Abstract : One of the main problems associated with the use of 6 DOF parallel robots remains the solving of their kinematic models. This is rarely possible to analytically solve their models thereby justifying the application of numerical methods. These methods are difficult to implement in an industrial controller and can cause solution bifurcations close to singularities resulting in following an unplanned trajectory. Recently, a 3-PPPS robot with U-shaped base was introduced where an analytical kinematic model can be derived. Previously, quaternion parameters were used to represent the orientation of the mobile platform. To allow for simpler model handling, this article introduces the use of Euler angles which have a physical meaning for the users. Compact writing of the direct and inverse kinematic model is thus obtained. Using algebraic and cylindrical decomposition for the workspace, this provides a simpler representation of the largest domain without singularity around the “home” configuration.

Damien Chablat, Luc Baron, Ranjan Jha, Luc Rolland. The 3-PPPS Parallel Robot with U-Shape Base, a 6-DOF Parallel Robot with simple Kinematics . Advances in Robot Kinematics 2018, Springer Proceedings in Advanced Robotics, Vol. 8, pp. 195-201, 2018. <Web Link>

Abstract : This paper presents the workspace, the joint space and the singularities of a family of delta-like parallel robots by using algebraic tools. The different functions of SIROPA library are introduced, which is used to induce an estimation about the complexity in representing the singularities in the workspace and the joint space. A Gröbner based elimination is used to compute the singularities of the manipulator and a Cylindrical Algebraic Decomposition algorithm is used to study the workspace and the joint space. From these algebraic objects, we propose some certified three-dimensional plotting describing the shape of workspace and of the joint space which will help the engineers or researchers to decide the most suited configuration of the manipulator they should use for a given task. Also, the different parameters associated with the complexity of the serial and parallel singularities are tabulated, which further enhance the selection of the different configuration of the manipulator by comparing the complexity of the singularity equations.

Ranjan Jha, Damien Chablat, Luc Baron, Fabrice Rouillier. Workspace, joint space and singularities of a family of delta-like robot. Mechanism and Machine Theory, Vol. 127, pp. 73-95, 2018. <Web Link>

Abstract : This paper presents variations in the workspace, singularities, and joint space with respect to design parameter k, which is the ratio of the dimensions of the mobile platform to the dimensions of the base of a 3-RPS parallel manipulator. The influence of the design parameters on parasitic motion, which is important when selecting a manipulator for the desired task, is also studied. The cylindrical algebraic decomposition method and Gröbner-based computations are used to model the workspace and joint space with parallel singularities in 2R1T (two rotational and one translational) and 3T (three translational) projection spaces, where the orientation of the mobile platform is represented using quaternions. These computations are useful in selecting the optimum value for the design parameter k such that the parasitic motions can be limited to specific values. Three designs of the 3-RPS parallel robot, based on different values of k, are analyzed.

Ranjan Jha, Damien Chablat, Luc Baron. Influence of design parameters on the singularities and workspace of a 3-RPS Parallel Robot. Transactions of the Canadian Society for Mechanical Engineering, 2018, 42(1): 30-37. <hal-01519620 Web Link>

Abstract : This paper presents the kinematic analysis of the 3-PPPS parallel robot with an equilateral mobile platform and a U-shape base. The proposed design and appropriate selection of parameters allow formulating simpler direct and inverse kinematics for the manipulator under study. The parallel singularities associated with the manipulator depend only on the orientation of the end-effector, and thus depend only on the orientation of the end effector. The quaternion parameters are used to represent the aspects, i.e. the singularity-free regions of the workspace. A cylindrical algebraic decomposition is used to characterize the workspace and joint space with a low number of cells. The discriminant variety is obtained to describe the boundaries of each cell. With these simplifications, the 3-PPPS parallel robot with proposed design can be claimed as the simplest 6 DOF robot, which further makes it useful for the industrial applications.

Damien Chablat, Luc Baron, Ranjan Jha. Kinematics and Workspace analysis of a 3PPPS Parallel Robot with U-Shaped Base. International Design Engineering Technical Conferences & Computers and Information in Engineering Conference, Aug 2017, Cleveland, United States. 2017. <hal-01521850 Web Link>

Abstract : Usually, the accuracy of parallel manipulators depends on the architecture of the robot, the design parameters, the trajec-tory planning and the location of the path in the workspace. This paper reports the influence of static and dynamic parameters in computing the error in the pose associated with the trajectory planning made and analyzed with the Orthoglide 5-axis. An error model is proposed based on the joint parameters (velocity and acceleration) and experimental data coming from the Orthoglide 5-axis. Newton and Gröbner based elimination methods are used to project the joint error in the workspace to check the accuracy/error in the Cartesian space. For the analysis, five similar trajectories with different locations inside the workspace are defined using fifth order polynomial equation for the trajectory planning. It is shown that the accuracy of the robot depends on the location of the path as well as the starting and the ending posture of the manipulator due to the acceleration parameters.

