A quasi-static state examination of handle forces and translational acceleration at impending planar motion for the four-caster manually manoeuvred vehicle

Abstract

Motion resistance, handle forces, and translational acceleration of a four-caster manually manoeuvred vehicle (FMV) are examined at impending planar motion.FMV-wheel angular acceleration directions occur in polygon regions of the FMV-body translational acceleration. The mass centre force and torque, which balance motion resistance, using a Coulomb model, are non-linear and discontinuous functions of FMV-body acceleration.The transformation from mass centre force and torque to a dynamically equivalent handleforce measure is examined. A reference manoeuvre with a single set of caster orientations shows that FMV-body translational acceleration has a substantial effect on handle-force measure variation: an almost three-fold variation exists.The reference manoeuvre analysis is repeated with a representative sample of all caster orientations. The mean handle-force measure for this sample also shows a substantial handle-force measure variation, e.g. relatively high handle forces occur when the translational acceleration is directed as the impending change of FMV heading. This effect is independent of motion resistance values. As the handle forces required to balance motion resistance vary substantially depending on FMV-body translational acceleration, spatial constraints may have a substantial effect on handle forces. A relationship between handle forces and spatial constraints indicates that architectural planning has health and safety implications for the FMV operator.

A novel four-caster manual vehicle manoeuvring investigation: Higher loading-weights require larger turning spaces

“…Theory predicts substantial variations in motion resistance related to manoeuvring space. 1 This theory is coherent with Health and Safety Laboratory (UK) commentary on operator injury potential when manoeuvring goods vehicles in small spaces 2 and with a patient hoist study 3 which found higher anterior/posterior spinal shear during confined turns.…”

“…All four-caster vehicle manoeuvres can be usefully represented by 13 manoeuvres distinguished by different centres of zero velocity. 18 These 13 manoeuvres can be visualised using Figure 1(a): the operator manoeuvres the vehicle so that the selected, labelled rod is maintained in the guide-ring centre as the vehicle is turned to face a new direction.…”

“…As experimental development and results are the focus of this work, a qualitative account is provided: the aim is to provide a useful, plausible explanation and avoid lengthy text. The interested reader will find initial treatment in Abraham and Johnson, 1 a complete account in Abraham 18 and a validation of the kinematic–dynamics relationship in Abraham et al 16…”

“…However, kinematic constraints reduce this number to a maximum of 41. 18 Casters will frequently be in an approximate trail position since relatively short translational motion produces this. 18 If casters are initially in the trail position, the number of combinations reduces to 13.…”

“…It has been shown that the centres of zero velocity have a substantial effect on motion resistance 16 and consequentially on the operator’s maximum comfortable loading weight (definition to follow). 18 The relationship between wall positions and maximum comfortable loading-weight is therefore of investigative interest for two reasons. First, in terms of ergonomics, are there wall and fixture arrangements that increase or decrease operator injury risks?…”