Vinten Radamec HS-2010MED Pan & Tilt Head - Manual (Page 65)

HS-2010MED Maintenance And Repair
User Manual 4-15
swap boards during troubleshooting. The jumper is on position 3 for Steer and
position 4 for Drive when used in the SP-2000. In the HS-2010MED (for Pan/
Tilt), no jumper is installed.
The four identical servo channels on the board are capable of controlling either
analog or digital servo motors. They 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. How-
ever, 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 seg-
ments. After each segment is computed, the output is generated 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 used to control zoom and focus on
the lens. The on-board 16-bit DAC709 D/A converter converts the position
demand data to a voltage between -10V and +10V. This control signal is fed to
the Z/F Driver board where the feedback loop is closed.
Digital
For the digital servo channels (pan, tilt), the servo loop is closed on the 4-chan-
nel board itself. Feedback is derived from an incremental encoder on the servo
motor which generates the position follow signal. This follow 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.
Some troubleshooting may be effected by probing for the TTL signals coming
back from the encoders on the motors. If the demand position and the follow
position are not the same, then the 4 channel board will be generating demand
signals at J3 through J6. For example, with a head that is operating normally,
you can pull gently on the head and watch these torque demand signals grow.
Zoom/Focus Driver
The Zoom/Focus Driver Board contains the motor drivers and servo loop cir-
cuitry for the zoom and focus servos (except when native lens control is