Chair,Particularly Conference or Office Chair, and Method for Manufacturing a Chair

Abstract

A chair, such as a conference or office chair, includes a seat support; a backrest support; a storage member formed as a force storage element; and a transmission coupling the seat support with the backrest support which allows a pivoting of the backrest support and the seat support between an upright position and a backwardly pivoted position according to a predetermined sequence of movements. The force storage element is coupled with the seat support and the backrest support such that the predetermined sequence of movements is facilitated and the storage member provides a force restoring in the upright position and wherein the flexibly elastic storage member forms in conjunction at least with a first articulated rotation point of the transmission a kinematic chain.

Claims

1. A chair, including a seat base, at which a supporting means of the chair is disposed, wherein: the supporting means has at least one seat support and at least one backrest support; the supporting means is provided with a transmission coupling the seat support to the backrest support which allows for pivoting the backrest support and the seat support between an upright position and a backwardly pivoted position using a predetermined sequence of movements, a flexibly elastic storage member is provided and installed at the transmission which, when the supporting means is charged, provides a force restoring to the upright position, and the flexibly elastic storage member in conjunction with at least one first articulated rotation point of the transmission forms a kinematic chain wherein the flexibly elastic storage member is one of (a) connected with the seat support, (b) formed on the seat support or (c) formed in one piece with the seat support.

2. The chair according to claim 1, wherein the transmission includes the first and a second articulated rotation point.

3. The chair according to claim 1, wherein the flexibly elastic storage member comprises at least two further rotation points of the kinematic chain or the storage member comprises at least two virtual rotation points.

4. The chair according to claim 3, wherein the at least one articulated rotation point of the transmission is coupled with the seat base and is fixedly arranged relative thereto and wherein the transmission has a first virtual and a second virtual rotation point which are comprised by the storage member, wherein the at least one articulated rotation point is coupled via a first link with a second articulated rotation point arranged at the storage member and the two virtual rotation points are coupled to each other via a second link, wherein the first link is fixedly connected with the backrest support or is integrally formed with the backrest support.

5. The chair according to claim 3, wherein the backrest support is rotatably supported at the at least one articulated rotation point with regard to the seat base and the storage member or the seat support connected thereto is provided at a free end with the second articulated rotation point, at which it is rotatably connected with the backrest support.

6. The chair according to claim 3, when the at least one articulated rotation point of the transmission is coupled with the seat base and is fixedly arranged thereto and wherein the transmission has a first virtual and a second virtual rotation point which are comprised by the storage member, wherein the at least one articulated rotation point is connected to a third virtual rotation point arranged at the storage member via a first link and the first and second virtual rotation point are coupled together via a second link, wherein the first link is fixedly connected with the backrest support or is integrally formed with the backrest support.

7. The chair according to claim 6, wherein the backrest support is rotatably supported at the at least one articulated rotation point with respect to the seat base and the storage member or the seat support connected thereto is at a free end flexibly connected with the backrest support via a bar, and thus forms the third virtual rotation point.

8. The chair according to claim 1, wherein the storage member of the transmission is formed from an elastic deformable plastic material, in particular a fiber-reinforced plastic.

9. A chair, including a seat base, at which a supporting means of the chair is disposed, wherein: the supporting means has at least one seat support and at least one backrest support; the supporting means is provided with a transmission coupling the seat support to the backrest support which allows for pivoting the backrest support and the seat support between an upright position and a backwardly pivoted position using a predetermined sequence of movements, a flexibly elastic storage member is provided and installed at the transmission which, when the supporting means is charged, provides a force restoring the seat support to the upright position, and the flexibly elastic storage member in conjunction with at least one first articulated rotation point of the transmission forms a kinematic chain, wherein the storage member has a bent shape, which in the idle position of the chair forms an acute angle between 1 and 40

10. The chair according to claim 9, wherein the acute angle is between 10 and 30.

11. The chair according to claim 1, wherein at the supporting means at least one arm rest support is arranged at a respective one of the at least one chair side, wherein each armrest support is connected with the seat support and/or the backrest support.

12. The chair according to claim 1, wherein the transmission has a first stop, which restricts a pivoting range of the seat support and the backrest support in the upright position such that when reaching the stop a bias of the storage member is applied holding the backrest support and the seat support in the upright position at the stop.

