JNIOSH

Abstract of Special Research Report (SRR-No.16)

National Institute of Occupational Safety and Health, Japan

Development of Devices and Working Systems for Promoting Safety of Aged Workers (Second Report)

Introduction

SRR-No.16-1
Shigeo UMEZAKI and Soichi KUMEKAWA

: As the aging society becomes actuality in Japan, an expansion of working fields and promoting safety for aged workers have become matters of great concern. For this trend, the specific research on "Development of Devices and Working Systems for Promoting Safety of Aged Workers" was conducted from 1990 to 1994.
    This research aimed mainly at promoting safety of aged workers in non-steady operations such as heavy work handling, trouble-shooting, repairing and maintenance. Following research subjects were conducted in this specific research.
(1) Improvement of environmental conditions for aged workers.
(2) Evaluation of abilities of aged workers to predict and avoid accidents.
(3) Improvement of operating equipments for aged workers.
(4) Development of assisting equipments for heavy work handling.
(5) Development of safety systems in warehouses for aged workers.
    This "Second Report" deals with research subjects (4) and (5), as the "First Report" published in 1993 described results of research subjects from (1) to (3).
    Chapter 2 and Chapter 3 are related to the research subject (4). The purpose of Chapter 2 was to develop an automatic work handling manipulator for assisting aged workers who handle heavy works by cranes. A cooperative control system between the crane and the work handling manipulator was designed for positioning heavy works accurately by a balance servo control.
    The purpose of Chapter 3 was to develop a supporting equipment for aged workers who operate a cart with full loads. An automatic chasing vehicle system which enables the vehicle to follow an aged worker was developed.
    From Chapter 4 to Chapter 7 are related to the research subject (5). The purpose of Chapter 4 was to develop safety systems for automated warehouses which sometimes force aged workers to climb up to the heights, to confirm safety over wide areas by their own eyes, or to carry out their works without stopping stacker cranes.
    The purpose of Chapter 5 was to develop a safety device of laser beam type for compensating visual ability of aged workers. The device is to be used for aged workers to confirm safety over wide areas such as automated warehouses and conveyors.
    The purpose of Chapter 6 was to develop a start-up alarm system for reducing work load of aged workers. The system sounds the alarm automatically by start operation and permits a machine to start when the system confirms that the alarm sounds without fail.
    The purpose of Chapter 7 was to theorize logical structures of guard systems for danger zones in automated warehouses. The entrance guard locking system which locks a door of danger zones until the stacker crane stops completely was necessary for the protection of danger zones.

Development of Safety Control System of Heavy Work Handing by the Cooperative Control of Crane and Manipulator

SRR-No.16-2
Noboru SUGIMOTO and Hiroyasu IKEDA

: The handling of a heavy work, for example, an operation to change heavy dies of a large press machine or injection machine, is a dangerous task. A crane is one of the suitable mechanisms to handle the heavy work, but it makes the suspended work vibration. In construction sites of building, many aged workers engage in handling a crane-loaded heavy work and they suffer from accidents of impact or crushing with the heavy work.
    This report proposes a heavy work handling system which consists of crane and manipulator remote-operated by workers. To secure safety of operator against misoperation, the manipulator is controlled to move with compliant motion by pneumatic actuators. An operation to decrease the sway and to secure the work at the possition proposed to be held, is conducted by an electromagnetic brake element which is installed at each joint of manipulator.
    The kinetic energy of swaying work dissipated in slip condition of the brake generates the possibility of turnover of the manipulator. The turnover mechanism is modelled in the manipulator. Based on this model, a cooperative control system between crane and manipulator is designed for decreasing a work sway and securing safe handling and positioning.
    This paper describes the practical load handling, especially, a newly developed position control method of pneumatic manipulator. In general, a pneumatic manipulator is hard to achieve an accurate positioning. To improve the low performance in operation of pneeumatic manipulator, an effective control method is introduced to settle the unsteady behavior of the manipulator by friction control. An elecrtomagnetic brake is used for this purpose. This element produces prompt damping force to fix their posture, and an inching motion control achieves the highly accurate control of the manipulator by this element. Consequently, this system realizes anti-sway handling operation of a heavy load in high efficiency and safety.

