Views: 10 Author: Site Editor Publish Time: 2019-04-24 Origin: Site
In constant speed applications, the fan motor typically runs at an approximate speed with little or no concern for acceleration and deceleration ramps. This type of application typically runs with cross-wire on/off control. Control circuits typically consist of branch circuits with contactor fuses, overloaded industrial motor starters and manual motor controllers or soft starters.
Both AC and DC motors are suitable for constant speed applications. DC motors provide full torque at zero speed and have a large installed base. AC motors are also a good choice because they have a high power factor and require little maintenance. In contrast, the high performance characteristics of a servo or stepper motor would be considered overkill for simple applications.
Variable speed applications often require strict speed and speed changes and defined acceleration and deceleration ramps. Slowing down industrial motors in applications, such as fans and centrifugal pumps, often increases efficiency by matching the power drawn by the load rather than running at full speed and throttling or suppressing the output. These are very important considerations for conveying applications such as bottling lines.
Both AC and DC motors with appropriate drives are suitable for variable speed applications. DC motors and drive configurations have long been the only variable speed motor options, and components have been developed and proven. Even now, DC motors are still popular in variable speed, low power applications and are useful in low speed applications because they can provide full torque at low speeds and constant torque over a wide range of industrial motor speeds.
Maintenance can be an issue with DC motors, however, as many require brushes for commutation, and they wear out from contact with moving parts. Brushless DC motors eliminate this problem, but they have a higher upfront cost and a smaller range of industrial motors available.
Brush wear is not an issue with AC induction motors, and variable frequency drives (VFDs) provide a useful option for applications over 1 hp, such as fans and pumping applications, increasing efficiency. Choosing the type of drive used to run an industrial motor can add some position awareness. An encoder can be added to the motor if the application requires it, and the drive can be specified to use encoder feedback. So this setup can provide servo-like speed.
Tight position control is achieved by continuously verifying the position of the motor as it moves. Applications such as positioning linear actuators can use stepper motors with or without feedback or servo motors with inherent feedback.
Steppers are designed to move exactly to a position at moderate speeds and then hold that position. When properly sized, an open-loop stepper system can provide powerful position control. While there is no feedback, the stepper will move the exact number of steps unless interrupted by a load that exceeds its capacity. As the speed and dynamics of the application increase, open-loop stepper control may not meet the system requirements, which requires an upgrade to a stepper or servo motor system with feedback.
The closed-loop system provides accurate, high-speed motion profiles and precise position control. Compared to steppers, servos will provide higher torque at high speeds, and they also work better in high dynamic loads or complex motion applications.
For high performance motion with low position overshoot, the reflected load inertia should match the servo motor inertia as closely as possible. In some applications, a mismatch of up to 10:1 can be sufficient, but a 1:1 match is optimal. Gear reduction is an excellent solution to the inertia mismatch problem because the reflected load inertia decreases as the square of the gear ratio, but the gearbox inertia must be included in the calculation.
Manufacturers offer a variety of motor options for industrial applications. Stepper, servo, AC and DC motors can meet most industrial automation requirements, but the ideal motor depends on the application. Whether it is a constant speed, variable speed or position control application, the user should work closely with the motor and push the supplier to select the right motor for the application.
By focusing on these key criteria, you will be able to quickly narrow your search and speed up the process of selecting a motor for your application. Even with this knowledge, choosing the right product mix for your application can be complicated. If you are not sure what product you need, please consult our experts for details, please contact us at email@example.com.