Ranjan Jha, Damien Chablat, Fabrice Rouillier, Guillaume Moroz. Influence of the trajectory planning on the accuracy of theorthoglide 5-axis. ASME International Design Engineering Technical Conference and the Computer and Information in Engineering Conference (IDETC/CIE), Aug 2016, Charlotte, NC, United States. Proceedings of the ASME 2016 International Design Engineering Technical Conference and the Computer and Information in Engineering Conference (IDETC/CIE), 2016. <hal-01309190 Web Link>

Abstract : There have been several research works on reconfig-urable parallel manipulators in the last few years. Some robots are reconfigurable in the sense that the position of the anchor points on the moving platform or the actuated joints can be changed. Some problems may arise when one intends to make a prototype and develop its control scheme. A reconfigurable planar parallel robot, named NaVARo, is a 3-DOF planar parallel manipulator with eight actuation modes. The subject of this paper is about a control scheme of NaVARo while taking advantage of multiple sensors such as motor encoders, additional absolute encoders and magnetic sensors used to determine the current assembly mode of the manipulator. Finally, a methodology is presented to determine the home configuration of NaVARo.

Damien Chablat, Ranjan Jha, Stéphane Caro. A Framework for the Control of a Parallel Manipulator with Several Actuation Modes. 14th International Conference on Industrial Informatics , Jul 2016, Poitiers, France. IEEE, 2016. <hal-01313376 Web Link>

Abstract : Trajectory planning is a critical step while programming the parallel manipulators in a robotic cell. The main problem arises when there exists a singular configuration between the two poses of the end-effectors while discretizing the path with a classical approach. This paper presents an algebraic method to check the feasibility of any given trajectories in the workspace. The solutions of the polynomial equations associated with the tra-jectories are projected in the joint space using Gröbner based elimination methods and the remaining equations are expressed in a parametric form where the articular variables are functions of time t unlike any numerical or discretization method. These formal computations allow to write the Jacobian of the manip-ulator as a function of time and to check if its determinant can vanish between two poses. Another benefit of this approach is to use a largest workspace with a more complex shape than a cube, cylinder or sphere. For the Orthoglide, a three degrees of freedom parallel robot, three different trajectories are used to illustrate this method.

Ranjan Jha, Damien Chablat, Fabrice Rouillier, Guillaume Moroz. An algebraic method to check the singularity-free paths for parallel robots. International Design Engineering Technical Conferences & Computers and Information in Engineering Conference, Aug 2015, Boston, United States. 2015. <hal-01142989 Web Link>

Abstract : Workspace and joint space analysis are essential steps in describing the task and designing the control loop of the robot, respectively. This paper presents the descriptive analysis of a family of delta-like parallel robots by using algebraic tools to induce an estimation about the complexity in representing the singularities in the workspace and the joint space. A Gröbner based elimination is used to compute the singularities of the manipulator and a Cylindrical Algebraic Decomposition algorithm is used to study the workspace and the joint space. From these algebraic objects, we propose some certified three dimensional plotting describing the the shape of workspace and of the joint space which will help the engineers or researchers to decide the most suited configuration of the manipulator they should use for a given task. Also, the different parameters associated with the complexity of the serial and parallel singularities are tabulated, which further enhance the selection of the different configuration of the manipulator by comparing the complexity of the singularity equations.

Ranjan Jha, Damien Chablat, Fabrice Rouillier, Guillaume Moroz. Workspace and Singularity analysis of a Delta like family robot. Robotics and Mechatronics, Springer, Vol. 37, Pp. 121 - 130, 2016. <hal-01142465 Web Link>

Abstract : The Accurate calculation of the workspace and joint space for 3 RPS parallel robotic manipulator is a highly addressed research work across the world. Researchers have proposed a variety of methods to calculate these parameters. In the present context a cylindrical algebraic decomposition based method is proposed to model the workspace and joint space. It is a well know feature that this robot admits two operation modes. We are able to find out the set in the joint space with a constant number of solutions for the direct kinematic problem and the locus of the cusp points for the both operation mode. The characteristic surfaces are also computed to define the uniqueness domains in the workspace. A simple 3-RPS parallel with similar base and mobile platform is used to illustrate this method.

