# US 7,609,736 B2 · Laser power control arrangements in electro-optical readers

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- Number: US 7,609,736 B2
- Document ID: US7609736B2
- Status: Granted
- Kind: B2
- Application number: 11/239,745
- Filed: 2005-09-30
- Published: 2007-06-14
- Granted: 2009-10-27
- Earliest claimed: 2005-09-30
- Assignees: Symbol Technologies, Inc.
- Inventors: Costanzo Difazio; Vladimir Gurevich; James Giebel; Gary G. Schneider; Matthew Blasczak; Mark A. Weitzner; Edward Barkan
- Web page: https://patentgrep.com/patent/US7609736B2

## CPC

- H01S 5/0014: {Measuring characteristics or properties thereof (measuring techniques per se G01J, G01K, G01N, G01R)}
- G06K 7/10851: {Circuits for pulse shaping, amplifying, eliminating noise signals, checking the function of the sensing device (basic electronic circuitry H03)}
- H01S 5/0617: {using memorised or pre-programmed laser characteristics}
- H01S 5/06808: {by monitoring the electrical laser parameters, e.g. voltage or current}
- H01S 5/06825: {Protecting the laser, e.g. during switch-on/off, detection of malfunctioning or degradation}
- H01S 5/0683: by monitoring the optical output parameters
- H01S: DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- G06K: GRAPHICAL DATA READING (image or video recognition or understanding G06V); PRESENTATION OF DATA; RECORD CARRIERS; HANDLING RECORD CARRIERS

## Abstract

Laser power control arrangements interrupt power to a laser used in electro-optical readers upon detection of an over-power condition not conforming to preestablished regulatory standards. In one embodiment, during an operational mode, a difference between laser drive currents at two operating points is compared to a difference between laser drive currents at the same two operating points during a calibration mode. The over-power condition is recognized when the difference during the operational mode exceeds the difference during the calibration mode by a predetermined amount. In another embodiment, the laser is only energized to emit the beam at a reduced power level well below regulatory standards for staring at even if a motor drive failed.

## Claims

### Claim 1

A laser power control arrangement for regulating output power of a laser beam emitted by a laser in an electro-optical reader for reading indicia, comprising:
a laser drive circuit for energizing the laser a plurality of times at substantially the same first temperature in a calibration mode to emit the laser beam with different, first and second output powers that respectively correspond to different, first and second, calibration drive currents, and for energizing the laser a plurality of times at substantially the same second temperature in an operating mode to emit the laser beam with the same first and second output powers that respectively correspond to different, first and second, operating drive currents;
a memory for storing a calibration difference between the first and second, calibration drive currents, the calibration difference being resistant to variations in the first temperature in the calibration mode, and the memory being further operative for storing an operating difference between the first and second, operating drive currents, the operating difference being resistant to variations in the second temperature in the operating mode; and
a controller operative in the operating mode for comparing the operating difference between the first and second, operating drive currents with the calibration difference between the first and second, calibration drive currents to resist variations between the first temperature and the second temperature, and for deenergizing the laser when the operating difference exceeds the calibration difference by a predetermined amount.

### Claim 2 (depends on 1)

The arrangement of claim 1, wherein the laser drive circuit includes a digital potentiometer controlled by the controller to set potentiometer settings that correspond to the first and second output powers.

### Claim 3 (depends on 2)

The arrangement of claim 2, wherein the memory is operative for storing the potentiometer settings.

### Claim 4 (depends on 1)

The arrangement of claim 1, wherein the controller includes a control switch connected to the laser, the control switch being opened by the controller to interrupt the operating drive currents from reaching the laser.

### Claim 5 (depends on 1)

The arrangement of claim 1, wherein the laser drive circuit includes a monitor photodiode for detecting the laser beam emitted by the laser, and a redundant feedback circuit for generating a feedback signal that redundantly deenergizes the laser based on detection by the monitor photodiode.

### Claim 6

A laser power control method of regulating output power of a laser beam emitted by a laser in an electro-optical reader for reading indicia, comprising the steps of:
energizing the laser a plurality of times at substantially the same first temperature in a calibration mode to emit the laser beam with different, first and second output powers that respectively correspond to different, first and second, calibration drive currents, and energizing the laser a plurality of times at substantially the same second temperature in an operating mode to emit the laser beam with the same first and second output powers that respectively correspond to different, first and second, operating drive currents;
storing a calibration difference between the first and second, calibration drive currents, the calibration difference being resistant to variations in the first temperature in the calibration mode, and storing an operating difference between the first and second, operating drive currents, the operating difference being resistant to variations in the second temperature in the operating mode; and
comparing during the operating mode the operating difference between the first and second, operating drive currents with the calibration difference between the first and second, calibration drive currents to resist variations between the first temperature and the second temperature, and deenergizing the laser when the operating difference exceeds the calibration difference by a predetermined amount.

### Claim 7 (depends on 6)

The method of claim 6, and the step of establishing digital potentiometer settings that correspond to the first and second output powers.

### Claim 8 (depends on 7)

The method of claim 7, and the step of storing the potentiometer settings.

### Claim 9 (depends on 6)

The method of claim 6, and the step of opening a control switch connected to the laser, to interrupt the operating drive currents from reaching the laser.

### Claim 10 (depends on 6)

The method of claim 6, and the step of detecting the laser beam emitted by the laser, and generating a feedback signal that redundantly deenergizes the laser based on the detecting step.