JP4803667B2 - Chair - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a chair securing an appropriate lumbar support function in a non-rocking state and securing a fitting property to a body in a rocking state. <P>SOLUTION: An intermediate member 19 is backward tiltably connected to the front part of a base 2 by a first spindle 22 and a seat 3 is fixed to the intermediate member 19. The intermediate member 19 has a back support 20a and the upper end of a backrest 4 is fixed to the upper end of the back support 20a. A rear frame 40 is connected to the rear end part of the base 2 by a second spindle 42. The second spindle 42 is connected to the back support 20a by a third spindle 49. The back face of a back inner shell 4a is pushed by a roller-shaped support body 54 provided in the upper end of the rear frame 40 and the lower part of the back inner shell 4a is vertically movably retained to a guide pin 56 and a guide body 57 to become non-separable from the rear frame 40. <P>COPYRIGHT: (C)2008,JPO&amp;INPIT

Description

  The present invention relates to a chair having a lumbar support function and a locking function.

  In a chair whose backrest tilts backward, the importance of supporting the seated lumbar vertebra (especially around the third lumbar vertebra) with the backrest (the lumbar support function) has been attracting attention in order to increase the posture stability of the seated person in the non-locking state. For this reason, the lower part of the backrest is projected in a forward convex shape in a longitudinal side view.

  However, in conventional rocking chairs, the side cross-sectional shape of the backrest is constant in both the non-locking posture (working posture) and the rocking posture, so if the shape of the backrest is matched to the shape in the non-locking state, There was a problem of feeling a strong push-up (a chair has also been proposed in which the lower part of the backrest protrudes relatively forward when locking, but in this case the push-up feel is even greater).

In order to solve this problem, the applicant of the present application provides a back column on a tilting frame (corresponding to the intermediate member of the present application) to which a seat is attached in Patent Document 1, and connects the upper part of the backrest to the upper end of the back column. On the other hand, an auxiliary frame (corresponding to the rear frame of the present application) that is tiltably connected to the base and the tilt frame are connected so as to be relatively rotatable, and a portion of the auxiliary frame that is above the connection point with respect to the tilt frame is backrested. We proposed a chair with a structure that can be moved relative to each other.
Japanese Patent Application No. 2005-33632

  According to this prior application, the degree of rearward tilting of the rear frame is greater than the degree of rearward tilting of the tilting frame. Therefore, it is possible to improve the fit by eliminating the feeling of pushing up the body due to the backrest when rocking.

  In other words, the lumbar vertebra can be accurately supported when not locked, and the entire back can be supported without a sense of incongruity for locking. In addition, the seat and the backrest are integrally tilted backward, but as the posture of the backrest is changed, the backrest is tilted backward at an angle larger than that of the seat.

  An object of the present invention is to improve the lumbar support function in the non-locking state and the fit in the locking state while basically adopting the configuration of the invention of the prior application.

  The chair according to the present invention includes a seat, a backrest that can be tilted rearwardly, a back strut to which an upper portion of the backrest is attached, and a rear frame (rear link) that supports a portion of the backrest that is below the attachment portion to the back strut from the rear. The backrest has flexibility so that the shape of the longitudinal side view can be easily deformed, and pushes the seated person's waist when not tilted backward It has a convex shape when viewed from the longitudinal side, and the rear frame tilts backward at a higher rate than the back column so that the backrest tilts backward and stretches toward a flat state when viewed from the longitudinal side. It has become.

  In the invention of claim 1, as a feature, the rear frame is provided with a support body that pushes a portion of the backrest that protrudes most forward in a longitudinal side view from the back, and the back frame includes the support body The part below the support body is held on the rear frame so that it cannot be separated and can move up and down.

  The invention of claim 2 includes, in addition to claim 1, a base supported by legs, and an intermediate member connected to the front part of the base so as to be able to move backward and backward, and the intermediate member includes Is provided with a back strut to which the seat is attached and to which the upper portion of the backrest is attached, while the rear frame is centered on the lower end of the rear portion of the base located near the rear end of the seat. The rear frame is attached so that it can be tilted rearward, and the rear middle part of the rear frame and the back column are connected so as to be relatively rotatable.

