GB2589914A

GB2589914A - Actuator for window blinds

Info

Publication number: GB2589914A
Application number: GB1918363.1A
Authority: GB
Inventors: Zeineddine Firas
Original assignee: Rotalink Ltd
Current assignee: Rotalink Ltd
Priority date: 2019-12-13
Filing date: 2019-12-13
Publication date: 2021-06-16
Also published as: WO2021116375A1; GB201918363D0

Abstract

The actuator 200 comprises a motor 210 and a compound gearbox. The gearbox itself comprises a first stage comprising an input sun gear 110, a first plurality of planet gears 122 in meshed engagement with the input sun gear and a fixed ring gear 130 in meshed engagement with the first plurality of planet gears wherein the motor is connected to the input sun gear to thereby be capable of directly driving the input sun gear. The gearbox also comprises a second stage comprising a second plurality of planet gears 124 and an output ring gear 140 in meshed engagement with the second plurality of planet gears wherein each of the second plurality of planet gears is rotatable in tandem with a respective one of the first plurality of planet gears. The actuator further comprises a coupling 220 rotatable in tandem with the output ring gear, the coupling being configured to be coupled with a rotatable element of a window blind to thereby drive the rotatable element. The first and second plurality of gears and the fixed and output ring gears may comprise a different effective diameter from one another.

Description

ACTUATOR FOR WINDOW BLINDS

TECHNICAL FIELD

This invention relates to an actuator for raising and lowering window blinds, and in particular to a gearbox of such an actuator.

BACKGROUND

It is known to operate window blinds using a remotely-controlled actuator installed in, or adjacent to, the blind headrail. Some known actuators for such applications comprise a worm gear driven by an electric motor, the worm gear meshing with a pair of bevel gears to enable an output drive shaft to be aligned with an input shaft of the motor.

SUMMARY OF THE INVENTION

The present inventors have found that the known worm gear arrangement described above is not suitable for all window blind applications. In particular, where a rail within the actuator must be located has a small transverse dimension, or diameter, it may prove difficult to achieve a sufficiently high torque with such an arrangement to raise and lower larger, or heavier, blinds.

In general terms, the present invention provides an actuator for driving a rotatable element of a window blind mechanism, the actuator comprising a motor driving, via a compound planetary gearbox, a coupling for engaging the rotatable element. A sun gear of the compound planetary gearbox is coupled to the motor, and the coupling is coupled to an output ring gear of the compound planetary gearbox.

Thus, a first aspect of the present invention provides an actuator for driving a rotatable element of a window blind to raise and lower the window blind, the actuator including: a motor; and a compound planetary gearbox including: a first stage comprising an input sun gear, a first plurality of planet gears in meshed engagement with the input sun gear, and a fixed ring gear in meshed engagement with the first plurality of planet gears, wherein the motor is connected to the input sun gear to thereby be capable of directly driving the input sun gear; and a second stage comprising a second plurality of planet gears, and an output ring gear in meshed engagement with the second plurality of planet gears, wherein each of the second plurality of planet gears is rotatable in tandem with a respective one of the first plurality of planet gears; and a coupling rotatable in tandem with the output ring gear, the coupling being configured to be coupled with a rotatable element of a window blind to thereby drive the rotatable element.

This arrangement enables a transverse dimension of the actuator to be minimised, since this dimension is controlled by the outer diameter of the fixed ring gear and/or output ring gear. Moreover, the arrangement is space-efficient, ensuring that the gear ratio is maximised for the available space.

A compound planetary gearbox would ordinarily not be considered ideal for such an application since they typically have a relatively low efficiency, and the rotating ring gear presents challenges in that there is no stationary front face to mount the gearbox in a typical fashion and there are unshielded rotating parts.

However, the present inventors have realised that the low efficiency can be beneficial in this application since it renders the gearbox inherently self-locking so that it cannot be back-driven. Moreover, they have realised that it is possible to directly couple the rotatable element (shaft) of a blind mechanism with an output ring gear by way of the claimed coupling. The claimed arrangement thus enables the gearbox to be mounted in a straightforward way without additional components, by coupling the fixed ring gear to the blind rail and the output ring gear to the coupling. No additional clutch or self-locking mechanism is required.

