JNIOSH

Abstract of Special Research Report (SRR-No.23)

National Institute of Occupational Safety and Health, Japan

A Study on Safety Measures for Exacavators Using Virtual Reality Technology

Introduction

SRR-No.23-1
Kiyoshi FUKAYA and Shigeo UMEZAKI

: In the field of the civil engineering and construction business, there are many accidents caused by construction machinery. The number of accidents is large next to that of fall accidents. Above all, the number of accidents due to excavators is greater number of accidents due to all construction machinery. The ratio of the fatal accidents due to excavators to the all of the civil and construction accidents is increasing.
    The accidents in relation to excavators were investigated and analyzed. These accidents were divided into 4 types; "caught and crushed", "overturn", "struck by falling or flying object" and the others. Nearly the half of the accidents belongs to the first type. Therefore the countermeasures against the "caught and crushed" were studied during 1997 - 1999 fiscal years.
    The "caught and crushed" accident has two factors, excavator and sufferer, and there are two approaches in prevention of the accident. Both approaches were studied.
    An excavator is controlled by a person and the prevention of an accident depends on the operator. Therefore human factors of the operators are very important, especially in the situation where accidents occur. From this point of view, researches to clarify operator's human factors were conducted. The devices that help operators also were studied.
    Sufferers could avoid the accidents unless they approached the excavator. Therefore the countermeasures to prevent a person from approaching an excavator were investigated.
    To sum up this specific research report, the following research subjects were conducted.
  (1) Development of the excavator simulation system in order to clarify operator's human factors, especially in dangerous situations such as presence of co-workers near the excavator.
  (2) Experiments using the simulator to clarify the operator's human factors, especially visual recognition of working circumstances.
  (3) Proposals of the methods to detect a person near an excavator in order to alarm the operator or to stop the excavator.
  (4) Proposal of the system to prevent workers from approaching an excavator.

Development of Excavator Operation Simulator

SRR-No.23-2
Kiyoshi FUKAYA, Shigeo UMEZAKI, Jian LU, Takahiro NAKAMURA and Yoshiyuki EGAWA

: In the field of the civil and construction work site, there are many accidents caused by construction machinery such as an excavator. Such machinery is operated by a person and the prevention of an accident is entrusted to the person. To take the safety measures knowing of operator's human factors is needed. Therefore to investigate the human factors of operators, the excavator simulator using virtual reality technology was developed.
    The simulator should meet the following requirements.
  (1) The simulator should have the function of simulating accident situations, such as presence of a worker near the excavator. From this requirement the simulator should be a virtual realty system.
  (2) The simulator should have not only front view but also back view to investigate operator's attention to the back, because many accidents occurred in the rear of excavators.
  (3) The simulator should have the function giving a sense of motion, because the sense is important to operate an excavator.
    Several plans such as the HMD system with a real excavator and the cabin on a turn table system were investigated, and following system has been developed.
    The simulator is composed of the image system and the motion system. The image system is composed of the image generator (graphic workstation), eight video projectors and eight 120 inch sized screens which are arranged in heptagon and surround the operator. The graphic workstation performs other functions at the same time, such as the system control function and the input-output control function for operation levers. The motion system has an operator seat on its motion base and give a sense of motion to the operator.
    The computer graphic images are made from 3D models. The simulator has two excavator models, medium sized one and small sized one. The views from their operator seat are different each other. It has several person models such as cooperation workers and walkers. They move about near the excavator. It has one work site model including an earth model which changes the shape corresponding the operation.

Eye Movement and Useful Field of View in the Operation of Exacavator

SRR-No.23-3
Takahiro NAKAMURA,Kiyoshi FUKAYA, Jian LU,Yoshiyuki EGAWA and Hikaru KOSHIMIZU

: What is the operator watching while he operates his machinery? Though this is a very simple question, it is very important in order to investigate the background factor for disasters caused by excavators. Because, the possibility to reduce the disaster depends how accurately the operators recognize and avoid nearby workers, dangerous events, and so on. However, researches, which answer such questions, have not been carried out so far.
    Therefore, the first experiment, in which the eye movement of operators was measured, was carried out using the newly developed excavator simulator, and the fundamental factors for the acquisition behavior of visual information in operating an excavator were examined. As the result, it was found that the operators gazed on the important objects to carry out work correctly and carefully, especially on the bucket.
    In addition, the second experiment, in which the target detection task was contained, was carried out. The factors that affect reaction time, miss rate and useful field of view of the operators were discussed. The effect of instruction was not significant, but the detection performance of the operators was influenced by the eccentricity of targets though the head- and body-movement were allowed to be free. The lever-pattern of operation had much influence on the performance. In case the lever-pattern is unfamiliar to the operator, it seems that the more experience the operator has, the greater the influence of that is. Such result means that the promotion of the standardization for lever-pattern must be dealt with cautiously and carefully.

Detection of Intrusion into the Dangerous Region by Image Recognition and Measurement

SRR-No.23-4
Jian LU and Kiyoshi FUKAYA

: As mentioned in the previous papers of this report, one purpose of this specific research is to clarify the attention ability of the excavator driver by ergonomics methods. Another purpose is to propose and develop the automatic safety device as a safety support means for reducing the accident resulted from the human error of the driver. The intrusion detection device which detects the intrusion into the dangerous region in the working area of an excavator is such a kind of automatic safety device. This paper involves the detection method used in intrusion detection device for excavators.
    Previously, some intrusion detection methods using various sensing devices such as infrared sensors, super-sonic sensors and laser sensors have been developed, but they have a number of problems difficult to be solved. In this paper, we study on intrusion detection by means of image recognition and image measurement. For the case that the intruders are nearby workers, the applicability of intrusion detection by means of image recognition was experimented and examined. As an example, intrusion detection by recognizing the color of the helmet was examined. For the case that the intruders are persons not limited to nearby workers (called general intrusion later), the intrusion detection method using the 3D measurement based on stereo vision is proposed.

Countermeasure Against Human's Approaching an Excavator

SRR-No.23-5
Kiyoshi FUKAYA

: There are two kinds of countermeasures against caught accidents by excavators. One is related to excavators and the other is related to co-workers. In this chapter the latter approach, that is, the countermeasures to prevent co-workers from approaching excavators were studied.
    Since the working areas of excavators are dangerous, the areas are often guarded by fences. In general the fences used in construction sites are usually simple except for the fences surrounding the construction sites. For example, the fences of color cones with side bars are widely used. Such simple fences may be stridden over by workers. On the other hand in factories the dangerous areas are guarded by tall fences and the entrances to the areas are monitored. In construction sites the dangerous areas change every day, so tall and strong fixed fences are impractical. Therefore the simple fence with the monitor system is proposed in this report.
    The experiment to estimate the intrusion prevention effect of the simple fence with side bars was carried out. The height of the side bar of the fence was changed and the behavior of the subjects such as striding over the bar, passing through under the bar, or detouring around the bar, was observed. All the subjects strode over the bar when it was low and passed though under the bar when it was high, and some subjects made a detour around the bar when it was middle height. The heights for detouring were from 65cm to 90cm, depending on the stature of the subject. The conclusions are that since the fence of the color cones of 70cm height with side bars is rather too low to prevent persons from entering the dangerous area, its effect is nothing but telling persons not to enter the area, and as the result the higher fences are needed.

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