Publications

2024

[Under review] 6R cuspidal robots: kinematic issues and guidelines for path planning and design

D. H. Salunkhe, T. Marauli, A. Mueller, D. Chablat, P. Wenger,

In
International Journal of Robotics Research,
(IJRR), 2024

Cuspidal serial robots can change inverse kinematic solutions (IKS) without crossing singularities in the joint space because they have multiple IKS in a singularity-free region. This property of robots has been researched for over three decades but has not been taken seriously in consideration while designing new robots. The presented work points out issues related to nonsingular change of IKS and path planning specific to the cuspidal robots that are present in existing commercial robots used in various applications. The multiple IKS at the initial end-effector pose allows the user to choose an initial IKS that may lead to a continuous and repeatable path. We analyze in detail how the choice of the initial IKS affects the feasibility and repeatability of the prescribed path. Cuspidal robots can be used safely if the workspace is analyzed taking into account the cuspidality property. For these reasons, we propose a methodology for path testing and planning that considers different path scenarios. Given the rise of unconventional designs in 6R robots, the identification of cuspidal properties in the design phase of a robot is of paramount importance. We recall all the known criteria for cuspidality and propose new methods to decide if a given 6R robot is cuspidal. Accordingly, a practical guideline is proposed for deciding the cuspidality of a generic 6R robot.

2023

Time-Optimal Point-To-Point Motion Planning and Assembly Mode Change of Cuspidal Manipulators: Application to 3R and 6R Robots

T. Marauli, D. H. Salunkhe, H. Gattringer, A. Mueller, D. Chablat, P. Wenger,

In
Proceedings of the International Conference on Intelligent Robots and Systems,
(IROS), 2023, Detroit, United States of America

The kinematics of cuspidal 3R regional robots was studied extensively in the past. Moreover, certain industrial 6R robots were found to be cuspidal (e.g. Fanuc CRX series, Kinova GEN2), which makes cuspidal robots finally interesting for practical applications. This necessitates optimal trajectory planning, respecting the dynamics and technical limits of the particular robot. In this paper, a method for singularity-free time-optimal point-to-point trajectory (PtP) trajectory planning is proposed. As a special case, this method is applicable to time optimal singularity-free assembly mode changing. Results are shown for 3R robots and a 6R FANUC CRX10iA/L.

Trajectory planning issues in commercial cuspidal robots

D. H. Salunkhe, D. Chablat, P. Wenger,

In
Proceedings of the International Conference on Robotics and Automation,
(ICRA), 2023, London, United Kingdom

Note: The α_{4} and α_{5} in Table I are 55 degrees instead of 90 degrees

A cuspidal serial robot can travel from one inverse kinematic solution to another without crossing a singularity. Cuspidal robots ask for extra care and caution in trajectory planning, as identifying an aspect related to one unique inverse kinematic solution is not possible. The issues related to motion planning with cuspidal robots are related to the inherent property arising from the geometric design of the robot. The cuspidality property has not been considered in recent industrial 6R robots with a non-spherical wrist. In this work, cuspidality is illustrated with the JACO robot (gen 2, non-spherical wrist), a serial arm by Kinova Robotics which is deployed in various applications and is cuspidal in nature. A nonsingular change of solutions for the robot is provided to highlight the effect of cuspidal robots on the interference with the environment. The pose with multiple inverse kinematic solutions in an aspect is presented. Problems in choosing the initial solution of the path in cuspidal robots, and its consequence, is illustrated with an example path in the workspace of the JACO robot. The paper presents the importance of cuspidality analysis of 6R robots and the implications of neglecting it.

2022

Deciding Cuspidality of Manipulators through Computer Algebra and Algorithms in Real Algebraic Geometry

D. Chablat, R. Prébet, M. Safey El Din, D. H. Salunkhe, P. Wenger,

In
Proceedings of the 2022 International Symposium on Symbolic and Algebraic Computation
(ISSAC), 2022, Lille, France

Cuspidal robots are robots with at least two inverse kinematic solutions that can be connected by a singularity-free path. Deciding the cuspidality of generic 3R robots has been studied in the past, but extending the study to six-degree-of-freedom robots can be a challenging problem. Many robots can be modeled as a polynomial map together with a real algebraic set so that the notion of cuspidality can be extended to these data. In this paper we design an algorithm that, on input a polynomial map in n indeterminates, and s polynomials in the same indeterminates describing a real algebraic set of dimension d, decides the cuspidality of the restriction of the map to the real algebraic set under consideration. Moreover, if D and τ are, respectively the maximum degree and the bound on the bit size of the coefficients of the input polynomials, this algorithm runs in time log-linear in τ and polynomial in ((s+d)D)O(n2). It relies on many high-level algorithms in computer algebra which use advanced methods on real algebraic sets and critical loci of polynomial maps. As far as we know, this is the first algorithm that tackles the cuspidality problem from a general point of view.

