I am a final year engineering student. In my final year project I will be using a closed loop process to determine the position of a roller in a roll bending process. I will be measuring the Force on the Roller pressing on the work piece, Curvature of the work piece, Distance Traveled (to determine and control slip if any). The bender will consist of 3 rollers with the middle roller movable and the outside 2 will be stationary at all times. The output of the system will be the automatic positioning of the middle roller, dependant on the output curvature of the machine.
I have a good experience with Allen Bradley, Mitsubishi and Siemens PLC's but I'm very rusty with the analogue side of things. If I give a PLC these Analogue inputs can the PLC do the math to control the process... e.g. Can it determine the Moment/Curvature Relationship?
If not... can anyone suggest a product that can...? I've heard Lab View will do the trick but I know nothing about Lab View.
All PLC's will do basic math functions, at least all of the ones you mentioned that I know about. If you need higher math functions then your going to need a higher priced unit.
LabView is a PC based product, MAC, Windows, Linux at least the way I understand it. I tend not to use PC's for control systems. Overhead is to high and they tend to have a lot of overhead that is not needed for a machine to produce a product in a lot of cases.
As has already been stated all PLC's will do some math functions. None of them are geared to anything too complex in the math department.
It strikes me that, if this controller is to be assigned to the machine, you will have at least two output actuators to control with about seven process sensor inputs (there may be other peripheral inputs and safety functions). The required actuators would seem to be the means for moving the middle roller up and down and the means to move the material to be bent with one or two degrees of motion (linear through and/or roll round). I know of a company that use such a machine already and it is a joy to watch the machine in operation bending pipework in quite fancy designs.
You need to sit down (with pencil and paper) to work out exactly what the system consists of in terms of all the inputs and outputs. Treat each actuator separately but note when the sensory feed for both is shared. At this early stage do not worry about what is going to provide the control. Just get the control plan very clearly described.
Once you have the control plan (which should include the relational formulae between inputs and outputs) you should then evaluate the operational speed and work out the required perfomance of the controller hardware. Modify the control plan to include this information. Only then will you be able to ask for further assistance with a well phrased and specific question about what hardware will properly suit the application. Do not forget to assess the safety factors for the machine and how you are going to protect the operators.
The above, I am sure you will be aware, is a more holistic approach to system development and should yield a control system architecture that fits the application really well (you may decide that two controllers are required instead of cramming all functionality into one). As you already know of some PLC products I expect you may look at those first. However, you may sometimes find that developing an embedded control system from a bought in SBC, and adding I/O conditioning to that, would be a less expensive option (there are lots of free tools available for a variety of languages and processor families). This would provide the means to do more complex mathematical functions in less time. The dis-advantage of the embedded approach is that you may loose the ability to update the programme with the system running (which most PLC's do quite well) unless you paid a lot of attention to retaining the ability to do that.
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