Abstract:
A motorized system for reeling and unreeling a flexible member on a roller tube between fully open wound and fully closed unwound conditions to minimize sound pressure level has a rotatable roller tube and a flexible member that winds on the tube. A d-c motor drives the tube through a gear reduction. The motor has a motor speed versus torque characteristic extending linearly from high maximum RPM, low minimum torque, to low minimum RPM high maximum torque with peak efficiency at a given RPM. The motor moves the member between the two positions at a motor speed less than the given peak efficiency RPM and less than 50% of high maximum RPM with efficiency less than 25% of peak efficiency, intentionally at a high torque and low efficiency. The motor has two or more modes each moving the member at predetermined different linear speed.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    The present application is a continuation under 37 C.F.R. §1.53(b) of prior U.S. Ser. No. 11/096,784, filed Apr. 1, 2005 in the name of Robert C. Newman, Jr. entitled MOTORIZED ROLLER TUBE SYSTEM HAVING DUAL-MODE OPERATION which is related to co-pending U.S. Ser. No. 11/096,783, filed Apr. 1, 2005 in the names of Jason O. Adams; Thomas W. Brenner; Brandon J. Detmer; Robert C. Newman, Jr.; and Joel Spira entitled DRIVE ASSEMBLY FOR A MOTORIZED ROLLER TUBE SYSTEM the co-pending application is incorporated herein by reference in its entirety. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to motorized roller tube systems, used for winding flexible members such as shades, screens and the like, and more particularly to a drive assembly for a motorized roller tube system. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0003]      FIG. 1  is a perspective view of a motorized roller tube system including a prior drive assembly. 
           [0004]      FIG. 2  shows the motor and gear assembly of the prior drive assembly of  FIG. 1 . 
           [0005]      FIG. 3  is a motor curve for the motor of  FIG. 2 . 
           [0006]      FIG. 4  is a perspective view showing a drive assembly for a motorized roller tube system according to the present invention. 
           [0007]      FIG. 5  shows the motor and the gear stages of the gear assembly of  FIG. 4  removed from the rest of the drive assembly. 
           [0008]      FIG. 6  is an exploded perspective view of the motor and gear assembly of  FIG. 4 . 
           [0009]      FIG. 7  is a motor curve for the motor of  FIGS. 4 and 5 . 
       
    
    
     BACKGROUND OF THE INVENTION 
       [0010]    Referring to  FIG. 1 , there is shown a motorized roller tube system  10  having a prior drive assembly  12 . The motorized roller tube system  10  includes a rotatably supported roller tube  14  and a flexible member  16 , such as a window shade fabric, windingly received by the roller tube  14 . The flexible member  16  is typically engaged to the roller tube  14  by securing an end portion of the flexible member  16 -to the roller tube  14 . There are a variety of well-known means for securing the flexible member  16  to the roller tube  14  including, for example, the use of double-sided tape, or by a clip member received over an end portion of the flexible member  16  in a locking channel provided on the exterior of the roller tube  14 . The roller tube  14  is driven in opposite rotational directions by the drive assembly  12  for winding and unwinding the flexible member  16  with respect to the roller tube  14 . The prior drive assembly  12  includes an elongated housing  18  and a puck  20  located adjacent an end of the housing  18 . The puck  20  engages an inner surface of the roller tube  14  to drive the roller tube  14  as the puck is rotated by the drive assembly  12 . 
         [0011]    The prior roller tube drive assembly  12  includes a motor  22  and gear assembly  24  located within an interior of the housing  18  and connected to the puck  20 . The motor  22  and gear assembly  24  are shown in  FIG. 2  removed from housing  18 . The motor  22  of prior drive assembly  12  is a DC motor. Referring again to  FIG. 1 , the drive assembly  12  is received within the interior of the roller tube  14 . For this reason, this type of roller tube drive assembly is referred to as an “internal” drive assembly. Other known motorized roller tube systems include drive assemblies that are located externally of the roller tube. 
         [0012]    The motor  22  includes an output shaft  23  that is rotated by the motor at a rotational speed referred to herein as the “motor speed”. The prior drive assembly  12  operates the motor at a motor speed of approximately 2000 rpm. The gear assembly  24 , which is connected to the output shaft of the motor  22 , reduces rotational speed from the relatively fast speed of 2000 rpm input from motor  22  to a relatively slow output rotational speed of approximately 27 rpm for roller tube  14 . The gear assembly  24  of the prior drive assembly  12 , therefore, has a gear ratio of approximately 74:1 (i.e., 2000/27). 
