Chairs and seats – Movable back – Tiltable
Patent
1997-08-15
1999-01-26
Nelson, Jr., Milton
Chairs and seats
Movable back
Tiltable
2974631, A47C 1500
Patent
active
058630996
DESCRIPTION:
BRIEF SUMMARY
The invention relates to an actuator for a lock of a chair adjustment mechanism of the type mounted between two mutually tiltable chair parts and in which the lock comprises at least two linearly movable locking members.
Such mechanisms have been known for a very long time. Numerous different types of lock have been provided and there has also been a wide variety of different actuators for user control of the locks. In one arrangement, the mechanism includes a gas piston to control mutual movement of parts of the chair. Such an arrangement is quite expensive and there was therefore a trend towards use of simple mechanical locks to perform this function.
The most common type of lock comprises a number of friction leaves which must be pressed together for locking. European Patent Specification No. EP160221A1 describes an actuator comprising a screw mechanism. The lock is opened and closed by rotating a handle which rotates a threaded spindle to cause the leaves to be clamped or released. A problem with such an arrangement is that the spindle may rotate a small amount to cause disengagement, especially after a prolonged period of time. Further, many people regard such actuators as being difficult to use, particularly as they must be tightened very carefully. The locking strength depends on the user's strength.
To overcome these problems actuators have been devised which are based on the principle of a spring applying pressure on the lock to provide a normally-closed lock state. For example, in GB2193884 a rod having a cam surface is acted upon by a torsion spring to clamp friction leaves together. The lock is opened by the user rotating the rod out of the clamping position. In US4636004, springs mounted within a channel-shaped mechanism housing act between a channel side wall and the friction leaves. In both of these examples, the actuator comprises a spring to exert pressure on the lock and various interconnecting elements which must be carefully positioned. This causes a high materials requirement and expensive production processes because of the difficulty in accurately mounting the various components. Another problem with these two actuators is that stresses are transmitted through the mechanism in the normally-closed position, thus possibly causing distortion over time.
In some other actuators operating according to the principle of a spring acting upon the lock for a normally-closed lock state, stresses are not transmitted through the mechanism to any great extent by in effect, pulling the lock towards a fixed wall such as a channel side wall. Examples of this type of actuator are described in EP499487A1 and EP22225. While the problem of stresses being transmitted through the mechanism is satisfactorily addressed in these actuators, these actuators still suffer from the problems of a relatively expensive materials requirement, and expensive production processes. For example, in EP499487A1, it is necessary to provide a spring, a washer and a U-shaped housing for the spring. Further, it is essential that the U-shaped bracket be accurately machined to provide a bearing for a cam which must be inserted at a fine tolerance.
In some actuators of the type having a spring acting on the lock, the user is allowed choose one of two stable positions--open and closed. In EP45925 this is achieved by a cam being rotated over-centre between a closed position at which it allows the spring to exert pressure and keep the lock closed, and an open position at which it presses against the spring to prevent it acting on the lock and allow it open. In WO90/14031 this is achieved by a pivoted arm rotating over-centre between the positions as described in relation to EP45925. While these actuators provide two stable positions, they still operate on the principle of a spring acting on the lock to exert pressure in a closed position, and a handle acting on the spring to remove the pressure in an open position. They thus suffer from the same materials and production disadvantages outlined above for the other spring-based actuators.
REFERENCES:
patent: 4292858 (1981-10-01), Lipsheild
patent: 4636004 (1987-01-01), Neumuller
patent: 5356200 (1994-10-01), Stumpf et al.
patent: 5588706 (1996-12-01), Neumueller et al.
Ashfield Engineering Company Wexford Limited
Jr. Milton Nelson
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