Weight responsive chair

A chair comprising:

• a base including a ground engaging portion;
• a seat supported on the base;
• a backrest connected to the seat and the base, the backrest pivotally connected to the base at a recline axis, the backrest pivotable about the recline axis between an upright position and a reclined position;
• a recline tension spring biasing the backrest in the upright position;
• and
• a weight responsive mechanism including:
• a front link pivotally connected between the base and the seat,
• a rear link pivotally connected between the seat and the backrest, and
• a resilient element connected between the seat, the rear link and the backrest,
• wherein the force of a user occupying the seat pivots the front link and the rear link against a resistance created by the resilient element an amount proportional to the weight of the user to increase the effective length of the moment arm between the user and the recline axis, such that the force to pivot the backrest about the recline axis varies as a function of the weight of the user;
• and
• including a secondary recline spring between the base and the backrest, the secondary recline spring contributing to the biasing force of the recline tension spring when the backrest is moved to the reclined position.

A chair comprising:

• a base having a ground engaging portion and a mechanism portion;
• a seat for supporting a user;
• and
• a backrest connected to the seat and the base, the backrest pivoting with respect to the base between an upright position and a reclined position about a recline axis, the backrest biased in the upright position by a recline spring;
• wherein the seat is supported on the base by a four-bar linkage, the four-bar linkage including the seat, the mechanism portion of the base, a front link between the seat and the mechanism portion of the base, and a rear link between the seat and the mechanism portion of the base, wherein the rear link includes an upper rear link and a lower rear link, the upper link connected to the seat, and the lower rear link connected to the base;
• wherein the four-bar linkage is biased in a first position by a weight sensing spring;
• wherein a force from a user sitting on the seat acts against the weight sensing spring and pivots the front link, the upper rear link and the seat downward and forward with respect to the backrest and the recline axis and increases the distance between at least a portion of the seat and the recline axis.

A chair comprising:

• a base having a ground engaging portion and a mechanism portion;
• a seat for supporting a user;
• and
• a backrest connected to the seat and the base, the backrest pivoting with respect to the base between an upright position and a reclined position about a recline axis, the backrest biased in the upright position by a recline spring;
• wherein the seat is supported on the base by a four-bar linkage, the four-bar linkage including the seat, the mechanism portion of the base, a front link between the seat and the mechanism portion of the base, and a rear link between the seat and the mechanism portion of the base, wherein the rear link includes an upper rear link and a lower rear link, the upper link connected to the seat, and the lower rear link connected to the base;
• wherein the four-bar linkage is biased in a first position by a weight sensing spring;
• wherein a force from a user sitting on the seat acts against the weight sensing spring and pivots the front link, the upper rear link and the seat forward with respect to the recline axis and increases the distance between at least a portion of the seat and the recline axis;
• and
• including a secondary recline spring between the base and the backrest, the secondary spring contributing to the biasing force of the recline tension spring when the backrest is moved to the reclined position.

A chair comprising:

• a base;
• a backrest supported by the base at a recline axis, the backrest pivotable about the recline axis between an upright position and a reclined position, the backrest biased in the upright position by a recline spring;
• a seat supported by the base and having a surface for supporting an occupant;
• and
• a weight responsive mechanism adjusting the force required to pivot the backrest to the recline position as a result of an occupant sitting on the seat, independent of the pivoting of the backrest, and as a function of the weight of the occupant, the weight responsive mechanism including:
• a front link between the base and the seat,
• an upper rear link between the seat and the backrest,
• a lower rear link between the upper rear link and the base, the backrest attached to the lower rear link, and
• a weight sensing spring urging the upper rear link toward a first position, wherein the force of an occupant on the surface of the seat acts against the weight sensing spring to pivot the front link and the upper rear link out of the first position and downwardly and away from the backrest.