Help Design Motion Control

Discussion in 'The Projects Forum' started by Mopar_Mudder, Feb 14, 2014.

  1. Mopar_Mudder

    Thread Starter Member

    Mar 13, 2012
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    I am looking for help or someone that offers a service to design a contorl system. This is just a one time project to control automation system in my house.

    Here is just a quick idea of what I am trying to do. I can get more detailed if someone is willing to help me out on this.

    I have a Reversable AC gear motor that moves a trolley along a 6' long straight track, I need to control where the trolley goes by IR remote. It needs to stop at 7 different spots along the track that could be triggered maybe by a switch or something at each stop. It needs to remember where it is so when you tell it to go to another loaction it will know which way to travel to get their.

    Right now I am controlling it by way of a Hall Effect sensor on the gear motor. This does work but their are a couple of things making it not ideal. The accuracy is not the best do to the gear motor traveling slightly when power is cut. It isn't much, maybe 1/8" but that adds up over time to being way off. Other problem is that the trolley could be moved by hand and the Hall Effect doesn't know it moved so then it is really off.

    Thanks for any help. I know just enough to know how I want it to work and ideas of how to do it. But not enough to know exactly what components to use or how to program it.
     
  2. MaxHeadRoom

    Expert

    Jul 18, 2013
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    You could go to a motion controller, but this may be expensive and overkill for what is essentially a point-to-point system.
    Just by simply applying a electro-magnetic brake could solve the problem?
    In what you describe, I would have though that the error would not be accumulative due to being corrected a the next sensor?
    If you want to introduce some memory and logic, you could look at one of the Smart Relay systems?
    Max.
     
  3. inwo

    Well-Known Member

    Nov 7, 2013
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    Sound similar to a scroll sign project I once designed.

    Only ten stops, so I used a crude "upc" type bar system and an slotted optic interrupter to count the bars.

    It remembered where it was (pic), so it knew which direction to run.

    When it counted the right number pulses in a set time it knew where it was and continued to the next "stop" indicator. (longer bar)

    So the placement of the "position" bars was not critical.

    I believe that, depending on direction, it reversed and always approached "stop" from the same direction.

    Kind of funky for your situation.
    It could have a separate sensor system for each direction.
    Then it wouldn't "hunt".

    I also tried a system that went home each time and counted "stops" from home. But this sign was only used for updating prices and needed the exorcise. :D
     
  4. Mopar_Mudder

    Thread Starter Member

    Mar 13, 2012
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    What I have done is cannibalized the parts of a antenna rotor control to run my system. Which actually is perfect in that it is 1) controlled by remote 2) has programmable memories 3) has a reset function to find "0" again.

    Problem is that it doesn't track the movement of the motor when it is not actively going to another position. So if you tell it to go to position #1 it tracks until it gets their and cuts power, now when it rolls 1/8" past the mark it has no idea, it simply thinks it is at #1. Same thing you can go and move it by hand a couple of inches and it has no idea as it doesn't actively track the position when it is not running.

    I have thought about the putting on a brake. And actually their is a brake made for the back of my gear motor. But I am using that shaft on the back of the motor as the point to track with the Hall sensor. Also the brake that is made for it need power to apply it. I would rather have a brake that is always locked and needs power to release it.

    I will look up Smart Relays, thanks
     
  5. Mopar_Mudder

    Thread Starter Member

    Mar 13, 2012
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    I have thought about optic or magnetic strip control. I just though a simple switch at the stop points would give less chances of something going wrong or getting out of sync. I can't have it hunting no, that would be distracting.
     
  6. djsfantasi

    AAC Fanatic!

    Apr 11, 2010
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    Just some ideas.

    The idea generally is when it is commanded to move, it starts to travel to the destination via what it believes us the shortest route. Then, on the track is a pattern that can be read. The pattern contains bar code with location information.

    All bar codes have a start sequence, then a code for each position on the track, then calibration bars, followed by the location code and finishing with the start code IN REVERSE. This last specification results in the location only being valid in one direction, so that the trolley is looking for the calibration lines at the right time. It also implies that this start code is different from right to left and left to right.

    No matter where the trolley is located, it heads toward the destination via the shortest path it believes. Eventually it will encounter a start code. It will do two things. Count the lines in the calibration code to determine the actual destination position. And determine if the location is where it expects to be.

    If the location is correct, "Life Is Good".

    If the location is off, the trolley recalculates the shortest route to its destination and starts there. The destination has not changed, but the trolley is 100% sure of where it is. This time the procedure above should result in getting successfully to its destination.

    The idea more accurately identifies the locations along the track. And if it was manually moved, it allows for the trolley to self-correct it's travels.
     
    Last edited: Feb 14, 2014
  7. djsfantasi

    AAC Fanatic!

    Apr 11, 2010
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    Simple switches don't account for momentum or slippage. When building robots, we use steppers for more accurate control, or DC motors with encoders. This scheme is similar to the latter solution.

    I can understand that you don't want it to hunt. However, in the above scenario, it would hunt only if someone had manually moved the trolley. Don't let anyone do that
     
  8. inwo

    Well-Known Member

    Nov 7, 2013
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    Starting over and building a remote controlled positioning system is a huge job.

