APPENDIX C – RESTART INTERLOCK CIRCUITS
C-2
CDS7324 (FORMERLY LSF-0819)
Rev. A
INSTALLATION & USER’S MANUAL
C.2 RESTART INTERLOCK FUNCTION
The Moog RIC safety function has been validated compliant with the provisions of category 3 as defined in the
harmonized standard EN-954-1:1996 by demonstrating that:
•
a single fault does not lead to the loss of the safety function
•
some, but not all, possible faults can be detected
•
the accumulation of undetected faults can lead to the loss of the safety function
The remaining risk is in the case where two errors/faults occur simultaneously in the power section; the motor
briefly rotates through a small angle (6-pole motor 60°, 8-pole motor 45°, 12-pole motor 30°, 16-pole motor 22.5°).
The drive controls the movements of an AC three-phase motor via the generation of a rotating magnetic field. To
do this, the microprocessor generates a complex model of pulses, which are amplified and used to drive the
power semiconductors.
The Restart Interlock function operates via hardware, with a relay which interrupts the auxiliary power supply to
the IGBT drivers, and via software by blocking the generation of PWM pulses.
As a result of a risk analysis and evaluation which must be carried out according to the Machinery Directive
98/37/EC modified and referring to standards EN ISO 12100-1, EN ISO 12100-2, EN 954-1 (EN ISO 13849-1)
and EN 1050 and, if it exists, the product standard (e.g. EN 775, safety requirements for robots), the machinery
manufacturer must configure the safety circuit for the complete machine taking into account all of the integrated
components of the safety chain, including the electric drives.
The approach to achieving category 3 safety is mainly characterized by structure, which is linked to the
consequences of the loss of the safety function and to the risk of a specific application.
The more the risk reduction is dependant on the circuit parts, the higher the performance level of these parts is
required to be.
To improve the reliability level of the safety function of the drive (one hardware channel and one software
channel) or to discriminate between the intervention of different protection systems on the machine by checking
the NC contacts, on the RIC board two relays are used, both of which are able to interrupt the auxiliary power
supply to the IGBT drivers.
For example, the product standard EN201/A2:2005 related to injection moulding machines with electrical axes,
specifies for the axis for the horizontal movement of the plate the use of both the relays in order to have two
independent hardware channels in addition to the standard SW channel.
Moreover the architecture of all the circuit parts (external to the drive) which are involved in the safety function
must be compliant with category 3 of EN 954-1 (EN ISO 13849-1).
The Restart Interlock function is included in the drive and prevents the need to power-off the drive and to re-do
the standard restart procedure.
The Restart Interlock safety function prevents the motor unexpectedly starting from standstill. This circuit can be
used in the “Safe Standstill” machine function. When the motor is rotating, the switching-on of the Restart
Interlock provides an uncontrolled stop (category 0 according to EN 60204-1:1997).
