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You are an expert at summarizing long articles. Proceed to summarize the following text: 
FIELD OF THE INVENTION 
     This invention relates to systems for opening and closing hinged closure panels, particularly the tailgate of a truck, in a controlled fashion. 
     BACKGROUND 
     Many light trucks have tailgates that can open to extend the bed and permit loading and unloading, and close to create a confined area. Typically, the range of motion of the tailgate is through about 90 degrees from the opened to the closed positions, with the inner surface of the tailgate being roughly aligned with the bed in the open position. 
     As technologies improve and proliferate, drivers of passenger cars and light trucks expect more automation and convenience, with automatic opening of the tailgate becoming a standard feature. However, power actuation is not always desired, as drivers may wish to operate the tailgate manually as well. Although complex systems involving a plurality of sensors and computer components could be developed, consumers prefer to have these features without the burden of excessive cost. 
     It has been a challenge to develop a mechanism for opening and shutting a tailgate which can be operated in a powered mode or by manual effort, and which is capable of tracking the position of the tailgate regardless of the mode in which the device is operated, and to do so with cost-effective components. Moreover, design requirements and constraints for this application include high torque loads necessary to move a tailgate between the positions while providing the desired manual actuation override and safety provisions. 
     SUMMARY OF THE INVENTION 
     In one aspect, the present disclosure provides an actuator for operating a hinge mechanism coupling a door to a body. The actuator has a motor for moving the hinge between a closed position and an open position, and the motor has a rotor which extends along a first axis. The actuator has a gear mounted on a gear shaft in rotatable connection with the rotor of the motor. The actuator also has a rotary position encoder coupled to the gear shaft. The rotary position encoder undergoes no more than one revolution when the hinge is moved between the closed position and the open position. There is also a hinge rod for driving the rotation of the door, the hinge rod extending along a second axis substantially parallel to the first axis. 
     In another aspect, the present disclosure provides an actuator for operating a hinge mechanism coupling a door to a body. The actuator has a motor for moving the hinge between a closed position and an open position. The motor has a rotor which extends along a first axis. The actuator also has a gear mounted on a gear shaft which is in rotatable connection with the rotor. The actuator has a rotary position encoder coupled to the gear shaft. Further, there is a clutch positioned between the gear shaft and the motor. The positioning of the rotary position encoder opposite the motor from the clutch allows the absolute position of the tailgate to be known independent of operation of the motor. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-sectional view of a power tailgate actuator in accordance with one embodiment of the present disclosure; 
         FIG. 2  is a perspective view of a power tailgate actuator in accordance with one embodiment of the present disclosure; 
         FIG. 3  is an exploded view of a gear reduction and position sensor in accordance with one embodiment of the present disclosure; 
         FIG. 4  is a cross-sectional view of a power tailgate actuator in accordance with another embodiment of the present disclosure; 
         FIG. 5  is a schematic view of the components associated with a power tailgate actuator within a tailgate in accordance with another embodiment of the present disclosure; 
         FIG. 6A  is a perspective view of the interfaces between the tailgate actuator and a truck tailgate in accordance with one embodiment of the present disclosure; 
         FIG. 6B  is a perspective view of the interfaces between the tailgate actuator and a truck tailgate in accordance with an embodiment of the present disclosure; 
         FIG. 6C  is a perspective view of the interfaces between the tailgate actuator and a truck tailgate in accordance with an embodiment of the present invention; 
         FIG. 7A  is a perspective view of a truck having a closed tailgate and in accordance with one embodiment of the present disclosure; 
         FIG. 7B  is a view of a positional sensor when the truck tailgate is positioned as depicted in  FIG. 7A ; 
         FIG. 8A  is a perspective view of a truck having an open tailgate in accordance with one embodiment of the present disclosure; and 
         FIG. 8B  is a view of a positional sensor when the truck tailgate is positioned as depicted in  FIG. 8A . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     It will be appreciated that drawings in this disclosure are not necessarily to scale, with some components enlarged relative to their actual size in order to show detail. 
     The terms “substantially,” “about,” or derivatives thereof will be understood to mean significantly, effectively, or in large part. 
       FIG. 1  shows a power tailgate actuator  10  in accordance with one embodiment of the present invention. The actuator  10  has a motor  32  which is enclosed within motor housing  12 . The motor  32  includes a rotor which turns to provide the mechanical energy to drive lifting and lowering of the tailgate  30 . The rotational motion of the rotor is transmitted through the planetary gearbox  34 . Planetary gearbox  34  is housed within gear housing  14 . The gears of the planetary gearbox provide a gear reduction from the rotation of the rotor of motor  32 . The planetary gearbox  34  is in turn connected to clutch  36 , the function of which will be described in detail below. 