         [0013]    The torque capability of a motor varies depending on the motor speed. Therefore, the motor of any motorized roller tube system must provide a torque capability at the operating motor speed that is sufficient to wind the flexible member  16  onto the roller tube  14 . Referring to  FIG. 3 , the performance characteristics for motor  22  of prior drive assembly  12  are shown graphically. Graphs of this type are referred to as “motor curves”. The relationship between motor speed (shown on the Y-axis) and motor torque capability (shown on the X-axis) is represented by line  26 . As shown, the maximum motor speed for motor  22  is approximately 3150 rpm and the maximum motor torque capability is approximately 280 m-Nm. As also shown, the motor torque capability for DC motor  22  varies linearly throughout the entire range of motor speeds. In other words, the motor will provide increasing torque capability with decreasing motor speed even at very slow speeds approaching zero. It should be understood the motor torque values on speed/torque line  26  of  FIG. 3  represent capability rather than fixed values of operating motor torque. In other words, the motor  22  is capable of operating at a given motor speed at any torque between zero (i.e., an unloaded condition) and the value represented on the speed/torque line  26 . At the operating speed of 2000 rpm, the torque capability of motor  22  is approximately 99 m-Nm. 
         [0014]    As shown in  FIG. 3  by curve  28 , the efficiency of motor  22  also varies depending on the motor speed. The efficiency, which is shown on the Y-axis with motor speed, is determined by reading vertically from the speed/torque line  26  to the efficiency curve  28 . Thus, at the operating motor speed of 2000 rpm, the motor  22  of prior drive assembly  12  has an efficiency of approximately 25 percent. As shown, the motor efficiency of 25 percent is the peak efficiency for motor  22 . The motor speed associated with peak efficiency is referred to herein as the peak efficiency motor speed. The peak efficiency motor speed represents approximately 65 percent of the maximum motor speed (i.e., 2000/3100). 
         [0015]    Although the particular values of motor speed, torque capability, and efficiency will vary for different DC motors, there are certain characteristics that are shared by all DC motors. Firstly, motor speed and motor torque capability will vary linearly, and inversely, throughout the entire range of motor speeds including very low speeds approaching zero. Secondly, motor efficiency will generally reach peak efficiency under light-duty conditions (i.e., relatively low torque capability at a motor speed greater than 50 percent of maximum motor speed). Prior drive assemblies include motors configured and operated by the drive assembly under light-duty conditions near the peak efficiency motor speed. As described below in greater detail, operation of the motors under such relatively light-duty conditions is in accordance with motor manufacturer recommended operation of the motor. 
         [0016]    The gear assemblies of known roller tube drive assemblies include planetary spur gears. Planetary spur gears are desirably economical in construction and provide efficient transmission compared to other types of gears. Spur gears, however, tend to be noisy in operation compared to other gear types because of sound generated as peripheral teeth contact each other. This contact sound associated with meshing teeth is sometimes referred to as “gear slapping” and increases as the rotational speed of the meshing gears is increased. Known gear assemblies also include gear stages having helical gears. Helical gears include elongated spiral flights that constantly engage with flights of other helical gears. The constant engagement of the flights eliminates the slapping noises associated with contact between the teeth of spur gears. Helical gears, however, tend to be less economical and less efficient than spur gears. 
         [0017]    The gear assembly  24  of prior drive assembly  12  includes three gear stages  30 ,  32 ,  34 . The gear assembly  24  is a hybrid gear system and includes a first stage  30  having helical gears and second and third stages  32 ,  34  each having planetary spur gears. The first gear stage  30  is located closest to the motor  22 . The gears of stage  30 , therefore, are rotated at the relatively fast motor speed of 2000 rpm. The rotational speed in the second and third stages  32 ,  34 , however, is stepped down from the 2000 rpm motor speed. Thus, the hybrid construction of prior drive assembly  12  represents a trade-off in which quieter, less efficient, more expensive helical gears are used in the relatively fast first stage  30 , while efficient, less expensive, but noisier, planetary spur gears are used in the relatively slower second and third stages  32 ,  34 . 
         [0018]    Prior motorized roller tube systems include systems providing for variable-speed control of a drive assembly motor. The variable-speed control feature is used in prior systems to provide for movement of the flexible member (known as “linear speed” or “fabric speed”) that is substantially constant. The variable motor speed adjusts the tube rotational speed to account for variation in the effective winding radius associated with the formation of winding layers as the flexible member is wound onto the roller tube. If the roller tube were to be rotated at a constant rotational speed, the fabric speed would change as the effective radius changed. Prior motorized roller tube systems control the motor speed to slow down the motor speed as the flexible member is wound onto the roller tube for substantially constant fabric speed. The prior motorized roller tube systems, however, do not provide for multiple modes of operation in which the fabric speed in each mode of operation is different from the fabric speed in the other modes of operation. 
