An Investigation on the Dynamic Stability of Scissor Lift

Abstract

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

Theoretical foundation, methods, and criteria for calibrating human vibration models using frequency response functions

“…1 shows a flowchart that outlines the theoretical basis and major activities of this study. Similar to the forward dynamic approach, the inverse dynamic approach can be applied to any model with linear or nonlinear dynamic properties [6–14]. The human body or segment has some nonlinear properties.…”

“…The results can be used to replace the linear stiffness and damping properties in the model to establish a nonlinear model. To efficiently analyze and discuss the model calibration methods, this study generally assumed the human body or segment can be approximately simulated as a linear system for each given test condition, although the inverse dynamic approach is generally applicable to any linear and nonlinear system [7,9,13,14]. Six models found in the literature are shown in Fig.…”

“…In principle, this imposed matching process passes the dynamic properties included in the reference data to the model, similar to the calibration of an accelerometer. In engineering modeling, this process is usually termed as parameter identification, as it is only used to identify the unknown values of one or a few well-defined parameters of a model that provides a close simulation of an engineering system [13,14]. In contrast, the vast majority of human vibration models are lumped-parameter models that only provide a very crude simulation of the complex human body structure.…”

A Numerical and Experimental Analysis of the Dynamic Stability of Hydraulic Excavators

“…Substituting the expression for kinetic (6) and potential (8) energy, and the expression for the dissipation function (13) into Lagrange's equations of the second kind (5), one obtains a system of six homogenous differential equations of the oscillating system:…”

“…Previous research in the area has been related to the development of mathematical models for the analysis of the static stability of hydraulic excavators [1][2][3][4]. However, the studies have shown that hydraulic excavators (and other hydraulic mobile machines) act like dynamic oscillating systems during their cyclic operation [5][6][7] where actuators (hydraulic motors and hydraulic cylinders) of the excavator drive mechanisms appear as extremely elastically dampened system members in the shape of hydraulic springs. They occur due to the compressibility of oil in the actuator displacement and ducts of the excavator hydrostatic drive system.…”