US3820144A

US3820144A - Electromechanical shutter

Info

Publication number: US3820144A
Application number: US00402554A
Authority: US
Inventors: E Neau; Hook A Van
Original assignee: US Atomic Energy Commission (AEC)
Current assignee: US Atomic Energy Commission (AEC)
Priority date: 1973-10-01
Filing date: 1973-10-01
Publication date: 1974-06-25
Anticipated expiration: 1991-06-25

Abstract

A fast, large aperture electromechanical shutter which uses a magnetically driven collapsing tubular, metal cylinder shutter arrangement is described.

Description

United States Patent [191 [111 3,820,144 Neau et al. June 25, 1974 ELECTROMECHANICAL SHUTTER [56] References Cited [75] Inventors: Eugene L. Neau; Arthur R. UNITED STATES PATENTS VanHmk, both of Livefmore, Calif- 3,185,063 5/1965 Ford 95/53 E [73] Assignee: The United States of America as represented by the At i Energy Primary Examiner-John M. Horan Commission, W hi D C Attorney, Agent, or Firm-J0hn A. Horan; Ignacio 221 Filed: 0a. 1, 1973 Resend App]. No.: 402,554

us. Cl g ;34 Int. Cl. G03b 9/60 Field of Search 95/53 I I I l I [57] ABSTRACT A fast, large aperture electromechanical shutter which uses a magnetically driven collapsing tubular, metal cylinder shutter arrangement is described.

4 Claims, 6 Drawing Figures I I 'IIIIIIIIIIII I I 1 I 1 1 PATENTEDJUH 25 1974 I I I PHOTODIODE ER URCE CAPACITOR BANK 7 SHUTTER I ASSEMBLY uen-r SOURCE PATENTEDJUHZBW 3820.144

SHEET 2 UF 2 I40 L4 FIG 3 w I m: m (VELOCITY Vs TURNS E 2 I00 5 3 B0 0.8 t m U 3 z 60 TIME Vs TURNS 0.6 u G E 40 0.4 I6 a g 0.2 E 6 I I I I I III I 2468l0l2l4l6l8 TURNS ON COIL ELECTROMECHANICAL SHUTTER BACKGROUND OF INVENTION The invention relates to fast closing photographic or the like shutter systems.

High speed drum and synchronous turbine type cameras with very short recording times have inherent problems, such as rewrite" problems which occur when the event light appears during the second occurrence of the viewing window giving a double exposure effect. Further, self-luminous events that occur late in time, such as high voltage arcs, may also cause these rewrite problems. Various methods or types of shutters have been employed in attempts to resolve these problems. In general, ordinary mechanical shutters cannot operate within the required time intervals, that is, less than about 100 microseconds. Kerr cells can and are being used as capping shutters in these time frames, but these have a serious disadvantage in that the polarizers required for their operation absorb light. The optical transmission of a typical photographic Kerr cell system in the open polarization condition is approximately percent. Another fast acting shuttering device that may be used is the image converter tube which has operation times comparable to those of the Kerr cells and very little light loss. The drawback of this type of tube is the lack of resolution, that is, no greater than about lines per millimeter. Explosive blast shutters have closing times of less than 100 microseconds but poor open-to-shut ratios. These may also be generally dangerous to handle due to the explosives involved.

Thus it is seen that previous devices have light loss and resolution problems and some, especially those requiring explosives, may be dangerous to handle and require special protective environments for their use.

SUMMARY OF INVENTION In view of the foregoing, it is an object of this invention to provide a fast closing shutter capable of closing such as a 2 inch aperture within 40 microseconds.

It is a further object of this invention to provide a shutter which comprises an efficient collapsing tube arrangement.

It is a further object of this invention to provide a fast closing shutter which blocks the optical path after closing thereby eliminating rewrite" problems.

It is a further object of this invention to provide a simple and inexpensive camera shutter which can close a 2 inch diameter aperture within 40 microseconds.

Various other objects and advantages will appear from the following description of the invention and the most novel features will be particularly pointed out hereinafter in connection with the appended claims. It will be understood that various changes in the details, materials, and arrangements of the parts which are herein described and illustrated in order to explain the nature of this invention may be made by those skilled in the art.

