CA1241904A - Chair with articulated flexible spring backrest - Google Patents
Chair with articulated flexible spring backrestInfo
- Publication number
- CA1241904A CA1241904A CA000504038A CA504038A CA1241904A CA 1241904 A CA1241904 A CA 1241904A CA 000504038 A CA000504038 A CA 000504038A CA 504038 A CA504038 A CA 504038A CA 1241904 A CA1241904 A CA 1241904A
- Authority
- CA
- Canada
- Prior art keywords
- strut
- frame
- chair
- frame members
- wire member
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- A—HUMAN NECESSITIES
- A47—FURNITURE; DOMESTIC ARTICLES OR APPLIANCES; COFFEE MILLS; SPICE MILLS; SUCTION CLEANERS IN GENERAL
- A47C—CHAIRS; SOFAS; BEDS
- A47C7/00—Parts, details, or accessories of chairs or stools
- A47C7/36—Support for the head or the back
- A47C7/40—Support for the head or the back for the back
- A47C7/44—Support for the head or the back for the back with elastically-mounted back-rest or backrest-seat unit in the base frame
-
- A—HUMAN NECESSITIES
- A47—FURNITURE; DOMESTIC ARTICLES OR APPLIANCES; COFFEE MILLS; SPICE MILLS; SUCTION CLEANERS IN GENERAL
- A47C—CHAIRS; SOFAS; BEDS
- A47C3/00—Chairs characterised by structural features; Chairs or stools with rotatable or vertically-adjustable seats
-
- A—HUMAN NECESSITIES
- A47—FURNITURE; DOMESTIC ARTICLES OR APPLIANCES; COFFEE MILLS; SPICE MILLS; SUCTION CLEANERS IN GENERAL
- A47C—CHAIRS; SOFAS; BEDS
- A47C7/00—Parts, details, or accessories of chairs or stools
- A47C7/36—Support for the head or the back
- A47C7/40—Support for the head or the back for the back
- A47C7/44—Support for the head or the back for the back with elastically-mounted back-rest or backrest-seat unit in the base frame
- A47C7/445—Support for the head or the back for the back with elastically-mounted back-rest or backrest-seat unit in the base frame with bar or leaf springs
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
- Y10T403/00—Joints and connections
- Y10T403/45—Flexibly connected rigid members
- Y10T403/453—Flexible sleeve-type coupling
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
- Y10T403/00—Joints and connections
- Y10T403/54—Flexible member is joint component
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
- Y10T403/00—Joints and connections
- Y10T403/55—Member ends joined by inserted section
Abstract
ABSTRACT
A chair which includes a seat frame having depend-ing leg members and a pair of upstanding, spaced apart members arranged to provide a lower backrest part for a chair and an upper backrest frame part having a pair of spaced apart depending members in registry with the up-standing members, said members being hollow with open extremities, and flexible spring means secured between each pair of members to provide an articulated, flexible spring backrest for the chair. Each flexible spring means includes a molded plastic support strut having a wire cable flexible core to maintain the strut under compression and limit the elongation thereof when a force is exerted on the backrest by a user of the chair. The seat frame may be integral with the depend-ing leg members.
A chair which includes a seat frame having depend-ing leg members and a pair of upstanding, spaced apart members arranged to provide a lower backrest part for a chair and an upper backrest frame part having a pair of spaced apart depending members in registry with the up-standing members, said members being hollow with open extremities, and flexible spring means secured between each pair of members to provide an articulated, flexible spring backrest for the chair. Each flexible spring means includes a molded plastic support strut having a wire cable flexible core to maintain the strut under compression and limit the elongation thereof when a force is exerted on the backrest by a user of the chair. The seat frame may be integral with the depend-ing leg members.
Description
CHAIR WITH ARTICULATED
PLEXIBLE SPRING PACRREST
This invention relates generally to chairs having flexible, articulated backrests and more particularly, to a novel chair frame having upper and lower backrest frame parts con30ined by flexible spring means.
Chairs having articulated, flexible backrest part foc achieving desired support ana comfort for the users are known in the art. 5uch chairs are used, for example, in banguet and conference facilities where back comfort for the seated~attendees is 80 desirable. Typically, such chairs are stackable and have molded backrest parts and peripheral frame parts of hollow construction to enable interconnection oS upper and lower backrest parts which are flexible. Various flexible spring arrangements for 30ining the upper and lower backrest earts of such chairs are shown in the following U.S. Patents: 2,0Z0,020 2,587,822:
PLEXIBLE SPRING PACRREST
This invention relates generally to chairs having flexible, articulated backrests and more particularly, to a novel chair frame having upper and lower backrest frame parts con30ined by flexible spring means.
