US3203732A

US3203732A - Chair having adjustable back and seat

Info

Publication number: US3203732A
Application number: US254128A
Authority: US
Inventors: William A Hoffman
Original assignee: Individual
Current assignee: Individual
Priority date: 1963-01-28
Filing date: 1963-01-28
Publication date: 1965-08-31
Anticipated expiration: 1982-08-31

Description

Aug. 31, 1965 W. A. HOFFMAN CHAIR HAVING ADJUSTABLE BACK AND SEAT Filed Jan. 28, 1963 2 Sheets-Sheet 1 a 54 2 3 f 5 3a .30 as l ra "7 .l u 24 /I/\ V fl/Y 71 19 5 W \L/ r Tm 3 INVENTOR.

William A. Hoffman Jmfii, f

ATTORNEYS 1, 1965 w. A. HOFFMAN 3,203,732

CHAIR HAVING ADJUSTABLE BACK AND SEAT Filed Jan. 28, 1963 2 Sheets-Sheet 2 2 ,120 T My 1 A M/ 7 1 1 INVENTOR. William A. Hoffman ATTORNEYS United States Patent 3,203,732 CHAIR HAVING ADJUSTABLE BACK AND SEAT William A. Hoffman, 670 Powder Horn Road, Atlanta, Ga. Fiied Ian. 28, 1963, Ser. No. 254,123 3 (Ilaims. (111. 297313) This invention relates to furniture and is more par ticularly concerned with a chair having adjustable back and seat.

In the past, many chair devices have been produced which will permit the adjustment of the back and the adjustment of the seat so as to alter the relative positions of the two with respect to each other. Usually, such an adjustable chair involves simply the tilting of the entire back which is hinged adjacent the seat or the simultaneous shifting of the back and the seat through a complicated linkage arrangement. Such devices are either utilized as outdoor furniture and are relatively unsuited for use indoors, or they are relatively expensive and comlicated, the mechanism being unsuitable for conventional straight back, lightweight chairs.

Briefly, the present invention, which seeks to overcome the disadvantages mentioned above, includes a chair frame which is a rigid structure, including a back subframe and a seat sub-frame disposed in fixed positions with respect to each other. Each of these sub-frames carries a plurality of pivotable arms disposed in substantially parallelogram relationship, the arms carrying the supporting members, namely the seat and back, for individual adjustment. Associated with each of the parallelogram arrangements are one or a plurality of stops which limit the swing of the parallelogram pivot arms and, in certain instances, lock the arms in an extreme position.

Accordingly, the primary object of the present invention is to provide a chair in which the height, pitch and depth of the seat, and the height and pitch of the back may be respectively altered. Another object of the present invention is to provide a chair having adjustable supporting members so that the relative position of the supporting members, with respect to the chair, may be altered.

Another object of the present invention is to provide a chair having adjustable supporting members, the chair being inexpensive to manufacture, durable in structure and efiicient in operation.

Other objects, features and advantages of the present invention will become apparent from the following description when taken in conjunction with the accompanying drawings wherein like characters of reference designate corresponding parts throughout several views, and wherein:

FIG. 1 is a fragmentary vertical sectional view of a chair constructed in accordance with the present invention.

FIG. 2 is an enlarged fragmentary side view of one of the pivot arm assemblies of the chair shown in FIG. 1, the pivot arm being utilized for supporting the back of the chair.

FIG. 3 is a fragmentary vertical sectional view of a chair seat showing a modified form of the present invention.

FIG. 4 is a side elevational view of the pivot mechanism of the chair shown in FIG. 3.

FIG. 5 is a cross-sectional view taken substantially along line 55 in FIG. 4.

Referring now in detail to the embodiments chosen for the purpose of illustrating the present invention, it being understood that in its broader aspects, the present invention is not limited to the exact details herein depicted, numeral denotes generally the main frame of a conventional upright or straight chair. The frame 19 includes 3,203,732 Patented Aug. 31, 1965 a pair of front legs, such as leg 11 and a pair of back legs, such as leg 12. The

legs

11 and 12 depend from the corners of a rectangular seat sub-frame 13 which, when the

legs

11 and 12 are resting on the floor, is disposed in a relatively stationary, essentially horizontal position. The seat sub-frame 13 includes a pair of parallel longitudinally extending side bars, such as bar 14, which are rectangular in cross section, the front ends of which are joined by a front bar 15 and the rear ends of which are joined by a rear bar 16. The side bars 14 are provided with parallel upper edges, such as edge 17, which are disposed in a common horizontal plane with the

upper edges

18 and 19 of the

bars

15 and 16 respectively.

