gripper-max-opening#

Code

GR.004

Validator

CheckPrim

Compatibility

open-usd

Tags

🔑

Summary#

Every gripper site prim must declare a gripper_maxOpening float attribute with a positive value (in meters) recording the maximum jaw separation.

Description#

gripper_maxOpening stores the maximum distance between the gripper fingertips when fully open, in meters. This is a kinematic property — the physical travel limit of the gripper joints — and is distinct from the gripper_grip_line segment length, which encodes the width of the grip pads (finger contact surface area).

Grasp planning algorithms consume this value to determine whether the gripper can physically open wide enough to fit around a given object before attempting a grasp.

The unprefixed attribute name custom:maxOpening is also accepted for existing assets. New assets should use gripper_maxOpening. When both are present the gripper_-prefixed name wins.

Why is it required?#

  • Grasp planners need the max opening to filter candidate grasps by object width.

  • Without it the gripper site does not provide sufficient information for autonomous grasping.

  • Expressed in meters for consistency with metersPerUnit = 1 USD convention.

Examples#

# Invalid: gripper_maxOpening not authored
def Xform "gripper_01"
{
    double3 xformOp:translate = (0, 0.15, 0)
    uniform token[] xformOpOrder = ["xformOp:translate"]
}

# Invalid: gripper_maxOpening is zero or negative
def Xform "gripper_01"
{
    float gripper_maxOpening = 0    # invalid — must be > 0
}

# Valid: 85 mm jaw opening (Robotiq 2F-85)
def Xform "gripper_01"
{
    double3 xformOp:translate = (0, 0.15, 0)
    uniform token[] xformOpOrder = ["xformOp:translate"]
    float gripper_maxOpening = 0.085

    def BasisCurves "gripper_forward_axis"
    {
        point3f[] points = [(0, -0.15, 0), (0, 0.15, 0)]
        int[] curveVertexCounts = [2]
        uniform token type = "linear"
    }

    def BasisCurves "gripper_grip_line"
    {
        point3f[] points = [(-0.04, 0, 0), (0.04, 0, 0)]
        int[] curveVertexCounts = [2]
        uniform token type = "linear"
    }
}

How to comply#

  • Author gripper_maxOpening as a float attribute on the gripper site prim (the unprefixed name custom:maxOpening is accepted for existing assets).

  • Set the value to the physical maximum jaw separation in meters.

  • Ensure the value is strictly positive (> 0).

  • The value must be greater than or equal to the gripper_grip_line segment length.

For More Information#