§ 1Smooth corners, not hard stops
Between any two moves, the naive controller would do the obvious thing: arrive fully at the waypoint, come to a complete stop, confirm position, then begin the next move. Clean, unambiguous — and slow. Every stop costs acceleration and deceleration time on both sides of the point. On a path with dozens of waypoints, those losses compound into a cycle time the engineer never intended.
Blending is the alternative. Instead of stopping at the intermediate waypoint, the controller starts curving toward the next destination while still approaching the current one. The arm never actually visits the corner; it rounds it, trading positional precision at that waypoint for continuous motion and preserved speed.
The geometry matters. A blend is defined by a zone — a radius around the taught point inside which the controller is permitted to begin the transition. Small zone, tight corner, some speed loss. Large zone, sweeping arc, maximum speed preservation but the arm departs noticeably from the nominal path. The programmer sets this per waypoint, and the choice is always a negotiation between path fidelity and cycle time.
Critically, a blended waypoint is a via point, not a target. The arm passes near it; it is not obliged to reach it. This matters wherever the intermediate position has a physical meaning — clearing a fixture edge, avoiding a cable bundle, threading through a gap. A generous blend zone on a point that exists only to shape the path is safe. A generous blend zone on a point chosen because the arm must physically be there is a programming error.
The distinction between joint moves and linear moves compounds this. Blending between two joint moves produces an arc in joint space, which traces an unpredictable path in Cartesian space. Blending between two linear moves keeps the tool closer to a smooth Cartesian curve. Mixing move types at a blended waypoint requires care, because the controller transitions between two different interpolation schemes mid-flight.
Where blending is suppressed — zone set to zero, or a deliberate fine-stop instruction inserted — the arm halts, the controller reads back the actual joint positions, confirms they are within tolerance, and only then proceeds. This is slower, but it is also the moment at which accumulated joint error is caught rather than carried forward. On long paths, strategic fine stops interspersed with blended via points give both speed and periodic ground-truth checks.
Blend zones also interact with speed limits. A zone so large that it overlaps the previous zone creates an undefined condition on some controllers; most handle it by contracting one or both zones automatically, but the result is geometry the programmer did not specify. The safe habit is to keep zones smaller than half the distance between adjacent waypoints.
Small zone, tight corner, some speed loss.