Geometry Based Analysis of 3R Serial Robots

D. H. Salunkhe, J. Capco, D. Chablat, P. Wenger,

In Advances in Robot
Kinematics
2022, Proceedings in Advanced Robotics
(ARK), 2022, Bilbao, Spain

Cuspidal robots can travel from one inverse kinematic solution (IKS) to another without meeting a singularity. This property can be analyzed by understanding the inverse kinematic model (IKM) as well as the singularities in the joint space and in the workspace. In this article, we revisit the geometrical interpretation of the IKM with conics. The conditions of getting different conics and their implication on singularities are discussed and the observations regarding the nature of the conics are presented. Further, a sufficient condition for a 3R robot to be binary (i.e. with up to 2 IKS) as well as quaternary (i.e. with up to 4 IKS) is put forth by analyzing the geometrical interpretation of the IKM. The possibility to derive a necessary and sufficient condition is presented too.

Necessary and sufficient condition for a generic 3R serial manipulator to be cuspidal

D. H. Salunkhe, C. Spartalis, J. Capco, D. Chablat, P. Wenger,

Mechanism and Machine Theory (MMT), 2022

Cuspidal robots can travel from one inverse kinematic solution to another without meeting a singularity. The name cuspidal was coined based on the existence of a cusp point in the workspace of 3R serial robots. The existence of a cusp point was proved to be a necessary and sufficient condition for orthogonal robots to be cuspidal, but it was not possible to extend this condition to non-orthogonal robots. The goal of this paper is to prove that this condition stands for any generic 3R serial robot. This result would give the designer more flexibility. In the presented work, the geometrical interpretation of the inverse kinematics of 3R robots is revisited and important observations on the nonsingular change of posture are noted. The paper presents a theorem regarding the existence of reduced aspects in any generic 3R serial robot. Based on these observations and on this theorem, we prove that the existence of a cusp point is a necessary and sufficient condition for any 3R generic robot to be cuspidal.

An efficient combined local and global search strategy for optimization of parallel kinematic mechanisms with joint limits and collision constraints

D. H. Salunkhe, G. Michel, S. Kumar, M. Sanguineti, D. Chablat,

Mechanism and Machine Theory (MMT), 2022

The optimization of parallel kinematic manipulators (PKM) involve several constraints that are difficult to formalize, thus making optimal synthesis problem highly challenging. The presence of passive joint limits as well as the singularities and self-collisions lead to a complicated relation between the input and output parameters. In this article, a novel optimization methodology is proposed by combining a local search, Nelder–Mead algorithm, with global search methodologies such as low discrepancy distribution for faster and more efficient exploration of the optimization space. The effect of the dimension of the optimization problem and the different constraints are discussed to highlight the complexities of closed-loop kinematic chain optimization. The work also presents the approaches used to consider constraints for passive joint boundaries as well as singularities to avoid internal collisions in such mechanisms. The proposed algorithm can also optimize the length of the prismatic actuators and the constraints can be added in modular fashion, allowing to understand the impact of given criteria on the final result. The application of the presented approach is used to optimize two PKMs of different degrees of freedom.

Geometric Atlas of the Middle Ear and Paranasal Sinuses for Robotic Applications

G. Michel, D. H. Salunkhe, P. Bordure, D. Chablat,

Surgical Innovation (SI), 2022

In otolaryngologic surgery, more and more robots are being studied to meet the clinical needs of operating rooms. However, to help design and optimize these robots, the workspace must be precisely defined taking into account patient variability. The aim of this work is to define a geometric atlas of the middle ear and paranasal sinuses for endoscopic robotic applications. Scans of several patients of different ages and sexes were used to determine the average size of these workspaces, which are linked by the similar use of endoscopes in surgery.

Design optimization of a parallel manipulator for otological surgery

D. H. Salunkhe, G. Michel, S. Kumar, E. Olivier, M. Sanguineti, D. Chablat,

In Proceedings of New Frontiers of parallel robotics, International Confernece on Robotics
and
Automation (ICRA), 2022

The use of an endoscope in otological surgery as compared to using a microscope provides many benefits in terms of visibility and access to the operating region. The disadvantage of using an endoscope is that it has to be handled by the surgeon during the surgery. A novel parallel kinematic mechanism has been proposed recently for manipulating the endoscope during surgery. This paper details the design requirements considered for the optimization of the process, after consulting surgeons with various expertise. The paper further presents the different evaluation strategies that can be used to optimize the design parameters as per the needs of the application. The contribution of the presented work is the implementation of the surgeons’ requirements into an objective function and the optimization of a proposed architecture of a parallel kinematic mechanism suitable for otological surgery.

