creo2urdf

Generate URDF model from CREO Parametric mechanisms.

Since it is under development, we cannot guarantee that the user interface of creo2urdf will not implement breaking changes. Be aware of this if you start using the code contained in this repository

CREO Parametric versions supported and tested

• 9.0.8.0

Assumptions & limitations

• To export the urdf of the robot, the CREO mechanism has to follow these guidelines.
• The joints are assumed to be in position 0.
• Right now it can handle only REVOLUTE, PRISMATIC and FIXED joints.

Installation from binaries

Warning

Users are encountering issues using the dll, see #84.

The DLL of v0.5.5 is broken: #118

Note

The provided dll has not been unlocked, therefore the Toolkit licence is required for using it

Download creo2urdf.zip from the assets of the latest release, and extract it in the folder you like.
This archive contains the dll of the plugin and the text folder for running it.
Follow the Usage section instructions for completing the installation.

Installation from sources

Dependencies

Right now the creo2urdf plugin needs its dependencies to be compiled and linked statically:

• Download vcpkg: git clone https://github.com/microsoft/vcpkg
• Bootstrap vcpkg: .\vcpkg\bootstrap-vcpkg.bat

Build creo2urdf

• Export CREO9_INSTALL_PATH pointing to the Creo9 installation folder, e.g. C:\Program Files\PTC\Creo 9.0.8.0\Common Files
• Pass -DCMAKE_TOOLCHAIN_FILE=[path to vcpkg]/scripts/buildsystems/vcpkg.cmake to the creo2urdf compilation.
• Run the CMake configure step, then build the project:
  • Within Visual Studio, you can do: Project > Configure creo2urdf, then Build > Build all

For those who use the CMake integration in Visual Studio, the -DCMAKE_TOOLCHAIN_FILE option should not be passed to CMake command arguments. Instead, the vcpkg.cmake file path must be passed in CMake toolchain file.

Usage

• Put in your CREO working directory the protk.dat that is automatically generated by CMake in ${PROJECT_BINARY_DIR} (e.g. C:\Users\ngenesio\icub-tech-iit\creo2urdf\build\x64-Release). Or create it by hand as follow:

name creo2urdf
Startup dll
Allow_stop True
Delay_start False
exec_file \path\to\creo2urdf.dll
text_dir \path\to\creo2urdf\src\creo2urdf\text
END

• Open CREO Parametric: on the first time, you will need to accept the plugin registration
• Load the assembly mechanism of which you want to export the urdf
• Press the button

• Select a yaml and csv configuration files with a format explained in the following sections, and the folder where both the urdf the meshes will be saved.

Test your installation

The folder examples contains a simple assembly with two links, called 2BARS.asm. You can open the assembly in Creo and then test the installation by clicking on the Creo2Urdf button. The plugin will ask you to select the related .yaml and .csv files, which are provided in the folder.

If the export process was successful, you should see three files": "bar.stl", "barlonger.stl" and "model.urdf".

YAML Parameter File

The YAML format is used to pass parameters to the plugin to customized the conversion process. The parameters accepted by the plugin are documented in the following.

Include Parameters

The YAML can eventually include other YAML files using the includes parameter, if so, the included files are merged with the main file. All internal groups are merged if they are maps, they are overwritten only if an element is not a map, taking precedence over the main file in case of conflicts.

Note

The includes parameter is not mandatory, but if it is present, it must be a list of strings, containing relative path respect the directory of the main YAML file.

Attribute name	Type	Default Value	Description
includes	List of strings	""	List of paths relative to the main YAML directory

Severity Parameters

Attribute name	Type	Default Value	Description
warningsAreFatal	Boolean	true	Used for throwing fatal errors in case some steps in the exportation of the urdf are failing.

Naming Parameters

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.

Root Parameters

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

Algorithm Parameters

Attribute name	Type	Default Value	Description
epsilon	Float	4*(Machine eps)	Set a custom value for testing whether a number is close to zero

Frame Parameters

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 frames starting w/ SCSYS 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.

Link Frames Parameters (keys of elements of linkFrames)

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

Exported Frame Parameters (keys of elements of exportedFrames)

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.

Mesh Parameters

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.
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.
meshFormat	String	stl_binary	Format of the meshes exported. Allowed values: stl_binary, stl_ascii, step
exportMeshes	Boolean	True	If false, the meshes will not be exported.

Assigned collision geometries (keys of elements of assignedCollisionGeometry)

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: shape: geometric shape type. Supported "box", "cylinder", "sphere". type dependent geometric shape parameters. Refer to SDF Geometry. origin: String defining the pose of the geometric shape with respect to the linkFrame.

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"

Inertia parameters

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.

Assigned Inertias parameters (elements of assignedInertias parameters)

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

Sensors Parameters

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..)

ForceTorque Sensors Parameters (keys of elements of forceTorqueSensors)

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.

Generic Sensors Parameters (keys of elements of sensors)

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

XML Blobs options

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>

CSV Parameter File

By using the a .csv file 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.

Format

The CSV file is loaded and parsed using the d99kris/rapidcsv library. Please refer to its documentation for supported dialects of the format.

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 plugin 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 plugin 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.

Maintainers

This repository is maintained by:

	@Nicogene
	@mfussi66