Abstract:
A drive mechanism including a rotary actuated motor configured to rotatably drive a drive arm between a first position to a second position and an actuator responsive to movement of the arm, wherein the actuator is thermally isolated from the arm in both the first position and the second position to create a thermal barrier. The drive arm is configured to engage and advance the actuator between the first position and the second position, while remaining physically spaced from the actuator in the first position and the second position. The drive arm includes a recess such as an opening, wherein the actuator has a member configured to reside in the recess and remain thermally isolated from the arm in both the first position and the second position. In one preferred embodiment, a shutter of an imaging device is positioned in response to the actuator, which shutter remains thermally isolated from the motor and arm. Other devices may be driven as well, such as switches.

Description:
TECHNICAL FIELD 
       [0001]    The present disclosure is directed in general to drive mechanisms and actuators, and more specifically to a drive arms and actuators utilized in thermally sensitive devices including but not limited to IR imaging shutters. 
       BACKGROUND OF THE DISCLOSURE 
       [0002]    Drive mechanisms including actuators are conventionally utilized to control the selective positioning of one or more members of a system. System design requirements dictate, and often limit, the specific design suitable for the application. In some environments, the system member to be controlled and/or manipulated is extremely thermally sensitive, such as infrared (IR) thermal imaging systems having movable shutters, including those operating in a true IR Dewer environment operating at cryogenic temperatures. Some conventional drive mechanisms are not suitable in such thermally sensitive systems where a thermal barrier needs to be maintained between a driving actuator and the driven device, such as to minimize or avoid stress, binding, wear and inconsistent operation of the system. Other conventional drive mechanisms have unreliable and inconsistent drive paths, and difficulty of meeting or staying within design tolerances. There is desired a drive mechanism that is reliably operable in thermally sensitive systems. 
       SUMMARY OF THE DISCLOSURE 
       [0003]    To address one or more of the above-deficiencies of the prior art, one embodiment described in this disclosure comprises a drive mechanism including a thermally isolated actuator reliably operable in thermally sensitive system. A drive mechanism including a rotary actuated motor is configured to rotatably drive a drive arm between a first position and a second position, wherein an actuator is responsive to movement of the arm. The actuator is thermally isolated from an actuatable member in both the first position and the second position to create a thermal barrier. The drive arm is configured to engage and advance the actuator between a first position and a second position, while remaining physically spaced from the actuator in the first position and the second position. The drive arm includes a recess, such as an opening, wherein the actuator has a member configured to reside in the recess and remain thermally isolated from the arm in both the first position and the second position. The spacing between the drive arm and the actuator also enables the drive arm to build momentum before engaging the actuator during actuation, converting the actuation mechanism from torque transfer to momentum transfer of energy. This additional momentum helps overcome magnetic detent forces of locking members, and also helps overcome any stiction that may be present. This spacing significantly increases the required force margin, and also allows the use of a less precise solenoid motor which has a relatively large amount of play. In one preferred embodiment, a shutter of an IR imaging device is positioned in response to the actuator, which shutter remains thermally isolated from the motor and arm. Other devices may be driven as well, such as switches. Although specific advantages have been enumerated above, various embodiments may include some, none, or all of the enumerated advantages. Additionally, other technical advantages may become readily apparent to one of ordinary skill in the art after review of the following figures and description. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0004]    For a more complete understanding of the present disclosure and its advantages, reference is now made to the following description taken in conjunction with the accompanying drawings, in which like reference numerals represent like parts: 
           [0005]      FIG. 1  illustrates a thermal imaging device including a shutter and a thermally isolated drive system configured to position the shutter according to an embodiment of the present disclosure; 
           [0006]      FIG. 2  illustrates the thermally isolated drive system of  FIG. 1  with the shutter removed; 
           [0007]      FIG. 3  illustrates a perspective view of one drive mechanism; 
           [0008]      FIG. 4  illustrates an exploded view of part of the drive system illustrating the drive arm having an elongated recess configured as an opening to receive a drive pin and roller of the shutter slider member; 
           [0009]      FIG. 5  illustrates the drive arm in a first “full open” position wherein the shutter slider member is in a corresponding first position; 
           [0010]      FIG. 6  illustrates the drive arm in a second “full closed” position wherein the shutter slider member is in a corresponding second position; 
           [0011]      FIG. 7  illustrates a top view of the arm and elongated opening receiving, but physically and thermally separated from, the slider pin and roller in the first and second position; 
           [0012]      FIG. 8  illustrates a top view of the arm in the first position showing the asymmetric clearance of the arm from the slider pin and roller, including the radial play of the actuator compared to this clearance; 
           [0013]      FIG. 9  illustrates a perspective view of the drive crank including the arms; and 
           [0014]      FIG. 10  illustrates a controller circuit configured to control the drive assembly. 
       
    
    
     DETAILED DESCRIPTION 
       [0015]    It should be understood at the outset that, although example embodiments are illustrated below, the present invention may be implemented using any number of techniques, whether currently known or not. The present invention should in no way be limited to the example implementations, drawings, and techniques illustrated below. Additionally, the drawings are not necessarily drawn to scale. 
