Limitations in iiwa 14

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javl0p

Limitations in iiwa 14

Post by javl0p »

Hi!

I'm using VREP in order to explore the limitations of an iiwa 14 robot based on its joint torque limits.

I created a simple scene in which I make the robot move in a straight line while applying a vertical force (as it was the weight of an object) to the end effector.

I already tried with loads of 100, 120, 150 N, and the robot seems to be ok. Joint torques are far from the limit {320, 320, 176, 176, 110, 40, 40} (N.m).

However, when reaching 160 N the robot falls down, not being able to cope with the load. What is going on exactly? Why isn't the iiwa able to create more torque in their joints in order to hold the position? Or, does VREP have incorporated joint torque limit values different that the ones i'm using?

I post the scene here:

https://www.dropbox.com/s/at2jmt6teu6xq ... t.ttt?dl=0

Thank you very much!

coppelia
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Joined: 14 Dec 2012, 00:25

Re: Limitations in iiwa 14

Post by coppelia »

Each of your joint has a specific PID controller, that will exert a constant force/torque, but modulate the velocity, as described here. Depending on the physics engine the velocity will also have an influence on the force/torque being exerted. Try with a different physics engine.
Then, at the same time, make sure to check the inertia and masses of the various links of the robot. The masses should be quite realistic, but the inertia are probably higher than real, in order for the simulated robot to also operate fine with engines such as Bullet and ODE.

Just noticed that you are using Vortex, which is the way to go. At the same time I am not sure what is not working as expected in your scene (the robot end-effector is correctly following the IK tip)

Cheers

javl0p

Re: Limitations in iiwa 14

Post by javl0p »

Thanks for the answer.

Actually, the problem came from the fact that the default max. torques in the iiwa 14 joints are much smaller than the ones specified by KUKA's catalogue, so once these limits were reached, the iiwa would inevitably fall. I have updated these values and the robot seems to work fine.

Regards!

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