Patent Publication Number: US-2013233496-A1

Title: Motorized window treatment having a belt drive

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a motorized window treatment, and more specifically, to a low-cost, quiet, battery-powered motorized window treatment having a belt drive that reduces the noise generated by the motorized window treatment and reduces the current draw by a motor from batteries of the motorized window treatment. 
     2. Description of the Related Art 
     Motorized window treatments typically include a flexible fabric or other means for covering a window in order to block or limit the daylight entering a space and to provide privacy. The motorized window treatments may comprise roller shades, cellular shades, Roman shades, Venentian blinds, and draperies. The motorized window treatments include a motor drive for movement of the fabric in front of the window to control the amount of the window that is covered by the fabric. For example, a motorized roller shade includes a flexible shade fabric wound onto an elongated roller tube with an electronic drive unit installed in the roller tube. The electronic drive unit includes a motor, such as a direct-current (DC) motor, which is operable to rotate the roller tube upon being energized by a DC voltage. 
     Prior art electronic drive units are typically powered directly from an AC mains line voltage (e.g., 120 VAC) or from a low-voltage DC voltage (e.g., approximately 24 VDC) provided by an external transformer. Unfortunately, this requires that electrical wires to be run from the power source to the electronic drive unit. Running additional AC main line voltage wiring to the electronic drive unit can be very expensive, due to the cost of the additional electrical wiring as well as the cost of installation. Typically, installing new AC main line voltage wiring requires a licensed electrician to perform the work. In addition, if the pre-existing wiring runs behind a fixed ceiling or wall (e.g., one comprising plaster or expensive hardwood), the electrician may need to breach the ceiling or wall to install the new electrical wiring, which will thus require subsequent repair. In some installations where low voltage (e.g., from a low-voltage DC transformer) is used to the power the electronic drive unit, the electrical wires have been mounted on an external surface of a wall or ceiling between the electronic drive unit and the transformer, which is plugged into an electrical receptacle. However, this sort of installation requires the permanent use of one of the outlets of the electrical receptacle and is aesthetically unpleasing due to the external electrical wires. 
     Therefore, some prior art motorized window treatments have been battery powered, such that the motorized window treatments may be installed without requiring any additional wiring. Examples of prior art battery-powered motorized window treatments are described in greater detail in U.S. Pat. No. 5,883,480, issued Mar. 16, 1999, entitled WINDOW COVERING WITH HEAD RAIL-MOUNTED ACTUATOR; U.S. Pat. No. 5,990,646, issued Nov. 23, 2009, entitled REMOTELY-CONTROLLED BATTERY POWERED-WINDOW COVERING HAVING POWER SAVING RECEIVER; and U.S. Pat. No. 7,389,806, issued Jun. 24, 2008, entitled MOTORIZED WINDOW SHADE SYSTEM; the entire disclosures of which are hereby incorporated by reference. 
     However, the typical prior art battery-powered motorized window treatments have suffered from poor battery life (such as, one year or less), and have required batteries that are difficult and expensive to replace. Thus, there is a need for a quiet, low-cost battery-powered motorized window treatment that has longer battery life. 
     SUMMARY OF THE INVENTION 
     The present invention provides a low-cost, quiet, battery-powered motorized window treatment for controlling the position of a covering material that is adapted to hang in front of an opening, such as a window. The motorized window treatment comprises a motor drive unit having a motor for rotating a drive shaft to thus raise and lower the covering material and batteries for powering the motor drive unit. The motor drive unit includes a belt drive that isolates noise generated by the motor from the gears and parts of the motor drive unit and the motorized window treatment. The belt drive includes a belt that is coupled between two pulleys and is sized to reduce the load on the motor, such that the motor draws less current from the batteries. As a result, the batteries have a much longer (and more practical) lifetime (e.g., approximately three years) than those of a typical prior art battery-powered motorized window treatment. 
     According to an embodiment of the present invention, a motor drive unit for a motorized window treatment comprises a motor having an output shaft, a first pulley coupled to the output shaft of the motor, a second pulley, and a flexible belt surrounding the first and second pulleys. The second pulley is coupled such that rotations of the second pulley result in rotations of a drive shaft of the motorized window treatment. At least one lift is rotatably received around the drive shaft and extends to a bottom of a covering material for raising and lowering the covering material between a fully-open and fully-closed position and to any position intermediate the fully-open and fully-closed positions. The flexible belt is coupled to the first and second pulleys, such that rotations of the motor and the first pulley result in rotations of the second pulley, and thus the drive shaft, so as to raise and lower the covering material by rotating the motor. 
     In addition, a gear assembly for a motor drive unit is also described herein. The gear assembly comprises: (1) an end portion; (2) a first pulley adapted to be coupled to an output shaft of a motor adjacent the end portion and to rotate with respect to the end portion; (3) a second pulley; (4) a flexible belt surrounding the first and second pulleys, such that rotations of the motor and the first pulley result in rotations of the second pulley, the belt having teeth adapted to engage teeth of the first and second pulleys; and (5) a first roller rotatably coupled to the end portion and contacting an outer surface of the belt. The first roller holds the belt against the first pulley to ensure that the belt and the first pulley have at least a predetermined angular contact length. 
