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448RE: [diy_3d_printing_and_fabrication] Re: Your thoughts please

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  • Boman33
    Mar 10, 2009
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      Hi Snow,

      I think it is extremely critical to keep the moving printer assembly’s weight to a minimum.  Here is why:

      All the printer normally has to do between each new line is to return the head (no change from normal operation) and move the paper ahead by the required distance.  The mass of the paper is extremely low, about 5 grams, so it takes very little force to accelerate it and then to stop at the new position.  The weight of the printer assembly is hundreds of times more so either it will be very slow or a lot of force will be required to move it quickly.  That translates to having a very rigid assembly and damping out lots of vibrations.   

       

      So my thought is to strip the carriage down to a minimum and leave all possible weight stationary.

       

      That brings us to you “toner” dispenser.  It is added weight to accelerate and stop for each line and it will easily create ripples in the deposited powder.  The engineering process and design requirements would be so much simpler if you let the cartridge follow (or lead) the carriage assembly separately and have a simple motor drive for constant speed.  Yes, an extra motor and a little electronics but the powder dispensing would be a smooth continuous operation for best quality and the carriage assembly weight would be much lower.

       

      As I mentioned earlier, also remember to apply the drive force on the carriage on its mass center point or symmetrically around that point to avoid rocking /twisting forces.

      Bertho

       

      From: snowmackenzie      Sent: Tuesday, March 10, 2009 04:38
      Hi Kevin
      It is in the files under Snow's Project.

      The printer that i'm using is a A3 one. It has ordernery Motor (Maybe Servos) with encoder feedback on both (I bet that will be a issue later). As the carriage assy is getting heavy i have to uprate the motor size and electronic drive as well.
      I was looking at using a Geko drive do do this as i have some. But i could also build one myself.
      The issue with this is i have to check to see how the HP printer works. Hopefully it detects the Y position (paperFeed) before it in gauges the X motor (Printer carriage). If it does then i can program a chip to to the ramping up/down PWM on a Tan cerve error rate difference. EG it add the pulses comming in and the encoder minuses the count of the comming in pulses. This them gives me a error figure to pass into a Tan logratham to set up the PWM that drives the Y motor.But from playing around with the geko drive I'm pretty sure it does something simular (Famous last words). But it all hinges on HP electronics that it waits so the paper to be in position before it starts the carriage....
      Thanks
      Snow

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