Patent Publication Number: US-6213551-B1

Title: Chair locking mechanism

Description:
BACKGROUND OF THE INVENTION 
     a) Field of the Invention 
     This invention relates to a new or improved locking mechanism for chairs and to a chair incorporating such locking mechanism. The invention is particularly although not exclusively useful with rocking and gliding arm chairs. 
     b) Description of the Prior Art 
     Numerous chair mechanisms have been proposed over the years for providing a rocking motion or a rocking and gliding motion of the chair seat, and frequently such chairs include mechanisms for locking the chair seat in a desired position relative to the chair base. Mostly these mechanisms are of considerable complexity, see for example U.S. Pat. No. 5,527,095 Marshall et al and U.S. Pat. No. 3,904,240 Rogers et al. A relatively simple locking mechanism is shown in U.S. Pat. No. 3,836,532 Caldemeyer wherein an upstanding rod pivoted to the base has serrations in its rear edge which are engageable with a pin mounted in a bracket that is affixed to the chair seat portion. A cam that is operated by a lever at the side of the seat can be swung into a position to hold the serrated rod in engagement with the pin. However this mechanism is relatively flimsy and it is doubtful that it could provide adequate resistance to the high disengagement forces which could be imposed upon the locking mechanism. 
     The aim of the present invention is to provide an improved locking mechanism is through a comparatively simple structure provides a strong and reliable locking action, and furthermore is convenient and easy for the occupant of the chair to utilize. 
     SUMMARY OF THE INVENTION 
     The present invention provides a locking mechanism for a chair having a base for supporting the chair on a floor and a chair seat positioned generally above the base and supported for movement thereon by a linkage connection, the locking mechanism being operable to immobilize said chair seat relative to said base, said locking mechanism comprising: a pin for attachment to one of said base and said seat and an elongate rack for attachment to the other of said base and said seat, said rack defining an array of teeth spaced along its length and presented towards said pin, said rack in use extending generally in a direction of movement of said chair relative to said base and being of such length that throughout at least a major part of said movement, said pin lies in register with said array of teeth; and an actuating mechanism selectively operable to effect relative movement of said pin and said rack towards one another to engage said pin with a registering tooth of said rack and thus lock said seat with respect to said base. 
     The rack is preferably pivotally attached at one end to the seat, the second end of the rack being swingable by a linkage mechanism to pivot the rack into or out of engagement with the pin on the base. The operating mechanism preferably comprises a lever handle carried on a pin and connected to a pair of pivoted strut links which can be moved through operation of the lever from a folded retracted position to at over center extended position. In the extended position the rack is advanced towards the pin to engage the latter with one of its teeth. 
     The above described locking mechanism is suitable for inclusion in many forms of chairs, and is particularly suitable for use in the kind of chair known as a gliding and rocking chair. The mechanism preferably includes a pin of substantial diameter, e.g. greater than ¼ inch, and preferably about ½ inch, engageable in deep teeth of corresponding size in the rack, this engagement providing a sufficient bearing surface to effect a secure locking action. For large chairs, and in particular for wide seating furniture such as sofas, the locking mechanism can be duplicated at opposite sides of the furniture. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
    
    
     The invention will further be described, by way of example only, with reference to the accompanying drawings wherein: 
     FIG. 1 is a top side perspective view of a rocking and gliding chair incorporating a locking mechanism in accordance with the invention; 
     FIG. 2 is a somewhat schematic side elevation of the rocking chair of FIG. 1; 
     FIG. 3 is a view similar to FIG. 2 showing the chair in a alternative position; and 
     FIG. 4 is an isometric view of the locking mechanism hardware of the chair. 
    
