Abstract of Special Research Report (SRR-No.26)

National Institute of Occupational Safety and Health, Japan

The Development of Comprehensive Safety Control Measures for Production and Construction Systems (Forth Report: Final Reports)



: As large scale computerized industrial systems such as chemical plants, factory automations and automated building construction systems were used in many industrial field, a comprehensive safety measure for these systems has become great concern for industrial safety. The specific research on "Development of Comprehensive Safety Control Measures for Production and Construction Systems" was conducted from 1997 to 2001 for above reason.
    This research aimed mainly at establishing systematic hazard evaluation methods, safety control measures and safety validation methods for many automated and computerized industrial systems. Following research subjects were conducted in this specific research.
  (1) Survey of actual conditions and specifications for industrial systems
  (2) Establishment of hazard evaluation methods for chemical plants
  (3) Establishment of hazard evaluation methods for large scale construction systems
  (4) Development of a human-error prediction estimator
  (5) Development of safety control system for construction robots
  (6) Development of safety control system for factory automations
    This "Forth Report" deals with newly added extent results in this research.
    Chapter 2 and 3 were related to the research subject (2). The purpose of Chapter 2 and 3 were to develop a extraction method of human-error accidents in chemical plants. The searching method developed in this research was not influenced by researcher's judgement criteria and ability.
    Chapter 4 and 5 were related to the research subject (3). The purpose of Chapter 4 was to introduce a hazard evaluation method for scaffolds using wind tunnel. The quantitative analysis result considering wind velocity and direction was obtained by the experiment using the simulator. The purpose of Chapter 5 was to introduce a probabilistic fracture analysis by the first-order reliability method(FORM). The breakdown probability could be evaluated at the sufficient accuracy by FORM.
    Chapter 6, 7 and 8 were related to the research subject (5). The purpose of Chapter 6 was to propose a risk reduction process and safety designing for construction robots. Safety independent layers were introduced to safety control systems of construction robots to realize human-robot cooperation. The purpose of Chapter 7 was to propose a navigation vision system for construction robots. Safety and flexible travel control was implemented by PC based vision system. The purpose of Chapter 8 was to propose a immunity system for construction robots. The general purpose software which could simulate a conducted disturbance on the shop floor was developed.
    Chapter 9 and 10 were related to the research subject (6). The purpose of Chapter 9 was to introduce a constitution method of the safety control system considering the coexistence of availability and safety. The drastic improvement in availability was achieved by clarifying and eliminating causes of machine stops. The purpose of Chapter 10 was to propose a safe design support system for man-machine systems. The automatically analyzed validity system such as the machine layout, maintenance easiness or workload was developed in this research.

Study on Search of Human-Error Cases in Accident Database of Chemical Plant (First Report: Development of a Searching Method of Human-Error Cases from Accident Database)

Ou-Sup HAN, Teruhito OTSUKA, Takaaki MIZUTANI and Yasuhiro FUJIMOTO

: Much information is written in a accident database, such as the situation when accident occurs, the factors which cause accident, the damage information by accident and so on. Such information related to accident provides not only the technical documents in case study of accident, but also the useful knowledge for development of technique to prevent the recurrence of similar accident. Therefore, from the viewpoint of efficient practical use, it would be important to make positive use of information on the accident database.
    Generally, most human-error case of accident database is written by various description and expression because accident database is produced by two or more person. And extracted information by searching of database varies in researcher's judgment criteria and the capability. Furthermore, much time and effort are required to examine manually information related to the human error from each accident case. Accordingly, it is difficult to explore objectively the accidents relevant to the human-error from the accident data base which is accumulated enormously.
    In this study, to solve problems described above, it was developed an searching method which is not influenced by researcher's judgment criteria and capability. For this, human-error keywords were extracted from a Japanese-English dictionary to examine objectively the accident case related to human error in data base. This searching method by the human-error keywords can be applicable in most accident databases, although a database will be accumulated in future. Also, using the searching technique of this research, knowledge obtained by searching result can be compared with other research's results by the same method. Although the number of accident case increases, searching results from database have the objectivity because it is not necessary to modify the based searching method or change the human-error keywords. However, as subject of future investigation, it would be necessary that the extension and investigation on human-error keywords improve and the technique to enhance searching accuracy would be modified.

