Night vision scope with voltage supply

Abstract: A night vision scope (10) incorporates an infrared light source (16) having a control circuit (S2, R1-R4) coupled between a voltage supply circuit and an infrared source, the control circuit comprising a resistive voltage divider arrangement (R2-R4) with a multi-position switch to give alternative illuminations of the infrared source.

Description: The invention relates to night vision scopes. Night vision scopes are used generally by military and law enforcement personnel for operations in low light conditions. This enables military and law enforcement personnel to use the night vision scopes to observe conditions at night and in dark buildings. A night vision scope allows the user to continue to make tactical advances and observe hostile tactical advances. New night vision scopes are also designed to assist pilots of helicopters and planes to more easily fly at night. Early night vision scopes allowed the user to observe light in the infrared spectrum. To do so, sufficient infrared light, invisible to the human eye, had to be supplied by beacons to illuminate an area. These scopes were used for only a limited period of time because of the concern that hostile forces could use similar night vision scopes to locate the infrared beacon and its user. Currently, night vision scopes utilize image intensification technologies. That is, the night vision scope receives ambient light from the environment and intensifies the image to produce an output image which is visible to the human eye. The present generation of night vision scopes operate to intensify low levels of visible light and make visible the light from the infrared spectrum. The image intensification process involves conversion of the received ambient light into electron patterns, intensification and energization of the electron patterns, and conversion of the electron patterns into light visible to the observer. Use by law enforcement officials and army personnel during active engagement with hostile forces requires that the night vision scopes be rugged and light weight. Further, it is important that the voltage supply for the night vision scope be dependable, light weight, and easily renewed. In constructing a rugged night vision scope it is important for the scope to be impervious to shocks and environmental conditions, such as moisture. Accordingly, the voltage supply must also be impervious to environmental conditions. Night vision scopes require batteries to supply the power. Either a single specialized battery or two conventional batteries can be used. Typical night vision scopes use two batteries. Since night vision scopes are designed to be light weight, using one battery is preferable to using two batteries. Any battery used in a night vision scope should be easily replaceable but sealed against water leakage into the battery area. When using two batteries, such as 1.5 volt DC batteries, the container for these batteries must be oval shaped to accept both batteries. If only one battery is used, a single cylindrical battery container can be used in combination with an O-ring of conventional construction to accomplish the seal desired. As disclosed in European Patent Application No. 91919511.5 (0502186), a voltage step-up circuit could be used as part of the voltage supply, in conjunction with a single battery, to increase the voltage supplied to a value above the voltage of the battery alone. Regardless of the voltage supply, it would be convenient also to have an infrared source to enable infrared radiation to be emitted for improved viewing facilities. It is known (US-A-4.672.194) to build such an infrared light source into a night vision scope. In this prior art, the infrared source may be switched on or off but may be operated at only one power level. According to the present invention, the infrared source may be operated at two different power levels. Thus, according to the invention there is provided a night vision scope comprising image intensifier means, voltage supply means for supplying an energizing voltage for the intensifier, and an infrared light source, characterised by an infrared light source control circuit means coupled between the voltage supply circuit and the infrared source and comprising a resistive voltage dividing arrangement and a multi-position switch, the switch being arranged in one position to provide illumination of the infrared source with a first voltage level via the voltage dividing arrangement, and in a second position providing a different illumination of the infrared source via the voltage dividing arrangement. For a better understanding of the invention and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, wherein: FIGS. 1A and 1B are illustrations of a night vision scope; FIG. 2 is a block diagram illustrating elements of the night vision scope; FIG. 3 is an illustration of the elements of an image intensifier in FIG. 2; FIG. 4 is a circuit diagram of a voltage source of FIG. 2; and