Paint Robot Tracking Boundary: Stroke Gate, Not Point Gate

A correctly commissioned tracking window releases each complete paint stroke only after that stroke has crossed the inbound boundary, then keeps every commanded point available until the robot TCP reaches it. Treat the boundaries as limits on a tracked stroke, not as simple triggers for individual points.

Boundary operating rules

The inbound boundary is therefore a stroke-release gate. It does not release the first paint point merely because that point has entered the tracking area. The outbound boundary is a destination-validity limit. It marks the last tracked position at which a future path point can remain executable.

Before anything else, confirm where each stroke begins and ends in the process program. A stroke begins at Gun=ON and ends at the next Gun=OFF. Any intervening motion points belong to the same admission and expiration decision.

Stroke-level tracking mechanism

Line tracking continuously transforms programmed path points from the moving workpiece reference into robot coordinates. As the conveyor advances, every unexecuted destination moves with that reference. The controller must decide when a complete process segment is available and when an unexecuted destination has moved beyond the permitted tracking window.

The complete-stroke inbound rule prevents the robot from starting a paint pass whose trailing points have not yet entered the usable region. This matters because an interrupted or partially available pass can produce an incomplete coating segment. Once the complete stroke passes inbound, it becomes eligible for execution; robot motion planning, process state, and other program conditions still determine when motion actually begins.

Outbound handling protects path validity. If conveyor motion carries a future point through the outbound boundary before the gun TCP reaches it, that point is no longer a valid tracked destination. The resulting Track Destination Gone alarm is not merely a gun-state warning. It identifies a geometry-and-timing failure: the moving path escaped the tracking window faster than the robot completed it.

Symptom and cause decisions

Separate an expected inbound wait from a true outbound failure. Waiting before stroke release does not by itself indicate lost tracking. A fault accompanied by Track Destination Gone means at least one required point passed outbound before TCP arrival.

Commissioning procedure

1. Map each process stroke. Locate every Gun=ON instruction and its following Gun=OFF. List all motion points between them. Do not move on until each tested point belongs to a clearly identified stroke.
2. Confirm boundary order and tracking direction. Observe the tracked reference moving through inbound, across the working region, and through outbound. The displayed tracking position must progress in the expected direction before path timing can be evaluated.
3. Test inbound qualification without painting. Run at a controlled commissioning condition with process output inhibited by the approved cell procedure. Watch the full stroke cross inbound. Confirm that execution remains withheld while any point in the stroke has not passed inbound.
4. Confirm stroke release. Continue tracking until the complete segment through Gun=OFF has passed inbound. Confirm that the controller can then execute the stroke. If release remains blocked, inspect program interlocks and motion readiness separately from the boundary rule.
5. Observe outbound margin. During execution, monitor the future points of the active stroke relative to outbound. Each point must remain inside the valid tracking region until the TCP reaches it. Do not move on if a future point approaches outbound before TCP arrival.
6. Repeat with the limiting production condition. Test the longest or slowest-executing stroke and the highest intended line-motion condition available under the commissioning plan. Confirm that the complete stroke qualifies inbound and finishes before any remaining destination crosses outbound.

Boundary placement, conveyor behavior, robot path length, process motion speed, and delays before stroke execution all consume the same tracking window. Read the actual values from the controller configuration and live diagnostics; no universal boundary distance or execution allowance applies.

Fault recovery and correction

When Track Destination Gone occurs, record the active stroke, tracked position, boundary state, and destination being pursued before resetting the fault. Resetting alone removes the symptom record but does not restore the expired destination.

1. Locate the active Gun=ON-to-Gun=OFF segment.
2. Find the first point the TCP had not reached when the alarm occurred.
3. Confirm that this point crossed outbound before TCP arrival.
4. Determine what consumed the window: late stroke release, path length, delayed robot start, reduced robot motion, unexpected conveyor motion, or boundary placement.
5. Correct the applicable path, sequence, motion condition, or configured boundary using the cell’s approved limits.
6. Restart from a process-safe state that does not duplicate or omit a paint segment.

Do not widen a boundary merely to suppress the alarm. A new boundary must still represent a region in which the robot can reach the tracked path without violating cell geometry, motion limits, or process requirements. Likewise, splitting a long stroke changes the process definition: each new Gun=ON-to-Gun=OFF segment receives its own inbound qualification.

Verification criteria

Use repeatable pass criteria rather than a single fault-free cycle. For every tested stroke, confirm all four states in order:

1. The controller withholds the stroke while any point through Gun=OFF remains before inbound.
2. The complete stroke passes inbound before execution begins.
3. The TCP reaches every point before that point passes outbound.
4. The cycle completes without Track Destination Gone.

Repeat the test across the production path set and the limiting line condition. A passing first point proves neither complete inbound qualification nor sufficient outbound margin; the full stroke is the verification unit.

Frequently asked questions