Pith. sign in

REVIEW 4 major objections 5 minor 28 references

Synthesizing Grasps and Regrasps for Complex Manipulation Tasks

T0 review · 4 major / 5 minor · reviewed 2026-08-10 · deepseek-v4-flash

Pith's one-line read The paper claims that a robot can compute the minimum number of grasps and the regrasping schedule for a complex manipulation task by checking whether graspable regions of consecutive constant-screw motion segments overlap after…

desk verdict Novel regrasp-by-overlap idea for constant-screw manipulation, but the printed Algorithm 1 cannot reproduce the paper's own α=2 example and the 'minimum' claim is unproved — fixable, and worth refereeing. read the letter →

arxiv 2501.18075 v1 pith:GXM67CVS submitted 2025-01-30 cs.RO

classification cs.RO
keywords graspsynthesisregraspingconstantscrewmotionpointcloudtask-orientedgraspingmanipulationplanningpivotingwrench-basedmetric
verification ladder T0 review T1 audit T2 compute T3 formal

The pith

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The reading

The paper sets out a problem that roboticists usually treat as two separate steps: first pick a grasp, then plan a motion. It claims both can be decided together when the task is expressed as a sequence of constant screw motions. Given a partial point cloud of the object and the motion-plan skeleton, the algorithm computes a graspable region for each segment and then measures, segment by segment, how much of that region survives when later segments' regions are pulled back into a common pose. Once the surviving overlap falls below a threshold, the algorithm declares that a new grasp is needed. The paper reports that this procedure predicts the minimum number of grasps for pivoting, sliding, and pouring tasks using realistic RGB-D point clouds.

What carries the argument

The key machinery is the combination of constant screws as a task representation and an overlap test on grasping regions. A constant screw motion is a rigid-body motion about and along a fixed screw axis—a one-parameter subgroup of $SE(3)$—so a plan skeleton is just a list of such screws. The grasping region for each screw is obtained from the point cloud using the grasp metric $\eta$ of [16] together with the learned region-finder of [17]; each region is thresholded at $\eta_{\mathrm{th}}$. To decide regrasping, regions are transformed into a common pose, the common set $I$ is computed, and the normalized score $\gamma = \min_i |I|/|I_{g_i}|$ is compared to $\gamma_{\mathrm{th}}$; only blocks of segments whose regions overlap at least that much share a single grasp.

What would settle it

For a fixed object and plan skeleton, compare the algorithm's predicted number of grasps $\alpha$ against an exhaustive search over grasps on the full object mesh; a single case where $\alpha$ is not the true minimum, or where the predicted common region $I$ cannot produce a working grasp in physical execution, would disprove the overlap criterion's sufficiency.

Watch

Extended reading notes

Core claim

The central claim is that grasping and regrasping for complex manipulation can be solved on the same representation used for motion planning. The paper formalizes the object's task as a plan skeleton $G = \{g_1,\dots,g_k\}$ where every consecutive pair $(g_i,g_{i+1})$ is a constant screw motion, and the object's geometry as a partial point cloud $O_{g_1}$ in the initial pose. For each segment it computes a grasping region $I_{g_i} \subseteq O_{g_i}$ by thresholding a task-dependent wrench-based grasp metric $\eta$, which measures the maximum wrench that can be exerted about the segment's screw axis while respecting friction cones at object–robot and object–environment contacts. It then transforms all regions to the initial frame and defines the score $\gamma = \min_i |I|/|I_{g_i}|$ on the common intersection $I$; with threshold $\gamma_{\mathrm{th}}$, a block of consecutive segments sharing $\gamma \geq \gamma_{\mathrm{th}}$ is assigned one grasp. The minimum number of grasps $\alpha$ is the number of blocks in a sequential partition of the segment index set, and regrasping must occur $\alpha-1$ times.

Load-bearing premise

The load-bearing premise is that when graspable point-cloud regions of consecutive motion segments overlap enough after being moved to a common pose, a real physical grasp exists that works for all of those segments; that depends on the grasp-quality measure and the grasp-detection network being complete enough.

