Safe drive controls with frequency converters (IFA Report 7/2013e)

Abstract: Machine drives with speed control are state of the art. As on drives without speed control, variable speed of movement of a machine part frequently gives rise to a hazard against which the users of the machine 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. Such cases require the machine to be operated with protective equipment disabled. In order to assure the user‘s safety despite this, the hazardous movements are performed in such cases at safely limited speeds and/or torques, and frequently in inching mode and/or only when an enabling switch is actuated. Safety 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 is intended for parties using drive control equipment who wish to use safety functions at a certain Performance Level to EN ISO 13849-1 in consideration of the application and risks. The basic safety functions of drive controls and the requirements relating to their use are presented. The principles of operation of frequency converters and DC-DC converters are described, and the concept of integrated safety functions explained. Examples of applied circuits are shown 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 converters and frequency converters with integral safety functions.

This report supplements BGIA Report 2/2008e, “Functional safety of machine controls”, and requires a basic understanding of Categories and Performance Levels.