Himanshu Chaudhary

Constraint Wrench Formulation for Closed-Loop Systems Using Two-Level Recursions

In order to compute the constraint moments and forces, together referred here as wrenches, in closed-loop mechanical systems, it is necessary to formulate a dynamics problem in a suitable manner so that the wrenches can be computed efficiently. A new constraint wrench formulation for closed-loop systems is presented in this paper using two-level recursions, namely, subsystem level and body level. A subsystem is referred here as the serial- or tree-type branches of a spanning tree obtained by cutting the appropriate joints of the closed loops of the system at hand. For each subsystem, unconstrained Newton-Euler equations of motion are systematically reduced to a minimal set in terms of the Lagrange multipliers representing the constraint wrenches at the cut joints and the driving torques/forces provided by the actuators. The set of unknown Lagrange multipliers and the driving torques/forces associated to all subsystems are solved in a recursive fashion using the concepts of a determinate subsystem. Next, the constraint forces and moments at the uncut joints of each subsystem are calculated recursively from one body to another. Effectiveness of the proposed algorithm is illustrated using a multiloop planar carpet scraping machine and the spatial RSSR (where R and S stand for revolute and spherical, respectively) mechanism.

Matrix Formulation of Constraint Wrenches for Serial Manipulators

A matrix formulation of the constraint forces and moments, together referred here as the wrenches, for serial manipulators is presented in this paper. The methodology is based on the Newton-Euler dynamic equations of motions of the manipulator at hand. The formulation provides joint forces and moments that are necessary for designing the robot links, as well those required by the joint actuators. The latter information is required in inverse dynamics. The formulation is based on writing the kinematic constraint equations using the Decoupled Natural Orthogonal complement (DeNOC) matrices, introduced elsewhere. The kinematic information in the form of the DeNOC matrices of a serial manipulator is used for the determination of the joint torques and forces, which lead to the development of a uniform analytical tool for control and design.

A NOVEL APPROACH FOR CUSTOMIZED PROSTHETIC SOCKET DESIGN

The manufacturing of limb prosthesis socket that is comfortable for the amputee depends greatly on prosthetic practitioner’s knowledge of socket biomechanics and skill. It involves multistage manual corrections depending upon the clinical condition of the patient’s residual limb which may be affected by shrinkage or possible damage of plaster of paris (PoP) mold. The current work describes a novel process simplified through digitization, it integrates conventional PoP processes, reverse engineering (RE), and additive manufacturing (AM) technologies to design and develop a socket. The stereolithography (STL) file generated from the scan data was modeled on a fused deposition modeling (FDM) based AM. Its fitment was assessed with the help of INSPECTPLUS and GEOMAGIC reverse engineering tools. This approach takes the guess work out of prosthetic practitioner’s job, ensures better fitment, and shortens the total fabrication time leading to improved patient satisfaction. The proposed method is a part of the on...

Minimization of Constraint Forces in Industrial Manipulators

Constraint force minimization is essential to improve the dynamic performance of an industrial manipulator. An optimization method is proposed to minimize the constraint forces using the concept of dynamically equivalent system of point-masses. It is shown that for the six-DOF PUMA robot the constraint forces are substantially reduced.

A VIRTUAL REVERSE ENGINEERING METHODOLOGY FOR ACCURACY CONTROL OF TRANSTIBIAL PROSTHETIC SOCKET

Computer-aided tools help in shortening and eradicating numerous repetitive tasks that reduce the gap between digital model and the actual product. Use of these tools assist in realizing free-form objects such as custom fit products as described by an stringent interaction with the human body. Development of such model presents a difficult situation for reverse engineering (RE), which are not analogous with the requirement for generating simple geometric models. Hence, an alternating way of producing more accurate three-dimensional models is proposed. For creating accurate 3D models, point clouds are processed through filtering technique, segmentation, mesh smoothing and surface generation. These processes help in converting the initial unorganized point data into a 3D digital model and simultaneously influence the quality of the model. This study provides an optimum balance for the best accuracy obtainable with maximum allowable deviation to lesser computer handling and processing time. In this paper, a realistic nontrivial case study of the free-form prosthetic socket is considered. The accuracy obtained for the developed model is acceptable for the use in medical applications and FEM analysis.

