Dooroo Kim

Input Shaping Control of Double-Pendulum Bridge Crane Oscillations

Large amplitude oscillation of crane payloads is detrimental to safe and efficient operation. Under certain conditions, the problem is compounded when the payload creates a double-pendulum effect. Most crane control research to date has focused on single-pendulum dynamics. Several researchers have shown that single-mode oscillations can be greatly reduced by properly shaping the inputs to the crane motors. This paper builds on those previous developments to create a method for suppressing double-pendulum payload oscillations. The input shaping controller is designed to have robustness to changes in the two operating frequencies. Experiments performed on a portable bridge crane are used to verify the effectiveness of this method and the robustness of the input shaper.

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.

Dynamics and Control of Bridge Cranes Transporting Distributed-Mass Payloads

The large-amplitude and lightly-damped oscillation of crane payloads is detrimental to safe and efficient operation. The problem is further complicated when the payload creates a double-pendulum effect. Previous researches have shown that single-mode oscillations can be greatly reduced by properly shaping the inputs to the crane motors. This paper builds on previous developments by thoroughly describing the double-pendulum dynamic effects as a function of payload parameters and the crane configuration. Furthermore, an input-shaping control method is developed to suppress double-pendulum oscillations created by a payload with distributed-mass properties. Experiments performed on a 10-ton industrial bridge crane verify the effectiveness of the method. A critical aspect of the testing was human operator studies, wherein numerous operators utilized the input-shaping controller to perform manipulation tasks. The performance improvements provided by the input-shaping controller, as well as operator learning effects, are reported.

Manipulation with Tower Cranes Exhibiting Double-Pendulum Oscillations

The payload oscillation inherent to all cranes makes it challenging for human operators to manipulate pay-loads quickly, accurately, and safely. Under certain conditions, the problem is compounded when the payload creates a double-pendulum effect. This paper presents an input-shaping control method for suppressing double-pendulum payload oscillations. Local and teleoperation experiments performed on a portable tower crane are used to verify the effectiveness of the method. Data from these experiments show that operators performed manipulation tasks faster and safer when input shaping was utilized to reduce payload sway. Furthermore, the teleoperation delays did not degrade the input shaping effectiveness.

Human Operator Learning on Double-Pendulum Bridge Cranes

Oscillation of crane payloads makes it challenging to manipulate payloads quickly, accurately, and safely. The problem is compounded when the payload creates a double-pendulum effect. This paper evaluates an input-shaping control method for reducing double-pendulum oscillations. Human operator performance testing on a 10-ton industrial bridge crane is used to verify the effectiveness and robustness of the method. The tests required the operators to drive the crane numerous times over a period of eight days. Data from these experiments show that human operators perform manipulation tasks much faster and safer with the proposed control scheme. Furthermore, considerably less operator effort is required when input shaping is used to limit the oscillation. These experiments also show that significant learning occurred when operators did not have the aid of input shaping. However, the performance never approached that achieved with input shaping without any training. With input shaping enabled, only moderate learning occurred because operators were able to drive the crane near its theoretical limit during their first tests.Copyright

Experimental Investigation of Thermal and Hydrodynamic Effects on Radially Grooved Thrust Washer Bearings

In this study, an experimental investigation on the effects of grooves on thrust washer bearings is investigated. Eight equally sized grooves are machined about 100 μ m deep into one side of a flat-faced steel washer. This thrust washer bearing is located between a helical gear and its carrier and is tested on a test rig capable of measuring frictional torque and the temperature of the bearing at different speeds. It is found that the grooved washers had lower bearing temperatures and failed at significantly higher loads than the control washer with no grooves. For a test procedure with varying operating conditions, the coefficient of friction is also significantly lower for the grooved washers. However, the grooved washers had about the same coefficient of friction as the control washers at each step when the speeds are very high. The results from various tests suggest that the increased amount of lubricant passing through the grooved surface of the washer removes heat from the washer bearing by convection. This decrease in stored heat conducted from friction deters thermoelastic instabilities and the reduction of hydrodynamic stiffness due to the decrease in viscosity. Enhanced hydrodynamic load-carrying capacity is also evident in the grooved washers test results. Review led by Jane Wang

Evaluation and integration of a wireless touchscreen into a bridge crane control system

Human manipulation of suspended payloads using cranes can be difficult. Cable sway is easily induced into the lightly damped system, which inhibits efficient, safe, and accurate payload manipulation. This problem is compounded when the payload forms a double-pendulum configuration. To aid operators, a wireless touchscreen controller was integrated into the control system of a 10-ton industrial bridge crane. This touchscreen allows an operator to move freely around the workspace and drive the crane with a simple graphical user interface. The operational effects of the touchscreen was compared to that of a standard pendent interface through a series of human operator performance studies. An oscillation suppression algorithm was used in conjunction with each interface. The touchscreen provides greater operator mobility while producing comparable manipulation performance.

A Dynamics-Based Hazard Analysis of Inverted-Pendulum Human Transporters Using Data-Mined Information

When a product is a complex dynamic system that interacts directly with a human, engineers must consider the wide range of possible motions and forces that the device could exert on the human. Such an analysis goes beyond a simple thought exercise and requires detailed knowledge about the system dynamics and the operating environment. This paper presents such an analysis of inverted-pendulum human transporters. The list of hazards is constructed by using knowledge of the dynamics and the mechanical design obtained through simulation and experimentation. However, the dynamics are so complex that the list is augmented with hazards that are revealed by studying accident videos posted on the Internet. The severity of the hazards are estimated using an energy-based measurement of the hazard onset conditions, as well as compounding factors from the mechanical design. In addition, experimental and simulation results of sample hazard conditions illustrate their danger and severity. The analysis reveals that inverted-pendulum human transporters have several hazards with unacceptable risk.

Virtual Model Control of Rotorcraft with Articulated Landing Gear for Shipboard Landing

Rotorcraft are essential to operations at sea, primarily due to their ability to perform vertical takeos and landings. However, due to the motion of the ship deck, ship landings can be dangerous for the pilot and result in damage to the helicopter. The addition of an articulated landing gear to a rotorcraft increases the number of degrees of freedom that can be used to land on a moving surface, such as a ship deck. Instead of relying solely on the rotor thrust magnitude and direction to land safely, the articulated landing gear can also be used to conform to the ship deck while maintaining a level fuselage, potentially allowing for quicker and safer landings. This paper presents a multi-body simulation tool to simulate the dynamics of a rotorcraft with robotic gear landing on a moving surface. A virtual model controller is developed to produce appropriate actuator torques. Dynamic simulation results show that an articulated, legged landing gear system can aid helicopters to landing on a moving ship deck.

Dynamic Modeling of Flat Belt Drives Using the Elastic-Perfectly-Plastic Friction Law

An analysis of a physically-motivated friction model called the Elastic/Perfectly-Plastic (EPP) friction model was performed on a steadily rotating flat belt drive. The EPP friction law is modeled as an elastic spring in series with an ideal Coulomb damper. The belt kinematics were developed and the nonlinear equations of motion and equilibrium solutions were derived using Hamilton’s Principle. Unlike the belt mechanics analyzed with Coulomb friction, the current study predicts the absence of adhesion zones. A stability analysis demonstrates that the non-linear equilibrium solution found is stable under local perturbation. A two-pulley belt drive with equal radii is analyzed and the dynamic response is studied. The results are compared to those computed using a dynamic finite element model. Excellent agreement between the two methods is documented.Copyright