The axial lengths of each of the gears, or stages, can be modified according to the specific application. For example, for high torque applications the axial lengths may be higher than for lower torque applications. Thus, the gearbox is scalable for different applications.

The first and second plurality of planet gears are preferably provided as a plurality of compound planets, each compound planet including a respective one of the first planet gears and a respective one of the second planet gears mounted on a common hub and common axis.

The rotatable element of a window blind preferably comprises an elongate rotatable shaft, optionally a shaft with a non-circular cross-section. For example, the rotatable shaft may have a generally polygonal cross-section, such as a square cross-section. The shaft may be rotated by a blind mechanism housed within a blind rail of the window blind. The actuator may also be located within the blind rail.

In preferred embodiments the first plurality of planet gears each have a different effective diameter to the second plurality of planet gears, optionally the second plurality of planet gears each have a smaller effective diameter than the first plurality of planet gears. By controlling the relative effective diameters of the first and second planet gears, respectively, the rotational speed of the output ring gear can be controlled. It is preferred that the second planet gears are smaller than the first planet gears such that the output ring gear is smaller than the fixed ring gear; in this way the rotating parts of the actuator can have a smaller transverse dimension than the non-rotating parts, leading to a simpler and more efficient mounting arrangement.

The difference between the effective diameters of the first and second planet gears controls the efficiency of the gearbox. That is, the closer the effective diameters, the lower the efficiency, the higher the gear ratio, and the more likely the mechanism will be self-locking. Thus, the effective diameters of the first and second planet gears are preferably close to one another. For example, the effective diameter of the second planet gears is preferably 80% or more, 90% or more, or 95% or more than the effective diameter of the first planet gears.

Similarly, the fixed ring gear preferably has a different effective diameter to the output ring gear, optionally the output ring gear has a smaller effective diameter than the fixed ring gear. By controlling the relative effective diameters of the fixed and output ring gears the rotational speed of the output ring gear can be controlled. It is preferred that the output ring gear is smaller than the fixed ring gear; in this way the rotating parts of the actuator can have a smaller transverse dimension than the non-rotating parts, leading to a simpler and more efficient mounting arrangement.

The fixed ring gear is preferably unable to rotate relative to the motor, for example a housing of the motor. That is, the fixed ring gear is preferably constrained in rotation relative to the motor. For example, the fixed ring gear may be mounted on a housing of the motor so that an output shaft of the motor is able to rotate relative to the fixed ring gear.

The actuator preferably comprises a non-rotatable housing and a rotatable housing, the rotatable housing including the coupling. The non-rotatable housing may be coupled to the rotatable housing to permit relative rotation therebetween but restrict relative axial movement. The non-rotatable housing may enclose the fixed ring gear and/or the rotatable housing may enclose the output ring gear.

The coupling may comprise an aperture in the rotatable housing that is configured to receive the rotatable element to permit transfer of torque from the coupling to the rotatable element of the window blind. This arrangement provides a particularly simple and space-efficient means of transferring rotation of the output ring gear to the rotatable element. The aperture may be centred on an axis of the output ring gear.

The rotatable housing is preferably configured to rotate in tandem with the output ring gear.

Thus, the output ring gear directly drives the rotatable housing. Optionally the rotatable housing is fixed to, or integral with, the output ring gear. In this way, the parts count is minimised and the efficient use of space is maximised.

The non-rotatable housing is preferably fixed to, or integral with, the fixed ring gear. This arrangement minimises parts count and maximises space-efficiency.

In preferred embodiments the rotatable housing has a largest dimension in a transverse direction of the actuator that is smaller than a largest dimension of the non-rotatable housing in the transverse direction. Thus, the non-rotatable housing can be mounted within a blind rail of a window blind such that the rotatable housing is free to rotate within the blind rail.

