Method and apparatus for calibrating optical sensors

• US 4,836,682 A
• Filed: 07/02/1986
• Issued: 06/06/1989
• Est. Priority Date: 07/02/1986
• Status: Expired due to Fees

• Current Assignee: E. I. du Pont de Nemours and Company (Corteva, Inc.)
• Original Assignee: E. I. du Pont de Nemours and Company (Corteva, Inc.)
• Inventors: Keenan, Paul C. III
• Primary Examiner(s): Rosenberger, Richard A.
• Application Number:
  US06/881,238
• Time in Patent Office: 1,070 Days
• Field of Search: 356/445, 356/73.1, 356/306, 356/338, 356/382, 356/389, 356/432, 356/433, 356/434, 356/435, 356/221, 356/256, 356/317, 356/323, 356/330, 356/217, 356/433, 356/226 , 356/223, 356/382, 250/262, 250/269, 307/311, 324/411, 324/414, 324/57 PS, 324/78 Z
• US Class Current: 356/445
• CPC Class Codes: G01S 7/497 Means for monitoring or calibrating
• CPC Class Codes: G01V 13/00 Manufacturing, calibrating, cleaning, or repairing instruments or devices covered by groups G01V1/00 – G01V11/00

Abstract

A self calibrating optical sensor is described in which a time varying response signal is provided which is a function of the reflectivity of a surface being detected and the overall response of the photodetector circuit. This response time is stored to establish a reference value to ascertain similar reflective surface are present.

Claims

1. A method for automatically calibrating the response of an optical sensor having a photoemitter portion and a photodetector portion and for determining the presence of different backgrounds comprising the steps of:

(a) applying an energizing pulse to the photoemitter portion, the energizing pulse having a predetermined time duration which is substantially controlled by a time duration of a first driving pulse;

(b) directing from the photoemitter portion to a reference background a first light pulse caused by the energizing pulse, the light pulse having a predetermined time duration substantially controlled by the time duration of the driving pulse and a predetermined time varying intensity characteristic that first gradually increases and then gradually decreases;

(c) sensing the time varying intensity characteristic of the light pulse from the reference background by the photodetector portion;

(d) measuring the time duration of the light pulse from the reference background at or above a predetermined intensity level;

(e) automatically storing the measured time duration;

(f) repeating the above steps (a) through (d) using another driving pulse having a time duration which is the same as the time duration of the first driving pulse to generate a light pulse having the same predetermined time duration and time varying intensity as the first light pulse for another background and in step (d) measuring the time duration of the light pulse from the another background at or above the same predetermined intensity level to provide another measured time duration; and

(g) automatically comparing the stored time duration and the another time duration to determine if like backgrounds were measured.

2. A self calibrating apparatus for detecting the presence of a surface comprising:

a light source for directing light pulses to a surface, each of the light pulses having a predetermined time duration and a predetermined time varying intensity characteristic that first gradually increases and then gradually decreases;

a source of energizing pulses, each of the energizing pulses having a predetermined time duration and a predetermined time varying intensity characteristic that first gradually increases and then gradually decreases, the source of energizing pulses connected to the light source for energizing the light source to produce the light pulses, the source of energizing pulses responsive to driving pulses;

means coupled to the source of energizing pulses for applying the driving pulses, each of the driving pulses having a predetermined time duration, such that the time durations of the driving pulses substantially control the time durations of the energizing pulses and the time duration of the light pulses;

sensing means for sensing light pulses from the light source modulated by the surface;

a threshold detector coupled to the sensing means for detecting the time duration of the modulated light occurring at or above a preselected intensity level;

means for automatically storing a first detected time duration of the modulated light; and

means for automatically comparing the stored first detected time duration to subsequent detected time durations of light from other surfaces at or above the preselected intensity level to determine the presence or absence of the other surfaces.

3. An apparatus as set forth in claim 2 wherein the light source is a light-emitting diode.

4. An apparatus as set forth in claim 2 wherein the light source and sensing means comprise a combined light emitting diode and phototransistor.

5. An apparatus as set forth in claim 2 wherein the light source includes an integrating circuit.

6. An apparatus as set forth in claim 5 wherein the integrating circuit is an R-C circuit.

7. An apparatus as set forth in claim 2 wherein the means for applying the driving pulses, storing means an comparing means comprise a digital computer.

8. An automatically self-calibrating apparatus for optically determining the presence or absence of objects comprising:

a source of energizing pulses of predetermined time duration,

means coupled to the pulse source for producing pulses of light, each said light pulse having a time duration corresponding to the preselected time duration and having a time varying intensity that first increases then decreases;

means for receiving light from the producing means affected by an object to be measured and for providing an output which varies in proportion to the intensity of the affected light received by the receiving means;

means connected to the receiving means for detecting the time duration of the affected light pulses at or above a preselected intensity level;

automatic means connected to the detecting means for storing the time duration of a first one of the affected light pulses and comparing the one stored time duration to subsequent time durations of the affected light pulses to determine if a like other object was present.