Homing / limits - the manual is misleading, possibly wrong

Re: homing and stopping distance
To clarify:

All homing moves use a single-joint trajectory
planner (simple_tp) that implements a trapezoidal
velocity profile using specified maximum speed and
acceleration (vmax,amax).

Note: Velocity is a vector quantity, speed is a scalar
measure of velocity magnitude. The terms are commonly
interchanged and misused in Linuxcnc documents and pin
names.

cmorley wrote:

In the below I am restricting the home position to a small portion of the table temporally.

Can you explain what you mean here, 'temporarily' confuses me - home position is not defined till the end of homing -it can't be until linuxcnc knows where the Origin is.

What soft limits goes with those settings?

Chris

Chris. these are the soft limits. but full disclosure I changed my home position from -20 to -200 so the limit below are correct with the home set at -20.
these settings are on a plasma table I am building the table is about 1260mm in X and 750mm in Y but I have a piece of MDF as a bench on it so I have cut the soft limits down so I don't move the gantry by mistake to far.
.
My switches are fitted top left on the machine but I will make my final home bot left so that my gcode will be +ve when using G54. If that makes sense

AXIS = Y
MIN_LIMIT = -200
MAX_LIMIT = 0

home = -200
home offset = .05
min = -200
max = 0

I don't see any problem with that nor does the docs say that's not ok. your machine coordinates are all negative but that doesn't really matter.

Chris

cmorley wrote:

home = -200
home offset = .05
min = -200
max = 0

I don't see any problem with that nor does the docs say that's not ok. your machine coordinates are all negative but that doesn't really matter.

Chris

home offset is 0.5

Yes Y G53 will be -ve but X is +ve

My machine homes without any problems.

Thanks again for the work you put in

linuxcnc.org/docs/devel/html/config/ini-homing.html

Looks great!

rodw wrote:

Chris,

Under Figure 1,

C is the home switch trip point

really should say

C is the home switch trip point (once triggered, home switch must remain active from the home switch 
position all the way to the hard limit)

Did you include something about this? Could not see it.

Did you include something about this? Could not see it.

Yes in the prerequisite

If using a separate homing switch, it’s possible to start homing on the wrong side of the home switch,
which combined with HOME_IGNORE_LIMITS option will lead to a hard crash.
You can avoid this by making the home switch toggle it’s state when the trip dog is on a particular side until it returns passed the trip point again.
Said another way, the home switch state must represent the position of the dog relative to the switch (ie before or after the switch),
and must stay that way even if the dog coasts past the switch in the same direction.

Hi rodw,

I've been posting recently under "Sharing Limit Switches and Homing on a Single Input" looking for help with setting up Homing and Limit Switches using a single input pin on my breakout board. I have successfully gotten the single pin deal to work and stumbled around until I managed to get Homing and soft limits etc. to work. However, it would be a significantly large understatement if I said I don't actually understand how to correctly set the different variables.

I've been struggling to make sense of the different sections of the manual and tie it all together. A large part of that is my limitations but I'm starting to suspect there might also be some errors and omissions in the manual and areas that could be more clearly stated.

I've read a few of your comments and would appreciate your insights and suggestions. Would you please check out my posting if you have time and let me know what you think ? I just updated it to include a copy of the "Figure 2. Demonstrative Shares Switch Layout" image from the manual with extensive mark-ups to help me try to understand how things fit together, and, some areas where I have questions or think the information may be incorrect. Per your comments on this thread I believe I'm using the version of the manual you recommended and have put that info on the image I submitted.

Thanks in advance for any help you can provide.

Jay