The actuator preferably comprises a bearing at an interface between the rotatable housing and non-rotatable housing. For example, the bearing may comprise a dry bearing providing a sliding interface between the rotatable and non-rotatable housings.

Similarly, the actuator preferably comprises axial retention means to restrict axial movement between the rotatable housing and non-rotatable housing. For example, the actuator may comprise snap-fit features configured to provide an engagement between the rotatable housing and non-rotatable housing that restricts such axial movement while enabling straightforward assembly of the rotatable and non-rotatable housings. Alternatively, the actuator may comprise an axially-extending pin with a shaft about which the rotating housing is able to rotate and a head that restricts axial movement of the rotating housing. The pin may be rotatable by the motor, for example it may be rotatable in tandem with an output of the motor or with the input sun gear.

In some embodiments the second stage of the compound planetary gearbox comprises a dummy sun gear in meshed engagement with the second plurality of planetary gears. The dummy sun gear is able to rotate freely, and thus not part of the gear train of the compound planetary gearbox. The dummy sun gear serves to maintain a consistent mesh between the second plurality of planet gears and the output ring gear, prevent 'skipping' of teeth, and improved the operating load of the gearbox.

Similarly, the first and/or second plurality of planet gears may be mounted on a dummy carrier. By maintaining the relative positions of axes of the first and/or second plurality of planet gears, respectively, the dummy carrier simplifies assembly of the gearbox, and reduces wobble (off-axis movement) of the first and/or second planet gears.

The compound planetary gearbox is preferably positioned between the motor and the coupling along an axial direction of the actuator. This linear arrangement minimises a radial and/or transverse dimension of the actuator, and maximises efficient use of space.

The actuator preferably comprises a communication link to enable remote operation of the motor. The communication link may be configured to provide a wireless or wired connection with a remote control device, for example.

The actuator preferably comprises one or more location features arranged to engage with corresponding location features of a window blind comprising the rotatable element. For example, the window blind location features may be provided on a blind rail of a window blind, or an actuator housing, such as a blind tube, configured to be located within a blind rail of a window blind. The location features of the actuator are preferably configured to engage with the corresponding location features of a window blind to prevent relative rotation therebetween, and optionally to permit relative axial movement during installation of the actuator.

The one or more location features preferably have a fixed position in relation to the fixed ring gear. In this way, engagement between the location features of the actuator and corresponding location features of a window blind prevents relative rotation between the fixed ring gear and the window blind location features.

The one or more location features are preferably located on the non-rotatable housing, for example on an outer face of the non-rotatable housing. The one or more location features optionally comprise elongate members extending in an axial direction of the actuator. This arrangement permits engagement by sliding of the actuator relative to e.g. a blind rail of the window blind.

A second aspect of the invention provides a blind rail for a window blind, the blind rail comprising an elongate shaft that is rotatable to raise and lower a window blind, and an actuator according to the first aspect wherein the coupling of the actuator is coupled with the elongate shaft to enable the actuator to drive the elongate shaft.

Wherein the blind rail comprises one or more location features engaging one or more location features of the actuator to thereby locate the actuator within the blind rail.

Wherein the one or more location features of the actuator are located on a non-rotating portion of the actuator.

Wherein the one or more location features of the blind rail and the actuator extend in an axial direction of the elongate shaft.

A third aspect of the invention provides a method of operating an actuator according to the first aspect, the method including the steps of: coupling the coupling of the actuator to a rotatable element of a window blind; and operating the motor to drive the input sun gear and thereby drive the rotatable element.

A fourth aspect of the invention provides a method of installing an actuator according to the first aspect in a blind rail for a window blind, the blind rail comprising a rotatable element for raising and lowering the window blind, the method including the steps of: installing the actuator within the blind rail; and coupling the coupling of the actuator to the rotatable element of the blind rail.

In preferred embodiments the method includes sliding the actuator along the blind rail until the coupling becomes coupled to the rotatable element.

