Technical data

MHD Sychronous motors Notes Application 16-13
DOK-MOTOR*-MHD********-PR05-EN-P
Sizing of Holding Brakes (Application)
The physical conditions of holding brakes require consideration of two
states. Beyond the normal operation also the incident must be viewed.
The effective braking torques are physically different.
Normal Operation
In normal operation, using the holding brake for clamping of an axis
standstill, the brake`s static torque (M4) rating in the data sheets applies
directly as static friction (M4) – stiction (friction coefficient
µ
H
).
Fault Condition (EMERGENCY STOP)
In fault conditions (i.e., EMERGENCY STOP), where the holding brake is
used to stop a moving axis, the “dynamic braking torque”, or sliding
friction (friction factor
µ
G
) applies.
The dynamic braking torque is reduced in comparison to the indicated
static holding torque M4. Therefore, note the following description of
dynamic sizing.
The load torque must be smaller than the minimum dynamic torque which
the brake can provide. Otherwise the dynamic brake torque is not
sufficient to stop the axis.
If a mass should be decelerated in a determined time or in a determinated
way, the additional moment of inertia of the whole system must be taken
into account.
Further important aspects for sizing:
The holding brake is not a safety brake (see DIN EN 954 / 03.97 and
vertical axis data sheet SMBG). As a result of uncontrollable influencing
factors such as rust film on the brake surface, the brake holding torque
can be reduced. Additionally, excessive voltage and temperature can
weaken the permanent magnets and the brake.
Bringing these factors together, the following recommendations can be
given for sizing the holding brakes to the axles.
The necessary holding torque required for the application must not
exceed a maximum of 60% of the static holding torque (M4) of the
used holding brake.
Note: Holding torque reduction and premature wear occur when
braking moving axles!
Do not use the holding brake to stop a moving axle! This is
permitted for EMERGENCY STOP situations only. In this
situation, the specified rated torque of the holding brake (M4)
is reduced to the value of the available dynamic braking
torque. Complete deterioration of brake holding capability can
be expected after approximately 20,000 revolutions of the
brake when clamped.
Observe the instructions on commissioning holding brakes as described
in the chapter “Startup, Operation, and Maintenance”.
Dynamic sizing
Sizing recommendation