Universal Robots UR3/CB3 User Manual page 159

14.6 Command: Fixed Waypoint
Blending
Blending enables the robot to smoothly transition between two trajectories, without
stopping at the waypoint between them.
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 trajectory (see figure 14.3):
Version 3.3.3
WP_1
• 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 initial/final speed of the robot)
O
II-75
WP_2
WP_3
CB3