Kodak DryView 8150, Руководство по обслуживанию, Страница: 222 / 470

Service Manual
6-20
7F3318 2005 July Rev. B
Scanner speed is controlled by a digital feedback loop on the Optics Module Control Board (OMCB). The
time interval between two adjacent scanner speed pulses is measured by a counter using a 16 MHz
clock. An error signal determined by the timing measurement is calculated by the microprocessor on the
OMBC and sent to the DAC, which feeds a correction voltage to the Spinner Motor.
S tart of Scan Sensing and Beam Power Monitoring ---- Start of Scan Detector PD1 on the OMCB
serves as both SOS detector and laser beam power monitor. The laser is turned off after completion of a
scan line, to avoid light scattering. Turn on of the beam is timed so that it will reflect onto PD1 at the
beginning of scan, generating the SOS pulse. This pulse is fed back to the MCS Board Pixel Clock
Generator to synchronize startup of the pixel clock.
To measure laser power, the laser is turned on constantly at a set driver level, and PD1 performs peak
detection for a number of scans. The power value is measured by an A/D Converter to provide a laser
power reading.
Laser Driver ----The laser driver, housed in the box which contains the laser diode, provides current to run
the laser. The current level is determined by the voltage present at the driver input. A feedback loop is
formed by reflection of the beam from lens L1 to a photodiode, which feeds a circuit that generates an
error signal for feedback control of the driver.
Beam Attenuator ----A linearly variable neutral density filter is used to attenuate beam power to
accommodate for variations in film speed. Use of the attenuator allows the laser drive current levels to
remain independent of film speed variations.
6-4-3-4. Optics Translation Assembly
The optics translation assembly (see Figure 6-10) moves the optics module in the cross-scan direction
during exposure. Speed and smoothness of motion must be precisely controlled. Speed variation during
translation will result in vertical bands or streaks of nonuniform density on the film image. Also, unstable
motion during translation can cause inaccurate placement of pixels, resulting in a variety of image
artifacts.
Translation Carriage ----The optics module is mounted on a translation carriage that slides on a pair of
cylindrical rails during translation. Kinematic support is achieved by a pair of V-shaped bearing surfaces
and a flat sliding surface built into the carriage. When the carriage slides on the rails, there is little friction
on the carriage in the translation direction, while its position is rigidly determined in the other directions.
The cylindrical rails are precision ground to reduce friction. Any marks or scratches on the rails can result
in nonuniformity in translation speed.
Drive Mechanism ----The carriage is driven by 4 nylon-coated steel cables (called a “quad” cable)
mounted on two pulleys: a drive pulley and an idler. The drive pulley is mounted on and coaxial with a
circular flywheel. The flywheel is friction-driven by a polyurethane tire mounted on the shaft of Optics
Translation Motor (STEP 4).