13. The chair according to claim 1, wherein the transmission has a second stop which restricts the pivoting range of the seat support and the backrest support in a maximally pivoted position and/or the transmission is provided with a locking element which fixes the seat support and the backrest support in a selectable pivoted position with regard to at least one movement direction.

14. The chair according to claim 4, wherein the length and/or the inclination of the first and second links are respectively provided such that a ratio of the pivoting angle of the backrest support to a pivoting angle of the seat support in the backwardly pivoted position is 2 to 1 to 4 to 1.

15. The chair according to claim 6, wherein the length and/or the inclination of the first and second links are respectively provided such that a ratio of the pivoting angle of the backrest support to a pivoting angle of the seat support in the backwardly pivoted position is 2 to 1 to 4 to 1.

16. The chair according to claim 1, wherein a manipulatable height adjustment means is provided and installed, which can be operated via a handle which is engageable and is arranged in the region of the seat support.

17. The chair according to claim 1, wherein a seat element is arranged at the seat support wherein the seat element is fixable or is fixed or is provided displaceable along the seat support by means of a guiding means.

18. A method for manufacturing a chair, comprising the steps of: providing a supporting means having a seat support, a backrest support and a transmission coupling the seat support to the backrest support which allows for pivoting the backrest support and the seat support between an upright position and a backwardly pivoted position using a predetermined sequence of movements; coupling a storage member provided and installed at the transmission to the supporting means so that the predetermined sequence of movement is facilitated and a force restoring to the upright position is provided by the storage member, wherein a kinematic chain is formed by the flexibly elastic storage member with at least one first articulated rotation point of the transmission, wherein the flexibly elastic storage member is one of (a) connected with the seat support, (b) formed on the seat support or (c) formed in one piece with the seat support.

19. The method according to claim 18, wherein the storage element has at least in a planar projection a bent shape with two legs which are connected at respectively one articulated rotation point with the backrest support.

20. A method for manufacturing a chair, comprising the steps of: providing a supporting means having a seat support, a backrest support and a transmission coupling the seat support to the backrest support which allows for pivoting the backrest support and the seat support between an upright position and a backwardly pivoted position using a predetermined sequence of movements; coupling a storage member provided and installed at the transmission to the supporting means so that the predetermined sequence of movement is facilitated and a force restoring to the upright position is provided by the storage member, wherein a kinematic chain is formed by the flexibly elastic storage member with at least one first articulated rotation point of the transmission, wherein the storage member has a bent shape, which in the idle position of the chair forms an acute angle between 1 and 40

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0043] The present invention will be explained with more detail hereinafter with reference to the embodiments stated in the schematic figures of the drawing. In the drawings:

[0044] FIG. 1 is a planar side view of a first embodiment of a chair in an upright position including a transmission with two articulated rotation points;

[0045] FIG. 2 a planar side view of a second embodiment of a chair in an upright position including a transmission with only one articulated rotation point;

[0046] FIG. 3 a planar side view of the chair of FIG. 1 including virtual rotation points which are additionally recognizable at the transmission;

[0047] FIG. 4 a perspective side view of the chair with its seat base and a storage member at which a seat support is arranged;

[0048] FIG. 5 a perspective side view of the chair of FIG. 4, at which a backrest support is connected with the storage member;

[0049] FIG. 6 a perspective side view of the chair of FIG. 5, at which a seat support is connected with the storage member;

[0050] FIG. 7 a planar side view of the chair of FIG. 3, with the supporting means once in the idle position and once in the pivoted position (dashed lines);

[0051] FIG. 8A a schematic drawing of the kinematics of a chair in an upright position;

[0052] FIG. 8B a schematic of the kinematics in accordance with FIG. 8A in a backward pivoted position; and

[0053] FIG. 9 a side view of a chair with a kinematics in accordance with FIG. 8A and FIG. 8B.

[0054] The attached figures of the drawing shall convey a further understanding of the embodiments of the invention. They illustrate embodiments and in connection with the description serve the explanation of the principles and concepts of the invention. Other embodiments and many of the stated advantages are apparent in view of the drawings. The elements of the drawings are not necessarily shown true to scale with regard to each other.

[0055] In the figures of the drawing the same, functionally same or equally acting elements, features and components are, unless otherwise stated, respectively provided with the same reference numerals.