Editorial extensions

If this is right

  • A robot can decide before moving whether one grasp suffices, avoiding unnecessary regrasps when the motion plan does not require them.
  • The same pipeline covers tasks beyond pick-and-place, including pivoting, sliding, pickup, and pouring, as long as the path constraints are expressed as constant screws.
  • The computed grasp regions plug directly into a motion planner to produce a joint-space trajectory; the reported robot trials completed roughly three-quarters of the planned motions.
  • Raising or lowering the threshold $\gamma_{\mathrm{th}}$ trades robustness against regrasp frequency, giving a user-controllable safety margin.
  • Because object geometry is a partial point cloud, the approach works with data from RGB-D sensors rather than requiring full CAD models.

Reading between the lines

Editorial extensions of the paper, not claims the author makes directly.

  • One could run the same overlap test online during execution: if a refreshed point cloud makes $\gamma$ drop below threshold mid-motion, the robot could trigger a regrasp before the grasp fails.
  • For longer plan skeletons, the sequential partitioning in Algorithm 1 compares each region to every later region; a hierarchical or incremental variant would be needed to keep the computation cheap as the number of segments grows.
  • The reported failures were all joint-limit violations, so folding manipulator reachability into the grasp-region computation (rather than filtering after the fact) should raise the success rate without changing the overlap logic.
  • The definition of $\gamma$ as a cardinality ratio treats every point in the intersection as equally useful; a weighted variant that prefers points with high margin under $\eta$ might predict grasp success more sharply than the current threshold.
Share X Bluesky LinkedIn Reddit HN

Signed reviews

No signed human review yet.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, and a circularity audit.

Referee Report

4 major / 5 minor

Summary. The paper formalizes the problem of grasp and regrasp synthesis for complex manipulation tasks in which the object is represented by a (partial) point cloud and the motion is specified as a sequence of constant screw motions. Graspable regions are computed for each constant-screw segment using the authors' prior grasp metric and neural-network-based point-cloud grasping method, and consecutive segments whose transformed graspable regions have sufficient overlap are grouped together. The output is the claimed minimum number of grasps and a partition of the segments into grasp groups. The approach is illustrated on a pivoting task and evaluated in simulation and on a Franka Emika Panda robot, with a reported success rate of about 75%.

Significance. The underlying formulation is attractive and timely: connecting task-oriented grasping to regrasping decisions via the common intersection of transformed, point-cloud-derived grasping regions is a natural and potentially useful step beyond pick-and-place regrasp planning. If made correct, the framework could provide a practical way to decide when a regrasp is necessary from sensor data. The authors provide real-robot experiments, an openly stated failure analysis (joint-limit violations), and a clear problem statement. However, the printed Algorithm 1 is internally inconsistent, the optimality claim lacks proof, and the experiments do not directly validate the necessity of the computed regrasp decisions. These issues currently block acceptance.

