Delta end stop sensor failure detection during homing
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It would be good to have an end-stop test to detect if an end-stop sensor locked in the "triggered" position.
I have had this happen twice on my TEVO little monster and it is not a pleasant experience. I have since changed the homing command after a print to a move to the top position but this is a mitigation of possible damage but not a solution.
The minimum nice to have would be a g-code to test all end-stops and if any of these are triggered then a sensor error is triggered, all axes are set to un-homed and no movement allowed until reset.
This would prevent the printer from homing if any of the sensors are triggered at start of operation but in normal operation this never happens and to recover the user would need to move the effector down a few mm manually. It is a small price to pay for additional safety.
I have experienced a sensor failure when a bad contact developed on the cable from the sensor to the DuetWifi. Both times this happened after a successful print and was nerve wracking because it was unexpected and threatened to damage the printer.
The homing of the printer resulted in one of the carriages to remain motionless (it's sensor was already triggered) while the other carriages kept moving up. The effector first pushed out to one side then rose above the carriage, finally everything locked and finished with the pulleys skipping over the timing belts.
Time between these failures was over a month of no issue printing so it appears to have developed in the normal printer operation, probably due to vibration.