The method may include an initial step of installing the actuator within an actuator housing, such as a rail tube, and the step of installing the actuator within the blind rail may include installing the actuator housing (with actuator therein) within the blind rail.

Throughout the description and claims of this specification, the words "comprise" and "contain" and variations of the words, for example "comprising" and "comprises", mean "including but not limited to", and do not exclude other components, integers or steps.

Moreover the singular encompasses the plural unless the context otherwise requires: in particular, where the indefinite article is used, the specification is to be understood as contemplating plurality as well as singularity, unless the context requires otherwise.

Preferred features of each aspect of the invention may be as described in connection with any of the other aspects. Within the scope of this application it is expressly intended that the various aspects, embodiments, examples and alternatives set out in the preceding paragraphs, in the claims and/or in the following description and drawings, and in particular the individual features thereof, may be taken independently or in any combination. That is, all embodiments and/or features of any embodiment can be combined in any way and/or combination, unless such features are incompatible.

BRIEF DESCRIPTION OF THE DRAWINGS

One or more embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figures 1A and 16 schematically illustrate examples of window blinds suitable for operation with an actuator according to the present invention; Figure 2 is an isometric view of an actuator according to a first embodiment of the invention; Figure 3 shows an exploded view of the actuator of Figure 2; Figure 4 is an axial cross-sectional view of an actuator according to a second embodiment of the invention; Figure 5 is an isometric partial section view of the actuator of Figure 4; Figure 6 shows an exploded partial section view of the actuator of Figures 4 and 5; Figure 7 schematically illustrates a first variant of a gearbox suitable for actuators according to the invention; Figure 8 schematically illustrates a second variant of a gearbox suitable for actuators according to the invention; Figure 9 schematically illustrates a general concept of a gearbox suitable for actuators according to the invention; Figure 10 provides a detail view of a portion of Figure 9; Figures 11 and 12 illustrate possible configurations of gearboxes suitable for actuators according to the invention; Figure 13 illustrates a rail tube sub-assembly including an actuator according to the invention, pre-assembly; Figure 14 illustrates the rail tube sub-assembly of Figure 13 after assembly; Figure 15 shows a typical blind rail and blind mechanism; and Figure 16 shows the rail tube sub-assembly of Figure 13 installed in the blind rail of Figure 15.

DETAILED DESCRIPTION

Introduction

The present invention is directed to actuators for lowering and raising window blinds. Example window blinds 10, 20 are schematically illustrated in Figures 1A and 1B. The blinds 10, 20 have in common a blind rail 12, 22 which houses a mechanism (not shown) for raising and lowering the blind 14, 24 itself. The mechanism typically includes an elongate shaft that is rotatable to effect movement of the blind 14, 24.

It is a key aim of the present invention to locate an actuator for remote raising and lowering of such blinds 10, 20 within the blind rail 12, 22. The dimensions of the actuator are therefore constrained by the transverse (or radial) and axial dimensions of the blind rail.

Figures 2 to 8 illustrate two embodiments of actuators 200, 300 according to the present invention. The actuator 200 of the first embodiment is illustrated in Figures 2 and 3, and the actuator 300 of the second embodiment is illustrated in Figures 4 to 6. The two embodiments have many features in common, and like components are referenced by the same reference numerals.

Each of the actuators 200, 300 includes a motor 210 that provides torque to a compound planetary gearbox 100, which in turn drives an output coupling 220 that, in use, is coupled with the elongate rotatable shaft 470 of the blind mechanism 460 (shown in Figures 15 and 16) to thereby drive that shaft.

Gearbox Concept Two variants of the gearbox 100 are illustrated schematically in Figures 7 and 8, respectively. The two gearboxes are identical, with the exception that the gearbox 100 of Figure 8 includes further 'dummy' components, as detailed further below. Either variant of the gearbox 100 can be incorporated into the actuator 200, 300 according to the first or second embodiments, respectively, or into any actuator embodying the present invention.

