Forces associated with pneumatic power screwdriver operation: statics and dynamics

Abstract

The statics and dynamics of pneumatic power screwdriver operation were investigated in the context of predicting forces acting against the human operator. A static force model is described in the paper, based on tool geometry, mass, orientation in space, feed force, torque build up, and stall torque. Three common power hand tool shapes are considered, including pistol grip, right angle, and in-line. The static model estimates handle force needed to support a power nutrunner when it acts against the tightened fastener with a constant torque. A system of equations for static force and moment equilibrium conditions are established, and the resultant handle force (resolved in orthogonal directions) is calculated in matrix form. A dynamic model is formulated to describe pneumatic motor torque build-up characteristics dependent on threaded fastener joint hardness. Six pneumatic tools were tested to validate the deterministic model. The average torque prediction error was 6.6% (SD = 5.4%) and the average handle force prediction error was 6.7% (SD = 6.4%) for a medium-soft threaded fastener joint. The average torque prediction error was 5.2% (SD = 5.3%) and the average handle force prediction error was 3.6% (SD = 3.2%) for a hard threaded fastener joint. Use of these equations for estimating handle forces based on passive mechanical elements representing the human operator is also described. These models together should be useful for considering tool handle force in the selection and design of power screwdrivers, particularly for minimizing handle forces in the prevention of injuries and work related musculoskeletal disorders.

Prolonged mechanical and physiological changes in the upper extremity following short-term simulated power hand tool use

“…The torsional stiffness (k) is the linear slope of frequency as a function of mass in the form of Equation (2). In previous studies (Lin et al 2001, 2003a,b,c, Sesto et al 2004, 2005a,b, 2006, the mass moment of inertia was calculated using intercept from Equation (2). The mass moment of inertia of the effective mass in the current study is calculated using the conservation of momentum principle.…”

Recent Advances in Biodynamics of Human Hand-Arm System

“…Electromyography (EMG) has been widely used for measuring hand forces in manual tasks 124,125) . Several studies have also applied this technique to measure the hand force on workers using powered hand tools [126][127][128] . A few investigators have also started to examine and improve a psychophysical technique known as force matching for the force measurement 129) .…”

Modeling of the hand–arm system for impact loading in shear fastener installation

“…Previous studies analyzing the hand-arm response for impulsive torques measured the response under the condition of maximum grip with the use of a simulated physical tool instead of a real tool (Lin et al, 2001(Lin et al, , 2003a. It resulted in an underestimation of the hand-arm deflection and an overestimation of the interface force between the tool and the hand when using a real tool.…”

“…However, these studies do not model the hand-arm system and require a large number of experiments to deduce the relationship between the probability of causing injuries and factors such as tool type and hand-arm posture. Previous attempts to model the hand-arm response to impulsive torques are based on the response of the hand-arm under conditions of maximum exertion (Lin et al, 2001(Lin et al, , 2003a. This resulted in an underestimation of the hand deflection and an overestimation of the contact force between the hand and the tool when using real tools.…”