     According to another embodiment of the present invention, a motorized window treatment comprises a covering material, a drive shaft, at least one lift cord rotatably received around the drive shaft and extending to a bottom end of the covering material, a motor drive unit having a motor comprising an output shaft, and at least one battery for powering the motor drive unit. The motor drive unit is coupled to the drive shaft for raising and lowering the covering material in response to rotations of the motor. The motor drive unit further comprises a first pulley coupled to the output shaft of the motor, a second pulley coupled such that rotations of the second pulley result in rotations of the drive shaft, and a flexible belt surrounding the first and second pulleys, such that rotations of the motor and the first pulley result in rotations of the second pulley, and thus the drive shaft, so as to raise and lower the covering material by rotating the motor. 
     Other features and advantages of the present invention will become apparent from the following description of the invention that refers to the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will now be described in greater detail in the following detailed description with reference to the drawings in which: 
         FIG. 1  is a perspective view of a motorized window treatment system having a battery-powered motorized window treatment and a remote control according to a first embodiment of the present invention; 
         FIG. 2  is a perspective view of the battery-powered motorized window treatment of  FIG. 1  in a full-opened position; 
         FIG. 3  is a right side view of the battery-powered motorized window treatment of  FIG. 1 ; 
         FIG. 4  is a front view of the battery-powered motorized window treatment of  FIG. 1 ; 
         FIG. 5  is an exploded view of a motor drive unit of the battery-powered motorized window treatment of  FIG. 1 ; 
         FIG. 6  is an enlarged perspective view of a motor and a gear assembly of the motor drive unit of  FIG. 5  showing a belt drive of the motor in greater detail; 
         FIG. 7  is a left side view of a belt drive of the gear assembly of  FIG. 6 ; 
         FIG. 8  is a front cross-sectional view of the belt drive of the gear assembly of  FIG. 6 ; 
         FIG. 9  is a simplified block diagram of a motor drive unit of the battery-powered motorized window treatment of  FIG. 1 ; 
         FIG. 10  is a simplified partial schematic diagram of an H-bridge motor drive circuit and a motor of the motor drive unit of  FIG. 9 ; 
         FIG. 11  is a diagram of a first output signal and a second output signal of a transmissive optical sensor circuit of  FIG. 9 ; 
         FIG. 12  is a simplified flowchart of a transmissive optical sensor edge procedure executed periodically by the controller of the motor drive unit of  FIG. 9 ; and 
         FIG. 13  is a simplified flowchart of a motor control procedure executed periodically by the controller of the motor drive unit of  FIG. 9 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The foregoing summary, as well as the following detailed description of the preferred embodiments, is better understood when read in conjunction with the appended drawings. For the purposes of illustrating the invention, there is shown in the drawings an embodiment that is presently preferred, in which like numerals represent similar parts throughout the several views of the drawings, it being understood, however, that the invention is not limited to the specific methods and instrumentalities disclosed. 
       FIG. 1  is a perspective view of a motorized window treatment system  100  having a battery-powered motorized window treatment  110  mounted in an opening  102 , for example, in front of a window  104 , according to a first embodiment of the present invention. The battery-powered motorized window treatment  110  comprises a covering material, for example, a cellular shade fabric  112  as shown in  FIG. 1 . The cellular shade fabric  112  has a top end connected to a headrail  114  (that extends between two mounting plates  115 ) and a bottom end connected to a weighting element  116 . The mounting plates  115  may be connected to the sides of the opening  102  as shown in  FIG. 1 , such that the cellular shade fabric  112  is able to hang in front of the window  104 , and may be adjusted between a fully-open position P FULLY-OPEN  and a fully-closed position P FULLY-CLOSED  to control the amount of daylight entering a room or space. Alternatively, the mounting plates  115  of the battery-powered motorized window treatment  110  could be mounted externally to the opening  102  (e.g., above the opening) with the shade fabric  112  hanging in front of the opening and the window  104 . In addition, the battery-powered motorized window treatment  110  could alternatively comprise other types of covering materials, such as, for example, a plurality of horizontally-extending slats (i.e., a Venetian or Persian blind system), pleated blinds, a roller shade fabric, or a Roman shade fabric. According to the first embodiment of the present invention, the motorized window treatment system  100  comprises an infrared (IR) remote control  118  for controlling the operation of the motorized window treatment  110 . 
       FIG. 2  is a perspective view and  FIG. 3  is a right side view of the battery-powered motorized window treatment  110  with the cellular shade fabric  112  in the fully-open position P FULLY-OPEN . The motorized window treatment  110  comprises a motor drive unit  120  for raising and lowering the weighting element  116  and the cellular shade fabric  112  between the fully-open position P FULLY-OPEN  and the fully-closed position P FULLY-CLOSED . By controlling the amount of the window  104  covered by the cellular shade fabric  112 , the motorized window treatment  110  is able to control the amount of daylight entering the room. The headrail  114  of the motorized window treatment  110  comprises an internal side  122  and an opposite external side  124 , which faces the window  104  that the shade fabric  112  is covering. 
