REVIEW 3 major objections 5 minor 29 references
23 DoF Grasping Policies from a Raw Point Cloud
T0 review · 3 major / 5 minor · reviewed 2026-08-12 · deepseek-v4-flash
Pith's one-line read A Neural Geometric Fabric policy directly predicts 23-DoF joint accelerations from a raw point cloud and, paired with a motion planner, grasps objects not seen in policy training.
desk verdict Solid NGF-to-point-cloud extension, but the 'unseen object' claim hinges on an unnamed autoencoder object set. read the letter →
The pith
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
The reading
What carries the argument
The Neural Geometric Fabric (NGF): a geometric fabric, a stable second-order differential equation of the form $\ddot{q} = e_h - M^{-1}\partial_q\psi - B\dot{q}$, whose metric, potential, and damping are neural-network functions of joint state and a latent object encoding. The fabric's stability guarantees and path consistency let the learned accelerations behave like a controller rather than an open-loop trajectory; the frozen point-cloud autoencoder supplies the object-conditioning feature $z$. The motion-planner-in-the-loop design is the other central mechanism: it restricts learning to the challenging grasp segment while traditional planning handles approach and lift.
What would settle it
Check the four YCB objects used to train the point-cloud autoencoder in Section III-D: if 'mustard' is among them, rerun the 100-trial mustard grasp evaluation with mustard excluded from encoder training. A materially lower success rate would show the reported generalization conflates grasp-policy novelty with encoder familiarity.
Extended reading notes
Core claim
The central discovery is that a Neural Geometric Fabric policy can output 23-dimensional joint accelerations that form smooth grasping trajectories directly from the latent code of a partial point cloud, and these trajectories generalize to an object whose point cloud was not part of grasp-policy training. The paper builds the fabric by parameterizing its metric, driving force, and damping with neural networks conditioned on a frozen PointNet-based autoencoder encoding of the scene. Trained with DAgger against a surrogate PD expert built from geometric-fabric-generated trajectories, the policy is evaluated in simulation on three objects; it consistently beats an MLP baseline, and point-cloud conditioning improves success over position-only conditioning. The authors combine the learned policy with a geometric fabric motion planner in a loop, using the planner for approach and lift while the policy handles only the contact-rich grasp, and report that this setup grasps a previously unseen object.
Load-bearing premise
The result depends on the test object 'mustard' not being one of the four YCB objects used to train the frozen point-cloud encoder; the paper never lists those four objects, so the 'previously unseen object' claim cannot be fully verified from the text.
Editorial extensions
If this is right
- High-DoF grasping can be cast as a learned second-order dynamical system rather than a per-scene optimization, so run-time grasp synthesis could be replaced by a single 30 Hz policy.
- Point-cloud encodings carry geometric information that improves grasping over position-only inputs, supporting the idea that raw perception can directly condition contact-rich policies.
- Because the fabric structure provides stability, the learned policy only needs to imitate the expert's accelerations rather than enforce constraint satisfaction from scratch.
- The same training pipeline, fabric-generated trajectories plus DAgger, could in principle be applied to other high-DoF manipulation skills without human demonstrations.
- Generalization over object shape and pose opens a route to multi-object grasping with a single policy, provided the encoder generalizes across the object distribution.
Reading between the lines
- The strongest interpretation of "novel object" applies only to the grasp policy; the frozen point-cloud encoder was trained on four YCB objects, so the paper's generalization claim is only fully about novel objects if the test object was not among those four, a detail the paper does not disclose.
- If the encoder had seen the test object, the result still demonstrates grasp-policy generalization but not end-to-end perception generalization; a clean test would retrain the encoder without the test object.
- The approach's reliance on a dataset lookup for the pre-grasp configuration means the method does not yet solve full pick-and-place from arbitrary configurations; learning that retrieval is an obvious next step the paper acknowledges.
