Electricity: motive power systems – With particular motor-driven load device – Power- or motion-transmitting mechanism
Reexamination Certificate
1999-09-15
2001-06-12
Ip, Paul (Department: 2837)
Electricity: motive power systems
With particular motor-driven load device
Power- or motion-transmitting mechanism
C318S015000, C318S466000, C192S048800, 27, C297S330000, C297S342000, C074S353000, C074S721000
Reexamination Certificate
active
06246191
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates, in general, to an electromotive linear drive mechanism, and in particular to a drive mechanism for a body of furniture.
Typical linear drive mechanisms for operating a body of furniture include a rotatable spindle which has placed thereon a nut forming an output member and secured against rotation, and a worm drive with a worm which is wedged onto the output journal of an electric motor. Linear drive mechanisms of this type are known in various designs to suit different use applications, and may be configured as a simple drive, i.e. with an electric motor and a spindle with a spindle nut, or as a dual drive with two electric motors and two threaded spindles with two spindle nuts, accommodated in a common housing. Also included here are small drives with an output of below 1 KW.
In conventional designs of linear drive mechanisms, the worm of the worm drive is made of steel whereas the worm gear, in mesh with the worm, is made from plastics. Although these material selections have been proven suitable, experience has also shown that the output journal of the electric motor, placed onto the worm, bends under load, albeit slightly. As a consequence, the overlap between worm and worm gear diminishes and the contact pressure increases. Thus, the flanks of the worm gear wear off and get crushed. This effect is further compounded during operation of the linear drive mechanism when the output journal of the electric motor heats up.
SUMMARY OF THE INVENTION
It is thus an object of the present invention to provide an improved electromotive linear drive mechanism, obviating the afore-stated drawbacks.
In particular, it is an object of the present invention to provide an improved electromotive linear drive mechanism, which is so constructed as to decrease wear of the worm gear in mesh with the wear, as a consequence of applied forces and possible heat, and to permit a transmission of higher forces.
These objects, and others which will become apparent hereinafter, are attained in accordance with the present invention by providing a worm drive with a worm which is secured to the output journal of an electric motor and in engagement with at least two worm gears arranged in a symmetric disposition with respect to the rotation axis of the worm.
The configuration of the worm drive in accordance with the present invention results in a substantial absorption of forces encountered at the worm during engagement. Thus, the output journal of the electric motor is not prone to flexure, as encountered by conventional drive mechanism to date, and is only loaded by torque being transmitted but not by forces directed perpendicular to its rotation axis.
According to one aspect of the present invention, the two worm gears in engagement with the worm are defined by rotation axes which are offset to one another by 180°, so that the worm gears are oriented in a common plane. Also, the number of components can thereby be kept to a minimum. Depending on the application, it may be appropriate to use the linear drive mechanism for elevation of a structure that is mounted to the spindle nut and for maintaining the structure in the elevated position after turning off the electric motor. Such a demand can be satisfied, by connecting each worm gear with a cylindrical gear which is in engagement with the cylindrical gear meshing with the other worm gear. Thus, a dual worm-cylindrical gear mechanism is realized which is self-locking as the overall efficiency is decreased by both cylindrical gears. The pitch diameter of both cylindrical gears are greater than the outer diameter of the worm gears and contact one another in the plane of the rotation axes of the worm. In addition, such a configuration realizes a distribution of the total torque, introduced by the worm, over two or more worm gears, so that such a gear mechanism is able to transmit a significantly greater maximum torque than a conventional worm gear mechanism.
The assembly can be simplified and the number of components can be kept to a minimum by designing each worm gear with pertaining cylindrical gear of single-piece construction. The cylindrical gears may be spur gears or oblique cylindrical gears.
According to another feature of the present invention, each worm gear and pertaining cylindrical gear may have mounted thereon an outwardly projecting bearing pin for attachment of a rolling-contact bearing or sliding bearing to thereby optimize a support of the worm gears and cylindrical gears. The entire gear mechanism is then supported on four places, thereby realizing a stable arrangement.
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Bokamper Ralf
Roither Andreas
Day Ursula B.
Dewert Antriebs-und Systemtechnik GmbH & Co. KG
Feiereisen Henry M.
Ip Paul
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