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    Discussion in 'The main mechanical design forum' started by Alborz_h87, Mar 28, 2012.

    1. Alborz_h87

      Alborz_h87 New Member

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      Hi,
      Linear Electromechanical actuators in which ball/roller screws are used can be categorized to the following categories:
      Type1-Rotating nut and moving screw
      Type2-Moving Nut and rotating screw
      Does any one know what is(are) exactly the difference(s) between above designs?
      I just know Type2 is faster with higher acceleration but I don't know why!
      Please give me reference..
      Thanks
       
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    3. Ramana Rao

      Ramana Rao Well-Known Member

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      Taking the momentum into consideration, acceleration depends on the mass of the moving body ( momentum = mass x acceleration). Now nut is the lighter of the two, and so it can move with higher acceleration.
       
    4. Robodavo

      Robodavo New Member

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      I'm not sure that your descriptions are quite accurate but there are two methods of using a Ballscrew.
      1. Mounting the screw in fixed mounts and then spinning a balanced nut in thrust bearings on the carriage. This is the fastest method.
      2. Fixing the nut to the carriage and mounting the screw in bearings. This is slower because the screw will start to whip and shake under high RPM. This is especially true when using a long screw.
       
    5. annalisexuereb

      annalisexuereb New Member

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      Hi,
      I am trying to design a Synchronous PM linear machine but do not know from where to start. The only known parameters are the required power and the maximum distance that the translator can move. Can anyone guide me on how to proceed please?
      Thanks
      Annalise
       
    6. kuldeep

      kuldeep New Member

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      Hi, i am also involved in a similar design. Rotating shaft and translating Nut seems to be a better option as the shaft can be supported at both ends and thrust bearing design on one shaft end is easier (SKF readily offers such flanged bearing ends).

      Whereas on the other hand, rotating follower and translating shaft can be little tricky design, shaft support is a concern is little axial loads are there.
      I feel based on your particular application call, you can choose between the 2 operational layouts.
      CHk this out - http://www.ejsong.com/mdme/memmods/MEM30009A/lifting_systems/lifting_systems.html
       
    7. kuldeep

      kuldeep New Member

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      This may not be entirely true, in this case the shaft is rotating then its rotational inertia will come into picture, which will add to torque requirement on motor, the longer the shaft, the J will add and also the stiffness of shaft will come into picture its its for high speed precision positioing system.
       

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