HP Color LaserJet CM1312 Service Manual - Page 105

Scanner system (base models) The flatbed image scanner captures an electronic image of the document on the glass. The scanner does this by illuminating the document with LEDs (red, green, and blue) and capturing the image in the image sensor to create an electronic format of the document. The flatbed scanner consists of three main elements ● CIS scanner. The CIS (contact image sensor) scanner captures an image using the product's optical path. Red, green, and blue LEDs sequentially illuminate a small strip of the document (often called a raster line), and the optical system captures each color in a single row of CCD sensors that cover the entire page width. Because only one color is captured for each line per exposure, the three colors are recombined electronically to create the full color image. For monochromatic scans or copies, all three LEDs are illuminated to create a white light for the scan so the raster line can be captured in one exposure. ● Mechanical carriage drive. The carriage drive moves the CIS scan head along the document length to create the image. In this product, a small DC motor with an optical encoder creates this motion. The speed of the carriage drive is proportional to the scan resolution (300 ppi is much faster than 1200 ppi) and also proportional to the type of scan (color scans are three-times slower than monochromatic scans). A 1200 ppi color scan moves so slowly that the product may appear to not be working, whereas a monochromatic copy scan moves at 50 times that speed and will be a little noisy. ● Image processing system (formatter). The formatter processes the scanner data into either a copy or a scan to the computer. For copies, the image data is sent directly to the product without being transmitted to the computer. Depending on user selections for the copy settings, the formatter enhances the scanner data significantly before sending it to the product. Image data is captured at 300 ppi for copies and is user selectable for scans to the computer. Each pixel is represented by 8 bits for each of the three colors (256 levels for each color), for a total of 24 bits per pixel (24bit color). Scanner power-on sequence of events When the product is turned on, it performs the following tests: ● Motor test. The product moves the motor left and right to confirm operation. It reports a scanner error 12 if no motion is detected in the motor encoder system. ● Wall find. The scan carriage moves slowly to the right while watching an encoder on the carriage motor to determine when the carriage has found the right side wall or stop. This enables the product to identify the document origin (position of the original). It reports a scanner error 13 if this process fails. ● LED check. The product moves the carriage to the white calibration label under the right side of the flatbed image scanner, and it verifies that the minimum and maximum response is acceptable. It reports a scanner error 14 if the response is unacceptable. ● Home find. The scan carriage uses the optical scanner to find physical reference features that relate to the document origin at the right side of the image glass. This process ensures accurate location of the first document pixels so that the user documents will have an accurate placement of the image on scans and copies. It reports a scanner error 6 message if the reference features are not found. ● Calibration. This test, also known as scanner color calibration, enables the product to identify the black and white on every pixel in the CCD. Calibration occurs in two major processes: a broad (analog) adjustment of all pixels to bring them into the target output range, and a pixel-by-pixel ENWW Scanner system (base models) 91