How to simulate grabbing an object on Simscape Multibody?

Hello Everyone,

I have been trying to simulate a process on Simscape Multibody, where a robot arm picks up an object and drops it in a box. I am having a problem with the grabbing and cannot get it done. I know I should use the spatial contact force and I have seen a couple of examples but they are very complicated with many subsystems connected to the block and I cannot really understand them. For example, how can I time in the block the moment that the robot arm has reaced the piece and should grab it now? would really appreciate any help.

Answer 1

[Nathan Hardenberg]

I made a very simple example for you (see attachment).

In general a "spatial contact force"-block has to be between all bodies that collide. Sometimes it is approximated with points since the simulation time can skyrocket when using contact forces (I have not done this). Thats why you need to set the following options in my example (you can also play around a bit):

• Solver Selection: Fixed-step
• Solver: ode8 (Dormand-Prince)
• Fixed-step size: 0.001

In general you have to calculate yourself when to close the gripper. It can be done with a Matlab-script, simply time based or something else. The gripper should also be acuated with a force and not a position. Otherwise the part maybe glitches and flies away.

[Ahmed Salaheldin Ahmed Farouk Salaheldin]

Thanks for your help! but actually I have the 2022b version so I can not open the model. could you please save it using "export to previous version"?

[Nathan Hardenberg]

@Ahmed Salaheldin Ahmed Farouk Salaheldin I will do that tomorrow!

[Nathan Hardenberg]

@Ahmed Salaheldin Ahmed Farouk Salaheldin Here the R2022b version of the Simulink file

[Ahmed Salaheldin Ahmed Farouk Salaheldin]

Thanks, Nathan! your example helped me alot but the moment one of the two grippers touch the box, I get this error.

"An error occurred while running the simulation and the simulation was terminated

Caused by:

• ['Electroplating_line/Main Configuratuion/Solver Configuration']: Error evaluating equations at time 7.6485. Stopping simulation. There may be a singularity in the solution. If not, try reducing the step size (either by reducing the fixed step size or by tightening the error tolerances)
• ['Electroplating_line/The metal Pieces/6-DOF Joint']: 'Electroplating_line/The metal Pieces/6-DOF Joint' has a degenerate mass distribution on its follower side. "

[Nathan Hardenberg]

Does this error occur in my example? If so check, if the options in my original answer are set the same. If not I sadly can't help you. Singularity-Errors can have a lot of reasons from my experience.