This tool was developed to convert CAD models to URDF ( http://wiki.ros.org/urdf ) models semi-automatically. It makes use of the XML files exported by the SimMechanics Link . Mathworks, makers of SimMechanics, have developed plugins for a couple of leading CAD programs, including SolidWorks, ProEngineer and Inventor.
More specifically, this library at the moment just support first-generation SimMechanics XML files, that in MathWorks documentation are also referred as PhysicalModelingXMLFile .
Based on the original version by David V. Lu!!.
Warning
This tool only works with MATLAB versions <= R2017b and PTC Creo versions <= 8. If you need to use either a newer version of MATLAB or a newer version of PTC Creo, you cannot use this tool.
No work is planned to update this tool to work with more recent MATLAB or Creo versions. Depending on the specific CAD tool you are using, you suggest you to use one of the following tools:
- Creo: creo2urdf
- SolidWorks: solidworks_urdf_exporter
- Autodesk Inventor: No tool is known to us at the moment, if you have any tool suggestion feel free to open an issue suggesting it.
This conversion script uses Python, so you have to install Python for Windows: https://www.python.org/downloads/windows/ .
To install the dependencies, a easy way is to have installed pip, that is installed
if you use the python version provided by homebrew.
If you have pip installed you can get all necessary dependencies with:
pip install lxml numpy pyyaml catkin_pkg
As the installation procedure at this moment suggest to install pip packages at the system level via administrative priviliges (such as sudo) at this moment it is suggest to follow it only on a dedicated environment, and not in your main development machine. See https://stackoverflow.com/a/22517157/1379427 for more details.
Install the necessary dependencies with apt-get:
sudo apt-get install python-lxml python-yaml python-numpy python-setuptools python-catkin-pkg
You can install urdf_parser_py from its git repository. Note that due to some regression in recent versions on the default branch of urdf_parser_py (see #36) it is recommended to use a specific commit of urdf_parser_py that is known to work, https://github.com/ros/urdf_parser_py/commit/31474b9baaf7c3845b40e5a9aa87d5900a2282c3 :
git clone https://github.com/ros/urdf_parser_py
cd urdf_parser_py
git checkout 31474b9baaf7c3845b40e5a9aa87d5900a2282c3
sudo python setup.py install
You can then install simmechanics-to-urdf:
git clone https://github.com/robotology/simmechanics-to-urdf
cd simmechanics-to-urdf
sudo python setup.py install
The SimMechanics Link creates an XML file (PhysicalModelingXMLFile) and a collection of STL files. The XML describes all of the bodies, reference frames, inertial frames and joints for the model. The simmechanics_to_urdf script takes this information and converts it to a URDF. However, there are some tricks and caveats, which can maneuvered using a couple of parameters files. Not properly specifing this parameters files will result in a model that looks correct when not moving, but possibly does not move correctly.
URDF allows robot descriptions to only follow a tree structure, meaning that each link/body can have only one parent, and its position is dependent on the position of its parent and the position of the joint connecting it to its parent. This forces URDF descriptions to be in a tree structure.
CAD files do not generally follow this restriction; one body can be dependent on multiple bodies, or at the very least, aligned to multiple bodies.
This creates two problems.
-
The graph must be converted into a tree structure. This is done by means of a breadth first traversal of the graph, starting from the root link. However, this sometimes leads to improper dependencies, which can be corrected with the parameter file, as described below.
-
Fixed joints in CAD are not always fixed in the exported XML. To best understand this, consider the example where you have bodies A, B and C, all connected to each other. If C is connected to A in such a way that it is constrained in the X and Z dimensions, and C is connected to B so that it is constrained in the Y dimension, then effectively, C is fixed/welded to both of those bodies. Thus removing the joint between B and C (which is needed to make the tree structure) frees up the joint. This also can be fixed with the parameter file.
You can call the script:
simmechanics_to_urdf {SimMechanics XML filename} --yaml [yaml_configfile] --csv-joint csv_joints_configfile --output {xml|graph|none}
The --output options defines the output. Selecting graph the script will output a graphviz .dot representation
of the SimMechanics model, useful for debugging, while selecting xml it will output the converted URDF.
