Machsupport Forum
Mach Discussion => General Mach Discussion => Topic started by: DNB on February 22, 2007, 02:17:27 AM
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Hello All,
I am strategizing the retrofit of my Enshu Accu-mill and have a question about the encoder. The P100 from Skyko states that it needs a quadrature encoder. My controller manual states that I have Fanuc Model 0 DC Servo motors with built in pulse coder. Are pulse coders the same as quadrature encoders? If not, how can I determine if they are quadrature?
Thanks,
David
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Pulse Coder is the Fanuc term for a quadrature encoder. Fanuc Pulse Coders are usually 2,000 or 2,500 pulses per revolution.
Darek
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So that means the signals are 5V A/-A, B/-B and index C/-C?? I also have a fanuc controller which may need replacing...not having to buy new encoders would be fantastic :) Figuring out how to do spindle alignment for tool change may be a challenge though :(
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^^^ Correct, but the encoder cout will be too high for Mach3, 2,000 count X 4 = 8,000 counts per turn. You can use it if the drives have a multiplier.
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Hi, David
It all depends on ball-screw ratio.
Not to disagree hear, but 2000 count encoders will work, may have to use 35k or 45k kernel speed on Mach to get the top speed back-up and might not archive the 300 ipm as before, speed isn't every thing.
How many turns of servo to move table one inch, I think I read another post where you stated that its a .0001 accuracy, thats a .8 inch per turn of servo / ball-screw ratio.
Lots of machines use 5 turn per inch ball-screws 200 steps per turn steppers gives them .001 accuracy, If it had a 8000 steps per turn servo I would agree.
Check your servo turns per inch, it all depends on ball-screw ratio.
Do plenty of research
You can probably use your servo amps with +-10 volt to step / dir input cards there several out there.
Just another opinion hear.
Hope this Helps, Chip
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One other point to consider about the 0 model servo is the tach signal for the Velocity Unit ( Fanuc's term for servo drive.) is generated by a F to V converter on the motherboard. By the time you built or bought a circuit to perform this you could probably just replace the Velocity Unit with a Rutex drive ( No tach signal needed.).
Which Fanuc control do you have?
Darek
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Hello all,
Thanks for your great input. I am gearing up for a retrofit and am just trying to finalize the details. I will post pics of the project as it progresses.
HillBilly: I have a Fanuc 3M-A and I believe the control unit is a honda tshushin m9 mr-20rma. I also believe the machine and controller were built in 1981. I see that the pulse coder goes to the control unit but I do not see anything in the wiring guide that it is passing through an F to V converter. Is it just part of the control unit? Also, I thought the pixie can handle this situation since it only asks for signals from a quadrature encoder. What am I missing?
afn09556: I have a maintenance manual, connecting manual, and general use manual. The machine manual is in storage. Arrrgh! As such, I do not have turns per inch data. You are right that it has .0001 inch accuracy. I also do not have figures on the pulse coders PPR information. Arrrgh again! Do you know how I can find this data without digging the manual out of storage? Also, you mentioned I could use +-10 volt to step / dir input cards. Do I need this? My wiring diagram states that the pulse coder uses 5 volt. I am researching like crazy. Good thing is its fun!
DennisCNC: What is a multiplier?
Thanks again. Also, I can't help but post some pictures below. Forgive my indulgence.
Picture of motor. Why did the prior owner paint the motor? I guess I'll have to scrape the paint for a view of the specs.
Picture of one of the drives
Picture of one of the current control board
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Hi, David
Your servo control uses the encoder to stay on track and bootstrap encoder info to the +-10 volt to step and dir cards, which interface to Mach3. Realy hard to say without the wiring Diag's Though.
I did a conversion, simmilar to yours on a Waterjet Cutter 4 axis, works Great.
Dig out the Manual's out of storage your going to need them
On the Ball-screws if you can get to one of them X or y turn it one turn measure table movement, are your servos direct-connect to ball-screws. Look's like you can turn the Y axis on front of Mill.
Where do you live?
Thanks, Chip
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In the last picture posted the 3 little black boxes labled A-PC06, in the lower center of the mother board, are the F to V converters. This is what is inside of them.
Darek
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Hi Guys,
Many points have been raised and I think many of these issues are addressed through the use of skyko's p100. I will summarize my understanding below. Please let me know where I am going wrong.
1. Fanuc pulse coders are usually 2,000 or 2,500. From my reading it seems that 2,000 is usually for Fanuc brush motors and 2,500 are the brushless motors that have Hall signals. I am 95% certain my pulse coder is 2,000. According to skyko the p100 is for 2000 count encoder Fanuc motors.
