TH38323A - Single-stage inclined chair with backrest seat and adjustable power mechanism. - Google Patents

Abstract

DC60 (18/01/42) The chair is equipped with a base assembly including the base frame, a backrest frame that is swivel-mounted to the base frame for movement between upright and reclined positions, and a seat that is slidingly supported on the base frame and swivel-mounted to the backrest frame, allowing the seat to move forward and its rear to move forward and down against the backrest frame when reclined. The flexible backrest is connected to the backrest frame at the top and bottom and is equipped with an improved lumbar support adjustment. The seat is equipped with a seat depth adjustment and active and passive thigh supports. A new power mechanism is provided, which includes a transverse spring, a moment arm and a moment arm slider for adjusting the spring tension on the backrest frame. The moment arm slider is easily adjustable and includes an overtorque protection device to prevent damage to the power mechanism components. The chair is equipped with a base assembly including the base frame, a backrest frame that is swivel-mounted to the base frame for movement between positions. The seat is adjustable in both upright and tilted positions, and is supported by a sliding mechanism on the base frame. It is rotatably attached to the backrest frame, allowing the seat to move forward, and its rear end to move forward and downward against the backrest when tilted. A flexible backrest is connected to the backrest frame at the top and bottom and is fitted with an improved lumbar support adjustment. The seat features a seat depth adjustment and active and passive thigh supports. A new power mechanism is provided, incorporating a transverse spring, arm, and moment arm slider for adjusting spring tension on the backrest frame. The moment arm slider is easily adjustable and includes an overtorque protection device to prevent damage to the power mechanism components.

Claims (102)

1. The seat consists of a base assembly including a control housing with opposing side wings and a lateral pivot positioned near one of the side wings. The backrest is rotatably attached to the base for movement between upright and reclined positions. The seat is rotatably supported on the base and connected to the backrest for simultaneous movement. A power mechanism acts to activate the backrest to the upright position. This power mechanism includes a compressible/retractable spring positioned transversely in the control housing, with one end supported on one of the side wings, and also includes an arm rotatably attached to the lateral pivot. The arm has a spring clamp that grasps the free end of the spring and an actuator that is functionally connected to the seat and lateral pivot. The spring clamp and seat actuator are spaced apart and positioned so that the spring activates the fulcrum arm, typically positioned on the lateral pivot, to actuate the backrest to the upright position. 2. The chair specified in claim 1, in which the lateral swivel includes an adjustable swivel element constructed to change the position of the pivot point on the arm when the swivel element is adjusted. 3. The chair specified in claim paragraph 2, in which the swivel parts and arms, including the interlocking surfaces, at least one of which is linearly curved. 4. The chair specified in claim 3, where the surfaces are joined together, including the teeth that interlock. 5. The chair specified in claim 4, whose arm consists of an L-shaped bell-shaped crank and whose pivot point is generally positioned along the middle section of one leg of the L-shaped crank. 6. The chair specified in claim 2, where the arm and swivel parts are fixed in a vertically axially rotatable manner and are able to move in a mutually horizontal plane, resulting in a compact position within the control housing. 7. The chair described in Reputation 1, in which the spring is supported by a control housing and held in place by arms in a manner that causes the free end of the spring to move in unison to one of the supported ends and also to move forward/backward during backrest tilting. 8. The chair described in claim 7, in which the armrests compress both longitudinal springs and cause the springs to bend sideways in a nonlinear manner during the tilting of the backrest. 9. In a chair with a housing containing a control unit that includes a rotating part, a tiltable backrest is functionally connected to the control housing for movement between the upright and tilted positions, and a power source in the control housing for activating the backrest to the upright position. An improved adjustable backrest tension control unit comprises an adjustable rotating part and an arm that holds the power source and the rotating part. The arm is functionally connected to the backrest for activating the backrest to the upright position. The arm and rotating part have non-slip contact surfaces; at least one of them has a linear curve to provide contact surface gripping to define the fulcrum for sliding when the arm is rotated during backrest tilting, and also to allow the fulcrum to change position when the rotating part is adjusted to change the arm moment on which the power source acts. 10. The chair specified in claim 9, whose arms consist of a bell-shaped crank with legs, which are held in a rotating manner at the center, with a rotating part to determine the fulcrum. 11. A chair as specified in claim 10, in which the arms rotate in a horizontal plane around a vertical axis to achieve compact positioning within the controller housing. 12. The chair specified in claim 11 includes the connecting arm and seat armrest, which are functionally connected to the axis by the connecting arm to enable the actuating arm, seat armrest, and seat to move in a backward direction. 13. The chair specified in claim 10, in which the rotating part is rotatably fixed to the control housing, at the pivot point away from the joint surface of the rotating part, the joint surface of the rotating part is curved and given a constant radius from the pivot point. 14. The chair specified in Claim 13, whose interlocking surfaces have teeth that engage in a manner similar to a rack and pinion. 15. The chair specified in claim 14, where the joint surfaces of the arms have a linear curved shape. 16. The chair specified in claim 9 includes an adjustment mechanism for angularly adjusting the pivot arm to change the length of the moment arm. 17. The chair specified in claim 16, where the adjustment mechanism includes an over-torque device to prevent excessive torque from being applied by the user when adjusting the rotating parts. 18. The chair specified in claim 9, in which the chair includes a functionally positioned seat on a control housing and is connected between the armrests and backrest. 19. The chair specified in claim 9, whose interlocking surfaces have teeth that engage in a rack-and-pinion manner. 20. The chair consists of a base assembly, a component comprising one section of the tiltable backrest and a movable seat, which is swivel-mounted to the base assembly for movement between the first and second positions, and a spring with one end supported on the base assembly and the other end functionally connected to a spring of a certain length. When the spring is moved from the first to the second position, it is compressed longitudinally along its length and simultaneously bent laterally in a direction perpendicular to that length, in the lower area and generally at least part of the back of the adult's lumbar region, and in the upper area positioned above the middle area and generally at least part of the back of the adult's chest region, cushions on the front surface of the backrest shell, and a vertically adjustable lumbar support positioned in front of the backrest shell. The lumbar support is movable on the backrest support and is molded for vertical adjustment to change the shape of the front surface of the backrest in the lumbar region of the adult. Such support includes a lateral control handgrip. 103. The chair consists of a base assembly that includes the control housing on the opposite wing, with a top edge and a lubricating cover welded to the top edge of the control housing. The lubricating cover includes a top surface that defines the track for the sliding part. The backrest frame is rotatably attached to the base assembly at the backrest pivot for movement between upright and reclined positions, and the seat support structure is functionally supported on the base assembly. The backrest frame includes a sliding part that securely attaches the control housing for general horizontal sliding movement, and includes a seat support carriage that is rotatably attached to the sliding part at the front seat pivot and also rotatably attached to the backrest frame at the rear seat pivot. 104. The chair specified in claim 103 includes the seat housing which is welded to the seat support structure. The seat housing includes a back section molded to comfortably support the thighs of a typical adult seated, a front section molded to comfortably support the hips of an adult seated and to support most of the adult's weight, and a flexible area connecting the back and front sections. 