Zaharuddin Mohamed

Vibration control of a single-link flexible manipulator using command shaping techniques

Abstract This paper presents experimental investigations into the development of feed-forward control strategies for vibration control of a flexible manipulator using command shaping techniques based on input shaping and low-pass and band-stop filtering. A laboratory-scale single-link flexible manipulator is used and various system responses are obtained. Initially, an unshaped bang-bang torque input is used to determine the dynamic response parameters of the system for design and evaluation of the control techniques. Feed-forward controllers are then designed based on the natural frequencies and damping ratios of the system. Experimental results of the response of the manipulator to the shaped and filtered inputs are presented in time and frequency domains. Performances of the techniques are assessed in terms of level of vibration reduction at the natural frequencies, time response specifications, robustness to natural frequency variation and processing time. The effects of the number of impulses and filter order on the performance of the system are investigated. Finally, a comparative assessment of input shaping and filtering techniques is presented.

Dynamic characterisation of a flexible manipulator system

This paper presents theoretical and experimental investigations into the dynamic modelling and characterisation of a flexible manipulator system. A constrained planar single-link flexible manipulator is considered. A dynamic model of the system is developed based on finite element methods. The flexural and rigid dynamics of the system as well as inertia effects and structural damping are accounted in the model. Performance of the algorithm in describing the dynamic behaviour of the system is assessed in comparison to an experimental test-rig. Experimental results are presented for validation of the developed finite element model in the time and frequency domains.

Techniques for vibration control of a flexible robot manipulator

This paper presents investigations into the applications and performance of positive and negative input shapers in command shaping techniques for the vibration control of a flexible robot manipulator. A constrained planar single-link flexible manipulator is considered and the dynamic model of the system is derived using the finite element method. An unshaped bang-bang torque input is used to determine the characteristic parameters of the system for design and evaluation of the input shaping control techniques. The positive and specified amplitude negative input shapers are designed based on the properties of the system. Simulation results of the response of the manipulator to the shaped inputs are presented in the time and frequency domains. Performances of the shapers are examined in terms of level of vibration reduction, time response specifications and robustness to parameters uncertainty. The effects of derivative order of the input shaper on the performance of the system are investigated. Finally, a comparative assessment of the impact amplitude polarities of the input shapers on the system performance is presented and discussed.

PSO-tuned PID controller for a nonlinear gantry crane system

This paper presents development of an optimal PID controller for control of a nonlinear gantry crane system. An improved PSO algorithm based on a priority-based fitness approach is implemented for finding optimal PID parameters. The system dynamic model is derived using Lagrange equation. A combination of PID and PD controllers are utilized for position and oscillation control of the system. System responses including trolley displacement and payload oscillation are observed and analyzed. Simulation is conducted within Matlab environment to verify the performance of the controller. It is demonstrated that the controller is effective to move the trolley as fast as possible to the desired position with low payload oscillation technique.

Finite difference and finite element approaches to dynamic modelling of a flexible manipulator

Abstract This paper presents a comparative investigation of the dynamic characterization of flexible manipulators on the basis of accuracy, computational efficiency and computational requirements using finite difference (FD) and finite element (FE) methods. A constrained planar single-link flexible manipulator is considered. Finite-dimensional simulations of the manipulator are developed using FD and FE methods. The simulation algorithms thus developed are implemented on two computing domains and their performances, on the basis of accuracy in characterizing the behaviour of the manipulator and computational efficiency, are assessed.

Hybrid Input Shaping and Feedback Control Schemes of a Flexible Robot Manipulator

This paper presents investigations into the development of hybrid control schemes for input tracking and vibration control of a flexible robot manipulator. A constrained planar single-link flexible manipulator is considered and the dynamic model of the system is derived using the assume mode method. To study the effectiveness of the controllers, initially a collocated PD control is developed for control of rigid body motion. This is then extended to incorporate input shaper control schemes for vibration control of the system. The positive and modified specified negative amplitude input shapers are designed based on the properties of the system. Simulation results of the response of the manipulator with the controllers are presented in time and frequency domains. The performances of the hybrid control schemes are examined in terms of level of input tracking capability, vibration reduction, time response specifications and robustness to parameters uncertainty in comparison to the PD control. Finally, a comparative assessment of the amplitude polarities of the input shapers to the system performance is presented and discussed.

Finite element approach to dynamic modelling of a flexible robot manipulator: Performance evaluation and computational requirements

This paper presents a performance evaluation and the computational requirements of using the finite element (FE) method for modelling flexible robot manipulators. A constrained planar single-link flexible manipulator is considered. Finite-dimensional simulation of the manipulator is developed using the FE method and is implemented on two computing domains. The simulation performance, on the basis of accuracy in characterizing the behaviour of the manipulator and computational efficiency, are assessed. Copyright

Linear matrix inequality-based robust proportional derivative control of a two-link flexible manipulator

This paper presents the design and development of a robust proportional derivative (PD) controller based on linear matrix inequality (LMI) for the control of a hub angular position and end-point deflection of a planar two-link flexible manipulator. The dynamics of the manipulator is uncertain and time varying due to the variation of payloads that result in large variations in the excitation of flexible modes. Practical design steps are presented in which the LMI-based conditions are formulated to obtain a robust PD gains to control the flexible manipulator. The robust controller has an advantage as compared to the Ziegler-Nichols tuned PD controller as the identified PD gains can be used to control the system under various loading conditions. The performances of the proposed controller are evaluated in terms of input tracking capability of the hub angular position response and level of deflection of both links of the flexible manipulator. Experimental results show that despite using the same sets of PD gains, LMI-PD control provides better robustness and system performance.

Dynamic modelling and characterisation of a two-link flexible robot manipulator

This paper presents an investigation into the dynamic modelling and characterisation of a two-link flexible robot manipulator. A planar two-link flexible manipulator incorporating structural damping, hub inertia and payload that moves in the horizontal plane is considered. A dynamic model of the system is developed using a combined Euler-Lagrange and assumed mode method. Simulation is performed to assess the dynamic model and system responses at the hub and end-point of both links are presented and analysed in time and frequency domains. Moreover, effects of payload on the dynamic characteristics of the flexible manipulator are studied and discussed.

Dynamic modelling of a two-link flexible manipulator system incorporating payload

This paper presents dynamic modelling of a two-link flexible manipulator based on closed-form equations of motion. The kinematic model is based on standard frame transformation matrices describing both rigid rotation and modal displacement, under small deflection assumption. The Lagrangian approach is used to derive the dynamic model of the structure. Links are modelled as Euler-Bernoulli beams with proper clamped-mass boundary conditions. A dynamic model of the system, incorporating structural damping, hub inertia and payload, is developed using finite assumed mode methods. Explicit equations of motions are detailed by assuming two modes of vibration for each link. Moreover, effects of payload on the response of the flexible manipulator are discussed. Extensive results that validate the theoretical derivation are presented in the time and frequency domains.