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(11) | EP 1 327 744 A1 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | Roller blind device with centrifugal brake |
| (57) A roller blind device comprising a centrifugal brake (20) which includes an overgear
device having a supporting element (42) that carries speed-increasing gears (44) which
co-operate with an output member (38) of the overgear device (40). The output member
(38) carries one or more centrifugal weights (28) designed to co-operate in a sliding-friction
relationship with a cylindrical braking surface (26). The aforesaid supporting element
(42) for supporting the overgear device (40) is connected to a stationary shaft (14)
with interposition of a torque-limiting device (58). |
[0002] Typically, a roller blind device comprises a stationary supporting shaft, a roller onto which the blind is designed to be wound and which is mounted in such a way that it can turn about the stationary supporting shaft, and a return spring which tends to cause the roller to rotate in the direction of winding of the blind. When the user lowers the blind manually, the roller loads the spring with elastic energy, which is used during the re-winding stage in order to cause the roller to rotate automatically in the direction of winding of the blind onto the roller itself. Generally, it is necessary for the spring for return of the roller to have a certain initial pre-loading, so as to obtain complete re-winding of the blind onto the roller even if the blind has been lowered just a few centimetres (for example, 30 cm) with respect to the condition of complete winding. In roller blind devices, the elastic return element generally consists of a helical spring set coaxially between the roller and the supporting shaft. At each complete revolution of the roller about its own axis there corresponds a turn of winding of the helical spring. Normally, the pre-loading of the spring necessary for guaranteeing complete re-winding of the blind onto the roller in every condition may be in the region of 8-15 complete turns of the spring. In addition to the said pre-loading, during operation the spring is loaded with a number of turns equal to the number of revolutions of the roller necessary for obtaining complete lowering of the blind. Consequently, the elastic energy that accumulates in the recall spring can reach considerably high values, corresponding, for example, to 25-30 turns of rotation of the spring. When the roller blind is released in the completely lowered position, the roller is subjected to a return torque having a very high value, which tends to cause it to accelerate violently. In order to prevent the problems deriving from an excessive acceleration of the roller during the return step, roller blind devices incorporating a centrifugal brake that slows down rising of the blind have already been proposed.
[0003] The present applicant has, however, noted that the centrifugal brakes of roller blind devices are subject to a high risk of failure, in particular in the cases where the installer of the blind imparts an excessive pre-load on the roller-return spring, or else selects an excessively rigid spring as compared to the weight of the blind. In fact, before the centrifugal brake is able to enter into action for slowing down rising of the roller, the static torque which is exerted upon the roller at the moment of disengagement of the blind produces a very high stress on the components of the centrifugal brake.
[0004] The purpose of the present invention is to provide an improved roller blind device that will overcome the aforesaid drawback.
[0005] According to the present invention, the above purpose is achieved by a device having the characteristics that form the subject of the main claim.
[0006] The characteristics and advantages of the present invention will emerge clearly from the ensuing detailed description, provided merely by way of non-limiting example, with reference to the attached drawings, in which:
- Figure 1 is a schematic perspective view of a roller blind provided with a device according to the present invention;
- Figure 2 is an exploded perspective view of the part indicated by the arrow II in Figure 1;
- Figure 3 is a partially sectioned side view of the part indicated by the arrow III in Figure 2;
- Figure 4 is a cross section according to the line IV-IV of Figure 3; and
- Figure 5 is an exploded perspective view of the part indicated by the arrow V in Figure 2.
[0007] With reference to Figures 1 and 2, number 10 designates a roller blind device comprising a pair of supports 12 which carry a stationary supporting shaft 14, around which a roller 16 is mounted so that it can turn, a blind 18 being wound on the roller 16. The roller blind device 10 comprises a return spring set coaxially between the stationary supporting shaft 14 and the roller 16, as well as an arrest device designed to withhold the roller against the action or return of the spring in a generic lowered position of the roller blind 18 chosen by the user. The structure and function of the spring return device and of the arrest device are not described in detail in so far as they do not fall within the scope of the present application and are well known to a person skilled in the sector.