105. The chair specified in claim 104 includes a gas spring that extends between the seat support structure and the front section. The gas spring is a self-locking, releaseable device. 106. The chair specified in claim 105 includes a rotatable shaft attached to the seat support structure and the front section and functionally connected to the gas spring. 107. The chair specified in claim 104 includes a functional front support plate spring on the seat support structure. 108. The chair specified in claim 103 includes a spring mechanism housed in a control housing. The spring mechanism is 109. The chair specified in claim 108, in which the spring mechanism includes a transversely mounted spring in the control housing and also includes an arm that is functionally rotatable attached to the control housing, an arm with one end that is functionally attached to the spring and the other end that is functionally attached to the seat support structure. 110. The chair consists of a base assembly that includes the control housing; a backrest that is rotatably attached to the base assembly at the backrest pivot for movement between the upright and reclined positions; a seat support structure that is functionally supported on the base assembly; and a backrest assembly that includes a sliding part that is rotatably attached to the sliding part at the front seat pivot for general horizontal sliding movement; and a seat support carriage that is rotatably attached to the sliding part at the front seat pivot and also rotatably attached to the backrest structure at the rear seat pivot. The spring mechanism is arranged in the control housing. The spring mechanism is functionally connected to the sliding part and includes a transversely mounted spring in the control housing and also includes an arm that is rotatably attached to the control housing. An arm with one end engaged by a working spring and the other end engaged by a working seat support structure; a rotating part; such rotating part and arm having interlocking surfaces, at least one of which is linearly curved, so that such arrangement functions similarly to a rack and pinion; the rotating part is adjustable to change the fulcrum point on the arm to adjust the arm length and moment that the spring acts on it. 111. The chair specified in Requirement 103 includes a backrest stopper housed in the control housing. The backrest stopper is formed to engage the seat support structure to limit the tilt of the backrest. 112. The chair specified in Requirement 111 in which the backrest stopper includes a cam mounted rotatably to the control housing for rotation around a vertical axis. The cams include a number of which can be selectively arranged to engage the seat support structure. 113. The chair consists of a base assembly including the control housing; a backrest mounted rotatably to the base assembly at the backrest pivot axis for movement between upright and tilted positions; and a seat support structure. The seat is supported by a base assembly and backrest frame that includes sliding components, a sliding control housing for general horizontal movement, and a seat support carriage that is rotatably attached to the sliding component on the front seat pivot axis and also rotatably attached to the backrest frame on the rear seat pivot axis, and a sliding seat housing supported on the seat support structure for selectable depth adjustment, where the depth of the seat housing can be selected relative to the backrest frame. 114. The chair consists of a base assembly that includes a control housing with side walls that define the seat track, with a front section that has bearings that hold the track in place. 21. The chair specified in claim 20 includes an armrest with one end connected to the other end of the spring and a second end connected to the component. 22. The chair specified in claim 21, in which the arms are swivel-mounted to the base. 23. The chair specified in claim 22, whose components include a seat. 24. The chair specified in claim 23 includes a backrest frame that is functionally attached to the seat for movement with it. 25. The chair consists of a base assembly including the control housing, a backrest frame rotatably attached to the base for movement between upright and reclined positions, and functionally welded to the seat so that the rotational movement of the backrest and the sliding movement of the seat are synchronized, and a power mechanism consisting of a spring of a certain length and an L-shaped torsion arm with the first leg grasping one end of the coiled spring and the second leg extending generally parallel to the length of the spring. The first leg rotatably grasps the control housing at a distance from the end of the spring, and the second leg is functionally welded to one of the seat and backrest frames so that the spring acts the torsion arm in a way that actsuates the backrest to the upright position. 26. The chair specified in claim 25, in which the first leg includes a linear curved surface which holds the rolling and swivel frame on the control housing when the backrest moves between the upright and reclined positions. 27. The chair specified in claim 26, where the structure on the control housing includes a rotating part with a shared surface that grips a linear curved surface on the first leg; such surface is formed to provide a positive grip to prevent unwanted slippage. 28. The chair consists of a base assembly that includes the control housing and a sliding-supported seat. On the control housing, a rotatable backrest is attached to the base for movement between upright and reclined positions and is functionally welded to the seat so that the rotational movement of the backrest and the sliding movement of the seat are synchronized. The control housing is enclosed in a relatively thin horizontal chamber beneath the seat, and the adjustable power mechanism is functionally housed within this chamber. The adjustable power mechanism includes an extendable power source, a functionally connected arm between the power source and the seat, and an adjustable part that allows the rotatable arm to control the force transmitted from the adjustable power source through the arm to the seat. The power source, arm, and adjustable part can only move in the horizontal direction to function within the relatively thin horizontal chamber. 29. The chair specified in claim 28, in which adjustable parts, including a swivel part, are functionally welded to the control housing for arm movement to adjust the arm fulcrum. 30. The chair controller consists of a controller housing, functionally welded components for controlling component movement, a handgrip for operating the actuator, and an overtorque protection device connecting the handgrip to the actuator. The overtorque protection device is designed to limit the force transmitted from the handgrip to the actuator to a maximum amount, preventing damage to the chair controller. 31. The chair controls specified in claim 30, which include an overtorque protection device, and a release mechanism formed to release the control hand, thus preventing the person from being subjected to excessive force on the control hand. 32. The seat control specified in claim 31, where the release mechanism includes a clutch. 33. The seat control specified in claim 32, in which the clutch, including the clutch ring and friction ring, engages the clutch ring for functional operation. 34. The chair control specified in claim 33, where the clutch ring, friction ring and control hand are mounted to the control housing for rotation of the common axis. 35. The chair specified in Reservion 1, in which the base assembly, including the base frame, works in conjunction with the casing. 36. The chair specified in Claim 20, where the base assembly, including the base frame, works in conjunction with the casing. 37. The chair specified in Claim 25, in which the base assembly, including the base frame, works in conjunction with the casing. 38. The chair specified in claim 28, where the base assembly, including the base frame, works in conjunction with the casing. 39. The controller consists of a controller housing, a single stored energy source housed within the housing which generates compression, an arm operable bypass to this single energy source for movement between upright and tilted positions, the single stored energy source is pre-tensioned to actuate the arm to the upright position and create tilting resistance during tilting, and a control device for controlling the pre-tension of the stored energy source and the tilt rate of the arm. The control device is designed for adjustment without the need for an operator to overcome the compression force of the single stored energy source. 40. The controller specified in claim 39, where the enclosure includes the adjusting device and arm and the adjusting device, shall determine a variable and adjustable microfullum. 