Press break

[DLTimmons]

I have a hydraulic press break that the PC (ISA card and Dos) based control that is acting up. Just got a quote to upgrade to a newer PC Windows 10 control at $22,000.00. It has features that we just don't need. I was looking at using a BRX to control it. It has two independent cylinders on each side that are controlled by a proportional valves based on encoders. Basically each side has the same control valves. I was thinking using a virtual axis and have each side follow it. What I don't know is can the followers keep each side in time. The proportional valves a +/- 10 volt input. the voltage out I used the velocity output time a scalar written out an analog output before but never trying to sink to side.

[Garyhlucas]

I would think this would be no problem to do. I think on a press brake, unlike CNC machining, that it is not so important that the two cylinders are exactly synched but very important they finish at the same point.  I would use the C-More 7" touch screen HMI with the BRX, best bang for the buck I think and the programming software is now free. 

I just built two cutting machines with BRX and C-more, and I am working on two drilling machines, one 2 axis and 5 spindles and the other with 3 axis and 16 spindles.

[DLTimmons]

Use several of the 7" C-mores along with the BRX's. Have one running the back gauge on another press break, one running a punch press  controlling the punch press and feeder. and one on a little roll former line. Used several D2 with Ctrio's over the years. It's looking like I have dead encoder at $3000.00 will be looking for options there.

[DLTimmons]

On studying this more I will need a basic servo lock. So if one side moves down it will respond buy send a command to move back into position. Does this sound like something that could be done?

[DLTimmons]

Would this work I gear axis 1 and axis 2 to Axis 0.Then control movement with axis 0.  What I do not know is if axis 1 or axis 2 could make small moves to correct there position based on encoder feed back while axis 0 was not moving if one or the other moves off position from valve leakage?

[deep6ixed]

Hydraulics guy here.

What about using a PID loop for each cylinder?  Convert the encoder to a 0-100% of travel signal and then just tie the SP of both loops to the desired position point.  If you have position drift, the loop should pull it back to the desired point.

[DLTimmons]

This press has both ends independent and uses gravity to pull the press down to a slow down point by opening a prefill valve from the tank. It controls the drop rate by back feeding the ram side of the cylinder thru a +/- 10 volt proportional valve. I am not sure how a PID loop would control the movement of the press and switching back and forth from a position loop to a PID loop would get tricky.

What I have done in the past with CTRIO's with encoder feed back is use the CurrentVelocity times a scaler value then write that out an analog port could get quite good results on position control that way. I feel that would do the cycle control that I need it the idle time that would be the issue as this old press have some leakage and will drift down. What we have is a fast approach by using a prefill valve then a slow down point that closes the prefill then a press to a set down point then decompress stage followed a fast return to the up stop point use the much small area of the ram side of the cylinder.

What I was wondering was if I leave the axis 1 & 2  geared to axis 0 would the motion control part of the BRX issue pulse to try to correct for the drift even if Axis 0 is not running a motion profile move?