Using kinematic reduction for studying grasping postures. An application to power and precision grasp of cylinders

Abstract

The kinematic analysis of human grasping is challenging because of the high number of degrees of freedom involved. The use of principal component and factorial analyses is proposed in the present study to reduce the hand kinematics dimensionality in the analysis of posture for ergonomic purposes, allowing for a comprehensive study without losing accuracy while also enabling velocity and acceleration analyses to be performed. A laboratory study was designed to analyse the effect of weight and diameter in the grasping posture for cylinders. This study measured the hand posture from six subjects when transporting cylinders of different weights and diameters with precision and power grasps. The hand posture was measured using a Vicon(®) motion-tracking system, and the principal component analysis was applied to reduce the kinematics dimensionality. Different ANOVAs were performed on the reduced kinematic variables to check the effect of weight and diameter of the cylinders, as well as that of the subject. The results show that the original twenty-three degrees of freedom of the hand were reduced to five, which were identified as digit arching, closeness, palmar arching, finger adduction and thumb opposition. Both cylinder diameter and weight significantly affected the precision grasping posture: diameter affects closeness, palmar arching and opposition, while weight affects digit arching, palmar arching and closeness. The power-grasping posture was mainly affected by the cylinder diameter, through digit arching, closeness and opposition. The grasping posture was largely affected by the subject factor and this effect couldn't be attributed only to hand size. In conclusion, this kinematic reduction allowed identifying the effect of the diameter and weight of the cylinders in a comprehensive way, being diameter more important than weight.

Sharing of hand kinematic synergies across subjects in daily living activities

“…Some of these studies came to the conclusion that the kinematic synergies are both task-dependent and subject-dependent 12 : a given subject is expected to use different grasps to perform two different tasks; and for a given task, two different subjects may engage different strategies. Conversely, synergies found in many studies, with different tasks and subjects, were quite similar 3,8,11,[13][14][15] , which seems to contradict the previous statement. A recent work 16 suggests that synergies used by the subjects are intrinsically sparse both in DoF and in actions (i.e., each synergy uses a limited set of DoF and each action is implemented with a combination of a limited number of synergies) and that there is a large set of synergies, shared across subjects.…”

“…However, we hypothesise that if PCA is applied to data from several subjects together, merged unreal synergies might appear, as different subjects may engage different strategies to perform a given task. In most previous works, PCA has been applied globally to the kinematic data of different subjects 8,13 . If our hypothesis is true, inferring single-person coordination patterns from those results may lead to unrealistic results, and in order to analyse real subject-specific coordination patterns, PCA should be applied per subject 11 .…”

“…Despite the existence of other methods for obtaining sparse synergies 16,19 , PCA with Varimax rotation has the advantage of the simplicity of the method and the low time of computation. However, it has been scarcely used in literature 13 .…”

Open‐source 3D printed sensors for hand strength assessment: Validation of low‐cost load cell and fabric sensor‐based systems

“…Lateral pinch grip was employed to obtain force readings. Given that the hand adopts many different postures to perform daily occupations (Jarque-Bou et al, 2016), the isolated measurement of lateral pinch strength presented in this study may not adequately reflect the dynamic nature of force exertion.…”

A large calibrated database of hand movements and grasps kinematics

“…Although studies are improving the understanding of hand kinematics [11][12][13][14][15] , scientific research in this field is still often affected by several limitations. First, most of the studies involve a small number of subjects (up to 10 subjects to our knowledge 13 ), lacking the possibility to generalize the results.…”