Chairs having articulated, flexible backrest part foc achieving desired support ana comfort for the users are known in the art. 5uch chairs are used, for example, in banguet and conference facilities where back comfort for the seated~attendees is 80 desirable. Typically, such chairs are stackable and have molded backrest parts and peripheral frame parts of hollow construction to enable interconnection oS upper and lower backrest parts which are flexible. Various flexible spring arrangements for 30ining the upper and lower backrest earts of such chairs are shown in the following U.S. Patents: 2,0Z0,020 2,587,822:
2,732,005, 3,183,034: 3,203,731: 3,351,378: 4,084,850: 4,157,203:
4,333,683.
The chair disclosed in the listed patents include articulated, flexible'backrests which are'of complex construction and relatlvely involved to install. Simplicity and economy of construction and installation for such chairs which are used in great numbers is a veey important and desirable~ob3ective.
Additionally, it is important to provide a-chair construction in which'the flexing parts are reliable and capable'of repeated use without breaking and which incorporate saftey features to prevent sudden failure of the flexible frame parts in the event such parts do fracture or otherwise break after extensive and repeated use.
Such safety ~eatur0~ are important to prevent possible in3ury to the user of the chair.
Accordingly, the invention pcovides a chair comprising, a 30' 8eat a8~embly whlch includes a support fcame and depending leg members, a lower backrest frame part having a pair of spaced apart frame members upstanding relative to the seat support frame, an upper backrest frame part having a pair of spac2d apart depending ~L2419~)4 fcame membec6 arranged in registry with the upstanding frame member, said frame members being hollow with open extremitie6, and spring members secured between each registered palr of frame members to provide an articulated, flexible~spring backrest for the chair, each 6pring means including a molded plastic.support stcut with an elongate passageway therein, a substantially non-exteAsible flexible member disposed within said passageway and means securing said flexible member at each end of said passageway 60 as to maintain the strut under longitudinal compression and limit the elongation chereof when a force is exerted on the backrest.
The present invention also provides ? spring member for use in a flexible backrest as6embly foc a chair wherein the assembly includss upper and lower backrest parts, said spring member capable of being secuced between said frame part6, said 6pring member comprising spring means including at least a molded plastic support strut having an elongated passageway extending .
substantially the length thereof and a f lexible insert disposed within said passageway to maintain the strut under compression and limit the elongat.ion thereof.
Further, the invention provides the seat support frame as unitary with said depending leg membees.
The preferred embodiments of this invention now will be described, by way of example, with eeference to the drawings accompanying this specification in which: ' Figure l is a perspective view of a chair embodying the invention and illustrating, in:phantom outline, the upeer backrest portion in f lexed displacement:
Figure 2 is a f ragmentary view of a portion of said chair 30 having the molded plastic elongate support strut of the invention installed thereon and shown in flexed displacement:
Figure 3 18 a fragmentary view similar to that of Figure 2 illustrating, in phantom outline, portions of the support 6trut disposed within the frame ends of the chair, and secured therein by optional fasteners:
- la -PAT 9408-l .
~241904 Figure 4 is a plan view of the molded plastic elongate support strut of the invention; - :
Figure 5 is an end view~of the strut: shown i~:Figure 4; :
Figure 6 is a partially fragmentary view of said support strut with a wire cable po6itioned and 8ecu~ed I
., ... ~,,~. . . :.
... .. . . .
~Z41~04 within the passageway thereof, and illustrating the manner in which an end of the strut is friction-fit within a frame end of the chair: and Figure 7 is a sectional view taken along the line 7-7 in Figure 6, in the direction indicated generally.
Referring to Figure 1, the chair embodying the invention is designated generally by the reference character 10. Chair 10 includes a frame 11 having an upper backrest portion designated generally 12 and a unitary seat and lower backrest portion designated 14.
The upper backrest portion 12 includes a peripheral, inverted U-shaped frame member 16 providing a pair of spaced apart, depending frame member ends 18 connected across the upper ends thereof by the curved bridging segment 20. A backrest pad or cushion 22 is secured between the frame member ends 18 in a connectional manner.
The lower extremities 24 of each frame member end 18 are open or hollow. The frame member 16 is formed of metal stock or tubing, the cross-sectional configuration of which can be rectangular, circular or any other suitable configuration. Strong molded synthetic plastic or composition materials also are feasible so long as they are rigid and hollow. Also, the precise configuration of the upper portion of frame member 16 forms no part of this invention; and suitable configurations other than the U-shape illustrated may be used.
The unitary seat and lower backrest portion 14 includes a unitary frame assembly formed of hollow tubular stock similar to that of frame member 16. The assembly includes a pair of like inverted U-shaped members, each providing a pair of depending legs 29 braced by a cross-member 30 in a conventional manner. Each pair of legs 29 is connected by an upper saddle or bridge segment 32.
The bridging segments 32 are spaced apart the distance between the conjoined leg pairs 29.
