S7 Program Help

Hi,

I'm after some help with some program development. I have an extrusion machine running at approx 2.2 meters per minute. This value varies as temp of product entering extruder, amount of product entering extruder. In order to try and control some of these issues I'm looking to install a frequency counter to calculate millimetres per second to then control the MM440 via profibus. I have a rotary wheel that sits on the exit of the extruder and a inductive sensor counting.

Wheel circumference = 221.44mm
Wheel input counts = 18

I would like some advice how to go about writing some code for this problem.

Regards

Hi
When I last worked with Extruders the width of the extrustion was critical... what is critical for you?

In my case I measured the output width every 10 seconds and did a calc to make minor speed adjustment to the extruder.

You may need IR temperature monitoring of your raw materials if it is affecting the process.

Provide a bit more info for a better answer

Hi thanks for your time and help. Know that I've studied the machine and have a bit more experience with extruding the infeed is not so critical now neither temp. These do still alter the extrusion but very minor. I have sorted the software to control this. I want to add loop to monitor the material extruded, I've made a wheel with 18 inputs per rev. Know I just struggling with the code as how to do it I was going to have a timer say 2 seconds and see how many pulses I get, then do calcs, then reset timer and carry on. Is this way ok or is there a better way?

Thanks again

What is the accuracy requirement?
0.1%? 5%?

Whats sort of Extruder is it ? Whats the output in Kgs/Hr ?

Hi
If my maths is correct your wheel is only giving you 1 count every 12.3mm which is probably a poor signal resolution if you require high accuracy. This is about 3 pulses per second at top speed. I would consider looking to fit a tacho onto the spindle of the wheel and get a lot more counts to improve resolution. Also consider the wheel diameter to get a sensible pulse width..maybe 10 per mm for example,depending on your desired accuracy

What product are you extruding? Rubber? Plastic? Aluminium? etc

You need to be aware that the wheel may slip on the product /takeoff conveyor and give a false reading. Additionally the product itself may slip on a take off belt/roller etc

Also I would try and measure as close as practicle to the extruder. As you make a speed change the adjustment may not be seen straight away which will cause you to over correct

As said , please give more info to get a good answer

Hi thanks again for your time and help,
Yep math's is correct, thanks for the resolution help I found his out after much trawling of the internet. I will now look into making a better measuring wheel. The product is rubber I've checked for slip on the current measuring wheel all is tracking the same "wheel and product" with hand held tachometer.
I've got the existing measuring wheel as you said mounted as close as possible to the tooling on the extruder.
Are you able to advise on measuring wheel sizes for best resolution? Sorry to be a pain but what other information will be a help? For the code I will sample in OB35 @100ms? Sorry but never really worked with extruders they are a bit of a dark art!!!

Thanks again for the help

Hi 5000 pulses per rev tacho and a 500mm wheel

cjd1965 said:

Hi 5000 pulses per rev tacho and a 500mm wheel

Click to expand...

This would be 0.1mm /pulse...you may not need to be as accurate.

What is the actual thing your trying to control? product thickness? width? weight?

Hi,
I did the calcs yesterday, might be a bit to accurate for this process, I'm possibly thinking 200mm circumference with 100 pulses = 2mm?? I'm also looking into analogue encoder?
I'm trying to control weight. But as you already know by the sounds, there's so many elements that can effect the extrusion as I'm learning! The extrusion is all in all very good but I just want to learn a bit more regarding the frequency counter, this can then just add that little bit more finer control. All the part weights are within the 2grams tolerance.
I've trolled the web for solutions for frequency counting and seems to be a few ways of doing it do you have any recommendations regarding best way? or is it trial and error!!!
Thanks again for your time and help it is very useful.

If you want weight and products are weighed why not look at weight average and then speed up or slow down.

Somthing like weigh 5 then discard heaviest and lightest then average the remaining three.

Maybe also introduce a deadband so minor variance is ignored

Hi,
Thanks again, I'm doing all the above mentioned already. I have an encoder counting each products size before it is cut to size if the weight's exceed the dead band tolerance I adjust the encoder counts instead. The only problem is I'm using a FM350-1 which you can only program to count or have a frequency measurement but I need he count for product size count. I just thought if I could try to control the extruder as best I could it might just help that little more. I've never done a frequency counter using a measuring wheel and inductive sensor, but I've created a function block now so going to try it Monday morning!

Thanks