       SUMMARY OF THE INVENTION 
       [0019]    According to the present invention, a motorized roller tube system comprises a rotatably supported roller tube and a flexible member engaging the roller tube for winding receipt of the flexible member by the roller tube. The motorized roller tube system also comprises a motor having an output shaft rotated at a motor speed and a gear assembly connected to the output shaft of the motor such that the gear assembly is driven by the motor. The gear assembly includes a plurality of gear stages adapted to produce an output rotational speed that is reduced with respect to the motor speed. 
         [0020]    The motorized roller tube system further comprises a controller connected to the motor for controlling the motor to wind or unwind the flexible member with respect to the roller tube. The controller of the present invention is adapted to provide at least two operating modes each providing for movement of the flexible member at a linear speed. The linear speed of each of the operating modes is different from the linear speed for the other modes. 
         [0021]    According to one embodiment, the operating modes include a set-up mode and an ultra low speed mode. The linear speed of the set-up mode is greater than the linear speed of the ultra low speed mode. According to one presently preferred embodiment, the linear speed of the set-up mode is at least 2 times faster than the linear speed of the ultra low speed mode. 
         [0022]    According to one embodiment, the motorized roller tube system produces a noise level when operating in the ultra low speed mode that is approximately 3 dBA or more below a noise level produced when the motorized roller tube system is operating in the set-up mode. 
         [0023]    According to one embodiment, the controller is responsive to an illuminance level input to the controller to adjust the position of the flexible member in response to the illuminance level input to the controller. 
       DESCRIPTION OF THE INVENTION 
       [0024]    Referring to the drawings, where like numerals identify like elements, there is shown in  FIGS. 4 through 6  a roller tube drive assembly  40  according to the present invention including a motor  42  and a gear assembly  44  contained within an elongated housing  41 . The drive assembly  40  of the present invention is adapted for receipt within a roller tube, such as the tube  14  of  FIG. 1 , to engage an inner surface of the roller tube for rotating the tube to wind or unwind a flexible member, such as a window shade fabric. The receipt and engagement of the drive assembly  40  is similar to that described above for the prior drive assembly  12 . As described below in greater detail, however, the drive assembly  40  of the present invention is configured in a novel manner providing for reduction in roller tube diameter for driving a given applied load or, alternatively, driving a large applied load for a given roller tube diameter. Also, the novel configuration generates limited noise for relatively quiet roller tube movements while desirably utilizing spur gear transmission throughout the gear assembly  44 . 
         [0025]    The motor  42  of drive assembly  40  is preferably a DC motor. Motor  42  has an output shaft  43  for transmission of mechanical power at a motor speed and torque. DC motors are highly reliable, relatively inexpensive and possess adequate torque capability in sufficiently small sizes for most roller tube applications. DC motors include brushed and brushless DC motors. Brushed and brushless DC motors have similar torque/speed curves. Brushless DC motors, however, have a wound stator surrounding a permanent-magnet rotor, which is an inverse arrangement to that of a brushed DC motor. The construction of the brushless motor eliminates the need for motor brushes, which allow current to flow through the wound rotor in a brushed motor. The stator windings of a brushless DC motor are commutated electronically requiring control electronics to control current flow. Brushed DC motors are presently readily available in large varieties and, therefore, are presently preferred for economic reasons. 
         [0026]    The majority of the noise generated by drive assembly  40  is created by motor  42  and by the gears in the gear assembly  44 . These noise generating elements are shown in  FIG. 5  removed from the rest of the drive assembly  40  to facilitate comparison with the corresponding elements of the prior drive assembly  12  of  FIG. 2 . The gear assembly  44  of drive assembly  40  includes first and second gear stages  46 ,  48  for reducing rotational speed from the rotational speed of motor  42  to the rotational speed desired for rotating a roller tube in which the drive assembly  40  is received. The gears in each of the stages  46 ,  48  of gear assembly  44  are planetary spur gears. As described above, the use of planetary spur gears throughout all stages of the gear assembly  44  is desirable because spur gears are economical and provide efficient gear transmission compared to other types of gears such as the helical gears in the first stage of prior drive assembly  12 . The planetary spur gears of gear assembly  44  are preferably made from plastic. 
