I've worked with Fanuc robots,and was amazed to find that none of the cables were shielded. The robot, with motors and encoders, is linked to the control box with a 6m cable. All unshielded. Ok, the power and signal cables are separate, but once installed, all extra cable is looped together next to the control box.
A while back I stripped some Motoman robots. Internal on the arm, all the motor wires, and encoder wires, are tightly bundled together. No shielding on either. On Mon, 21 Jun 2021 at 22:15, Thaddeus Waldner <thadw...@gmail.com> wrote: > > Okuma machine builders really don’t like quantization noise so they use 40 > million CPR encoders on the axis motors. > > > On Jun 21, 2021, at 11:34 AM, Chris Albertson <albertson.ch...@gmail.com> > wrote: > > > > Quantization noise is fundamental and present in all digital systems. > > There is absolutely no way to avoid it. All you can do is minimize it. > > > > To know how fast a shaft is spinning or how far it moves, you have to > count > > edges and if you get 100 counts you just can not know if you are closer > to > > 100 or to 101 counts. Basically the counter always rounds down even if > at > > 100.99999 it tells you "100". So the cound is "wrong" 50% of the time. > > This applies not only to encoders, but A/D converts and every other kind > of > > measurement. > > > > This is the nature of digital data, of representing the world with a > fixed > > number of bits. > > > >> On Sat, Jun 19, 2021 at 4:00 PM John Dammeyer <jo...@autoartisans.com> > >> wrote: > >> > >> But doesn't the 7i92 FPGA deal with quadrature encoders and therefore > >> doesn't really need to deal with a sampling process but instead looks at > >> edges? And because of the way quadrature works, with the A/B phasing > you > >> don't get the same types of errors compared to polling a bit level X > times > >> per second and trying to decide when it's high/low. > >> > >> John > >> > >> > >>> -----Original Message----- > >>> From: Chris Albertson [mailto:albertson.ch...@gmail.com] > >>> Sent: June-19-21 3:21 PM > >>> To: Enhanced Machine Controller (EMC) > >>> Subject: Re: [Emc-users] Machining question > >>> > >>> There are two kinds of noise, > >>> 1) electrical noise superimposed on the signal. > >>> 2) quantization noise from the sampling process. What happens here is > >> that > >>> the computer counts the number of line crossings during a given time. > it > >>> is just random luck when the time starts so on average there is a plus > or > >>> minus one count error. > >>> > >>> So a one count error sounds small but lets say we have a 600 count > >>> encoder and we are running at 500 RPM and sampling 100 times per > second. > >>> This works out to 50 counts per period. a one count error is a 2% > >> error. > >>> You will see a larger percent error at slower speeds or with a lower > >>> resolution encoder. > >>> > >>> So even with perfect wires and perfect grounding and zero electrical > >> noise > >>> the RPM speed is going to jump around randomly over a 4 RPM range > because > >>> of unavoidable quantization error. > >>> > >>> The solutions either the use a larger sample time apply a low-pass > >> DIGITAL > >>> filter to the signal. No amount of analog filters on the wires will > >> work. > >>> > >>> On Sat, Jun 19, 2021 at 2:55 PM Gene Heskett <ghesk...@shentel.net> > >> wrote: > >>> > >>>> On Saturday 19 June 2021 12:59:19 John Dammeyer wrote: > >>>> > >>>>> I need to do a couple of things. For one the AC Servo makes a lot of > >>>>> electrical noise. The frame of the motor is connected to earth > >>>>> through power line ground. But my bench setup has the control side > >> 5V > >>>>> not isolated from the 'PC' side (optos are kind of useless here) and > >>>>> although the Pi4 doesn't appear to have any trouble the scope shows a > >>>>> pretty noisy encoder signal. > >>>> > >>>> You are about to learn the star ground system I think. > >>>> > >>>> Thats where all grounds go to a single bolt, and no other grounds are > >>>> allowed anyplace. > >>>> > >>>> Shielding in motor cables ends without touching the motor, only > >> connected > >>>> to this same single bolt which is grounded. The common line of any > >> power > >>>> supply is connected only to this bolt, and the common grounds to every > >>>> piece of pcb in the system comes from that bolt. The used to be green > >>>> static ground wire in any power cord is rerouted to this bolt. And > >>>> static grounds on a power supply are fed from this single bolt. > Because > >>>> the psu case is usually bolted down wherever its at, you may have to > >>>> uncover the supply and remove any connection from the earth labeled > >>>> terminal, and the psu's case. It may be a screw in the corner of a > pcb, > >>>> but it needs to be removed. > >>>> > >>>> Anything connected to ground at some other point in addition to that > >> bolt > >>>> becomes an antenna, is called a ground loop, picking up both magnetic > >>>> and electrostatic noises. I had to learn that the hard way while > >>>> building the Sheldon, blowing two 7i90HD boards out by picking up 80 > >>>> volts p-p of switching noise that reached up to the bandwidth limits > of > >>>> both of my 100mhz scopes. Hell on an fpga with a 3 volt limit. I > >> killed > >>>> the power and redid it to