MXPA98000973A - Height adjustment mechanism for the support of any si - Google Patents

Abstract

The present invention relates to an adjustment mechanism for releasably retaining a backrest in a plurality of selected positions relative to a seat, the adjustment mechanism comprising: a channel member adapted to be rigidly secured to one of said backrest and seat; a support member slidably received by said channel member and adapted to be rigidly secured to the other of said backrest and seat, a first plurality of vertically aligned rack teeth extending in a generally lateral direction from one of the channel member and the support member: a second plurality of vertically aligned rack teeth extending from said one of the channel member and the support member in the same direction as the first plurality of rack teeth, said second plurality of rack teeth being separated and generally parallel to said first plurality of teeth of cr rack, and a pin having a first ratchet and a second ratchet adapted to selectively couple simultaneously the first and second respective plurality of rack teeth, wherein said pin slides in a plane defined by the first and second plurality of teeth of rack and place the first and second pawls in engagement with the first and second plurality of rack teeth, whereby the backrest is retained and does not fall from a desired vertical position by coupling the first and second pawls with the first and second pawls. plurality of cremalle teeth

Description

MECHANISM OF HEIGHT ADJUSTMENT FOR THE SUPPORT OF A CHAIR BACKGROUND OF THE INVENTION The present invention relates in general to a mechanism for adjusting the height of a backrest in relation to the seat of the chair, and more particularly, to a rack and ratchet mechanism that will facilitate the assembly of the chair in the user's place after being embarked in a semi-armed condition. An assembled chair requires a large shipping carton that increases the cost of freight. For this reason, it is advantageous and economical to ship products such as chairs in a partially assembled or "semi-assembled" condition. Another advantage of boarding products such as saddles in the "semi-armored" condition is that the individual components can be packaged so that the chances of damage during boarding are reduced compared to the boarding of the fully assembled chair. However, when a product is shipped in the "semi-armed" condition, the final assembly is the responsibility of the consumer. For this reason, it is important that the products that will be shipped in the "semi-armed" condition are designed and constructed for an easy final assembly by the consumer. The position of the backrest of a chair in relation to the seat of the chair is an important consideration for the comfort of the user. In this way, it is important to provide an adjustment mechanism that is easy and convenient for the user. An operator can locate the most suitable location for the backrest if the adjustment is made while the user is sitting in the chair. It is also important that the backrest can be adjusted in small increments to obtain the most suitable location. Since some chair users want to adjust the backrest to suit the particular task they are performing or to adjust in different locations and provide a variety of sitting postures, it is important that the backrest can be adjusted easily and quickly . Due to the above reasons, there is a need for an adjustable backrest for a chair that can be produced inexpensively, assembled conveniently and easily after being shipped in the "semi-armed" condition, and that is simple and practical of driving to readjust after the final assembly.

BRIEF DESCRIPTION OF THE INVENTION The present invention is directed to an apparatus that can be easily assembled after having been shipped in the "semi-armed" condition, and which can be adjusted in small increments by the operator while sitting so that the person making the adjustment can feel when the backrest is in its optimal location. According to the invention, the portion of the adjustment mechanism carried by the backrest can be assembled completely before boarding and the backrest only needs to be slid over the seat support bar to complete the local assembly. The adjustment mechanism will allow the backrest to be adjusted upward by exerting an upward force on the backrest. This is particularly important when small increment adjustments are desired. To achieve such upward adjustment, the person performing the adjustment can place both hands and exert upward pressure on both sides of the backrest. This adjustment could also be achieved with just one hand. The lever for releasing the pin mechanism is accessible from the front or back of the chair and by a person seated in the chair. This lever must be depressed when you want to decrease the location of the backrest. This invention consists of a chair, including an adjustment mechanism for releasably retaining a backrest in a plurality of selected positions relative to a seat, which can be shipped in a "semi-armed" condition and easily assembled by the consumer. Furthermore, this invention consists of an adjustment mechanism comprising a channel member that is adapted to be rigidly secured to one of said backrest and seat, and a support member slidably received by the channel member and adapted to be rigidly secured to the other of said backrest and seat so that the backrest and seat can be assembled by a simple sliding operation. The adjustment mechanism of this invention consists of vertically aligned rack teeth that extend from the support member, and a movable pin having ratchets that are adapted to engage the rack teeth, movement of the pin engages the ratchets in engagement with the rack teeth to prevent downward movement of the backrest from a selected vertical position. The present invention, together with additional objects and advantages, will be better understood by reference to the above detailed description taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a perspective view of a chair backrest locked in a selected position in relation to a chair support member. Figure 2 is an exploded perspective view of a chair back and a chair support member.

