Patent Publication Number: US-2021189798-A1

Title: Window covering

Description:
BACKGROUND OF THE DISCLOSURE 
     1. Field of the Disclosure 
     The present disclosure relates generally to a window covering, and more particularly to a window covering which uses a motor to extend and retract (i.e., to raise and lower) the covering material thereof. 
     2. Description of the Prior Art 
     When installed to cover building openings, window coverings can provide specific effects, such as keeping privacy, insulating heat, and blocking light. Typically, a conventional window covering includes a headrail and a covering material; in the headrail, there are usually a spindle, a decelerator, a motor, and a control device. The covering material is located below the headrail, and can be driven through a cord which is connected to the spindle. The decelerator is connected between the spindle and a shaft of the motor. The control device can be used to control the motor, whereby the shaft is able to, through the decelerator and the spindle, drive the covering material to be extended or retracted. 
     If the covering material is hindered or even pulled downward by someone or some objects during its collapsing or ascending and therefore is unable to rise smoothly, such situation may cause damages to the blocking objects. In addition to this, the force that holds the covering material back will be also transferred to the motor through the spindle, becoming a force exerted on the motor in a direction opposite to its rotating direction. The covering material, the power transmitting mechanism, or even the motor itself may get damaged as a result. On the other hand, while the covering material is expanding (i.e., closing), the motor will not stop operating until receiving a stop command, and therefore the covering material will keep descending even if it bumps into any blocking object. A continuously lowering covering material is possible to damage the blocking object, or, since the bottom of the covering material is obstructed by the blocking object, the covering material is likely to expand or lower unevenly with unbalanced tension, and the rest of the cord which is still wound around the spindle may become misarranged or loose, affecting the smoothness of the operations taken place next time. 
     In addition, the upper and lower limits corresponding to the complete retracted and extended states of the covering material have to be set up before the window covering is ready to use so that the motor can automatically stop operating when the window covering is fully opened or closed. The conventional way to do the set-up is to manually stop the motor through a control device when the covering material is fully raised or lowered. A position detector connected to the shaft of the motor is then used to detect and collect the location information corresponding to the current states of the window covering, and the location information will be saved in the control device. Once the position detector is rotated to a recorded position information as being concurrently driven by the shaft of the motor, the control device sends out a command to make the motor stop operating. However, this manual way to set up the upper and lower limits requires additional preparation in advance, and the information deviation of the position detector can accumulate after a period of use, leading to imprecise upper and lower limits that have to be recalibrated, which unnecessarily increases the inconvenience of using a window covering. 
     SUMMARY OF THE DISCLOSURE 
     The present disclosure provides a window covering which includes a headrail, a covering material, a rotating member, a driving device, and a control device. The headrail has a longitudinal direction. The covering material is provided below the headrail. The rotating member is provided in the headrail and connected to the covering material, wherein the rotating member is adapted to drive the covering material to be extended or retracted. The driving device is provided in the headrail and coupled to the rotating member, wherein the driving device drives the rotating member to rotate. The control device is provided in the headrail and electrically connected to the driving device. When a moving speed of a lower end of the covering material decreases and such situation lasts for a predetermined time, the control device controls the driving device to stop operating. 
     With the above design, the control device could control the driving device to stop operating when the moving speed of the lower end of the covering material decreases and the situation lasts for a predetermined time. In this way, no matter whether the covering material is fully expanded to a fully expanded (i.e., fully lowered) position, is fully collapsed to a fully collapsed (i.e., fully raised) position, or encounters resistance during its movement, the driving device could be controlled to stop operating, whereby the covering material could be stopped from continuously moving. As a result, the components and procedures required for setting up the upper and lower limits could be reduced or even omitted. Furthermore, in any circumstances that a window covering bumps into a blocking object, the window covering could be prevented from further colliding with the blocking object, and therefore the blocking object and the window covering would not be damaged. 
     These and other objectives of the present disclosure will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present disclosure will be best understood by referring to the following detailed description of some illustrative embodiments in conjunction with the accompanying drawings, in which 
         FIG. 1  is a perspective view of the window covering of a first embodiment of the present disclosure; 
         FIG. 2  is a partial exploded perspective view of the window covering of the first embodiment; 
         FIG. 3  is a schematic view showing the connection relation of the control device of the first embodiment; 
         FIG. 4  is a chart showing the relation between the rotating speed of the rotating member of the first embodiment and time; 
         FIG. 5  is a perspective view of the detecting assembly located on the left side of the first embodiment; 
         FIG. 6  is a perspective view of the detecting assembly located on the right side of the first embodiment; 
         FIG. 7  is an exploded perspective view of the detecting assembly located on the left side of the first embodiment; 
         FIG. 8  is a schematic view showing the cord is located at a predetermined position; 
         FIG. 9  is a schematic view showing the winding portion of the torsion spring presses the switch; 
         FIG. 10  is a schematic view showing the detecting assembly of a second embodiment of the present disclosure; 
         FIG. 11  is a schematic view, showing the operation rod of the switch retreats into the main body; 
         FIG. 12  is a schematic view, showing the situation when the lower end of the covering material encounters resistance at a location within the first predetermined distance; and 
         FIG. 13  is a schematic view, showing the situation when the lower end of the covering material encounters resistance at a location out of the first predetermined distance. 