  According to a third aspect of the present invention, in the first or second aspect, the support body is formed in a roller shape rotatable around a horizontal axis. According to a fourth aspect of the present invention, in the third aspect, the roller-shaped support body is formed in a substantially hourglass shape in which the portion of the longitudinal center line of the backrest has the smallest diameter and the outer diameter increases from the longitudinal center line to the outside. Has been.

  In the present invention, the backrest is in a state of being pushed forward by the support body of the rear frame, with the portion attached to the back support and the portion held in the rear frame inseparable as upper and lower fulcrums. First, the portion of the backrest that protrudes most forward in the longitudinal side view (that is, the portion that pushes the person's waist) is pushed from behind by the support body, so the forward protrusion of the backrest is retracted by body pressure. Therefore, the lumbar support can be securely held.

  In addition, the lower part of the backrest is pushed forward by the part that hits the support body, and the part that is held away from the rear frame is pulled backwards. As a result, the longitudinal section has a forwardly convex shape, so that the portion below the portion on which the support body hits can also be deformed in a longitudinal side view. For this reason, the backrest can be curved in a forward-convex shape with a natural roundness when non-locking, and the backrest can be deformed in the stretching direction throughout the locking state (on the back of the upper body of a person). It can be deformed so as to follow the profile), and is therefore excellent in fit to the user's body.

  A synchro-type chair in which the seat moves backward and backward in conjunction with the backward tilting of the backrest has an advantage of preventing or suppressing a so-called shirt-spinning phenomenon due to the separation of the seat and the backrest when rocking. However, in a synchro-type chair, the back tilt of the backrest and the backward and backward tilt of the seat are supported by a single spring, so if the spring force of the spring is weak, the seat will be retracted and tilted backward as soon as the seat is seated. May cause discomfort. If the spring strength is increased, the smooth back tilt of the backrest may be hindered.

  On the other hand, when configured as in claim 2, since the rear frame is connected to the base at the site from the rear end of the seat, the load due to seating does not act to tilt the rear frame backward, The rear frame is in a state of supporting the intermediate member from the rear, so that it is possible to prevent the seat from being retracted and tilted backward when sitting.

  If the support body is formed in a roller shape (or roller shape) as in claim 3, the support body can move smoothly on the back surface of the backrest, so that the backrest can smoothly change its cross-sectional shape by tilting. There are advantages. Further, when the support body is formed in a substantially drum shape as in claim 4, since the support body hits the back of the backrest from both the left and right sides, it can be prevented that the spine of the seated person is pushed by the backrest through the support body, For this reason, it is more excellent in the lumbar support function and fit.

  Next, an embodiment of the present invention will be described with reference to the drawings.

(1). Outline of chair First, the outline of the chair will be described with reference to FIGS. 1A is a front view, FIG. 2B is a right side view, FIG. 2A is a plan view, FIG. 1B is a cross-sectional view taken along the line IIB-IIB in FIG. Is a rear view, (D) is a longitudinal side view of only the seat and the backrest, and FIG. 3 is a longitudinal side view of the chair.

  The chair includes a leg 1, a base 2 attached to the upper end of the leg 1, a seat 3 disposed above the base 2, and a backrest 4 disposed behind the seat 3. The leg 1 includes a pedestal 5 made of a gas cylinder, and branch legs 6 extending radially from the pedestal 5, and a caster 7 is provided at the tip of each branch leg 6. The lock of the pedestal 5 can be released by operating a lever 8 (see FIG. 1A) provided on the base 2.

  As shown in FIGS. 2 (D) and 3, the seat 3 includes front and rear inner shells (seat plates) 9 and 10 made of resin and a cushion body 11 stretched so as to extend in series on the upper surface thereof. Therefore, the seat 3 includes a seat rear portion 3b that does not move unless locked, and a seat front portion 3a that can be tilted forward. Although details are omitted, the front inner shell 9 and the rear inner shell 10 are connected by a horizontally long connecting pin 12, and the seat front portion 3 a is inclined forward about the connecting pin 12.

  The backrest 4 has a structure in which a cushion 4b is stretched on the front surface of the back inner shell 4a, and a back cover 13 extending over substantially the entire height of the back inner shell 4a is disposed behind the back inner shell 4a ( The back cover 13 is fixed to a back column which will be described later.)

