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Choice of motor - application query

simonturner83
Hi

I am currently working on a design concept for a motion system - I would be very grateful for any advice that could be given on a suitable type of motor for the application (e.g. servo, stepper, DC motor etc.).
 The related requirements for the motion system are as follows:
  1. Rotate a cylindrical object placed on its side on friction rollers to allow inspection, where rotation occurs around the axial axis as per test tube rollers or pipe weld rollers.
    1. Details of the cylindrical object:
      1. It is unattached to the rollers, i.e. placed on for rotation / inspection then removed.

    2. Can weigh up to 20kg.



  • The cylindrical object is required to rotate at a very slow speed, typically 1rpm and lower, where the upper limit is likely to be in the region of 15rpm. The friction rollers on the motion system will be in the region of 1/10 to 1/20 of the circumference of the cylindrical object.

  • The rotation of the cylindrical object is required to be significantly consistent, i.e. smooth rotation with minimal stepping / juddering.

  • The motion  profile is likely to just be one full rotation of the cylindrical object at a fixed speed, but there may be a requirement to perform the rotation in increments with pauses in between (i.e. one full rotation split into 6x moves). The duty will be low, i.e. 5-10 such operations per day.

  • Allow some basic position/speed control, where closed-loop is preferable.

Many thanks.



  • 0
    How many are you going to make? Let's assume it is one, then you need the easiest to get working. If it is millions then you go for the cheapest to manufacture. For 1 off the easiest is probably a stepper motor with a reduction belt so that the step size is too small to detect. For millions, it is probably a servo controlled DC motor, exactly sized to accelerate the load as needed but no bigger. A stepper gives easy position and speed control, but is fairly expensive.


    I hope that helps, it's all very debatable, I assume this is a college project?
  • 0
    So you want to turn something, slowly, smoothly,  and possibly steppily.

    How much torque, how much inertia, and how much accuracy do you need on the angular positioning ? You may need clutching or brakes if there is a requirement to come to a dead stop at a known angle from rapid motion.

    You are probably correct to think in terms of electricity as your preferred prime mover, but if you had said it was a missile and weighed tonnes I'd suggest you consider hydraulics with the oil controlled by solenoids.  I still might if the diameter is very large.

    Stepper motors are good for small controlled angles of rotation, as you can literally count the clicks, but be aware of starting and break-away torque limits, so you have a top speed limit and load limit to consider as well as a low starting torque

    You may servo any kind of motor on either shaft speed or angular position (and this can be very good - open a roller ball mouse to see how it can be done very precisely indeed) DC motors are easier to arrange if you have a wide speed range, for low speeds inverters and induction motors are probably not precise enough, some geared or belt driven reduction may well be needed.


    If it really is test tubes, then buy something from Festo or Rockwell, no need to design these days for any problem that has already been solved.
  • 0
    simonturner83:

    Hi

    I am currently working on a design concept for a motion system - I would be very grateful for any advice that could be given on a suitable type of motor for the application (e.g. servo, stepper, DC motor etc.).
     The related requirements for the motion system are as follows:
    1. Rotate a cylindrical object placed on its side on friction rollers to allow inspection, where rotation occurs around the axial axis as per test tube rollers or pipe weld rollers.
      1. Details of the cylindrical object:
        1. It is unattached to the rollers, i.e. placed on for rotation / inspection then removed.

      2. Can weigh up to 20kg.



    • The cylindrical object is required to rotate at a very slow speed, typically 1rpm and lower, where the upper limit is likely to be in the region of 15rpm. The friction rollers on the motion system will be in the region of 1/10 to 1/20 of the circumference of the cylindrical object.

    • The rotation of the cylindrical object is required to be significantly consistent, i.e. smooth rotation with minimal stepping / juddering.

    • The motion  profile is likely to just be one full rotation of the cylindrical object at a fixed speed, but there may be a requirement to perform the rotation in increments with pauses in between (i.e. one full rotation split into 6x moves). The duty will be low, i.e. 5-10 such operations per day.

    • Allow some basic position/speed control, where closed-loop is preferable.

    Many thanks.



     


    A geared down hand cranked system is simplest and best. No electricity required and very reliable. Rotate some rubber covered rollers at slow speed to grip and rotate the work being inspected. Similar to the old fashioned washing mangle.

    you tube old washing mangle - Bing video


    Z.


  • 0
    A geared DC motor would do the job.  They can be bought off-the-shelf.  An optical rotary encoder attached to one of the drums would tell you how far it has turned.  Use a little microcontroller to read the encoder, and turn the motor on and off.  Use PWM if you need to control the speed.
  • 0
    The load weighs 20kg people. He is after an electrical solution. Not a problem for steppers, take my CNC lathe which has them and you wouldn't want to try to stop them! If you want a closed loop for steppers this is not a problem and not difficult to implement, but you will need a high-resolution position sensor ie. a shaft encoder. Stepper motors are a very good solution for accurate positioning and are much less complex than full servo implementations, and do not have many of the snags such as needing full data on the load inertia, stability calculations, zero drift, integral or differential control etc. They are more expensive for higher power and large quantities, but I already said that above. 3,4&5 above become fairly trivial, which is not true of a conventional full servo. The trick which you need to know is called micro-stepping. Digital is generally better and easier!
  • 0
    How about the load inertia Simon?
  • 0
    davezawadi (David Stone):

    The load weighs 20kg people. He is after an electrical solution. 


     



    1. The motion  profile is likely to just be one full rotation of the cylindrical object at a fixed speed, but there may be a requirement to perform the rotation in increments with pauses in between (i.e. one full rotation split into 6x moves). The duty will be low, i.e. 5-10 such operations per day.



    Why electrical? The thing will only get very occasional use and is for inspection of a cylinder. Just turn it by hand.


    Z.


  • 0
    It also makes a big difference to the inertia if it is a thin shell at large diameter like an empty  hot water tank, or long thin and sold like a 10m length of rebar.
  • 0
    simonturner83:

    Hi

    I am currently working on a design concept for a motion system - I would be very grateful for any advice that could be given on a suitable type of motor for the application (e.g. servo, stepper, DC motor etc.).
     The related requirements for the motion system are as follows:
    1. Rotate a cylindrical object placed on its side on friction rollers to allow inspection, where rotation occurs around the axial axis as per test tube rollers or pipe weld rollers.
      1. Details of the cylindrical object:
        1. It is unattached to the rollers, i.e. placed on for rotation / inspection then removed.

      2. Can weigh up to 20kg.



    • The cylindrical object is required to rotate at a very slow speed, typically 1rpm and lower, where the upper limit is likely to be in the region of 15rpm. The friction rollers on the motion system will be in the region of 1/10 to 1/20 of the circumference of the cylindrical object.

    • The rotation of the cylindrical object is required to be significantly consistent, i.e. smooth rotation with minimal stepping / juddering.

    • The motion  profile is likely to just be one full rotation of the cylindrical object at a fixed speed, but there may be a requirement to perform the rotation in increments with pauses in between (i.e. one full rotation split into 6x moves). The duty will be low, i.e. 5-10 such operations per day.

    • Allow some basic position/speed control, where closed-loop is preferable.

    Many thanks.



    A search online for industrial rotators will give you some ideas.


    Z.


     


  • 0
    These items already exist and are quite inexpensive.

    Motorized Screw Adjustable Welding Rotator - Buy Hot Selling Creditable Rotators Welding Manufacturers,Best Selling Turning Roller Frame For Welding In Industrial Pipe Welding Rotator,High Quality New Rotator Welding Turning Rolls Product on Alibaba.com


    Z.

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