Velocity and flow issues with Rexroth HACD

saultgeorge

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Join Date
Jul 2015
Location
Detroit
Posts
535
Hey, folks. Here's a good one. Hope one of you pros can shed some light on this. I'm doing a job where 2 hydraulic cylinders work alternately to dispense slurry to make foam car parts, the foam stuff you find under your hood that deadens sound and wraps Freon lines. The cylinders supply a system that mixes other materials after the slurry is dispensed and then it goes through a mixhead and gets dispensed into a mold. The dispensing set-up and mixhead are on a robot, and I don't control any of that. My only task is to get these cylinders to dispense a certain volume (grams) in a certain time (seconds) with my PLC program.
Instead of using a PID, the company has these HACD controllers made by Rexroth. We are a Rexroth dealer.
My immediate question is this: The cylinders will not dispense a uniform amount of slurry and it hasn't hit the weight setpoint yet. (36/grams per sec) Every time it dispenses slurry, it's called a "shot". We discovered two lines plugged in the mixhead, and then we also determined the mixhead was plugged. The cylinders have a 1,500 psi limit. The company says that isn't the problem, the shot should be correct. The slurry circulates through the mixhead when not called for a shot. Since it couldn't circulate, I believe that the HACD's cannot compensate fast enough at the 1,500 psi to give an accurate volume.
Anyone had any experience with this and has some insight to these HACD's? Besides the 722 page manual. Thanks for reading and for your help. Attached please find spreadsheet used for volume/sec calcs and a snip of the logic to send to the HACD

cylinder logic 04 02.jpg
 

Attachments

  • Cylinder Flow Rate Calcs 032318.xlsx
    14 KB · Views: 10
Not sure what the final answer was but the spreadsheet has the wrong formula for the area of the cylinder. In calculating the radius, they did not divide the diameter by 2.

It's also unclear how the system coordinates the accel/ decel of the two cylinders when one takes over from another but generally giving them the same acceleration and deceleration and starting the change at the same time will work.
 

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