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UBC Theses and Dissertations

A study of production and ergonomic factors in grapple yarding operations using an electronic data logger system de Souza, Amaury Paulo


This thesis reports a study of production and ergonomic factors in a grapple yarding operation, observed during 1982 at MacMillan Bloedel Ltd's Shawnigan Logging Division, near Duncan, British Columbia. Optimizing safety, health and performance requires detailed evaluation of factors affecting man-machine relationships during actual industrial operations. In the case of grapple yarding, these factors were divided into two groups: (1) Production factors: yarding distance; mainline speed and tension; load volume, weight and number of logs; and climatic, ground and stand conditions; (2) Ergonomic factors: operator's heart rate; cab noise level, temperature and humidity; and triaxial vibration at the operator's seat. The research objectives were to: develop and evaluate an electronic Data Logger system for man-machine studies; automatically determine work-cycle, work-element and delay times; test hypothesized relationships among production and ergonomic variables; analyze trends in the duration of work-element times over the working shift; and compare measured ergonomic conditions with recommended standards. Data were simultaneously sampled and recorded using the Data Logger, a microprocessor-controlled, multi-channel, digital signal-recording instrument, newly developed for this specific research. Reliable field performance confirmed the ability of the Data Logger to function as a practical research tool in forest harvesting operations. Development of pattern-recognition computer programs allowed automated and consistent interpretation of recorded signals into machine work cycles, work elements and certain delays. Time measurement accuracy of 0.001 min together with automated data recording allowed identification of fast grapple yarding activities not previously identified. Correlation and regression analyses examined inter-relationships among measured factors in the complex grapple yarding system. Yarding distance was the most important variable affecting grapple travel time, but was not significantly associated with hookup time. Work-element times were not significantly related to cumulative working time over the shift. Weak associations were found between most pairs of production and ergonomic variables. The grapple yarder operator's work load, based on measured heart rate, was judged "very low". This also indicated a relatively low level of emotional or mental stress placed on the experienced operator during grapple yarding activity. Ergonomic factors associated with the grapple yarder man-machine system were, in general, acceptable; however, they could be improved. For instance, vibration acceleration levels exceeded the International Organization for Standardization (ISO) limits for "fatigue-decreased proficiency" and "reduced comfort". Noise level (Leq) was below the recommended Workers' Compensation Board of British Columbia (WCB) hearing risk limit, but high enough to cause concern to many ergonomic specialists. Cab climatic conditions were not completely satisfactory. To improve workplace conditions to meet the ergonomic standards, measures should be taken to reduce noise and vibration levels, and to maintain optimum climatic conditions inside the operator's cab. Future studies could usefully investigate: long-term health effects; operator's visibility of the working area; ergonomic and production characteristics of other forest machines and their crews under different site, stand and climatic conditions. These studies should enlist the operators in explaining extraordinary observations, as well as their opinions on machine workplace conditions. Suggested improvements of the electronic Data Logger include: on-site, signal-monitoring controls and displays; a faster data recording system; and, a method for registering causes of delays, in the field.

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