Koichi Futsuhara

Realization of a fail-safe train wheel sensor using electromagnetic induction

A wheel detector is described as a method for detecting the approach of a train on a railroad without using any vehicle-mounted devices. Wheels of the train are detected as the change in the magnetic coupling between two coils located on either side of the rail. The coils are placed on one metal plate so that high sensitivity and reliability can be achieved. The wheel detector produces two fail-safe output signals having different characteristics when it fails. One output signal indicates the wheel detection state by the failure of any detector component, while the other indicates the wheel nondetection state by the failure of any detector component. Fail-safe window comparators are used to obtain these characteristics. The two binary output signals are related as mutually negative information and are produced as complementary output signals with double rails. The output signals allow fail-safe logic operations, including logic negations. >

A Study of Risk Assessment Method Containing Hygiene Aspect and Safety Aspect

The most characteristic point of food processing machines is that they require hygiene measures for risk reduction against contamination of manufactured food products for consumers, as well as safety measures for risk reduction to ensure safety for operators. The measures of risk reduction for safety aspects do not always match the risk reduction measures for hygiene aspects. The protective measures of safety aspects may increase the hygiene risk. Therefore, ISO 14159 has defined to decide the suitable protective measures for risk reduction by comparing both safety and hygiene. However, not only ISO14159 but also other standards do not illustrate a concrete method by comparing safety risk and hygiene risk. Harm contents differ between safety risk and hygiene risk, so methods of safety risk estimation are inapplicable to hygiene risk estimation. Consequently it has been an important issue in Food-processing machine industry to develop method of risk assessment by comparing the safety risk and hygiene risk, because of these circumstances. Authors devise the reduction measure of the hygiene aspects to be included in the process of the limits of the machine. We consider it is possible to perform both risk assessments, according to risk reduction process described in ISO 12100-1, without comparing both different risks. This paper mentions about the unprecedented assessment method including different risks.

A Method for Implementing a Safety Control System Based on Its Separation into Safety-Related and Non-Safety-Related Parts

International safety standards recommend that control systems should be separated into safety-related and non-safety-related parts. The control circuit is required to have such an interlock function that the control output of the safety-related part gives permission to the control output of the non-safety-related part. This paper describes the methods of separating and combining the safety-related and non-safety related parts in Chapter 2. In Chapter 3, a configuration example of the control circuit for producing a control output is presented. The control circuit is constructed by two fail-safe techniques, or dynamic fail-safe signal processing and voltage-above-supply-voltage processing. The proposed control circuit has such a fail-safe characteristic that it produces no output when the frequent check of its functioning detects a failure in any of its elements. An interlock device constructed by using the two fail-safe processing techniques and containing high-output semiconductor switching elements is shown.

Logic of Antirepeat Control and its Application to Man-Machine Work Systems.

Antirepeat is one of basic concepts for safe operation of industrial machines. It is regarded as safety control concerned with start of operating. In this paper, logic of antirepeat control is discussed and the concept of antirepeat is evaluated by using multiple-valued logic based on the degree of safety. It is shown that two different strategies exist for achievement of the antirepeat control and basic construction methods based on fail-safe signal processing are presented. An example of automated restarting confirmation based on antirepeat control, which is superior to manual restarting in safety assurance of multiple workers, is proposed in this paper.

Application of fail-safe multiple-valued logic for control of power press

The logical construction of a safety control for the operation of a power press is explicated. Fail-safe dual two-rail system signal processing and fail-safe multivalued logic operations as methods for achieving this control as a fail-safe system are described. A circuit for generating fail-safe two-rail run button signals based on ternary logic for concrete operation of the power press and an operation control circuit for confirming brake performance for each cycle of slide operation by using the run button signals are presented.<<ETX>>