Patent Publication Number: US-2017371152-A1

Title: Shutter with Linear Actuator

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to optical shutter apparatus and more particularly relates to optical shutter apparatus with a linear actuator. 
     BACKGROUND OF THE INVENTION 
     Optical shutters use an actuator to drive each of one or more radiation-blocking elements or “shutter blades”, between a first, closed position that blocks the path of light through at least a portion of an aperture and a second, open position that is spaced apart from the first position and that allows light through the aperture. The light radiation that is directed toward the aperture can generally be any form of electromagnetic radiation, such as ultra-violet, visible or infrared radiation, for example. The aperture can be in a frame or baseplate that is directly or indirectly coupled to the actuator. The frame can additionally support the actuator and can include features that retain the shutter blade or blades and that define the travel path of the shutter blade or blades. The actuator can be electromagnetically activated (an “electromagnetic actuator”) so that it responds to an electrical signal to translate the shutter blade or blades between the open and closed positions. Electromagnetic actuators typically used for this purpose include linear solenoids, rotary solenoids, or brushed or brushless commutated motors, for example. 
     Actuators for optical shutters can support monostable or bistable operation. Monostable shutters have a single stable position to which the actuator returns when power is removed. Bistable actuators are able to remain in the last position held at the time power is removed. 
     Monostable solenoid actuators have a coil of wire that generates a magnetic field when electrical power is applied. The magnetic field applies a force to pull or rotate a soft magnetic core in a given direction. Monostable actuators with soft magnetic cores typically utilize a spring or other mechanical element to return the core to an original position when power is removed. One disadvantage of monostable actuators for shutter control relates to their behavior upon power loss; these actuators require continuous power to remain in the electrically driven state. 
     Bistable actuators are stable in the state held when power is removed, whether open or closed. Bistable actuators can be created using geared motor drives that lock in a given position when unpowered. In other embodiments, an over-center spring can be used to create a locking force in either of the open aperture or closed (blocked aperture) positions. 
     The soft magnetic core of a monostable solenoid can be replaced with a hard magnet that adheres to soft magnetic material in each of its two positions to create a bistable shutter. For example, commonly assigned U.S. Pat. No. 8,508,828 to Durfee describes a magnetic voice-coil actuator that operates a rotary shutter using a pair of supporting permanent magnets. 
     Conventional rotary shutters are characterized by arrangements of shutter blades and supporting features that can be mechanically complex, sizable, and relatively costly. 
     Thermal imaging apparatus require periodic calibration in order to provide continuous and trouble-free operation, with shutter arrangements that allow calibration to be easily performed. As these types of systems become smaller, lightweight, and less expensive, there is a corresponding demand for shutter systems that are more compact than conventional shutter apparatus and offer simple operation at low cost. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to advance the art of optical shutter design. Embodiments of the present invention provide a shutter apparatus that has a bistable linear actuator, with a minimum of components and with a compact footprint. 
     According to one aspect of the present invention, there is provided an optical shutter apparatus comprising
         a baseplate that defines an aperture in a plane and that has at least first and second tabs that extend outward from the plane;   at least a first linear actuator that is coupled to the first tab and that drives a first magnetic shaft between the first and second tabs according to an electrical signal; and   a first shutter blade that is coupled to the first magnetic shaft and that is linearly translatable, along a translation path in the direction of the plane, between a first and a second position, wherein the first shutter blade blocks at least a first portion of the aperture in the first position and unblocks the first portion of the aperture in the second position.       

     These objects are given only by way of illustrative example, and such objects may be exemplary of one or more embodiments of the invention. Other desirable objectives and advantages inherently achieved by the disclosed invention may occur or become apparent to those skilled in the art. The invention is defined by the appended claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing and other objects, features, and advantages of the invention will be apparent from the following more particular description of the embodiments of the invention, as illustrated in the accompanying drawings. The elements of the drawings are not necessarily to scale relative to each other. 
         FIG. 1  is a perspective view of a shutter with a linear actuator in an open position. 
         FIG. 2  is a perspective view of a shutter with a linear actuator in a closed position. 
         FIG. 3  is a perspective view showing a solenoid assembly coupled to a shutter blade. 
         FIG. 4A  is a perspective view showing a partial assembly of a shutter apparatus according to an embodiment of the present disclosure.  FIG. 4B  is a perspective view showing a partial assembly of a shutter apparatus according to an embodiment of the present disclosure, with an added spacer. 