         [0027]    Referring to  FIG. 7 , the motor curve for motor  42  is shown. Similar to the motor curve of  FIG. 3  for motor  22 ,  FIG. 7  graphically illustrates various performance characteristics for motor  42  including motor speed, motor torque capability and motor efficiency. As shown by line  51 , the motor speed and motor torque capability for motor  42 , like those of motor  22 , are inversely proportional to each other throughout the entire range of motor speeds including very slow speeds approaching zero. The maximum motor speed for motor  42  is approximately 4200 rpm and the maximum motor torque capability is approximately 122 m-Nm. As shown by efficiency curve  53 , the motor efficiency for motor  42  reaches a peak of approximately 75 percent when the motor is operated at a speed of approximately 3700 rpm. 
         [0028]    The motor curve of  FIG. 7  includes a manufacturer&#39;s recommended operating range, which is shown by shaded area  55 . As shown, the manufacturer&#39;s recommended operating range for motor  42  includes motor speeds corresponding to relatively light-duty conditions (i.e., relatively high speeds and relatively low motor torque). Not surprisingly, the manufacturer&#39;s recommended operating range includes the peak efficiency motor speed of 3700 rpm. As discussed above, the motors of prior roller tube drive assemblies are operated by the drive assemblies under light-duty conditions in accordance with the manufacturer&#39;s recommendations. Specifically, the manufacturer for motor  42  recommends that the motor be operated at motor speeds above approximately 3200 rpm, which represents speed ranging between approximately 76 percent and 100 percent of the maximum motor speed for motor  42 , which is 4200 rpm. Also similar to motor  18 , the recommended operating range for motor  42  includes the peak efficiency motor speed of 3700 rpm. 
         [0029]    Operating the motor of a roller tube drive assembly within the manufacturer&#39;s recommended range in conformance with established convention in the art would appear to be intuitively preferred. As discussed above, the recommended operating range includes the peak efficiency motor speed. Therefore, operation of the motor in the recommended range results in efficient operation of the motor. Also, the relatively light-duty conditions (i.e., relatively low torques) associated with the recommended range serves to limit overheating damage that could result from heavy-duty operation of the motor, thereby promoting motor life. 
         [0030]    The drive assembly  40 , however, is not configured to operate the motor  42  in the manufacturer&#39;s recommended range in conformance with established convention. Instead, the motor  42  of drive assembly  40  is preferably operated under heavy-duty conditions (i.e., relatively high torque) in a range of motor speeds represented in  FIG. 7  by shaded area  57 . As shown, the preferred operating range  57  includes motor speeds between 0 rpm and approximately 1500 rpm. The upper end of 1500 rpm for the preferred operating range represents approximately 36 percent of the maximum motor speed of 4200 rpm for motor  42 . Most preferably, the drive assembly  40  operates the motor  42  at a speed of approximately 850 rpm, which represents only approximately 20 percent of the maximum speed. As shown by line  51  of  FIG. 7 , the motor torque capability for motor  42  when operated at a speed of 850 rpm is approximately 98 m-Nm. As shown by curve  53 , the motor efficiency for motor  42  is approximately 19 percent when the motor is operating at the preferred speed of 850 rpm. This motor efficiency represents only approximately one-fourth of the peak efficiency for motor  42  (i.e., 19175). The drive assembly  40  of the present invention is configured to operate the motor  42  at a motor speed that is well outside the recommended range under conditions that are very inefficient for the motor. 
         [0031]    The torque capability of 98 m-Nm provided by motor  42  at its operating motor speed of 850 rpm is roughly equivalent to the 99 m-Nm provided by motor  22  of prior drive assembly  12  at its operating motor speed of 2000 rpm. However, the diameter of motor  22  is 1.65 inches while the diameter of motor  42  is only approximately 1.22 inches. The present invention, therefore, by operating inefficiently outside of the recommended operating range, provides similar torque capability for driving similar applied loads while allowing for reduction in the diameter of the motor. By reducing motor diameter, a corresponding reduction in the required roller tube diameter is provided. Limiting the roller tube diameter is desired aesthetically to avoid an installation that is bulky in appearance. It should be understood that, instead of decreasing motor diameter, the present invention could be used to increase torque capability for a given motor for increasing the applied load that is driven by the motor. 
         [0032]    The motor  22  of prior drive assembly  12  has a length of approximately 2.7 inches. The aspect ratio (i.e., length/diameter) of motor  22 , therefore, is approximately 1.64 (i.e., 2.7/1.65). This aspect ratio is typical for standard torque motors. Motor  42  of the present drive assembly  40  also has a length of approximately 2.7 inches. The aspect ratio of motor  42 , therefore, is approximately 2.21 (i.e., 2.7/1.22). The effect of this increase in the aspect ratio of motor  42  can be seen by comparing  FIGS. 2 and 5 . It is known that torque capability for a motor varies in proportion to BID 2 L, where B is magnetic flux, I is current, and D and L are respectively diameter and length of the motor. Thus, the motor torque capability can be increased by increasing any one of B, I, D or L. Because the aspect ratio has been increased from that which is associated with standard torque motors, the motor  42  of the present drive assembly is considered a “high” torque motor. The increased torque capability for motor  42  provided by increased aspect ratio (i.e., increased length) partially offsets the decreased torque capability associated with the decreased diameter. Of course, the reduction in diameter has a much greater impact on torque capability than the increased in length because the diameter is squared in the above relationship (i.e., BID 2 L). The present invention, therefore, also provides fot increase in torque capability by operating the smaller diameter motor under the above-described heavy-duty conditions associated with the preferred range  57 . 
