Position-adjusting apparatus for mounting a reclining chair on a pedestal base
BACKGROUND OF THE INVENTION 
     1. Field: 
     The invention is in the field of reclining chairs for dental and medical patients and especially of so-called &#34;conversion units&#34; whereby modern styles of chairs of this type can replace older chairs on existing pedestal bases. 
     2. State of the Art: 
     Conversion units for such chairs have in most instances utilized the old mechanism contained in the pedestal base. However, several years ago, I designed an advanced type of conversion unit which contained its own position-adjusting mechanism. The mechanism of that conversion unit comprised a mounting plate, for fixed attachment to the existing pedestal base, and an articulated, elongate, two section, chassis frame containing an easily replaceable power package. Linkage mechanism, operable through a master bell crank that was pivotally attached to an end of a reciprocating motivator, rocked the chassis frame relative to the mounting plate on which the chassis frame was cradled to adjust the position of the chair to the work to be performed on the reclining patient. 
     3. Objective: 
     A principal objective in the making of the present invention has been retention of the advantageous features of such advanced type of conversion unit while providing improved stability for the so-mounted chair. 
     SUMMARY OF THE INVENTION 
     A feature of the invention in accomplishing the foregoing objective is resilient coupling of the pivotally attached back and seat frame sections of the chassis frame to one another. 
     The resilient coupling is accomplished by the provision of a transverse, rigid shaft between and pivotally mounting one set of corresponding ends of at least a pair of transversely spaced rods that pass through correspondingly spaced bracket members affixed to the chair seat frame section of the chassis frame. The shaft is pivotally attached to the chair back frame section of the chassis frame and the rods carry coil springs, respectively, between and with opposite ends bearing against shaft and bracket members for compression as the chair back frame section is rocked to its lowermost position. The motion-imparting linkage is pivotally attached to the shaft. 
     Further features for achieving improved stability are the relocation of a transverse leaf spring so that its ends are below the chair seat section of the chassis frame, rather than above, and the replacement of the former &#34;hinging&#34; device pivotally interconnecting the two chassis frame sections at opposite sides of the chassis frame with a uniquely rigid interconnection that still provides the required &#34;hinge&#34; movement. 
    
    
     THE DRAWINGS 
     The best mode presently contemplated for carrying out the invention commercially is illustrated in the accompanying drawings, in which: 
     FIG. 1 represents a perspective view of an upholstered dental chair incorporating the conversion unit of the invention applied to an existing pedestal base; 
     FIG. 2, a top plan view of the conversion unit per se, with the chair back frame section raised and with the pedestal indicated by broken lines; 
     FIG. 3, a righthand end elevation looking from the line 3--3 of FIG. 2 but shown as projected from FIG. 2; 
     FIG. 4, a longitudinal vertical section taken along the line 4--4 of FIG. 2; 
     FIG. 5, a view corresponding to that of FIG. 4 but with the chair back lowered and the chair seat raised; and 
     FIG. 6, a fragmentary vertical section taken along the line 6--6 of FIG. 5 and drawn to a larger scale. 
    
    
     DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENT 
     As shown in FIG. 1, an upholstered conversion unit 10 of the invention constituting a modern, reclining, dental chair is mounted in usual manner on a typical existing pedestal base 11 from which an older style dental chair had been removed. 
     In the present embodiment of the invention shown in FIGS. 2-4, articulatively joined chair back and chair seat chassis frame sections 12 and 13, respectively, of an elongate chassis frame are pivotally connected to each other end-to-end at opposite sides, but with ends overlapped, by respective pivot pins 14. These, contrary to the spring-loaded &#34;hinge&#34; arrangements previously used, enable the chair back to be fully lowered to the horizontal position shown in FIG. 5. 
     Both frame sections are rectangular in configuration, but the chair back frame section 12 is relatively short compared to the chair seat frame section 13, which is longer so as to accommodate and support the lower trunk and legs of a patient in a reclining position. Extending transversely beneath frame section 13, adjacent to but at a level below frame section 12, is a heavy mounting plate 15 provided with holes for receiving bolts 16 used in attaching the conversion unit to the base pedestal 11. Such mounting plate is pivotally attached to frame section 13 at the opposite ends of its edge lying closest to frame section 12, by pivot pin extensions 15a, respectively, FIG. 6, passing through bearing blocks 13a that are attached to and depend from frame section 13, see also FIGS. 4 and 5. 
     The two frame sections 12 and 13 are articulatively interconnected for movement relative to each other by a pair of double links 17, respectively, that extend longitudinally of mounting plate 15 below such plate. Each set of such double links 17 is pivotally connected at one end 17a to a corresponding arm 18 depending rigidly from frame section 12 at a side thereof and, at the other end 17b, to the lower arm 19a of a corresponding bell crank 19 at the same side of the frame section. The upper arm 19b of the bell crank is pivotally connected at 20 to a corresponding end of a transverse rocker shaft 21, which is itself journaled by transversely spaced bracket members 15b upstanding from fixed attachment, as by welding, to the upper surface of mounting plate 15. Bell cranks 19 are pivotally attached to a cross-member 13a of chassis frame section 13 by pairs of double links 22, which have one set of ends pivotally attached at 22a to a corresponding bell crank 19 intermediate the arms thereof and the other set of ends pivotally attached at 22b to a corresponding lug 23 projecting fixedly from frame cross-member 13a. Accordingly, chassis frame section 13 is cradled intermediate its length by rocker shaft 21 for back or forth movement about it as an axis. 