41. The chair consists of a base assembly including a control housing, a single stored energy source housed in the control housing which generates compression force, and a backrest support which is functionally connected to this single energy source for movement between upright and tilted positions. This single stored energy source is pre-tensioned to actuate the backrest support to the upright position and allows for sliding. It also includes a seat back assembly including a seat housing with a flexible front support section, a rotatable backrest attached to the base assembly, and a detachable rotatable arm attached to the seat for movement between upright and tilted positions. The back of the seat is rotatably attached to the backrest to allow the seat to move forward, and the back of the seat moves forward and downward in a synchronized motion when the backrest is tilted. A spring mechanism housed in the control housing and functionally connected to the seat acts to actuate the seat backward. This spring mechanism includes a compression/extension spring housed in the control housing and an arm rotatably attached to the control housing, with the moment arm controlled by a spring. Energy is transferred from the spring to the seat, acting to push the backrest to an upright position, and a gas spring, functionally connected between the front part of the housing and the rest of the seat, is modified to support the weight of an adult in a typical seat. The gas spring can act to adjust the position of the front part relative to the rest of the seat. 115. The chair specified in claim 114 in which the gas spring is self-locking and releaseable. 116. The chair specified in claim 115 includes a control unit connected to the seat and includes a connecting arm functionally connected to the gas spring for release and adjustment. 117. The chair consists of a base assembly including a control housing with side walls defining the seat track, a seat section with a front section bearing that securely holds the track in place, and a seat back assembly including a seat housing with a front section that is flexibly supported. The backrest is swivel attached to the base assembly and is swivel detachable attached to the seat for movement between upright and reclined positions. The back of the seat is swivel attached to the backrest to allow the seat to move forward, and the back of the seat moves backward. Forward and forward movement is achieved through synchronized motion when the backrest is tilted. A spring mechanism, housed in the control housing and functionally connected to the seat, acts to propel the seat backward. This spring mechanism includes a compression/retention spring housed in the control housing and a rotatable arm attached to the control housing. The arm's moment is controlled by a spring to transfer energy from the spring to the seat, propelling the backrest to the upright position. Leaf springs are positioned between and flexibly support the front and rear sections of the seat. 118. The chair consists of a base assembly including the control housing with side walls defining the track, a seat with a front section bearing a sliding track clamp, and a rear section including the seat housing and depth adjustment structure for adjusting the depth of the seat housing relative to the backrest. The backrest is rotatably attached to the base assembly and selectively rotatably attached to the seat for movement between upright and tilted positions. The rear section of the seat is rotatably attached to the backrest, allowing the seat to move forward, and the rear section of the seat moves forward and downward. 118. The chair in question includes a seat containing a seat carriage supporting the seat housing and a spring mechanism mounted in the control housing and functionally connected to the seat to actuate the seat backward. The spring mechanism includes a compression/extension spring mounted in the control housing and an arm that is rotatably attached to the control housing and spring-loaded to transmit energy from the spring to the seat to actuate the seat back to the upright position. 119. The chair in question 118 includes a seat carriage supporting the seat housing and linear bearings for sliding attachment of the housing to the seat carriage. 120. The chair in question 119 includes a functional extension bolt between the seat carriage and the housing to hold the housing at a selected depth. 121. The chair in question 120 includes a control unit connected to the seat for the operation of the extension bolt. 122. The chair consists of a base assembly including the control housing and a tiltable backrest frame that is rotatably attached to the assembly. The base for movement between the upright and fully reclined positions; the seat is movably supported on the control housing and rotatably supported on the backrest frame; and the variable backrest stop mechanism is movably supported on the seat clamping base to stop the seat and simultaneously halt the backrest tilt at a selected position before reaching the fully reclined position. The variable backrest stop mechanism includes a seat clamping element and an actuator arm for the adjustable movement of the seat clamping element. The seat clamping element and arm include interlocking teeth for non-slip handling. 123. The chair specified in claim 122 in which the seat clamping element includes a movable cam with a molded step for selective seat clamping. 124. The chair specified in claim 123 in which the variable backrest stop mechanism includes a spring damper for holding the cam in a selected stop position, the specific one of which 125. The chair specified in claim 124 includes an actuator connected to a cam for rotating the cam to select a specific step. 126. The chair comprises a base assembly including a control housing, a tiltable backrest frame rotatably attached to the base for movement between the upright and fully tilted positions, a seat movably supported on the control housing and rotatably supported on the backrest frame, a variable backrest stop mechanism operably supported on the seat attachment base to provide resistance to the tilt of the backrest support when tilting, and a control device for controlling the pretension of the stored energy source and the tilt rate of the backrest support. The control device includes an adjustable fulcrum pointing arm which can be adjusted without overcoming the pressure of the single stored energy source. 42. The chair specified in claim 41 includes the seat, the fasteners and the connection of the backrest to the power source. 43. The controller consists of a controller housing, a stored energy source enclosed within the controller housing, a first arm supporting the backrest, which is functionally connected to the stored energy source for movement between the upright and tilted positions. The stored energy source is pre-tensioned to actuate the first arm to the upright position and creates tilting resistance on the first arm when tilting. A control device is used to control the pre-tension of the stored energy source on the first arm. The control device includes a crank arm within the controller housing. This crank arm has one end that grips the stored energy source and the other end is functionally connected to the first arm. A section of the crank arm between these two ends forms a fulcrum, allowing the energy source to actuate the crank arm around the fulcrum, thereby acting the first arm to the upright position. 44. The controllers specified in claim 43 include adjustable rotating parts that determine the movable fulcrum point on at least one of the crank arms of the rotating parts and such crank arm parts with linearly curved surfaces where the movable fulcrum point is positioned. 45. The controller comprises a controller housing, a stored energy source housed within the housing, and a first arm functionally connected to the stored energy source. For movement between the upright and tilted positions, the stored energy source is pre-tensioned to actuate the first arm to the upright position and to create tilt resistance on the first arm when tilting. An adjustable control device allows for adjustable pre-tensioning of the stored energy source. The control device includes a manual lever for controlling the pre-tension of the stored energy source and an overtorque protection device formed to limit the physical forces transmitted from the lever to the control device. 46. The chair consists of a base assembly, a seat supported on the base, a backrest rotatably attached to the base for movement between upright and reclined working positions, a flexible backrest connected to the backrest at least one upper connection point and to the chair at least one lower connection point away from the vertical of the upper connection point. The lower connection point is generally aligned with the hips and spine of the seated person in such a way that the flexible backrest forms a controlled curvature between the upper and lower connection points. The seat has a front section that is sliding supported on the base and a back section that is rotatably attached to the backrest, allowing the seat to move forward in sync with the backrest during the reclined position of the backrest. 47. The chair specified in claim 46, in which the flexible backrest, including the upper and lower sections which are swivel attached, is swivel attached to the backrest frame for counter-rotating movement; at the upper and lower sections which include the forward-extending wings which are swivel attached to the backrest frame; at the lower section, the distance backward from the lower section to the anterior surface of the lower section is approximately equal to the distance from the seater's hip joint to the seater's posterior/inferior lumbar spine; thus, the flexion of the seater's lower back causes the flexible backrest to curve in accordance with the curvature of the seater's lower spine. 