DESCRIPTION OF THE EMBODIMENTS

[0056] Referring first to FIG. 1 to FIG. 3, these figures show a chair generally denoted with 1 which is as an example embodied as office swivel chair including a pedestal 35 with wheels 26.

[0057] In each of the plane side views of FIG. 1 to FIG. 3 a chair 1 is recognizable at which at a seat base 9 a supporting means 4 of the chair 1 is arranged. The supporting means 4 of the chair is provided with a seat support 2 and a backrest support 3 as well as with a transmission 5 coupling the seat support 2 with the backrest support 3.

[0058] The transmission 5 enables a pivoting of the backrest support 3 and the seat support 2 between an upright and a backwardly pivoted position in a predetermined sequence of movements.

[0059] At the transmission 5 there is provided and installed a flexibly elastic storage element 8 which when charging the supporting means provides a restoring force into the upright position. Furthermore, the flexibly elastic storage member 8 forms a kinematic chain 15 in conjunction with at least a first articulated rotation point 10.

[0060] The aforementioned kinematic chain 15 is a feature of the system built by the transmission 5 which presents a gear and is configured for the transfer of movements and torques. This is most easily recognizable from FIG. 3 which illustrates the chair of FIG. 1 with its first articulated rotation point 10 as well as its second articulated rotation point 11 and furthermore also the further virtual rotation points 12, 13 which are provided in the structure of the storage member 8 and around which the flexibly elastic storage element is capable to carry out rotational movements due to its shape in conjunction with its material properties.

[0061] Furthermore, it is also illustrated for the chairs 1 of FIG. 1 and FIG. 3 that the first articulated rotation point 10 of the transmission 5 is coupled with the seat base 9 and is fixedly arranged in relation thereto. The transmission 5 has a first virtual and a second virtual rotation point 12, 13 which are comprised by the storage member 8, and the first articulated rotation point 10 is coupled to the second articulated rotation point 11 arranged at the storage member 8 via a first link 16 which is illustrated with the dashed line connection of the two articulated rotation points 10, 11 in FIG. 1 and FIG. 3.

[0062] In this connection a virtual rotation point means a structural portion which by means of its elastic bending property allows a certain pivoting of two adjoining structural portions.

[0063] Also, the two virtual rotation points, 12, 13 are coupled to each other, via a second link 17, which is additionally illustrated in FIG. 3 with the dashed line. The dashed line connection of the second articulated rotation point 11 to the first virtual rotation point 12 only serves illustration of their coupling to the kinematic chain 15. The aforementioned first link 16 is connected fixedly with the backrest support 3 and in FIG. 1 and FIG. 3 it is for example formed integrally with the backrest support 3.

[0064] On the other hand, FIG. 2 illustrates a chair 1 according to the invention where in contrast to the illustrations of FIG. 1 and FIG. 3 the second articulated rotation point 11 is replaced by a third virtual rotation point 14 at approximately the same location on the storage member 8 or the seat support 2 which is, as described above for the other virtual rotation points 12, 13, integrated into the structure of the storage member 8 such that the kinematic chain 15 a is maintained. Thus, in this embodiment there are provided at the flexibly elastic storage member 8 three virtual rotation points 12, 13 and 14, configured according to the specifications of the shape and the material properties, and only one real articulated rotation point 10.

[0065] The mapping into virtual rotation points 12, 13, 14 of the storage member 8 of the transmission 5 at the chair 1 of FIG. 2 is here attributed for example to a fiber reinforced plastic material, similarly as before in FIG. 1 and FIG. 3 to the configuration of the storage member 8 in an elastically deformable material. This plastic material may be formed by polyamide.

[0066] Referring now to FIG. 4 to FIG. 7, FIG. 4 first of all shows a partially assembled chair 1 according to the invention the seat base 9 of which supports the supporting means 4 of the chair 1 versus the pedestal 35 including wheels 26 configured as rotating pedestal and which for this purpose is coupled with a height-adjustable pressure spring portion.