Development of Chasing Carriage Vehicle

SRR-No.16-3
Hiroyasu IKEDA and Noboru SUGIMOTO

: There are still lots of manual handling works in which aged workers are engaged. In these manual working conditions, aged workers often use carriage vehicles, such as hand trucks and hand carts, in order to support their physical strength.
    These vehicles tend to be used by operators with less attention, but there are dangers of collisions between operators and vehicles with full loads because of poor visibility and a possibility of failure in operation. Especially, eyesight and physical abilities of aged workers are too weak to avoid collisions. On the other hand, aged workers are often exhausted mentally and physically because they must pay attention to the surroundings while steering and pushing the vehicles with their full strength.
    To solve these problems, the authors proposed a powered carriage vehicle system which enables the vehicle to follow an aged worker as a guide automatically. The aims to develop this kind of vehicle are to release the aged worker from their exhaustion. A safety function such as an anti-collision is essential to the chasing carriage vehicle. A chasing control function is required to keep chasing the guide and not to stop unnecessarily.
    In this chapter, a structural concept of the system to confirm safety was logically discussed. As the result, the chasing carriage vehicle guided by aged workers must have:
  1) the safety confirmation method which stops the tracking operation in the event of coming up to the guide,
  2) the safety function to keep an adequate distance between the guide and the vehicle. In the distance confirmation method, reflecting type of infrared sensors were used to satisfy the above-mentioned requirement, that is, they can output a guide detecting signal which means the adequate distance, only when they normally work.
    In order to achieve the chasing control of the vehicle, moving speed and steerage should be controlled in real-time. Here defined six detectable areas by four infrared sensors for the chasing control, and the adequate distance between the guide and the vehicle was judged by these sensors only when the guide existed in any one of the six areas. These sensors were able to measure distance between the guide and the vehicle by use of a special cloth of the guide, and to produce the corresponding signal.
    Furthermore, this chasing carriage vehicle can sound an alarm when turning right or left. This alarm system made improvement of operation efficiency because the alarm prompted the guide to walk constantly and smoothly.
    Practical experiments proved that the chasing carriage vehicle was composed as the safety confirmation system with infrared sensors.

Development of Safety Systems of Automated Warehouses for Assisting Aged Workers

SRR-No.16-4
Shigeo UMEZAKI,Kiyoshi FUKAYA, Soichi KUMEKAWA and Shoken SHIMIZU

: There are many non-steady operations in automated warehouses such as trouble-shooting, picking, repairing and maintenance. In order to conduct these operations, workers are sometimes forced to climb up to the heights, to confirm safety over wide areas by their own eyes, or to carry out their work without stopping stacker cranes. They are required to have physical abilities such as good body balance, quick response and good eyesight, but these abilities naturally declines with age. As a result, aged workers sometimes meet with serious accidents during above operations.
    In this report, safety systems of automated warehouses for assisting aged workers are proposed. These systems are summarized as follows:
(1) Manipulating system for trouble-shooting
    The manipulating system for trouble-shooting was developed so that the aged worker can correct the arrangement of loads on a upper rack from the outside of the movable range of the stacker crane. The manipulator is remotely controlled by a monitoring system.
(2) Safety system for picking operation
    The safety system for picking operation was developed so that the aged worker can carry out picking operations without entering into the movable range of the stacker crane. The picking area is limited and is shielded by a rotating shutter.
(3) Safety system for manual operation
    The safety system for operations such as trouble-shooting, repairing and maintenance was developed so that the aged worker can avoid any crash with the stacker crane. The system can stop the stacker crane immediately in the event of an unexpected runaway due to a misoperation by a worker or a malfunction of a controller.
(4) Prevention system against unsuitable start operation
    A safety device of laser beam type was developed which confirms the absence of workers in the movable range of the stacker crane in order to prevent a third person from starting the stacker crane erroneously.
(5) Prevention system against entering into the movable range of the stacker crane
    A system which prevents a worker from entering into the movable range of the stacker crane was developed. The worker can enter the movable range of the stacker crane from a interlocked door only when the stacker crane stops or in low power mode such as a manual operation.

