Hey Gene, > If you've got noises bad enough to mess with the encoder, I'll bet a > bottle of suds your grounding system violates the single point "star" > rule. You want shielded cables yes, but all shields and all ground > commons come back to a single long bolt, and none of it is grounded any > place else. Any other ground, including the 3rd static ground in the > power cords is a ground loop and will intro noise. Only one master > connection to the reference ground should be allowed.
You haven't read the CUI data sheet then. My mouth dropped when I read the specs and looked at the cable they make for this encoder. It's shielded 14 or 18 conductor depending on the model. At the encoder end there's a teensy little connector along with a loose wire with a ring terminal The data sheet clearly says this ring terminal is connected to the 5V ground and should be fastened to the motor frame. (which ultimately leads back of course to your big ground bolt). The other end of this 36" cable has 6" unshielded and a 3 length connected to the shield. That one of course should go to your big bolt. But that they want me to connect 3 different motors 5V Gnd at dramatically different parts of the frame to the frame boggles my mind. The reason I'm trying a replacement encoder is because Henrik Olsson had nothing but troubles with his HP_UHU servo drives and the US Digital encoders. He was fortunate enough to have several other brands handy and had absolutely no overrun errors ever. Even with the cables wrapped around the motors a number of times. But put the US Digital one back in and constant overrun errors. Mine aren't as bad as his but then mine are a slightly different model. So although I've got a clean system and signals that look perfect on the scope (like his did) I thought it was time to at least verify that the encoders weren't the problem. I even went as far as buying braided shielded twisted pair 16g motor cable. Not cheap. So if the new encoders work then we know it's something with the US Digitals. And I am using differential pairs for A and B. The receiver is a 75115. I've even wired in termination at the encoder end so the cable is a properly balanced transmission line. So at the moment we're thinking that the US Digital units are sensitive to magnetic interference from the acceleration or deceleration heavy current. (105VDC power supply and a motor rated to momentarily draw 40A but steady current at 9A). And it doesn't matter whether the PC is running LinuxCNC or MACH3. Henrik designed and sells a replacement CPU module that plugs in place of Uli's UHU Atmel processor. It's dsPIC based and has the hardware quadrature support. So he doesn't use interrupts on encoder edges and perhaps might not have the problems. But I agree with him that if I can get overrun errors from the Atmel UHU processor then switching to something else won't solve the problem. Might only just hide it. If I use the stepper motor power supply (60VDC) I can mount my two Gecko Servo Drives in place of the HP_UHU but then I'd never get full speed from the motors and I still wouldn't know if I was having problems until I would perhaps see a home not agree with my Shumatech DRO. And be aware this mill conversion project with the HP_UHUs started back in 2008. And just gets postponed by a year or so every once in a while. The mill with the scales and DRO has been adequate for most precise operations that I need to do. One of My Electronic Lead Screw controllers driving the GECKO 950oz/in knee motor through a 3:1 toothed belt has made raising the knee simple. Another ELS on my rotary table as simplified much of that work. At the moment I don't really 'need' CNC on the mill. I just want it. I think I posted a youtube link before with a BeagleBone Black, Xylotex Cape and MachineKit exercising the knee and the Y axis. The motor mounts are all castings. This link is with MACH3 running the roadrunner.tap GCode sample. https://youtu.be/OUQzyp-3WXY That's when I discovered the move to home after it was done was out by a few thou. So for now it's been two steps backwards and one step forward. You can see the US Digital encoder on the X motor. Nice totally shielded aluminium cover. The CUI has more plastic bits. I'll let you know how it works out. John _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
