Ehsan Maleki

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.

Dynamics and Control of a Small-Scale Boom Crane

Cranes are vital to many manufacturing and material-handling processes. However, their physical structure leads to flexible dynamic effects that limit their usefulness. Large payload swings induced by either intentional crane motions or external disturbances decrease positioning accuracy and can create hazardous situations. Boom cranes are one of the most dynamically complicated types of cranes. Boom cranes cannot transfer the payload in a straight line by actuating only one axis of motion because they have rotational joints. This paper presents a nonlinear model of a boom crane. A large range of possible motions is analyzed to investigate the dynamic behavior of the crane when it responds to operator commands. A command-shaping control technique is implemented, and its effectiveness on this nonlinear machine is analyzed. Experimental results verify key theoretical predictions.

Swing Dynamics and Input-Shaping Control of Human-Operated Double-Pendulum Boom Cranes

Boom cranes are used for numerous material-handling and manufacturing processes in factories, shipyards, and construction sites. All cranes lift their payloads by hoisting them up using overhead suspension cables. Boom cranes move payloads by slewing their base about a vertical axis, luffing their boom in and out from the base, and changing the length of the suspension cable. These motions induce payload oscillation. The problem of payload oscillation becomes more challenging when the payload exhibits double-pendulum dynamics that produce two varying frequencies of oscillation. This paper studies the swing dynamics of such cranes. It also applies input shaping to reduce the two-mode oscillatory dynamics. Experiments confirm several of the interesting dynamic effects.

Increasing Crane Payload Swing by Shaping Human Operator Commands

Cranes are commonly used to swing wrecking balls that demolish unwanted buildings and other structures. The crane operator moves the machine back and forth to increase the wrecking ball swing and then attempts to direct the swinging ball at the desired point of impact. By increasing the oscillation, the wrecking ball has more damaging force at impact. The rudimentary control interface, the sluggish dynamic response of the crane, and the limited field of view make this a challenging problem for the human operator. Although shaping human operator commands has traditionally been used to reduce oscillation, a related design process can be used to develop oscillation-amplifying commands. This paper presents such a command-shaping method that aids the operator in maximizing the swing of a crane payload. The effectiveness of the command shapers is verified through numerous simulations and experiments.

Experimental Analysis for Wind Induced Disturbance Rejection on Bridge Crane Structures

This paper describes the development of a feedback controller for rejecting wind disturbances on a crane payload. The goal of this research is to perform in-situ parameter sensitivity testing that is specific to a given crane structure. Through experimentation, this paper evaluates the robustness of a closed-loop controller that implements station keeping on a bridge crane. A set of general trends were developed to describe how altering system parameters and operating conditions affected controller performance. Such findings are not limited to single parameter characterization and can be extended to multiple variables given specific system specifications.Copyright

Dynamic Analysis and Control of a Portable Cherrypicker

Cherrypickers are an important class of machines that can lift people to great heights. Understanding the dynamics and stability of these machines is crucial for efficient and safe operation. A dynamic model has been developed to capture the oscillatory dynamics of the machine as a function of the configuration and mass properties. Simulation studies reveal the complex dynamic behavior of the machine. In many cases, the oscillation of the endpoint bucket causes difficulties and dangers for the operators. An input-shaping controller has been added to the system to decrease the oscillatory dynamics. A portable cherrypicker is being developed for use in both education and research. The cherrypicker will be used as an experimental testbed in an advanced controls course at the Massachusetts Institute of Technology. The MIT students will use the machine to verify their theoretical models of the dynamic behavior, as well as evaluate control systems they develop to improve performance. Concurrently, students at the Georgia Institute of Technology will use the machine in teleoperation mode to conduct similar experiments. The MIT and Georgia Tech students will work together to conduct meaningful research on the cherrypicker testbed for their course projects. This paper describes the developments and results of the project to date.Copyright

Dynamic Response of a Dual-Hoist Bridge Crane

Cranes are used in manufacturing facilities, throughout nuclear sites, and in many other applications for various heavy-lifting purposes. Unfortunately, the flexible nature of cranes makes fast and precise motion of the payload challenging and dangerous. Certain applications require the coordinated movement of multiple cranes. Such tasks dramatically increase the complexity of the crane operation. This paper studies the dynamic behavior of a dual-hoist bridge crane. Simulations and experiments are used to develop an understanding of the dynamic response of the system. Various inputs and system configurations are analyzed and important response characteristics are highlighted.Copyright

A small-scale cherrypicker for experimental and educational use

Cherrypickers are a useful class of machines that lift people to great heights. However, a major drawback of cherrypickers is that they oscillate when they move. Under-standing the dynamics and stability of these machines is crucial for efficient and safe operation. To this end, a small-scale cherrypicker was constructed for experimental dynamic analysis and educational use. Experimental results confirm the benefits of the vibration-control techniques developed for this machine. The cherrypicker was used during Fall 2010 as an experimental apparatus in an advanced graduate controls course taught simultaneously at the Georgia Institute of Technology and the Massachusetts Institute of Technology. Details of its educational use are discussed.

Positioning and control of boom crane luffing with double-pendulum payloads

Boom cranes are used for numerous material-handling and manufacturing processes in factories, shipyards, and construction sites. They move payloads by hoisting up and down, slewing their base about a vertical axis, and luffing their boom in and out from the base. Many boom cranes are designed to automatically level luff, wherein the payload stays at the same height while the boom luff angle changes. All of these motions induce payload oscillation. The problem of payload oscillation becomes more challenging when the payload exhibits double-pendulum dynamics that produce two varying frequencies of oscillation. In this paper, input shaping is used to reduce the two-mode oscillatory dynamics of such systems. Furthermore, a small-step control mode is designed to allow the operator to make short and precise motions without causing oscillations.

Dynamics and zero vibration input shaping control of a small-scale boom crane

Cranes are vital to many manufacturing and material-handling processes. However, their physical structure leads to flexible dynamic effects that limit their usefulness. Large payload swings induced by either intentional crane motions or external disturbances decrease positioning accuracy and can create hazardous situations. Mobile boom cranes are one of the most dynamically complicated types of cranes. Boom cranes cannot move the payload in a straight line by actuating only one axis of motion because they have rotational joints. This paper presents a nonlinear model of a mobile boom crane. Then, a large range of possible motions is analyzed to investigate the dynamic behavior of the crane. A command-shaping control technique is applied to this nonlinear machine and its effectiveness is analyzed. Experimental results confirm the predicted oscillation phenomenon.