     The motor drive unit  120  comprises an actuator  126 , which is positioned adjacent the internal side  122  of the headrail  114  may be actuated when a user is configuring the motorized window treatment  110 . The actuator  126  may be made of, for example, a clear material, such that the actuator may operate as a light pipe to conduct illumination from inside the motor drive unit  120  to thus be provide feedback to the user of the motorized window treatment  110 . In addition, the actuator  126  may also function as an IR-receiving lens for directing IR signals transmitted by the IR remote control  118  to an IR receiver  166  ( FIG. 9 ) inside the motor drive unit  120 . The motor drive unit  120  is operable to determine a target position P TARGET  for the weighting element  116  in response to commands included in the IR signals received from the remote control  118  and to subsequently control a present position P PRES  of the weighting element to the target position P TARGET . As shown in  FIG. 2 , a top side  128  of the headrail  114  is open, such that the motor drive unit  120  may be positioned inside the headrail and the actuator  126  may protrude slightly over the internal side  122  of the headrail. 
     The battery-powered motorized window treatment  110  also comprises a plurality of batteries  138  (e.g., four D-cell batteries), which are electrically coupled in series. The series-combination of the batteries  138  is coupled to the motor drive unit  120  for powering the motor drive unit. The batteries  138  are housed inside the headrail  114  and thus out of view of a user of the motorized window treatment  110 . Specifically, the batteries  138  are mounted in two battery holders  139  located inside the headrail  114 , such that there are two batteries in each battery holder as shown in  FIG. 4 . According to the embodiments of the present invention, the batteries  138  provide the motorized window treatment  110  with a practical lifetime (e.g., approximately three years), and are typical “off-the-shelf” batteries that are easy and not expensive to replace. Alternatively, the motor drive unit  120  could comprise more batteries (e.g., six or eight) coupled in series or batteries of a different kind (e.g., AA batteries) coupled in series. 
       FIG. 4  is a front view of the battery-powered motorized window treatment  110  with a front portion of the headrail  114  removed to show the motor drive unit  120 . The motorized window treatment  110  comprises lift cords  130  that extend from the headrail  114  to the weighting element  116  for allowing the motor drive unit  120  to raise and lower the weighting element. The motor drive unit  120  includes an internal motor  150  ( FIG. 5 ) coupled to drive shafts  132  that extend from the motor on each side of the motor and are each coupled to a respective lift cord spool  134 . The lift cords  130  are windingly received around the lift cord spools  134  and are fixedly attached to the weighting element  116 , such that the motor drive unit  120  is operable to rotate the drive shafts  132  to raise and lower the weighting element. The motorized window treatment  110  further comprises two constant-force spring assist assemblies  135 , which are each coupled to the drive shafts  132  adjacent to one of the two lift cord spools  134 . Each of the lift cord spools  134  and the adjacent constant-force spring assist assembly  135  are housed in a respective lift cord spool enclosure  136  as shown in  FIG. 4 . Alternatively, the motor drive unit  120  could be located at either end of the headrail  114  and the motorized window treatment  110  could comprise a single drive shaft that extends along the length of the headrail and is coupled to both of the lift cord spools  134 . 
       FIG. 5  is an exploded view of the motor drive unit  120 . The motor drive unit  120  comprises two enclosure portions  180 ,  182  for housing the motor  150  and a gear assembly  185 . The two enclosure portions  180 ,  182  are connected and held together by a plurality of screws  184 . The gear assembly  190  is held together by two end portions  186 ,  188  and comprises a belt drive, and specifically, a belt  190  coupled between a first pulley  191  that is coupled to the output shaft of the motor  150  and a second pulley  192  that is coupled to the other gears of the gear assembly. The motor drive unit  120  comprises output gears  194  that are located on both sides of the motor drive unit and are coupled to the drive shafts  132 . The gear assembly  185  is coupled to the output gears  194  via a coupling member  195 , such that the rotations of the output shaft of the motor  150  result in rotations of the drifts shafts  132 . 
       FIG. 6  is an enlarged perspective view of the motor  150  and the gear assembly  185  showing the belt drive in greater detail. For example, the belt  190  may comprise a flexible toothed belt having teeth  196  ( FIG. 8 ) that engage teeth  198  ( FIG. 8 ) of the first and second pulleys  191 ,  192 . For example, the outside diameter of the first and second pulleys  191 ,  192  may be approximately 0.235 inch and 0.591 inch, respectively, resulting in a gear ratio of approximately 2:5. Since the second pulley  192  is coupled to the first pulley  191  via the flexible belt  190 , noises generated by the rotations of the motor  150  are not coupled from the first pulley  191  to the second pulley  192 . Accordingly, the total noise generated by the gear assembly  185  is reduced. 