~24~9~4 A combination seat and lower backrest frame 34 is secured between the bridging or saddle parts 32. The combination frame 34'Iikewise is formed of tubular stock and includes a horizontally oriented seat-retaining portion 36 of generally U-shaped configuration and an upstanding backrest portion formed as an extension of the seat portion 36.' The seat portion 36 includes a pair of side s0gments 40 connected at the front end of the chair by front segment 42., Extending upwardly from each segment 40 at the rear end of the chair are straight segments 44 which are hollow and open at their respective upper extremities 46. The segments 44 are arranged in parallel relationship and spaced apart laterally the same distance as the depending frame member ends 18. The upstanding segments 44 thereby cooperate to provide the lower backrest frame portion of the chair 10.
As seen in Figure 1, the members 18 and 44 are interconnected, i.e., each member 18 is aligned and in registry with a respective member 44. The joint or juncture between each of the interconnected members 18 and 44 is concealed by a bellows-like appearing flexible sleeve 46 so that the backrest 12 of the chair appears to be unitary., A seat pad or cushion 48 is installed on the seat frame members 40 and 42, and an optional lower backrest pad S0 is installed between the lower backrest segments 44. The chair construction is such that lower backrest pad 50 may be omitted, if desired, without sacrif,icing the utility of the chair.
The flexible spring means for cojoining or inter-connecting the upper and lower backrest parts isdesignated generally 52. A pair of identical spring means 52 is utilized as seen in Figure 1, so only one need be described in detail. Each spring means includes a molded plastic support strut 54 of generally elongate configuration with opposite terminal ends 56,58. The cross-sectional configuration of strut 54 is rectangular .
~4~9{~4 to conform to the configuration of the frame parts of chair 10. It is to be understood, however, that the configuration could be other than rectangular and need only be suitable to be engageable in the chair frame portion as described hereinafter.
Strut 54 has a centrally-located bellows-like portion 46 disposed between opposite end parts 60,62. Portion 46 has a plurality of radially projecting circumferential ribs 64 spaced along the surface thereof. End parts 60,62 are adapted to be disposed within the hollow frame ends of the upper and lower backrest portions 18,44 with portion 46 exposed therebetween as seen in Figures 1, 2 and 3.
Each end part 60,62 has a plurality of axially-extending ribs 66 formed on the external surface thereof to provide an interference fit with the inner-facing walls 68 of frame parts 14,44 so as to facilitate tight or friction engagement between the end parts 60,62 when they are positioned within frame parts 18,44.
Strut 54 includes a longitudinally extending passage-way 69 formed through the length thereof to permitpositioning of a cable 70 therewithin. Cable 70 may be formed of ~.ircraft wire, chain or other linkage material and terminates beyond the ends 56,58 of strut 54. Cable 70 i8 retained in passageway 68 by clips 72 which are crimped or otherwise secured at locations 74 and thereby maintain the plastic from which strut 54 is formed under compression. When.the cable 70 is secured in place in passageway 68 by clips 72, the cable limits the elongation and ultimate yield or breakage point of strut 54.
The terms "wire member" will be used to include all suitable linkage materials referred to herein.
Strut 54 i8 positioned between frame parts 18,44 by force-fitting end parts 60,62 into the terminal hollow ends 24,46. As this positioning is effected, portions 35 80 of ribs 66 are sheared off (see Figure 6) and may be discarded as scrap, thus ensuring a tight, friction-fit.
~24~9~4 of strut 54 within frame parts 18,44. As added assurance for maintaining the assembly of strut 54 within frame parts 18,44, fasteners 82 may be inserted through frame parts 18,44 into respective end parts 56,58 of strut 54, as shown in Figure 3.
The invention in such that chair back 14 may be flexed as desired to accommodate the posture of a person sitting in the chair for extended periods of time. The cross-sectional configuration and length of strut 54 with wire cable 7-0 therein is selected to be sufficient to limit the elongation, flexibility and ultimate yield strength to allow the chair back to flex and return to the original position without overstressing the elasto-metric material from which strut 54 is formed. The cable 70 limits the elongation and ultimate yield point of the plastic strut 54 in that the plastic material from which strut 54 is constructed has a compression strength which is higher than its tensile strength. By positioning the cable in passageway 68 which is located centrally or slightly closer to the larger or front curve 85 of the strut (see Figure 2), the portions of the strut closer to the rear curve 87 are compressed before the material on the front curve 85 can-stretch or elongate. This limits the overstressing of the surface of the elastometric material.
The chair back should flex approximately 20 degrees rearward when a force of 75 pounds is applied perpend-icular to the back at a point 16 inches above the sitting surface. For optimum user comfort, the flex point should be between three (3) and five (5) inches above the sitting surface. Using the following formula, the load applied at the flex point will be Load = Moment arm length x force;
975 Inch lbs = 13 inches x 75 lbs.
This load would be divided between the two struts 54 giving an individual spring loading of 487.5 lbs. The ~.2419~)4 , elastic modulus in flexure of the plastic material used must correspond to the required cross section and the above mentioned flexural requirements.
