12 - 5
12. CHARACTERISTICS
12.3 Dynamic brake characteristics
12.3.1 Dynamic brake operation
(1) Calculation of coasting dista nce
Fig. 12.6 shows the pattern in which the servo motor comes to a stop when the dynamic brake is
operated. Use Equation 12.2 to calculate an approximate coasting distance to a stop. The dynamic
brake time constant varies with the servo motor and machine operation speeds. (Refer to (2) in this
section.)
V0
Time constant
Emergency stop(EMG) OFF
ON
Machine speed
teTime
Fig. 12.3 Dynamic brake operation diagram
Lmax 60
V0JL
JM
te1.......................................................................................................................(12.2)
Lmax : Maximum coasting distance .................................................................................................[mm][in]
Vo : Machine rapid feed rate ........................................................................................ [mm/min][in/min]
JM: Servo motor inertial moment................................................................................. [kg cm2][oz in2]
JL: Load inertia moment 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 ex ternal relay and a delay of the
magnetic contactor built in the external dynamic brake.
(2) Dynamic brake time constant
The following shows necessary dynamic brake time constant for the equations (12.2).
Speed[r/min]
0
14
16
2
4
8
10
6
12
0 500 1000 1500 2000 2500 3000
13
73
23
43
053
Time constant [ms]
0 500 1000 1500 2000 2500 3000
73
23
43
053
13
Speed [r/min]
Time constant [ms]
20
18
16
14
12
10
8
6
4
2
0
HC-KFS series HC-MFS series