Fanuc Spindle has low power
I've got an old Fanuc AC Spindle drive A06B-6044 on a Fanuc 6M controlled machine. The spindle motor is a Fanuc 3.
I can't figure out why this machine has low spindle "power" compared to it's sister machine sitting right next to it. It's been this way for the 2 years I've owned it, but lately I've been using it more and more and noticed this is a problem and not just the way the machine was made. For instance, the load meter stays under 10% all the way up until just over 4,000 RPM, Then as it gets faster RPM the load gets higher. At max 5,000 RPM the load meter creeps up to about 75%. On identical cuts from each machine, this machine is always about twice the load at the spindle compared to it's sister machine. Lately when the sister machine spins up it's spindle, this machine will alarm out because of excessive speed deviation. Basically the spindle has a hard time keeping up speed when the voltage in the shop dips a bit from the sister machine spinning up it's spindle. I've tuned up the logic top board for the encoder feedback signals to be the proper square wave height and offsets, so I don't think it's a logic issue. It seems to be related to power.
Also when the sister machine spins up the spindle it can get up to 150% load while accelerating. This machine pegs the meter at 200% while accelerating. I thought it was just the load meters themselves being different, but you can hear this machine bog right down when it's doing a medium heavy cut, where the sister machine performs the same cut with ease.
I tested the amperage on each leg going to the motor. The three wires are within 1 ampre of each other, this is consistent with both machines. This happens at all RPM speeds, slow or fast. Does this indicate anything?
I've just started reading about replacing transistors and capacitors in the Spindle Drive which seems easy enough. But I'm not sure if the problem is that, or the motor windings, or something else. I've checked all the fuses that I can find in the drive and they are all good. I also checked the 220V vs 200V switch.
I'm about to swap the entire spindle drive from one machine to the other to see if the problem moves. What do you think is causing the low power at the spindle? Anyone run into this issue before? Thanks for your help in figuring this out.
Benjamin
Barch Designs
877-201-9771
Re: Fanuc Spindle has low power
I swapped the spindle drives between the machines last night and this machine still has low cutting power. I'm starting to think there's a problem with the motor itself. Since the spindle turns with ease by hand I don't think any bearings are bad or sticky. I just replaced all the spindle bearings last year.
Is repairing a motor something I should tackle myself or is there some specialized equipment that is needed? Any other ideas what could be causing it?
Thanks,
Benjamin
Barch Designs
877-201-9771
Re: Fanuc Spindle has low power
Ben,
A quick check on Ebay indicates that the Fanuc 3 could be either DC or AC driven. Do you know if your motor is a DC or AC motor? Can you get the actual motor part number (the A06B number above is the drive unit)? There could be a couple of possibilities - if the motor is DC the magnets in the rotor could be losing their strength and thus require a higher current input to keep the spindle at speed. If AC the encoder could be misaligned which would then cause the drive to be out of sync with the rotor - if the motor has permanent magnets then weak magnets could also be a problem. In either case it sounds like the windings are probably ok as you have the same current through each. Repairing the motor yourself is probably out of the question as it will require special tools to re-magnetize/rewind the core. Have you considered a used Ebay motor? or looked online for companies that repair Fanuc motors? This place came up when I searched the web for "Fanuc 3": A06B-1003-B100 Fanuc 3 Spindle Motor - CNC Electronics .
Cj
ps.. After rereading your post you probably have the 3 phase motor.
Re: Fanuc Spindle has low power
Benjamin,
I would first make sure your motor code is correct in the parameters. Looking at the parameter book you will see that the motor model code sets a bunch of other parameters related to speed and HP. I have seen this many times in the past, and do you have the motor encoder controlling the speed or a separate encoder? Just a few things to check. I worked for a CNC machine builder for 31 years and have seen all kinds of crazy things. Some new motors have dual windings also, one for high speed, low torque and another for low speed, high torque.
Re: Fanuc Spindle has low power
Spiker - I thought the same thing, but Ben mentioned that he swapped the drive units. If indeed the motors are the same as stated "sister machines" then swapping the good unit over should run the motor correctly. This brings up and interesting test... Ben - swap the drive in the machine that is not working into the good machine and see if the "good" machine still functions normally. This will eliminate the drive unit/parameters as the problem.
Cj
Re: Fanuc Spindle has low power
The motor is an AC Fanuc Model 3 A06B-0704-B001 (which Fanuc tells me is discontinued and replaced by A06B-1003-B150) That replacement number doesn't seem right to me, but maybe...
