Hello Thomas, I will come back with some suggestions about, I work in high performance hydraulic systems since a dozen of years,

Ciao

Thank you Carlo.

Also, I've been trusted to design a 20t capacity hydraulic hexapod, stewart platform, to use as a load actuator... It's gonna cost a hell of a lot, and consume a lot of space.

calculating the worst case scenarios for all 6 dof. of loading at 6 dof. displacement combinations is quite a thing. Maybe you've encountered those hexapods.

Input would be valuable. In a perfect case - a parametric excess sheet, where you enter the wished for stroke lengths in 6 dof, and wished for loading capacity in each direction... and it outputs the power and size of required pistons.

I've got rough estimates but would be good to double check

Nice discussion.

Hello Thomas.

Well in my experience, basically the 3 stage servovalves are used when a big flow rate is required and a big performance are required too.

Personally I have used the D672 Moog valves, and the 4WSE3E Rexroth servovalves with good exeprience both on performance and robustness.

Moreover, the D672 is a DIGITAL valve (so, internal parameters, can be remotely adjusted via a fieldbus)

For my knowledge, is the exapod that system used on the flight simulators ?

what is the 6 dof , that you mentions?

If you have some more specific questions and I can provide some answers, I will be happy about,

Have a nice evening

Interesting.....

Carlo Moiola

We got these MTS pistons. 150kN. They seem to have large secondary coil chambers (see pics attached). So, is it correct to say that, the second coil serves as "precision control" while the main one is brute first stage "porelad", for power distribution?

We did Moog pistons before. Now MTS... had our own PID controllers too. All of them are the same thing, in essence. The industrial software suites are just over complicated PID controllers with simple load history generators (ramp, wave, sequence, sampling managers...). We deal with complex nonlinear material, though. So, "standard" solutions are inadequate. We develop scripts which compensate for nonlinear stiffness changes. In Moog it was Ruby scripting. MTS seems like python (not there yet)... When making DIY equipment, C and Matlab work together well... Must say it's a bit annoying how little "manual control" options industrial options have. It's all hidden behind layers of copy righted modules and extra complex, unnecessary data bases, licenses... eh...

The hexapod is indeed like the ones in flight simulators. The purpose being slightly different. We need to apply combinations of 3 axial loads and 3 rotation loads on structures (x, y, z axial and rotation). The hexapod is attached to 6 d.o.f. load cell, then the position / force vector is controlled using real time simulation of positioning in 3D. It sounds more complex than it is. It's all linear algebra...

We deal with nonlinear behaviors though. Large changes in stiffness within soil (we test foundations), impact loads, loading rate dependent phenomenon... you could describe it as applying loading cycles along 6 d.o.f. while encountering cracks (loss of stiffness) and impact loads (instant recovery of stiffness). Thus, standard PID is not good enough. We have to develop control algorithms which do partial simulations of the phenomenon being tested. To avoid excess loading rate accumulation when stiffness is lost, and overloading when stiffness instantaneously reappears.

Thus, the need to understand performance of individual components. Such as the 3 stage servo valve. To reduce noise, resonance, over/under loading, etc...

Following

Tomas Sabaliauskas , yes I see in the first picture the servovalvole. It can be just the pilot valve (it looks like a G761 of Moog, a small servovalve without electronics). It is possible but i don't see in the picture this is only the pilot valve for the bigger valve (the other 1 or 2 stage servovalve). I will come back later to you with more details/ impressions.

Now the application is clear , sorry 6 dof = 6 degree of freedom.

Very interesting, keep cooperating.

Tomas do you have knowledge or experience about Electr- Hydraulic Systems ? they are very innovative, interesting, and complicated too...

Thanks and have a nice sunday

Valuable discussion.....

thanks Omar Ali Al-Khashman , I will try to find the time to go more in detail, regarding the last info's from Tomas (MTS Cylinders)

Ciao

i need know what is the aplication of each type of servovalve ?single stage ?two stage?three stage??

@Mahmoud - same application in all of them. To push things...

They got two params essentially - push force and push speed (and stroke length but that's limited not by the valve type)

The bigger the valve, the more volume of oil you can push in without losing pressure - the faster the piston can go without losing much push force.

In our lab we're trying to push things with 250kN of power. At speeds within range of 20cm in 0.1s. So we got pistons with two compesators (elastic containers with pressurised oil attached to the piston directly). And we got valves with large holes. The large valves are opened by a small piston, to get the big piston going. Thus two stage valves.... Extra power.

The piston can generate quite a strong punch. If PID calibration goes wrong, the whole building shakes... It's pretty cool. Makes students respect the machines.

Tomas Sabaliauskas thank you vary much , but i need to know one application fro each type ?