    If you tell us exactly what it is, maybe we could come up with short cuts.

    Can you control it more manually? If it's in sight you could have stop markers at each position.

    Then command it to "take two steps back" or "take one step forward", etc.

    That could really simplify.
     
  9. Mopar_Mudder

    Thread Starter Member

    Mar 13, 2012
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    It is a masking system for a theater screen. Basically a black fabric is rolled out in front of the screen to change the size of the screen and also cover the entire screen when not in use.

    It need so be controlled by remote so you can have it change the aspect ratio of the screen to fit the movie you are watching.

    Here is how it works. Masking is totally closed in front of the screen when you enter. Turning on the theater with an IR remote also sends a command to the masking system to open up to a 16:9 aspect ratio (this in normal TV ratio). When you start a movie you can push a button on the remote to adjust the size of the screen to preset aspect ratio's (1.33, 1.77, 1.85, 2.35, and 2.40). When you turn off the system a command it sent to close the masking all the way again.

    I do also have manual controls for it so I can open and close it with a button up by the screen, but that is not practical when watching a movie.

    I don't know if it would help or make it more complicated, but I could also tie this into the Windows PC that is in the theater. Could it be used to control the system some how?
     
  10. inwo

    Well-Known Member

    Nov 7, 2013
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    Thanks, I can't picture the mechanics.

    Horizontal or vertical?

    There is a curtain on each end that moves towards the middle to close?
    From the top down.

    Is the motor on the trolley or is the trolley moved by a cable?

    A picture would be helpful.
     
  11. Mopar_Mudder

    Thread Starter Member

    Mar 13, 2012
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    Here are some shots from the SketchUp model of it. I could take some video of it in action if it would help at all.
     
  12. MaxHeadRoom

    Expert

    Jul 18, 2013
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    The answer maybe to look for a stepper motor controller, I don't have the links, but there were a couple of projects out there that used a small programmer to plug in positions for a single axis controller, the advantage of a stepper is no limits are required and they hold position, even with no power there is some holding torque present.
    Max.
     
  13. Mopar_Mudder

    Thread Starter Member

    Mar 13, 2012
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    I would be open to that. I am assuming then I would need an entire new stepper motor correct?

    Has to be around 14 rpms and min of 70 in.lb. of torque.
     
  14. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    Is this a cable car with motor at a fixed location? If so it makes it more difficult for feedback from car. What is minimum non accumlitative stopping error- a little more than 1/8 in??
    I liked post # 6. With 1/8 in resolution, a 10 track binary coded strip & digital comparators on car would have absolute location and direction control. Maybe split between high @ low order bits, so speed could be reduced when high order was reached, then low order to stop on a dime.
     
  15. Mopar_Mudder

    Thread Starter Member

    Mar 13, 2012
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    Motor is fixed. If I can get it accurate to with in 1/4" I would be happy.

    Not sure how to slow the speed down. That would require another control to slow the gear motor down.
     
  16. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Should be no problem, you say you are using a G.B. anyway?
    What is the nature of the AC motor you have?
    Max.
     
  17. Mopar_Mudder

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    Mar 13, 2012
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  18. MaxHeadRoom

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    Jul 18, 2013
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    One problem with that motor it is a simple 1ph Induction motor, so you will not have any control over RPM or accurate positioning.
    Max.
     
  19. Mopar_Mudder

    Thread Starter Member

    Mar 13, 2012
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    That is what I figured
     
  20. bertz

    Member

    Nov 11, 2013
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    It seems to me that the solution to your problem is pretty straightforward and there is no need to re-invent the wheel.

    Step 1. Convert your electro-mechanical system to a DC servo motor with a rotary encoder. What does this accomplish? First it has gobs of torque; second, the encoder allows the system to "memorize" the locations where you want the mask to stop. If it overshoots, it will correct itself. If someone tries to move it, it will resist. DC servo motors can be a little pricey compared to AC gearmotors or (UGH) stepper motors, but you don't need to take out a second mortgage. Also, some good can be had on e-bay. As I said, there is no need to re-invent the wheel here. DC servo motors have been the basis for machine tool motion control for a long time.

    http://www.teknic.com/products/clea...=27793230486&gclid=COzU647zzLwCFSzNOgodvS8A_A

    Step 2. How to control this sucker. The motor is supplied with a control package which includes a thing we refer to as a "drive". Now most of the drives I have come across have either a 0-5 or 0-10 VDC control input for speed and a feedback loop using the encoder for position control. Typically we used to control these bad boys with a PLC, but we have used a windows based PC with a special "servo" card for control.

    http://www.automationtechnologiesin...axis-cnc-usb-card-mach3-200khz-breakout-board

    There is no reason why a PIC based microprocessor could not be interfaced with the USB servo card. Hardware and software could easily be incorporated to include an IR decoder based on the Sony SIRC protocol. Thus you could use any after market remote to control your system. Then all you have to do is program in your stops, and after a little trial and error your good to go.

    Good luck

    Al

    P.S. I don't do this anymore, I'm happily retired and more interested in catching fish and flying model helicopters.:D
     
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