Chair seat mounting mechanism

Abstract: A chair seat mounting mechanism includes a stationary base member (1) adapted to be mounted on a chair base, a seat-mounting member (9) that is adapted to be attached to a chair seat and is rotatably attached to the base member (1) by a pivot shaft (7) and springs acting between the base member (1) and the seat-mounting member (9) and biasing the seat to a neutral position intermediate of a forward tilted position and a rearward tilted position. An intermediate member (12) is pivotally attached to the pivot shaft (7), and at least one first spring (13) is engaged between the intermediate member (12) and the seat-mounting member (9) such as to bias the seat-mounting member relative to the intermediate member toward the neutral position and to permit the seat to tilt forward against the bias. At least one second spring (17) is engaged between the base member (1) and the intermediate member (12) such as to bias the intermediate member relative to the base member toward the neutral position and to permit the seat to tilt rearward against the bias. The pivot shaft (7) is spaced apart a substantial distance from the center of the chair seat in the direction of the front edge of the seat botton (10) so as to limit the amount of vertical motion of the front edge when the seat tilts forward and backward from the neutral position.

Description: Background of the Invention The present invention relates to a mounting mechanism for the seats of office chairs and, in particular, to a mounting mechanism that permits the seat to tilt both forward and backward. There is an increasingly felt need in the office furniture field for chairs that tilt not only backward, which have long been widely available, but also tilt forward. This need has arisen primarily because of the widespread use of computer and word-processing systems by both office staff and management. It has become necessary to have chairs that afford a comfortable and ergonomically correct position under conditions of normal writing at one's table or desk and under conditions of operating a computer keyboard, which is usually located at a height lower than desk-top level. Lastly, there is also a need for office chairs that provide a slightly backward tilted position of active rest. A number of different mounting mechanisms have been proposed to achieve these variations in the seat position with respect to the horizontal plane. Many of the mechanisms have various disadvantages, such as the provision of separate pivot shafts to provide tilting of the seat both forward and backward, which makes the mechanism of large size and requires a large number of parts and, hence, increases the cost and the possibility of malfunctioning. A mounting mechanism having two different pivot shafts to provide for forward and backward tilting is known from EP-A-0 292 444. Due to the separate pivot axes spaced apart from each other the front of the seat moves up and down to different degrees during tilting thus requiring the sitter to change leg positions. Many of the known mounting mechanisms provide for rotation of the seat about an axis or axes located a substantial distance from the front edge of the seat bottom, which results in large vertical movements of the front edge and requires the user to change the positions of his or her legs or to change sitting posture to compensate for the change in the height of the front edge of the seat bottom. EP-A-0 392 984 discloses a mounting mechanism having a pivot shaft that is spaced apart a substantial distance from the center of the chair seat in the direction of the front edge of the seat bottom. This known mounting mechanism, however, is only adapted for rearward tilting and thus does not meet with all the needs demanded from today's modern office chairs. U. S. Patent No. 4,131,260 (Ambasz, Dec. 26, 1978) describes and shows several embodiments of chair seat mounts that provide for tilting of the chair seat both backward and forward from a neutral position. Two sets of springs bias the chair seat toward the neutral position, one set resisting backward tilting and the other forward tilting. A lock device is provided for preventing the chair seat from tilting backward. U. S. Patent No. 4,345,733 (Ambasz et al., Aug. 24, 1982) discloses a chair seat mount that permits a chair seat to tilt forward from a normal upright position, to which it is biased by an adjustable spring. A lock device allows the user to lock the chair seat in the forward tilted position. The seat mounts of the aforementioned patents provide for pivoting of the chair seat about a pivot axis located very close to the column of the chair base, which means that the front edge of the seat bottom moves a relatively large distance vertically when the chair seat is tilted from the neutral position. As mentioned above, this requires the user to change his or her sitting posture when the chair seat is tilted from the neutral position. Summary of the Invention One object of the present invention is to provide a seat-mounting mechanism that provides for both forward and backward tilting of the seat from a neutral position that is normally maintained by springs. Another object is to provide a seat-mounting mechanism in which forward and backward tilting occur with only a relatively small amount of vertical movement of the front edge of the seat bottom so that the user can keep his legs and, hence, his or her overall sitting posture, unchanged in all work positions. Yet another