48. The chair specified in claim 46 in which the flexible backrest includes a backrest shell with rigid upper and lower sections connected by a flexible area generally positioned at the lumbar region of the seated person. 49. The chair specified in claim 48, in which the lumbar support area includes a number of horizontal channels that extend generally across the lumbar support but terminate to allow for a continuous strip of material at the opposite edge of the lumbar support area. 50. The chair specified in claim 49 includes a torsion lumbar support mechanism that is welded to the backrest shell. The torsion lumbar support mechanism activates the shell to form a convex shape forward for effective lumbar support. 51. The chair specified in claim 50 includes a vertically adjustable lumbar support that is attached to the flexible backrest for vertical adjustment to change the shape of the front surface of the flexible backrest in the lumbar region of the seated person. 52. The chair specified in claim 51, in which the vertically adjustable lumbar support, including the lateral control arm, is constructed to grasp and track the perimeter of the flexible backrest and is constructed to grasp the vertically adjustable lumbar support in a sliding manner to allow the control arm to adjust in and out along the perimeter. 53. The chair specified in claim 46 includes a torsion lumbar support mechanism welded to one of the lower connecting parts to activate the flexible backrest to form a convex forward shape. 54. The chair specified in claim 46, in which a vertically adjustable lumbar support is attached to the front surface of the flexible backrest, the lumbar support is attached to the seat and stops the backrest tilt at a selected position before reaching the maximum tilt position; a variable backrest stop mechanism, including a movable cam with steps formed to selectively engage the seat, and including a spring damper to hold the cam at the selected stop position, in which specific steps are arranged to engage the seat, and an actuator attached to the cam to rotate the cam to select the specific step; the actuator includes an arm attached to the rotatable control housing, the arm and cam include interlocking teeth. 127. The chair specified in claim 128, in which the actuator includes a rotatable handgrip attached to the movable control housing. 128. The chair specified in claim 127, in which the actuator includes a rod connecting the handgrip to the arm. 129. The chair specified in claim 127, in which the handgrip includes a radial extension and is connected to the arm by a swivel/sliding joint allowing the handgrip to rotate around the first axis and allowing the arm to rotate around a second axis which is tilted and not parallel to the first axis, without the handgrip's rotation being obstructed. 130. The chair consists of a base assembly including the control housing, a tiltable backrest frame that is swivel-mounted to the base assembly for upright and extreme tilt positions, a seat that is swivel-supported on the control housing and swivel-supported on the backrest frame, and a variable backrest stop mechanism that is functionally mounted on the seat attachment base to hold the seat in place and simultaneously stop the seat tilt at a selected position before reaching the extreme tilt position. The variable backrest stop mechanism includes a movable cam with molded steps for selective seat clamping. The cam also includes a wavy surface modified to selectively engage the damper for seat clamping in the seat clamping position, and also includes teeth modified to meet the matching teeth on the actuator for operating the cam. 131. The seat structure for the chair consists of a flexible seat shell that includes a front section molded to comfortably support the thighs of a typical adult, a back section molded to support the buttocks of the adult and comfortably support most of the adult's weight, and a flexible middle section connecting the front and back sections. The front section is positioned around the middle section or in front of it on the seat shell and generally in front of the intended area of the adult's hip joint so that the adult's weight is relatively supported by the back section for the adult. The seat cushion is supported on the seat shell. The tray-shaped seat support that supports the back of the seat shell includes an forward projection that extends beneath the flexible central section and is extra-spaced beneath and not connected to the flexible central section, and an adjustable thigh flexion support mechanism that functionally supports the front of the seat shell on the forward projection of the seat support, allowing the front section to be adjusted relative to the rear section to apply pressure to the thighs and effectively support a seated adult. The adjustable thigh flexion support mechanism includes pre-tensioned transverse spring plates. 132. The seat structure for the chair consists of a flexible seat shell that includes a molded front section to comfortably support the thighs of a typical seated adult, a molded front section to comfortably support the buttocks of a seated adult, and to comfortably support most of the weight of a seated adult, and a flexible central section that connects the front and rear sections. The front section is positioned to support the central or anterior section from there on the seat shell and generally in front of the intended area of the thigh joint. The seat's support system, designed to distribute the adult's weight more evenly across the seat's back, includes a tray-shaped support for the rear of the seat shell. The support system incorporates an forward extension beneath the flexible central section, an extension further apart and not connected to the central flexible section, and an adjustable thigh flexion mechanism that operates on the front of the seat shell's forward extension. This allows the front section to adjust relative to the rear, providing optimal thigh pressure and support for the seated adult. The adjustable thigh flexion mechanism includes a flexible rod. The gas spring block is released to rotate the bending rod and then secures the bending rod in the selected position and direction. 133. The seat structure consists of a flexible seat shell that includes a front section molded to support the thighs of a typical adult, a rear section molded to comfortably support the thighs of an adult and to comfortably support most of the adult's weight, and a flexible middle section. The T-shaped seat tray has a bottom panel that defines the full-width rear section and a partial-width front section that is narrower than the full-width rear section and extends forward from the center of the rear section. The full-width rear section is molded to support the rear of the shell, while the vertically adjustable front section is molded to change the support force on the front surface of the flexible backrest in the lumbar region of the seated person. 55. The chair specified in claim 54 includes at least one control arm which grasps the vertically adjustable lumbar support and slides in the general horizontal direction. The control arm is formed to move along the perimeter of the flexible backrest for vertical adjustment to the vertically adjustable lumbar support. 56. The chair specified in claim 46, where the upper connection includes a swivel upper connection. 57. The chair specified in claim 56, where the upper swivel connection includes a T-shaped cantilever joint on the backrest frame and a matching channel in the flexible backrest, the channel is formed to receive and frictionally hold the T-shaped cantilever joint to connect the flexible backrest to the backrest frame. 58. The chair specified in claim 46, in which the flexible backrest, including the armrests and belt straps, are attached to the lower edge of the flexible backrest and the armrests and belt straps, including the wings that define part of the lower joint. 59. The chair specified in claim 58 includes an adjustable torsion-type lumbar support mechanism attached to one of the lower joints. 60. The chair specified in claim 46, in which the backrest frame forms an inverted linear curve. 61. The chair specified in claim 46, in which the backrest frame includes an internal metal reinforcement and an external polymer cover that encloses all sides of the central portion of the internal metal reinforcement. 62. The chair specified in claim 46, where the backrest frame includes the formed ends placed on the opposite sides of the back of the seat; the formed ends are defined as the first swivel for swivel connection to the backrest frame and the second swivel for swivel connection to the seat. 63. The chair consists of a base assembly, a swivel backrest frame attached to the base for movement between upright and reclined working positions, and a flexible backrest functionally attached to the backrest frame at the upper connection point and functionally attached to the chair at the lower connection point. The flexible backrest, including its forward-extending wings, is generally positioned along its lower edge, forming a swivel axis at the lower connection point. This axis is positioned at or behind the posterior aspect of the seated person's pelvis so that when the seated person bends their lower back backward, the pelvic support of the flexible backrest rotates downward and backward around the lumbar axis. The lumbar region of the flexible backrest generally moves flexiblely backward to form a more flatter position with the pelvic support, and the thoracic support of the backrest rotates around the upper connection point. This creates support for the seated person's back that is highly consistent with the seated person's back bending and movement of the torso and spine. The back of the person sitting. 