Damien Chablat, Ranjan Jha, Fabrice Rouillier, Guillaume Moroz. Workspace and joint space analysis of the 3-RPS parallel robot. ASME 2013 International Design Engineering Technical Conferences & Computers and Information in Engineering Conference, Aug 2014, Buffalo, United States. Volume 5A, pp.1-10, 2014. <hal-01006614 Web Link>

Abstract : Having non-singular assembly modes changing trajectories for the 3-RPS parallel robot is a well-known feature. The only known solution for defining such trajectory is to encircle a cusp point in the joint space. In this paper, the aspects and the characteristic surfaces are computed for each operation mode to define the uniqueness of the domains. Thus, we can easily see in the workspace that at least three assembly modes can be reached for each operation mode. To validate this property, the mathematical analysis of the determinant of the Jacobian is done. The image of these trajectories in the joint space is depicted with the curves associated with the cusp points.

Damien Chablat, Ranjan Jha, Fabrice Rouillier, Guillaume Moroz. Non-singular assembly mode changing trajectories in the workspace for the 3-RPS parallel robot. Advances in Robot Kinematics, Springer, Pp. 149 - 159, 2014. <hal-00956325 Web Link>

Abstract : Minimally invasive surgery is a modern surgical technique in which the operating tools are inserted into the patient through small incisions. Robotic applications in general surgery have evolved from simple surgical assist devices, to more sophisticated systems capable of enhancing surgical performance. The primary class of robots used in general surgery today, are ‘master-slave’ machines, where the robot mimics the movement of the surgeon. A major drawback with the master-slave robotic systems is the motion coordination between the two. The paper discusses the techniques of motion transfer from master to slave and to implement force feedback from slave to master. Motion is transferred from master surgeon handle to the robotic arm depending on the encoder pulses from master configuration. The pulses from the encoder are processed and fed to the slave, which mimics the hand motion of master configuration. A two channel encoder with DC motor is used in master-slave configuration. The proposed configuration with force feedback capability enables the exact motion coordination between surgeon and robotic surgical system. This technique has a wide application, with accuracy, efficiency, safety and overall user experience that provide superior performance and reliability in master-slave robot-assisted interventions.

Ranjan Jha, Varun Dhiman, Sanjeev Kumar, Amod Kumar. Implementation of motion transfer in robotic Surgery. Int. J. Medical Engineering and Informatics, Vol. 6, No. 4, pp. 289-296, 2014. [Web Link]

Abstract : During Otologic surgery, and more broadly during microsurgery, the surgeon encounters several difficulties due to the confined spaces and micro-manipulations. The purpose of the paper is to design a robot with a prescribed regular workspace shape to handle an endoscope to assist the Otologic surgery. A spherical parallel mechanism with two degrees of freedom is analysed in its design parameter space. This mechanism is composed of three legs (2USP-U) to connect the base to a moving platform connected to a double parallelogram to create a remote center of motion (RCM). Its kinematic properties, i.e. the singularity locus and the number of direct kinematic solutions, are investigated. For some design parameters, non-singular assembly modes changing trajectories may exist and have to be investigated inside the prescribed regular workspace shape. Two sets of design parameters are presented with their advantages and disadvantages.

Damien Chablat, Guillaume Michel, Philippe Bordure, Swaminath Venkateswaran, Ranjan Jha. Workspace analysis in the design parameter space of a 2-DOF spherical parallel mechanism for a prescribed workspace: Application to the otologic surgery. Mechanism and Machine Theory, Volume 157, 2021, 104224, ISSN 0094-114X, [Web Link]

Abstract : Rehabilitation of ankle injuries must be under supervision of a therapist to prevent severe injuries. However, relying on a therapist is not consistent and accurate. In the present days, parallel manipulators play a key role as an ankle rehabilitation device to overcome the problem imposed by a therapist. The ankle rehabilitation device should be able to sustain the external forces and moments exerted from the patient’s feet. The external forces and moments applied to the platform can cause deflections, either translation or rotational deflections. These deflections depend mostly upon the stiffness properties of the device. The stiffness property is one of crucial factors to be considered in designing the ankle rehabilitation device. Therefore, this paper aims to analyse and establish the static and stiffness model of the 3-RPS parallel manipulator which is employed as an ankle rehabilitation device. Each RPS leg applies one constraint force and one actuation force intersecting the centre of spherical joint. By collecting all constraint forces and actuation forces, the Jacobian matrix can be formulated according to the Screw theory and Quaternion parameters. Influences of actuators and base-and-platform configuration are identified by using stiffness index, namely eigenvalues of the stiffness matrix. The base-and-platform configuration is described by the distance of each joint to the origin of coordinate frame and the angle among three legs. For given external wrenches, numerical simulations have been performed to determine the optimal distributions of actuators and base-and-platform configuration by taking into account the stiffness.

