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| 28 (Figure 1). Both work on a similar principle: Turning the threaded screw pushes the nut directly forward or backward depending on the motor's direction of rotation. The difference between the two solutions is that the lead screw has a nut threaded like a screw, and the ball screw uses ball bearings to navigate along the thread. Both techniques have their advantages and disadvantages. For example, the ball screw has less friction and therefore needs less torque to drive, while the lead screw is self-locking, making it a better choice for vertical applications. Linear actuator designs often include gears, making them suitable for loads that require large amounts of force. The downside of the extra force is that linear actuators tend to be slower than other methods of providing linear motion. Their other drawback is that they have more components and rely on friction to operate, meaning they may require regular maintenance. An alternative way of achieving linear motion is to use a motor designed for that specific purpose. Linear motors operate similarly to conventional motor types, with a rotor, a stator, poles, electromagnets, and permanent magnets. Like conventional motors, linear motors can be manufactured with different types of rotor construction to provide traits that suit the application. The most common types of motors used in linear motor designs are based on brushless DC (BLDC), synchronous, and induction motors. Linear motors have an "unrolled" stator that lies flat instead of being the continuous loop that is found in other motors (Figure 2). To operate, the linear motor's controller energizes the stator's electromagnetic poles in sequence to move the permanent magnet rotor forward and backward along the length of the stator. The rotor is often manufactured as a carriage that attaches to the load. To provide further flexibility, the specifications of linear motors can be tailored for different purposes, such as providing thrust force or offering accurate positioning. Linear motors are most often used in direct drive applications that need high speed and accuracy. They have fewer moving parts, meaning that they are very reliable. However, the amount of force they can generate is limited by the strength of the magnetic field in the stator, making them less useful than a linear actuator for applications that require a lot of force. A second type of linear motor design that has been growing in popularity recently is the tubular linear motor. Here, disc-shaped permanent magnets are embedded in a long tube, with the stator electromagnetic windings arranged Figure 1: Changing rotational torque to linear motion can be as easy as adding a ball screw. The motor turns the screw, moving the nut and the load it carries. (Source: "dizfoto1973/stock.adobe.com") Figure 2: A linear motor is basically an unrolled version of a traditional motor. (Source: Wikipedia/Schnibbi678, Linearmotorprinzip, CC BY-SA 3.0)