     The gear assembly  185  further comprises a first roller  199 A ( FIG. 4A ) and a second roller  199 B ( FIG. 6 ) that are rotatably coupled to the end portion  186  that is located adjacent the motor  150 .  FIG. 7  is a left side view of the belt  190 , the first and second pulleys  191 ,  192 , and one of the rollers  199 A.  FIG. 8  is a front cross-sectional view of the belt  190 , the first and second pulleys  191 ,  192 , and the rollers  199 A,  199 B taken through the center of the belt  190  as shown in  FIG. 7 . The belt  190  contacts the rollers  199 A,  199 B, which operate to hold the belt against the first and second pulleys  191 ,  192  and to ensure that the belt and the first gear have an appropriate angular contact length θ C  (e.g., approximately 136°) as shown in  FIG. 8 . For example, if the rollers  199 A,  199 B are not provided in the motor drive unit  120 , the belt  190  may have an angular contact length θ c  with the first pulley  192  of approximately 30°. With the rollers  199 A,  199 B installed in the gear assembly  185 , the belt  190  can have a larger diameter than if the rollers were not provided and still achieve the appropriate angular contact length θ C  between the belt and the first pulley  191 . It was discovered that loosening the belt  190  and providing the rollers  199 A,  199 B led to a decreased current consumption in the motor  150  as compared to when the rollers were not provided, the belt was tighter, and the same angular contact length θ C  between the belt  190  and the first pulley  191  was achieved (i.e., approximately 136°). In addition, the diameters of the rollers  199 A,  199 B can be adjusted to change the angular contact length θ C . 
       FIG. 9  is a simplified block diagram of the motor drive unit  120  of the battery-powered motorized window treatment  110 . The motor drive unit  120  comprises a controller  152  for controlling the operation of the motor  150 , which may comprise, for example, a DC motor. The controller  152  may comprise, for example, a microprocessor, a programmable logic device (PLD), a microcontroller, an application specific integrated circuit (ASIC), a field-programmable gate array (FPGA), or any suitable processing device or control circuit. The controller  152  is coupled to an H-bridge motor drive circuit  154  for driving the motor  150  via a set of drive signals V DRIVE  to control the weighting element  116  and the cellular shade fabric  112  between the fully-open position P FULLY-OPEN  and the fully-closed position P FULLY-CLOSED . The controller  152  is operable to rotate the motor  150  at a constant rotational speed by controlling the H-bridge motor drive circuit  154  to supply a pulse-width modulated (PWM) drive signal having a constant duty cycle to the motor. The controller  152  is able to change the rotational speed of the motor  150  by adjusting the duty cycle of the PWM signal applied to the motor and to change the direction of rotation of the motor by changing the polarity of the PWM drive signal applied to the motor. 
       FIG. 10  is a simplified schematic diagram of the H-bridge motor drive circuit  154 . The H-bridge motor drive circuit  154  may comprise four transistors, such as, for example, four field effect transistors (FETs) Q 1 , Q 2 , Q 3 , Q 4 . Each FET Q 1 -Q 4  may be driven by the controller  152  via four respective drives signals V DRIVE     —     1 , V DRIVE     —     2 , V DRIVE     —     3 , V DRIVE     —     4 . The FETs Q 1 -Q 4  are coupled such that, when two of the FETs are conductive (e.g., FETs Q 3 , Q 4 ), a positive DC voltage is applied to the motor  150  to cause the DC motor to rotate in a clockwise direction. When the other two FETs of the H-bridge circuit  154  are conductive (e.g., FETs Q 1 , Q 2 ), a negative DC voltage is applied to the motor  150  to cause the motor to rotate in the reverse (i.e., counter-clockwise) direction. To control the speed of the motor  150 , the controller  152  drives at least one of FETs of the H-bridge circuit  154  with a PWM control signal. When the motor  150  is idle (i.e., at rest), the controller  152  drives only the FET Q 1  to be conductive and controls FETs Q 2 , Q 3  and Q 4  to be non-conductive. 
     Referring back to  FIG. 9 , the controller  152  receives information regarding the rotational position and direction of rotation of the motor  150  from a rotational position sensor, such as, for example, a transmissive optical sensor circuit  155 . The rotational position sensor may also comprise other suitable position sensors or sensor arrangements, such as, for example, Hall-effect, optical, or resistive sensors. The controller  152  is operable to determine a rotational position of the motor  150  in response to the transmissive optical sensor circuit  155 , and to use the rotational position of the motor to determine a present position P PRES  of the weighting element  116 . The controller  152  may comprise an internal non-volatile memory (or alternatively, an external memory coupled to the controller) for storage of the present position P PRES  of the shade fabric  112 , the fully open position P FULLY-OPEN , and the fully closed position P FULLY-CLOSED . 
