The tip-over of scissor lifts in operation has frequently resulted in the death and/or severe injuries of workers. The objective of this study is to enhance the understanding of its major mechanisms and factors influencing scissor lift stability. Both experimental and modeling approaches were used in this study. Two series of experiments were performed under possible tip-over scenarios: curb impact and pothole depression. Based on the dynamic characteristics identified from the experimental results, a lumped-parameter model of the scissor lift was developed. It was applied to investigate the effect of scissor structure flexibility on the tip-over potential of the lift, to understand tip-over mechanisms, and to ex-plore preventive strategies. This study found that the fundamental natural frequencies of the lift were generally in a range of 0.30 - 2.08 Hz, which are likely related to the tip-over. Increasing flexibility of the lift structure generally increased the tip-over potential. The tip-over threshold was also a function of both ground slope and tilt speed of the lift. The results suggest that the lift should not be elevated on largely deformable and/or uneven surfaces such as bridged wood board or a soft soil base. The worker on the lift platform should avoid any large continuous periodic movement or forceful action in the horizontal plane, especially when the lift is fully elevated. Besides the tilt angle of the lift, the tilt speed should be monitored to help prevent the tip-over
Tip-over/rollovers are the most frequent cause of fatalities associated with the use of scissor lifts. The objective of this study is to develop a dynamic model of a scissor lift to investigate tip-overs. A multibody dynamic model of a typical scissor lift was created using an advanced modeling platform-ADAMS ®. This model was statically validated and dynamically calibrated based on experimental results from center of gravity, curb impact, and pothole depression tests. The dynamic responses of the scissor lift model were consistent with the experimental data. Once calibrated/validated, the model was used to simulate hazardous scenarios while varying the scissor lift's flexibility. Results of the simulations indicate that increased flexibility reduces the scissor lift's stability. This developed scissor lift model could be used to perform additional simulated conditions and for design optimization.
Objective:The current study is intended to evaluate the stability of a scissor lift and the performance of various fall-arrest harnesses/lanyards during drop/fall-arrest conditions and to quantify the dynamic loading to the head/ neck caused by fall-arrest forces.Background: No data exist that establish the efficacy of fall-arrest systems for use on scissor lifts or the injury potential from the fall incidents using a fallarrest system.Method: The authors developed a multibody dynamic model of the scissor lift and a human lift operator model using ADAMS TM and LifeMOD TM Biomechanics Human Modeler. They evaluated lift stability for four fall-arrest system products and quantified biomechanical impacts on operators during drop/fall arrest, using manikin drop tests. Test conditions were constrained to flat surfaces to isolate the effect of manikin-lanyard interaction.Results: The fully extended scissor lift maintained structural and dynamic stability for all manikin drop test conditions. The maximum arrest forces from the harnesses/lanyards were all within the limits of ANSI Z359.1. The dynamic loading in the lower neck during the fall impact reached a level that is typically observed in automobile crash tests, indicating a potential injury risk for vulnerable participants.Conclusion: Fall-arrest systems may function as an effective mechanism for fall injury protection for operators of scissor lifts. However, operators may be subjected to significant biomechanical loadings on the lower neck during fall impact.Application: Results suggest that scissor lifts retain stability under test conditions approximating human falls from predefined distances but injury could occur to vulnerable body structures.
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