Research Article - (2013) Volume 3, Issue 4
Faculty of Natural Resource, Sari Agricultural Sciences and Natural Resources University, Iran
Time study is one of the techniques which are used to evaluate the performance of forest machinery. This study is time consuming and expenses. According to appearance of new technologies in recent years, it is possible to use this method in time study. It is necessary to investigate the accuracy and efficiency of the results of this method in scientific researches. GPS is based on geographical information system which can record local and time data. This system has a high accuracy to record all movements of machine in forest. In this study the possibility of the application of trip recorder was assessed for time studies forest machinery. The studied skidding machine was wheeled skidder Timber jack 450c.31 skidding cycle recorded. Results indicated that 29 cycles of 31 skidding cycle was determined and assessed by GPS. The time study with GPS was along with 7% error and 93% confidence. The mean of skidding time in each cycle was 968.79 seconds for stop watch (traditional method) and 959.21 seconds for GPS. The error was 0.01%. In investigation of the components of skidding cycle, there were most variations in skidding distances. The distances in GPS method was 11% less than that of traditional method. In stop watch method 15 minutes per cycle was spend for measuring of skidding distance. This additional time was removed in GPS method. Results show that with using GPS the time and cost of time study can be reduced.
GPS, Time Study, forest, machinery
Nowadays, the application of machinery on forest harvesting has been developed. According to high cost of harvesting and high investments for buying machinery, it is necessary for managers and experts of forest to have accurate information about the efficiency of forest machinery to improve economic status of a project [1]. The estimation of the efficiency of forest equipments is an important part of cost management in a forestry unit which causes to decrease operations cost [2].
Work study is one of the main approaches to access machines information such as efficiency and cost [5].Work study are included the techniques of method and time studies. Time study is a main tool in studying the effects of management factors on performance of harvesting system [3]. Time study is techniques to determine work elements accuracy, separate effective work from ineffective work (delay times) as well as necessary time to perform especial operations which has been recognized [4].
The assumption of work study is a work conditions which has been defined previously. In other words the work condition must be stable. There are different tools for time study which the stop watch is a traditional method. This job is time consuming and expensive. Today, with development of technology and appearance of geographical positioning system we can analysis the movement of forest machinery and work elements.GPS or global positioning system is tracking satellite systems which have accurate watch. Different researches have been conducted to time study of forest machinery. Thor et al. (1997) used the GPS to investigate the cutting operation of harvester in thinning. Thompson et al. (1998) used the GPS to determine the track of skidder routes on skid trails and prepare the map of routes network and traffic. Veal et al. (2002) investigate the accuracy rate of GPS special data for tracking skidder. Mc Donald & Fulton (2005) compared the handle time study and automated method (GPS). Results showed that the error of times measured by handle and GPS method was less than 10%. This study attempts to investigate the possibility of the use of GPS in time study of forestry machines in northern forest of Iran.
Global Positioning System (GPS)
GPS or Global Positioning Systems is a satellite navigating and tracking system which is included network with at least 24 satellites. This satellite are constructed by suggestion of war ministry of United States and located in earth orbit. At first GPS are prepared to military consumptions but science 1980 its public usage was released. The services of this collection are free and accessible in each weather condition and each pint of earth. This system is a collection of 27 satellites which is moved around the earth. 24 satellites are working and 3 additional satellites are activated when a problem is appeared in main satellites. The distances of satellite from earth are 12000 miles. The mapping and controlling of transportation and traffic is one of the applications of global positioning system.
Description of the study area: this study was conducted in watershed number of 73 in northern forests of Iran. In this research a compartment in annual harvesting area was selected. The forest area was 59.38 hectare, the direction was southern, density was 125 trees per hectare, forest type was faugus-carpinetum, altitude was 600-930 meter and harvesting method was single tree selection cutting.
Figure 1: Location of study area in Iran
The rubber tire skidder Timberjack 450c was used in this study. This skidder was constructed in Canada and imported in Iran at decade of 1990. The engine power of skidder was 177hp with 6 cylinders. Its fuel was gasoline and it has a winch motor with tension power of 40 tones.
A handle receptor of GPS 550 Oregon constructed by Garmin Company was used to record local data and movement model of skidder. This instrument can record 2000 points and 200 different routes. It has three axle magnetic clinometers with three dimensional views.