       FIG. 11  is a timing diagram of a first output signal  176  and a second output signal  178  of the transmissive optical sensor circuit  155 . The output signals  176 ,  178  are provided to the controller  152  as a train of pulses. The frequency, and thus the period T, of the pulses of the output signals  176 ,  178  is a function of the rotational speed of the motor output shaft  172 . The relative spacing S between the pulses of the first and second output signals  176 ,  178  is a function of rotational direction. When the motor  150  is rotating in a clockwise direction of the output shaft  172 , the second output signal  178  lags behind the first output signal  176  by the relative spacing S. When the motor  150  is rotating in the opposite direction, the second output signal  178  leads the first output signal  176  by the relative spacing S. 
     The controller  152  stores the present position P PRES  of the weighting element  116  in the memory as a number of optical sensors edges between the present position P PRES  of the weighting element and the fully-open position P FULLY-OPEN . An optical sensor edge is, for example, the low-to-high transition  179  of the first output signal  176  as shown in  FIG. 11 . The operation of the H-bridge motor drive circuit  154  and the use of sensor devices to track the direction and speed of the motor drive unit  120  is described in greater detail in commonly-assigned U.S. Pat. No. 5,848,634, issued Dec. 15, 1998, entitled MOTORIZED WINDOW SHADE SYSTEM, and commonly-assigned U.S. Pat. No. 6,497,267, issued Dec. 24, 2002, entitled MOTORIZED WINDOW SHADE WITH ULTRAQUIET MOTOR DRIVE AND ESD PROTECTION, the entire disclosures of which are herein incorporated by reference. 
     Referring back to  FIG. 10 , the H-bridge motor drive circuit  154  is operable to provide a manual movement wake-up signal V MAN     —     WAKE  to the controller  152 . In the event that the cellular shade fabric  112  is moved manually, the motor  150  can be back-driven and provide the manual movement wake-up signal V MAN     —     WAKE  to the controller  152 . The manual movement wake-up signal V MAN     —     WAKE  indicates that the cellular shade fabric  112  is being moved manually (i.e., pulled by a user), and the signal can cause the controller  152  to wake up (i.e., become fully energized) in the event that the controller is sleeping (i.e., operating in a low power mode). Thus, the controller  152  can continue to monitor the output of the transmissive optical sensor circuit  155 . As shown in  FIG. 10 , one terminal of the motor  150  is coupled to the base of an NPN bipolar junction transistor Q 5  via a resistor R 1 . The collector of the transistor Q 5  is coupled to the supply voltage V CC  via a resistor R 2 . The manual movement wake-up signal V MAN     —     WAKE  is generated at the junction of the collector of the transistor Q 5  and the resistor R 2 , which is coupled to the controller  152 . When the motor  150  is rotated in response to a manual action, a back electromagnetic force (EMF) is generated across the motor  150  and the transistor Q 5  becomes conductive, thus driving the manual movement wake-up signal V MAN     —     WAKE  low. The controller  152  may be operable to wake-up automatically in response to detecting such a high-to-low transition on one of its input ports. 
     Once the controller  152  wakes up in response to the manual movement wake-up signal V MAN     —     WAKE , the controller  152  monitors the output of the transmissive optical sensor circuit  155  to track the position of the motor  150  by executing a transmissive optical sensor edge procedure  200 , which will be discussed in greater detail below with reference to  FIG. 12 . In addition, the controller  152  may further wake-up periodically (e.g., once each second) to execute the transmissive optical sensor edge procedure  400  to determine whether the cellular shade fabric  112  is moving or has moved as a result of a manual adjustment. 
       FIG. 12  is a simplified flowchart of the transmissive optical sensor edge procedure  200  executed periodically by the controller  152 , e.g., every 10 msec, to determine the rotational position and direction of the motor. In addition, the transmissive optical sensor edge procedure  200  may be executed by the controller  152  in response to receiving the manual movement wake-up signal V MAN     —     WAKE . If the controller  152  has not received a transmissive optical sensor edge at step  210 , the transmissive optical sensor edge procedure  200  simply exits. However, if the controller  152  has received a transmissive optical sensor edge from the transmissive optical sensor circuit  155  at step  210 , the controller determines the direction of rotation of the motor  150  by comparing the consecutive edges of the first and second output signals  176 ,  178  at step  212 . If the motor  150  is rotating in the clockwise direction at step  214 , the controller  152  increments the present position P PRES  (i.e., in terms of transmissive optical sensor edges) by one at step  216 . If the motor  150  is rotating in the counter-clockwise direction at step  214 , the controller  152  decrements the present position P PRES  by one at step  218 . After the present position P PRES  is incremented or decremented at steps  216  and  218 , respectively, the transmissive optical sensor edge procedure  200  exits. 