The YAML format is used to pass parameters to the script to customized the conversion process. The file is loaded using the Python (yaml)[http://pyyaml.org/] module. The parameter accepted by the script are documented in the following.
| Attribute name | Type | Default Value | Description |
|---|---|---|---|
robotName |
String | model name set in the file PhysicalModelingXMLFile | Used for setting the model name, i.e. the parameter <robot name="..."> in the URDF model file. |
rename |
Map | {} (Empty Map) | Structure mapping the SimMechanics XML names to the desired URDF names. |
| Attribute name | Type | Default Value | Description |
|---|---|---|---|
root |
String | First body in the file | Changes the root body of the tree |
originXYZ |
List | empty | Changes the position of the root body |
originRPY |
List | empty | Changes the orientation of the root body |
| Attribute name | Type | Default Value | Description |
|---|---|---|---|
epsilon |
Float | 4*(Machine eps) | Set a custom value for testing whether a number is close to zero |
| Attribute name | Type | Default Value | Description |
|---|---|---|---|
linkFrames |
Array | empty | Structure mapping the link names to the displayName of their desired frame. Unfortunatly in URDF the link frame origin placement is not free, but it is constrained to be placed on the parent joint axis, hence this option is for now reserved to the root link and to links connected to their parent by a fixed joint |
exportAllUseradded |
Boolean | False | If true, export all SimMechanics frame tagged with USERADDED in the output URDF as fake links i.e. fake link with zero mass connected to a link with a fixed joint.. |
exportedFrames |
Array | empty | Array of displayName of UserAdded frames to export. This are exported as fixed URDF frames, i.e. fake link with zero mass connected to a link with a fixed joint. |
| Attribute name | Type | Default Value | Description |
|---|---|---|---|
linkName |
String | Mandatory | name of the link for which we want to set the frame |
frameName |
String | Mandatory | displayName of the frame that we want to use as link frame. This frame should be attached to the frameReferenceLink link. The default value for frameReferenceLink is linkName |
frameReferenceLink |
String | empty | frameReferenceLink at which the frame is attached. If frameReferenceLink is empty, it will default to linkName |
| Attribute name | Type | Default Value | Description |
|---|---|---|---|
frameName |
String | Mandatory | displayName of the frame in which the sensor measure is expressed. The selected frame should be attached to the referenceLink link, but referenceLink can be be omitted if the frameName is unique in the model. |
frameReferenceLink |
String | empty | frameReferenceLink at which the frame is attached. If referenceLink is empty, it will be selected the first USERADDED frame with the specified frameName |
exportedFrameName |
String | sensorName | Name of the URDF link exported by the exportedFrames option |
additionalTransformation |
List | Empty | Additional transformation applied to the exported frame, it is expressed as [x, y, z, r, p, y] according to the semantics and units of the SDF convention for expressing poses. If the unmodified transformation of the additionalFrame is indicated as linkFrame_H_additionalFrameOld, this parameter specifies the additionalFrameOld_H_additionalFrame transform, and the final transform exported in the URDF is computed as linkFrame_H_additionalFrame = linkFrame_H_additionalFrameOld*additionalFrameOld_H_additionalFrame . If not specified it is assume to be the [0, 0, 0, 0, 0, 0] element and the specified frame is exported in the URDF unmodified. |
| Attribute name | Type | Default Value | Description |
|---|---|---|---|
filenameformat |
String | %s | Used for translating the filenames in the exported XML to the URDF filenames, using a formatting string. Example: "package://my_package//folder/%sb" - resolves to the package name and adds a "b" at the end to indicate a binary stl. |
filenameformatchangeext |
String | %s | Similar to filenameformat, but use to also change the file extensions and not only the path of the filenames |
forcelowercase |
Boolean | False | Used for translating the filenames. Ff True, it forces all filenames to be lower case. |
scale |
String | None | If this parameter is defined, the scale attribute of the mesh in the URDF will be set to its value. Example: "0.01 0.01 0.01" - if your meshes were saved using centimeters as units instead of meters. |
stringToRemoveFromMeshFileName |
String | None | This parameter allows to specify a string that will be removed from the mesh file names. Example: "_prt" |
assignedCollisionGeometry |
Array | None | Structure for redefining the collision geometry for a given link. |
assignedColors |
