The accuracy of measurements in a time study of harvester operations

Grzegorz Szewczyk,Janusz M. Sowa

doi:10.1186/s40490-017-0105-3

Grzegorz Szewczyk, Janusz M. Sowa

Open Access

https://doi.org/10.1186/s40490-017-0105-3

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Abstract

BackgroundWork time measurements are the starting point for any calculation of unit costs of machine exploitation; therefore, the accuracy of evaluating these costs determines the economic effectiveness of technological solutions employed in forest work. The research aimed to determine the level of measurement error of harvester operation times by means of a chronometric method.MethodsDifferent methods for measuring the components of the work cycle in cut-to-length harvesting operations were compared. These operations consisted of a thinning and a clear-cut harvesting operation in two Scots pine (Pinus sylvestris L.) stands in central Poland. The average duration of a work cycle was determined from cumulative timing using either the on-board PSION microcomputers or analysis of video footage. Results from these two methods were compared with the standard method used in work study which is snap-back timing (i.e. the timer is reset at the end of each activity within the work cycle, the average time for each activity calculated and then summed to give the average cycle time) using the PSION microcomputer.ResultsThe average duration of the work cycles estimated from cumulative timing of video footage were 55.0 and 52.3 s for the thinning and clear-cut operations, respectively. The cumulative timing method using the PSION on-board computer underestimated these cycle times by ca. 14% in thinning operations and by 22% in clear-cut operations. The snap-back timing method, which measures the duration of certain operations separately, underestimated the average work cycle time in the clear-cut operation by 6% but overestimated it by ca. 12% in the thinning operation. In both operations, most of the difference in work cycle time estimates were due to differences in the time recorded for delimbing and bucking activities.ConclusionsThe accuracy of work time measurement taken using the standard methods—snap-back timing—depends on the variability of work cycles. The hitherto employed method of snap-back timing is more accurate than the cumulative timing method with respect to both stable and more changeable work cycles.

Highlights

Work time measurements are the starting point for any calculation of unit costs of machine exploitation; the accuracy of evaluating these costs determines the economic effectiveness of technological solutions employed in forest work
Duration of a work cycle In the thinning operation, the mean duration of a harvester work cycle, determined using the cumulative timing PSION method, was 48 s (Table 3), which was significantly shorter than the work cycle recorded using the cumulative timing VIDEO method (Z = 4.23; p < 0.01)
The accuracy of work time measurements employing chronometric methods is of particular importance for investigation of highly variable technological operations, with short-lasting activities, which is typical of harvester operation

Summary

Introduction

Work time measurements are the starting point for any calculation of unit costs of machine exploitation; the accuracy of evaluating these costs determines the economic effectiveness of technological solutions employed in forest work. The research aimed to determine the level of measurement error of harvester operation times by means of a chronometric method. A key advancement in the field of work time research was the division of a work process into its basic elements, such as operations, treatments, activities and movements. This approach was proposed by F.W. Taylor at the beginning of the twentieth century and has been commonly employed in work-related investigations ever since (Sajkiewicz 1981; Palmroth 2011).

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