[0067] In FIG. 4 the chair 1 is partially assembled insofar as only the storage member 8 which is fixedly connected with the seat base 9 and provides the transmission 5 is shown at the supporting means 4. In the perspective view of FIG. 4 it is illustrated that the storage member 8 includes a kind of bent frame 18 the frame portions 18a-18d of which surround a recess 19. In an assumed planar projection from the side, similarly as the illustrations in FIG. 7, the two frame portions 18b, 18c associated with the chair sides respectively form a curved frame side with an upper and a lower leg 20, 21 of which the lower legs 21 will form the second link 16 of the kinematic chain 15 to be established at the chair. Here, the storage member 8 which has a bent shape in the aforementioned projection forms an approximately acute angle in the order of 25 with the two legs 20, 21 in the idle position of the chair 1.

[0068] By imposing a bias on the storage member 8, the storage member 8 is in FIG. 5 coupled with the backrest support 3 at two articulated rotation points 10, 11 which are connected by the first link 16 as part of the backrest support 3. Furthermore, in FIG. 6 the chair 1 is provided with a seat support 2 such that the seat support 2 and the backrest support 3 are coupled by the transmission 5 of the support member 8. Furthermore, it is shown that the backrest support 3 is rotatably supported at the at least one articulated rotation point 10 in relation to the seat base 9 and that the storage member 8 or the seat support 2 connected thereto is provided in an end portion of its upper leg 20 with a second articulated rotation point 11 at which it is rotatably connected with the backrest support 3.

[0069] In the embodiment of FIG. 2 the coupling of the end portion of the upper legs 20 of the storage member 8 is not realized as in FIG. 5 to FIG. 7 via a second articulated rotation point 11 but via a further virtual rotation point 4 such that the storage member 8 or the seat support 2 arranged thereto is rotatably fixedly connected with the backrest support 3 via a bar 22. FIG. 2 further illustrates that the aforementioned bar 22 then forms the first link 16 such that, in contrast to the embodiments with two articulated rotation points 10, 11, it is not directly part of the backrest support. However, since clearly in the embodiment of FIG. 2 the storage member 8 is integrally formed with the backrest support 3, the first link 16 is at least in this sense formed as part of the backrest support 3. The upper leg 20 of the storage member 8 is with its free end which forms the bar 22 or the link 16, when the bias is imposed, connected with the articulated rotation point 10 arranged in the region of the seat base 9.

[0070] Furthermore, FIG. 5 and FIG. 6 also illustrate that the backrest support 3 is essentially constituted by a backrest frame 30 which in turn surrounds a recess 31 and which can hold for example a not further illustrated padding or also a textile supporting braid.

[0071] FIG. 6 shows that here the flexibly elastic storage member 8 is connected to the seat support 2 which in turn is provided with a seat padding 32 shown in FIG. 7 as a seating element. Not shown is here the displaceable guide of the seating element.

[0072] The transmission 5 of the storage member 8 determines the sequence of movements of the supporting means with the seat support 2 and the backrest support 3 when pivoting from the upright position into a backwardly pivoted position as are shown in unison in FIG. 7 in which the latter position is illustrated with dashed lines. To this end the storage member 8 is as shown embodied and arranged such that it allows the sequence of movements of the seat support 2 and the backrest support 3 predetermined by the transmission 5. Furthermore, the storage member 8 provides the restoring force into the upright position, by means of the entire sequence of movements, and furthermore this force is also imposed in the upright position as a result of the coupling with bias.

[0073] Referring again to all figures and in particular to FIG. 3 and FIG. 7, it is clear that when charging the respective chair 1, for example by a person who is in the process to sit down, the backrest support 3 is pivoted backwards to a pivoting angle, as is particularly shown in FIG. 7. The first link 16 extending between the first and the second articulated rotation point 10, 11 is, in conjunction with the backrest support 3, pivoted to the same angle. Due to the inclination of the first link 16 and the seat support 2 and thus of the storage member 8, also the second link 17 is pivoted.

[0074] Both links 16 and 17 are inclined forwardly in the upright position as well as in the backwardly pivoted position such that a gravitational force of a person sitting on the chair 1 causes a restoring torque and such that storage member formed as a force storage element only needs to work against the backrest force. The backwardly pivoted position is achieved by the person sitting on the chair 1 leaning backwards and thus exerting on the backrest support 3 a back leaning force which exceeds a spring force of the storage member 8.

