Frank J. Fronczak

Forces associated with pneumatic power screwdriver operation: statics and dynamics

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.

A Dynamic Mechanical Model for Hand Force in Right Angle Nutrunner Operation

A deterministic mechanical model based on physical tool parameters was used for estimating static and dynamic hand forces from kinematic measurements. We investigated the effects of target torque (25, 40, and 55 Nm) and threaded fastener joint hardness (35-, 150-, 300-, 500-, and 900-ms torque buildup time) on hand force. Estimated hand force was affected by target torque and joint hardness. Peak and average dynamic hand force was least for the hard joint (35-ms buildup) and greatest for the medium hardness joint (150-ms buildup). Tool inertia played the major role in reducing hand reaction force. Estimated hand force decreased when the inertial force component increased. Inertial force decreased by 366% when buildup time increased from 35 to 300 ms. Static modeling overestimated hand force; the error ranged from 10% for a soft joint to 40% for a hard joint. Results from direct hand force measurements using a strain gauge dynamometer showed that the dynamic model overestimated peak hand force by 9%. However, average hand force and force impulse were not significantly overestimated.

Simulated and Experimental Results for a Hydraulic Actuator Controlled by two High-Speed on\off Solenoid Valves

Abstract Research was completed to investigate the use of high-speed on\off valves in the control of a hydraulic actuator. This work was completed as part of efforts to improve the accuracy and smoothness of travel for a six-degree-of-freedom testing machine. A mathematical representation of the system was developed that correctly predicted experimental results when a single command pulse was sent to the valves. For experiments involving a series of pulses to the valves the simulated and experimental results generally agreed at lower duty cycles, however, at higher duty cycles there was some separation in the results due to assumptions made in the simulation.

A Mechanical Model of Hand Force in Power Hand Tool Operation

A three-dimensional static equilibrium mechanical model of power hand tool operation was developed and used for comparing hand force associated with use of nutrunners having similar operating parameters (i.e. torque and feed force) but different physical parameters (i.e. shape, size, and mass distribution). The model used a Cartesian coordinate system relative to the orientation of the handle grasped in the hand using a power grip. Several important relationships between tool parameters and required hand force were revealed. Resultant hand force associated with different torque and feed force requirements were compared between four pistol grip nutrunners, and between pistol grip and right angle tools used for the same operation. Accessory handles and counterbalancers are also included in the model. Further development and validation of this model will be useful to power hand tool designers and tool engineers.

Hydraulic Drive Systems and Potential Use for Automobiles and Airplanes

Utilization of hydrostatic drives for power transmission, along with hydropneumatic accumulator energy storage can provide significant opportunities for improvements in vehicle design. These advantages are particularly relevant when considering advanced concept vehicles such as flying automobiles. Research and development in this technology has primarily focused on the fuel economy improvements that can be achieved in automobiles using a hydrostatic transmission and hydropneumatic accumulator energy storage. The accumulator permits the engine power to be uncoupled from the road load, thus enabling the engine to be operated at a more efficient point. By using wheel drive units that can operate as either motors (when driving) or pumps (when braking), regenerative braking can also be achieved, with the energy stored in the accumulator. In addition to improved fuel economy, several other significant design opportunities can be exploited. The drivetrain concept that has been most

Design of a Modified Hypocycloid Engine

Abstract : The modified hypocycloid engine incorporates a unique geared drive that imparts straight-line, sinusoidal motion to the one-piece piston and rod assembly. These kinematic characteristics provide a variety of potential benefits not possible with traditional slider-crank kinematics. Perfect engine balance is achieved through the use of two sets of counterweights. The absence of piston side thrust promises reductions in piston assembly friction and piston slap, even with smaller piston skirts. Additional potential benefits include improved combustion characteristics and reduced piston manufacturing costs. Although simpler hypocycloid designs provide the same motion, the modified hypocycloid engine reduces gear and crankshaft loading. A description and design details of a prototype engine currently under construction are presented. Patented design improvements over previous hypocycloid designs are described. These improvements reduce crankshaft stresses, ensure a compact crankshaft with convenient assembly and disassembly, and control deviations from the desired straight-line piston motion that are caused by gear tooth backlash.

