# WorkCell Format¶

The workcell file describes workcell elements such as frames, joints, DAFs, devices and the properties that relate to these elements such as name, parent name, joint limits, position and orientation, collision geometry, drawing geometry and even user defined properties.

The basic structure of a workcell is frames. Frames are connected in a tree like fashion such that each frame has a parent and [0;many] children. The root of the frame tree is called the world frame and this frame is the only frame that has no parent (except detached DAF frames). The world frame is named WORLD.

Frames come in many different types: fixed frame, movable frame, prismatic joint, revolute joint, and so on. They can be freely defined and connected in the workcell file, though often frames will be grouped into devices.

A device is a robot with one or more joints. It defines a scope where frames that belong to that device can be described. A device always has a base frame which is the frame belonging to the device that has a parent that does not belong to the device. That is, a device defines a sub tree in the frame tree. There exists several device types: serial device, tree device, parallel device and so on, that allow different sort of connections between the joints of the device.

User properties can be attached to any frame. A property has a name and a string value. The property is saved in the frame such that the user can retrieve it and parse the string himself.

A collision setup is a set of include or exclude rules that tell which frame pairs that should not or should be tested for collision. Ex. two neighboring links on a robot will usually collide in their attachment points, which is undesirable, the collision setup should in this case be used to exclude those frames from collision checking.

## Scopes¶

An important thing to notice is that some xml elements are scope dependent. In general the refframe and refjoint attributes are optional and if not defined then scope rules will define them instead.

Ex. when defining a frame in workcell or a device scope the frame will automatically be attached to the previously defined frame.

<WorkCell name="testwc">
...
<Frame name="A" refframe="WORLD" />

<Frame name="B" />

<Frame name="C" refframe="A" />
</WorkCell>


in the above example A attaches to world and B and C attaches to A.

Another example illustrates how properties defined inside a frame can omit the refframe attribute.

<WorkCell name="testwc">
...
<Frame name="A" refframe="WORLD">
<Property name="A_Property"> some string value</Property>
</Frame>

<Property name="A_nother_Property" refframe="A">some string value</Property>
...
</WorkCell>


## Preparser¶

The RobWork preparser is used as the first thing when loading a RobWork XML file. Preparsing happens before processing the file for the tags defined in the remainder of this page. It makes it possible to reuse XML definitions in different ways.

### Define & Use¶

To define a reusable block of XML, it is possible to use the Define tag:

<Define id="SomeID">
<!-- definition goes here -->
</Define>


The code defined can then be reused with the Use tag. The definition is substituted in without any modification.

<Use id="SomeID" />


The Define/Use tags are often used when defining grippers that can have multiple identical kinematic chains as part of its structure.

### Include¶

It is also possible to include other XML files with the Include tag:

<Include file="some.file.xml" />


This is very convenient. For instance, it makes it possible to include the same robot definition in multiple WorkCells that use the same type of robot.

Warning

If you load a WorkCell and save it afterwards, the preparsing information will be lost. This means that only one big file will be generated with no Include, Define or Use tags.

## WorkCell Structure¶

Before going deep into the grammar of the rw xml format some common structure need be explained. The complete kinematic description is based on a construct named Frame. The Frame has a name and a transform relative to its parent frame or refframe. This means that a kinematic Frame tree can be described with multiple frames. The Frame can be of different types the simplest being Fixed, which means that the frame transform is unchangeable.

Another common structure is the Drawable and CollisionModel tags. These are defined relative to the frames, and adds geometry to the workcell.

Properties are linked to a frame and has a name, description and a value. Properties are used to link different information to frames, such as camera or scanner information.

In the xml file format, frames are grouped logically in container type elements. These elements are WorkCell and device types. To avoid name clashes, frames belonging to a container type will have the container name prepended. Example: a frame named “base” specified in a device named “PA10” will have the unique name “PA10.base”.

The WorkCell element is the root element in the fileformat. It implicitly defines a Fixed frame named World. This world frame is the root frame in the kinematic frame tree.

## WorkCell¶

Element WorkCell

Attributes

• name: a string identifying the workcell.

Child elements:

Example

<WorkCell name="scene">
...
</WorkCell>


## Device¶

The different device types are much alike when considering the child elements that they allow. Though they vary somehow in the implicit rules of frame attachment.

