JP2015092966A - Backrest of chair - Google Patents

Abstract

PROBLEM TO BE SOLVED: To simplify assembly in a backrest provided with a reinforcement metal fitting.SOLUTION: A backrest 5 is provided with a back outer shell 12 and a back inner shell 13. The back outer shell is attached by a reinforcement metal fitting 37 that has a joint bar 38 in advance, and a rear end part of the joint bar 38 is an upward standing part 38b. The back inner shell 13 is engaged with the standing part 38b from above. The back inner shell and the back outer shell 12 are held by engagement between male shape catches 50 to 52 and female shape catches 53 to 55 in a vertically and horizontally non-displaceable manner. While the back inner shell is engaged with the upward standing part 38b and moved downward, the male shape catches 50 to 52 are automatically engaged with the female shape catches 53 to 55.

Description

  The present invention relates to a chair backrest.

  The back of the chair has a variety of structures, but when a cushion is provided, the back inner shell is generally stretched with a cushion in front of the back inner shell (back plate) that can be bent and deformed by human body pressure. It is often attached to the back outer shell arranged on the back side.

  As a means for attaching the back inner member to the back outer member, there is a screw stop, but there is a catch method that does not use a screw, and an example thereof is disclosed in Patent Document 1, for example.

JP 2002-10870 A

  In the method of Patent Document 1, when the back inner member is moved downward along the front surface of the back outer member, the catches provided on both of them are fitted, and the back inner member is moved back and forth, left and right, It is held so that it cannot be displaced in either the upper or lower direction. Therefore, assembly is easy.

  In a normal case, this is sufficient, but there are cases where it is desired to connect the back outer member and the back inner member also by a reinforcing metal fitting. For example, the back outer member is generally made of resin, but there are cases where it is desired to reduce the number of reinforcing ribs as much as possible and make most of them only have a cover function. In this case, the lower part of the back outer member has a large number of ribs. When this part and the back inner member are connected with a reinforcing metal fitting, a wide range of the back outer member can be configured without ribs (or fewer ribs), so ribs are formed after molding. It is possible to improve the quality by eliminating sink marks (dents) that are likely to occur at the locations.

  When the reinforcing metal fittings are provided in this way, if the reinforcing metal fittings are not screwed but simply fitted, the number of members can be reduced and the cost can be reduced. However, if the connection by the reinforcing metal fitting and the connection by the catch are not matched, the ease of assembly, which is an advantage of the catch method, may be hindered.

  The present invention was made based on such an idea, and aims to ensure the ease of assembly when a reinforcing metal fitting and a catch are used together to attach the back inner member to the back outer member. It is.

  The present invention includes the structures of the claims. Of these, the invention of claim 1 has a back inner member, a back outer member disposed behind the back inner member, and a reinforcing metal fitting connecting the back outer member and the back inner member, and a rear surface of the back inner member. The basic structure that the back inner member is held so as not to move back and forth with respect to the back outer member by fitting the front catch provided on the back to the rear catch provided on the front surface of the back outer member. It is.

  The reinforcing metal fitting has a configuration in which the reinforcing metal fitting has an upward standing portion extending upward from the back outer member, and a back inner member is fitted into the reinforcing metal fitting from above. A member is fitted, and then the catch is fitted by the guide action of the reinforcing bracket.

  The present invention also includes the invention of claim 2. In this invention, the reinforcing metal fitting includes a plurality of left and right joint bars made of a pipe material or a bar material, and the joint bar is first attached to the back outer member, and the rear end portion is the upwardly rising portion. Then, the catch is started to be fitted after the back inner member is fitted to the upward standing portion.

  According to a third aspect of the present invention, in the same basic configuration as in the first aspect, the reinforcing metal fitting has a hanging portion extending downward from the back inner member, and is fitted into the back outer member from above. The back outer member is fitted to the reinforcing bracket, and then the catch is fitted by the guide action of the reinforcing bracket.

  The invention according to claim 4 is the tilt according to any one of claims 1 to 3, wherein either one or both of the rear catch and the front catch is used to invite the front catch to the rear catch. A guide portion is provided.

  As a specific example of the invention of claim 2, in claim 5, the front catch of the back inner shell is male and the rear catch of the back outer shell is female, and the back catch is directed downwardly of the back inner shell. The guide portion that guides the front catch when moving is provided in a posture that is substantially parallel to or inclined forward from the upward rising portion of the reinforcing bracket in a side view.

