Understanding the main types of loads, motors, and applications can help simplify the selection of industrial motors and accessories. There are many aspects to consider when choosing an industrial motor, such as application, operation, mechanical and environmental issues. Generally speaking, you can choose AC motors, DC motors or servo/stepping motors. Knowing which one to use depends on the industrial application and whether there are any special needs. Depending on the type of load the motor drives, industrial motors require a constant or variable torque and horsepower. The size of the load, the required speed and acceleration/deceleration—especially when the speed is fast and/or frequent—will determine the required torque and horsepower. It is also necessary to consider the requirements for controlling the speed and position of the motor.

There are four types of industrial automation motor loads:

1. Adjustable horsepower and constant torque: Variable horsepower and constant torque applications include conveyors, cranes and gear pumps. In these applications, the torque is constant because the load does not change. The horsepower required may vary depending on the application, which makes constant speed AC and DC motors a good choice.

2. Variable torque and constant horsepower: An example of the application of variable torque and constant horsepower is machine rewinding paper. The speed of the material remains the same, which means that the horsepower will not change. However, as the diameter of the roll increases, the load changes. In small systems, this is a good application for DC motors or servo motors. Regenerative power is also an issue worthy of attention, which should be considered when determining the size of an industrial motor or selecting an energy control method. AC motors and encoders, closed-loop control, and full-quadrant drives may benefit larger systems.

3. Adjustable horsepower and torque: fans, centrifugal pumps and agitators require variable horsepower and torque. As the speed of industrial motors increases, the load output also increases as the required horsepower and torque increase. These types of loads are the beginning of the discussion of motor efficiency. Inverter loads AC motors use variable speed drives (VSDs).

4. Position control or torque control: Applications like linear drives require precise movement to multiple positions, tight position or torque control, and often require feedback to verify the correct motor position. Servo motors or stepper motors are the best choice for these applications, but DC motors with feedback or inverter-loaded AC motors with encoders are usually used in steel or paper production lines and similar applications.

Different types of industrial motors

Although there are more than 36 types of AC/DC motors used in industrial applications. Although there are many types of motors, there is a large amount of overlap in industrial applications, and the market has pushed to simplify the choice of motors. This reduces the actual selection of motors in most applications. The six most common motor types, suitable for most applications, are brushless and brushed DC motors, AC squirrel cage and winding rotor motors, servo and stepper motors. These motor types are suitable for most applications, while other types are only used for special applications.

Three main types of industrial motor applications

The three main applications of industrial motors are constant speed, variable speed, and position (or torque) control. Different industrial automation situations require different applications and problems as well as their own problem sets. For example, if the maximum speed is less than the reference speed of the motor, a gearbox is required. This also allows a smaller motor to run at a more efficient speed. Although there is a lot of information on how to determine the size of a motor, users must consider many factors because there are many details to consider. Calculating load inertia, torque and speed requires the user to understand the parameters, such as the total mass and size (radius) of the load, as well as friction, gearbox loss, and machine cycle. Load changes, acceleration or deceleration speed, and application duty cycle must also be considered, otherwise the industrial motor may overheat. AC induction motors are a popular choice for industrial rotary motion applications. After selecting the motor type and size, users also need to consider environmental factors and motor housing types, such as washing applications with open frames and stainless steel housings.

How to select industrial motors

Three main problems in the selection of industrial motors

1. Constant speed application?

In constant speed applications, the motor usually runs at an approximate speed, with little or no consideration of acceleration and deceleration ramps. This type of application usually runs with full-line on/off control. The control circuit usually consists of a branch circuit fuse with a contactor, an overload industrial motor starter and a manual motor controller or soft starter. Both AC and DC motors are suitable for constant speed applications. The DC motor provides full torque at zero speed and has a large installation base. AC motors are also a good choice because they have a high power factor and require very little maintenance. In contrast, the high-performance characteristics of a servo or stepper motor can be considered excessive for a simple application.

2. Variable speed app?

Variable speed applications usually require tight speed and speed changes, as well as defined acceleration and deceleration ramps. In practical applications, reducing the speed of industrial motors, such as fans and centrifugal pumps, usually improves efficiency through power consumption matching the load, rather than running at full speed and throttling or suppressing output. These are very important considerations for conveying applications, such as bottling lines. The combination of AC motor and VFD is widely used to improve efficiency and works well in various variable speed applications. Both AC and DC motors with appropriate drives work well in variable speed applications. For a long time, the DC motor and drive configuration have been the only choice for variable speed motors, and its components have also been developed and verified. Even now, DC motors are popular in variable speed and fractional horsepower applications, and are also useful in low-speed applications because they can provide full torque at low speeds and constant torque at various industrial motor speeds. However, the maintenance of DC motors is an issue that needs to be considered, because many motors require brushes for commutation and wear out due to contact with moving parts. Brushless DC motors eliminate this problem, but they are more expensive upfront and the range of available industrial motors is smaller. Brush wear is not a problem with AC induction motors, and variable frequency drives (VFD) provide a useful option for applications with more than 1 horsepower (such as fans and pumping) that can increase efficiency. Choosing the drive type to run industrial motors can add some position perception. If required by the application, an encoder can be added to the motor, and the drive can be designated to use encoder feedback. Therefore, this setting can provide a servo-like speed.

3. Do you need position control?

Tight position control is achieved by constantly verifying the position of the motor as it moves. Applications such as positioning linear drives can use stepper motors with or without feedback or servo motors with inherent feedback. The stepper accurately moves to a certain position at a moderate speed and then maintains that position. The open loop stepping system provides powerful position control, if the size is appropriate. When there is no feedback, the stepper will move the exact number of steps unless it encounters a load interruption beyond its capabilities. As the speed and dynamics of the application increase, the open-loop stepper control may not meet the requirements of the system, which requires an upgrade to a stepper or servo motor system with feedback. A closed loop system provides precise, high-speed motion profile and precise position control. Servo system provides higher torque than stepper at high speed, and can work better in high dynamic load or complex motion applications. For high-performance motion with low position overshoot, the reflected load inertia should match the servo motor inertia as much as possible. In some applications, a mismatch of up to 10:1 is sufficient, but a 1:1 match is optimal. Gear reduction is a good way to solve the problem of inertia mismatch, because the inertia of the reflected load is reduced by the square of the transmission ratio, but the inertia of the gearbox must be considered in the calculation.