In general a device defines a scope. This scope has the same name as the device. Any frames defined inside the scope of a device gets the device name appended. Ex. given a device “dev” and a frame “base” in the device the complete frame name becomes: “dev.base”

### SerialDevice¶

The serial device only allows joints to be connected in a serial chain. And it also only allows one single endeffector.

Element SerialDevice

Attributes

• name: a string identifying the device.

Child elements:

Example

<SerialDevice name="RobotArm">
...
</SerialDevice>


### TreeDevice¶

The tree device allows joints to be connected in a tree like structure. And it also allows for multiple endeffectors.

Element TreeDevice

Attributes

• name: a string identifying the device.

Child elements:

Example

<TreeDevice name="RobotHand">
...
</TreeDevice>


### ParallelDevice¶

The parallel device is like a number of serial devices (with same base) with all endeffectors rigidly connected together. The initial configuration of the robot is required to make all endeffectors align in the same pose. For devices that are connected in multiple places, it is also possible to define so-called junctions. Each Junction must specify two or more chains, where each chain referes to a list of previously defined SerialChains. Notice that each of these chains must start and end in equivalent frames. If no junctions are defined, one implicit junction is created, assuming that each of the defined serial chains must end in the same endeffector frame.

Attributes

• name: a string identifying the device.

Child elements:

In any order:

Final elements:

• Junction

• Q

Example

Take the following kinematic structure as an example:

                                ___
/--------------------|-C |
/             ___     |   |
/-- B ------------|-D-|----|-E |
/     \    ___     |   |    |___|
/       ---|-F |    |   |
/           |   |    |   |
A -----------|-G-|----|-H-|
|___|    |___|


Each of the 8 serial chains, A to H, can contain one or more joints. The boxes show three places where the device must be connected. This can be specified in the device with Junction tags:

<ParallelDevice name="RobotHand">
...
<Junction>
<Chains>C</Chains>
<Chains>D E</Chains>
</Junction>
<Junction>
<Chains>B D</Chains>
<Chains>G H</Chains>
</Junction>
<Junction>
<Chains>B F</Chains>
<Chains>G</Chains>
</Junction>
...
</ParallelDevice>


Notice that the first serial chain (A) was left out in all the cases, as it is equal for all chains. For the junction ending after chains C and E, both A and B was left out, as they do not provide any extra information.

### MobileDevice¶

The mobile device defines a two wheeled mobile robot where the two wheels are on the same axel displaced from the center of the axel with some width AxelWidth.

Attributes

• name: a string identifying the device.

• basename: name of the mobile device base.

Child elements:

Example

<MobileDevice name="Pioneer" basename="Base">
...
</MobileDevice>


### SerialChain¶

Attributes

• name: a string identifying the chain.

Child elements:

## Frame¶

Attributes

• name: a string identifying the frame.

• refframe: name of the parent frame (optional).

• type: (Fixed|Movable|EndEffector) a frame type identifier - default is Fixed (optional).

• daf: (true|false) boolean defining if the frame is a daf or not - default is false (optional)

Child elements

!((Pos >> RPY) | (RPY >> Pos) | Transform) >> *(Property | CollisionModel | Drawable)

Example

<Frame name="myframe" refframe="WORLD">
</Frame>


### Joint¶

Attributes

• name: a string identifying the frame.

• refframe: name of the parent frame (optional).

• type: (Prismatic|Revolute|Universal|Spherical|PrismaticUniversal|PrismaticSpherical) a joint type identifier.

• state: (Active|Passive) joint state - default is Active (optional)

Child elements

!((Pos >> RPY) | (RPY >> Pos) | Transform) >> *(PosLimit | VelLimit | AccLimit | Depend | Property | CollisionModel | Drawable)

Example

### DHJoint¶

A joint that is defined from the Denavit Hartenberg notation. The Craig DH variant is used. This can only specify Revolute or Prismatic joints

Attributes

• name: a string identifying the frame.

• alpha: in degrees

• a:

• One of the following:

• d: Revolute joint

• theta: Prismatic joint

• b: HGP Revolute joint

• beta: HGP Prismatic joint

• offset:

• state: (Active|Passive) joint state - default is Active (optional)

• type: (craig|schilling|HGP) type of DH joint (optional)

Child elements

!((Pos >> RPY) | (RPY >> Pos) | Transform) >> *(PosLimit | VelLimit | AccLimit | Depend | Property | CollisionModel | Drawable)

Example

### Depend¶

A tag used in Joint and DHJoint for making one joint depend on another.