The general principle of the compound planetary gearbox 100 is illustrated in Figures 9 and 10, and described below. The gearbox 100 is based on a Wolfrom gear train.

The gearbox 100 includes an input sun gear 110 which meshes with a plurality (four in the illustrated example) of compound planets 120 which orbit around the input sun gear 110 as it rotates. Each compound planet 120 comprises a first planet gear 122 that meshes with a fixed ring gear 130, and a second planet gear 124 that meshes with a rotatable output ring gear 140. Each second planet gear 124 has a smaller effective diameter than its respective first planet gear 122, and similarly the rotating output ring gear 140 has a smaller effective diameter than the fixed ring gear 130.

The input sun gear 110 drives the planets 120 around the fixed ring gear 130. At the effective diameter, also referred to as the pitch diameter or the diameter of the pitch circle, the instantaneous speed of the point where each planet 120 (first planet gear 122) meshes with the fixed ring gear 130 is zero. This is shown in Figure 10 as the point Vpi. Similarly, the tangential speed of the point where each planet 120 (first planet gear 122) meshes with the sun gear 110 is Vs which is the tangential speed of the sun gear 110. From this analysis the theoretical carrier speed, Vc, (i.e. the speed of rotation of the axes of each of the planets 120 about the axis of the input sun gear 110) can be calculated to be Vs/2.

Since the output ring gear 140 is engaged to the second planet gear 124 of each compound planet 120, which has a slightly different effective diameter, the tangential velocity of the output ring gear 140, R2, is non-zero. The velocity is calculated according to Equation 1, where Dpi and Dp2 are the pitch diameters of the first 122 and second 124 planet gears, respectively. Equation 1 shows that the output velocity, VR2, approaches zero as DR1 approaches DP2.

Equation 1: Dp -Dp2 vs V = R2 2DP1 The full derivation of the gear ratio, R, is possible using Equation 1 and the constraint that both ring gears 130, 140 and each compound planet 120 must share the same Vc. The calculation steps are omitted but the final result is shown in Equation 2.

Equation 2: 2 NR2Npi(Npr+ Ns) Ns(Np1NR2-Np2Ns -2NpiNp2) where N number of teeth of: Ns sun gear N1 compound planet gear -input Np2 compound planet gear -output NR2 ring gear -output A very high ratio can be achieved by reducing the denominator factor in Equation 2, as shown in Equation 3.

Equation 3: R -> cio as NpiNR2 -N p2Ns -2Np, Np2 -> 0 Equation 4 is derived from the geometric constraints of the gearbox and must be satisfied to ensure the gears mesh correctly.

Equation 4: NRi = Ns + 2Npi Combining Equation 3 and Equation 4 yields Equation 5. Equation 5: R -> Co as Np1NR2 -Np2NR1-> 0 Turning to the variants illustrated in Figures 7 and 8, the gearbox 100 of the Figure 8 variant is generally identical to the gearbox 100 of the Figure 7 variant, with the addition of a dummy sun gear 150 and dummy carrier 160 for the compound planets 120.

The dummy sun gear 150 meshes with the second planet gears 124 of the compound planets 120 and is able to freely rotate about its axis such that it is not an active part of the gear train. The dummy sun gear 150 thus acts solely as a means to support the compound planets 120 in the radial direction, and in particular serves to maintain a meshed engagement between the second planet gears 124 and the rotating output ring gear 130.

Each of the compound planets 120 is mounted on the dummy carrier 160 such that the relative circumferential spacing of the compound planets 120 around the input sun gear 110 is maintained. The dummy carrier 160 thus rotates in tandem with the input sun gear 110 during operation of the gearbox 100. The dummy carrier 160 is not an active part of the gear train, but instead acts to support the compound planets 120 and maintain their relative positions.

