Micro-g LaCoste FG5, Руководство пользователя

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Adjustment and Maintenance
4
slip can cause the cart to drive into the bottom or top of the dropping
chamber and burn out the motor.
4.5.2.Analog Servo
The analog servo has three different sections. They are: Cart-position, Cart-
velocity, and Sphere-position. The cart servos use the rotary shaft encoder as
a position/velocity sensor. The sphere servo uses the optical sensor mounted
on the cart.
4.5.2.1.Cart-Position
The cart position is given by an optical shaft encoder that is mounted on the
motor shaft. The base resolution is 500 counts per revolution. The outputs
are two quadrature signals which give information about the amount and
direction of shaft rotation.
The shaft encoder quadrature outputs are preconditioned by a custom
programmed gate array logic (GAL) chip called the AXQD2X. The outputs of
the AXQD2X are glitch-free clock pulses and an up/down bit. The resolution
of the shaft encoder is multiplied by two, giving 1000 counts per revolution.
The AXQD2X also has logic that helps clear the counters and keeps them
from an overflow or underflow condition.
The sixteen-bit counters feed a twelve-bit digital to analog chip (DAC) for use
in the analog servo. The top seven bits are also fed to a comparator that is
used for level settings that trigger different phases of the servo. The output of
the DAC is available on the front panel BNC called CART position.
The DAC output has a programmable offset corresponding to either (1) the
manual position controlled by the front panel knob, or (2) the hold position
trimpot on the controller board. The servo adds in some derivative or
damping that is set by the CART DAMP trimpot on the PC-board. The
overall gain is set by the HOLD GAIN trimpot on the PC-board.
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