Hello All,

I need a tip and or suggestion because I've to put hands on a control system with some control problems.

The system is basically a beam, with section 250x250mm long about 5000mm: the beam travel for a less than 2000m over linear guides moved by two pinions that rolls over a rack (without helicals tooths that are NOW mounted on) the two pinions was moved by ONLY ONE hydraulic motor at one end, with reversible mechanical reducer, and a 5000mm long transmission shaft (coupled and supported at mid length).

The system is designed to move about 10 metric tons of iron block over a surface under the beam: results? When the load is placed unbalanced (near one end) the displacement of the beam was about 20mm: the required displacement is less than 1mm.

The hydraulic motor was moved by two couple (one for each direction forward / backward) of electric valves that with two flow reducers that does something a fast or slow speed.

At one (the same of the motor) is placed an absolute encoder, coupled with his own rack and his own pinion for measuring purposes only: the system is born to be driven forward and backward with a joystick and a display indicates the measure of the position of the beam.

When is asked my support someone has decided that THE SOLUTION must be putting another hydraulic motor at the other end of beam, removing the shaft, which drive the pinion, remove the on-off electric valves with the flow reducers and put two proportional valves (with analog setpoint and feedback) and ask me to drive them with the same setpoint (I've made a new HMI setup page with two setpoints: one for fast and one for slow speed and some other button for drive one valve at time - for alignment purposes only).

Obviously the new system didn't work as expected (!) the displacement error has been reduced from 20mm to only 8 mm but is much more than the desired  value (less than 1mm)

Obviously everyone has asked me HOW to obtain a result: the better way (that must be designed from beginning) is two syncro electrical motor , with reversible reducers, with ball screw putted in gear motion solution (as many other machine), but because they cannot rebuild half machine and half electrical box has asked me to design a motion gear solution (with another absolute encoder at other end) : than my first trouble: with a control system with a very long control chain: from my PLC (S7-1500), analog output, proportional valves, hydraulic motors, mechanical reducers, the coupling between driven pinion and rack, the coupling between encoder pinion and his own rack, the signal trasmission between PN-IO absolute encoder and PLC how I can trim or setup a unstable motion gear solution system? What are the parameter on motion block (V6 - TIA V17) that I could touch to obtain not the better result but at least something like?

I've see that there are some tracing function inside motion block: how I can use them to trace my setpoint - feedback control loop? There's something (like Sinamics drive) auto-tuning function to provide a loop roughly adjusted that I can refine by me?

Any doc, suggestion or other tip are welcome: I think that this topic could be a base for help technician to setup control loops with high backlash.

Thanks in advance to all.

Hello,

very thanks for the answer but I have some doubt about:

- the solution is valid for S7 1500 "basic" or only for T version?

- the solution is valid also for V6? I think that changing CPU to Fw 3.x one isn't an option (I'm not the person who decides, I've only the problem to solve)

I'm start to study what suggested and plain a solution.

Thanks again

Hello, the past week I've to do the commission of this system over teleservice and 9000Km distance, on the plant side I've a very good guy that helped me with right suggestion and stopped the system during the first phases of commissioning when I've not fully clear the direction of moving and the signs in the position closed control loop.

The startup was more easy than expect (and than some much more people in real life have prognosticate: the system when the sign in control loop control all the loop because my target is maintain a position and follow with the slave axis the position of the master.

A complex idea that I've written to change the regulation gains of both axis at the end was a bad, or at least a useless idea: starting with kv at 10 and kp at 100 was the goal.

Until the oil pump is active I've disable the hydraulik brakes on the motor shaft: the control loops must be always active to maintain the position: when the system is apparently not moving both setpoints of the valve still at 150~200 points (to 27648) so the system need to maintain the valve slightly driven to hold the position.

With a travel space of  1160mm at 1300 mm/min speed the system position with no load within 0.1 mm precision from master to slave,  with 5 metric tons moving in the same way the position displacement is worst but always less than 1 mm that is the maximum value accepted, when get fine positioning at 50mm/min the displacement return at 0,1 mm from one side to other.

When the system is working (is a very large blade saw) the position is fully maintained with open brakes and the position loops enabled within the value of the lower bit of position encoder: 0,004 mm that, compared with the force in action, is nothing.

I'll get thanks to Siemens tech personnel that help me for found the right solution to apply without have no time and no possibility to fail.