Verifying Grasps

verifying-grasps

Three instruments on one grasp attempt, at three different moments. A graph may use any of them alone; together they separate "the hand never got there" from "it got there and closed on nothing" from "it closed on something and dropped it", which a single check cannot.

verify_reach compares the commanded grasp pose with the observed one and routes missed when the distance exceeds the object's own smallest half-extent (clamped to floor_m..ceiling_m). The tolerance is the object's size rather than a constant because the question is whether the object can still be between the pads, and that is a question about the object. Cheap -- no camera, no motion -- and it fires before the close, when the graph can still do something about it.

verify_grip reads robot.get_gripper and converts through robot.describe_gripper's width_fit, routing empty when the gap is within empty_margin_m of the mechanical stop. Also cameraless. It reports expected_width_m alongside, which is context and not a test: a planner that grasps at a fitted line's centre may legitimately hold a wide part of the body.

verify_grasp raises the end effector by lift_m along world Z with a Cartesian move, takes a fresh observation, and looks for object_description (then marker_description, when given) first in the camera whose name contains wrist_camera_keyword and then in overhead_camera_name. The first segmentation at or above score_min is back-projected; the grasp is verified only when the cloud has at least min_points valid depth points, its median lies at least min_above_table_m above robot.describe_workspace().surface_z, and within max_hand_distance_m of the lifted hand. Every failed gate returns route: not_held with a reason.

score_min is deliberately low: a small held object occupies only a few dozen wrist pixels and true positives score in the hundredths. Confidence admits a candidate; geometry decides.

Boundaries

• The lift in verify_grasp is the only motion any of the three makes; the object is neither released nor moved elsewhere.
• No force or tactile reading is consulted. verify_grip uses the jaw gap, which every parallel hand reports; torque and slip belong to a connector's own grasp check when it has one.
• Only a rig without a wrist camera raises, and only from verify_grasp. A missing input elsewhere routes the benign way -- reached, unknown -- because absent evidence is not evidence of a failed grasp.