Figure 3 is a perspective view of the bottom surface of the stop pad or support member. Figure 4 is a plan view of the bottom surface of the stop pad or support member. Figure 5 is a side view of the abutment pad or support member. Figure 6 is an end view of the abutment pad or support member. Figure 7 is a perspective view of the pin. Figure 8 is a plan view of the pin. Figure 9 is a side view of the pin. Figure 10 is a bottom view of the pin. Figure 11 is a side view of the lever. Figure 12 is a bottom view of the lever. Figure 13 is a rear view of the backrest and the seat support member, with the backrest in its lowermost adjusted position and with a portion of the channel open to expose the teeth engaged from the zipper and ratchet. Figure 14 is a cross-sectional view of the backrest and seat support member taken along the lines 14-14 of Figure 13. Figure 15 is a rear view of the backrest and the seat support member with a portion of the open channel to expose the uncoupled teeth of the rack and ratchet.

Figure 16 is a rear view of the backrest and the seat support member, with the backrest in its highest adjusted position, and with a portion of the channel open to expose the teeth coupled to the rack and ratchet. Figure 17 is a cross-sectional view of the backrest and chair support member taken along lines 17-17 of Figure 16. Figure 18 is a partial cross-sectional view of the rack, ratchet and lever, taken along lines 18-18 of Figure 15.

DETAILED DESCRIPTION OF THE PREFERRED MODALITY Referring to the drawings, Figure 1 shows the back of a chair backrest 10 adjustably connected to a chair or bar support member 40.