     It will be appreciated that while the embodiment  FIG. 1  is a tailgate for a light truck, the invention of the present disclosure can be applied to any hinged mechanism which couples a first portion (such as a door) to a second portion (such as a body. The motor moves the hinge between a closed position and an open position. 
     In the illustrated embodiment, on the opposite end of clutch  36  from planetary gearbox  34  is pinion gear  38 . Pinion gear  38  is mounted on pinion shaft  57 , which rotates in proportion to the rotation of the motor  32  when clutch  36  is engaged. In the embodiment illustrated in  FIG. 1 , the pinion shaft  57  is substantially coaxial with the rotor of motor  32 . 
     Pinion gear  38  meshes with compound gear having spur gear portions  40  and  42 . Spur gear portions  40  and  42  surmount gear shaft  59 , which is on a second axis running parallel to the axis running through pinion shaft  57 . The compound gear provides another gear reduction, and coupled to gear shaft  59  is rotary position sensor  46 . In the embodiment illustrated in  FIG. 1 , which is shown in exploded view in  FIG. 3 , the gear reduction is such that the gear shaft  59  rotates through less than one-half revolution. In the illustrated embodiment, the gear shaft  59  rotates about 0.42 revolutions or between about 150 degrees and about 160 degrees, particularly about 151.2 degrees. Many other configurations are possible, including gear reductions which rotate through about 0.25 revolutions, about 0.33 revolutions, about 0.5 revolutions, about 0.66 revolutions, about 0.75 revolutions, about 0.8 revolutions, about 0.99 revolutions, and between about 0.25 revolutions and about 0.99 revolutions, inclusive. 
     Any device capable of collecting and reporting positional information may be used as a rotational position sensor. In one embodiment, the sensor  46  may be a Hall effect sensor. In a preferred embodiment, the rotary position sensor is in the form of a rotary potentiometer. 
     A rotary potentiometer is a particularly attractive option for use with rotary position sensor  46  for a number of reasons. First, these components are simple to use and install and are inexpensive. Second, the analog rotary potentiometer can provide a reliable, absolute position signal related to the position of the tailgate. Installing the rotary position sensor  46  at the position illustrated in  FIG. 1  ensures that the gear shaft  59  always turns in proportion to the amount the output shaft (or hinge rod)  20  turns, regardless of engagement of the clutch; if the output shaft  20  rotates, the wiper of the rotary potentiometer moves in concert with it. If it does not, the wiper remains stationary at its position on the resistive track of the rotary potentiometer. Sensor wire  47  is attached to the rotary position sensor  46 , providing a means of transmitting positional information from the sensor to other portions of the tailgate actuation system. Typical and inexpensive rotary potentiometers are capable of rotation over less than one full turn (360°). Such devices may be used as rotary position sensor  46  since gear shaft  59  rotates less than a full revolution. 
     Vertically below the axis to which the rotary position sensor  46  is coupled, and meshing with the larger gear portion  40  of spur gear  40  and  42 , is sector gear  61 . Sector gear  61  is capable of making about a quarter of a rotation and drives the rotational movement of shaft  44 . Shaft  44  extends along a third longitudinal axis which runs substantially parallel to the first axis and the second axis. Shaft  44  terminates in output shaft coupling  16 , which is mated to output shaft  20 , which ultimately provides the motion and energy for raising and lowering of tailgate  30 . As mentioned previously, truck tailgates typically move through a 90-degree range of motion from the closed position to the open position. Hence, sector gear  61 , by providing substantially a quarter of a revolution of rotational range, controls the extent of the rotation of output shaft  20 . Output shaft  20  passes through the side of the tailgate  30  and into output cup  22  and governs the motion of double-D interface  24 . 
     The tailgate of  FIG. 1  is illustrated in cross-sectional view. The outermost wall (that is, the wall that would be furthest from the cab of the truck) is cut away to expose a view of the tailgate actuator assembly  10  which is housed within the tailgate  30  itself. The tailgate has an outer panel, an interior panel (which encloses the bed in the closed position and extends the bed in the open position) and an interior space between the outer panel and the interior panel. It is in this space that the power tailgate actuator  10  is mounted. The axial displacement of the hinge rod  20  from the rotor axis of motor  32  permits the actuator to be of a size which is capable of producing the power required to lift and lower the tailgate, but still be compact enough to fit within the interior of the tailgate, particularly as the interior space narrows at the top and the bottom of the tailgate. 
