Actuators are a vital part of the automated system. They help with controlling equipment using pneumatic, hydraulic, or sometimes electronic signals. As you know, linear actuators are very common since they form the applications used in the equipment control moving along a lateral axis.
That said, it’s crucial to note that several other types of actuators are also found in robotic arms. Let’s check them out and help you choose the right actuator.
An actuator is a component of a machine responsible for controlling and moving a system or mechanism. For example, DC motors are one type of actuator.
A rotary actuator is an actuator that produces a rotary motion or torque. A basic actuator is completely mechanical, where linear motion in one direction produces rotation. Common actuators are usually electrically powered; others are either powered pneumatically hydraulically or, or may use energy stored in springs.
Alternating current (AC) is not common in mobile robots as they are mostly powered with DC or direct current generating from batteries. Because electronic components utilize DC, having the same power supply type for actuators makes sense.
A DC motor converts electrical energy into mechanical energy. It features an output shaft that rotates at significantly high speeds, typically in the rpm range of 5 000-10 000. Although they rotate quickly, most aren’t robust (low torque). So, you can add a gear to reduce speed and enhance the torque.
To add motors into robotics, you must adjust the motor’s body to the robot’s frame. DC motors operate in both counter-clockwise (CCW) or clockwise (CW) rotation. You can measure the turning shaft’s angular motion using shaft encoders or potentiometers.
DC Gear Motors
A geared DC motor is an all-in-one combination of a gearbox and motor. The addition of a gear head to a motor reduces the speed while improving the torque output.
A servo motor uses either a linear or rotary actuator to control linear or angular positions via velocity and acceleration. They usually operate between 4.5V to 6V, running through power, ground, and control wires. The DC motor of a servo rotates at a high RPM on low torque.
Industrial Servo Motors
Industrial servo motors are typically built from a large AC motor, gear down and encoder that provides feedback regarding speed and angular position. These motors aren’t commonly used in mobile robots due to their size, weight, complexity, and cost.
A stepper motor is a DC motor that moves in discrete steps. It has multiple coils organized in groups labeled as “phases”. Through energizing each phase sequentially, the motor rotates one step at a time. With a computer-controlled stepping, you can obtain precise positioning and speed control.
A linear actuator is the type of actuator that generates motion in a straight line, as opposed to a traditional electric motor’s circular motion. Linear actuators are mostly used in places where there’s a need for linear motion, like in printers, disk drives, valves, dampers, industrial machinery, and machine tools.
DC Linear Actuators
A linear actuator driven by a DC power source is called a DC linear actuator. These actuators are commonly used in industrial applications to activate a variety of secondary mechanisms.
A solenoid is an electromagnet that generates a controlled, robust magnetic field via a coil wound inside a packed helix. In 1823, the term Solenoids was invented by André-Marie Ampère to indicate a helical coil. A “Linear Solenoid” is an electromagnetic device that converts electrical energy into a mechanical pushing or pulling motion or force.
Drive shafts connect the gearbox to the wheel and is responsible for transferring the turning energy into the wheels. Each wheel needs its own drive shaft and these are often prone to break. Usually you would want to change all drive shafts when you change one, but depending on the problem you might be able to just find a single semi truck drive shaft for sale and just change the one that was broken. If you go this route make sure the numbers add up as you don’t want any difference in the four drive shafts in terms of how much they can pull and their ratings for weight etc.
Muscle Wires are thin, deeply processed strands of a nickel-titanium alloy known as Nitinol— a type of Shape Memory Alloy which can assume completely different forms or “phases” at different temperatures. These actuators aren’t very strong but are far more convenient when working with small parts.
Pneumatic actuators boast a piston inside a hollow cylinder. Pressure from a manual pump or external compressor moves the piston inside the cylinder.
Hydraulic actuators operate quite similarly to pneumatic actuators, except an incompressible liquid from a pump moves the cylinder, instead of pressurized air.
How to Choose an Actuator?
We’ve developed the following FAQs to help you choose the right actuator for your specific task.
#1. Will the actuator be used to move a wheeled robot?
Generally, automobiles use a rack and pinion steering while robots use skid steering. If you go with skid steering, DC gear motors are the best options for robots with tracks and wheels as they rotate continuously. If you go for rack and pinion, a drive motor along with a motor to steer the front wheels is required.
#2. Will the motor be used to turn or lift heavy stuff?
Torque is gained at the cost of speed. You must use a high gear ratio gearbox and a heavy-duty DC motor/linear actuator besides clamps to prevent the mass from tripping when the power’s down.
#3. Will the range of motion be limited to 180-degree?
R/C servos are used to make small walking robots as their range of motion is limited to 180 degrees without much torque.
#4. Do you require a precise angle?
You can use stepper motors in place of R/C servos for high precision angular motion. However, some R/C servos using digital encoders provide great precision.
#5. What if the motion is in a straight line?
Experts suggest linear actuators are ideal for positioning moving objects along a straight line. Muscle wire can help if very little force is involved. Solenoids are ideal for fast motion and DC linear actuators for strong forces.
So, there you have it! Now that you know the basics of actuators, you’ll be able to choose one for your next project. Leave a comment below if you have any further questions.