I called Fanuc this morning to see if they could help in diagnosing if it is a motor problem or something else. I checked the motor legs between each other and each test was 0.5 - 0.6 ohms. Then I tested each motor leg to ground and each test was over 20 Mohm (The upper limit of my ohmmeter). This seems to indicate the motor electrical is "good". Could weak magnets really be this issue? I have considered an eBay motor and it's been my go-to place for previous CNC equipment. If it was an easy swap I might be more inclined to just try it and see, but the motor is 160 pounds and on top of the machine. Not something I want to swap unless I absolutely have to.
Next I called my 3 phase converter company. After many tests we thought the wire going from the 3 phase converter to the CNC may be too small. I had 8awg copper and now replaced it with 2awg Aluminum. This didn't affect the load on the spindle after putting in the bigger wire.
I did have some success bouncing some ideas off of Fanuc. I have 240v 3 phase power. The drive was powered from a 200v transformer and drive's switch set to 170-220V (selector switch for 170-220V vs 220-242V). If the transformer is undersized, the drive could be starved for amperage. This transformer also powers all the other general motors around the machine. So I changed the switch to 220-242V and bypassed the transformer. Surprisingly this lowered the load at max 5,000 RPM. It went from 80% previously down to 40% now. I can now get up to about 4,500 RPM before the load meter starts to creep up. This is better, but I really don't think it's "right"
As far as feedback, It uses a pulse generator built into the motor. The drive's circuitry turns that into quadrature square waves. Long story short I have the service manual for the drive and a few months ago I adjusted the variable pots to set the feedback to nice quadrature square waves with proper offset and amplitude. It was giving me some issues of dropping sync which led to that "tune-up" and buying a spare Fanuc board. Before I knew how to tune the Fanuc drive I actually replaced the Fanuc Drive with a brand new Delta VFD and ran the machine for a while like that. I didn't pay much attention to the load (load meter wasn't hooked up) when using the Delta drive last year as I wasn't using the machine very often.
I have a replacement eBay spindle motor saved and can go pick it up tomorrow from a machine stripper on the other side of the state. But again, I really want that to be the last thing to do as it's 160 pounds and on top of the machine. Do weak magnets or dirty motors affect the load similar to what I am seeing. If it really does turn out to be the motor I will end up replacing the motor with an eBay spare and sending the original out for refurbishment.
Parameters related to spindle/motor I've found in the manual are following. I don't see any obvious things that need changing.
037 SPGST (0-255) [15] spindle motor rev at spindle gear shift
038 SPSOR (0-255) [30] spindle speed at spindle orientation
119 SPDLC (-8191 to +8191) [0] Spindle Speed offset compensation
132 GRLMAX (1-9999) [1124] low gear RPM at 10V velocity command voltage
133 GRHMAX (1-9999) [5000] high gear RPM at 10V velocity command voltage
134 GRHMIN (1-9999) [1125] lower limit of high speed gear
135 SPDMIN (1-4095) [73] lower limit of output value to spindle motor
136 SPDMAX (1-4095) [4095] upper limit of output value to spindle motor
140 SANGN (700-1250) [1000] data of adjustment for gain in spindle analog output
my parameters stop at 4127. I didn't see anything about motor codes in the manual parameter area or any charts. Both machines are a Fanuc 6M
CJ, It's heavy, but I feel the final test is indeed to put Thing 2's drive over in Thing 1 and see if it will run that motor ok. That will guarantee the drive is OK. (Currently my project for the rest of tonight)
Thanks,
Benjamin
Barch Designs
877-201-9771
Re: Fanuc Spindle has low power
Ben
"The motor is an AC Fanuc Model 3 A06B-0704-B001 (which Fanuc tells me is discontinued and replaced by A06B-1003-B150) That replacement number doesn't seem right to me, but maybe..."
I'll take Fanuc's word on that one.
"I called Fanuc this morning to see if they could help in diagnosing if it is a motor problem or something else. I checked the motor legs between each other and each test was 0.5 - 0.6 ohms. Then I tested each motor leg to ground and each test was over 20 Mohm (The upper limit of my ohmmeter). This seems to indicate the motor electrical is "good". Could weak magnets really be this issue? I have considered an eBay motor and it's been my go-to place for previous CNC equipment. If it was an easy swap I might be more inclined to just try it and see, but the motor is 160 pounds and on top of the machine. Not something I want to swap unless I absolutely have to."
I hear you on the weight... I have lifted a red cap this same size off a mill.
"Next I called my 3 phase converter company. After many tests we thought the wire going from the 3 phase converter to the CNC may be too small. I had 8awg copper and now replaced it with 2awg Aluminum. This didn't affect the load on the spindle after putting in the bigger wire."
Is the converter running the other mill as well? I helped someone else a while back who couldn't get his spindle going... He was getting a Low Voltage error when he tried starting the spindle. I would expect the same to happen in your case if your converter/wire were undersized.