FIG. 5 is a circuit diagram showing how components of a night vision scope are supplied power by the voltage source of FIG. 4. Reference will now be made in detail to a present preferred embodiment of the invention, an example of which is illustrated in the accompanying drawings. A night vision scope utilizing the teachings of the presently preferred embodiment is illustrated in FIG. 1. Night vision scope 10 intensifies a received image. Night vision scope 10 includes an eye piece 12, a lens 14, an infrared light source 16, and an infrared light source lens 17. A housing 18 contains the electronics and optics required for operation of the invention. Mounted on one face of housing 18 is an operating switch 15 and cap 13 for the single battery which generates a voltage for night vision scope 10. The single battery is housed in a battery chamber which includes cap 13. The chamber cap 13 is sealed with a standard O-ring. Utilization of an O-ring reduces the complexity and construction costs of night scope 10 since an off the shelf element may be used. Night vision scope 10 includes a light receiving means for receiving an image. In the present preferred embodiment, lens 14 receives the light image and magnifies it. The user of night vision scope 10 places his eye adjacent to eye piece 12 to observe the resultant intensified received image. Infrared light source 16 may be activated to emit infrared light in the direction which lens 14 is directed. Preferably, infrared light source 16 is an infrared light emitting diode. A focus lens 17 is mounted on swing arm 19 to be optionally positioned over infrared light source 16. Lens 17 may be positioned over infrared light source 16 to focus the infrared light, such as for using light source 16 for a spot light. FIG. 2 illustrates a block diagram of the functional elements of night vision scope 10. Like reference numerals indicate like structures. Accordingly, FIG. 2 illustrates objective lens 14 and infrared light source 16. Night vision scope 10 further includes an image intensifier 20, an output window 22 and voltage source 24. Voltage source 24 supplies the voltage to both infrared light source 16 and image intensifier 20. An image is received through lens 14 and transmitted to image intensifier 20. After image intensification a visible image is output from image intensifier 20 to output window 22. Observer 26 views the intensified image in output window 22. FIG. 3 illustrates the image intensification process in conjunction with the structural elements of image intensifier 20. Image intensifier 20 includes an input window 30, a photo cathode 32, a micro channel plate 34, and a phosphor screen 36. In a preferred embodiment of the present invention the elements of image intensifier 20 are constructed in a wafer tube configuration with the elements being configured as wafers. Photo cathode 32 is located between input window 30 and micro channel plate 34. On the opposite face of micro channel plate 34 is located phosphor screen 36 at the input to output window 22. The eye piece receives the output from output window 22. An observer 26 observes an intensified output image through eye piece 12. During operation of night vision scope 10 the light from object 38 is received through objective lens 14. In the presently preferred embodiment, objective lens 14 is a convex lens which gathers light and magnifies the image. Light passes through input window 30 onto photocathode 32. Photocathode 32 responds to the received light by generating a number of electrons in proportion to the intensity of received light. The number of electrons are proportional to the intensity of the received light to form a pattern of electrons corresponding to the received image. Photocathode 32 is sensitive to infrared light as well as light in the visible Spectrum so that electrons are produced in response to infrared light passing through the objective lens and input window onto photocathode 32. Electrons from photocathode 32 are emitted into micro channel plate 34. The energy of the electrons from photocathode 32 is increased because of a voltage applied across the two faces of micro channel plate 34. Micro channel plate 34 consists of a disk of optical fibers each of whose primary cylindrical axis is oriented parallel to the direction of received electrons from photocathode 32. The optical fibers in micro channel plate 34 are held together with reflective cladding between the fibers. Further, each face of micro channel plate 34 has an electrode deposited thereon so that a potential may be generated between the two faces to accelerate and energize the electrons entering the optic fibers. Micro channel plate 34 also multiplies the number of electrons by adding additional electrons. The energized and multiplied electron pattern from micro channel plate 34 exits the micro channel plate and strikes phosphor screen 36. Phosphor screen 36 generates a visible light image corresponding to the image received through objective lens 14. Phosphor