Abstract:
Two braking magnets are attached to the housing of a motor of a motorized component such as a window covering, with one magnet north face down and the other magnet south face down. With this structure the motor is braked from turning under the weight of the window covering when deenergized, while during operation the average null value of the braking field results in minimal drag on the motor.

Description:
RELATED APPLICATIONS 
   This is a continuation-in-part of U.S. patent application Ser. No. 10/445,149, filed on May 23, 2003 now U.S. Pat. No. 6,794,778 titled “Braking System for Powered Window Covering” and co-pending U.S. patent application Ser. No. 10/786,351, filed Feb. 25, 2004 titled “Piezo-Based Encoder with Magnetic Brake for Powered Window Covering” from which priority is claimed and which are incorporated herein by reference. 

   FIELD OF THE INVENTION 
   The present invention relates generally to motorized window coverings, awnings, security screens, projection screens, and the like. 
   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. Pat. 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. 
   While effective, the present invention recognizes that even though the braking field does not unduly affect motor operation when the motor is energized, it is possible to even further reduce brake drag on the motor when it is operating. 
   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. 
   The magnets can be disk-shaped and can be mounted on a housing of the motor side by side each other on the housing. DC batteries can be the sole source of power for the motor. Or, the braking magnets may be parallelepiped shaped. Shallow recesses may be formed in the housing of the motor in which the braking magnets can be disposed to shorten the distance between the magnets and the motor core and, hence, strengthen the braking power of the magnets. In addition, a concentrator bar can be placed over the top of the braking magnets to close the magnetic field outside the motor and, hence, to concentrate the braking field within the motor. 
   In another aspect, a drive assembly for a movable object including a rod includes an electrically-powered drive structure couplable to the rod to move the object when the drive structure is energized. The drive structure has a rotating member. First and second braking magnets are closely spaced from the rotating member and are oriented with the north pole of the first magnet being substantially co-planar with the south pole of the second magnet. 
   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. 
   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 
       FIG. 1  is a perspective view of a window covering actuator, shown in one intended environment, with portions of the head rail cut away; 
       FIG. 2  is a perspective view of a first embodiment of the motor showing disk-shaped braking magnets; 
       FIG. 3  is a perspective view of a second embodiment of the motor showing parallelepiped shaped braking magnets; 
       FIG. 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 
       FIG. 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  FIG. 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) 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 such as those commonly marketed under the trade names “Silhouette”, “Shangri-La”, etc. 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. Pat. 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. 
     FIG. 1  shows that the actuator  10  can include a control signal generator, 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. 
     FIG. 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  FIG. 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  FIG. 2 , in one non-limiting implementation the motor  32  includes a motor housing  42  inside of which a rotor  44  may rotate. 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. 
     FIG. 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  FIG. 3  can be parallelepiped shaped. 
     FIG. 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  FIG. 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. 
     FIG. 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  FIG. 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. 
   While the particular MAGNETIC BRAKE FOR POWERED WINDOW COVERING as herein shown and described in detail is fully capable of attaining the above-described aspects of the invention, it is to be understood that it is the presently preferred embodiment of the present invention and thus, is representative of the subject matter which is broadly contemplated by the present invention, that the scope of the present invention fully encompasses other embodiments which may become obvious to those skilled in the art, and that the scope of the present invention is accordingly to be limited by nothing other than the appended claims, in which reference to an element in the singular is not intended to mean “one and only one” unless explicitly so stated, but rather “one or more.” All structural and functional equivalents to the elements of the above-described preferred embodiment that are known or later come to be known to those of ordinary skill in the art are expressly incorporated herein by reference and are intended to be encompassed by the present claims. Moreover, it is not necessary for a device or method to address each and every problem sought to be solved by the present invention, for it is to be encompassed by the present claims. Furthermore, no element, component, or method step in the present disclosure is intended to be dedicated to the public regardless of whether the element, component, or method step is explicitly recited in the claims. No claim element herein is to be construed under the provisions of 35 U.S.C. section 112, sixth paragraph, unless the element is expressly recited using the phrase “means for.”