Safe drive controls with frequency inverters

Abstract

Machine drives using closed-loop speed control are state of the art. As on drives without closed-loop speed control, the movement of a machine part at varying speeds frequently gives rise to a hazard against which the machine operators must be protected. The simplest means of preventing movements during manual intervention in danger zones is the (safe) disconnection of the energy driving the relevant motors. This is however often not possible, for example when intervention is required whilst the machine is running for the purpose of clearing faults, setup, during test operation, etc. Scenarios such as these require the machine to be operated with protective equipment disabled. In order for the operators‘ safety to be assured nonetheless, Annex I, Section 1.2.5 of the Machinery Directive sets out the required measures. Safety sub-functions for drive controls have been defined for implementation of the machine functions required for this purpose. Examples are STO (safe torque off), SLS (safely limited speed) and SS1 (safe stop 1).

This report addresses the use of drive control equipment that implements safety sub-functions at a certain Performance Level according to ISO 13849-1 in consideration of the application and risks. The basic safety sub-functions of drive controls and the requirements relating to their use are presented. The principles of operation of frequency inverters and DC converters are described, and implementation of the safety sub-functions are explained. Examples are provided of application circuits by which the various machine safety functions can be implemented. The corresponding SISTEMA files for quantification of these safety functions are available for download free of charge. The examples include both standard frequency inverters and frequency inverters with integrated safety functions.

This report supplements IFA Report 2/2017, "Functional safety of machine controls", and requires a basic understanding of Categories and Performance Levels according to ISO 13849-1.