Patent Publication Number: US-2020284093-A1

Title: System and method for reducing friction in a counterbalancing spring of a roller shade

Description:
BACKGROUND OF THE INVENTION 
     Technical Field 
     Aspects of the embodiments generally relate to roller shades, and more particularly to systems, methods, and modes for attachment of a counterbalancing spring to a shade drive unit of a roller shade in a manner that reduces friction in the counterbalancing spring. 
     Background Art 
     Motorized roller shades provide a convenient one-touch control solution for screening windows, doors, or the like, to achieve privacy and thermal effects. A motorized roller shade typically includes a rectangular shade material attached at one end to a cylindrical rotating tube, called a roller tube, and at an opposite end to a hem bar. The shade material is wrapped around the roller tube. An electric motor, either mounted inside the roller tube or externally coupled to the roller tube, rotates the roller tube to unravel the shade material to cover a window. To uncover the window, however, a lot of torque and motor power are required to initially lift the entire weight of the shade material and the hem bar. This is in particular detrimental to battery operated motors as rolling up the shade quickly drains the battery. 
     Various methods exist for counterbalancing roller shades using springs mounted inside the roller tubes in an effort to reduce torque requirements on shade motors. As the roller shade is unraveled, tension builds up in the spring. The tension is released when the roller shade is rolled up, thereby assisting the motor in lifting the shade material. One approach uses a conventional torsion spring comprising a plurality of coils. As a torsion spring is wound up, it builds up torque. When the torsion spring is let go, the amount of torque exerted by the torsion spring progressively reduces in a linear fashion as the torsion spring winds down.  FIG. 1A  shows a diagram  100  representing the performance of a conventional torsion spring in assisting rolling up an exemplary sized roller shade. Line  105  represents the torque profile necessary to roll up an exemplary sized roller shade from a rolled down position, when the shade material is fully unraveled, up to a rolled up position, when the shade material is fully wrapped about the roller tube. Initially, more torque is required to lift the entire weight of the fully unraveled shade material and the hem bar as represented by maximum torque (T max ) value  102 . As the roller tube turns, the shade material wraps around the roller tube, resulting in less shade material hanging from the roller tube. Accordingly, as the roller tube keeps turning, less torque is required to lift the weight of the remaining shade material until a minimum torque (T min ) value  103  is reached. Line  106  represents the torque exerted by the torsion spring during the roller shade travel. As shown, the torsion spring torque  106  decreases at a slope in a linear fashion to a zero value as the torsion spring winds down. 
     Currently, a torsion spring is chosen with a torque  106  that approaches the T max  value  102  required to lift the shade material and the hem bar. The resulting torque, shown by line  108  in the figure, required to be exerted by the motor to roll up the roller shade is equal to the difference between the torque of the roller shade  105  and the spring torque  106 .  FIG. 1B  shows a diagram  101  representing the resulting power  110  required of the motor to roll up the shade. As the roller shade begins to roll up from a fully unrolled position, the torsion spring releases its built up torsion energy. Then its energy progressively diminishes as the roller shade continues to roll up. At the end of the rolling up cycle, the torsion spring unravels back to zero torsion assistance. Thus, a conventional torsion spring assists the motor significantly more when the roller shade begins to roll up than during the remainder of the rolling up cycle. In the example of  FIGS. 1A and 1B , initially about 0.1 N m of torque and less than 1 W of power are required to lift up the roller shade. That number climbs up to above 0.8 N m of torque and above 6 W of power at the end of the roll up cycle. Thus, while the conventional torsion spring decreases the amount of torque required to roll up the roller shade in the beginning, the amount of torque and power required to finish rolling up the roller shade remains quiet high. In order to further assist in reducing torque in rolling up the roller shade, the counterbalancing spring may be pretensioned in the factory or during installation of the roller shade. 
     During operation, however, a torsion spring may introduce frictional forces that interferes with its counterbalancing efficiency, which are further exacerbated when the spring is pretensioned. During winding of the spring, the coils get tighter and the spring longitudinally extends causing friction to be formed at the point of contact between the torsion spring coils when winding and unwinding the spring. This friction is increased as the spring continues to be wound (i.e., when lowering the shade material) and is reduced during unwinding of the spring (i.e., when lifting the shade material). However, in pretensioned springs where the spring does not return to a relaxed state, this friction remains to be present. Friction is also increased in a close wound springs, which are preferred in roller shade due to space restrictions. Additionally, friction is further built between typical roller shade system components that allow for axial translation of the torsion spring within the roller tube of the roller shade, which further intensifies the coil friction in the spring. 
     Therefore, a need has arisen for systems, methods, and modes for counterbalancing a roller shade with pretensioned spring and for attachment of the counterbalancing spring to a shade drive unit of the roller shade in a manner that reduces friction in the counterbalancing spring. 
     SUMMARY OF THE INVENTION 
     It is an object of the embodiments to substantially solve at least the problems and/or disadvantages discussed above, and to provide at least one or more of the advantages described below. 
     It is therefore a general aspect of the embodiments to provide systems, methods, and modes for counterbalancing a roller shade with pretensioned spring and for attachment of the counterbalancing spring to a shade drive unit of the roller shade in a manner to reduce friction in the counterbalancing spring. 
     This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter. 
     Further features and advantages of the aspects of the embodiments, as well as the structure and operation of the various embodiments, are described in detail below with reference to the accompanying drawings. It is noted that the aspects of the embodiments are not limited to the specific embodiments described herein. Such embodiments are presented herein for illustrative purposes only. Additional embodiments will be apparent to persons skilled in the relevant art(s) based on the teachings contained herein. 
     DISCLOSURE OF INVENTION 
     According to one aspect of the embodiment a roller shade is provided comprising a roller tube, a shade material attached to the roller tube, and a shade drive unit at least partially disposed within the roller tube and comprising a drive assembly adapted to rotate the roller tube to lower or raise the shade material between a rolled up position and a rolled down position. The shade drive unit comprises a stationary spring carrier, a rotating spring carrier operably connected to the roller tube, a counterbalancing spring connected to and longitudinally extending between the stationary spring carrier and the rotating spring carrier, and an output mandrel comprising a first end operably connected to the drive assembly and a second end attached to the rotating spring carrier. The spring comprises an active portion having a plurality of coils located between the stationary spring carrier and the rotating spring carrier. The output mandrel extends within the spring between the stationary spring carrier and the rotating spring carrier and comprises a length that maintains the spring in a stretched state such that the plurality of coils at the active portion of the spring do not contact each other when the shade material is at the rolled down position. 
     According to an embodiment, at the rolled down position the spring is at a maximum tension, and the length of the output mandrel between the stationary spring carrier and the rotating spring carrier equals to or is larger than a deflected length of the active portion of the spring at the maximum tension. According to an embodiment, the deflected length of the active portion of the spring at the maximum tension is a factor of a diameter of a wire of the spring, a number of coils at the active portion of the spring, and a number of turns between the rolled up position and the rolled down position. According to an embodiment, the length of the output mandrel is determined using the following formula: 
     
       
      
       l 
       mandrel 
       =l 
       deflected 
       +l 
       clearance 
       +l 
       components  
      
     
     where,
         l mandrel  is the length the output mandrel,   l deflected  is the deflected length of the active portion of the spring at the maximum tension,   l clearance  is a predetermined clearance factor, and   l components  is an adjustment factor that accounts for assembly of the shade drive unit.
 
According to a further embodiment, the deflected length of the active portion of the spring at the maximum tension is determined using the following formula:
       

         l   deflected   =d   wire (( N   coils   −N   fastened ×2)+ N   turns +1)
 
     where,
         d wire  is a diameter of a wire of the spring,   N coils  is a total number of coils of the spring,   N fastened  is a number of coils at each end of the spring that are attached to one of the stationary and the rotating spring carriers,   N turns  is a number of turns between the rolled up position and the rolled down position.       

     According to an embodiment, the spring is pretensioned when the shade material is at the rolled up position, and wherein the deflected length of the active portion of the spring at the maximum tension is a factor of a diameter of a wire of the spring, a number of coils at the active portion of the spring, a number of turns between the rolled up position and the rolled down position, and a number of pretension turns in the spring at the rolled up position. According to a further embodiment, the spring is pretensioned when the shade material is at the rolled up position, and wherein the deflected length of the active portion of the spring at the maximum tension is determined using the following formula: 
         l   deflected   =d   wire (( N   coils   −N   fastened ×2)+ N   turns   +N   pretension +1)
 
     where,
         d wire  is a diameter of a wire of the spring,   N coils  is a total number of coils of the spring,   N fastened  is a number of coils at each end of the spring that are attached to one of the stationary and the rotating spring carriers,   N turns  is a number of turns between the rolled up position and the rolled down position, and   N pretension  is a number of pretensioned turns in the spring at the rolled up position.       