Study on Search of Human-Error Cases in Accident Database of Chemical Plant (Second Report: Quantification Analysis on Human-Error Keywords and Accident Reports)

Yasuhiro FUJIMOTO, Teruhito OTSUKA, Takaaki MIZUTANI and Ou-Sup HAN

: In this paper, the results of the categorization of human-error keywords and accident reports with quantification analysis are reported. The procedures are follows;
  1) Summarization of the human-error search keys with regular expressions.
    The search keys were summarized from 817 to 747 words by regular expressions. For example, a Chinese character and their Japanese phonetic characters are described using one regular expression.
  2) Quantification analysis on the summarized keys.
    The quantification analysis with the keys and the 1487 human-error keywords gave many axes with almost same eigen values. Because of the difficulty of the selection of effective 2 axes by eigen values, the alternative method was tried, which method was to pallarelize each samples (summarized keys) to the axis which has the maximum score for the sample. Four axes which pallarelized decades of samples were found, and these axes could be shown more effective than the two axes with the maximum eigen values.
  3) Quantification analysis on the human-error reports searched with the summarized keywords.
    The quantification with the keys and human-error accident reports could show that the effective two axes for the reports. Each axis was defined as 'Internal-factor axis' and 'Interaction-factor axis'.
    Further analysis to categorize the keys and/or the accident reports using cluster analysis would be proceeding with the result of this report which shows the improved selection of effective axes for categorize.

Hazard Evaluation of Scaffolds Against Wind Load Using Construction-Environmental-Simulator Wind Tunnel

Katsutoshi OHDO, Yasumichi HINO and Songpol PHONGKUMSING

: Construction accidents caused by wind frequently happen and the workers are often injured and killed. One important problem that leads to the engineering concern nowadays is the accident of the scaffolds. Temporary scaffolds are typically covered with sound barrier panels or plastic sheets to prevent construction materials and debris from falling from scaffolds. In Japan, the design of scaffolds mainly considers wind loads that are directly acting on the exterior surface of the scaffolds. However, due to these sheets and the wind direction, wind entering the gap between the building and scaffolds through the wall openings, etc. results in significant increase of wind load acting on the scaffolds. The increase of wind pressures can affect the stability of the scaffolds and lead to the total collapse of the large scale scaffolds which can cause injury or loss of life as well as economic loss and construction time delay.
    In this study, a series of wind tunnel experiments using the Construction-Environmental-Simulator was conducted to measure the wind pressures acting on the 1/150 scale 0% porosity simplified scaffolds models. As a first step, a building model without opening was used and a uniform wind condition was considered. Based on the wind tunnel experimental results, the wind direction that caused the maximum pressure was identified. Moreover, there were high pressures around the connection corner of the front and side panels of the scaffolds in a certain case that wind was not directly acting on the scaffolds. This is because there were high pressures acting on the inner surface of the scaffolds that face the building model due to wind that entered the gap between the building and scaffolds. Thus, the wind pressures acting on the scaffolds are greatly influenced by the existence of the building.
    An analysis for the hazard evaluation of scaffold was also performed to ascertain the probability of scaffold collapse. The probability of scaffold system failure was found to be sensitive to the wind speed and direction. In a certain wind direction, there was a high risk caused by the pressure due to wind blowing behind the building and scaffolds.