Optimal dynamic design of planar mechanisms using teaching–learning-based optimization algorithm

A two-stage optimization method for optimal dynamic design of planar mechanisms is presented in this paper. For dynamic balancing, minimization of the shaking force and the shaking moment is achieved by finding optimum mass distribution of mechanism links using the equimomental system of point-masses in the first stage of the optimization. In the second stage, their shapes are synthesized systematically by closed parametric curve, i.e. cubic B-spline curve corresponding to the optimum inertial parameters found in the first stage. The multi-objective optimization problem to minimize both the shaking force and the shaking moment is solved using evolutionary optimization algorithm – “Teaching-learning-based optimization (TLBO) algorithm”. The computational performance of TLBO algorithm is compared with another evolutionary optimization algorithm, i.e. genetic algorithm.

A novel gait-based synthesis procedure for the design of 4-bar exoskeleton with natural trajectories

Background/Objective Human walking involves the coordination of brain, nerves, and muscles. A disturbance in their coordination may result in gait disorder. The gait disorder may be treated through manually assisted gait training or with the aid of assistive devices/robotic devices. These robotic devices involve mechanisms which are synthesized using complex conventional procedures. Therefore, in this study, a new gait-based synthesis procedure is proposed, which simplifies the mechanism synthesis and helps to develop a mechanism which can be used in rehabilitation devices, bipeds, etc. Methods This article presents a novel procedure for the synthesis of 4-bar linkage using the natural gait trajectories. As opposed to the conventional synthesis procedures, in this procedure, a global reference frame is considered, which allows the use of hip trajectory while moving. Moreover, this method is divided into two stages, and five precision points are considered on the hip trajectory in each stage. In the first stage, the 4-bar linkage is designed, thereafter, the configurations of the linkage for the remaining precision points are determined in the second stage. The proposed synthesis procedure reduces the complexity involved in the synthesis and helps in the simplification of the problem formulation. A two-stage optimization problem is formulated for minimizing the error between the generated and desired hip trajectories. Two nature-inspired algorithms are used for solving the optimization problem. The obtained best results are presented, and the designed linkage is simulated in MATLAB. Results The best design of the linkage is obtained using particle swarm optimization. The trajectories generated by the designed linkage using the proposed methodology can accurately track the desired path, which indicates that designed linkage can achieve all the orientations required during walking. The positions of a whole lower limb at all the desired precision points are demonstrated by stick diagram for one gait. Conclusion The proposed methodology has reduced the complexity of synthesis procedures and used optimization techniques to obtain a feasible design of the mechanism. The stick diagram of the designed mechanism obtained using the proposed method indicates that the designed mechanism can walk smoothly. Hence, the designed mechanism can be used in the rehabilitation devices. Furthermore, a conceptual design of an exoskeleton knee is also presented. The Translational Potential of this Article Many hospitals and individuals have used the immobile and portable rehabilitation devices. These devices involve mechanisms, and the design of mechanism plays a vital role in the functioning of these devices; therefore, we have developed a new synthesis procedure for the design of the mechanism. Besides synthesis procedure, a mechanism is developed that can be used in the rehabilitation devices, bipeds, exoskeletons, etc., to benefit the society.

