Radiant energy – Invisible radiant energy responsive electric signalling – Infrared responsive
Reexamination Certificate
2001-07-18
2004-02-10
Porta, David (Department: 2878)
Radiant energy
Invisible radiant energy responsive electric signalling
Infrared responsive
C250S347000
Reexamination Certificate
active
06690018
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to passive infrared motion detectors, occupancy sensors and similar devices, and more particularly to the infrared input section of these devices.
2. Description of the Related Art
Passive infrared motion detectors and occupancy sensors employ an array of Fresnel lenses covering an entrance aperture. This lens array is illuminated by thermal infrared radiation from the object of interest. For any particular angle of incidence each of the elements in the array of Fresnel lenses covering the entrance aperture generates a focal spot. The array of Fresnel lenses is designed so that as the object of interest moves across its field of view the system of focal spots moves across the sensitive area of a detector. The varying electrical output signal generated by the detector is processed to yield information about the state of motion of the object of interest.
Each element of the array of Fresnel lenses is designed to focus incident infrared radiation in a small angular range onto the sensitive area of a detector. The angular sectors, in which the elements of the array of Fresnel lenses focus onto one of the active areas of a detector, are interlaced by angular sectors which are not focused onto any sensitive area of any detector by any element of the array of Fresnel lenses. Moving infrared radiators are detected when they move from one angular sector across a boundary into an adjacent angular sector, leading to a rapid change in the amount of infrared power falling on the active area of a detector. Ordinarily all of the sectors are of the same angular size so that the maximum angle through which an object of interest can move without being detected, i.e. the angular resolution of the system, is equal to the angular size of one of these sectors. This assumes that the size and velocity of the radiating object and its distance from the entrance aperture are such that the infrared signal is greater than the minimum that can be detected by the system electronics.
One way to improve the angular resolution of the system is to increase the number of elements in the lens array. More specifically, the angular resolution of the system is approximately inversely proportional to the number of elements in the lens array. Thus, in order to achieve the smallest angular resolution, a lens array with as many elements as possible must be employed. On the other hand, the sensitivity and effective range of the system decrease if the size of the individual lenses of the array is decreased. The phrase “sensitivity of the system” refers to the size of the smallest radiating object that can be detected as a function of its distance from the detector. Thus, compromises must be made between the size of the entrance aperture, sensitivity, range and angular resolution of the system. For example, for any desired sensitivity and range there is a minimum size for each of the individual lenses of the array and hence a maximum number of elements for an entrance aperture of fixed size and a corresponding minimum angular resolution. The terms “focus” and “focusing” as used herein are intended to embrace any change in spot size and thus includes partially focusing and defocusing (e.g. dispersing energy).
SUMMARY OF THE INVENTION
The present invention is a new input lens configuration which can be employed, for example, to: 1) increase the sensitivity and range of motion detectors and occupancy sensors with an entrance aperture of fixed size without decreasing the angular resolution of the system or, 2) improve the angular resolution of a system with an entrance aperture of fixed size without decreasing the sensitivity or range of the system or, 3) decreasing the size of the entrance aperture required for a given sensitivity, range and angular resolution, or 4) reduce the distance that the unit must protrude in, for example, a wallbox installation in order to achieve acceptable performance at wide angles. In one implementation the angular resolution of the system is reduced to zero, i.e. moving infrared radiators anywhere in the field of view of the system are detected, not just radiators that cross the planes separating a sequence of angular sectors. The relative importance of each of these characteristics of motion detectors and occupancy sensors depends on the application in which the system is employed.
Two-dimensional implementations of the input lens configuration disclosed herein in wallbox installations, for example, have the capability to detect vertical motion as well as horizontal angular motion. Further, such systems can detect horizontal radial motion (e.g. motion directly towards or away from the detector) which is not possible with prior art systems which can only detect infrared radiators moving across the planes which separate a sequence of angular sectors. It is also possible to design two-dimensional systems which can determine the angular size and range of infrared radiators. This is useful in systems which must filter out signals due to various infrared noise sources.
In simplest terms, the infrared input section disclosed herein consists of a lens array, which may be similar to the Fresnel lens array used in the prior art, preceded by one or more, possibly segmented, pre-focusing lenses, which may or may not be Fresnel lenses. For the purpose of illustration, suppose that a certain range and angular resolution can be achieved by employing some particular lens array. If the number of elements of this array is doubled, for example, the angular resolution is improved by approximately a factor of two. However, without changing the size of each element, so as not to affect the sensitivity or range of the system, the size of the array is doubled. This doubling in size can be avoided by employing a pre-focusing lens in front of the customary lens array to focus the beam from any particular incident direction to say, one-half or less of the size of an original lens element. With this configuration the number of elements in the lens array can be effectively doubled, with a corresponding improvement of the angular resolution by a factor of two, without increasing the total size of the lens array or decreasing the sensitivity or range of the system.
In fact, in the above example, both the sensitivity and range of the system are increased as almost all of the infrared power entering the entrance aperture is focused onto the sensitive area of a detector, rather than only the infrared power entering one element of a lens array as in prior art configurations. In other words, in the prior art the infrared power incident on the entrance aperture is focused into many spots, only one of which is effective in activating a detector when the infrared radiator of interest is in a certain angular sector. This is to be contrasted with the input configuration disclosed herein in which there is a single focal spot which contains almost all of the infrared power incident on the entrance aperture. In this situation the amount of infrared power incident on the detector is larger than that incident on the detector in the prior art configurations by a factor approximately equal to the number of elements in the lens array. For some applications the optimum design will employ a small array of pre-focusing lenses as opposed to a single element. It should be noted that depending on the performance characteristics desired, the lens array may be positioned on either side of or in the focal plane of the pre-focusing lens. Further, again depending on the desired performance characteristics, some of the individual elements of the lens array may be converging while others are diverging, neutral or absent.
With a high degree of pre-focusing, the size of the individual lens elements making up the final lens array preceding the detector may become too small to be realized by current Fresnel lens technology. In this situation microlens and diffractive optics technology can be employed to produce elements with the same functionality as an array of Fresnel lense
Carter DeLuca Farrell & Schmidt LLP
Electro-Optic Technologies, LLC
Gabor Otilia
Porta David
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