     
    
    
     DETAILED DESCRIPTION 
     A window covering  100  of a first embodiment of the present disclosure is shown in  FIG. 1  to  FIG. 10  which includes a headrail  10 , a covering material  12 , a rotating member  14 , a driving device  16 , and a control device  24 . 
     The headrail  10  is a frame having a receiving space  10   a  therein. The covering material  12  is located below the headrail  10 , and the covering material  12  has a lower end  12   a  away from the headrail  10 . 
     The rotating member  14  is provided in the receiving space  10   a  of the headrail  10 , and includes a spindle  142  and two spools  144 . The spindle  142  extends in a longitudinal direction of the headrail  10 . The spools  144  fixedly fit around the spindle  142 , and are apart from each other by a certain distance. Each of the spools  144  has a cord  44  wound therearound, wherein an end of each of the cords  44  is fixed at the corresponding one of the spool  144 . 
     Each of the cords  44  passes through a cord hole  102  located on a bottom of the headrail  10 , and goes through the covering material  12  in a vertical direction, with another end thereof reaching the lower end  12   a  of the covering material  12 . The lower end  12   a  of the covering material  12  includes a bottom rail  122 , wherein the another ends of the cords  44  are connected to the bottom rail  122 . In some embodiments, the number of the spools  144  and the cords  44  are not limited to be two as exemplified above, but could be only one or more than two. 
     The driving device  16  is provided in the receiving space  10   a  of the headrail  10 , and includes a casing  18 , a motor  20 , and a decelerator  22 , wherein the motor  20  and the decelerator  22  are located in the casing  18 . The motor  20  is coupled to the spindle  142  through the decelerator  22 , wherein a shaft  202  of the motor  20  is connected to the decelerator  22 , and the decelerator  22  is connected to an end of the spindle  142 . In an embodiment, the decelerator  22  is a planetary gearing decelerator; however, this is not a limitation of the present disclosure. The motor  20  drives the spindle  142  to rotate, and the spools  144  fixedly fitting around the spindle  142  would be concurrently driven to rotate as well, whereby the spools  144  could release out or reel in the cords  44  to drive the covering material  12  to expand (close) or collapse (open). A length of a segment of each of the cords  44  which can be fully released out from the corresponding spool  144  due to the driving of the motor  20  is slightly longer than a length of the covering material  12  when it is fully expanded or lowered. Understandably, in any embodiments described or implied in the present disclosure, the so mentioned length of the segment of each of the cords  44  released out from the corresponding spool  144  refers to the segment length that each cord  44  gets released out from the respective spool  144  by the driving of the motor  20 , not a distance between each of the spools  144  and the lower end  12   a  of the covering material  12 . 
     The control device  24  is provided in the receiving space  10   a  of the headrail  10 , and is electrically connected to the motor  20 , wherein the control device  24  is adapted to control the motor  20  to rotate, whereby to drive the covering material  12  to expand or collapse. Furthermore, the control device  24  would control the motor  20  to stop operating when a moving speed of the lower end  12   a  of the covering material  12  decreases and such situation lasts for a predetermined time. In this way, when the covering material  12  is expanded to eventually reach a fully expanded (i.e., fully lowered) position, is collapsed to eventually reach a fully collapsed (i.e., fully raised) position, or encounters resistance during its expanding or collapsing, the control device  24  could stop the covering material  12  from moving because the moving speed of the lower end  12   a  of the covering material  12  would decrease for some time at least equal to or even longer than the predetermined time. Whereby, the covering material  12  could stay in a fully expanded state or a fully collapsed state. In addition, the covering material  12  would not exert further force on the blocking object which it bumps into during the expanding or collapsing process, and the window covering  100  could be prevented from being damaged as well. 
     In an embodiment, the control device  24  includes a control module  26  and a detecting module  30 , wherein the control module  26  controls the motor  20  through a driving circuit  28  to drive the spindle  142  of the rotating member  14  to rotate in a first rotating direction D 1  or a second rotating direction D 2 . When the spindle  142  of the rotating member  14  rotates in the first rotating direction D 1 , the spools  144  which fixedly fit around the spindle  142  would be driven by the spindle  142  to rotate as well, whereby to reel in the cords  44  and therefore to collapse or retract the covering material  12 ; when the spindle  142  of the rotating member  14  rotates in the second rotating direction D 2 , the spools  144  which fixedly fit around the spindle  142  would be driven by the spindle  142  to release out the cords  44 , whereby to expand or lower the covering material  12 . 