     According to an embodiment, the drive assembly comprises a motor adapted to drive a motor output shaft operably connected to the output mandrel. According to another embodiment, the shade drive unit comprises a motor housing adapted to house the motor therein and comprising the stationary spring carrier, wherein the output mandrel extends from an opening in the motor housing, and wherein during operation of the motor rotation of the motor output shaft causes rotation of the rotating spring carrier and thereby the roller tube while the motor housing and the motor remain stationary. According to an embodiment, the drive assembly further comprises at least one selected from the group consisting of a planetary gear, a clutch, or any combinations thereof. According to another embodiment, the output mandrel comprises a first mandrel portion connected to a second mandrel portion, wherein the first mandrel portion is operably connected to the drive assembly and wherein the second mandrel portion is attached to the rotating spring carrier. 
     According to yet another embodiment, wherein during assembly of the shade drive unit: the spring is adapted to be positioned over the output mandrel and be attached at a first end of spring to the stationary spring carrier, the rotating spring carrier is adapted to be slidably mounted over the output mandrel to allow a second end of the spring to be attached to the rotating spring carrier while the spring is in an unstretched state, and the rotating spring carrier is adapted to be slidably pulled away from the stationary spring carrier to stretch the spring to the stretched state and be attached to the second end of the output mandrel. 
     According to an embodiment, the shade drive unit comprises a drive wheel having a cylindrical body operably connected to the roller tube that extends from a first end to a second end, wherein the rotating spring carrier extends from the first end of the cylindrical body, and the second end of the cylindrical body is adapted to retain a washer, wherein the washer is adapted to be attached to the second end of the output mandrel to maintain the spring in the stretched state. According to a further embodiment, the drive wheel comprises a bore that traversely extends through the cylindrical body and the rotating spring carrier, wherein the bore is shaped to mate with an external surface of the output mandrel such that rotation of the output mandrel causes rotation of the drive wheel. According to a further embodiment, the cylindrical body of the drive wheel comprises a washer receiving cavity recessed into the second end of the cylindrical body that is defined by an opening at the second end of the cylindrical body and a biasing surface within the cylindrical body of the drive wheel, wherein the washer is adapted to be retained within the washer receiving cavity and biased against the biasing surface. According to yet another embodiment, the washer comprises locking arms and wherein the opening in the cylindrical body comprises circumferentially and inwardly extending washer retaining arms adapted to engage the locking arms of the washer. According to a further embodiment, the washer is adapted to be inserted through the opening in the second end of the cylindrical body by aligning the locking arms of the washer with a space between the retaining arms of the cylindrical body of the drive wheel and inserting the washer into the washer receiving cavity, wherein the washer is adapted to be retained within the washer receiving cavity by turning the washer until the locking arms of the washer engage the retaining arms of the drive wheel. According to another embodiment, the washer is secured to the output mandrel via a screw adapted to be inserting through a hole in the washer and screwed into a threaded hole in the second end of the output mandrel. 
     According to another aspect of the embodiments, a roller shade is provided comprising a roller tube, a shade material attached to the roller tube, and a shade drive unit at least partially disposed within the roller tube and adapted to rotate the roller tube to lower or raise the shade material from a rolled up position to a rolled down position. The shade drive unit comprises a motor adapted to drive a motor output shaft, a motor housing adapted to house the motor therein and comprising a first spring carrier, an output mandrel comprising a first end operably connected to the motor output shaft and a second end that extends out of an opening in the motor housing, a drive wheel attached to the second end of the output mandrel and comprising a second spring carrier, wherein the drive wheel is operably connected to the roller tube, and a counterbalancing spring longitudinally extending from a first end to a second end and comprising a plurality of coils, wherein the first end of the counterbalancing spring is connected to the first spring carrier and the second end of the counterbalancing spring is connected to the second spring carrier, wherein the output mandrel extends within the counterbalancing spring. The output mandrel comprises a length that maintains the spring in a stretched state such that the plurality of coils of the spring located between the first and second spring carriers do not touch when the shade material is at the rolled down position. 
     According to another aspect of the embodiments, a roller shade is provided comprising a roller tube, a shade material attached to the roller tube, and a shade drive unit at least partially disposed within the roller tube and comprising a drive assembly adapted to rotate the roller tube to lower or raise the shade material between a rolled up position and a rolled down position. The shade drive unit comprises a stationary spring carrier, a rotating spring carrier operably connected to the roller tube, a counterbalancing spring connected to and longitudinally extending between the stationary spring carrier and the rotating spring carrier, and an output mandrel comprising a first end operably connected to the drive assembly and a second end attached to the rotating spring carrier. The spring comprises an active portion having a plurality of coils located between the stationary spring carrier and the rotating spring carrier, wherein at the rolled down position the spring is at a maximum tension. The output mandrel extends within the spring between the stationary spring carrier and the rotating spring carrier, wherein a length of the output mandrel between the stationary spring carrier and the rotating spring carrier equals to or is larger than a deflected length of the active portion of the spring at the maximum tension. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other objects and features of the embodiments will become apparent and more readily appreciated from the following description of the embodiments with reference to the following figures. Different aspects of the embodiments are illustrated in reference figures of the drawings. It is intended that the embodiments and figures disclosed herein are to be considered to be illustrative rather than limiting. The components in the drawings are not necessarily drawn to scale, emphasis instead being placed upon clearly illustrating the principles of the aspects of the embodiments. In the drawings, like reference numerals designate corresponding parts throughout the several views. 
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
         FIG. 1A  illustrates a torque diagram of a prior-art roller shade using a conventional torsion spring. 
         FIG. 1B  illustrates a power diagram of a motor required to lift the prior-art roller shade using the conventional torsion spring. 
         FIG. 2A  illustrates a torque diagram of a roller shade using a pretensioned torsion spring according to one aspect of the embodiments. 
         FIG. 2B  illustrates a power diagram of a motor required to lift the roller shade using the pretensioned torsion spring according to one aspect of the embodiments. 
         FIG. 3A  illustrates an end view of a roller shade in a fully rolled down position according to one aspect of the embodiments. 
         FIG. 3B  illustrates an end view of the roller shade in a fully rolled up position according to one aspect of the embodiments. 
         FIG. 4  illustrates a partially exploded perspective view of a roller shade according to one aspect of the embodiments. 
         FIG. 5  shows an illustrative block diagram of a shade drive unit according to one aspect of the embodiments. 
         FIG. 6  shows a first side perspective view of the shade drive unit according to one aspect of the embodiments. 
         FIG. 7  shows a second side perspective view of the shade drive unit according to one aspect of the embodiments. 
         FIG. 8  shows an exploded perspective view of a portion of the shade drive unit according to one aspect of the embodiments. 
         FIG. 9  shows a cross-sectional view of the portion of the shade drive unit according to one aspect of the embodiments. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The embodiments are described more fully hereinafter with reference to the accompanying drawings, in which embodiments of the inventive concept are shown. In the drawings, the size and relative sizes of layers and regions may be exaggerated for clarity. Like numbers refer to like elements throughout. The embodiments may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the inventive concept to those skilled in the art. The scope of the embodiments is therefore defined by the appended claims. 
     Reference throughout the specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with an embodiment is included in at least one embodiment of the embodiments. Thus, the appearance of the phrases “in one embodiment” or “in an embodiment” in various places throughout the specification is not necessarily referring to the same embodiment. Further, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. 
     LIST OF REFERENCE NUMBERS FOR THE ELEMENTS IN THE DRAWINGS IN NUMERICAL ORDER 
     The following is a list of the major elements in the drawings in numerical order.
           100  Torque Diagram of a Roller Shade Using a Conventional Torsion Spring     101  Power Diagram of a Motor     102  Maximum Torque     103  Minimum Torque     105  Torque Profile of a Roller Shade     106  Torque of a Conventional Torsion Spring     108  Torque of a Motor     110  Power of a Motor     200  Torque Diagram of a Roller Shade Using a Pretensioned Torsion Spring     202  Maximum Torque     203  Minimum Torque     206  Torque Profile of Roller Shade&#39;s Spring     208  Torque of a Motor     210  Power of a Motor     300  Roller Shade     301  Roller Tube     303  Shade Material     304  Hem Bar     306  Radius of the Roller Tube     308  Radius of the Roller Tube plus the Thickness of the Shade Material Layers Wrapped over the Roller Tube (if any) when the Shade Material is at the Rolled Down Position     309  Thickness of the Shade Material (Single Layer)     310  Overwrap     311  Radius of the Roller Tube plus the Thickness of the Shade Material Layers Wrapped over the Roller Tube when the Shade Material is at the Rolled Up Position     312  Thickness of the Shade Material Layers over the Roller Tube     313  Shade Material Layers     314  Thickness of the Shade Material Layers over the Roller Tube     400  Roller Shade     401  Roller Tube     402  Shade drive unit     403  Idler Assembly     405   a  Mounting Bracket     405   b  Mounting Bracket     406  Shade Material     407  Motor Housing     408  Idler Body     409  Idler Pin     410  Hem Bar     411   a  First End of Roller Tube     411   b  Second End of Roller Tube     413  Pin Tip     416  Crown Adapter Wheel     417  Idler Crown Wheel     418  Keyhole     419  Flange     420  Counterbalancing Spring     421  Drive Wheel     422  Channels     423   a  First End of Counterbalancing Spring     423   b  Second End of Counterbalancing Spring     424  Projections     425  Teeth     426  Flange     427  Motor Head     428  Power Cord     432  Terminal Block     434  Inner Surface     495  Ball Bearings     500  Block Diagram of the Shade drive unit     502  Power Supply     504  Controller     506  Memory     507  Light Indicator     509  User Interface     510  Communication Interface     601  Motor     602  Motor Control Module     603  O-Ring     604  Rubber Locking Strip     605  Motor Output Shaft     606  First Stage Planetary Gear     608  Clutch     609  Final Stage Planetary Gear     610  Output Mandrel     611  First Mandrel Portion     612  Second Mandrel Portion     614  Keyed Bore     615  Motor Housing Opening     616  Keyed Grooves     617  Retaining Clip     621  First Spring Carrier     622  Second Spring Carrier     623  Threads     625  Cylindrical Body     626  Outer Surface     627   a  First End     627   b  Second End     628  Washer Biasing Surface     629  Washer Retaining Arms     630  Washer Receiving Cavity     631  Opening     632  Keyed Bore     633  Distance     640  Washer     641  Hole     642  Locking Arms     643  Screw     645  Threaded Hole       