- Because the fabric expert itself only succeeds on a fraction of its own training trajectories (59% for one object), the policy's ceiling is coupled to expert data quality; improving the expert's success rate before collecting training data should raise the learned policy's success rate.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The paper proposes an imitation-learning pipeline for 23-DoF grasping from a single fixed RGBD camera. The authors first generate successful grasp configurations using a DexGrasp-1M-derived grasp set and a geometric-fabric motion planner, then reverse the resulting trajectories and train a Neural Geometric Fabric (NGF) policy, with an MLP baseline, to predict joint accelerations. Object information is supplied either by object position or by a frozen PointNet-based autoencoder latent encoding of the partial point cloud. Experiments compare NGF and MLP with position and point-cloud encodings on three objects, of which mustard is labeled as not seen.
Significance. If the empirical claims hold, the paper would support a useful design: a second-order fabric-structured policy that can be trained without human demonstrations and deployed in a loop with an off-the-shelf motion planner, with the learned component handling only the final grasping motion. The expert construction and loss in Eqs. (1)-(2) are standard, and the NGF parameterization is a coherent extension of geometric fabrics. The paper also gives credit to the geometric-fabric literature and clearly separates the learned grasping component from the motion-planner loop. However, the evidence for the headline claim of generalization to novel object geometry is incomplete: the autoencoder's training objects are not disclosed, no uncertainty or significance measures are reported, and the underlying dataset for one training object has only a 59% successful-lift rate.
major comments (3)
- [Section III-D and Section IV, Fig. 5] The autoencoder is trained on point clouds of '4 YCB objects' but the objects are not named. The evaluation object 'mustard' is labeled '(not seen)' in Fig. 5, but the label only says it was not seen by the grasp-policy training; the paper never states whether mustard was among the four autoencoder training objects. If mustard was included, the 'novel object' experiment tests generalization of the grasp head but not generalization of the perception-to-grasp system to an unseen shape, which is the central contribution claimed in the abstract and introduction. Please disclose the four objects and, if necessary, retrain the autoencoder with mustard excluded before re-evaluating.
- [Section IV, dataset note] The paper reports that only 59% of the generated trajectories for 'sugarbox' successfully lift the object, versus 93% for 'bleach'. Since the policies are trained to imitate these trajectories, the upper bound on achievable success for sugarbox is at most 59% under the current data-generation process, independently of policy architecture. This directly qualifies the introductory claim that the model 'reliably predicts a smooth 23-DoF grasping trajectory' and should be discussed explicitly as an upper bound and addressed, for example by filtering the training set to successful demonstrations or by reporting per-object ceiling performance.
- [Section IV and Fig. 5] No error bars, confidence intervals, or statistical tests are reported for the 100-trial success rates. For a binary outcome with n=100, the 95% Wilson interval has half-width around 5-10 percentage points, so the reported differences between NGF-PCD and MLP-PCD, and between PCD and POS encodings, may not be significant. Please report exact counts, intervals, and tests (or at least multiple random seeds) for each bar.
minor comments (5)
- [Section III-A] The word 'postive' in the description of the damping matrix should be 'positive'.
- [Fig. 3 caption] The caption says 'course geometry' but should read 'coarse geometry'.
- [Section III-B and Eq. (5)] In Eq. (5), B is introduced as a positive semi-definite damping matrix, but the definition B = beta_f M^{-1} dot-q appears to produce a vector rather than a matrix. Please clarify the intended construction.
- [Section II-A] The notation K is used in |D_tau| = M K but K is not defined; it should be explicitly tied to the number of object poses |G| times the number of objects |O|.
- [Section III-D] Training details of the autoencoder, such as latent dimension, number of epochs, regularization weight, and point-cloud preprocessing, are missing and are needed for reproducibility.
Circularity Check
No circularity found: the policy is trained by imitation of fabric-generated trajectories and evaluated by physical grasp success, with no success signal used as a training input.
