Abstract:
A rotary actuator suitable for use in a refrigerator ice-dispensing door provides a rotating shaft driven by a DC permanent magnet motor through a gear train and subject to a returning force of an internal spring. The gear train communicates with a switch to reduce current to the motor when a limit of travel is reached and a shunting path is provided around the motor to produce generative braking when power is removed from the motor and the actuator rotates backward to its initial position.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is National Phase of PCT/US2012/046689 filed Jul. 13, 2012 and claims the benefit of U.S. provisional application 61/508,345 filed Jul. 15, 2011 and hereby incorporated by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to a compact rotary actuator and in particular to an electrically actuated door through which ice cubes may be dispensed, using such an actuator. 
     BACKGROUND OF THE INVENTION 
     Consumer refrigerators may have ice dispensers that dispense ice through an opening in a freezer compartment door. Typically, the opening in the freezer door includes a dispenser door that automatically opens and closes to restrict the entry of ambient air into the freezer compartment. 
     The dispenser door is normally held closed by a bias spring. When ice is requested by the user, the dispenser door is opened, typically by a solenoid triggered by a switch. The switch may be positioned near the dispenser door to be activated, for example, by the lip of a drinking glass positioned near the dispenser door. 
     In the time period during which the dispenser door is held open for the discharge of ice, power must be applied to the solenoid. Solenoids consume significant power during operation and are prone to buzzing when supplied with unregulated power. The rapid action of the solenoid can produce a loud popping sound when the doors open and close. 
     SUMMARY OF THE INVENTION 
     The present invention provides an actuator for an ice dispenser door that employs a low-power DC motor. A gear train connecting to the DC motor and the self regulating properties of DC motors moderate the speed of opening of the dispenser door when power is applied to the motor. Further, generative electrical braking through the motor slows the closing speed of the dispenser door. In this way, door impact sounds are substantially reduced. A switch system lowers the power to the motor when the dispenser door is opened to limit the holding state power consumption to much less than required by a solenoid. 
     In one embodiment, the present invention provides an ice dispenser door system having a door plate attached to a door frame defining a door opening to pivot about an axis on a door shaft to one side of the door opening. A DC permanent magnet motor providing a rotating motor shaft and reducing gear train provides a first gear attached to the motor shaft to rotate therewith and a last gear attached to the door shaft to rotate the door shaft with rotation of the motor. A stop limits rotation of the door shaft in a first direction as driven by the motor through the gear train when power is applied to the motor; and a spring biases rotation of the door shaft in a second direction opposite the first direction, the spring sized to rotate the door shaft in the second direction when power is not applied to the motor. 
     It is thus a feature of at least one embodiment of the invention to provide an energy efficient ice door employing a DC motor over a higher power consumption solenoid. It is another feature of at least one embodiment of the invention to provide a replacement ice door that may use the same signals as would be provided to a solenoid. 
     The ice dispenser door system may further include an electrical switch actuating when the rotary shaft is rotating in the first direction before being limited by the stop to add a resistance in series with the motor. 
     It is thus a feature of at least one embodiment of the invention to provide a positive holding of the door in an open state with reduced power consumption below a power level necessary to open the door. 
     The electrical switch may be actuated by an intermediary gear in the gear train before the last gear. 
     It is thus a feature of at least one embodiment of the invention to provide high accuracy power control for the motor. By increasing a relative movement of the switch operator with respect to the door through the gear train, high accuracy switching may be obtained in a compact switch. 
     The electrical switch may be a rotary electrical switch attached to a shaft communicating with the intermediary gear. 
     It is thus a feature of at least one embodiment of the invention to provide a simple switch element well adapted for activation by rotating shafts. 
     The gear train and motor may retain engagement with the door shaft with movement of the door shaft in the first and second directions and the ice door delivery system may further include a shunting element allowing current flow through the shunting element as generated by the motor with movement of the door shaft in the second direction whereby a damping of that movement may be obtained by electrical resistive dissipation. 
     It is thus a feature of at least one embodiment of the invention to slow the closure of the door by dissipating spring energy in electrical power generated by the motor. 
     The shunting element may be a diode back-biased when the power is applied to the motor. 
     It is thus a feature of at least one embodiment of the invention to provide shunting only during door closure without diverting power during door opening, making use of the selective conduction direction of the diode. 
     The ice dispenser door system may further including a second stop limiting rotation of the door shaft in a second direction. 
     It is thus a feature of at least one embodiment of the invention to provide a self-contained actuator element that may be shared among other applications. 
     The spring may be a helical torsion spring fitting coaxially around the door shaft. 
     It is thus a feature of at least one embodiment of the invention to provide a self-contained spring limiting the need for external returning mechanisms, for example an external spring or a weighting of the door. 
     The ice dispenser door system may further include a housing containing the motor, gear train, spring, stop and first portion of the door shaft and having an opening providing a journal through which the door shaft may extend to expose a second portion of the door shaft outside of the housing. 
     It is thus a feature of at least one embodiment of the invention to provide a self-contained actuator that may be tested in isolation. 