The invention comprises a shutter system incorporating a coil into which is disposed a collapsible metal tube such that the tube opening is in registry with an optical axis of the camera, and further incorporating a capacitor electrically connected to the coil such that on activation a magnetic field is generated inducing a current in the tube which creates an opposing field thereby forcing a radial collapse of the tube and closing the aperture to the camera optics.

DESCRIPTION OF DRAWING FIG. 1 is a cross section of a preferred embodiment of the shutter assembly of this invention;

FIG. 2 is a diagrammatic representation of a typical layout used to measure shutter closing times.

FIG. 3 graphically plots turns on coil versus closure time and impact velocity.

FIG. 4 is a schematic representation of tlyer plate and capacitor bank circuits.

FIG. 5 is a perspective drawing of a tubular cylinder before collapse.

FIG. 6 is a perspective drawing of a tubular cylinder after collapse.

DETAILED DESCRIPTION FIG. 1 illustrates in cross section a shutter assembly 10 which includes a multiturn, helical coil 16 embedded in an encapsulant or housing 18. The encapsulant may be a suitable resin such as polyurethane resin and may provide a suitable voltage standoff gradient between turns of sufficient level such as 40 kilovolts or more to prevent shorting between coil windings. Encapsulant 18 also provides mechanical support to the coil. The mechanical support should be sufficient to minimize or prevent dimensional changes effected by the applied magnetic field pressure. The inner surface of the coil 16 may have a layer 22 of a suitable plastic material for the purpose of increasing the insulation strength between a tube to be collapsed and the coil. A suitable material for insulative layer 22 may be such as a polycarbonate resin of a'thickness of from about 0.20 to about 0.50 millimeters and preferably about 0.25 millimeters.

FIG. 3 illustrates a correlation between the number of turns on coil 16 and close time in usec and impact velocity in millimeters per second. The plot indicates that an eight turn coil and a suitable energy source would give the fastest closure with the highest impact velocity. Because of mehanical advantages such as ease of fabrication and assembly, it may be desirable for coil 16 to include three turns as shown although any number of turns may be used depending upon the shutter operation requirement. From FIG. 3 it may be seen that a'three turn coil provides a closure time within 15 percent of minimum closure time.

The tube or hollow cylinder 26 to be collapsed may be made of a highly electrically conductive and ductile metal, for example, of aluminum or an alloy of aluminum, copper, brass or the like. The hollow cylinder 26 is preferably made from a deep drawn aluminum beverage-type can with ends or portions thereof removed to provide an opening preferably greater than the aperture size at the remaining end, as is illustrated in FIGS. 1 and 5. A portion of one end 28 of a can used as tube 26 may be retained in order to provide a rigid end structure and thereby collapse the end of tube 26 opposite end 28.

It may be preferred that the diameter of hollow cylinder 26 by slightly smaller, such as from about I to about 2 millimeters smaller, than the diameter of chamber 29 formed by the encapsulant wall 30 which supports the coil 16. This dimension permits locating of the can or tube within chamber 29 and retention of same in this position during operation of the shutter system. The length of the tube" 26 may be varied depending upon the opening of the aperture, the closure speed required, and the like. It may be desired that the end of the tube 26 extend slightly beyond the coil, such as a distance of from about 5 to about millimeters, to insure complete closure of the shutter.

Line 31 illustrates what would be a typical optical axis for the system shown in FIG. 1. Upon appropriate trigger command a high level, rapidly changing discharge current is applied through the

eon'isv'ia terminals

32a, 32b generating a rapidly increasing, large and concentrated magnetic field within coil 16. The increasing magnetic field will induce currents in the tube 26 and an opposing magnetic field which will force a rapid, radial collapse of the tube 26 thereby blocking the light along the optical axis 31. Line 34 schematically illustrates a can or tube profile in flight after activation of the coil 16.

It may be desirable, in order to insure that'there is no light leakage due to rebound of the can surfaces after closure of the shutter, to provide a pair of transparent plates or the like 40a, 40b disposed at each open end of the encapsulant l8.