Attributes

• on: the joint that this joint depends on.

• gain: numeric value giving a multiplication factor of the other joint value.

• offset: numeric value giving an offset.

## Drawable¶

A Drawable will be rendered as part of the visualisation in RobWorkStudio. It is also used for collision detection. If you want a model that is only for collision detection, see CollisionModel.

Attributes

• name: the name of the drawable.

• refframe: the frame that the drawable is to be attached to (optional).

• colmodel: (Enabled|Disabled) if enabled the drawable will also be used as collision model - default is Enabled (optional).

Child elements

!((RPY >> Pos) | (Pos >> RPY) | Transform) >> *(RGB) >> *(Polytope | Plane | Sphere | Box | Cone | Cylinder | Tube | Custom)

Example

<Drawable name="Joint1Geo" refframe="Joint1">
<Pos>0 0 0</Pos>
<RPY>-90 0 0</RPY>
<Polytope file="geometry/czlon1"/>
</Drawable>


Example

If the model geometry file does not contain colour information. It is possible to add the RGB tag to give it a custom colour. The default colour will otherwise be gray RGB(0.6,0.6,0.6). Example below shows how to make a drawable green.

<Drawable name="Joint1Geo" refframe="Joint1">
<Pos>0 0 0</Pos>
<RPY>-90 0 0</RPY>
<RGB>0 1 0</RGB>
<Polytope file="geometry/czlon1"/>
</Drawable>


## CollisionModel¶

A CollisionModel will not be rendered as part of the visualisation in RobWorkStudio. It is only used for collision detection. If you want a model that is also visualised, see Drawable.

Attributes

• name: name of the model

• refframe: place model relative to this frame (optional)

Child elements

!((RPY >> Pos) | (Pos >> RPY) | Transform) >> *(Polytope | Plane | Sphere | Box | Cone | Cylinder | Tube | Custom)

Example

CollisionModel and Drawable can be used together, in order to use different models for visualisation and collision detection. Often it is useful to have a more coarse model for collision detection, and a finer model for visualisation.

<Drawable name="BaseGeo" refframe="Base" colmodel="Disabled">
<Pos>0 0 0.1331</Pos>
<RPY>90 0.0 90</RPY>
<Polytope file = "Geometry/Geo_fine"/>
</Drawable>
<CollisionModel name="BaseGeo" refframe="Base">
<Pos>0 0 0.1331</Pos>
<RPY>90 0.0 90</RPY>
<Polytope file = "Geometry/Geo_coarse"/>
</CollisionModel>


## Property¶

Attributes

• name: name of the property

• type: type of property (string, double or Q) - string is default (optional)

• reframe: frame to attach property to (optional)

• desc: description of the property (optional)

Child elements

• string value (if type is string)

• double value (if type is double)

• list of doubles separated by space (if type is Q)

Example

A user property for defining a camera on a frame. The string value can be parsed by the user to get image dimensions [640;480] and field of view 40

<Property name="Camera" refframe="WORLD" desc="[fovy,width,height]">
40 640 480
</Property>


When the ‘Camera’ property name is used, this will also, when opened in RobWorkStudio, draw the outline of the camera frame. In this case the camera parameters will always be interpreted in the order fovy,width,height, as shown above, ignoring the description given.

Example

A user property for enabling the display of the frame axis. This will automatically execute the TreeView plugin action of turning on the visibility of the frame axis.

<Frame name="my_frame">
<RPY>0 0 0</RPY>
<Pos>0 0 1</RPY>
<Property name="ShowFrameAxis">true</Property>
</Frame>


## Transform¶

Attributes None

Child elements All real values are parsed into a rotation matrix R and a position P

R00 >> R01 >> R02 >> P0 >>
R10 >> R11 >> R12 >> P1 >>
R01 >> R21 >> R22 >> P2


Example Loads the identity rotation and the (0.1,0.1,0.1) position. Values are seperated by whitespace.

