an opening 61 between 
them and have three engagement tabs 40 extending inwardly into the opening 
61. When the hub 30 is disposed in the opening, the engagement tabs 40 
engage the hub 30. When installing the hub fastener 35, the beveled ends 
38 are placed against the hub 30 and a lateral inward force is applied to 
the enlarged portion 39, thereby biasing the resilient members 37 
outwardly as the members translate past the hub 30. 
The beveled ends 38 provide an initial guide for positioning the hub 
fastener 35 on the hub 30 and facilitate the installation process by 
providing for a ramped installation force, whereby the lateral inward 
force applied to the fastener 35 is necessarily increased as the resilient 
members 37 slide past the hub 30 and are biased outwardly. Thus, a lesser 
force is required at the beginning of the installation, which 
appropriately corresponds to the point in time when the fastener 35 is not 
stabilized by the hub 30 and is guided only by the user. When the hub 30 
is disposed in the opening, the resilient members 37 return to their 
original position so that the engagement tabs 40 engage the hub 30. 
The hub fastener 35 is removed by applying an outward force to the enlarged 
portion 39. As the hub fastener 35 moves laterally outwardly, the 
resilient members 37 are biased laterally outwardly by the hub 30. When 
disengaged from the hub 30, the resilient members 37 return to their 
original position. Thus, the hub fastener 35 can be used repeatedly 
without destroying it. Moreover, because the hub fastener 35 is not 
fixedly attached to either the hub 30 or the carrier tube 13, it can be 
replaced easily and inexpensively without correspondingly having to 
replace the carrier tube 13 or pneumatic cartridge 17. 
To remove and replace the pneumatic cartridge 17, the hub fastener 35 is 
removed and the seat 5, support housing 6 and carrier tube 13 are 
disengaged from the support tube 7 and pneumatic cartridge 17. The shaft 
fastener 51 is then removed, whereby the pneumatic cartridge 17 can be 
removed. Thus, the cartridge 17 can be replaced without having to remove 
the support housing 6 from the carrier tube 13 in order to access the hub 
30. 
In a preferred embodiment, the hub 30 has a circumferential groove 31 
defined by a lower shoulder 63 and an upper shoulder 65. The resilient 
members 37 are disposed in the groove 31 and engage the upper shoulder 65 
thereby preventing the hub 30 from passing downwardly through the opening 
15 in the carrier tube 13. In the preferred embodiment, the hub fastener 
35 is curved and has a lower concave surface 67, which is biased against 
the support housing 6 and a top surface 75 of the carrier tube 13 as shown 
in FIG. 2, 3 and 5. The hub fastener 35 also has an upper convex surface 
69, which is biased against the upper shoulder 65 of the hub 30. The hub 
fastener 30 is curved so as to bias the cartridge 17 upwardly against the 
shoulder 59 of the carrier tube 13, thereby eliminating any unintentional 
slackening or chatter of the chair when lifted upwardly by the seat 5. In 
addition, the hub fastener 35 acts as a secondary retention device as 
previously described. Because the beveled ends 38 and enlarged portion 37 
of the hub fastener 35 engages the support housing 6, the support housing 
6 is prevented from becoming disengaged from the carrier tube 13. 
In a preferred embodiment, the hub fastener 35 is made out of steel and has 
a thickness of about 0.030 to 0.050 inches. However, it should be 
understood that a variety of other materials and thicknesses are 
acceptable for the intended purpose of the fastener. Because the hub 
fastener 35 is located externally of the carrier tube 13, its thickness 
does not interfere with or decrease the stroke of the column. 
As shown in FIGS. 4 and 6, the shaft 23 of the pneumatic cartridge 17 is 
attached to a support plate 12 that is mounted to a bottom end 10 of the 
support tube 7. The bottom end 10 of the support tube 7 is generally open 
and includes a shoulder 71. The support plate 12 engages the shoulder 71 
formed at the bottom end 10 of the support tube 7 as show in FIGS. 4 and 
6. The tube 7 is crimped above the support plate 12 to secure it in place. 
Alternatively, the support plate can be welded to the support tube. 
In another embodiment, the bottom end does not include a shoulder. Rather, 
the support plate is positioned in the opening of the bottom end and 
welded to the support tube. In yet another embodiment, the support plate 
is threaded and engages the corresponding threads disposed in the support 
tube. 
The shaft 23 has a bottom end 27 which passes thorough an opening 14 in the 
support plate 12. The bottom end 27 of the shaft 23 has a groove 29. A 
shaft fastener 51 is disposed in the groove 29 so as to prevent the shaft 
23 from passing back through the opening 14 in the support plate 12. 