Factors influencing power hand tool fastening accuracy and reaction forces.

Objective: A laboratory study investigated the relationship between power hand tool and task-related factors affecting threaded fastener torque accuracy and associated handle reaction force. Background: We previously developed a biodynamic model to predict handle reaction forces. We hypothesized that torque accuracy was related to the same factors that affect operator capacity to react against impulsive tool forces, as predicted by the model. Method: The independent variables included tool (pistol grip on a vertical surface, right angle on a horizontal surface), fastener torque rate (hard, soft), horizontal distance (30 cm and 60 cm), and vertical distance (80 cm, 110 cm, and 140 cm). Ten participants (five male and five female) fastened 12 similar bolts for each experimental condition. Results: Average torque error (audited − target torque) was affected by fastener torque rate and operator position. Torque error decreased 33% for soft torque rates, whereas handle forces greatly increased (170%). Torque error also decreased for the far horizontal distance 7% to 14%, when vertical distance was in the middle or high, but handle force decreased slightly 3% to 5%. Conclusion: The evidence suggests that although both tool and task factors affect fastening accuracy, they each influence handle reaction forces differently. We conclude that these differences are attributed to different parameters each factor influences affecting the dynamics of threaded faster tool operation. Fastener torque rate affects the tool dynamics, whereas posture affects the spring-mass-damping biodynamic properties of the human operator. Application: The prediction of handle reaction force using an operator biodynamic model may be useful for codifying complex and unobvious relationships between tool and task factors for minimizing torque error while controlling handle force.

Simulated Helical Gear Pump Analysis Using a New CFD Approach

The purpose of this paper is to focus on cavitation prediction at high-speeds in helical gear pumps for the purpose of hydrostatic dynamometer system development. Details of the fluid motion will be described through various stages of fluid transfer from the pump inlet to the outlet using various mesh densities. Using the results of these simulations, a discussion of design improvements for high-speed hydrostatic dynamometer operation is included. Conducting CFD simulations on external gear pumps is a difficult problem depending upon the complexity of the individual components. Simulating helical gears is especially taxing due to the complexity of the gear tooth profile. The additional detail in a helical gear pump model leads to an increase of the required mesh density and therefore increased computation time. A less computationally complex approach to simulating helical gears is to consider a helical gear as a series of thin spur gears rotated according to a predetermined helix angle. Details of this approach and results are discussed in this paper.Copyright

Techniques for improving the efficiency of agricultural fluid power systems

Techniques pour augmenter le rendement des systemes hydrauliques utilises sur le materiel agricole

Predicting Tool Operator Capacity to React Against Torque within Acceptable Handle Deflection Limits in Automotive Assembly

The proportion of tool operators capable of maintaining published psychophysically derived threaded fastener tool handle deflection limits were predicted using a biodynamic tool operator model, interacting with the tool, task and workstation. Tool parameters, including geometry, speed and torque were obtained from the specifications for 35 tools used in an auto assembly plant. Tool mass moments of inertia were measured for these tools using a novel device that engages the tool in a rotating system of known inertia. Task parameters, including fastener target torque and joint properties (soft, medium or hard), were ascertained from the vehicle design specifications. Workstation parameters, including vertical and horizontal distances from the operator were measured using a laser rangefinder for 69 tool installations in the plant. These parameters were entered into the model and tool handle deflection was predicted for each job. While handle deflection for most jobs did not exceed the capacity of 75% females and 99% males, six jobs exceeded the deflection criterion. Those tool installations were examined and modifications in tool speed and operator position improved those jobs within the deflection limits, as predicted by the model. We conclude that biodynamic tool operator models may be useful for identifying stressful tool installations and interventions that bring them within the capacity of most operators.