Hi, I was just wondering why the Pneumo-Hydraulic Actuator does not have a mechanical translational conserving port associated with the cylinder clamping structure as other cylinders available in simhydrualics do. Should we assume it is connected to a Mechanical Translational Reference? Alex
MATLAB: Pneumo-Hydraulic Actuator ports
pneumo-hydraulic actuatorSimscapeSimscape Fluidssimulink
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Hi Alex,
1. You are right. The L port is equivalent to the R port in a traditional Mechanical Simscape block. If you want access to the C port for whichever reason, you may have to build your own "custom" Pneumo-Hydraulic actuator. In other words, combine a hydro-mechanical converter, mass, and pneumatic piston chamber from the Simscape Foundation Library.
2. I'm not sure about this one. My guess would be that the simplified equations don't require the component to keep the pressure stored internally in its equations, so you don't need initial conditions. The equations simply look at (Pa - Pb) at a particular time to figure out the force transmitted.
Again, don't quote me on this one. You could log the pressure across this cylinder block (with varying initial conditions) to test it out for yourself.
3. I think you're right here too. While the Simple block lists assumptions about friction, the documentation for the regular (non-simplified) block also lists this:
Basic Assumptions and Limitations
- No leakage, internal or external, is taken into account.
- No loading on piston rod, such as inertia, friction, spring, and so on, is taken into account. If necessary, you can easily add them by connecting an appropriate building block to cylinder port R.
- Sebastian
Sounds like the question is resolved. Will paste the comments here:
Yifeng Tang
Hi Thomas,
Looks like you are using a much earlier version of MATLAB. I wonder whether it would help to see if where is any shipping demo using that variable displacement pump. In R2020a shipping demo, there is one example with that pump and a reservior, which, if available in your version, can be a good reference.
https://www.mathworks.com/help/releases/R2019b/physmod/hydro/examples/hydraulic-motor-driven-by-load-sensing-variable-displacement-pump.html
I also believe that "displacement" quantity refers to the ratio between flowrate and angular velocity, instead of the instaneous location of the pistons, so you won't see any reciprocal motion.
Thanks for your answer, i couldn't adapt an exemple to my need but i added a reservoir with ckeck valves at the entry of my pump and it worked (even though this don't represent a closed loop circuit anymore).
After doing some research, i think the better solution tu resolve the solver problem " pressure fell bellow absolute zero " would be to upgrade my version of matlab, as newer version can continue the simulation after this problem, but not the 2013 version.
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