WO1997031293A1

WO1997031293A1 - Apparatus and method for eliminating the fogging of intraoral camera images

Info

Publication number: WO1997031293A1
Application number: PCT/US1997/002944
Authority: WO
Inventors: William W. Stevens
Original assignee: New Image Industries, Inc.
Priority date: 1996-02-22
Filing date: 1997-02-20
Publication date: 1997-08-28
Also published as: AU1974897A

Abstract

An improved apparatus and method for minimizing fogging of the camera image caused by water vapor condensation on a transparent element (12 or 300) in an intraoral camera's optical path is provided. The intraoral camera has a distal end for placement in a subject's mouth. The camera also contains an optical train and a heating element (50). The optical train includes the transparent element (12 or 300) which is located at the distal end. The heating element (50) is thermally coupled to the transparent element (12 or 300). The heat minimizes condensation that would prevent light from entering the transparent element (12 or 300).

Description

APPARATUS AND METHOD FOR ELIMINATING THE FOGGING OF INTRAORAL CAMERA IMAGES

BACKGROUND OF THE INVENTION The present invention is directed generally to intraoral cameras, and more particularly to apparatus and method for eliminating the fogging of intraoral camera images.

An intraoral camera is a device used by a dentist or others to examine a person's mouth (also referred to as a patient's oral cavity) . The intraoral camera is typically an elongate instrument having a distal end that is inserted in the patient's mouth and a proximal end that is kept outside the patient's mouth. An optical train forms an image of a portion within a field of view inside the patient's mouth and relays this image to a video camera located at the proximal end. The camera may have a dedicated illumination system. Thus, the optical train may also communicate light from a source at the proximal end to the distal end to illuminate the field of view. The light source can also be located at the distal end of the camera device. If the camera device does not include a dedicated illumination system, the operatory light can be used to illuminate the field of view.

The optical train and other components are typically located in an opaque housing formed with a distal end opening that allows illumination light to exit the housing and allows light from the object of interest to be captured by the optical train. The opening is covered by a transparent element, such as a lens, a prism, or a window that is at the distal end of the optical train. It is common practice to cover at least the distal portion of the intraoral camera with a thin, transparent, disposable sheath or a transparent, rigid cap for sanitary reasons, since the camera is typically not sterilizable. Thus, these protective sheaths and caps are often used by dentists and others to prevent microbiological cross contamination from one patient's oral cavity to another's and to the hands of the operator.

Figs. 1A and IB are bottom and side-sectional views of a prior art intraoral camera. A camera housing/ handpiece 10 contains the video pick-up and the optical train, which extends between the distal and the proximal ends . As shown in the side view of Fig. IB, the camera is characterized by a field of view 20 directed 90 degrees to the axis of the handpiece. A reflecting element such as a reflective prism or mirror 30 is used to deflect incoming light by approximately 90 degrees. The optical image from field of view 20 is directed from the prism along an optical path to a video camera pick-up 32. An initial lens, which may be a gradient index lens, forms an image of the field of view, and relay optics such as a series of lenses 34 relay and magnify the images to the video camera pick-up.

The light sensitive video pick-up is used to convert optical images from optical element 12 into electrical (or television/video) images. These electrical images are provided via a camera cable 14 for real-time display. The optical element is just one example of a transparent element located at the distal end of the camera housing. If a dedicated illumination system is provided, fiber optics located within cable 14 along with light source 24 are used to provide the illumination 22. Thus, field of view 20 is illuminated.

Regardless of the particular optical configuration, there will be a surface of a transparent element in the optical path that is exposed to the atmosphere inside the patient's mouth. This may be the outer surface of the element at the distal end of the optical train, or it may be the outer surface of the protective sheath or cap. This surface will be referred to as the exposed surface in the optical path.

The atmosphere in the oral cavity of a patient is warm and moist compared to the typical atmosphere outside the oral cavity. A common phenomenon with intraoral cameras is the condensation of water vapor onto the surfaces at the distal end, due to the fact that the intraoral cameras are typically somewhat cooler than the atmosphere in the oral cavity. The optical train can include elements which have no optical power (e.g., the protective sheath) . Thus, fogging occurs when a cool object comes in contact with the warm moist air in the patient's mouth, and when condensation is present on a transparent element in the optical path, it causes the image produced by the camera to be blurred.

Several schemes have been employed to minimize or eliminate water vapor condensation on transparent elements. For example, a stream of air can be passed over the exposed surface subject to fogging to prevent condensation as shown in Fig. 2. Fig. 2 shows a prior art technique for defogging the distal end of an intraoral camera. To prevent fogging in this arrangement, an air stream 40 can be provided via a tube 42 to the other exposed surface subject to fogging.

