Startup repeatability

[JamesNewton]

Having a way for Dexter to find "home" position automatically would be a wonderful help. This will both allow it to accurately interact with a work surface or other object via "dead reckoning" (no need to touch or be guided to a starting point). It will also removed the need to calibrate Dexter on startup because the prior calibration can be applied immediately.

Currently, the solution to this is to add a "dial" or little knob to each motor shaft. The robot is set to a perfect zero position once during manufacture (with a test stand) then the dials are installed and their correct positions marked. While powered off, the robot is move close to the home position, then each dial is turned until it lines up with the known home position.

Automated methods of solving this problem include:

• An index pulse on each joint encoder. The issue with this is the cost of an addition sensor and extra size of the disk. It may be possible to get the same effect by filling in one of the regular slots with a semi-transparent material (it looks like "Elmers Washable Clear Glue" works well) so that the slot is still there, still the same width, but doesn't "open" as far as the other slots. On power up, each joint would be "wiggled" until the index slot is detected. Redundancy is provided by the fact that each sensor should see the same effect, some fixed number of degrees apart.
• A mechanical home switch on each motor shaft. Just like the dials, the arm would be preset to near the home position, then on power up, each joint would be "wiggled" until the home switch closes.
• A "garage" or "dock" where the tool interface must be placed by the user before power up. The robot can even drive the tool interface into the edges of the dock to ensure it is well seated before setting that position as home. Or that position may be "pre-home" and home is a known number of degrees on each joint away from the pre-home position. So the robot finds pre-home, translates each joint to a new position (home) and then zeros out it's position making that home.

[JamesNewton]

In order to find position faster after power up in an unknown position, a set of index pulses, instead of just one, could be used.

If the gap between index pulses is different on the two sides of the center "home" index pulse, then the correct direction to rotate to reach home. E.g. if there are an odd number of regular sized eyes between index pulses on one side of home and an even number on the other side, a small movement in any direction from any position should tell us which way to move to reach home.

If the count of regular sized eyes between index pulses increases as you move away from home, then the exact position can be found faster. E.g. on one side, there might be 4, then 6, 8 regular eyes between indexes and on the other side, 5, 7, and 9.

[cfry]

Clever! _____ Lots of games could be played here. For instance, the idea of partially covering a slot means we effectively get 2 bits from it, ie "that it is a slot" and that it is "partial or full". But can we get more bits out of it? ie 1/4 covered, 1/2 covered, 3/4 covered? and apply that to James N's trick to tell how far a slot is from home? Maybe this interferes too much with the normal accuracy. A 2nd row of slots, closer to disc center, lower rez but more bits per slot as I describe above? Transparently colored slots? Just throwing some more cards on the table.

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On Sun, May 19, 2019 at 1:09 PM JamesNewton ***@***.***> wrote: In order to find position faster after power up in an unknown position, a set of index pulses, instead of just one, could be used. If the gap between index pulses is different on the two sides of the center "home" index pulse, then the correct direction to rotate to reach home. E.g. if there are an odd number of regular sized eyes between index pulses on one side of home and an even number on the other side, a small movement in any direction from any position should tell us which way to move to reach home. If the count of regular sized eyes between index pulses increases as you move away from home, then the exact position can be found faster. E.g. on one side, there might be 2 then 4, 6, 8 regular eyes between indexes and on the other side, 3, 5, 7, and 9. — You are receiving this because you are subscribed to this thread. Reply to this email directly, view it on GitHub <#5?email_source=notifications&email_token=AAJBG7JFNWNNQBNYBRNI5OLPWGCT5A5CNFSM4FMTH5MKYY3PNVWWK3TUL52HS4DFVREXG43VMVBW63LNMVXHJKTDN5WW2ZLOORPWSZGODVXGLCA#issuecomment-493774216>, or mute the thread <https://github.com/notifications/unsubscribe-auth/AAJBG7IK6IDYLXHCTC3QHXDPWGCT5ANCNFSM4FMTH5MA> .

[JamesNewton]

this issue is effectively closed for the HDI robots.

[JamesNewton]

Kamino cloned this issue to HaddingtonDynamics/OCADO