Method and apparatus for detecting the presence of a surface bearing a bar code symbol
First Claim
Patent Images
1. In a device for convening machine readable symbols on a surface to information signals, a low power apparatus for detecting the presence of the surface, the apparatus comprising:
- a light source that is pulsed at a carrier frequency, the light source producing a pulsed light beam;
a light detector that receives portions of the pulsed light beam that are reflected off of the surface, the light detector producing a reflection signal having amplitude variations that are proportional to reflective characteristics of the surface;
a synchronous demodulator having a first input that is coupled to receive the reflection signal having amplitude variations that are proportional to the reflective characteristics of the surface, the synchronous demodulator having a second input that is coupled to a signal having a frequency that approximates, and is in phase with the carrier frequency so that the synchronous demodulator produces a demodulated signal that isolates the amplitude variations in the reflection signal that are proportional to the reflective characteristics of the surface;
a comparator having a first input coupled to the first input of the synchronous demodulator to receive the reflection signal and a second input coupled to a reference potential, an output of the comparator producing a surface detection signal as a function of the reference potential relative to a value of the first input of the comparator, the surface detection signal having a first state indicating that the surface is present and a second state indicating that the surface is not present; and
a synchronizer that monitors the output of the comparator at the frequency that approximates, and is in phase with, the carrier frequency to produce a detect signal indicating the detection of the surface in response to the surface detection signal occurring at the carrier frequency.
1 Assignment
0 Petitions
Accused Products
Abstract
A method and apparatus for detecting the presence of a surface which may bear a bar code symbol. The apparatus generates a series of pulses having a duty cycle which depends upon whether light reflected from a surface bearing a bar code symbol has been detected recently. If such a surface has been detected, the duty cycle is maintained at a high rate. Otherwise, the duty cycle is reduced substantially until such a surface is again detected to save battery power.
50 Citations
5 Claims
-
1. In a device for convening machine readable symbols on a surface to information signals, a low power apparatus for detecting the presence of the surface, the apparatus comprising:
-
a light source that is pulsed at a carrier frequency, the light source producing a pulsed light beam; a light detector that receives portions of the pulsed light beam that are reflected off of the surface, the light detector producing a reflection signal having amplitude variations that are proportional to reflective characteristics of the surface; a synchronous demodulator having a first input that is coupled to receive the reflection signal having amplitude variations that are proportional to the reflective characteristics of the surface, the synchronous demodulator having a second input that is coupled to a signal having a frequency that approximates, and is in phase with the carrier frequency so that the synchronous demodulator produces a demodulated signal that isolates the amplitude variations in the reflection signal that are proportional to the reflective characteristics of the surface; a comparator having a first input coupled to the first input of the synchronous demodulator to receive the reflection signal and a second input coupled to a reference potential, an output of the comparator producing a surface detection signal as a function of the reference potential relative to a value of the first input of the comparator, the surface detection signal having a first state indicating that the surface is present and a second state indicating that the surface is not present; and a synchronizer that monitors the output of the comparator at the frequency that approximates, and is in phase with, the carrier frequency to produce a detect signal indicating the detection of the surface in response to the surface detection signal occurring at the carrier frequency. - View Dependent Claims (2, 3, 4)
-
-
5. An apparatus for detecting a presence of a surface, the apparatus comprising:
-
a light source that is pulsed at a carrier frequency, the light source producing a light beam; a light detector that receives portions of the light beam that are reflected off of the surface, the light detector producing a signal having amplitude variations that are proportional to reflective characteristics of the surface; a comparator that produces a surface detection signal when the amplitude variations of the signal produced by the light detector indicate that the light detector has detected a presence of a surface, the comparator having a first input and a second input, the first input of the comparator being coupled to the signal produced by the light detector and the second input of the comparator being coupled to a reference potential; a monitoring device that evaluates, at a frequency that is substantially in phase with the carrier frequency, the comparator to determine whether the surface detection signal is being produced; a disabling circuit that produces a duty cycle adjustment signal when the monitoring device has not observed the surface detection signal for a predetermined amount of time, the duty cycle adjustment signal reducing a duty cycle of the carrier frequency; and a synchronous demodulator having a first input, a second input, and an output, the first input of the demodulator being coupled to the first input of the comparator, the second input of the demodulator being coupled to a signal having the carrier frequency, the output of the demodulator providing a demodulated signal that isolates the amplitude variations that are proportional to the reflective characteristics of the surface.
-
Specification