<Transform>
1 0 0 0.1
0 1 0 0.1
0 0 1 0.1
</Transform>


## RPY¶

Attributes None

Child elements Loads RPY values seperated by whitespace

roll >> pitch >> yaw


Example A rotation matrix with 90 degree rotation around z-axis

<RPY> 90 0 0 </RPY>


## RGB¶

Attributes None

Child elements Defines the simple material colours for the visual model. This material is used if the model does not support the colour/material information (e.g. when geometric primitive or STL model is used).

r >> g >> b >> *a


Example

Simple material color with RGB values [1.0, 0.0, 0.0] (red color).

<RGB> 1.0 0.0 0.0 </RGB>


Example

Simple material color with transparency: RGBA values [1.0, 1.0, 0.0 0.5] (transparent yellow color).

<RGB> 1.0 1.0 0.0 0.5 </RGB>


## Pos¶

Attributes

Child elements Loads pos values seperated by whitespace

x >> y >> z


Example

<Pos> 0.1 0.1 0.2 </Pos>


## Geometry¶

Geometries are used in Drawable and CollisionModel definitions. The following types of geometries are currently supported: Polytope, Plane, Sphere, Box, Cone, Cylinder, and Tube. Also, a Custom type is possible, which can be used together with the RobWork plugin structure to define custom geometry.

### Polytope¶

Attributes

• file: the geometry file

Example

<Polytope file="c:/geometry/object.stl" />


### Plane¶

Attributes None

Example

<Plane />


### Sphere¶

Attributes None

• level: (optional, default=20) mesh resolution.

Example

<Sphere radius="0.05" />

<Sphere radius="0.05" level="20" />


### Box¶

Attributes

• x: length in x-axis

• y: length in y-axis

• z: length in z-axis

Example

<Box x="0.1" y="0.1" z="0.1" />


### Cone¶

Attributes

• z: height of cone.

• level: (optional, default=20) mesh resolution.

Example

<Cone radius="0.1" z="0.1" />

<Cone radius="0.1" z="0.1" level="10"/>


### Cylinder¶

Attributes

• z: length of cylinder

• level: (optional, default=20) mesh resolution.

Example

<Cylinder radius="0.1" z="0.1" />

<Cylinder radius="0.1" z="0.1" level="20"/>


### Tube¶

Attributes

• thickness: thickness of the tube surface.

• z: height of the tube.

• level: (optional, default=20) mesh resolution.

Example

<Tube radius="0.1" thickness="0.01" z="0.1"/>

<Tube radius="0.1" thickness="0.01" z="0.1" level="10"/>


### Custom¶

The Custom type allows the user to add user-defined geometry to RobWork and use it in the WorkCell definition. The user must register an extension to the rw.loaders.GeometryFactory extension point, for instance by providing a RobWork plugin. The extension should have a property called type. It is this property that is used to match the extension with the type parameter in the Custom tag. If no type property is found, the name of the extension itself is used instead. The extension can provide any geometry object that implements the rw::geometry::GeometryData interface, but the parameters given in the param parameter is only passed to the object if it is of the more specific type rw::geometry::Primitive.

Attributes

• type: name identifying the type of geometry.

• param: arbitrary length list of doubles separated with space.

## Calibration¶

Attributes

• file: name of the calibration file.

## CollisionSetup¶

Attributes

• file: the file where the collision setup is described

Example

<CollisionSetup file="../mydevice/colsetup.xml" />


## ProximitySetup¶

Attributes

• file: the file where the proximity setup is described

Example

<ProximitySetup file="../mydevice/colsetup.xml" />


## PosLimit¶

Attributes

• refjoint: the joint which the limit is valid for. (optional)

• min: the minimum joint value

• max: the maximum joint value

Example

<PosLimit refjoint="joint1" min="-90" max="90" />


## VelLimit¶

Attributes

• refjoint: the joint which the limit is valid for. (optional)

• max: the maximum joint velocity value

Example

<VelLimit refjoint="joint1" max="180" />


## AccLimit¶

Attributes

• refjoint: the joint which the limit is valid for. (optional)

• max: the maximum joint acceleration

Example

<AccLimit refjoint="joint1" max="180" />


## Q¶

Attributes

• name: name identifying the configuration. The special name “Home” specifies the home position of a device.

Example

<Q name="Home">1.57 -2.4 2.4 -1.57 -1.57 0</Q>
`