The invention relates to back support mechanisms. Mass produced chairs and the like formed with a fixed back support structure do not provide adequate lumbar support for many users. Various attempts have been made using selective padding of back rest zones in order to provide comfort together with adequate lumbar support for a variety of users. Of course individual requirements vary and to date such attempts have not been entirely successful. Also back rests have been formed on adjustable mountings to vary the inclination thereof. However, such adjustment cannot accommodate variations in individual back configurations.

The present invention aims to alleviate the disadvantages associated with such prior art devices and to provide a back support mechanism which can be incorporated in backrests and which will be effective and efficient in use. It is also an object of this invention to provide such a mechanism which can be adjusted to suit individual requirements,

With the foregoing and other objects in-view, this invention provides a back support mechanism for a backrest of a chair including: operating means; adjustable support means mounted to the operating means; control means foractuating said operating means to move said support means out of the plane of the backrest for a chosen degree.

Preferably the adjustable support means bearing pad is movable in a direction substantially at right angles to the plane of the backrest. If desired however, the bearing pad could be movable or pivotal for adjustment in any suitable manner so as to provide support in the lumbar region of a user. In a preferred form the bearing pad is centrally disposed and pivotally connected to the opposed supports arranged for movement towards or away from one another and the pivotal connection being such that such movement causes a

corresponding movement of the bearing pad substantially in the direction at right angles to the plane of movement of said supports. The supports can be adapted to move trans¬ versely or in an up and down direction and of course if desired the bearing pad could be coupled to a single support or it could be located by other actuating mechanisms. Preferably the supports engage a threaded actuating shaft having external actuating means whereby rotation of the shaft will cause the supports to move together or away from one another.

The invention will now be described by way of example with reference to the accompanying drawings in which:

Figure 1 is a perspective view illustrating a typical application of the present invention;

Figure 2 is a perspective view of a preferred form of back support mechanism;

Figure 3 is a plan view of the mechanism illustrated in figure 2;

Figure 4 is a broken away view illustrating the operation of the back support mechanism;

Figure 5 illustrates a modified mounting arrangement for the support mechanism;

Figure 6 illustrates another modified mounting arrangement for the support mechanism; and

Figure 7 shows a view illustrating the mode of adjustment of the mechanism of figure 6.

As illustrated the support mechanism 10 is adapted to be supported between the side rails 11 of the backrest 12 of a chair. The side rails 11 are upholstered and control means such as an operating knob 13 is supported in an accessible position projecting outwardly from the backrest as illustrated in figure 1. The backrest 12 may include fixed upper and lower backrest panels 14 and an intermediate backrest panel 15 which is separately upholstered and movable with respect to the adjacent panels 14 such that adjustment

of the panel 15 will not pull on the fixed upholstery fabric in the panels 14 and about the side rails 11 and cause creases and the like to form in the upholstery fabric.

The back support mechanism 10 includes adjustable support means comprising a central substantially rectangular bearing pad 16 which is connected pivotally at

opposite sides to laterally spaced link members 17 each having upper and lower slotted arms 18 remote from the pad 16 which engage about mountings or posts 19. Posts 19 are supported slidably on upper and lower guide rails 20. The inner end portions 21 of the link members 17 extend inwardly beyond their pivotal connections 23 with the bearing pad 6 and are formed with meshing projections 25.

Control means for moving a threaded shaft 24 having opposite hand threads at the respective end portions thereof extends between the side rails 11 and engages threadedly with the respective central portions of the posts 19 such that upon rotation of shaft 24 the posts are both simultaneously moved either towards or away from one another, depending upon the direction of rotation of the shaft 24 along the supporting rods 20. A control knob 13 is provided for rotating shaft 24. In use, the back support mechanism is provided with suitable padding and is encased within suitable upholstery forming the intermediate section 15.

A user supported in the chair 9 can.byrotation of the knob 13 move the bearing pad 16 forwards or rearwards to provide thedesired amount of support at the lumbar region. When the control knob is rotated in one direction the mounting posts 19 will move towards one another to cause the links 17 to pivot outwardly and carry the bearing pad 16 outwardly with their inner ends to an outer position as illustrated in figure 4. Since both parts will move a corresponding amount the outer face of the bearing pad 16 is maintained in a parallel relationship with the supporting plane of the backrest 12. If the knob 13 is rotated in the opposite direction the posts 19 will move apart enabling the links to retract towards the position illustrated in figure 2.

If desired return springs can be provided to cause retraction of the links 17, or the end parts on the slotted arms 19 could be adapted to encircle the respective post such that the links 17 would be drawn to their retracted position.

Alternatively the upholstery tension or the weight of a user may be used to cause retraction of the bearing pad 16. In the illustrated embodiment the meshing of the teeth 25 between the inner ends of the links 17 will ensure even retraction thereof.

Figure 5 illustrates a modified mounting for the guide rails 20a whereby the bearing pad 16a can be tilted about an axis coincident with the shaft 24. In this embodiment the ends of the guide rails 20a are located in sockets in respective side brackets 30 connected pivotally to a mounting plate 31 screwed to the inside face of the respective side rails 11. The brackets (not shown) adjacent the control knob 13 pivot freely about a bias on the mounting plate 31 while the opposite bracket 30 is associated with a further control knob or lever on the outside of the side rails 11 such that it can be pivotal for indexed movement between a normal position, as illustrated and opposed inclined positions.

For this purpose a sleeve on the bracket 30 extends through an aperture in the plate 31 and the side rails 11. The inner end of the sleeve supports the bar 24 while the outer end supports the tilting control. Suitable indexing means may be provided and a locking nut may be threaded about the sleeve to hold the brackets 30 in their selected inclinat¬ ion to selectively position the bearing pad 16a.

In one embodiment the shaft 24 is spring biased at one end by spring 40. The other end of the shaft 24 is formed with radial projections 41 which engage in a selected one of a plurality of notches provided in the adjacent mounting plate 31. That end of the shaft has an operating knob 42 which may be manipulated by pressing it in the direction of the arrow A to cause it to compress the spring. This action disengages the radial projection from the notch. This action will enable relative rotation between side brackets 30 and plate 31. When the knob is released the projection

may be located in a different one of the notches. In this fashion the angle at which the bearing pad projects out of the plane of the backrest may be varied. In an alternative arrangement (not illustrated) a spline connection maybe provided between the shaft and the plate 31. By depressing the shaft in the manner mentioned above the shaft may be rotated and relocated in the plate 31 at a different angular position. In this way the angle at which the bearing pad projects from the backrest may be adjusted. 0 In an alternate form the control knob actuates a cam member which upon rotation bears against the back face of the bearing pad in a camming action to control its position. Also adjustable mounting means may be provided to move the bearing pad in an up and down position to suit a user. ³ Furthermore, the bearing pad could be supported by a scissors type linkage or any suitable mechanical or electrical linkage or otherwise as desired. The shaft 24 could be electrically driven and provided with remote control means.

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