There are several problems with passing air over the exposed surface. For example, this technique becomes impractical when using a sterile sheath or cap over the camera because of the difficulty of maintaining a sanitary barrier over the camera while still getting air to flow over the outer surface of the sheath or cap where fogging is likely to occur. The jet of air used for defogging can also cause patient discomfort if the patient has teeth sensitive to having air blown over them. Finally, the air can introduce foreign, undesirable objects into the oral cavity.

A stream of fluid can also be passed over the surface subject to fogging to prevent condensation. There are several problems with passing a stream of water or other fluid over the optical element. A method must be supplied to turn the fluid stream on or off, and a method must be supplied to remove the spent fluid from the patient's mouth. Also, the optical surface must maintain good optical properties and not distort the camera image after being wetted by the fluid.

Finally, the optical elements can be coated with a coating that inhibits condensation. Unfortunately, there is no practical special coatings to permanently prevent fogging without the coating being periodically reapplied. Further, it does no good to apply an anti-fogging coating to the optical element if a sheath or cap is to be used. Therefore, it is desirable to provide an improved scheme for minimizing or eliminating water vapor condensation on optical elements.

SUMMARY OF THE INVENTION

The present invention provides an improved apparatus and method for eliminating blurring of the intraoral camera image caused by water vapor condensation on the exposed surface in the intraoral camera's optical path. This is accomplished without having to introduce air or liquid into the patient's mouth and without having to rely on anti-fogging coatings .

In brief, the invention contemplates heating a portion of the camera structure so as to raise the temperature of the exposed surface in the optical path to a point where condensation is reduced or eliminated. This may be accomplished by heating the surface directly, or by heating other portions of the structure and providing sufficient thermal coupling between the heated structure and the exposed surface. In a specific embodiment, a resistive heater is mounted to a supporting structure for the distal element in the optical train; in other embodiments the distal element is provided with a transparent resistive coating or is heated radiatively. The heating can be open loop or closed loop, but it is preferred to control the heating in a closed loop fashion. In a specific embodiment, a temperature sensor is mounted to a portion of the camera structure whose temperature correlates with that of the exposed surface in the optical path. The amount of applied heat is directly related to the sensed temperature, and thus the exposed surface temperature is maintained within a prescribed range. In a specific embodiment, the surface temperature is maintained at a temperature above the dew point in the patient's mouth. It has been found that maintaining the exposed surface above about 90°F generally works, with a preferred temperature of approximately 94°F. These and other advantages will become apparent to those skilled in this art upon a reading of the following detailed description of the invention, which should be taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS Figs. 1A and IB are bottom and side-sectional views of a prior art intraoral camera;

Fig. 2 shows a prior art technique for defogging the distal end of an intraoral camera;

Fig. 3 illustrates schematically an open loop heater that provides heat to the optical element of an intraoral camera;

Fig. 4 illustrates schematically a method of controlling the temperature of the optical element;

Fig. 5 is a schematic of a circuit which controls the temperature of the optical element;

Fig. 6 shows a specific arrangement for mounting the heater and temperature sensor to a support structure; Fig. 7 shows schematically an embodiment where heat is supplied by irradiating the sheath or cap with infrared radiation;

Fig. 8 shows schematically an embodiment where heat is supplied by a resistive coating or film located on the optical element; and

Fig. 9 shows schematically an embodiment where heat is supplied by irradiating the optical element with infrared radiation.

DESCRIPTION OF SPECIFIC EMBODIMENTS

The present invention uses heat to prevent the fogging of surfaces that can degrade intraoral camera images . Heat is applied to the area subject to fogging; this area is usually on or near the distal optical element. The area subject to fogging is also referred to as the exposed surface. An exposed surface may have gaps which allow a small amount of the oral cavity environment to pass by that exposed surface. The heat maintains the area subject to fogging at a temperature that is above the dew point of the camera's operating environment. Thus, a minimum of condensation develops on the optical elements (or other nearby area) of the camera. Heating the optical elements (or other nearby areas which are subject to fogging) introduces no foreign materials into the oral cavity of the patient, and no audible noise is emitted from the defogging mechanism. Furthermore, the defogger can be "on" all of the time so the only "warm-up" occurs when the cameral has its initial power applied. This method of heating brings the camera hand piece tip to a temperature at or near body temperature so there is no patient discomfort related to the cold feeling from an unheated intraoral hand piece in the patient's mouth. Additionally, when heat is used, there is no need for an air supply compressor in the camera unit, or a hook-up to an operatory air supply.

