Thats one thing I'm not totally positive about yet, but from how it
looks in the source I can use home_offset on one the second joint to
correct skew, leaving the first at zero.
For instance..
Distance between homes switches is 2in.
INI Specifies
Joint0, home_offset = 0
home = 0
Joint1, home_offset = -2in
home = 0
Both linked joints will travel towards home switch. Joint0 trips first,
puts Joint1 in follow mode. After joint0 completes it's home it loads
its position with 0(home_offset) then it moves to home.. (which will
just be a bit of overshoot)
After Joint0 stops, Joint1 starts homing and Joint0 goes into follow mode..
They both travel towards joint1 home. After Joint1 completes its home
it's loaded with -2(home_offset). Because Joint0 was following it should
also be at -2 as well.. so they are now both loaded with -2 for position.
On second thoughts It might be better to stop homing joint0 at the
HOME_FINAL_MOVE_START state instead of HOME_FINISHED.. Then start homing
joint1.. after they are both this far and loaded with their home_offset
values they stop following each other and both drive to their HOME
positions and at the end of the move any skew should be corrected? right?
I guess I need to add another error check to make sure both joints HOME
value is the same.
Thats what I was thinking about, I'm still new to EMC so not sure if
this will work the way I'm thinking.
Alex Joni wrote:
> HI Cliff,
>
> looks good so far.
> What happens when both are homed, but the home position is different (slight
> skew).
> Does it get corrected? Does the offset get remembered?
> (At least that's what I think happens if one joint _always_ follows the
> other one during homing).
>
> Regards,
> Alex
>
>
> ----- Original Message -----
> From: "Cliff Blackburn" <cblackb...@powertechrepairs.com>
> To: <emc-developers@lists.sourceforge.net>
> Sent: Tuesday, April 20, 2010 10:11 AM
> Subject: [Emc-developers] Coordinated Gantry Homing by Linked Joints
>
>
>
>> I started working on a modification to homing.c so you can home a gantry
>> style machine properly I have started working on it but have more work
>> before i find how many bugs I created in the process. It adds a option
>> to link 2 joints together. The joints will home themselves one at a time
>> while maintaining the same velocities. Quite a few commercial machines
>> can do this out of the box and I think EMC should too.
>>
>> Ideally I don't want to touch what already works and think the best
>> solution is to introduce custom homing modules (simple, gantry,
>> crazymach) which can do coordinated motion if needed. Although this
>> seems like the most configurable + ideal way it's also is the most work
>> :( This way *seems* simple with minimal changes.
>>
>> This is the basic plan so far.....What do you think, good/bad idea? is
>> it useful to anyone? or should I go a completely different method.
>>
>> Plan
>> - Add a HOME_LINK_JOINT property to the joints. This property defines
>> which joint is linked linked to it.
>> - It will at all times will insure both joints move together. (Const vel
>> at least)
>> - The first joint to come into contact with it's switch will put the
>> second into a HOME_LINK_WAIT waiting state.
>> - While the second is in the waiting state the first will complete it's
>> home and follow all of it's moves.
>> - The move following is done in the home_start_move() funtion
>> - Once the first joint has come to a complete stop after homing it will
>> be sent to HOME_FINISHED state.
>> Now it will set the second joints state to HOME_START
>> - The second joint will now follow the first until it also hits the
>> HOME_FINISHED state
>> - The joints will check each other see they are both completed and sets
>> the HOMING flag off and HOMED true...etc...
>>
>> Error Checking
>> - Must check all velocities, accels, etc.. are equal between joints, if
>> not it's a warning and use the smallest values from the two.
>> - Joints which are linked must have the same home_sequence. If not it is
>> a critical error and quit
>> - Joints can only link to 1 other joint, and that joint can only link
>> back to the orig. (e.g. cannot link 3 or have some kinda chain..
>> Simplicity)
>>
>> Requirements
>> - Make minimal changes to the homing configuration.
>> - Don't break working home procedures...!
>> - Allow all current home methods even if the 2 linked joints use a
>> different procedure.
>> - Up to user to specify home offset values to adjust for table skew and.
>> - Doesn't matter which joint homes first
>> - Always stay in sync.
>> - An error in one will trip the other
>>
>> ------------------------------------------------------------------------------
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>>
>
>
> ------------------------------------------------------------------------------
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