William Singhose

While input shaping is an effective control technique for reducing residual oscillation in systems with continuous actuation, many systems can only be actuated at discrete time steps. Thus, to apply this control technique to discrete time systems the input shapers must be discretized. This process can reduce the effectiveness of the shapers. Furthermore, nonlinearities in frequency behavior, such as those observed in linear resonant actuators (LRAs), can further diminish the effectiveness of input shapers. This paper examines the effectiveness of previously proposed discretization approaches and seeks to develop an improved approach for creating input shapers for linear resonant actuators (LRAs). LRAs are often utilized in consumer electronics to generate haptic signals. This application presents the dual challenge of minimizing residual peak accelerations while maintaining large transient peak accelerations. Both challenges are addressed herein.

Rolling contact is a complex phenomenon that is dependent on a host of physical properties, as well as relative motion. Simplified treatments of rolling often rely on point or line contact and use nonslip kinematic constraints to treat rolling. However, during rolling motion, the deformation of the contacting bodies leads to energy dissipation and contact forces that oppose the rolling motion. Given the importance of rolling contact in mobile and multibody systems, the problem has received considerable attention over the years and has motivated a number of different modeling approaches. This paper examines rolling from a macroscopic perspective that accounts for the deformed area and presents an approach for defining the resultant tangential and normal reaction forces under the assumption of no-slip. Deformations in the normal direction are modeled using bilinear springs and dampers, while the forces in the tangential direction are calculated using reaction forces computed from a constrained Lagrangian approach. One particular motivation for the development of the model in this paper is for the prediction of how multiple payloads being lifted by a single crane can roll relative to each other. The modeling approach is applied to the planar case of a disk rolling under conditions of acceleration, deceleration, and constant speed. Results are also presented for the application of the model to a planar disk-on-disk rolling system.

Large upright heterogeneous flexible cylinders need to be transported by huge cranes in some safety-critical industrial applications. Unfortunately, the coupling effects between swing and twisting of the cable-suspended load, as well as bending and torsion of the flexible cylinder, degrade efficiency and safety of the material transportation. Although many publications have been directed at understanding compound-pendulum dynamics and beam vibrations, little attention has been focused on the coupled dynamics between load swing and twisting, as well as bending and torsion of cylindrical payloads. A three-dimensional model of a bridge crane moving an upright heterogeneous flexible cylinder has been developed to study such dynamic coupling. Furthermore, a control method has been developed to attenuate vibrations induced by the complex coupling effects. Several experiments have been performed to verify the effectiveness of the proposed dynamic model and control methods.

As the height of telescoping-boom aerial lifts increase, the severity of tip-over accidents obviously increases. To reduce the probability of tip-over accidents, manufacturers use countermeasures such as outriggers and wheel axels that expand in width to provide a more stable base, counterweights to offset the moments generated by the telescoping boom, and controllers that limit the machine configurations to within stable envelopes. The size of stability margins is determined by industry standards that set the approved load capacity of the machine to less than the load that would induce tip-over. This paper investigates the effectiveness of such load-based safety margins for very tall aerial lifts with telescoping-booms. The results indicate that the industry standards result in both inconsistent and often low safety margins.

Linear resonant actuators (LRAs) are used extensively in consumer electronic devices such as cell phones and fitness trackers to provide haptic signals to users. This work presents a dynamic model of LRAs based, principally, on the electromagnetic aspects of the these devices. The model predicts that the natural frequency exhibited by an LRA can deviate significantly from that predicted by conventional spring-mass-damper dynamic models. Preliminary experimental results appear to support theoretical findings.

Crawler crane designers continually extend the height of the machines. Models that reach over 500 feet high are commercially available. Of course, as the crane height increases, so do the hazards associated with tip-over accidents. Destabilizing tip-over moments are generated by the boom and the suspended payload when they extend beyond the base of support. Stabilizing moments are generated by the crane base and counterweights. Counterweights are normally secured by mechanical fasteners such as pins, bolts, or chains. However, some cranes use unrestrained counterweights that are held in place only with friction. This paper investigates the dynamic behavior of such unrestrained counterweights during tip-over accidents. The analysis shows that counterweight blocks can break free and slide off the crane when the tip angle is as small as 20 degrees. Scale-model testing of cranes with unsecured counterweights demonstrates that the fall path of the spilling counterweights on certain crane models intersects the operator cab and thus presents a deadly hazard.

Self-balancing transporters apply wheel torque in order to accelerate, turn, and regain balance. However, these control efforts require sufficient traction between the wheels and the ground so that appropriate wheel-ground forces are generated. When this is not the case, the stability is compromised and machine behavior can be unexpected and destabilizing. Experiments were performed to quantify the reduction in wheel-ground friction that can occur in common real-life conditions, such as on wet surfaces or surfaces with debris. A simulation has been developed to show that common transporter motions that are safe on dry surfaces lead to unstable or unpredictable behavior when the available wheel-ground friction is reduced by amounts similar to those seen in the experiments.