Probabilistic Elastic-Plastic Fracture Analysis of Circumferential Through-Wall-Cracked Pipes Using the First-Order Reliability Method

Tetsuya SASAKI

: To prevent fractures of pressure vessels and pipes, which are widely used at industrial sites like chemical plants, is essentially important to assure safety of workers and a neighborhood. Since fractures of pressure vessels and pipes usually result from cracks contained in materials, any crack-like defects have not been allowed to exist by regulations. However, it is more economical to continue to operate plants ignoring small cracks contained in materials as long as they are not critical, and the recent development of fracture mechanics has already made it possible to realize such damage tolerant operation. In making such economical and technical circumstance to be a background, so-called fitness-forservice standards for pressure vessels and pipes have being developed in the United States, EU countries and Japan. These fitness-for-service standards tend to adopt the two-parameter approach to evaluate structural integrity of components with crack-like flaws. Some probabilistic methods have also been developed to make quantitative assessments of structural reliability based on the two-parameter approach because there exist a large amount of uncertainties in the assessment parameters. However, most of them employ restricted numerical integration or tedious Monte Carlo simulation methods to calculate failure probabilities, and it is difficult to efficiently assess the reliability of many components included in the large-scale system using such methods. In this paper, making use of the first-order reliability method (FORM) is suggested to efficiently and generally compute failure probabilities of circumferential through-wall-cracked pipes subject to bending based on the two-parameter approach. The fracture of a circumferential through-wall-cracked pipe is one of the most important fractures which must be considered to ensure the plant safety. To confirm adequacy of employing FORM, the failure probabilities are computed by FORM and Monte Carlo simulation methods considering uncertainties in major parameters of the two-parameter approach such as crack size, tensional stress, yield stress and fracture toughness. The results show that FORM provides satisfactory estimates for the wide range of fracture mechanics parameters. The effect of a correlation of yield stress and fracture toughness on the failure probability is also investigated. It is revealed that a positive correlation between yield stress and fracture toughness results in the increase of the failure probability.

Study on Risk Reduction Process and Safety Designing for Construction Robots

Hiroyasu IKEDA, Shoken SHIMIZU, Tsuyoshi SAITO, Jian LU and Masanori ONISHI

: For the industrial robots with the fixed movable space, the safety measures have already been specifically stipulated by the relevant international safety standards. However, since these standards are not applicable to the mobile robots due to impossibilities to prepare fixed guards, the application of the safety design principles for general machines to the mobile robots is tried. In this research, for designing a construction robot categorized as a mobile robot, a concept of the safety designing based on risk assessment and procedure for realizing such concept are proposed.
    Under the risk assessment principles, the risks of hazards assumedly caused by the construction robots are estimated and evaluated. The risk estimation is made on the risk factors utilized by general risk assessment techniques (i.e., severity of hazards, frequency of exposure, possibility of avoidance). In addition to the judgment parameters applied to the conventional industrial robots, the allowable risk ranking described above is applied as one of the judgment parameters. Then, according to the magnitude of the risks, the safety performance of the required risk reduction means is stipulated.
    Then, the procedures for layered safe designing along risk reduction activity are descried and applied to the designing of the construction robot equipped with the mobile platform and manipulators, which can be operated in the environment with the presence of workers around. Assumable typical hazards lead to hazardous events that the manipulator squeezes a worker and that the robot body collides with a worker.
    The manipulator is provided with the inherently safe designing with the force output and speed of the actuator controlled by a brake and a clutch, and the robot mobile mechanism is applied with safety measures for the risk reduction since it is difficult to provide the same inherently safe designing as that for the actuator. Particularly, as the safety measures to prevent the collision of the robot bodies with workers, an ultrasonic radar sensor, a photoelectric reflective sensor and a soft-touching bumper switch are hierarchically managed by a safety controller. According to the size of the detection area for these human detection measures, the safety requirements for them are stipulated, and according to the intervals between the mobile construction robots and individual workers, the human detection measures are hierarchically functioned.
    The construction robot provided with the risk reduction activity can freely behave as long as it is physically secluded from workers. However, when it is approaching a worker, the robot functionally secures the safety in such a way that it can avoid the worker or stop its operation before it makes dangerous contact with the worker. As described above, in whatever the status of robots and workers, it is a requirement of the construction robots to functionally secure the safety in the low-risk status and inherently secure the safety in the high-risk state.

