Simscape Multibody (SimMechanics) - obtaining symbolic dynamic model

Hi everyone,

I am trying to model a parallel robot using MATLAB. I've tried the robotics toolbox (which supports symbolic modeling), but it only supports serial robots (i.e. no closed-loop kinematics), unfortunately.

I haven't been able to figure out if Simscape Multibody has the ability to create a dynamic model - symbolically - from a given system of bodies. Basically, given a parametric model of the robot, can I obtain the general expressions describing the system dynamics? (actuator and passive-joint torques, to be precise)

If not, any other recommendation of how to go about solving this would be greatly appreciated.

Thanks,

Guy

[Swarooph]

Hello Guy,

I am not sure if there is a way to get a graphical version of a robot based on an existing set of equations. I'll let others chime in about that. Some information below to help you get started:

1. You can build your model in Simscape multibody (SimMechanics). Look at the example here.

2. You can import an existing CAD model into Simscape multibody. Look at the examples here.

3. How a Differential Equation Becomes a Robot webinar - This could help.

[Guy Lalkin]

Hi Swarooph, thanks for the answer!

I'm actually looking for "the other way around" - given a graphical representation of a robot - and by graphical, I just mean a Simscape Multibody model, can I obtain the governing dynamics equations?

I heard about a program called SYMORO, but I'd much rather work with MATLAB/Simulink.

[Swarooph]

Hello Guy,

I know there are ways to get a 'linearized' version of your model into something like a state space model. Other than that I am not sure if there are other ways to get the dynamic equations provided you have the graphical model..

Technically, the thing that you call the graphical model is not just graphics. It has all the necessary dynamics modeled underneath. Can I ask you why you need the equations? Maybe there are ways to workaround to achieve your final goal without getting these equations..

[Guy Lalkin]

For sure-

I need it to find optimal link lengths/sizes, to minimize actuator torques. It could be done in trial and error without a parametric model, but it would take a whole lot of time! Ha.

[Swarooph]

Hello Guy,

Maybe you already know this. But a product called Simulink Design Optimization can actually run your simulation model to try to find optimal model parameters so the objectives/goals that you set are met. Take a look at the video here to see that in action with a mechanical engineering example.

[Guy Lalkin]

Ah, I hadn't considered using that product. Thanks, I'll read up about it some more. And thanks for all the help!

Answer 1

[Steve Miller]

As answered above, the desired task (finding optimal link lengths/sizes, to minimize actuator torque) does not require a full symbolic representation, it requires a parameteric model which Simscape Multibody enables you to create. Automated parameter tuning is possible using Simulink Design Optimization.

--Steve