Development of Safety Device of Laser Beam Type for Compensating Visual Ability of Aged Workers

SRR-No.16-5
Shigeo UMEZAKI, Kiyoshi FUKAYA and Hiroyasu IKEDA

: In automated warehouses, workers are forced to confirm a human absence in a movable range of a stacker crane before they operate it. Especially for aged workers, whose visual abilities decline with age, it is extremely difficult to confirm the human absence. As a result, aged workers may start it erroneously in spite of the human existence in the movable range of a stacker crane.
    In this report, the prevention system against the erroneous start operation by aged workers was developed. The safety device of laser beam type was developed which confirmed the absence of human body in the wide movable range of the stacker crane automatically instead of eyes of aged workers. The characteristics of the safety device are summarized as follows:
    (1) The safety device uses laser beam for monitoring wide range. A long exposure of the laser beam to human eyes may become harmful. Therefore, the one-shot laser beam of a very short period is used. If the one-shot laser beam reaches the receiver (photo sensor), this means that human body does not exist in the movable range, and the safety device permits radiation of the next shot and this process is repeated. On the other hand, if the one-shot laser beam does not reach the receiver, this means that the human body exist in the movable range, and the safety device stops the next radiation. This control method can be called the "Consecutive Confirmation Control Type". The human eyes are never harmed by this control because the exposing of the laser beam to human eyes can be limited within the very short period.
    (2) The exposing period of the beam shot can be reduced to less than 27ms under the condition that the wavelength of the laser beam is 670nm and its output power is 1.5mW. The safety classification of this device corresponds to CLASS 1 (as defined IEC825) in comparison with CLASS 3A of a normal laser beam sensor.

Start-up Alarm System for Reducing Work Load on Aged Workers

SRR-No.16-6
Kiyoshi FUKAYA

: Before a start-up of a large machine, such as an automatic warehouse and a long belt conveyor, it is indispensable to confirm the safety condition, which means nobody is in the movable zone of the machine. In many cases this safety confirmation should be conducted by the operator of the machine, but it is difficult especially for an aged worker who is weak-sighted. Because actually many accidents occurred in the start-up process, safety measures which assist the operator to confirm safety are needed.
    One of the safety measures is an alarm system for workers in the movable zone of the machine.
The alarm system, however, has some defects. For example, a skip of the alarm operation or a failure of the alarm system makes the alarm ineffective. Therefore, the alarm system with foolproof and fail-safe characteristics has been developed.
    This alarm system has the following features.
  (1) This system sounds the alarm automatically by start operation of the machine in order to ensure foolproof.
  (2) This system confirms that the alarm really sounds and permits the machine to start in a fail-safe manner.
  (3) In order to make the system fail-safe, fail-safe ICs are used for signal processing.
  (4) The sound frequency of the alarm is rather low, because the aged worker has a tendency to miss a high tone.
  (5) There is a rather long period from the start operation to an actual power supply to the machine, because the worker in the movable zone of the machine needs time to escape out of there.
    This system consists of an operation block, an alarm generation block, a sound detection block and a control block. The start-up sequence begins by start-up operation, which makes the alarm sound. When the sound detector detects the alarm, it triggers an on-delay timer to count the time for escape. When the time is up, the machine is powered. If any element of the system fails, the sequence stops at this failure.