In one embodiment of the present invention, the temperature is raised above the dew point temperature by applying heat directly to the optical element. This raises the temperature sufficiently above ambient to be above the dew point such that the exposed surface is not subject to fogging. In this embodiment, this temperature is usually over 90 degrees and preferably around 95 degrees. The temperature is not raised to a point where a patient might experience discomfort from the heat . There are several ways to heat the particular optical surfaces that are subject to fogging. In one embodiment, heat is applied from a heating element to the optical surface (s) . A resistor mounted to the metal block that holds the optical element is used to provide the heat in this arrangement.

Fig. 3 illustrates schematically an open loop heater 50 that provides heat to an optical element 60 of an intraoral camera. This open loop heater embodiment does not include a temperature sensor. Heat is provided from heater 50 to optical element 60 via one or more known heat transfer mechanisms such as conduction, convection, and radiation. This may be done by heating the element directly or by heating other structures that are thermally coupled to the optical element. Thus, a small amount of power, applied to the heater, can prevent fogging of the exposed surface.

Fig. 4 shows another embodiment of the present invention, where a closed loop system incorporates a temperature sensor 120 in conjunction with heater 50 to regulate the temperature of the heater and/or optical element 60 subject to fogging. In this arrangement, the regulated temperature is maintained above the dew point of the intraoral cavity. In this embodiment, temperature sensor 120 monitors the temperature of optical element 60 and provides a temperature-dependent electrical signal to an amplifier 130, which controls the power to heater 50. A reference signal is also applied to amplifier 130 such that heater 50 applies more or less heat to optical element 60 depending on the feedback information from temperature sensor 120.

Fig. 5 is a schematic of a circuit which controls the temperature of the optical element. In this embodiment, the heater is a surface mount resistor 200 while the temperature sensor is a thermistor 202. Resistor 200 is in series with a transistor 205, and the current through resistor 200 is controlled by an amplifier 210. Amplifier 210 acts as a comparator which receives at its inputs (a) a temperature- dependent voltage provided by a first voltage divider that incorporates thermistor 202 and (b) an adjustable reference voltage provided by a second voltage divider that incorporates a variable resistor 220. In the specific implementation, amplifier 210 and transistor 205 are part of the same circuit package, so the designation of inverting and non-inverting inputs are with respect to the output terminal defined by the collector of transistor 205. LED 222 is an optional element located in parallel with heater 200 such that LED 222 is illuminated when heater 200 is "on. " This circuit design can also be used with the embodiments described below. Fig. 6 shows a specific arrangement for mounting the heater and temperature sensor to a support structure. The distal end of the camera device is illustrated in Fig. 6. As stated above, in the preferred embodiment, a resistor mounted to metal block 240 that holds the optical element is used to provide heat to the exposed surface. In this embodiment, heater 250 provides heat to the optical element, and temperature sensor 252 monitors the temperature of the block at a point near heater 250. Temperature sensor 252 can also monitor other elements whose temperature correlates with that of the exposed surface. Both heater 250 and temperature sensor 252 are mounted directly to a portion of the distal end of the camera device. Electrical conductors 254-257 connect the heater and sensor to the remaining portions of the circuit, which are located at the proximal end. Optical fiber cable 262 provides illumination to the camera field of view via aperture 260 (there is also an aperture on the other side of optical element) . Fig. 7 shows schematically an embodiment where heat is supplied by irradiating the sheath or cap with infrared radiation. A protective sheath 300, cap or other plastic device can be placed over hand piece 10. Heat can then be conducted or radiated to warm the sheath 300 or cap. When this occurs, heat is transferred between the optical surface and the plastic device. Conduction or convection occurs when the sheath or cap is placed in close proximity to another heated element (e.g., the optical element) . For radiation, material which absorbs infrared energy can be placed in the sheath or cap. Infrared radiation directed toward the sheath or cap would then warm it. The light for the illumination of the field of view can be used to provide the infrared radiation for warming the sheath or cap. This is an open loop system, so sheaths with varying amounts of absorption could be used for different ambient conditions.

Fig. 8 shows schematically an embodiment where heat is supplied by a resistive coating or film located on the optical element. In the preferred embodiment, a coating or film 310 is in contact with optical element 12. This coating/ film 310 can also be placed on the prism or on any other transparent element in the optical path. In this arrangement, current is passed through the coating/ film 310 to provide resistive heating. Thus, coating/ film 310 acts as a resistor to provide the desired heat .

Fig. 9 shows schematically an embodiment where heat is supplied by irradiating the optical element with infrared radiation. Optical (or other transparent) element 12 absorbs infrared radiation or a similar electromagnetic source of energy. In this arrangement, a source of infrared radiation 320 has an output beam 322 directed at optical element 12. Thus, in this embodiment, light beam 322 is used to heat the surface of the optical element 12 or other area which is subject to fogging. Output beam 322 can also be directed to other structures that are thermally coupled to the optical element 12. In another embodiment, infrared radiation can be passed via optical fiber 330 to radiate on exposed surface 12 such that it is heated. This optical fiber 330 can be the same optical fiber used to illuminate the camera's field of view.

