Registers – Coded record sensors – Particular sensor structure
Reexamination Certificate
1998-07-27
2001-02-27
Le, Thien M. (Department: 2876)
Registers
Coded record sensors
Particular sensor structure
C235S454000, C235S455000, C235S447000, C385S001000, C385S010000
Reexamination Certificate
active
06193157
ABSTRACT:
FIELD OF INVENTION
This invention relates to a frequency division multiplexed bar code scanner, and more particularly to such a scanner which detects the bar code and the distance of the object bearing the bar code over a large depth of focus.
BACKGROUND OF INVENTION
Bar code readers are required to read bar codes on objects of a wide variety of sizes wherein the bar codes may be at varying distances from the scanner. This requires a wide range of depths of focus in order to read the bar code clearly and accurately over the entire distance in which they may be presented, typically as much as two meters. In one approach two or more lasers focused at different distances are switched on and off alternately so that only one is on at a time. This requires a switching device to switch between them so that the scan rate is divided by the number of lasers and thus significantly reduced. Thus a faster, more expensive motor is needed to rotate the scanning wheel at a higher rate, or higher speed scanning cannot be done. Alternatively, additional systems may be used to intelligently switch the lasers at optimum times but this is a more complex and expensive approach. In another approach a number of separate scanning channels are used each including its own laser, optics, and receiver which increases cost and complexity. In still another approach mechanical auto focus mechanisms are used but these have many moving parts and are relatively slow, expensive and prone to wear out.
SUMMARY OF INVENTION
It is therefore an object of this invention to provide an improved, frequency division multiplexed bar code scanner.
It is a further object of this invention to provide such an improved, frequency division multiplexed bar code scanner which detects the bar code and the distance to the object bearing the bar code over an enlarged depth of focus.
It is a further object of this invention to provide such an improved, frequency division multiplexed bar code scanner which may use but a single optical channel including laser, optics, and receiver.
It is a further object of this invention to provide such an improved, frequency division multiplexed bar code scanner which has an enlarged depth of focus without additional moving parts.
It is a further object of this invention to provide such an improved, frequency division multiplexed bar code scanner which does not require automatic intelligent control.
It is a further object of this invention to provide such an improved, frequency division multiplexed bar code scanner which implements bar code reading and distance measurement in one integrated system.
It is a further object of this invention to provide such an improved, frequency division multiplexed bar code scanner which employs the same scanner source modulation to increase the reading range and accurately determine the distance.
It is a further object of this invention to provide such an improved, frequency division multiplexed bar code scanner which has a capability to utilize distance measurement information to improve the bar code reading capability of the scanner.
It is a further object of this invention to provide such an improved, frequency division multiplexed bar code scanner which has a capability to intelligently select between lasers to improve the distance measurement accuracy of the scanner.
The invention results from the realization that an improved bar code reader and/or distance measuring system can be effected by amplitude modulating a plurality of laser sources, each with different focal lengths and modulating frequencies, to allow them to share the same optical path thus simply extending the bar code reading range; to use the same modulation to determine the distance by measurement of the phase difference between the outgoing and return laser beam; and to provide the capability of using distance information to improve bar code reading performance.
This invention features a frequency division multiplexed bar code scanner system including a plurality of radiation sources for simultaneously providing a plurality of source beams and a modulator circuit for modulating the intensity of each source beam at a different frequency. There are means for combining the source beams and directing them along a path to a bar code to be read. There are means for receiving the returning combined source beams amplitude modulated by the bar code and means responsive to the returning combined source beams for detecting the amplitude modulation of at least one of the source beams representative of the bar code read.
In a preferred embodiment the radiation sources may be lasers. The modulator circuit may include means for varying the amplitude of each radiation source at the modulating frequency. The means for combining may include means for coaxially combining the source beams or means for collinearly combining them. The means for receiving may include collection optics for collecting the radiation of the returning source beams and a sensor circuit for converting the returning source beams to an electrical signal. The means for detecting amplitude modulation may include a phase locked loop circuit. There may be means for determining which of the source beams to detect for decoding the bar code.
The invention also features a frequency division multiplexed scanner system including a plurality of radiation sources for simultaneously providing a plurality of source beams. A modulator circuit modulates the intensity of each beam at a different frequency for defining a different distance range. There are means for combining the source beams and directing them along a path to a target. There are also means for receiving the returning combined source beams reflected from the target and means responsive to the returning combined source beams for detecting the phase shift of at least one of the source beams representative of the distance of the target from the scanner.
In a preferred embodiment the radiation sources may be lasers. The modulator circuit may include means for varying the power to each radiation source at the modulating frequency. The means for combining may include means for coaxially combining the source beams or collinearly combining the source beams. The means for receiving may include collection optics for collecting the radiation of the returning source beams and a sensor circuit for converting the returning source beams to an electrical signal. The means for detecting the phase shift may include a phase comparator circuit. There may be means for determining which of the source beams to detect for indicating the phase shift.
The invention also features a frequency division multiplexed bar code scanner system including a plurality of radiation sources for simultaneously providing a plurality of source beams and a modulator circuit for modulating the intensity of each source beam at a different frequency. There may be means for combining the source beams and directing them along a path to a bar code bearing object. There are means for receiving the returning combined source beams reflected from the object amplitude modulated by the bar code and phase shifted in accordance with the distance between the object and scanner. There are means responsive to the returning combined source beams for detecting the amplitude modulation of at least one of the source beams representative of the bar code read and for detecting the phase shift of at least one of the source beams representative of the distance of the object from the scanner.
In a preferred embodiment the radiation sources may be lasers. The modulator circuit may include means for varying the power to each radiation source at the modulating frequency. The means for combining may include means for coaxially combining the source beams or means for collinearly combining them. The means for receiving may include collection optics for collecting the radiation of the returning source beams and a sensor circuit for converting the returning source beams to an electrical signal. The means for detecting amplitude modulation includes a phase locked loop cir
Crole Peter V.
Dickson Karen M.
Dwinell John F.
Ci-Matrix
Felten Daniel S
Iandiorio & Teska
Le Thien M.
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