object is to provide a seat-mounting mechanism that permits the seat, at the option of the user, to be locked against tilting in a neutral position, a forward tilted position and a rearward tilted position. It is also to desired that the mechanism be of relatively small size, have a low number of parts, and be easy to assemble. The foregoing and other objects are attained, according to the present invention, by a chair seat mounting mechanism having the features as set out in claim 1. In a preferred embodiment, the pivot shaft is spaced apart a substantial distance from the center of the chair seat in the direction of the front edge of the seat bottom so as to limit the amount of vertical motion of the front edge when the seat tilts forward and backward from the neutral position. Interengageable stop surfaces act among the members for limiting the amounts of rotation of each of them relative to the others and establishing maximum forward and rearward tilt positions. A lock device prevents movement of the seat-mounting member relative to the base member and is selectively operable by the user to fix the seat in the neutral position, a maximum rearward tilted position and a maximum forward tilted position. The lock device includes an abutment on the base member and a lock member movably mounted on the seat-mounting member, the lock member having spaced-apart surfaces, each of which is engageable individually with the abutment in a different one of the fixed positions of the seat-mounting member upon movement of the lock plate relative to the seat-mounting member to a locking position and is clear of engagement with the abutment upon movement to a release position. Preferred embodiments of the present invention have many advantages over previously known chair seat mounting mechanisms. The present invention provides improved comfort for the user by minimizing the amount of vertical movement of the front edge of the seat bottom when the inclination of the seat is changed. Accordingly, the user does not have to change the position of his or her legs or slide forward or backward on the seat bottom when changing the inclination. In the backward tilt position, the front of the seat bottom does not apply pressure to the backs of the user's legs. The user is given the choice of locking the seat in a desired position or leaving it unlocked so that it automatically moves to different positions in response to forces applied to it by the user when he or she changes sitting posture. It is important to avoiding fatigue for an office worker to change seating posture from time to time, thereby moving the muscles and in many positions stretching and tensing the muscles. The mechanism allows the user to easily alter the configuration of the chair to attain a desired posture and a desired relationship between the chair seat position and the forces he or she applies to it. The ability to lock the chair in the forward tilted position is especially beneficial to users who operate a keyboard located, as is conventional, at a lower height than the top of a standard desk The present invention is of compact construction and fits into a small volume under the center of the seat bottom. It does not present an unsightly appearance -- indeed, the outer shape can be made to fit the contour of the underside of the seat. The location of the spring-adjustment knob in front of the column of the chair base makes it easy to reach and operate. Likewise, the operating arm of the lock mechanism is conveniently located, and the mechanism is easy to operate. For a better understanding of the invention, reference may be made to the following description of exemplary embodiments, taken in conjunction with the accompanying drawings. Description of the Drawings Fig. 1 is a top plan view of one embodiment; Fig. 2 is a side cross-sectional view of the embodiment of Fig.1, taken along the lines II-II of Fig. 1; and Figs. 3a, 3b and 3c and 4 are side cross-sectional views taken along the lines IIIA-IIIA, IIIB-IIIB, IIIC-IIIC and IV-IV, respectively, of Fig. 1 and also show the mechanism in different positions. Description of the Embodiments As Figures 1 and 2 show, one embodiment of the chair seat mounting mechanism, according to the present invention, comprises a stationary base member 1 having a sleeve portion 2 that defines a vertical socket that is adapted to receive a support column 3 of a pedestal base of the type commonly used for office chairs and having radially extending legs 4 with casters. Immediately in front of the sleeve of the stationary member 1 is a cup-shaped projection 5 provided with a center hole 5a and having its axis inclined with respect to the axis of the support column 3. At the front end of the member 1, and located a substantial distance in front of the column 3, are a pair of laterally spaced-apart vertical flanges 1c with aligned holes 6 that receive a pivot shaft 7. The shaft 7 extends laterally outwardly on both sides beyond the flanges 1c and receives rotationally a pair of spaced apart vertical sleeves 9a, 9b of a seat-mounting member 9, which is adapted to be affixed to the underside of a chair seat bottom 10 by means of screws passing through fastening holes 11. Received between the stationary base member 1 and the seat-mounting member 9 of the mechanism is a pivotable intermediate member 12, the front end of which is pivotally coupled by means of curved flanges 12c to the pivot shaft 7. The back end 12b of the member is free and has inturned stop