[0008] With reference to Figures 2 and 3, the roller blind device 10 comprises a centrifugal brake, designated as a whole by 20. The centrifugal brake 20 comprises a cylindrical body 22 inserted inside the roller 16 and fixed in rotation to the latter. The centrifugal brake 20 comprises an annular element 24 which is fixed with respect to the body 22 and has an internal cylindrical braking surface 26. Two or more centrifugal weights 28 are mounted so that they can turn inside the surface 26 and are set in such a way that, by the centrifugal effect, they are pressed against the surface 26, thus providing a braking contact. Preferably, the centrifugal weights 28 are provided with brake pads 30. In the embodiment illustrated in the figures, the annular element 24 is made as a component separate from the body 22 in so far as it is preferably made of a material having higher characteristics of wear resistance as compared to the material forming the body 22. For example, the body 22 may be made of a plastic material, whereas the annular element 24 may be made of brass. In a variant of the present invention, the annular element 24 could be eliminated, and in this case the centrifugal weights 28 would co-operate with a braking surface formed integrally with the body 22. In the embodiment illustrated by way of example in the figures, the annular element 24 is housed in a cover 32 fixed to the body 22 by means of screws 34. The centrifugal weights 28 are mounted in an oscillating way about respective pins 36 carried by a disk-shaped element 38 that constitutes the output member of an overgear device of a planetary-gear type, designated as a whole by 40. The overgear device 40 comprises a supporting element 42 which carries, in such a way that they can rotate freely, a plurality of planetary gears 44 which mesh with an internal toothing 46 of the body 22. The planetary gears 44 moreover mesh with a ring gear 48 which is fixed with respect to the element 38 that carries the centrifugal weights 28. The overgear mechanism 40 is represented in a simplified way, with a single speed-increasing stage of a planetary-gear type. In order to augment the speed-increasing ratio, the overgear mechanism 40 could be provided with two or more speed-increasing stages of planetary-gear type cascaded together.
[0009] The supporting element 42 of the overgear device 40 co-operates with a unidirectional-transmission device 48, which comprises a helical spring 50 set coaxially outside a cylindrical portion 52 of the supporting element 42. A tubular sleeve 54 has a cylindrical seat 56 which surrounds the helical spring 50 externally. One end 58 of the spring 50 is inserted inside a slit 60 of the sleeve 54. The purpose of the unidirectional-actuation device 48 is to prevent the centrifugal brake from going into action when the roller 16 rotates in the direction for lowering of the blind.
[0010] The roller blind device according to the present invention moreover comprises a torque-limiting device 58 which has the purpose of limiting the torque transmitted to the centrifugal brake 20. In the embodiment illustrated in the figures, the torque-limiting device 58 comprises a stationary member 60 fixed to one end of the stationary supporting shaft 16. Preferably, the stationary member 60 has a square-section hole 62, which engages, in such a way that it cannot turn, the stationary supporting shaft 14, which also has a square cross section. For retention in the axial direction of the stationary member 60 on the shaft 14, also an omega-shaped retention clip 64 may be provided. As may be seen in particular in Figure 4, the stationary member 60 of the torque-limiting device 58 comprises a plurality of arms 66 which are elastically deformable in the radial direction. Preferably, the stationary member 60 consists of a monolithic body made of injection-moulded plastic material, and the arms 66 extend in cantilever fashion in the tangential direction. A free space 68 is provided in a position corresponding to each arm 66 in order to enable the arm to deform elastically in a radial direction inwards. The elastically deformable arms 66 of the stationary member 60 co-operate with an internal toothing 70 formed on an internal cylindrical surface of the sleeve 54. Preferably, the arms 66 have substantially hook-shaped ends 72 that form seats, within which respective pins 74 that co-operate with the toothing 70 are housed. The radial elasticity of the arms 66 and the degree of interference between the arms 66 and the toothing 70 are determined in such a way as to obtain a pre-set torque for entry into action of the device 58. When the torque that tends to cause the sleeve 54 to rotate with respect to the stationary member 60 is lower than the pre-set torque level, the sleeve 54 remains fixed to the stationary sleeve 60. When, instead, the sleeve 54 receives a torque about its own axis that exceeds the value of the torque for entry into action of the torque-limiting device 58, the sleeve 54 rotates about its own axis with respect to the stationary member 60. During this movement of rotation, the torque-limiting device 58 operates like a sliding-friction clutch which dissipates a certain amount of energy, performing a braking action which opposes the torque that tends to cause the sleeve 54 to rotate with respect to the stationary member 60. The sleeve 54 is free to rotate about its own axis with respect to the body 22 and is withheld axially with respect to the body 22 by a cover 72 fixed to the body 22.