     The power tailgate actuator  10  can be mounted to the interior of tailgate  30  by any conventional method. In the embodiment illustrated in  FIG. 1 , mounting bracket  28  is attached to motor cover  12  and to the base of the interior of tailgate  30 . Reinforcing bracket  26  is attached at its first portion to the base of the interior of tailgate  30 , angles away from the base to form a second portion having a hole formed therethrough to accommodate the output shaft  20 , and is angled again toward an interior sidewall of the tailgate  30 . The reinforcing bracket  26  acts to reinforce the tailgate  30  in order to compensate for the high torsional load that accompanies operation of the actuator. L bracket  18  is mounted to reinforcing bracket  26  and has a hole which houses and guides the output shaft  20 . 
     In the embodiment of  FIG. 1 , the power tailgate actuator  10  is depicted with a clutch  36  positioned between the planetary gearbox  34  and the pinion shaft  57 . The clutch  36  may be of any construction known in the art. In a preferred embodiment, the clutch  36  is an electromagnetic clutch. The clutch  36  serves a number of purposes. 
     As mentioned previously, the tailgate actuator  10  has an automatic operation mode, in which an electronic control unit sends a signal to the tailgate actuator and instructs it to open or close, and a manual operation mode, in which a human user manually opens and closes the tailgate. 
     In the power actuated mode, the clutch  36  is active in both the opening and the closing directions. While in power actuated mode, the actuator system monitors the position of the tailgate and processes the signal from the rotary position sensor  46  in order to control the speed of the door and as an anti-pinch precaution. 
     When the system is in manual mode and the tailgate  30  is being opened manually by the operator, the clutch  36  and the motor  32  are active to facilitate action by the user. When the rotary position encoder  46  detects that the tailgate  30  is opening and the electronic control unit  50  is in manual mode, the clutch  36  engages to slow and control the speed at which the tailgate opens. Incorporating the rotary position encoder  46  at a point in the actuator  10  such that absolute position can be ascertained allows the clutch  36  to be used, if desired, as the sole means of damping, minimizing the number of components that need to be incorporated into the tailgate assembly. 
     When the system is in manual mode and the tailgate  30  is being closed, the clutch and the motor are both inactive. Because the rotary position sensor  46  is positioned on the opposite side of the clutch  36  from planetary gearbox  34  and motor  32 , it is able to continue to reflect the correct, absolute position of the tailgate as the user closes it, while the clutch decouples the rotation of the output shaft  20  from that of the planetary gearbox  34 . Thus, the gears of the planetary gearbox, which provide a significantly high gear reduction, are not backdriven by manual closing of the tailgate, avoiding damage to the assembly. 
     The clutch  36  further has the capacity to slip when situations that could damage the actuator  10  arise. For instance, if a heavy load has been placed on the tailgate and a user instructs the system to lift the tailgate, the clutch will inactivate, preventing the transmission of an excessive load to the gear train. Further, if the system is in power actuated mode and a user attempts to close or open the tailgate more quickly or in uncontrolled fashion, the clutch will slip for the same reason. 
       FIG. 2  illustrates the view of power tailgate actuator  10  of  FIG. 1 , though without a cutaway view of the internal components. In this figure, the attachment of mounting bracket  28  to the motor cover  12  can be clearly seen. Rotary position encoder  46  is enclosed by housing  49 . 
       FIG. 3  provides a view of components that make up the power tailgate actuator  10  individually. A component of clutch  36  is positioned near pinion  38  and its shaft. Pinion  38  meshes with spur gear portion  40  of compound spur gear  40  and  42 , which rotates in conjunction with gear shaft  59 . Gear shaft  59  transmits rotation to sensor coupling  68 , which in turn acts to rotate rotary position encoder  46 . Rotary position encoder is wired to printed circuit board  54  and housed with it in housing  49 , and is capped with grommet  70 . 
     In this embodiment, spur gear portion  42  of compound gear  40  and  42  meshes with sector gear  61 , which is positioned on shaft  46 . Shaft  46  terminates in output shaft coupling  16 , which engages the output shaft and drives lowering and raising of the tailgate. 
     In the embodiment of  FIG. 3 , the gear assembly is housed within gear housing cover  14 , which is illustrated in  FIG. 3  as two separate halves. The two halves of housing cover  14  come together surrounding the gears and shafts illustrated and meet at gear housing seal  66 . Bolts  64  hold the two halves of gear housing cover  14  together. 
       FIG. 4 . illustrates another embodiment of a power tailgate actuator  110  in accordance with the principles of the present disclosure. In this embodiment, motor  132  is housed in motor cover  112 . Rotational motion from the rotor of motor  132  undergoes a gear reduction via planetary gearbox  134 , which is connected to clutch  136 . On the opposite end of clutch  136  from the planetary gearbox  134  is shaft  138 , which is coupled to rotary position encoder  146 . In one embodiment, shaft  138  may be a pinion shaft having a pinion positioned thereon. Further gear reductions  140  are housed within gear housing  114  and are coupled via output shaft coupling  116  to ultimately drive the rotary motion of output shaft  120 , which in turn drives tailgate motion between the open and closed positions. 