     Other features and advantages of the invention will become apparent to those skilled in the art upon review of the following detailed description, claims and drawings in which like numerals are used to designate like features. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a simplified side elevational view of an ice cube dispenser door, for example, in the door of a refrigerator for dispensing ice cubes into an adjacent glass; 
         FIG. 2  is an exploded perspective view of the dispenser door of  FIG. 1  showing its constituent rigid shell member, insulating member and an elastomeric gasket communicating via a shaft with a rotary actuator of the present invention; 
         FIG. 3  is a perspective view of an internal mechanism of the rotary actuator showing an electrical switch for controlling power to the internal DC motor as a function of door angle; 
         FIG. 4  is an exploded perspective view of the mechanism of  FIG. 3 ; 
         FIG. 5  is a cutaway view of the housing of the rotary actuator of  FIG. 2  showing the internal mechanism of  FIG. 3  as fitting therein; and 
         FIG. 6  is a schematic representation of the circuitry of the rotary actuator. 
     
    
    
     Before the embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of the components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced or being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein are for the purpose of description and should not be regarded as limiting. The use of “including” and “comprising” and variations thereof is meant to encompass the items listed thereafter and equivalents thereof as well as additional items and equivalents thereof. 
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to  FIG. 1 , an ice cube dispensing mechanism  10  per the present invention may fit inside a refrigerator door  12  or the like to provide a pivoting dispenser door  14  on a divider wall  16 , the divider wall  16  separating a refrigerated volume  17  of a refrigerator from outside air  18 . 
     The dispenser door  14  may pivot about an axis  20  to cover or uncover an opening  19  through the divider wall  16  and, in the open position, to provide an unobstructed path  22  for ice cubes  24  to pass down a chute  26  into a glass  28  or the like. Activation of the door  14  to pivot about axis  20  may be provided by a rotary actuator  30  controlled, for example, by electrical dispenser switch  32  operated by a lip of the glass  28 . 
     Referring now to  FIGS. 1 and 2 , the door  14  may include a rigid flapper  34  pivoting about an axle  36  extending along the axis  20  and engaging in one direction with an output shaft  35  of the rotary actuator  30 . The axle  36  may be retained in journals  40  in a frame  38 , the latter of which may attach against the inside of the divider wall  16  above the opening  19 . The rigid flapper  34  may provide a cylindrical cup-shaped cavity  46  facing inward toward the refrigerated volume  17  receiving an insulating foam element  48  (expanded polystyrene). The foam element  48  may be captured within the cylindrical cup-shaped cavity  46  by an elastomeric gasket  50  fitting over a lip of the cylindrical cup-shaped cavity  46 . 
     Referring now to  FIGS. 2 and 3 , the axle  36  extending toward the rotary actuator  30  may include a bore fitting over the output shaft  35  of the rotary actuator  30  and having an internal shelf to engage a flat  37  in the output shaft  35  allowing the two to rotate together along axis  20  when the rotary actuator  30  is slid axially into engagement with retention elements  39  on the frame  38 . 
     Referring now to  FIGS. 3 and 4 , the internal mechanism  31  of the rotary actuator  30  includes a sub-fractional horsepower DC electric motor  52  (having an operating power of less than 25 watts and preferably less than 10 watts). The DC electric motor  52  includes a permanent magnet stator and brushes, the latter of which may attach to a printed circuit board  54  by means of conductive motor terminals  56  and  57  extending from a base of the motor  52 . The motor shaft  58  extending opposite from the base along an axis  60  parallel to axis  20  may hold a spur gear  62  engaging with a reducing gear train  64 . 
     The reducing gear train  64  includes: gear set  61 ,  63  and partial gear  72 . Gear set  61  has a larger diameter gear communicating with the spur gear  62  and a co-rotating smaller diameter gear communicating with a larger diameter gear of gear set  63 . A smaller diameter gear of gear set  63 , co-rotating with the larger diameter gear of gear set  63 , communicates with a partial gear  72  which is attached directly to the output shaft  35 . 
     A shaft  65  rotating with gear set  63  also attaches to a rotary switch  66  formed by an inner engagement of a conductive wiper  68  held on the shaft  65  and conductive traces  67  on the printed circuit board  54  as will be described in more detail below. 
     The gear set  63  communicating with a partial gear  72  drives the output shaft  35  such that the angular range of the shaft  35  in opening and closing the door  14  corresponds to the door movement range of about 55 degrees. Generally, the corresponding rotation of the shaft  65  attached to the gear set  63  before the partial gear  72 , with full rotation of the shaft  35 , will be much larger than the rotation of the shaft  35  as a result of the gearing between these two shafts  65  and  35  (a gear ratio of approximately 3.5:1). As a result, the rotation of the rotary switch  66  will be more than 180 degrees with opening or closing of the door  14 . By attaching the rotary switch  66  to the shaft  65 , instead of to the shaft  35  to rotate directly with rotation of the rigid flapper  34 , much better precision may be obtained in the switch point of the rotary switch  66  as will be described below. 
