Radiant energy – Photocells; circuits and apparatus – Photocell controlled circuit
Reexamination Certificate
2000-05-30
2001-11-27
Bruce, David V. (Department: 2882)
Radiant energy
Photocells; circuits and apparatus
Photocell controlled circuit
C250S574000
Reexamination Certificate
active
06323477
ABSTRACT:
TECHNICAL FIELD
The invention pertains to the field of recognition of objects on a transparent pane, perhaps a windshield of a motor vehicle. In particular, the invention pertains to a method for detecting objects present on a transparent pane using a pickup unit containing an optical sensor array. The invention additionally pertains to a device for detecting illuminated objects present on a transparent pane, a pickup unit with an optical sensor array for detecting light beams emitted from an illumination apparatus and reflected, as well as an evaluation unit.
BACKGROUND ART
Such a method is employed, for instance, for detecting raindrops present on the windshield of a motor vehicle to control a wiper motor. Such a device is accordingly referred to as a rain sensor. Such a method as well as such a rain sensor is known from U.S. Pat. No. 4,867,561. The detection method described in this document operates according to the reflection principle, utilizing total reflection on the outside of the windshield. To this end, the rain sensor comprises an infrared diode (IR diode) constructed as an illumination apparatus, the emitted beams of which are directed from the inside onto a section of the windshield to be observed. As a pickup unit, an optical sensor array which is preceded by a lens for imaging [light from] the IR diode onto its photosensitive surface is used. The illumination apparatus and the pickup unit are positioned with respect to one another such that light beams emitted from the light-emitting diode that are reflected by total reflection of the windshield are imaged onto the sensor array in case of a clean windshield. The previously known method uses the fact that said total reflection of the light beams emitted from the illumination apparatus occurs from the outside of the windshield to the sensor array in case of the absence of objects on the windshield. On the other hand, if raindrops are present on the outside of the windshield, light beams are output coupled by the raindrops, so that only a part of the light beams is reflected to the sensor array. Consequently, the light intensity that can be detected by the sensor array in case of the presence of objects on the windshield is lower compared to the light intensity detected for total reflection.
The signals of the sensor array are first filtered in an evaluation unit downstream of the sensor array in order that those signal components which cannot be associated with the light beams emitted from the illumination apparatus are not further evaluated. To this end, the filtering is designed to be wavelength-specific. The filtered sensor array output signal is then fed to a comparator element in which a threshold value comparison of the detected light intensity to a specified threshold value is performed. If the detected light intensity is lower than the threshold value, a control signal, which is applied to a microcomputer for triggering the wiper motor, is present at the output of the comparator element.
Even if the method or device described in this document permits an improved detection over and against older ones, the method is nonetheless subject to error influences. Sunbeams or other light beams refracted on the windshield, whose refraction also produces infrared components which can then impinge on the sensor array, can be considered interfering factors. Since the evaluation of the light intensity detected in the sensor array is adapted by specification of the threshold value to the emitted light intensity of the illumination apparatus, such secondary influences can superimpose the output coupling of light beams by raindrops adhering to the windshield, so that the resulting evaluation outcome no longer corresponds to the actual conditions.
Furthermore, the previously known method is not suited to detect objects on the windshield for which an output coupling of light beams does not occur, such as dust or the like.
SUMMARY OF THE INVENTION
Starting from the prior art as just discussed, the problem of the invention is, first of all, to propose a method for detecting objects present on a transparent pane with which a more exact detection of objects present on the windshield is guaranteed, with simultaneous suppression of irrelevant light signals or interfering influences. The invention is also based on the problem of providing a corresponding device.
The problem related to the method is solved according to the invention by a method for detecting objects present on a transparent pane that produce reflections of light when illuminated, said method using an analysis unit containing one or more optical sensor arrays and comprising the following steps:
illumination of the pane to generate light reflections in or on objects present on the pane from that side of the pane behind which the pickup unit is arranged;
imaging detection of an illuminated pane section with the pickup unit by provision of two pane section images forming an image pair, in which two pictures the light reflection or reflections of an object present on the pane are respectively located at pixels with different positions;
acquisition of the difference image of the two images of an image pair by subtraction of the contents of pixels of equal position on the one pane section image from those of the other pane section image and subsequent analysis of the acquired difference image with respect to the contents associated with the individual pixels.
The device-related problem is solved, first of all, in that as a pickup unit a single sensor array is provided in an arrangement with respect to the pane such that the surface of the pane section detected by the sensor array which is to be observed lies in the depth of focus range of the imaging system depicting the pane section on the photosensitive surface of the sensor array and in that the illumination apparatus comprises at least two mutually separated light sources illuminating the pane section observed by the pickup unit from different directions.
The device-related problem is additionally solved in that the pickup unit comprises two mutually separated optical sensor arrays in a stereoscopic arrangement with respect to the pane in which the surface to be observed of the pane section detected by the sensor array lies in the depth of focus range of the imaging system depicting the pane section on the photosensitive surface of the sensor array, which optical sensor array for observing a pane section is arranged such that the background located a given distance from the pane to be observed is imaged on the two sensor arrays at pixels with the same position.
According to the proposed method, an analysis of the observed pane section takes place not only on the basis of a single image of on the basis of the contents of its pixels, but on the basis of two individual images, each referred to in these writings as a pane section image and jointly as an image pair. It is also provided that the same pane section can be reproduced with the two pane section images, but that the light reflections produced by the illumination of an object located on the pane are imaged in each pane section image at pixels with different positions, or only on one pane section image. Influences that can be traced back to light reflections not generated by the illumination from the objects present on the pane, on the other hand, are imaged at identical points in the two pane section images. The illumination of the pane section to be detected can be done by available ambient light (daylight) or by an additional illumination apparatus. In the subsequent stage of ascertaining the difference image from the two pane section images, the contents of pixels with the same positions are subtracted from one another. Ultimately this leads to a difference image in which the contents of those pixels which are the result of the subtraction of pixels with the same position have the value 0. On the other hand, those pixels whose contents are different—due perhaps to the detection of light reflections of differing positions—receive a value different from
Bendicks Norbert
Bläsing Frank
Brooks & Kushman P.C.
Bruce David V.
Leopold Kostal GmbH & Co. KG
Song Hoon K.
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