Robot Mechanisms and Mechanical Devices Illustrated - Profe Saul

60 Chapter 1 Motor and Motion Control Systems
will usually be converted to digital data by an integrated circuit analogto-digital
converter (ADC). Accuracies of 0.05% can be obtained from
an instrument-quality precision multiturn potentiometer, and resolutions
can exceed 0.005º if the output signal is converted with a 16-bit ADC.
Precision multiturn potentiometers have wirewound or hybrid resistive
elements. Hybrid elements are wirewound elements coated with
resistive plastic to improve their resolution. To obtain an output from a
potentiometer, a conductive wiper must be in contact with the resistive
element. During its service life wear on the resistive element caused by
the wiper can degrade the precision of the precision potentiometer.
SOLENOIDS AND THEIR APPLICATIONS
Solenoids: An Economical Choice for Linear or
Rotary Motion
A solenoid is an electromechanical device that converts electrical energy
into linear or rotary mechanical motion. All solenoids include a coil for
conducting current and generating a magnetic field, an iron or steel shell
or case to complete the magnetic circuit, and a plunger or armature for
translating motion. Solenoids can be actuated by either direct current
(DC) or rectified alternating current (AC).
Solenoids are built with conductive paths that transmit maximum
magnetic flux density with minimum electrical energy input. The
mechanical action performed by the solenoid depends on the design of
the plunger in a linear solenoid or the armature in a rotary solenoid.
Linear solenoid plungers are either spring-loaded or use external methods
to restrain axial movement caused by the magnetic flux when the
coil is energized and restore it to its initial position when the current is
switched off.
Cutaway drawing Figure 1-50 illustrates how pull-in and push-out
actions are performed by a linear solenoid. When the coil is energized,
the plunger pulls in against the spring, and this motion can be translated
into either a “pull-in” or a “push-out” response. All solenoids are basically
pull-in-type actuators, but the location of the plunger extension
with respect to the coil and spring determines its function. For example,
the plunger extension on the left end (end A) provides “push-out” motion
against the load, while a plunger extension on the right end terminated
by a clevis (end B) provides “pull-in” motion. Commercial solenoids
perform only one of these functions. Figure 1-51 is a cross-sectional
view of a typical pull-in commercial linear solenoid.