         [0033]    As described above, the torque capability of 98 m-Nm provided by motor  42  at its operating motor speed of 850 rpm is roughly equivalent to the 99 m-Nm provided by motor  22  of prior drive assembly  12  at its operating motor speed of 2000 rpm. The present invention, however, is not limited to any particular torque capability. Therefore, it is conceivable, therefore, that the drive system could be configured to include a smaller diameter motor having a reduced torque capability compared to motor  42  for use within a smaller diameter roller tube. For example, a motor having a maximum torque capability between 50 m-Nm and 75 m-Nm could be used to drive a roller tube having a diameter less than approximately 1.625 inches. 
         [0034]    As discussed above, planetary spur gears are a preferred gear type because of their economy and their gear efficiency but also tend to be undesirably noisy when driven at the relatively high rotational motor speeds associated with prior art drive assemblies. By reducing the motor speed to approximately 850 rpm, however, the present invention desirably allows for the use of spur gears in each stage of the gear assembly  44  without excessive noise being generated in the first stage  46  from gear slapping. As discussed above, the reduction in motor speed to 850 rpm also reduced the gear ratio required by gear assembly  44  to approximately 20:1. As a result, it was possible to reduce the number of gear stages from three to two. Such a reduction in the number of stages provides for a reduction in the total number of gears in the assembly thereby further reducing the noise generated by the gear assembly. 
         [0035]    It is desirable that the drive assembly of a motorized roller tube system is capable of variable speed control of the drive assembly motor. Such variable speed control is desirable to account for changes in the effective winding radius for substantially constant movement of a flexible member being wound onto the roller tube. As a flexible member is wound onto a tube, the flexible member forms layers (or “windings”) such that the effective radius at which the flexible member is received by, or delivered from, the roller tube changes. Thus, if a roller tube were to be driven at a constant rotational speed, the speed at which the flexible member is moved (sometimes referred to as the “linear speed” or the “fabric speed”) would vary because of change in the effective winding radius. It should be understood that rotational speed will need to be reduced as the flexible member is wound onto a tube in order to maintain a constant fabric speed and, therefore, that the rotational speed will be greatest when the roller tube is being driven at or near the point at which the flexible member is fully unwound from the roller tube (i.e., a “fully-lowered” or “fully-closed” position). Also, the least amount of material is wound onto the tube when the flexible member is at the fully-lowered position of the flexible member such that the flexible member provides the least amount of sound attenuation for the roller tube in this position. The sound level produced by the motorized roller tube system, therefore, is greatest when the drive assembly is driving the roller tube at or near the fully-lowered position of the flexible member. 
         [0036]    The present invention provides a drive assembly  40  that desirably includes spur gears in each stage of its gear assembly  44  while also limiting noise that is generated by the drive assembly. A motorized roller tube system including the drive assembly  40  housed within a 1.625 inch diameter roller tube was used to drive a typical applied load of approximately 8.1 in-lb (i.e., a 10 pound flexible member applied at 0.81 inch radius). Sound levels generated by the motorized roller tube system were measured using a sound pressure meter at a distance of approximately 3 feet from the driven end of the roller tube. The sound pressure level produced by the motorized roller tube system in an ambient of approximately 38 dBA when the drive assembly  40  is driving the roller tube at or near the fully-lowered position of the flexible member (i.e., the maximum sound level produced by the motorized shade assembly) is approximately 43 dBA. An ambient level of 38 dBA is a sound pressure level in a relatively quiet office setting such as a private office with the door closed, for example. A sound pressure level of between approximately 40-44 dBA generated by a motorized roller tube system in such a setting is considered non-distracting and even pleasant. The sound level generated by the present drive assembly having spur gears driven at rotational speeds well below the speeds associated with the motor manufacturer&#39;s recommended operating range compares favorably with that of prior motorized roller tube systems having spur gears driven at the faster rotational speeds recommended for the motor. Such motorized roller tube systems include systems generating sound pressure levels exceeding 50 dBA at approximately 3 feet in an ambient of approximately 38 dBA. Sound pressure levels exceeding 50 dBA in such an ambient environment are considered distracting and even annoying. 