In addition to the above stress requirement (which has been tested cyclically), the struts must withstand a functional test loading of 150 pounds, one time without failure, and a proof loading of 250 pounds, one time without a failure that would cause injury to the chair's occupant. It is on this 250 pound proof loading that the stress requirements are based. These tests are further described in American National Standards Institute, Inc.
Business and Institutional Furniture Manufacturing Associates (BIFMA), ANSI X5 1-1977 Test Standards, Sections 5 and 16.
From page 418 of "The Twenty-First Edition of Machinery's Handbook," the stress in the extreme outer fibers of the spring is calculated to be as follows:
6x length of moment arm x load Stress in outer fibers =(~idth of flex member x (thickness of flex member)3 Length of moment arm = 13 inches Load = 250 lbs/2 struts = 125 lbs.
Width of flexural member = .690 in.
Thickness of flexural member = .690 in.
6 x 13 in. x 125 lbs = 9.750 in Stress in outer fibers = lbs. .690 in x (.690 in)3 -(.3285 in) = 29,860 lbs/in2 The tensile strength of the plastic used in an operating A embodiment, DuPont Delrin-Supertough lOOST~acetal resin, is given by DuPont at 6,500 psi with an elongation factor of 200% at breakage. By use of a steel cable 70 to control the elongation of the outer fibers, tensile failures are prevented by ensuring that the outer fibers of strut 54 do not exceed the tensile limits of the material.
c en .2gl904 The flexing or deflection of the central portion 46 of struts 54, as seen in Figure 2, enables the upper backrest part to be displaced from the normal plane of the backrest assembly or relative to the lower backrest S part, as illustrated in phantom outline 80 in Figure 1.
This flexing or displacement of the upper backrest part relative to the lower backrest part is the desired feature for seating comfort by the user. Upon rising from the seat pad 48 or withdrawing from the backrest pad 22, the upper backrest part will return automatically to the normal solid outline condition of the backrest illustrated in Figure 1.
Summarizing, herein there has been described a novel chair having a seating frame which includes a lower lS backrest portion upstanding thereon and an upper backrest frame portion. The backrest portions are interconnected by flexible spring means secured between the lower and upper backrest portions. Each spring means includes a molded plastic support strut of elastomeric material with a flexible core of sufficient strength to limit the elongation, flexibility and ultimate yield strength thereof.
It should be noted that each spring means has a molded plastic elongate support strut with a passageway extending the length thereof. A strong, flexible core member formed from wire cable, chain, linkage, or the like, is positioned within the passageway and secured therein with retaining clamps at opposite extremities of the support strut to hold and maintain the strut under compression. The molded plastic support strut has a centrally-located bellows-like portion between opposite end parts adapted to be inserted into and secured within the respective depending and upstanding frame ends to retain the same together with the spring means secured therebetween.
The opposite end parts of the strut have mutliple ribs formed thereon to abut against the inner-facing walls g lZ4~9~4 of the frame ends for friction fit of the plastic support strut within the frame ends.
The spring means serve positively to join the upper and lower backrest portions to prevent translational movement therebetween. As the spring means are flexed, the wire cable secured in the passageway of the plastic support strut limits the elongation and ultimate yield or breaking point of the strut. The cable controls elongation of the strut to permit flexing and yet prevents tensile failure by insuring that the plastic support strut is not flexed beyond the tensile limit of the material from which it is constructed.
The simplicity and economy of the spring means 52 and its installation between the upper and lower backrest frame parts can be readily appreciated. Simple tooling and parts are involved. Minor variations in dimensions and configuration of component parts of the invention may occur to the skilled artisan without departing from the scope of the invention as set forth in the appended claims.
4,333,683.
The chair disclosed in the listed patents include articulated, flexible'backrests which are'of complex construction and relatlvely involved to install. Simplicity and economy of construction and installation for such chairs which are used in great numbers is a veey important and desirable~ob3ective.
Additionally, it is important to provide a-chair construction in which'the flexing parts are reliable and capable'of repeated use without breaking and which incorporate saftey features to prevent sudden failure of the flexible frame parts in the event such parts do fracture or otherwise break after extensive and repeated use.
Such safety ~eatur0~ are important to prevent possible in3ury to the user of the chair.