         FIG. 5  is a perspective view showing a partial assembly of a shutter apparatus with a spacer and the shutter blade in an open position. 
         FIG. 6  is a perspective view showing a partial assembly of a shutter apparatus having a top cover or plate. 
         FIG. 7  is a cross-sectional side view that shows how a gap is formed to allow sliding movement of a shutter blade across an aperture area. 
         FIG. 8  is a cross-sectional view of a solenoid assembly in an energized state. 
         FIG. 9  is a cross-sectional view of a solenoid assembly in a de-energized state that retains the shutter blade. 
         FIG. 10  is a perspective view that shows a shutter apparatus having two solenoid assemblies. 
         FIG. 11  is a perspective view that shows a shutter apparatus having a retainer formed from a folded back portion of the baseplate material. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Figures provided herein are given in order to illustrate principles of operation and component relationships according to the present invention and are not drawn with intent to show actual size or scale. Some exaggeration may be necessary in order to emphasize basic structural or functional relationships or principles of operation. Some conventional components that would be needed for implementation of the described embodiments, such as support components used for providing power, for packaging, and for mounting, for example, are not shown in the drawings in order to simplify description of the invention. In the drawings and text that follow, like components are designated with like reference numerals, and similar descriptions concerning components and arrangement or interaction of components already described may be omitted. 
     Where they are used, the terms “first”, “second”, and so on, do not necessarily denote any ordinal or priority relation, but may be used for more clearly distinguishing one element or time interval from another. The term “plurality” means at least two. 
     In the context of the present disclosure, the term “energizable” describes a component or device that is enabled to perform a function upon receiving power and, optionally, upon also receiving an enabling signal. 
     In the context of the present disclosure, positional terms such as “top” and “bottom”, “upward” and “downward”, and similar expressions are used descriptively, to differentiate different surfaces or views of an assembly or structure and physical relationships of components relative to each other and do not describe any necessary orientation of the assembly in an optical apparatus. Two flat surfaces can be considered “substantially orthogonal” where their angle of intersection is within 75-105 degrees. The terminology of a surface lying in a plane has its conventional meaning as understood by those skilled in the mechanical arts and indicates that the surface extends in the direction of the plane. 
     In the context of the present disclosure, the term “coupled” is intended to indicate a mechanical association, connection, relation, or linking, between two or more components, such that the disposition of one component affects the spatial disposition of a component to which it is coupled. For mechanical coupling, two components need not be in direct contact, but can be linked through one or more intermediary components. 
     “Non-magnetic materials”, in the context of the present disclosure, are materials that are negligibly affected by magnetic fields and that exhibit no perceptible magnetic attraction and are thus not perceptibly pulled toward a magnet. In general, non-magnetic materials have a low relative magnetic permeability, typically not exceeding  1 . 0  at room temperature. Some exemplary non-magnetic materials include copper, aluminum, certain types of stainless steel, a number of metals and alloys; various ceramics; wood and paper composite materials; glass; plastics and other polymers; fiberglass; and various composite materials such as phenolic materials. 
     By contrast to non-magnetic materials, “magnetic materials” have higher relative permeability and are considered to be “magnetically responsive” and therefore attracted to a magnet. This can include ferromagnetic materials and various compounds of rare earth materials, for example, that exhibit attraction to a magnet that can be readily perceived without requiring instrumentation. 
     Soft magnetic materials can carry magnetic field but retain little if any field after conducting a magnetic field and are not used as permanent magnets. Soft materials are readily magnetized and demagnetized. Their capability to respond rapidly in response to magnetic fields is desirable, and makes these materials suitable for use in AC generators and transformers. In general, coercivity (Hc) of a soft magnetic material is no more than 12.5 Oersted (Oe), preferably less than 1.1 Oe. An ideal soft magnetic material has very low coercivity (Hc), generally ranging from about 0.01-0.1 Oersted. Common examples of soft magnetic materials include iron-silicon alloys, nickel-iron alloy, ferritic stainless steels, and pure grades of iron. 
     Hard magnetic materials, with coercivity (Hc) values well above 100 Oe and typically in thousands of Oersteds, can be permanently magnetized by a strong magnetic field and are used to supply a fixed magnetic field. Common examples of some hard magnetic materials include alloys composed of iron, cobalt, and aluminum, and other rare-earth element materials such as neodymium-iron-boron (NdFeB). 
