Conveyor tracking

[ABlearner 2]

Hello Guys,

I have a Mitsubishi A8000 series vfd with an encoder card and also encoder. With analog (0-10V) signal i can read back the current speed.

The conveyor convey paper sheets. Occasionally they change the width of the paper but the the two type of paper is connected. We have a camera on the begging of the conveyor, and we would like to lets say cut it 2 meter later. But the position should be very precise otherwise we are not cut it in the good position. The cutting procedure would happen also an asynchronous motor or with servo motor. 

Is it possible to write a tracking program and cut paper sheet in a good position ?

My plane is to stop the CV in the position and waiting for the cut and go on. 

The plc is Allen Bradley, control logix 5580.

Any tip would be appreciated.

Thank you so much. 

[panic mode 246]

using speed control allow you to control the speed but it will not get you precision when it comes to position. for precise position cuts you need position feedback. doe your axis have an encoder?

[ABlearner 2]

Hello thank you for the answer. 

Yes i have an encoder on the the conveyor motor. Is it enough ? Or do i have to apply also an i dependent one on the conveyor directly ?

 

Thanks. 

[pturmel 160]

I'm not familiar with that particular drive, but the general requirements for the application described are:

• Capture an encoder count or position value, at the required level of precision, when the leading edge of the material enters the cut zone, and
• Command the drive to stop at the required ending position, again, to the required level of precision.

Drives with positioning modes built in can generally do both of these operations, as long as some leading edge sensor is wired directly to the drive (for high speed capture).

If your drive doesn't have any positioning functionality, or lacks the high-speed position capture feature, it all becomes much more complicated.  And possibly requires encoder signals to be brought to the PLC itself.

[ABlearner 2]

Thank you for the thorough answer.

Lets assume the drive cant do it. 

In this case do i need an encoder on the conveyor ? The conveyor maximum speed is 20 m/min. In this case do i need a high speed counter module too in the plc ?  The precision should be within 3 mm.

Thanks. 

[pturmel 160]

11 hours ago, ABlearner said:

encoder on the conveyor

Maybe.  I've typically added an encoder repeater so the one on the motor can transmit to two systems, isolated.  Usually cheaper than another encoder.

11 hours ago, ABlearner said:

a high speed counter module too in the plc

Yes.  With a leading edge sensor wired to one of its Z inputs, where that input is configured to "latch and continue".

Then, use a high-speed output on the encoder card to stop the analog drive at the target position, with an appropriate (speed-compensated) lead for deceleration.  If deceleration from normal speed is not sufficiently precise for your 3mm tolerance, use additional logic to slow down the drive early, then stop from the slower speed.