IVYXSTUDIO · IVY NODE

Choose a grasp

ivy.node.choose-grasp · v0.1.0

ivyx✓

Decides how to take an object from its size: the jaw yaw across its narrow side and the approach height above it. A decision node: it computes, the robotics steps move.

#robotics#grasp#pick#decision

Inputs

Field	Type	Description
sizerequired	object	The object's half extents in metres, as robotics.scene.locate answers them: x, y, z.
pose	object	The object's pose, passed through.
jawOpening	number	How wide the jaws open, metres; the grasp goes across the side that fits.
clearance	number	Metres between the object's top and the jaws on the approach.

Outputs

Field	Type	Description
yawrequired	number	The jaw yaw about the vertical, radians: 0 across x, pi/2 across y.
approachrequired	number	Metres above the object's centre the jaws arrive before coming down.
fitsrequired	boolean	True when a side of the object fits between the jaws.
pose	object	The object's pose, passed through.

Source

python

# Input preparation
inp = __ivy_ctx__["nodes"][__ivy_node_id__]["input"]

# Compute
import math

class ChooseGrasp:
    """
    Decides how to take an object from its half extents: the jaw yaw across
    its narrower side and the height above its centre the jaws arrive at.
    """

    def __init__(self, jaw_opening: float = 0.03, clearance: float = 0.03):
        if jaw_opening <= 0:
            raise ValueError("jawOpening must be a positive number of metres")
        if clearance < 0:
            raise ValueError("clearance must be zero or a positive number of metres")
        self.jaw_opening = jaw_opening
        self.clearance = clearance

    def run(self, size: dict) -> dict:
        hx = float(size.get("x", 0.0125))
        hy = float(size.get("y", 0.0125))
        hz = float(size.get("z", 0.0125))
        across_x = 2 * hx
        across_y = 2 * hy
        # The jaws close across the narrower side: a yaw of 0 closes across x, pi/2 across y.
        yaw = 0.0 if across_x <= across_y else math.pi / 2
        return {
            "yaw": yaw,
            "approach": round(hz + self.clearance, 4),
            "fits": min(across_x, across_y) <= self.jaw_opening,
        }

result = ChooseGrasp(float(inp.get("jawOpening", 0.03)), float(inp.get("clearance", 0.03))).run(inp.get("size") or {})
result["pose"] = inp.get("pose")

# Output collection (the runner reads it here)
out = __ivy_ctx__["nodes"][__ivy_node_id__]["output"]
out.update(result)

Tests

Requires: python:3.9

cube-across-x
A cube is taken across x, the jaws arriving 4.25 cm above its centre, and it fits.
bar-across-y
A bar wider in x than the jaws is taken across y.
too-wide
A block wider than the jaws on both sides does not fit.