WO2001011582A1

WO2001011582A1 - Optical ice detector

Info

Publication number: WO2001011582A1
Application number: PCT/US2000/021837
Authority: WO
Inventors: Thomas J. Bachinski; Brett A. Muehlhauser; Robert D. Rutkiewicz; Timothy T. Golly; Douglas M. Holm
Original assignee: Rosemount Aerospace Inc.
Priority date: 1999-08-10
Filing date: 2000-08-10
Publication date: 2001-02-15
Also published as: AU6629100A

Abstract

An optical ice detector (12A, 12B, 12C, 12I, 86) uses an optical element (22) mounted in a position to receive ice. The light reflected from a prism (22, 51, 88) is sensed and as ice collects on the exterior of the prism (22, 51, 88) the amount of light reflected changes proportionately, thereby providing an indication of icing or other conditions that contaminate a surface.

Description

OPTICAL ICE DETECTOR

BACKGROUND OF THE INVENTION

The present invention relates to ice detectors, and more particularly, to optical ice detectors capable of detecting and measuring a liquid water and/or ice accumulation layer, such as can occur on the surface of an air vehicle

A major application of the invention lies in aviation where, during cold periods, it is important to know prior to aircraft takeoff whether the surfaces of its lift structures are clean, and to detect ice and icing conditions in flight. The detection of contaminants, and in particular, ice and frost on the ground and ice during flight is critical for safe air vehicle operation.

A number of different kinds of contaminant detectors have been utilized for air vehicles. Among these types are ultrasonic contaminant detectors, which utilize ultrasonic energy transmitted through a buffer or plate. Networks of flexible microstrip antennas multiplexed into a microcomputer are also used to detect surface contaminates by measuring the electrical properties of compounds on the surface over the sensor. Other detectors use lasers, fluorescent dyes or vibrating probes.

Optical sensors used for measuring liquid level are well known. Thus, sensing circuitry for optical sensors is available. Vickers, Inc. of Maumee, Ohio, USA and Gems Sensor, Inc. of Plainsville,

Connecticut, USA, provide liquid level optical sensors.

SUMMARY OF THE INVENTION

The present invention is a light refractory optical ice detector. The principle of operation makes use of the difference in the optical refraction of light in air, liquids and ice. A light source sends a light beam into a prism or other optically reflective shape. If the outer surface of the prism is free from liquid or ice, the majority of the light beam is reflected through its normal path back to a phototransistor . When the prism is exposed to liquid or ice, some of the light is refracted into the liquid or ice and a less intense light beam is collected by the phototransistor. Sensing circuitry activates warning lights, deicing mechanisms or the like depending on the intensity of the light beam collected by the phototransistor.

In most applications, the optical ice detector would be subject to exposure to light from ambient light sources such as the sun. This ambient light can off set the sensitivity of an optical ice detector by flooding the phototransistor with light thus reducing or eliminating it's capability to detect ice. Because of this, the present invention employ electronic modulation/filtration methods and/or optical filtering methods of reducing or eliminating the effects of the ambient light.

The use of optics for ice detection, as disclosed herein, offers several desirable advantages, among which are significantly lower costs, greater simplicity and increased reliability. As with other contaminant detection methods, optical ice detection can be used in combination with decontamination methods for removing ice from the surface.

Other possible applications for optical ice detectors include carburetor ice detection, ice management systems and ground ice detection in aerospace . BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a top view of an airplane where ice detectors are typically mounted on the wing and fuselage; Figure 2 is a cross section taken on line 2--2 in Figure 1, illustrating the placement of optical ice detectors at possible locations on the wing surface;

Figure 3 is a side view of an optical ice detector using a prism-shaped reflective surface; Figure 4 is a top view of the prism-shaped optical ice detector of Figure 3 ;

Figure 5A is a side view of the optical detector of Figure 3 illustrating the internal reflection of light when there is no ice or water build- up on the detector's exterior face;

Figure 5B is a side view as in Figure 5A, but with ice or water build-up on the exterior surface of the optical detector;

Figure 6 is a side view of an optical ice detector using a flat reflective surface to allow for flush surface mounting;

Figure 7 is a perspective view of an optical ice detector mounted in a modified housing that has a particle separating inlet shroud; Figure 8 is a front view of the modified housing design shown in Figure 7 illustrating the position of the inlet shroud and the optical ice detector in the housing;

Figure 9 is a cross section taken on Line 9- -9 in Figure 8 showing the modified housing and particle separating shroud separating particles over the optical ice detector;

Figure 10 is a schematic side elevational view of a helicopter having an optical ice detector made according to the present invention installed on the rotor; and

Figure 11 is a sectional view showing the ice detector mounted in the rotor and taken along line 11-- 11 in Figure 10.

