Backrest height adjustment device for office furniture chairs

Claim 2

In a backrest for office chairs including a support member having its lower end adapted for securement to the chair and a backrest mounted on the upper end of the support member, a device for adjusting the backrest vertically of said support member, said device comprising: a housing positioned on said support member adjacent the upper end thereof for movement vertically thereof and having the backrest secured thereto, said support member upper end having an elongated slot formed therein, said slot extending longitudinally of said support member and being rectilinear in longitudinal configuration, said slot defining spaced parallel sidewalls extending longitudinally of said support member, and a cam lock member journaled in said housing, said cam lock member being journaled for pivotal movement about an axis extending transversely of said support member and said slot and defining a cam lock portion concentric with said axis and received in said slot, said cam lock portion defining a pair of oppositely disposed cam locking surfaces proportioned transversely of said axis to have equal but opposite binding engagement with said slot side walls within said slot when in contact therewith at points lying on radii extending from said axis that make an angle with the horizontal having a tangent that is less than the coefficient of static friction between said cam lock portion and said slot side walls, said cam locking surfaces being separated by opposed cam surfaces proportioned transversely of said axis to have slip fit relation with said slot side walls whereby the backrest has free sliding adjustment relative to the support member when said cam locking surfaces are out of contact with said support member slot side walls, means for selectively pivoting said cam lock member about said axis relative to said housing, and means for guiding the movement of said housing longitudinally of said slot when said cam locking surfaces are free of binding engagement with said slot side walls.

Claim 3

In a backrest for office chairs including a support member having its lower end adapted for securement to the chair and a backrest mounted on the upper end of the support member, a device for adjusting the backrest vertically of said support member, said device comprising: a housing positioned on said support adjacent the upper end thereof for movement vertically thereof and having the backrest secured thereto, said support member upper end having a pair of elongated slots formed therein in coplanar relation, said slots extending longitudinally of said support member in vertically spaced relation and being rectilinear in longitudinal configuration, a bushing mounted in said housing and received in one of said slots in backrest movement guiding relation therewith, and a cam lock member journaled in said housing, said cam lock member being journaled for pivotal movement about an axis extending transversely of said support member and defining a cam lock portion concentric with said axis and received in the other of said slots, said other slot defining spaced parallel side walls extending longitudinally of said support member, said cam lock portion defining a pair of oppositely disposed Cam locking surfaces and proportioned to make equal but opposite binding engagement with said other slot side walls when in contact therewith at points lying on radii extending from said axis that make an angle with the horizontal having a tangent that is less than the coefficient of static friction between said cam lock portion locking surfaces and said other slot side walls, said cam locking surfaces being separated by a pair of opposed cam portion surfaces having slip fit relation with said other slot side walls when said cam locking surfaces are free of contact with said other slot side walls, and means for pivoting said cam lock member about said axis relative to said housing to selectively move said cam locking surfaces into and out of engagement with said other slot side walls, whereby said cam lock portion cam locking surfaces when in binding engagement with said other slot side walls fix the backrest against movement longitudinally of said support member slots free of clamping stress applied to said housing.

Claim 4

In a backrest for office chairs including a support member having its lower end adapted for securement to the chair and a backrest mounted on the upper end of the support member, a device for adjusting the backrest vertically of said support member, said device comprising: a housing positioned on said support adjacent the upper end thereof for movement vertically thereof and having the backrest secured thereto, said support member upper end having a pair of elongated slots formed therein in coplanar relation, said slots extending longitudinally of said support member in vertically spaced relation and being rectilinear in longitudinal configuration, a bushing mounted in said housing and received in one of said slots in backrest movement guiding relation therewith, and a cam lock member journaled in said housing, said cam lock member being journaled for pivotal movement about an axis extending transversely of said support member and defining a cam lock portion concentric with said axis and received in the other of said slots, said other slot defining spaced parallel side walls extending longitudinally of said support member, said cam lock portion defining a pair of oppositely disposed Cam locking surfaces and proportioned to make equal but opposite binding engagement with said other slot side walls when in contact therewith at points lying on radii extending from said axis that make an angle with the horizontal having a tangent that is less than the coefficient of static friction between said cam lock portion locking surfaces and said other slot side walls, said cam locking surfaces being separated by a pair of opposed cam portion surfaces having slip fit relation with said other slot side walls when said cam locking surfaces are free of contact with said other slot side walls, and means for pivoting said cam lock member about said axis relative to said housing to selectively move said cam locking surfaces into and out of engagement with said other slot side walls, whereby said cam lock portion cam locking surfaces when in binding engagement with said other slot side walls fix the backrest against movement longitudinally of said support member slots free of clamping stress applied to said housing.