     List of Acronyms Used in the Specification in Alphabetical Order 
     The following is a list of the acronyms used in the specification in alphabetical order.
         ASICs Application Specific Integrated Circuits   BLDC Brushless Direct Current   CAT5 Category 5 Cable   C friction  Constant Representing the Friction between the Spring Coils   DC Direct Current   d coils  Mean Diameter of the Spring Coils   d wire  Diameter of the Spring Wire   E Elastic Modulus   IR Infrared   k Slope of the Torque Profile of the Roller Shade   LAN Local Area Network   LED Light Emitting Diode   l clearance  Clearance Factor to Ensure that the Spring Coils do not Touch when the Spring is Fully Tensioned at the Rolled Down Position   l components  Adjustment Factor to Account for the Assembly Components of the Shade Drive Unit Assembly   l deflected  Deflected Length of the Active Portion of the Spring at Maximum Tension   l mandrel  Length the Second Mandrel Portion   l overwrap  Length of Shade Material Overwrap   l spring  Total Length of the Spring   N m Newton Meter   N coils  Total Number of Coils in the Spring   N fastened  Number of Nonactive Fastened Coils   N pretension  Number of Pretensioned Turns   N turns  Number of Turns Between Rolled Up and Rolled Down Position   PoE Power Over Ethernet   RAM Random-Access Memory   RF Radio Frequency   ROM Read-Only Memory   r down  Radius of the Roller Tube Plus the Thickness of the Shade Material Layers over the Roller Tube (if any) When the Shade Material is at the Rolled Down Position   r tube  Radius of the Roller Tube   r up  Radius of the Roller Tube Plus the Thickness of the Shade Material Layers over the Roller Tube When the Shade Material is at the Rolled Up Position   T max  Maximum Torque   t material  Thickness of the Shade Material (Single Layer)   T min  Minimum Torque   w material  Weight of the Shade Material   w hembar  Weight of the Hem Bar       

     MODE(S) FOR CARRYING OUT THE INVENTION 
     For 40 years Crestron Electronics, Inc. has been the world&#39;s leading manufacturer of advanced control and automation systems, innovating technology to simplify and enhance modern lifestyles and businesses. Crestron designs, manufactures, and offers for sale integrated solutions to control audio, video, computer, and environmental systems. In addition, the devices and systems offered by Crestron streamlines technology, improving the quality of life in commercial buildings, universities, hotels, hospitals, and homes, among other locations. Accordingly, the systems, methods, and modes of the aspects of the embodiments described herein can be manufactured by Crestron Electronics, Inc., located in Rockleigh, N.J. 
     The different aspects of the embodiments described herein pertain to the context of counterbalancing and pretensioning roller shades, but is not limited thereto, except as may be set forth expressly in the appended claims. While the roller shade is described herein for covering a window, the roller shade may be used to cover over types of architectural openings, such as doors, wall openings, or the like. The embodiments described herein may further be adapted in other types of window or door coverings, such as inverted rollers, Roman shades, Austrian shades, pleated shades, blinds, shutters, skylight shades, garage doors, or the like. In addition, the embodiments described herein can be used in shade drive units that comprise a motor to drive the roller shade, as described herein, or they can be implemented in non-motorized window treatments that implement a counterbalancing spring without departing from the scope of the present embodiments. 
     Disclosed herein are systems, methods, and modes for counterbalancing a roller shade with one or more pretensioned springs, and more particularly for the attachment of the counterbalancing spring and pretensioning the spring to lower the torque load on the motor of the roller shade throughout the rolling up or rolling down cycles of the roller shade. Disclosed are also systems, methods, and modes for a motor pretensioned roller shade that can be pretensioned using the motor to a preset amount and which locks and maintains the pretension. 
     To efficiently counterbalance a roller shade, a preset number of pretensioning turns first need to be determined for a given roller shade and its spring. In one embodiment, a torsion spring is utilized. However, other types of springs may be used without departing from the scope of current embodiments. Referring to  FIG. 2A , line  105  represents the roller shade torque profile across the number of turns required to roll up an exemplary sized roller shade from a rolled down position, when the shade material is fully unraveled, up to a rolled up position, when the shade material is substantially fully wrapped up around the roller tube. The y-axis represents the torque required in Newton Meter (N m) to roll up a roller shade, and the x-axis represents the number of 360 degree turns the roller shade rotates during the rolling up cycle (i.e., traveling right along the x-axis). Initially, more torque is required to start lifting all the weight of the shade material and the hem bar. As the roller tube rotates, the shade material wraps around the roller tube, resulting in less shade material hanging from the roller tube. Accordingly, as the roller tube keeps rotating, less torque is required to lift the weight of the remaining shade material plus the hem bar. T max    102  represents the maximum torque required to start lifting the entire weight of the shade material and hem bar, while T min    103  represents the minimum torque required to finish lifting the shade material and the hem bar during the rolling up cycle. 
     Line  206  represents the torque profile of the roller shade&#39;s spring. It is desired that the T max    202  and T min    203  values of the spring be set to be substantially equal to the T max    102  and T min    103  values, respectively, of the roller shade torque profile  105 . Alternatively, as shown in  FIG. 2A , the T max    202  and T min    203  values of the spring may be offset down by a predefined amount from the roller shade T max    102  and T min    103  values, respectively. Reducing the T max    202  and T min    203  values of the spring with respect to the roller shade T max    102  and T min    103  values will ensure that the shade material naturally drops down when the roller shade is rolled down and does not tend to roll back up. As shown in  FIG. 2A , T min    103  required to finish lifting the roller shade is not zero. There is always some torque required to finish lifting the shade because of the weight of the hem bar across the width of the shade, some pulling created by the shade material, and the inertia and weight of the roller tube itself. Accordingly, T min  set point  203  of the spring has to be brought up from zero to substantially equal to, or slightly offset below T min    103  of the roller shade. This is accomplished by pretensioning the torsion spring such that when the roller shade is fully rolled up, the torsion spring still exerts a preset amount of torque  203  that is substantially equal to or slightly offset below from T min    103  of the roller shade. 
     With optimally pretensioned torsion spring, the spring assists rolling up the roller shade throughout the rolling up cycle of the roller shade. As a result, the resulting torque  208  required to be exerted by the motor to roll up the roller shade is minimal and substantially steady throughout the rolling up cycle of the roller shade. Similarly, the resulting power  210  shown in  FIG. 2B  is significantly reduced and is substantially steady throughout the rolling up cycle of the roller shade. As illustrated in the example of  FIGS. 2A and 2B , the maximum torque required to be exerted to lift an exemplary sized roller shade is below 0.15 N m, compared to above 0.8 N m of torque required to lift the same sized shade by a motor with the aforementioned prior art counterbalancing system. Similarly, the maximum power required to lift an exemplary sized roller shade is around 0.8 W, compared to 6 W of power required to lift the same sized shade by a motor with the aforementioned prior art counterbalancing system. 
     In addition, the optimally pretensioned torsion spring also assists the motor to steadily lower the roller shade throughout the entire rolling down cycle (i.e., traveling left along x-axis in  FIG. 2A ). 
     The torque profile  105  of a roller shade is effected by various properties of the roller shade. For example, the torque profile  105  of a roller shade varies depending on various factors, such as the roller tube diameter and radius, the diameter and radius of the shade material as it wraps about the roller tube, the shade material thickness, the width and length of the shade material, the number of layers of the shade material about the roller tube, the weight of the shade material, and the weight of the hem bar. Therefore, depending on the window size and the fabric selection, the pretension parameters of the required torsion spring will change. The systems, methods, and modes of the embodiments described herein provide a motorized roller shade assembly that can be pretensioned using its integrated motor by an optimal number of pretension turns such that the T min  value  203  of the torsion spring corresponds to the T min  value  103  of the roller shade. 
     The embodiments described herein may be used to quickly and precisely pretension torsion springs to be used in customized roller shades, during the assembly of the customized roller shades at the factory, right after the customer has placed their order. The embodiments described herein may be also used to pretension torsion springs for use in stock roller shades sold in a number of predetermined sizes and shade materials. In yet another embodiment, the pretension of the roller shade may be adjusted or corrected, if necessary, in the field by removing the shade drive unit containing the motor from the roller tube, pretensioning the spring, and reinserting the drive unit into the roller tube. In addition, if a defective motor needs to be replaced, the customized pretensioning information of the defective motor may be transmitted to the replacement motor and used to pretension its spring. 
     According to an embodiment, to determine the preset number of pretension turns, initially the roller shade properties are determined.  FIG. 3A  illustrates an end view of a roller shade  300  in a fully rolled down position, and FIG.  3 B illustrates an end view of the roller shade  300  in a fully rolled up position. The roller shade properties include one or more of the diameter or radius  306  of the roller tube  301 , the weight of the shade material  303 , the thickness  309  of the shade material  303  (single layer), the width and length of the shade material  303 , and the weight of the hem bar  304 , among others. For customizable roller shades, for example, initially a customer will measure the window dimensions and select the style of the roller shade they want. The customer may pick from a selection of mounting brackets and hardware, hem bars, fabric designs, fabric attributes, such as transparency, translucency, and blackout materials, and the like. A customer may use the Crestron® Design Tool, a one-stop Web-based platform for all the Crestron® Shading Solutions designing, available from Crestron Electronics, Inc. of Rockleigh, N.J. Then, the customer will submit their order to the manufacturer. The manufacturer may use computer software to convert the customer requirements to manufacturing specifications for production, as is known in the art. The manufacturing specifications specify, for example, the radius  306  of the roller tube  301  to use, how long to cut the roller tube  301 , how long and wide to cut the shade material  303 , and what type of hardware to use in assembling the customized roller shade, including the type of hem bar  304 . All of the above customized properties will drive the weight of the shade material  303  and hem bar  304 , and thereby the roller shade torque profile  105 . 
     Using the aforementioned roller shade properties, the T max  and T min  values of the roller shade  300  are determined. T max  represents the maximum torque required to start rolling up the roller shade  300  when the shade material  303  is at the rolled down position and is substantially fully unraveled from the roller tube  301 . Thus, as shown in  FIG. 3A , the substantially entire weight of the shade material  303  plus the weight of the hem bar  304  need to be pulled up. T max  may be determined by the following formula: 
         T   max   =r   down λ( w   material   +w   hembar )  (1)
 