       FIGS. 1 and 2  are perspective views, from different angles, that show a shutter apparatus  10  for selectively blocking or un-blocking a light energy path according to an embodiment of the present disclosure.  FIG. 1  shows shutter apparatus  10  in an open position. A solenoid assembly  40  drives a shutter blade  30  to either of two positions, one closed position for blocking the light energy path, one open or unblocking position. Shutter blade  30  is translated forward, to the left in  FIG. 1 , allowing light through an aperture A that is defined in a plane by a baseplate  20  and by a top cover  65 .  FIG. 2  has shutter blade  30  moved in the opposite, blocking or closed direction. Aperture A is blocked or covered (not visible) due to shutter blade  30 , which blocks light in the closed position view of  FIG. 2 . 
     Referring to  FIGS. 1 and 2 , planar baseplate  20  of shutter apparatus  10  can be formed from a non-magnetic material, such as a single piece of sheet aluminum, for example. Baseplate  20  has a solenoid tab  24  and an open-position tab  26  that project outward orthogonally from the plane of the baseplate and that define the linear travel limits for solenoid assembly  40  and its coupled shutter blade  30 . One or both tabs  24  and  26  can be folded outward (or, if considered with respect to the layout of components of shutter apparatus  10 , folded “inward”) to project orthogonally relative to the plane of baseplate  20 . 
     Solenoid assembly  40  is a linear actuator that is coupled, along one end, to solenoid tab  24 . Solenoid assembly  40  has a magnetic shaft  48  that is coupled to shutter blade  30 . Magnetic shaft  48  is a permanent magnet, preferably formed from a hard magnetic material such as neodymium-iron-boron (NdFeB), with a high field strength. Magnets of this type are typically coated with a protective nickel plating. 
     Blade  30  is formed from a flat sheet of magnetically soft material, such as low-carbon steel or ferritic stainless steel. Blade  30  motion is provided by magnetic shaft  48 . Blade  30  includes a blade tab  34  that is magnetically attracted to the end of shaft  48 . Magnetic shaft  48  can also be adhesively bonded to shutter blade  30 , for example. 
     To block or unblock aperture A, magnetic shaft  48  is linearly translatable to one of two positions along a planar translation path according to the state of a controlling electrical signal. In a first, unblocked position, solenoid  40  drives magnetic shaft  48  outward to contact open-position tab  26 . Tab  26  acts as a detent, limiting linear travel of shaft  48  and temporarily retaining shaft  48  in extended position, using an additional magnetic feature described in more detail subsequently. In this first, open position, shutter blade  30  is driven forward, unblocking aperture A as shown in  FIG. 1 . In a second, blocked position, solenoid  40  drives magnetic shaft  48  inward along the translation path, according to an alternate state of the controlling electrical signal. Shutter blade  30  is correspondingly driven backward, blocking aperture A as shown in  FIG. 2 . 
     It must be noted that, with appropriate changes to the design of shutter blade  30  or position of aperture A, the two corresponding states of the linear actuator, solenoid assembly  40 , can be reversed. This reversed arrangement would allow aperture A to be blocked when shaft  48  is extended and unblocked when shaft  48  is retracted. 
       FIGS. 3 through 7  show various assembly details for the components and construction of shutter apparatus  10  according to an embodiment of the present disclosure.  FIG. 3  shows solenoid assembly  40 , separated from its mount to baseplate  20 . Solenoid assembly  40  has a spool  42  with an arrangement of internal wire coils  46  energizable to drive shaft  48  to its forward or retracted position according to the state of a received electrical signal  32 . 
     Spool  42  can be formed from a non-magnetic material, such as a polymer or aluminum. Spool  42  is preferably made of material that provides a low-friction, low-wear surface between on the surface facing magnetic shaft  48 , such as nylon or acetal Polyoxymethylene (POM). Polymer material can contain one or more low-friction additives or can have a low-friction coating. 
       FIGS. 4A and 4B  are perspective views that show partial assembly of shutter apparatus  10 , with solenoid assembly  40  mounted onto baseplate  20  at solenoid tab  24 . Shutter blade  30  is shown in the closed position, covering aperture A (traced in outline in  FIG. 4A ) defined by baseplate  20 . Shutter blade  30  has a raised blade tab  34  that is magnetically coupled to shaft  48 , as noted previously. Solenoid assembly  40  can be adhesively mounted to solenoid tab  24  or can be press-fitted into its position against solenoid tab  24 , such as into a slot or hole formed in solenoid tab  24  for example. By being mounted against solenoid tab  24 , solenoid assembly  40  is raised slightly above the plane of baseplate  20 , allowing space for a portion of shutter blade  30  to pass beneath solenoid assembly  40 , sliding between the solenoid and baseplate  20  in moving between open and closed positions. 