  The space between the back cover 13 and the base 2 is closed by a rear cover 14, and a front cover 15 is mounted in front of the base 2. A front lever knob 16 for tilting the front portion 3a is exposed. The front cover 15 is attached to the front inner shell 9 of the seat 3. Reference numeral 17 shown in FIGS. 1 and 2 is a lever that switches the backrest 4 between a state in which the backrest 4 can be tilted backward and a state in which the backrest cannot be tilted.

(2) Details of the seat Next, the seat and its peripheral part will be described in detail with reference to FIGS. 4 and 5 are separated perspective views showing the support mechanism of the seat 3, FIG. 6 is a plan view with the seat omitted, FIG. 7 is a sectional view taken along the line VII-VII in FIG. 6, and FIG. -VIII sectional view.

  The base 2 has a housing shape opened upward, and an intermediate member 19 to which the seat 3 and the backrest 4 are attached is disposed between the seat 3 and the base 2, for example, as shown in FIG. 4. The intermediate member 19 includes two left and right pipes 20 as main members, and the rear end of the pipe 20 extends upward to form a back column 20a. That is, in this embodiment, the seat 3 and the backrest 4 are attached to one intermediate member 19.

  A front bracket 21 having an U-shape opening upward as viewed from the front is fixed to the front part of the left and right pipes 20 constituting the intermediate member 19 by welding. Then, left and right laterally long first support shafts (slide shafts) 22 are fixed to the left and right front brackets 21 by welding, and the horizontal portions of the left and right pipes 20 are a first connection body 23 and a second connection body. 24 are integrally connected. The first support shaft 22 is disposed below the pipe 20.

  As shown in FIG. 3, a resin seat outer shell (seat support plate) 25 is disposed below the rear inner shell 10, and the rear inner shell 10 is detachably fixed to the seat outer shell 25. The seat outer shell 25 is fixed to the first connecting body 23 of the intermediate member 19 with screws or the like.

  As can be understood from FIGS. 4, 7, and 8, the first support shaft 22 of the intermediate member 19 is sandwiched between a lower receiving member 26 and an upper receiving member 27 that are vertically overlapped. The members 28 are overlapped, and these three members are fastened together with screws (not shown) to the base 2 in a state of being overlapped with each other.

  For example, as shown in FIG. 5, the bottom receiving member 26 has four front and rear, left and right engagement holes 29 penetrating vertically, while the base 2 has a boss body in which the engagement holes 29 fit tightly. 2a is integrally formed, and the lower receiving member 26 is held immovably in the horizontal direction by fitting the lower receiving member 26 into the boss body 2a. The pressing member 28 is fastened to the boss body 2a with screws. Since the boss body 2a is narrowed, the lower receiving member 26 is easily fitted and held so as not to be displaced.

  The base 2 is formed with a center protrusion 2b with which the rear end of the lower receiving member 26 comes into contact, a hole 2c in which the pedestal 5 is fitted, an overhang portion 2d for attaching an armrest (not shown), and the like. The base 2 and the upper and lower receiving members 26 and 27 are die-cast products such as aluminum, and the pressing member 28 is a sheet metal product. Of course, materials and processing methods can be arbitrarily selected.

  The upper and lower receiving members 26 and 27 are formed with long grooves 30 that allow the first support shaft 22 to slide back and forth. The upper and lower elongated grooves 30 are elongated holes by overlapping each other. A spring (compression coil spring) 31 is disposed between the upper and lower receiving members 26 and 27, and a rear wall 32 for supporting the spring 31 from the rear is formed at the rear end of the lower receiving member 26. On the other hand, a front spring receiver 33 that supports the spring 31 from the front is overlapped with the first support shaft 22 of the intermediate member 19.

  Therefore, the intermediate member 19 (and the seat 3 and the backrest 4) can slide rearward against the spring 31 and can tilt backward about the first support shaft 22. The first support shaft 22 may be directly attached to the base 2 without using the upper and lower receiving members 26 and 27.

  As shown in FIGS. 9 and 10, the long grooves (long holes) 30 of the upper and lower receiving members 26 and 27 extend in the horizontal direction. For this reason, even if the spring force of the spring 31 is not excessively large, the seat 3 does not tilt backward only by a person sitting on the seat 3.