     where,
         T max  is the maximum torque required to lift the shade material  303  and hem bar  304 ,   r down  is the radius  308  of the roller tube  301  plus the thickness  312  of the shade material layers wrapped over the roller tube  301  (if any) when the shade material is at the rolled down position where substantially the entire shade material  303  is unraveled from the roller tube  301 ,   w material  is the weight of the entire shade material  303 , and   w hembar  is the weight of the hem bar  304 .
 
According to one embodiment, in roller shades where the entire shade material  303  is unraveled from the roller tube  301  in the rolled down position, radius (r down ) 308 equals to the radius (r tube ) of the roller tube  301 . In another embodiment, the roller shade may comprise an overwrap  310  where some length of shade material remains to be wrapped about the roller tube  301  when the shade material  303  is in the rolled down position. Thickness  312  represents the total thickness of the shade material layers that are wrapped over the roller tube  301 . Typically, the overwrap  310  will form a single layer of shade material  303  over the roller tube  301  and as such total thickness  312  would equal to thickness  309  of a single layer of shade material  303 . However, the overwrap  310  may form more than a single layer, resulting in greater overall thickness  312  of the shade material layers over the roller tube  301 . The shade material overwrap  310  may be used to hide the roller tube  301  and/or to eliminate the pull by the shade material on the point of contact between the shade material  303  and the roller tube  301  and prevent disengagement. In such a case, r down  is the radius  308  of the roller tube  301  plus the thickness  312  of the shade material layers over the roller tube  301  that remains to be wrapped about the roller tube  301  in the rolled down position to account for the additional shade material overwrap  310 . According to an embodiment, radius (r down )  308  may be determined using the following formula:
       

     
       
         
           
             
               
                 
                   
                     r 
                     down 
                   
                   = 
                   
                     
                       
                         
                           
                             t 
                             material 
                           
                           × 
                           
                             l 
                             overwrap 
                           
                         
                         π 
                       
                       + 
                       
                         
                           ( 
                           
                             r 
                             rt 
                           
                           ) 
                         
                         2 
                       
                     
                   
                 
               
               
                 
                   ( 
                   2 
                   ) 
                 
               
             
           
         
       
     
     where,
         r down  is the radius  308  of the roller tube  301  plus the shade material  303  (if any) at the rolled down position,   t material  is the thickness of the shade material  303  (single layer),   l overwrap  is the length of shade material overwrap  310  (if any), and   r tube  is the radius  306  of the roller tube  301 .
 
While the formulas above and below utilize the radius as the measuring parameter, for example for radius  306 ,  308 , and  311 , the formulas herein can instead use the diameter parameter without departing from the scope of the present embodiments.
       

     T min  represents the minimum torque required to finish rolling up the roller shade  300  when the shade material  303  is at the rolled up position and is substantially fully wrapped around the roller tube  301 . As shown in  FIG. 3B , the only weight that is being lifted at the end of the rolling up cycle substantially consists of the weight of the hem bar  304 . T min  may be determined by the following formula: 
         T   min   =r   up   ×w   hembar   (3)
 
     where,
         T min  is the minimum torque required to lift the shade material  303  and hem bar  304 ,   r up  is the radius  311  of the roller tube  301  plus the thickness  314  of the shade material layers wrapped over the roller tube  301  when the shade material is at the rolled up position where substantially the entire shade material  301  is wrapped around the roller tube  301 , and   w hembar  is the weight of the hem bar  304 .
 
Total thickness  314  of the shade material layers wrapped over the roller tube  301  represents the thickness  309  of the shade material  303  times the number of layers  313  that are wrapped about the roller tube  301  at the rolled up position. According to an embodiment, radius (r up )  311  may be determined using the following formula:
       

     
       
         
           
             
               
                 
                   
                     r 
                     up 
                   
                   = 
                   
                     
                       
                         
                           
                             t 
                             material 
                           
                           × 
                           
                             ( 
                             
                               
                                 l 
                                 material 
                               
                               + 
                               
                                 l 
                                 overwrap 
                               
                             
                             ) 
                           
                         
                         π 
                       
                       + 
                       
                         
                           ( 
                           
                             r 
                             tube 
                           
                           ) 
                         
                         2 
                       
                     
                   
                 
               
               
                 
                   ( 
                   4 
                   ) 
                 
               
             
           
         
       
     
     where,
         r up  is the radius of the roller tube  301  plus the shade material  303  at the rolled up position,   t material  is the thickness  309  of the shade material  303  (single layer),   l material  is the length of the shade material  303  that hangs from the roller tube  301  during the rolled down position,   l overwrap  is the length of shade material  303  overwrap  310  (if any), and   r tube  is the radius  306  of the roller tube  301 .       

     Exemplary T max    102  and T min    103  values are illustrated in  FIG. 2A . Using the T min  and T max  values, a slope is determined for the rate of change of the natural torque profile of the roller shade. The slope is determined using the following formula: 
     
       
         
           
             
               
                 
                   
                     k 
                      
                     
                       ( 
                       
                         
                           N 
                            
                           
                               
                           
                            
                           mm 
                         
                         turn 
                       
                       ) 
                     
                   
                   = 
                   
                     
                       
                         T 
                         max 
                       
                       - 
                       
                         T 
                         min 
                       
                     
                     
                       N 
                       turns 
                     
                   
                 
               
               
                 
                   ( 
                   5 
                   ) 
                 
               
             
           
         
       
     
     where,
         k is the torque slope of the roller shade,   T max  is the maximum torque required to lift the shade material  303  and hem bar  304 ,   T min  is the minimum torque required to lift the shade material  303  and hem bar  304 , and   N turns  is the number of turns between a rolled up position ( FIG. 3B ) and a rolled down position ( FIG. 3A ) of the roller shade.
 
According to an embodiment, N turns  may be determined using the following formula:
       

     
       
         
           
             
               
                 
                   
                     N 
                     turns 
                   
                   = 
                   
                     
                       ( 
                       
                         
                           r 
                           up 
                         
                         - 
                         
                           r 
                           down 
                         
                       
                       ) 
                     
                     
                       t 
                       material 
                     
                   
                 
               
               
                 
                   ( 
                   6 
                   ) 
                 
               
             
           
         
       
     
     where,
         r down  is the radius  308  of the roller tube  301  plus the shade material  303  (if any) at the rolled down position,   r up  is the radius  311  of the roller tube  301  plus the shade material  303  at the rolled up position, and   t material  is the thickness of the shade material  303 .       