     In order to provide force for retaining the shaft  48  in open position as shown in  FIG. 1 , open-position tab  26  is coupled to a magnetic attraction element  50 , such as by a clip mechanism or using an adhesive or fastener, for example. Magnetic attraction element  50  is not a magnet but can be, for example, a flat metallic element in the shape of a coin or washer and formed from a soft magnetic material or, alternately, from a hard magnetic material. Correspondingly, a second magnetic attraction element  55  that is coupled to solenoid tab  24  helps to provide a retaining force for holding magnetic shaft  48  in closed position. Magnetic attraction elements  50 ,  55  can be formed from a soft magnetic material, such as low-carbon steel or ferritic stainless steel. This type of material for elements  50 ,  55  allows a magnetic field to be induced, generating an attractive force for holding magnetic shaft  48  in position. 
     A retainer is used to maintain shutter blade  30  along its translation path and to prevent unwanted movement of blade  30  orthogonal to its intended translation path. In the partially assembled configuration of  FIG. 4B , a spacer  60  is added, fitted into place against baseplate  20 , such as fastened using an adhesive. In the fully assembled shutter apparatus  10  shown in  FIGS. 1 and 2 , spacer  60  may not be visible, but defines the height of a retaining sleeve or gap between top cover  65  and baseplate  20  through which shutter blade  30  translates, as described in more detail subsequently. 
       FIG. 5  is a perspective view of partially assembled shutter apparatus  10  that shows solenoid assembly  40  with magnetic shaft  48  in its extended configuration, in contact with open-position tab  26 , driving shutter blade  30  to the open, unblocking position. 
       FIG. 6  shows the position of a flat, apertured top cover  65  that mounts onto spacer  60  and extends around aperture A, acting as a retainer  82  for shutter blade  30  translation. Top cover  65  is formed from a non-magnetic material such as aluminum or a polymer material and is substantially planar. For better visibility of underlying features of shutter apparatus  10 , apertured top cover  65  is shown in  FIG. 6 , but the aperture A would not be visible in the closed view position shown. Top cover  65  can be adhesively coupled to spacer  60  to define, between cover  65  and baseplate  20 , a planar translation path  52  for shutter blade  30  travel. Translation path  52  extends in parallel to the surface of baseplate  20 , with shutter travel along translation path  52  in the direction of the dashed line as shown. Any of a number of mechanical fasteners such as screws or clips can be used to secure spacer  60  and top cover  65  in position on baseplate  20 . 
     The schematic side view of  FIG. 7  shows spacer  60  separating the retaining top cover  65  from baseplate  20  by a distance d to form a gap G that extends parallel to the plane P in which baseplate  20  lies. Gap G allows space for sliding translation of shutter blade  30  along a planar translation path  52  that extends across the surface of baseplate  20  and parallel to plane P to block or unblock the aperture. Top cover  65 , in defining the translation path  52  over a portion of gap G acts as retainer  82  to help retain shutter blade  30  along its intended translation path  52 , so that the blade does not inadvertently move or shift in a direction orthogonal to the translation path  52  and jam or shift out of its intended position. 
     The schematic side views of  FIGS. 8 and 9  show, for closed and open positions, respectively, a cross-section of solenoid assembly  40 , showing features of electromagnetic operation of shutter blade  30 . Solenoid assembly  40  includes spool  42 . To form the solenoid, coils  46  of electrically conductive wire are wound circumferentially around spool  42 . For clarity, only a few of the coils  46  are represented, only showing a few representative cross sections in  FIG. 8 . Coil windings are formed of non-magnetic, electrically conductive material such as copper or aluminum. Spool  40  includes a mounting plug  44  or other feature that can be inserted into or bonded to a corresponding socket or cavity on solenoid tab  24 , as described previously with reference to  FIG. 4A . 