full rationale
The paper's derivation chain is empirical rather than formal. Grasp trajectories are generated in simulation by geometric fabrics [20], reversed, and stored; a PD controller (Eq. 1) forms the surrogate expert, and the policy is trained by DAgger to match the expert's accelerations (Eq. 2). The expert's target is a dataset trajectory, not the grasp-success label; success is measured only after execution in Section IV and is never used as a training objective. Hence no prediction reduces by construction to a fitted parameter or to the training signal. The NGF architecture is inherited from prior work [21], but this is a structural choice tested directly against an MLP baseline in Section IV and Figure 5, so the self-citation is not load-bearing. The point-cloud autoencoder in Section III-D is trained on a reconstruction task and then frozen; its latent vector is an input feature to the policy, not a prediction of grasp outcome. One disclosure gap should be flagged: the paper says the autoencoder was trained on '4 YCB [26] objects' without naming them, and Figure 5 labels 'mustard' as '(not seen)' while Section IV states the grasp policies were trained on bleach and sugarbox only. If mustard was among the four autoencoder objects, the 'previously unseen object' claim would be weakened for perception generalization. This is an experimental-support ambiguity, not a circularity by construction: no equation or fitting step equates the test output to the training data. Score 0.
Assumptions & free parameters
free parameters (6)
- Additional damping scalar beta =
5
- Number of grasp poses per object N =
7
- Number of trajectories per object pose M =
256
- PD gains kp, kd in surrogate expert =
not reported
- Autoencoder latent dimension =
not reported
- Number of random Fourier features =
1000
assumptions (5)
- standard math Geometric fabrics are provably stable and produce path-consistent motion (citing [20])
- domain assumption The simulator physics and fixed-camera point cloud faithfully represent the real robot environment
- domain assumption The surrogate expert with PD control can reliably track dataset trajectories and provides a valid teaching signal for DAgger
- domain assumption The point-cloud autoencoder trained with Chamfer distance preserves information sufficient for grasping
- ad hoc to paper The sampled start region above the object (based on bounding box) is sufficient for the policy to generalize
Cite this review
Pith. "Pith review of 23 DoF Grasping Policies from a Raw Point Cloud." pith.science (2026). https://pith.science/paper/FTIFB54C
@misc{pith2026241114400,
author = {Pith},
title = {Pith review of: 23 DoF Grasping Policies from a Raw Point Cloud},
year = {2026},
howpublished = {\url{https://pith.science/paper/FTIFB54C}},
note = {Machine review of arXiv:2411.14400}
}
read the original abstract
Coordinating the motion of robots with high degrees of freedom (DoF) to grasp objects gives rise to many challenges. In this paper, we propose a novel imitation learning approach to learn a policy that directly predicts 23 DoF grasp trajectories from a partial point cloud provided by a single, fixed camera. At the core of the approach is a second-order geometric-based model of behavioral dynamics. This Neural Geometric Fabric (NGF) policy predicts accelerations directly in joint space. We show that our policy is capable of generalizing to novel objects, and combine our policy with a geometric fabric motion planner in a loop to generate stable grasping trajectories. We evaluate our approach on a set of three different objects, compare different policy structures, and run ablation studies to understand the importance of different object encodings for policy learning.
Figures
Figures from the paper (2 more)
Reference graph
Works this paper leans on
-
[1]
Hand posture subspaces for dexterous robotic grasping,
M. T. Ciocarlie and P. K. Allen, “Hand posture subspaces for dexterous robotic grasping,” Intl. Journal of Robotics Research , vol. 28, no. 7, 2009
work page 2009
-
[2]
A probabilistic framework for uncertainty-aware high-accuracy precision grasping of unknown objects,