  In the present invention, the back outer member and the back inner member include both a shell-like form and a frame-like form opened in the front-rear direction. When the back inner member has a shell shape, a cushion is often disposed on the front surface of the back inner member. On the other hand, the back inner member is configured in a frame shape and a mesh material is stretched on it, or the back outer member is configured in a frame shape as disclosed in JP 2011-92537 A, and a support portion such as a band plate is provided inside the frame. It is also possible to have a configuration in which Therefore, the present invention can also be applied to a backrest in which a back outer member such as JP 2011-92537 is opened back and forth (in this case, the reinforcing bracket is inserted into the left and right vertically elongated portions of the back inner member). Is preferred).

  According to the first and third aspects of the invention, since the connection between the back outer member and the back inner member is reinforced by the reinforcing metal fitting, the support strength of the backrest load is improved, and the range in which the rib is provided on the back outer member is reduced. Thus, the occurrence of sink marks can be prevented or suppressed.

  In addition, both the connection with the reinforcing bracket and the connection with the catch are fitted, and the fitting of the catch is automatically guided by fitting into the reinforcing bracket, so the assembly of the backrest is easy and reliable with one touch. Can be done.

  If the structure in which the upright standing portion is provided in the reinforcing metal fitting and the back inner member is fitted therein is adopted as in claim 2, the reinforcing metal fitting can be fitted into the back inner member without any trouble even if the upright upstanding portion of the reinforcing metal fitting is long. This is an advantage that the strength-up effect can be improved.

  If the catch is provided in the catch as in claims 4 and 5, it is preferable that the catch can be more reliably guided. In particular, as in claim 5, if the catch of the back inner shell is male and the catch of the back outer shell is formed female and a guide portion is provided on the rear catch, it is easy to visually recognize the mating condition. There is an advantage of good workability.

It is an external view of the chair which concerns on embodiment, (A) is the perspective view seen from the front, (B) is the perspective view seen from back. It is a partial fracture perspective view in the state where a cushion was omitted. It is a partial fracture separation perspective view in the state where a cushion was omitted. It is a vertical side view of a center part. It is a perspective view around a back outer shell and a base. It is an isolation | separation perspective view in the state which fell the seat board. It is the perspective view turned over and shown in order to show a clerk. It is a separate perspective view which shows the attachment method of a seat board. It is the perspective view which isolate | separated the element of the backrest. (A) is the perspective view which looked at the back inner shell to which the reinforcement metal fitting was attached from back, (B) is the partial perspective view of a back inner shell, (C) is the partial perspective view of a back outer shell. It is a separation perspective view of a back outer shell and a back inner shell. It is a figure which shows the attachment procedure of a back inner shell.

  Next, an embodiment of the present invention will be described with reference to the drawings. In the following description, the words “front and rear” and “left and right” are used to indicate the direction. These front and rear and left and right words are used by a person who normally sits on a rocking chair (hereinafter simply referred to as a chair). It is based on the direction.

(1). Outline First, the outline will be explained. The chair of this embodiment is applied to a so-called swivel chair that is frequently used for office work. As shown in FIGS. 1 to 4, the chair includes a leg column (gas cylinder) 2 and branch legs as main elements. A leg 1 having a base 3, a base 3 fixed to the upper end of the leg support 2, a seat 4 disposed above the base 3, and a backrest 5 connected to the base 3 so as to be tilted rearwardly. A caster is provided at the tip of each branch leg constituting the leg 1. Note that left and right armrests can be attached to the left and right side surfaces of the base 3 as optional items.

  As shown in FIG. 5, the base 3 is made of sheet metal, has a box shape with an upward opening having a bottom plate and left and right side plates 3 a, and is long in the front-rear direction. Further, as clearly shown in FIG. 4, the base member 3 includes a lower member 6 having an upward opening in the base 3, and an upper end of the leg support 2 is fitted to a bush 7 penetrating the lower member 6 and the base 3. It is fitted. A support member 8 for attaching an armrest is provided in front of the leg column 2 in the base 3. As clearly shown in FIG. 5, left and right side flanges 3 b that are long in the front-rear direction are provided at the upper ends of the left and right side plates 3 a constituting the base 3.

