Moving to feeder location when not homed

[Mark Patton]

I just discovered that if I turn my PnP machine on and start Open PnP but not home the machine, then go to one of the feeders and move the head to reference hole location, the head will move from wherever it happens to be.  This new location could be anywhere.

Can anyone think of a reason why popping up an error with "Machine not homed" or some such error would be a bad idea? 

I could home the machine when the host connects, but I can think of reasons why that could be ill advised.  Unexpected head motion, for instance. 

[mark maker]

That's a valid concern.

It is one of these functionalities that are so "primal" that we don't think much about them anymore, i.e. quite out of place, now that bar for adequate safety is much higher than back in the beginnings.

Because these functions with motion are virtually everywhere, this needs some thinking... I have an idea, though.

_Mark

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[Mark Patton]

Thanks Mark!

[ma...@makr.zone]

Hi everybody

NOTE: this affects everybody, please read.

From the description:

On unhomed machines the current position is not known by the controller, they often power-up/reset to zero coordinates at the position the machine randomly happens to be. Positioning the machine to a prerecorded location can therefore lead to a crash. Only few actions in OpenPnP check if the machine is homed and prevent that. Most notably the generic Position to Location buttons do not.

This PR makes this safer. In doing so, it distinguishes two types of motion:

• Jog motion is allowed, when the current controller machine position is positively known to OpenPnP. It is assumed that the user observes the true machine position and will avoid jogging into obstacles.
• Non-jog motion is generally disallowed on unhomed machines.

The machine homing safety checks are centrally administered inside the motion planner, so motion generated from all sources is covered.

The behavior can be overridden on the driver, in case it proves too restrictive, e.g. for controllers where absolute linear encoders are available and homing is simply not required, or where homing is inherently and safely done when powering up. This option can be controlled per driver, i.e. it can be treated differently if multiple drivers/controllers with different capabilities are involved. The drivers assigned to axes determine which drivers are relevant for a certain motion.

Details:

https://github.com/openpnp/openpnp/pull/1540

This is now in the OpenPnP test version. Please allow some minutes to deploy.

_Mark