General Motion Control

Choosing the best motion control solution

Author: Bob Parente | January 4, 2011

Our last posting asked: What are the criteria for choosing the best motion control solution?

I think the first test is price and performance, or what are the least expensive motor and control that meet the application’s requirement?

I believe the following list defines the least expensive to the most expensive motor technologies:

  • AC Motors with no control. (Line driven.)
  • DC Motors and controls
  • AC Motors and controls
  • Brushless motors and controls
  • Stepper motors and controls
  • Servo motors and controls
  • Direct drives and controls

All of the above motor systems have a motor shaft, or at least a mounting surface, that rotates. Remember we’re not going to deal with linear motors.
To choose the best solution we have to ask some additional questions:

What do you want the motor shaft to do?
I remember asking customers this question and getting a “Duh! I want it to rotate.”
And I’d follow up with:

  • It can Rotate:
    • Clockwise
    • Counter clockwise
    • Fast
    • Slow
    • At a constant speed
    • A variable speed or just multiple speeds
    • Have controlled acceleration
    • Have controlled deceleration
    • Stop in any position
    • Stop in an exact position
    • Hold it’s position when stopped
    • Be able to do many starts and stops
    • Have high or low starting toque
    • Have high or low running torque

This long list of things a shaft could do usually elicited a “surprised” response, some not printable here. But you can see the customer needs to know what their application requires.

We can move on to more questions, once the shaft requirements are defined

What environment does the motor operate in?

  • Indoors
  • Outdoors
  • Wet
  • Wind blown rain
  • Wash down
  • Food grade
  • Dry
  • Cold
  • Hot
  • High altitude
  • Vacuum
  • Mounting orientation
  • Dusty environment
  • Chemical environment
  • Explosive environment

Did you think you’d see 15 environmental issues? Can you think of more?
How about:

  • Physical size
  • Mounting style
    • Foot mount
    • NEMA face/size
    • Integrated motor system
  • Motor type
    • Totally Enclosed Non Ventilated (TENV)
    • Totally Enclosed Fan Cooled (TEFC)
    • Totally Enclosed Air Over (TEAO)
    • Open Drip Proof (ODP)
    • NEMA

Next on our question list is:
What is the motor or control’s power source?

  • Single phase. 120, 240 VAC, 50 and/or 60 Hz.
  • Three phase. 208, 277, 460 VAC, 50 and/or 60 Hz.
  • Battery power, voltage and current
  • DC power supply, voltage and current.

Let’s go back to our fan application and assume some of the application requirements as if it’s going to be used on a pedestal fan in a home or office environment:

  • The motor only needs to spin its shaft in the clockwise direction. It’s blowing air not exhausting it. Plus we could always turn the fan around and have it blow in the opposite direction.
  • We don’t need and infinite number of speeds, so we don’t need a speed control. Unless the speed control saves us money. Three speeds (low, medium, high) in this application will work well.
  • We don’t care if the motor accels or decels in a particular time frame or stops in an exact position.
  • It should hold its set speed reasonably well once it reaches it. (What is reasonably well, +/- 5%, 10 %?)
  • It’s going to operate indoors in a home or office type environment. Fans don’t work well in a vacuum, even though some people think that their office operates in one.
  • It or its control is going to operate from a 120 VAC, 60 Hz line.

Do we have enough information to make a choice?

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