13 May 2016

2.77 PUPDate! (PUPS 10 Part 2)

What a ride this class has been! Almost done!

In the last PUPDate, it's made obvious that everything works to some extent.
But how well does it work? What didn't exactly work? What would I change in a second iteration? 

I tested the axis positioning repeatability and backlash to validate the module's design. Because both the clamp and nut driver axes are based on the same design, and because most axes are hard to reach or to instrument (instrumentate?), I decided to test only the X- axis. 



Here, the FASBot consistently moved slightly under the 0.005" it was commanded to move, implying a systematic error. This is possibly due to rounding errors in the conversion from mm to inches in the grbl firmware, which add up after a few hundred steps. 

After moving left, I attempted to switch directions and move right in order to measure the axis backlash. I kept track of how many jog commands it took before it began to move again. The backlash is 0.025", just under 1/32". This is probably due to the exact locations of the tooth engagement and the series spring compression. I can probably use a stiffer spring with a longer stroke, or disassemble the axis and find the right combination of nut rotation that allows for the most spring compression and the least backash. 

The repeatability test had the FASBot continually moving its X-axis between 4 and 3 inches in order to move past the backlash hysteresis. The dial indicator was zeroed for the first data point reaching 4 inches. I measured each data point when the carriage stopped at 4 inches and manually entered it into MATLAB. 


3 Test Trials were conducted, with the FASBot being homed after each one. 


Tests 1 and 2 exhibit similar behavior, with the machine always reaching farther and farther away from the original position. Test 2 was the worst, with the FASBot moving further and further away from the zero'd position after each move. The maximum deviation was 0.035 inches, more than the axis backlash! I imagine this behavior can be attributed to the stepper motor skipping steps every time it moves, perhaps because it must overcome static frictional torque. If my axes are overconstrained, I can add a flexure to or machine the sides of one of my axis bushings in order to eliminate this overconstraint. 

Microstepping may have also been useful to prevent skipping steps due to motor vibration. I conducted these tests with full stepping, in order to maximize motor torque, but the sharp vibrations in the stepper motor during acceleration/deceleration could have been enough to cause it to skip steps. I could switch to half- or quarter-stepping and see if I can achieve smoother motion with no continuous deviation. All of the error can be eliminated using feedback control. 


The best repeatability was achieved in Test 3, with a maximum deviation of 0.0055 inches. Perhaps after all of the previous trials, the bearings had smoothed out and the static friction was decreased, or maybe I just got lucky with the motor vibrations. 

10 comments:

  1. This text is worth every attention. It's wonderful.
    www.Qcredit.pl

    ReplyDelete
  2. This article describes everything very well.

    ReplyDelete
  3. Latvia is considered to be a developed nation. The developmental stage of a nation is determined by a number of factors including, but not limited to, economic prosperity, life expectancy, income equality, and quality of life. As a developed nation, Latvia is able to provide its citizens with social services like public education, healthcare, and law enforcement. Citizens of developed nations enjoy a high standard of living and longer life expectancies than citizens of developing nations. Each year, Latvia exports around $12.67 billion and imports roughly $15.56 billion. http://www.confiduss.com/en/jurisdictions/latvia/economy/

    ReplyDelete
  4. Here, the FASBot consistently moved slightly under the 0.005" it was commanded to move, implying a systematic error. This is possibly due to rounding errors in the conversion from mm to inches in the grbl firmware, which add up after a few hundred steps. pakistani silk suits online , 2 piece suit for ladies

    ReplyDelete
  5. Dear Sir / Madam

    Do you need funds to start up your own business? Do you need loan to settle your debt or pay off your bills or start a nice business? Do you need funds to finance your project? We Offers guaranteed loan services of any amount and to any part of the world for (Individuals, Companies, Realtor and Corporate Bodies) interest rate of 2% within 1 year to 50 years repayment duration period to any part of the world. We give out loans within the range of $1,000 to $100,000,000 USD. Our loans are well insured for maximum security is our priority.

    For application and more information send replies to the following

    Lender's Name: Scott Tucker
    Lender's Email: scotttuckerloanfund@gmail.com
    What app Number: +16182279611

    ReplyDelete
  6. Thanks for sharing this information if you want to read about top mba schools in canadathen do please visit our blog.

    ReplyDelete
  7. For my approval for foreign tour i was requires best Livescan Fingerprinting Frederick, Maryland near me and the ABUZZ FINGERPRINT SERVICES, LLC provides live fingerprint scanning services .Live Scan is an inkless, electronic means of capturing fingerprints in a digitized format .

    ReplyDelete
  8. We use Connectwise Manage every day. We use it to enter everything we do, from project plans to password resets. We also use it to create quotations. It helps us manage our daily schedule using built-in and customizable workflow.

    ReplyDelete
  9. Attention Everybody, I am Colin Byrne by names, from United States. I want use this medium to say a special thanks to this awesome company who made it possible for me to improve my business. I was stuck in a financial crisis and i needed to refinance my business, i tried seeking loans from various loan firms both private and corporate but never with success and most banks declined my credit, until i met this company pennymac financial Services who helped me out with a loan sum of ($570,000) without any stress i truly want to thank Mr penny mac who made it possible and helped me through and ensure i got my loan. So i want use this means to advise everyone out there searching for a loan that if you must contact any firm with reference securing a loan with low interest rate and better repayment schedule to contact Mr pennymac at (pennymacfinancialservice0147@gmail.com)or what-app number; +16182279611 . for a fast, safe and easy loan today...

    ReplyDelete
  10. I am so delighted I found your weblog, I really found you by accident,
    while I was researching on Bing for something else, Regardless I am here now and would just I saw this FAKE UK DRIVING LICENCE THAT WORKS FROM THE DVLA an will like to say thank you. (I also love the theme/design), I don’t have time to go through it all at the minute but I have bookmarked it and also added your RSS feeds, so when I have time I will be back to read a lot more, Please do keep up the excellent job.

    Y’all don’t forget to join this DVLA EXPERTS TELEGRAM GROUP for more information about new drivers license and updated materials being used along the production process of the DL . You can also take advantage to learn and meet many Experts who will guide you on numerous techniques for anyone who love hacking and don’t know how to go about it .

    ReplyDelete