WO2012093092A1

WO2012093092A1 - Driving mechanism for a winding shaft of an architectural covering and improved architectural covering

Info

Publication number: WO2012093092A1
Application number: PCT/EP2012/000044
Authority: WO
Inventors: Lars Koop; Jörg Bohlen
Original assignee: Hunter Douglas Industries B.V.
Priority date: 2011-01-06
Filing date: 2012-01-06
Publication date: 2012-07-12

Abstract

A driving mechanism (13) for a winding shaft (3) of an architectural covering (1) that is adapted to be associated with a fixed architectural mounting structure. The driving mechanism (13) includes a driving member (23), and a driven member (21) for inducing rotation to the winding shaft (3) of the architectural covering (1). A torque limiting clutch (57) is operatively engaged between the driving member (23) and the driven member (21) and a non- rotatable stationary member (51) for mounting of the driven member (21) to said fixed mounting structure. A first limit stop (85) is associated with the non- rotatable stationary member (51) and a second limit stop (87) on the driven member (21) is adapted to be engaged by the first limit stop (85) only after a predefined number of rotations of the driven member (21) from a first rotational end position to a second rotational end position. A lost motion mechanism (79, 81) is interposed between the driven member (21) and the stationary member (51) to allow the predefined number of rotations of the driven member (21) from the first to the second rotational end position and vice versa. The stationary member (51) is locked with respect to the fixed mounting structure by a locking tab (37), but can be unlocked for rotation with the driven member (21) by disengaging the locking tab (37).

Description

Title: DRIVING MECHANISM FOR A WINDING SHAFT OF AN

ARCHITECTURAL COVERING AND IMPROVED ARCHITECTURAL COVERING

The invention relates to a driving mechanism for a winding shaft of an architectural covering and to an architectural covering provided with such a driving mechanism. More in particular the invention relates to such a driving mechanism that includes an end stop or limit stop system to limit the fully extended position of the architectural covering.

Mechanical limit stop systems for defining the fully extended position of architectural coverings, such as window coverings, are known in the art. Best known are the so-called spindle and nut-limit stops. A spindle and nut, limit stop system generally includes a threaded shaft, a wandering or travelling nut threaded on the shaft and at least one fixed limit stop on the shaft. For roller blinds and other blinds where a roller is rotated to wind and unwind a covering material or lift cords about the roller, it generally is the case that the nut is keyed to a driven portion of the blind and the shaft is stationary, such that when the blind is driven the nut rotates and is displaced in an axial direction along the threaded shaft or spindle. When the nut reaches the limit stop, the nut can no longer be displaced along the shaft and since the driven portion of the blind is keyed to the nut either directly or by way of the shaft, rotation of the driven blind portion will be stopped at the same time.

When the driven member of a blind rotates with a considerable speed, the nut will reach the limit stop at a considerable speed too. In order dampen the impact on the limit stop, it is known to add a shock absorber.

It is known from applicant's US 2010/0212843 (Al) to use, in retractable coverings for architectural openings, limit stops with impact-absorbing means which are bi-directionally cushioning. While, in this arrangement, the limit stop will remain at a preselected position, even after being impacted, there is no safety mechanism against excessive torque being applied and damaging the limit stop.

It is further known from CH 661560 (A) to the force of manual crank drives for blinds by inserting an element for limiting the rotary force at the transition point from a universal joint and a drive rod. This torque limiting element consists of inner and outer sleeves which engage one another. The outer sleeve has catch recesses on its inside and the inner sleeve has axial slot openings for receiving cylindrical bodies. In the central cavity, an elastic compression element is inserted. By selecting the number of cylindrical bodies and/or the Shore hardness of the elastic compression element, the force limitation can be adapted to the respective blind.

Accordingly, it is an object of the present invention to provide an improved driving mechanism for a winding shaft of an architectural covering. In a more general sense it is an object of the invention to overcome or ameliorate at least one of the disadvantages of the prior art. It is also an object of the present invention to provide alternative structures which are less cumbersome in assembly and operation and which moreover can be made relatively inexpensively. Alternatively, it is also an object of the invention to at least provide the public with a useful choice.