D. Chen, V . Dietrich, Z. Liu, and G. von Wichert, “A probabilistic framework for uncertainty-aware high-accuracy precision grasping of unknown objects,” Journal of Intelligent & Robotic Systems , vol. 90, no. 1, 2018
work page 2018
-
[3]
Examples of 3d grasp quality computations,
A. Miller and P. Allen, “Examples of 3d grasp quality computations,” in IEEE Intl. Conf. on Robotics and Automation , vol. 2, 1999, pp. 1240–1246 vol.2
work page 1999
-
[4]
Computation of independent contact regions for grasping 3-d objects,
M. A. Roa and R. Suarez, “Computation of independent contact regions for grasping 3-d objects,” IEEE Trans. on Robotics , vol. 25, no. 4, 2009
work page 2009
-
[5]
Synthesizing grasp configurations with specified contact regions,
C. Rosales, L. Ros, J. M. Porta, and R. Su ´arez, “Synthesizing grasp configurations with specified contact regions,”Intl. Journal of Robotics Research, vol. 30, no. 4, 2011
work page 2011
-
[6]
Coping with the grasping uncertainties in force-closure analysis,
Y . Zheng and W.-H. Qian, “Coping with the grasping uncertainties in force-closure analysis,” Intl. Journal of Robotics Research , vol. 24, no. 4, 2005
work page 2005
-
[7]
Hierarchical fingertip space: A unified framework for grasp planning and in-hand grasp adaptation,
K. Hang, M. Li, J. A. Stork, Y . Bekiroglu, F. T. Pokorny, A. Billard, and D. Kragic, “Hierarchical fingertip space: A unified framework for grasp planning and in-hand grasp adaptation,” IEEE Trans. on Robotics, vol. 32, no. 4, 2016
work page 2016
-
[8]
M. S. Siddiqui, C. Coppola, G. Solak, and L. Jamone, “Grasp stability prediction for a dexterous robotic hand combining depth vision and haptic bayesian exploration,” Frontiers in Robotics and AI , 2021
work page 2021
Show all 29 references
-
[9]
Planning Multi-Fingered Grasps as Probabilistic Inference in a Learned Deep Network,
Q. Lu, K. Chenna, B. Sundaralingam, and T. Hermans, “Planning Multi-Fingered Grasps as Probabilistic Inference in a Learned Deep Network,” in Intl. Symposium on Robotics Research , 2017
2017
-
[10]
Modeling Grasp Type Improves Learning- Based Grasp Planning,
Q. Lu and T. Hermans, “Modeling Grasp Type Improves Learning- Based Grasp Planning,” IEEE Robotics and Automation Letters , 2019
2019
-
[11]
Multi- fingered grasp planning via inference in deep neural networks,
Q. Lu, M. V . der Merwe, B. Sundaralingam, and T. Hermans, “Multi- fingered grasp planning via inference in deep neural networks,” IEEE Robotics & Automation Magazine , 2020
2020
-
[12]
Multi-Fingered Active Grasp Learning,
Q. Lu, M. V . der Merwe, and T. Hermans, “Multi-Fingered Active Grasp Learning,” in IEEE/RSJ Intl. Conf. on Intelligent Robots and Systems, 2020
2020
-
[13]
Learning Continuous 3D Reconstructions for Geometrically Aware Grasping,
M. Van der Merwe, Q. Lu, B. Sundaralingam, M. Matak, and T. Her- mans, “Learning Continuous 3D Reconstructions for Geometrically Aware Grasping,” in IEEE Intl. Conf. on Robotics and Automation , 2020
2020
-
[14]
Planning visual-tactile precision grasps via complementary use of vision and touch,
M. Matak and T. Hermans, “Planning visual-tactile precision grasps via complementary use of vision and touch,” IEEE Robotics and Automation Letters, vol. 8, no. 2, pp. 768–775, 2023
2023
-
[15]
6-dof graspnet: Variational grasp generation for object manipulation,
A. Mousavian, C. Eppner, and D. Fox, “6-dof graspnet: Variational grasp generation for object manipulation,” in Intl. Conf. on Computer Vision, 2019
2019
-
[16]
Dynamical movement primitives: learning attractor models for motor behaviors,
A. J. Ijspeert, J. Nakanishi, H. Hoffmann, P. Pastor, and S. Schaal, “Dynamical movement primitives: learning attractor models for motor behaviors,” Neural computation, vol. 25, no. 2, pp. 328–373, 2013
2013
-
[17]
Rie- mannian motion policies,
N. D. Ratliff, J. Issac, D. Kappler, S. Birchfield, and D. Fox, “Rie- mannian motion policies,” arXiv preprint arXiv:1801.02854 , 2018
2018 arXiv
-
[18]
Rmp flow: A computational graph for automatic mo- tion policy generation,
C.-A. Cheng, M. Mukadam, J. Issac, S. Birchfield, D. Fox, B. Boots, and N. Ratliff, “Rmp flow: A computational graph for automatic mo- tion policy generation,” in Algorithmic Foundations of Robotics XIII: Proceedings of the 13th Workshop on the Algorithmic Foundations of Robot...
