Dimitar Chakarov | Bulgarian Academy of Sciences (original) (raw)

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Papers by Dimitar Chakarov

Consider complex problems or complex environment, where the introduction of robotized automation ... more Consider complex problems or complex environment, where the introduction of robotized automation is needed. Then, as outlined in a number of papers, manipulation robots should have more inputs than the necessary minimum

In the present work a methodology is developed for synthesis of closed structures for microand na... more In the present work a methodology is developed for synthesis of closed structures for microand nano-applications, utilizing the advantages of structured piezo-ceramics, tense piezo-actuators and closed robot kinematics structures. The synthesis of closed kinematic structure with piezoceramic actuators is investigated for three case studies: А) Synthesis for parallel structures in which the basic links are connected in between, only by means of driving chains of the piezoceramic actuators. B) Synthesis for parallel structures in which the basic links are connected in between in a serial chain. The driving chains of the piezoceramic actuators are attached parallel to the links of the basic serial chain. C) Synthesis for parallel structures in which the basic links are connected in between in a parallel chain. The driving chains of the piezoceramic actuators are attached parallel to the links of these chain. A synthesis of kinematics schemes with definite degrees of mobility based on t...

This paper presents actually work from development of mechatronic handling devices able to accomp... more This paper presents actually work from development of mechatronic handling devices able to accomplish certain microand/or nano operation tasks. Piezo ceramic structures with (3,1)-piezoelectric effect integrated into the mechatronic system will be used an actuation element. The subject of this paper is structures with more than 1 degrees of freedom appropriate for different microand nano-applications.The kinematic design of the actuator involves specifying the kinematic structure and required raw geometric data like actuator force and motion. Here the synthesized kinematic structures using the structured piezo ceramics are tense integrity closed structures. A fine tuning of geometric and material parameters is performed in an iterative process based on a lot of partial tasks to be achieved, with respect to: modeling, FE-simulation, design, control and experimental investigation of mechatronic handling device for microand nano-operations.

Theory and Practice of Robots and Manipulators, 1995

The present paper studies parallel manipulators and the possibilities for synthesis of their impe... more The present paper studies parallel manipulators and the possibilities for synthesis of their impedance parameters — damping and compliance. A mechanical model is presented, accounting for the closeness of the mechanical structure. Synthesis of impedance parameters of the end effector is performed as a function of the impedance parameters in the manipulator joints, at different manipulator structures. The influence of the manipulator position and geometry on the impedance parameters is considered. An optimization procedure for stiffness synthesis is proposed, by choosing the optimization parameters to be stiffnesses in joints as well as manipulator geometric parameters.

In present work a development of the passive approach is made to design of human oriented robots.... more In present work a development of the passive approach is made to design of human oriented robots. Model of robots with controllable compliance modules on the base and cable transmissions is developed that creates a natural security in the interaction with human. In the paper computer model of 4R robot is developed and simulated using Solid Dynamics 2004+ program software. Computer simulations of the robot compliance behavior are carried out. Influence of the compliance on the position control and on the motor torques is been evaluated when changing based mechanical characteristics. The results obtained from calculation of the mechanical parameters are also illustrated graphically. A model with animation of motion is obtained.

International Journal of Advanced Robotic Systems, 2015

An important task for the precize manipulators desigh is the ensuring realization of the complian... more An important task for the precize manipulators desigh is the ensuring realization of the compliance motion. There exist two known methods for this task-active and passive one. In this paper the possibilities for realization of passive compliance are investigated which are more effective for humanmanipulator interaction. Two basic approaches are clearly pointed out for this purpose -by means of controllable complient ellements in the joints and by antagonistic complient joint actuators. The influence of the constant and variable actuator stiffness is investigated in this work in case of their linear and non-linear joint allocation. The possibilities are revealed for the different approaches for the stiffness modulling and the possibilities for its decoupling from possition.

The paper treats hybrid manipulators comprising a serial anthropomorphic kinematic chain and redu... more The paper treats hybrid manipulators comprising a serial anthropomorphic kinematic chain and redundant number of parallel actuating kinematic chains for linear displacements.The manipulator stiffness is presented in the study, as a function of the redundant actuating forces. Schemes for manipulator control are outlined, based on the antagonistic stiffness. To apply those schemes, approaches of generating the compliance admissible bounds are proposed. Computer simulations are performed and the results are graphically illustrated.

The robots sharing space and surrounding environment with human being are called friendly with ma... more The robots sharing space and surrounding environment with human being are called friendly with man robots. They must posses compliance, to emanate safety and security, to be shock protected. In the work presented in this paper basic mechanical characteristics are pointed out determining the safety in the "human-robot" interaction and some approaches for their modulation. A special attention is paid to the passive approaches, which are more suitable for the securing safety in the "human-robot" interaction. Some algorithms are shown for modulation of inertia, damping and stiffness in the passive variant. The disadvantages of this approach are pointed out and some alternative solutions are developed.