"I did have some success bouncing some ideas off of Fanuc. I have 240v 3 phase power. The drive was powered from a 200v transformer and drive's switch set to 170-200V (selector switch for 170-200V vs 200-242V). If the transformer is undersized, the drive could be starved for amperage. This transformer also powers all the other general motors around the machine. So I changed the switch to 200-242V and bypassed the transformer. Surprisingly this lowered the load at max 5,000 RPM. It went from 80% previously down to 40% now. I can now get up to about 4,500 RPM before the load meter starts to creep up. This is better, but I really don't think it's "right""
Not surprised... any time you go to a higher voltage the current in the motor will be lower. And yes something is still off. I would expect your load meter to be less than 5% with no load.
"As far as feedback, It uses a pulse generator built into the motor. The drive's circuitry turns that into quadrature square waves. Long story short I have the service manual for the drive and a few months ago I adjusted the variable pots to set the feedback to nice quadrature square waves with proper offset and amplitude. It was giving me some issues of dropping sync which led to that "tune-up" and buying a spare Fanuc board. Before I knew how to tune the Fanuc drive I actually replaced the Fanuc Drive with a brand new Delta VFD and ran the machine for a while like that. I didn't pay much attention to the load (load meter wasn't hooked up) when using the Delta drive last year as I wasn't using the machine very often."
Hmm.... If you used a standard VFD (one without programming for a Permanent Magnet (PM) motor) on your motor there is a possibility that you can demagnetize the magnets or re-magnetize them incorrectly. This is due to the VFDs use of the full voltage when operating. The VFD uses Pulse Width Modulation (PWM) at several kHz to create an "average" voltage. What this means is that your spindle motor is getting hit with super fast pluses that create large current spikes in the core. With enough power you can demagnetize/re-orient the magnetic field. A little background on motors: Any motor in good shape once spun up will generate a "back current (also called back emf)" (I'm simplifying this a bit) that opposes the incoming power, aka in an unloaded state the motor should be drawing very little current. When you load the motor the input current climbs as the motor adjusts to maintain the speed. for instance - I helped a guy out with a shaper that used 120 Hz rated motors (spun at 7000 rpm). He was trying to use them at 60 Hz and confused as to why the motor was cooking itself. Basically, the motor was running at half speed at the full voltage and the current was about twice what you would expect - all because the motor could not generate the correct back emf at 60 Hz . How does this affect you? If the magnets are damaged or weak the motor will not create the required back emf and your current requirements will be through the roof.
"I have a replacement eBay spindle motor saved and can go pick it up tomorrow from a machine stripper on the other side of the state. But again, I really want that to be the last thing to do as it's 160 pounds and on top of the machine. Do weak magnets or dirty motors affect the load similar to what I am seeing. If it really does turn out to be the motor I will end up replacing the motor with an eBay spare and sending the original out for refurbishment."
The motor is a sealed unit - it really should be clean inside.
Cj
Re: Fanuc Spindle has low power
After putting Thing 2's spindle drive in Thing 1 to see what would happen it runs the spindle just fine. The load meter stays low even at max RPM. So both drives run Thing 1 spindle ok, but both drives report 40% on the load meter at max RPM on Thing 2.
But......I've made an embarrassing discovery. Everything is not identical between the 2 machines. Sure the AC drive is exactly the same, but the problematic Thing 2 has the Fanuc Model 3 spindle motor and Thing 1 actually has a Model 6 (A06B-1006-B100). So even though the electrical plate is almost identical, the motors look the same size, they have the same RPM and voltages, The model 6 has lots more power/torque. That explains the difference in spindle loads for the same cut.
The Model 3 is 5.5kW for 30 minutes (3.7kW cont)
The Model 6 is 7.5kW for 30 minutes (5.5kW cont)
But does it explain why Thing 2 stays at 5% load up to 4,500 RPM and then quickly rises to 40% as it heads to 5,000 RPM? That part still seems weird and not right.
I see some possibilities
1) Thing 2 motor magnets are weak
2) It's just the way this machine is
I don't remember testing the difference in amperage going through Thing 2's Spindle Motor between 4,000 RPM and 5,000 RPM to see if it indeed pulls lots more amperage. Is it actually pulling that much amperage or is it just reporting high load?
I couldn't get Thing 2 to alarm out by spinning up Thing 1's Spindle. Of course they were both just cutting air so that may change once I start making chips and loading up the spindles. After running bigger service wire to Thing 2 and rewiring Thing 2's Spindle drive directly from 240V, bypassing the transformer, I'm hoping that may "fix" my problem. At the end of the day I can live with a weak motor if both machines can stay running simultaneously. I'm going to put everything back together and start cutting and see what happens.