     Chassis frame section 13 is rocked about its cradle mounting axis, provided by transverse shaft 21, by means of a power package replaceably fastened in such frame section 13 and comprising a reversible motor 24, a gear box 25, and an elongate screw-threaded power output shaft 26 that extends and is screwed into an internally threaded actuator tube 27. As motor 24 rotates shaft 26 in one direction, it pulls tube 27. In the other direction it pushes tube 27. Thus, tube 27 reciprocates back or forth as power is applied to motor 24 for driving it in one direction or the other under the control of the dentist operating a push button 28 in the electrical circuitry supplying power to the motor. 
     The free end of actuator tube 27 is pivotally secured between dual upper arms 29a, respectively, of a master bell crank 29, whose dual lower arms 29b, respectively, are pivotally fastened at 30a to one set of ends of corresponding sets of double links 30, the opposite set of ends of such sets of double links 30 being pivotally fastened at 30b to corresponding arms of a set of transversely spaced arms 31 rising from rigid securement, as by welding, to frame cross-member 13a. Master bell crank 29 is journaled between its arms 29a by rocker shaft 21. Accordingly, as drive tube 27 reciprocates, it either lifts or lowers that end portion of chassis frame section 13 to which master bell crank 29 is attached and concurrently lowers or lifts the opposite end portion of such chassis frame section 13 positioned on the opposite side of the rocker axis. 
     For the purpose of enhancing stability of the chair, it is especially advantageous that a leaf spring 32 be fastened along with mounting plate 15 to pedestal base 10 by some, here two, of the bolts 16 and that it extend transversely across, but with its opposite ends below, chassis frame section 13 so as to be free to descend relative to its midportion for cushioning the approach of such chassis frame section to such pedestal base. A block 32a is interposed centrally of and between leaf spring 32 and mounting plate 15 to support the midportion of such spring and prevent its descent, thereby enabling spring to act as a shock absorber under the impact of chassis frame section 13. The leaf spring attachment bolts 16 pass through block 32a to hold it in place. 
     For the purpose of better stabilizing the chair in adjusted positions thereof and during positional adjustments thereof, the means constituting the pivotal connections 17a of the double links 17 with the depending arms 18 of chassis frame section 12 is a transverse shaft 33, and pivotally attached to such shaft in transversely spaced relationship is one set of ends 34a of a pair of transversely spaced, longitudinal rods 34, respectively, whose opposite ends 34b pass slidably through receiving openings in corresponding bracket members 35 of a pair of such bracket members depending from rigid securement, as by welding, to a frame cross-member 36 positioned across chassis frame section 13 adjacent to chassis frame section 12. Additional rods may be provided, e.g. a third one intermediate the two shown in an embodiment of chair in which the seat section remains horizontal and is not moved relative to the back section. Positioned on such longitudinal rods 34, for compression and expansion between shaft 33 and bracket members 35 as chassis frame section 12 is lowered and raised, respectively, are respective coil springs 37. 
     Tubular fittings 38 are carried in fixed positions laterally of chassis frame 13 by brackets 39 welded to the side members of frame 13 for receiving rigid attachment posts 40a, respectively, FIG. 1, of upholstered arm rests 40. 
     The manner in which chassis frame section 12 is &#34;hinged&#34; to chassis frame section 13 should be noted. Thus, chassis frame section 13 has end members 13b rigidly fastened as by welding to opposite sides thereof, respectively, FIGS. 4 and 5, and angled upwardly in elbow fashion to receive, in overlapping relationship adjacent their free ends, side members 12a, respectively, of chassis frame section 12, through which overlapped members the pivot pins 14 extend from fixed securement to the free end portion of frame member 13b. Interposed between the overlapped frame members of each set is a slippery faced washer 41, preferably of &#34;Teflon&#34; plastic adherant to the confronting face of overlapping frame end member 13b, pivot pin 14 being preferably molded or otherwise securely fixed to the overlapping portion of side member 12a of chassis frame section 12 and having its free end upset in pivot fashion against the confronting face of end frame member 13b. This arrangement could, of course, be reversed. 
     Also, by mounting the transverse leaf spring 32 under chassis frame 13 so its opposite ends are beneath the longitudinal side members of chassis frame section 13, as indicated in FIGS. 2 and 5, such chassis frame section 13 is cushioned by spring 32 acting as a shock absorber as such chassis frame section 13 descends toward the mounting pedestal 11. This is an important feature in achieving improved stability over the earlier forms of conversion unit wherein a similar leaf spring had its end mounted above chassis frame section 13. 
     Whereas this invention is here illustrated and described with specific reference to an embodiment thereof presently contemplated as the best mode of carrying out such invention in actual practice, it is to be understood that various changes may be made in adapting the invention to different embodiments without departing from the broader inventive concepts disclosed herein and comprehended by the claims that follow.