DETAILED DESCRIPTION OF THE ILLUSTRATIVE EMBODIMENTS Figure 1 is a top view of an airplane. Ice detectors 12A, 12B and 12C are shown on the top of the wing 10 and on the fuselage 13. Figure 2 is a cross sectional view of wing 10.

Optical ice detectors are shown at two possible locations 12A and 12B at the top and leading edge of the wing. Placement or application of the optical ice detector is not restricted by the drawings of the present invention. The ice detectors can be located at any desired location, for example, on fuselage surfaces, turbine inlets and other locations where ice is likely to initially accumulate.

Figure 3 is a side view of an optical ice detector 12 shown in Figures 2 and 4 that is mounted on a wing 10. Optical ice detector 12 consists of housing 20, for attachment of detector components, and a prism 22 for reflecting light. The prism is exposed to ambient conditions, and can be recessed slightly to minimize air flow disruption over the mounting surface. The prism can be small in size so it does not substantially disrupt air flow. A light source 24, typically a light emitting diode (LED) , emits a continuous or pulsed light beam 30A into the prism 22 that reflects from or passes through interior face 26A of the prism 22. If reflected from face 26A, light beam 30B passes to the opposite side of prism 22 to either reflect from or pass through another interior face 26B. If reflected from face 26B, the light beam is collected by a phototransistor 32, thus completing a circuit.

Figure 5A illustrates light beam 30A undergoing little change as it is reflected from face 26A because face 28A is free of water or ice. Therefore, the light beam 30C collected by the phototransistor 32, completes a circuit and an electronic signal indicating the lack of ice, water or other contamination on the surface of the prism 22 is sent by the sensing circuitry 42 through cable 40 for processing and control.

When the prism exterior faces 28A and 28B are bombarded by rain droplets or any other moisture that absorbs the light beam, some of the light beams 30A and 30B are refracted through interior faces 26A and 26B into the moisture. A weaker light beam 30C, often sporadically weaker with rain droplets, is then collected by phototransistor 32 and an electronic signal indicating the presence of liquid water is sent by the sensing circuitry 42.

Figures 3 and 5B illustrate when the prism exterior faces 28A and 28B are exposed to ice build-up. Light beams 30A and 3OB are partially refracted through 26A and 26B into the ice. The amount of refraction is directly dependant on the amount of ice and the type of ice. Light beam 30C is reduced in intensity and the sensing circuit 42 senses this difference in optical amplitude and triggers a signal proportional to the icing condition present on the prism surface. The signal indicating icing conditions can be used to activate warning lights, energize deicing heaters or other systems such as ultrasonic vibrations of surfaces on which ice accretes. The sensitivity of the circuit 42 can be set to various thresholds depending on the application. For example, it can be set to detect a light frost, or only a heavy icy condition. Icing rate can be determined up to the point of refraction saturation, where no measurable light in beam 30C exists. This is accomplished by the sensing circuit differentiating the optical amplitude with respect to time to determine if ice is increasing or decreasing in accumulation rate. The system can be distinguish between rain and ice, because of different refraction characteristics, therefore eliminating false icing readings from rain. Further, the shape of the reflector can be prism shaped, as in Figures 2-5, flat to allow for a flush mount surface, as illustrated in Figure 6, or any other optically reflective surface shape.

Figure 4 is a top view of optical ice detector 12. The housing 20 is square in this design with the light source 24 and phototransistor 22 symmetrically positioned in the housing.

Figure 6 illustrates a flush mount optical ice detector 121. This design utilizes a prism 51 oriented upside down relative to the prism arrangement of Figure 3. In this configuration, the light beam 50A emitted from light source 54 is reflected only once, from prism interior face 56, before collection of the light beam 50B by phototransistor 55. Although the design of Figure 6 has the advantage of a flush mounting surface, it has the limitation of only one reflective surface. The housing 20, circuitry 42 and cable 40 can be the same, as previously discussed. Multiple reflective surfaces, as illustrated in Figure 3, provide more opportunities for refraction of the light beams 30A and 30B into the water or ice on exterior faces 28A and 28B of the optical ice detector 12. The results of multiple refraction is a greater range of light beam intensities entering phototransistor 32.

