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4 Characteristics
MITSUBISHI CNC
4 - 14
4-1-8 Magnetic brake
(1) Motor with magnetic brake
(a) Types
The motor with a magnetic brake is set for each motor. The "B" following the standard motor model
stands for the motor with a brake.
(b) Applications
When this type of motor is used for the vertical feed axis in a machining center, etc., slipping and
dropping of the spindle head can be prevented even when the hydraulic balancer's hydraulic pressure
reaches zero when the power turns OFF. When used with a robot, deviation of the posture when the
power is turned OFF can be prevented.
When used for the feed axis of a grinding machine, a double safety measures is formed with the
deceleration stop (dynamic brake stop) during emergency stop, and the risks of colliding with the
grinding stone and scattering can be prevented.
This motor cannot be used for the purposes other than holding and braking during a power failure
(emergency stop). (This cannot be used for normal deceleration, etc.)
(c) Features
[1] The magnetic brakes use a DC excitation method, thus:
• The brake mechanism is simple and the reliability is high.
• There is no need to change the brake tap between 50Hz and 60Hz.
• There is no rush current when the excitation occurs, and shock does not occur.
• The brake section is not larger than the motor section.
[2] The magnetic brake is built into the motor, and the installation dimensions are the same as the
motor without brake.
(d) Cautions for using a timing belt
Connecting the motor with magnetic brakes and the load (ball screw, etc.) with a timing belt as
shown on the left below could pose a hazard if the belt snaps. Even if the belt's safety coefficient is
increased, the belt could snap if the tension is too high or if cutting chips get imbedded. Safety can
be maintained by using the method shown on the right below.
1. The axis will not be mechanically held even when the dynamic brakes are used. If the machine
could drop when the power fails, use a servomotor with magnetic brakes or provide an external
brake mechanism as holding means to prevent dropping.
2. The magnetic brakes are used for holding, and must not be used for normal braking. There may be
cases when holding is not possible due to the life or machine structure (when ball screw and
servomotor are coupled with a timing belt, etc.). Provide a stop device on the machine side to
ensure safety.
3. When operating the brakes, always turn the servo OFF (or ready OFF). When releasing the
brakes, always confirm that the servo is ON first. Sequence control considering this condition is
possible by using the brake contact connection terminal on the servo drive unit.
4. When the vertical axis drop prevention function is used, the drop of the vertical axis during an
emergency stop can be suppressed to the minimum.
CAUTION
Motor
Timing belt
Ball screw
Brake
Top
Bottom
Load
Motor
(No brakes)
Timing belt
Ball screw
Top
Bottom
Load
Brake