Jason Lawrence

Human Operator Performance Testing Using an Input-Shaped Bridge Crane

The payload oscillation inherent to all cranes makes it challenging for human operators to manipulate payloads quickly, accurately, and safely. An input-shaping controller was implemented on a large bridge crane at the Georgia Institute of Technology to reduce crane payload oscillation. The crane was used to study the performance of human operators as they drove the crane through obstacle courses. An image processing system was implemented to track the movement of the crane payload. Data from these experiments show that operators performed manipulation tasks faster, safer, and more effectively when input shaping was utilized to reduce payload sway.

Command Shaping for Nonlinear Crane Dynamics

Motion-induced vibration can be greatly reduced by properly shaping the reference command. Input shaping is one type of reference shaping method that is based largely on linear superposition. In this paper we document the impact of nonlinear crane dynamics on the effectiveness of input shaping. As typical bridge cranes are driven using Cartesian motions, they behave nearly linearly for low- and moderate-velocity motions. On the other hand, the natural rotational motions of tower cranes make them more nonlinear. The nonlinear equations of motion for both bridge and tower cranes are presented and experimentally verified using two portable cranes. The effectiveness of input shaping on the near-linear bridge crane is explained. Then, a command-shaping algorithm is developed to improve vibration reduction during the more nonlinear slewing motions of the tower crane. Experimental results demonstrate the effectiveness of the proposed approach over a wide range of operating conditions.

Command Generation for Flexible Systems by Input Shaping and Command Smoothing

DOI: 10.2514/1.50270Aggressive motions are often discouraged when a system has flexible dynamics. Common practice suggests thatsmooth commands, such as S-curves, should be used to drive the system. However, smooth commands cannot beimplementedonsomeactuators,suchastheon/offthrustersusedonspacecraftoron/offvalvesusedwithhydraulicsand pneumatics. Furthermore, smooth commands can lead to sluggish response. A rigorous comparison of smoothand nonsmooth reference commands is presented in this paper. The evaluation is performed by treating smoothcommandprofilesasinput-shapedfunctions.Inputshapingisamethodofreducingresidualvibrationbyconvolvinga sequence of impulses with a baseline reference command. By interpreting smooth commands as input-shapedfunctions, a common criterion for comparing smooth and nonsmooth commands is developed. The results of thiscomprehensive comparison indicate that input-shaped step functions are usually more efficient for reducingvibration than commonly used smooth commands. A portable tower crane is used to experimentally verify thecomparison between input-shaped and smooth commands.

AN INTERNET-DRIVEN TOWER CRANE FOR DYNAMICS AND CONTROLS EDUCATION

Abstract An advanced controls class taught at both the Georgia Institute of Technology and the Tokyo Institute of Technology focuses on command generation, remote manipulation, and human interaction with control systems. To aid in teaching these concepts, a portable tower crane was constructed. The tower crane can follow pre-programmed trajectories or be driven manually. It can also be operated from anywhere in the world with an internet connection. The crane can perform both feedback and command shaping anti-swing control while measuring trolley position and payload swing. The system enables students to perform a variety of useful and interesting laboratories and student projects. The students participated in and studied the effects of remote operator behavior, non-linear system dynamics, and advanced command generation techniques. The paper describes the tower crane and the results of this new educational endeavor.

Friction-Compensating Command Shaping for Vibration Reduction

Fast and accurate point-to-point motion is a common operation for industrial machines, but vibration will frequently corrupt such motion. This paper develops commands that can move machines without vibration, even in the presence of Coulomb friction. Previous studies have shown that input shaping can be used on linear systems to produce point-to-point motion with no residual vibration. This paper extends command-shaping theory to nonlinear systems, specifically systems with Coulomb friction. This idea is applied to a PD-controlled mass with Coulomb friction to ground. The theoretical developments are experimentally verified on a solder cell machine. The results show that the new commands allow the proportional gain to be increased, resulting in reduced rise time, settling time, and steady-state error.

Command Shaping Slewing Motions for Tower Cranes

Input shaping has been shown to be a practical and effective control scheme for reducing payload swing on industrial bridge and gantry cranes. However, when applied to tower cranes, standard input shapers will have degraded performance due to the nonlinear dynamics of rotational motion. To alleviate this problem, two new command generators for tower cranes are developed for a point-to-point slewing motion. It is shown that standard shaping techniques greatly reduce oscillation and the new tower crane command generators cause even less residual vibration. Simulations and experiments verify the results.

Study of operator behavior, learning, and performance using an input-shaped bridge crane

Input shaping is a simple way of reducing vibration in bridge cranes. Reduction of payload sway is particularly important if the crane must operate in a cluttered workspace or has to accurately position payloads. An input shaping controller has been implemented on a large bridge crane at the Georgia Institute of Technology. It is used to study the response of operators and their learning patterns while driving the crane through obstacle courses both with and without input shaping. An image processing technique was implemented to track the movement of the crane payload. Data from these experiments show that the operators performed tasks more fastly, safely, and effectively when input shaping is used.

An analytical solution for a zero vibration input shaper for systems with Coulomb friction

Systems with actuator limits and Coulomb friction are examined with the goal of moving the system in a point-to-point motion as quickly as possible with very little vibration or steady state error. An input shaper is designed to compensate for the nonlinear effects of Coulomb friction. This shaper makes it possible to increase the proportional gain to move the system quickly without the detrimental effects of increased vibration. Experimental tests on a solder cell machine validate the proposed solution.

Use of Input Shaping to Decrease the Effects of Stiction

Abstract Stiction can be a major detriment to the performance of machines that move at low velocities or attempt to position with high accuracy. The control of machines with stiction is further complicated if the machine has flexible dynamics that lead to vibration and transient deflection. Command generation schemes have recently been shown to eliminate many of the problems associated with flexible dynamics. This paper investigates the use of command generation techniques for reducing the effects of stiction, as well as vibration. It is shown that command generation allows the positioning feedback gains to be increased, thereby reducing the positioning error associated with stiction, without increasing vibration.

Improving trajectory tracking for systems with unobservable modes using command generation

Trajectory tracking with flexible systems is extremely difficult. This difficulty is increased when there are unobservable modes. Optimal PID control can be used for standard trajectory tracking, whereas sliding mode control can be used in systems with parametric uncertainties. Command shaping has been proven to be beneficial in eliminating unwanted vibration. This paper shows that command generation can be utilized to eliminate unwanted vibration from a system with an unobservable mode. Both optimal PID and sliding mode control can be used in conjunction with command generation for enhanced system performance.