  As shown in FIG. 4, the seat 4 includes a resin seat inner shell (seat plate) 9 and a cushion 10 disposed thereon as main elements, and the cushion 10 is a skin material (not shown) such as cloth or leather. )). A hinge portion 9a having a large number of horizontally long recesses is formed at the rear portion of the seat inner shell 9, and the rear rear portion 9b can tilt backward relative to the front portion by the hinge portion 9a. As shown in FIGS. 2 and 3, the seat inner shell 9 is covered with a lower cover (seat outer shell) 11.

  For example, as shown in FIGS. 3 and 4, the backrest 5 includes a resin-made outer back shell 12 as an example of a back outer member, a resin-made back inner shell (back plate) 12 as an example of a back inner member, and a back inner. A cushion 14 disposed on the front surface of the shell 13 is a main element, and the cushion 14 is covered with a skin material such as a cloth.

  As can be understood from FIGS. 2 to 4, the back outer shell 12 has a submerged portion 15 that enters under the seat 4. The submerged portion 15 has a bifurcated shape separated left and right so as to be positioned on both the left and right sides of the base 3, and a left and right longitudinal support shaft 16 is spanned between the front ends of the left and right submerged portions 15. Is attached to the front end of the submersion 15 via a bearing 17. The bearing 17 is made of resin, is fitted into the tip of the submerged portion 15 from the outside, and overlaps the flange 3 b of the base 3 from above. A portion overlapping the flange 3b is a flat surface.

  As shown in FIGS. 2 to 5, a rocking spring (compression coil spring) 18 that expands and contracts in the front-rear direction is disposed inside the base 3. The locking spring 18 is supported by front and rear spring receivers 19 and 20, and the rear spring receiver 20 is fixed to the left and right intermediate portion of the support shaft 16. Accordingly, the rear spring receiver 20 moves back and forth together with the support shaft 16. On the other hand, the front spring receiver 19 is fixed to the front surface of the base 3 by welding, and a laterally long support bar 21 is fixed to the upper end of the front spring receiver 19.

  As shown in FIG. 5, the base 3 is formed with a rearward projecting portion 3c protruding rearward between the left and right submerged portions 15 of the back outer shell 12, and the rear end portion of the rearward projecting portion 3c has a laterally long lateral shape. The guide shaft 22 is fixed. The guide shaft 22 protrudes to the left and right outside of the rear end portion of the rearward projecting portion 3 c, and the protruding tip portion is fitted in a guide groove 23 provided on the inner surface of the submerged portion 15 in the back outer shell 12.

  The guide groove 23 has a substantially upwardly concave circular arc shape when viewed from the side, and the back outer shell 12 (backrest 5) tilts backward about the support shaft 16 while being guided by the guide groove 23 and sinking. That is, it tilts backward while moving the pivot fulcrum toward you.

  Although details are omitted, the flange 3b of the base 3 is held from below by a holding piece provided on the seat inner shell 9, and the seat inner shell 9 is held so that it cannot be pulled out. The seat inner shell 9 is supported by the flange 3b of the base 3 via the bearing 17 so as to be movable back and forth, and is also supported by the support bar 21 so as to be movable back and forth.

(2). Connection structure between the back outer shell and the seat inner shell The back outer shell 12 and the seat inner shell 9 are connected, and when rocking, the backrest 5 descends while tilting backward about the support shaft 16. The seat 3 moves forward with this movement. In addition, the rear portion of the seat 9 tilts backward when moving forward.

  Therefore, a connection structure between the back outer shell 12 and the seat inner shell 9 will be described. As shown in FIGS. 6 and 7, a lower front catch 27 having left and right inward claws 26 is provided in the rear portion of the seat inner shell 9 near the left and right ends, while the back outer shell 12 is submerged. The part 15 is provided with a rear catch 28 into which the front catch 27 is fitted from the front. The rear catch 28 is provided with an outward claw 29 with which the inward claw 26 of the front catch 27 is engaged so that it cannot be pulled upward.

  In addition, a stopper claw 30 extending toward the front is provided on the left and right inner sides of the rear catch 27 of the seat inner shell 9, while the stopper claw 30 fits into the submerged portion 15 of the back outer shell 12 from above. A stopper hole 31 is provided.