[0011] Operation of the device according to the present invention is described in what follows. When the user lowers the blind manually, the roller 16 turns in a first direction around the stationary shaft 14. The body 22 of the centrifugal brake 20 rotates together with the roller 16 and draws in rotation the planetary gears 44 of the overgear device 40. The planetary gears 44 apply a torque that tends to cause the supporting element 42 of the overgear device 40 to rotate in the aforesaid first direction. The unidirectional-actuation device 48 is set in such a way as to leave the supporting element 42 free to rotate with respect to the sleeve 54 in the first direction. In this way, the overgear device 40 is "idle" and does not increase the speed of the output member 38. The result of the foregoing is that, during lowering of the blind, the centrifugal weights 28 do not exert a braking action.
[0012] When the user releases the blind from the lowered position, the roller 16 rotates under the action of return of the spring (not illustrated) in a second direction, namely in the direction of winding of the blind onto the roller. The body 22 imparts a rotation on the planetary gears 44 in the second direction. The planetary gears 44 tend to cause the supporting element 42 to rotate in the second direction. In this case, the unidirectional-transmission device 48 goes into action and blocks the supporting element 42 with respect to the sleeve 54. The supporting element 42 is thus stationary. In this condition, the overgear device 40 performs an increase of the speed of rotation of the output member 38 with respect to the speed of rotation of the body 22. The centrifugal weights 28 are then driven in rotation by the output member 38 and move outwards against the internal surface 26 of the annular element 24, thus performing a braking action. The reaction torque necessary for keeping the supporting element 41 in a stationary position passes through the torque-limiting device 58. If the said torque exceeds the limit for entry into action of the torque-limiting device 58, the sleeve 54 rotates in the second direction, producing a dissipation of energy as a result of the relative movement of the toothing 70 with respect to the elastically deformable teeth 66. If the sleeve 54 rotates in the second direction, the overgear 40 is idle and does not perform any speed increase. In this way, an excessive torque of return of the roller 16 in the winding direction is prevented, which could produce excessive stress on the centrifugal brake. Entry into action of the torque-limiting device 58 has an energetic braking action and rapidly reduces the value of the return torque. As soon as the torque drops below the limit for entry into action of the torque-limiting device 58, the overgear 40 enters into operation, and braking of the roller 16 is performed by the centrifugal weights 28.
[0013] Of course, without prejudice to the principle of the invention, the details of construction and the embodiments may vary widely with respect to what is described and illustrated herein, without thereby departing from the scope of the present invention as defined in the ensuing claims.
[0014] In particular, it is understood that the torque-limiting device 58 could be implemented in different ways, without prejudice to the fact of providing a device which keeps an element fixed to the shaft 14 if the torque that acts on the said element is lower than a pre-set limit and which enables freedom of movement of said element when the torque acting thereon exceeds the pre-set limit value.
1. A roller blind device comprising a centrifugal brake (20) which includes an overgear
device having a supporting element (42) that carries speed-increasing gears (44) which
co-operate with an output member (38) of the overgear device (40), said output member
(38) carrying one or more centrifugal weights (28) designed to co-operate in a sliding-friction
relationship with a cylindrical braking surface (26), characterized in that the aforesaid supporting element (42) for supporting the overgear device (40) is
connected to a stationary shaft (14) with interposition of a torque-limiting device
(58).
2. The device according to Claim 1, characterized in that the aforesaid supporting element (42) of the overgear device (40) is moreover associated
to a unidirectional-actuation device (50).
3. The device according to Claim 2, characterized in that the torque-limiting device (58) comprises a stationary member (60) and a sleeve (54)
which is able to rotate with respect to the stationary member (60) when it is subjected
to a torque higher than a pre-set limit.
4. The device according to Claim 3, characterized in that the aforesaid stationary element (60) and the aforesaid sleeve (54) co-operate together
by means of elastically deformable arms (66), carried by one between said stationary
member (60) and said sleeve (54), and a toothing (70), carried by the other between
said stationary member (60) and said sleeve (54).
5. The device according to Claim 4, characterized in that the aforesaid unidirectional-actuation device (48) comprises a helical spring (54)
set coaxially between a cylindrical portion (52) of the aforesaid supporting element
(42) of the overgear mechanism (40) and a cylindrical surface (56) of the aforesaid
sleeve (54) of the torque-limiting device (58).
6. The device according to Claim 1, characterized in that the aforesaid overgear mechanism (40) comprises one or more speed-increasing stages
of a planetary-gear type, each of which carries a gear-train carrier (42) and a plurality
of planetary gears (44) which mesh with an internal toothing (46) of a body (22) fixed
to the roller (16).
7. The device according to Claim 6, characterized in that the aforesaid supporting element (42) of the overgear mechanism (40) constitutes
a gear-train carrier of an speed-increasing stage of a planetary-gear type.