As is well known in the art, the support member is rigidly secured to the seat of a chair; the back of the chair 10 is formed by a hard cast plastic shell 20 having a portion of a receptacle 11 integrally formed therein for receiving the support member or bar 40. The receptacle 11, (see figure 2) includes a rib 12 extending horizontally and extending outward from the shell. As will be described in more detail, the shell 12 acts as a stop contacting the upper edge of the stop pad or support member 70 when the backrest 10 is lowered to its lowermost position. The receptacle 11 also includes walls 13 and 14 that extend vertically and join with the rib 12 at their upper ends. Projections 15 and 16 extend towards each other from vertically extending walls 13 and 14. The receptacle 11 is reinforced by a plurality of radially extending ribs 17 and internal ribs 18 which are all integrally cast with the hard cast plastic shell 20. Other ribs define a horizontally extending channel 19 that is open on the side right for a purpose that will be described later. The receptacle 11 is completed by a U-shaped channel member 30 which includes outwardly extending mounting flanges 32 which are connected to the walls 13 and 14 which extend vertically by means of fastening devices 34. The mounting flanges 32 extend under the projections 15 and 16. With the channel member 30 secured to the walls 13 and 14 that extend vertically, a vertically extending receptacle and having a rectangular cross-section is provided, which is adapted to receive the upper end of the bar or support member 40. Referring now to Figures 2, 7, 8, 9 and 10, the pin 48 will be described. Figure 2 is similar to Figure 1, however, the bar or support member 40 has been removed from the receptacle and a section of the channel member 30 has been opened to expose the pin 48. The pin 48, as best seen in Figures 7-10, has a generally rectangular shape and includes an angled end surface 50. The pin 48 is slidably received in the horizontally extending channel 19 which is formed integrally with the shell Hard cast plastic. The pin 48 and the channel 19 are configured so that although the pin can move horizontally in the slot, it is limited to sliding in a straight line movement as a result of the slidable engagement of the pin 48 with the walls of the channel 19. The pin 48 has an outer surface 49 which is in a vertical plane when the pin is installed as seen in Fig. 2. A first ratchet 52 and a second ratchet 54 exit outward from the surface 49 of the pin 48. The first ratchet 52 it includes a plurality of vertically aligned pin teeth 56, the upper ends of which are inclined and whose lower ends are horizontal. The second ratchet 54 includes a plurality of vertically aligned pin teeth 58, the upper edges of which are inclined and whose lower edges are horizontal. The first ratchet 52 and the second ratchet 54 are spaced in the horizontal direction, and the teeth 56 and 58 extend in the same direction. The channel 19 is open on the right side as seen in Figure 2, and the angled end surface 50 of the pin 48 is located at the open end of the slot. The angled end surface 50 is in slidable engagement with an end surface 64 angled in complementarity to a lever 62. As best seen in Figure 10, the pin 48 has a spring receiving notch 51 at its end opposite the angled end surface. 50. A spiral spring 60 bears against the vertically extending wall 13 on a guide pin 21 and extends into the notch 51. The spiral spring 60 functions to urge the pin 48 to the right as seen in FIG. Figures 2, 13 and 8. The lever 62, shown in isolation in Figures 11 and 12, has an upper portion that extends generally horizontally 67 and a lower portion that extends generally vertically 66. It should be noted Figure 12 is a bottom view of the lever 62 and thus appears inverted to the position in which it appears in the other figures. The portion 67 extending generally horizontally terminates in a complementary angle end surface 64 which is in slidable engagement with the angled end surface 50 of the pin 48. The lever 62 is limited to the vertical sliding movement on the surface of the shell. hard plastic 20 by a guide pin 22 and a slot 26 which are, in the preferred embodiment, integrally cast with the hard plastic shell 20. The lever 62 has a reinforced slot 63, dimensions for slidably receiving the pin 22, formed in its portion that extends generally vertically 66. The lever 62 has a vertically extending and vertically extending shoulder 25 (see Figure 12) that slides in the groove 26 formed in the hard shell. The edge guides 23 which are integrally cast with the hard plastic shell 20, are located on each side of the reinforced slot 63. The edge guides 23 engage flat surfaces on the upper surface of the lever 62 and function to retain the lever 62 against the surface of the hard plastic shell 20. The lever 62 is provided with a flange 65 around its edge, which works to reinforce it. The rim 65 is removed (see Figure 11) from the upper surface of the lever 62 in the area in which the edge guides 23 are located. The lowermost edge of the generally vertically extending portion 66 is a handle 68. It should be noted that a flat surface of the handle 68 slides against a complementary flat surface 24 of the hard plastic shell 20. The lower edge 69 of the handle 68 extends below the lower edge of the backrest 10 and thus, It can be observed and manipulated from the front, as well as from the back of the chair. Figure 13 describes the preferred embodiment of the reinforcing ribs extending radially 17. Figure 13 is a rib added as additional C 17a and ribs 17 extending radially, and are not described in the embodiment described in the other figures. Isolated illustrations of the abutment pad or support member 70 are shown in FIGS. 3 to 6. The abutment pad or support member 70 has a cross section similar to that of an I-beam. Plate 78 has flanges 84 and 82 along their longitudinal edges. The surface 79 of the plate 78 observed in FIGS. 3 and 4 is the surface facing toward the backrest 10. A portion of the opposite surface 80 of the plate 78 can be seen in FIG. 2 below the open portion of the bar or support member 40. The bar 40 is secured to the surface 80 of the stop pad or support member 70. The