I. Field of the Invention The present invention relates generally to motorized window coverings, awnings, security screens, projection screens, and the like.

II. Background of the Invention The present assignee has provided several systems for either lowering or raising a window covering, or for moving the slats of a window covering between open and closed positions, under control of a hand-held remote or other control device. These systems include a motor that is coupled through gears to the window covering activation mechanism. When the motor is energized in response to a user command signal, the activation mechanism moves the window covering. Such assemblies are disclosed in U.S. Patent No. 6,433,498, incorporated herein by reference.

The present assignee has also provided systems for determining the position of the window coverings based on counting motor pulses, and for braking the motor from turning when it is not energized. By knowing the position of the window coverings, features such as automatic repositioning the window covering to a preset position can be provided. The present invention likewise provides structure and methods for braking an object in the absence of power while minimizing the effects of the brake during motor operation.

In the parent application, one or more permanent magnets are disclosed that are juxtaposed with the rotor to generate a magnetic field which interferes with the rotor slots and thereby creates an extra reluctance torque on the motor shaft. The extra reluctance torque establishes a static brake, to hold the rotor from undesirably turning under the weight of the window covering when the motor is deenergized. It has been noticed that the braking magnetic field has a negative effect on the electromagnetic operating of the motor.

The aim of the invention is to provide a powered assembly that allows the aforementioned drawbacks to be overcome and that provides an improvement with respect to the known assemblies of the state of the art. In particular, the invention allows a powered assembly in which the negative effect on the electromagnetic operating of the motor is minimized. The invention also relates to a method for operating an object.

SUMMARY OF THE INVENTION A powered assembly includes an object that can be moved between a first configuration and a second configuration. The object may be selected from the group consisting of window coverings, awnings, skylight coverings, curtains, and screens. A motor is provided, and an actuator is coupled to the motor and the object to move the object when the motor is energized. First and second magnets are juxtaposed with the rotating member and are magnetically coupled thereto. The first magnet is oriented with its north pole toward the rotating member and the second magnet is oriented with its south pole toward the rotating member.

Various embodiments of the powered assembly are defined by dependent claims 2 to 11.

In still another aspect, a method for operating an object that can be moved between a first configuration and a second configuration, with the object being selected from the group consisting of window coverings, awnings, skylight coverings, curtains, and screens, includes providing a drive structure and coupling the drive structure to the object such that the object is moved when the drive structure is energized. The method also includes closely juxtaposing at least first and second magnets with the drive structure. Using the magnets, the drive structure is braked when the drive structure is not energized. On the other hand, the magnets are oriented such that when the drive structure is energized, the average magnetic field within the drive structure is at a null. That is, when the motor is energized, little or no back electromotive force (emf) is created because the effect of the field created by the braking magnets on the rotor during operation has a null average value.

Various embodiments of the method are defined by dependent claims 13 to 15.

The details of the present invention, both as to its construction and operation, can best be understood in reference to the accompanying drawings, in which like numerals refer to like parts, and which:

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a perspective view of a window covering actuator, shown in one intended environment, with portions of the head rail cut away; Figure 2 is a perspective view of a first embodiment of the motor showing disk-shaped braking magnets; Figure 3 is a perspective view of a second embodiment of the motor showing parallelepiped shaped braking magnets; Figure 4 is a perspective view of a third embodiment of the motor showing braking magnets in shallow recesses that have been formed in the housing of the motor; and Figure 5 is a perspective view of a fourth embodiment of the motor showing braking magnets and a magnetic concentrator.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring initially to Figure 1 , a motorized window covering is shown, generally designated 10, that includes an actuator such as a rotatable rod 12 of a window covering 14, such as but not limited to a shade assembly having raisable (by rolling up) - A - and lowerable (by rolling down, or unrolling) shade 16. As shown, the tilt rod 12 is rotatably mounted by means of a block 18 in a head rail 20 of the window covering 14.

While a roll-up shade is shown, it is to be understood that the principles herein apply to a wide range of window coverings and other objects that are to be moved by motors. For example, the invention applies to raisable and lowerable pleated shades and cellular shades as well as to projector screens, awnings, etc. that can be raised and lowered. Moreover, while needed less in applications that require only tilting slats such as in horizontal blinds, the invention may also apply to these systems. Thus, for example, the rod 12 may be a roll-up rod of a shade, awning, or projector screen, or a tilt rod of a horizontal (or vertical) blind, or other like operator. It is thus to be further understood that the principles of the present invention apply to a wide range of window coverings and other objects including, but not limited to the following: vertical blinds, fold-up pleated shades, roll-up shades, cellular shades, skylight covers, etc. Powered versions of such shades are disclosed in U.S. Patent No. 6,433,498, incorporated herein by reference.

In the non-limiting illustrative embodiment shown, the window covering 14 is mounted on a window frame 22 to cover a window 24, and the rod 12 is rotatable about its longitudinal axis. The rod 12 can engage a user-manipulable baton (not shown). When the rod 12 is rotated about its longitudinal axis, the shade 16 raises or lowers between an open configuration and a closed configuration.

