# US 6,297,488 B1 · Position sensitive light spot detector

> Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt

- Number: US 6,297,488 B1
- Document ID: US6297488B1
- Status: Granted
- Kind: B1
- Application number: 09/300,445
- Filed: 1999-04-29
- Granted: 2001-10-02
- Earliest claimed: 1999-04-29
- Assignees: National Research Council of Canada
- Inventors: J. Angelo Beraldin; Francois Blais; Marc Rioux; Jacques Domey
- Web page: https://patentgrep.com/patent/US6297488B1

## CPC

- G01J 1/4204: {with determination of ambient light (solar light G01J2001/4266)}
- G01C 3/08: Use of electric radiation detectors
- G01D 5/30: the beams of light being detected by photocells
- G01J 1/1626: {Arrangements with two photodetectors, the signals of which are compared}
- G01J 1/42: using electric radiation detectors (optical or mechanical part G01J1/04; by comparison with a reference light or electric value G01J1/10)
- G01J: MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY (light sources F21, H01J, H01K, H05B; investigating properties of materials by optical means G01N)
- G01C: MEASURING DISTANCES, LEVELS OR BEARINGS; SURVEYING; NAVIGATION; GYROSCOPIC INSTRUMENTS; PHOTOGRAMMETRY OR VIDEOGRAMMETRY (measuring liquid level G01F; radio navigation, determining distance or velocity by use of propagation effects, e.g. Doppler effects, propagation time, of radio waves, analogous arrangements using other waves G01S)
- G01D: MEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR

## Abstract

The present invention provides a method and an apparatus for detecting a position of a light spot in a light distribution that can include stray light components (e.g. from other lasers, ambient lighting etc.) The apparatus includes a continous response position sensitive detector (CRPSD, e.g. lateral effect photo-iode) for determining a first centroid of the light distribution and a discrete response position sensitive detector (DRPSD, e.g. multiplexed array) for determining a second centroid of the light distribution within a reading window defined about the first centroid and within the light distribution. The second centroid represents the position of the light spot in the light distribution. This multiple stage approach exploits the high resolution and speed offered by traditional CRPSDs together with the accuracy under variable lighting conditions offered by traditional DRPSDs.

## Claims

### Claim 1

An apparatus for detecting a position of a light spot in a light distribution comprising:
(a) means for determining a first centroid of the light distribution; and
(b) means for determining a second centroid of the light distribution within a reading window defined about the first centroid and within the light distribution, said second centroid being the position of the light spot in the light distribution.

### Claim 2 (depends on 1)

The apparatus of claim 1, wherein the means for determining the first centroid of the light distribution includes:
(i) a continuous response position sensitive detector having N photo-elements for receiving the light distribution and producing a first and a second photo-current; and
(ii) means for calculating the first centroid based on the first and second photo-currents.

### Claim 3 (depends on 2)

The apparatus of claim 2, wherein the first centroid is defined by: P = I 2 - I 1 I 1 + I 2 , P ∈ [ - 1 , 1 ]
where P represents the centroid and I1, and I2 represent the first and second photo-currents respectively.

### Claim 4 (depends on 2)

The apparatus of claim 2, further comprising:
(i) an analog-to-digital converter for converting the first centroid into a digital representation; and
(ii) an adder for shifting the digital representation of the first centroid by a predetermined amount based on the reading window.

### Claim 5 (depends on 4)

The apparatus of claim 4, wherein the means for determining the second centroid includes:
(i) a discrete response position sensitive detector for reading M photo-elements, wherein M represents a size of the reading window and M is less than N; and
(ii) a circuit for detecting the second centroid based on determining a peak of the digital representation of the first centroid.

### Claim 6 (depends on 2)

The apparatus of claim 2, wherein the continuous response position sensitive detector is a transparent lateral effect photo-diode having a first sensor and a second sensor whereby the light distribution passes through the first sensor to the second sensor.