upper edge of the bar 40 has a notch 42 formed therein which receives a box segment 86, which described later, when the bar 40 is secured to the surface 80 of the stopper pad or support member 70. in the preferred embodiment, a foam pad 44 is used (see figures 5 and 18) having adhesive on both surfaces , to secure the bar 40 to the surface 80; however, other adhesive means or fastening devices may be used. It should be noted that the foam pad 44 observed in FIGS. 5 and 18 is not included in the other figures in an effort to simplify and clarify the drawings. A first set or plurality of rack teeth 72 extend upward from the surface 79 of the plate 78 and extending parallel to flange 82. A second set or plurality of rack teeth 74 extend upward from the surface 79 of the plate 78 and they extend parallel to the flange 84. The rack teeth 72 and 74, as seen in FIGS. 3 and 4, have flat horizontal upper surfaces and flat inclined lower surfaces. A box segment 86 exits from the upper central portion of the surface 80. The upper surface 87 (see Figure 2) of the box segment 86 lies in the plane of the edges of the flanges 82 and 84. A projection in the form of hook 46 extends upwards and then downwards from the upper surface 87. As best seen in Figure 4, grooves 88 that terminate in tension relief holes 89 are cut in the upper surface 87 to provide an assembly of spring cantilever projecting hook 46. the mounting cantilever spring for projecting hook 46 permits it to be depressed when the bar 40 with the stopper pad or support member 70 secured thereto is inserted through the channel formed on the backrest 10 and then spring back out when the upper edge of the stop pad or support member has come out of the channel. After the backing 10 has been assembled on the bar 40, the hook-shaped projection 46 is free to engage a notch 36 as seen in Figure 2, formed at the upper edge of the U-shaped channel member. and therefore functioning as a limiting stop when the backrest is in its highest position. A spring member 85 is provided on the outer surface of the rim 84, which engages the inner surface of the U-shaped channel member 30 to ensure a smooth sliding action therebetween. The backing 10 is assembled by the manufacturer with the components positioned as shown in Figure 2. With the components thus positioned, the spring 60 urges the pin 48 to the right, causing its angled end surface 50 to exert pressure against the complementary angled end surface 64 of the lever 62, which causes the lever 62 to move downwardly towards the place where the pin 22 engages the upper end of the slot 63. the pin 48 can be raised from its position in the horizontally extending channel 19 but preventing it from exiting the channel 19, by means of the U-shaped channel member 30. The backrest 10 can be lowered onto the bar or chair support member 40 so that the upper edge of the stop pad or support member 70 is inserted into the receptacle 11. Upon entering the upper edge of the stop pad or support member 70 into the receptacle 11, the edge incli- The hook 46 meets the edge of the U-shaped channel member 30. The hook 46, as a result of its cantilever spring assembly, is depressed and slides along the inner surface of the channel member in the form U when lowering the backrest on the bar 40 and the stop pad or support member 70. When the hook 46 reaches the groove 36 formed in the U-shaped channel member 30, it snaps outwardly. If the backing 10 is then moved upward, the hook 46 engages the horizontal edge of the notch 36 and prevents further upward movement of the support 10. If desired to remove the support 10 of the bar 40, the hook 46 is depressed manually to raise the backrest 10. When the backrest 10 is installed on the bar 40, the lever 62 must be coupled to move the pin 48 from right to left as seen in Figure 2. The lever 62 is engaged by applying a rising pressure on the handle 68, which causes the angled end surface 64 to move towards above. The end surface 64 is coupled to the angled end surface 50 which is displaced to the left in response to upward movement of the angled end surface 64. If the lever 62 is not depressed when the backrest 10 is installed on the bar 40, the surfaces flat tops of the rack teeth 72 and 74 would meet the flat bottom surfaces of the pin teeth 56 and 52, which would prevent further downward movement of the backrest 10. The displacement of the pin 48 to the left leads to the teeth of pin 56 and 58 with this and, as seen in figure 2, allows the rack teeth 72 and 74 to pass to the right of the pin teeth 56 and 58. After the backrest 10 has been installed, the lever 62 is released and the teeth 56 and 58 of the pin move to the right to engage the rack teeth 72 and 74. It should be noted that the inclined surfaces of the pin teeth 56 and 58 are moved away from each other. see inside the surface a coupling with the inclined surfaces of the rack teeth 72 and 74 when the lever 62 is released. With these surfaces in engagement, if the backrest is moved upward, the pin teeth 56 and 58 will be transported to the left by the inclined surfaces of the rack teeth 72 and 74. When the pin teeth 56 and 58 reach the peak of the rack teeth 72 and 74, the spiral spring 60 will cause them to be inserted into the surface and make surface contact with the next set of rack teeth 72 and 74. In this way, step-by-step ratchet feeding is provided. backrest 10 upwards in the bar 40. The teeth 56, 58, 72 and 74 have a vertical dimension of approximately 6.35 mm and in this way, the height of the backrest can be raised in increments of 6.35 mm. As mentioned above, if it is desired to lower the backrest 10 relative to the bar 40, the lever 62 must be depressed and the backrest descended while depressed. The backrest 10 will lock in the location it is in when the lever 62 is released. It is desired that the annexed drawings and the above detailed description be considered in all respects as illustrative and not as restrictive; it is intended that the scope of the invention encompass any equivalents, alternatives and / or modifications of elements that fall within the spirit and scope of the invention, and that all changes within the meaning and scale of equivalences of the claims are designed therefore to be covered in it.