In the paper, different approaches for compliance control for human oriented robots are revealed.... more In the paper, different approaches for compliance control for human oriented robots are revealed. The approaches based on the nonantagonistic and antagonistic actuation are compared. In addition, an approach is investigated in this work for the compliance and the position control in the joint by means of antagonistic actuation. It is based on the capability of the joint with torsion leaf springs to adjust its stiffness. Models of joint stiffness are presented in this paper with antagonistic and non-antagonistic influence of the spring forces on the joint motion. The stiffness and the position control possibilities are investigated and the opportunity for their decoupling as well. Some results of numerical experiments are presented in the paper too.

To execute high- value added operation, such as fine motion control and many other manufacture ta... more To execute high- value added operation, such as fine motion control and many other manufacture tasks, one need to incorporate into the control strategy inputs whose number is larger than the needed minimum. If the number of the actuators is larger than that of the degrees of mobility, the resulting redundancy is called “actuation redundancy”. Actuation forces balance each other in a closed structure and do not execute effective work, but generate stiffness. One can use this property to design control strategies, most generally known as stiffness control by redundant actuation. In the paper are shown schemes of passive stiffness control, feedback stiffness control and stiffness control realized by means of antagonistic actuation.

In the work presented in this paper a class of robots is revealed scheduled for mutual interactio... more In the work presented in this paper a class of robots is revealed scheduled for mutual interaction with the human being. These are robots that can join together mobility and manipulation. Mobile manipulator systems hold promise in many industrials and service applications including manipulations, assembly, inspection and work in hazardous environments. Virtual variants of wheeled mobile robots WMR are derived in the present investigation. A generalised kinematics model of nonholonomic WMR is presented in this work. The direct and reverse problem of the kinematics of nonholonomic WMR is also shown. The usage of the kinematics model for control of WMR in mobile tasks or in mobile manipulation tasks is suggested.

The paper treats an approach of stiffness control scheme of a serial-parallel manipulator. It com... more The paper treats an approach of stiffness control scheme of a serial-parallel manipulator. It comprises an anthropomorphic kinematic chain and redundant number of parallel actuating chains, fixed to the serial one. The manipulator stiffness is presented in the study as a function of the manipulator position, joint stiffness and antagonistic actuating forces. To realize the stiffness control, an approach of stiffness numerical specification is created. Distributing the internal actuating forces performs the specification of a desired stiffness of the end effector. This approach guarantees the compliance upper bound along a given direction in operation space. A control scheme to generate the required redundant actuating forces and to realize the stiffness control is given in the paper. Computer simulations are performed, applying a minimization procedure in order to generate admissible compliance along a given direction. Desired end effector compliance in operation space is presented ...

A number of researchers (1), (2) outline that purposeful motion under external mechanical disturb... more A number of researchers (1), (2) outline that purposeful motion under external mechanical disturbances and in the absence of any offered feedback is executed in human and in animal natural limb. This is possible because a given level of co- activation of antagonistic muscles defines an equilibrium condition of the joint. Deviation of the limb from this equilibrium state results

International Journal of Intelligent Mechatronics and Robotics, 2013

This work deals with modelling and experimenting of a compliant serial-parallel robot. Using Pseu... more This work deals with modelling and experimenting of a compliant serial-parallel robot. Using Pseudo-Rigid-Body Modelling (PRBM) of elastic structures, a kinematics and stiffness model of a serial-parallel structure has been built. Several approaches for pre-tensioning of a parallel structure with elastic joints were developed in order to eliminate backlashes and improve the performance of its actuators. In this work a robot is designed to inject biological cells with size in the range of 10-30μm. The approaches used for pre-tensioning of the robot have been analysed and subjected to numerical evaluation. Assessing the mechanical parameters of the tensed manipulator has been performed using the following methods: PRBM and Finite Element Analysis (FEA). An experimental set-up for testing a robot prototype has been developed, using an optical system and correlation technique for digital image processing. The experimental results obtained are compared to data received from the numerical experiment.

The subject of this paper is motion study of the mechatronic system for manipulation and processi... more The subject of this paper is motion study of the mechatronic system for manipulation and processing of micro/nano operations. First it was synthesized the kinematic chain of the system. Then this system was modelled and simulated in Solid Dynamics (SDS) 2004+ environment. The obtained results are necessary for final development of the real prototype. Three piezoelements with range of motion 8 μm are used, realizing 1 translation and 2 rotations, necessary for micro/nano scanning operations. They are suitable for many micro/nano manipulations requiring high dynamics and velocity. An experimental stage was created for investigation of the end-effector motion trajectory. The experimental study was performed by means of the digital speckle photography method and Fourier transforms. The obtained results are presented.

