Grip force was measured along two orthogonal axes and vector summed. Sixty-one participants recruited from a manufacturing facility (29 men and 32 women) grasped instrumented cylinders (2.54, 3.81, 5.08, 6.35, and 7.62 cm diameter) using a maximal voluntary power grip. Two orthogonal force measurements relative to the third metacarpal were resolved into a magnitude and corresponding angle. On average, magnitude increased 34.8 N as handle diameter increased from 2.54 cm to 3.81 cm, and then monotonically declined 103.8 N as the handle diameter increased to 7.62 cm. The average direction monotonically decreased from 59.2 degrees to 37.7 degrees as handle diameter decreased from the largest to the smallest. When the diameter was smallest, the greatest force component, Fx (168.6 N), was in the direction where the fingertips opposed the palm. Conversely, when the diameter was largest, the smallest component, Fx (77.7 N), was in the same direction. These values are averaged for the left and right hand. The angle for the largest diameter increased with increasing hand size. These relationships should be useful for the design of handles that require gripping in specific directions, such as for hand tools and controls. Actual or potential applications of this research include the design of handles that require gripping in specific directions, such as for hand tools and controls, that reduce effort, and that prevent fatigue and overexertion.
This study investigated external grip force vectors when grasping cylindrical handles of varying diameters. Forty-eight subjects (18 males and 30 females) grasped strain gage instrumented cylinders (2.54, 3.8 1, 5.08, 6.35, and 7.62 cm diameter) using a maximal voluntary exertion for a five-fmger power grip and standardized postures. The third metacarpal bone was parallel to the axis of sensitivity to measure the force being exerted by the fingers against the palm. Each condition was presented to every subject in a random order and on a different day. The subjects were recruited from a manufacturing facility in the Midwest and consisted of a mixture of office and production personnel. Their ages ranged from 22 to 59 years. Hand length ranged from 15.2 cm to 20.9 cm. Two measurements were resolved into a force vector magnitude and associated force direction. On average, total grip force monotonically increased as handle diameter increased from 2.54 cm to 3.81 cm (30 N and 33 N increases for the left and right hands, respectively), and then decreased as diameter increased further. Average force direction for the resolved vector on the dominant hand was 57.5 degrees, 52.1 degrees, 46.7 degrees, 42.8 degrees and 36.3 degrees for handle diameters of2.54 cm, 3.81 cm, 5.08 cm, 6.35 cm, and 7.62 cm respectively. The smallest contribution to the total force magnitude (39.3%) was produced in the direction where the fingertips opposed the thumb tip when the cylinder diameter was small. Conversely, the smallest contribution of the total force magnitude (42.1%) was produced in the direction where the fmgertips opposed the palm when the cylinder diameter was large. These data are useful in the design of handles that require exertions to be directed in a specific direction relative to the hand.
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