2020
-
[19]
A unified approach for motion and force control of robot manipulators: The operational space formulation,
O. Khatib, “A unified approach for motion and force control of robot manipulators: The operational space formulation,” IEEE Journal on Robotics and Automation , vol. 3, no. 1, pp. 43–53, 1987
1987
-
[20]
Geometric fabrics: Generalizing classical mechanics to capture the physics of behavior,
K. Van Wyk, M. Xie, A. Li, M. A. Rana, B. Babich, B. Peele, Q. Wan, I. Akinola, B. Sundaralingam, D. Fox, B. Boots, and N. D. Ratliff, “Geometric fabrics: Generalizing classical mechanics to capture the physics of behavior,” IEEE Robotics and Automation Letters , vol. 7, no. 2...
2022
-
[21]
Neural geometric fabrics: Efficiently learning high-dimensional policies from demonstration,
M. Xie, A. Handa, S. Tyree, D. Fox, H. Ravichandar, N. D. Ratliff, and K. V . Wyk, “Neural geometric fabrics: Efficiently learning high-dimensional policies from demonstration,” in 6th Annual Conference on Robot Learning , 2022. [Online]. Available: https://openreview.net/foru...
2022
-
[22]
Learning robust real-world dexterous grasping policies via implicit shape augmentation,
Q. Chen, K. V . Wyk, Y .-W. Chao, W. Yang, A. Mousavian, A. Gupta, and D. Fox, “Learning robust real-world dexterous grasping policies via implicit shape augmentation,” in 6th Annual Conference on Robot Learning , 2022. [Online]. Available: https: //openreview.net/forum?id=bUUf1CT1sNu
2022
-
[23]
A reduction of imitation learning and structured prediction to no-regret online learning,
S. Ross, G. Gordon, and D. Bagnell, “A reduction of imitation learning and structured prediction to no-regret online learning,” in Proceedings of the Fourteenth International Conference on Artificial Intelligence and Statistics , ser. Proceedings of Machine Learning Research, ...
2011
-
[24]
Dexgrasp-1m: Dexterous multi-finger grasp generation through differentiable simulation,
D. Turpin, T. Zhong, S. Zhang, G. Zhu, E. Heiden, M. Macklin, S. Tsogkas, S. Dickinson, and A. Garg, “Dexgrasp-1m: Dexterous multi-finger grasp generation through differentiable simulation,” in IEEE Intl. Conf. on Robotics and Automation , 2023
2023
-
[25]
Generalized nonlinear and finsler geometry for robotics,
N. D. Ratliff, K. Van Wyk, M. Xie, A. Li, and M. A. Rana, “Generalized nonlinear and finsler geometry for robotics,” in 2021 IEEE International Conference on Robotics and Automation (ICRA) , 2021, pp. 10 206–10 212
2021
-
[26]
The ycb object and model set: Towards common benchmarks for manipulation research,
B. Calli, A. Singh, A. Walsman, S. Srinivasa, P. Abbeel, and A. M. Dollar, “The ycb object and model set: Towards common benchmarks for manipulation research,” in 2015 International Conference on Advanced Robotics (ICAR) , 2015, pp. 510–517
2015
-
[27]
Pointnet: Deep learning on point sets for 3d classification and segmentation,
R. Q. Charles, H. Su, M. Kaichun, and L. J. Guibas, “Pointnet: Deep learning on point sets for 3d classification and segmentation,” in 2017 IEEE Conference on Computer Vision and Pattern Recognition (CVPR), 2017, pp. 77–85
2017
-
[28]
Fast graph representation learning with PyTorch Geometric,
M. Fey and J. E. Lenssen, “Fast graph representation learning with PyTorch Geometric,” in ICLR Workshop on Representation Learning on Graphs and Manifolds , 2019
2019
-
[29]
Deconstructing the inductive biases of hamiltonian neural networks,
N. Gruver, M. Finzi, S. Stanton, and A. G. Wilson, “Deconstructing the inductive biases of hamiltonian neural networks,” arXiv preprint arXiv:2202.04836, 2022
2022 arXiv
Reviewed August 12, 2026 · model on record in the stance chip above.
Discussion (0). Continue with ORCID to comment.