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marcinmrag

relationship between piston stroke and pressure function

6 posts in this topic

Hello experts,

Maybe someone can help me.

I would like to create some function which detect the material from which the pressed element is made. I know that is a relationship between material and how fast pressure is build up. I would like detect two materials : aluminum and copper. I have research, which shows that the pressure builds up faster for copper than aluminum. Aluminum is more flexible. Maybe someone has some idea how to create function which will detect what kind of material is pressed? Im thinking to use linear function. It is a good way? Maybe someone have some good ideas and can help me a little :)

 
 
 

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You would use a pressure sensor into an analog input.  You would start a timer when you apply the pressure.  When you reach the level that is desired, you can record the timer value and determine which material you are using.  Do you have a PLC?  If so, what kind?

 

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Yes i have CP1H Omron PLC . But how i can determine which material is using? Can you explain your idea?

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What @Michael Walsh suggested is that you set a certain threshold value of the pressure.

1. For example you set the threshold to 1 kPA. This threshold is to be read by an Analog pressure sensor, so you need to scale the analog conversion value to the pressure units.
2. Start the pressing action, and at the same time you run a Timer inside the PLC.
3. Your pressing action should be controlled in the same way for both materials (same speed or same target torque)
4. Compare the value of the analog reading, is that already reaching the said Threshold or not.
5. If the analog reading has reached the threshold, you stop the Timer and the pressing action, then you check the time.
6. You should have a standard time value for each material and compare the Timer value to those standard values. From that you can determine what material were you pressing.

That method may work, but it requires you to know/conducting research beforehand on what Timer value is expected for each material.


Another way is that you need to measure the Gradient of the pressure relative to time. It should be simpler, but you need to know the Gradient of each material, like this :

1. Start the pressing action, and at the same time you run a Timer inside the PLC.
2. For a said sampling interval, you sample the current pressure level read by the analog pressure sensor
3. For example, each 500 ms you read the current pressure level.
4. You measure the gradient by the following formula : (CurrentPressure - PreviousPressure)/(CurrentTime - PreviousTime)
5. This way you will get the Gradient of the pressure relative to time and compare it with the expected Gradient of each material to determine what material is it.

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3 hours ago, innoaloe said:

4. You measure the gradient by the following formula : (CurrentPressure - PreviousPressure)/(CurrentTime - PreviousTime)

I agree @innoaloe, another simple way to state this is the "rate of change of the pressure".    @marcinmrag, the experiment that you have conducted should have provided you with either a time to reach a pressure, or a rate of change.  What you may have to be concerned with is if the rate of change is not linear and therefore may be the same at some point during the process for both materials.

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But the problem is that i need to detect kind of material on some short distance when the pressure is going up more aggressive for copper and than continue pressing with different parameters for aluminum and copper. The idea is to create intelligent electric press which detect kind of material, size of connector and stop pressing with two different ways for copper and aluminum.  I hope that i describe the problem enough clear.

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