Sprint Goal:
The machine can knit a small, multiple row sample.
After the lack of productivity in previous sprint, we decided to move to have sprint task distributed into have sprint intervals (aka one week tasks instead of two week tasks) .

Sprint 3a Goal: Each member of the team has made 1-2 improvements to the cam/needle system.
Sprint 3b Goal: Actuate stitches with yarn
Overview:
Needle bed and cam now play well together. Stitches can be hand actuated and will work as such. Sensor code now functional. Motor attachment slightly less janky, but not by much. Tensioner not working. Needles don't move out quite far enough to complete stitches automatically. Two-sided verge added to hold fabric in place during knitting.
Sprint Events (A):

Event: Website Redirect headed by Joe
  • ​We now have our official class URL! It's:
    poe.olin.edu/2015/grandmasfavorite
  • It features everything this site has and more! "What more could it possibly have?" you might ask. Well, the answer is simple: a redirect! That's right, that URL redirects directly to this website. One small step for us, one minuscule step for mankind.

Event: Encoder Strip Improvement headed by Claire
  • The old encoder was the black and white paper that the sensor used to figure out how far it had gone. We want a slightly more formal build, hopefully with a greater difference between the light and dark values to make thresholding easier.
  • The new encoder is black tape on an the clear acrylic bar
    • The clear acrylic has very little light reflection and as such as the "dark" strip. The black electrical tape strip is shiny and reflective and acts like the white or mirror like surface. Irony.
  • The difference between values is much greater. The new bar works very well

Event: Website Improvement headed by Claire
  • You may notice that a first attempt at a project overview page has been made. Not this will not be the final iteration of the page and it will change, likely without notification. In the future, the page with hopefully include a gif of stitch actuation, more description how knitting machines exist and how they function, and links our final post, cad files, BOM, and github account.

Task: Cam Support to be moderated by Claire
Bridges are attached over the channel of the linear cam to increase the stability of the cam. Bridges must be high enough to not block follower motion.
  • Originally the wood of the cam was unconstrained except at the edges. When the cam moved over the needles, the middle of the cam was able to be forced upward by the needles causing an downward force on the needles.
  • Metal flat braces were bent with plies and hot glued to nylon spacers. These formed the bridges over the needle slot in the cam to help stabilize it. It worked moderately well but needles still jam when the carriage moves in one direction
Task: Needle Bed to be moderated by Aubrey
10-needle bed of 0.25" acrylic. Needle bed constrains needles upright. Front of needles are constrained. Aluminum sheet cover contains appropriately sized slots that allow for off motion and
are constrained on the front.
  •  Aubrey and Sean laser cut several test beds with differing slot sizes to try to find a slot size that would allow for the cam have a moderately steep angle and to hold the needles upright in their slots.
  • This took quite a bit of iteration, but we finally have the perfect slot sizes for the needles in the needle bed. This has eliminated the jamming mentioned above entirely.
  • However an aluminum sheet was not added to the top of the bed to keep the needles in their slots nor was needle spacing conserved

Task: Cam Follower Rollers to be moderated by Joe
Bushing-style rollers have been added to the needle cam followers. Rollers are stable enough to handle pressure without deformation. Rollers are smaller than cam channel to allow for motion through channel.
  • Attempt was made to find bushings to fit on the cam followers. This task was made difficult by the need for the inner diameter to be larger than 4mm (size of followers) but the outside diameter needed to be smaller than 5mm (size of the needle channel).
    • Joe tries spring, nylon spacers, and considered using cut straws
  • After the needle bed was re-cut the task became moot as the cam/follower interaction was smooth
Task: Cam Friction Decrease to be moderated by Claire
Add a slick material to both sides of the linear cam channel to decrease friction between the linear cam and the cam followers
  •  Claire tried several materials to try to decrease friction between the cam and followers.
    • First hot glue hut it create too thick a coat and hat to be peeled off.
    • Second a sheet spring. However it resisted being cut down to a size that could fit beneath the cam bridges
  • After the needle bed was re-cut the task became moot as the cam/follower interaction was smooth