The first step in time study is the determination of work elements. A skidding cycle includes travel empty, establishment, hooking, winching, travel loaded and unhooking. Then, 31 working cycle of skidder was studied using chronometer. This study is recognized as watch. Moreover, a GPS was used to record data. Information was recorded in time study forms. In GPS each stage of skidding cycle was marked and at the end of each element was marked. Indeed this point is the start point of nest stage.
The instrument determined from number of 1. It is possible to edit the name of points according to Table 1. It was done in Map Source software to facilitate point determination. For example at start of empty movement the recorded point is recognized as St-Empty Travel and at the end of this stage and in considered time it is marked and recognized with En-Empty Travel. The end point of each stage is saved.
Figure 2: Rubber tire skidder Timberjack 450c
Indeed this point is the start point of next stage. The name of each point in GPS receptor has been determined in GPS. At the end of each cycle, the information is unloaded from receptor and saved entitled cycle number in computer. This time study method is called as GPS.
Table 1: Name of skidding elements in GPS receiver
Figure 3. Information of points in Mapsource
An example of recorded data by GPS has been shown in Figure 4. Indeed GPS can record all points along with determined data in image. Finally with calculation of temporal distance among recorded points, the duration of each stage was achieved. The distance of each element and skidding distance was extracted from GPS receptor. One Sample k-s was used to investigate normality of data. In watch method the skidding distance was measured using tape meter. After the collection of the information of time study and GPS, the data was analyzed and compared in SPSS software and T-test.
Figure 4. Handle GPS Oregon 550
In Table 2, the results of time study by clock and GPS has been illustrated for 29 skidding cycle.
Table 2: Skidding cycles times (second) and Distance (M)
the data were normalized using K-S1 method. In stop watch method, 15 minute per cycle spend for measuring of skidding distance by tape meter. This additional time was removed in GPS method. With using GPS the time and cost of time study can be reduced.
Table 3: The total skidding time by clock and GPS
Table 4 shows that the P-value was 0.876 at probability level of 95%. Therefore, the difference among total time of skidding in 29 cycle was not significant, because the mentioned value was more than 0.05.
Table 4: The statistics of total skidding time by clock and GPS
Table 5: T-Test between total skidding time by clock and GPS
Figure 5: Compare of average time of elements skidding cycle for two methods
Table 6: Average time and share time segments by two methods
29 cycles of 31 skidding cycle was determined and assessed by GPS. The time study was along with 7% error and 93% confidence which were in agreement with Mc Donald (2005) findings. He estimated the error 6%. The main reason of the removal of two skidding cycle was loss of GPS signal. The mean of skidding time for each cycle was 968.79 seconds for stop watch (traditional method) and 959.21 seconds for GPS. The error was 0.01%. In investigation of the components of skidding cycle, there were most variations in skidding distances. The distances in GPS method was 11% less than that of traditional method which were in agreement with Mc Donald (2005) findings. This rate was 7% by Mc Donald (2005), because the GPS can’t consider the gradient of slope during the distance measuring. GPS calculates the distance on surface and without measuring the variation between the elevations of two points, whereas in time study by watch the distances are measured using tape meter on slope.
The relationship between skid distance and cycle time was estimated using both methods. Figure 6 and Figure 7 are graphs of one-way skid distance as a function of total cycle time, along with fitted linear regressions. The model, in both cases, was significant with adjusted R2 being 0.77 and 0.78 for the GPS and clock data, respectively.
Figure 6: one-way skid distance as a function of total cycle time For GPS method
Figure 7: one-way skid distance as a function of total cycle time For clock method
The time study of different works in forest is necessary to improve performance, scheduling and control of future works and decision making. To determine the work elements accurately and separate effective works from ineffective works we should divide work to smaller elements and then the time of each element must be recorded. Continues time study is used in forest engineering projects. The traditional system is time consuming and tiresome. Application of chronometer makes eyes tired and reduce the accuracy of time records, because the ability of human is limited to measure a few skidding cycle. GPS increase the speed of measuring and decrease the delay and cost. Moreover it is possible to tracking machines routes in forest. With record of the tracks of machines and comparison to trails we can assess the density and optimum density of skid trails.
