Design of servopresses - Safety recommandations

Servopresses are innovative machines whose sales are increasing. The evolution of servomotors and recent arrival on the market of power drive systems including safety functions have contributed to their emergence. For example, servomotors are used to participate in safe stopping of the slide when protective devices are actuated.<br/>
There is still no European or international standard for these specific presses, a draft is scheduled at ISO standardization level.<br/>
This document presents an inventory of specific techniques of servopresses and the results of their detailed study in normal operation and in case of occurrence of a failure. It particularly points out that a safety-related power drive system, when affected by a failure, reacts to the latter by initiating a failsafe position, which may be different from the initially intended safety function. In the case of the servopresses, it can result in a degradation of safety functions performances. <br/>
Recommendations regarding the safety functions supported by the power drive system are proposed. For example, safe stop types have been defined, describing the different steps assigned to servomotors and for example those that require a complementary mechanical brake to stop the slide in the absence of torque motor.<br/>
In conclusion, the paper describes in which conditions the means of protection that are listed in the standards for the design of "traditional" machines can ensure their function.