On Saturday 09 October 2021 04:20:48 Peter Hodgson wrote: > Thank you Gene. > > I’m in the UK and lightning strikes are unlikely where I am but I > guess should always be a consideration. > > The grounding in my machine is not currently from one ‘star’ point so > I will correct that. Shielding is only terminated at one end. > > Is the single point best on the machine frame or in the control panel > chassis or does it not matter?
The ground point I am using now, an inch of 10-32 bolt tightened solidly into a drilled hole in the bottom of the box. Its hangingf on the back of a pole frame I installed to hold a 4 foot led shop lamp over the bed of the lathe as it just inside the garage door, and the door moves over the top of it when open. That box contains the psu's and motor drivers, and all io cabling goes by it on it way out to the lathe. The pi, the 7i90HD and the three 7i42TA's are all in another, slightly smaller box mounted on the outside of the rusty boxes lid, along with a corfam brick wall filter between the AC feed and a 5 volt, 5 amp supply that runs the pi and the interface cards. All grounds in the controller box are connected to this bolt on the way by it. The pi and the interfaceing cards are all made into a one piece assembly, connected stair step fashion by nylon standoffs. There is on the right side of that rusty box, a 650WA cyberpower ups that doesn't have enough load to see it, and has a 2 minute shutdown time that apparently isn't adjustable, but it only has to hold up 5 seconds as there is a 20kw nat gas fired generator in the back yard. I installed it several yearss ago so the wife would have nonstop power for her oxygen generator as she had COPD, but she has now passed on. Frankly its all a big kluge, but it works. I, since I had i/o to throw away have another small box with two 40 qmp 600 volt crydom SSR's in it that controls all motor power to the machine but not to the pi and interfacing, so its on 24/7 but the machine is powerless until I start LinuxCNC and hit F1 to allow control, and F2 to enable motion. And that is all interlocked in the hal file with the fault signals from the new, 3 phase stepper/servo motors and drivers I recently installed. If you are using steppers, these are the "next big thing", and cost around $130 per axis. I can turn the chuck to put a jaw in the tools way, jog left to approach the chuck and jog the tool into the chuck jaw, the driver detects the increased load and kills its outputs, and sends a fault signal back to LinuxCNC which shuts the machines AC power off by toggling F2. If it ever happens while working, empty the qcth post, hit F2 to re-enale motion, fix why it shut down, rehome the machine, put the tool back on the post and hit R again. But it has yet to do that in normal operation. The final test is whether it Just Works, and it does. The spring in the system bounces it back about 10 thou clear of the jaw, and does the the shutdown without damaging the carbide chip in the tool if the jog speed isn't excessive. These 3 phase motor controllers use the error from an encoder in the motor, fed back to the controller, to control motor current, and the motors run quite cool, not to mention they doubled the machines rapid speeds. And they move a lot like casper the ghost. Very quiet. The 2 phase motors I took off regulaly shook tools off the machine onto the floor. At my age and the abuse I've put on this old carcass, bending over to pick up a tool hurts. Avoiding that is definite plus. :o) > It’s great to have the support of such experienced senior engineers !! They can jail me in texas for calling myself an "engineer". Born with a higher IQ, I quit school just passed the 8th grade and went to work fixing the then brand new things called televisions for a living. That was something over 70 years ago. Its been quite a ride and I still have my hands on the steering wheel. Some failing parts have been replaced though, like a pacemaker and a TAVR heart valve. Take care Pete. > > > On 8 Oct 2021, at 23:34, Gene Heskett <[email protected]> wrote: > > > > On Friday 08 October 2021 15:22:23 Peter Hodgson wrote: > >> Hello All, > >> > >> I'm hoping someone with more electrical control experience than me > >> may be able to offer advice on why I am seeing occasional rogue > >> index pulses which are messing up my G76 cycles on larger threads. > >> > >> The Halscope below shows an example of the occasional ghost index > >> pulse which can create a new 'thread start' and trash my parts as > >> photo above. > >> > >> A schematic of the encoder setup which is a quadrature 500ppr > >> incremental encoder can be downloaded here: > >> > >> > >> https://www.purbrookengineering.com/index.php?option=com_content&vi > >>ew= article&id=11 > >> > >> > >> The signal goes to a Pico Systems USC board via a voltage level > >> shifter. We have a 0.75uF capacitor to filter the 5v supply to the > >> voltage shifter and 1kohm resistors in series on the input signals > >> from the encoder. The encoder cable is shielded, grounded only at > >> the encoder case end and is not close/parallel to any power cables. > >> The 12v supply to the encoder is from a voltage regulator and the > >> 5v supply to the level shifter is from the Pico control board. > >> > >> Jon @ Pico provided me with excellent support to get me this far > >> with the setup which now cuts smaller threads quite reliably but > >> with larger threads on my small lathe I need many passes and I > >> haven't been able to get rid of these occasional ghost pulses which > >> eventually cause a bad pass. Jon Elson @ Pico is a very good man, he has modified his pwm-servo amps to make them into CCS rated spindle motor drivers, with which I'm abusing a couple 1hp rated motors to around 2hp peak, with zero problems. [...] Cheers, Gene Heskett. -- "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author, 1940) If we desire respect for the law, we must first make the law respectable. - Louis D. Brandeis Genes Web page <http://geneslinuxbox.net:6309/gene> _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