Latifah Nurahmi, Rath Kautsar, Ranjan Jha. Stiffness Distribution of 3-RPS Parallel Manipulator Based on the Base-and-platform Configuration. In: Sen D., Mohan S., Ananthasuresh G. (eds) Mechanism and Machine Science. Lecture Notes in Mechanical Engineering. pp 57-68, Springer, Singapore. [Web Link]

Abstract : Rehabilitation of ankle injuries must be under supervision of a therapist to prevent severe injuries. However, relying on a therapist is not consistent and accurate. In the present days, parallel manipulators play a key role as an ankle rehabilitation device to overcome the problem imposed by a therapist. The ankle rehabilitation device should be able to sustain the external forces and moments exerted from the patient’s feet. The external forces and moments applied to the platform can cause deflections, either translation or rotational deflections. These deflections depend mostly upon the stiffness properties of the device. The stiffness property is one of the crucial factors to be considered in designing the ankle rehabilitation device. Therefore, this paper aims to analyse and establish the static and stiffness model of the 3-RPS parallel manipulator which is employed as an ankle rehabilitation device. Each RPS leg applies one constraint force and one actuation force intersecting the center of spherical joint. By collecting all constraint forces and actuation forces, the Jacobian matrix can be formulated according to the Screw theory and Quaternion parameters. Influences of actuators and base-and-platform configuration are identified by using the stiffness index, namely eigenvalues of the stiffness matrix. The base-and-platform configuration is described by the distance of each joint to the origin of coordinate frame and the angle among three legs. Forgiven external wrenches, numerical simulations have been performed to determine the optimal distributions of actuators and base-and-platform configuration by taking into account the stiffness.

Vikash Shaw, Parul Rani, Yogesh Kumar, Ranjan Jha, Dinesh Pankaj and Sanjeev Kumar. Real time implementation of motion transfer mechanism for master slave robotic configuration. 2019 3rd International Conference on Recent Developments in Control, Automation & Power Engineering (RDCAPE), 2019, pp. 390-394. [Web Link]

Abstract : This present study describes the design of the finger probe to be working with near-infrared (NIR) and infrared (IR) light sources for the diagnosis of common blood disorder called as anemia non-invasively. The probe has been designed in 3D CAD system and fabricated with ABS plastic using Fortus 250mc 3D printer. In the probe the cushion has been used to provide comfort for the subject and flexibility to be used for all age groups of subjects (excluding children). The probe has been tested on multiple volunteers (male/female to record the neat and clean noise free photoplethysmographic (PPG) waveform. The output of the probe has been recorded using LabVIEW. The developed probe can be helpful to detect anemic conditions of the patient non-invasively which is a big concern now a days in society.

Yogesh Kumar, Vikash Shaw, Parul Rani, Varun Dhiman, Ranjan Jha and Sanjeev Kumar. Design and Development of finger probe for diagnosis of Anemia non-invasively. 2019 3rd International Conference on Recent Developments in Control, Automation & Power Engineering (RDCAPE), 2019, pp. 384-389. [Web Link]

Abstract : This present study describes the design of the finger probe to be working with near-infrared (NIR) and infrared (IR) light sources for the diagnosis of common blood disorder called as anemia non-invasively. The probe has been designed in 3D CAD system and fabricated with ABS plastic using Fortus 250mc 3D printer. In the probe the cushion has been used to provide comfort for the subject and flexibility to be used for all age groups of subjects (excluding children). The probe has been tested on multiple volunteers (male/female to record the neat and clean noise free photoplethysmographic (PPG) waveform. The output of the probe has been recorded using LabVIEW. The developed probe can be helpful to detect anemic conditions of the patient non-invasively which is a big concern now a days in society.

Yogesh Kumar, Vikash Shaw, Parul Rani, Varun Dhiman, Ranjan Jha and Sanjeev Kumar. Design and Development of finger probe for diagnosis of Anemia non-invasively. 2019 3rd International Conference on Recent Developments in Control, Automation & Power Engineering (RDCAPE), 2019, pp. 384-389. [Web Link]

Jha R., Chablat D., Rouillier F., Moroz G., “A partition of the workspace and jointspace of parallel robots using algebraic tools”, Applications of Parallel and Cable-driven Robots, INNOROBO, 2014. [WEB LINK]

Jha R., Dhiman V., Kumar S. and Kumar A., “Force Feedback Approach In Implementation Of Haptics”, National Symposium on Instrumentation (NSI-37), CSIR-CSIO, India, 2012. [POSTER]