Title page for ETD etd-01262003-204800


Type of Document Dissertation
Author Omar, Hanafy M.
Author's Email Address haomar@vt.edu
URN etd-01262003-204800
Title Control of Gantry and Tower Cranes
Degree PhD
Department Engineering Science and Mechanics
Advisory Committee
Advisor Name Title
Nayfeh, Ali H. Committee Chair
Adjerid, Slimane Committee Member
Hendricks, Scott L. Committee Member
Kachroo, Pushkin Committee Member
Ragab, Saad A. Committee Member
Keywords
  • Fuzzy Control
  • Gain-Scheduling Feedback
  • Anti-Swing Control
  • Tower Crane
  • Time-Delayed Feedback
  • Gantry Crane
Date of Defense 2003-01-24
Availability unrestricted
Abstract
The main objective of this work is to design robust, fast, and

practical controllers for gantry and tower cranes. The controllers are

designed to transfer the load from point to point as fast as

possible and, at the same time, the load swing is kept small

during the transfer process and completely vanishes at the load

destination. Moreover, variations of the system parameters, such

as the cable length and the load weight, are also included.

Practical considerations, such as the control action power, and

the maximum acceleration and velocity, are taken into account. In

addition, friction effects are included in the design using a

friction-compensation technique.

The designed controllers are based on two approaches. In the

first approach, a gain-scheduling feedback controller is designed

to move the load from point to point within one oscillation

cycle without inducing large swings. The settling time of the

system is taken to be equal to the period of oscillation of the

load. This criterion enables calculation of the controller

feedback gains for varying load weight and cable length. The

position references for this controller are step functions.

Moreover, the position and swing controllers are treated in a

unified way. In the second approach, the transfer process and the

swing control are separated in the controller design. This

approach requires designing two controllers independently: an

anti-swing controller and a tracking controller. The objective of

the anti-swing controller is to reduce the load swing. The

tracking controller is responsible for making the trolley follow

a reference position trajectory. We use a PD-controller for tracking, while the anti-swing controller is designed using three different methods: (a) a classical PD controller, (b) two controllers based on a delayed-feedback technique, and (c) a fuzzy logic controller that maps the delayed-feedback controller performance.

To validate the designed controllers, an experimental setup was

built. Although the designed controllers work perfectly in the

computer simulations, the experimental results are unacceptable

due to the high friction in the system. This friction

deteriorates the system response by introducing time delay, high

steady-state error in the trolley and tower positions, and high

residual load swings. To overcome friction in the tower-crane

model, we estimate the friction, then we apply an opposite

control action to cancel it. To estimate the friction force, we

assume a mathematical model and estimate the model coefficients

using an off-line identification technique using the method of

least squares.

With friction compensation, the experimental results are in good

agreement with the computer simulations. The gain-scheduling

controllers transfer the load smoothly without inducing an

overshoot in the trolley position. Moreover, the load can be

transferred in a time near to the optimal time with small swing

angles during the transfer process. With full-state feedback,

the crane can reach any position in the working environment

without exceeding the system power capability by controlling the

forward gain in the feedback loop. For large distances, we have to

decrease this gain, which in turn slows the transfer process.

Therefore, this approach is more suitable for short distances. The

tracking-anti-swing control approach is usually associated with

overshoots in the translational and rotational motions. These

overshoots increase with an increase in the maximum acceleration

of the trajectories . The transfer time is longer than that

obtained with the first approach. However, the crane can follow

any trajectory, which makes the controller cope with obstacles in

the working environment. Also, we do not need to recalculate the

feedback gains for each transfer distance as in the

gain-scheduling feedback controller.

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