Re: Mazak Impulse - Oak retrofit build log
Posted: Sat Jun 19, 2021 3:13 am
A few progress steps made today. I finally gave in and moved the home switches. For two reasons; to get rid of the dead band past them where if the machine was to stop there, next home would crash and so that one of my travel limits could be zero to enable screw compensation.
Firstly I want to get off my chest that I think Centroids homing is rubbish (yes I understand how it works and about switches and index pulses). It overshoots the home switches by 3mm (1/8") and crashes into the hard stops! Even at lower speeds like 1500 mm/min. You have to set the home rate super slow to minimize overshoot. Then the jog rate is affected. Why aren't these separate settings! If you move the home switches back so there is more room after them before the hard stops, then you lose travel. But you cant gain that travel back by setting your + limit a few mm higher because then screw compensation doesn't work. Why does that even care about travel limits! Just reference the table off the zero position! A better homing mechanism is to have wide home switch dogs so you can detect the leading edge and slow down enough to not overshoot the trailing edge. They could do all the above back in the early 90s! Yes I know all machines are different. Rant over...
Anyways, after finding a happy medium and adjusting the motor to lead screw orientation to get my index pulses nice and close to my home switches, I ran the system test. All systems are go! I tidied up my home macro to also perform a spindle rotation to ensure spindle index is found.
I also wrote a PID control in the PLC to perform spindle orientation. It works OK but the motor drive cant do zero RPM so it twitches a lot as it constantly goes in and out of zero RPM.
I then wrote a macro to do manual tool changing. This used to require manually jogging to tool change position so it is nice to now have a button on the jog panel to do it now.
I ran a few of the sample g code programs just because. I noticed the X axis shudders at low speeds so more work is needed on the DYN4 tuning. To be honest I have lost confidence that these drives are ever going to work nicely!
Next mission is to finish off auto tool changing. I am not sure that the spindle orient is going to be good enough though. It has to be quite precise otherwise the tool collides with the locator. Fingers crossed. If not its yet another spindle drive which would be a pain!
Firstly I want to get off my chest that I think Centroids homing is rubbish (yes I understand how it works and about switches and index pulses). It overshoots the home switches by 3mm (1/8") and crashes into the hard stops! Even at lower speeds like 1500 mm/min. You have to set the home rate super slow to minimize overshoot. Then the jog rate is affected. Why aren't these separate settings! If you move the home switches back so there is more room after them before the hard stops, then you lose travel. But you cant gain that travel back by setting your + limit a few mm higher because then screw compensation doesn't work. Why does that even care about travel limits! Just reference the table off the zero position! A better homing mechanism is to have wide home switch dogs so you can detect the leading edge and slow down enough to not overshoot the trailing edge. They could do all the above back in the early 90s! Yes I know all machines are different. Rant over...
Anyways, after finding a happy medium and adjusting the motor to lead screw orientation to get my index pulses nice and close to my home switches, I ran the system test. All systems are go! I tidied up my home macro to also perform a spindle rotation to ensure spindle index is found.
I also wrote a PID control in the PLC to perform spindle orientation. It works OK but the motor drive cant do zero RPM so it twitches a lot as it constantly goes in and out of zero RPM.
I then wrote a macro to do manual tool changing. This used to require manually jogging to tool change position so it is nice to now have a button on the jog panel to do it now.
I ran a few of the sample g code programs just because. I noticed the X axis shudders at low speeds so more work is needed on the DYN4 tuning. To be honest I have lost confidence that these drives are ever going to work nicely!
Next mission is to finish off auto tool changing. I am not sure that the spindle orient is going to be good enough though. It has to be quite precise otherwise the tool collides with the locator. Fingers crossed. If not its yet another spindle drive which would be a pain!