[Emc-users] using fanuc drives and motors
Gentlemen, Unfortunately necessity breeds investigation. The Fanuc 11M on my Enshu is dying. In concert with Fanuc we can find no cause. It is now at the point of beginning a random board replacement until the culprit is eliminated. This could be expensive. The other option is EMC2!! - that is an option I like. After review of a previous discussion on the necessary tach signal for the amp I have questions bouncing around in my head. If the 11 control is S SLOOO in program execution would that control not process the tach signal at a relative slow speed compared to today's capability? If that generated tach signal was sufficient for the amps in the late 70's would the current technology be able to at least match it? If today's tach signal generation is suboptimal for a servo amp how did Fanuc do it acceptably 30 years ago? If synthesized tach signals are problematic why does/did Fanuc use them as their primary design? Fanuc seems to have a decent reputation for servo systems and controls. :) I insist on believing there is no magic nor magic chip in a Fanuc control. just asking thanks Stuart -- dos centavos -- This SF.net email is sponsored by Sprint What will you do first with EVO, the first 4G phone? Visit sprint.com/first -- http://p.sf.net/sfu/sprint-com-first ___ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
Re: [Emc-users] using fanuc drives and motors
On Sun, Jul 18, 2010 at 09:32:40AM -0500, Stuart Stevenson wrote: If that generated tach signal was sufficient for the amps in the late 70's would the current technology be able to at least match it? I have several competing ideas in my head about this. I will list them in order from least daring to most daring. 1. You could add tachs 2. I have some servo dynamics amps that take A,B encoder inputs as velocity feedback. This makes me think there is a simple way to do frequency-to-voltage conversion to get a velocity signal from quadrature. I bet many on the list are experienced enough in analog design to easily do this. 3. You could get extra DACS (an extra 7i33 mesa card) and send Mesa's high quality encoder velocity signal directly out an extra DAC. 4. You could assume that all the amp does with these two velocity signals is act according to the difference, command minus feedback. You could generate this difference in HAL by subtracting the encoder velocity signal from the pid output, and feed that difference out a single DAC. On the amp, just null out the other input. Frankly I'd try these in reverse order and see what gives you a stable loop. -- This SF.net email is sponsored by Sprint What will you do first with EVO, the first 4G phone? Visit sprint.com/first -- http://p.sf.net/sfu/sprint-com-first ___ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
Re: [Emc-users] using fanuc drives and motors
Stuart Stevenson wrote: The other option is EMC2!! - that is an option I like. After review of a previous discussion on the necessary tach signal for the amp I have questions bouncing around in my head. If the 11 control is S SLOOO in program execution would that control not process the tach signal at a relative slow speed compared to today's capability? If that generated tach signal was sufficient for the amps in the late 70's would the current technology be able to at least match it? If today's tach signal generation is suboptimal for a servo amp how did Fanuc do it acceptably 30 years ago? Low bandwidth. You can figure it out, given the encoder resolution. The amplifier would have a velocity bandwidth of maybe 100 Hz at the max, but I'm guessing probably less on that system. So, what speed would the machine need to move at for the encoder counts to be coming in at less than 100 Hz? Processing the tach signal is not the important factor. Fanuc had a custom chip made to do the conversion, it was literally all in one chip plus an op-amp. There are several outfits making a converter now. US Digital has one with LOTS of options, and there's a guy in Bulgaria making a 2-channel unit for 100 Euros. If synthesized tach signals are problematic why does/did Fanuc use them as their primary design? Yes, I've often wondered that! If you are a control manufacturer, of course, they aren't problematic. They figured the problem out, standardized the solution, and built it into their controls. Problem solved, period. The only problematic thing is replacing the function when you pull the control. Fanuc seems to have a decent reputation for servo systems and controls. :) I insist on believing there is no magic nor magic chip in a Fanuc control. Oh, there IS, INDEED, a magic chip! It is similar to one made by ST microelectronics, a bi-directional frequency to voltage converter, but it has been out of production for years. That is the L290, see http://pdf1.alldatasheet.com/datasheet-pdf/view/87940/STMICROELECTRONICS/L290.html for info on how it works. Pretty sad there's no current replacement, as this does everything you need. Jon -- This SF.net email is sponsored by Sprint What will you do first with EVO, the first 4G phone? Visit sprint.com/first -- http://p.sf.net/sfu/sprint-com-first ___ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
Re: [Emc-users] using fanuc drives and motors
Analog devices also made f to v's AD650 goes either way and still in production http://www.analog.com/en/analog-to-digital-converters/voltage-to-frequency-converters/ad650/products/product.html Dave Caroline -- This SF.net email is sponsored by Sprint What will you do first with EVO, the first 4G phone? Visit sprint.com/first -- http://p.sf.net/sfu/sprint-com-first ___ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
Re: [Emc-users] using fanuc drives and motors
Peter C. Wallace wrote: The AD650 has bipolar output but not quadrature input so would probably not be useful as a bidirectional tachmometer replacement. A quadrature to direction pulse converter would be a very simple circuit to make. The L290 interestingly enough is a sine/cosine quadrature input device, probably emulated easily with a DSPIC if needed. I think it will work fine with a digital input signal, too, if it were only still available. On the other hand if the velocity estimation from the encoder counter is good enough, why not drop all the external futzy whatziz and do all the PID loop in EMC... Yes, some people have advocated that, switch the servo amps to torque mode, and use PID2. Do the Fanuc drives need a analog velocity signal? That is, is their encoder/velocity feedback not built into the drives themselves? Yes, the typical Fanuc servo amp, from way back to relatively recently, were run in velocity servo mode, and a component of the control converted the encoders to velocity signals to give the amps the velocity feedback. It is possible to convert even old Fanuc amps to torque mode, but it requires moving wires and components on the board to bypass the velocity error amp. They do not take encoder signals, just enable, velocity command and tachometer. Jon -- This SF.net email is sponsored by Sprint What will you do first with EVO, the first 4G phone? Visit sprint.com/first -- http://p.sf.net/sfu/sprint-com-first ___ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
Re: [Emc-users] using fanuc drives and motors
Dave Caroline wrote: Analog devices also made f to v's AD650 goes either way and still in production http://www.analog.com/en/analog-to-digital-converters/voltage-to-frequency-converters/ad650/products/product.html I certainly don't see how you can get bipolar output from this chip, all by itself. it has no direction or sign input. Just Fin. You could connect two of them up to get a difference between the chip handling + and the one doing minus. That is what the L290 did, but it had a matched pair in the same package, so it would presumably remain balanced better. The reason why you need two sections is because of encoder dither. When the encoder is dithering back and forth across one count, that does not equate to real velocity, no matter how fast it is dithering. Any scheme using a single F/V converter and flipping the sign of the analog output based on the most recent direction would produce a significant output magnitude in response to dither. The dual scheme with difference would rightly produce a near-zero output. Jon -- This SF.net email is sponsored by Sprint What will you do first with EVO, the first 4G phone? Visit sprint.com/first -- http://p.sf.net/sfu/sprint-com-first ___ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