  The stopper claw 30 has a free end at the front end, and a claw portion formed at the front end has an inclined surface that becomes higher as going back. For this reason, when the seat inner shell 9 is shifted rearward with the front catch 27 fitted to the rear catch 28, the stopper pawl 30 is elastically deformed so as to be raised upward, and then the seat inner shell 9 is fully pushed. The original posture is restored by the elastic restoring force, and the claw portion of the stopper 30 is fitted into the stopper hole 31 from above. Thereby, the seat inner shell 9 is held so as not to move back and forth.

  A hook-like rear claw 33 is provided rearward at the rear end of the seat inner shell 9, and a rib 34 is provided in the submerged portion 15 of the back outer shell 12 so that the rear claw 33 cannot be moved upward. This forcibly lowers the rear end of the seat inner shell 9 together with the back outer shell 12 during locking.

(3). Structure of the backrest Next, the structure of the backrest 5 will be described. The back outer shell 12 of the backrest 5 functions as a strength member. For example, as shown in FIG. 5, a large number of reinforcing ribs 36 are provided in the submerged portion 15 and a portion connected thereto.

  More precisely, as shown in FIG. 5 with reference numerals, the back outer shell 12 is composed of an upright portion 12a extending generally in the vertical direction and an inclined portion 12b connected to the lower end of the back outer shell 12 toward the lower side of the seat. In the inclined portion 12b, about half of the tip side is the submerged portion 15, but reinforcing ribs 36 are provided on the entire inclined portion 12b and the lower end portion of the standing portion 12a. Therefore, most of the upright portions 12a are not provided with the reinforcing ribs 36 (this is not intended to exclude the reinforcing ribs and is not necessary).

  As shown in FIGS. 5 to 8, the back outer shell 12 and the back inner shell 13 are connected via a substantially H-shaped reinforcing metal fitting 37. The reinforcing metal fitting 37 is composed of a vertically elongated left and right joint bar 38 and a horizontally elongated stay 39 that integrally connects the left and right joint bars 38.

  The joint bar 38 is made of, for example, a round pipe such as a steel pipe, and has a forward facing lower portion 38a, an upward standing portion 38b, and an intermediate portion 38c that connects the two, and adjacent portions are recessed toward the front in a side view. It is bent into a square shape. The forward-facing lower portion 38 a is fitted from behind to the tunnel portion 40 formed in the sinking portion 15 of the back outer shell 12. The intermediate portion 38 c is fitted in a holding groove 41 provided in the back outer shell 12. The upward standing portion 38 b of the joint bar 38 is fitted into a cylindrical portion 42 of a downward opening provided on the rear surface of the back inner shell 13.

  In this case, the joint bar 38 is not fixed with respect to the back outer shell 12 and the back inner shell 13 but is simply fitted. The joint bar 38 is fitted to the tunnel portion 40, the holding groove 41, and the cylindrical portion 42 with a slight play (backlash, clearance). The clearance can be a few millimeters to a millimeter.

  As shown in FIGS. 8 and 9, the periphery of the back inner shell 13 is constituted by an outer peripheral rib 43. Inside the outer peripheral rib 43, two left and right vertical main ribs 44 and two upper and lower (two pairs) horizontally long A main rib 45 is formed, and a crossed center rib 46 is provided in a portion surrounded by the vertically long main rib 44 and the horizontally long main rib 45. Further, upper ribs 47 are provided on the upper and lower sides, and side ribs 48 are provided on the left and right sides.

  By the group of these ribs, the back inner shell 13 functions as a strength member that supports the load (body pressure) of the seated person. Therefore, the back inner shell 13 has a rigid structure that does not deform due to the body pressure of the seated person (the rib for maintaining the strength is not limited to the illustrated mode, and various modes can be adopted). The cylindrical portion 42 is configured by opening the lower end of the vertically long main rib 44 downward.

  In particular, as shown in FIGS. 9 and 10, two pairs of left and right upper male catches 50 and a pair of left and right sides arranged on the left and right sides are provided on the inner side of the upper rib 46 and the side rib 47 on the rear side of the back inner shell 13. An intermediate male catch 51 and a pair of left and right lower male catches 52 arranged on the left and right side portions are provided, while an upper female catch 50 in which the upper male catch 50 is fitted to the back outer shell 12 from above is provided. 53, an intermediate female catch 54 into which the intermediate male catch 51 fits, and a lower female catch 55 into which the lower male catch 52 fits. The female catches 50 to 52 are examples of the front catch described in the claims, and the female catches are examples of the rear catch described in the claims.

