Rotary actuators produce rotary motion from an energy source. Electric rotary actuators are the most common and can use a stepper motor or servo motor to produce fixed or continuous motion. Servos require a position encoder to determine the angular position and are commonly used in radio controlled models. A newer type of electric rotary actuator uses memory wire for low weight.
A rotary actuator is a device that produces rotary motion from an energy source. The simplest actuator of this type uses linear motion in a single direction to produce rotation. Electric rotary actuators use a source of electrical energy such as an electric motor. This type of rotary actuator is the most common, although rotary actuators can also use hydraulic energy from pneumatic tubes or mechanical energy from springs.
An electric rotary actuator can produce continuous rotation when its power source is a typical electric motor. It could also produce a fixed motion in a specific position when its power source is a stepper motor or servo motor. A torque motor is similar to a stepper motor, except that it produces a specific torque. Engine torque causes a specific rotation unless an opposing torque balances it.
A stepper motor is a type of electric motor that travels a fixed distance for each application of power. It can produce continuous motion by rotating at a fixed speed and can move to a specific angular position. A rotary actuator can use one or more reference sensors with any position encoder, allowing a stepper motor to move to any angular position.
A servo motor, or servo for short, is a device made up of several specific components. It requires a motor which is usually electric, although servos can also use hydraulic motors. Servos need a gear system to convert the high rotational speed of the motor into a slower rotational speed that produces more torque. A servo also requires a position encoder.
The servo position encoder allows the servo control system to determine the angular position of the electric rotary actuator. The position encoder sends a signal to the control system, indicating the desired angular position. The controller subtracts the encoder’s current position from the desired position to obtain an error code. This error code allows the controller to activate the motor, spinning it until the motor is in the correct position. An electric rotary actuator using a servo is common in radio controlled models.
A newer type of electric rotary actuator uses memory wire to achieve very low weight. The wire receives an electric current which heats the wire above a specific temperature, causing the wire to change shape. This change in shape applies torque to the motor shaft, causing it to rotate. The wire cools down when it no longer receives current, causing it to assume its previous shape. This removes torque from the drive shaft.
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