Plates

40a, 40b coact with a coating 44 on inner surface of cylinder 26 to insure complete closure as is described hereinbelow. These

plates

40a, 40b may be made of a rigid and transparent vinyl polymer such as a methyl methacrylate vinyl polymer. Other suitable materials may also be used such as glass and other acrylic resin or the like polymers Prior to disposing the tube 26 within the shutter assembly 10, the inner surface 44 of tube 26 may be coated with a film of a suitable grease such as a vacuum type grease, or any other similar suitable material, to a suitable thickness such as from about 0.] to about 1 millimeters. The grease, which may be translucent, may contain therein a suitably sized powder which will render the grease opaque, such as a charcoal powder of a diameter size of from about greater than 0 to about 4 microns or greater. This powder may be mixed with the grease prior to coating of the surface or may be thereafter sprinkled upon the grease. As an alternative, an opaque grease may be used without mixing any powder. Upon activation of the coil 16, the tube will close and, in effect, throw the powder and grease upon the

plates

40a, 40b thereby filling interstices which may remain in the collapsed tube, thus insuring against light leakage.

In order to insure most prompt response, the distance between coil 16 and tube 26 is minimized as stated hereinabove. Layer 22 disposed on coil 16 on the inner I surface of the coil as illustrated in FIG. 1 increases the insulation strength between the can or cylinder 26 and the coil allowing the coil to be closer to the can and thus permitting the use of smaller diameter coils. The encapsulant 18 may extend or contain a lip 46 which retains or locates the can or tubular cylinder 26 and prevents same from being ejected from the coil. A further purpose of lip 46 is to close the viewing aperture from the size of the tube or beverage container of about 6.3 centimeters to a desired open shutter diameter, such as about 5 centimeters in a preferred embodiment. Lip 46 size may also further enhance closure.

time by allowing thecylinder 26 to be triggered early in time such that only the final portion of the closure is used. Thus in the preferred embodiment, the can may close about 1.3 centimeters before blocking any light eliminating thereby the initial acceleration time from the useable closure time.

FIG. 4 schematically represents a simplified circuit for the collapsing can and capacitor bank arrangement. Upon closure of switch 70, the circuit is completed and the charge on capacitor 72 dissipates through inductor 74 an d resi storjq. The rapigl discharge and changing current rate generates an iriduced electromagnetic field by inductor 74 which will induce a current through the collapsing can equivalent circuit as schematically illustrated in FIG. 4. Resistor represents the collapsing can resistance and inductor 82 represents the collapsing can acting as an inductor. The triggering of the

capacitor bank

72, 47 may be timed either from the event being photographed or at any other time from a delay generator not shown).

The shutter assembly 10 may be connected as shown in FIG. 2 to a capacitor bank 47 or other source of high current, by a short section of an appropriate low inductance cable 48 in order to keep the total bank inductance as low as possible yet maintaining a relatively flexible assembly which may be built into a variety of optical designs. A fast closing shutter as described in this invention may be most valuable or useful if it contains a 2 inch diameter or 5 centimeter diameter aperture closing I in less than about 50 microseconds. Smaller size apertures may be closed faster, and these may be located either in the internal optics of the camera or at the apex of external optics to prevent objectionable vignetting with the subsequent loss of optical information. The 5 centimeter aperture selected may be located in almost any position depending on the image size and the optics of any particular camera or other optical system.

In order to close a 5 centimeter diameter cylinder 26 with an approximate moving mass of 2.5 grams, as illustrated by line 34 in FIG. 1, in 50 microseconds or less, an average closing velocity of 0.5 millimeters per microsecond and 310 joules of kinetic energy may be required.

A suitable capacitorbank satisfying these requirements may be built around a 14 microfarad, 20 kilovolt capacitor satisfying the energy requirements of 3 kilojoules assuming 10 percent energy conversion and also having a low internal inductance (l5 nanohenries). Although any high voltage switch may be used, it may be desirable to usea swinging cascade gap for the high voltage switch which contains its own biasing network and trigger capacitor. During normal operating conditions in a typical embodiment the gap may be triggered from about 6 to about 27 kilovolts thusallowing for a wide range of operating conditions. Current discharge may typically be from about 40 to about 50 kiloamperes at a 5 to 10 microsecond rate of discharge.