     The printed circuit board  54  may also provide finger terminals  74  that may connect to a wiring harness in the refrigerator (not shown). It will be appreciated, therefore, that the printed circuit board  54  may provide for all electrical interconnections necessary for the rotary actuator  30  between the components of the motor  52 , the diodes  80  and  84 , the resistor  76 , the rotary switch  66  (as well as providing for one contact of the rotary switch  66 ) and the finger terminals  74  eliminating any hand wiring. 
     Referring now to  FIG. 5 , the internal mechanism  31  of the rotary actuator  30  may fit within a housing  73  so that the finger terminals  74  and the output shaft  35  may extend therefrom. A torsion spring  77  fits coaxially about the output shaft  35  within the housing  73  between a wall of the housing  73  and a catch portion  79  on the partial gear  72  to bias the output shaft  35  in rotation so as to generally close the door  14  absent power to the motor  52 . The self-contained torsion spring  77  allows full functional testing of the rotary actuator  30  independent of its attachment to other elements of the door mechanism. 
     The housing  73  may include catches  83  allowing it to snap together with a corresponding housing component (not shown) to fully enclose the internal mechanism  31  except for the output shaft  35  and the finger terminals  74  as noted. 
     Referring now to  FIGS. 4 ,  5  and  6 , the rotary switch  66  may be positioned in series with the motor  52  between two terminals of the fingers  74 . A source of DC electrical power  81  may be applied across terminals  74  through dispenser switch  32  so that a positive voltage (typically 13.2 volts DC and preferably less than 20 volts) is received directly by one terminal  56  of the motor  52  when a glass  28  is activating (closing) the dispenser switch  32 . 
     The return for the DC electrical power  81  is received by the cathode of a diode  80  which serves to prevent damage to the rotary actuator  30  in the event of an improper reverse polarity connection of the rotary actuator  30  to power. 
     The anode of diode  80  connects to rotary switch  66  which in turn connects to the remaining terminal  57  of the motor  52 . The terminals  56  and  57  of motor  52  are shunted by diode  80  whose cathode attaches to the terminal  56  directly receiving positive voltage. Likewise the rotary switch  66  is shunted by resistor  76 . 
     Initially, when the dispensing door  14  is closed and the dispenser switch  32  is open (not activated by a glass  28 ), no power is applied to the motor  52  and the rotary actuator  30  remains stationary. At this time, rotary switch  66  is in a closed state  85  shorting resistor  76 . 
     When dispenser switch  32  is closed, for example by pressing against it with a glass  28 , power is applied to motor  52  through rotary switch  66  and forward biased diode  80  causing the motor  52  to rotate to open the door as indicated by arrow  82 . Substantially zero current passes through diode  84  because it is back-biased and because rotary switch  66  is in a closed state  85  shorting resistor  76  so that substantially no current passes through resistor  76 . As is understood in the art, the DC motor  52  is speed limited by back electromagnetic force (EMF) being proportional to the applied voltage and its limited speed is moderated by the gear train  64  to control the opening speed of the door  14  to reduce door opening impact sounds. In one embodiment the motor draws 500 milliamps at 13 volts providing substantially 6.5 watts to the motor  52 . 
     Just before the door  14  is fully opened, rotary switch  66  moves to an open state  89  and power to the motor  52  must pass through resistor  76 . Resistor  76  reduces the current through motor  52  to an amount necessary to hold the door open against the torsion spring  77  but substantially less than a power used to drive the rotary actuator  30  to open the door  14 . Importantly, resistor  76  prevents over current to the motor  52  in the stall condition when the impedance of DC motors drops radically. In one embodiment, resistor  76  limits the current to the motor  52  to an amount providing substantially less than 6.5 watts to the motor  52 . The resistor  76  reduces power consumption of the rotary actuator  30  (the total of power consumed by the motor  52  and the resistor  76 ) and concomitant heating of the actuator  30 . 
     When dispenser switch  32  is opened, (for example by removal of the glass  28 ) the force of the torsion spring  77  causes the shaft  35  to rotate backward as indicated by arrow  90  in the opposite direction of arrow  82  also causing motor  52  to rotate backward. This rotation causes the motor  52  to generate electrical power forward biasing diode  84  to pass current therethrough. The resulting electrical power is dissipated in the diode  84  and the windings of the motor  52  and thereby serves to provide a generative braking of motion on the motor  52  slowing closure of the door  14  and reducing door closure impact sounds. 
     Various features of the invention are set forth in the following claims. It should be understood that the invention is not limited in its application to the details of construction and arrangements of the components set forth herein. The invention is capable of other embodiments and of being practiced or carried out in various ways. Variations and modifications of the foregoing are within the scope of the present invention. It also being understood that the invention disclosed and defined herein extends to all alternative combinations of two or more of the individual features mentioned or evident from the text and/or drawings. All of these different combinations constitute various alternative aspects of the present invention. The embodiments described herein explain the best modes known for practicing the invention and will enable others skilled in the art to utilize the invention.