Development of Navigation Vision System for Construction Robots

Jian LU, Hiroyasu IKEDA and Katsumi YASUDA

: In this paper, a navigation vision system is proposed for the industrial mobile robots that are mainly used in unfixed work place, or planned to travel along changeable routes. Instead of the traditional navigation method in which magnetic tags or lanes are constructed on the floor to indicate the route, a series of navigation-signs (briefed as signs in the following) are placed along the route. By change the order and the types of signs in the series, the route can be planned and adjusted simply and flexibly on the spot. The navigation vision system recognizes these signs, detects large non-sign objects as obstacles, and sends these results to the travel control system.
    The vision system is a hybrid system, consisted of two functions, i.e., the object detection function and the sign recognition function. The former is used to determine roughly the 3D position and the size of large objects, including signs, within the travel space of the robot. The later is used to recognize the specific type or meaning of a sign. This paper gives the overview of the vision system, describes details about the implementation approaches related to the two functions of the vision system. By experiments and discussions, it was verified that the design specification can be achieved practically by these approaches.
    The results and significance of this study are mainly as the follows:
  (1) In the research field of robot travel control, for the requirements of the changeable work fields such as the construction work, where task and travel route often change, the navigation method with flexible and easy route-setting is proposed, and the approach for implementing the system is shown.
  (2) In the research field of robot vision, it is shown that the recognition method for 2D image is applicable even to wide 3D space, in case that the focus objective is effectively controlled according to the 3D information from stereo vision.
  (3) As the application of disparity image and stereo vision, the methods for 3D measurement and object extraction are developed. Although the example object used in this paper is the navigation sign of 30 x 30cm, the method is applicable to other types of objects simply by learning their features.

Development of a Construction Robots Immunity System Simulating Conducted Disturbances on the Shop Floor

Hajime TOMITA and Toshiyuki UEKI

: Electric and electronic devices, equipment, or systems are exposed to various kinds of electromagnetic disturbances on the shop floor, such as static electricity and industrial electromagnetic sources, bursts, and surges. To prevent these devices, equipment, and systems from producing improper operating signals due to those electromagnetic disturbances, immunity tests are commonly carried out by the manufacturer before distribution.
    As the current immunity tests do not cover all kinds of electromagnetic disturbances on the shop floor, it has been reported that some equipment, although having passed the immunity tests, produces improper operating signals on the shop floor. As a solution, an immunity system using purpose-built software which can simulate radiatic disturbances on the shop floor has already been developed.
    As reported here, an immunity system for a construction robot using general-purpose software which can simulate conducted disturbances on the shop floor has been developed. The software is used for the calculation of fast Fourier transformation, the division of complex numbers, and inverse fast Fourier transformation. The transfer function of the immunity system is then obtained. The input waveform is obtained as the result of compensating for the transmission characteristics of the immunity system. The applicability of a current-injection probe, electromagnetic clamp (EM-clamp), capacitive coupling clamp, and coupling and decoupling networks (CDN) used for test-signal injection in the current immunity test to simulate conducted disturbances on the shop floor is considered. The usability of the developed system was tested using a model circuit, and a photoelectric safety device for a power press was used as an example of a control device for a construction robot. The current-injection probe, EM-clamp, capacitive coupling clamp, and CDN were able to generate the intended test signals after compensating for the transmission characteristics of the system.