64. The chair specified in claim 63 includes an adjustable torsion spring lumbar support mechanism that activates the torsion spring backrest to form a forward-projecting convex shape for optimal lumbar support for the seated person. 65. Chairs as specified in claim 64, in which the backrest is flexible and the shell is compressed with a flexible lumbar support. 66. The chairs specified in claim 65 include armrests, seat belts attached to the lower edge of the shell, and molded coverings. 67. The chair specified in claim 66 includes a vertically adjustable support section that is functionally welded to the front of the flexible backrest. 68. The chair specified in Reservation 63, where the upper connection, including the overhang on the base frame and the corresponding channel on the flexible backrest, is formed to receive and hold the overhang by friction. 69. The chair specified in claim 63 includes a vertically adjustable lumbar support that is attached to the flexible backrest in the seated area to change the shape of the front surface of the flexible backrest in that area. 70. The chair specified in claim 69 includes a handgrip that holds the vertically adjustable body support in place and is formed to move along the perimeter of the flexible backrest during the vertical adjustment of the vertically adjustable body support. 71. The chair specified in claim 63, in which the backrest frame has a formed end positioned on the opposite side of the flexible backrest; the formed end that defines the backrest tilt axis, the seat tilt axis, and the lower tilt axis of the backrest shell, which are positioned posteriorly to the backrest tilt axis and the seat tilt axis; the lower tilt axis of the backrest shell is generally positioned at the adjustable torsional lumbar spring mechanism. 72. The chair specified in claim 63, in which the flexible backrest includes a cover which at least part of its fastening material is a fastening material for keeping the cover taut on the flexible backrest during the bending of the flexible backrest. 73. The chair specified in claim 72, where the fastening part includes a strip of fastening textile sewn to the lower edge of the cover. 74. The chair specified in claim 73, in which the flexible backrest includes the backrest shell and includes an extruded part bonded to a strip of flexible textile; the extruded part is bonded to the underside of the backrest shell. 75. The chair specified in claim 74, in which the extruded part includes notches for receiving strips of fastening textile and is sewn to the strips of fastening textile along the notches. 76. In chairs where the seat base, backrest frame is rotatably attached to the base and a first power mechanism is used to actuate the backrest frame to an upright position. The improvement consists of a partial width extension located beneath the front section and an adjustable thigh support mechanism that is adjustablely attached to and supports the front section on the partial width front section. 134. Seat structures specified in claim 133 where the adjustable thigh support mechanism includes a pre-tensioned transverse leaf spring. 135. Seat structures specified in claim 134 where the adjustable thigh support mechanism includes a flex rod and a lockable/releaseable gas spring for rotating the flex rod and then securing the flex rod in a selected position. 136. In chairs with a tiltable seat and a movable seat that is functionally supported for synchronized movement with the backrest, the improvement consists of a seat support carriage with a T-shaped housing that includes the front and back sections and includes linear bearings arranged on each. 137. The chair specified in claim 136, where one of the seat carriages and the seat frame includes a swivel shaft modified to mount the seat carriage to the swivel support for movable seating relative to the tiltable backrest; the seat frame includes a flat-surfaced underside panel with the associated sliding linear bearings, where the seat frame is adjustable in depth on the seat carriage. 138. The chair specified in claim 137, where the seat carriage includes a set of notches protruding forward/backward, and the other of the seat carriage and seat frame includes a bolt for selectively securing the notches. 139. The chair specified in claim 137, where the seat carriage includes a formable upper side bar and includes an upper mounted limiter welded to the seat frame, a limiter with a downward protrusion through the seat frame and which is formable to hold. 139. The chair specified in claim 136 in which the seat frame includes at least two bearing-holding wings to prevent the seat frame from being lifted vertically out of the seat carriage. 140. The chair consists of a base assembly which includes a control housing with at least one additional wing and sliding cast bearings supported on each wing; a backrest frame which is rotatably attached to the base assembly at the backrest pivot for movement between the upright and reclined positions; and a seat support structure which is rotatably supported on the base assembly and the backrest frame includes sliding parts that slide the lubricated cast bearings of each wing for general horizontal sliding movement; and includes a seat carriage which is rotatably attached to the sliding part at the front seat pivot and also rotatably attached to the backrest frame at the rear seat pivot. 141. The chair specified in claim 140 in which at least one wing extends, including two parallel side wings on the control housing. 142. The chair specified in claim 141 in which each lubricated bearing consists of a polymer part bonded to the upper edge of the side wings. 143. The chair specified in claim 140 in which the base assembly includes the base frame, which includes the housing, and also includes the side arms supporting the backrest frame at the backrest swivel. 144. The chair specified in claim 103 in which the base assembly includes the base frame, which includes the housing, and also includes the side arms supporting the backrest frame at the backrest swivel. 145. The chair specified in claim 110 in which the base assembly includes the base frame, which includes the housing, and also includes the side arms supporting the backrest frame at the backrest swivel. 146. The chair specified in claim 113 in which the base assembly includes the base frame, which includes the housing, and also includes the side arms supporting the backrest frame at the backrest swivel. 147. The chair consists of a base assembly that includes opposing side arms; a backrest frame with formed ends that are swivel-attached to the side arms on the backrest pivot for rotation around the backrest tilt axis; a seat that is swivel-attached to the formed ends on the seat pivot for rotation around the seat tilt axis and at least one backrest pivot and seat pivot axis including swivel bearing components and supporting components; flexible bearing components for rotational movement that is not aligned with the relative tilt axis of at least one pivot axis, so that the bearing components rotate around the stud without jamming even if the stud is not aligned with the relative tilt axis. 148. The chair specified in claim 147 in which the supporting components include flexible material. 149. The chair specified in claim 148 in which the supporting components include rubber. 150. The chair specified in claim 147 in which the backrest pivot includes 151. The chair specified in claim 150 in which the seat pivot includes a second stud fixed to the opposite side protruding inward. 152. The chair specified in claim 151 in which the first stud is welded into position and in which the formed end defines a recess for receiving the first stud at the backrest pivot and the second stud at the second pivot. 153. The chair specified in claim 152 in which the second stud is welded into position and in which the backrest frame is adjustable, including the side arms, and in which the seat includes bearings that slide the side arms. 194. The chair specified in claim 189 in which the back is formed to support the buttocks of the seated adult and most of the adult's weight, and the front is formed to support the lower part. 195. The chair is described in claim 189, whereby the seat includes a seat carriage, the seat is movably supported on the base assembly and the backrest is movably secured, and also includes a seat shell whose depth can be adjusted manually on the seat carriage. 