Above the sub-frame 13 is the seat supporting member which includes a flat rectangular seat plat-form 20 and a backing frame 21. The backing frame 21 is secured to the back of platform 20 and is a smaller rectangular member of essentially the same dimensions as the sub-frame 13 therebelow for registering therewith. This backing frame 21 includes a pair of side struts, such as strut 22, a front strut 23 and a rear strut 24. The arrangement is such that under normal conditions, the seat supporting frame 21 sits upon the sub-frame 13. In other words, the struts, such as strut 22, rest upon the side bars, such as bar 14, while the strut 23 rests upon the front bar 15 and the strut 24 rests upon the back bar 16. Thus, the latform 20 is disposed in its normal predetermined position.

In the embodiment here illustrated, the platform 20 is provided with such upholstery as desired, such as the usual cushion 24- which is secured to the upper or front surface of platform 29, forming with platform 20 the seat of the chair.

According to the present invention, the seat supporting member, i.e., frame 21, is movably secured to the subframe 13 by means of a plurality of pivot arm assemblies, such as assemblies 25 and 26. Pivot arm assembly 25 includes a pair of flat rectangular bracket 27 and 28, respectively, provided with inwardly protruding pivot pins 29 and 30. One end of a flat rectangular pivot arm 31 is pivotally carried by pivot pin 29 while the other end of arm 31 is pivotally carried by pivot pin 30.

Bracket 27 is secured by means of a pair of screws 32 to the inside central surface of side bar 14, adjacent but in spaced relationship to the back bar 16. In like manner, screws 33 secure the bracket 28 to the inside surface of strut 21, adjacent the back strut 24. Bracket 28 is disposed above and rearwardly of bracket 27, the arrangement being such that the pivot arm 31 projects upwardly and rearwardly from the bracket 27 at approximately a 45 degree angle, when the backing frame 21 is in registry with the sub-frame 13.

In a like manner, the pivot arm assembly 26 includes a pair of brackets 37 and 38 provided respectively with inwardly extending pivot pins 39 and 40, the brackets being secured respectively to the inside surface of side bar 14 and side strut 21 by means of

screws

42 and 43. The pivot pins 39, 4t pivotally carry the respective ends of a pivot arm 41.

It will be seen in FIG. 1 that the brackets 37 and 38 are so disposed that the pivot arm 4-1, when the backing frame 21 is in registry with the sub-frame 13, extend rearwardly and upwardly at approximately degrees from the horizontal and that pivot arm 41 is about the same length as or slightly longer than pivot arm 31.

It will be understood that the chair illustrated in FIG. 1 is symmetrical and therefore there is a complementary pivot arm assembly opposite the pivot arm assembly 25 and a second complementary pivot arm assembly opposite the pivot arm assembly 26, the two pivot arm assemblies (not shown) being secured to the inside surfaces of the side bar and side strut opposite the side bar 14 and the side strut 21.

Between the two forward pivot arm assemblies, such as assembly 26, and depending from the bottom surface of the platform 20, is a cross-bar 44 which is wider or extends further down than the front strut 23. The cross bar 44 is spaced rearwardly of the front strut 23 by a distance equal to the distance which the platform may be moved forwardly in shifting from its normal position, as shown in full lines in FIG. 1, to its raised position, as shown in broken lines in FIG. 1. The shifting of the seat assembly forwardly is accomplished by simply urging the seat upwardly and forwardly whereby the first arms 31 and 41-pivot respectively about their

pivot pins

29 and 39, passing in arcuate paths beyond their respective vertical positions so as to terminate in upwardly and forwardly inclined positions.

When the platform 20 is in its raised position, the bottom edge of the cross-bar 44 rests upon the top edge 18 of the front bar 15. Furthermore, the rear bottom edges of the side struts, such as strut 22, rest upon the top edges, such as edge 17, of the side bars, such as bar 14. In such a position, the seat is shifted forwardly from its normal position and pitched, tilted or inclined rearwardly, the rear position of platform 20 being at essentially the same height from the floor as it was previously. The forward edge portion of the platform 20 is, however, substantially raised, thereby giving a feeling that the entire seat has been raised.

