Additional axes can be added to some robot kinematics to allow the tool's orientation to be changed. In the simplest case this is a fourth axis at a XYZ gantry that turns the gripper. In more complex situations the tool can also be tilted, e.g. to do manipulations at the workpiece's side.

The igus Robot Control supports this in three ways: The tilt/swivel joints, the legacy fourth axis and as external axes. This guide explains the different approaches and how to set them up.

External Axes

Adding the tool joint(s) as external axes is the easiest and most flexible approach. These can simply be added via the configuration section in the PC software. Please follow the external axes guide on how to set these up.

Advantages:

Easy to set up
Motion not limited to +/- 179°
Supported by all kinematics

Limitations:

Not coupled to the cartesian ABC orientation, therefore cartesian motion commands including the DXF path command may not turn the axes as you expect.

Tilt/Swivel Joints

The tilt / swivel joint configuration links up to three robot axes to the cartesian ABC orientation. The first axis (e.g. A4 on a XYZ gantry) is linked to A, the second to B, the third to C, where A turns the tool around the Z axis and B/C tilt it around Y and X.

Advantages:

Motion is coupled to the cartesian ABC orientation
Supports offsets between each axis

Limitations:

Motion limited to +/- 179°
Needs to be set up in the Robot Configuration File
Supported from igus Robot Control version 15.1

Supported kinematics:

XYZ room gantries
XY flat gantries
XZ line gantries
further kinematics may be added on demand, please contact us

Configuration

In the Robot Configuration File add the following:

In line "<Joints NrOfJoints="3" />" increase the number of robot joints by the number of tilt/swivel joints.
Below this line you should find an entry for each axis, e.g. "<Joint0...", "<Joint1...>" etc. Add new entries for each joint and increase the number in the XML tag name. Set up the parameters as usual (you need to set at least the CAN ID and the GearScale parameters).
Change line "<Kinematic..." as follows (do not change the parameters within the "Kinematic" line). Add a "<SwivelJoint..." line for each joint and set the offset to the next flange in mm (in most cases as "zOffset").

 <Kinematic Type="Cartesian" FourthAxis="False" dirA1="1 0 0" dirA2="0 1 0" dirA3="0 0 -1" xOffset="0" yOffset="0" zOffset="0">
   <SwivelJoint xOffset="0" yOffset="0" zOffset="50"/>
   <SwivelJoint xOffset="0" yOffset="0" zOffset="50"/>
   <SwivelJoint xOffset="0" yOffset="0" zOffset="50"/>
 </Kinematic>

Change the motion limits in line "<SoftwareMinMax" so that the corresponding axes (for a 3 axis gantry A4-A6, for a 2 axis A3-A5) move no more than +/- 179°.
Change the speed and acceleration in lines "<JointVelocities...", "<JointAccelerations..." etc.

Visualization

If you like to visualize the joints in the 3D view you can add 3D models in OBJ format to the robot configuration directory (next to the robot configuration file). These files must be named as follows:

"SwivelJoint0.obj" - the static base of the first joint, this connects to the previous robot joint (e.g. the gantry's Z axis)
"SwivelJoint1.obj" - the first joint that rotates around Z (cartesian A orientation)
"SwivelJoint2.obj" - the second joint that rotates around Y (cartesian B orientation)
"SwivelJoint3.obj" - the third joint that rotates around X (cartesian C orientation)

If less than 3 tilt/swivel axes are defined elements 2 and 3 may not be displayed, the last element is the flange to the tool.

Fourth Axis

The legacy configuration parameter "Fourth Axis" links an additional axis to the cartesian A orientation, turning the tool around the Z axis. This effectively is equivalent to the tilt/swivel joint approach with only one joint.

Advantages:

Motion is coupled to the cartesian A orientation

Limitations:

Motion limited to +/- 179°
Does not support cartesian B and C orientation
Needs to be set up in the Robot Configuration File

Supported kinematics:

XYZ room gantries
DeltaLinear
SCARALRRR, SCARARRLR
further kinematics may be added on demand, please contact us

Configuration

In the Robot Configuration File add the following:

In line "<Joints NrOfJoints="3" />" increase the number of robot joints by one.
Below this line you should find an entry for each axis, e.g. "<Joint0...", "<Joint1...>" etc. Add a new entry and increase the number in the XML tag name. Set up the parameters as usual (you need to set at least the CAN ID and the GearScale parameters).
In line "<Kinematic..." change parameter "FourthAxis" to "True".
Change the motion limits in line "<SoftwareMinMax"
Change the speed and acceleration in lines "<JointVelocities...", "<JointAccelerations..." etc.