    
     The chair  10  shown in FIG. 1 is of the type known as a rocking and gliding chair and comprises a seat  11  supporting a back  12  and a pair of arms  13 , the central area of the seat being omitted for ease of illustration. The chair base  14  has an elevated platform section  15  which on each side provides pivotal support for front and rear pivotal links  16 ,  17  respectively. At their lower ends these links are pivoted to respective side frame rails  18  on which the seat  11  is rigidly supported by means of spaced rods  19 . As will be understood, the platform  15  together with the front and rear links  16  and  17  and the rails  18  form on each side of the chair a four bar linkage, the two linkages guiding the chair for a rocking and gliding movement relative to the base. 
     To provide for locking of the chair  10  relative to the base at different selected positions, a locking mechanism  20  (which is best seen in FIG. 4) is provided. The locking mechanism in FIG. 4 is shown isolated from the chair for clarity of illustration and comprises on each side a rear mounting bracket  21  for attachment on the underside of the chair seat  11  and an elongate toothed rack  22  having a rear end that is pivoted to the bracket  21  on a transverse axis by a pivot pin  23 . The rack  22  is oriented in a vertical plane and is upwardly arched over its length, having on its underside a series of large rounded teeth  24 . The forward end of the rack  22  is connected through a pivot pin  25  to an operating mechanism which comprises a pair of struts  26 ,  27  that are pivotally interconnected at adjoining ends by a pivot pin  28 . Forwardly of the pivot pin  25 , each rack  22  supports a laterally outwardly projecting abutment pin  25 . 1 , the function of which will become clear as this description proceeds. 
     On each side the strut  27  is fixed at its other end to a transverse square shaft  29  the opposite ends of which are journalled in brackets  30  designed for attachment to opposite sides of the seat  11 . One end of the shaft carries a plate  31  adapted to mount an operating lever  32  affixed thereto, in use the operating lever being disposed at the right hand side of the chair seat  11  in a position where it is convenient for manipulation by the occupant of the seat. 
     The locking mechanism also includes for each of the toothed racks  22  a corresponding locking pin  33  projecting laterally inwardly from a mounting plate  34  designed for attachment to the platform  15  of the chair. The various parts of the locking mechanism are fabricated in steel, and are conveniently attached to wooden portions of the chair by means of threaded screws (not shown). 
     The operation of the locking mechanism will now be described. With the pivoted rack  22  in its retracted position as shown in broken lines in FIG. 2, the teeth  24  of the rack are raised well clear of the pin  33  and therefore the rocking and gliding motion of the chair can take place without any interference from the locking mechanism. It will be noted that in this position the struts  27 ,  28  are folded relative to one another. When it is desired to lock the chair in a particular position within its range of movement relative to the base, the lever  32  is manipulated to rotate the shaft  29  which in turn unfolds the struts  26 ,  27  to a more straightened position thus effecting downwards pivotal movement of the toothed rack  22  in a vertical plane about the transverse axis defined by the rear pivot pin  23 . 
     The two toothed racks  22  pivot in unison with the shaft  29  so that the teeth  24  thereof move simultaneously into engagement with the locking pins  33  which are fixed on the platform  15 . Each of the racks  22  includes a series of teeth  24  extending along its length so that the tooth-to-pin engagement can be effected at selected positions throughout a relatively large range of movement of the chair relative to its base, as illustrated by the different positions of engagement seen in FIGS. 2 and 3. The pins  33  are of relatively large diameter, e.g. at least 0.25 inches, and are comfortably accommodated in the oversize teeth receptacles  24 , the entire locking structure being of adequate strength to withstand the bearing and other loads imposed on the locking mechanism by the occupant by the chair. 
     As seen in FIGS. 2 and 3, in the locked position, the pivoted struts  26 ,  27  are in an over-center position so that the locking mechanism is stable when locked. In other words, since in moving to the locked position the axis of the pivot pin  28  has passed slightly beyond the plane containing the axes of the pivot pin  25  and of the square shaft  29 , downward forces applied on the locking mechanism by the weight of the occupant in the chair will not tend to restore the locking mechanism to the retracted position. The locking mechanism is supported in the locking position by the abutment pin  25 . 1  at the forward end of each toothed rack  22 , this abutment pin being positioned to be engaged by the strut  26  and provide support thereto. 
     When it is desired to release the locking mechanism, the operating lever  32  is swung (in a clockwise sense as seen in FIG. 2) to move the strut linkage  26 ,  27  back through the over-center position, whereupon it can easily be restored to the folded retracted position as shown in broken lines in FIG.  2 . This unlocking movement can be performed even with an occupant seated in the chair since the mechanism is sufficiently strong and the lever  32  provides sufficient mechanical advantage to effect this unlocking movement against the imposed load.