3. SIGNALS AND WIRING
3 - 50
3.7.3 Vertical axis freefall prevention function
The vertical axis freefall prevention function avoids machine damage by pulling up the shaft slightly like the
following case.
When the servo motor is used for operating vertical axis, the servo motor electromagnetic brake and the
base circuit shut-off delay time function avoid dropping axis at forced stop. However, those functions may not
avoid dropping axis a few μm due to the backlash of the servo motor electromagnetic brake.
The vertical axis freefall prevention function is enabled with the following conditions.
Other than "0" is set to [Pr. PC54 Vertical axis freefall prevention compensation amount].
The servo motor speed decelerates lower than the value of zero speed by turning off EM2 (Forced stop
2) or by an alarm occurrence.
The base circuit shut-off delay time function is enabled.
EM2 (Forced stop 2) turned off or an alarm occurred while the servo motor speed is zero speed or less.
(1) Timing chart
ON
OFF
Electromagnetic
brake
Set the base circuit shut-off delay time.
([Pr. PC16])
SON (Servo-on)
MBR
(Electromagnetic
brake interlock)
ON
OFF (Enabled)
Base circuit
(Energy supply to
the servo motor)
ON
OFF
Release
Activate
Position Travel distance
ON
OFF (Enabled)
EM2 (Forced stop 2)
(2) Adjustment
Set the freefall prevention compensation amount in [Pr. PC54].
While the servo motor is stopped, turn off the EM2 (Forced stop 2). Adjust the base circuit shut-off delay
time in [Pr. PC16] in accordance with the travel distance ([Pr. PC54). Adjust it considering the freefall
prevention compensation amount by checking the servo motor speed, torque ripple, etc.
3.7.4 Residual risks of the forced stop function (EM2)
(1) The forced stop function is not available for alarms that activate the dynamic brake when the alarms
occur.
(2) When an alarm that activates the dynamic brake during forced stop deceleration occurs, the braking
distance until the servo motor stops will be longer than that of normal forced stop deceleration without the
dynamic brake.
(3) If STO is turned off during forced stop deceleration, [AL. 63 STO timing error] will occur.
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