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SmoothStepper and PLC with Modbus
« on: November 18, 2011, 12:25:12 AM »
Hy, brand new on this forum.
So... let’s go into it.
I have a milling 3 axes with gecko drive, spindle with servo, and automatic tool change. All do by myself. The motor control is made by Mach3 and all the rest is made by a Fatek PLC. I feel it's more reliable and safe to dedicate a PLC to control limits and estop because it's closer to the energy that way.
The spindle has 1 HP at 10000 RPM and all axes are mounted on 0 backlash ball screw and linear bearing. That makes the machine pretty fast.
I use tis milling on the past 2 year, toke me 3 year to build it.

A couple of day ago, I run my biggest and complicated G-code on that mill. An 3D mold for plastic part. The finishing run toke 25000 line of G-Code.  After the machining end up, I realise that there is some missing step. I look upon this forum and conclude that the tension on my PP wasn’t high enough. Then I decide to use SmoothStepper drive to overpass this problem. In fact, if I still miss some step, I can simply put some encoder on the step motor. Till yet, everything look fine.
After installing the SS driver and updating Mach3 to the lasts version, thing became worst.  All my input from Modbus stop working. I try to reinstall and reconfigure all the communication on the  Mach3 seting but never work.
When I open Mach3, SS throw me a error screen who tell me that Limits and estop are on another port than the SS port. All my input are set to the port 0 (Modbus port) when I open the debugger screen of Mach3, I see the led blinking as it normally do when I push my estop button on limits. So the config is good but something in the SS driver cut the communication or I don’t know what.
If I restart Mach3 on PP without SS, all input work well. Is there something I can do to fix this?
Really sorry for my poor English, I try to do my best

Offline Jeff_Birt

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Re: SmoothStepper and PLC with Modbus
« Reply #1 on: November 21, 2011, 08:51:25 AM »
Quote
The motor control is made by Mach3 and all the rest is made by a Fatek PLC. I feel it's more reliable and safe to dedicate a PLC to control limits and estop because it's closer to the energy that way.


My friend you are simply wrong. Your EStop circuit should NOT depend on a PLC, the SS, the PC, etc to run correctly. You have in fact made your system more unsafe by using your PLC to control your EStop.

Also, the limit switches MUST be tied directly to the motion control device. You cannot run them through modbus as there is too long of a delay in the signal reach Mach.
Happy machining , Jeff Birt
 
Re: SmoothStepper and PLC with Modbus
« Reply #2 on: November 22, 2011, 10:07:57 PM »
I have no delay problem with the limit switch, eache time i run the machine full speed into the limit, i don't crash. The main reason is that the limit trig a Estop.
The Estop shut down all drive directly and aply brake on the spindle with a releay who is normaly open. If we talk security, i think it's a again law and security principle of machine to not have a estop wiered like this. If worker use the machine and an accident occure, the worker security agency (CSST in Canada) will make an big investigation and close the shop. I mean if it's a small shop who can't pay the several k$ penalty. Im not realy sure about all this but...

So what you think about those sentence? i am right?
Re: SmoothStepper and PLC with Modbus
« Reply #3 on: November 22, 2011, 11:55:10 PM »
A couple of comments.

There is NO problem running the limits through a PLC as long as the delay in getting the limit signal to Mach3 are catered for. This is particularly true if the PLC is dealing with the limits and is only informing Mach3 that a limit has been activated.

Also, having the PLC process the limits and activate an ESTOP as a result is also NOT a problem, as long as you also have the mandatory manual ESTOP buttons within reach of the operator. These switches need to remove power from the drives in accordance with the safety class of the machine.

In some classes of machines it is more dangerous to just remove power than to do a controlled ESTOP sequence. If you are only relying on your PLC to manage your ESTOP inputs, you need to ensure that your PLC is of a type accredited to do so.

As to a conflict between Modbus and the SS, what Mach3 Modbus Interface are you running? It has two, an older legacy one where Port 0 is defined as the Modbus port,
and a later one that supports plugins.

If you are using the older one, my guess is that the SS is trampling over and using the port 0 inputs/outputs that were assigned for Modbus use.

Another problem is that I'm not sure as to whether you can tell the SS to ignore some of the inputs such as limits, if you want to manage them via a different method, such as Modbus.

I hope this helps.

Cheers,

Peter.

----------------------------------------------------
Homann Designs
http://www.homanndesigns.com
email: peter at homanndesigns.com

Offline Hood

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Re: SmoothStepper and PLC with Modbus
« Reply #4 on: November 23, 2011, 06:28:31 PM »
SS works fine with the old style interface, its what I use on all my machines.

What you may need to do is use an output from the PLC that signifies the E-Stop and put it in to the SS and configure in Ports and Pins for the E-Stop.
Hood
Re: SmoothStepper and PLC with Modbus
« Reply #5 on: November 24, 2011, 10:22:55 AM »
Good, i finaly redo the config and realise that i have some problem in the modbus config. Estop, limit, all working fine.
Now i want to make solid threding with my servi spindle and have couple of question.
The spindle is a Parker brushless servo motor with his drive.
I use Step and Dir to command the drive via the pin 9 and 14 on the port 1 on the SS board
I get feedback from the drive on the diférential input port 3 on the SS
Feedback is has the form of A-B encoder.
I set the encoder 1 to map the port 3 pin 4 and 5 from de SS in Port and pin mach config.
I try to set the index pulse to port 3 pin 4 and 5 but the encoder has 1000 pulse per turn and DRO RPM show a way to high speed
But then, im a bit confuse.
How can i use this encoder to show the actual speed on the DRO RPM.
How can i use this encoder to control the pid loop for spindle feedback?
Do i need feedback loop to make solid threading?

Thanls in advance

Offline Hood

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Re: SmoothStepper and PLC with Modbus
« Reply #6 on: November 24, 2011, 01:31:19 PM »
You can not do rigid tapping, well you can but its not a case of encoder feedback.
Ok so first things, you really need the index pulse of the encoder rather than the A and B pulses, you then set that as Index in Mach and you will get the spindle reading. You could possibly use either the A or B pulse and use the ratio in the pulley setup but best just to use the index as its simpler and will be more reliable.

Now rigid tapping, as you have a servo on the spindle you can use SwapAxis() in Mach to turn the spindle temporarily into an A axis and then you can rigid tap or you can use a floating holder without swapping axis, and tap  in the normal way. The floating holder will allow slight variance if needed and is an easier way to do things as you can just use a G84 instead of having to work out A and Z axis motion, not really too much of a hassle but certainly more complicated than G84.

Hood