2. Motor speed will usually be slow using a 2000 count encoder and mach 3. However, the ball-screw ratio may improve the speed and the 35 or 45 kernel speed may need to be used. If slow you can use a multiplier to speed things up again. I do not have the information on the ball-screw ratio at this time. However, the skyko p100 comes with a step multiplier just for this purpose.
3. The Model 0 servo uses a F to V converter to provide the tach signal for the velocity unit. This is a frequency to volt converter? I think the p100 can be wired directly to the encoder and it will handle any necessary conversions. For reference I have copied the wiring diagram below. I think it is ok to post here as this is free to download from Skyko.com. Am I missing something? Skyko says it needs the 5v A and B signals from the encoder and nothing else.
Additionally, Skyko says the following: "The Pixie implements a Proportional, Integral, Derivative (PID) control loop using position feedback from the motor shaft in the form of quadrature encoder signals (denoted by channel A and channel B). Each time through the loop, the Pixie calculates analog reference voltages to control the speed and direction of the motor to bring the current actual position of the motor shaft to the desired position (usually commanded by a control host through the step and direction signal lines). It does this calculation 10,000 times per second to achieve and maintain the desired position through a changing load."
4. Regarding the need for +-10 volt to step / dir input cards to interface with Mach 3. Skyko says, "[the p100] has a jumper selectable analog output range of ±10v or ±5v which is compatible with many commercial motor amplifiers." Is this the function needed?
I really appreciate your input.
David
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The problem is your velocity control unit (drive) will not function properly without the tach signal. These units are velocity drives not current drives ( Current drive is what the pixie wants to see with its PID.). I modified the Pixie diagram to show this. If you do use a F to V converter ( US Digital ect...) the I and D terms in the Pixie will be basically useless ( This part of the tuning will be in the drive.).
Darek
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Thanks Darek,
I have a few more questions and thanks so much for your insight thus far.
1. Is this the type of F to V board I will need: http://www.eidusa.com/Interface_Boards_F_to_V.htm
2. Were the rest of my assumptions in my prior post correct?
3. If the I and D functions are useless, is the p100 the way to go? Will the board still work even though it won't handle the encoder signal? Is there an alternative board or combination of boards to use?
4. Suppose I was ready to junk the entire control system. Meaning, I will only have the machine, motors, and external devices (spindle motor, coolant, etc). What system would you reccommend I use? I don't want to break the bank but I want a system that is appropriate for my machine. Let me know if you need additional specs.
5. The machine is currently using 3 phase. If changing the controller setup, would it remain three phase or is that dictated by the motors?
Thanks so much.
David
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The F to V converter has to be bipolar, positive voltage for one direction and negative for the other ( I don't think the ones you posted will do that.). It also needs to output 3V per 1000RPM. Here is a link to the US Digital one.
http://www.usdigital.com/products/etach2/
Once you figure the price of this with the Pixie You would probably be better off with the Rutex step and direction drive.
http://www.rutex.com/us/home/index.htm
You will need a DC power supply for the Rutex drives. You should be able to use the existing servo transformer and add some bridge rectifiers and capacitors. If you are running this machine on a phase converter this would be preferred over the existing system. To elaborate your Fanuc velocity control units are the ones with six SCR's that fire on the three phase power. I have found these drives to be finicky on phase converters. You sure can not perform the scope pulse alignment as covered in the maintenance manual.
Darek
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Hello Darek,
Do you think that is better a Rutex or original amps. with bigger servo motors? I have fanucs 20M and I am thinking of rutex R2020, but my servos are 213V , 18 A continuos, 40 A peak. Do you think rutex can handle it. Or can I use pixies with etach2 conected directly to the servo amp.
George.
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George,
Rutex has a file MYSTIQUE.PDF about motor and drive sizing on this page.
http://www.rutex.com/us/home/index.htm
My opinion would be the R2020's would work fine for the Fanuc Model 0 and 5 servoes. The Model 10 would be boarder line and NO WAY on Model's 20, 30 and H10. I would not want to use a breaking resistor in series with the armature as suggested in the MYSTIQUE.PDF.
Darek
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Darek,
What would you do in my situation??
Thanks,
George
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Your velocity control units should have a DC power supply with PWM output (A20B 0009 0320). These are good drives. I would try to use them. With that being said a tachometer or a F/V convertor must be used.
Once you have the drives working stand alone, +/-10v analog signal, without the 6M mother board. At this point you can either choose a step a direction to analog converter or a controller board such as Galil or Delta Tau.
Darek
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Darek,
Do you think that this Glentek CEMF to Velocity Feedback Conversion Card will work as a F/V converter? (http://)
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I have never seen that one. I could not find any support documentation for it on the Glentek site.
Darek
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A friend has broken Enshu Accu-mill just like the one pictured here. I offered to try to repair it. Does anyone happen to have the schematic diagrams for it or know where they can be downloaded from.
vr/rik