With respect to the back of the chair, it includes a back sub-frame 49 which comprises a pair of upright standards, such as standard 58, which project from and are integrally joined to the upper end of the legs 12, the upper ends of the standards, such as standard 50, being connected by cross bar 51. The supporting member includes a rectangular backing frame 52 which is provided with vertically extending side bars, such as bar 53, and horizontally extending

cross bars

54 and 55 which connect the ends of the side bars, such as bar 53. Connected to the front surface of the backing frame 52 is the back board, plate, or platform 56 which may include such upholstery as desired or may be contoured to fit the shape of the back of a person, all as being well known by those skilled in the art.

According to the present invention, the backing frame 52 is movably connected to the sub-frame 49 of the back by means of a plurality of pivot arm assemblies, in a manner very similar to the connecting of the backing frame 21 to its sub-frame 13. In more detail, backing frame 52 is connected to the sub-frame 49 by means of a plurality of pivot arm assemblies, such as upper pivot arm assembly and lower pivot arm assembly 66.

The upper pivot arm assembly includes, as seen in FIGS. 1 and 2, a pair of brackets 67 and 68, secured respectively to standard 50 and side bar 53, in the same manner as the securing of brackets 27 and 28 to their respective frames. Brackets 67 and 68 are provided with

pivot pins

69 and 70, respectively, the

pins

69 and 70 extending inwardly toward the central portion of the chair and respectively journaling the ends of a pivot arm 71.

The difference between the

pivot arm assembly

25 and 65 is that the pivot arm assembly 65 is provided with a means for locking the arm 71 in one extreme position. This means includes a key-hole slot 73 in the end of arm 71 which is pivoted about pivot pin 69. For cooperating with the keyhole slot 73, the pivot pin 69 is provided with flat opposed parallel chordal portions 74, these chordal portions being spaced apart by a distance approximately the width of the slotted narrow portion of the key-hole slot 73. On the other hand, the diameter of the pivot pin 69 is substantially the diameter of the widened or cylindrical portion of key-hole 73, to provide the normal hearing portion of the pivot pin 69. It will be observed in FIG. 2 that the chordal portions 74 are disposed in an upwardly and forwardly protruding direction with respect to the bracket 67 and, hence, with respect to the standard 50. Therefore, the arm 71 must be disposed in an upwardly and forwardly protruding position with respect to pivot pin 69 in order that the chordal portions 74 be aligned With and be adapted to be received in the narrow portion of the slot 73, upon rearward movement of arm 71.

The pivot arm assembly 66 is essentially the same as the pivot arm assembly 26 and therefore is not described in detail. Normally, the

arms

71 and 81 of the respective

pivot arm assemblies

65 and 66 are disposed parallel to each other, as shown in full lines in FIG. 1. To prevent further clockwise; i.e. downward, movement of these

pivot arms

71 and 81, the standard 50 is provided with a pair of blocks 82 and 83 which protrude inwardly below the

pivot arms

71 and 81 at an appropriate position to hold such arms in essentially horizontal positions.

As mentioned previously, since the chair here disclosed is symmetrical, there are complementary pivot arm assemblies (not shown) which are opposed to the

pivot arm assemblies

65 and 66 and are connected to the sub-frame 49 and the backing frame 52 of the back on the opposite side from the side containing the

pivot arm assemblies

65 and 66.

t should now be apparent that while the normal position of the platform 56 and its backing frame 52 is shown in full lines in FIG. 1, this frame may be shifted to a position shown in broken lines in FIG. 1 by simply lifting the platform 56 and its backing frame 52 so that the pivot arms 71 and S1 pivot upwardly in arcuate paths about their pivot pins, such as pin 69. When the pivot arm 71 is positioned in alignment with the chordal portions 74 of pivot pin 69, the upper portion of platform 56 and its backing frame 52 may be urged inwardly, thereby urging the pivot arm 71 inwardly with respect to pivot pin 69 such that the chordal portions 74 are received in the narrow portion of key-hole slot 73. Thus, the broken line position shown in FIG. 1 is attained and the stationary pivot pin 69 prevents downward pivoting of the platform 56 and its backing frame 52, to maintain them in that position.

Referring now to FIGS. 3, 4 and 5 of the drawings, it will be seen that, if it is desirable to provide a variable height for the platform of the seat, this may be accomplished by providing shiftable pivot pins on the pivot arm assemblies. In more detail, it will be seen that the portion of the chair illustrated, includes a sub-frame 113 having side bars 114 and end

bars

115 and 116, all arran ed in the same manner as the arrangement of the sub-frame 13. Further, the sub-frame 113 is supported by legs, such as leg 111, so that it is disposed in an essentially horizontal position.