         [0037]    The above-described gear assembly  44  includes two gear stages  46 ,  48 . The number of gear stages, however, is not critical. A drive assembly according to the present invention, therefore, could include more than the two stages that are shown in the above-described embodiment. As discussed above, however, reducing the number of gear stages desirably provides for reduction in the total number of gears in the gear assembly and, accordingly, a reduction in gear slapping noise. 
         [0038]    As discussed above, inefficient operation of the motor  42  by drive assembly  40  under heavy-duty conditions is counter-intuitive. In addition to inefficient operation of the motor, sustained operation of a motor under the heavy-duty torque conditions associated with the preferred operation range  57  could overheat the motor potentially causing life-shortening damage of the motor. The motors of motorized roller tube systems, however, are not ordinarily operated in a continuous fashion. In a typical motorized roller tube system, such as a window shade for example, the shade fabric might be raised in the morning, lowered at night, and possibly adjusted to a number of other positions at infrequent intervals during the day. Therefore, except in the most unusual situations, the inefficient operation of drive motor  42  will not appreciably effect the motor in terms of longevity. To protect the motor  42 , however, it is conceived that the drive assembly  40  could be configured to track the run time of motor  42 . The motor  42  could then be disabled in the event that excessive run time has occurred during a given period of time that could adversely affect the motor if the motor were otherwise permitted to continue running. Alternatively, the condition of the motor could be monitored based on the temperature of the motor or related components, or the temperature of surrounding areas, using thermal-couples, thermistors, temperature sensors, or other suitable sensing devices. 
         [0039]    Referring again to  FIG. 4 , some additional details of the construction of drive assembly  40  will now be discussed. The elongated housing  41  is tubular defining an interior in which the drive motor  42  and gear assembly  44  are housed. The drive assembly  40  preferably includes an electronic drive unit (“EDU”)  50  for controlling the operation of the drive motor  42 . The EDU controller  50  includes a printed circuit board  52  for mounting control circuitry (not shown) of the controller  50 . The controller  50  could be configured to track run time of the motor  42  in the above-described manner and to disable the operation of motor  42  in the event that overuse of the motor  42  within a given period of time could damage the motor  42 . The EDU controller  50  includes a bearing sleeve  54  and bearing mandrels  56  adjacent an end of the housing  41 . Electronic drive units for motorized roller tube systems are known and no further description is necessary. 
         [0040]    The drive assembly  40  includes a drive puck  58  located adjacent an end of the housing  41  opposite the EDU bearing sleeve  54  and mandrels  56 . The drive puck  58  is connected to a puck shaft  60  that is rotatably supported with respect to the housing  41  of drive assembly  40  by a drive bearing  62 . The puck shaft  60  is connected to the gear assembly  44  of drive assembly  40  such that actuation of the drive motor  42  drivingly rotates the drive puck  58 . The drive puck  58  includes longitudinal grooves in an outer periphery to promote engagement between the outer surface of the puck  58  and an inner surface of a roller tube when the drive assembly is received within a roller tube. The drive assembly  40  is adapted for receipt within the interior of a roller tube such that the EDU bearing sleeve  54  and mandrels  56  are located adjacent an end of the roller tube. The drive assembly  40  also includes brake  64  having a brake input  66 , a brake output  68  and a brake mandrel  70 . The brake  64  defines an interior in which the puck shaft  60  is received. The brake  64  is adapted to engage the puck shaft  60  to prevent relative rotation between the motor  42  and the drive puck  58 . The engagement of the brake  64  prevents a flexible member from unwinding because of load applied to a roller tube by an unwound portion of the flexible member and any hem bar carried by the member, thereby holding the flexible member in a selected position. Brakes for roller tube drive assemblies are known and no further description is necessary. 
         [0041]    Referring to  FIG. 6 , an embodiment of the motor  42  and gear assembly  44  of drive assembly  40  is shown in greater detail. The gear assembly  44  includes a ring gear  72  received within an interior of a ring gear cover  74 . A motor adapter  76  is located between the motor  42  and the ring gear cover  74  and engages an end of the ring gear cover  74 . The ring gear cover  74  includes a tab  78  received by a correspondingly shaped notch  80  of the motor adapter  76  to limit relative rotation therebetween. The ring gear cover  74  also includes an end fitting  82  received by the brake mandrel  70 . 
