Masayoshi Sakai

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>>

Logic and Method for Safety in Controlling a Power Press.

Standards have been established by the Japanese Ministry of Labor on the mechanical structure of the power press. These standards provide for the slide to the effect that the power press should be equipped with an overrun monitor function which enables the slide to be forcedly stopped in case the slide fails to stop within a specified allowable range around the upper dead point. This paper regards the press operation as a human-machine system in which both the operator and the machine may cause an error, and defines the overrun monitor function as a requirement for safety operation. Furthermore, this paper establishes a signal processing method for the infallible operation of the overrun monitor function and specifically shows a fail-safe overrun monitoring system based on this signal processing method.