screen 36 in the preferred embodiment acts as means for converting the electron pattern generated by photocathode 32 into a visible light image of the received image. Since the objective lens 14 inverts the image of the observed object 38, input image 40 is upside down during the image intensification process and results in an upside down image on the output of phosphor screen 36. Accordingly, output image 42 must be inverted for observer 26. Output window 22 transmits output image 42 to eye piece 12 and observer 26. Output window 22 is made of optical fiber. In order to invert output image 42, the optical fiber output window 22 is softened and rotated 180° from its origin to the output during manufacture. Observer 26 will observe a correctly oriented output image 42 through eye piece 12 as a virtual image 44. In this case virtual image 44 is magnified in size due to objective lens 14 as well as its light being intensified. FIG. 4 is a simplified circuit diagram of the voltage supply 24. Voltage supply 24 includes battery 50, a step-up circuit 52, a rectifying circuit 54, and a low battery indicator circuit 56. Preferably, battery 50 supplies a first voltage of 1.5 V and is a commercially available 1.5 volt battery. The night vision scope includes a means for supplying a second voltage to the light converting means, the means for increasing the energy of the electrons, and the electron converting means. The second voltage is proportionately greater than the first voltage. In the preferred embodiment of the present invention, voltage supply circuit 24 produces an output voltage V out which is greater than the voltage supplied by battery 50. In the preferred embodiment, voltage V out is two times the voltage supplied by battery 50, i.e. 3 volts. Other voltage values and proportions may be used. The voltage of battery 50 is input to step-up circuit 52. Step-up circuit 52 includes an inductor L1 and a switching circuit S1. The output of step-up circuit 52 is fed to rectifying circuit 54. Step-up circuit 52 operates by oscillating switch S1 open and closed. When the switch is closed, current builds up in the coil, creating a magnetic field. Next, switch S1 is opened and the magnetic field collapses in inductor L1. Accordingly, the voltage across the inductor reverses polarity. This voltage across the inductor L1 adds to the voltage of battery 50 to produce a total voltage which is greater than the voltage produced by battery 50 alone. In order to supply a constant voltage at V out , rectifier circuit 54 is utilized to smooth out the variations in voltage due to the cycling of switch S1. Rectifier circuit 54 includes diode D1 and capacitor C1. Rectifier circuit 54 works in a conventional manner to smooth out voltage variations at V out . A zener diode D2 is included in rectifying circuit 54 to facilitate utilization of a battery 50 which supplies a voltage greater than the voltage required by night vision scope 10. Zener diode D2 has an operational value slightly greater than the required voltage. Accordingly, voltage V out does not exceed a maximum value determined by zener diode D3. Preferably, zener diode is rated as a 3.3 volt zener diode so that the output voltage has a maximum output of 3.3 volts. For operation of the present preferred embodiment in extremely cold temperatures, the 1.5 volt alkaline battery does not function properly. Therefore, a 3.9 volt lithium battery is used in voltage supply circuit 24. Output voltage V out is then limited to a maximum value of 3.3. volts. As the lithium battery wears down below the required output voltage of 3.0 volts, voltage step-up 52 will function to increase the battery voltage as described above. In order to detect a low voltage condition of battery 50 a low voltage detecting circuit 56 is provided. This low voltage circuit produces a reference voltage V out which is compared to the voltage of battery 50 by comparator 58. If the battery voltage is lower than the reference voltage V ref current flows through resistor R1 and through light emitting diode LED1. Accordingly, light emitting diode LED1 will light when the voltage of battery 50 goes below V ref . In a preferred embodiment of the invention, battery 50 produces a 1.5 volt output, and V ref Is selected to be 1.17 volts. In the preferred embodiment of the invention a switching circuit which is used to implement switch S1 is an off the shelf component. In the presently preferred embodiment a Maxim Low Voltage Step-Up DC-DC Convertor, catalog number MAX657 manufactured by Maxim is utilized. FIG. 5 illustrates the application of output voltage V out to the elements of night vision scope 10 of the presently preferred embodiment. That is, as discussed above, output V out is applied to image intensifier 20 and its associated components. The voltage V out is also applied to provide voltage to an infrared light source 16 and the light emitting diode (LED) infrared indicator 60. LED infrared indicator 60 indicates the status of infrared light source 