Task: Cam/Follower Improvement to be moderated by Sean
Make improvement to the linear cam and needle follower system
  •  Independent attempt at cam/needle system improvement not attempted
  • After the needle bed was re-cut the task became moot as the cam/follower interaction was smooth

Task: Cam/Follower Improvement to be moderated by Paul
Make improvement to the linear cam and needle follower system
  •  Independent attempt at cam/needle system improvement not attempted
  • After the needle bed was re-cut the task became moot as the cam/follower interaction was smooth
"Stop shouting, dearie. I can hear you just fine." ~ Grandma
"Now where did I set down my reading glasses?" ~Grandma
Sprint Events (B):

Event: Added Weighted Comb headed by Claire and Joe
  • In order to cast off yarn during stitch actuation, the fabric of hte scarf needs to be in tension downward. This is normally done by adding a weighted comb to the fabric after a couple rows have been knit. 
    • Before we had the comb we used a set of hex wrenches to hold the fabric in tension
  • Claire CADed up a quick comb for a 6.5mm gap, 10-needle bed
  • Joe 3D printed the comb in PLA.
    • The printer we used had a curved printing bed causing issues with the print. Once this was discovered we started using a a different 3D printer

Event: Corrected Sensor Code headed by Sean, Claire, and Paul
  • After much iteration, the (re-)addition of debouncing code, and adding counting code the motor now moves across the needle bed a number of needles equal to the input scarf width and then back
    • The code does not account for the width of the carriage at current so will need some more work before it will met our needs for our MVP

Event: Stitch Actuation Proof of Concepts headed by Claire
  • With the end of the sprint fast approaching and no MVP in sight, we tried a couple proof of concepts to see if we were on the right track
  • By actuating the needles by hand instead of with the carriage, and holding the fabric in place, It was shown that the needles could create the correct motion to actuate stitches. Two important changes would need to be made
    • First we would need to constrain both sides of the fabric with the verge, not just one
    • Second we would need the needle to move slightly farther outward

Event: Yarn Tensioner headed by Sean and Aubrey
  • Added a zip tie as a yarn tensioner
    • The tension is a bit too high, but we will iterate.
    • Knitting works better just using the yarn guide or laid by hand.

Event: Two-Sided Verge headed by Sean and Aubrey
  • Added a verge channel to help constrain the fabric and allow the stitches to and yarn to clear the latch of the needle instead of being pulled forward with the needle
    • Does not quite clear latches yet, but upon increasing range of motion for the needles they will
    • To increase latch cleanse, we cut off about 7mm of the verge. While this allowed the yarn to clear the latch, the yarn no longer moved completely of the head of the needle.
Previous Goals:
We desire to have a knitting machine that is stable enough to create a multiple row knitted sample without mistake, repeatedly.  The trade-off is less features.

Personal Goals:
Mechanical Goals:
  • Understanding how the 1D needle motion can actuate a stitch, including scale of motion and location of needle head
  • Understanding how linear cams work, and the specifications that are required for smooth, correctly-scaled motion
  • Research and practice of method for driving linear
  • Expand knowledge of mechanical joints and joinings
  • Gain greater familiarity with laser cutting, including materials and tolerances
Electrical Goals:
  • Learn more about motion tracking systems, such as various types of encoders
  • Practice using embedded system components, such as the arduino and motor shield, in circuits
Software Goals:
  • Research the easiest methods of creating websites that can be moved into the POE hosting solution
  • Make a gui from the PyGtk to expand knowledge of python graphics libraries

Risks:
We still have not met our minimum viable product going into the final sprint, which is bad. We wanted to build a 20-30 needle version, but our 10 needle version is not yet functional. It needs to become functional very, very soon. The biggest risk is sacrificing time on the smaller machine for the larger one might bite us when we try and fix everything.
Decision:
​Let's do this. We have one sprint to go, and we have to make our project work at all costs. We've gotten out many of the kinks, but there is still plenty to fix. Our plan is to divide and conquer in teams rather than individually, splitting into two groups so we can tackle the remaining problems faster.