Question about SimHydraulics/SimScape multibody

Hi guys! ,

So I was looking at how to connect hydraulic systems to mechanical system in simulink, I found some good models in Mathworks libraries, such as the backhoe model: https://se.mathworks.com/matlabcentral/fileexchange/39520-backhoe-model-in-simscape and hydraulic lift https://se.mathworks.com/matlabcentral/fileexchange/39120-lift-table-model-in-simscape. But the thing i do not understand in both of these models, is the connection between the pristmatic joint from simscape multibody and the hydraulic cylinder from SimHydraulics. I have included some pictures showing this connection. Looking at the pictures, how does the combination of motion coming from the hydraulic cylinder and the velocity from the prismatic joint convert into Force? Why is it setup this way?

1:

2:

3:

[omar almasri]

Hello,

this is my email.

[e-mail]

I need your help please

Answer 1

[Steve Miller]

When you connect a 3D mechanical model in Simscape Multibody to any 1D Simscape domain, we recommend letting Simscape calculate the force applied to the mechanical system, actuating the joint in Simscape Multibody with that force and synchronizing the mechanical motion of the 1D system using a 1D velocity source in Simscape. This is simplest way to connect the two systems that will avoid an algebraic loop.

If you need to synchronize the initial mechanical positions of the two systems, we recommend passing the position of the joint to the Simscape 1D network. This will also help avoid numerical drift between the two systems, which is typically only a problem if your tolerances are too low and you have high frequency cyclic motion.

You can find many examples that show the different methods for connecting 3D models and 1D models in the File Exchange entry Simscape Multibody Multiphysics Library.

[Bilal Ahmad Khan]

Thank you very much for the explanation Steve!, I was wondering if you can look at my model and see what is wrong? I have connected it the same way as the pictures above and it does not move as I want to. I have tried connecting my hydraulic system with the backhoe model to first check if its something wrong with the hydraulic system itself, but once I run that model, the hydraulic model worked as desired. However, once I connect it to my mechaincal model ( which is supposed to be a lifting crane), even when the hydraulic cylinder is directly connected to the pump and tank, the force experienced in the prismatic joints are very strange, often resulting in way too high numbers.

The solids:

The solids

Making this work is very important as my university is looking to fully focus on using Simulink/Simscape in its mechatronics courses instead of SimulationX, which has previously been the main software for this type of modeling. As our thesis is one of the first using SimScape's multibody to model a combined mechatronic model in our university, and with our documentation on how this process has been, it will also determine if its something the school wants to fully dedicate itself into.

Answer 2

[omar almasri]

Hey

I have the same problem as you. I'm doing my master thesis. I can't progress because of this problem, I have already finished and simulated my mechanical system and my hydraulic system.

I want to link the two together and simulate them together.

I have tried to connect the prismatic joint directly to the cylinder. But it did not work.