Flexible or portable closure – partition – or panel – Plural strip – slat – or panel type – Venetian blind type
Patent
1997-07-02
1998-09-08
Purol, David M.
Flexible or portable closure, partition, or panel
Plural strip, slat, or panel type
Venetian blind type
160321, E06B 936
Patent
active
058031480
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention concerns an operating device for a screening arrangement comprising an input shaft which by one end is connected with a driving means, in particular including a rotatable wheel for receiving an operating means such as an endless cord, and which by the other end is coupled to an output shaft connected in a rotationally locked manner with the screening arrangement via a transmission shifting device, in particular a planet gear with one or more transmission stages.
Such a device is known, among others, from U.S. Pat. Nos. 4,657,060, 5,137,037 and 4,848,433. In operating devices of this type, the transmission shifting device performs the function either--in case of manual operation as in the two first-mentioned patents--of ensuring an easy operation without using great forces, or--in case of eg. electrical operation by a motor having a relatively high velocity of rotation--of providing the accuracy aimed at when adjusting the position of the screening arrangement.
A drawback when using transmissions in this connection is, however, that the load on the parts of the screening arrangement is considerably increased if the transferred driving torque becomes too large. For instance, if the screening arrangement hits an end stop in one of its end positions, in the form of a top case or a bottom or top section of the sash or the main frame and the operation cord is still being pulled, the driving torque may at worst cause damage in parts of the screening arrangement.
SUMMARY OF THE INVENTION
Consequently, it is the purpose of the invention to provide an operating device which protects the screening arrangement against damage of its parts and, at the same time, has a relatively simple and compact structure.
To this end, the operating device according to the invention is characterized in that between the transmission shifting device and the output shaft, a sliding clutch is engaged for limitation of the transferred driving torque and comprises a first coupling part in connection with the transmission shifting device and a second coupling part in connection with the output shaft, which coupling parts are in a mutual driving torque transferring engagement when the driving torque is below a predetermined threshold value, but is brought out of engagement when the driving torque exceeds said threshold value.
By this embodiment the screening arrangement is in a structurally simple manner prevented from being damaged if eg. it hits one of its end stops.
In the sliding clutch, either the first or the second coupling part may comprise a toothed shaft and the corresponding second or first coupling part a slotted and toothed rim. During normal operation of the screening arrangement, ie. where the sliding clutch transfers the driving torque from the input shaft to the output shaft, this design provides a good transmission, at the same time as the teeth in the slotted rim and on the toothed shaft are allowed to ridge or slide over each other at the given threshold value for the driving torque.
On the outside of the rim, there is preferably provided a ring acting as a spring which partly serves the function of keeping the first and second coupling parts together, and partly permits the threshold value of the driving torque to be varied simply by varying the spring characteristic of the ring.
In an embodiment of the invention, the operating device has as a further advantage also a braking means for retaining the screening arrangement in an arbitrary position and comprising an essentially semicircular ring element positioned above the wheel of the driving means and on the outside of the cord and having a slot for passage of the in- and outgoing sections of the cord, which ring element, when operating the screening arrangement, assumes a first position where the slot allows free passage of said cord sections, but at termination of operation, is moved in the peripheral direction as a consequence of the cord load stemming from the weight of the screening arrangement to another position where t
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patent: 4848433 (1989-07-01), Bresson et al.
patent: 5137073 (1992-08-01), Huang
patent: 5399129 (1995-03-01), Ciolli
Purol David M.
V. Kann Rasmussen Industri A/S
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