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What is the Difference between a Rotary and a Linear Actuator?

Actuators can be divided into two types based on their motion. There are two primary types of actuators: rotary and linear. In a rotary actuator, something is rotated a certain number of degrees in a circle, it may be a limited number or an infinite number.  A linear actuator moves something along a straight line, usually back and forth. An electric motor is an example of a rotary actuator since it converts an electrical signal into a rotating motion of its shaft. Upon application of current to a basic motor, the motor rotates. By connecting a motor directly to a load, you can create a direct drive rotary actuator. Rotating actuators are often combined with mechanisms that act as mechanical levers (an advantage) to decrease rotational speed and increase torque. If the output of this assembly is rotational, it is still a rotary actuator. In contrast, linear actuators are connected to mechanisms that translate rotational motion into a back-and-forth motion. What are these mechanisms I am referring to? These include ball screws, belts, pulleys, racks, and pinions. All of these mechanisms are mechanical devices that convert energy in some manner. Typically, ball screws and roller screws are used in machining centers to convert rotary motion into a precision linear motion. Belts and pulleys can be used to translate the rotary motion of a motor into linear motion (e.g. conveyor).  The rack and pinion mechanism is typically used to multiply torque, reducing the speed of a rotary motion. However, it may also be used in conjunction with a mechanism that will translate the rotary motion into a linear motion. As a word of caution, whenever a translation of motion occurs between multiple bodies, an element of compliance is introduced, which affects the actuator's ability to respond rapidly - to achieve high bandwidth. It is therefore advisable to use a system that is as close to the load as possible, such as a stepper motor or linear stepper motor solution, to achieve the highest bandwidth.