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Related Concept Videos

Torque01:10

Torque

Torque is an important quantity for describing the dynamics of a rotating rigid body. We see the application of torque in many ways in the world, such as when pressing the accelerator in a car, which causes the engine to apply additional torque on the drivetrain. Here, we define torque and provide a framework to create an equation to calculate torque for a rigid body with fixed-axis rotation.
Torque can be considered as the rotational counterpart to force. Since forces change the translational...
Net Torque Calculations01:19

Net Torque Calculations

When a mechanic tries to remove a hex nut with a wrench, it is easier if the force is applied at the farthest end of the wrench handle. The lever arm is the distance from the pivot point (the hex nut in this case) to the person’s hand. If this distance is large, the torque is higher. Only the component of the force perpendicular to the lever arm contributes to the torque. Therefore, pushing the wrench perpendicular to the lever arm is more advantageous. If multiple people apply force to rotate...
Screw: Problem Solving01:21

Screw: Problem Solving

In mechanical engineering, the interaction between a threaded screw shaft and a plate gear involves analyzing the resisting torque on the plate gear that can be overpowered when a specific torsional moment is applied to the shaft. To better comprehend this concept, consider a generic situation with a threaded screw shaft with a given mean radius and lead and a plate gear with a specified mean radius. The coefficient of static friction between the screw and gear is also provided.
To evaluate the...
Angle of Twist: Problem Solving01:13

Angle of Twist: Problem Solving

An electric motor applies a torque of 700 N·m to an aluminum shaft, triggering a stable rotation. Two pulleys, B and C, are subjected to torques of 300 N·m and 400 N·m, respectively. The modulus of rigidity is provided as 25 GPa. With the knowledge of the length and diameter of each segment, the twist angle between the two pulleys can be computed. First, a section cut is made between pulleys B and C, and the cut cross-section is analyzed using a free-body diagram. Given that the torque exerted...
Residual Stresses in Circular Shafts01:10

Residual Stresses in Circular Shafts

In materials that exhibit elastic and plastic behavior, known as elastoplastic materials, residual stresses can accumulate when these materials experience plastic deformation. This deformation arises from either high levels of shearing stress or significant strains. Residual stresses are internal stresses that persist within a material after removing the external force causing deformation. This phenomenon is demonstrated when observing the behavior of a shaft under torque; notably, the shaft's...
Transmission Shafts: Problem Solving01:09

Transmission Shafts: Problem Solving

Designing a solid shaft that transmits power from a motor to a machine tool involves a series of calculations to ensure the shaft can withstand the stresses applied by bending moments and torques. First, calculate the torque exerted on the gear, considering the power transmitted by the shaft and its rotational speed. Following this, compute the tangential forces acting on the gears, which directly relate to the torque and the gear radius.
Next, use bending moment diagrams for the shaft to...

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Method to Measure Tone of Axial and Proximal Muscle
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Published on: December 14, 2011

Predicting subjective perceptions of powered tool torque reactions.

Jia-Hua Lin1, Raymond W McGorry

  • 1Liberty Mutual Research Institute for Safety, Hopkinton, MA, USA. Jia-hua.lin@libertymutual.com

Applied Ergonomics
|April 1, 2008
PubMed
Summary

Powered hand tools can cause discomfort and injury. Grip force and tool reaction forces are key factors influencing discomfort and acceptability, informing safer workstation design and exposure limits.

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Area of Science:

  • Occupational Ergonomics
  • Biomechanics
  • Human Factors Engineering

Background:

  • Powered hand tools generate reaction forces potentially linked to upper extremity musculoskeletal disorders.
  • Understanding subjective responses to these forces is crucial for preventing work-related injuries.

Purpose of the Study:

  • To investigate the association between reaction forces from powered hand tools and subjective ratings of discomfort and acceptability.
  • To identify key factors, including grip force and tool handle displacement, influencing these subjective responses.

Main Methods:

  • Collected subjective ratings of discomfort and acceptability from 20 participants operating pneumatic nutrunners in three configurations.
  • Measured grip force and tool handle displacement across nine locations and various working heights.
  • Analyzed data to determine significant factors correlating with subjective responses.

Main Results:

  • Normalized grip force during torque buildup was a significant predictor of subjective ratings.
  • A higher ratio of hand moment impulse to tool torque impulse correlated with unacceptable torque reactions.
  • Increased working height (30 cm) for pistol grip tools on vertical surfaces raised the odds of unacceptable ratings by 1.6 times.

Conclusions:

  • Grip force and reaction force characteristics are significant determinants of discomfort and acceptability.
  • Workstation design and exposure control strategies can be informed by prediction models based on handle displacement and grip force.
  • These findings can aid in establishing objective exposure limits for powered hand tool use.