     Optionally, as discussed above, the T max    202  and T min    203  values of the spring may be offset from the natural torque profile  105  of the roller shade. This can be accomplished through a static offset, as shown by formula 7 below, or a percentage offset, as shown by formula 8 below. 
         T   min_offset ( N  mm)= T   min −offset  (7)
 
         T   min_offset ( N  mm)= T   min ×(1−offset percentage )  (8)
 
     Once the slope and offset T min    203  value are determined, the number of preset pretension turns can be determined using the following formula: 
     
       
         
           
             
               
                 
                   
                     N 
                     pretension 
                   
                   = 
                   
                     
                       T 
                       
                         min 
                          
                         _ 
                          
                         offset 
                       
                     
                     k 
                   
                 
               
               
                 
                   ( 
                   9 
                   ) 
                 
               
             
           
         
       
     
     where,
         N pretension  is the number of pretensioned turns,   T min_offset  is the offset minimum torque required of the spring, and   k is the torque slope of the roller shade.
 
If no offset is being made, then T min  offset is substituted with T min    103  in the above formula. As shown, the number of pretension turns is determined using the slope of the natural torque profile of the roller shade to bring the minimum torque of the torsion spring up from zero torque to the desired minimum torque value, in this example T min    203 . As a result, when the determined preset number of pretension turns are put in the spring, T min    203  of the spring is either substantially equal to T min    103  of the roller shade  300 , or as shown in  FIG. 2A , it is slightly offset below T min    103  of the roller shade  300  by a predetermined amount. According to an embodiment, the preset number of pretension turns may comprise full 360 degree turns. However, since the pretension is achieved via motor rotation and may be locked via clutch  608  at any orientation, the preset number of pretension turns may include any fraction of 360 degree incremental turns. For example, the preset number of turns could comprise 35.4 turns.
       