major comments (4)
  1. [Section V-B, Algorithm 1] The pseudocode as printed does not produce the results reported in the paper. Line 6 initializes the inner loop at j=2 regardless of i instead of at j=i+1, and line 8 appends the transformed region to Cu before the score is computed. When γ<γ_th, lines 10-12 store Cu containing the just-rejected region and then set i=j. Tracing this on the paper's own CheezIt example (C={Ig1,Ig2,Ig3}, γ_th=0.25) gives Cu={Ig1,Ig2,Ig3} with γ=0 at j=3, so Z={{Ig1,Ig2,Ig3}} and α=1, contradicting the reported Z={{Ig1,Ig2},{Ig3}} and α=2 in Section V-C. If lines 10-12 are corrected to exclude the failing region and set i=j, the while condition i<k-1 then exits with i=3 without ever processing the last region as a new subset, again yielding α=1. The algorithm must be fixed and the example re-traced.
  2. [Section V-B, Eq. (1) vs Algorithm 1] The optimization problem (1) minimizes α over arbitrary partitions of the index set subject to each block having a non-empty common intersection, but Algorithm 1 computes a contiguous-block (interval) partition using a greedy longest-prefix rule. No proof is given that a contiguous partition achieves the same optimum, nor that the greedy rule is optimal. The distinction matters: for three regions with I1∩I2=∅, I2∩I3=∅, and I1∩I3≠∅, an arbitrary partition achieves α=2, whereas the contiguous greedy partition requires α=3. Without either a proof of optimality or an explicit statement that the problem is restricted to contiguous partitions, the use of the word 'minimum' in the problem statement is unsupported.
  3. [Section V-C and VI-B] The central proxy assumption is not validated. The algorithm certifies that a single grasp works for a set of segments when the cardinality ratio γ of the common intersection of sampled point-cloud grasping regions exceeds a threshold. This assumes that point-cloud overlap is a faithful surrogate for the existence of a physical grasp that contacts the same object region across all segments, and that the cardinality ratio is a meaningful estimate of usable common area. The real-robot experiments (Table I) show that the computed grasps execute the motion in 15/20 trials, but they never attempt the same plan with one fewer grasp or with a deliberately wrong regrasp timing, so the experiments do not demonstrate that the computed regrasp decisions are necessary or that α is minimal. In addition, γ is computed as a ratio of point counts even though it is described as a fraction of area; point-cloud density in partial scans varies with pose and occlusion, so the interpretation should be clarified or the measure justified.
  4. [Section VI] The experimental evaluation does not substantiate the minimality claim. The simulation study in Section VI-A reports α values for 48 trials but includes no ground truth, no baseline, and no check against exhaustive enumeration for small instances; the real-world trials in Section VI-B attribute failures to joint limits without examining whether the regrasp decisions themselves were correct in the failed trials. Since the paper's main formal claim is that the algorithm computes the minimum number of grasps, the experiments need either to validate that claim under controlled conditions or to explicitly state that minimality rests on the (currently missing) theoretical proof rather than on the experiments.
minor comments (5)
  1. [Section V-A] The text says 'the corresponding set C consists three elements Ig1 , Ig3 and Ig3'; this should read 'Ig1 , Ig2 and Ig3'.
  2. [Eq. (1)] The intersection symbol in the constraint appears as a backslash; it should be a proper intersection operator, e.g., ⋂_{j∈Ju} I_{g_j} ≠ ∅.
  3. [Algorithm 2] In line 4, 'I = nT i=1 Cu' is unclear; it should denote the intersection of all regions in the set Cu, for example I = ⋂_{I∈Cu} I.
  4. [Section V-C] The phrase 'fraction of the area' is used to describe γ_i, but the computation uses the cardinality of point sets; the paper should state the assumption that the point cloud is approximately uniformly sampled or use an area-based measure instead.
  5. [Section VI-A] The sentence 'there are no existing algorithm that is capable of synthesizing grasps for the type of tasks that we consider' is grammatically incorrect and should be rephrased as 'no existing algorithm that is capable...'.

Circularity Check

0 steps flagged · score 0.0 of 10

No circularity: the regrasp-count algorithm is a self-contained computation on externally defined grasp regions; self-citations are component reuse, not load-bearing reductions.

full rationale

The paper does not fit alpha to data or define its inputs in terms of its outputs. Given the point cloud and plan skeleton, the grasp regions I_gi are computed by the independently published task-dependent grasp metric [16] and network [17]; the paper's own contribution is the overlap partition (Section V-B, Eq. (1)) that computes alpha from those regions. That partition is not statistically fitted to the reported alpha values, and it is checked against real-robot executions (Table I), so the central claim is externally falsifiable rather than equivalent to its inputs. The self-citations are ordinary component reuse, not a uniqueness theorem or ansatz smuggled by citation. The main concerns are correctness, not circularity: Algorithm 1 as printed (inner loop from j=2 and line 12's i=j break) is inconsistent with the prose (j=i+1) and does not trace to the reported alpha=2 for the CheezIt example; the 'minimum' in Eq. (1) is also asserted without an optimality proof for the greedy contiguous-block partition. These are validity gaps, not circular reductions, and under the stated rules do not raise the circularity score.