To this end, the invention provides a driving mechanism for a winding shaft of an architectural covering, the driving mechanism being adapted to be associated with a fixed mounting structure and include: a driving member; a driven member for inducing rotation to the winding shaft of an architectural covering; a torque limiting clutch operatively engaged between the driving member and the driven member; a non-rotatable stationary member for mounting the driven member on the fixed mounting structure; a first limit stop associated with the non-rotatable stationary member; a second limit stop on the driven member and adapted to be engaged by the first limit stop after a predetermined number of rotations of the driven member from a first rotational end position to a second rotational end position; a lost motion mechanism interposed between the driven member and the stationary member to allow the predetermined number of rotations of the driven member from the first rotational end position to the second rotational end position and vice versa, wherein the stationary member is locked with respect to the fixed mounting structure by a locking tab but can be unlocked for rotation with the driven member by disengaging the locking tab. With such an improved driving mechanism, it has become possible to quickly adjust and limit a fully extended position of an architectural covering associated with the improved driving mechanism. Moreover, providing a torque limiting clutch between the driving member and the driven member allows cushioning and dampening of the impact on abutment of the limit stops, without changing their relative positions. The torque limiting clutch also prevents excessive torque from being imposed on the mechanism and protects it from damage. Incorporating the torque limiting clutch in the driving mechanism also eliminates any need for external torque limiting devices in auxiliary crank drives or the like.

Advantageously the lost motion mechanism includes a travelling nut on a screw threaded spindle, and preferably, the nut is non-rotatably guided along the non-rotatable stationary member and the screw threaded spindle extends integrally from the driven member.

It is of further advantage in the driving mechanism according to the invention that the torque limiting clutch is a wrap spring clutch. In this regard it may also be preferred, when the wrap spring clutch includes a wrap spring with a first radially extending spring end and a second radially extending spring end, that one of the first and second spring ends is selectively

engageable by a radially inwardly extending formation on the driven member in favour of right-hand and left-hand rotational options.

According to a further advantageous embodiment of the invention, the driving member includes a drive gear and a drive coupling for driving a central drive shaft. In such an embodiment, the drive gear may preferably be adapted to be mounted to a fixed mounting structure by a mounting bracket. In this regard, it may also be advantageous that an external housing having a lower periphery is attached to the drive gear. The locking tab is then preferably held within the lower periphery of the external housing for movement between a retracted and an extended position with respect to the external housing.

Additionally or alternatively, the non-rotatable stationary member may be adapted to engage the fixed mounting structure by a plurality of radially spaced and distributed complementary formations, so as to offer some tolerance for misalignments that could otherwise impair proper functioning. In particular, it is then of advantage, when a receiving disc is rotatably mounted with respect to the drive gear and concentrically with respect to the drive coupling, that the receiving disc has a plurality of radially extending teeth on its outer circumference for engagement with a number of complimentary teeth on the locking tab. The receiving disc may then further have a plurality of radially positioned openings and the stationary member may have an axial end flange with corresponding protrusions for disconnectably engaging the openings of the receiving disc. The drive coupling is then preferably also disconnectably engageable with a drive cavity of the central drive shaft.

With all these variations of drive mechanisms according to the

invention, the driving member may advantageously be adapted to be drivingly engaged by a crank drive, a ball chain drive or a cord drive associated with the fixed mounting structure.

Irrespective of the variation of the invention, the fixed mounting structure may include a pair of mounting brackets, between which the winding shaft is rotatably received.

The winding shaft may in one application of the invention be a roller blind roller for winding a blind fabric. With such an architectural covering, the roller blind roller may advantageously be a substantially hollow roller blind tube. The invention in general also provides an architectural covering that includes the driving mechanism in any one of the preferred or advantageous variations.