     The next section describes an embodiment of a shade drive unit comprising a counterbalancing assembly having a torsion spring that may be pretensioned using the integrated motor of the roller shade and which assists the roller shade to raise and lower the shade during operation. Using the motor, the torsion spring of the counterbalancing assembly can be pretensioned at the factory, or thereafter, to a preset number of turns as required for a particular roller shade to effectively counterbalance the roller shade according to the systems, methods, and modes described above. 
     Referring to  FIG. 4 , there is shown a perspective view of a roller shade  400  according to one aspect of the embodiments. Roller shade  400  generally comprises a roller tube  401 , a shade drive unit  402 , an idler assembly  403 , shade material  406 , and a hem bar  410 . Shade material  410  is connected at its top end to the roller tube  401  and at its bottom end to the hem bar  410 . Shade material  406  wraps around the roller tube  401  and is unraveled from the roller tube  401  to cover a window, a door, a wall opening, or any other type of architectural opening. In various embodiments, shade material  406  comprises fabric, plastic, vinyl, or other materials known to those skilled in the art. 
     Roller tube  401  is generally cylindrical in shape and longitudinally extends from a first end  411   a  to a second end  411   b . In various embodiments, the roller tube  401  comprises aluminum, stainless steel, plastic, fiberglass, or other materials known to those skilled in the art. The first end  411   a  of the roller tube  401  receives the shade drive unit  402 , and the second end  411   b  of the roller tube  401  receives the idler assembly  403 . 
     The idler assembly  403  of the roller shade  100  may comprise an idler pin  409  and an idler body  408  inserted into the second end  411   b  of the roller tube  401 . The idler body  408  may be rotatably connected about the idler pin  409 . It is inserted into the roller tube  401  and is operably connected to the roller tube  401  such that rotation of the roller tube  401  also rotates the idler body  408 . The idler body  408  may comprise a flange  419  to prevent the idler body  408  from sliding entirely into the roller tube  401 . The idler body  408  may comprise ball bearings therein (not shown) allowing the idler body  408 , and thereby the roller tube  401 , rotate with respect to the idler pin  409 . The idler pin  409  may include a pin tip  413  disposed on its terminal end to attach the roller shade  400  to a mounting bracket  405   b.    
     During installation, the roller shade  400  is mounted on or in a window between the first and second mounting brackets  405   a  and  405   b . The roller shade  400  may first be mounted to the second mounting bracket  405   b  by inserting the idler pin tip  413  into a keyhole  418  of the second mounting bracket  405   b . The roller shade  400  may then be mounted to the first mounting bracket  405   a  by snapping the motor head  427  of the shade drive unit  402  to the first mounting bracket  405   a  or coupling the shade drive unit  404  to the first mounting bracket  405   a  using screws. The mounting brackets  405   a  and  405   b  can comprise similar configuration to the CSS-DECOR3 QMT®3 Series Décor Shade Hardware, available from Crestron Electronics, Inc. of Rockleigh, N.J. Other types of brackets may be utilized without departing from the scope of the present embodiments. 
     The shade drive unit  402  may comprise a motor head  427 , a crown adapter wheel  416 , a motor housing  407  containing a motor control module  602  and motor  601  ( FIG. 6 ) therein, an idler crown wheel  417 , a counterbalancing spring  420 , and a drive wheel  421 . The shade drive unit  402  may be inserted into the roller tube  401  from the first end  411   a . The crown adapter wheel  416 , idle crown wheel  417 , and drive wheel  421  are generally cylindrical in shape and are inserted into and operably connected to roller tube  401  through its first end  411   a . Crown adapter wheel  416 , idle wheel  417 , and drive wheel  421  may comprise a plurality of channels  422  extending circumferentially about their external surfaces. Channels  422  mate with complementary projections  424  radially extending from an inner surface  434  of roller tube  401  such that crown adapter wheel  416 , idle crown wheel  417 , drive wheel  421 , and roller tube  401  rotate together during operation. Crown adapter wheel  416  and idler crown wheel  417  can further comprise a plurality of teeth  425  extending circumferentially about their external surfaces to form a friction fit with the inner surface of the roller tube  401 . Crown adapter wheel  416  can further comprise a flange  426  radially extending therefrom. Flange  426  prevents the crown adapter wheel  416  from sliding entirely into the roller tube  401 , such that the motor head  427  remains exterior to the roller tube  401 . The crown adapter wheel  416  removably and releasably couples the shade drive unit  402  to the roller tube  401 . The drive wheel  421  is operably connected to the output shaft  605  of the motor  601  as will be later described such that rotation of the motor output shaft  605  also rotates the drive wheel  421 . The crown adapter wheel  416  may be rotatably attached to a first end of the motor housing  407  via ball bearings therein (not shown), while the idle wheel  417  may be rotatably attached to a second end of the motor housing  407  via ball bearings  495  ( FIG. 9 ) therein. This ensures that the motor  601  ( FIG. 6 ) is held concentric to the roller tube  401  at the front and the rear of the motor housing  407  by the crown adapter wheel  416  and the idle wheel  417 . 
     In operation, the roller shade  400  is rolled down and rolled up via the shade drive unit  402 . Particularly, the motor  601  drives the drive wheel  421 , which in turn engages and rotates the roller tube  401 . The roller tube  401 , in turn, engages and rotates the crown adapter wheel  416 , idle crown wheel  417 , and idler body  408  with respect to the motor  601 , while the motor housing  407 , including the motor  601  and motor control module  602 , remain stationary. As a result, the shade material  406  may be lowered from an opened or rolled up position, when substantially the entire shade material  406  is wrapped about the roller tube  401 , to a closed or rolled down position, when the shade material  406  is substantially unraveled, and vice versa. 
       FIG. 5  is an illustrative block diagram  500  of the shade drive unit  402  according to one embodiment. The shade drive unit  402  may comprise the motor  601  and a motor control module  602 . The motor control module  602  operates to control the motor  601 , directing the operation of the motor, including its direction, speed, and position. The motor control module  602  may comprise fully integrated electronics. The motor control module  602  can comprise a controller  504 , a memory  506 , a communication interface  510 , a user interface  509 , and a light indicator  507 . 
     Power supply  502  can provide power to the circuitry of the motor control module  602 , and in turn the motor  601 . Power can be supplied to the motor control module  602  through a power cord  428  ( FIG. 4 ) by connecting a terminal block  432  to a dedicated power supply  502 , such as the CSA-PWS40 or CSA-PWS10S-HUB-ENET power supplies, available from Crestron Electronics, Inc. of Rockleigh, N.J. In another embodiment, the shade drive unit  402  may be battery operated and as such may be connected to an internal or external power supply  502  in a form of batteries. In yet another embodiment, the shade drive unit  402  may be powered via solar panels placed in proximity to the window to aggregate solar energy. 
     Controller  504  can represent one or more microprocessors, and the microprocessors can be “general purpose” microprocessors, a combination of general and special purpose microprocessors, or application specific integrated circuits (ASICs). Controller  504  can provide processing capability to provide processing for one or more of the techniques and functions described herein. Memory  506  can be communicably coupled to controller  504  and can store data and executable code. In another embodiment, memory  506  is integrated into the controller  504 . Memory  506  can represent volatile memory such as random-access memory (RAM), but can also include nonvolatile memory, such as read-only memory (ROM) or Flash memory. 
     Motor control module  602  may further comprise a communication interface  510 , such as a wired or a wireless communication interface, configured for receiving control commands from an external control point. The wireless interface may be configured for bidirectional wireless communication with other electronic devices over a wireless network. In various embodiments, the wireless interface  510  can comprise a radio frequency (RF) transceiver, an infrared (IR) transceiver, or other communication technologies known to those skilled in the art. In one embodiment, the wireless interface  510  communicates using the infiNET EX® protocol from Crestron Electronics, Inc. of Rockleigh, N.J. infiNET EX® is an extremely reliable and affordable protocol that employs steadfast two-way RF communications throughout a residential or commercial structure without the need for physical control wiring. infiNET EX® utilizes 16 channels on an embedded 2.4 GHz mesh network topology, allowing each infiNET EX® device to function as an expander, passing command signals through to every other infiNET EX® device within range (approximately 150 feet or 46 meters indoors), ensuring that every command reaches its intended destination without disruption. In another embodiment, communication is employed using the ZigBee® protocol from ZigBee Alliance. In yet another embodiment, wireless communication interface  510  may communicate via Bluetooth transmission. 
     A wired communication interface  510  may be configured for bidirectional communication with other devices over a wired network. The wired interface  510  can represent, for example, an Ethernet or a Cresnet® port. Cresnet® provides a network wiring solution for Crestron® keypads, lighting controls, thermostats, and other devices. The Cresnet® bus offers wiring and configuration, carrying bidirectional communication and 24 VDC power to each device over a simple 4-conductor cable. 
     In various aspects of the embodiments, the communication interface  510  and/or power supply  502  can comprise a Power over Ethernet (PoE) interface. The controller  504  can receive both the electric power signal and the control input from a network through the PoE interface. For example, the PoE interface may be connected through category 5 cable (CAT5) to a local area network (LAN) which contains both a power supply and multiple control points and signal generators. Additionally, through the PoE interface, the controller  504  may interface with the internet and receive control inputs remotely, such as from a homeowner running an application on a smart phone. 
     Motor control module  602  can further comprise a local user interface  509 , such as a buttons disposed on the motor head  427  (not shown), that allows users to set up the shade drive unit  402  at the factory, for example to pretension the shade drive unit  402 , or after installation in the field, for example to set the shade upper and lower limits. Furthermore, the motor control module  602  may comprise a light indicator  507 , such as a multicolor light emitting diode (LED) disposed on the motor head  427  (not shown), for indicating the motor status. 
     The control commands received by the controller  504  may be a direct user input to the controller  504  from the user interface  509  or a wired or wireless signal from an external control point. For example, the controller  504  may receive a control command from a wall-mounted button panel or a touch-panel in response to a button actuation or similar action by the user. Control commands may also originate from a signal generator such as a timer or a sensor. Accordingly, the motor control module  602  can integrate seamlessly with other control systems using the communication interface  510  to be operated from keypads, wireless remotes, touch screens, and wireless communication devices, such as smart phones. Additionally, the motor control module  602  can be integrated within a large scale building automation system or a small scale home automation system and be controllable by a central control processor, such as the PRO3 control processor available from Crestron Electronics, Inc., that networks, manages, and controls a building management system. 
       FIGS. 6-9  illustrate various views of the shade drive unit  402  in greater detail. Specifically,  FIG. 6  shows a first side perspective view of the shade drive unit  402 ;  FIG. 7  shows a second side perspective view of the shade drive unit  402 ,  FIG. 8  shows an exploded perspective view of a portion of the shade drive unit  402 , and  FIG. 9  shows a cross-sectional view of a portion of the shade drive unit  402 . Referring to  FIGS. 6-9 , shade drive unit  402  includes a motor housing  407  that houses the motor control module  602  and the motor  601 . According to an embodiment, the motor  601  is suspended in the motor housing  407  using a rubber O-ring  603  at the front of the motor  601  and a rubber locking strip  604  at the rear of the motor  601 . This allows the motor  601  to be substantially centered within the motor housing  407 . The motor  601  may comprise a brushless direct current (BLDC) electric motor. In another embodiment, the motor  601  comprises a brushed direct current (DC) motor, or any other motor known in the art. 
     The motor  601  drives the drive wheel  421  through a series of drive train components that in combination provide efficiency and counterbalancing to the roller shade, including a first stage planetary gear  606 , a clutch  608 , and a final stage planetary gear  609 , which are described in more detail in U.S. patent application Ser. No. 15/872,467, filed on Jan. 16, 2018, and titled “Motor Pretensioned Rolle Shade”, the entire contents of which are hereby incorporated by reference. In one embodiment, the first and final stage planetary gears  606  and  609  may be configured for providing speed reduction and torque increase to achieve efficient operation of the motor  601 . According to another embodiment, the first and final stage planetary gears  606  and  609  may be configured for providing increased speed and decreased torque. According to various aspects of the embodiment, the shade drive unit  402  may comprise less, additional, or no planetary gears. In operation, the output shaft  605  of the motor  601  drives into the first stage planetary gear  606 , which in turn drives into an input stage of a clutch  608 , which drives into an input stage of the final stage planetary gear  609 , which drives the output mandrel  610 , and which drives the drive wheel  421 . 
     Referring to  FIG. 8 , the output mandrel  610  extends from a first end connected to the final stage planetary gear  609  within the motor housing  407 , out of an opening  615  in the motor housing  407 , and to a second end connected to the drive wheel  421 . According to one embodiment, output mandrel  610  may comprise a single body. Yet according to another embodiment, the output mandrel  610  may comprise a first mandrel portion  611  and a second mandrel portion  612 . The first mandrel portion  611  can comprise a keyed bore  614  while the second mandrel portion  612  can comprise an extrusion with keyed grooves  616  configured to mate with the keyed bore  614  of the first mandrel portion  611 . The second mandrel portion  612  can be inserted into the keyed bore  614  of the first mandrel portion  611  and be secured using a retaining clip  617  such that rotation of the first mandrel portion  611  by the motor  601  also rotates the second mandrel portion  612 . 
     The counterbalancing spring  420  longitudinally extends from a first end  423   a  to a second end  423   b . Spring  420  is mounted about the output mandrel  610 , which holds and stabilizes the spring  420  within the roller tube  401 , preventing the spring  420  from sagging within the roller tube  401 . Motor housing  407  may comprise a first spring carrier  621  configured for engaging and retaining the first end  423   a  of the spring  420 . On the opposite end, drive wheel  421  may comprise a second spring carrier  622  configured for engaging and retaining the second end  423   b  of the spring  420 . According to one embodiment, each spring carrier  621  and  622  can comprise a cylindrical body comprising threads  623  adapted to retain the coils of the spring. According to an alternate embodiment, the spring  420  may be retained over the spring carriers  621  and  622  using retaining clips in a similar configuration as disclosed in U.S. patent application Ser. No. 16/855,694, filed on Apr. 22, 2020. and titled “Counterbalancing Spring Fasteners”, the entire contents of which are hereby incorporated by reference. 
     The drive wheel  421  comprises a cylindrical body  625  comprising an outer surface  626  that slidably contacts the inner surface  434  of the roller tube  401 . The cylindrical body  625  of drive wheel  421  is dimensioned and constructed such that it can longitudinally travel within the roller tube  401  via channels  422  and projections  424  along center axis  604 . This translation allows the drive wheel  421  to be displaced longitudinally when the shade drive unit  402  is inserted into the roller tube  401  during installation. The cylindrical body  625  of the drive wheel  421  extends from a first end  627   a  to a second end  627   b . The second spring carrier  622  extends from the first end  627   a  of the cylindrical body  625 . The cylindrical body  625  further comprises a washer receiving cavity  630  recessed into the second end  627   b  of the cylindrical body  625  that is defined by an opening  631  at the second end  627   b  of the cylindrical body  625  and a biasing surface  628  within the cylindrical body  625  of the drive wheel  421 . In addition, washer retaining arms  629  circumferentially and inwardly extend from the cylindrical body  625  at the opening  631 . The drive wheel  421  may further comprise a keyed bore  632  that traversely extends through the cylindrical body  625  and the second spring carrier  622  of the drive wheel  421 . The keyed bore  632  is adapted to slidably retain the second mandrel portion  612  therein. As discussed above, the second mandrel portion  612  can comprise an extrusion with keyed grooves  616  configured to mate with the keyed bore  632  such that rotation of the second mandrel portion  612  also rotates the drive wheel  421 . The drive wheel  421  may be attached to the second end of the second mandrel portion  612  using a washer  640  and screw  643 . The washer  640  may comprise a hole  641  for receiving the screw  643  and locking arms  642  adapted to engage the retaining arms  629  of the drive wheel  421 . 
     According to an embodiment, shade drive unit  402  can be stocked with only the first mandrel portion  611  extending out of the motor housing  407  through opening  615 . After a customer places an order for a customized size roller shade  400 , the manufacturing specifications may be determined as discussed above to specify the type of required assembly components, their sizes, as well as the pretension specifications. Using the manufacturing specifications, an appropriate counterbalancing spring  420  is chosen, with specified wire diameter, coil diameter, and length. According to an embodiment, for each roller tube diameter, a factory may maintain an inventory of springs with the same wire diameter and coil diameter. The spring  420  may be cut to a specified length based on the manufacturing specifications. According to another embodiment, the factory may maintain an inventory of springs with lengths at 1 inch or half inch increments that can be chosen for assembly based on the manufacturing specifications. According to an embodiment, for each roller tube diameter with predetermined wire diameter and coil diameter, the following formula may be used to determine the total number of coils of the required spring  420 : 
     