         [0016]      FIG. 1  illustrates a top perspective view of a IR thermal imaging shutter apparatus  10  including a shutter mechanism comprising a plate  12  and a sliding aperture blade  14  configured to be driven by a pair of drive mechanisms generally shown at  16 A and  16 B. Each drive mechanism  16 A and  16 B comprises a rotary motor  18  (see  FIG. 3 ) having a rotatable actuator pin  20  coupled to and driving a balanced rotatable drive crank  22 . Each drive crank  22  has a radially extending elongated arm  24  (see  FIG. 2 ), configured to selectively rotate arm  24  between a first “full open” position and a second “full closed” position as shown in  FIG. 5  and  FIG. 6 , as will be discussed shortly. Each arm  24  has a distal end having a recess  26 , as shown in  FIG. 2 , the recess  26  preferably comprising an elongated opening in one preferred embodiment as shown. The recess  26  could also comprise a slot or other open ended structure if desired, and limitation to an opening is not to be inferred. Each arm recess  26  is configured to receive, but is spaced from, a respective actuatable member  30  and roller  34  (see  FIG. 4 ) rotatably disposed thereabout. Each member  30  preferably comprises a shutter pin secured to one respective end of the aperture blade  14  as shown in  FIG. 4 . Each member  30  is also secured to, and extends downwards towards, a respective slidable magnetic detent latch  32 , wherein each detent latch  32  is securingly and slidably received in a respective dovetail slot  35  (see  FIG. 2 ) defined in a frame  36 . Each detent latch  32  is preferably comprised of a dovetail plug configured to slide linearly inside the corresponding dovetail slot  35  in frame  36 , along with respective shutter pin  30  and roller  34  when manually adjusted, and locked into position when positioned in the final desired location by a set screw  37  pressing the plug  37  upwards into the dovetail slot  35 , providing an accessible locking feature while inducing minimal additional linear motion. Upon rotation of the arms  24 , the respective openings  26  engage the respective roller  34  encompassing the respective shutter pin  30  to linearly move the aperture blade  14  between a first full open position and a second full closed position, wherein the roller  34  rotates in the opening  26  during transition, and is then spaced therefrom at the end of the transition. 
         [0017]      FIG. 2  depicts the apparatus  10  with the shutter plate  12  and aperture blade  14  removed, illustrating the drive mechanisms  16 A and  16 B including the respective arms  24  having openings  26 , the magnetic detent latches  32  without shutter pins  30 , as well as a pair of proximity sensors  40  (see  FIG. 3 ) to indicate the final position of the arm, preferably comprised of Hall effect sensors. Each drive crank  22  has a proximity indicating arm  42  including a magnet  44  disposed at a distal end therein and selectively extending over one of the proximity sensors  40  as a function of the arm  24  position. When the arm  24  is in the first full open position as shown in  FIG. 5 , the first proximity sensor  40  indicates the drive crank  22  is in place at the open position, and when the arm  24  is in the second full closed position as shown in  FIG. 6 , the second proximity sensor  40  indicates the drive crank  22  is in place at the closed position. Magnetic cogging, created internally to the actuator  18  and in the detent magnetic latch  32 , forces the arms  42  and  46  against the set screws  54  in stops  50  and  52  and prevents any play at the end of travel. 
         [0018]      FIG. 3  depicts a perspective view of one drive mechanism  16  with arm  24  positioned between the first and second position, illustrating the travel path of the arm, which may be, for instance, 24 degrees, although limitation to this path is not to be inferred. 
         [0019]      FIG. 4  depicts an exploded view of one drive mechanism  16  and one end of the shutter plate  14  configured to be positioned as a function of the drive mechanism positions. The shutter pin  30  consists of a cylindrical post which captures roller  34  to prevent sliding along the distal slot  26 , and a magnet below provides detent pulling when in close proximity of the shutter pin  30 , but not contacting, to the arms of the detent magnetic latch  32 . 
         [0020]    Each drive crank  22  further comprises a radially extending arm  46 , wherein each of arms  42 , and  46  are shorter than the elongated arm  24  as shown in  FIGS. 5 and 6 , as well as  FIG. 9 . Each of arms  24 ,  42 , and  46  are balanced about the center of the drive crank  22 , such that the center of gravity of drive crank  22  is balanced when coupled to the respective actuator pin  20 . This makes system  10  far less sensitive to extremely high shock requirements. Each arm  42  and  46  has a travel stop limit comprising a stop member  50  and  52 , respectively, of which each contains an adjustable travel limit set screw  54 . Stop member limit screws  54  in turn establish the precise travel path and limit of arm  24 , and thus the precise limit position of the driven shutter plate  14 . Again, proximity sensors  40  indicate whether the drive crank  22 , and thus the arm  24  and shutter plate  14 , is in one of two positions. 