Claims (25)

NOVELTY OF THE INVENTION CLAIMS

1. - An adjustment mechanism for releasably retaining a backrest in a plurality of positions selected in relation to a seat, the adjustment mechanism comprising: a channel member adapted to be rigidly secured to one of said backrest and seat; a support member slidably received by said channel member and adapted to be rigidly secured to the other of said backrest and seat; a first plurality of vertically aligned rack teeth that extend in a generally lateral direction from one of the channel member and the support member; a second plurality of vertically aligned rack teeth extending from said one of the channel member and the support member in the same direction as the first plurality of rack teeth, said second plurality of rack teeth being spaced apart and generally parallel to each other. said first plurality of rack teeth; and a pin having a first ratchet and a second ratchet adapted to selectively couple the first and second respective plurality of toothed teeth simultaneously; wherein said pin slides in a plane defined by the first and second plurality of rack teeth and places the first and second pawls in engagement with the first and second plurality of rack teeth; whereby the backrest is retained and does not fall from a desired vertical position by engaging the first and second pawls with the first and second plurality of rack teeth.

2. The adjusting mechanism according to claim 1, wherein the first and second pawls are aligned horizontally and extend in the opposite direction to the first and second plurality of rack teeth, and wherein said pin is adapted to moving in a horizontal and linear direction to releasably couple said first ratchet with selected teeth of said first plurality of rack teeth and said second ratchet with teeth selected from said second plurality of rack teeth.

3. The adjusting mechanism according to claim 2, further comprising a spring for driving the first and second pawls in engagement with said first and second plurality of rack teeth, and a coupling lever operable with the pin, said The pin has an angled end portion in slidable engagement with a complementary angled end portion of the lever so that the movement of the lever causes a cam action that moves the pin in said lateral, horizontal and linear direction.

4. The adjusting mechanism according to claim 3, wherein the lever has a lower vertical portion that is slidably mounted to the backrest, whereby the vertical actuation of the lever results in the horizontal actuation of the pin.

5. The confymetry adjustment mechanism of claim 1, wherein the first ratchet comprises a first plurality of vertically aligned pin teeth engaging selected teeth of a first plurality of rack teeth, and the second ratchet comprises a second plurality of vertically aligned pin teeth engaging selected teeth of said second plurality of rack teeth.

6. The adjusting mechanism according to claim 1, wherein the first and second plurality of rack teeth and the first and second ratchets are configured so that the backrest moves upwardly when coupling the first and second ratchets the first and second plurality of rack teeth in a ratchet type shape.

7. The adjustment mechanism according to claim 6, wherein the first and second plurality of rack teeth extend from the support member that is rigidly secured to the seat., and each of the first and second plurality of rack teeth are defined by a substantially horizontal upper edge and a lower edge inclined upwards, and each of the first and second pawls are defined by an upper edge inclined upwardly and lower edge substantially horizontal.

8. An adjustment mechanism for releasably retaining a backrest in a plurality of positions selected in relation to a seat, the adjustment mechanism comprising: a channel member adapted to be rigidly secured to the backrest; a support member slidably received by said channel member and adapted to be rigidly secured to the seat; a first plurality of vertically aligned rack teeth that extend in a generally lateral direction from the support member; a second plurality of vertically aligned rack teeth that extend from the support member in the same direction as the first plurality of rack teeth, said second plurality of rack teeth being spaced apart and generally parallel to said first plurality of rack teeth; a pin having first and second horizontally aligned and spaced ratchets extending in the opposite direction to the first and second plurality of rack teeth, said pin being slidably mounted to one of the channel member and the support member, wherein the activation the pin causes the movement thereof in a linear and horizontal direction to simultaneously and selectively engage the first and second pawls with the first and second respective plurality of rack teeth; and a spring acting against the pin for driving the first and second pawls in engagement with the first and second plurality of rack teeth; whereby the backrest is retained and does not fall from a desired vertical position by engaging the first and second pawls with the first and second plurality of rack teeth.

9. The adjustment mechanism according to claim 8, wherein the pin is adapted to be slidably mounted to the backrest.

10. The adjusting mechanism according to claim 9, wherein the first and second plurality of rack teeth exit toward the pin from the support member, and the first and second ratchets exit toward the support member from the support member. pin for said first and second plurality of rack teeth and first and second ratchets to be in the same plane when the first and second detents are in the engaged and uncoupled positions.

11. The adjusting mechanism according to claim 8, wherein the pin is slidably mounted within a channel formed in the backrest.

12. The adjustment mechanism according to claim 8, further comprising a rib extending outwardly from the backrest to act as a stop contacting an upper edge of the support member when the backrest is lowered to the lowest position.