         [0042]    The gear assembly  44  includes a sun gear  45  that is attached to the output shaft  43  of motor  42  such that the sun gear  45  rotates with the output shaft  43 . Preferably, the sun gear  45  is pressed onto the output shaft  43 . Each of the first and second stages  46 ,  48  of gear assembly  44  includes three planetary spur gears that meshingly engage longitudinal teeth  96  formed on an inner surface of the ring gear  72 . The sun gear  45  meshingly engages the spur gears of the first stage  46  such that the spur gears of the first stage  46  are rotated by the sun gear  45  at the motor speed. The spur gears of the first stage  46  are rotatingly received on pins  90  of a sun carrier  88 . The spur gears of the second stage  48  are rotatingly received on pins  94  of a hex carrier  92 . A sun gear  98  is fixed to the sun carrier  88  opposite the pins  90  and meshingly engages the spur gears of the second stage  48  to rotate the second stage gears as the sun carrier  88  is driven by the first stage  46 . A hex socket  100  is fixed to the hex carrier  92  opposite the pins  94 . The gear assembly  44  also includes a second stage adapter  102  including a hex head  104  received by the hex socket  100  of the hex carrier  92  and a socket  106  opposite the hex head  104  receiving an end of the drive puck shaft  60 . The second stage adapter  102  transfers rotation from the hex carrier  92  to the drive puck  58  as the hex carrier  92  is driven by the second stage  48 . 
         [0043]    The controller  50  of drive assembly  40  preferably provides variable-speed control of the motor speed of motor  42 . Such variable-speed control is desirable in a roller tube drive assembly for speed adjustments to account for winding of the flexible member onto the roller tube such that the movement of the flexible member (referred to as “linear speed” or “fabric speed”) is substantially constant. An example of such a control system is disclosed in U.S. patent application Ser. No. 10/774,919, filed Feb. 9, 2004, entitled “Control System for Uniform Movement of Multiple Roller Shades”, which is incorporated herein by reference in its entirety. As the flexible member is wound onto the roller tube, the material of the flexible member is formed into layers (or “windings”). The layering of the fabric changes the radius at which the fabric is received by, or delivered from, the roller tube. Thus, if the roller tube is driven at a constant rotational speed, the speed of the flexible member will tend to increase as the member is being wound onto the roller tube. It is known to control motor speed for a DC motor by controlling the voltage to the motor using pulse-width modulation. An example of a motorized roller tube system using pulse-width modulation for variable motor speed is disclosed in U.S. Pat. No. 5,848,634, which is incorporated herein by reference. 
         [0044]    The motor  42  of the above-described drive assembly is a DC motor, preferably a brushed DC motor. There may be applications, particularly when the applied load to be driven by the motor is relatively large, where an AC induction motor may be preferred over a DC motor. Such a situation could arise, for example, where a single motor is driving multiple roller tubes arranged in end-to-end fashion. For variable-speed control using an AC induction motor, the frequency and the applied voltage to the motor are modulated instead of just the voltage. An AC induction motor is typically wound with a set of stator windings, each driven with an AC voltage waveform. Typically, there are three separate windings spaced about the periphery of the motor stator to be driven by three phases of an AC voltage waveform. The phase displacements of the drive voltage waveforms sets up a rotating field in the rotor section of the motor. The reaction between the induced fields in the rotor and the fields in the stator creates a net torque on the rotor. The speed at which the rotor turns is related to the frequency of the drive waveform and the number of electrical poles created by the winding structure of stator. This relationship is stated in the following equation: n=120×FIP, where n is the rotor speed in rpm, F is drive voltage frequency in Hertz, and P is the number of electrical poles. 
         [0045]    Commercially available AC induction motors typically include 2 or 4 poles. This configuration facilitates manufacture of stator windings. AC induction motors having 2 poles and 4 poles will typically run at nominal speeds of 3600 rpm and 1800 rpm, respectively, when driven with a 60 Hz drive voltage waveform. To operate these type of motors at speeds of about 750 to 900 rpm, a reduction pf operating frequency is required. This is accomplished with a frequency controlled inverter circuit. By way of example, a 4 pole AC induction motor will need to be operated with a drive frequency of about 25 Hz to run at a rotor speed of about 750 rpm. 
         [0046]    As described above, the drive assembly  40  of the present invention is adapted for receipt within a rotatably supported roller tube, such as the roller tube  14  depicted in  FIG. 1 . It should be understood, however, that the present invention is not limited to use within cylindrical tubes. The rotatably supported tube, therefore, could be any elongated member capable of being rotatably supported and adapted for winding receipt of a flexible member. Therefore, the roller tube could have a non-circular cross section such as hexagonal or octagonal for example. The non-circular cross section could also conceivably be a non-symmetrical shape such as an oval for example. 
