Radiant energy – Photocells; circuits and apparatus – Optical or pre-photocell system
Reexamination Certificate
2000-08-08
2002-06-04
Allen, Stephone (Department: 2878)
Radiant energy
Photocells; circuits and apparatus
Optical or pre-photocell system
C250S201200, C356S400000, C362S277000
Reexamination Certificate
active
06399937
ABSTRACT:
COPYRIGHT NOTICE
A portion of the disclosure of this patent document contains material which is subject to copyright protection. The copyright owner has no objection to the facsimile reproduction by anyone of the patent disclosure, as it appears in the U.S. Patent and Trademark Office patent files or records, but otherwise reserves all copyright rights whatsoever.
FIELD OF THE INVENTION
The present invention relates to optical focusing systems and more particularly relates to a computer-based semi-automatic focusing and assembly apparatus and method for focusing and assembling optical devices, such as laser diode assemblies, used in bar-code scanning systems.
BACKGROUND OF THE INVENTION
Bar-code scanning systems are widely used in retailing, postal and parcel delivery services, manufacturing, warehousing and distribution and other industries for fast data transaction applications. The benefits of such scanning systems are countless. For example, in manufacturing, the use of bar code scanners could result in accurate raw material inventory, production routing, work-in-progress tracking, labor efficiency, inventory control, quality assurance, shipping precision, and so on.
One of the key elements of bar-code scanners is the laser diode assembly that provides the light source for the scanners. The focusing characteristics of the assembly have significant effects on the correct reading of bar codes. If the laser beam emitted from the laser diode assembly is not focused accurately, it will result in a weak signal level and therefore possible loss of information when it scans across the bar-code. The end result is that one has to scan several times before correct information can be captured. For bar-code scanners to be effective over a range of distances, the beam width of the laser beam has to be within tolerance at several specified distances (normally three distances corresponding to the near, mid and far fields are specified). To ensure that the beam width requirement is met and therefore high scanner accuracy is achieved, every laser diode assembly needs to be focused in high precision during production.
Currently such focusing adjustments are performed manually in most of the bar-code scanner production processes which limits productivity as well as focusing performance of the laser diode assemblies. The manual focusing setup typically used in manufacturing laser diode (LD) assemblies consists of the following components: the laser diode assembly consisting of a light beam emitting laser diode, a focusing lens, a lens holder with an aperture, a spring, and a diode holder; a mechanical fixture to hold the LD assembly; a beam scan head including a cylindrical rotating drum with a slit for beam width measurement, a photo detector for beam power measurement, and a level for gain adjustment; a guide rail to move the scan head for beam width measurement at different distances (the height of the scan head can also be adjusted); a beam scan block which controls the scan head and displays the beam width (the outputs of the scan block include an analog beam profile signal, a trigger signal, and a clock reference signal); a current source that supplies the current to the laser diode; and a laser power meter which is used to measure the intensity of a laser beam during the laser diode power-up stage.
The first step of the focusing process is to assemble the laser diode, the spring, and the lens together in the diode holder and use a clamp to hold the parts in place. Next, this assembly is placed in the mechanical focusing fixture. The clamp is lifted and the assembly is now ready for focusing. For each type of assembly, the operator is usually given three specified locations at which the beam width should be focused (i.e., near, mid and far fields). The operator's next task is to connect the current source to the laser diode and slowly increase the current to a specified value. The operator then manually slides the scan head to the nearest specified location and adjusts the orientation of the LD so that the beam is centered in the aperture of the scan head. The operator then adjusts one or more focusing knobs of the focusing fixture so that the beam width displayed on the scan head is within a specified tolerance. The process is then repeated at mid and far field locations. If the operator is successful in achieving beam widths within the specified tolerances at all locations, glue is carefully applied to the lens holder to fix the lens with respect to the LD. After the curing time of the glue has elapsed, the operator removes the assembly and starts focusing the next assembly. If the operator is not able to focus the beam to acceptable beam widths at all locations, the assembly is rejected.
Following are some of the major problems associated with the manual focusing setup and procedures:
Moving Scan Head
One of the major concerns of the current setup is that the operator has to repeatedly move the scan head on the rail back and forth during focusing. For mass production, the time spent on moving the beam scan head significantly reduces productivity.
Time Consuming Focusing Check After Curing
After curing, the beam widths at specified distances have to be checked again to see if they are still within tolerances. To do this in the existing manual setup, the operator has to move the scan head to different locations again, which further slows down the process.
Human Factor
In the existing setup, the focusing criteria is quite subjective with the operator making most of the decisions based on intuition and experience. In addition, the operator is not required to optimize focusing.
Wasted Time During Curing
Currently, the operator focuses only one LD assembly at a time. During the curing period, the operator is basically idle. This period of time can be utilized more efficiently if the operator can start focusing the next assembly. With the current setup this is not possible.
No Check on Beam Centering
Another concern is that the operator cannot accurately point the laser beam to the center of the scan head aperture due to the lack of an accurate beam centering target. Because of this pointing error, the beam width displayed on the scan block may not be an accurate indication of the true beam width at the specified clip level.
Focusing Inconsistency
Currently, the operator's task is simply to bring the beam widths within the specified tolerances. No targeting of specific beam width values within the specified ranges is required. The result of this practice is that the assembled LD assemblies lack focusing consistency from assembly to assembly, which in turn may result in performance inconsistency of bar-code scanner products.
Lack of Process Tracking
During the focusing process, some of the focusing parameters may change systematically due to errors in the focusing setup or systematic defects in the laser diodes and focusing lenses. Since no focusing data are recorded in the current focusing process, no process tracking can be done to detect such problems. Also, if a laser diode assembly results in a defective product when assembled into a bar-code scanner, no trouble shooting can be done because no data regarding to the focusing condition of the laser diode assembly at the time of assembling is available.
No Control Over the Amount of Glue Dispensed
After focusing, the amount of glue applied for curing and the way how glue is applied are crucial. The operator has to be very careful in making sure that no excessive amount of glue is applied. If this operation is not carried out with care, then the focal distance may change and the focusing may go out of tolerance. In the currently process, there is no control over the amount of glue dispensed, which could cause serious problems if the operator is not careful or not skillful.
No Access to Beam Profile Information
Another concern is that the engineers do not have easy access to the beam profile information at different distances, especially that for the assembled laser diode assemblies, to perform a comprehensive analysis of the proce
Huang Peisen S.
Kao Imin
Allen Stephone
Hoffmann & Baron , LLP
The Research Foundation of State University of New York
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