Further advantageous aspects of the invention will become clear from the appended description of preferred embodiments, which are described in reference to the accompanying drawings, in which:

Figure 1 is a partly exploded view of a roller blind embodying the invention;

Figure 2 is a further exploded detail view of a drive arrangement according to the invention;

Figure 3 is an exploded view of some of the components of Figure 2, but viewed from an opposite direction;

Figure 4 is a detailed longitudinal cross section of the driving mechanism that is illustrated in Figures 1, 2 and 3;

Figure 5 is a transverse cross section according to the line V-V of

Figure 4;

Figure 6 is a transverse cross section according to the line VT-VI of

Figure 4;

Figure 7 is a cross section of the assembled parts of Figure 2;

Figure 8 (A) is a partial elevation in cross section of the assembled structure of Figure 1 showing a disengaged locking tab;

Figure 8 (B) is a transverse cross section according to the line B-B of Figure 8 (A);

Figure 8 (C) is a partial elevation in cross section of the assembled structure of Figure 1 showing an engaged locking tab;

Figure 8 (D) is a transverse cross section according to the line D-D of Figure 8 (C); and

Figure 9 is a longitudinal cross section similar to Figure 4 of an alternative embodiment. Referring first to Figure 1, an architectural covering in the form of a roller blind 1 is shown. The roller blind 1 includes a winding shaft or blind roller 3 to which a blind fabric 5 is attached to be wound and unwound therefrom by rotation of the blind roller 3. A free end of the blind fabric 5 is provided with a bottom bar 7 for keeping the unwound portion of the blind fabric taut. The bottom bar 7 is also useful in limiting the fully wound up position of the blind fabric.

On one of its ends, the blind roller 3 is equipped with an end plug 9 for rotatably journaling the blind roller 3 to a mounting bracket 11. A similar mounting bracket 11 on an opposite end of the blind roller 3 supports a drive unit, or drive arrangement, generally indicated by a reference 13. The drive unit 13 can be an electric motor drive, a spring, a manual ball chain, a cord drive or a manual crank drive as in the preferred embodiment of Figure 1. Thus, the drive unit 13 has a universal joint 15 to allow angular deflection of a crank drive rod or shaft 17. A protruding drive mechanism 19 is adapted to be accommodated in, and engage, the tubular hollow interior of the blind roller 3. The drive mechanism 19 has a rotatable driven member 21 for inducing rotation of the blind roller 3.

In Figure 2, the principal elements forming the drive unit 13 are shown in an exploded arrangement. A conventional drive gear 23, including a worm gear transmission, transmits rotation of the crank drive shaft 17 into rotation of a central drive sleeve 25. The central drive sleeve 25 drivingly engages a hexagonal shaft portion of a drive coupling 27. The drive coupling 27 extends through a receiving disc 29 and an external housing 31. The external housing 31, when assembled as shown in Figure 1, fits over the drive gear 23 and is attached by mounting screws 33 and a securing element 35 to the mounting bracket 11 (shown in Figure 1, but deleted from Figure 2). A locking tab 37, upon assembly of the elements shown in Figure 2, is held within the lower periphery of the external housing 31. The locking tab 37, as is more clearly seen in Figure 3, has a plurality of teeth 39 for engaging a selected plurality of the teeth 41 on the outer circumference of the receiving disc 29. Figure 3 shows the drive mechanism 19 and the drive coupling 27 from a direction opposite to the viewing direction of the same elements in Figure 2. As further illustrated in Figure 3, the receiving disc 29 has also a plurality of radially positioned openings 43. A corresponding plurality of protrusions 47 on an axial end flange 45 of the drive mechanism 19 is adapted to be received in the radial openings 43 of the receiving disc 29. The drive mechanism 19 also has a central drive shaft 49 which is adapted to be drivingly engaged by the drive coupling 27, to drive the driven member 21 by engagement in a drive cavity 53. The end flange 45 and a cylindrical outer housing 51 of the drive mechanism 19, in use, will be held stationary with respect to the mounting bracket 11 (shown in Figure 1) by being in non-rotatable engagement with the receiving disc 29. The receiving disc 29 in normal use will be held stationary in the external housing 31 by the locking tab 37.

