On Wednesday 12 February 2020 01:43:33 andrew beck wrote: > Hi guys > > wondering if anyone has any ideas here. > > I have a heidanhain spindle motor that runs up to 10000 rpm and has a > 5v sin cos encoder on it. I am currently controlling the motor with a > schiender vfd. I am talking to the support engineers here in New > Zealand about buying a encoder card so I can get better low down > torque. If I run the card in full encoder closed loop control in the > vfd I can get 200 percent of the torque right down to 0 rpm for 30 > seconds or so which is pretty useful. I am currently just running the > drive in Variable frequency control which rapidly looses torque at low > rpm. > > Anyway they have a bunch of cards I can use but don't have a encoder > card that is suitable for sin cos encoders. I have no trouble > changing the encoder but am not sure if I can get a source of encoders > that spin up to 10k rpm. > > Anyone have any suggestions?
I have an encoder, not a sin/cos, but an A/B/Z quadrature on my Sheldon lathes bull gear. I because the vfd is pretty stiff, haven't even a PID in its circuit. But by programming my 1.5 hp rated clone vfd to fit the motor, specifically to boost the low frequencies but limited to the nameplate FLA amps, can run a 1hp 3 phase down to 5hz while cutting steel for long enough to get the job done, nearly an hour in one instance while still being able to lay a hand on the motor at the end of the job. And the encoder there is only used for threading, including rigid tapping. I bought a 6040 gantry machine a year ago, it all ran on 120 volts, but the electronics were junk, so I junked them and fitted new. Including locating a 120 volt clone vfd, whose manual was somewhat less than useful, and it took a months worth of experimentation to find the registers that controlled that, but I did finally get that water cooled 24k motor to turn 500 revs while plowing a 1/8" mill thru 1/8" of alu with mister coolant. No encoder on/in that motor. So it will never do rigid tapping. I have dreams of carving gunstocks with it eventually. Generally speaking, the slip angle of hz vs speed seems to be a fixed thing depending on the coil current the vfd can get into the motor, up to the motors FLA, What currant you can get at the higher speeds is limited by the coils inductance, so by the time its up to 200hz on the lathe, coil current is under an amp and the slip angle becomes quite large, to the point where an increase in the hz isn't matched by an actual increase in the motor rpms. That particular motor came off a 50 yo air compressor, so its first intro to a vfd was when I hooked it up about 4 years ago after putting fresh bearings in it. Definitely NOT an inverter rated motor, but it still gets the job done. What I'm saying is that due to the slip angles at low speed, unless the vfd is properly programmed, low speed torque is far more a function of vfd programming than it will be obtained by putting the vfd's hz under PID control. If the excitation current isn't there, neither will the available torque to maintain the desired speed. For water cooled 24k motors it can be educational to stick an lcd thermometer on the side of the coolant tank although a 4 gallon tank takes a while to respond. So can an amprobe on a motor leg. Getting the low speed boost up to nameplate FLA will be much more helpfull than the encoder feedback. And beware of amprobes that lie like a rug at low frequencies, one of mine shows half the current actually passing at 30 hz. Its a 50 yo genuine Amprobe. Only accurate at 60 hz. Check it with an auto headlamp possibly with a shunting R in series with a motor coil, its brightness will NOT lie to you like the amprobes can. But its uncalibrated at any hz, so if in doubt. check its brightness at 60 hz, and the correct currant, then maintain that brightness as the hertz goes down. You are then actually delivering the same current if the headlamp is the same brightness. HTH Andrew. 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