196. The chair consists of a base assembly which includes the side arms; a backrest frame which is movably secured to the base assembly at the swivel axis; a backrest for movement between a number of working positions, including an upright and an inclined working position; a seat which is movably secured to the backrest frame at the seat swivel axis and is movably supported at the front of the backrest frame; the backrest frame includes the right and left formed ends which are positioned on opposite sides of the seat and between the sides of the seat and the corresponding ones of the side arms; formed ends which support the first swivel bearing at the seat swivel axis and the second swivel bearing at the backrest swivel axis, allowing the seated person to continue working while Movement between upright and tilted working positions 197. The chair consists of a base assembly with multiple movable legs that includes the housing, controls, and upward-extending side arms; an inverted U-shaped backrest frame with formed ends, which is positioned adjacent to its relative ends and swivel-attached to it at the backrest pivot axis; each backrest pivot axis consists of a first stud and a first swivel bearing that holds the first stud; the seat, which is movably supported on the control housing; the seat, which includes a seat support carriage that is swivel-attached to the formed ends at the seat pivot axis; each seat pivot axis consists of a second stud and a second swivel bearing that holds the second stud; the seat pivot axis and the backrest pivot axis are spaced apart; and an adjustable power mechanism that includes a transverse spring, a spring-attached arm, and a working seat for activating the seat to the tilted position and, conversely, activating the backrest frame to the upright position; and an adjustable pivot section that attaches the adjustable arm to determine the fulcrum, which moves. During tilting, and which can be adjusted manually to reposition the fulcrum for adjustable control of the spring force on the seat. 198. The base assembly consists of a control housing which includes opposing side wings, a lower and a front wing that defines the chamber for receiving the power mechanism; a rear wing of the housing that defines the transverse rotation; a rigid upright structure which includes a transverse tubular section, a compatible transverse rail clamp and is welded to it, and includes rigid upright arms extending from the ends of the transverse tubular section which define the seat swivel axis on the inboard side and the backrest swivel axis on the outboard side. The seat swivel and backrest swivel axes are modified to support the seat and backrest, respectively, rotatably, and a transverse reinforcing section and is welded to the transverse tubular section and a lower section for reinforcing the tubular section. The reinforcing section and the lower section include vertically aligned holes modified to receive the vertically adjustable central axis on the chair base. 199. The base assembly specified in claim 198, where the side wings of the control housing include linear bearings modified to support the seat rotatably. 200. A chair as specified in claim 181 in which the seat includes springs that provide flexible support to the right and left sides of the front section for freely bending motion to increase comfort for the user. 201. A chair as specified in claim 181 in which the seat includes lockable, detachable gas springs that provide adjustable front support for adjustable motion to increase comfort for the user. 202. A chair consisting of a base assembly including a control housing, a power source positioned within the control housing, a seat that is functionally supported on the base for general horizontal movement between forward and backward positions, with the seat functionally connected to the power source, a backrest assembly including a backrest housing and a backrest frame supporting the backrest housing, with the backrest frame including a first swivel in which the backrest frame is rotatably connected to the base for movement of the backrest between upright and reclined positions, and a second swivel in which the backrest frame is connected. 202. A chair in which the first axis of rotation is approximately aligned with an axis through which the seat passes through the hip joint of the seated adult. 203. A chair in which the seat consists of a seat front slider modified to slide forward and backward on a control housing, a seat carriage connected to such control housing and such front slider rotating, a seat frame in a sliding attachment manner to such seat carriage and a seat housing modified to support the hips and thighs of the seated adult. 204. A chair in which the seat housing includes a back section molded to support the hips of the seated adult and to support most of the weight of the seated adult and also includes a front section modified to support. 206. The chair specified in claim 202 includes a variable backrest stop mechanism supported on the base assembly and functionally clamped to the seat. The variable backrest stop mechanism is molded to clamp the seat and simultaneously stop the tilt of the backrest support at a number of selectable positions between the upright and reclined positions. 207. The chair comprises a base assembly that includes a control housing, a power source positioned within the control housing, and a functionally clamped seat on the base assembly for general horizontal movement between forward and backward positions, where the seat is functionally connected to such power source. The seat includes a seat shell with a back section modified to support the buttocks of the seated adult and a front section modified to support the thighs of the seated adult. The backrest support, including the backrest shell and the backrest frame supporting the backrest shell, and the backrest frame including the first pivot point to which the backrest frame is rotatably connected to the base assembly and the second pivot point to which the backrest frame is rotatably connected to the seat (Clause 207, page 52, figure 31), is flexible for bending to allow the formed ends to be positioned on the first and second studs. 154. The chair specified in Clause 153, in which the depression is formed in the shape of a truncated cone. 155. The chair specified in Clause 154, in which each backrest pivot point and each seat pivot point includes one rotatable bearing component and one rubber component. 156. The chair specified in Clause 147, in which each formed end includes the first wing which forms a depression for the compatible reception of the rubber component. 157. The chair specified in Clause 156, in which the second wing 158. The chair specified in claim 157 in which the angling is formed into a truncated cone and the rubber components are formed to fit the angling together. 159. The chair specified in claim 147 in which the formed ends on each side of the seat are positioned between and adjacent to their corresponding ends of the side arms and the sides of the seat. 160. The chair consists of a base assembly that includes the side arms, a backrest frame with formed ends that are swivel-attached to the side arms, a backrest pivot axis for rotation around the backrest's angling axis, the backrest frame is sufficiently flexible to allow the formed ends to be bent outwards during assembly, the formed ends and the side arms with adjacent surfaces in which one surface has a channel, and the arrangement of bearings on each backrest pivot axis that swivel-connect the side arms to each formed end, the arrangement of bearings that include studs to which other to the channels and bearings. 161. The chair specified in claim 160 in which the bearing includes a rotatable stud-holding bearing component and a flexible component that flexibly supports the bearing component so that the bearing component can self-align with the stud to prevent jamming during the rotation of the backrest frame around the backrest tilt axis. 162. The chair specified in claim 160 in which the bearing includes a rotatable stud-holding bearing component and a flexible component that flexibly supports the bearing component so that the bearing component can self-align with the stud to prevent jamming during the rotation of the backrest frame around the backrest tilt axis. 162. The chair specified in claim 161 in which the span defines a truncated conical basin and in which the bearing is formed to securely clamp the basin. 163. The method of assembling the chair consists of the following steps. 163. The method specified in claim 163 where the chair components consist of a seat and include the preparation of a base assembly with side arms and also include the bending of the formed ends of the backrest assembly and at the same time the placement of the formed ends of the formed ends on the extensions and the release of the backrest assembly so that the backrest assembly flexibly returns to its original shape, which holds the backrest assembly in position and connects the backrest assembly to the chair components rotatably. 164. The method specified in claim 164 where the chair components consist of a seat and include the preparation of a base assembly with side arms and also include the bending of the formed ends to place the formed ends between the side arms of the seat and the side arms of the base assembly. 