  Further, a pair of left and right stopper claws 56 that extend upward are provided on the inner side of the lower male shell 52 in the back inner shell 13, while the stopper claws 56 are hooked and engaged with the front surface of the back outer shell 12. A stopper wall 57 is provided.

  Each male catch 50, 51, 52 protrudes backward, and the upper male catch 50 and the lower male catch 51 are provided with one claw piece 58 on the left and right outer sides, and the intermediate male catch 51 A claw piece 58 is provided. On the other hand, each of the female catches 53, 54, 55 has a substantially box shape having left and right walls and a bottom plate 59 so that the male catches 50, 51, 52 fit from above. The lower female catch 55 is provided with one inward restricting piece 60 that holds the claw pieces 58 of the upper and lower male catches 50 and 52 in front of each other, and the intermediate female catch 54 has an intermediate male catch 54. Corresponding to 51 having left and right claw pieces 58, a pair of left and right inward restriction pieces 60 are provided.

  The male catches 50, 51, 52 are held by the female catches 53, 53, 55 so that they cannot move left and right, cannot move back and forth, and cannot move downward. Further, the male catches 50, 51, 52 are fitted into the female catches 53, 53, 55 from above, but the upper ends of the respective restricting pieces 60 are provided to guide (invite) the fitting of the male catches 50, 51, 52. Is provided with a guide portion 60a that is inclined (tilted forward) toward the front.

  Then, as shown in FIG. 11, in the side view, the inclination posture of the upward standing portion 38b in the reinforcing bracket 37 and the inclination posture of the guide portion 60a of each regulating piece 60 are set to be substantially the same (the upward standing portion 38b and the guide). The cylindrical portion 42 of the back inner shell 13 is fitted to the upward standing portion 38b by a certain size (for example, several tens of mm), and then the male catches 50, 51 are set. , 52 are set so as to fit into the respective female catches 53, 54, 55.

  For this reason, when the back inner shell 13 is fitted into the upright rear portion 38 b of the reinforcing metal fitting 37 and moved downward, the male catches 50 to 52 are automatically fitted into the female catches 53 to 55. Therefore, the back inner shell 13 can be easily attached with one touch. The forward tilt angle of the guide portion 60a may be slightly larger than the forward tilt angle of the upward standing portion 38b (that is, the guide portion 60a may be tilted forward relative to the upward standing portion 38b). .

  The lowering lower limit of the back inner shell 13 is regulated by each male catch 50-52 hitting the bottom plate 59 of the female catch 53-55. Then, the stopper claw 56 hits the stopper wall 57 by the downward movement of the back inner shell 13 and is elastically deformed so as to fall down to the near side. Then, when the back inner shell 13 is completely lowered, the stopper claw 56 returns and rotates. Migrate below. Thereby, the back inner shell 13 is held immovable upward. On the upper surface of the stopper wall 57, a guide rib 61 inclined in a side view is provided in order to guide the downward movement of the stopper claw 56.

  As described above, the back inner shell 13 is formed in the vertical direction, the front-rear direction, and the left-right direction by the male catch catches 50 to 52 and the female catches 53 to 55, and the stopper claw 56 and the stopper wall 57. It is attached to the back outer shell 12 in a state where there is no backlash.

  The back inner shell 13 receives a backward moment due to the backward load applied by the seated person, and the moment acts strongly on the lower portion of the back inner shell 13. The back inner shell 13 and the back outer shell 12 are provided with the reinforcing bracket 37. Therefore, the moment acting on the back inner shell 13 is firmly supported by the lower portion of the back outer shell 12 via the reinforcing metal fitting 37.

  Accordingly, only the lower portion of the back outer shell 12 functions as a strength member, and most of the upright portions 12a do not need to maintain high strength. Therefore, most of the upright portions 12a have no or almost no reinforcing ribs 36. Can be molded into a state that does not. Thereby, quality degradation due to the occurrence of sink marks can be prevented.

  Further, since the joint bar 38 is fitted to the back outer shell 12 and the back inner shell 13 with a little play, as described above, not only is the assembly easy, but also the back inner shell 13 is subjected to an uneven load. It is possible to prevent the stress concentration due to the difference in thermal expansion coefficient and the advantage of preventing stress concentration when acting.

