PR2 Optical (IR) Beam Sensor

This is an instruction of setting up the optical (IR) beam sensor, for both hardware and software, on an actual PR2 robot.

Hardware Setup

Attach the sensor according to the following photo: Alt text

Several important things:

When the LED on the gripper is facing up, the emitter (with 4 transparent diodes) should be installed on the left finger, and the receiver (with 4 black diodes) is on the right finger.
The emitter should be installed before the receiver on each gripper. This is to make sure the emitter can draw enough power from the motor control board. If later on you found the sensors are not working correctly, you may want to try doing this in the correct order again.
Remember to insert the FFC cable into the connector on the sensor.

Software Setup (Fuerte)

Running ROS Fuerte on the PR2
Build system: rosbuild

###Clone and compile the required packages * pr2_pretouch_sensor_optical * pr2_ethercat_drivers * pr2_robot

using rosinstall:

cd ~
rosinstall optical_ws /opt/ros/fuerte/ https://bitbucket.org/uwsensors/pr2_pretouch_sensor_optical/raw/fuerte-dev/pr2_sensor_optical.rosinstall
source optical_ws/setup.bash
rosmake pr2_robot
rosmake pr2_ethercat_drivers
rosmake pr2_pretouch_sensor_optical

You can change the workspace name optical_ws above to whatever you like.

Overlay this workspace on top of your environment automatically on new terminals by adding this to your .bashrc:

source $HOME/optical_ws/setup.bash

Software Setup (Hydro)

Running ROS Hydro on the PR2 (instruction)
Build system: catkin

###Clone and compile the required packages * pr2_pretouch_sensor_optical * pr2_ethercat_drivers * pr2_robot

using wstool:

cd ~
mkdir optical_ws && cd optical_ws
wstool init src https://bitbucket.org/uwsensors/pr2_pretouch_sensor_optical/raw/hydro-dev/pr2_sensor_optical.rosinstall
cd src && wstool update -j8
cd .. && rosdep install --from-paths src -i -y
catkin_make

You can change the workspace name optical_ws above to whatever you like.

Overlay this workspace on top of your environment or add this to your .bashrc file:

source $HOME/optical_ws/devel/setup.bash

Upgrade the gripper (WG006) firmware (Do it only once)

Important: this step only needs to be done once on each PR2 robot. The upgrade will be persistent. Please make sure the robot is not running (robot stop), and the robot's power cable is plugged into the outlet. Otherwise this firmware upgrade may brick the gripper's motor control board.

./pr2_ethercat_drivers/wg006_fingertip_dev/upgrade_wg006_firmware.sh

Power cycle the PR2 to make this upgrade effective.

Upload the Picoblaze firmware for the gripper’s FPGA (Do it everytime the robot is power-cycled)

If this is the first time you do this, you need to compile the picoasm binary:

cd pr2_ethercat_drivers/wg006_fingertip_dev/picoasm
make

Run this bash script to upload the firmware for the optical sensors:

./pr2_ethercat_drivers/wg006_fingertip_dev/upload_optical_firmware.sh

Run this bash script to upload the firmware for the standard pressure sensors which came with the PR2:

./pr2_ethercat_drivers/wg006_fingertip_dev/upload_pressure_firmware.sh

The firmware is not persistent, and will be lost if the robot is power-cycled. To make it persistent, one way is to call the above script into the system startup script.

Start the Optical Sensor Publisher

Start the Robot, and verify the raw data is published.

robot start
rostopic list | grep raw_pressure

You should see:

/raw_pressure/l_gripper_motor

/raw_pressure/r_gripper_motor

Start the optical sensor publisher:

roslaunch pr2_pretouch_sensor_optical optical_pretouch_both_gripper.launch

Verify the sensor data for the right gripper:

rostopic echo /optical/right

You should see the sensor readings like this:

header: 
  seq: 809
  stamp: 
    secs: 1396376917
    nsecs: 471429109
  frame_id: ''
data: [768, 780, 744, 792]
broken: [False, False, False, False]

Verify the sensor data for the left gripper in the same way:

rostopic echo /optical/left

Visualize the sensor readings

Run a realtime visualization of the sensor readings for verifying the sensor. The photo below shows the suitable configuration for testing. You may want to run this program on a workstation other than the robot and set the ROS_MASTER_URI to the robot. Alternatively you can run it in a ssh -X session.

rosrun pr2_pretouch_sensor_optical visualizer.py

The red color means the beam is broken between the emitter and the receiver (something is in between to block the light).

Alt text

How to use the sensor data

The sensor data is published to the /optical/right and /optical/left topics as a OpticalBeams message.

Header header
uint16[] data
bool[] broken

The data and broken fields are both an array of length 4. The broken field is False when the beam is not broken, and is True when the beam is broken by some object in between. The data field contains the raw sensor readings. By default, a reading with value larger than 800 is defined as a broken beam. You may change the threshold value in pub_optical.py. A smaller value meaning higher sensitivity to sense object in between. The default value usually works fine.

You can simply subscribe to the topics to receive the data. The data rate is 500 Hz.

Wiki

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