Benjamin
Barch Designs
877-201-9771
Re: Fanuc Spindle has low power
Ben,
Took a look at the two motors I have in my shop. I have a Model 3s with the same ratings as yours. Did a quick check and it is a standard non-PM 3 phase motor. I also watched the load meter my bigger mill while it was running a project (it has the Fuji equivalent of your Model 6 - also a non-PM motor). At 4800 rm the load was up to 10% while at speeds less than 3500 it floats around 4 to 5% - it is turning a gear set and a bt50 spindle (I had it in high gear so 1:1 ratio). So your motor is most likely just fine. Is your mill geared? Or belt driven with any ratio that is not 1:1? Gearing will require additional power at higher speeds. I agree that a jump to 40% load seems a little off.
Cj
Re: Fanuc Spindle has low power
CJ, yes it is a geared spindle setup. Both machines are 6,000 RPM motors, but Thing 2 is geared 1.2:1 so 5,000 RPM at the spindle in high gear. Thing 1 is geared 1:1 so it goes to 6,000 RPM and it stays around 10-15% during all RPM's with an empty spindle in high gear.
On Thing 2 I was able to take load readings during spin up and see what ampres are being pulled at different RPMs while seeing what the load meter reports as well.
During spin up it is pulling 28 Amps
5% load 2,000 RPM = 4.5A
5% load 4,000 RPM = 9A
50% load 5,000 RPM = 14 A
Later today I will have Thing 1 all put back together. I will try to get Thing 2 to alarm out as it did before. If it does, my next step is the motor replacement and I'll take a drive to pick it up tomorrow.
Benjamin
Barch Designs
877-201-9771
Re: Fanuc Spindle has low power
Looking at your current readings - something is weird.. Your more than 50% load as full load is 17 amps (at least for the 3.7kW). Thing 2 may be geared 1:1 but limited on the top speed in the parameters. My 11m is that way. At this point I'd hesitate to replace the motor, but you have swapped the drives back and forth. If anything I'd upgrade - especially as the motor is not going to be easy to get in and out. I get nervous about buying parts when there isn't a cut and dried cause.
Cj
Re: Fanuc Spindle has low power
Gotta ask, since I've run in to this several times doing service, do you have the correct gauge wire to the machine?
Sent from my A3-A20FHD using Tapatalk
Re: Fanuc Spindle has low power
Yes, I now have 2 awg aluminum going to the machine (2-2-2-2). I had 8 awg copper (8-8-8-8) a few days ago, but my 3 phase company suggested going higher. There was no difference in load readings after upgrading the wire size. I'm powering the machines on this morning to test both machines running. In a few hours I will know if Thing 2 is working any better from bypassing the 200V transformer and running the drive from 240V.
Benjamin
Barch Designs
877-201-977
Re: Fanuc Spindle has low power
Well so far so good. I was running Thing 2 at max RPM cutting medium heavy cuts (load was about 90%) and it stayed strong even while Thing 1 was cutting/changing tools/spinning up.
I'll let both machines cut the rest of the day and see if anything weird happens. At this point I am tentatively calling this solved. I believe it may have been a combination of the amperage starvation from an undersized transformer trying to power all the motors on the machine (coolant pump, hydraulic motor, etc) along with the spindle drive. Removing the spindle drive from the transformer and running bigger gauge wire to the machine seems to have helped enough so far that both machines can stay running.
While Thing 2 load still seems a too high at max RPM, it doesn't seem to load up anymore when Thing 1 spins up. Thanks everyone for your advice. Sometimes it's good to have others help who don't see the machines on a daily basis.
Thanks again,
Benjamin
Barch Designs
877-201-9771
Re: Fanuc Spindle has low power
An unexpected pleasant surprise! My face mill cuts look nicer. Previously I could see oscillations in the cut, even though it felt smooth. I bet that was from the spindle drive starving for power to stay consistent. Now it's a nice consistent cut and looks fabulous. My customers are going to love the way this looks.
Benjamin
Barch Designs
877-201-9771
Re: Fanuc Spindle has low power
Nice! Just out of curiosity what type of phase converter are you using? Is it rotary or electronic?
Cj
Re: Fanuc Spindle has low power
Both machines just completed a full run of parts simultaneously at max RPM and it went fine. No spindle speed issues at all.
I installed a 40HP rotary style (which uses a heavy 300lb 33kW idler motor) around 2012 from American Rotary. I've been very happy with it and the company service. I run both my CNC machines and a 1.5HP Bridgeport from it. They told me their new models are better regulated and have higher starting torque. They offered a trade in/upgrade price for the control box.
Benjamin
Barch Designs
877-201-9771
