Motors and drives are where the action is. They convert electrical power into the torque and speed necessary to keep industry turning. The editors of Motion System Design conducted a survey among industry experts, asking for their feedback and analysis. Here are their responses, which we hope you’ll find useful.

Challenges

When using motors and drives, what applications present the most challenges in terms of machine productivity and why?

JOHN/BALDOR: In any application, the greatest challenge comes when the system integrator, designer, or user must select the best motor technology. After doing this, probably the most challenging applications are when the user tries to cut corners. Too many compromises in performance or repeatability are the result. This may lead to disappointing machine performance and productivity. In short, results of compromises from shortcuts must be understood. Communication and clearly defined expectations are a must.

MAX/LEESON: The motor and drive applications that present the most challenges in terms of machine productivity are those in washdown environments in the food processing industry. Productivity in this industry depends on the up-time of the machines. Because an electric motor is frequently the prime mover for a machine, a rugged and reliable motor is required to ensure maximum up-time. In a food-processing washdown environment, all equipment — including the motor — is frequently exposed to harsh chemicals such as bleach, caustics, acids, and surfactants. If not properly excluded, these chemicals can penetrate the motor and damage internal components. Eventually, the motor will fail.

DOUGLAS/BOSCH REXROTH: Machines that require high accuracy, high force and high speed simultaneously, such as grinding machines or large mold-making machines, can be very challenging. You can always use a ball screw to achieve high force, but you will be limited by the speed. Therefore, linear motors are a perfect solution for these types of applications.

CHRIS/DANAHER: The most challenging applications are generally those requiring extremely high levels of accuracy and throughput at high operational speeds. Challenges stem not so much from the motor-drive design, but rather from the design engineer’s need for an exact solution without added lead-time or cost.

Pitfalls

What are the worst cases of improper design and implementation you’ve seen?

CHRIS/DANAHER: Coupling high-performance motion components to a load with ordinary gearboxes, compliant couplings, or even belts, is quite common and easily preventable. These arrangements defeat the purpose of utilizing high-performance components and can create significant control issues.

• Another problem, which can be difficult to diagnose, is using moderate or low-quality cables between the drive and motor. Time and again, these lower-quality cables are responsible for intermittent electrical noise issues that have a significant negative impact on system operation. It simply doesn’t make sense to have high performance motion components connected with cables that are not up to the task.

• A third common error is not matching motors and drives, which results in low performance, overheating, or both. The drive should be specified along with a motor.

• A fourth common error is utilizing inappropriate feedback devices. Using the wrong feedback device keeps the system from operating at its intended level of performance.

DOUGLAS/BOSCH REXROTH: Improper sizing of a linear motor is, by far, the most improper implementation that we have seen. With a rotary motor, you can typically up-size your motor, add a gearbox or modify gearing to overcome inertia mismatches. This is not possible with linear motors; they are an integral part of the machine.

MAX/LEESON: The worst cases of improper design and implementation occur when the wrong motor is selected for the application. For instance, a generalpurpose motor is much less expensive than a washdownduty motor — this is especially true of stainless steel motors. However, general-purpose motors will last days or weeks in a washdown environment, whereas a washdown-duty motor will last months or years.

Best Practices

Describe best practices in designing with motors and drives.

DOUGLAS/BOSCH REXROTH: Proper sizing of both motor and drive is key. For the motor, you want to make sure that the inertia of the motor is equal to the load inertia. Too high load inertia can lead to lost control, and if the motor inertia is too high, you can waste energy just to accelerate the motor.

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