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Areeb

Speed in meter/mint

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Hi Everyone!  I wanted to determine the speed of my printing machine in meter per minute. The machine is very simple it consists of 2 roller one is unwinding the paper roll and 2nd is winding the paper roll and in between them printing process take place. I just wanted to determine how ma meter per minute machine is printing.

 

Thanks & Regards,

M.Areeb

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Hi Areeb.

You can do this by 2 ways- use 2 static values such as a speed frequency or inverter speed and work out how many rotations it gives you per minute- then you can work out a scaling factor using conveyor travel.

If you are using incremental encoder for example- work out number of increments per meter of conveyor travel (maybe use some trap software for this). Then you can measure number of increments per (increments over 10 seconds x6) /Scale Factor= Speed in Meters per min.

You can modify the forumla or optimise depending on your system requirements. 

 

Regards

Daniel

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can u further explain me by giving some sort of numerical base examples and  how I determine the scaling factor? 

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If I multiply the circumference of the shaft with RPM so is it fine or not ?

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4 minutes ago, Areeb said:

If I multiply the circumference of the shaft with RPM so is it fine or not ?

Circumference of the shaft is not relevant to conveyor travel unless you work out the ratio between them- this is the value you need to calculate, either by Encoder Increments of another form of Conveyor Speed.

What feedback devices have you got to work this out? 

 

Regards

 

Daniel

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Till now I use incremental  encoder from which I got the RPM of the machine, now  after that I am confused. The idea is very simple is that I just wanted to know that on how many meter per minutes my machine is covering the paper roll in shaft.

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Circumference=2*pi*r =>   pi*d

Speed(Meter/Mint)=  C*RPM;

I just used the encoder only nothing else.

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Just now, Areeb said:

Circumference=2*pi*r =>   pi*d

Speed(Meter/Mint)=  C*RPM;

I just used the encoder only nothing else.

So I would work out how many encoder incrments you get per metre of travel....this will be your scaling factor. You can do this manually using a trap- once you have this count write it down.

Then you can capture your increments in second intervals- and apply the scaling factor to get your travel per minute.

 

Regards

Daniel

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okay if I am not wrong u are saying that for instance my conveyor cover 1 meter in 800 increments and after 800 the encoder is reset and again calculate for 2nd third and so on till timer of 1 minute and after every 800 increment there will be increment of 1 count in counter so in this way after 1 mint it shows the speed in meter per minute ?

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So 800 increments = 1 Metre of Travel.

Capture number of increments over a set period of time.

You now have a time and distance, now you just need to get everything into metres/minute.

-Set this as a high priority task (10ms) if possible.

-You need to account for overflow in your code (32,767)

-Your final value will be a REAL, so you may need to take your inputs and convert to REALs in order to complete the calculation.

 

 

Regards

Daniel.

 

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If you have 800 increments the "resolution" will be very low- so you may have to calculate over a larger time base .

 

Regards

Daniel.

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To measure linear speed correctly you need in two sensors: the one for RPM measuring, the second for measuring the diameter of roll (an encoder or a resistor; the paddle, laying on roll, transfers the angle, related to the diameter of roll, to the sensor's shaft)

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@Inntele which type of sensor ? can u tell me the name of that sensors which is used to calculate the rpm and diameter of the shaft.

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@Gambit I just assumed 800 increments for 1 meter of travel as an example. can u tell me that this strategy is right or wrong ?

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sensors don't calculate, they sense....

controller (your PLC) calculates...  bases on values received from sensors. 

as mentioned, linear speed of paper roll depends both on RPMs and radius (or diameter) of the roll. 
circumference of a circle is L=2*pi*R

but if encoder is monitoring position of the shaft where the product is rolled/unrolled, radius R will keep on changing and this complicates things. so you need to know the R value and this is why you need a distance sensor of some sort. if the rotational sensor is mounted on roller that is just following/guiding product (maybe mounted on a tension roller or a capstan wheel), radius is fixed and you do not need distance sensor to measure radius. 

Next, you are measuring speed or rate. You can get meter/minute by measuring distance product traveled in one minute (use timer). But i would not want to stare at display for a minute to see value chang, specially if the printing speeds are anywhere near printing machines i am familiar with. I would want to see readout change at least every second for example. But that output could look crude with low resolution encoder.  

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Check the SPD instruction... , but i use different method.

I usually use A phase interrupt rising edge on X0 and B phase on X1.

Each interruption incremnts common data register... let's say D0

And that's how you can use 1000 pulse/rev encoder to read 2000 pulses/rev for greater accuracy.

You can use the falling edge interrupts on 2 more inputs like X3 and X4 and you have 4000 pulses per rev.

Every 100ms timer T0 moves current value of D0 to D10 and resets D0 and it self

Now you have D10 accumulating the pulses for 100ms interval.

MUL D10 K10 D20 gives the pulses per second.

MUL D20 K60 D30 gives pulses per minute.

It remains only to know pulse count for 1m and make the calculation program.

This method may seem awkward, but proven over time as flawless.

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