     The detecting module  30  is electrically connected to the control module  26 , and is adapted to detect a rotating speed of the rotating member  14  or of the shaft  202  of the motor  20 . While the covering material  12  is being collapsed (i.e., being raised), the control module  26  could, based on the detected rotating speed, determine whether the moving speed of the lower end  12   a  of the covering material  12  is lower than the moving speed moments ago, and whether such situation lasts for the predetermined time. This way the control module  26  could learn if the covering material  12  has reached the fully collapsed position or if it encounters a blocking object during the process of collapsing. The detecting module  30  could further detect if any of the cords  44  has shifted away from a predetermined position P 0 , and the result of such detection could be used as an indication. Specifically speaking, if it is detected that at least one of the cords  44  has completely shifted away from the predetermined position P 0 , the control module  26  would realize that the moving speed of the lower end  12   a  of the covering material  12  has become lower than the moving speed moments ago, and such situation has lasted at least for the predetermined time. Therefore, the control module  26  could use said indication to determine if the covering material  12  has reached the fully expanded position or if it encounters resistance from a blocking object during the process of expanding or lowering. The control module  26  would control the motor  20  to stop operating if it determines that the covering material  12  is in any of the following circumstances: the covering material  12  has been completely collapsed or raised to reach the fully collapsed position, has been completely expanded or lowered to the fully expanded position, or encounters resistance during the expanding or collapsing process. In an embodiment, the control module  26  could further include a microcontroller to make all kinds of judgments mentioned above. It has to be clarified that the predetermined time mentioned in some embodiments could be defined in the control device  24  as required. However, it should be a sufficient period of time so that the control device  24  could recognize the situation when the moving speed of the lower end  12   a  of the covering material  12  decreases or even becomes 0. 
     In the following paragraphs, we are going to explain the mechanism of how to determine if the covering material  12  has been fully collapsed (in other words, fully opened) or if it encounters resistance during the process of collapsing. 
     The detecting module  30  includes a rotating speed detecting member  32 , which is adapted to measure the rotating speed of the rotating member  14 . In an embodiment, the rotating speed detecting member  32  is a Hall sensor, and a magnet  34  is provided on the rotating member  14  as shown in  FIG. 3 , wherein the magnet  34  is provided on the spindle  142 . When the spindle  142  rotates, the rotating speed of the spindle  142  could be measured through the calculation of the changing on the magnetic field induction between the magnet  34  and the rotating speed detecting member  32 . 
     A lower rotating speed limit for the rotating member  14  could be set in advance in the control module  26 , as shown in  FIG. 4 . When the control module  26  controls the motor  20  to drive the rotating member  14  to rotate in the first rotating direction D 1  (i.e., when the covering material  12  is being collapsed or retracted), the control module  26  would receive a signal of the rotating speed measured by the rotating speed detecting member  32 . The rotation of the rotating member  14  would be hindered if the covering material  12  has been fully collapsed (retracted or raised) and any parts of the cords  44  which can be wound have already been wound around the spools  144 , or if the covering material  12  encounters resistance during the process of collapsing and the resultant pulling and tugging cause the cords  44  unable to be further wound around the spools  144 . As a result, the rotating speed of the rotating member  14  would decrease, and therefore the moving speed of the lower end  12   a  of the covering material  12  which is driven by the rotating member  14  would decrease as well. Once the rotating speed measured by the detecting module  30  is lower than the lower rotating speed limit, and such situation lasts for the predetermined time, the control module  26  would control the motor  20  to stop rotating. Whereby, no matter the covering material  12  is fully collapsed, or bumps into a blocking object during the process of collapsing, the motor  20  would be stopped from operating. If the rotating speed measured by the detecting module  30  returns to a speed higher than the lower rotating speed limit within the predetermined time, the control module  26  would determine that the covering material  12  bumps into a blocking object only for a brief moment, and the moving speed of the lower end  12   a  of the covering material  12  would not be affected by the blocking object so the covering material  12  would be still able to collapse or retract normally. Therefore, the control module  26  could, through the driving circuit  28 , control the motor  20  to keep operating. In an embodiment, the lower rotating speed limit is half of the rotating speed of the motor, and the predetermined time period is 100 ms to 200 ms. 
     In an embodiment, the magnet  34  could be provided on the spool  144  or the shaft  202  of the motor  20  instead. However, since a rotating speed of the shaft  202  of the motor  20  is higher than the rotating speed of the rotating member  14 , in an embodiment that the magnet  34  is provided on the shaft  202  of the motor  20 , the lower rotating speed limit should be adjusted to match the rotating speed of the shaft  202  of the motor  20 . In other embodiments that the rotating speed detecting member  32  is provided on the shaft  202  of the motor  20 , said rotating speed detecting member  32  could be an encoder, a resolver, or any device capable of measuring the rotating speed of the shaft  202  of the motor  20 . 