Assumptions & free parameters 2 free parameters · 6 assumptions · 0 invented entities

The method relies on two hand-set thresholds, the prior grasp metric and network of the same authors, and a core modeling assumption that point-cloud overlap implies physical grasp feasibility. No new physical entities are introduced.

free parameters (2)
  • gamma_th = 0.25
    Threshold on the overlap score gamma; chosen by hand in Section V-C with no sensitivity study. It directly controls when a regrasp is declared, so alpha depends on it.
  • eta_th = 0.75
    Threshold on the task-dependent grasp metric eta used in computeMetric to define graspable regions; chosen by hand. The paper claims different values only scale gamma_i but gives no derivation or experiments.
assumptions (6)
  • standard math Any SE(3) path can be approximated arbitrarily closely by a sequence of constant screw motions (Chasles-Mozzi theorem).
    Invoked in Section I to justify representing manipulation plans as constant screw segments.
  • domain assumption The task-dependent grasp metric eta from [16] correctly identifies all object-robot contact regions that can impart a given constant screw motion while satisfying friction cone constraints.
    Adopted wholesale from prior work by the same authors; the present paper does not re-derive or independently validate it.
  • domain assumption The neural network from [17] correctly computes graspable regions on partial point clouds.
    Used in computeMetric (Section V-A) and for pouring (Section VI-B); no independent evaluation inside this paper.
  • domain assumption The object is rigid and stably placed on a support surface during regrasping, and the regrasp can be executed by breaking and re-establishing contact.
    Assumed in Section II and following [5]; no physical validation of the regrasp transition itself.
  • ad hoc to paper If the common intersection of sampled point-cloud grasping regions has size at least gamma_th relative to each region, then a physically realizable grasp exists for the whole segment set.
    This is the core modeling assumption of Algorithm 2: point-set cardinality is used as a proxy for continuous graspable area, and the threshold is imposed for robustness without a theoretical justification.
  • ad hoc to paper The greedy sequential interval partition in Algorithm 1 yields the minimum number of grasps.
    No proof is provided; it relies on monotonicity of the overlap property, which is plausible but not stated or justified.

how reviews work

0 comments
Cite this review

Pith. "Pith review of Synthesizing Grasps and Regrasps for Complex Manipulation Tasks." pith.science (2026). https://pith.science/paper/GXM67CVS

@misc{pith2026250118075,
  author       = {Pith},
  title        = {Pith review of: Synthesizing Grasps and Regrasps for Complex Manipulation Tasks},
  year         = {2026},
  howpublished = {\url{https://pith.science/paper/GXM67CVS}},
  note         = {Machine review of arXiv:2501.18075}
}
read the original abstract

In complex manipulation tasks, e.g., manipulation by pivoting, the motion of the object being manipulated has to satisfy path constraints that can change during the motion. Therefore, a single grasp may not be sufficient for the entire path, and the object may need to be regrasped. Additionally, geometric data for objects from a sensor are usually available in the form of point clouds. The problem of computing grasps and regrasps from point-cloud representation of objects for complex manipulation tasks is a key problem in endowing robots with manipulation capabilities beyond pick-and-place. In this paper, we formalize the problem of grasping/regrasping for complex manipulation tasks with objects represented by (partial) point clouds and present an algorithm to solve it. We represent a complex manipulation task as a sequence of constant screw motions. Using a manipulation plan skeleton as a sequence of constant screw motions, we use a grasp metric to find graspable regions on the object for every constant screw segment. The overlap of the graspable regions for contiguous screws are then used to determine when and how many times the object needs to be regrasped. We present experimental results on point cloud data collected from RGB-D sensors to illustrate our approach.

Figures

Figures reproduced from arXiv: 2501.18075 by the authors.

Figure 1
Figure 1. Example task considered in this paper where the robot has to pivot a CheezIt box three times. The partial point cloud of the object [PITH_FULL_IMAGE:figures/full_fig_p002_1.png] view at source ↗
Figure 2
Figure 2. Solution overview with pivoting a CheezIt box three times. Using the [PITH_FULL_IMAGE:figures/full_fig_p004_2.png] view at source ↗
Figure 3
Figure 3. Result where two grasps, i.e., one regrasping suffice to perform the task given by the plan skeleton [PITH_FULL_IMAGE:figures/full_fig_p004_3.png] view at source ↗
Figures from the paper (1 more)
Figure 4
Figure 4. Figure 4: Results where a single grasp is sufficient to perform the task (a) Plan skeleton [PITH_FULL_IMAGE:figures/full_fig_p006_4.png]

Discussion (0). Continue with ORCID to comment.