Figures 11 and 12 illustrate example configurations for the various gear components of the gearbox 100 in an arrangement with four or five compound planets 120, respectively. In each of these arrangements it can be seen that the output ring gear 140 has a smaller effective diameter than the fixed ring gear 130. In addition, the output ring gear 140 has fewer teeth than the fixed ring gear 130; in the illustrated example, the output ring gear 140 has one less tooth than the fixed ring gear 130. This arrangement has the effect of requiring the first 122 and second 124 planet gears of each of the compound planets 120 to be angularly offset from one another by different amounts.

In gearboxes 100 according to the invention each of the components may be formed from metal or a plastics material, for example by moulding, machining or additive manufacture (3D printing). Each compound planet 120 may be formed as one unitary part, or the first planet gear 122 and second planet gear 124 can be formed separately and subsequently fastened together, for example by bonding with an adhesive.

First Embodiment The actuator 200 of the first embodiment, illustrated in Figures 2 and 3, comprises an electric motor 210 with an output shaft 212 that is coupled to the input sun gear 110 of the gearbox 100 such that the motor 210 directly drives the input sun gear 110. The gearbox 100 may be configured according to any of the variants described herein or their equivalents.

The gearbox 100 is enclosed within a housing that includes a non-rotating portion 170 and a rotating portion 180. The non-rotating portion 170 comprises a generally cylindrical tube portion, an inside face of which incorporates the fixed ring gear 130 of the gearbox 100 in the form of a ring of radially inwardly protruding teeth (not shown). The meshed input sun gear 110 and first planet gears 122 of the compound planets 120 of the gearbox are thus enclosed within the non-rotating housing 170.

An outer face of the generally cylindrical tube part of the non-rotating housing 170 carries a plurality of (four in the illustrated example) elongate location projections 172 that extend along an axial direction of the actuator 200. The location projections 172 are shaped to engage with corresponding elongate grooves in the blind rail of a window blind (or an actuator housing, such as a rail tube, located within the blind rail) to prevent rotation of the non-rotating housing 170 and motor 210 relative to the blind rail.

The rotating housing 180 comprises a generally cylindrical tube portion having a slightly smaller outer diameter than that of the non-rotating housing 170. In this way, the rotating housing 180 is able to rotate within the blind rail of a window blind without fouling, when the non-rotating housing 170 is located within the blind rail as described above. An interface between the rotating housing 180 and non-rotating housing 170, for example a dry bearing or other bearing, permits relative rotation therebetween.

An inside face of the generally cylindrical tube portion incorporates the output ring gear 140 of the gearbox 100 in the form of a ring of radially inwardly protruding teeth (not shown).

The second planet gears 124 of the compound planets 120, and optionally the dummy sun gear 150, are thus enclosed within the rotating housing 180, the first planet gears 122 protruding beyond an open end face of the cylindrical tube portion.

The rotating housing 180 has a substantially closed end face opposite to the open end face, the closed end face including a generally square-shaped aperture forming the output coupling 220 that, in use, is coupled with the elongate rotatable shaft 470 of the blind mechanism 460. Thus, as the output ring gear 140 is driven in rotation, the coupling 220 is rotated.

In this embodiment the non-rotating housing 170 is coupled to the rotating housing 180 via a plurality of snap fit connections, each snap fit connection comprising a radially-inwardly protruding member provided on a respective one of a plurality of axially-extending fingers 174 formed in the non-rotating housing 170. Each finger 174 is in the form of a cantilever such that it is able to flex in the radial direction as the non-rotating portion 170 is slid over the rotating portion 180, thus allowing the snap fit connections to engage a circumferential groove, step or shoulder of the rotating housing 180.

This arrangement provides a quick and straightforward assembly method, resulting in a coupling that prevents relative axial movement of the non-rotating 170 and rotating 180 housings but permits relative rotational movement via the dry bearing or other rotation-permitting interface as described above.

Second Embodiment The actuator 300 of the second embodiment, illustrated in Figures 4 to 6, has many features in common with the actuator 200 of the first embodiment. Like features are indicated by like reference numerals.

The actuator 200 comprises an electric motor 210 with an output shaft 212 that is coupled to the input sun gear 110 of the gearbox 100 such that the motor 210 directly drives the input sun gear 110. The gearbox 100 may be configured according to any of the variants described herein or their equivalents.