For a further explanation of the drive mechanism 19, reference will be made to a schematic longitudinal cross section shown in Figure 4. Blind roller 3 is rotatingly journaled on the stationary held cylindrical outer housing 51 adjacent its end flange 45, by means of end plug bearing ring 55. The central shaft 49, by being driven from its drive cavity 53 by the drive coupling 27, is adapted to drive the driven member 21 through a torque limiting clutch 57. The driven member 21 is fixed for rotation to the blind roller by an internal ridge 3A. As also shown in Figure 5 - a view across the line V-V in Figure 6 - the torque limiting clutch 57 includes a wrap spring 59 that is frictionally engaged on a cylindrical wrap spring drum 61. The torque limiting clutch 57 is conveniently accommodated within a central cavity in the driven member 21. The wrap spring drum 61 is firmly attached to the central drive shaft 49 by a driving square 63 and may be held in position by a locking ring 65. The wrap spring 59 has radially extending first and second spring ends 67, 69. A selected one of the first and second spring ends, in this case the first spring end 67, is engaged between inwardly extending ridges 71, 73 of the driven member 21. The other one of the first and second spring ends, in this case the second spring end 69, remains unengaged. The unengaged first or second spring end 67, 69 points to a corresponding marker 75 for "R" or 77 for "L" on the driven member 21 to assist with a correct assembly of the torque limiting clutch for right hand (RH) or left hand (LH) winding as required by the winding shaft or blind roller 3. The RH and LH rotation options will be discussed in more detail herein below.

Figure 4 further shows that the driven member 21 in the form of an axial extension is provided with a screw spindle 79. Engaged about this screw spindle 79 is a nut 81. The nut 81, as is shown in the cross section of Figure 6, has a radially extending notch 83 engaged in an inwardly opening longitudinal groove 51A in the cylindrical housing 51. The nut 81 further has an axially extending first limit stop 85, which confronts a second limit stop 87 on the driven element 21. With the cylindrical outer housing 51 being stationary, rotation of the screw spindle 79 and driven member 21 will result in axial travelling of the nut 81. Thereby the assembly of screw spindle 79, stationary housing 51 and nut 81 will act as a lost-motion mechanism, allowing a predefined number of rotations of the driven member 21 before the first and second limit stops 85, 87 will engage one another. Upon engagement of the first limit stop 85 with the second limit stop 87 further rotation of the driven member 21 and the winding roller 3 will be arrested by the stationary housing 51. Such an arresting of the winding roller 3 will be useful when the roller blind fabric 5 has reached the fully extended position with the bottom bar 7 just slightly above the window sill. In that position it would be undesirable when the blind fabric 5 could be unwound any further from the blind winding roller 3. Further unwinding could damage the bottom bar 7 or blind fabric 5, or worse, could loosen the blind fabric 5 from the roller 3.

Limiting the fully wound position of the roller blind 1 is achieved in that the bottom bar 7 cannot get between the mounting brackets 11 and the roller 3. In both the fully lowered and fully raised positions, when further rotation of the roller 3 and driven member 21 is arrested, any damage to the mechanism that could be caused by further rotation of the crank rod 17, is prevented by the torque limiting clutch 57.

Figure 7 shows a somewhat simplified cross section of the parts of

Figure 2 in an assembled arrangement. For clarity the torque limiting clutch has been deleted and the screw spindle 79 and driven member 21 are represented as one unitary element directly driven by the drive coupling 27.

For a description of the individual parts indicated in Figure 7, reference can be made to the description of the previous drawing Figures. A main purpose of Figure 7 is to illustrate how these individual parts come together when assembled into a functioning unit. In particular the

arrangement of the retaining disc 29 within the external housing 31 and the locking tab 37, will now be clarified in relation to the end flange 45 engaging the retaining disc 29. Double arrow 89 indicates the locking and unlocking movement of the locking tab 37. As shown in Figure 7, the locking tab 37 is in its unlocked position, which will allow the receiving disc 29 to rotate together with the end flange of the cylindrical outer housing 51 of the drive mechanism 19.