flanges 12a (Fig. 3B) that are located so as to engage the undersides of a stop flanges 1b on the base member 1 when pivoted clockwise about the shaft 7 under the bias of springs (described below). Located in the space between the base member 1 and intermediate member 12 are two sets of springs, one set of which biases the seat-mounting member 9 counterclockwise about the pivot shaft 7 relative to the intermediate member 12 and the other set of which biases the intermediate member 12 clockwise about the pivot shaft 7 relative to the base member 1. The first set consists of two springs 13 (see Fig. 3b) located symmetrically on opposite sides of the front to back center line of the mechanism and engaged between seats 14 on the member 12 and spring retainers 15 threaded onto screws 16, the heads 16a of which bear against the top of the member 9. The screws enable the preload of springs 13 to be adjusted when the mechanism is assembled. The second set of springs consists of two non-adjustable springs 17 (see Fig. 3b) located symmetrically on opposite sides of the centerline of the mechanism and an adjustable spring 18 located in the lateral center of the mechanism (see Fig. 2). Each spring 17 is held in place at each end by a flange that forms a seat. The upper end of the spring 18 engages a seat 19 on the intermediate member 12, and the lower end engages a spring retainer 20 that is rotatably received on a threaded shaft 21. The shaft threads into a hole 5a in the cup-shaped portion 5 of the base member 1 and has a knob 22 affixed to it. The user can adjust the force applied by the spring 18 by turning the knob 22. The mechanism, according to the invention, also includes a mechanical locking device for locking the chair seat in different positions. The locking device includes an operating arm 23 provided at its outside end with a handle 24 and extending laterally into the seat-mounting member 9. It is received for lengthwise movement in holes in flanges 25 on the seat-mounting member and has affixed to it a lock member having two plate portions 26 that are shaped at their rearward portions (to the left in the figures) in profile (see Fig. 2, for example) to engage the member 9 so that the lock member cannot rotate. Each plate portion has a groove 26a that is engageable with a corresponding abutment 1a that projects rearwardly from the base member 1. The upper and lower edges at the fronts of the plate portions 26 are also engageable with the abutments 1a. The abutments are laterally spaced apart. When the operating arm 23 is pulled out laterally away from the base member 1, the position shown in Fig. 1, the plate portions 26 of the locking device are received in the spaces between the abutments 1a, which is the unlocked position of the locking device. When the operating arm is pushed in, which is the locked condition of the locking device, the plate portions engage the abutments in a selected one of three positions of the mechanism, namely, a neutral, relatively upright position, a backward tilt position and a forward tilt position. The locked and unlocked conditions are retained against moderate forces on the operating arm 23 by a detent acting between a center plate portion 26c and a grooved boss 9c on the seat-mounting member (see Fig. 1). The front part of the center plate portion 26c of the lock member also works with the center abutment 1a of the base member. The device according to the invention functions as follows: when the user assumes a relatively upright sitting posture, the chair seat is biassed by the two sets of springs to the neutral position shown in Fig. 2. The springs 13 pull the seat-mounting member down, such that it engages the top of the intermediate member. The springs 17 and 18 push the intermediate member up relative to the base member 1 to a stop position corresponding to the neutral position of the chair seat maintained by engagement of the stop flanges 12a on the seat-mounting member with the stop flanges 1b (Fig. 3b) on the base member. In the neutral position, the seat bottom slopes down slightly from front to back at an angle of about 5° with respect to the horizontal. The seat can be locked in the neutral position by pushing the operating arm in (to the left in Fig. 1 from the position shown in Fig. 1), which moves the lock member to a position in which the abutments 1a are received in the notches 26a (Fig. 2) of the plate portions 26 and 26c. If the seat is unlocked by pulling the operating arm out, the user can apply forces to the chair seat by changing his or her seating posture that cause the seat to tilt either backward or forward against the biassing forces of the respective springs. if the user leans forward, such as to operate a keyboard, the springs 13 will yield to the force applied by the user to the seat and allow the seat-mounting member to pivot clockwise about the pivot shaft 7 to the forward tilted position shown in Fig. 3b. The maximum forward tilt position is a rearward slope of the seat bottom of about 1.5° to the horizontal. In the forward tilt position, the intermediate member 12 remains stationary, stopped by engagement of the flanges 12a of the intermediate member against the flanges 1b of the base member 1. If desired, the user may lock the seat in the forward tilt position by pushing in the operating arm 23, thereby causing the abutments 1a to be engaged by the lower front edges of the corresponding plate portions 26 of the locking device, as shown in Fig. 3c. In the full forward tilt