For registry with the sub-frame 113 there is a backing frame 121 which carries the seat platform 120. The backing frame 121 includes side struts, such as strut 122, and front and back struts 123 and 124, respectively. Protruding inwardly from side struts, Such as strut 124, are pivot pins, such as pin and 140, which respectively pivotally carry the pivot arms, such as pivot arms 131 and 141. These pivot arms, of course, normally extend downwardly and forwardly from the backing frame 121 and terminate within the sub-frame 113, being provided with inwardly protruding pivot pins 129 and 139, respectively. It will be understood that, in this embodiment, the pivot pins 129 and 139 are each fixed with respect to their pivot arms 131 and 141 and, hence, are rotated with these arms.

The pivot pins 129 and 139 protrude, respectively, through irregularly shaped slots denoted generally by the

numerals

133 and 143 in

brackets

127 and 137.

Brackets

127 and 137 are substantially identical to each other in configuration, however, as seen in FIG. 3, the bracket 137 is larger than the bracket 127 and, likewise, the slot 143 is longer than the slot 133. Each bracket, such as bracket 137, is spaced inwardly from the side bar, such bar 114,

to which it is attached, so as to provide for the free pivoting through a limited arc, of the pivot arm which it carries. The mounting of the bracket is essentially identical for each of

brackets

129 and 137. For example, bracket 137 is provided with a plurality of spacer lugs 144 through which bolts or screws 145 protrude into side bar 114.

Referring now to the pivot pin 139, which is best seen in FIG. 4, this pin is flattened on opposite sides so as'to provide parallel chordal surfaces 146 which are essentially parallel with the axis of pivot arm 141. The pivot pin 139 is also provided with a wide, fiat head 147, inwardly of the bracket 137 so as to retain the pivot pin in the slot 143.

The slot 143, as best seen in FIG. 4, is vertically elongated and includes a pair of

circular openings

148 and 149 at the upper and lower extremities of slot 143. Extending between these

circular openings

148 and 149 which define the limits of the slot 143 is a narrowed passageway 160 which is interrupted at one or a plurality of spaced locations therealong, by circular openings such as opening 150. The

circular openings

148, 149 and 150 are of essentially the same diameter as each other and of the major diameter of the pivot pin 139 whereby the pivot pin may be selectively journaled in any one of these

openings

148, 149 or 150. It will be understood that when, and only when, the axis of pivot arm 141 is aligned with the axis of slot 143, the chordal surfaces 146 will be aligned with the passageway 160 and thus the pivot pin 139 may be shifted to any one of the

circular openings

148, 149 or 150. When disposed in one of these

circular openings

148, 149 or 150, and upon movement of the pivot arm 141 out of alignment with the slot 143, the pivot pin becomes locked in the selected

circular opening

148, 149 and 150.

The slot 133 is essentially the same as the slot 143, except that it is not as long as the slot 143. Therefore, no detailed description of this slot is necessary. Furthermore, the pivot pin 129 is substantially identical to the pivot pin 139 and, hence, no detailed explanation of this pivot pin is necessary. It will be understood, however, that since the pivot arms 131 and 141 are essentially parallel, and remain so at all times, the axis of pivot arm 131 may be aligned with the axis of its slot 133 at the same time that the axis of pivot arm 141 becomes aligned with its slot 143. Hence, at that position, the platform 120 may be raised or lowered by manually shifting it upwardly or downwardly whereby the pivot pins 129 and 139 are simultaneously shifted from one circular opening to the other in their

respective slots

133 and 143.

Referring now to FIG. 3 of the drawings, it will be seen that a pair of arresting blocks 182 and 183 protrude inwardly from the side bar 114, adjacent its upper edge and in front, respectively, of the

brackets

127 and 137. The arresting blocks 182 and 183 cooperate respectively with stops 184 and 185, each stop being a downwardly protruding member secured to the backing frame 121. The stops 184 and 185 are provided with lower edges which are saw-tooth in arrangement so as to provide step-like ledges 186 and 187, respectively, which may be selectively received on the blocks 182 and 183. Preferably, the step-like ledges 186 and 187 are inclined in a forwardly and downwardly direction while the upper surfaces of the blocks 182 and 183 are inclined in a like manner so as to permit the ledges 186 and 187 to mate therewith.

