Improving Accuracy and Repeatability
The robot does not consistently move to the desired position or consistently moves to an undesired position.
Although accuracy and repeatability in robotics continues to advance, there are still limitations and several factors that can contribute to issues getting the desired results. How do accuracy and repeatability differ? Accuracy is the difference between the desired result and the actual result of a move, while repeatability is the ability to achieve the same results repeatedly. While many applications only require approximate accuracy and are forgiving of the occasional discrepancy in position, this is not always acceptable.
Most commonly these inaccuracies are caused by inappropriate or undesired velocities moving to the specified pose. Either the robot was programmed to move at a speed that is too fast, or moving close to a kinematic singularity is causing the robot to move at an unpredictable velocity.
For moves where a waypoint is defined and each subsequent move is based on that position, such as grid or pattern moves, even a slight inaccuracy will compound as it progresses through each point.
Try setting a waypoint as an approach position before the waypoint where you’re seeing the issue. Then, slow the move between these two points. This is especially useful when cycle time is critical, allowing the robot to move quickly where accuracy is less important, then moving slowly where accuracy is essential.
If the speed of the robot seems erratic as it moves to a waypoint, it may be moving close to a singularity. Try adding additional waypoints to avoid that position, or use a “Joint Jump” to set an absolute position for each joint to avoid singularities.
For grid moves, verify that your three waypoints are set perfectly, or there will be noticeable drift the further you progress through the grid. Additionally, use the approach point method mentioned above to improve accuracy moving to the grid.