Peter Mitrouchev

Contact identification for assembly–disassembly simulation with a haptic device

Assembly/Disassembly (A/D) simulations using haptic devices are facing difficulties while simulating insertion/extraction operations, such as removing cylinders from holes. In order to address this configuration as well as others, an approach based on contact identification between components is presented in this paper. This approach can efficiently contribute either to a new A/D simulation preparation process relying on two types of shape representations (mesh and CAD NURBS models), or directly to the real time simulation process when it is performed with 6D haptic devices. The model processing pipeline is described and illustrated to show how information can be propagated and used for contact detection. Then, the contact identification process is introduced and illustrated through an example.

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.

Disassembly operations’ efficiency evaluation in a virtual environment

Disassembly operations play a very important role during the initial design phase of industrial products. The available disassembly evaluation methods today seldom make disassembly as the preferred end-of-life solution for the reuse of parts or components in an economically sustainable way for lower value products. In virtual environment (VE), for instance, a human model is often involved in a digital mock-up model for assembly/disassembly (A/D) evaluation. However, it has limited application areas because of the high cost investment. Focusing on the evaluation of disassembly operations in a VE, a method based on five new criteria – visibility of a part, disassembly angles, number of tools’ changes, path orientation changing, and sub-assembly stability – is proposed here. All five criteria are presented by automatically calculated dimensionless coefficients, thus allowing the evaluation of the complexity of disassembly sequences in a VE. For this purpose, a mixed virtual reality disassembly environment based on Python programming language has been developed, using Visualisation Toolkit and Open Dynamics Engine libraries. The results of the analysis and findings demonstrate the feasibility of the proposed approach thus providing significant assistance for the evaluation of disassembly sequences during Product Development Process.

Analysis of inverse kinematics and dynamics of a novel 6-degree-of-freedom wire-driven parallel gantry crane robot

Every type of wire-driven parallel robots can be used in cargo handling as a robot crane. Concerning the 6-degree-of-freedom (DOF) wire-driven parallel robot with three wires, its mechanism configuration belongs to URPMs (Under Restrained Positioning Mechanisms), if one translational or rotational DOF rigid mechanism is added to each of its kinematic chains. In this case the mechanism becomes a new type 6-DOF robot. It has been found, in the research survey that the mechanism configuration of such kind of 6-DOF robot CABLEV is not powerful enough because of its limited workspace. A novel 6-DOF parallel crane robot containing three rigid-and-flexible hybrid sub-chains is proposed which can access to a larger workspace. The differential flatness of its inverse kinematics and dynamics is analyzed by a simulation. The results of this simulation will lay a basis for the future trajectory tracking control of the payload.

Disassembly Process Simulation in Virtual Reality Environment

Integration of disassembly operations simulation during product design is an important issue today. A method for ergonomic evaluation of disassembly operations is presented here. It is based on three new criteria, presented by dimensionless coefficients: visibility score, neck score and bending score. The method is integrated in a Virtual Reality Disassembly Environment (VRDE) based on Python programming language using mixed VTK (Visualization Toolkit) and ODE (Open Dynamics Engine) libraries. The framework is based on STEP, WRL and STL exchange formats. The proposed method is tested and an example for disassembly sequences evaluation is presented. The results of the analysis and findings demonstrate the feasibility of the proposed approach thus providing significant improvement in Product Development Process (PDP).

Enumeration of Driving Mechanisms in Robotics by Combinatorial Analysis Method

This research deals with the development of a new method for restricted morphological number enumeration for planar pin-jointed driving mechanisms of mobility 1 and 2. It is based on combinatorial analysis by using the symmetries of kinematic chains. Since the restricting criterion is the position of the robot’s frame, different cases of symmetries are addressed. New expressions for calculating the number of positions of the actuators in a mechanism are presented. These help to reduce the number of chains by avoiding those that are isomorphic with regard to the position of the robot frame. The expressions offer a corrected formulation for counting the number of actuators for planar mechanisms in robotics. Different examples of applications for various planar pin-jointed driving mechanisms of mobility 1 and 2 are presented.

Implementation of a Controllable Damper for Suppressing Vibration in the Technological Process

The paper deals with the problem of suppressing vibration of the arm of Motoman SSF200 robot within the frame of the technological process. Based on an overview of literature, a semi-active vibration control system was selected and a double ended magnetorheological damper (MR) was designed. After testing the acceleration of the robot arm in milling operation without the MR damper, the device was employed and the acceleration of the robot arm in four operation modes was experimentally tested.The conducted research has proved that the double ended MR damper can be practically applied for suppressing the vibration of the robot arm. The higher power to the electromagnet of the MR damper is exposed, the better vibration suppression is. This means that by changing the strength of current, the technological process of the robot arm is under control. Thus, control over the technological process is simplified when the physical characteristics of the milled material, milled tool or operation vary.

3D geometric removability analysis for virtual disassembly evaluation

In recent years, Virtual Reality interface has been wildly used to simulate various processes and in particular assembly/disassembly operations during the initial stage of product design. This paper deals with a method for 3D geometric removability analysis for disassembly operation evaluation. It is based on the visibility calculation of 3D Geometric and Removability Analysis. For this purpose three new parameters for evaluation are proposed. They are presented by dimensionless coefficients automatically calculated thus allowing evaluating disassembly sequences complexity in a virtual environment. The proposed method is tested and an example for disassembly operations of a mechanical assembly is presented. Results showed that the Removability is great different within different possible disassembly sequences.

Least Levels Disassembly Graph Method for Selective Disassembly Planning

As known, the number of possible disassembly sequences increases significantly with the number of parts in a product. For selective disassembly, for instance, it is important to eliminate the components unrelated with the target component prior to sequence generation. In order to address this configuration, a method for disassembly sequences generation in the case of selective disassembly is presented in this paper. Based on the least levels of disassembly product graph it allows reducing computation resources. Instead of considering the geometric constrains for each pair of components, the proposed method considers the geometric contact and collision relationships among the components in order to generate the disassembly graph for sequences planning. The method is applied for automatically generating the selective disassembly sequences thus allowing reducing the computation resources and is illustrated through an example.Copyright

Number Enumeration of Planar Pin-Joined Driving Mechanisms

This paper deals with the development of a new method for the morphological number enumeration for planar pin-jointed driving mechanisms applied in robotic design. The method is based on linkage graph presentation by using geometrical symmetries of kinematic chains and combinatorial analysis. The restricting criteria being the position of: the frame, the end-effector and the actuators (motors) of the robot, different cases of symmetries for planar pin-jointed driving mechanisms of mobility 1 and 2 are addressed. New expressions for calculating the number of different possibilities to position the frame, the end-effector and the actuators in a mechanism are presented, thus reducing the number of the possible solutions by avoiding those that are isomorphic. A further consequence of the present work is the ability for it to be extended to mechanisms with three degrees of mobility and more.Copyright