[0075] The entire seating surface formed by the seat support provided with a seating padding is lifted slightly and additionally also pivoted, though compared to the backrest support 3 to a much lesser degree. The storage member 8, as best apparent from FIG. 7, is in its tensioned state charged according to both pressure and bending and is hence elastically compressed and bent. The backwardly pivoted position of the supporting means 4 is reached when a person sitting on the chair leans backwards and thus exerts a backwards leaning force on the backrest support 3 which exceeds a spring force of the storage member 8.

[0076] Notwithstanding the large pivoting region possible with the configurations of the figures, all visible components of the chair 1, in particular the backrest support 3, the first link 13, the seat base 9 and the second link 14 as well as the seat support 2, are configured very slender. The same applies for the storage member 8.

[0077] Furthermore, no additional components are arranged between the seat support 2 and the seat base 9 and between the seat support 2 and the backrest support 3, respectively. In this manner in total a greatly slender design is created without jeopardizing functionality compared to a conventional synchronizing mechanism.

[0078] Not shown in the figures of the drawing is a first stop restricting the pivoting region of the seat support 2 and the backrest support 3 in the upright position as well as a second stop restricting a pivoting region of the seat support 2 and the backrest support 3 in the pivoted position. These stops are provided in the region of the first or if provided of the second articulated rotation points 10, 11 in the form of stop wedges which are supported at respectfully suitable points in the upright position and in the pivoted position.

[0079] The stops are arranged and configured such that when reaching the first stop still a bias of the storage member 8 holding the backrest support 3 and the seat support 2 in the upright position is exerted. In this manner, a defined setting of the transmission 5, the seat support 2 and the backrest support 3 is guaranteed also in the upright position.

[0080] FIG. 8A shows a schematic drawing of the kinematics of a chair 101 in an upright position.

[0081] A swivel chair base 104 of the chair is here illustrated schematically as fixed bearing. In the case of a swivel chair the seat base can of course also include a degree of freedom around the vertical axis.

[0082] The seat base is coupled to a seat support 102. The seat support 102 includes a seat receiving portion 105 for receiving a seating surface, a base receiving portion 107 for receiving the swivel chair base 104 and a force storage 108 formed integrally with the seat receiving portion 105 and the base receiving portion 107. The seat support is here in particular formed in one piece. The portions, therefore, thus only form functional portions which are, however, formed integrally to each other.

[0083] The chair 101 further includes a backrest support 103 which is coupled to the seat support 102 at two locations. To this end a transmission 109 coupling the seat support 102 to the backrest support 103 is provided wherein the transmission 109 allows a pivoting of the backrest support 103 and the seat receiving portion 105 with a predetermined sequence of movements between an upright position and a backwardly pivoted position. The transmission 109 includes a first rotation point 110 which couples the backrest support 103 to the base receiving portion 107 of the seat support 102 rotatably. Furthermore, a second rotation point 111 of the transmission 109 is provided which couples the backrest support 103 to the seat receiving portion 105 rotatably.

[0084] The force storage 18 of the seat support 102 provides a predetermined elastic deformation. A pivoting of the backrest support 103 thus causes an elastic deformation of the seat support in the region of the force storage 108. Due to the integral formation of the force storage 108 with the base receiving portion 107 and the seat receiving portion 105 a certain relative movement of the seat receiving portion 105 relative to the base receiving portion 107 is thus provided. A predetermined sequence of movements associated with this relative movement is predetermined by the configuration of the force storage 108.

[0085] In the illustrated upright position the force storage 108 is essentially released. A pivoting of the backrest support 103 and by means of the kinematic coupling via the transmission 108 also of the seat receiving portion 105 causes an elastic deformation of the force storage 108. In this manner the force storage 108 provides a force restoring the backrest support 13 and the seat receiving portion 105 into the upright position when it is shifted into a backwardly pivoted position.

[0086] FIG. 8B shows a schematic drawing of the kinematics according to FIG. 8A into a backwardly pivoted position.

[0087] Here, the force storage 108 is illustrated as correspondingly elastically deformed. While the base receiving portion 107 of the seat support maintains its original position, the seat coupling portion 105 is relative thereto shifted by means of the transmission 109. To this end the transmission 109 includes a link 113 mounted at the backrest 303 or formed integrally therewith.

[0088] In the upright position according to FIG. 8A the link 113 is, relative to the gravitational direction here extending vertically, pivoted forwardly. When pivoting the backrest support 103 backwardly, the link 113 is hence pivoted into a position which approximates the gravitational direction. In this manner the seat receiving portion 105, when pivoting backwards, on the one hand is lifted and on the other hand is displaced backwardly.

