Joshua Vaughan

Control of Tower Cranes With Double-Pendulum Payload Dynamics

The usefulness of cranes is limited because the payload is supported by an overhead suspension cable that allows oscillation to occur during crane motion. Under certain conditions, the payload dynamics may introduce an additional oscillatory mode that creates a double pendulum. This paper presents an analysis of this effect on tower cranes. This paper also reviews a command generation technique to suppress the oscillatory dynamics with robustness to frequency changes. Experimental results are presented to verify that the proposed method can improve the ability of crane operators to drive a double-pendulum tower crane. The performance improvements occurred during both local and teleoperated control.

Reducing Vibration by Digital Filtering and Input Shaping

The residual vibration of flexible systems can be reduced by shaping the reference command with notch filters, low-pass filters, and input shapers. Since the introduction of robust input shaping, there has been substantial evidence that input shaping is better than both notch and low-pass filtering for suppressing vibration in mechanical systems. Much of this evidence is empirical comparisons between traditional filters and robust input shapers. Given the large variety of filters and shapers and the large number of design strategies and parameters, there is still some uncertainty as to which approach is better. This paper seeks to end this debate by proving that notch and low-pass filters are never better than input shapers for suppressing mechanical vibration. This paper expands on previous efforts by presenting a proof showing that input shapers suppress vibration more quickly than notch or low-pass filters. The problem of suppressing multi-mode vibration is also examined. Experimental results from a portable bridge crane verify key theoretical results.

Robust Negative Input Shapers for Vibration Suppression

Input shaping is a control method that limits motion-induced oscillation in vibratory systems by intelligently shaping the reference command. As with any control method, the robustness of input shaping to parameter variations and modeling errors is an important consideration. For input shaping, there exists a fundamental compromise between robustness to such errors and system rise time. For all types of shapers, greater robustness requires a longer duration shaper, which degrades rise time. However, if a shaper is allowed to contain negative impulses, then the shaper duration may be shortened with only a small cost of robustness and possible high-mode excitation. This paper presents a thorough analysis of the compromise between shaper duration, robustness, and possible high-mode excitation for several negative input-shaping methods. In addition, a formulation for specified negative amplitude, specified insensitivity shapers is presented. These shapers provide a continuous spectrum of solutions for the duration/robustness/high-mode excitation trade-off. Experimental results from a portable bridge crane verify the theoretical predictions.

Predictive Graphical User Interface Elements to Improve Crane Operator Performance

Operating cranes is challenging because the payload significantly lags behind the control input and can undergo large amplitude oscillations. While significant work has been directed at reducing the payload swing, little effort has been placed on reducing the time lag. There is a good reason for neglecting the time lag; it cannot be eliminated. It is a result of the physical limitations of the crane; motor torque limits coupled with the very large inertia of cranes and their payloads cause sluggish behavior. Experienced crane operators become accustomed to the time lag and develop the skill to start decelerating the crane well before the desired stopping location. This paper presents a control method that aids the human operator by graphically displaying a prediction of where the crane will stop. This predictive element is combined with an input-shaping controller that both reduces the payload swing and simplifies the implementation of the predictive element. Results from a study of crane operators show that the proposed control system significantly improves tower crane performance, in terms of both task completion time and positioning accuracy.

Advantages of using command shaping over feedback for crane control

Cranes are the primary heavy lifters for a wide variety of industries. However, all cranes share the same important limitation on efficiency: payload oscillation. Given the significance of cranes, it is not surprising that a large amount of research has been dedicated to eliminating this oscillation. Much of this research has been directed toward feedback control methods. Another portion of the work has focused primarily on command-shaping methods. This paper explores the problems with using feedback for crane control, which include the difficulty in sensing the crane payload, widely varying system dynamics, and human-operator compatibility. In light of these problems, input shaping is shown to be a favorable solution.

Control of Crane Payloads That Bounce During Hoisting

Crane payloads exhibit unwanted motions such as swings, twists, and bounces that cause safety hazards and decrease performance. Numerous controllers have been developed to reduce payload swing. However, much less consideration has been given to bouncing in the vertical direction, which in some cases can also excite pitching of the payload. This dynamic effect most often arises when the payload is heavy and the suspension cables are long. This brief presents a mathematical model of a bouncing crane payload. Then, a method for generating commands to suppress the oscillations is developed and evaluated. Experiments on a tower crane demonstrate the improved performance provided by the proposed control method.

DYNAMICS AND CONTROL OF CRANE PAYLOADS THAT BOUNCE AND PITCH DURING HOISTING

The natural sway of crane payloads is detrimental to safe and efficient operation. Most crane control research has focused on oscillation induced by motion of the overhead trolley that is perpendicular to the vertical suspension cables. Little consideration has been given to bouncing oscillation in the hoist direction and pitching oscillation with respect to mass center of the payload. These dynamic effects arise in cases when the suspension cables are very long. These oscillations may interfere with the ability of the crane operators to accurately unload the payload at its desired position and orientation. This paper presents a method for generating shaped commands that suppress payload oscillations of bouncing and pitching. Theoretical models are initially used to develop and evaluate the input-shaping control algorithm. Then, experiments performed on a portable tower crane are used to demonstrate the improved response provided by the proposed approach.Copyright

Reducing Overshoot in Human-Operated Flexible Systems

Input shaping accomplishes vibration reduction by slightly increasing the acceleration and deceleration periods of the command. The increase in the deceleration period can lead to system overshoot. This paper presents a new class of reduced-overtravel input shapers that are designed to reduce shaper-induced overtravel from human-operator commands. During the development of these new shapers, an expression for shaper-induced overtravel is introduced. This expression is used as an additional constraint in the input-shaper design process to generate the reduced-overtravel shapers. Experiments from a portable bridge crane verify the theoretical predictions of improved performance. Results from a study of eight industrial bridge crane operators indicate that utilizing the new reduced-overtravel input shapers dramatically reduces task completion time, while also improving positioning accuracy.

Input shapers for reducing overshoot in human-operated flexible systems

Input shaping is a command generation method for creating commands that result in low levels of residual vibration. The vibration reduction is accomplished by slightly increasing the acceleration and deceleration periods of the command. The increase in the deceleration period can lead to system overshoot. This paper presents a new class of Zero Overtravel (ZO) input shapers that are designed to reduce shaper-induced overtravel from human-operator commands. During the development of these new shapers, an expression for shaper-induced overtravel is introduced. This expression is used as an additional constraint in the input shaper design process to generate the ZO shapers. Experiments from a portable bridge crane verify the theoretical predictions.

A study of crane operator performance comparing PD-control and input shaping

Cranes are the primary heavy lifters for a wide variety of industries. However, all cranes suffer from payload oscillation. Numerous feedback-based control methods have been proposed to reduce oscillation. Command-shaping is another method that has received significant attention. This paper compares the two methods for crane control. It also presents a study of twelve novice crane operators using representative input-shaping and feedback control methods. Both feedback control and input shaping reduced average task completion time from the manually controlled case, with input shaping providing the lowest average completion time. Input shaping also allowed the operators to move the trolley through a shorter total path length toward the target, suggesting that input shaping may save energy compared to the feedback and manual control methods.