An outer face of the generally cylindrical tube part of the non-rotating housing 170 carries a plurality of (four in the illustrated example) elongate location projections 172 that extend along an axial direction of the actuator 200. The location projections 172 are shaped to engage with corresponding elongate grooves in the blind rail of a window blind (or an actuator housing, such as a blind tube, located within the blind rail) to prevent rotation of the non-rotating housing 170 and motor 210 relative to the blind rail.

The rotating housing 180 has a substantially closed end face opposite to the open end face, the closed end face including a generally square-shaped aperture forming the output coupling 220 that, in use, is coupled with the elongate rotatable shaft of the blind mechanism. Thus, as the output ring gear 140 is driven in rotation, the coupling 220 is rotated.

In this embodiment the non-rotating housing 170 is coupled to the rotating housing 180 via an axially-extending rotating pin 176 that is attached to the motor output 212 or input sun gear 110. The rotating housing 180 is able to rotate about the shaft 177 of the pin 176, while the head 178 of the pin 176 prevents relative axial movement between the non-rotating 170 and rotating 180 housings via the dry bearing or other rotation-permitting interface as described above.

Installation in Blind Rail In some embodiments the actuator 200, 300 is initially installed inside an actuator housing, which in the illustrated embodiments takes the form of a rail tube 400, as shown in Figures 13 and 14. This arrangement facilitates straightforward assembly of the actuator within a blind rail 450 of a window blind, as illustrated in Figure 16.

The actuator 200, 300 is first inserted into the rail tube 400 via a sliding fit so that the elongate locating projections 172 engage the corresponding grooves 430 of the rail tube 400. Thus, relative rotation between the non-rotating housing 170 (and the motor 210) and the rail tube 400 is prevented.

First 410 and second 420 end caps are fitted at either end of the rail tube 400. The first end cap 410 extends over the rotating housing 180 so that the rotating housing 180 is not engaged by the first end cap 410 and thus is not prevented from rotating. The first end cap 410 has an opening in an end face thereof to permit the rotatable shaft of the window blind mechanism to pass therethrough. The second end cap 420 similarly has an opening for power cables 214 supplying the motor 210 to pass therethrough. The first 410 and second 420 end caps each have outer sealing portions formed from an elastomeric material to provide a sealing engagement with the rail tube 400. The end caps 410, 420 serve to maintain a desired axial position of the actuator 200, 300 within the rail tube 400. Alternatively, or in addition, a pin or other fastener (not shown) may be installed to prevent axial movement of the actuator within the rail tube.

Figure 14 shows the actuator 200, 300 installed within the rail tube 400 to form a rail tube sub-assembly 440, and ready to be installed in the blind rail 450.

Figure 15 illustrates an example blind rail 450 with operating mechanism 460 installed therein. The operating mechanism 460 includes an elongate shaft 470 that is rotatable to raise or lower a window blind (not shown). In the final assembly step, the rail tube sub-assembly 440 is slid along the blind rail 450 until the elongate shaft 470 is coupled with the coupling 220 of the actuator 200, 300, as shown in Figure 16. An end cap (not shown) may be installed at the open end of the blind rail 450 to prevent post-installation axial movement of the rail tube-sub-assembly 440 and/or actuator 200, 300. Alternatively, or in addition, a pin or other fastener (not shown) may be installed to prevent axial movement of the rail tube-sub-assembly 440 and/or actuator 200, 300 within the blind rail 450.

In other embodiments the rail tube 400 may be omitted, and the actuator 200, 300 may instead be installed directly into the blind rail 450, with the locating projections 172 of the actuator engaging corresponding grooves of the blind rail 450.

