Tubularfab
Member
Ok, first of all I'm completely new to PLC's, but at least have a basic understanding and a computer programming history. Right now I'm looking for ideas on the best (economical) approach to a problem. Here is the machine info:
It's a home built mandrel tube bender. 20hp motor driving a large hydraulic pump. 6 directional control valves, 5 separate cylinders. Direct logic 205 Plc controlling it all. The main bend cylinder is actually a dual piston design with 4 ports so it can either run fast as a single cylinder or get twice the force as a dual cylinder.
Here's the issue. The bend cylinder speed is adjusted via a flow control valve on the "b" port. The problem is that at normal bend speeds the delay from the Plc hitting the set point to the bend arm stopping equates to up to 3 degrees, and it's completely dependent on the temp of the oil and the bend speed. This is a big problem when trying to hold fractions of a degree tolerance.
I want to devise a way to slow it down a couple of degrees before the setpoint then creep up on it. One idea I had was adding a second flow valve in series with the existing one that also has a normally open solenoid in parallel with it. At bend angle minus a couple degrees close the new solenoid forcing he new flo valve to take over at a much reduced setting. I've also thought about adding some kind of actuator to the existing flow control that the Plc could engage to slow it down.
What would the most elegant way to do this be? There is a tight budget here... I assume all of the digital / proportion controls would be way too expensive?
Thanks for any suggestions!
It's a home built mandrel tube bender. 20hp motor driving a large hydraulic pump. 6 directional control valves, 5 separate cylinders. Direct logic 205 Plc controlling it all. The main bend cylinder is actually a dual piston design with 4 ports so it can either run fast as a single cylinder or get twice the force as a dual cylinder.
Here's the issue. The bend cylinder speed is adjusted via a flow control valve on the "b" port. The problem is that at normal bend speeds the delay from the Plc hitting the set point to the bend arm stopping equates to up to 3 degrees, and it's completely dependent on the temp of the oil and the bend speed. This is a big problem when trying to hold fractions of a degree tolerance.
I want to devise a way to slow it down a couple of degrees before the setpoint then creep up on it. One idea I had was adding a second flow valve in series with the existing one that also has a normally open solenoid in parallel with it. At bend angle minus a couple degrees close the new solenoid forcing he new flo valve to take over at a much reduced setting. I've also thought about adding some kind of actuator to the existing flow control that the Plc could engage to slow it down.
What would the most elegant way to do this be? There is a tight budget here... I assume all of the digital / proportion controls would be way too expensive?
Thanks for any suggestions!