Radiant energy – Photocells; circuits and apparatus – Optical or pre-photocell system
Reexamination Certificate
1999-04-08
2001-08-07
Lee, John R. (Department: 2878)
Radiant energy
Photocells; circuits and apparatus
Optical or pre-photocell system
C250S2140RC, C318S434000, C318S469000, C049S026000
Reexamination Certificate
active
06271512
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to the optical detection of a small object within a fixed plane, and more particularly the invention relates to an optical detection system that prevents objects such as hands and fingers from being pinched by a power window of an automobile as the window closes.
DESCRIPTION OF THE RELATED ART
Various techniques that rely on the measurement of applied force have been utilized to detect obstructions in the plane of an open automobile window. Presently, the indirect measurement of mechanical force applied by a window is the leading solution. Indirect measurement of mechanical force involves estimating the required torque of a window motor based upon the position of the window, window weight, closing rate, and mechanical advantage. The amount of force applied by the window motor is estimated based on the window motor current and on the window motor rotation rate. If the estimated force applied by the window motor exceeds the estimated torque requirement, the window motor is stopped or reversed.
The compressive force of a window against an obstructing object can also be directly measured by a compressive membrane located within a window gasket of a window frame. If force is applied to the membrane non-uniformly, as in the case of an object trapped between the window and the window frame, the membrane is pinched and the window motor is stopped or reversed. Although the techniques relying on the measurement of mechanical force may work well for their intended purposes, detection of an obstruction within the window plane requires direct contact between the obstructing object and the window. For example, an arm must weigh down the window or a finger must be partially pinched between the window and the window frame before stoppage or reversal of the motor is triggered.
Optical detection techniques are also utilized for detecting obstructions in the plane of an object that is closing. Known techniques involve measuring the attenuation of a signal through an optical waveguide or measuring the change of capacitance in a multilayer capacitor structure. While these techniques may work well for their intended purpose, there are important design considerations that these techniques may not adequately address.
A critical design consideration for an optical obstruction detection system for use in an automobile having power windows is that the system must be able to detect a small object, such as a finger, that is located in the plane of an open window. Detection of a small object is difficult, because the signal response is often hard to distinguish from various background and/or interfering signals. The various background and/or interfering signals may be caused, for example, by the movement of the window or reflections from a person that is seated near the window. The optical sensing circuitry must be able to distinguish interfering signals caused by direct sunlight or scattered light that is incident on the detectors of the obstruction detection system.
In view of the prior art shortcomings, what is needed is an optical detection system that has the sensitivity to detect small obstructing objects and the ability to distinguish interfering signals (e.g., from the closing of a window) in order to prevent false detections of an obstructing object when no obstructing object is actually present.
SUMMARY OF THE INVENTION
An obstruction detection system utilizes a segmented optical detector and detector-specific signal processing to optically detect the presence of a small object within a defined plane and to screen out interfering signals. In one embodiment of the obstruction detection system, the segmented optical detector includes a series of segmented detector elements that are generally perpendicular to the defined plane. In another embodiment, the segmented optical detector includes segmented detector elements that are generally parallel to the defined plane. In the preferred application, the system is utilized with an automatically closing window to prevent small objects, such as fingers, from being pinched by the window.
The complete obstruction detection system includes an optical emitter, the segmented optical detector, and a signal processor. The system is ultimately connected to a window motor controller and a window motor so that closing of a window can be halted if an obstruction is detected. In the preferred embodiment, the optical emitter is a laser diode and the segmented optical detector is an array of photodiodes. Both the optical emitter and the segmented optical detector are located in a single corner of a window frame. The optical emitter projects light toward the interior of the window frame. The segmented optical detector receives portions of the emitted light that are reflected by the interior of the window frame, by an obstructing object, and/or by other nearby objects or surfaces.
The preferred signal processor is an application-specific integrated circuit (ASIC) that detects differences in the amount and pattern of light that is reflected when there is an obstruction in the plane of the window versus the amount and pattern of light that is reflected when there is no obstruction in the plane of a window. If the signal processor determines that there is an obstruction in the window plane, the signal processor generates a signal that is used to disable or reverse the window motor. The detection algorithm that is utilized by the signal processor depends upon the type of segmentation that is utilized for the segmented optical detector. Two alternative embodiments of the segmented optical detector and signal processor are described in further detail below.
In the first embodiment, the segmented optical detector is formed of detector elements that are generally perpendicular to the window plane. The segmented detector elements are interconnected by separate conductive traces that are ultimately connected to related signal pads. In one embodiment, the segmented detector elements are divided into four separate groups and each detector element is connected to one and only one signal pad by a respective conductive trace. The four detector groups are distributed in a repeating pattern and the detector elements are spaced apart at distances that optimize the detection of a small object, such as a finger. The segmented optical detector is oriented, with respect to the window plane, such that the lengthwise (horizontal) dimension of the detector is generally parallel to the window frame and such that the segmented detector elements are generally perpendicular to the window plane.
A spatial filtering algorithm is implemented by the signal processor in conjunction with the segmented optical detector in order to distinguish gradual spatial changes in light intensity from abrupt changes in light intensity. The gradual changes are typically caused by interference, or the illuminated background while the abrupt changes in intensity are likely to be caused by the presence of a small object. The spatial filtering algorithm involves summing the signals received from different combinations of the segmented detector elements and comparing the sums. The circuitry required to implement the preferred spatial filtering algorithm is contained within the signal processor. Within the signal processor, the segmented detector groups are connected to group-specific signal amplifiers and then to a processing circuit that performs the sum and difference functions of the spatial filtering algorithm. The results of the functions are forwarded to absolute value units, where the absolute value of each function is obtained. The absolute values are then transmitted to a comparator unit and compared to a reference signal in order to determine if either signal deviates from the reference signal enough to trigger a condition that is responsive to the presence of an obstructing object.
In the other embodiment, the segmented optical detector includes detector elements that are generally parallel to the window plane. In a preferred embodiment, there are multiple
Infineon Technologies Corporation
Lee John R.
Pyo Kevin
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