Incremental printing of symbolic information – Light or beam marking apparatus or processes – Scan of light
Reexamination Certificate
1999-01-06
2001-06-26
Tran, Andrew Q. (Department: 2824)
Incremental printing of symbolic information
Light or beam marking apparatus or processes
Scan of light
C347S236000, C347S237000, C347S234000, C347S233000, C347S246000, C347S247000, C347S248000
Reexamination Certificate
active
06252622
ABSTRACT:
FIELD OF THE INVENTION
The invention herein disclosed relates to laser diode recording systems and more specifically to printing systems employing laser diode arrays for recording.
BACKGROUND OF THE INVENTION
Laser diodes have been used in many prior art recording techniques as have monolithic laser diode arrays. Monolithic laser diode arrays used in recording typically contain 10-100 diodes and the recording is done with either photonic exposure or thermal exposure. Photonic systems react to the total exposure to photon energy, such that each photon striking the recording surface helps to expose it. Conversely thermal systems respond to peak temperatures and must reach a certain threshold for exposure to occur. Thermal systems usually operate in the infrared (IR), while photonic systems usually operate in the visible or ultraviolet (UV) range, but either system can operate in any range of the spectrum. Each diode may be a single mode source or a short multiple mode stripe and is said to record a particular “track” on the recording surface. Diode arrays can contain anywhere from 10 to 1000 diodes. In typical printing applications, the tracks on the recording surface are spaced between 10 and 20 microns apart, but for data storage applications, the tracks can be as close together as 0.5 microns, in order to permit high density recording.
A current problem associated with the use of monolithic laser diode arrays is the diode spacing within the array. Current technology in semiconductor fabrication can only produce arrays in which the diodes are spaced in the neighborhood of 10-100 microns and, as mentioned above, recording requires data spacing down to 0.5 microns. The laser diodes can not be de-magnified optically because of the large numerical aperture of the laser emission. Consequently, to achieve the required density of tracks on the recording surface, a non-optical method is required to reduce the effective diode spacing. Such methods normally include one of two techniques: angled diode arrays and interleaving.
An angled diode array is depicted in FIG.
1
. The diode array
1
is maintained at an angle &thgr; with respect to the perpendicular of the scan direction
11
. Diode spacing a is typically between 10 and 100 &mgr;m on the array, but because the array is angled, the spots
7
which are printed in the tracks on the recording surface
6
are more closely spaced with separations of b=a.cos &thgr;. Printing the data onto the recording surface
6
in a linear fashion requires that the diodes of the angled array
1
be activated in a delayed fashion. The desired location of the printing dots
7
is in a horizontal line on the printing surface
6
. Because the printing surface
6
is scanning (i.e. moving relative to the laser diode array
1
) in direction
11
, the various lasers must be delayed so that they are not activated until the desired location
7
on the printing surface
6
is reached. Diode
1
a
is not delayed, and data is fed straight into it. However, data flowing to diode
1
b
must be delayed slightly until spot
7
b
is directly under diode
1
b.
The required delay t is easily determined from the diode spacing a, the array angle &thgr; and the scan velocity. The delay required for the other diodes
1
c,
and
1
d
is simply a multiple of that required for
1
b.
Using this technique of coupling the angled diode array with digital delays, the effective track spacing can be reduced on the recording surface overcoming the diode spacing limitation of semiconductor fabrication technology.
A second method of overcoming the diode spacing limitation requires interleaving. Interleaving involves multiple passes with a diode array, such that each pass fills in only a limited number of tracks and then subsequent passes fill in the remaining tracks in order to complete the recording. Both slanting and interleaving are well known and discussed in “High Power Multi-Channel Writing Heads”, by Dan Gelbart, published in the “IS&T Tenth International Congress on Advances in Non-Impact Printing”, Nov. 1994, which is hereby incorporated by reference.
A second major problem associated with monolithic diode arrays and their use in recording is the failure rate of the diodes. Moreover, if any of the diodes in the array fails, then the entire array is ruined and can no longer be used as a recording means. A need exists for a technique to overcome isolated failures of single diodes within the array, so that the array may still function.
Accordingly, it is an object of this invention to provide a fault tolerant diode array recording system which is capable of overcoming isolated diode failures within a diode array, so as to effectively record data onto a recording surface.
SUMMARY OF THE INVENTION
A fault tolerant laser diode array apparatus is disclosed. The apparatus is operative to record multiple parallel tracks on a recording surface and is comprised of a plurality of laser diodes made up of several smaller groups of diodes. Each group of diodes is assigned to a different one of the parallel tracks. Within each group, there is a designated diode called the primary diode which is operative to receive input data, emit optical energy in correspondence with the data, and record the data on the assigned track.
The apparatus also comprises a selection subsystem which, in the case of a failure of any of the primary diodes, is operative to selectively activate a functional secondary diode within the group of diodes that contains the failure.
Because the groups contain at least two diodes and the selection subsystem is able to selectively activate one diode from within each group, there is always a functional diode assigned to each one of the parallel tracks.
Preferably, the selection subsystem may be further operative to detect a failure in any one of the primary diodes.
The plurality of laser diodes may be comprised of at least two distinct laser diode arrays and the groups of diodes may comprise one diode from each array.
The apparatus may also comprise a delay network operative to compensate the primary diodes so as to ensure that the primary diodes are operative to record in the correct location on the recording surface independent of the primary diodes being located on any of the distinct laser diode arrays.
Advantageously, the plurality of laser diodes may be single mode laser diodes or multi-mode laser diodes and the method of recording on the recording surface may be thermal or photonic in nature.
The apparatus may contain many groups of diodes. The number of diodes in each group may range between 10 and 1000.
A second aspect of the invention involves a fault tolerant monolithic laser diode array apparatus operative to record multiple parallel tracks on a recording surface. The apparatus comprises two monolithic laser diode arrays which are arranged face to face in a manner such that a pair of diodes (one from each of the arrays) is assigned to each one of the parallel tracks. The pair of diodes consists of one active diode and one secondary diode. The primary diode is operative to receive input data, emit optical energy in correspondence with the data, and record the data in the assigned track.
The apparatus also comprises a selection subsystem which, in the case of a failure of the primary diode, is operative to activate the secondary diode within the pair of diodes that contains the failure, making the secondary diode into the primary diode.
Preferably, the selection subsystem may be further operative to detect a failure the primary diode.
The apparatus may also comprise a delay network operative to compensate the primary diode, so as to ensure that the primary diode is operative to record in the correct location on the recording surface independent of the primary diode being located on either of the monolithic laser diode arrays.
Advantageously, the laser diode arrays may comprise diode which are single mode laser diodes or multi-mode laser diodes and the method of recording on the recording surface may be thermal or photonic in nature.
The apparatus may be opera
Creo Products Inc.
Oyen Wiggs Green & Mutala
Tran Andrew Q.
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