Literature Review on Endoscopic Robotic Systems in Ear and Sinus Surgery

G. Michel, D. H. Salunkhe, P. Bordure, D. Chablat,

Journal of Medical Devices (JMD), 2022

In otolaryngologic surgery, endoscopy is increasingly used to provide a better view of hard-to-reach areas and to promote minimally invasive surgery. However, the need to manipulate the endoscope limits the surgeon's ability to operate with only one instrument at a time. Currently, several robotic systems are being developed, demonstrating the value of robotic assistance in microsurgery. The aim of this literature review is to present and classify current robotic systems that are used for otological and endonasal applications. For these solutions, an analysis of the functionalities in relation to the surgeon's needs will be carried out to produce a set of specifications for the creation of new robots.

2016-2020

A new RCM mechanism for an ear and facial surgical application

G. Michel, D. H. Salunkhe, D. Chablat, P. Bordure,

In Advances in Service and Industrial Robotics, (RAAD), 2020

In otolaryngologic surgery, endoscopy is increasingly used to provide a better view of hard-to-reach areas and to promote minimally invasive surgery. However, the need to manipulate the endoscope limits the surgeon's ability to operate with only one instrument at a time. Currently, several robotic systems are being developed, demonstrating the value of robotic assistance in microsurgery. The aim of this literature review is to present and classify current robotic systems that are used for otological and endonasal applications. For these solutions, an analysis of the functionalities in relation to the surgeon's needs will be carried out to produce a set of specifications for the creation of new robots.

Motion planning for multi-mobile-manipulator payload transport systems

R. Tallamraju, D. H. Salunkhe, S. Rajappa, A. Ahmad, K. Karlapalem, S. V.
Shah,

In Proceedings of International Conference on Automation Science and Engineering ,
(CASE), 2019

In this paper, a kinematic motion planning algorithm for cooperative spatial payload manipulation is presented. A hierarchical approach is introduced to compute realtime collision-free motion plans for a formation of mobile manipulator robots. Initially, collision-free configurations of a deformable 2-D virtual bounding box are identified, over a planning horizon, to determine a convex workspace for the entire system. Then, 3-D payload configurations whose projections lie within the convex workspace are computed. Finally, a convex decentralized model-predictive controller is formulated to plan collision-free trajectories for the formation of mobile manipulators. Our work facilitates real-time motion planning for the system and is scalable in the number of robots. The algorithm is validated in simulated dynamic environments.

Sensorless full body active compliance in a 6 DOF parallel manipulator

A. Dutta, D. H. Salunkhe, S. Kumar, A. D. Udai, S. V. Shah,

Robotics and Computer-Integrated Manufacturing, (RCIM), 2019

Parallel manipulators are being used extensively to cater to the needs of a multitude of industrial automation applications. Due to its kinematic accuracy and structural stiffness, parallel manipulators have proven considerable advantage over their serial counterparts. In modern applications, humans train, collaborate and interact with the manipulators in order to maximize the productivity and the quality of the final product. The critical factor in this human-robot interaction is safety and the ability of the mechanism to comply with human intentions. It thus becomes a necessity for the manipulator to detect external disturbances and interactions, and be able to react accordingly. In this research, a methodology for sensor-less full body active compliance is proposed on a 6-DOF RSS (Rotary-Spherical-Spherical) parallel manipulator. By using the proposed approach, the manipulator can detect and comply with the external forces on any part of its body without using any explicit force/torque sensor at the joint or the end-effector. This is done by utilizing the estimated joint torque based on the actuator current feedback only. A three-layer cascaded impedance controller for active compliance and reaction to various human interactions are reported. The proposed design and unique methodology for compliance exhibits an effective and inexpensive yet reliable alternative to be used in safe human-robot interactions and force controlled manufacturing applications.