165. The method specified in claim 164 where the side arms include a second opposite extension and where the formed ends include a second slot and include the placement of the second slot on the second extension. 166. The method specified in claim 165 where the extension 167. The method specified in claim 1478 in which the base assembly includes a base frame consisting of a shell in which the opposite side arms extend laterally and upward from the shell. 168. The chair specified in claim 160 in which the base assembly includes a base frame consisting of a shell in which the opposite side arms extend laterally and upward from the shell. 169. The method specified in claim 164 in which the base assembly includes a base frame consisting of a shell in which the opposite side arms extend laterally and upward from the shell, and includes the placement of the formed ends inside the upper ends of the side arms but outside and above the shell in general. 170. The chair consists of a base assembly for supporting the chair on the surface of the floor while the seated person is working; a backrest frame that is rotatable and fixed to the base assembly at the pivot point; the backrest for movement between a number of positions, including the upright and reclined working positions. 171. A chair that is rotatably fixed to the backrest frame at the pivot point. The seat is positioned further back and lower than the backrest pivot point. The seat is supported slidingly at the front of the base assembly. For horizontal movement, the backrest pivot point and the seat pivot point are connected and positioned to move the seat generally forward and also move the rear of the seat forward by synchronized rotational movement when the backrest frame is tilted, thus the user is comfortably supported in upright and reclined working positions and thus the user can continue working while moving between upright and reclined working positions without moving and adjusting the base assembly backward and forward in a stationary manner. 172. A chair that is specified in claim 171 in which the base assembly includes a control housing in which the power mechanism is provided, which engages one of the backrest and seat frames to activate the backrest frame to the upright position. 173. A chair that is specified in claim 171 in which the base assembly includes side arms that extend upward generally adjacent to the seat. 173. Chairs specified in claim 172 in which the backrest is swivel attached to the side arms. 174. Chairs specified in claim 173 in which the seat is swivel attached to the backrest in a relatively close proximity to the side arms. 175. Chairs specified in claim 174 in which the power mechanism includes a transversely arranged spring in the control housing and includes an arm connecting the spring to one of the seat and the functional backrest. 176. Chairs specified in claim 175 include an adjustment mechanism for adjusting the arm to change the force transmitted from the spring to the seat; the adjustment mechanism includes the arm and sets an adjustable moment on the arm to actuate the backrest to an adjustable upright position. 177. Chairs specified in claim 171 include a transversely arranged spring within the control housing and also include an arm connecting the spring to one of the seat and the functional backrest. 178. The chair is described in claim 177 in which the arm can rotate around a vertical axis, with one end attached to a spring and the second end connected to the seat to actuate the seat backward and, conversely, actuate the backrest to an upright position. 179. The chair is described in claim 171 in which the control housing includes the opposite side wings and the seat includes bearings that allow the side wings to slide. 180. The chair is described in claim 171 in which the seat includes a seat sliding piece which allows the control housing to slide and also includes a seat carriage that allows the seat sliding piece to rotate on the first axis of rotation and allows the backrest to rotate on the second axis of rotation. 181. The chair is described in claim 180 in which the seat includes a flexible seat housing with a back section modified to support the buttocks of the seated adult and also includes a front section modified to support the thighs of the seated adult, and which is flexibly connected to the back section. The back section is supported and held by the seat carriage. 182. The chair specified in claim 170 includes a seat carriage that is movably connected to the base assembly and movably connected to the swivel backrest frame, and also includes a seat shell that is movably supported on the seat carriage for manual depth adjustment. 183. The chair specified in claim 171 includes a backrest stop mechanism that is movably connected to the control shell and is formed to selectively restrain the seat to limit forward movement of the seat and thus selectively limit the tilt of the backrest frame. 184. The chair specified in claim 170 includes a flexible backrest assembly that is movably connected to the backrest frame at least two vertically separated areas. The flexible backrest assembly is formed to flex between at least two vertically separated areas to provide effective lumbar support. 185. The chair is described in claim 184, whereby the flexible backrest assembly includes a single, flexible shell. 186. The chair is described in claim 1847, whereby the flexible backrest assembly includes a series of interconnected components, each with a surface supporting a portion of the person's back. 187. The chair comprises a movable base assembly; a backrest that is rotatably attached to the base for movement between upright and reclined positions; a functional seat supported on the base and connected to the backrest for movement between a relatively backward and forward working position; the seat, including the front section which is movably attached to the base, moves horizontally forward with the recline of the backrest so that the seated person's legs are not unnecessarily raised from the surface of the floor during recline; and the seat, including the back section which is flexibly attached to the front section and which is connected to the functional backrest, moves downward and forward with the recline. Thus, the seated person is comfortably supported and positioned well during tilting by the intense angular movement of the seat and backrest, and therefore the maximum forward movement of the seat and the maximum angular movement of the backrest are limited by a range which keeps the seated person's hands relatively stable during tilting, so that the seated person can continue to work in various seating positions easily and comfortably. 188. The chair is described in claim 187 in which the base assembly includes a housing, a control unit containing a power mechanism for activating the backrest to the upright position. 189. The chair is described in claim 188 in which the base assembly includes side arms that rotatably support the backrest at a position generally aligned with the seated person. 190. The chair is described in claim 187 in which the base assembly includes a spring mechanism arranged transversely in the control housing and also includes an arm that rotatably grasps the spring mechanism and is functionally connected to the seat for activating the seat to the working position backward and at the same time activating the backrest to the upright position. 191. The chair, as described in claim 190, includes a flexible front support spring for flexion motion to provide increased comfort for the seated person. 192. The chair, as described in claim 191, includes a lockable, releaseable front support gas spring that operates for adjustable motion to provide adjustable comfort for the seated person. 193. The chair, as described in claim 190, includes a flexible backrest shell that flexes to conform to different linear curves to provide consistent lumbar support for the seated person, and armrests with forward-extending wings that connect the flexible backrest to the swivel backrest frame at the first connection point. The flexible backrest, including the second connection point, connects the flexible backrest to the swivel backrest frame at a second vertically oriented point from the first connection point in such a way that the backrest The flexible backrest is forced to move within a certain range, limited by the first and second connecting parts, and a second power mechanism which includes a force-generating mechanism typically positioned at one end of the first and second connecting parts and designed to activate the armrests, in turn activating the lumbar portion of the flexible backrest forward relative to the chair. 