  As shown in FIG. 6, a bearing member 35 for rotatably holding the front lever 34 is attached to the front end portion of the left and right front bracket 21, and the cam member 36 is supported by the bearing member 35. . Although details are omitted, when the front lever 34 is rotated around the rotation support shaft 34a by placing the hand on the knob 16, the cam member 36 rotates the crank portion 33b of the front lever 33, thereby The front portion 3a is switched between a horizontal posture and a forward tilt posture.

(3). Backrest Mounting Structure Next, the mounting structure of the backrest 4 will be described with reference to FIGS. 9 to 13 in addition to FIG. 3. 9 is an exploded perspective view of the main member, FIG. 10A is a front view of the back inner shell, FIG. 9B is a sectional view taken along the line BB of FIG. 10A, and FIG. C sectional view, FIG. 11 is an exploded perspective view of the main member, FIG. 12 is a perspective view with the backrest 4 removed, (A) without the cover, and (B) with the cover attached. FIG. 13 is a longitudinal side view of the main part.

  As shown in FIG. 3, the backrest 4 includes a resin-made back inner shell 4a and a cushion 4b stretched on the front surface thereof (a cross is also stretched), and the back inner shell 4a is formed as shown in FIG. As shown in FIG. 5, by forming a large number of horizontally long slits 38, flexibility is given so that the shape of the longitudinal side view can be easily changed.

  As shown in FIGS. 9 and 12, the upper ends of the left and right back struts 20a are connected by an upper connecting body 39 having a U-shaped cross section, and the upper end portion of the back inner shell 4a is attached to the upper connecting body 39 so as not to be separated. It has been. In this case, as shown in FIG. 10B, a locking portion 4c is formed on the upper portion of the back inner shell 4a, and the locking portion 4c is fitted to the upper coupling body 39.

  As a support mechanism for the backrest 4, a rear frame 40 having a substantially L-letter shape in side view, in which two pipe members on the left and right sides are main members, is disposed. A horizontally long second support shaft 42 is integrally fixed to front end portions of the left and right pipes constituting the rear frame 40 via a bracket plate 41. The second support shaft 42 is sandwiched between the rear portion of the base 2 so as to be rotatable by vertically split bearings 43 and 44, and the bearings 43 and 44 are fixed to the base 2 with screws by a pressing member 45. ing. Therefore, the rear frame 40 can tilt about the third support shaft 42. The rear frame 40 may be connected to the base 2 with pins.

  In FIG. 3, the bearings 43 and 44 should originally be displayed in a cross-section, but the cross-section display (hatching) is not performed because of complexity. In FIG. 11, only the upper bearing member 43 is shown.

  A third connecting body 46 made of a metal plate is integrally fixed to the lower part of the left and right pipes constituting the rear frame 40, and a fourth connecting body 47 made of a metal plate is integrally attached to the upper ends of the left and right pipes. It is fixed to. The fourth connecting body 46 includes a forward groove 46a and upper and lower blades 46b, and a third support shaft 49 is integrally fixed to the lower part of the left and right back struts 20a via a bracket material 48.

  Then, as clearly shown in FIG. 13, the third support shaft 49 is rotatably sandwiched between upper and lower split-type bearing bodies 50, 51, and the front and rear bearings 50, 51 are sandwiched from the front through a pressing member 52. It is fixed to the third connector 46. Accordingly, the intermediate member 19 (back strut 20a) and the rear frame 40 rotate in conjunction with each other. The rear bearing 50 is fitted in the forward groove 46a of the third connecting body 46, and the pressing member 52 is fixed to the blade plate 46b of the third connecting body 46 with screws.

  The fourth connecting body 47 in the rear frame 40 is integrally formed with a pair of left and right bearing pieces 47a extending upward, and a roller 52 (or roller-like) support body is provided on the pin 52 inserted through the left and right bearing pieces 47a. 54 is rotatably fitted, and the support body 54 is brought into contact with the back surface of the back inner shell 4a. The back inner shell 4a is pushed and bent in a forwardly convex shape in a side view so that a portion where the support body 54 abuts is positioned closest to the back. Further, the forward apex portion of the back inner shell 4a is set to be substantially the same height as the third lumbar vertebra of the seated person.

  As shown in FIG. 3, a box-shaped bracket portion 54 protruding rearward is formed on a portion of the rear surface of the back inner shell 4 a located between the third connecting body 46 and the fourth connecting body 47 of the rear frame 40. The left and right laterally long guide pins 56 are formed integrally with each other (the guide pins 56 may be separate members from the back inner shell 4a).

