Score During one –on-one interview, all three crane operators expressed their excitement about the system. One comment regarding the information content was that they would like to see the current load information displayed on the anti-collision system on the navigation system.
6. Perceived usefulness
The perceived usefulness was tested by video-recording and comparing the frequency of using the tower crane navigation system and the anti-collision system in actual steel construction work. The anti-collision system is commonly used today when operating a crane with blind spots. If the crane operator looked at (relied on) the navigation system during a lifting task, then the crane operator perceived that the navigation system was more useful for the task than the anti-collision system and vice versa.
The usefulness experiment was conducted as part of the usability analysis of the second system. Use of the anti-collision system (fig. 1) and our tower crane navigation system by the same three crane operators who had participated in the second ease-of-use test was video recorded for 71 days from behind the tower crane operators using a webcam (fig. 11) and analyzed. The video were analyzed on the task level. One lifting cycle was counted as one task. Each lifting task took about 2 to 5 min. A total of 345 tasks were observed. The tasks were categorized into six groups: 1) only the anti-collision system was used during the task, 2) only the navigation system was used, 3) the anti-collision system was used longer, 4) the navigation system was used longer, 5) the anti-collision system and the navigation system were almost equally used, and 6) none was used. In the analysis, actual use of the devices was distinguished from crane operators’ non-meaningful behaviors such as turning their heads from one side to the other out of habit or just as an action to relax their neck. Based on our experience and observation, it took at least 2 s to perceive the location
Information from a lifting supportive device (the navigation system or the anti-collision system).The event durations were included in the total amount of time spent using a lifting supportive device only when the crane operators looked at either the anti-collision system or the navigation system for more than 2 s.
Table 1 and Fig.12 summarize the analysis results. The analysis results show that, for 90 task (26.09%) out of 345, the tower crane operators used neither the navigation system nor the anti-collision system, because a tower crane operator sometimes can see and life an object without a blind spot in the case of low-rise buildings ( a seven-story building in our experiment ). However, for most cases (255 tasks out of 345 ), the tower crane operators used either the tower crane navigation system or the anti-collision system. When the tower crane operators used either the tower crane navigation system or the anti-collision system, they relied heavily on the tower crane navigation system during the lift tasks (99.33%). The crane operator used the anti-collision system only for the other 17 cases (6.67%). Out of 255 tasks that used either the tower crane navigation system or the anti-collision system, 197 task (77.25%) were conducted solely using the tower crane navigation system, and in 41 task (16.08%), the crane operators used the tower crane navigation system longer than the anti-collision system. No case was observed where the tower crane navigation system and the anti-collision system were used equally. Although the number of test subjects in this experiment was small, the test results clearly indicate that the tower crane operators perceived the new tower crane navigation system as more useful than the existing anti-collision system during blind lifts.
7. Conclusions
This paper presented a hardware system and a software system of a tower crane navigation system developed by the authors through five years of effort, and reported the used experiment test results. This system was developed to assist operation of a tower crane during blind lifts. Developed system showed the location of a lifted object in the context of a building and surroundings using an imported BIM model and data collected through sensors and a video camera. The system showed the location of a lifted object from the top and side points of view of a 3D BIM model and the actual camera view from the lifted object.
Even if a good technology is invented, if the technology is not accepted by users, the technology will be abandoned. Potential user acceptance of the tower crane navigation system was tasted from two perspectives, “perceived ease of use” and “perceived usefulness” based on Fred Davis’s Technology Acceptance Model (TAM) theory
The perceived ease of use was tested through the usability of the hardware and the software aspects of the system. Both the interview and the quantitative analysis showed that the perceived ease of use of the tower crane operators increased after they used the second version of the system. The first prototype of the system was tested with six tower crane operators. An interesting finding was that the operators felt that the location of a lifted object was easier to understand in 2D representations