On Wed, 15 Jun 2011 14:17:27 -0700, Ibrahim Awwal  wrote:  

Hi all,


In our work with clothing at Berkeley, we often need to grasp clothing
articles. Currently we basically approach a point that we think the
clothing article is at and alternate closing the gripper and moving closer
until the gripper does not close all the way, which is not terribly
reliable (false negatives occur sometimes with thin articles) and also
slower than it could be. We would like to be able to simply slide the
gripper under the article and then close when an article is detected by the
fingertip sensors. I have looked at some data and it seems like it should
be possible to detect a change in pressure resulting from the gripper
moving under a clothing article, although the response is somewhat small
compared to say, me touching the gripper sensor with my finger. 

I just
wanted to check before I go ahead and do this, is there anything out there
that already does this? I.e. something where the gripper moves toward a
point and closes once it senses a pressure increase. It seems like the
current fingertip pressure controllers are intended for situations where
you first position the gripper in the correct place and then the sensors
are used to apply just enough force to keep the grasp instead of closing
all the way every time. 

One thing I was wondering about is how do people
generally deal with the fingertip pressure readings? It seems like there is
noticeable drift in the values over time, so do you just re-zero the data
periodically, or is there a better way to compensate? Also, I would
appreciate any tips on how to go about creating such a controller, because
I've never done anything with low level control on the PR2. Thanks!  
--

-Ibrahim Awwal

Oops, I meant this for ros-users, >.