Accordingly, the invention pcovides a chair comprising, a 30' 8eat a8~embly whlch includes a support fcame and depending leg members, a lower backrest frame part having a pair of spaced apart frame members upstanding relative to the seat support frame, an upper backrest frame part having a pair of spac2d apart depending ~L2419~)4 fcame membec6 arranged in registry with the upstanding frame member, said frame members being hollow with open extremitie6, and spring members secured between each registered palr of frame members to provide an articulated, flexible~spring backrest for the chair, each 6pring means including a molded plastic.support stcut with an elongate passageway therein, a substantially non-exteAsible flexible member disposed within said passageway and means securing said flexible member at each end of said passageway 60 as to maintain the strut under longitudinal compression and limit the elongation chereof when a force is exerted on the backrest.
The present invention also provides ? spring member for use in a flexible backrest as6embly foc a chair wherein the assembly includss upper and lower backrest parts, said spring member capable of being secuced between said frame part6, said 6pring member comprising spring means including at least a molded plastic support strut having an elongated passageway extending .
substantially the length thereof and a f lexible insert disposed within said passageway to maintain the strut under compression and limit the elongat.ion thereof.
Further, the invention provides the seat support frame as unitary with said depending leg membees.
The preferred embodiments of this invention now will be described, by way of example, with eeference to the drawings accompanying this specification in which: ' Figure l is a perspective view of a chair embodying the invention and illustrating, in:phantom outline, the upeer backrest portion in f lexed displacement:
Figure 2 is a f ragmentary view of a portion of said chair 30 having the molded plastic elongate support strut of the invention installed thereon and shown in flexed displacement:
Figure 3 18 a fragmentary view similar to that of Figure 2 illustrating, in phantom outline, portions of the support 6trut disposed within the frame ends of the chair, and secured therein by optional fasteners:
- la -PAT 9408-l .
~241904 Figure 4 is a plan view of the molded plastic elongate support strut of the invention; - :
Figure 5 is an end view~of the strut: shown i~:Figure 4; :
Figure 6 is a partially fragmentary view of said support strut with a wire cable po6itioned and 8ecu~ed I
., ... ~,,~. . . :.
... .. . . .
~Z41~04 within the passageway thereof, and illustrating the manner in which an end of the strut is friction-fit within a frame end of the chair: and Figure 7 is a sectional view taken along the line 7-7 in Figure 6, in the direction indicated generally.
Referring to Figure 1, the chair embodying the invention is designated generally by the reference character 10. Chair 10 includes a frame 11 having an upper backrest portion designated generally 12 and a unitary seat and lower backrest portion designated 14.
The upper backrest portion 12 includes a peripheral, inverted U-shaped frame member 16 providing a pair of spaced apart, depending frame member ends 18 connected across the upper ends thereof by the curved bridging segment 20. A backrest pad or cushion 22 is secured between the frame member ends 18 in a connectional manner.
The lower extremities 24 of each frame member end 18 are open or hollow. The frame member 16 is formed of metal stock or tubing, the cross-sectional configuration of which can be rectangular, circular or any other suitable configuration. Strong molded synthetic plastic or composition materials also are feasible so long as they are rigid and hollow. Also, the precise configuration of the upper portion of frame member 16 forms no part of this invention; and suitable configurations other than the U-shape illustrated may be used.
The unitary seat and lower backrest portion 14 includes a unitary frame assembly formed of hollow tubular stock similar to that of frame member 16. The assembly includes a pair of like inverted U-shaped members, each providing a pair of depending legs 29 braced by a cross-member 30 in a conventional manner. Each pair of legs 29 is connected by an upper saddle or bridge segment 32.
The bridging segments 32 are spaced apart the distance between the conjoined leg pairs 29.
~24~9~4 A combination seat and lower backrest frame 34 is secured between the bridging or saddle parts 32. The combination frame 34'Iikewise is formed of tubular stock and includes a horizontally oriented seat-retaining portion 36 of generally U-shaped configuration and an upstanding backrest portion formed as an extension of the seat portion 36.' The seat portion 36 includes a pair of side s0gments 40 connected at the front end of the chair by front segment 42., Extending upwardly from each segment 40 at the rear end of the chair are straight segments 44 which are hollow and open at their respective upper extremities 46. The segments 44 are arranged in parallel relationship and spaced apart laterally the same distance as the depending frame member ends 18. The upstanding segments 44 thereby cooperate to provide the lower backrest frame portion of the chair 10.
As seen in Figure 1, the members 18 and 44 are interconnected, i.e., each member 18 is aligned and in registry with a respective member 44. The joint or juncture between each of the interconnected members 18 and 44 is concealed by a bellows-like appearing flexible sleeve 46 so that the backrest 12 of the chair appears to be unitary., A seat pad or cushion 48 is installed on the seat frame members 40 and 42, and an optional lower backrest pad S0 is installed between the lower backrest segments 44. The chair construction is such that lower backrest pad 50 may be omitted, if desired, without sacrif,icing the utility of the chair.