### Claim 7 (depends on 2)

The apparatus of claim 2, wherein the continuous response position sensitive detector is a split sensor having a pair of spaced apart wedges to reduce thermal noise whereby the light distribution impinges the pair of spaced apart wedges and wherein each wedge generates one of the respective first and second photo-currents.

### Claim 8 (depends on 5)

The apparatus of claim 5, wherein the continuous response position sensitive detector is transparent and overlays the discrete response position sensitive detector.

### Claim 9 (depends on 5)

The apparatus of claim 5, further comprising a beam splitter for splitting the light distribution between the continuous response position sensitive detector and the discrete response position sensitive detector, wherein the continous response position sensitive detector and the discrete response position sensitive detector are separated.

### Claim 10 (depends on 5)

The apparatus of claim 5, further comprising a diffraction grating for directing the light distribution between the continuous response position sensitive detector and the discrete response position sensitive detector, wherein the continuous response position sensitive detector and the discrete response position sensitive detector are separated.

### Claim 11 (depends on 1)

An apparatus for detecting a position of a multiple wavelength light spot in a light distribution comprising the apparatus of claim 1 for each wavelength and means for computing a first estimate of the centroid of the multiple wavelength light spot.

### Claim 12 (depends on 11)

The apparatus of claim 11, wherein the multiple wavelength light spot is composed of a red (R,r) wavelength component, a green (G,g) wavelength component, a blue (B,b) wavelength component and wherein the means for determining the first centroid of the light distribution includes:
(i) a continuous response position sensitive detector having N photo-elements for receiving the light distribution and producing a first and a second photo-current; and
(ii) means for calculating the first centroid based on the first and second photo-currents.

### Claim 13 (depends on 12)

The apparatus of claim 12, wherein the first centroid for each wavelength component (R,G,B) is defined by: P = I 2 - I 1 I 1 + I 2 , P ∈ [ - 1 , 1 ]
where P represents the centroid and I1 and I2 represent the first and second photo-currents respectively for each wavelength component (R,G,B) where pr, pg and pb represent light spot positions for each wavelength component and Ir, Ig and Ib represent wavelength intensities value for each wavelength component and where Ir,g, or b=I1+I2.

### Claim 14 (depends on 13)

The apparatus of claim 13, wherein the means for computing includes a weighted estimator for receiving the wavelength intensities and Ir, Ig and Ib and the light spot positions pr, pg and pb and generating the first estimate of the centroid of the multiple wavelength light spot, said first estimate being used as input to the means for determining the second centroid.

### Claim 15 (depends on 14)

The apparatus of claim 14, wherein the first estimate of the centroid of the multiple wavelength light spot is calculated using: p = 1 τ g 2 ∑ ⁢ ⁢ p g + 1 τ r 2 ∑ ⁢ ⁢ p r + 1 τ b 2 ∑ ⁢ ⁢ p b , ⁢ where ⁢ ∑ = 1 τ g 2 + 1 τ r 2 + 1 τ b 2
where p is the first estimate, pg. pr, pb represent the position of light spots, and τr2, τg2, τb2 represent a variance of the three light spot positions pg, pr, pb.

### Claim 16 (depends on 15)

The apparatus of claim 15, wherein the variance of the three light spot positions are obtained using: τ g 2 = K g ⁢ I g 2 , τ r 2 = K r ⁢ I r 2 , τ b 2 = K b ⁢ I b 2
where Kg,r,b represent a width of the reading window.

### Claim 17

A method of detecting the position of a light spot in a light distribution comprising the steps of:
(a) calculating a first centroid of the light distribution;
(b) determining a reading window defined about the first centroid and within the light distribution; and
(c) calculating a second centroid of the light distribution within the reading window, said second centroid being the position of the light spot in the light distribution.

### Claim 18 (depends on 17)

The method of claim 17, wherein step (a) is determined by impinging a first detector with the light. distribution and obtaining a first and a second photo-current where the first centroid is calculated by: P = I 2 - I 1 I 1 + I 2 , P ∈ [ - 1 , 1 ]
where P represents the first centroid and I1 and I2 represent the first and second photo-currents respectively.