Claims

CLAIMS1. An actuator for driving a rotatable element of a window blind to raise and lower the window blind, the actuator including: a motor; and a compound planetary gearbox including: a first stage comprising an input sun gear, a first plurality of planet gears in meshed engagement with the input sun gear, and a fixed ring gear in meshed engagement with the first plurality of planet gears, wherein the motor is connected to the input sun gear to thereby be capable of directly driving the input sun gear; and a second stage comprising a second plurality of planet gears, and an output ring gear in meshed engagement with the second plurality of planet gears, wherein each of the second plurality of planet gears is rotatable in tandem with a respective one of the first plurality of planet gears; and a coupling rotatable in tandem with the output ring gear, the coupling being configured to be coupled with a rotatable element of a window blind to thereby drive the rotatable element.
2. An actuator according to claim 1, wherein the first plurality of planet gears each have a different effective diameter to the second plurality of planet gears, optionally wherein the second plurality of planet gears each have a smaller effective diameter than the first plurality of planet gears.
3. An actuator according to claim 1 or claim 2, wherein the fixed ring gear has a different effective diameter to the output ring gear, optionally wherein the output ring gear has a smaller effective diameter than the fixed ring gear.
4. An actuator according to any preceding claim, wherein the fixed ring gear is unable to rotate relative to the motor.
5. An actuator according to any preceding claim, comprising a non-rotatable housing and a rotatable housing, the rotatable housing including the coupling.
6. An actuator according to claim 5, wherein the coupling comprises an aperture in the rotatable housing that is configured to receive the rotatable element to permit transfer of torque from the coupling to the rotatable element.
7. An actuator according to claim 5 or claim 6, wherein the rotatable housing is configured to rotate in tandem with the output ring gear, optionally wherein the rotatable housing is fixed to, or integral with, the output ring gear.
8. An actuator according to any of claims 5 to 7, wherein the non-rotatable housing is fixed to, or integral with, the fixed ring gear.
9. An actuator according to any of claims 5 to 8, wherein the rotatable housing has a largest dimension in a transverse direction of the actuator that is smaller than a largest dimension of the non-rotatable housing in the transverse direction.
10. An actuator according to any of claims 5 to 9, comprising a bearing at an interface between the rotatable housing and non-rotatable housing.
11. An actuator according to any of claims 5 to 10, comprising axial retention means to restrict axial movement between the rotatable housing and non-rotatable housing.
12. An actuator according to any preceding claim, wherein the second stage of the compound planetary gearbox comprises a dummy sun gear in meshed engagement with the second plurality of planetary gears.
13. An actuator according to any preceding claim, wherein the first and/or second plurality of planet gears are mounted on a dummy carrier arranged to maintain a relative position of axes of the first and/or second plurality of planet gears, respectively.
14. An actuator according to any preceding claim, wherein the compound planetary gearbox is positioned between the motor and the coupling along an axial direction of the actuator.
15. An actuator according to any preceding claim, wherein the actuator comprises a communication link to enable remote operation of the motor.
16. An actuator according to any preceding claim, wherein the actuator comprises one or more location features arranged to engage with corresponding location features of a window blind comprising the rotatable element.
17. An actuator according to claim 16, wherein the one or more location features have a fixed position in relation to the fixed ring gear.
18. An actuator according to claim 16 or claim 17 and any of claims 5 to 11, wherein the one or more location features are located on the non-rotatable housing.
19. An actuator according to any of claims 16 to 18, wherein the one or more location features comprise elongate members extending in an axial direction of the actuator.
20, A blind rail for a window blind, the blind rail comprising an elongate shaft that is rotatable to raise and lower a window blind, and an actuator according to any preceding claim wherein the coupling of the actuator is coupled with the elongate shaft to enable the actuator to drive the elongate shaft.
21, A blind rail according to claim 20, wherein the blind rail comprises one or more location features engaging one or more location features of the actuator to thereby locate the actuator within the blind rail.
22. A blind rail according to claim 21, wherein the one or more location features of the actuator are located on a non-rotating portion of the actuator.
23. A blind rail according to claim 21 or claim 22, wherein the one or more location features of the blind rail and the actuator extend in an axial direction of the elongate shaft.