The flexible spring means for cojoining or inter-connecting the upper and lower backrest parts isdesignated generally 52. A pair of identical spring means 52 is utilized as seen in Figure 1, so only one need be described in detail. Each spring means includes a molded plastic support strut 54 of generally elongate configuration with opposite terminal ends 56,58. The cross-sectional configuration of strut 54 is rectangular .
~4~9{~4 to conform to the configuration of the frame parts of chair 10. It is to be understood, however, that the configuration could be other than rectangular and need only be suitable to be engageable in the chair frame portion as described hereinafter.
Strut 54 has a centrally-located bellows-like portion 46 disposed between opposite end parts 60,62. Portion 46 has a plurality of radially projecting circumferential ribs 64 spaced along the surface thereof. End parts 60,62 are adapted to be disposed within the hollow frame ends of the upper and lower backrest portions 18,44 with portion 46 exposed therebetween as seen in Figures 1, 2 and 3.
Each end part 60,62 has a plurality of axially-extending ribs 66 formed on the external surface thereof to provide an interference fit with the inner-facing walls 68 of frame parts 14,44 so as to facilitate tight or friction engagement between the end parts 60,62 when they are positioned within frame parts 18,44.
Strut 54 includes a longitudinally extending passage-way 69 formed through the length thereof to permitpositioning of a cable 70 therewithin. Cable 70 may be formed of ~.ircraft wire, chain or other linkage material and terminates beyond the ends 56,58 of strut 54. Cable 70 i8 retained in passageway 68 by clips 72 which are crimped or otherwise secured at locations 74 and thereby maintain the plastic from which strut 54 is formed under compression. When.the cable 70 is secured in place in passageway 68 by clips 72, the cable limits the elongation and ultimate yield or breakage point of strut 54.
The terms "wire member" will be used to include all suitable linkage materials referred to herein.
Strut 54 i8 positioned between frame parts 18,44 by force-fitting end parts 60,62 into the terminal hollow ends 24,46. As this positioning is effected, portions 35 80 of ribs 66 are sheared off (see Figure 6) and may be discarded as scrap, thus ensuring a tight, friction-fit.
~24~9~4 of strut 54 within frame parts 18,44. As added assurance for maintaining the assembly of strut 54 within frame parts 18,44, fasteners 82 may be inserted through frame parts 18,44 into respective end parts 56,58 of strut 54, as shown in Figure 3.
The invention in such that chair back 14 may be flexed as desired to accommodate the posture of a person sitting in the chair for extended periods of time. The cross-sectional configuration and length of strut 54 with wire cable 7-0 therein is selected to be sufficient to limit the elongation, flexibility and ultimate yield strength to allow the chair back to flex and return to the original position without overstressing the elasto-metric material from which strut 54 is formed. The cable 70 limits the elongation and ultimate yield point of the plastic strut 54 in that the plastic material from which strut 54 is constructed has a compression strength which is higher than its tensile strength. By positioning the cable in passageway 68 which is located centrally or slightly closer to the larger or front curve 85 of the strut (see Figure 2), the portions of the strut closer to the rear curve 87 are compressed before the material on the front curve 85 can-stretch or elongate. This limits the overstressing of the surface of the elastometric material.
The chair back should flex approximately 20 degrees rearward when a force of 75 pounds is applied perpend-icular to the back at a point 16 inches above the sitting surface. For optimum user comfort, the flex point should be between three (3) and five (5) inches above the sitting surface. Using the following formula, the load applied at the flex point will be Load = Moment arm length x force;
975 Inch lbs = 13 inches x 75 lbs.
This load would be divided between the two struts 54 giving an individual spring loading of 487.5 lbs. The ~.2419~)4 , elastic modulus in flexure of the plastic material used must correspond to the required cross section and the above mentioned flexural requirements.
In addition to the above stress requirement (which has been tested cyclically), the struts must withstand a functional test loading of 150 pounds, one time without failure, and a proof loading of 250 pounds, one time without a failure that would cause injury to the chair's occupant. It is on this 250 pound proof loading that the stress requirements are based. These tests are further described in American National Standards Institute, Inc.
Business and Institutional Furniture Manufacturing Associates (BIFMA), ANSI X5 1-1977 Test Standards, Sections 5 and 16.
From page 418 of "The Twenty-First Edition of Machinery's Handbook," the stress in the extreme outer fibers of the spring is calculated to be as follows:
6x length of moment arm x load Stress in outer fibers =(~idth of flex member x (thickness of flex member)3 Length of moment arm = 13 inches Load = 250 lbs/2 struts = 125 lbs.
Width of flexural member = .690 in.
Thickness of flexural member = .690 in.
