Linear Actuators Mechanisms and Mechanical Devices Sourcebook, 5th Edition
To start with In the GLOSSARY OF ROBOTIC TERMS in Mechanisms and Mechanical Devices Sourcebook, 5th Edition
Actuator is defined as Any transducer that converts electrical, hydraulic, or
pneumatic energy into power to perform motions or tasks.
Examples are electric motor, air motor, and solenoid.
DC and AC Motor Linear Actuators Chapter follows
Actuators for motion control systems are available in many different forms, including both linear and rotary versions. One popular configuration is that of a Thomson Saginaw PPA, shown in
section view in Fig. 16. It consists of an AC or DC motor mounted
parallel to either a ballscrew or Acme screw assembly through a
reduction gear assembly with a slip clutch and integral brake
assembly. Linear actuators of this type can perform a wide range
of commercial, industrial, and institutional applications.
One version designed for mobile applications can be powered
by a 12-, 24-, or 36-VDC permanent-magnet motor. These
motors are capable of performing such tasks as positioning
antenna reflectors, opening and closing security gates, handling
materials, and raising and lowering scissors-type lift tables,
machine hoods, and light-duty jib crane arms.
Other linear actuators are designed for use in fixed locations
where either 120- or 220-VAC line power is available. They can
have either AC or DC motors. Those with 120-VAC motors can
be equipped with optional electric brakes that virtually eliminate coasting, thus permitting point-to-point travel along the
stroke.
Where variable speed is desired and 120-VAC power is available, a linear actuator with a 90-VDC motor can be equipped
with a solid-state rectifier/speed controller. Closed-loop feedback
provides speed regulation down to one-tenth of the maximum
travel rate. This feedback system can maintain its selected travel
rate despite load changes.
Thomson Saginaw also offers its linear actuators with either
Hall-effect or potentiometer sensors for applications where it is
necessary or desirable to control actuator positioning. With
Hall-effect sensing, six pulses are generated with each turn of
the output shaft during which the stroke travels approximately
1 over 32 inches (0.033 in. or 0.84 mm). These pulses can be counted by
a separate control unit and added or subtracted from the stored
pulse count in the unit’s memory. The actuator can be stopped
at any 0.033-in. increment of travel along the stroke selected by
programming. A limit switch can be used together with this
sensor.
If a 10-turn, 10,000-ohm potentiometer is used as a sensor, it
can be driven by the output shaft through a spur gear. The gear
ratio is established to change the resistance from 0 to 10,000 ohms
over the length of the actuator stroke. A separate control unit
measures the resistance (or voltage) across the potentiometer,
which varies continuously and linearly with stroke travel. The
actuator can be stopped at any position along its stroke.
Stepper-Motor Based Linear Actuators
Linear actuators are available with axial integral threaded shafts
and bolt nuts that convert rotary motion to linear motion.
Powered by fractional horsepower permanent-magnet stepper
motors, these linear actuators are capable of positioning light
loads. Digital pulses fed to the actuator cause the threaded shaft
to rotate, advancing or retracting it so that a load coupled to the
shaft can be moved backward or forward. The bidirectional digital linear actuator shown in Fig. 17 can provide linear resolution
as fine as 0.001 in. per pulse. Travel per step is determined by the
pitch of the leadscrew and step angle of the motor. The maximum
linear force for the model shown is 75 oz.
Sclater, N. (2011). Mechanisms and mechanical devices sourcebook. McGraw Hill.