A modification to the invention is the use of an inlet shroud 60 shown in Figures 7, 8 and 9. The shroud is designed to accelerate and alter the airflow 74, over the ice detector 12. Large, heavier particles 70, shown in FIG. 9, are not able to overcome gravitational forces and impact optical ice detector 12, while small, lighter particles 72 are carried along with the airflow indicated at 76 and fly over the prism. With this modification, the optical detector is selectively sensitive to Super Large Droplet (SLD) icing. In Figure 10, a helicopter 80 is illustrated.

The helicopter has a rotor 82 driven in the normal manner from an engine, and the helicopter rotor 82 has an outer end portion 84 in which an optical sensor 86 made according to the present invention is installed. As shown in Figure 11, the rotor outer portion 84 is hollow, and the sensor 86 is mounted into place. An outer prism shown at 88 is made out of a natural diamond to avoid abrasion commons, and is used as the light reflecting element as explained in connection with the previous figures. The sensor 86 would include a light source, such as that shown at 24, and sensing circuitry.

The circuitry provided in the readout is indicated at 90 and can be on board the helicopter.

Suitable wires 92 can carry the needed information to the circuitry 90.

The optical lens piece, when it is made out of a natural diamond, gives great wear abrasion properties as is needed out on the outer tip of the rotor. The sensor is small and lightweight, so that it can be mounted near the tip portion and thus sense any buildup of ice where the rotor blade is spinning the fastest. The sensor will send out a digitized signal that is transferred down the mast for the rotor, using inductions and or radio frequency sensing in the circuitry 90. Thus the sensor of the present invention can be mounted in remote places such as the tip of a rotor of a helicopter to provide information relating to buildup of ice in a timely manner. Various types of baffles can be used for separation of the particles.

A further modification to the invention is the use of a specific frequency circuit and/or filters to eliminate or reduce sensitivity of the sensing circuitry to sunlight and other extraneous light sources using such filters is well known.

Specific examples of electronic modulator/filtration methods and/or optional filtering methods to reduce or eliminate the effects of ambient light include using a source consisting of a single or narrow frequency or single color component. Electronic modulation of the sensors emitting light source can be used to provide differentiation from ambient light sources. Optical filtering can block external optical light sources and geometric filtering is used in some applications to reflect off external light sources or shield the sensor from external light sources.

Using sensors which also detect and measure any external light sources and subtracts this amount from the phototransistor will provide an accurate net light refraction.

If the emitting light source is strong enough initially, ambient light becomes noise and can be filtered out. Other known methods of accommodating ambient light can be used.

Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention.

Claims

WHAT IS CLAIMED IS:

1. An optical ice detector comprising: an optical element normally reflecting light when an exterior surface is free of material and refracting light when covered with water or ice; a light source emitting light into the optical element; the exterior surface of the optical element being exposed to ambient conditions and receiving light from the light source on an interior face; a photo transistor receiving light reflected from the interior face of the optical element ; sensing circuitry for sensing an output of the photo transistor as a function of reflected light which varies as water or ice accumulates on the exterior surface.

2. The optical ice detector of claim 1, wherein the contaminant comprises ice accumulating on the exterior surface.

3. The optical ice detector of claim 2 and a deicing system activated by the signal sent from the sensing circuitry.

4. The optical ice detector of claim 2 and a warning device activated by the signal sent from the sensing circuitry.

5. The optical ice detector of claim 1 used in combination with a mounting for a rotor on a helicopter, with the ice detector being positioned near an outer tip of the rotor.

6. The optical ice detector of claim 5, wherein the ice detector optical element comprises a natural diamond.

7. The optical ice detector of claim 1, wherein the optical element comprises a flat surface lens.

8. The optical ice detector of claim 1, wherein the optical element comprises a prism.

9. The optical ice detector of claim 8, wherein said prism has a pair of surfaces and the light reflection beams being reflected on the inner sides of each of the pair of surfaces to provide individually reflected beams.

10. The optical ice detector of claim 1, wherein the ice detector is used in combination with an air vehicle having a surface on which ice accumulates, said optical ice detector being mounted on said surface with the optical element open to ambient conditions.

11. The optical ice detector of claim 8, wherein said phototransistor receives light from one of the surfaces of the prism that is reflected from the other surface of the prism.

12. An ice detector for mounting onto an air vehicle surface on which ice accretes, said ice detector comprising an optical element having an exterior surface extending through the air vehicle surface, said optical element normally reflecting light when the exterior surface is free of contaminant materials, and refracting light when covered with one of the contaminants consisting of water and ice, a light source in the detector for emitting light into the optical element, the exterior surface of the optical element receiving light from the light source on an interior face thereof, a phototransistor receiving light reflected from the interior face of the optical element, and sensing circuitry for sensing an output of the phototransistor as a function of the reflected light.