  On the other hand, as shown in FIG. 13, a guide body 57 into which the guide pin 56 of the backrest 4 is fitted is fixed to the third connection body 46 and the fourth connection body 47 of the rear frame 40 with screws. The guide body 57 has a guide groove 57a that is vertically long and has a lower portion opened forward. The guide pin 56 is fitted into the guide groove 57a so that the back inner shell 4a cannot be separated forward from the rear frame 40. And it is held (locked) so as to be movable up and down. The reason why the lower portion of the guide groove 57a is opened forward is to allow the guide pin 56 to be fitted and removed from the near side.

  The rear frame 40 is covered with an auxiliary cover 59 from the front, and as shown in FIG. 12 (B), a portion excluding the periphery of the support body 54 in the mechanism portion that supports the backrest 4 is a front cover 58. Covered. The front cover 58 has a window hole 59a for exposing the substantially upper half of the auxiliary cover 59. Although the nail | claw for attaching this is provided in the back cover 13, display is abbreviate | omitted in FIG. As shown in FIG. 12, the hanger 59 can be attached to the upper coupling body 39 of the back column 20a.

  As can be understood from FIG. 3, the rear frame 40 is attached to the base 2 at a portion near the rear end of the seat 3. For this reason, a load acts on the rotation fulcrum of the rear frame 40 when a person is seated. It is shifted backward from the center point (the position of the white arrow in FIG. 3). For this reason, when a person is seated and not leaning against the backrest 4, the intermediate member 19 (and the back column 20 a) is supported upward from the rear by the rear frame 40. The first support shaft 22 is prevented from moving backward simply by being seated.

(4). Movement of the seat and the backrest FIG. 14 is a diagram schematically showing the framework of the chair, and the movement of the seat and the backrest 4 will be described based on FIG.

  Since the rear frame 40 and the back column 20a (intermediate member 19) are connected, the rear frame 40 also tilts backward in conjunction with the rearward tilt of the back column 20a. Therefore, the rear frame 40 tilts backward at a larger angle than the back column 20a. Further, since the intermediate member 19 also moves backward, the rear frame 40 tilts backward while being pushed rearward, and the rear frame 40 also tilts backward at a higher rate than the back column 20a.

  For this reason, the support body 54 tilts backward relative to the back column 20a. And since the lower part of the back inner shell 4a has the guide pin 52 fitted to the guide member 57 and is held so as not to be separated from the rear frame 40, when the support body 54 moves backward relative to the back column 20a, The back inner shell 4a is stretched and deformed from a state of being greatly deformed in a forwardly convex shape in a longitudinal side view to a state close to flat (the guide pin 52 and the guide member 45 have an action of stretching the back inner shell 4a. Prepared.)

  When a seated person performs an operation such as keyboard operation with the upper body in an upright posture or a slightly tilted posture, the lumbar vertebra (especially around the third lumbar vertebra) is supported by the backrest 4 so that the person maintains a stable posture. it can. On the other hand, if the backrest 4 remains largely curved in a forwardly convex shape when locked, the upper body of the person is bent into a state of sliding, but this is not comfortable, but in the present invention, the backrest 4 is flat in the locked state. Because it becomes selfish, it does not give the body a sense of incongruity.

  Further, since the backrest 4 is extended toward the flat shape, the backrest 4 is inclined rearward at a larger angle than the seat 3 as a result. Therefore, the seat 3 and the backrest 4 are attached to the intermediate member 19. However, the back tilt angle required for the backrest 4 can be maintained. Further, since the forward projecting portion of the backrest 4 is pushed by the support body 54, the forward projecting portion of the backrest 4 is not retracted by the human body pressure, and the lumbar support function can be firmly retained.

  Further, since the back inner shell 4a can be easily deformed in the longitudinal side view as well as the part below the forward projecting portion, the entire back inner shell 4a has a natural rounded shape in the non-locking state. While the lumbar support function can be improved by softly pushing the waist of the body, it can be extended and deformed into a very loosely curved state in the locked state, and the fit can be improved even in the locked state.

  In addition, since the support body 54 is formed in a substantially drum shape whose outer diameter increases toward both sides across the longitudinal center line of the back inner shell 4a, the user's spine is supported via the back inner shell 4a. The body 54 is not pushed and, as a result, even if the support body 54 is a hard resin product, the user does not feel lumpy on the spine, and the softness can be ensured.