Force/position control of 3 dof delta manipulator with voice coil actuator

A. D. Udai, D. H. Salunkhe, A. Dutta, S. Mukherjee,

In Proceedings of Advances in Robotics, (AIR),
2017

Parallel manipulators are widely used in the industries for several applications. Due to its precision in motion as well as its robustness, parallel manipulators have proved its advantage over serial manipulators. In this paper, a 3DOF parallel manipulator is presented and force control of the manipulator is demonstrated. The proposed manipulator uses a direct drive voice coil arc actuators to achieve compliance required for human-robot interaction or soft mechanical manipulations. Its implementation in the proposed delta manipulator is discussed in the paper. The paper has discussed a unique method of controlling position as well as the force at the end-effector of the delta manipulator. The method used in making the manipulator compliant does not need an explicit force sensor and is convenient to implement. The method is inexpensive and works satisfactorily in a human interactive environment which is demonstrated through experiments discussed in the paper. The proposed design finds its application in robot-assisted assembly, surface finishing, cooperative manipulation, haptics etc.

Design, trajectory generation and control of quadrotor research platform

D. H. Salunkhe, S. Sharma, S. Topno, C. Darapaneni, A. Kankane, S. V.
Shah,

In Proceedings of Robotics and Automation for Humanatarian Applications,
(RAHA), 2016

We describe the modeling, estimation and control of a quadrotor in 3D environment using the 3DR Pixhawk PX4 as controller through Robot Operating System(ROS). The paper discusses a method to measure moment of inertia of quadrotor about its principal axes to achieve better results in an inexpensive way. We also present the trajectory generation and segment optimization of the trajectory commanded to the quadrotor. We describe a method of controlling the quadrotor through ROS by providing necessary inputs to the flight controller using the built-in firmware.

Theses

2024

Cuspidal robots: theoretical study, classification, and application to commercial robots

Durgesh Haribhau Salunkhe

Cuspidal robots are robots that have at least one connected region with multiple inverse kinematic solutions. This allows cuspidal robots to change solutions without crossing singularites. This doctoral thesis presents theoretical study on the cuspidal analysis of 3 revolute jointed (3R) serial robots. The thesis also presents identification algorithms to decide cuspidality of generic 6R robots. Later, the application of cuspidality is presented by discussing issues and developing a trajectory planning framework of cuspidal commercial robots. A closure to the conjecture in 3R cuspidal robots is provided as a result of the presented work, and the question on number of aspects in generic 3R robot is concluded. A proof for the existence of reduced aspects for a generic 3R robot is presented too. A presented proof on cuspidality in 6R robots is reinvestigated, and the need of attention to the topic of cuspidality in path planning is further motivated. The critical issues existing in commercial 6R robots that are largely ignored are shown, and a path planning framework for their mitigation is presented.

2020

The use of endoscope in otological surgery provides many benefits in terms of visibility and access to the operating region but needs to be handled by the surgeon at all time making such surgeries cumbersome. A mechanism that can act as an assistant to the surgeon for manipulating endoscope can have a huge positive impact on the efficiency of the surgeon and the surgeries. This thesis explains the technical requirements, constraints and optimization process for proposing a mechanism for such application. The importance of analysis and synthesis of the kinematic properties of the structure for an optimized output is highlighted in the study. The author presents a novel implementation of an optimization algorithm for the design optimization. Various approaches researched in the past for the optimization are presented and their advantages and disadvantages are pointed out too. The effect of parametrization, different constraints as well as rewarding strategies are discussed to stress the complexities in the optimization of closed loop kinematic chains. The thesis also presents approaches used to consider the constraints for the passive joint limits as well as avoiding internal collision in the mechanism. A novel methodology is used for a faster and efficient global search of the optimization space. The work concludes by presenting the optimised result as well as by discussing open questions regarding the future of mechanism design.

Talks

Book chapters

Optimisation of parallel mechanisms with joint limits and collision constraints

D. H. Salunkhe, S. Kumar, D. Chablat, In Biologically Inspired Series-Parallel Hybrid Robots, 2024

In this chapter, a new optimization methodology for parallel kinematic manipulator (PKM) is
proposed, addressing constraints related to singularities, passive joint limits, and
self-collisions. The proposed optimization approach combines a local search method
(Nelder-Mead algorithm) with global search methodologies such as low discrepancy distribution.
This combination allows for faster and more efficient exploration of the optimization space.
The algorithm optimizes a global kinematic quality along with the length of the prismatic
actuators. The design constraints can be introduced modularly. This allows for a better
understanding of the impact of specific criteria on the final result. The chapter also discusses
the effect of the dimension of the search space. It is shown that initial knowledge on PKM can
help reduce the dimension of the search space and result in more intuitive results. The
presented approach is applied to optimize a PKM with a motion constraint generator of 2 degrees
of freedom. This case study demonstrates the effectiveness of the proposed methodology in
addressing the challenges associated with the optimization of PKMs.

Keywords: parallel mechanisms, optimization, Nelder-Mead