Journal of Theoretical and Applied Mechanics, 2014

Consider complex problems or complex environment, where the introduction of robotized automation ... more Consider complex problems or complex environment, where the introduction of robotized automation is needed. Then, as outlined in a number of papers, manipulation robots should have more inputs than the necessary minimum

In the present work a methodology is developed for synthesis of closed structures for microand na... more In the present work a methodology is developed for synthesis of closed structures for microand nano-applications, utilizing the advantages of structured piezo-ceramics, tense piezo-actuators and closed robot kinematics structures. The synthesis of closed kinematic structure with piezoceramic actuators is investigated for three case studies: А) Synthesis for parallel structures in which the basic links are connected in between, only by means of driving chains of the piezoceramic actuators. B) Synthesis for parallel structures in which the basic links are connected in between in a serial chain. The driving chains of the piezoceramic actuators are attached parallel to the links of the basic serial chain. C) Synthesis for parallel structures in which the basic links are connected in between in a parallel chain. The driving chains of the piezoceramic actuators are attached parallel to the links of these chain. A synthesis of kinematics schemes with definite degrees of mobility based on t...

This paper presents actually work from development of mechatronic handling devices able to accomp... more This paper presents actually work from development of mechatronic handling devices able to accomplish certain microand/or nano operation tasks. Piezo ceramic structures with (3,1)-piezoelectric effect integrated into the mechatronic system will be used an actuation element. The subject of this paper is structures with more than 1 degrees of freedom appropriate for different microand nano-applications.The kinematic design of the actuator involves specifying the kinematic structure and required raw geometric data like actuator force and motion. Here the synthesized kinematic structures using the structured piezo ceramics are tense integrity closed structures. A fine tuning of geometric and material parameters is performed in an iterative process based on a lot of partial tasks to be achieved, with respect to: modeling, FE-simulation, design, control and experimental investigation of mechatronic handling device for microand nano-operations.

Theory and Practice of Robots and Manipulators, 1995

The present paper studies parallel manipulators and the possibilities for synthesis of their impe... more The present paper studies parallel manipulators and the possibilities for synthesis of their impedance parameters — damping and compliance. A mechanical model is presented, accounting for the closeness of the mechanical structure. Synthesis of impedance parameters of the end effector is performed as a function of the impedance parameters in the manipulator joints, at different manipulator structures. The influence of the manipulator position and geometry on the impedance parameters is considered. An optimization procedure for stiffness synthesis is proposed, by choosing the optimization parameters to be stiffnesses in joints as well as manipulator geometric parameters.

In present work a development of the passive approach is made to design of human oriented robots.... more In present work a development of the passive approach is made to design of human oriented robots. Model of robots with controllable compliance modules on the base and cable transmissions is developed that creates a natural security in the interaction with human. In the paper computer model of 4R robot is developed and simulated using Solid Dynamics 2004+ program software. Computer simulations of the robot compliance behavior are carried out. Influence of the compliance on the position control and on the motor torques is been evaluated when changing based mechanical characteristics. The results obtained from calculation of the mechanical parameters are also illustrated graphically. A model with animation of motion is obtained.

International Journal of Advanced Robotic Systems, 2015

An important task for the precize manipulators desigh is the ensuring realization of the complian... more An important task for the precize manipulators desigh is the ensuring realization of the compliance motion. There exist two known methods for this task-active and passive one. In this paper the possibilities for realization of passive compliance are investigated which are more effective for humanmanipulator interaction. Two basic approaches are clearly pointed out for this purpose -by means of controllable complient ellements in the joints and by antagonistic complient joint actuators. The influence of the constant and variable actuator stiffness is investigated in this work in case of their linear and non-linear joint allocation. The possibilities are revealed for the different approaches for the stiffness modulling and the possibilities for its decoupling from possition.

The paper treats hybrid manipulators comprising a serial anthropomorphic kinematic chain and redu... more The paper treats hybrid manipulators comprising a serial anthropomorphic kinematic chain and redundant number of parallel actuating kinematic chains for linear displacements.The manipulator stiffness is presented in the study, as a function of the redundant actuating forces. Schemes for manipulator control are outlined, based on the antagonistic stiffness. To apply those schemes, approaches of generating the compliance admissible bounds are proposed. Computer simulations are performed and the results are graphically illustrated.

The robots sharing space and surrounding environment with human being are called friendly with ma... more The robots sharing space and surrounding environment with human being are called friendly with man robots. They must posses compliance, to emanate safety and security, to be shock protected. In the work presented in this paper basic mechanical characteristics are pointed out determining the safety in the "human-robot" interaction and some approaches for their modulation. A special attention is paid to the passive approaches, which are more suitable for the securing safety in the "human-robot" interaction. Some algorithms are shown for modulation of inertia, damping and stiffness in the passive variant. The disadvantages of this approach are pointed out and some alternative solutions are developed.

