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SP-2000/X-Y
The Dolly Board has an Auto Setup feature. After each successful targeting
operation, the voltage excursions of each individual sensor are sensed and an
offset voltage is stored in memory so that the voltage swing is kept symmetrical
with respect to the 2.5V threshold.
4-Channel Servo Boards
Two of these boards form the core of the pedestal servo electronics (a third for
pan, tilt, zoom and focus is in the head). Each board can control up to four
motors. The board contains a microprocessor and related circuitry, local power
supply regulation and data interconnections.
Although the three boards are electrically identical, the Shunt jumper (J1) in the
lower right corner must be changed if you swap boards during troubleshooting.
The jumper is on position 3 for Steer and position 4 for Drive. In the head for
Pan/Tilt, no jumper is installed.
The four identical servo channels receive data commands from the controller via
the local data bus at a frame rate of 25ms. This fast frame rate supports the
highly responsive behavior of the AutoCam system to joystick commands.
However, this rate is too coarse to feed the motors directly since it would cause
rough movement. Therefore, the 25ms interval is linearly interpolated into
shorter segments of a few milliseconds each. After each segment is computed, it
is outputted as a position demand signal to the appropriate servo channel.
Each of the four servo channels is configured as either an analog channel with a
position demand output, or a digital channel with a torque demand output.
Analog
The analog position demand output mode is only used to control zoom and
focus on the lens. The circuitry is not used in the SP-2000/X-Y.
Digital
For the digital servo channels (steer, drive, height, pan, tilt), the servo loop is
closed on the 4-channel board itself. Feedback is derived from an incremental
encoder on the servo motor which generates the position follow signal. This fol-
low signal is in the form of quadrature TTL signals which are counted by the on-
board HCTL-2000 ICs. The follow signal is relayed to the microprocessor
where it is compared to the interpolated demand signal. The difference between
these two signals is the position error signal.
The servo produces a motor velocity which is proportional to the position error.
The motor velocity (computed by differentiating the position follow signal, or
subtracting subsequent motor positions) is subtracted from the position error to
derive the velocity error. The servo controls the motor current to reduce the
velocity error to zero by feeding the error to the on-board DAC and converting it
to a voltage between -10V and +10V to generate the current (or torque) desired
in the motor. The current demand signal leaves the board to feed the motor
amplifier.
User Manual
Maintenance And Repair
4-35
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