Configuring a Tool Offset

You can set the offset between the flange coordinate system of the kinematics (XYZ) and the TCP coordinate system of the kinematics (X'Y'Z') by means of configuring a tool offset. This tool offset acts on all subsequent movements.

TCP: Tool Center Point

The tool offset is specified by a shift v=(x,y,z) and a rotation r=(A,B,C) in ZYZ Euler angles. Shift and rotation are expressed relative to the flange coordinate system of the kinematics.

When you configure a tool offset, it can be incompatible with the current kinematics. As a result, a tool offset can cause the kinematics to be incapable of achieving orientations. In this situation, an error is issued and the tool offset is ignored. For example, you can configure a tool offset in the Z-direction for the kinematics Kin_Scara2_Z. On the other hand, an offset with parts in the X- or Y-direction results in an error. When kinematics have these kinds of restrictions, they are described with the kinematics.

Function block: SMC_GroupSetTool

The function block configures the tool offset specified at the input ToolOffset (type MC_COORD_REF) for an axis group. However, as long as the axis group is in the state GroupDisabled or GroupErrorStop, no tool offset can be configured.

If the tool is not compatible with the current kinematics, then the POU issues the error SMC_AXIS_GROUP_TOOL_OFFSET_INCOMPATIBLE_WITH_KINEMATICS. This error is also issued if the interface ISMKinematicsWithOrientationImage has not been implemented for the kinematics description.

Function block: SMC_GroupReadTool

This function block reads the tool offset: output ToolOffset (type MC_COORD_REF). In this process, the ReadMode input determines whether the tool of the active movement, the last commanded movement, or the tool currently set in the axis group should be read.

Compatible kinematics

Not all kinematics support every tool offset. The following list shows which tools are suitable for which kinematics.

Kinematics	Compatible Tool
SCARA 2 kinematics `Kin_Scara2_Z`	Tools with position offset in the Z-direction and offset in the orientation
SCARA 3 kinematics `Kin_Scara3_Z`	All tools
Polar kinematics `Kin_Polar`, `Kin_Polar_Z`	Tools with position offset in the Z-direction and offset in the orientation
3-axis articulated robot `Kin_Pos_RRR`	Tools with an offset in the orientation
6-axis articulated robot `Kin_ArticulatedRobot_6DOF`	All tools
4-axis palletizer `Kin_4AxisPalletizer`	All tools
Bipod `Kin_Bipod_Rotary`	All tools
5-axis gantry `Kin_5Axes`	All tools
Gantry systems	All tools
H-gantry system	All tools
T-gantry system	All tools
Rotary or linear tripod	All tools

Tip

If a kinematic system does not have 3 degrees of freedom for the orientation, then it may be the case that not every tool offset is compatible.

For custom kinematics

In order to use your custom kinematics with a tool offset, you need to implement the ISMKinematicsWithOrientationImage interface. To add a tool offset for your custom position kinematics, you first have to implement the interface ISMPositionKinematics2.

Interface: ISMKinematicsWithOrientationImage

The kinematic interface provides the method GetFlangeOrientationImage with the variable mR_Flange of data type SMC_Matrix3, which contains the commanded orientation of the flange. As a consequence, the method returns possible resulting orientations oriInfo as data type OrientationSpace.

Behavior of the interface

In particular, when the orientation of the flange in the commanded orientation is known, dof = zero is returned and mOriZero is set to the known orientation.
If the orientation R of the flange is only partially known in the form R*vU = vRot (where vU and vRot are known unit vectors), then dof = one is returned.mOriZero is set to an orientation in the reachable space.
Otherwise, dof = three is returned.

A specified tool offset is compatible with kinematics if the flange position can be calculated uniquely while taking the calculated orientation into account. This is always the case when the calculated orientation can be achieved by the kinematics. The tool offset may be incompatible only if not all orientations can be reached. Moreover, if the method GetFlangeOrientationImage returns dof = zero, then every tool offset is compatible. If the method returns dof = one, then only the tool position offset v_off parallel to the unit vector vU is compatible. In this case, R*v_off = R*vU*x = vRot*x does not depend on the unknown parts of the orientation matrix R. This also includes a tool offset with v_off = 0 (where x = 0). If dof = three is returned, then only position shifts without an offset in x/y/z are compatible.

Implementation notes

Implement the interface ISMOrientationKinematicsWithOriImage2 for orientation kinematics. Then a tool offset can be used for coupling the orientation kinematics with position kinematics. The interface has the method GetOrientationImage2 with the variable VAR_IN_OUT CONSTANT mR_Flange of data type SMC_Matrix3, which contains the commanded orientation of the flange.
The method returns csTool and oriinfo with the data type OrientationSpace in the base coordinate system of the orientation kinematics.
Moreover, the method returns in bActive whether the degrees of freedom from orinfo are active (TRUE) or passive (FALSE).

Example of active degrees of freedom: Kin_CAxis. The rotation about the z-axis is controlled by the orientation kinematics axis.

Example of passive degrees of freedom: Kin_Wrist2. The remaining degree of freedom is the rotation of X/Y about the Z-axis, which points in the direction programmed by the user.

Important

When both the last commanded movement and the new movement are CP movements (both movements linear or rotary) during a tool change, the buffer mode of the subsequent movement is changed from Blending or Aborting to Buffered.

Important

If you configure a new tool offset after MC_GroupInterrupt and before MC_GroupContinue, then the old tool offset is used for the interrupted movements. The new tool offset is used only for movements that are commanded afterwards.

Important

When the kinematics are changed (MC_SetKinTransform), the tool offset is reset (no shift, no rotation).