6 x 13 in. x 125 lbs = 9.750 in Stress in outer fibers = lbs. .690 in x (.690 in)3 -(.3285 in) = 29,860 lbs/in2 The tensile strength of the plastic used in an operating A embodiment, DuPont Delrin-Supertough lOOST~acetal resin, is given by DuPont at 6,500 psi with an elongation factor of 200% at breakage. By use of a steel cable 70 to control the elongation of the outer fibers, tensile failures are prevented by ensuring that the outer fibers of strut 54 do not exceed the tensile limits of the material.
c en .2gl904 The flexing or deflection of the central portion 46 of struts 54, as seen in Figure 2, enables the upper backrest part to be displaced from the normal plane of the backrest assembly or relative to the lower backrest S part, as illustrated in phantom outline 80 in Figure 1.
This flexing or displacement of the upper backrest part relative to the lower backrest part is the desired feature for seating comfort by the user. Upon rising from the seat pad 48 or withdrawing from the backrest pad 22, the upper backrest part will return automatically to the normal solid outline condition of the backrest illustrated in Figure 1.
Summarizing, herein there has been described a novel chair having a seating frame which includes a lower lS backrest portion upstanding thereon and an upper backrest frame portion. The backrest portions are interconnected by flexible spring means secured between the lower and upper backrest portions. Each spring means includes a molded plastic support strut of elastomeric material with a flexible core of sufficient strength to limit the elongation, flexibility and ultimate yield strength thereof.
It should be noted that each spring means has a molded plastic elongate support strut with a passageway extending the length thereof. A strong, flexible core member formed from wire cable, chain, linkage, or the like, is positioned within the passageway and secured therein with retaining clamps at opposite extremities of the support strut to hold and maintain the strut under compression. The molded plastic support strut has a centrally-located bellows-like portion between opposite end parts adapted to be inserted into and secured within the respective depending and upstanding frame ends to retain the same together with the spring means secured therebetween.
The opposite end parts of the strut have mutliple ribs formed thereon to abut against the inner-facing walls g lZ4~9~4 of the frame ends for friction fit of the plastic support strut within the frame ends.
The spring means serve positively to join the upper and lower backrest portions to prevent translational movement therebetween. As the spring means are flexed, the wire cable secured in the passageway of the plastic support strut limits the elongation and ultimate yield or breaking point of the strut. The cable controls elongation of the strut to permit flexing and yet prevents tensile failure by insuring that the plastic support strut is not flexed beyond the tensile limit of the material from which it is constructed.
The simplicity and economy of the spring means 52 and its installation between the upper and lower backrest frame parts can be readily appreciated. Simple tooling and parts are involved. Minor variations in dimensions and configuration of component parts of the invention may occur to the skilled artisan without departing from the scope of the invention as set forth in the appended claims.
Claims (12)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A chair comprising, a seat assembly which includes a support frame and depending leg members, a lower backrest frame part having a pair of spaced apart frame members upstanding rel-ative to the seat support frame, an upper backrest frame part having a pair of spaced apart depending frame members arranged in registry with the upstanding frame members, said frame mem-bers being hollow with open extremities, and spring members secured between each registered pair of frame members to provide an articulated, flexible spring backrest for the chair, each spring means including a molded plastic support strut with an elongate passageway therein, a substantially non-extensible flexible member disposed within said passageway and means secur-ing said flexible member at each end of said passageway so as to maintain the strut under longitudinal compression and limit the elongation thereof when a force is exerted on the backrest.
2. A chair as defined in claim 1 in which said support frame is unitary with said depending leg members and said lower backrest frame part has a pair of upstanding spaced apart frame members integral with the seat support frame.
3. A chair as defined in claims 1 or 2 in which said flex-ible member is a metal wire member secured within said passageway by fastening means affixed to the wire member proximate opposite ends of the strut.
4. A chair as defined in claims 1 or 2 in which said flex-ible member is a metal wire member secured within said pas-sageways by fastening means affixed to the wire member proximate opposite ends of the strut, said strut includes a centrally lo-cated bellows-like portion disposed between opposite end parts and said spring means are secured between the registered pair of frame members with the end parts disposed within the frame and the bellows-like portion positioned between the frame members.
5. A chair as defined in claims 1 or 2 in which said flexible member is a metal wire member secured within said passageway by fastening means affixed to the wire member proximate opposite ends of the strut, said strut includes a centrally located bellows-like portion disposed between opposite end parts and said spring means are secured between the registered pair of frame members with the end parts disposed within the frame mem-bers and the bellows-like portion positioned between the frame members, the opposite end parts having a plurality of axially-extending ribs formed on the external surface thereof, said ribs being constructed and arranged to cooperate with the inner-facing walls of said frame members to provide an interference fit between the strut and the frame members in the installed position thereof.
6. A chair as defined in claims 1 or 2 in which said flex-ible member is a metal wire member secured within said passageway by fastening means affixed to the wire member proximate opposite ends of the strut and the strut includes a centrally located bellows-like portion disposed between opposite end parts and said spring means are secured between the regis-tered pair of frame members with the end parts disposed within the frame members, the bellows-like portion positioned between the frame members, portions of said ribs being sheared off when the strut is positioned within said frame members.