         [0047]    The flexible members wound by a roller tube system incorporating the drive assembly of the present invention may include shades, screens, curtains or the like that blocks or reflects, or partially blocks or reflects, light. The flexible member may be formed of paper, cloth, or fabrics of any sort. Examples of flexible members include window shades, window screens, screens for projectors including television projectors, curtains that block or partially block entry of light or that reflect light, and curtains used for concealing or protecting objects. 
         [0048]    Operation of the motor  42  at various speeds by the controller  50  allows for additional features. Running the motor at a nominal speed of approximately 1000 rpm allows for very quiet operation and when commanded to move by the operation of a user interface control, such as a wall control station, the movement of the flexible member is considered to be visually responsive to command inputs such as a raise or a lower command. That is to say, that upon the pressing of a raise button, the flexible member moves at an adequate speed to give visual feedback to the user to acknowledge the action being requested. It has been found that a speed of about 3 inches per second for the flexible member satisfies the feedback requirement of human operators. However, when a command is given to move the flexible member to a particular predetermined position, the requirement of visual feedback is greatly diminished. The operator knows that the flexible member, upon being commanded to travel to a predetermined position, requires no additional input from the user. That is, once commanded, the flexible member will be moved to the predetermined position without requiring the user to hold the button that commanded the action. The user is, therefore, inclined to press the button and then proceed to some other activity. This mode of operation affords additional benefits. Since the need for visual feedback of the movement of the flexible member is not required for preset operation, the motor can be caused to run very slowly such that flexible member is moved at a very slow linear speed (herein referred to as “ultra-low speed operation”). 
         [0049]    There are at least two significant advantages provided by an ultra low speed operation. First during this mode of operation, the noise generated by the motorized roller tube system is further reduced below the approximate 43 dBA level to approximately 40 dBA. In many ambient conditions, a sound level of 40 dBA is undetectable by humans. Second, the ultra low speed of the motor  42  can be selected such that the movement of the flexible member is on the order of about 1 inch per second. This corresponds to a motor speed of about 300 rpm. At this speed, the movement of the flexible member is barely noticeable by room occupants, thus creating less of a distraction to activities being carried out in the room. A motorized roller tube system of this type lends itself to the use of automatic controls such as photo cell sensors. 
         [0050]    Conventional lighting systems include systems in which an artificial light source may supplement natural light, such as those including controllable fluorescent lamps located adjacent a window. It is common to provide a control system that measures the total light in the space and adjusts the output of the controllable fluorescent lamps to maintain the room ambient light level at a predetermined value. The ability to control a motorized roller tube system for adjustment of the natural light entering the space, however, has been limited to open loop control, whereby a flexible shade member of the roller tube system is moved in response to manual control, or using a time clock control, or by measuring outdoor illuminance level using a sensor. Previous attempts to measure actual indoor illuminance level for adjustment of a flexible shade member in response results in movement of the flexible shade member that is either too fast or too slow, thereby allowing either too much or too little light into the space. This results in an under-damped oscillating control loop system. Additionally, overly rapid movement of the shades would be annoying to the occupants. The ultra low speed operation of the present invention, and the associated very slow movement of a flexible member, allows for matching between the slow movement of the flexible member with the desired response rate of the indoor illuminance level, thereby preventing the control system from oscillating and causing annoyance to occupants of the lighted space. 
         [0051]    The present invention provides a motorized roller tube system having at least two distinct operating modes. In the first mode, the motor of the roller tube system is driven at an operating motor speed of approximately 1000 rpm such that the associated flexible member is moved at a linear speed of about 3 inches per second. The first mode is useful for movement of the flexible member to a selected position in which the operator uses and holds a raise/lower type command to move the flexible member to move to the desired position. The first mode of operation will herein be referred to as “the set-up mode”. 
         [0052]    In a second mode of operation, the motor of the roller tube system is driven at a speed of approximately 300 rpm such that the associated flexible member is moved at a speed of about 1 inch per second. The second mode of operation is referred to herein as “the ultra low speed mode”. The second mode of operation is particularly useful for moving the flexible member to a predetermined position (sometimes referred to as a “preset”) or for regulating the contribution of natural light into a room during operation in a closed loop control system as described above. 
         [0053]    The foregoing describes the invention in terms of embodiments foreseen by the inventor for which an enabling description was available, notwithstanding that insubstantial modifications of the invention, not presently foreseen, may nonetheless represent equivalents thereto. 
         [0054]    In the appended claims, the term “flexible member” should be interpreted broadly as including any member capable of being wound that blocks or reflects, or partially blocks or reflects, light. Non-limiting examples of flexible members include shades, screens and curtains.