Safe motion: System examination

Safe drive technology merges two issues which individually already involve a high level of complexity. The  challenge is to provide the user with transparent, comprehensible logic in the lifecycle of a safe motion application. The difficulty in configuring and selecting safe drive components is in translating the various influencing factors to the product requirements. Or to put it another way: in selecting products for an optimum, safe drive solution, which parameters are to be derived from which specifications?



The machine design and the functionality demanded by the end customer are essentially the factors that determine which drive technology will be used and how the machine will be operated in control technology terms. The resulting parameters are:

• How many drive axes are there?
• Does the system use servo amplifiers or frequency converters?
• Are the drives decentralized – i.e. outside the control cabinet?
• Which safe drive functions are required and how are the parameters to be set?
• Does the movement to be monitored involve an elliptical curve, synchronous drive axes or, in the simplest case, a single movement?

Specifications from the B and C standards and risk analyses will provide the safety integrity requirement (SIL and PL). These, of course, will also influence the required safety functions. The reaction times of the safe drive components are part of the overall machine design and must be fine-tuned as part of an iterative process. Factors such as stopping performance, safety distances, inertia of the moved mass or the reaction capability of the machine control system play a key role.

General requirements may be whether or not the machine is to be retrofitted with safe drive functions, for example. In some circumstances, existing components must continue to be used, a situation which will often favor an external safety solution. These criteria and parameters must be converted into a concept. The result is a safe drive solution, made up of standard market components.