In the paper, different approaches for compliance control for human oriented robots are revealed.... more In the paper, different approaches for compliance control for human oriented robots are revealed. The approaches based on the nonantagonistic and antagonistic actuation are compared. In addition, an approach is investigated in this work for the compliance and the position control in the joint by means of antagonistic actuation. It is based on the capability of the joint with torsion leaf springs to adjust its stiffness. Models of joint stiffness are presented in this paper with antagonistic and non-antagonistic influence of the spring forces on the joint motion. The stiffness and the position control possibilities are investigated and the opportunity for their decoupling as well. Some results of numerical experiments are presented in the paper too.

To execute high- value added operation, such as fine motion control and many other manufacture ta... more To execute high- value added operation, such as fine motion control and many other manufacture tasks, one need to incorporate into the control strategy inputs whose number is larger than the needed minimum. If the number of the actuators is larger than that of the degrees of mobility, the resulting redundancy is called “actuation redundancy”. Actuation forces balance each other in a closed structure and do not execute effective work, but generate stiffness. One can use this property to design control strategies, most generally known as stiffness control by redundant actuation. In the paper are shown schemes of passive stiffness control, feedback stiffness control and stiffness control realized by means of antagonistic actuation.

In the work presented in this paper a class of robots is revealed scheduled for mutual interactio... more In the work presented in this paper a class of robots is revealed scheduled for mutual interaction with the human being. These are robots that can join together mobility and manipulation. Mobile manipulator systems hold promise in many industrials and service applications including manipulations, assembly, inspection and work in hazardous environments. Virtual variants of wheeled mobile robots WMR are derived in the present investigation. A generalised kinematics model of nonholonomic WMR is presented in this work. The direct and reverse problem of the kinematics of nonholonomic WMR is also shown. The usage of the kinematics model for control of WMR in mobile tasks or in mobile manipulation tasks is suggested.

The paper treats an approach of stiffness control scheme of a serial-parallel manipulator. It com... more The paper treats an approach of stiffness control scheme of a serial-parallel manipulator. It comprises an anthropomorphic kinematic chain and redundant number of parallel actuating chains, fixed to the serial one. The manipulator stiffness is presented in the study as a function of the manipulator position, joint stiffness and antagonistic actuating forces. To realize the stiffness control, an approach of stiffness numerical specification is created. Distributing the internal actuating forces performs the specification of a desired stiffness of the end effector. This approach guarantees the compliance upper bound along a given direction in operation space. A control scheme to generate the required redundant actuating forces and to realize the stiffness control is given in the paper. Computer simulations are performed, applying a minimization procedure in order to generate admissible compliance along a given direction. Desired end effector compliance in operation space is presented ...

A number of researchers (1), (2) outline that purposeful motion under external mechanical disturb... more A number of researchers (1), (2) outline that purposeful motion under external mechanical disturbances and in the absence of any offered feedback is executed in human and in animal natural limb. This is possible because a given level of co- activation of antagonistic muscles defines an equilibrium condition of the joint. Deviation of the limb from this equilibrium state results

International Journal of Intelligent Mechatronics and Robotics, 2013

This work deals with modelling and experimenting of a compliant serial-parallel robot. Using Pseu... more This work deals with modelling and experimenting of a compliant serial-parallel robot. Using Pseudo-Rigid-Body Modelling (PRBM) of elastic structures, a kinematics and stiffness model of a serial-parallel structure has been built. Several approaches for pre-tensioning of a parallel structure with elastic joints were developed in order to eliminate backlashes and improve the performance of its actuators. In this work a robot is designed to inject biological cells with size in the range of 10-30μm. The approaches used for pre-tensioning of the robot have been analysed and subjected to numerical evaluation. Assessing the mechanical parameters of the tensed manipulator has been performed using the following methods: PRBM and Finite Element Analysis (FEA). An experimental set-up for testing a robot prototype has been developed, using an optical system and correlation technique for digital image processing. The experimental results obtained are compared to data received from the numerical experiment.

The subject of this paper is motion study of the mechatronic system for manipulation and processi... more The subject of this paper is motion study of the mechatronic system for manipulation and processing of micro/nano operations. First it was synthesized the kinematic chain of the system. Then this system was modelled and simulated in Solid Dynamics (SDS) 2004+ environment. The obtained results are necessary for final development of the real prototype. Three piezoelements with range of motion 8 μm are used, realizing 1 translation and 2 rotations, necessary for micro/nano scanning operations. They are suitable for many micro/nano manipulations requiring high dynamics and velocity. An experimental stage was created for investigation of the end-effector motion trajectory. The experimental study was performed by means of the digital speckle photography method and Fourier transforms. The obtained results are presented.

Journal of Theoretical and Applied Mechanics, 2014