Citation

Weck M, Frentzen B. J. Occup. Accid. 1986; 8(1-2): 99-107.

Copyright

(Copyright © 1986, Elsevier Publishing)

DOI

unavailable

PMID

unavailable

Abstract

Stored program controls are being introduced, on an increasing scale, for applications that may be critical to safety in areas such as nuclear reactor monitoring, medical technology and traffic light management. In addition to the objective of preventing damage to persons or objects and minimizing shutdown periods and rejects, fail-safe systems are gaining increasing importance in the control and monitoring of manufacturing processes.Examples may be found in controls for robotics and presses as well as in systems monitoring security of personnel.

A system for controlling the safety of presses is presented and test results to date reported. With the aid of three microcomputers operating independently and cross-checking themselves by matching routines implemented at software level, a majority-decision system has been devised. The reason for relying on three components was that this number was sufficient to trace the source of the error distorting the partial result without needing to take heavily into account the failure rate, which increases as a function of the number of elements and tends to produce a negative influence upon overall system reliability.

Software for the interlinked microcomputers consists of program modules for ensuring control functions, synchronization and data exchange between the computers as well as for matching computational results. Using the data exchanged the units cross-check them-selves and, in the event of error, will exclude the erroneous computer from the majority decision-process and generate an error report. This essential ingredient of automatic error recognition in the system concept was extended to include the capability of replacing defective computer modules without affecting overall system availability. Integration and synchronization of a repaired or replacement module into the majority process is automatic.In addition to detailing the software concept and data exchange within the system, significant characteristics of the hardware in use are presented. This hardware includes the computer components and specialized test and display items, e.g. status indicators of the computer systems.

Experience and test results available to date on the system's behaviour under simulated error and failure conditions are reported. This review is confined to the processing of information in the component systems. The purpose of present and future research work is the development of speciaslized hardware for linking this type control to manufacturing processes.