     A user of the window treatment system  100  is able to adjust the position of the weighting element  116  and the cellular shade fabric  112  by using the remote control  118  to transmit commands to the motor drive unit  120  via the IR signals. Referring back to  FIG. 9 , the IR receiver  166  receives the IR signals and provides an IR data control signal V IR-DATA  to the controller  152 , such that the controller is operable to receive the commands from the remote control  118 . The controller  152  is operable to put the IR receiver  166  to sleep (i.e., disable the IR receiver) and to periodically wake the IR receiver up (i.e., enable the IR receiver) via an IR enable control signal V IR-EN , as will be described in greater detail below. An example of an IR control system is described in greater detail in U.S. Pat. No. 6,545,434, issued Apr. 8, 2003, entitled MULTI-SCENE PRESET LIGHTING CONTROLLER, the entire disclosure of which is hereby incorporated by reference. Alternatively, the IR receiver  166  could comprise a radio-frequency (RF) receiver or transceiver for receiving RF signals transmitted by an RF remote control. Examples of RF control systems are described in greater detail in commonly-assigned U.S. patent application Ser. No. 12/033,223, filed Feb. 19, 2008, entitled COMMUNICATION PROTOCOL FOR A RADIO-FREQUENCY LOAD CONTROL SYSTEM, and U.S. patent application Ser. No. 13/415,084 filed Mar. 8, 2012, entitled MOTORIZED WINDOW TREATMENT, the entire disclosures of which are hereby incorporated by reference. 
     As previously mentioned, the motor drive unit  120  receives power from the series-coupled batteries  138 , which provide a battery voltage V BATT . For example, the batteries  138  may comprise D-cell batteries having rated voltages of approximately 1.5 volts, such that the battery voltage V BATT  has a magnitude of approximately 6 volts. The H-bridge motor drive circuit  154  receives the battery voltage V BATT  for driving the motor  150 . In order to preserve the life of the batteries  138 , the controller  152  may be operable to operate in a sleep mode when the motor  150  is idle. 
     The motor drive unit  120  further comprises a power supply  156  (e.g., a linear regulator) that receives the battery voltage V BATT  and generates a DC supply voltage V CC  for powering the controller  152  and other low-voltage circuitry of the motor drive unit. The controller  152  is coupled to the power supply  156  and generates a voltage adjustment control signal V ADJ  for adjusting the magnitude of the DC supply voltage V CC  between a first nominal magnitude (e.g., approximately 2.7 volts) and a second increased magnitude (e.g., approximately 3.3 volts). The power supply  156  may comprise, for example, an adjustable linear regulator having one or more feedback resistors that are switched in and out of the circuit by the controller  152  to adjust the magnitude of the DC supply voltage V CC . The controller  152  may adjust the magnitude of the DC supply voltage V CC  to the second increased magnitude while the controller is driving the FETs Q 1 -Q 4  of the motor drive circuit  154  to rotate the motor  150  (since the controller may require an increased supply voltage to drive the gates of the FETs). The controller  152  adjusts the magnitude of the DC supply voltage V CC  to the first nominal magnitude when the controller is not controlling the motor drive circuit  154  to rotate the motor  150  (e.g., when the controller is in the sleep mode). The magnitude of the idle currents drawn by the controller  152 , the IR receiver  166 , and other low-voltage circuitry of the motor drive unit  120  may be significantly smaller when these circuits are powered by the first nominal magnitude of the DC supply voltage V CC . 
     The motor drive unit  120  further comprises a battery monitoring circuit  158  that receives the battery voltage V BATT  and provides a battery-monitor control signal V MON  representative of the magnitude of the battery voltage V BATT  to the controller  152 . The battery monitoring circuit  158  may comprise for example a resistive voltage divider circuit (not shown) coupled in series between the battery voltage V BATT  and circuit common, such that the battery-monitor control signal V MON  is simply a scaled version of the battery voltage V BATT . The controller  152  may include an analog-to-digital converter (ADC) for receiving and measuring the magnitude of the battery-monitor control signal V MON  to thus determine the magnitude of the battery voltage V BATT . The battery monitoring circuit  158  may further comprise a controllable switch, e.g., a NPN bipolar junction transistor (not shown), coupled in series with the resistive divider. The controller  152  may be operable to render the controllable switch conductive, such that the battery-monitor control signal V MON  is representative of the magnitude of the battery voltage V BATT , and to render the controllable switch non-conductive, such that the resistive divider does not conduct current and energy is conserved in the batteries  138 . 
     According to an aspect of the present invention, the controller  152  is operable to determine that the magnitude of the battery voltage V BATT  is getting low in response to the battery-monitor control signal V MON  received from the battery monitoring circuit  158 . Specifically, the controller  152  is operable to operate in a low-battery mode when the magnitude of the battery voltage V BATT  drops below a first predetermined battery-voltage threshold V B-TH1  (e.g., approximately 1.0 volts per battery). For example, the controller  152  may control the motor drive circuit  154  so that the motor  150  is operated at a reduced speed (e.g., at half speed) to reduce the instantaneous power requirements on the batteries  138  when the controller  152  is operating in the low-battery mode. This would serve as an indication to a consumer that the battery voltage V BATT  is low and the batteries  138  need to be changed. 