  When the support body 54 is formed in a drum shape, if the whole is an integrated resin product, smooth rotation may be hindered by sink marks on the inner peripheral surface of the center hole. Therefore, it can be rotated smoothly. Further, the back inner shell 4a and the cushion 4b are covered with a cloth bag. In this case, a vertically long fastener for opening and closing the bag extends along a vertically long center line on the back surface of the backrest 4. However, if the support body 54 is formed in a drum shape (in other words, a shape in which the left and right intermediate portions are constricted), the support body 54 can be prevented from being buffered by the fastener. This is also an advantage of this embodiment.

(5). Others Although the embodiment of the present invention has been described above, the present invention can be embodied in various other forms. For example, the shape of each member such as a base, a seat, an intermediate member, a rear frame, and a backrest can be any shape as long as the function is maintained. For example, both the intermediate member and the rear frame can be made of sheet metal products or die-cast products. A portion of the intermediate member located below the seat may be a die-cast product, and the back strut may be made of a pipe.

  Further, the support body does not necessarily have a roller shape. It is also possible to form the support body in a cylindrical roller shape and to wind a soft cushioning material such as an elastomer around the outer peripheral surface thereof. In addition, as a mechanism for tilting the rear frame backward at a rate larger than that of the back column, a link mechanism including a plurality of links may be employed. The support body may be an integral structure without being separated left and right, or conversely, it may be composed of three or more roller-shaped members.

It is the front view and right view of a chair. It is a top view of a chair, a IIB-IIB view sectional view of Drawing 1 (A), a rear view, and a vertical side view only of a seat and a backrest. It is a vertical side view. It is a separate perspective view of the member which comprises a seat part. It is a separate perspective view of a base and a lower receiving part seat. It is a partial top view in the state where a seat was omitted. FIG. 7 is a sectional view taken along the line VII-VII in FIG. 6. FIG. 8 is a sectional view taken along the line VIII-VIII in FIG. 6. It is an isolation | separation perspective view of the member which comprises a back part. It is a figure which shows the structure of a back inner shell. It is a separation perspective view of the member which constitutes the mechanism which changes the shape of a backrest. It is a perspective view of the back part in the state where a member was incorporated. It is a partial vertical side view of a back part. It is a figure which shows a motion of a backrest and a seat.

Explanation of symbols

1 leg 2 base 3 seat 4 backrest 4a back inner shell 22 first support shaft 19 intermediate member 20a back strut 40 rear frame 42 second support shaft 49 third support shaft 54 support body 55 box-shaped bracket portion 56 in the back inner shell 56 Back inner shell guide pin 57 Guide member

Claims (4)

A seat, a backrest that can be tilted rearward, a back column to which an upper portion of the backrest is attached, and a rear frame that supports a portion of the backrest that is lower than a mounting portion with respect to the back column from the rear, the backrest being Flexibility is provided so that the shape of the longitudinal side view can be easily deformed, and in a non-reclined state, the shape of the rear frame is a convex shape facing forward so as to push the waist of the seated person. By tilting backward at a larger rate than the back column, the backrest is designed to stretch and deform toward a flat state in a longitudinal side view while tilting backward,
A chair called
The rear frame is provided with a support body that pushes a portion of the backrest that protrudes most forward in a longitudinal side view from the rear, and a portion of the backrest that is below the support body is separated from the rear frame. It is impossible to hold it so that it can move up and down,
Chair. The base further includes a base supported by a leg and an intermediate member connected to the front portion of the base so as to be able to move backward and backward. The intermediate member has the seat attached thereto and the backrest. On the other hand, the rear frame is attached to the rear part of the base located near the rear end of the seat so that the rear frame can tilt backward with the lower end as the center, Furthermore, the upper and lower halfway part of the rear frame and the back column are connected so as to be relatively rotatable.
The chair according to claim 1. The support body is formed in a roller shape rotatable around a horizontal axis.
The chair according to claim 1 or 2. The roller-shaped support body is formed in a substantially hourglass shape in which the portion of the longitudinal center line of the backrest has the smallest diameter and the outer diameter increases toward the outside from the longitudinal center line.
The chair according to claim 3.

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