Mitsubishi Electronics MR-J3- B, MR-J3-B - page 201

10 - 6
10. CHARACTERISTICS
10.3 Dynamic brake characteristics
10.3.1 Dynamic brake operation
(1) Calculation of coasting distance
Fig. 10.3 shows the pattern in which the servo m otor comes to a stop when the dynamic brake is operated.
Use Equation 10.2 to calculate an approxim ate coasting distance to a stop. The dynamic brake time
constant varies with t he servo motor and machine operation speeds . (Refer to (2)(a), (b) of this section.)
V0
Time constant
Forced stop(EM1) OFF
ON
Machine speed
teTime
Fig. 10.3 Dynamic brake operation diagram
Lmax 60
V0JL
JM
te1.......................................................................................................................(10.2)
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 valu e on servo motor shaft............ [kg cm2][oz in2]
: Brake time constant.......................................................................................................................... [s]
te : Del ay time of control section............................................................................................................. [s]
For 7kW or less servo, there is internal relay delay time of about 30m s. For 11k to 22kW servo,
there is delay time of about 100ms caused by a delay of the external re lay and a delay of the
magnetic contactor built in the external dynamic brake.
(2) Dynamic brake time constant
The following shows necessary dynamic brake t ime constant for the equat ions (10.2).
(a) 200V class servo motor
Speed [r/min]
00 1000 2000
5
10
15
20
25
3000 4000 5000 6000
43
053
13
2373
Time constant [ms]
00 1000 2000
5
10
15
20
25
3000 4000 5000 6000
43
053
13
23
73
Speed [r/min]
Time constant [ms]
HF-MP series HF-KP series