       
         
           
             
               
                 
                   
                     N 
                     coils 
                   
                   = 
                   
                     
                       
                         N 
                         fastened 
                       
                       × 
                       2 
                     
                     + 
                     
                       
                         
                           
                             ( 
                             
                               
                                 d 
                                 wire 
                               
                                
                               
                                 / 
                               
                                
                               1000 
                             
                             ) 
                           
                           4 
                         
                         × 
                         
                           ( 
                           
                             E 
                             × 
                             1000000 
                           
                           ) 
                         
                       
                       
                         ( 
                         
                           
                             C 
                             friction 
                           
                           × 
                           
                             ( 
                             
                               
                                 d 
                                 coils 
                               
                                
                               
                                 / 
                               
                                
                               1000 
                             
                             ) 
                           
                           × 
                           
                             ( 
                             
                               k 
                                
                               
                                 / 
                               
                                
                               1000 
                             
                             ) 
                           
                         
                         ) 
                       
                     
                   
                 
               
               
                 
                   ( 
                   10 
                   ) 
                 
               
             
           
         
       
     
     where,
         N coils  is the total number of coils of the required spring,   N fastened  is the number of nonactive coils at each end of the spring that are attached to the spring carrier  621 / 622 ,   d wire  is the diameter of the spring wire,   E is the elastic modulus (MPa), which is the elasticity property of the spring metal,   C friction  is a constant representing the friction between the spring coils,   d coils  is the mean diameter of the spring coils, and   k is the slope of the torque profile of the roller shade.
 
Using the total number of coils of the required spring, the total length of the required spring may be determined using the following formula:
       

     
       
      
       l 
       spring 
       =N 
       coils 
       ×d 
       wire  
      
     
     where,
         l spring  is the total length of the spring,   N coils  is the total number of coils of the required spring, and   d wire  is the diameter of the spring wire.
 
The required spring  420  may be cut in length to the determined total length (l spring ).
       

     In addition, the manufacturing specifications will also specify the required length of the second mandrel portion  612 , which may be cut to size to accommodate the length (l spring ) of the required spring  420 . According to the present embodiments, the ends  423   a  and  423   b  of the spring  420  are fixidly mounted to the shade drive unit  402  such that the spring  420  is maintained at a constant length and cannot translate in length. The second mandrel portion  612  comprises a length such that the spring  420  is maintained in a stretched out state. Stretching out the spring  420  prevents the individual spring coils from touching each other and therefore reducing friction created by the spring  420  as it is being tensioned. Furthermore, according to the present embodiment, the determined length of the second mandrel portion  612  accounts for the deflection of the spring  420  when it is pretensioned as well as when it is further tensioned during the operation of the roller shade  400 . Specifically, as the spring  420  is tensioned during its pretensioning at the factory and further during operation when the roller shade  400  rolls down to the rolled down position, the coils of the spring  420  will become tighter causing the space between the coils to become smaller. As such, the construction of the motor drive unit  402  of the present embodiments stretches out the spring  420  and maintains it in a stretched out state such that its individual coils do not contact when the spring  420  is fully tensioned when the roller shade  400  is at the rolled down position. To account for the maximum tensioning of the spring  420 , the following formula may be used to determine the length of the spring  420  at a maximum tension—i.e., as the spring would be at the rolled down position of the roller shade  400 : 
         l   deflected   =d   wire (( N   coils   −N   fastened ×2)+ N   turns   +N   pretension +1)  (12)
 
     where,
         l deflected  is the deflected length of the active portion of the spring  420  at maximum tension,   d wire  is the diameter of the spring wire,   N coils  is the total number of coils of the required spring,   N fastened  is the number of nonactive coils at each end of the spring that are fastened to a spring carrier  621 / 622 ,   N turns  is the number of turns between a rolled up position and a rolled down position of the roller shade, and   N pretension  is the number of pretensioned turns.       

     The length of the second mandrel portion  612  is determined to ensure that the spring  420  is maintained at a stretched out state between the terminal ends of first mandrel portion  621  and the second mandrel portion  621  when the roller shade  400  is at the rolled down position. As such, the length of the second mandrel portion  612  accounts for the deflection of the spring  420  at the rolled down position as well as the assembly factors, and may be determined using the following formula: 
         l   mandrel   =l   deflected   +l   clearance   +l   components   (13)
 
     where,
         l mandrel  is the length the second mandrel portion  612 ,   l deflected  is the deflected length of the active portion of the spring  420  at maximum tension,   l clearance  is a clearance factor that is added to ensure that the spring coils do not touch when the spring  420  is fully tensioned at the rolled down position, and   l components  is an adjustment factor to account for the assembly components of the shade drive unit assembly.
 
Particularly, the adjustment length factor l components  accounts for the additional length required for the second mandrel portion  612  to be fastened into the first mandrel portion  621  and into the second mandrel portion  622 , minus the length of the first mandrel portion  611  that extends out of the first spring carrier  621 . The second mandrel portion  612  may then be cut to the determined length specification (l mandrel ).
       

