Rockwell Automation 2094-EN02D-M01-S1 Kinetix 6200 and Kinetix 6500 Safe Speed Monitoring Safety Reference Manual - Manual (Page 19)

Rockwell Automation Publication 2094-RM001C-EN-P - May 2013 19
Safety Concept Chapter 1
A safety rating up to and including SIL CL3, PLe, and CAT 4 can be achieved in
a single-encoder application with these requirements:
• The motor is a permanent magnet (PM) brushless AC motor.
• The motor controller must be configured as a closed-loop application with
field-oriented control by using the single-encoder for commutation.
• The motor-to-encoder coupling is designed to exclude shaft slippage as a
dangerous failure mechanism.
• The encoder is of the Sin/Cos type and is suitable for the desired safety
rating of the application.
An encoder that is suitable for SIL CL3 applications must follow one of
these two conventions:
– Use independent Sine/Cosine signals and be incapable of producing
simulated signals when under an error condition.
– Use simple or discreet circuitry with no complex or programmable
internal devices.
• Encoder voltage monitoring in Kinetix 6200 and Kinetix 6500 drives can
be enabled, depending on the feedback configuration.
• The system design of the motor/encoder-to-load coupling excludes shaft
slippage and breakage as a dangerous failure mechanism.
Understanding Commutation
Permanent magnet (PM), brushless AC motors are a class of synchronous motor
that depends on electronic brushless commutation for their operation. In PM
brushless motors, an electromagnetic field is created by the permanent magnets
on the rotor. A rotating magnetic field is created by a number of electromagnets
commutated electronically with IGBT’s at the right speed, order, and times.
Movement of the electromagnetic field is achieved by switching the currents in
the coils of the stator winding. This process is called commutation. Interaction of
the two electromagnetic fields produces magnetic force or torque.