Dynamic modelling and control of a flexible manipulator.

This thesis presents investigations into dynamic modelling and control of a flexible
manipulator system. The work on dynamic modelling involves finite element and symbolic
manipulation techniques. The control strategies investigated include feedforward control
using command shaping techniques and combined feedforward and feedback control
schemes. A constrained planar single-link flexible manipulator is used as test and verification
platform throughout this work.
Dynamic model of a single-link flexible manipulator incorporating structural
damping, hub inertia and payload is developed using the finite element method. Experiments
are performed on a laboratory-scale single-link flexible manipulator with and without
payload for verification of the developed dynamic model. Simulated and experimental system
responses to a single-switch bang-bang torque input are presented in the time and frequency
domains. Resonance frequencies of the system for the first three modes are identified. The
performance and accuracy of the simulation algorithm are studied in comparison to the
experimental results in both domains. The effects of damping and payload on the dynamic
behaviour of the manipulator are addressed. Moreover, the impact of using higher number of
elements is studied.
The application of a symbolic manipulation approach for modelling and performance
analysis of a flexible manipulator system is investigated. System transfer function can be
retained in symbolic form using this approach and good approximation of the system transfer
function can be obtained. Relationships between system characteristics and parameters such
as payload and hub inertia are accordingly explored. Simulation and experimental exercises
are presented to demonstrate the effectiveness of the symbolic approach in modelling and
simulation of the flexible manipulator system.
Simulation and experimental investigations into the development of feedforward
control strategies based on command shaping techniques for vibration control of flexible
manipulators are presented. The command shaping techniques using input shaping, low-pass
and band-stop filters are considered. The command shaping techniques are designed based on
the parameters of the system obtained using the unshaped bang-bang torque input.
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Abstract
Performances of the techniques are evaluated in terms of level of vibration reduction, time
response specifications, robustness to error in natural frequencies and processing times. The
effect of using higher number of impulses and filter orders on the system performance is also
investigated. Moreover, the effectiveness of the command shaping techniques in reducing
vibrations due to inclusion of payload into the system is examined. A comparative assessment
of the performance of the command shaping techniques in vibration reduction of the system
is presented.
The development of hybrid control schemes for input tracking and vibration
suppression of flexible manipulators is presented. The hybrid control schemes based on
collocated feedback controllers for rigid body motion control with non-collocated PID
control and feedforward control for vibration suppression of the system are examined. The
non-collocated PID control is designed utilising the end-point deflection (elastic deformation)
feedback whereas feedforward control is designed using the input shaping technique. The
developed hybrid schemes are tested within the simulation environment of the flexible
manipulator with and without payload. The performances of the control schemes are
evaluated in terms of input tracking capability and vibration suppression of the flexible
manipulator. Initially, a collocated PD utilising the hub-angle and hub-velocity feedback
signals is used as a feedback controller. Subsequently, to achieve uniform performance in the
presence of a payload, a collocated adaptive control is designed based on pole-assignment
self-tuning control scheme. Lastly, a comparative assessment of the performance of the
hybrid control schemes is presented.