System Examination: Motors

The relevant properties for the motor in terms of its use in safety-related systems are:

• Type of movement (rotating, linear)
• Acceleration capability (inert asynchronous motor or air-borne linear drive)
• Integrated motor encoder
• Integrated holding brake incorporated into the safety concept

The motor’s acceleration capability influences the system’s maximum permitted overall reaction time. Highly dynamic linear motors have extremely low electrical time constants on the winding and a high overload capability, so that a multiple of the rated power is present in just a few milliseconds. Resolvers are widely used as motor encoders in servo drive technology. They are used in rotating motors and are both robust and economical. The measuring system provides an absolute position within a motor rotation, but has limited resolution due to the function principle. Only rarely can resolver signals be evaluated by safe monitoring components. For this reason, motor encoder systems with sine/cosine analogue tracks are preferable in safety-related applications with motion monitoring. Motor encoder systems with an all-digital interface can only be monitored using special manufacturer-specific safety components. Third party products cannot be connected.