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Flashcards in Mechanics of the Hand Deck (12):

what two forces are involved when gripping and litfting an object?

the grip and load force


what is the slip ratio referring to?

the inverse of the coefficient of friction between the object and the hand


to maintain grasp stability...

the grip/load ratio must exceed the slip ratio


when gripping an object, the rate of change of the grip and load forces are...



what is the safety margin called when holding an object?

difference between the grip/load force applied by the subject and the corresponding slip ratio


when gripping an object in the hand, what mechanisms occur when the arm is swayed back and forth?

the grip force is modulated in phase with fluctuations in load force that are induced by the arm movement indicating ancipitory control strategy.


what happens to the grip force as a subject moves an object up or down?

this load force can be anticipated and thus the grip force is exactly as high as needed at every point in time and tracks the load force without delay.


what are the two main components of the stereotypically automatic response?

a brisk grip force increase called catch up response, followed by a grip force increase that runs in parallel with increasing load force called the tracking response


whats special about the catch up response?

The catch-up response is scaled by sensory input (rate of the load force increase and friction) at the time of its initiation to compensate for delay due to reaction time


what are the four types of tactile fingertip receptors?

stretch, pressure, pain and temperature


whats practically impossible to measure via a prosthesis?

the force of friction


whats one experiment which is conducted to investigate the biomedical mechanism of friction encoding

setup consists of a robotic manipulator applying normal and tangential forces to the fingertip, ultrasonic friction modulation device (friction plate), light source to generate high contrast fingertip image as light is absorbed where fingertip skin ridges contact the friction
plate. Fingerprint before the tangential force was applied and processed fingerprint image showing tracking points in blue and micro-slips in magenta when normal:tangential force ratio was approaching the slip ratio.