[0089] In the completely backwardly pivoted position of the backrest support 103 illustrated in FIG. 8B there is still provided a minor remaining forward angulation of the link 113. In this manner a weight charged on the seat receiving portion 105 by a person sitting on a seating surface mounted thereon acts in an restoring manner additionally to the bias of the force storage 108. In this manner, a restoring force is advantageously always automatically adapted to the weight of a person sitting on the chair. The link 113 thus serves a self-regulating adaptation of the restoring force to a weight charged on the seating surface which is supported with the seat receiving portion 105.

[0090] Accordingly the chair remains in the backwardly pivoted position if a person sitting on the chair displaces his/her weight on a backrest coupled to the backrest support 103. However, if the backrest is released, the backrest support 103 automatically straightens up by means of the restoring force stored in the force storage 108 and by means of the restoring force caused by the angulation of the link 113 with the intrinsic weight of the person.

[0091] FIG. 9 shows a side view of a swivel chair including a kinematics according to FIG. 8A and FIG. 8B.

[0092] The swivel chair 101 illustrated here is an office swivel chair with a rotating pedestal 114 provided with wheels. However, of course other configurations without such wheels are envisaged, for example for a conference swivel chair.

[0093] The solid lines here illustrate an upright position and the dashed lines illustrate a backwards pivoted position.

[0094] The backrest support 103 acts in this configuration simultaneously as backrest frame and is thus integrally formed with the backrest 115. Furthermore, the link 113 is formed integrally as one piece with the backrest support 103. To this end the backrest support 103 is angled in the region of the second articulated point 11.

[0095] Furthermore, the seat support 102 describes, starting from the second rotation point 111, a single-piece bracket shape extending to the first rotation point 110. From the second rotation point 111 to the first rotation point 110 the bracket shape here forms an angle of roughly 210 in the upright position. This angle is of course adaptable to the geometry and the design of the seat support and is in a range >180, preferably in a range between 200 to 240. In this manner, the seat support, with an appropriate material selection, can be tensioned or extended like a spring and can thus be employed as force memory.

[0096] The bracket shape can advantageously be divided into different functional portions. The legs of the bracket shape serve here as the base receiving portion and the seat receiving portion. They are accordingly formed relatively rigid. In between there is provided a bar connecting the two legs wherein the bar is configured as spring arm 112 and is formed accordingly elastically deformable. The spring arm 112 is angled with respect to the base receiving portion 107 and the seat receiving portion 105 and forms a part of the bracket shape therewith.

[0097] A seating surface 106 is mounted on the seat receiving portion 105 wherein the seating surface 106 includes a structural part or a seating shell introducing the seating forces into the seat support, and a seating padding. In further embodiments also a configuration without padding of a seating shell is possible.

[0098] Although the present invention has been completely described with reference to preferred embodiments, the invention is not limited thereto but can be modified in various kinds and manners.

LIST OF REFERENCE NUMERALS

[0099] 1 chair [0100] 2 seat support [0101] 3 backrest support [0102] 4 supporting means [0103] 5 transmission [0104] 8 storage member [0105] 9 seat base [0106] 10 first articulated rotation point [0107] 11 second articulated rotation point [0108] 12 further or first virtual rotation point [0109] 13 further or second virtual rotation point [0110] 14 further or third virtual rotation point [0111] 15 kinematic chain [0112] 16 first link [0113] 17 second link [0114] 18 frame part [0115] 18A-18D frame portions [0116] 19 recess [0117] 20 upper leg [0118] 21 lower leg [0119] 22 bar [0120] 25 locking element [0121] 26 wheel [0122] 27 height adjustment means [0123] 30 backrest frame [0124] 31 groove [0125] 32 seat padding [0126] 35 pedestal [0127] 101 swivel chair [0128] 102 seat support [0129] 103 backrest support [0130] 104 swivel chair base [0131] 105 seat receiving portion [0132] 106 seating surface [0133] 107 base receiving portion [0134] 108 force storage [0135] 109 transmission [0136] 110 first rotation point [0137] 111 second rotation point [0138] 112 spring arm [0139] 113 link [0140] 114 rotating pedestal [0141] 115 backrest