Figure 1 shows that the motorized window covering 10 can include a control signal receiver, preferably a signal sensor 26, for receiving a user command signal. Preferably, the user command signal is generated by a hand-held user command signal generator 28, which can be an infrared (IR) remote-control unit or a radio frequency (RF) remote-control unit. Or, the user command signal may be generated by any other means of communication well known in the art, such as by manipulable manual switches 29. The user command signals can include open, close, raise, lower, and so on.

An electronic circuit board 30 can be positioned in the head rail 20 and can be fastened to the head rail 20, e.g., by screws (not shown) or other well-known method. The preferred electronic circuit board 30 includes a microprocessor for processing the control signals.

Figure 1 shows that a small, lightweight electric motor 32 is coupled to a gear enclosure 34, preferably by bolting the motor 32 to the gear enclosure 34. The gear enclosure 34 is keyed to the rod 12, so that as the gears in the gear enclosure 34 turn, the rod 12 rotates.

It is to be understood that the motor 32 is electrically connected to the circuit board 30. To power the motor 32, one or more (four shown in Figure 1) primary dc batteries 36, such as type AA alkaline batteries or Lithium batteries, can be mounted in the head rail 20 and connected to the circuit board 30. Preferably, the batteries 36 are the sole source of power for the motor, although the present invention can also be applied to powered shades and other objects that are energized from the public ac power grid.

As set forth in the above-referenced U.S. Patent, a user can manipulate the signal generator 28 to generate a signal that is sensed by the signal sensor 26 and sent to signal processing circuitry in the circuit board 30. In turn, the electrical path between the batteries 34 and the motor 32 is closed to energize the motor 32 and move the window covering open or closed in accordance with the signal generated by the signal generator 28, under control of the processor on the electronic circuit board 30. When the motor is deenergized, the braking magnets disclosed below advantageously brake the motor from turning under the weight of the window covering 14. Now referring to Figure 2, in one non-limiting implementation the motor 32 includes a motor housing 42 inside of which a rotor 44 may rotate. Only the shaft of the rotor is shown on the figure as such rotors are well known by the man skilled in the art. The rotor 44 may have, e.g., three poles. First and second permanent braking magnets 46, 48 are closely juxtaposed with the motor. The non-limiting magnets are disk-shaped with opposing magnetic poles for each magnet being established by the flat faces of the disk. Preferably, the magnets 46, 48 are attached to the housing 42 on a flat portion thereof by, e.g., solvent bonding the magnets to the housing 42, with the magnets being positioned side by side each other.

In accordance with present principles, the first magnet 46 is oriented with its south pole "S" against the housing 42 and, hence, facing the rotor 44, while the second magnet 48 is oriented with its north pole "N" against the housing 42. Stated differently, the north pole "N" of the magnet 48 is substantially co-planar with the south pole "S" of the magnet 46.

With this structure, the magnets 46, 48 are magnetically coupled to the rotor 44 sufficiently to stop it from rotating when the motor 32 is deenergized. However, when the motor 32 is energized, the average magnetic field effect on the rotor generated by the magnets 46, 48 is at a null, thereby causing little or no drag on the rotor 44 as it rotates.

Figure 3 shows an alternate embodiment having a motor 50 on which is mounted braking magnets 52 with opposed polarities as shown. The braking magnets 52 shown in Figure 3 can be parallelepiped shaped.

Figure 4 shows another alternate embodiment having a motor 54 on which is mounted braking magnets 56 with opposed polarities as shown. The braking magnets 56 shown in Figure 4 can be disk shaped as shown or they can have other shapes (e.g., they can be parallelepiped shaped.) In any case, shallow recesses 58 that are preferably configured to match the contours of the braking magnets 56 are formed in the housing of the motor (but not through the case). With this structure, the distance between the magnets 56 and the core of the motor is shortened and, hence, the braking force of the magnets on the motor strengthened.

Figure 5 shows yet another alternate embodiment having a motor 60 on which is mounted braking magnets 62 with opposed polarities as shown. The braking magnets 62 shown in Figure 5 can be disk shaped as shown or they can have other shapes (e.g., they can be parallelepiped shaped.) In any case, a magnetic concentrator 64, such as an elongated ferromagnetic bar, can be placed on top of the braking magnets 62 to sandwich the magnets 62 between the concentrator 64 and motor 60 and thereby close the magnetic field beyond the braking magnets opposite the motor 60. This serves to strengthen the magnetic braking field inside the motor, permitting the use of smaller magnets if desired. The concentrator 64 can have rounded ends as shown to match the contours of the braking magnets 62 in the event that the braking magnets 62 are disk shaped. The length of the non-limiting concentrator can equal the diameters of the braking magnets plus the distance between the braking magnets as shown.

The concentrator is a flux guide made from soft ferromagnetic material. When a very efficient concentrator is used, a soft iron part may replace one of the braking magnets also. Only one permanent magnet will create the braking flux (for instance with a North pole oriented towards the rotor) but all this flux will circulate in the rotor and leave the rotor to enter in the soft iron part exactly as it would enter in the South pole of a permanent magnet.