Claim 5

In a backrest for office chairs including a support member having its lower end adapted for securement to the chair and a backrest mounted on the upper end of the support member, a device for adjusting the backrest vertically of said support member, said device comprising: a housing positioned on said support member adjacent the upper end thereof and having the backrest secured thereto, said housing comprising: a pair of housing members secured together to define between same a socket in which said upper end of said support member is received, said support member upper end having a pair of elongated rectilinear slots formed therein disposed in coplanar relation, said slots extending longitudinally of said support member and each defining parallel planar side walls extending longitudinally of said support member, a bushing carried by said housing and mounted within said socket and in one of said slots in backrest movement guiding relation with said one slot, and a cam lock member mounted in said housing, said cam lock member being journaled between said housing members for pivotal movement about an axis extending through said other slot and transversely of said support member, and defining a cam lock portion concentric with said axis and disposed in said socket and said other slot, said cam lock portion defining a pair of oppositely disposed cam locking surfaces proportioned radially of said axis to make equal but opposite binding engagement with said other slot side walls, respectively, when moved into contact therewith at points lying on radii extending from said axis that make an angle with the horizontal having a tangent that is less than the coefficient of static friction between said cam locking surfaces and said other slot side walls, said cam locking surfaces being separated by a pair of oppositely disposed cam surface portions having slip fit relation with said other slot side walls when said cam locking surfaces are free of contact with said other slot side walls, and a handle member keyed to said cam lock member for pivoting said cam lock member about said axis relative to said housing to move said cam locking surfaces into and out of said binding engagement with said other slot side walls, whereby said cam lock portion cam locking surfaces when in binding engagement with said other slot side walls fix the backrest against movement longitudinally of said support member slots free of clamping stress applied to said housing.

Claim 6

In a backrest for office chairs including a support member having its lower end adapted for securement to the chair and a backrest mounted on the upper end of the support member, a device for adjusting the backrest vertically of said support member, said device comprising: a housing positioned on said support member adjacent the upper end thereof and having the backrest secured thereto, said housing comprising: a pair of housing members secured together to define between same a socket in which said upper end of said support member is received, said support member upper end having a pair of elongated rectilinear slots formed therein disposed in coplanar relation, said slots extending longitudinally of said support member and each defining parallel planar side walls extending longitudinally of said support member, a bushing carried by said housing and mounted within said socket and in one of said slots in backrest movement guiding relation with said one slot, and a cam lock member mounted in said housing, said cam lock member being journaled between said housing members for pivotal movement about an axis extending through said other slot and transversely of said support member, and defining a cam lock portion concentric with said axis and disposed in said socket and said other slot, said cam lock portion defining a pair of oppositely disposed cam locking surfaces proportioned radially of said axis to make equal but opposite binding engagement with said other slot side walls, respectively, when moved into contact therewith at points lying on radii extending from said axis that make an angle with the horizontal having a tangent that is less than the coefficient of static friction between said cam locking surfaces and said other slot side walls, said cam locking surfaces being separated by a pair of oppositely disposed cam surface portions having slip fit relation with said other slot side walls when said cam locking surfaces are free of contact with said other slot side walls, and a handle member keyed to said cam lock member for pivoting said cam lock member about said axis relative to said housing to move said cam locking surfaces into and out of said binding engagement with said other slot side walls, whereby said cam lock portion cam locking surfaces when in binding engagement with said other slot side walls fix the backrest against movement longitudinally of said support member slots free of clamping stress applied to said housing.

Claim 7

The device set forth in claim 3 wherein: said cam locking surfaces and said other slot side walls are formed from steel, and wherein said angle is no more than about 8*.

Claim 8

The device set forth in claim 4 wherein: said support is formed from steel, and said cam lock portion is formed from powdered metal and has a hardness in the range of 25 - 35 Rockwell C.

Claim 9

The device set forth in claim 3 wherein: saiD slots are aligned longitudinally of said support member.

Claim 10

The device set forth in claim 4 wherein said slip fit cam surface portions of said cam lock portion are struck on arcs eccentric with said axis and having a radius exceeding that of said cam locking surfaces, with said slip fit cam surface portions smoothly connecting said cam locking surfaces.

Claim 11

The device set forth in claim 3 wherein: said housing members are each of channel configuration defining side flanges separated by a web, said housing members being in nesting relation with their webs separated to define said socket therebetween, with one of said housing members being received within the other of said housing members to provide said nesting relation, and with the other of said housing members having the backrest applied thereto, said cam lock member including a flange exterior of said housing and concentric with said axis and positioned within said inner housing member, said handle member being keyed to said flange for swinging movement in a plane exterior of said housing.