Hi,
I’ve been running a series of tests with a UR3e involving movement along two long (50mm) or short (10mm) lines using MoveL and the UR RTDE library, with differing angles between lines, target velocity/acceleration, and blend radius.
While these tests run, I am constantly recording the TCP velocity and position. The speed is recorded using the x/y/z velocity from rtde_read.getActualTCPSpeed, and then finding sqrt(x^2 + y^2 + z^2) to find the velocity magnitude.
When moving at lower velocities, the robot will travel at its target velocity during the straight part, accelerate when passing through the blend, and then return to its target velocity at the second straight. This behaviour was observed at 1mm/s at 2mm/s^2 with the long lines, and 1mm/s at 2mm/s^2 and 5mm/s at 10mm/s^2 with the short lines.
Long lines: It reaches the target velocity of 1mm/s until the blend, and suddenly shoots up to 10mm/s. The sudden acceleration is visible on camera footage. It decelerates before the end of the blend back to 1mm/s.
Short lines: Both acceleration and deceleration behaviour is observed.
At higher velocities, this behaviour is not present.
Another thing that I noticed is that, when viewing the TCP position data, it’s visible that the robot begins the blend late. When moving along the 50mm lines, the robot only starts the blend after travelling about 47/50mm even though the blend radius is set to 20mm.
Is this expected behaviour for the robot during blended MoveL motion? What’s the reasoning behind the sudden acceleration during blends?