For a better understanding of the limit stop adjustment, using the locking tab 37, reference will now be made to Figures 8(A) to 8(D). Figure 8(A) shows the situation of Figure 7 except that a blind roller 3 has been added and the crank rod drive has been deleted. Figure 8(B) is a cross sectional view according to line B-B of Figure 8(A) and shows the locking tab 37 disengaged from the receiving disc 29.

A basic adjustment of a lower rotational end position is obtained as follows.

Upon installation of the roller blind 1 at an architectural opening the mounting brackets 11 (see also Figure 8(B)), are first mounted to a wall surface in the vicinity of the architectural opening. Before the blind roller 3 with the end plug 9 attached to one of its ends and the drive mechanism 19 attached to the other end, is offered up to the brackets 11, it will be necessary to ensure that the first limit stop 85 is engaged with the second limit stop 87 (see Figure 4). Preferably the drive unit 19 is supplied with the driven member 21 and the cylindrical outer housing 51 in a relative position with the first limit stop 85 on the nut 81 in engagement with the second limit stop 87 on the driven member 21. This relative position can be temporarily fixed by a piece of removable tape fixing the end flange 45 to the roller 3. This tape then is to be removed before mounting the roller 3 between the mounting brackets 11 and the protrusions 47 on the end flange 45 being engaged in the openings 43 of the receiving disc 29. In case the first and second limit stops 85, 87 would not yet be engaged this initial position can be established by rotating the end flange 45 with respect to the blind roller 3, before engaging the end flange 45 with the receiving disc 29.

With the drive mechanism 19 in its initial position and the blind fabric 5 and bottom bar 7 fully wound on the roller 3, the installation between the mounting brackets 11 is effected. Then the locking tab 37 is moved to the extended position shown in Figures 7 and 8(A), so that the end flange 45 can freely rotate with the receiving disc 29. In this position the bottom bar 7 is lowered to the desired position of maximum deployment, preferably hovering with a slight gap above the window sill, or like lower boundary of the

architectural opening. After reaching this lower most position for the bottom bar 7 the locking tab 37 is pushed back to a retracted position, as shown in Figures 8(C) and 8(D), where it arrests the confronting radially extending teeth of the receiving disc 29. After setting of the lower end position as described, the roller blind can be raised and lowered by manual rotation of the crank drive rod 17. In the lowermost position the first and second limit stops 85, 87 will repeatedly engage one another and further rotation of the crank drive rod 17, will only result in the torque limiting clutch 57 starting to slip. Moving from the lowermost position in an upward winding direction, the first and second limit stops 85, 87 will start to travel in an axial direction away from the driven member 21 by the action of the rotating screw spindle 79. The uppermost position is reached when the bottom bar 7 abuts the mounting brackets 11, or is caught between the mounting brackets 11 and the roller. Alternatively also dedicated stops may be provided on the bottom bar 7 and the mounting brackets 11 to arrest further rotation of the blind roller 3. Also in the uppermost end position of the roller blind 1 any forced further rotation of the crank drive rod 17 will only result in slippage of the torque limiting clutch 57.

As may be appreciated from the above description, the screw spindle

79 and the axially travelling nut 81 are effectively functioning as a lost motion mechanism interposed between the driven member 21 and the cylindrical outer housing 51. As the skilled person is well aware, such lost motion mechanisms exist in a variety of forms and are quite commonly used in architectural coverings. Examples include rotating discs with mutually abutting protrusions such as in applicant's US 5,390,721 and US 6,637,492, or a convoluted length of cord between two relatively rotatable elements. Such examples may be employed to replace the spindle and nut assembly of the present invention, without departing from the inventive concept.

In roller blinds it is common to offer the option of having the drive mechanism at either a right hand (RH) or a left hand (LH) side of the blind. It is also a common option in roller blinds to chose for the blind fabric 5 to unwind tangentially from a rear side of the roller 3, as shown in Figure 1, or alternatively from a front side of the blind roller. To be able to offer these options, it is usually necessary to have different drive units 13 for RH and LH rotation. With the nut and spindle mechanism as shown in Figure 4 this would require to have available a RH threaded spindle 79 and ditto nut 81, as well as RH threaded versions of these components.