7. A chair as defined in claims 1 or 2 in which said flex-ible member is a metal wire member secured within said pas-sageway by fastening means affixed to the wire member proximate opposite ends of the strut, said fastening means including fasteners positioned between the frame members and the strut to maintain assembly thereof.
8. A chair as defined in claims 1 or 2 in which said flex-ible member is a metal wire member secured within said pas-sageway by means affixed to the wire member proximate opposite ends of the strut, said fastening means being clips which are crimped to said wire member.
9. A chair as defined in claims 1 or 2 in which said flex-ible member is a metal wire member secured within said pas-sageway by fastening means affixed to the wire member proximate opposite ends of the strut, the opposite end parts having a plurality of axially-extending ribs formed on the external sur-face thereof, said ribs being adapted to cooperate with the inner-facing walls of said frame members to provide an interference fit between the strut and the frame members in the installed position thereof.
10. A spring member for use in flexible backrest assembly for a chair wherein the assembly includes upper and lower back-rest parts, said spring member capable of being secured between said frame parts, said spring member comprising spring means in-cluding at least a molded plastic support strut having an elongated passageway extending substantially the length thereof and a flexible insert disposed within said passageway to maintain the strut under compression and limit the elongation thereof.
11. The spring member as defined in claim 10 in which said flexible insert is a wire member secured within said passageway by fastening means affixed to the wire member proximate opposite ends of the strut.
12. The spring member as defined in claim 10 in which said flexible insert is a wire member secured within said passageway by fastening means affixed to the wire member proximate opposite ends of the strut, said strut including a centrally-located bellows-like portion disposed between opposite end parts, said spring means being secured between the frame parts with the end parts disposed within the frame parts and the bellows-like por-tion positioned between the frame parts.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US06/764,557 US4603904A (en) | 1985-08-12 | 1985-08-12 | Chair with articulated, flexible spring backrest |
| US764,557 | 1985-08-12 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1241904A true CA1241904A (en) | 1988-09-13 |
Family
ID=25071056
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000504038A Expired CA1241904A (en) | 1985-08-12 | 1986-03-13 | Chair with articulated flexible spring backrest |
Country Status (11)
| Country | Link |
|---|---|
| US (1) | US4603904A (en) |
| EP (1) | EP0233189A4 (en) |
| JP (1) | JPS63500431A (en) |
| KR (1) | KR870700306A (en) |
| AU (1) | AU578882B2 (en) |
| CA (1) | CA1241904A (en) |
| DK (1) | DK184887A (en) |
| ES (1) | ES296773Y (en) |
| IL (1) | IL78183A (en) |
| WO (1) | WO1987001018A1 (en) |
| ZA (1) | ZA862228B (en) |
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-
1985
- 1985-08-12 US US06/764,557 patent/US4603904A/en not_active Expired - Fee Related
-
1986
- 1986-03-06 JP JP61501627A patent/JPS63500431A/en active Pending
- 1986-03-06 WO PCT/US1986/000478 patent/WO1987001018A1/en not_active Application Discontinuation
- 1986-03-06 EP EP19860902135 patent/EP0233189A4/en not_active Withdrawn
- 1986-03-07 AU AU55482/86A patent/AU578882B2/en not_active Expired - Fee Related
- 1986-03-13 CA CA000504038A patent/CA1241904A/en not_active Expired
- 1986-03-19 IL IL78183A patent/IL78183A/en unknown
- 1986-03-25 ZA ZA862228A patent/ZA862228B/en unknown
- 1986-04-08 ES ES1986296773U patent/ES296773Y/en not_active Expired
-
1987
- 1987-04-10 DK DK184887A patent/DK184887A/en not_active Application Discontinuation
- 1987-04-11 KR KR870700315A patent/KR870700306A/en not_active Application Discontinuation
Also Published As
| Publication number | Publication date |
|---|---|
| AU578882B2 (en) | 1988-11-03 |
| EP0233189A4 (en) | 1988-01-28 |
| EP0233189A1 (en) | 1987-08-26 |
| ZA862228B (en) | 1987-11-25 |
| JPS63500431A (en) | 1988-02-18 |
| ES296773U (en) | 1988-01-16 |
| AU5548286A (en) | 1987-03-10 |
| DK184887D0 (en) | 1987-04-10 |
| IL78183A0 (en) | 1986-07-31 |
| IL78183A (en) | 1989-02-28 |
| US4603904A (en) | 1986-08-05 |
| DK184887A (en) | 1987-04-10 |
| KR870700306A (en) | 1987-12-28 |
| WO1987001018A1 (en) | 1987-02-26 |
| ES296773Y (en) | 1988-10-01 |
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Legal Events
| Date | Code | Title | Description |
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| MKEX | Expiry |