In yet another embodiment of the present invention, more than one optical element is located in the intraoral camera. In this arrangement, the multiple optical elements are heated to prevent condensation.

While a full and complete disclosure of the invention has been provided herein above, it will be obvious to those skilled in the art that various modifications and changes may be made.

Claims

WHAT IS CLAIMED IS:

1. Apparatus for use in an intraoral camera having a distal end for placement in a subject's mouth, the apparatus comprising: an optical train having a transparent element at the distal end; and a heating element thermally coupled to the transparent element; whereby condensation that would prevent light from entering the transparent element is minimized.

2. The apparatus of claim 1, wherein: the transparent element is mounted to a thermally conductive support; and the heating element is mounted to the thermally conductive support so that the thermally conductive support transfers heat from the heating element to the transparent element.

3. The apparatus of claim 1, wherein the heating element maintains the transparent element at a temperature above the dew point of the environment of the distal end of the intraoral camera.

4. The apparatus of claim 1, further comprising a temperature sensor for monitoring the temperature of the optical element.

5. The apparatus of claim 4 , further comprising control circuitry coupled to the temperature sensor and the heating element, the control circuitry operating to change the heat generated by the heating element when the temperature sensor detects that the temperature of the optical element is outside a predetermined temperature range.

6. The apparatus of claim 1, wherein the heating element comprises an electrical resistor that generates heat as a result of current flow therethrough.

7. The apparatus of claim 1, wherein the heating element is an electrically resistive transparent film deposited on a surface of the transparent element.

8. The apparatus of claim 1, wherein: the transparent element absorbs infrared radiation; and the heating element comprises a source of infrared radiation having an output beam directed at the transparent element .

9. The apparatus of claim 1, wherein: the intraoral camera is used in conjunction with a transparent sheath covering the distal end, the transparent sheath making intimate contact with the transparent element; and the heating element maintains the optical element and the transparent sheath above the dew point of the environment of the distal end of the intraoral camera.

10. The apparatus of claim 1, wherein the transparent element is at least one of an optical element, a window, a prism, a sheath, a cap, a coating covering an optical element and a film covering an optical element.

11. A defogging element in an intraoral camera, the intraoral camera including an optical train with an transparent element, comprising: a heating element for generating heat; and means for providing heat from the heating element to a portion of the optical train; whereby condensation that would prevent light from entering the transparent element is minimized.

12. The defogging element of claim 11, wherein the heated portion of the optical train maintains a temperature above the dew point of the intraoral camera environment.

13. The defogging element of claim 11, further comprising a temperature sensor for monitoring the temperature of the transparent element.

14. The defogging element of claim 13, further comprising means for changing the heat generated by the heating element when the temperature sensor detects the temperature of the transparent element is outside a predetermined temperature range.

15. A method of controlling transparent element temperature in an intraoral camera, comprising the steps of: heating an transparent element with a heating element; monitoring a temperature of the transparent element with a temperature sensor; and changing the amount of heat generated by the heating element when the temperature sensor detects the temperature of the transparent element is outside a predetermined temperature range.

16. The method of claim 15, wherein a closed loop servo is used to monitor the temperature and change the amount of heat generated.

17. The method of claim 15, wherein the transparent element maintains a temperature above the dew point of the intraoral camera environment .

18. A defogging apparatus in an intraoral camera, the intraoral camera including an transparent element, comprising: a film for generating heat, the film coating the transparent element, wherein the film is heated; whereby condensation on the transparent element of the intraoral camera is minimized.

19. The defogging apparatus of claim 18, wherein current is passed through the film to provide resistive heating.

20. The defogging apparatus of claim 18, wherein the film is a resistive coating.

21. The defogging apparatus of claim 18, wherein the transparent element maintains a temperature above the dew point of the intraoral camera environment .

22. A defogging element in an intraoral camera, the intraoral camera including an optical train with an transparent element, comprising: a light beam for generating heat; and means for providing heat from the light beam to a portion of the optical train, wherein the transparent element maintains a temperature above the dew point of the intraoral camera environment; whereby condensation that would prevent light from entering the transparent element is minimized.

23. A defogging element in an intraoral camera, the intraoral camera including an optical train with an transparent element, comprising: a light beam for generating heat; at least one of the group of a sheath and a cap for covering the distal end of the intraoral camera; and means for providing heat from the light beam to at least one of the sheath and the cap, wherein at least one of the sheath and the cap maintains a temperature above the dew point of the intraoral camera environment; whereby condensation that would prevent light from entering the transparent element is minimized.