13. The adjusting mechanism according to claim 8, further comprising a hook extending outward from an upper portion of the support member to act as a stop contacting an upper edge of the channel member when the Backrest is raised to the highest position.

14. The adjusting mechanism according to claim 8, further comprising a lever in operable engagement with the pin, said pin having an angled end portion in slidable engagement with an angled end portion complementary to the lever so that the movement of the lever originates a cam action that moves the pin in said lateral, horizontal and linear direction.

15. The adjusting mechanism according to claim 14, wherein the lever has a lower vertical portion that is slidably mounted to the backrest, whereby the vertical activation of the lever results in the horizontal activation of the pin.

16. The adjusting mechanism according to claim 8, wherein the first ratchet comprises a first plurality of vertically aligned pin teeth engaging selected teeth of said first plurality of rack teeth, and the second ratchet comprises a second plurality of vertically aligned pin teeth engaging selected teeth of said second plurality of rack teeth.

17. The adjusting mechanism according to claim 8, wherein each of said first and second plurality of rack teeth are defined by a substantially horizontal upper edge and a lower edge inclined upwards, and each of the first and second pawls is defined by an upper edge inclined upwards and a substantially horizontal bottom edge, whereby the backrest moves upwardly when the first and second pawls engage the first and second plurality of rack teeth in a ratchet-like manner.

18. An adjustment mechanism for releasably retaining a backrest in a plurality of selected positions relative to a seat, the adjustment mechanism comprising: a channel member adapted to be rigidly secured to the backrest; a support member slidably received by said channel member and adapted to be rigidly secured to the seat, said support member has a first plurality of vertically aligned rack teeth and a second plurality of vertically aligned rack teeth that exit therefrom the backrest in a generally lateral direction, said first and second plurality of rack teeth forming first and second arrangements that are parallel and spaced apart from one another; a pin slidably mounted to the backrest and limited to movement in a linear and horizontal direction, said pin having a first plurality of vertically aligned pin teeth and a second plurality of vertically aligned pin teeth exiting therefrom to the support member, so that said first and second plurality of rack teeth remain in the same plane as the first and second plurality of rack teeth, said first plurality of pin teeth forming an arrangement that is separate and parallel to an arrangement formed by said second plurality of pin teeth, and said first and second plurality of pin teeth extend in the opposite direction to the first and second plurality of rack teeth, whereby the movement of the pin in said linear and horizontal direction places the first and second pins. plurality of pin teeth in a selective and simultaneous coupling Aneo with the first and second respective plurality of toothed teeth; and a spring acting against the pin to urge the first and second plurality of pin teeth in engagement with the first and second plurality of rack teeth; whereby the backrest is retained and does not fall from a desired vertical position by coupling the first and second plurality of pin teeth with the first and second plurality of rack teeth.

19. The adjustment mechanism according to claim 18, wherein the pin is slidably mounted within a channel formed in the backrest.

20. The adjusting mechanism according to claim 18, comprising a rib extending outwardly from the backrest to act as a stop contacting an upper edge of the support member when the backrest is lowered to the position more inferior.

21. The adjusting mechanism according to claim 18, further comprising a projection extending outwardly from an upper portion of the support member to act as a stop contacting an upper edge of the channel member when the Backrest is raised to the highest position.

22. The adjustment mechanism according to claim 18, further comprising a lever in operable engagement with the pin, said pin having an angled end portion in slidable engagement with an angled end portion complementary to the lever so that the movement of the lever originates a cam action that moves the pin in said lateral, horizontal and linear direction.

23. The adjusting mechanism according to claim 22, wherein the lever has a lower vertical portion that is slidably mounted to the backrest, whereby the vertical activation of the lever results in the horizontal activation of the pin.

24. The adjusting mechanism according to claim 18, wherein each of said first and second plurality of rack teeth are defined by a substantially horizontal upper edge and a lower edge inclined upward, and each of the first and second pawls are defined by an upper edge inclined upwards and a substantially horizontal lower edge, whereby the backrest moves upwards while the first and second pawls engage the first and second plurality of rack teeth in a ratchet-like manner.

25. The apparatus according to claim 18, wherein the adjustment mechanism comprises a plate mounted to an upper portion of the support member, a projection extending rearwardly from an upper edge portion of the plate.; and said plate has said first and second plurality of rack teeth extending therefrom for operable engagement with said first and second plurality of pin teeth.