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13. SERVO AMPLIFIERS WITH A LARGE CAPACITY (30k TO 55kW)
13.8.3 Dynamic brake characteristics
(1) Dynamic brake operation
(a) Calculation of coasting distance
Fig. 13.2 shows the pattern in which the servo motor comes to a stop when the dynamic brake is
operated. Use Equation 13.1 to calculate an ap proximate coasting distance to a stop. The d ynamic
brake time constant var ies with the servo motor and machine operatio n speeds. (Refer to (b). Please
contact us for the servo motor not indicated.)
te
Forced stop (EM1)
Machine speed
Time constant
Time
OFF
ON
V0
Fig 13.2 Dynamic Brake Operation Diagram
60
Lmax
Vo te1JM
JL ·················································································································· (13.1)
Lmax : Maximum coasting distance ··············································································· ··························· [mm]
V0 : Machine rapid feed rate ······················································································· ······· [mm/min][in/min]
JM : Servo motor inertial moment ······················································································ [kg cm2][oz in2]
JL : Load inertia mom ent converted into equivalent value on servo motor shaft ·············· [kg cm2][oz in2]
: Brake time constant ····························································································· ····························· [s]
te : Delay time of control section ··············································································· ····························· [s]
For 7kW or less servo, there is internal relay delay time of about 30ms . For 11k to 22kW servo, there
is delay time of about 100ms caused by a delay of the external relay and a d elay of the magnetic
contactor built in the external dynamic brake.