Robot Mechanisms and Mechanical Devices Illustrated - Profe Saul

Chapter 1 Motor and Motion Control Systems 51
stator terminals will be the vector sum of the voltages across the two
connected coils. Accuracies of ±1 arc-minute can be achieved.
In feedback loop applications, the stator’s sinusoidal output signals
are transmitted to a resolver-to-digital converter (RDC), a specialized
analog-to-digital converter (ADC) that converts the signals to a digital
representation of the actual angle required as an input to the motion
controller.
Tachometers
A tachometer is a DC generator that can provide velocity feedback for a
servosystem. The tachometer’s output voltage is directly proportional to
the rotational speed of the armature shaft that drives it. In a typical servosystem
application, it is mechanically coupled to the DC motor and
feeds its output voltage back to the controller and amplifier to control
drive motor and load speed. A cross-sectional drawing of a tachometer
built into the same housing as the DC motor and a resolver is shown in
Figure 1-42. Encoders or resolvers are part of separate loops that provide
position feedback.
As the tachometer’s armature coils rotate through the stator’s magnetic
field, lines of force are cut so that an electromotive force is induced
in each of its coils. This emf is directly proportional to the rate at which
Figure 1-42 Section view of a
resolver and tachometer in the
same frame as the servomotor.