Motion Control and Motor Drives

[dluu13]

Hello everyone,

I have two axes on the platform that I am trying to program here.  One with larger motors (more inertia), and one with smaller motors (barely any inertia)

I am able to find the forward and home reference of one of the axes (the one with the smaller motors).

I notice that the axis with larger motors does not home properly.  I will describe this in detail.  I have reduced the reference finding procedure for the larger axis to just homing, as the same problem exists in the forward reference finding as well.

The homing procedure proceeds as usual until it hits the home limit switch and releases it (so as to stop at the falling edge of the switch's signal).  This is when problems start to arise.  The homing procedure doesn't stop as the switch is released.  If I look in MAX, even though the switch is released, the "home switch activated" indicator is still on.  However, on the NI fanout board, the "home switch" indicator is off (which is correct).  

Unless I press the limit switch again by hand, the "home switch" indicator in MAX will stay on, and the VI will continue searching for that falling edge.  One thing to note is that when the switch is depressed by hand, the indicator light on the fanout board turns on, while the indicator on MAX turns off even though the switch is depressed.  Only when the switch is released does the movement on the motor stop.  When there is no movement, the indicator lights on MAX and the fanout board behave as expected.

Another thing to note is that if I depress the switches by hand slowly, and then release them, instead of letting physical blocks hit the switches, the homing sequence completes correctly.  I have also tried setting the home search speed to a slower speed,   but it does not make a difference.  However, if I start my search sequence very close to the home switch, the homing sequence finishes properly.

I have also made sure my settings look the same as the settings on the axis that works (using MAX).  I have also tried reversing some settings.

Is this some sort of polling issue?  Switch bouncing?  Is there a way to force the movement to wait after touching the home switch before moving off?

cheers,

dluu

[Cole_R]

Hi dluu13,

Judging from when you said the home switch indicator is off on the board and on in MAX, it sounds as though you have a polarity issue in software.  What happens if you change the active polarity settings of the home switch in the Motion I/O settings in MAX?

[dluu13]

The strange thing is that the problem only surfaces during a home move, and not any other time.

[Cole_R]

Would it be possible to post some screenshots of how the Axis Status indicators in MAX when you execute the move?  Do the 'Axis is currently moving' and 'Move is complete' indicators show appropriately when executing the home command?

[dluu13]

I haven't got any screenshots right now.

However, the "Axis is moving" is on for as long as the axis moves (appropriate).  As far as I can tell, the only problem is that the software does not seem to detect that the axis has moved off of the limit.  The move complete indicator is active after I press the limit switch by hand and the axis stops moving.

[Cole_R]

Another thing we can check is the Smart Enable setting in the find Reference setting.  It this is not selected we would need to manually enable or disable the limits.  

[dluu13]

I spoke with a colleague of mine and in the past, he has had the exact same problem as I did.  He was unable to solve the problem himself, so he wrote his own function.  I will try that myself as well, and I will try and report back the results.

The key feature that I will try to incorporate is a sort of delay timer so that the actuator will sit on the switch for a little bit before moving off.

[Cole_R]

You may also want to try enabling/disabling the home switch when you need or don't need the home switch.  Check out this KB for some more information.  

http://digital.ni.com/public.nsf/allkb/BE713663C048225586256A0A005A6A20