     In the above paragraphs, we have explained the mechanism of the current embodiment regarding how to determine if the covering material  12  has been fully collapsed, or if it encounters resistance from a blocking object during its process of collapsing. Then, in the following paragraphs, we are going to describe the mechanism of how to determine if the covering material  12  has been fully expanded, or if it encounters resistance from a blocking object during the process of expanding (i.e., while on its way toward the fully expanded position). 
     As shown in  FIG. 1  to  FIG. 3 , and  FIG. 6  to  FIG. 9 , the detecting module  30  further includes two sets of detecting assemblies  36  provided in a symmetric manner, each of which is respectively located near one of the spools  144  (as shown in  FIG. 5  and  FIG. 6 ). Each of the detecting assemblies  36  has the same structure, and we take the detecting assemblies  36  illustrated on the left side of  FIG. 5  as an example for explanation hereinafter. 
     This detecting assembly  36  includes an elastic member, which is a torsion spring  38  as an example, and a switch  40 . The torsion spring  38  includes a winding portion  382  and two extending arms  384  connected to the winding portion  382 . An end of each of the extending arms  384  has a bent section  384   a . The winding portion  382  is located above the cord hole  102  on the left side of the headrail  10 , and the cord  44  on this side passes through both the winding portion  382  and the cord hole  102 . The winding portion  382  forms a restricting ring which confines the cord  44  in there. The switch  40  has an operation rod  402  and a main body  404 , wherein the switch  40  is electrically connected to the control module  26 . When the winding portion  382  of the torsion spring  38  is located at an original position (i.e., when it has no external force exerted thereon), it pushes against the operation rod  402  so that the operation rod  402  is forced to contact the main body  404  of the switch  40 . 
     In an embodiment, each of the detecting assemblies  36  further includes a fixing seat  42  which is fixed at the headrail  10 , and the torsion spring  38  and the switch  40  are provided on the fixing seat  42 . The fixing seat  42  has a receiving hole  422  and two narrow holes  424 , wherein the receiving hole  422  is located above the cord hole  102 . In a short axial direction of the headrail  10 , the receiving hole  422  is located between the two narrow holes  424 . A longitudinal direction of each of the narrow holes  424  is parallel to the short axial direction of the headrail  10 . The winding portion  382  is located in the receiving hole  422 , with the bent section  384   a  of each of the extending arms  384  going into one of the narrow holes  424 . By pulling the winding portion  382  to move in the longitudinal direction of the headrail  10 , each of the bent sections  384   a  could be moved in the longitudinal direction of the respective narrow hole  424 . 
     As shown in  FIG. 8 , during the process of extending the covering material  12 , an expanded length of the covering material  12  equals to the length of the segment of each of the cords  44  released due to the driving of the motor  20 , which means the cords  44  would be taut. At this time, each of the cords  44  is located at the predetermined position P 0  in the respective cord hole  102 , and exerts a force on the respective winding portion  382  in a direction away from the respective operation rod  402 , so that the torsion spring  38  would be forced to leave the original position, accumulating an elasticity. Meanwhile, the main body  404  of the switch  40  is not touched by the operation rod  402 , and the control module  26  could control the motor  20  through the driving circuit  28 , whereby the rotating member  14  could be rotated in the first rotating direction D 1  or the second rotating direction D 2 , driving the covering material  12  to open or close. 
     As shown in  FIG. 9 , when the covering material  12  is fully expanded and the moving speed of the lower end  12   a  of the covering material  12  has been decreased to zero, the length of the segment of each of the cords  44  fully released from the respective spool  144  due to the driving of the motor  20  would be slightly longer than the fully expanded length of the covering material  12 . As a result, the motor  20  would still drive the cords  44  to be released from the spools  144  at least for the predetermined time (at this time, the moving speed of the lower end  12   a  of the covering material  12  is zero, and this situation lasts for the predetermined time). When the cords  44  are fully released by the driving of the motor  20 , the tension of the cords  44  are no longer stretched by the length of the covering material  12 , and therefore would be slack. As a result, the cords  44  would be no longer able to exert force on the winding portions  382 , and therefore each of the torsion springs  38  would return to its original position through the accumulated elasticity, driving the corresponding cord  44  to shift and leave its predetermined position P 0 . Once the torsion springs  38  go back to the original position, the winding portion  382  of each of the torsion springs  38  would press against the corresponding operation rod  402 , whereby to trigger the switches  40 , making the switches  40  to switch from a first state into a second state, e.g., from an open circuit state to a short circuit state. After the switches  40  are touched and therefore serve as a trigger, the control module  26  would, as responsive to the trigger, control the motor  20  to stop operating. In this way, when the covering material  12  is fully expanded, the motor could stop automatically. When the control module  26  controls the rotation of the motor  20  in a direction of retrieving the covering material  12 , the control module  26  would ignore the current state of the switches  40  and reel up the cords  44 . When the cords  44  are reeled up by the driving of the motor  20  to a extend that the released length of the cords  44  equals the expanded length of the covering material  12 , the cords  44  would drive the lower end  12   a  of the covering material  12  to move in the direction of collapsing or ascending. 