Reference graph

Works this paper leans on

28 extracted references · 28 canonical work pages

  1. [16]

    Computing a task-dependent grasp metric using second-order cone programs,

    A. Fakhari, A. Patankar, J. Xie, and N. Chakraborty, “Computing a task-dependent grasp metric using second-order cone programs,” in 2021 IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS). IEEE, 2021, pp. 4009–4016

  2. [17]

    Task-oriented grasping with point cloud representation of objects,

    A. Patankar, K. Phi, D. Mahalingam, N. Chakraborty, and I. Ramakr- ishnan, “Task-oriented grasping with point cloud representation of objects,” in 2023 IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS) . IEEE, 2023

  3. [1]

    On screw linear interpola- tion for point-to-point path planning,

    A. Sarker, A. Sinha, and N. Chakraborty, “On screw linear interpola- tion for point-to-point path planning,” in 2020 IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS) . IEEE, 2020, pp. 9480–9487

  4. [2]

    Z. L. Richard Murray and S. Sastry, A Mathematical Introduction to Robotic Manipulation. CRC Press, 1994

  5. [3]

    Human-guided planning for complex manipulation tasks using the screw geometry of motion,

    D. Mahalingam and N. Chakraborty, “Human-guided planning for complex manipulation tasks using the screw geometry of motion,” in 2023 IEEE International Conference on Robotics and Automation (ICRA). IEEE, 2023, pp. 7851–7857

  6. [4]

    R. P. C. Paul, Modelling, trajectory calculation and servoing of a computer controlled arm . Stanford University, 1972

  7. [5]

    Regrasping,

    P. Tournassoud, T. Lozano-P ´erez, and E. Mazer, “Regrasping,” in Proceedings. 1987 IEEE international conference on robotics and automation, vol. 4. IEEE, 1987, pp. 1924–1928

  8. [6]

    Complete and rapid regrasp planning with look-up table,

    K. Cho, M. Kim, and J.-B. Song, “Complete and rapid regrasp planning with look-up table,” Journal of Intelligent and Robotic Systems, vol. 36, pp. 371–387, 2003

Show all 28 references
  1. [7]

    Generating and evaluating regrasp operations,

    F. Rohrdanz and F. M. Wahl, “Generating and evaluating regrasp operations,” in Proceedings of international conference on robotics and automation, vol. 3. IEEE, 1997, pp. 2013–2018

  2. [8]

    Motion planning of intelligent ma- nipulation by a parallel two-fingered gripper equipped with a simple rotating mechanism,

    H. Terasaki and T. Hasegawa, “Motion planning of intelligent ma- nipulation by a parallel two-fingered gripper equipped with a simple rotating mechanism,” IEEE Transactions on Robotics and Automation, vol. 14, no. 2, pp. 207–219, 1998

  3. [9]

    Planning of regrasp operations,

    S. A. Stoeter, S. V oss, N. P. Papanikolopoulos, and H. Mosemann, “Planning of regrasp operations,” in Proceedings 1999 IEEE interna- tional conference on robotics and automation (Cat. No. 99CH36288C), vol. 1. IEEE, 1999, pp. 245–250

  4. [10]

    Planning of regrasping operations for a dextrous hand in assembly tasks,

    D. R. Rapela, U. Rembold, and B. Kuchen, “Planning of regrasping operations for a dextrous hand in assembly tasks,” Journal of intelli- gent and Robotic Systems , vol. 33, pp. 231–266, 2002

  5. [11]

    A single-query manipulation plan- ner,

    P. Lertkultanon and Q.-C. Pham, “A single-query manipulation plan- ner,” IEEE Robotics and Automation Letters , vol. 1, no. 1, pp. 198– 205, 2015

  6. [12]

    A regrasp planning component for object reorientation,

    W. Wan, H. Igawa, K. Harada, H. Onda, K. Nagata, and N. Yamanobe, “A regrasp planning component for object reorientation,” Autonomous Robots, vol. 43, pp. 1101–1115, 2019

  7. [13]

    Improving regrasp algorithms to analyze the utility of work surfaces in a workcell,