It will be understood, of course, that the stops 184 and 185 are spaced rearwardly of the blocks 182 and 183 when the backing frame 121 is in registry with the sub-frame 113. However, depending upon which of the circular openings the

pins

129 and 139 are in, the stops 184 and 185, upon shifting of the platform 120 forwardly and upwardly are positioned over the blocks so that one of the ledges 186 rests upon the block 182, as one of the ledges 187 rests upon block 183. Thus, the platform 120 and its backing frame 121 may be shifted from the position shown in full lines in FIG. 3 to the position shown 6 in broken lines therein. When shifted from its rearmost or normal position to its forwardmost position, the platform will be provided with a greater pitch, as shown in broken lines in FIG. 3.

In an intermediate position of platform 120, arms 131, 141 space the platform 120 from its sub-frame 113; however, in either extreme position of platform 120, arms 131 and 141 are either extending forwardly and upwardly or rearwardly and upwardly and hence, pins 129 and 139 cannot shift upwardly or downwardly in their

slots

133 and 143 while in such extreme position. At an intermediate position of platform 120, however, the height of platform 120 may be selectively altered through one of a plurality of positions of

pins

129 and 139.

From the foregoing description, it will be understood that the pivot pins of each support member pivot in parallel longitudinal planes and that the pivot pins therefor extend transversely parallel to each other. Further, in shifting of the seat supporting member from one position to the other, the pivot arms are sufficiently long thatthey space the seat backing frame from the sub-frame at an intermediate position of the support member.

While I have chosen to describe my invention with reference to a straight chair for which it is particularly adapted to provide an inexpensive means by which the support platforms are rendered adjustable with respect to the :chair frame, it will be understood that the present invention is suited for use in other forms of furniture, such as in loveseats and in upholstered chairs, or the like.

It will be obvious to those skilled in the art that many variations may be made in the embodiments here chosen for the purpose of illustrating the present invention without departing from the scope thereof as defined by the appended claims.

I claim:

1. A chair comprising a seat sub-frame, legs extending from said seat-sub-frame for supporting said seat subframe in about a horizontal position, a seat support member disposed over said seat sub-frame, said seat support member being characterized by a backing frame adapted to rest upon said seat sub-frame in one position of said seat support member, a seat platform carried by said seat sub-frame, a plurality of forward and rear seat pivot arm assemblies connecting said seat sub-frame and said seat backing frame, said pivot arm assemblies including pivot arms and pivot pins pivotally connecting the ends of said pivot arms respectively to said seat sub-frame and said seat backing frame, said pivot arms being pivotal in parallel longitudinal planes, said pivot arms extending rearwardly and upwardly from said sub-frame when said seat backing frame is resting upon said seat sub-frame, said seat support member being movable with respect to said seat sub-frame from its position resting upon said seat subframe to a position shifted forwardly thereof, said pivot arms extending forwardly and upwardly from said subframe when said seat support member is in its shifted position, and a stop extending downwardly from said seat support member and engageable with said seat sub-frame when said seat support member is in its forwardly shifted position.

2. A chair comprising a rectangular seat sub-frame, legs extending from said seat sub-frame for supporting said seat sub-frame in about a horizontal position, a seat support member disposed over said seat sub-frame, said seat support member being characterized by a backing frame adapted to register with said seat sub-frame in one position of said seat support member, a seat platform carried by said seat sub-frame, a plurality of forward and rear seat pivot arm assemblies connecting said seat subframe and said seat backing frame, said pivot arm assemblies including pivot arms and pivot pins pivotally connecting the ends of said pivot arms respectively to said seat sub-frame and said seat backing frame, said pivot arms being pivotal in parallel longitudinal planes, said pivot arms extending rearwardly and upwardly from said sub-frame when said seat backing frame is in registry with said seat sub-frame, said seat support member being movable with respect to said seat sub-frame from its position in registry with said seat sub-frame to a position shifted forwardly thereof, said pivot arms extending forwardly and upwardly from said sub-frame when said seat support member is in its shifted position, and a stop extending downwardly from said seat support member and engageable with said seat sub-frame when said seat support member is in its forwardly shifted position, said forward pivot arm assemblies being of a different configuration than said rear pivot arm assemblies by which a pitch is imparted to said seat support member as said seat support member is moved to its forwardly shifted position.