     When the magnitude of the battery voltage V BATT  drops below a second predetermined battery-voltage threshold V B-TH2  (less than the first predetermined battery-voltage threshold V B-TH1 , e.g., approximately 0.9 V per battery) while operating in the low-battery mode, the controller  152  may shut down electrical loads in the motor drive unit  120  (e.g., by disabling the IR receiver  166  and other low-voltage circuitry of the motor drive unit) and prevent movements of the cellular shade fabric  112  except to allow for at least one additional movement of the cellular shade fabric to the fully-open position P FULLY-OPEN . Having the cellular shade fabric  112  at the fully-open position P FULLY-OPEN  allows for easy replacement of the batteries. The second predetermined battery-voltage threshold V B-TH2  may be sized to provide enough reserve energy in the batteries  138  to allow for the at least one additional movement of the cellular shade fabric  112  and the weighting element  116  to the fully-open position P FULLY-OPEN . 
     When the magnitude of the battery voltage V BATT  drops below a third predetermined battery-voltage threshold V B-TH3  (less than the second predetermined battery-voltage threshold V B-TH2 , e.g., approximately 0.8 V per battery), the controller  152  may be operable to shut itself down such that no other circuits in the motor drive unit  120  consume any power in order to protect against any potential leakage of the batteries  138 . 
     Referring back to  FIG. 9 , the motor drive unit  120  comprises an alternate (or supplemental) power source, such as a backup battery  159  (e.g., a long-lasting battery), which generates a backup supply voltage V BACKUP  (e.g., approximately 3.0 volts) for powering the controller  152 . The DC supply voltage V CC  generated by the power supply  156  is coupled to the controller  152  via a first diode D 1 , and the backup supply voltage V BACKUP  is coupled to the controller via a second diode D 2 . The alternate power source provides the controller  152  with power when the batteries  138  are removed for replacement, or otherwise depleted, such that the position data relating to the position of the window treatment that is stored in the memory of the controller  152  is maintained. Alternatively, a large bus capacitor or an ultra-capacitor can be coupled to the controller  152  (rather than the backup battery  159 ), so that even when the batteries  138  are removed for replacement, an adequate charge will remain in the bus capacitor or ultra capacitor to maintain adequate voltage to keep the controller  152  charged for the period of time necessary to replace batteries  138  and thereby prevent loss of stored data in the memory of the controller. 
     These embodiments allow the motor drive unit  120  to keep track of the position of the weighting element  116  of the window treatment  110  even when the batteries  138  are removed and the window treatment is manually operated (i.e., pulled). In such embodiments, the controller  152  continues to receive signals from transmissive optical sensor circuit  155 , even when the batteries  138  are removed. Because it remains powered, the controller  152  will continue to calculate the position of the window treatment  110  when manually adjusted. It should be pointed out that the window treatment  110  of the present invention allows a user at any time to manually adjust the position of the window treatment, and that the position of the window treatment is always calculated both when the window treatment is moved by the motor or manually. 
     Another feature of the invention is that the controller  152  is preferably arranged to prevent the motor drive circuit  154  from operating to lower the cellular shade fabric  112  until an upper limit for the fabric is reset after a loss of power, e.g., if the batteries  138  are depleted. Thus, the motor drive unit  120  will not lower from the current raised position in the event of power loss. The user will be required to raise the cellular shade fabric  112  to the fully-open position before being able to lower the shade fabric. 
     As shown in  FIG. 9 , the motor drive unit  120  comprises an internal temperature sensor  160  that is located adjacent the internal side  122  of the headrail  114  (i.e., a room-side temperature sensor), and a external temperature sensor  162  that is located adjacent the external side  124  of the headrail (i.e., a window-side temperature sensor). The room-side temperature sensor  160  is operable to measure an interior temperature T INT  inside the room in which the motorized window treatment  110  is installed, while the external temperature sensor  162  is operable to measure an exterior temperature T EXT  between the headrail  114  and the window  104 . The motor drive unit  120  further comprises a photosensor  164 , which is located adjacent the external side  124  of the headrail  114 , and is directed to measure the amount of sunlight that may be shining on the window  104 . Alternatively, the exterior (window-side) temperature sensor  162  may be implemented as a sensor label (external to the headrail  114  of the battery powered motorized window treatment  110 ) that is operable to be affixed to an inside surface of a window. The sensor label may be coupled to the motor drive unit  120  through low voltage wiring (not shown). 
     The controller  152  receives inputs from the internal temperature sensor  160 , the external temperature sensor  162 , and the photosensor  164 . The controller  152  may operate in an eco-mode to control the position of the weighting element  116  and the cellular shade fabric  112  in response to the internal temperature sensor  160 , the external temperature sensor  162 , and the photosensor  164 , so as to provide energy savings. When operating in the eco-mode, the controller  152  adjusts the amount of the window  104  covered by the cellular shade fabric  112  to attempt to save energy, for example, by reducing the amount of electrical energy consumed by other control systems in the building in which the motorized window treatment  110  is installed. For example, the controller  152  may adjust the present position P PRES  of the weighting element  116  to control the amount of daylight entering the room in which the motorized window treatment  110  is installed, such that lighting loads in the room may be turned off or dimmed to thus save energy. In addition, the controller  152  may adjust the present position P PRES  of the weighting element  116  to control the heat flow through the window  104  in order to lighten the load on a heating and/or cooling system, e.g., a heating, air-conditioning, and ventilation (HVAC) system, in the building in which the motorized window treatment  110  is installed. 