     During the process of extending the covering material  12 , if the covering material  12  bumps into a blocking object and the moving speed of the lower end  12   a  of the covering material  12  therefore decreases, the cords  44  would be still released out by the driving of the motor  20 , and the moving speed of the lower end  12   a  of the covering material  12  would decrease (to even zero) for a predetermined time as the cords  44  being released. If the length of the segment of any one of the cords  44  released by the driving of the motor  20  is greater than the current expanded length of the covering material  12 , said cord  44  would become loose (i.e., the force exerted by said cord  44  on the corresponding torsion spring  38  would be dismissed), and therefore the corresponding torsion spring  38  would return to its original position, which could drive said cord  44  to shift and leave the predetermined position P 0 . The torsion spring  38  that returns to its original position would make the winding portion  382  move toward and eventually press against the operation rod  402 , whereby to trigger the switch  40 . As a result, the switch  40  would be switched from a first state into a second state, e.g., from an open circuit state into a short circuit state. The control module  26  would control the motor  20  to stop operating if any of the switches  40  is triggered, whereby to stop the covering material from expanding or lowering. In this way, the covering material  12  could stop expanding if bumps into a blocking object during its expanding process, and therefore the covering material  12  or the blocking object could be prevented from being damaged. 
     After the covering material  12  stops moving upon encountering a blocking object during its expanding, if the control module  26  is going to control the motor  20  to rotate in a direction of collapsing or raising the covering material  12 , the control module  26  would ignore the current state of the switches  40 , and start to reel in the cords  44 . When the length of the segment of each of the cords  44  released by the driving of the motor  20  equals the expanded length of the covering material  12 , the cords  44  would drive the lower end  12   a  of the covering material  12  to move in the collapsing direction. 
     A detecting assembly  46  of a second embodiment of the present disclosure is shown in  FIG. 10  and  FIG. 11 , which can be also applied to the window covering  100  of the first embodiment. The detecting assembly  46  of the current embodiment includes a switch  48  and a restricting ring  50 , wherein the switch  48  has an operation rod  482  and a main body  484 . The restricting ring  50  is connected to the operation rod  482 , and, on each side, one of the cords  44  passes through the restricting ring  50 . When the cord  44  on any given side is taut, said cord  44  is located at the predetermined position P 0 , and exerts a force to the restricting ring  50  in a direction away from the switch  48 . The restricting ring  50  would pull the operation rod  482 , forcing the switch  48  to be in a first state (e.g., open circuit). If the lower end  12   a  of covering material  12  reaches a fully expanded position or bumps into an obstruction, and such situation lasts for a period of time, the cords  44  would become loose since the lengths of the segments of the cords  44  released by the driving of the motor  20  are greater than the expanded length of the covering material. Meanwhile, the force exerted by the cords  44  on the corresponding restricting rings  50  would be dismissed. At this time, an elastic member (not shown) inside the main body  484  of the switch  48  would drive the operation rod  482  to move in an opposite direction, whereby the switch  48  would be in a second state (e.g., short circuit). Furthermore, the restricting ring  50  could pull the cord  44  on the same side to shift and leave the predetermined position P 0 . The control module  26  would control the motor  20  to stop operating when the switch  40  is in the second state. Whereby, the motor  20  could be stopped from operating when the covering material  12  is fully expanded or when the covering material  12  bumps into an obstruction during the process of expanding. 
     As mentioned above, through the control device, the window covering provided in the present disclosure could control its motor to stop operating when the moving speed of the lower end of the covering material decreases for a predetermined time. In this way, the motor could be turned off to stop the covering material from further moving in each of the following situations: when the covering material is expanded to the fully expanded position; when the covering material is collapsed to the fully collapsed position; or when the covering material encounters resistance during the process of expanding or collapsing (i.e., while on its way toward the highest or lowest possible positions). With such design, the process and components required for setting up the upper and lower limits could be reduced or even omitted. Furthermore, if the covering material bumps into a blocking object during its movement, it could be prevented from further colliding with the blocking object or getting damaged. In addition, in each of the above-mentioned embodiments, the number of the detecting assemblies of the detecting module is two; however, this is for the purpose of explanation, and in practice, the number of the detecting assemblies could be at least one as well. 
