Dimitar Chakarov

Study of the passive compliance of parallel manipulators

This paper studies the characteristic mechanical stiffness or compliance by means of which the interaction of a manipulator with the environment is controlled. A mechanical model of manipulators with parallel structure is presented in which compliance is determined by the shaft stiffnesses in the joints and by the antagonistically acting driving forces. An optimization procedure of the stiffness of a manipulator with a variable structure is proposed. Computer experiments on the compliance of a parallel manipulator have been performed. The results are visualized by means of the compliance ellipses and ellipsoids.

Adjustable Compliance Joint with Torsion Spring for Human Centred Robots

Human-centred robots should be human-friendly, safe and impact-free. The present work is devoted to the problem of adjustable compliance implementation during the human friendly robots design. A new solution of a compliant joint with passive compliance adjustment based on a leaf torsion spring with variable length is presented. It allows independent positioning and stiffness regulation in a wide range. Some basic characteristics of the leaf torsion spring such as: stiffness, compliance, allowable torque, angle of elastic deformation and generated potential energy are analyzed. Thereafter numerical simulations are performed and the influence of the structural parameters on the basic compliant joint characteristics is estimated. Tests with a specially realized prototype of adjustable compliant joint are carried out and the basic characteristics of the prototype are evaluated. The results from the experimental assessment show a very good correlation with the numerical ones.

Synthesis of parallel manipulators with linear drive modules

Abstract A procedure is presented for the synthesis of the mechanical structure of hybrid parallel-serial manipulators with a principal anthropomorphic kinematic chain and infinite number of linear drives. An algorithm for structural synthesis of the manipulators is proposed and some basic structures are created. In addition a dynamical model and a procedure for optimizing synthesis are built. As parameters of optimization, the coordinates of fixing points of linear drives are chosen. Some numerical and physical experiments were performed.

New Exoskeleton Arm Concept Design And Actuation For Haptic Interaction With Virtual Objects

Abstract In the work presented in this paper the conceptual design and actuation of one new exoskeleton of the upper limb is presented. The device is designed for application where both motion tracking and force feedback are required, such as human interaction with virtual environment or rehabilitation tasks. The choice is presented of mechanical structure kinematical equivalent to the structure of the human arm. An actuation system is selected based on braided pneumatic muscle actuators. Antagonistic drive system for each joint is shown, using pulley and cable transmissions. Force/displacement diagrams are presented of two antagonistic acting muscles. Kinematics and dynamic estimations are performed of the system exoskeleton and upper limb. Selected parameters ensure in the antagonistic scheme joint torque regulation and human arm range of motion.

Web-Based Synthesis of Robot Structures for Micro and Nano Manipulations

This paper describes how the web technologies are utilized for a robot system synthesis. A web application is created for automation of the synthesis of closed structures for micro- and nano-applications, utilizing the advantages tense piezo-actuators and closed robot kinematical structures. The algorithm, integrated into the developed web based application, offers a synthesis of robot kinematic chains without extensive knowledge in this domain. The aim is to facilitate synthesis of such kind of kinematic chains from specialists who will generate optimal solutions for automation and robotisation of the requested micro- and nano-process.

Design and Control of a Force Reflecting Arm Exoskeleton for Virtual Reality Applications.

In this paper, the design of an exoskeleton for the upper limb is presented, aimed primarily at training and rehabilitation in virtual environments. A mechanical model of the exoskeleton arm as haptic device is built up and impedance control scheme is selected as the most suitable for force reflection at the arm. The design of a grounded exoskeleton prototype is revealed in the paper. A driving system based on braided pneumatic muscle is selected to ensure natural security in the interaction. Antagonistic drive system for each joint is shown, using pulley and Bowden cable transmissions. An approach is presented for the joint moments control by antagonistic interaction of bundles with different numbers of pneumatic muscles. Control scheme of joint torque by antagonistic interaction is given, too. Computer simulations are performed to provide power reflection by virtual reality (VR), according to scenario of virtual gymnastics.

Powered Upper Limb Orthosis Actuation System Based on Pneumatic Artificial Muscles

Abstract The actuation system of a powered upper limb orthosis is studied in the work. To create natural safety in the mutual “man-robot” interaction, an actuation system based on pneumatic artificial muscles (PAM) is selected. Experimentally obtained force/contraction diagrams for bundles, consisting of different number of muscles are shown in the paper. The pooling force and the stiffness of the pneumatic actuators is assessed as a function of the number of muscles in the bundle and the supply pressure. Joint motion and torque is achieved by antagonistic actions through pulleys, driven by bundles of pneumatic muscles. Joint stiffness and joint torques are determined on condition of a power balance, as a function of the joint position, pressure, number of muscles and muscles

Exoskeleton with Soft Actuation and Haptic Interface

This work presents an active orthotic device with a wearable structure corresponding to the natural motions of the human that can be used for motion capturing and mobility assisting. The exoskeleton structure includes left and right upper limb, left and right lower limb fabricated with light materials and powered by pneumatic artificial muscles. The proposed exoskeleton provides more than fifteen degrees of freedom and can operate in three modes: Motion tracking and data exchange with virtual reality (VR); Haptic device with force-feedback that can display sensory information from a virtual reality to the user; Assistive and rehabilitation device in cases of impaired muscles.

Adjusting the natural stiffness of a pneumatic powered exoskeleton designed as a virtual reality haptic device

This study describes the natural stiffness of a pneumatic powered exoskeleton arm, designed as a haptic device in virtual reality applications. It is important for the haptic device to provide a natural, safe, and comfortable physical mutual human–robot interaction as well as realism for the haptic feedback. To meet these requirements, an exoskeleton possessing an actuation system based on pneumatic artificial muscles and feedforward impedance control is presented. A natural stiffness controller is included to passively adjust the desired stiffness of the exoskeleton. The parameters of the actuation system that determine the natural exoskeleton stiffness are analyzed. A scheme is constructed for joint torque control and end-effector stiffness adjustment under the antagonistic action of the pairs of pneumatic actuators. An optimization-based approach is created for specifying the parameters determining the natural stiffness of the exoskeleton arm. Computer simulations are conducted for a preliminary assessment of options for adjusting the Cartesian stiffness. Additional experiments are performed for specifying the object stiffness according to the scenario of virtual gymnastics.

Mechatronic Scanning System with Integrated Micro Electro Mechanical System Position Sensors

Abstract In this paper, a study of a mechatronic scanning system for application in the microbiology, microelectronics research, chemistry, etc. is presented. Integrated silicon micro electro mechanical system (MEMS) position sensor is used for monitoring the displacement of the scanning system. The utilized silicon MEMS sensors with sidewall embedded piezoresistors possess a number of key advantages such as high sensitivity, low noise and extremely low temperature dependence. Design of 2D scanning system with a travel range of 22 × 22 μm2 has been presented in present work. This system includes a Compliant Transmission Mechanism, (CTM) designed as a complex elastic mechanism, comprising four parallelograms. Computer aided desigh (CAD) model and finite element analysis (FEA) of the Compliant Transmission Mechanism mechanisms have been carried out. A prototype of the scanning system is fabricated, based on CAD model. An experimental set-up of an optical system and a correlation technique for digital image processing have been used for testing the scanning system prototype. Results of the experimental investigations of the prototyped scanning system are also presented.