Parallelogram gripper

Looped linkages

One slider opens and closes two parallelogram fingers whose jaws stay vertical.

Play0.00 s

¼×½×1×2×

Loop

The steel preset (the default), recordedon an NVIDIA RTX PRO 6000 Blackwell.

Run it

cd examples
# the default preset (steel), then the others
uv run shelf play loop_parallel_gripper
# change solver settings live
uv run shelf tune loop_parallel_gripper

Source: examples/shelf/05_looped_linkages/loop_parallel_gripper/ · ported from common/loop_mechanisms.py, mechanism gripper

Presets

Preset	Solver	Status	Checked
steeldefault	steel	works	2026-11-10, newton f6fc82a8b, NVIDIA RTX PRO 6000 Blackwell Server Edition

Solvers with no row are untested on this example. The full settings are inpresets.toml.

Code

example.py

examples/shelf/05_looped_linkages/loop_parallel_gripper/example.py

# SPDX-FileCopyrightText: Copyright (c) 2026 Skild AI and the Steel contributors
# SPDX-License-Identifier: Apache-2.0

###########################################################################
# Example Parallelogram gripper
#
# One prismatic actuator pulls two rods that swing the upper bars of two parallelogram fingers, so the
# jaws translate symmetrically and stay vertical. Four planar loops (revolute closures); 1 DOF.
#
# The mechanism comes from common/loop_mechanisms.py and runs through common/loop_linkage.py. check compares
# the tracked bodies with reference.json, an exact-constraint reference integration.
#
# Command: python -m shelf run loop_parallel_gripper
#
###########################################################################

from typing import ClassVar

import newton.examples

from common.loop_linkage import LoopLinkageExample


class Example(LoopLinkageExample):
    file = __file__
    mechanism = "gripper"
    period = 2.0  # [s] the trajectory repeats with this period once its one-second ramp is over
    camera: ClassVar = {"eye": (-0.152, -0.416, 0.578), "target": (0.0, 0.0, 0.5)}


if __name__ == "__main__":
    parser = Example.create_parser()
    viewer, args = newton.examples.init(parser)
    newton.examples.run(Example(viewer, args), args)

example.py on GitHub

presets.toml

examples/shelf/05_looped_linkages/loop_parallel_gripper/presets.toml

example = "loop_parallel_gripper"
source = "common/loop_mechanisms.py, mechanism gripper"
default = "steel"

[check]
# Arguments `python -m shelf check` passes in test mode: a 4 s run, the frames in reference.json.
args = ["--num-frames", "200"]

[gallery]
short = "One slider opens and closes two parallelogram fingers whose jaws stay vertical."
title = "Parallelogram gripper"
frame = 75

[xpbd]
status = "untested"

[vbd]
status = "untested"

[mujoco]
status = "untested"

[featherstone]
status = "untested"

[semi_implicit]
status = "untested"

[feather_pgs]
status = "untested"

[steel]
status = "works"
# loop-closing joints need the "immediate" response (this Newton's Steel enforces BALL and REVOLUTE closures only there).
# 2 substeps x 48 iterations: the fastest setting (RTX PRO 6000 sweep, 2026-11-07, mean 1.13 ms per frame) within
# 0.5 mm of the exact reference on both jaws (0.33 mm) and a 0.25 mm loop gap (0.14 mm). Four revolute loops in a
# chain through the slider converge slowly: 2 x 32 leaves the jaws 0.78 mm off, 4 x 16 0.65 mm. Tuned with solve_mode
# "split", which newton f6fc82a8b removed (it runs "serial"); re-checked there at 1.12 ms.
sim = { fps = 50, substeps = 2 }
solver = { solve_mode = "serial", iterations = 48, articulated_contact_response = "immediate" }
checked = "2026-11-10, newton f6fc82a8b, NVIDIA RTX PRO 6000 Blackwell Server Edition"

[kamino]
status = "untested"

[implicit_mpm]
status = "untested"

[style3d]
status = "untested"

presets.toml on GitHub

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