Hello I'm Lionel Broglia with Siemens PLM Software. Today I'm going to prepare a model of an hydraulic excavator
for real-time applications. My presentation will be splitted in three parts.
The first part will be presentation of the actual model of the hydraulic
actuator, the working scenarios, some results and already some tips in order to
maintain the simulation time acceptable. The second step will be to present the
methodology of model reduction together with different tools that support
this methodology. And as a third step I will explain how we can use this real-time model
within LMS Amesim environment.
So the first step is to present the actual model of
hydraulic excavator. So what we have here is a full model starting from the combustion engine to the mechanisms.
So the model includes the combustion engine with first level model of the engine control.
All the actuation system included into the excavator starting from
the swing motor and all the hydraulic cylinder for the boom, the dipper and the bucket.
All these hydraulic actuation systems are connected also with a 3D mechanism which is
represented in this part of the system. In order to simulate the working scenario
we use the state chart functionnality of LMS Amesim. The state chart functionality
will define the different steps of the working cycling and the working cycle
will be the traditional JCMAS cycle that is used for regulation.
So some results of the simulation, here we have access to the displacement of the actuators so hydraulic jack
for the boom, the dipper, the bucket and also the swing angle.
So here we see the working scenario including the digging face, then the boom is raising at the same time
the turret rotates so we release the bucket inside the truck and we come back to the initial position.
So in order to perform this cycle it takes 20 seconds of working cycle time.
Let's have a look now at the CPU. So the CPU time of the simulation so simulating 30 seconds
takes one hundred and eighty seconds of simulations
so roughly six times the real time so we are six times slower than the real time.
So how to make this model real-time?
So we are going to use a first tool which is the performance analyzer.
So within the performance analyzer we have access to some information of of the solver.
For example the current integration step and also the state contributions.
Meaning which part of the system are CPU time-consuming.
With frequency analysis we have the possibility to visualize what is the maximum at the different CPU time.
So we can see here that we have a very huge frequency around 22 seconds
which is around 100 kilo Hertz. So this frequency is indeed very high and we will try to
reduce this frequency but to reduce this frequence we need to understand what
are the components that create that very high frequency.
So once the simulation is finished we can have a look at the results of the
model projection tool. So this tool is a graphical tool that allows to show for
each linearization time what are the high frequency and what are the components that are involved in this high frequency.
So here we click on te maximum frequency of the system close to 100kHz
and we can see that two components are involved in this high frequency
and these components are two hydraulic chambers which are included into the dipper actuation system.
What's happening at 20.4 seconds of the simulation
we see here that we have the pressures that are almost equivalent and
we have cross-sectional area between the two chambers which is very high.
That's create a very high frequency. So one solution could be either to reduce the size of the
orrifice or to increase the volume.It's what has been done with the step 2 model where the volume of
chamber has increased from 2 liters to 10 liters.
As a consequence the high frequency has been removed and the calculation time has been reduced
So now let's compare the results of the simplified model
with the initial one. So first we compare the results of a simulation so of course the modification in the parametrisation
should not impact the result of the simulation.
So here we compare the displacement of the deepper cylinder between the initial model and the simplified model.
So we see that we have limited modification in term of results.
It's up to the engineer to understand if this modification is acceptable or not.
But if we look in term of CPU-time we will see is that
we have a huge benefit from the modification of the volume of the
chambers because here we have reduce CPU time from 180 seconds
to roughly 85 seconds, so we have almost divided more than two the CPU time.
So step by step we continue the analysis still using the two different tools that
I presented before: the performance analyzer and the model projection tool
and we can reach almost real-time. The last step is to make sure that the model can run
with a fixed steps solver. In our case the model is stable with a Euler fixed step solver
at 0.15 miliseconds. So let's have a look at the simulation and
here you can see that definitely the CPU time is real-time almost and
the results of the simulation are in line with expectations meaning that they are the same
as the initial results. So now we have different possibilities of using this real-time model.
The first one can be for control unit validation.
So this model can be exported to any real-time platform
dSPACE, ETAS and so on and can be used by control engineers to validate their
real ECU. Another way of using these real-time simulator is to perform
human-in-the-loop simulation meaning that we have the possibility to interact directly with
a model and see the reaction of the excavator in function of
the sequence requires by the operator.
To do this we can use the dashboard functionality of LMS Amesim
together with the interactive signals that can be connected with the different servo-valves
of the system. So let's run now the simulation and we will interact with the model.
So we set a final time of five minutes for example and then running the
simulation we have the possibility
to interact with the model so for example we rotate the bucket, the swing.
An output of the model here is the power that is requested by the excavator that is
required to rotate. So we can see how the system
behaves with the real mechanism.
As a conclusion I've demonstrated the capabilities of LMS Amesim to develop a real-time model of an hydraulic excavator starting from a non-real time model
to reach real-time simulation, using the performance analyzer and the model projection tool.
Now the model can be used either for human or operator interaction or for the validation of control strategies.
Thank you for watching for more information please visit our website