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  • Elevator, concepts of drive needed + few more things.

    Discussion in 'The main mechanical design forum' started by MartinR, Nov 9, 2013.

    1. MartinR

      MartinR Member

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      Hello,

      I have a student task which contains study concepts of drive in elevator (electric engine). Concepts should include things like transmission gear, self-locking, auto inhibit, how to operate when is no electricity , etc.
      Could you please share your conception, especially transimision gear options (which one and why ?) + auto inhibit.

      What else should I consider designing elevator ?

      Thanks for reasonable answers ;)
       
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    3. Paul.R

      Paul.R Member

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      Designing an elevator drive is an energy management problem. The passengers are being moved from one energy state to another.
      In the case of lifting, the passenger is moved to a higher gravitational potential energy state - this takes energy.
      In the case of lowering, the passenger is moved to a lower state - this releases energy.
      The passenger is only able to absorb a certain amount of energy safely: if he accelerates or decelerates too quickly, he can be seriously injured or killed.

      As such, the design of an elevator drive needs to manage the energy required to lift and lower the passenger. Practically speaking, that means that the drive must be able to bring the elevator to a controlled stop whether it is going up or down. In practice:
      1. The motor size should be chosen based on the load capacity being lifted (i.e. design load X design overload factor).
      2. The motor brake and cables should be based on the absolute maximum capacity (i.e. if the elevator is overloaded and the motor cannot move the load, the motor brake and cables must be able to support the load safely).
      3. The motor drive must be sized appropriate to the motor and it must be capable of incorporating a brake resistor or some other way of dissipating the energy of a free-falling load so that it does not exceed a maximum velocity. This is really important: when an elevator is lowering a load, the motor is acting like a generator because the energy from the falling load is driving the rotation of the motor - that means the energy being generated has to go somewhere safe (i.e. heat, regenerative circuit, etc.) in order to control the descent of the elevator.
      4. Finally, in the event of a complete free-fall, some kind of mechanical means of stopping the load is needed (springs to absorb the energy of the falling load or something similar) - these should be designed to absorb the kinetic energy of a free falling load so that the passenger remains safe.

      Oh - and don't use worm gears as a load holding device: I've heard of a few instances/legal cases where after the initial wear-in period, the worm gear was not longer self-locking and passengers were seriously injured. Any device that involves mechanical wear (i.e. acme screw drive, worm gear) runs the risk of catastrophic failure once the load holding element wears to a critical threshold.

      Other things to take into account besides the drive are operator entrapment, safe conditions for opening and closing doors, overriding in event of emergency, etc.
       
    4. MartinR

      MartinR Member

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      I wonder about following things:

      - How elevator with drive other then counterweight is protected from free fall ?
      - How speed of drive is programmed ?
       
    5. Paul.R

      Paul.R Member

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      Programming the drive depends on the manufacturer of the drive. I would suggest researching drives for your application (some manufacturers you can look at would be ABB, Schneider, Emerson to name a few). Lower end drives may not have the ability to incorporate a braking resistor, so it is important to discuss with your supplier what the application is.

      Generally speaking, a VFD is used to control the speed of an AC motor by varying the frequency to the motor. If you plug an AC motor directly into the wall at 60Hz power without a drive - it will run at the rated speed on the motor. If you connect the motor to a VFD drive, you can now run the motor at a different frequency, which in turn will correspond to the motor speed. For example, if you set the VFD drive to run at 30Hz - the motor will run at half-speed.

      If you are going this route, please note that the motor must be 'inverter' capable - any old AC motor won't be suitable for the application. When selecting the motor, be sure to specify that you need an 'Inverter Duty' motor so that your supplier knows you will be running it off of a VFD.
       
    6. leocassim

      leocassim New Member

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      lets email;leocassim21@gmail.com
       

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