Map | {} (Empty Map) | If a link is in this map, the color found in the SimMechanics file is substituted with the one passed through this map. The color is represented by a 4 element vector of containing numbers from 0 to 1 representing the red, green, blue and alpha component. |
| Attribute name | Type | Default Value | Description |
|---|---|---|---|
linkName |
String | Mandatory | Name of the link for which the collision geometry is specified. |
geometricShape |
Dictionary | Mandatory | This dictionary contains the parameters used to define the type and the position of the geometric shape. In particular we have:
|
assignedCollisionGeometry:
- linkName: r_foot
geometricShape:
shape: cylinder
radius: 0.16
length: 0.06
origin: "0.0 0.03 0.0 1.57079632679 0.0 0.0"
- linkName: l_foot
geometricShape:
shape: box
size: 0.4 0.2 0.1
origin: "0.0 0.0 0.0 0.0 0.0 0.0"
Parameters related to the inertia parameters of a link
| Attribute name | Type | Default Value | Description |
|---|---|---|---|
assignedMasses |
Map | {} (Empty Map) | If a link is in this map, the mass found in the SimMechanics file is substituted with the one passed through this map. Furthermore, the inertia matrix present in the SimMechanics file is scaled accounting for the new mass (i.e. multiplied by new_mass/old_mass). The mass is expressed in Kg. |
assignedInertias |
Array | empty | Structure for redefining the inertia tensor (at the COM) for a given link. |
| Attribute name | Type | Default Value | Description |
|---|---|---|---|
linkName |
String | Mandatory | name of the link for which we want to set the frame |
xx |
String | empty | If defined, change the Ixx value of the inertia matrix of the link. Unit of measure: Kg*m^2 . |
yy |
String | empty | If defined, change the Iyy value of the inertia matrix of the link. Unit of measure: Kg*m^2 . |
zz |
String | empty | If defined, change the Izz value of the inertia matrix of the link. Unit of measure: Kg*m^2 . |
assignedMasses:
link1: 1
link2: 3
assignedInertias:
- linkName: link1
xx: 0.0001
- linkName: link1
xx: 0.0003
yy: 0.0003
zz: 0.0003
Sensor information can be expressed using arrays of sensor options. Note that given that the URDF still does not support an official format for expressing sensor information, this script will output two different elements for each sensor:
- a
<gazebo>element, necessary to simulate the sensor in Gazebo when loading the URDF, as documented in http://gazebosim.org/tutorials?tut=ros_gzplugins . - a more URDF-like
<sensor>element, in particular the variant supported by the iDynTree library, as documented in https://github.com/robotology/idyntree/blob/master/doc/model_loading.md .
| Attribute name | Type | Default Value | Description |
|---|---|---|---|
forceTorqueSensors |
Array | empty | Array of option for exporting 6-Axis ForceTorque sensors |
sensors |
Array | empty | Array of option for exporting generic sensors (e.g. camera, depth, imu, ray..) |
| Attribute name | Type | Default Value | Description |
|---|---|---|---|
jointName |
String | empty | Name of the Joint for which this sensor measure the ForceTorque. |
directionChildToParent |
Bool | True | True if the sensor measures the force excerted by the child on the parent, false otherwise |
sensorName |
String | jointName | Name of the sensor, to be used in the output URDF file |
exportFrameInURDF |
Bool | False | If true, export a fake URDF link whose frame is coincident with the sensor frame (as if the sensor frame was added to the exportedFrames array). |
exportedFrameName |
String | sensorName if defined jointName otherwise |
Name of the URDF link exported by the exportFrameInURDF option |
frameName |
String | empty | Name of the frame in which the sensor measure is expressed. Mandatory if exportFrameInURDF is set to yes. |
linkName |
String | empty | Name of the parent link at which the sensor is rigidly attached. Mandatory if exportFrameInURDF is set to yes. |
frameReferenceLink |
String | linkName |
link at which the sensor frame is attached (to make sense, this link should be rigidly attached to the linkName. By default referenceLink is assumed to be linkName. |
frame |
String | empty | The value of this element may be one of: child, parent, or sensor. It is the frame in which the forces and torques should be expressed. The values parent and child refer to the parent or child links of the joint. The value sensor means the measurement is rotated by the rotation component of the <pose> of this sensor. The translation component of the pose has no effect on the measurement. |
sensorBlobs |
String | empty | Array of strings (possibly on multiple lines) represeting complex XML blobs that will be included as child of the <sensor> element of type "force_torque" |
Note that for now the FT sensors sensor frame is required to be coincident with child link frame, due to URDF limitations.