77. The chair specified in claim 76, in which the armrests, seatbelts, and side wings are positioned, generally, at the back of the seated person's pelvis so that when the seated person bends his/her lower back backward, the pelvic region of the backrest moves downward and backward, the lumbar region of the backrest generally curves backward to form a more flatter position with the pelvic region, and the thoracic region of the backrest rotates around the second connection, and the pelvic, lumbar, and thoracic regions curve in a manner that is well in accordance with the movement of the seated person's back. 78. The chair structure consists of a base assembly, a seat, a backrest frame that is swivel-attached to the base for movement between upright and reclined positions, and a flexible backrest that is swivel-attached to the backrest frame at the rigid upper connection point. It also includes forward-extending wings that are swivel-attached to one of the seat-backrest frames and the base assembly at the lower connection point. The distance behind the lower connection point to the middle surface of the lower front of the flexible backrest is approximately equal to the distance behind the user's hip joint to the user's spine, so that the flexion of the user's spine and lower back causes the flexible backrest to curve accordingly, and similar to the flexion of the user's back and spine. 79. The chair structure specified in claim 78, in which the lower connection link the flexible backrest wings to the backrest frame. 80. The chair structure described in claim 79, in which the flexible backrest consists of relatively rigid upper and lower sections connected by a flexible section. 81. The backrest structure of the chair consists of a backrest frame including upper and lower sections, and a flexible backrest that is rotatable and attached to the upper and lower connecting sections, respectively. The flexible backrest has a relatively rigid pelvic support that rotates around the lower connecting section at an axis of rotation positioned anterior to the pelvic support and at or behind the hip joint of the seated person. The flexible backrest also has a relatively rigid thoracic support that rotates around the upper connecting section at an axis of rotation positioned posterior to the thoracic support. The pelvic and thoracic supports are connected for flexion in the lower back area of the seated person. The flexible backrest is forced to flex in accordance with the upper and lower rotating axes, in a manner consistent with the spine of the seated person during back flexion. 82. The backrest structure of the chair as specified in Claim 81, in which the flexible backrest includes a flexible lumbar support connecting the lumbar support and the thoracic support. 83. The chair consists of a base assembly, an inverted U-shaped backrest frame with a central upper section and a pair of molded end sections that are swivel-attached to the base assembly, a T-shaped upper joint extending from the upper section and a pair of lower joints at the molded end sections, a flexible backrest including a molded upper channel to receive and hold the upper joint with friction, and a belt armrest along the lower edge with opposite wings extending forward a certain distance to connect to the lower joints, and a swivel connecting mechanism that connects the opposite wings to the lower joints near but slightly behind the seated person's hip joint. 84. A chair as specified in claim 83 in which the flexible backrest includes a flexible lumbar support and in which the distance the wings extend forward is a few inches and is approximately equal to the distance from the hip joint of the seated person to the lower spine of the seated person in such a way that the flexible backrest, when bent, will bend in a manner consistent with the spine of the seated person. 85. The backrest structure for a chair consists of a backrest frame, a flexible backrest with an forward-extending lumbar support that can move backward in a manner similar to the sitter's back, upper and lower swivel connections between the flexible backrest and the backrest frame, and an adjustable torque-generating mechanism that is connected to one or both of the flexible backrest and the backrest frame to activate the lumbar support forward, providing beneficial lumbar support for the sitter's back. 86. The backrest structure specified in claim 85, where the torque-generating mechanism is functionally installed at the lower connection point to the backrest structure and the flexible backrest. 87. The backrest structure specified in claim 86, in which the flexible backrest includes a relatively rigid thoracic support and a relatively rigid pelvic support, connected by a lumbar support. 88. The backrest structure specified in claim 87, in which the lumbar support consists of a flexible material sheet. 89. The backrest structure specified in claim 86, in which a torque-generating mechanism, including springs and a control hand, is able to rotate to coil and uncoil to adjust the tension of the springs. The springs are functionally connected between the flexible backrest and the backrest frame to actuate the lumbar support of the flexible backrest to form an forward convex shape. 90. The backrest structure specified in claim 89, in which the torque-generating mechanism includes an arm that provides a mechanical advantage when adjusting the spring tension. 91. The chair consists of a base assembly including a control housing with a power source located therein, and a backrest support functionally connected to the power source for movement between upright and reclined positions. The backrest support includes the backrest frame and the backrest housing. The backrest housing consists of a flexible polymer sheet molded to support the back of the adult seated, with a semi-rigid lower area generally positioned at least partially behind the adult's pelvis, a flexible middle area positioned above this lower area and at least partially behind the adult's lumbar region, and a semi-rigid upper area positioned above this middle area and at least partially behind the adult's chest region. The backrest frame has a first attachment point connecting this upper area of the backrest housing to the backrest frame and several second rotatable attachment points connecting this lower area of the backrest housing to the backrest frame. The second attachment point controls the movement of the lower area. To create a consistent, controlled curvature in the lumbar region, ensuring continuous and comfortable lumbar support for the adult's spine during seated spinal flexion. 92. A chair as specified in claim 91, in which the backrest frame includes a first swivel on which the backrest frame is swivel-attached to the base assembly for the movement of the backrest support between upright and reclined positions, where the first swivel axis is approximately aligned with the axis established by the hip joint of the seated adult. 93. The chair specified in Requisition 91, where the center area contains a number of lateral openings in the said panel, which generally extend horizontally across a portion of the center area of the backrest support, and where these openings terminate before the perimeter of the said panel, and where these openings define a number of long horizontal flexible strips in the said center area, each of which is modified and dimensional to provide flexible support for an adult seated in the chair. 94. The chair specified in claim 93, in which the underside of the backrest shell, including the forward-extending reinforcement wings, is swivel connected to the second connecting link of the backrest frame; such reinforcement and swivel connecting link provide stable, movable support for at least part of the pelvic area of the seated person. 95. The chair specified in claim 91, in which a second swivel connection link for the lower section of the said backrest shell to the rotating backrest frame, and a stimulator for stimulating the middle section of the backrest shell in an anterior direction. 96. The chair specified in claim 95, whereby the said lower area of the said rear shell, including the forward wings, is rotatably connected to the second link of the backrest frame, and the said actuator, including the torsion spring, is functionally connected to the said forward wings. 97. The chair specified in claim 96 where such actuating device includes a means for pre-tensioning the torsion spring. 98. The chair specified in Reservation 91, in which the underside of the backrest shell, including the forward wings, forms an axis of rotation at the second swivel attachment of the backrest frame; such axis of rotation is positioned at or toward the posterior aspect of the pelvis of the seated adult so that when the seated adult bends his lower back backward, the underside of the backrest shell moves downward and backward, and the middle of the backrest shell generally curves backward to form a more flatter position relative to the lower aspect. 99. The chair specified in claim 91, in which the backrest frame shall form a linear curve. 100. The chair specified in claim 91, in which the backrest frame contains internal metal reinforcement enclosed in a flexible polymer covering. 101. The chair specified in claim 91 includes a seat that is functionally installed on a base unit, a seat with forming armrests, and a connection that links the backrest to a power source. 102. The chair consists of a base assembly which includes a control housing containing the power source, and a movable base supported on the base assembly, and includes a backrest support which is functionally connected to the power source. The backrest support includes the backrest frame and backrest housing. The backrest housing consists of a flexible polypropylene sheet molded to support the back of the adult seated on it, with a lower area generally positioned behind, at least a portion of, the adult's pelvis in the middle, positioned above the back.