ROS URDF for XELA Sensors

NOTE: There is currently no module to broadcast sensor readings to the model. If there is a need, please make note of the joint names and make own joint_publisher node and enable taxel visualization
NOTE: As each hand is different, some elements in URDF files need to be changed manually
NOTE: Gravity compensation must be calibrated after adding sensors. It will be the responsibility of the user

Installation

Unpack the xela_models directory into your catkin workspace src directory and set it up to be used like any other package for ROS

Use

To use sensors with your URDF files, import XELA xacro file by adding <xacro:include filename="$(find xela_models)/urdf/xela.xacro" /> to your xacro URDF file.

Visualization (XACRO)

To run the visualization of the model, use following command;

roslaunch xela_models display.launch model:=<model>

Available models:

sensor_model	Description
4x4	default 4x4 sensor (XR1844, XR1944)
1x6	specific sensor layout of 3xXR1921
4x6	default 4x6 sensor
aftc	curved fingertip sensor (for Allegro hand)
aftf	flat fingertip sensor (for Allegro hand)
allegro_hand_right	Allegro hand full assembly (right)

You may also take a look in the specific files in xela_models/urdf
Do not edit the xela.xacro file.

Visualization (URDF)

To run the visualization of the model, use following command;

roslaunch xela_models urdf.launch model:=<model>

Available models:

sensor_model	Description
ahrcpcpn	Allegro hand full assembly (right) with curved fingertips, phalange sensors (covers on back), palm sensors and no visual taxels

Available default sensors (XACRO):

Model	Linking tag
XR1944	<xacro:sensor4x4 sequence="1" parent="base_link" />
XR1946	<xacro:sensor4x6 sequence="1" parent="base_link" />

Required arguments you will need to specify (XACRO):

Argument	Description	Example
sequence	Unique name for the sensor	sequence=”1”
parent	Parent link the sensor should be attached to	parent=”base_link”

Optional arguments you can edit (XACRO):

Argument	Description	Example
x	To set base position on x axis	x=”0.01”
rx	To set rotation over x axis (in degrees)	rx=”90”
y	To set base position on y axis	y=”0.01”
ry	To set rotation over y axis (in degrees)	ry=”90”
z	To set base position on z axis	z=”0.01”
rz	To set rotation over z axis (in degrees)	rz=”90”
col	To set one of the default colors: black, blue, green, grey, orange, brown, red, white	col=”blue”
body	To include or exclude the shell of the sensor (set to 0 if your mesh already has sensor shape)	body=”0” Note: by default body=”1”
taxels	To show or hide taxels	taxels=”0” Note: single sensors by default will have taxels on, whilst Allegro hands will have them off

Available special sensors (XACRO):

Model	Linking tag	arguments
Allegro hand (right) full assembly	<xacro:allegro_hand_right sequence="1" parent="base_link" />	Same as regular sensors, except no col Plus covers, palm, tips, phalanges
3xXR1921	<xacro:sensor1x6 sequence="1" parent="base_link" />	Same as regular sensors

Special arguments (XACRO):

Argument	Description	Example
covers	To enable or disable controller covers	covers=”0” Default: covers=”1”
palm	To enable or disable sensors on the palm	palm=”0” Default: palm=”1”
phalanges	To enable or disable phalange sensors	phalanges=”0” Default: phalanges=”1”
tips	To set the type of fingertips curved, flat, default Note: default means Allegro Hand’s own tips You can also set to none to have no tips	tips=”curved” Default: tips=”flat” Note: set to default if you wish the original tips without sensors
defaultnames	To enforce using default link and joint names	defaultnames=1 Default: defaultnames=0
baseispalm	enforce naming of the hand's base_link to be called palm_link (allegro default)	baseispalm=1 Default: baseispalm=0

Changelog and notes

2021/10/14

• Change links to official ones for v4 without sensors and use sensor bodies as fixed link
• Modify some initial values to match the hand for testing
• Add ahrcpcpn.urdf with new details (Allegro Hand Right with Curved Fingertips, Phalange sensors, Phalange covers and Palm sensors)

Known issues

• Encoders can report slightly different data between hands
• Accuracy of the Allegro hand -> TF is separate from URDF and would need to be manipulated by separately (not supported by XELA)

2021/10/12

• Add baseispalm parameter to enforce default name for allegro ROS node
• Update link names to be fully compatible with allegro's

2021/10/04

• Add more options for custom use cases
  • Inertias can be disabled for individual sensors if calculated into parent link
  • Hand links can be with default names by using defaultnames parameter
• All links that move and sensors have defined inertias and masses for simulation (calculated with trimesh library for Python)

2021/09/13

• Replace the link between base and finger
• Move finger up by 4 mm due to the change in the link
• Edit sensors to have an option to turn on/off taxel positions
  • Allegro Hand will have by default taxels turned off
  • Regular sensors will have by default taxels turned on
• Add new parameter "taxels" for sensors and hands/grippers

To Do

• Add XR1911
• Add XR1921
• Add XR1922
• Add Robotiq Gripper
• Add Schunk Gripper
• Add SAKE Gripper
• Add Allegro Hand - Left
• Add pure URDF files of configurations

Contributors

Photo	Contributor	Relation
	@mcsix	XELA Software Engineer