| Attribute name | Type | Default Value | Description |
|---|---|---|---|
linkName |
String | Mandatory | Name of the Link at which the sensor is rigidly attached. |
frameName |
String | empty | displayName of the frame in which the sensor measure is expressed. The selected frame must be attached to the referenceLink link. If empty the frame used for the sensor is coincident with the link frame. |
frameReferenceLink |
String | linkName | link at which the sensor frame is attached (to make sense, this link should be rigidly attached to the linkName. By default referenceLink is assumed to be linkName. |
sensorName |
String | LinkName_FrameName | Name of the sensor, to be used in the output URDF file |
exportFrameInURDF |
Bool | False | If true, export a fake URDF link whose frame is coincident with the sensor frame (as if the sensor frame was added to the exportedFrames array) |
exportedFrameName |
String | sensorName | Name of the URDF link exported by the exportFrameInURDF option |
sensorType |
String | Mandatory | Type of sensor. Supported: "altimeter", "camera", "contact", "depth", "gps", "gpu_ray", "imu", "logical_camera", "magnetometer", "multicamera", "ray", "rfid", "rfidtag", "sonar", "wireless_receiver", "wireless_transmitter" |
updateRate |
String | Mandatory | Number representing the update rate of the sensor. Expressed in [Hz]. |
sensorBlobs |
String | empty | Array of strings (possibly on multiple lines) represeting complex XML blobs that will be included as child of the <sensor> element |
SimMechanics Link has some problems dealing with mirrored mechanism, in particularly when dealing with exporting inertia information. For this reason we provide an option to use for some links not the inertial information (mass, center of mass, inertia matrix) provided in the SimMechanics XML, but instead to "mirror" the inertia information of some other link, relyng on the simmetry of the model.
TODO document this part
IF you use extensions of URDF, we frequently want to add non-standard tags as child of the <robot> root element.
Using the XMLBlobs option, you can pass an array of strings (event on multiple lines) represeting complex XML blobs that you
want to include in the converted URDF file. This will be included without modifications in the converted URDF file.
Note that every blob must have only one root element.
| Attribute name | Type | Default Value | Description |
|---|---|---|---|
XMLBlobs |
Array of String | [] (empty array) | List of XML Blobs to include in the URDF file as children of <robot> |
Using the --csv-joints options it is possible to load some joint-related information from a csv
file. The rationale for using CSV over YAML for some information related to the model (for example joint limits) is to use a format that it is easier to modify using common spreadsheet tools like Excel/LibreOffice Calc, that can be easily used also by people without a background in computer science.
The CSV file is loaded by loaded by the python csv module, so every dialect supported
by the csv.Sniffer() is automatically
supported by simmechanics-to-urdf.
The CSV file is formed by a header line followed by several content lines, as in this example:
joint_name,lower_limit,upper_limit
torso_yaw,-20.0,20.0
torso_roll,-20.0,20.0
The order of the elements in header line is arbitrary, but the supported attributes are listed in the following:
| Attribute name | Required | Unit of Measure | Description |
|---|---|---|---|
| joint_name | Yes | - | Name of the joint to which the content line is referring |
| lower_limit | No | Degrees | lower attribute of the limit child element of the URDF joint. Please note that we specify this limit here in Degrees, but in the urdf it is expressed in Radians, the script will take care of internally converting this parameter. |
| upper_limit | No | Degrees | upper attribute of the limit child element of the URDF joint. Please note that we specify this limit here in Degrees, but in the urdf it is expressed in Radians, the script will take care of internally converting this parameter. |
| velocity_limit | No | Radians/second | velocity attribute of the limit child element of the URDF joint. |
| effort_limit | No | Newton meters | effort attribute of the limit child element of the URDF joint. |
| damping | No | Newton meter seconds / radians | damping of the dynamics child element of the URDF joint. |
| friction | No | Newton meters | friction of the dynamics child element of the URDF joint. |