     Moreover, the control device  24  may be realized according to various design considerations. In another embodiment, when the lower end  12   a  of the covering material  12  moves and encounters resistance, instead of simply stopping the driving device  16 , the control device  24  may further configure the driving device  16  to rotate reversely. For example, if the driving device  16  originally rotates in the second rotating direction D 2  and the control device  24  configures the driving device  16  to rotate reversely, the control device  24  configures the driving device  16  to stop and then rotate in the first rotating direction D 1 . In the process of configuring the driving device  16  to rotate reversely, the control device  24  may explicitly configure the driving device  16  to rotate in a first rotating direction, stop for a human noticeable duration, and then rotate in a second rotating direction. In another embodiment, the control device  24  may also configure the driving device  16  to operate as if the driving device  16  changes the rotating direction without a halt. There is, however, at least a small amount of time, even if human-unnoticeable, in which the rotating speed of the driving device  16  approaches zero and behaves like being stopped. Whether the duration of time that the driving device  16  remains stopped is noticeable by human or not, when referring to the process of rotating the driving device  16  reversely, the driving device  16  is considered to stop from rotating in the previous rotating direction and then rotate in the other direction. Accordingly, the lower end  12   a  of the covering material  12  is considered to stop from a previous moving direction and then move in the other direction. 
     When the lower end  12   a  of the covering material  12  moves downward and encounters resistance, the cords  44  may become loose and tangled, and therefore fail to function properly anymore. In another embodiment, when the lower end  12   a  of the covering material  12  moves downward and encounters resistance, instead of simply stopping the driving device  16 , the control device  24  configures the driving device  16  to rotate reversely. Thus, a suitable length of the cords  44  may be reeled in to the spools  144 , and the cords  44  may remain taut as a result. The tangle of the cords  44  and the consequent malfunction can be prevented. The reeled-in length of the cords  44  may be configured to be a predetermined length, a length determined by rotating the driving device  16  for a predetermined time, or dynamically determined by the control device  24 . For example, in the process of rotating the driving device  16  reversely, once the state of the switch  40  changes, indicating that the cords  44  are taut, the control module  26  accordingly configures the driving device  16  to stop rotating reversely. 
     Moreover, the control device  24  may also calculate the position of the lower end  12   a  of the covering material  12  according to the output of the rotating speed detecting member  32 . For example, the rotating speed detecting member  32  detects the rotating direction and the rotating speed of the rotating member  14  and/or the driving device  16  according to information such as the rotating speed(s) of the spindle  142 , the spool  144  and/or the output shaft  202  of the motor  20 . The control device  24  would be able to calculate the length of the cords  44  released from the headrail  10  based on the rotating direction, the rotating speed, and the rotating time of the rotating member  14  and/or the driving device  16  according to the output(s) of the rotating speed detecting member  32  and/or other component(s) (e.g., an encoder, a resolver, a timer circuit and a memory unit). In addition to the released length of the cords  44 , the control device  24  also has the knowledge of the positions of the upper limit and the lower limit of the covering material  12 , and therefore can calculate the position of the lower end  12   a  of the covering material  12 . 
     In another embodiment, when the lower end  12   a  of the covering material  12  encounters resistance, the position of the lower end  12   a  of the covering material  12  may incur different problems which require different solutions. The control device  24  may further configure the driving device  16  to rotate reversely for moving the lower end  12   a  of the covering material  12  for different distances in response to various scenarios. For example, the lower limit of the lower end  12   a  of the covering material  12  may be configured by a lowermost position of the lower end  12   a  of the covering material  12  when touch or approach a reference surface position. The reference surface position may be the positions of a sill, a floor, a ground, or other suitable horizontal levels (may be a tilt and/or uneven surface as well). The lower end  12   a  of the covering material  12  may encounter resistance in the vicinity of the reference surface position due to inaccurate installment, aging of the cords  44  and/or the spool  144 , small objects near the reference surface position (e.g., shoes, books and toys), etc. Even if the lower end  12   a  of the covering material  12  encounters resistance in the vicinity of the reference surface position, the lower end  12   a  of the covering material  12  should still not move below the lower limit, and therefore, in such circumstances, the cords  44  cannot get loose too much. In this situation, the possibility of the cords  44  getting tangled is lower, so reeling in a smaller length of the cords  44  for moving the lower end  12   a  of the covering material  12  in the reverse direction for a smaller distance may suffice. Whereas, when the lower end  12   a  of the covering material  12  encounters resistance at a distance away from the reference surface position, there is more room for the cords  44  to loosen and the probability of tangling the cords  44  is higher. It may, therefore, be better to reeling in a greater length of the cords  44  for moving the lower end  12   a  of the covering material  12  for a greater distance to prevent the tangle of the cords  44 . In the above embodiment, the reference surface position corresponds to physical positions in the real world. In other embodiments, the reference surface position may be configured according to the upper limit of the covering material  12 , the lower limit of the covering material  12 , the position of the headrail  10 , and/or the output of the rotating speed detecting member  32 . The control device  24  may therefore configure the driving device  16  to rotate, stop and rotate reversely according to the reference surface position. For example, the control module  26  may configure the reference surface position to be the position where the lower end  12   a  of the covering material  12  will reach after the driving device  16  rotating for 15 seconds for releasing the lower end  12   a  of the covering material  12  from the position of the headrail  10 . In another embodiment, the control device  24  may be configured to have multiple reference surface positions. 