  The joint bar 38 and the stay 39 can be embodied in various forms such as a square pipe or a sheet metal. It is also possible to make the reinforcing metal fitting 37 an integral product made of sheet metal or aluminum die cast. For example, two joint bars 38 may be arranged on the left and right. Needless to say, the back outer shell 12 does not need to include the sinking portion 15.

  Therefore, the reinforcing metal fitting 37 is constituted by a single member having a certain right and left width and is arranged at the left and right middle part of the back outer shell, and the joint bar is arranged at three places of the right and left middle part and both sides thereof. Is also possible. The point is that any material or shape can be used for the reinforcing bracket 37 as long as it can maintain at least the strength that can withstand a backward moment from the seated person. The catch means is not limited to the illustrated form, and various structures (combinations) can be adopted.

  The retaining means for preventing upward movement of the back inner shell is not limited to the combination of the stopper claw and the stopper wall as in the embodiment, and various structures and combinations such as a hook between the claw and the claw can be adopted.

  Although the cushion 14 is affixed to the back inner shell 13 of the embodiment, the back inner shell 13 may be configured in a frame shape that is open forward and backward, and a flexible member such as a mesh may be stretched thereon. In this case, the back outer shell does not cover most of the back inner shell 13.

  Although illustration explanation is omitted, it is also possible to attach the reinforcing metal fitting to the back inner member first. In this case, the reinforcing metal fitting is provided with a downward hanging portion, and the back outer member is provided with a cylindrical portion (or hole) into which the downward hanging portion is fitted. When using a set of a male catch and a female catch as in the embodiment, a female catch may be provided on the back inner shell and a male catch may be provided on the back outer shell. Further, the guide portion for guiding may be provided in any place.

  The present invention can be embodied in a chair back. Therefore, it can be used industrially.

3 base 4 seat 9 seat inner shell 12 back outer shell (back outer member)
13 Back inner shell (back inner member)
DESCRIPTION OF SYMBOLS 15 Submerged part 36 Reinforcement rib 37 Reinforcement metal fitting 38 Joint bar 39 Stay 40 Tunnel part 41 Holding groove 42 Cylindrical part 50-52 Male catch (front catch)
53-55 Female catch (rear catch)
56 Stopper Claw 57 Stopper Wall

Claims (5)

A back inner member, a back outer member disposed behind the back inner member, and a reinforcing metal fitting connecting the back outer member and the back inner member;
A front catch provided on the rear surface of the back inner member is fitted to a rear catch provided on the front surface of the back outer member from above, so that the back inner member is held so as not to move back and forth with respect to the back outer member. While
The reinforcing metal fitting has an upward standing portion extending upward from the back outer member, and the back inner member is fitted into the reinforcing metal fitting from above, and the back inner member is first fitted into the reinforcing metal fitting, and then It is set so that the catch is fitted by the guide action of the reinforcing bracket,
The back of the chair. The reinforcing metal fitting includes a plurality of left and right joint bars made of pipe material or bar material, and the joint bar is first attached to the back outer member, and the rear end portion is the upward standing portion, and the back The engagement of the catch is started after the inner member has been fitted to the upward standing portion,
The chair back according to claim 1. A back inner member, a back outer member disposed behind the back inner member, and a reinforcing metal fitting connecting the back outer member and the back inner member;
A front catch provided on the rear surface of the back inner member is fitted to a rear catch provided on the front surface of the back outer member from above, so that the back inner member is held so as not to move back and forth with respect to the back outer member. While
The reinforcing bracket has a hanging portion extending downward from the back inner member and is fitted into the back outer member from above, and the back outer member is fitted into the reinforcing bracket first, and then the reinforcing It is set so that the catch is fitted by the guide action of the bracket,
The back of the chair. Either one or both of the rear catch and the front catch is provided with an inclined guide portion for guiding the front catch into the rear catch.
The backrest of the chair described in any one of Claims 1-3. The front catch of the back inner shell is male and the back catch of the back outer shell is female, and a guide portion for guiding the front catch to the rear catch when the back inner shell moves downward is shown in a side view. Provided in a posture that is substantially parallel to or upwardly inclined from the upward rising portion of the reinforcing bracket,
The chair back according to claim 2.

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