The capacitor bank 47 is electrically connected by means of electrical cable 49 to a suitable power source 50 used to charge bank 47. The shutter assembly 10 may be inserted in a system which may be used to measure closing times as shown in FIG. 2 wherein light source 52 provides the light for the event to be re corded on photodiode 60. Shown disposed at both ends of shutter assembly 10 are diffuser elements 54a and 54b made of a suitable material. Disposed between photodiode 60 and diffuser element 54b is a lens 58 suitable for converging the incident light from light source 52 onto photodiode 60. The assembly between the light source 52 and the photodiode 60 may be incorporated within a closed container to prevent stray light from entering.

In using this invention, a typical setup may include an event light in lasscfithe ht snares a camera place of ph otodiode 60, together with shutter assembly 10, lens 58, capacitor bank 47, power source 50 and appropriate

electrical connectors

48, 49.

The shutter assembly and capacitor bank 47 having the properties described hereinabove and using a 5 centimeter long can fired with a capacitor voltage of kilovolts has repetitively provided a closure Within approximately 40 microseconds. Further, coating of the inner surface 44 with vacuum grease and charcoal powder and effecting closure thereafter has insured that no light passes after the approximate 40 microsecond closure. By placing the system in a vacuum such as less than about 10 Torr, the effects of the air cushion and shock wave have been removed and this has resulted in a subsequent decrease in closure time to 31 microseconds on a repetitive basis. I

FIG. 5 and FIG. 6 illustrate the appearance of the tubular cylinder before and after collapse, respectively. The length L of a 5 cm and an 8.25 cm can before collapse was reduced to a length L of about 1.9 cm and about 4.5 cm respectively after use in this invention.

A positive and simple closure may be obtained by charging the abovedescribed capacitor bank to 14 kilovolts and using an 8.25 centimeter long tube 26. The longer tube and lower voltage also provides a longer time requirement for positive closure in this case but these have been consistently performed at less than 200 microseconds in this mode.

Should a faster closure be desired, the shutter assembly maybe placed at the optical apex (i.e., the focal point of the single lens) and triggered early such that the final portion of the closure is used. Use of this latter method of closing and locating of the shutter assembly may depend on the amount of vignetting that can be tolerated. In both a simple closure and a fast closure where the shutter assembly is disposed adjacent the optical apex,

plates

40a and 40b may not be required.

What is claimed is:

1. A fast closing photographic shutter comprising an open-ended coil, a hollow, open-ended electrically conductive, ductile metallic cylinder within the confines of and extending at least partially through said coil, said cylinder having an inner wall having disposed thereon a layer of opaque material, transparent plates disposed adjacent to and covering said cylinder ends, and means including a capacitor for supplying rapidly changing current to said coil for collapsing said cylinder and closing the opening therethrough, activation of said coil resulting in said opaque material coating said plates to prevent light transmission tnrough said shutter assembly.

2. The apparatus of claim 1 wherein said coil has a layer of polycarbonate material disposed on its inner surface intermediate said coil and said cylinder.

3. The method of rapidly closing a photographic shutter comprising disposing a hollow, open-ended, electrically conductive cylinder in registry with an optical path between an event light source and a camera, disposing transparent plates over said open ends of said cylinder, coating the inner wall of said cylinder with an opaque coating, producing a magnetic field about the periphery of said cylinder to induce currents in said cylinder and a counter magnetic field thereby collapsing the walls of said tube, said collapsing of said cylinder dispersing said opaque coating onto said transparent plates preventing light passage and effecting closing of said optical path.

4. The method of claim 3 wherein said opaque coating is taken from the group consisting of opaque grease and translucent vacuum grease including charcoal powder of diameter size of from about greater than 0

Claims

4. The method of claim 3 wherein said opaque coating is taken from the group consisting of opaque grease and translucent vacuum grease including charcoal powder of diameter size of from about greater than 0 to about 4 microns.