Safe Speed Monitor (Ssm) - Mitsubishi Electric MELSEC Q Series Programming Manual

1 OVERVIEW

1.4.3 Safe speed monitor (SSM)

(3) Safely-limited Speed function guarantees the motor control (the motor rotation
speed), but it does not guarantee the actual machine safety speed. Make sure to
set parameters so that the safety speed of the machine is the same as the safety
speed of the motor.
(4) When using Safely-limited Speed function when there is no speed command from
the Motion controller or the command speed is 0, using an external encoder
(external auxiliary input pulses), or a safety encoder and switching to Safe
Operating Stop (SOS) is required.
(5) The accuracy of safety speed observation depends on the performance of the
external auxiliary pulses, or the safety encoder. Therefore, when using external
auxiliary pulses, the number of the external input pulses for safety speed must be
determined considering the external auxiliary pulses resolution and the allowance
input pulse frequency.
(6) Check if the rotation speed of the monitored servo axis is the same as the actual
speed by using a tachometer, etc. considering the speed includes an error caused
by the encoder resolution of the external auxiliary input pulses.
(7) The defect of the mechanical section such as slid of shaft and wanting of a timing
belt, etc is not covered. Be sure to eliminate the risk of mechanical section before
operation.
(8) Speed monitoring error detection time is set in the unit of 10ms, but the time
resolution in the actual operation is 25ms. Error in shorter than this time are not
detected.
(9) Create sequence program so that Scan time is within 25ms to make sure that PLC
CPU performs the safety observation function within a certain process time. If
scan time is 25ms or longer, PLC CPU should be added to distribute the load of
the process.
(10) Safety observation error (shutdown signal OFF) does not occur during the time
set by the safety observation parameters after speed is over the limit. Make sure
that safety can be ensured during this period.
(11) The error occurs when detected speed is different between the motor encoder
and the external auxiliary input pulse, and the time required to detect the error
depends on the frequency of the external auxiliary pulse. Determine the number
of external input pulse considering the error detection risk.
(1) If the safety output condition of SSM is used as a restart trigger, incidental start-up
cannot be prevented. A restart interlock must comply with EN60204-1. However,
using it as the operation ready signal is possible.
1 - 11