     Moreover, since the covering material  12  may be elastic or stretchable to some degree, it might not be easy to precisely detect the distance when the control device  24  configures the lower end  12   a  of the covering material  12  to move. Therefore, in another embodiment, when the control device  24  configures the lower end  12   a  of the covering material  12  to move, the distance of the covering material  12  to be moved may be related to the length of the cords  44  to be reeled in by the driving device  16 . 
     In another embodiment, as shown in  FIG. 12 , when the lower end  12   a  of the covering material  12  encounters resistance within a first predetermined distance DN measured from the reference surface position R, the control device  24  configures the driving device  16  to reel in the cords  44  for a first length L 1  for moving the lower end  12   a  of the covering material  12  upward for a first distance DS 1 . On the other hand, as shown in  FIG. 13 , when the lower end  12   a  of the covering material  12  encounters resistance at a position out of the first predetermined distance DN measured from the reference surface position R, the control device  24  configures the driving device  16  to reel in the cords  44  for a second length L 2  for moving the lower end  12   a  of the covering material  12  upward for a second distance DS 2 . In this embodiment, the first length L 1  is configured to be smaller than the second length L 2 , so that the first distance DS 1  is smaller than the second distance DS 2 . Moreover, the first length L 1  may also be configured to be greater than or equal to the second length L 2  for accommodating different scenarios. In another embodiment, the first length L 1  is configured to be greater than the second length L 2  for solving another problem. When the lower end  12   a  of the covering material  12  encounters resistance at a position out of the first predetermined distance measured from the reference surface position, the control device  24  configures the driving device  16  to reel in the cords  44  for the second length L 2  for moving the lower end  12   a  of the covering material  12  upward for a shorter second distance DS 2 . In this embodiment, the reference surface position and the lengths L 1  and L 2  may be respectively configured to be different from the counterparts in the previous embodiment. The shorter second length L 2  and the shorter second distance DS 2  may prevent the lower end  12   a  of the covering material  12  from bumping into the headrail  10 , whereby to avoid unnecessary reactions and/or damages of the components. For example, the power consumption may be lower for not executing unnecessary reactions which may take place when the lower end  12   a  of the covering material  12  bumps into the headrail  10 . Moreover, the control device  24  may configure the driving device  16  to reel in the cords  44  for moving the lower end  12   a  of the covering material  12  upward for the same distance every time it encounters resistance, or, the control device  24  may also configure the driving device  16  to reel in the cords for moving the lower end  12   a  of the covering material  12  fora distance which is to be determined depending on the distance between the reference surface position and the position where the lower end  12   a  of the covering material  12  encounters resistance. For example, if the lower end  12   a  of the covering material  12  encounters resistance in the vicinity of the reference surface position and the headrail  10 , the control device  24  configures the driving device  16  to reel in the cords  44  for moving the lower end  12   a  of the covering material  12  upward for a shorter distance. On the contrary, if the lower end  12   a  of the covering material  12  encounters resistance elsewhere, the control device  24  configures the driving device  16  to reel in the cords  44  for moving the lower end  12   a  of the covering material  12  upward for one or more greater distances. 
     Moreover, if the control device  24  configures the driving device  16  to move the lower end  12   a  of the covering material  12  upward for too much distance, a gap may be left or even widened in the vicinity of the reference surface position, allowing light to pass through, which usually bothers the users. In another embodiment, when the lower end  12   a  of the covering material  12  encounters resistance in the vicinity of the reference surface position, the control device  24  configures the driving device  16  to move the lower end  12   a  of the covering material  12  upward for a short distance and check whether the state of the switch  40  changes as the cords  44  become taut. The control device  24  iterates the operations of moving the lower end  12   a  of the covering material  12  upward for a short distance and checking the state of the switch  40  until the switch  40  changes its state to indicate that the cords  44  are taunt or until a predetermined number of iterations are performed. Therefore, the gap caused by moving the lower end  12   a  of the covering material  12  upward may be eliminated or narrowed. 