In Figure 9 an alternative drive mechanism 119 is shown that can be employed for both RH and LH options. Figure 9 is substantially similar to Figure 4 and like components are referred to by like reference numerals preceded by "1". The lines V-V and VI-VI refer to the identical transverse cross sections of Figures 5 and 6. The drive mechanism 119 allows the use of one and the same screw spindle 179 and nut 181 to obtain both RH and LH rotating options. As a consequence, of being able to use the same screw spindle 179 also only one single driven member 121 will be required when this is integrally formed with the screw spindle 179. To this end a third limiting stop 191 on a detachable flange part is provided at the free end of the screw spindle 179. A nut 181 differs from the nut 81 in Figure 4 in that it is provided with an additional fourth limiting stop 193 that confronts the third limiting stop 191. The third limiting stop 191 is preferably detachable to allow the nut 181 to be mounted on the screw spindle 179. However, it would also be possible to make the nut 181 detachable in two halves, in which case the third limiting stop 191 may be integral with the screw spindle 179 and driven member 121. With the alternative arrangement of Figure 9 the third and second limiting stops 191, 193 can be used to limit the lowermost position of the bottom bar 7 in a RH rotation option while the first and second limiting stops 185, 187 are used in a LH rotation option. As will be clear to the skilled person, the inverse situation may apply when the screw spindle 179 and nut 181 use left hand rather than right hand screw threads.

When reference is again made to Figure 5, the torque limiting clutch 57, 157 is seen to have different torque limit values depending on whether force is applied to the wrap spring 59, 159 in a direction of widening the individual windings. As viewed in Figure 5, engaging the driven member 21, 121 for rotation in a clockwise direction will allow the torque limiting clutch 57, 157 to start slipping at a lower torque value than when it would be driven for rotation in a counter clockwise direction. This difference in torque limiting is convenient in that the torque required for driving the roller 3 also differs between the upper and lower end positions. Accordingly the marking 75 for "R" or right hand and 77 for "L" or left hand on the driven member 21 indicate the position for the free spring end to obtain the appropriate torque limiting characteristic for the RH or LH rotation options.

Thus is disclosed a driving mechanism (drive unit 13) for a winding shaft (blind roller 3) of an architectural covering (roller blind 1) that is adapted to be associated with a fixed architectural mounting structure. The driving mechanism (13) includes a driving member (drive gear 23), and a driven member (21) for inducing rotation to the winding shaft (3) of the architectural covering (1). A torque limiting clutch (57) is operatively engaged between the driving member (23) and the driven member (21) and a non-rotatable stationary member (cylindrical outer housing 51) for mounting of the driven member (21) to the fixed mounting structure. A first limit stop (85) is associated with the non-rotatable stationary member (51) and a second limit stop (87) on the driven member (21) is adapted to be engaged by the first limit stop (85) only after a predefined number of rotations of the driven member (21) from a first rotational end position to a second rotational end position. A lost motion mechanism (screw spindle 79, and travelling nut 81) is interposed between the driven member (21) and the stationary member (51) to allow the predefined number of rotations of the driven member (21) from the first to the second rotational end position and vice versa. The stationary member (51) is locked with respect to the fixed mounting structure by a locking tab (37), but can be unlocked for rotation with the driven member (21) by disengaging the locking tab (37).

It is thus believed that the operation and construction of the present invention will be apparent from the foregoing description. The invention is not limited to any embodiment herein described and, within the purview of the skilled person; modifications are possible which should be considered within the scope of the appended claims. Equally all kinematic inversions are considered inherently disclosed and to be within the scope of the present invention. In the claims, any reference signs shall not be construed as limiting the claim. The term 'comprising' when used in this description or the appended claims should not be construed in an exclusive or exhaustive sense but rather in an inclusive sense. Thus the expression 'comprising' as used herein does not exclude the presence of other elements or steps in addition to those listed in a claim. Furthermore, the words 'a' and 'an' shall not be construed as limited to Only one', but instead are used to mean 'at least one', and do not exclude a plurality. The mere fact that certain measures are recited in mutually different claims does not indicate that a combination of these measures cannot be used to advantage. Expressions such as: "means for ..." should be read as: "component configured for ..." or "member constructed to ..." and should be construed to include equivalents for the structures disclosed. The use of expressions like: "critical", "preferred", "especially preferred" etc. is not intended to limit the invention. Features which are not specifically or explicitly described or claimed may be additionally included in the structure according to the present invention without deviating from its scope.