the single bolt model, and that 80 volts of > >>>> noise was reduced to under 100 millivolts. Took me about a week to > find > >>>> all the connections that should not have been made. Even a small > bypass > >>>> capacitor to a local ground instead of back to that bolt can become a > >>>> lethal weapon to the elecronics. Its a noise injector in that case. > >>>> > >>>> The whole idea is to make the ground, if it bounces from a lightning > >>>> strike on the can on the pole that powers your place, which may make > >> the > >>>> whole system bounce 100+ kilovolts, and if you are in that circuit at > >>>> that instant it WILL get your attention. BUT, everything tied to that > >>>> bolt should bounce in unison, meaning an individual board input will > >>>> only see the difference signal its being fed with, and it should > >> survive > >>>> that lightning strike with no damage. > >>>> > >>>> My soap box as a CET just collapsed, so I'll do an Andy Capp and > >> shudup. > >>>> > >>>> > >>>>> ===================== HAL code =================== > >>>>> Second is some of the HAL parameters and reducing to 0.003 makes the > >>>>> display more stable. # Use ACTUAL spindle velocity from spindle > >>>>> encoder > >>>>> # spindle-velocity bounces around so we filter it with lowpass > >>>>> # spindle-velocity is signed so we use absolute component to remove > >>>>> sign # ACTUAL velocity is in RPS not RPM so we scale it. > >>>>> > >>>>> setp scale.spindle.gain 60 > >>>>> setp lowpass.spindle.gain 0.003 > >>>>> net spindle-vel-fb-rps => scale.spindle.in > >>>>> net spindle-fb-rpm scale.spindle.out => > >>>>> abs.spindle.in net spindle-fb-rpm-abs abs.spindle.out > >>>>> => lowpass.spindle.in net spindle-fb-rpm-abs-filtered > >>>>> lowpass.spindle.out > >>>>> ===================== end HAL code =================== > >>>>> > >>>>> But I'm still using the original signal for at speed and the LED > >> never > >>>>> comes on nor does it know it's at speed. I should probably be > >>>>> filtering the RPS rather than RPM I think? > >>>>> > >>>>> ===================== HAL code =================== > >>>>> net spindle-vel-fb-rps => spindle-near-speed.in1 > >>>>> net spindle-ramped => spindle-near-speed.in2 > >>>>> > >>>>> # ---Setup spindle at speed signals--- > >>>>> # the output from spindle-near-speed 'near' component is sent to > >>>>> spindle.0.at-speed # and when this is true motion will start. The LED > >>>>> in the pyvcp-panel.xml is renamed to be a LED. net > >>>>> spindle-near-speed-led <= spindle-near-speed.out => > >> spindle.0.at-speed > >>>>> ===================== end HAL code =================== > >>>>> > >>>>> John > >>>>> > >>>>>> -----Original Message----- > >>>>>> From: andy pugh [mailto:bodge...@gmail.com] > >>>>>> Sent: June-19-21 2:48 AM > >>>>>> To: Enhanced Machine Controller (EMC) > >>>>>> Subject: Re: [Emc-users] Machining question > >>>>>> > >>>>>> On Sat, 19 Jun 2021 at 07:11, John Dammeyer < > >> jo...@autoartisans.com> > >>>> wrote: > >>>>>>> I'm finding the AXIS Spindle speed oscillates about +/- 5 RPM. > >> I > >>>>>>> thought that I was filtering it. > >>>>>> > >>>>>> It generally needs to be filtered, but it is possible you are > >>>>>> filtering it, but not enough to get a steady reading. > >>>>>> > >>>>>> For whatever reason encoder velocity does always seem to be a bit > >>>>>> noisy, despite the counters using timetamped edges and all the > >> other > >>>>>> tricks that might help. > >>>>>> > >>>>>> -- > >>>>>> atp > >>>>>> "A motorcycle is a bicycle with a pandemonium attachment and is > >>>>>> designed for the especial use of mechanical geniuses, daredevils > >> and > >>>>>> lunatics." > >>>>>> ? George Fitch, Atlanta Constitution Newspaper, 1912 > >>>>>> > >>>>>> > >>>>>> _______________________________________________ > >>>>>> Emc-users mailing list > >>>>>> Emc-users@lists.sourceforge.net > >>>>>> https://lists.sourceforge.net/lists/listinfo/emc-users > >>>>> > >>>>> _______________________________________________ > >>>>> Emc-users mailing list > >>>>> Emc-users@lists.sourceforge.net > >>>>> https://lists.sourceforge.net/lists/listinfo/emc-users > >>>> > >>>> > >>>> 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) > >>>> 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 > >>>> Emc-users@lists.sourceforge.net > >>>> https://lists.sourceforge.net/lists/listinfo/emc-users > >>>> > >>> > >>> > >>> -- > >>> > >>> Chris Albertson > >>> Redondo Beach, California > >>> > >>> _______________________________________________ > >>> Emc-users mailing list > >>> Emc-users@lists.sourceforge.net > >>> https://lists.sourceforge.net/lists/listinfo/emc-users > >> > >> > >> > >> _______________________________________________ > >> Emc-users mailing list > >> Emc-users@lists.sourceforge.net > >> https://lists.sourceforge.net/lists/listinfo/emc-users > >> > > > > > > -- > > > > Chris Albertson > > Redondo Beach, California > > > > _______________________________________________ > > Emc-users mailing list > > Emc-users@lists.sourceforge.net > > https://lists.sourceforge.net/lists/listinfo/emc-users > > > _______________________________________________ > Emc-users mailing list > Emc-users@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/emc-users > _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
