Page 55 - Concise Encyclopedia of Robotics

CABLE DRIVE C
A cable drive is a method of transferring mechanical energy in a robotic
system from an actuator to a manipulator or end effector. This type of
drive can also be used in wheel-drive propulsion systems and in cer-
tain indicating devices. The system consists of a cable, or cord, and a
set of pulleys.
The main asset of the cable drive is its simplicity.The principal limitation
is the fact that the cable can slip on the wheels or pulleys, and over time, the
cable can degenerate, and ultimately break without warning. Anyone who
has been stranded on a highway because of a failed automotive fan belt
can attest to the problems this can cause. Compare CHAIN DRIVE.
CAPACITIVE PRESSURE SENSOR
A capacitive pressure sensor consists of two metal plates separated by a
layer of nonconductive (dielectric) foam. The resulting variable capac-
itor is connected in parallel with an inductor; the inductance/capacitance
(LC) circuit determines the frequency of an oscillator. If an object strikes
the sensor, the plate spacing momentarily decreases. This increases the
capacitance, causing a drop in the oscillator frequency. When the ob-
ject moves away from the transducer, the foam springs back, the plates
return to their original spacing, and the oscillator frequency returns to
normal. The illustration is a functional block diagram of a capacitive
pressure sensor.
The output of the sensor can be converted to digital data using an
analog-to-digital converter (ADC) and then sent to a robot controller.
Pressure sensors can be mounted in various places on a mobile robot,
such as the front, back, and sides. Then, for example, physical pressure on
the sensor in the front of the robot might send a signal to the controller,
which tells the machine to move backward.

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