     One difference between the device of  FIG. 1  and the device of  FIG. 4  is the location of the rotary position encoder  46 / 146 . The device of  FIG. 4  places the rotary position encoder  146  in the first stage gear reduction, whereas the device of  FIG. 1  places the rotary position encoder  46  in a second stage gear reduction. In a device of either construction which has an analog rotary position encoder capable of tracking and reporting the absolute position of the tailgate, the shaft to which the position encoder is mounted must rotate through less than one full rotation. Thus, in the device of  FIG. 4 , the first stage gear reduction must be configured so that shaft  138  rotates less than a full revolution. Contrarily, no such requirement is in place for the first stage reduction of the device  10  of  FIG. 1 , so long as the second stage reduction decreases the rotation of the gear shaft to less than one revolution. However this configuration may not enable use of a rotary potentiometer. The electromagnetic clutch  136  of actuator  110  may need to be of a higher capacity than clutch  36  of device  10  in order to compensate for the very high gear reduction that causes the shaft  138  to rotate one time or fewer during operation. 
       FIG. 5  illustrates an actuator  10  in accordance with the principles of the present disclosure. The rotor of motor  32  rotates about axis A, and axis B is substantially parallel to axis A. Output shaft  20  rotates about axis B. Sensor wire  47  connects the rotary position encoder to electronic control unit  52 , which in turn communicates with central brain plate  50 . Cinch latches  48  provide a latching closure for the tailgate. 
       FIG. 6A  provides a view of torsion rod  56 , which provides counterweight torsion for reducing the mechanical effort needed for moving the door between the closed position and the open position in any operation mode. As shown in  FIG. 6B , the torsion rod  56  extends through the side of the tailgate and is fixed to an interface  24  which is surrounded in part by output cup  22 . The interface  24  as illustrated has a double-D geometry and can be mounted to a fixed vehicle bracket. Such a construction allows for simplified assembly and disassembly to the vehicle body structure. 
     The output shaft  20 , as shown in  FIG. 6C , also emerges through the side of the tailgate in a similar fashion. However, because this shaft is on the power-driven side of the tailgate, an additional reinforcement plate  26  is used to mount the actuator  10 . L bracket  18  further constrains the output shaft  20 . 
     To illustrate the operation of a power tailgate actuator  10 / 110 , a light truck  80  is shown in  FIG. 7A  with its tailgate  30  in the closed position  82 . In one embodiment, the rotary position sensor  46 , as shown in  FIG. 7B , may be a rotary potentiometer. When the tailgate  30  is in the closed position  82 , the wiper  58  is in a first position  60  along track  55 . The rotary potentiometer has a characteristic first resistance associated with the wiper (and therefore the tailgate) being in the first position  60 , which when transmitted to the electronic control unit, allows or permits certain actions. For instance, if the actuator  10  is in power actuated mode, the indication that the tailgate  30  is in the closed position  82  indicates that the clutch should be active. 
       FIG. 8A  illustrates the same truck  80 , but the tailgate  30  is now in the open position  84 . In response, the wiper  58  of rotary position encoder  46  has moved to its second position  62  ( FIG. 8B ), which is associated with a second resistance different from the first resistance. Such a second resistance, when detected by the electronic control unit, may, in one embodiment, cause the clutch to become inactivated if the actuator  10  is in manual operation mode, since doing so will prevent the planetary gearbox from being backdriven upon manual closure of the tailgate. 
     Should the tailgate  30  be stopped in its motion from open position  84  to closed position  82 , the analog rotary position encoder  46  will have a resistance intermediate between the first resistance and the second resistance. The electronic control unit may be programmed with a protocol which could, in one embodiment, produce a warning that the tailgate is stuck, and could, for example, inactivate the clutch in order to minimize damage to the gear structures. 
     While the above description constitutes the preferred embodiment of the present invention, it will be appreciated that the invention is susceptible to modification, variation, and change without departing from the proper scope and fair meaning of the accompanying claims.

Summary:
An actuator for opening and closing a hinged device is provided. In particular, the actuator is a power tailgate actuator. The actuator comprises a motor with a rotor, and an output shaft that rotates on an axis which is substantially parallel to the axis on which lies the rotor of the motor. The actuator has a rotary position sensor such as a rotary potentiometer which positively identifies the position of the tailgate. The tailgate also comprises a clutch which can engage and disengage depending on the mode of operation.