Issue link: https://resources.mouser.com/i/1525523
29 | along the inside of the tube. This type of design can provide both high speed and high force. Tubular linear motors are highly efficient because the force generated by permanent magnets and stator coils is perpendicular to the magnetic field and the current. Both linear actuators and linear motors are more precise, efficient, and versatile than hydraulic and pneumatic methods of providing linear motion. As applications for linear motion become more sophisticated and demanding, these advantages are increasingly important. They also tend to be safer and more environmentally friendly because they don't rely on high-pressure gas or liquid. There are still some niche cases where both pneumatic and hydraulic linear motion methods can find a role; for example, pneumatics are often installed in hazardous and flammable areas as air is less of a danger than electricity or liquids, and hydraulic linear actuators are ideal for applications that require simultaneous high force and high speed. Positioning Motors can also be deployed in applications that require highly precise positioning, such as pick-and-place machines, printers, robotics, and power tools. Traditional motor designs can be used for positioning applications, but their accuracy is typically not as good as motors designed for that purpose. In addition to the positional linear motor design previously mentioned, two other types of motors are widely used for positional applications: stepper motors and servo motors. Stepper Motors Stepper motors are an adaptation of the motors highlighted in previous articles in this series but are specifically designed for positional precision. They are most often based on BLDC motors, variable reluctance motors, and hybrid synchronous motors. These motors can be effective positioning devices, but their accuracy depends on the quality of the angular sensor used. Stepper motors are designed to have maximum holding torque, while traditional motor designs target continuous motion. To get that maximum holding torque, the stator's electromagnets have windings with additional turns that provide a stronger magnetic field. That stronger magnetic field has the drawback of generating more back-EMF, meaning that the maximum speed of the design is reduced. The windings are always supplied with maximum current, no matter the load, which generates heat. Stepper motors must usually be specially designed to ensure that the excess heat does not cause demagnetization of the magnets in the rotor. The other main physical difference between the stepper motor and BLDC motor designs is that the stepper motor has more poles on the rotor (Figure 3). The larger the number of poles, the more steps the motor can take in one 360° rotation. This usually ranges from twelve steps of 30° up to 200 steps of 1.8°. However, the trade- offs are that the motor becomes more expensive as the number of poles increases, the amount of available torque decreases, and stepper motor torque inherently tails off at higher speeds. In theory, as the controller always knows the position of the rotor, no feedback loop is required, and the stepper motor can be operated as an open-loop system. However, Figure 3: The exploded view of a stepper motor shows many poles on the rotor, allowing the motor to be used for more accurate positioning. (Source: "Madalin/stock.adobe.com")