Universal Robots UR3/CB3 Original Instructions Manual page 176

Example Consider a pick and place application as an example (see figure 14.2), where the
robot is currently at Waypoint 1 (WP 1), and it needs to pick up an object at Waypoint 3 (WP 3).
To avoid collisions with the object and other obstacles (O), the robot must approach WP 3 in the
direction coming from Waypoint 2 (WP 2). So three waypoints are introduced to create a path that
fulfils the requirements.
Figure 14.2: WP 1: initial position, WP 2: via point, WP 3: pick up position, O: obstacle.
Without configuring other settings, the robot will make a stop at each waypoint, before continuing
the movement. For this task a stop at WP 2 is not optimal since a smooth turn would require less
time and energy while still fulfilling the requirements. It is even acceptable that the robot does not
reach WP 2 exactly, as long as the transition from the first trajectory to the second happens near this
position.
The stop at WP 2 can be avoided by configuring a blend for the waypoint, allowing the robot to
calculate a smooth transition into the next trajectory. The primary parameter for the blend is a
radius. When the robot is within the blend radius of the waypoint it can start blending and deviate
from the original path. This allows for faster and smoother movements, as the robot does not need
to decelerate and re-accelerate.
Blend parameters Apart from the waypoints, multiple parameters will influence the blend tra-
jectory (see figure 14.3):
• the blend radius (r)
• the initial and final speed of the robot (at positions p1 and p2, respectively)
• the movement time (e.g. if setting a specific time for a trajectory this will influence the ini-
tial/final speed of the robot)
• the trajectory types to blend from and to (MoveL, MoveJ)
If a blend radius is set, the robot arm trajectory blends around the waypoint, allowing the robot
arm not to stop at the point.
Blends cannot overlap, so it is not possible to set a blend radius that overlaps with the blend radius
of a previous or following waypoint as shown in figure 14.4.
CB3
WP_1
O
II-78
14.6 Command: Fixed Waypoint
WP_2
WP_3
Version 3.10