Abstract of Special Research Report (SRR-86-1)

National Institute of Occupational Safety and Health, Japan

Study on Preventing Occupational Accidents Due to Falling Construction Works for Elderly Workers


Hidenori BODA and Soichi KUMEKAWA

: A lot of industrial accidents have occurred in working of machinery in Japan. Recently, the industrial accidents that have caused by machinery become about 30 percents of all industrial accidents in Japan.
    Then, the special research for hazard control technique and the application to man-machine systems, in order to prevent those industrial accidents that are caused by machinery.
    This special research includes two thesises. One of them is the development and improvement of measuring system for prevention of hazards in man-machine systems. And, another is the practical application of hazard control technique to man-machine systems.
    The followings are studied according to the above two thesises ;
  (1) on the detection of a man coming close with an infraredray-sensor
  (2) on the prevention of squeezing injuries with a touch-sensor
  (3) on the prevention of hazards in man-machine systems with an electro-sensitivity device
  (4) on the interlock mechanism between sensing systems of guard and machinery
  (5) on the warning devices applied the alarm-sound in a factory
  (6) on hazard assessment of man-machine systems using system safety technique
    Results of the special research are given as following three sections in this report.
  (I) Fail-Safe Mechanism and Application for Man-Machine Systems
  (II) Acoustic Countermeasures for Safety
  (III) On Hazard Assessment of Innovative Systems
    The results of the special research would be very useful to prevent for hazards in man-machine systems.

Fail-Safe Mechanism and Application to Man-Machine Systems

Soichi KUMEKAWA, Noboru SUGIMOTO, Kiyoshi FUKAYA and Shoken SHIMIZU

: Safety discussions are always heated one. Particularly with the development of safety for new types of machinery with a minimum record of accidents, safety that is traded off with economy is subjectively evaluated and intensive discussions sometimes fall through due to "differences of opinion".
    Not only innovative machinery such as robot, numerical control machinery, automatic guided vehicle, stacker crane, machining center but various kinds of conventional automated machine are no exception in this sense.
    To bring to end now a repetition of subjective discussions on safety and to approach the safety of automated machines from a common point of view, in this paper, establishment of a "principle of safety" is tried. According to the Principle, safety discussions can be continued for machinery with a short accident record, like robots, from a common standpoint. And conclusion satisfactory to everyone concerned can be reached.
    This paper presents the development of the Principle by discussing construction of safety sensor sensing human accessing to danger zone/point and interlocking mechanism to be reasonable. And robot-related human operation in Shuttle-working system and pneumatic grinding system improved in fail-safe are developed and evaluated from a point of view of the Principle.

Acoustic Countermeasures for Safety

Kiyoshi FUKAYA and Yoshiyuki EGAWA

: 3.1 Sound control Emergency Stop device
      by Kiyoshi FUKAYA
    The development of automation has brought about many changes in factories. One of them is underpopulation of workers, i.e. work range has broadened and no colleague is around the worker in automated line. When such a worker happen to meet an accident, even though he cries for help, he can not expect help from colleagues. In these circumstances, a device which recognizes voice for help and stops the machine will be great help. The possibility of application of speech analysis technology to emergency stop device was investigated.
    The system consists of two sub-system : voice input system and voice recognition system. The system must have the function of distinguishing voice from background noise. In this research, the input system bears this function.
    Voice input system consists of microphone and radio wave transmitter and receiver. In order to give worker the freedom of movement, use of radio device is necessary.
    In order to lessen the influence of noise, the bone transmitting microphone was used. It detects the vibration which arise in vocal cords and is transmitted through head bone, and therefore it has low sensitivity for sound. The measurement of sensitivity showed sufficient faculty.
    Two voice recognition devices of speaker dependent type were tested. Recorded voices were registered and were recognized in various playback condition ; normal, low/high tone, low/high speed, small/large voice, etc. They recognized poorly voices which were not played back but pronounced each time and voices which were played back in high speed. The shift of voice to high pitch resembles the voice in time of emergency. It seemed that they can not cope with the fluctuation of human voice.
    In order to distinguish stop command, simple algorithm was adopted : large voice which lasts for a certain duration considered as command for emergency stop. Simple device which fulfills the algorithm was made and tested. The test showed that the total system has the possibility of practical use.
    The device developed do not have fail safe function, which is indispensable to "safety device". Therefore this is not safety device but safety assist device. To give them the fail safe function is future problem.

3.2 Selection of Auditory Warning Alarm According to Different Unsafe Condition
      by Yoshiyuki EGAWA
    For evaluating the characteristics of auditory warning which were safety measurements using acoustics, this: report investigated them from the two points of view as follows.
  I. Warning alarm should have the characteristics not to be masked by ground noise in the factory.
  II. Warning alarm should be made up of wave forms which are suitable for utility purposes of warning usage.
    About I theme, the data which we had measured about fifty kinds of ground noises in many factorys were classified as eight patterns model-noise by cluster analysis. According to form in 1/3 Oct. analysis, their models were named "Pink-noise, 2 tsu-yama (koiki), Chuiki-yama, Teiiki-ochi, Owan, Chuiki-ochi, Koiki-yama, and Teiiki-yama."
    Next, spectrum analysis of warning alarm being made use of various occasions was performed. As the result analysis, four types of alarms were found in auditory warning.
    From a frequency band viewpoint, it was found that warning alarm had two types which were Wide band type and Narrow band type.
    Further, there were two types, which were named Noise spect.-type and Linear Spect.-type from a spectrum form.
    Experiments on discrimination four types alarm from eight patterns model-noise were conducted. As the result of experiments on discrimination, Wide band type alarm was more available than Narrow band type in all model-noises and Noise spect.-type alarm was more discriminative than Linear spect.-type in Chuiki-yama model noise.
    Regarding as shift type alarm (like a siren) being made use of emergency car (i.e. fire engine) , the siren was most discriminative in the case when the parameter indicated 1000 ˜ 2000 Hz/2 sec.
    About II theme, we arranged auditory warning alarm according to the wave form and purpose of warning usage.
    This result was illustrated in Table 3.2-5.

Hazard Assessment of Innovative Systems

Yoshinobu SATO

: In this paper the problem of how to assess hazards posed in innovative man-machine systems is discussed. First, the procedure of hazard assessment for innovative systems with fewer operation data is discussed. Secondly, action-change and action-chain models for identification of hazards are presented, and useful identification results of hazards that could be posed in present or future human-robot systems are shown. Thirdly, the second step of hazard assessment that is minute qualitative analysis of accident-causing-mechanisms is discussed, and requisites to safety interlock systems or safety monitoring systems are mentioned quoting fault trees extracted as subsets of comprehensive logic models which analyze general accident-causing-mechanisms. Lastly, methodology of quantitative evaluations is described especially emphasizing sequential nature of basic events for quantification of cut sets.

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