Patent Application
20090101829
The present invention relates generally to ultraviolet lamp systems and, more particularly, to detection of light from ultraviolet lamp systems.
Ultraviolet (“UV”) lamp systems are commonly used for heating and curing materials such as adhesives, sealants, inks, and coatings. Certain ultraviolet lamp systems have electrodeless light sources and operate by exciting an electrodeless plasma lamp (“bulb”) with microwave energy. In an electrodeless ultraviolet lamp system that relies upon excitation with microwave energy, the bulb is mounted within a metallic microwave cavity or chamber. One or more microwave generators, such as magnetrons, are coupled via waveguides with the interior of the microwave chamber. The magnetrons supply microwave energy to initiate and sustain a plasma from a gas mixture enclosed in the bulb. The plasma emits a characteristic spectrum of electromagnetic radiation strongly weighted with spectral lines or photons having ultraviolet and infrared wavelengths.
The bulb in an electrodeless UV lamp system lights when excited by microwave energy and has no direct electrical connections to the other portions of the lamp system. Therefore, a light sensor in the microwave cavity is used to determine if the bulb is lit. Without the light sensor, the UV lamp system has no indication of the status of the bulb (on or off). Conventional light sensors detect light intensity inside the lamp box but are not oriented directly at the bulb. However, in some applications, another lamp may be positioned such that it shines enough light into the cavity to activate the light sensor and cause it to falsely indicate that the bulb is lit.
One method to reduce the false detections from stray light sources has been to place the light sensor in the microwave chamber and orient it such that it is directed toward the bulb. This method reduces the effects of incoming light from other sources; however, this method also exposes the light sensor to very intense UV light that must be reduced to a level compatible with the sensor's operating range. In some instances, colored glass filters have been used to reduce the intensity, though with extended exposure to the intense UV light, these filters often change or cloud over and this can adversely affect the calibration of the light sensors. Additionally, at sufficient intensities, incoming light from external sources can still activate the sensor.
Another method used to avoid the challenges with filters is to direct the light sensor at a highly polished surface and detect the reflected light from the bulb. While this method may help in overcoming some of the challenges with the sensor oriented directly toward the bulb, it still can produce false detections if external light is also reflected from the highly polished surface.
A light sensor is provided for an ultraviolet lamp system of the type having an electrodeless lamp excited by microwave energy. The light sensor includes an elongated channel having a first aperture and a second aperture. The first aperture is directed generally toward the electrodeless lamp. The second aperture is configured to receive at least a portion of light received in the first aperture and transmit it to a detector. The light received in the first aperture typically includes ultraviolet, visible, and infra-red components. In one embodiment of the light sensor, the elongated channel includes a first elongated channel portion and a second elongated channel portion. The first elongated channel portion is oriented generally transverse to the second elongated channel portion, such that the first elongated channel portion and the second elongated channel portion are not in a direct line of sight. The detector for this embodiment includes light detection circuitry that is configured to detect light reflected in the second elongated channel portion at the second aperture.
In an alternate embodiment of the light sensor, a lens intersects the elongated channel and is positioned between the first aperture and the second aperture. The lens allows infrared radiation to pass through while substantially blocking visible light. In this embodiment, the detector includes infrared detection circuitry that is configured to detect infrared radiation in the elongated channel at the second aperture.
The accompanying drawings illustrate embodiments of the invention and, together with a general description of the invention given above, and the detailed description given below, serve to explain the principles of the invention.
Referring now to the drawings where like numbers denote like components among the several views,
Referring now to
Additional channel portions may also be connected with channel portions 36, 38 as illustrated in the embodiments shown in
As illustrated in
Sizes of the apertures and channels in some embodiments range, for example, from approximately 0.5 mils to approximately 10 mils. These sizes may be larger or smaller in other embodiments as appropriate for the channel lengths and light intensities of those embodiments. The sizes and configurations of the channel portions are dependent on the range of the detector circuitry 44. For example, in the present embodiment the first and second channel portions 36, 38 may have different sized cross sections to accommodate the detection range of the detector circuitry 44. The cross sections of the channel portions 36, 38 may be the same for other embodiments. Similarly, the first and second channel portions 36, 38, in some embodiments, intersect each other at the ends opposite the first and second apertures 34, 42, or as with this embodiment, the first channel portion 36 intersects the second channel portion 38 between the second aperture 42 and the end of the second channel portion 38 opposite the second aperture 42.
The light sensor 30 may be positioned anywhere in the microwave chamber 14 as long as it can be oriented generally toward the bulb. Positioning the light sensor 30 such that it is not directly in line with the chamber outlet 22 assists in reducing the number of false detections. In addition, while stray light 70 from an external light source 72 is able to enter the microwave chamber 14 through the chamber outlet 22, elongated channel 35 in the light sensor 30 assists in attenuating the stray light 70 from the external light source 72. This in turn also assists in reducing the number of false detections.
Another embodiment of the light sensor 80, illustrated in
The light sensor, in some embodiments, is machined from a block of aluminum. The walls of the channel (or channel portions) do not require a specific reflectivity; however, the wall properties should not degrade or change over time, as that would change the light input to the sensor, possibly causing the sensor output to be unreliable. The reflectivity of the channel walls may be a design parameter that is considered when the detection circuitry is selected. If a certain reflectivity is required, the walls can be treated by, for example, a gold plating or Teflon coating, though any type of reflective coating that would tolerate the harsh conditions of the environment could be used.
While the present invention has been illustrated by a description of various embodiments and while these embodiments have been described in considerable detail, it is not the intention of the applicants to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications will readily appear to those skilled in the art. The invention in its broader aspects is therefore not limited to the specific details, representative apparatus and method, and illustrative examples shown and described, for example, other embodiments of the light sensor may utilize combinations of the first and second elongated channel portions in the embodiment in
