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Platen ProfilerReal-time print-head diagnostic instrumentR&D and Manufacturing Applications Real-Time f-˜ lens adjustments Real-time GRIN lens array adjustment Spot Size, Bow and Linearity Measurement Final Test and Quality Assurance Configure, Test and Verify Designs Basic Measurements Spot size Spot X and Y centroid position Power/Energy Derived Measurements Scan bow Scan jitter Start-of-scan jitter Linearity Distortion Facet-to-facet tilt Photon's Platen Profiler is a real-time print-head diagnostic instrument designed for manufacturing, aligning, and testing Laser Scan Units (LSU) and laser printers; it profiles a beam along the entire print length in <1/10 second. What can be Measured? The Platen Profiler is a laser printer diagnostic instrument designed to measure CW or pulsed laser beam characteristics at multiple positions along the print plane. The instrument is able to measure beams in a dynamically operating print head or laser scan unit (LSU), without the need to stop the polygonal scanning mirror. Using this system the entire raster scan can be acquired and analyzed at once, with an update rate of up to 15Hz. This makes it possible to perform, for example, real-time dynamic adjustments of f-˜ lenses in print heads with air bearing spindles or to measure the characteristics of polygonal scanners across the entire scan plane in seconds. Details Speed is of the Essence LSUs for laser printers operate by modulating a laser beam, or beams, reflected off a facet of a rapidly spinning polygonal mirror and focusing the resultant dot, or PEL, on to the scan plane of the printer platen. Each facet sweeps the entire scan length and represents one raster scan of the printer. Traditionally, the optics for this operation are adjusted and tested by stopping the polygon and manually aiming the laser spot to various points on the platen where a beam profiler has been positioned. Although this can be automated to some extent, it is still very time-consuming, requiring multiple measurements and either the physical translation of the beam profiler across the platen plane or the use of multiple profilers. Using a combination of fiber optic transfer optics and a CCD camera, the Platen Profiler allows the simultaneous collection of data across the entire platen plane. This means that the data can be collected from a fully operational LSU with the polygon spinning at full speed. Depending on the control circuits of the LSU, PELs from a single raster scan, multiple raster scans or even sequential polygon facets can be collected and analyzed. The Platen Profiler collects beam size, position and irradiance data from all sensor positions simultaneously with an update rate of 15Hz. By controlling the modulation of the LSU's laser, any pattern of PELs can be written to the profiler and then analyzed to derive such features as focus, scan bow, linearity, uniformity, facet jitter or tilt. The real power of the Platen Profiler is the speed with which it can make these measurements. The sensors are read simultaneously, and the entire scan line can be profiled in less than 1/10th second. Figure 1 shows an example of the standard measurement platen configuration. The profiler operates either as a stand-alone instrument or integrated into automated test and measurement systems. As a standalone instrument, it is useful in research and development applications to configure, test and verify designs, and in manufacturing and production for real-time adjustments of print-head optics. As an automated system, it finds applications as a tool for final test and quality assurance of assembled print heads. In either case, the system provides considerable savings in time and improves productivity and throughput. This second generation profiler has no moving parts. It comes in two standard 15-sensor configurations for 216mm or 320mm laser printer platens, and a 17-sensor, 216mm configuration. Also, it can be custom configured to measure focused spots at practically any location across a scan plane. Beam Characterization Laser beam parameters can be obtained from simple measurements of beam profile: width, amplitude, and position. The normal of each mirror facet should ideally lie in the scan plane; however, due to fabrication tolerances, each facet will have a slightly different orientation, or facet-to-facet tilt. The scan from each mirror facet is slightly deflected from the next, and print pattern is slightly displaced from line to line. The result can be a blurred print pattern. Analysis of the differences in beam position determines the facet-to-facet tilt. Figure 2 ­ Bow and linearity Another typical optical misalignment is scan line bow (See Figure 2). This occurs when the middle of the scan is either bowed up or down in reference to a straight line. Figures 3-6 show simplified examples of how the LSU can be controlled to determine some of the print plane characteristics using the Platen Profiler. Figure 3 ­ LSU with polygonal mirror of six facets Figure 3 illustrates the LSU with a polygon rotation of 20,000 rpm. This translates to 333.33 rps and with six facets, 2000 scans per second. Thus, each raster scan is 0.5ms in duration. Using this information, the LSU can be controlled to write one PEL on each of the 15 evenly spaced sensors, as shown in Figure 4. Figure 4 ­ Timing diagram illustrating the writing of one PEL to each sensor from one facet In order to measure the jitter that is the result of any wobble in the spinning polygonal mirror the LSU should be controlled to write a series of PELs from one facet. Figure 5 shows the timing that will write a series of 15 PELs each time the ith facet comes around for a full 66.67ms camera cycle. Since each revolution of the polygon takes 3ms, it will be possible to collect 22 repetitive PELs from the ith facet for jitter analysis. Figure 5 ­ Measure jitter caused by wobble of the polygonal mirrorby writing a PEL of one (ith) facet over k revolutions To compare the jitter caused by facet-to-facet tilt, the LSU should be controlled to write the 15 PELs from each facet. In this case, shown in Figure 6, PELs are written as each facet makes a raster scan for one full revolution of the polygon. Figure 6 - Measure jitter caused by facet-to-facet tilt by writingPELS from each facet over one full revolution of the polygonal mirror Software Analysis The software reports beam parameters either to the standalone graphical user interface (GUI) or to an ActiveX server interface for integration into custom manufacturing or inspection applications using for example, Visual C/C++, Visual Basic or LabView. An automation controller example illustrating the use of the automation interface is included. Additionally the software can be custom designed to answer the specific questions posed by the user¹s application. Figure 1 ­ Standard platen configuration Using the sample measurements of beam size, position and power, the Platen Profiler software can report scan linearity, scan bow, jitter, uniformity of power and myriad other important parameters of the scan engine. Knowledge of these parameters can be combined with information about the scanning operation, such as the identity of the facet producing a given series of spots, to deduce other characteristics like facet-to-facet tilt and scan start jitter. Specifications Platen Profiler System Specifications Wavelength Response: VIS to NIR (user specified) XY Position Accuracy within sensor: ±3µm Beam Size Accuracy 100µm: 1/e2 = 5% FWHM = 3% 75µm: 1/e2 = 8% FWHM = 5% 50µm: 1/e2 = 10% FWHM = 8% Acquisition System Data Collection Rate: Up to 15Hz Gain Adjustment Range (shuttering): 30dB Optical Dynamic Range: 35dB Digitization: 12 Bit Options Sensor placement - can place sensors on different centers Number of sensors to meet customer's need External energy/power with preamp detector