         [0021]    When the shutter plate  14  is in the full open position, the arm  24  of drive mechanism  16 A is in the full open position and the shutter pin  30  of drive mechanism  16 A is positioned at a distal end of a slot  60  defined in one end of plate  12  as shown in  FIG. 5 . Correspondingly, the arm  24  of drive mechanism  16 B is in the full open position, and the shutter pin  30  of the drive mechanism  16 B is outwardly advanced in an opposing slot  60  defined at the opposing end of plate  12 . The converse is true when the shutter plate  14  is in the closed position, as can be seen in  FIG. 1  and  FIG. 6 . 
         [0022]    Advantageously, as illustrated in  FIG. 7  and  FIG. 8 , each shutter pin  30  and the corresponding roller  34  remain physically and thermally separated from the respective arm  24  when in the first position and the second position due to a spacing created therebetween in both positions, thus creating a thermal barrier, also referred to as thermal isolation. The arm  24  only engages the rollers  34  disposed about the shutter pin  30  for a very short time period during movement/actuation of the shutter plate  14  from one position to the other. Thus, the drive mechanisms  16 A and  16 B and all parts thereof are thermally isolated from the driven shutter plate  14  when in the operable full open or full closed position. The shutter mechanism including the plate  12  and shutter plate  14  are preferably configured in a vacuum having a true IR Dewer cryogenic environment. 
         [0023]    Moreover, the spacing of the arms  24  from rollers  34  provides the motors  18 , and thus the respective arms  24 , time to accelerate from the respective first rest position or second rest position which advantageously builds momentum in the arms  24  before engaging and driving the respective rollers  34 , converting the actuation mechanism from torque transfer to momentum transfer of energy. This additional momentum helps overcome the magnetic detent forces of the magnetic detent latch  32  acting against the shutter pin  30 , holding arms  42  or  46  against the stop posts  50  or  52 . The impact of the arm  24  engaging the roller  34  during rotation also helps overcome any stiction that may be present. This spacing increases the required force margin from 25% to 900%. The spacing also allows the use of a less precise solenoid motor  18 , which has a relatively large amount of play and thus is less suitable for driving the arm  24  directly. Each arm opening  26  provides a loose fitting about the respective shutter pin  30  and roller  34 , such that the motor loose play does not impair operation of the shutter aperture. Conversely, the loose tolerances of the arm openings  26  mitigate the risk of an inadvertent rebound. The aperture blades  14  have internal stops, which engage prior to the holding arms  42  or  46  contacting their respective stop. Since the shutter pin  30  is not firmly engaged within the distal slot  26 , the aperture blade can rebound before the arm  42  or  46  contacts the stop set screw  54  and rebounds. Additional margin is provided by the fact that the arm has much higher inertia than the aperture blade, and rebounds correspondingly slower. The high level of damping in the actuator bearings in  18  diminishes the magnitude of the arm rebound. These features prevent a situation where the rebounding arm  24  impacts the shutter pin  30  and roller  34  while traveling in the opposite direction. Such impact could exert extremely high forces onto the shutter pin  30  due to the arm&#39;s much higher inertia. 
         [0024]    As shown in  FIG. 8 , the clearance between the respective roller  34  and arm opening  26  is slightly asymmetric, although it may be symmetric if desired. In one preferred implementation, there is about 1.4 degrees of clearance, also referred to as a dead zone, equating to about a 0.011 inch clearance, although limitation to this angular spacing or clearance is not to be inferred. The arm travel limit set stops established by screws  54  are preferably set to detent to within ⅕ of the dead zone, about 0.28 degrees. 
         [0025]    In one preferred embodiment, a rotary solenoid is used as motor  18  as it provides consistent reliability and an adjustable stroke, such as manufactured by Brandstrom Instruments of Ridgefield Conn. The fine adjustment features of the drive crank  22  using the travel limit screws  54  in the stationary motor mount stop limit members  50  and  52  help establish this stroke. This design is superior to a piezo drive motor that is inherently unreliable, although is functionally acceptable. Alternate rotary motors could comprise DC stepper motors, and limitation to the particular rotary motor is not to be inferred. This invention has advantages over motors and linkages that may allow motor over-travel which may overstress driven parts. 
         [0026]      FIG. 9  illustrates a perspective view of the drive crank  22 , including the four balanced arms. 
         [0027]      FIG. 10  illustrates a control circuit at  60  that is configured to selectively drive each of motors  18 , to control the positioning of the arms  24  and thus drive the shutter plate  14  between the first and second positions. The control circuit includes a controller  62  having a processor configured to control drive electronics  64  that interface with motors  18  of drive mechanisms  16 A and  16 B. 
         [0028]    Modifications, additions, or omissions may be made to the systems, apparatuses, and methods described herein without departing from the scope of the invention. The components of the systems and apparatuses may be integrated or separated. Moreover, the operations of the systems and apparatuses may be performed by more, fewer, or other components. The methods may include more, fewer, or other steps. Additionally, steps may be performed in any suitable order. As used in this document, “each” refers to each member of a set or each member of a subset of a set. 
         [0029]    To aid the Patent Office, and any readers of any patent issued on this application in interpreting the claims appended hereto, applicants wish to note that they do not intend any of the appended claims or claim elements to invoke paragraph 6 of 35 U.S.C. Section 112 as it exists on the date of filing hereof unless the words “means for” or “step for” are explicitly used in the particular claim.