Sergey Khalapyan

Bio: Sergey Khalapyan is an academic researcher from National University of Sciences and Technology. The author has contributed to research in topics: Parallel manipulator & Robot. The author has an hindex of 2, co-authored 7 publications receiving 12 citations.

Conceptual Design and Control of a Sitting-Type Lower-Limb Rehabilitation System Established on a Spatial 3-PRRR Parallel Manipulator

Abstract: The conceptual design of a new sitting-type lower-limb rehabilitation robot along with simplified motion control for its passive range of motion therapies is put forth here The suggested system’s design is demonstrated and verified using computer-based numerical simulations For this, the desired motion trajectory is generated with the help of a clinically obtained gait data-set The robustness of the proposed simplified motion control scheme is verified with the variation of the physical parameters of the patients’ limb

Intelligent Computing Based on Neural Network Model in Problems of Kinematics and Control of Parallel Robot

Abstract: Implementation of a closed-loop control system for a parallel robot is rather difficult due to impossibility of a mechanism output link position direct detection. In order to overcome this, a direct kinematics problem should be solved according to states of the mechanism drive links. However, such approach application requires a solution of a system of nonlinear equations. It is even more complicated for mechanisms with ambiguity of such solution. In this paper, we propose a method to determine the “correct” solution of the direct kinematics problem for such mechanisms using a tripod, a robot with three degrees of freedom, as an example. The method is based on artificial neural networks usage. The data of the mobile platform previous position are used as networks input information. In this paper, it is shown that in this case the adequacy of the obtained neural network based model is sufficiently improved since the neighborhood is defined, where the “correct” solution is located. As a result, both the reliability of the output link position determination and positioning speed and accuracy are improved. The obtained neural network based model can be directly used for the tripod control, and the method to develop this model can be used to synthesize models of other parallel robots.

Synthesis of Parallel Robots Optimal Motion Trajectory Planning Algorithms

Abstract: The article considers the problem of planning the optimal trajectory of the tripod robot movement. The movement of the output link includes working displacements that are performed for the purpose of machining the workpiece and are completely determined by the surface of the workpiece, as well as the movement of the tool to the beginning of the next stage of processing, which can be relatively free, however, taking into account working area and workpiece surface limitations. The working area is limited by the range of permissible lengths of the drive links and the sign of the Jacobian. Additional restrictions are introduced, related to the dimensions of the workpiece. Chebyshev’s metric makes a significant ambiguity in the choice of the trajectory. Therefore, it is proposed to supplement the original objective function with the Euclidean metric taken with a small weighting factor. Optimization was carried out with restrictions on the size of the working area and workpiece.

Two-Stage Method for Controlling the Movement of a Parallel Robot Based on a Planar Three-Revolute-Prismatic-Revolute Mechanism

Abstract: A two-stage method for organizing control of a robot with parallel kinematics is proposed. The method involves the transfer of all complex resource-intensive computational procedures to the stage of the trajectory formation. During the operational control of the robot’s movement, a ready-made trajectory is used, recorded as points in the input coordinate space of the mechanism. Method application allows avoiding multiple solutions of the forward and inverse kinematics during the robot movement, significantly increasing the performance of the control system. Experimental verification of the method was carried out using the planar 3-RPR mechanism as an example.

Motion Control of 6-DOF Relative Manipulation Device

Abstract: The article discusses a robotic system based on a 6-DOF relative manipulation device consisting of two modules. The lower module is based on a parallel planar 3-RPR mechanism, and the upper module is based on a parallel 3-RPS tripod module. Such robotic system can be used in mechanical engineering as a robot-machine for the mechanical processing of parts. The mathematical model was built in the MATLAB package to analyze the prospects for using a 3-RPS robot. An alternative description of the rotation of the robot’s mobile platform is proposed to organize a simpler control of it within the framework of a system of interacting robots. A technique has been developed to compensate for the movable tripod platform’s horizontal displacements and take into account the geometric dimensions of the replaceable tool and the relative positions of the 6-DOF system modules during the control process. The results of the mathematical simulation are presented.

Synthesis of Parallel Robots Optimal Motion Trajectory Planning Algorithms

Abstract: The article considers the problem of planning the optimal trajectory of the tripod robot movement. The movement of the output link includes working displacements that are performed for the purpose of machining the workpiece and are completely determined by the surface of the workpiece, as well as the movement of the tool to the beginning of the next stage of processing, which can be relatively free, however, taking into account working area and workpiece surface limitations. The working area is limited by the range of permissible lengths of the drive links and the sign of the Jacobian. Additional restrictions are introduced, related to the dimensions of the workpiece. Chebyshev’s metric makes a significant ambiguity in the choice of the trajectory. Therefore, it is proposed to supplement the original objective function with the Euclidean metric taken with a small weighting factor. Optimization was carried out with restrictions on the size of the working area and workpiece.

Two-Stage Method for Controlling the Movement of a Parallel Robot Based on a Planar Three-Revolute-Prismatic-Revolute Mechanism

Abstract: A two-stage method for organizing control of a robot with parallel kinematics is proposed. The method involves the transfer of all complex resource-intensive computational procedures to the stage of the trajectory formation. During the operational control of the robot’s movement, a ready-made trajectory is used, recorded as points in the input coordinate space of the mechanism. Method application allows avoiding multiple solutions of the forward and inverse kinematics during the robot movement, significantly increasing the performance of the control system. Experimental verification of the method was carried out using the planar 3-RPR mechanism as an example.

Small normalized boolean circuits for semi-disjoint bilinear forms require logarithmic conjunction-depth

Abstract: We consider normalized Boolean circuits that use binary operations of disjunction and conjunction, and unary negation, with the restriction that negation can be only applied to input variables. We derive a lower bound trade-off between the size of normalized Boolean circuits computing Boolean semi-disjoint bilinear forms and their conjunction-depth (i.e., the maximum number of and-gates on a directed path to an output gate). In particular, we show that any normalized Boolean circuit of at most ϵlogn conjunction-depth computing the n-dimensional Boolean vector convolution has ω(n2−4ϵ) and-gates. Analogously, any normalized Boolean circuit of at most ϵlogn conjunction-depth computing the n × n Boolean matrix product has ω(n3−4ϵ) and-gates. We complete our lower-bound trade-offs with upper-bound trade-offs of similar form yielded by the known fast algebraic algorithms.

Synthesis of Trajectory Planning Algorithms Using Evolutionary Optimization Algorithms

Abstract: The article considers the problem of planning the optimal trajectory of a delta robot. The workspace of the robot is limited by the range of permissible values of the angles of the drive revolute joints, interference of links and singularities. Additional constraints related to the presence of obstacles have been introduced. Acceptable values of the robot’s input coordinates are obtained based on the inverse kinematics, taking into account the constraints of the workspace, represented as a partially ordered set of integers. For the given initial and final coordinates, a randomly generated family of trajectories belonging to a valid set is obtained. Optimization of each of the trajectories of the family based on evolutionary algorithms is performed. The optimization criterion is a function proportional to the duration of movement along the trajectory. The results of modeling are presented.