Claims

1. Driving mechanism for a winding shaft of an architectural covering, the driving mechanism being adapted to be associated with a fixed mounting structure and includes:

a driving member;

a driven member for inducing rotation to said winding shaft of an architectural covering;

a torque limiting clutch operatively engaged between the driving member and the driven member;

a non-rotatable stationary member for mounting of the driven member to said fixed mounting structure;

a first limit stop associated with the non-rotatable stationary member; a second limit stop on the driven member and adapted to be engaged by the first limit stop after a predefined number of rotations of the driven member from a first rotational end position to a second rotational end position;

a lost motion mechanism interposed between the driven member and the stationary member to allow the predefined number of rotations of the driven member from the first to the second rotational end position and vice versa,

wherein the stationary member is locked with respect to the fixed mounting structure by a locking tab, but can be unlocked for rotation with the driven member by disengaging the locking tab.

2. Driving mechanism according to claim 1, wherein the lost motion mechanism includes a travelling nut on a screw threaded spindle.

3. Driving mechanism according to claim 2, wherein the nut is non- rotatably guided along the non-rotatable stationary member and wherein the screw threaded spindle extends integrally from the driven member.

4. Driving mechanism according to claim 1, 2, or 3, wherein the torque limiting clutch is a wrap spring clutch.

5. Driving mechanism according to claim 4, wherein the wrap spring clutch includes a wrap spring with a first radially extending spring end and a second radially extending spring end, one of the first and second spring ends being selectively engageable by a radially inwardly extending formation on the driven member in favour of right-hand and left-hand rotational options.

6. Driving mechanism according to any preceding claim, wherein the driving member includes a drive gear and a drive coupling for driving a central drive shaft.

7. Driving mechanism according to claim 6, wherein the drive gear is adapted to be mounted to a fixed mounting structure by a mounting bracket.

8. Driving mechanism according to claims 6 or 7, wherein an external housing having a lower periphery is attached to the drive gear.

9. Driving mechanism according to claim 8, wherein the locking tab is held within the lower periphery of the external housing for movement between a retracted and an extended position with respect to the external housing.

10. Driving mechanism according to claim 7, 8 or 9, wherein the non- rotatable stationary member is adapted to engage said fixed mounting structure by a plurality of radially spaced and distributed complementary formations, so as to offer some latitude to misalignments that could otherwise impair proper functioning.

11. Driving mechanism according to claim 10, wherein a receiving disc is rotatably mounted with respect to the drive gear and concentrically with respect to the drive coupling, and wherein the receiving disc has a plurality of radially extending teeth on its outer circumference for engagement with a number of complimentary teeth on the locking tab.

12. Driving mechanism according to claim 11, wherein the receiving disc further has a plurality of radially positioned openings and the stationary member has an axial end flange with corresponding protrusions for

disconnectably engaging the openings of the receiving disc.

13. Driving mechanism according to any one of claims 6 to 12, wherein the drive coupling is disconnectably engageable with a drive cavity of the central drive shaft.

14. Drive mechanism according to any preceding claims, wherein the driving member is adapted to be drivingly engaged by one of a crank drive, a ball chain drive, and a cord drive associated with said fixed mounting structure.

15. Drive mechanism according to any preceding claim, wherein the fixed mounting structure includes a pair of mounting brackets between which the winding shaft is to be rotatably received.

16. Drive mechanism according to any preceding claim, wherein the winding shaft is a roller blind roller for winding a blind fabric.

17. Drive mechanism according to claim 16, wherein said roller blind roller is a substantially hollow roller blind tube.

18. Architectural covering including the driving mechanism of any one of the preceding claims.