Shape synthesis of an assistive knee exoskeleton device to support knee joint and rehabilitate gait

Abstract Purpose: The assistive knee exoskeleton device is used for supporting the surrounding ligaments, tendons, and muscles of the injured knee joint. Various knee exoskeletons have been discussed; however, their shape synthesis is not reported. This study aims to present the shape synthesis of the assistive knee device. Moreover, four-bar linkage is used for the knee exoskeleton, in this study. Methods: Clinical biomechanical data are adapted from gait database for one gait cycle. Using the clinical gait data, position and static force analyses are performed to obtain a set of orientations and unknown forces. Simultaneously, CAD models are prepared, and the obtained forces are applied to the CAD models of the four-bar linkage knee exoskeleton. Consequently, the threshold is obtained for each component of the knee exoskeleton and the unwanted material below the threshold is removed. Results: A reduction of 45% in the peak actuating force is observed in comparison with the literature. Besides, a total reduction of 21% in the mass of four-bar knee exoskeleton is observed in contrast to the base models when shape synthesis is performed. Conclusions: An assistive knee exoskeleton is developed using the shape synthesis methodology in which four-bar linkage is used. New shapes of thigh and shank attachments are obtained. The developed knee exoskeleton can be used by persons with the injured knee for supporting the ligaments, tendons, and muscles. Besides, control technology can be implemented to make it useful for persons with monoplegia. Implications for rehabilitation Assistive knee exoskeleton devices proved to be an important tool for providing support to injured knee joints. Typically single axis joints are observed in the lower limb exoskeletons which can be replaced with linkage mechanisms to obtain the desired range of motion. In this study, four-bar linkages are used for the knee exoskeleton in which cranks and rockers are connected to the lateral and medial sides of the knee joint, for connecting shank and thigh attachments. Shape synthesis is performed on the components of four-bar exoskeleton through the evaluated reaction forces. The components are assembled to form an assistive knee exoskeleton which can be used by any person with injured knee joint.

A modified algorithm of Particle Swarm Optimization for form error evaluation

Abstract The set of measured data points acquired from the Coordinate Measuring Machine (CMM) need to be processed and analyzed for evaluating the form errors inside the manufactured components. This paper presents a modified algorithm of particle swarm optimization (MPSO) for assessing the form error from the set of coordinate measured data points. In the classical algorithm of the particle swarm optimization (PSO), the value of the candidate solution is updated from its existing value without actually comparing the value obtained in the consecutive iterations for fitness. This behaviour attributes to a lack of exploitation ability in the defined search space. The proposed algorithm generates new swarm position and fitness solution for the objective function through an improved and modified search equation based on a proposed heuristic step. In this step, the swarm searches around the best solution of the previous iteration for improving the swarm exploitation capability. The particle swarm uses greedy selection procedure to choose the best candidate solution. A non-linear minimum zone objective function is formulated mathematically for different types of form errors and then optimized using proposed MPSO. Five benchmark functions are used to prove the effectiveness of the modified algorithm, which is verified by comparing its solution and convergence with those obtained from the established algorithms namely PSO and genetic algorithm (GA). Finally, the result of the proposed algorithm for form error evaluation is compared with previous work and other established nature-inspired algorithms. The results demonstrate that the proposed MPSO algorithm is more efficient and accurate than the other conventional heuristic optimization algorithms. Furthermore, it is well suited for form error evaluation using CMM acquired data.

Ergonomic assessment and prevalence of musculoskeletal disorders among washer-men during carpet washing: guidelines to an effective sustainability in workstation design

The development of musculoskeletal disorders (MSDs) is the most common problem among the workers employed in carpet industry working at any stage of production. This study investigates the problems encountered during washing stage and establishes the guidelines for an ergonomically efficient workstation. The data about pain occurrence at different body and hand regions of male washer-men were collected by questionnaire. Postural assessment techniques were used to identify the postural risks and a mannequin was developed in CATIA for biomechanical analysis associated with washing. Most of the participants reported discomfort in different body and hand regions. A significant difference between the physical and physiological factors pre- and post- activity (p < 0.05) was reported. Postural techniques revealed that the working posture during carpet washing requires necessary action. This study proposes certain workstation guidelines that may reduce the symptoms of MSDs, lead to the improvement in working posture and efficiency of the worker.