    W. Wan, M. T. Mason, R. Fukui, and Y . Kuniyoshi, “Improving regrasp algorithms to analyze the utility of work surfaces in a workcell,” in 2015 IEEE International Conference on Robotics and Automation (ICRA). IEEE, 2015, pp. 4326–4333

  8. [14]

    Regrasp planning using 10,000 s of grasps,

    W. Wan and K. Harada, “Regrasp planning using 10,000 s of grasps,” in 2017 IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS). IEEE, 2017, pp. 1929–1936

  9. [15]

    Reorientating objects with a gripping hand and a table sur- face,

    ——, “Reorientating objects with a gripping hand and a table sur- face,” in 2015 IEEE-RAS 15th International Conference on Humanoid Robots (Humanoids). IEEE, 2015, pp. 101–106

  10. [18]

    Autonomous bimanual functional regrasping of novel object class instances,

    D. Pavlichenko, D. Rodriguez, C. Lenz, M. Schwarz, and S. Behnke, “Autonomous bimanual functional regrasping of novel object class instances,” in 2019 IEEE-RAS 19th International Conference on Hu- manoid Robots (Humanoids) . IEEE, 2019, pp. 351–358

  11. [19]

    Learning to regrasp by learning to place,

    S. Cheng, K. Mo, and L. Shao, “Learning to regrasp by learning to place,” in Conference on Robot Learning. PMLR, 2022, pp. 277–286

  12. [20]

    Learning to predict diverse stable placements for extrinsic manipulation on a support plane,

    P. Xu, Z. Chen, J. Wang, and M. Q.-H. Meng, “Learning to predict diverse stable placements for extrinsic manipulation on a support plane,” IEEE Transactions on Cognitive and Developmental Systems , 2023

  13. [21]

    Learning to reorient objects with stable placements afforded by extrinsic supports,

    P. Xu, H. Cheng, J. Wang, and M. Q.-H. Meng, “Learning to reorient objects with stable placements afforded by extrinsic supports,” IEEE Transactions on Automation Science and Engineering , 2023

  14. [22]

    Dynamic control of sliding by robot hands for regrasping,

    A. A. Cole, P. Hsu, and S. S. Sastry, “Dynamic control of sliding by robot hands for regrasping,” IEEE Transactions on robotics and automation, vol. 8, no. 1, pp. 42–52, 1992

  15. [23]

    Regrasping by fixtureless fix- turing,

    N. Chavan-Dafie and A. Rodriguez, “Regrasping by fixtureless fix- turing,” in 2018 IEEE 14th international conference on automation science and engineering (CASE) . IEEE, 2018, pp. 122–129

  16. [24]

    Dynamic regrasping using a high-speed multifingered hand and a high-speed vision system,

    N. Furukawa, A. Namiki, S. Taku, and M. Ishikawa, “Dynamic regrasping using a high-speed multifingered hand and a high-speed vision system,” in Proceedings 2006 IEEE International Conference on Robotics and Automation, 2006. ICRA 2006. IEEE, 2006, pp. 181–187

  17. [25]

    A long horizon planning framework for manipulating rigid pointcloud objects,

    A. Simeonov, Y . Du, B. Kim, F. Hogan, J. Tenenbaum, P. Agrawal, and A. Rodriguez, “A long horizon planning framework for manipulating rigid pointcloud objects,” in Conference on Robot Learning . PMLR, 2021, pp. 1582–1601

  18. [26]

    Motion and force plan- ning for manipulating heavy objects by pivoting,

    A. Fakhari, A. Patankar, and N. Chakraborty, “Motion and force plan- ning for manipulating heavy objects by pivoting,” in 2021 IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS) . IEEE, 2021, pp. 9393–9400

  19. [27]

    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 ad- vanced robotics (ICAR) . IEEE, 2015, pp. 510–517

  20. [28]

    Cvxpy: A python-embedded modeling language for convex optimization,

    S. Diamond and S. Boyd, “Cvxpy: A python-embedded modeling language for convex optimization,” The Journal of Machine Learning Research, vol. 17, no. 1, pp. 2909–2913, 2016

Pith tools

Reviewed August 10, 2026 · model on record in the stance chip above.