Grasping metric

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neostek
Posts: 21
Joined: 15 Feb 2013, 10:26

Grasping metric

Post by neostek »

I saw that a robot in V-rep could grasp an object (like in MTB tutorial example). I want to ask you if some metrics of the grasping are available, i.e. a measure of the quality of the grasp (e.g. force closure). I have to develop a grasping algorithm and a measure is really important for me. As negative case, do you think it is possible to import such a calculation in V-rep?

Thanks in advance for any reply,

Neostek

coppelia
Site Admin
Posts: 7928
Joined: 14 Dec 2012, 00:25

Re: Grasping metric

Post by coppelia »

Hello Neostek,

In V-REP you can read and record the force/torque exerted in a joint or force/torque sensor, given that the objects are dynamically enabled.

Refer to simJointGetForce and simReadForceSensor

In the case of the Barrett hand, you could directly read the associated force sensors, or joints. In another construction, you could simply add auxiliary force sensors if you want to read a specific force/torque.

Cheers

neostek
Posts: 21
Joined: 15 Feb 2013, 10:26

Re: Grasping metric

Post by neostek »

Hello,

thanks for your response. If it is possible, is there any metric? I mean to measure the grasp quality (i.e. not only grasp/non grasp but also a metric) such as force closure?

As alternative, can I import an algorithm in V-rep? Do you suggest as LUA script or as plugin?

Thank you,

Neostek

coppelia
Site Admin
Posts: 7928
Joined: 14 Dec 2012, 00:25

Re: Grasping metric

Post by coppelia »

I am not sure I understand what you mean with metric. The data that the mentioned functions return are in Newton or Newton*meter. So you can figure out with what force the hand is grasping an object for instance. You can also imagine having an special object that can read force applied to it (one would have to decompose the object into smaller parts, then link them via force sensors).
For a higher-level metric, you will have to implement this yourself, based on force/torque readings.

And yes, you can always use your own algorithms. When possible, always use a child script, this this is the most portable controller (i.e. it is saved/loaded/copy/pasted together with the model/robot, does not require compilation, has no compatibility/dependency problems on other platforms, operates synchronously, etc.).
Plugins work fine too, but they don't have the same advantages as child scripts. Refer to this page for a good overview of the different possibilities to include your controller/algorithm.

Also, from V-REP 3.0.2 on, there will be the possibility to write custom low-level joint callback controllers. The release is planned for mid-March 2013

Cheers

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