Gursel Alici

Optimum synthesis of planar parallel manipulators based on kinematic isotropy and force balancing

This paper deals with an optimum synthesis of planar parallel manipulators using two constrained optimisation procedures based on the minimization of: (i) the overall deviation of the condition number of manipulator Jacobian matrix from the ideal/isotropic condition number, and (ii) bearing forces throughout the manipulator workspace for force balancing. A revolute jointed planar parallel manipulator is used as an example to demonstrate the methodology. The parameters describing the manipulator geometry are obtained from the first optimisation procedure, and subsequently, the mass distribution parameters of the manipulator are determined from the second optimisation procedure based on force balancing. Optimisation results indicate that the proposed optimisation approach is systematic, versatile and easy to implement for the optimum synthesis of the parallel manipulator and other kinematic chains. This work contributes to previously published work from the point of view of being a systematic approach to the optimum synthesis of parallel manipulators, which is currently lacking in the literature.

Special class of positive definite functions for formulating adaptive micro/nano manipulator control

This paper presents a special class of positive definite functions for the formulation of adaptive control strategies, specifically in the research of an effective control algorithm for piezoelectric actuation systems in micro/nano manipulation. To deal with the control problems of unknown system parameters, nonlinear hysteresis effects, and disturbances in the piezoelectric actuation systems, an adaptive control methodology is proposed. Using the saturation function derived from a positive definite function to formulate the control methodology, the closed-loop system stability can be guaranteed. Furthermore, the control methodology is proposed to track a desired motion trajectory in position, velocity, and acceleration. In this paper, a special positive definite function is introduced and a control formulation as well as a stability analysis is detailed. Implementation of the control methodology is practical and requires only a knowledge of the initial estimate of the system parameters. In this study, control experiments conducted using the proposed control approach on a piezoelectric actuation system has demonstrated a promising ability in tracking a specified motion trajectory. With this control capability in the presence of unknown system parameters, hysteresis, and external disturbance, the adaptive methodology is very attractive in the field of micro/nano manipulation in which high performance control applications could be realised

A mathematical model for a pneumatically actuated robotic fibre placement system

In this paper, a lumped parameter model of a robotic fibre placement system consisting of a Motoman SK-120 robot, a force/torque sensor, a pneumatic actuator and a stiff workpiece holder is developed and experimentally verified for the purpose of predicting and characterising the dynamic behaviour of the fibre placement system. Special attention has been given to the dynamics of the actuator which is represented as a mass confined to move between two non-linear springs and dampers. The overall model containing manipulator, force sensor, pneumatic actuator and the workpiece holder dynamics is of the tenth order. Step response experiments were conducted to verify the model and to determine the approximate values of the parameters in the mathematical model. The results prove that the established model is accurate enough to explain the dynamic behaviour of the fibre placement system and it can be employed to quantify the influence of the dynamics of the pneumatic actuator on the constant force-based fibre placement. The well-known fact that the dynamics of the pneumatic actuator varies with the piston position has also been experimentally demonstrated.

Constrained structural optimisation of a revolute-jointed planar parallel manipulator

This paper addresses kinematic analysis and constrained structural optimisation of a five-bar planar parallel manipulator articulated with revolute joints only. The kinematics of the manipulator is investigated, and its Jacobian matrix as a function of the input joint positions has been formulated. An objective function based on minimizing the overall deviation of the condition number of the manipulator Jacobian matrix from the ideal condition number throughout the workspace of the manipulator has been employed to determine the link lengths subjected to a set of optimisation constraints. Optimisation results indicate that the proposed optimisation method is systematic, versatile and easy to implement for the optimal synthesis of the five-bar parallel manipulator and other kinematic chains.

Kinematic identification of a closed-chain manipulator using a laser interferometry based sensing technique

This paper focuses on a technique for the identification of parameters needed for kinematic modeling of an industrial manipulator, Motoman SK 120, with a parallel five-bar mechanism. Two classical estimation techniques, nonlinear and linear least squares, are employed to determine the parameters from a number of manipulator end point positions measured by a high precision laser tracking system with a single beam laser interferometer. The kinematics parameters of the five-bar mechanism in the topology of the manipulator are considered during kinematic modeling and parameter identification procedure. Numerical results presented demonstrate that the root mean square position error can be improved by at least 60% with the identified parameters. Although slightly different parameters are obtained from both estimation techniques, the resulting root mean square position errors remain the same. When the kinematics parameters of the five-bar mechanism are not included in the model for parameter estimation, the improvement in the root mean square position errors has been limited to 35%.

Contact type determination for cylindrical pair adjustment

Adjustment for a cylindrical pair is a fundamental manipulation, which can be utilised in dynamic assembly and reconfigurable workholding systems. In this paper, a comprehensive dynamic analysis associated with the adjustment of a cylindrical pair for a single DOF motion case is developed and its relevance to the adjustment operation is investigated. It is assumed that the inner link of the lower pair is attached to a Cartesian manipulator, which is considered to be the active device and the outer link is attached to an articulated robot. Also, a methodology to uniquely identify the type of contact between the two links is developed. The type of contact determines the appropriate translation/orientation adjustment. Analysis results indicate that, depending on the size of the outer link and the friction coefficient, the contact type is either single point (translational) or double point (orientation).

Experimental Investigation of 2D Cylindrical Pair Height Adjustment in a Static Environment

Abstract In this paper, a new method for adjusting the height of a cylindrical pair in a static environment is presented. Generic force formulations are established. A technique to uniquely identify the type of contact based on the force and torque data provided by a wrist mounted F/T sensor is developed. For small clearances between the links, the assumption of using zero misalignment in the formulations is justified by means of simulations. Friction, which is a key parameter for contact type identification is experimentally determined. Preliminary experimental results indicate that the presented technique is effective in determining the type of contact for the height adjustment operation.

Description and kinematic analysis of a planar micromanipulation system based on flexure joints

This paper addresses description and kinematic analysis of a micromanipulation system based on revolute typeflexure joints. It is a five-bar planar parallel manipulator dedicated to applications requiring micro/nano scale motion. The forward kinematics problem is formulated and then solved by employing two separate approaches; (i) linearising the trigonometric functions (TF) and (ii) employing an approximate method based on linearising generalised velocity relationship for small joint space and Cartesian space displacements. Further, the velocity of the manipulator in Cartesian space is determined and compared to the results obtained from (i) linearising TF in the Jacobian matrix and, from (ii) using a constant Jacobian matrix. Numerical results prove that linearising TF in the kinematics equations and Jacobian matrix gives results close to the exact results. Using a constant Jacobian approach for analysing kinematics of micromanipulation systems contradicts the order of accuracy expected from such systems.

Model Development and System Identification of a Cartesian Manipulator Using a Laser-Interferometry Based Measurement System

Abstract This paper describes the development and verification of a dynamic model for a Cartesian manipulator. Experiments and simulations are performed in order to determine the parameters of the established model. Optical shaft encoder feedback was proven to be unsatisfactory predominantly due to elasticity of the couplings and ball-nut backlash. As a result, a laser interferometry-based measurement system was used for position data acquisition. Experimental results highlight the occurrence of limit-cycles due to inherent friction by the rails, ball-nuts and bearings. The derived model parameters were determined both by theoretical calculations and experimental response observation.