     Moreover, if the lower end  12   a  of the covering material  12  moves at a high speed when encounters resistance, the rotating speed of the rotating member is high and a large amount of the cords  44  may become loose. The possibility that the cords  44  get tangled and have malfunction may therefore be higher. In another embodiment, the control device  24  configures the driving device  16  to move the lower end  12   a  of the covering material  12  for different distances according to different rotating speed of the driving device  16  and/or the rotating member  14 . When the rotating speed of the driving device  16  and/or the rotating member  14  is lower than a predetermined speed threshold, the control device  24  configures the driving device  16  to reel in the cords  44  for a third length L 3  for moving the lower end  12   a  of the covering material  12  upward for a third distance DS 3 . When the rotating speed of the driving device  16  and/or the rotating member  14  is higher than the predetermined speed threshold, the control device  24  configures the driving device  16  to reel in the cords  44  for a fourth length L 4  for moving the lower end  12   a  of the covering material  12  upward for a fourth distance DS 4 . In this embodiment, the third length L 3  is configured to be smaller than the fourth length L 4 , so that the third distance DS 3  is smaller than the fourth distance DS 4 . In another embodiment, the third length L 3  may also be configured to be greater than or equal to the fourth length L 4  for accommodating different scenarios. Moreover, the control device  24  may also configure the driving device  16  to reel in the cords  44  for moving the lower end  12   a  of the covering material  12  upward for a distance which is to be determined according to the rotating speed of the driving device  16  and/or the rotating member  14 . 
     Moreover, the above embodiments may be properly combined to accommodate different scenarios. In another embodiment, when the lower end  12   a  of the covering material  12  encounters resistance within the first predetermined distance measured from the reference surface position, the control device  24  configures the driving device  16  to stop without rotating reversely. When the lower end  12   a  of the covering material  12  encounters resistance at a position out of the first predetermined distance measured from the reference surface position, the control device  24  configures the driving device  16  to reel in the cords  44  for moving the lower end  12   a  of the covering material  12  upward for an appropriate distance. In another embodiment, when the lower end  12   a  of the covering material  12  encounters resistance within the first predetermined distance measured from the reference surface position, the control device  24  configures the driving device  16  to reel in the cords  44  for a fifth length L 5  for moving the lower end  12   a  of the covering material  12  upward for a shorter fifth distance DS 5 . When the lower end  12   a  of the covering material  12  encounters resistance at a position out of the first predetermined distance measured from the reference surface position, the control device  24  configures the driving device  16  to reel in the cords  44  respectively for a sixth length L 6  and a seventh length L 7  for moving the lower end  12   a  of the covering material  12  upward respectively for a sixth distance DS 6  and a seventh distance DS 7  according to the rotating speed of the driving device  16  and/or the rotating member  14 . Moreover, the sixth length L 6  and the seventh length L 7  are different but both greater than the fifth length L 5 . In another embodiment, when the lower end  12   a  of the covering material  12  encounters resistance and the rotating speed of the driving device  16  and/or the rotating member  14  is higher than the predetermined speed threshold, the control device  24  configures the driving device  16  to move the lower end  12   a  of the covering material  12  upward. Whereas when the lower end  12   a  of the covering material  12  encounters resistance and the rotating speeds of the driving device  16  and/or the rotating member  14  is lower than the predetermined speed threshold, the control device  24  configures the driving device  16  to stop. 
     In the drawings, the motor  20  and the decelerator  22  of the driving device  16  are respectively drawn as a single element for the purposes of conciseness and clear explanation. In the above embodiments, the driving device  16  may also comprise more than one motor and/or more than one decelerator. For example, when the control device  24  configures the driving device  16  to drive the rotating member  14  in the first rotating direction D 1 , the motor  20  and a first decelerator (not shown in the figures) may be used to drive the rotating member  14  in the first rotating direction D 1 . Whereas, when the control device  24  configures the driving device  16  to drive the rotating member  14  in the second rotating direction D 2 , the motor  20  and a second decelerator (not shown in the figures) may be used to drive the rotating member  14  in the second rotating direction D 2 . In another embodiment, when the control device  24  configures the driving device  16  to drive the rotating member  14  in the first rotating direction D 1 , a first motor (not shown in the figures) and the decelerator  22  may be used to drive the rotating member  14  in the first rotating direction D 1 . Whereas, when the control device  24  configures the driving device  16  to drive the rotating member  14  in the second rotating direction D 2 , a second motor (not shown in the figures) and the decelerator  22  may be used to drive the rotating member  14  in the second rotating direction D 2 . In another embodiment, when the control device  24  configures the driving device  16  to drive the rotating member  14  in the first rotating direction D 1 , the first motor and the first decelerator may be used to drive the rotating member  14  in the first rotating direction D 1 . Whereas, when the control device  24  configures the driving device  16  to drive the rotating member  14  in the second rotating direction D 2 , the second motor and the second decelerator may be used to drive the rotating member  14  in the second rotating direction D 2 . 
     It must be pointed out again that the embodiments described above are only some embodiments of the present disclosure. All equivalent structures which employ the concepts disclosed in this specification and the appended claims should fall within the scope of the present disclosure. 
     Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the disclosure. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.