16. That is, infrared light source 16 can be elected to be either off or on at two different power settings. Infrared light source 16 may be selectively activated with switch S2. If position 1 of switch S2 is selected, the infrared light source remains inactive and no infrared light is emitted. If position 2 of switch S2 is chosen, a low power condition of infrared light source is activated and LED infrared indicator 60 indicates this low power status. That is, a low level of infrared light is emitted from infrared light source 16. This low level of light is generated because of the low level of power supplied through resistor R4 to infrared light source 16. Further, LED infrared indicator 60 is activated but at a low level due to the amount of power supplied through resistor R3. The LED infrared indicator 60 is located so that it may be viewed through eye piece 12 of night vision scope 10. A high level or high intensity of infrared light will be emitted from infrared light source 16 if position 3 of switch S2 is selected. The LED infrared indicator 60 will indicate this higher intensity output of infrared light source 16. The higher intensity of infrared light emitted from infrared light source 16 will be due to the increased power supplied to infrared light source 16 through resistor R2. Resistor R2 will be selected to have a lower resistance value than resistor R4 since greater power must flow through resistor R2 for a fixed voltage. Likewise, the resistance of resistor R1 will be chosen to be less than the resistance of resistor R3. The two different levels of infrared light emitted from infrared light source 16 allows the user of night vision night scope 10 to select two different modes of infrared light emission. In the low level mode the user of the night vision scope 10 can inspect maps with the aid of image intensifier 20 at night or do other tasks at close range requiring a low level of illumination. If a higher level of infrared light is required for viewing objects in, for example a room in a house which is dark, the high level of infrared light emitted from infrared light source 16 may be selected. It will be apparent to those skilled in the art that various modifications and variations could be made in the night vision scope of the present invention without departing from the scope of the invention as set out in the claims. As an example, the invention may be used in a device that takes the form of a single viewing device with optics for two eyes, or two viewing devices for both eyes.

Claims: A night vision scope (10) comprising image intensifier means (20), voltage supply means (50) for supplying an energizing voltage for the intensifier, and an infrared light source (16), characterised by an infrared light source control circuit means (S2, R1-R4) coupled between the voltage supply circuit and the infrared source and comprising a resistive voltage dividing arrangement (R1, R2, R3, R4) and a multi-position switch (S2), the switch being arranged in one position to provide illumination of the infrared source with a first voltage level via the voltage dividing arrangement, and in a second position providing a different illumination of the infrared source via the voltage dividing arrangement. A scope according to claim 1, wherein the dividing arrangement (R1-R4) comprises two resistances (R2, R4) coupled to the infrared light source (16) to provide two alternative resistive paths coupled to the switch (S2). A scope according to claim 1 or 2 and including a voltage rectifier circuit (D1) for minimizing variations in the voltage output from said voltage supply means (50). A scope according to claim 1, 2 or 3 and including limiting circuit means (D2) for limiting the output voltage to a predetermined value. A scope according to claim 4, wherein said limiting circuit means includes a zener diode (D2). A scope according to claim 4 or 5, wherein said predetermined value is 3.3 volts. A scope according to any one of the preceding claims, wherein the image intensifier means (20) includes: light converting means (30, 32) for converting the light in an image into electrons in proportion to the intensity of the received light to form a pattern of electrons corresponding to said received image; energization means (34) for increasing the energy of the electrons in the electron pattern; and electron converting means (36) for converting the electron pattern into a visible light image of the received image. A scope according to any one of the preceding claims, wherein the voltage supply means comprises a battery (50). A scope according to claim 8, wherein the voltage supply means comprises a substantially cylindrical battery chamber for housing a simple battery, the chamber including a cap (13) and an o-ring for sealing said cap.

Inventors: GRAMER MARK EVERETT, MORRIS TERRY D, GRAMER, MARK EVERETT, MORRIS, TERRY D.
Applicants: LITTON SYSTEMS INC, LITTON SYSTEMS, INC.
Application year: 1991
Main classification: H01J29
IPC codes: H01J29, G02B23