position, there is enough clearance between the abutments 1a and the plate portions 26 to enable the plate portions to slide into the lock position. if the user leans back in the chair from the neutral position (Fig.2), the chair seat tilts backward to any desired extent up to a maximum rearward slope of the seat bottom of about 15° (Fig. 4). The force applied by the user's body to the chair seat in leaning back is transmitted from the seat-mounting member 9 to the intermediate member 12 and overcomes the forces of the springs 17 and 18, thereby enabling the members 9 and 12 to pivot together counterclockwise about the pivot shaft 7. The maximum backward tilt position is established by engagement of portions 12d of the top wall portion of the intermediate member 12 near the junctures with the rear flanges 12b with portions of the upper edge of the stop flanges 1b of the base member 1 -- one of the aforementioned portions 12d is visible in Fig. 3b, where it can be seen that the flange 1b acts as a stop in conjunction with the portions 12a and 12d of the base member to limit the range of pivoting of the intermediate member relative to the base member. If desired, the user can lock the chair seat in the maximum backward tilt position by pushing in the operating arm 23, which moves the plate portions of the lock member 9 into engagement with the undersides of the abutments 1a, as shown in Fig. 4. The force required to be exerted by the user to move the seat to the backward tilt position can be varied to suit the user's desire by adjustment of the force of the spring 18, using the knob 22 to turn the threaded shaft 21 and either tighten or loosen the spring 18. It is apparent from the above description that the mechanism for providing changes in the inclination of the seat of an office chair, according to the present invention, has a single shaft 7 for both rotations, clockwise (forward) and counterclockwise (backward), which is located a substantial distance in front of the column of the chair base in the direction of the front edge of the seat 10. Accordingly, the amount of vertical movement of the front edge of the seat is limited, and it is not necessary for the user to change the position of his or her legs and sitting posture when the inclination of the seat is changed. The mechanism is compact in size and fits unobtrusively under the center of the seat bottom within a small area and a small volume.

Claims: A chair seat mounting mechanism having a stationary base member (1) adapted to be mounted on a chair base, a seat-mounting member (9) that is adapted to be attached to a chair seat and is rotatably attached to the base member (1) by a pivot shaft (7) and springs acting between the base member (1) and the seat-mounting member (9) and biasing the seat to a neutral position intermediate of a forward tilted position and a rearward tilted position, characterized in that an intermediate member (12) is pivotally attached to the pivot shaft (7), at least one first spring (13) is engaged between the intermediate member (12) and the seat-mounting member (9) such as to bias the seat-mounting member relative to the intermediate member about the pivot shaft (7) in a direction such as to lower the rear of the seat relative to the front to the neutral position and to permit the seat to tilt forward relative to the intermediate member (12) against the bias of the first spring (13), and at least one second spring (17) is engaged between the base member (1) and the intermediate member (12) such as to bias the intermediate member (12) and the seat-mounting member (9) in tandem in a direction such as to raise the rear of the seat relative to the front to the neutral position and to permit the seat to tilt rearward against the bias of the second spring (17). A chair seat mounting mechanism according to claim 1 and further characterized in that the pivot shaft (7) is spaced apart a substantial distance from the center of the chair seat in the direction of the front edge of the seat bottom (10) so as to limit the mount of vertical motion of the front edge when the seat tilts forward and backward from the neutral position. A chair seat mounting mechanism according to claim 1 and further characterized in that there are stop means (1b, 12a) acting among the members for limiting the amounts of rotation of each of them relative to the others and establishing maximum forward and rearward tilt positions. A chair seat mounting mechanism according to claim 1 and further characterized in that there is a lock means for preventing movement of the seat-mounting member (9) relative to the base member (1) and selectively operable to lock the seat in the neutral position, a maximum rearward tilted position and a maximum forward tilted position. A chair seat mounting mechanism according to claim 1 and further characterized in that the lock means includes an abutment (1a) on the base member (1) and a lock member movably mounted on the seat-mounting member (9), the lock member having spaced-apart surfaces, each of which is engageable individually with the abutment (1a) in a different one of the fixed positions of the seat-mounting member (9) upon movement of the lock member relative to the seat-mounting member (9) to a locking position and is clear of engagement with the abutment (1a) upon movement to a release position.

Inventors: AMBASZ EMILIO, AMBASZ, EMILIO
Applicants: AMBASZ EMILIO, AMBASZ, EMILIO
Application year: 1991
Main classification: A47C3
IPC codes: A47C7, A47C3