3. A chair comprising a rectangular seat sub-frame, legs extending from said seat sub-frame for supporting said seat sub-frame in about a horizontal position, a seat support member disposed over said seat sub-frame, said seat support member being characterized by a backing frame adapted to register with said seat subframe in one position of said seat support member, a seat platform carried by said seat sub-frame, a plurality of forward and rear seat pivot arm assemblies connecting said seat subframe and said seat backing frame, said pivot arm assemblies including pivot arms and pivot pins pivotally connecting the ends of said pivot arms respectively to said seat sub-frame and said seat backing frame, said pivot arms being pivotal in parallel longitudinal planes, said pivot arm-s extending rearwardly and upwardly from said sub-frame when said seat backing frame is in registry with said seat sub-frame, said seat support member being movable with respect to said seat sub-frame from its position in registry with said seat sub-frame to a position shifted forwardly thereof, said pivot arms extending forwardly and upwardly from said sub-frame when said seat support member is in its shifted position, a stop extending downwardly from said seat support member and engageable with said seat sub-frame when said seat support member is in its forwardly shifted position, said forward pivot arm assemblies being of a different configuration than said rear pivot arm assemblies by which a pitch is imparted to said seat support member as said seat support member is moved to its forwardly shifted position, and means for varying the position of certain of said pivot pins for varying the height of said seat supporting platform.

References Cited by the Examiner UNITED STATES PATENTS 301,913 7/84 Miller 297-313 956,681 5/10 Clarke 108-4 1,258,640 3/18 Abramson 108-4 1,829,288 10/31 May 108-4 1,835,048 12/31 Hottel 297-383 2,292,618 8/42 Davis 297-338 2,549,902 4/51 Hibbard et a1. 297-325 2,646,839 7/53 Hillman 297-313 2,766,088 10/56 Jackson 108-138 2,767,777 10/56 Kriger et a1. 297-383 2,780,276 2/57 Valente 297-338 FOREIGN PATENTS 14,505 1888 Great Britain. 515,788 12/39 Great Britain. 6,767 5 93 Switzerland.

FRANK B. SHERRY, Primary Examiner.

Claims

1. A CHAIR COMPRISING A SEAT SUB-FRAME, LEGS EXTENDING FROM SAID SEA-SUB-FRAME FOR SUPPORTING SAID SEAT SUBFRAME IN ABOUT A HORIZONTAL POSITION, A SEAT SUPPORT MEMBER DISPOSED OVER SAID SEAT SUB-FRAME, SAID SEAT SUPPORT MEMBER BEING CHARACTERIZED BY A BACKING FRAME ADAPTED TO REST UPON SAID SEAT SUBFRAME IN ONE POSITION OF SAID SEAT SUPPORT MEMBER, A SEAT PLATFORM CARRIED BY SAID SEAT SUB-FRAME, A PLURALITY OF FORWARD AND REAR SEAT PIVOT ARM ASSEMBLIES CONNECTING SAID SEAT SUB-FRAME AND SAID SEAT BACKING FRAME, SAID PIVOT ARM ASSEMBLIES INCLUDING PIVOT ARMS AND PIVOT PINS PIVOTALLY CONNECTING THE ENDS OF SAID PIVOT ARMS RESPECTIVELY TO SAID SEAT SUB-FRAME AND SAID SEAT BACKING FRAME, SAID PIVOT ARMS BEING PIVOTAL IN PARALLEL LONGITUDINAL PLANES, SAID PIVOT ARMS EXTENDING REARWARDLY AND UPWARDLY FROM SAID SUB-FRAME WHEN SAID SEAT BACKING FRAME IS RESTING UPON SAID SEAT SUB-FRAME, SAID SEAT SUPPORT MEMBER BEING MOVABLE WITH RESPECT TO SAID SEAT SUB-FRAME FROM ITS POSITION RESTING UPON SAID SEAT SUBFRAME TO A POSITION SHIFTED FORWARDLY THEREOF, SAID PIVOT ARMS EXTENDING FORWARDLY AND UPWARDLY FROM SAID SUBFRAME WHEN SAID SEAT SUPPORT MEMBER IS IN ITS SHIFTTED POSITION, AND A STOP EXTENDING DOWNWARDLY FROM SAID SEAT SUPPORT MEMBER AND ENGAGEABLE WITH SAID SEAT SUB-FRAME WHEN SAID SEAT SUPPORT MEMBER IS IN ITS FORWARDLY SHIFTED POSITION.