PLC used as CNC to control Mill

starman

Member
Join Date
Jun 2003
Location
Wisconsin
Posts
2
Hello, I'm looking for advice. First of all I am new to the world of PLC's. I am getting involved into machines and PLC's for fun. I have a large copy milling machine that I am interested in changing to a full CNC capable mill. I have some interest in using the TI-405 series PLC's to control the mill because I have some and cost is low. The mill has rotory encoders to control the servo drives. There are tachogenerators for feedback and also the mill has glass linear encoders that I can use for feedback also. I am wondering what the capabilities of the TI-405 (435) are and if it is a good possibility to use them to control the mill. I am not worried about my ability because I have time. :) Also if there is anyone that has some knowledge about how DirectSoft32 will help me out here I would appreciate that too.

The project: Copy Mill to CNC using PLC's
The Copy Mill: HC-1600 from OKK full working order
The PLC's: TI-405 series with many I/O's to choose from
The programmer: 405 series handheld

Thanks.

starman.
 
What are you planning to keep from the existing controls for the milling machine? The motors? The drives? I don't think that Koyo offers a motion controller module for the 405. I didn't see one in my old (1999) catalog, but I also didn't go to the website to check.

When you say 'full CNC', what do you mean? You won't be able to create part programs using G codes in a PLC. You won't be able to do interpolation between axes. If you try to use the PLC to close the position loop, you'll probably be disappointed with the results. I'm not saying that you can't use a PLC to do motion control. I'm only saying that you have to bear in minnd that you'll be dealing with scan times in the 5 - 10 millisecond range or longer. That's an eternity when you're trying to achieve tight tolerance and rapid response. You may be able to position accurately and repeatably, but you won't be able to do it quickly.

Let us know more details of what you hope to accomplish. We may be able to offer some suggestions, or at least tell you whether your expectations are too high.
 
You are going to do this with handheld programmer?
eek2.gif
 
starman:

Unless the TI has cards made specifically for servo control (I have no experience w/ TI so don't know) you will not be able to achieve a CNC-like controller. Although PLC scan times can be quite fast, they usually don't have what it takes to do closed loop servo control... especially on multiple axes (The newer AB control logix can do this but it still requires a special card besides the processor).

Also, if you want to enter programs in G-code that would be a really tough nut to crack on any plc. They just aren't made to handle all the text parsing required for it. Maybe they have a BASIC language card which could help with that.

I'm not meaning to burst your bubble. Heck if I had that hardware and spare time to play with it I'd be in heaven :)
 
More indepth goal.

Ok, first of all-thanks for the responses they are helpful. As I mentioned earlier, I am a beginner. I plan to learn more about PLC's whether or not I can use them on my Mill. I just thought maybe put the two together for a much more cool project. The copy mill is awesome; I got it about a year ago and have been spending some time on it. It was hooked to 460VAC at one time and is 3 phase. So my work was cut out for me as I have only single phase coming to the shop. I built a single to three phase converter and rewired the 5 three phase motors and 5 transformers (that run the 10 AC-DC converters and 40+ circuit cards) to run on 240VAC (thank goodness for schematics!). After that it needed much work to get the basic funtions working and now it is almost fully functional. So that in itself was enough fun. But I heard about how close PLC's are getting to be able to be used for CNC control so I thought I would see what I can do with what I have. I have MANY I/O modules and CPU's. I have some Omiron and AB but "my best option" I have are the TI-405 series. I say my best only because of the amount I have and from what I read they have some good software that allows them to be controlled with a PC easily and with hobby priced software (DirectSoft32). I do have the handheld programmer but with the size programs I think the software is a must. I have heard AB are the top dogs in the industry but I only have the SL-150's. Ok-bored yet? I do want to have a CNC mill but if I will be disappointed using the PLC's I have then I will try another route. I will want to keep my existing controls (Copy ability) just because it is so darn cool to watch :) The mill is amazingly accurate for its size and age so I don't want to screw it up. All of the the encoders,tachogenerators and sync-transformers are working. There are 4 Minertia servo motors on it, one each for X and Y and 2 for the Z axis. It can copy a Dime to like quality and also the mill spindle has a travel of about 40"X40"X34" so you can do large projects also. I would keep the existing control cabinet with all the existing servo drives because they are good. If it is impossible to use PLC control for this project in your opinion let me know. Also if you all have other suggestions, I have an open mind. Hope this helps you to understand what I am doing and if you have specific questions; feel free to ask.

starman
 

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