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  • Destiny
    Destiny

    Member • Dec 10, 2008

    Precise motion

    Hello everybody!

    Im new here, but I read the forum for a while now and since I need some extra ideas I decided to ask for your help.

    English is not my native language so this might be slightly hard to explain. I will try though 😀

    I am looking for all different ways of 'creating' motion that are currently avaiable. Ideally they are capable of running from dc power supply as the device that will be used in is suppose to be portable/hand held.
    The end motion ideally will be a precise (controlled by pressure exerted) vertical motion in down direction and then the motion upwards to go back to the start position.
    The distance of travel is very small - we are really talking about couple of cm maximum.

    What I was thinking of for a start was:
    - stepping motor linked with a gear mechanism
    - stepping motor to provide screw-in/out motion
    - electromagnets?
    - LVDT?

    The key factor is power and life time - it would be no good if it worked once and you would have to recharge/change battery.

    Just throw any ideas you might think of.
    Thanks in advance!


    If you need more explanations just ask. I will try to clarify that as much as possible.
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  • flash319

    Member • Dec 20, 2008

    I think you are on the right track for accuracy. Your key will be feedback to the system. If you use a stepper motor you will be limited to the steps that it can take. This must be considered. You will have to match your resolution of feedback to the capabillity of the motor or drive system. If you couple a high step (micro stepping motor) to a ball screw with a very high resolution optical scale you will have a very accurate device. A linear optical scale (used in CNC tables) will give .0001 of an inch if you spend enough money.
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  • Destiny

    Member • Dec 21, 2008

    Hey flash319!

    Thanks for an answer.
    I nearly thought I will get no answers at all...

    Anyway, things moved slightly further and I now know that the movement will not be more than 10mm, but not less than 5mm.
    The type of precision you suggested, flash, though is far too much.
    The whole 'system' will look similar to this:

    -lowering down, until feedback of pressure exerted onto the flat surface haven't reached our limit (couple of psi max)
    - keep it there for a certain period of time
    - take it back up at a constant rate to the start position.

    I found some linear stepper motors as well as servos used in rc models but I am not sure about their power capabilities. The weight that might be required to 'move' shouldn't exceed 500g.

    I was also thinking about memory wires yet I can see some problems with controlling them, as well as maintaining constant speeds...

    Any more comments are welcome!
    Thanks!
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  • flash319

    Member • Dec 21, 2008

    Sounds like you are more interested in rate then precision. A stepper motor with a microstepping drive will do what you want. You can set the step rate to whatever you want. You can also set acceleration and deceleration curves. Some drives will give you current feedback and through this you can figure out how much pressure you are applying as well. AC servo motors are better at that task but are more expensive and complicated to get working.

    Since you are moving such a small amount you may be able to find a linear motor that will do what you want. This all depends on how large the setup is going to be.
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  • Destiny

    Member • Dec 21, 2008

    Thanks!

    The only problem is that I cant use AC motors... since the whole thing needs to be portable and I want to use batteries to power it. Recharchables, standard alkaline or something else.

    Setup shouldnt be any bigger than lets say... a 14V power drill, without the handle...
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  • flash319

    Member • Dec 21, 2008

    I would say that you can probably just take a printer apart and you will have everything that you need. The drive for the print head will be running on a stepper motor and you will also have the drive screw. You may be able to use the control as well. Just write some code into a PIC to make it do what you want. A PIC can also do the stepping for you.😁
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  • Destiny

    Member • Dec 21, 2008

    Yeah I know about pics. Useful little things 😉
    I'll check the printer though 😀 good idea 😀 thanks!
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