     Referring to  FIG. 8 , during assembly of the roller shade  400  to customer specifications, the cut second mandrel portion  612  is inserted into the keyed bore  614  of the first mandrel portion  611  and secured using the retaining clip  617 . Then, the spring  420  is slipped over the second mandrel portion  612  and the first end  423   a  of the spring  420  is concentrically mounted about the first spring carrier  621  by twisting the spring coils onto threads  623  of the first spring carrier  621 . The drive wheel  421  is then mounted over the second mandrel portion  612  by inserting the terminal end of the second mandrel portion  612  through bore  632  in the drive wheel  421  until the second end  423   b  of the spring  420  can be concentrically mounted about the second spring carrier  622  by twisting the spring coils onto threads  623  on the second spring carrier  622 . After attaching the spring  420  to the second spring carrier  622 , the drive wheel  421  is pulled to pull the second end  423   b  of the spring  420  away from the first end  421   a  of the spring  420  and stretch out the spring  420  until the terminal end of the second mandrel portion  612  is fully inside bore  632  and does not extend out of the bore  632  of the drive wheel  421 . Washer  640  may then be inserted through opening  631  in the second end  627   b  of the cylindrical body  625  of the drive wheel  421  by aligning the locking arms  642  of the washer  640  with the space between any two retaining arms  629  of the cylindrical body  625  of the drive wheel  421 . The washer  640  may then be inserted into the washer receiving cavity  630  and biased against the washer biasing surface  628  and turned until the locking arms  642  of the washer  640  engage the retaining arms  629  of the drive wheel  421 . The washer  640  may then be secured to the drive wheel  421  by inserting the screw  643  through the hole  641  in the washer  640  and screwing it into a threaded hole  645  in the terminal end of the second mandrel portion  612 . The washer  640  secures the drive wheel  421  to the terminal end of the second mandrel portion  612  such that the spring  420  is maintained in a stretched state to add separation between the spring coils and thereby eliminate any friction between the coils. As previously discussed, the spring  420  is stretched to a length that mains a distance  633  between the spring coils even when the roller shade  400  is at a rolled down position by accounting for the tensioning and resulting deflection of the spring  420  at the rolled down position. 
     Using the above discussed assembly, the roller shade  400  may then be pretensioned by the above determined pretension turns (N pretension ) in either a clockwise or counterclockwise direction, depending in which direction the shade drive unit  402  needs to turn to unravel the shade material  406  from the roller tube  401  and the direction of the spring coils. For example, if the roller shade  400  is configured to lift the shade material  406  from a closed position to an opened position in a counterclockwise direction, the spring  420  should be pretensioned in a clockwise direction. On the other hand, if the roller shade  400  is configured to lift the shade material  406  from a closed position to an opened position in a clockwise direction, the spring  420  should be pretensioned in a counterclockwise direction. 
     To pretension the roller shade  400 , the shade drive unit  402  may enter into a pretensioning mode to pretension the spring  420  according to the predetermined number of pretension turns, for example in a counterclockwise direction. For example, the pretensioning mode may be initiated by pressing a button or a combination of buttons using the user interface  509 . According to an embodiment, the motor controller  504  may indicate that it is in the pretensioning mode by blinking the light indicator  507  red. The determined number of pretension turns may be communicated to the motor controller  504  in a variety of ways. According to an embodiment, a technician may connect the shade drive unit  402  to a programming computer or tool (not shown) via the communication interface  510  and enter shade parameters and spring parameters into the programming computer. The programming computer may calculate the preset number of pretension turns and communicate that information to the motor controller  504 . According to another embodiment, the technician may enter the preset number of pretension turns via the user interface  509 . The motor controller  504  may store the predetermined number of pretension turns in memory  506 . 
     The shade drive unit  402  is pretensioned while it is located outside the roller tube  401 , such that rotation of the drive wheel  421  is located outside the roller tube  401  and is not hindered by any object. According to an embodiment, the shade drive unit  402  may be placed on a rack that holds the motor housing  407  still, but which does not contact the drive wheel  421 . According to another embodiment, the technician may hold the motor housing  407 , without contacting the drive wheel  421 , during pretensioning. 
     The motor controller  504  will then signal the motor  601  to rotate the motor output shaft  605  a predetermined number of turns in the counterclockwise direction while the motor housing  407  is held stationary. Because the shade drive unit  402  may comprise a plurality of planetary gear assemblies  606  and  609 , the actual number of revolutions that the motor output shaft  605  needs to turn to achieve the predetermined number of pretension turns at the spring  420  may be adjusted by a predetermined ratio depending on the configuration of the planetary gear assemblies  606  and  609 . As discussed above, the motor output shaft  605  will drive the output mandrel  610  and drive wheel  421  through the first stage planetary gear  606 , clutch  608 , and final stage planetary gear  609 . As the drive wheel  421  rotates in the counterclockwise direction, the second spring carrier  622  also rotates in a counterclockwise direction, while the first spring carrier  621  and motor housing  407  remain stationary. This results in pretensioning the counterbalancing spring  420  as its second end  423   b , connected to the second spring carrier  622 , rotates in a counterclockwise direction with respect to its first end  423   a , connected to the first spring carrier  621 . Pretensioning turns are then applied by continual rotation of the drive wheel  421  with respect to the motor housing  407  until the predetermined number of pretensioning turns is reached. 
     After the desired number of pretensioning turns is reached, the motor  601  may stop and the motor controller  504  may exit the pretensioning mode, stop blinking the light indicator  507  red, and turn the light indicator  507  green to indicate that the pretensioning mode is complete. The clutch of the drive train prevents any rotational motion back from the drive wheel  421  such that clutch can lock the pretension in the spring  420 . The technician may then complete assembling the roller shade  400  by inserting the pretensioned shade drive unit  402  into the roller tube  401  and packaging the roller shade  400 . After its assembly, the roller shade  400  is shipped out to the customer to be installed in a window. 
     After installation and during operation, to roll down the roller shade  400 , the motor  601  rotates the drive wheel  421  and thereby the second spring carrier  622  and roller tube  401  in a first direction, while the motor housing  407  and thereby the first spring carrier  621  remain stationary. Rotation of the motor  601 , as well as the increasing weight of the shade material  406  and the hem bar  410 , cause the counterbalancing spring  420  to progressively build torque. The pretensioning ensures that the rolling down cycle of the roller shade  400  starts at the desired T min  value  203 , as discussed above with reference to  FIG. 2A . As the roller shade  400  rolls down, counterbalancing spring  420  continues to build torque in substantially a linear fashion (traveling left along the x-axis in the diagram of  FIG. 2A ) until the T max  value  202  is reached. As the roller shade  400  rolls down, the shade material  406  gradually unravels and progressively more shade material  409  hangs down from the roller tube  401 . The increasing weight of the shade material  406  and the hem bar  410  assist the motor  601  to build torque in the counterbalancing spring  420  throughout the rolling down cycle without the motor  601  requiring to exert much power, as shown by the exerted motor torque  208  and power  210 . In addition, as the spring  420  continuously builds torque, it is tensioned causing its coils to tighten and come closer to each other until the roller shade  400  reaches the rolled down position. However, because the spring  420  was stretched over the output mandrel  610  to a length that accounted the length of the spring deflection plus a clearance factor, at the fully tensioned state the spring coils do not touch or rub and do not add any friction to the shade drive unit  402 . 
     When rolling up the shade  400 , the torque that was built up in the counterbalancing spring  420  during the rolling down cycle assists the motor  601  to roll up the shade  400  during the entire rolling up cycle (traveling right along the x-axis in the diagram of  FIG. 2A ). As the roller shade  400  rolls up, counterbalancing spring  420  releases torque in a substantially linear fashion until the T min  value  203  is reached. The decreasing weight of the shade material  406  and the hem bar  410  combined with the progressively released torque by the spring  420  effectively assist the motor  601  to roll up the shade material  460  throughout the rolling up cycle without the motor  601  requiring to exert much power, as shown by the exerted motor torque  208  and power  210 . Spring  420  assists the motor  601  to finish rolling up the shade material  406  all the way through the end of the rolling up cycle because the torque of the counterbalancing spring  420  does not return to zero, but returns to the T min  value  203  as a result of the pretension. 
     At the end of each rolling up cycle, the pretension put into the spring  420  continues to be locked by the clutch  608 . The pretension continues to be locked even if the roller shade  400  is knocked down or hit accidentally, or when the shade needs to be removed and reinstalled. Beneficially, the roller shade  400  may be easily serviced by a field technician or repaired as the roller shade may be easily disassembled and the factory specified pretension turns may be put back into the spring  420 . In addition, if a defective motor needs to be replaced, the customized pretensioning information of the defective motor stored in memory  506  may be transferred to and used by the replacement motor to pretension its spring. 
     According to further aspects of the embodiments, pretensioning of the roller shade  400  can be accomplished in a clockwise direction in a substantially similar manner as discussed above, but with rotation of the motor output shaft  605 , and thereby drive wheel  421 , in a clockwise direction with respect to the motor housing  407 . According to an embodiment, a different torsion spring may be used with coils winding in a clockwise direction. Pretension of the roller shade  400  may then be locked in a clockwise direction and the roller shade  400  can rotate in a clockwise direction to roll down the shade material  406 , and in counterclockwise direction to roll up the shade material  406  in substantially the same way as discussed above. 
     INDUSTRIAL APPLICABILITY 
     To solve the aforementioned problems, the aspects of the embodiments are directed toward systems, methods, and modes for counterbalancing and pretensioning a roller shade via a motor to lower the torque load on the motor of the roller shade throughout the rolling up or rolling down cycles. It should be understood that this description is not intended to limit the embodiments. On the contrary, the embodiments are intended to cover alternatives, modifications, and equivalents, which are included in the spirit and scope of the embodiments as defined by the appended claims. Further, in the detailed description of the embodiments, numerous specific details are set forth to provide a comprehensive understanding of the claimed embodiments. However, one skilled in the art would understand that various embodiments may be practiced without such specific details. 
     Although the features and elements of aspects of the embodiments are described being in particular combinations, each feature or element can be used alone, without the other features and elements of the embodiments, or in various combinations with or without other features and elements disclosed herein. 
     This written description uses examples of the subject matter disclosed to enable any person skilled in the art to practice the same, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the subject matter is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims. 
     The above-described embodiments are intended to be illustrative in all respects, rather than restrictive, of the embodiments. Thus the embodiments are capable of many variations in detailed implementation that can be derived from the description contained herein by a person skilled in the art. No element, act, or instruction used in the description of the present application should be construed as critical or essential to the embodiments unless explicitly described as such. Also, as used herein, the article “a” is intended to include one or more items. 
     All United States patents and applications, foreign patents, and publications discussed above are hereby incorporated herein by reference in their entireties. 
     Alternate Embodiments 
     Alternate embodiments may be devised without departing from the spirit or the scope of the different aspects of the embodiments. The embodiments described herein may be used for covering windows as well as doors, wall openings, or the like. The embodiments described herein may further be adapted in other types of window or door coverings, such as inverted rollers, Roman shades, Austrian shades, pleated shades, blinds, shutters, skylight shades, garage doors, or the like. 
     Moreover, the processes described herein are not meant to limit the aspects of the embodiments, or to suggest that the aspects of the embodiments should be implemented following these processes. The purpose of the aforementioned processes is to facilitate the understanding of one or more aspects of the embodiments and to provide the reader with one or many possible implementations of the processes discussed herein. The steps performed during the aforementioned process are not intended to completely describe the processes but only to illustrate some of the aspects discussed above. It should be understood by one of ordinary skill in the art that the steps may be performed in a different order and that some steps may be eliminated or substituted.