Mitsubishi Electric Melservo-Jet HG-KNS Series, Руководство пользователя, Страница: 13 / 108

1 INTRODUCTION
1.5 Electromagnetic brake
11
1
Selection of surge absorbers for electromagnetic brake circuit
The following shows an example of how to select a varistor as a surge absorber.
■
Selection condition
■
Tentative selection and verification of surge absorber
• Maximum permissible circuit voltage of varistor
Tentatively select a varistor whose maximum permissible voltage is larger than Vb [V].
• Brake current (Ib)
• Energy (E) generated by brake coil
• Varistor limit voltage (Vi)
From the energy (E) generated in the brake coil and the varistor characteristic diagram, calculate the varistor limit voltage (Vi)
when the brake current (Ib) flows into the tentatively selected varistor during opening of the circuit.
Vi is favorable when the varistor limit voltage (Vi) [V] is smaller than the desired suppressed voltage (Vs) [V].
If Vi is not smaller than Vs, reselect a varistor or improve the withstand voltage of devices.
• Surge current width (
τ )
Given that the varistor absorbs all energies, the surge current width ( τ ) is as follows.
• Examining surge life of varistor
From the varistor characteristic diagram, find the guaranteed current value (Ip) in which the number of the surge application
life is N at the surge current width (
τ ). Calculate the guaranteed current value (Ip) ratio (Ip/Ib) to brake current (Ib).
If a sufficient margin is ensured for Ip/Ib, the number of the surge application life N [time] can be considered as favorable.
Other precautions
A leakage magnetic flux occurs at the shaft end of the servo motor with an electromagnetic brake. Note that chips, screws,
and other debris are attracted.
Item Condition
Electromagnetic brake specification R [ Ω ]: Resistance
L [H]: Inductance
Vb [V]: Power supply voltage
Desired suppression voltage Vs [V] or less
Durable surge application time N times
U
Relay
Varistor Brake coil 24 V DC
Vb
Ib = [A]
R
L × Ib
2
E = [J]
2
Vi × Ib
= [S]
E
τ