PhD Oral Exam - Yumeng Yao, Mechanical Engineering

When studying for a doctoral degree (PhD), candidates submit a thesis that provides a critical review of the current state of knowledge of the thesis subject as well as the student’s own contributions to the subject. The distinguishing criterion of doctoral graduate research is a significant and original contribution to knowledge.

Once accepted, the candidate presents the thesis orally. This oral exam is open to the public.

Abstract

Hand-transmitted vibration (HTV) arising from hand-held power tools has been associated with an array of disorders of the hand arm system, collectively referred to as the hand-arm vibration syndrome (HAVS). The risk of HAVS among hand-held power tools operators has been related to the nature of HTV exposure and the mechanical coupling of the hand with a tool handle, which is neglected in the current standardized exposure assessment method (ISO 5349, 2001). Anti-vibration (AV) gloves are considered as convenient and effective means to reduce exposure to HTV. The effectiveness of AV gloves is, invariably, assessed on the basis of the handle vibration transmitted to the palm of the hand. The method does not consider the vibration responses of the fingers, which differ significantly from that of the palm. The AV gloves adversely influence the manual dexterity and grip strength of the operators, which are considered as primary factors discouraging the usage of AV gloves. The current standardized method, however, does not consider the loss of dexterity and grip strength caused by wearing these gloves.

This thesis proposes a methodology for evaluating the integrated performance of AV gloves, considering the distributed vibration transmission to the palm and fingers through gloves, manual dexterity and grip strength. In order to establish the methodology, independent experiments were designed to quantify each performance measure. Three series of experiments were designed to evaluate vibration responses distributed over the palm and fingers, manual dexterity and grip strength performance of gloves. Each experiment design involved ten different gloves and 15 adult male subjects. Visco-elastic properties of vibration isolation materials used in the AV gloves were also characterized under a constant preload. In the first series, the fine fingers and hand dexterity were investigated using the Two-Hand Turing & Placing Minnesota and ASTM F2010 methods. Subsequently, the handle vibration transmitted to the palm and mid phalanges of the index and middle fingers of the glove hand were measured along the three translational axis using the palm and fingers’ adapters, respectively. In the final series, the influence of AV gloves on the operator’s grip strength were investigated via direct as well as indirect methods. A flexible thin-film hand sensor was designed and verified for direct measurement of the contact force developed at the rigid as well as flexible hand-handle, and hand-glove interfaces. The activities of four different forearm muscles were also measured via surface electromyography (EMG) under different hand grip forces imposed by the gloved hand.

The correlations among the individual performance measures of AV gloves and the material properties were analyzed via Pearson’s correlation coefficient, which provided essential knowledge on the roles of design factors and the design guidance. A relationship among the hand grip, push and contact forces imposed on flexible hand-handle was developed via multiple linear regression analysis. The individual measures of AV gloves were also analyzed via two-factor repeated analyses of variance (ANOVA) and multivariate analysis of variance (MANOVA) to evaluate significance of different independent variables such as glove type, test method, frequency range, and hand grip force. The glove type yielded significant effect on all the measures (p<0.05). Post-Hoc tests were subsequently conducted via Bonferroni and Tukey HSD (honest significant difference) test for discriminating difference among the gloves.

The combination of extensor carpi radialis longus (ECR) and flexor carpi radialis (FCR) muscles activities revealed highest sensitivity to discriminate among gloves, and could serve as an effective indirect measure of the grip strength performance. Increasing the glove thickness resulted in improved vibration isolation by the glove but reduced manual dexterity and enhanced muscles activities. Strong correlation was observed between the material stiffness and wh-weighted palm vibration transmissibility in the high frequency range (r>0.90), while a weak correlation was evident between the manual dexterity and the wp-weighted fingers’ vibration transmissibility. Strong positive correlations were observed among the palm vibration isolation, material properties and material thickness in the 25-1250 Hz frequency range.

The results also revealed conflicting glove design requirements imposed by the individual measures. A methodology based on analytical hierarchy process (AHP) is proposed to identify weightings for the conflicting performance measures for a given work condition, classified in accordance with the frequency ranges of predominant vibration (low and high) together with assembly/disassembly tasks. The methodology is applied for identifying task/tool-specific optimal AV glove. The effectiveness of the proposed method is demonstrated considering individual performance measures for five different AV gloves.