[ros-users] PR2 fingertip sensor based grasping

[Kaijen Hsiao]

Hi Ibrahim,

On Wed, Jun 15, 2011 at 2:18 PM, Ibrahim Awwal
<ibrahim.awwal at berkeley.edu> wrote:
> 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.

Not that I am currently aware of.

> 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

When I use them, I just re-zero the data whenever I'm fairly certain
I'm not touching anything.

> 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!

I would guess that you mostly just need a node that listens to the
fingertip sensor readings and sends a command to the gripper to close
when you see the readings you're looking for.  It doesn't have to be a
real-time controller.  Although if you did want to write a real-time
controller, a good example is Joe Romano's
pr2_gripper_sensor_controller package:
http://www.ros.org/wiki/pr2_gripper_sensor_controller
(For a non-real-time example in Python, look at
hand_sensor_listeners.py and reactive_grasp.py in
pr2_gripper_reactive_approach/src/pr2_gripper_reactive_approach.)

-Kaijen