The Corner Problem in Robotic Dispensing: TCP Speed Variation and Vibration Effects

The problem

In robotic dispensing and gluing applications, bead consistency depends on maintaining a constant relationship between TCP speed and material flow rate. When the robot follows a contour that includes corners or direction changes, two control-level effects degrade bead quality:

TCP speed variation at corners. The robot must decelerate to change direction. Even with corner blending or look-ahead enabled, the TCP speed drops as the arm navigates the corner. If the dispensing system maintains a constant flow rate, the slower TCP speed produces excess material at the corner — a thicker bead, a pool, or a drip. Conversely, if the flow rate is reduced to match the slowdown, timing mismatches between the flow controller and the robot motion create thin spots on either side of the corner.

Residual vibration after direction changes. After navigating a corner, the arm's flexible modes are excited, causing the TCP to oscillate briefly. This produces waviness in the bead immediately after the corner — the dispense nozzle traces a wavy path instead of a straight line. The amplitude depends on the arm's stiffness, the speed of the preceding motion, and the sharpness of the corner.

These effects are particularly problematic in sealant applications (where consistent bead width determines seal integrity), structural adhesive bonding (where excess or insufficient material affects joint strength), and conformal coating (where uniformity is critical for dielectric protection).

Conventional mitigations include slowing down before corners (reduces throughput on complex contours), tuning corner blending parameters per geometry (labor-intensive for complex parts), and adjusting dispensing parameters dynamically (requires a dispensing controller that supports speed-synchronized flow control, adding system complexity).

How software-based compensation addresses this

Vibration compensation shapes trajectory commands to reduce excitation of the arm's flexible modes during direction changes. The TCP follows the intended path with less post-corner oscillation, reducing bead waviness.

Accuracy compensation corrects kinematic model errors and compensates for dynamic tracking errors (joint compliance under the weight of the dispensing head, thermal drift during long runs). The TCP follows the programmed contour more closely, particularly on complex geometries with many direction changes.

Both operate as a feedforward layer between the trajectory planner and the robot SDK. They modify the motion commands — not the dispensing parameters — so the robot's physical motion more closely matches the intended path.

Performance

• Greater than 80% vibration reduction at TCP, directly reducing post-corner bead waviness

• Up to 5.7x TCP accuracy improvement, reducing path deviation on complex contours

• Compatible with speed-synchronized dispensing systems — the improvement comes from better motion, not changed speed profiles

• Feedforward architecture — no production sensors required beyond the existing dispensing system

Integration

• Operates between trajectory planner and robot SDK — no dispensing system modifications

• Calibration uses a temporarily mounted accelerometer (removed before production)

• Currently supported on Standard Bots, UFACTORY, Trossen, and Denso platforms

• Cloud-based model identification; local runtime for real-time compensation

Business context

Dispensing defects — excess material, thin spots, bead waviness — drive rework, scrap, and field failures. In automotive sealing, a failed bead can mean a water leak in the field. In electronics conformal coating, an uneven bead can leave circuitry unprotected. Software-based compensation addresses the motion-quality root cause, improving bead consistency without sacrificing throughput or adding dispensing system complexity.