Adaptive Robot Control for Ultimate Accuracy

 Some robot applications require the highest possible accuracy – close to the robot’s repeatability, i.e. typically < 0.1mm – which robot-cell calibration alone cannot achieve, especially in the case of external dynamic forces (e.g. the pressure exercised by drilling). The required accuracy should be achieved not just at the robot’s final resting position (as is the case in Robot Guidance – see “Robot Guidance for Part-to-Part Variation”), but along the entire path followed by the robot’s TCP.  

Adaptive Robot Control with the DynaGuide™ system is the solution for these kinds of applications. A measurement sensor continuously track the robot’s TCP while it moves along the desired path, and any deviation from that path is instantly compensated. Typical sensors used for such application are external 3D or 6DOF measurement systems, the latter type of system allowing the actual measurement targets on the end-effector to be physically located remotely from the TCP. The calculated compensation is generally applied at the TCP’s level for each point along the path.

Adaptive Robot Control can be performed ‘upfront’ at the initial setup of the robot-cell only, or ‘throughout production’. In the latter case, the used measurement system (typically an external 3D or 6DOF device) needs to be operating on the plant floor with a line of sight of the robot’s TCP at all times during the production process: this might make the entire process prohibitively expensive and might not always be feasible. With upfront Adaptive Control, the measurement system is used at setup only, therefore not only reducing overall cost but also allowing measurement of the TCP in potentially different conditions than when in production (e.g. when the part might obstruct view of the TCP). Of course, upfront Adaptive Control is only possible if the initial robot programs will not need to be changed later on throughout production (no change in fixture location, no constantly changing parts, etc.); a Temperature Compensation solution should generally also be implemented in such cases.

Adaptive Robot Control benefits from robot-cell calibration for the same reasons as Robot Guidance – i.e. accurate displacement, minimum collisions, and quick crash recovery – with the additional benefit of maximizing the efficiency of the compensation process at the TCP for each point along the path. Indeed, making the robot as accurate as possible at initial setup, minimizes the magnitude of the compensation to be applied at the TCP, which in turn allows points be compensated at a lower frequency, while minimizing the need for possible iterations – therefore altogether improving cycle time.

The DynaGuide system is a highly sophisticated software package, integrating several key technologies: it can interface with multiple measurement sensors, automatically communicates with virtually any robot controller, incorporates robot-cell calibration, interacts with standard PLC’s, and can populate customer’s data servers. ‘Scripts’ (which have been pre-defined or can be created from scratch) define what sensor data to use for what purpose, what calculation to perform based on the measurement data, what tolerance level to accept, what sequence of operations to follow, etc. The DynaGuide system includes both an Adaptive Robot Control solution as well as a Robot Guidance one (see “Robot Guidance for Part-to-Part Variation”).