       FIG. 13  is a simplified flowchart of a motor control procedure  300  executed periodically by the controller  152  (e.g., every two msec). If the motor  150  is not presently rotating at step  310  and the present position P PRES  is equal to the target position P TARGET  at step  312 , the motor control procedure  300  simply exits without controlling the motor. However, if the motor  150  is not presently rotating at step  310  and the present position P PRES  is not equal to the target position P TARGET  at step  312 , the controller  152  controls the voltage adjustment control signal V ADJ  to adjust the magnitude of the DC supply voltage V CC  to the increased magnitude (i.e., approximately 3.3 volts) at step  314 . The controller  152  then begins to control the H-bridge drive circuit  154  to drive the motor  150  appropriately at step  315 , so as to move the weighting element  116  towards the target position P TARGET . 
     If the motor  150  is presently rotating at step  310 , but the present position P PRES  is not yet equal to the target position P TARGET  at step  316 , the controller  312  continues to drive the motor  150  appropriately at step  318  and the motor control procedure  300  exits. If the motor  150  is presently rotating at step  310  and the present position P PRES  is now equal to the target position P TARGET  at step  316 , the controller  152  stops driving the motor at step  320  and controls the voltage adjustment control signal V ADJ  to adjust the magnitude of the DC supply voltage V CC  to the nominal magnitude (i.e., approximately 2.7 volts) at step  322 . The controller  152  then waits for a timeout period (e.g., approximately 200 msec) at step  324 , and puts the IR receiver  166  back to sleep at step  325 . 
     As previously mentioned, the controller  152  operates in a low-battery mode when the magnitude of the battery voltage V BATT  is getting low. Specifically, if the magnitude of the battery voltage V BATT  has dropped below the first battery-voltage threshold V B-TH1  at step  326 , the controller  152  begins at step  328  to operate in the low-battery mode during which the controller  152  will operate the motor at a reduced speed (i.e., at half speed). If the magnitude of the battery voltage V BATT  is less than or equal to the second battery-voltage threshold V B-TH2  at step  330 , the controller  152  allows for one last movement of the cellular shade fabric  112  and the weighting element  116  to the fully-open position P FULLY-OPEN  by setting a FINAL_MOVE flag in memory at step  332 . At step  334 , the controller  152  shuts down all unnecessary loads of the motor drive unit  120  (e.g., the external temperature sensor  162 , the photosensor  164 , the internal temperature sensor  160 , and the IR receiver  166 ) and prevents the motor  150  from moving the cellular shade fabric  112  and the weighting element  116  except for one last movement to the fully-open position P FULLY-OPEN . If the magnitude of the battery voltage V BATT  is less than or equal to the third battery-voltage threshold V B-TH3  at step  336 , the controller  152  shuts itself down at step  338  such that no other circuits in the motor drive unit  120  consume any power to thus protect against any potential leakage of the batteries  138 . Otherwise, the motor control procedure  300  exits. 
     While the present invention has been described with reference to the battery-powered motorized window treatments having the cellular shade fabric  112 , the concepts of the present invention could be applied to motors of other types of motorized window treatments, such as, for example, roller shades, draperies, Roman shades, Venetian blinds, and tensioned roller shade systems. An example of a roller shade system is described in greater detail in commonly-assigned U.S. Pat. No. 6,983,783, issued Jan. 10, 2006, entitled MOTORIZED SHADE CONTROL SYSTEM, the entire disclosure of which is hereby incorporated by reference. An example of a drapery system is described in greater detail in commonly-assigned U.S. Pat. No. 6,994,145, issued Feb. 7, 2006, entitled MOTORIZED DRAPERY PULL SYSTEM, the entire disclosure of which is hereby incorporated by reference. An example of a Roman shade system is described in greater detail in commonly-assigned U.S. patent application Ser. No. 12/784,096, filed Mar. 20, 2010, entitled ROMAN SHADE SYSTEM, the entire disclosure of which is hereby incorporated by reference. An example of a Venetian blind system is described in greater detail in commonly-assigned U.S. patent application Ser. No. 13/233,828, filed Sep. 15, 2011, entitled MOTORIZED VENETIAN BLIND SYSTEM, the entire disclosure of which is hereby incorporated by reference. An example of a tensioned roller shade system is described in greater detail in commonly-assigned U.S. Pat. No. 8,056,601, issued Nov. 15, 2011, entitled SELF-CONTAINED TENSIONED ROLLER SHADE SYSTEM, the entire disclosure of which is hereby incorporated by reference. 
     Although the present invention has been described in relation to particular embodiments thereof, many other variations and modifications and other uses will become apparent to those skilled in the art. It is preferred, therefore, that the present invention be limited not by the specific disclosure herein, but only by the appended claims.