The Basic Study on the Construction Method of the Safety Control System Considering the Coexistence of Availability and Safety

Shigeo UMEZAKI and Shoken SHIMIZU

: The coexistence of availability and safety is a very important problem in the field of the industrial safety. However, the availability is sometimes decreased by improving safety when a trade-off model is established in the relation between safety and availability. The self developing spiral model was proposed for replacing the conventional trade-off model.
    Two types of spiral models were examined in this study. The first model has no priority between safety and availability (described in Fig.2). Accidents might be occurred when the initial safety level was not sufficient. On the other hands, the second model put the priority in safety (described in Fig.3). The possibility of accident occurrence was very small because the complete safety measures were carried out before the operation start.
    Following results were obtained from the consideration of new spiral model.
  (1) The fully safety measure such as the application of safety confirmation system is required in this model. The availability decreases because the machine stops frequently for ensuring safety of the operator. However, the drastic improvement in availability can be possible by clarifying and eliminating causes of machine stops. The availability is improved from 93% to 99.8% in a real automated product line.
  (2) The application range of the dependability concept is examined in this study, and it is proved that this concept is limited to the system which can not sufficiently reduce the risk to the acceptable level in the design stage.
  (3) There are two types of methods for improving availability, that is, the space-depend-type and the time-depend-type. Though the former can drastically improve the availability, the certainty is not enough. On the other hands, the latter is a reverse type for improving availability.

Development of the Safety Design Supporting System for the Purpose of the Optimum Design of Man-Machine System

Shoken SHIMIZU and Shigeo UMEZAKI

: This report proposes a new safety design supporting system which is called the "information shared development model". The conventional safety design process depended on intuition and experience of the personal. Safety measures were sometimes not proper in this case for that reason. The new systematic safety design supporting system was developed for that purpose.
    The "information shared" means that the machine designer and user share the information by using the latest information technology such as the database(DB) and the virtual factory(VF). The systematic cooperated safety design between designer and user was executed by sharing the databese of labor accidents or safety measures. The evaluation of safety design was also executed by sharing the software tools of virtual factory. It could estimate the defect in the layout, the work load for the operator, the easiness of the maintenance work, and the effectiveness of safety measures.
    The "development" means that the supporting system develops itself by the integration of the knowledge of safety design. The design principle of new supporting system was based on that the knowledge developed by the interaction of the inside of the database and the inside of the head of the designer. The self-developed spiral model was proposed based on such principles.
    The new supporting system was applied to the real production line or robot systems, and it was proved that this system has a ability to evaluate not only the validity of safety design but also the appropriateness of human suitability.



: This specifc research report proposed the new safety technology for large scale industrial systems such as chemical plants, construction sites, construction robots or factory automations. Results obtained from this research are summarized as follows:
(1) Development of hazard evaluation technology for chemical plants
    A new retrieval method of human-error accidents database which arised in the chemical plants was developed. It was less influenced by the human judgement criteria and ability because the keyword concerning human-error was selected automatically and conjugational words using morphological analysis were normalized by the new retrieval system.
(2) Development of hazard evaluation technology for large scale construction systems
    The simulator to evaluate the environmental condition around the large scale construction system has been developed. This simulator was used to evaluate the wind environment around the buildings to study the effect of wind on the scaffolds quantitatively. Furthermore, based on the recently developed knowledge of the fracture mechanics, the technique to quantitatively evaluate the failure probability of the structure members in the large scale construction system was also established.
(3) Development of safety control technology for construction robots
    A mobile robot for construction work was developed on the concept of the safety designing based on risk assessment. This robot, taking a form of a trackless mobile robot mounted with a twin-arm manipulator, carries the object while being sign-recognized by a vision system and after stopping at a target position, sets the object in collaboration with an operator. In addition, a new EMI evaluation system for robot work places was developed and its efficiency was verified. The EMI evaluation method could be accurately simulated in an actual electromagnetic field.
(4) Development of safety control technology for large scale industrial systems
    The new safety control technology using the programmable electronic equipment with the triple redundancy, diversity and the self-checking mechanism was proposed. The new concept of the "distributed safety bus control" was also proposed in this study. Many safety measures such as the laser sensor for confirming safety in large scale working areas, discrimination systems between human bodies and objects, runaway monitoring systems for the robot etc. were developed. Optimum designs for man-machine systems such as the constitution methods of safe control system considering the coexistence of availability and safety, the safety design supporting system with the function of evaluating the work load, and the easiness of the maintenance were also developed.

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