Preferably, the shaft fastener 51 comprises a clip. Alternatively the 
shaft can have a hole in the bottom end adapted to receive a cotter pin. 
The bottom end can also be threaded to receive a nut. 
The shaft 23 also includes a shoulder 25 located near the bottom end 27 of 
the shaft 23. The shoulder 25 is an integral part of the shaft 23. In 
alternative embodiments, the shoulder can be comprised of a nut screwed 
onto the shaft or a washer welded to the shaft. 
A bearing set 41 is disposed on the shaft 23 between the support plate 12 
and the shoulder 25 as shown in FIG. 4 and 6. The bearing set 41 includes 
a first washer 42, a second washer 43 and a plurality of ball bearings 44 
captured between the washers. The bearing set 44 permits the pneumatic 
cartridge 17 and carrier tube 13 to rotate about a vertical axis as the 
user rotates the seat 5 about that axis. The bearing set 41 also prevents 
the shoulder 25 from passing through the opening 16 in the support plate 
12. Alternatively, the shoulder can have a greater diameter than the 
opening and can directly bear up against the support plate. As shown in 
FIG. 4 and 6, a cushion member 45 is disposed on the shaft 23 around the 
shoulder 25 and extends above the upper surface of the shoulder 25. 
Preferably, the cushion member 45 is made out of rubber. The cushion 45 is 
interposed between the bottom surface 53 of the cylinder 19 and the 
shoulder 25 when the column is in a fully compressed position. The cushion 
45 prevents the shoulder 25 from coming into contact with and damaging the 
bottom surface 53 of the cylinder 19. 
When occupied by a user, the seat 5 imparts a vertical load to the carrier 
tube 13, which transfers the load to the pneumatic cartridge 17 through 
the carrier tube shoulder 59. The pneumatic cartridge 17 carries the 
vertical load through the shaft 23 and transfers it to the bearing set 41 
through the shoulder 25 on the shaft 23. The bearing set 41 then transfers 
the vertical load to the support tube 7 through the support plate 12. 
Finally, the load is transferred from the support tube 7 to the base 3. 
Because the cartridge 17 is secured within the carrier tube 13 at the top 
of the carrier tube 13, the cartridge 17 is not forced to carry any 
bending loads. If fixed to a lower portion of the carrier tube, the 
cartridge would be forced to resist the bending moment applied to it by 
exerting a coupled reaction force, one reaction force exerted at the point 
of the cylinder attachment and the other at the point where the shaft is 
attached to the support tube. Such an arrangement would force the 
cartridge to carry the bending moment and react against it. The resultant 
force exchanged between the shaft and the cylinder would accelerate the 
wear and degradation of the seal interfacing those two elements. To the 
contrary, when the cylinder is attached at the top of the carrier tube, 
the cartridge is not forced to carry the moment. 
The present invention also relates to a method for assembling the pneumatic 
height adjustable column. The method includes inserting the pneumatic 
cartridge 17 in the carrier tube 13 so that the hub 30 passes through the 
opening 15 in the top portion 14 of the carrier tube 13. When so 
positioned, the top surface of the cylinder 19 engages the shoulder 59 of 
the carrier tube 13. A hub fastener 35 is then attached to the hub 30 to 
secure the pneumatic cartridge 17 within the carrier tube 13. A cushion 45 
is disposed on the shaft 23 around the shoulder 25 and a bearing set 41 is 
disposed on the end of the shaft 27 below the shoulder. The carrier tube 
13 and attached pneumatic cartridge 17, including the cushion 45 and the 
bearing set 41, are then inserted into the support tube 7. The carrier 
tube 7 is pushed downwardly until the bottom end 27 of the shaft passes 
through the opening 14 in the support plate 12, thereby capturing the 
bearing set 41 between the shoulder 25 and the support plate 12. A shaft 
fastener 51 is then attached to the end of the shaft 23 to secure the 
shaft to the support plate 12. It should be understood that there is no 
required order for performing these steps and that they can be reordered 
so as to achieve the same result. 
Although the present invention has been described with reference to 
preferred embodiments, those skilled in the art will recognize that 
changes may be made in form and detail without departing from the spirit 
and scope of the invention. As such, it is intended that the foregoing 
detailed description be regarded as illustrative rather than limiting and 
that it is the appended claims, including all equivalents thereof, which 
are intended to define the scope of the invention.