How-tos

Here are short sections that explain some concepts in more detail.

Blending parameters

The motion planner will report the maximum blend radius guaranteed to give a collision-free blending motion for each Waypoint in the planned path. However, different robot brands vary in how they accept blending parameters, or if they support blending at all. How to interpret the blend radius for each waypoint therefore depends on the robot in use:

Single-valued TCP blending

This is the type of blending that most commercial-off-the-shelf robots support. As an example, this value is what you would use in the Zone argument for an ABB MoveJ instruction (except that ABB uses millimeters, not meters). Note that with this type of blending, the entry and exit value in the BlendRadius are guaranteed to be equal and always expressed in meters in 3D space.

Single-valued TCP blending example

Separate entry and exit blend radius

For robots that accept separate blending values for the start and end of the blending motion, the entry and exit values in the BlendRadius are not necessarily equal.

1. The first value is the distance from the current waypoint to the blend entry point. The blend entry point lies on the robot trajectory between the previous and the current waypoint, and denotes where blending must start.

2. The second value is the distance from the current waypoint to the blend exit point. The blend exit point lies on the robot trajectory between the current and the next waypoint, and denotes where blending must end.

Blending from the blend entry point to the blend exit point is safe and guaranteed collision-free.

Blending example with a separate entry and exit blend radius

Note that whether an entry/exit blend radius is expressed in joint space or in 3D space depends on the movement type of the path segment that corresponds to the entry/exit value. For a given waypoint, the movement type that corresponds to the entry radius is the movement type of that given waypoint. While the movement type corresponding to the exit radius is the movement type of the next waypoint in the trajectory.

For segments with linear movement type, the blend radius is given in meters in 3D space. The blending value then represent the distance the current TCP is from its position at the waypoint configuration when blending should start or end.

For segments with joint movement type, the blend radius is given in joint space. The blending value then represents the euclidean distance (L2-norm) between the waypoint configuration and the joint configuration where the blending should start or end. When computing the distance in joint space, rotational joints are represented in radians and if the robot has any linear joints they are represented in meters.

How to modify the cell

The robot and cell setup can be modified by updating the associated URDF files. See the official URDF documentation for more detail: https://wiki.ros.org/urdf.

The data files used by the Zivid Motion planner must be regenerated after any changes to the robot model. See the Quickstart article for instructions on how to re-generate.