Logical Study on Danger Zone Guard System in Automated Warehouses

SRR-No.16-7
Kiyoshi FUKAYA, Soichi KUMEKAWA and Shigeo UMEZAKI

: Safety measures were analyzed logically from the standpoint of protection against a danger zone. In this analysis an accident is represented logically by coexistence of a man and a machine. Consequently basic principle of safety measures is a spatial or temporal separation of a man and a machine. Spatial separation means a division of the space into a danger zone in which machinery moves and a safety zone in which men exist. Temporal separation means stop of machinery during men's existence in the danger zone. To control separation, an interlock structure is needed. There are two type of interlock. One is an interlock to human and another is an interlock to machine. If there is no time delay in control system, either interlock can realize the separation. But there is a time delay in any control system and it must be compensated in control structure. There are two methods of compensation. One is "the confirmation precedence method" in which both type of interlock structure are applied, that is, a human entrance into the danger zone is permitted after confirming stop of the machine and start of machine operation is permitted after nobody's existence in the danger zone. Another is "the prediction method" in which a human approach to the danger zone is predicted and a machine is stopped. This method is an enhancement of an interlock to machine and control is based not only on the human existence in the danger zone but also on the prediction of human existence. Therefore certainty of the prediction and of control, especially stop control of machine, is needed.
    In an automatic warehouse the prediction methods can not be applied, because an emergency stop of a stacker crane may cause other accidents such as fall of loads. Furthermore, aged workers in Japan have the tendency to avoid a stop of a machine, and they often overcome the safety device to enter the danger zone without stopping the machine. Consequently the confirmation precedence method should be applied. To prevent men from entering the danger zone, the safe guards must surround thoroughly the danger zone including the opening for loads and it was moved to 2nd floor level out of human space. To permit a man to enter the danger zone a door with lock was used and a man must wait the unlock of the door until the stacker crane stops.
    The guard system against danger zone with entrance door lock is necessary for the machinery in which emergency stop is not preferable.

Conclusion

SRR-No.16-8
Shigeo UMEZAKI and Soichi KUMEKAWA

: The aim of this specific research was to promote safety of aged workers engaged in nonsteady operations. To realize this purpose, several safety measures were proposed based on physical and mental characteristics of aged workers. Results of these studies are summarized as follows.
(1) Development of safety control system of heavy work handling by the cooperative control of crane and manipulator.
    The automatic work handling manipulator was developed for assisting aged workers who handle heavy works by cranes. This manipulating system controls compliance of the manipulator by a friction torque of an electro-magnetic brake. A cooperative control system between a crane and the manipulator was designed to position the heavy work accurately by the balance servo control.
(2) Development of chasing carriage vehicle.
    The chasing carriage vehicle system was developed which enables the vehicle to follow the aged worker automatically. To realize safe and efficient chasing, the vehicle was designed to have functions that it keeps an adequate distance between the aged worker and itself and to stop in the event of coming up to the worker or its failure.
(3) Development of safety systems of automated warehouses for assisting aged workers.
    The manipulating system for trouble-shooting, the safety system for picking operations and the safety system for manual operations etc. were developed. By the first system, an aged worker can correct the arrangement of loads on a upper lack without entering the movable range of the stacker crane. By the second system, a worker can also carry out picking operations without entering this area. By the third system, a worker can avoid a crash with the stacker crane when a worker executes trouble-shooting, repairing and maintenance.
(4) Development of safety device of laser beam type for compensating visual ability of aged workers.
    The safety device of laser beam type was developed which confirms the absence of human body in the movable range of stacker crane automatically. As a long exposure of the laser beam to human eyes may be harmful, the one-shot laser beam should radiate during a very short period to this movable range. The exposing time of laser beam to human eyes can be reduced within 27ms.
(5) Development of start-up alarm system for reducing work load on aged workers.
    This system sounds the alarm automatically by the start operation and permits the machine to start when it confirms that the alarm autually sounds without fail. The sound frequency of the alarm is set around 300 Hz, bacause aged workers have a tendency of missing a higher frequency sound.
(6) Logical Study on danger zone guard system in automated warehouses.
    The danger zone guard system can be divided into the safety stop system and the entrance protection system. The former system is the emergency stop system which stops a machine immediately after the sensor detects a human body entering the danger zone. The latter system is the guard locking system which keeps the entrance door to the danger zone locking until the machine stops completely. The entrance protection system is preferable for aged workers, because it can prevent them from entering danger zones perfectly.

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