Positioning

[Guest eaygin]

Hi, I am a mechanical engineer studying some otomation systems for HIPAK A.S, where I work. I am working on a project at which we are trying to control a milling machine by PLC. The main and the biggest problem is the result of job being done by the machine. To achive tolerances such as 0,002 mm is my goal. Does anyone have experiences about this subject? Can I make positioning control without using FX2n-1PG? Can you show me some reference documents? Thanks to everybody from now... AYGIN, Ertem

[panic mode]

0.002" in a mill? Is it a paper mill? And to answer you question, positioning can be done in numerous ways and all PLCs. Some are better suited for certain things but they all can be used for one or the other way of positioning. One common way is to use VFD or servo. FX series PLCs would use first inputs for position feedback (quadrature encoder) and first outputs as pulse train generator to control the servo or stepper drive. The high speed outputs required for pulse trains must be transistor style. Check the Product Selection Guide for details. Models with transistors have "MT" in the part number Can you provide more details on your application?

[Guest eaygin]

This is a vertical milling machine at which the tool holder is fixed and the workpiece table moves in 3 axis. I am trying to set up a system to work in tolerances (SI) 0,002 mm. This is my main goal, but tolerances like (SI) 0,01 mm will be enough accurate. We are using the milling machine for broach manufacturing. So, I see that, I will not have any problems while programming the PLC. The latest thing I am scared about is the linear encoder. Is there any special brand that works perfectly with Mistsubishis? Thanks again... AYGIN, Ertem

[panic mode]

Why not simply use rotary encoder attached to the top of ballscrew of your vertial axis? For example if the pitch is 5mm and you use 1024 count encoder, you would get resolution of 5mm/1024=0.00488mm and the 4096 counts encoder you would get resolution of 0.00122mm. Those are very common encoders (read cheaper) but you can go with higher resoultion like 8192 or 16384 counts and get even better presission if that's what you want. I would not recommend connecting encoder to the motor because you have to take into account stretching and slipping of the belt or play of the gearbox (or whatever system you use to connect motor to the ballscrew). Just keep it simple and connect encoder to the final shaft.