     In solenoid operation, coils  46  can have an applied voltage which provides electrical current to generate a coil flux path  72  along the axis of spool  42 , as shown in  FIG. 8 . Magnetic shaft  48  has a magnet flux path  70  relative to coil flux path  72 , to axially force magnetic shaft  48  to move in a forward or reversed direction depending on the direction of the current. Interaction between coil flux path  72  and magnet flux path  70  moves magnetic shaft  48  linearly, based on the direction of current through coils  46 . With this arrangement, the applied electromagnetic field can drive magnetic shaft  48  into either the closed position of  FIG. 8  or the open position of  FIG. 9 . Magnet flux path  70  of magnet  48  and the coil flux path  72  of coils  46  are shown in an attracting polarity that draws magnetic shaft  48  into solenoid assembly  40 . Reversing the current flowing through coils  46  reverses the coil flux path  72  and drives magnetic shaft  48  in the opposite, outward direction. 
     In  FIG. 9 , shutter assembly  10  is in the de-energized state. Coils  46  are not carrying current and there is no coil flux path  72 . The attraction of magnetic shaft  48  to either of magnetic attraction elements  50  and  55  provides a retention force for magnetic shaft  48  and shutter blade  30 . Magnetic attraction elements  50  and  55  can be soft magnetic material such as low carbon steel or ferritic stainless steel that are attached to corresponding non-magnetic tabs  24 ,  26  that protrude from baseplate  20 . Alternately, elements  50  and  55  can be magnets oriented to provide a measure of retention force for shaft  48 . When an end of magnetic shaft  48  is adjacent to a magnetic attraction element  50 ,  55  as shown in  FIG. 9 , magnetic shaft  48  induces a flux path  74  in the magnetic attraction element, causing force in an attracting direction. The flux path  74  forms a field of attraction between magnetic shaft  48  and the corresponding magnetic attraction element  50 ,  55 . As a result, magnetic attraction between magnetic shaft  48  and either of magnetic attraction elements  50 ,  55  retains shutter blade  30  in position in the absence of current through coils  46 . Magnetic retention of shaft  48  and its coupled shutter blade  30  helps to stabilize and maintain blade  30  position and provides a measure of resistance to disruptive gravitational or shock force. 
       FIG. 9  also shows mounting plug  44  of spool  42  coupled to baseplate  20  at solenoid tab  24 . This arrangement couples at least the end portion of solenoid assembly  40  to baseplate  20 . Mounting plug  44  in this case is a single circular extension that fits into a hole in solenoid tab  24 . Mounting plug  44  can be glued or heat staked to solenoid tab  24 , for example. Mounting plug  44  could alternately include more complex fasteners, such as threaded fasteners, for attachment to solenoid tab  24  or other portion of baseplate  20 . Spool  42  has a membrane across the bore, spool stop  45  ( FIG. 8 ) to provide a stop for magnetic shaft  48  when shaft  48  is retracted into solenoid assembly  40 . 
     The perspective view of  FIG. 10  shows a shutter apparatus  80  having two solenoid assemblies  40 , each driving its associated shutter blade  30   a ,  30   b  in a respectively opposite direction, so that each shutter blade  30   a ,  30   b  blocks or unblocks a portion of aperture A. First shutter blade  30   a  is traced in outline in  FIG. 10 , shown in blocking position. To fully block aperture A, an edge of the second shutter blade  30   b  can butt against or overlap an edge of the first shutter blade  30   a . Cover  65  acts as retainer  82  for both shutter blades  30   a  and  30   b.    
     According to an embodiment of the present disclosure, a linearly translatable shutter uses a single metal sheet to form shutter blade  30  and a blade interface. The blade is magnetically soft for coupling to magnetic shaft  48 . A single piece, non-magnetic frame, such as an aluminum frame, forms baseplate  20  that defines an aperture and holds the solenoid assembly between two tabs  24 ,  26  that define the extent of solenoid shaft travel and stop position. Tabs  24 ,  26  also support magnetic attraction elements to maintain the shutter blade in either open or closed position. The elements of solenoid assembly  40  are selected to provide sufficient urging force for translating shutter blade  30  along its travel path. The perspective view of  FIG. 11  shows a shutter apparatus  90  in closed position, having retainer  82  formed from the baseplate  20  material. This arrangement provides the needed functions of retainer  82  and eliminates the spacer and cover parts described previously, along with needed fasteners or adhesives. To form retainer  82 , a portion of baseplate  20 , along its edges, is folded back or inward to extend over a nearby edge of the shutter blade  30  and to constrain out-of-plane shutter blade  30  travel. 
     The invention has been described in detail with particular reference to a presently preferred embodiment, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention. The presently disclosed embodiments are therefore considered in all respects to be illustrative and not restrictive. The scope of the invention is indicated by the appended claims, and all changes that come within the meaning and range of equivalents thereof are intended to be embraced therein.