“ANALYSIS: Linear actuators provide powerful one-dimensional movement, best suited to high-precision and high-force requirements when other alternatives will not suffice.“
One of our teachers with a manufacturing background brought up the potential use for linear actuators for some robotic designs, particularly large stationary robotics like CNC systems that could add functionality to a school makerspace. Linear actuators are available through many industrial equipment supplies and through online sites such as EBay, but are not likely to be found in serviceable surplus equipment.
Available in a variety of sizes and formats, electromechanical (EM) linear actuators use motors to control a linear-action shaft output (meaning it goes back and forth, rather than around and around). EM linear actuator designs make use of DC motors and stepper motors for motive power, so control and power for either will follow the same requirements as noted previously based on the implementation. Linear actuators are heavier than their motor counterparts due to the addition of the actuator assembly.
Electrical linear motors essentially unroll a stepper motor to allow the rotor to move along its length in a linear fashion. Students may be familiar with this type of control from studies into Maglev designs for linear magnetic propulsion. Because linear motors rely on rare-earth magnets along their entire length of travel, they are more expensive than their rotary stepper motor counterparts.
Pneumatic linear actuators are also available and have found use in many bio-mimetic robots that need to simulate musculature. These designs rely on an external source of compressed air and high-pressure tubing for operation. They are efficient, but relatively complex to control via pressure valves and compressor manipulation.
Hydraulic linear actuators are used in many industrial applications requiring higher levels of force than provided through equivalently sized electromechanical systems. Like their air-powered cousins, hydraulic linear actuators require an external source for fluid pressurization and high-pressure feed hoses that must be considered in robotic designs. Unlike pneumatic actuators, a leak from hydraulic equivalents can foul equipment and require additional clean up procedures depending on the type of fluid used. Control is complex, involving compressor control and hydraulic valves.
More exotic forms of linear actuation are used in industrial and manufacturing equipment, including magnetic, magnetostrictive, and wax actuators. Many of these operate over very restrictive distances with high precision or require environmental and power controls not possible on small mobile robots. Many of these devices are special-purpose items trading high precision for increased cost.
Summary for Linear Actuators:
- Price: Very Expensive (hundreds of dollars and up) with additional components required
- Availability: Sourced from specialty electronic suppliers
- Control: Can be controlled by digital electronics through additional driver components
- Operation: Linear in continuous or stepwise operation based on technology
- Outputs: As per the fundamental type of motor or actuator function employed
- Caveats: Costly, heavier than base alternatives, more complex, not commonly available, may require additional measures for operation and clean-up
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