Page 350 - Sensors and Control Systems in Manufacturing

Advanced Sensors in Pr ecision Manufacturing
digital motor-control circuits that execute a PID control algorithm 305
with programmable gain (one such control circuit dedicated to each
servomotor) and modules that contain the motor-power switching
circuits, digital-to analog buffer circuits for the feedforward control
signals, and analog-to-digital buffer circuits for the feedback signals
from the shaft-angle encoders (one such module located near, and
dedicated to, each servomotor).
Besides being immune to noise, optical fibers are compact and
flexible. These features are particularly advantageous in robots,
which must often function in electromagnetically noisy environments
and in which it would otherwise be necessary to use many stiff bulky
wires (which could interfere with movement) to accommodate the
required data rates.
Figure 6.22 shows schematically the fiber-optic link and major
subsystems of the control loop of one servomotor. Each digital motor-
control circuit is connected to a central control computer, which pro-
grams the controller gains and provides the high-level position com-
mands. The other inputs to the motor-control circuit include the sign
of the commanded motor current and pulse-width modulation repre-
senting the magnitude of the command motor current.
The fiber-optic link includes two optical fibers—one for feedfor-
ward, one for feedback. The ends of the fibers are connected to identi-
cal bidirectional interface circuit boards, each containing a transmit-
ter and a receiver. The fiber-optic link has a throughput rate of 175
MHz; at this high rate, it functions as though it were a 32-bit parallel
link (8 bits for each motor control loop), even though the data are
multiplexed into a serial bit stream for transmission. In the receiver,
the bit stream is decoded to reconstruct the 8-bit pattern and a pro-
grammable logic sequencer expands the 8-bit pattern to 32 bits and
checks for errors by using synchronizing bits.

6.21 Acoustooptical/Electronic Sensors for Synthetic-
Aperture Radar Utilizing Vision Technology
An acoustooptical sensor operates in conjunction with analog and
digital electronic circuits to process frequency-modulated synthetic-
aperture radar (SAR) return signals in real time. The acoustooptical
SAR processor will provide real-time SAR imagery aboard moving
aircraft or space SAR platforms. The acoustooptical SAR processor
has the potential to replace the present all-electronic SAR processors
that are currently so large and heavy and consume so much power
that they are restricted to use on the ground in the postprocessing
of the SAR in-flight data recorder.
The acoustooptical SAR processor uses the range delay to resolve
the range coordinates of a target. The history of the phase of the train
of radar pulses as the radar platform flies past a target is used to