Baumuller b maXX BM3400 Series - Safe Stop Procedures

Safe stop 2.12T
2.12 Safe stop
In order to exclude dangers for persons, e.g. operators, service- and maintenance technicians, a machine
must be brought to a safe stop during operation in its danger range (safe stop).
This is why the dependable prevention of an unexpected starting is demanded (amongst others Machine
directive 89/392/EWG, attachment I, 1.6.3, last para.; EN 292-2, 4.1.4; EN 60204-1, 5.4). Under unexpected
starting one understands each starting that can c ause a risk when appearing unexpected for persons (EN
292-1).
Moreover, besides the transition of the enable- to the operating status of the machine also the unexpected
ramp-up of the machine, this means the transition from the safe stop into an unsafe moving must be con-
sidered. This is necessary, because the unexpected ramp-up usually is to be led back to an interruption of
the control loop of the machine. In this case the drive is, because of its control system, anxious to a chieve
highest speed at maximum a c celeration. If an unexpected starting occurs, the operator therefore doesn’t have
the possibility anymore to remove himself or his hand from the danger area. This is why the drive has to be
stopped and has to be kept safe in its ’off-position’, when having opened, electrical interlocked safety devices.
The motor must not have a torque and therewith cannot generate dangerous movement.
The avoiding of an unexpected starting of the machine can be reached by electrical separated safety devices,
e.g. contactors. At some machine types it must be done without the isolation of the drive from the mains.
This is necessary, if the drive, which is supplied via a conver ter is operationally often shut down or started
again. The continuous charg ing a nd discharging of the DC-link is a great burden for the modules. This leads
to interfering waiting times and/or to failures of parts.
The precondition for the starting of a three-phase a.c. motor is the existence of a rotating field. For this at
controlled variable-speed triple phase a.c. motors usually a complex pulse pattern is generated in the micro-
processor. The pulses are amplified and control the power semiconductor. If there is no defined pulse pattern
or the amplifying connection is interrupted, e.g. by switching off the current supply with a relay (safety relay),
no rotating field can be generated. An error during the pulse pattern generation cannot lead to a starting of
the motor, as long as the second precondition, the interruption of the amplifying current supply, is existent
and vice versa. The protection against an unexpected starting is reached by an electromechanic measure,
which is higher-levelled than the electronics. The measure is a safe isolation outside the load circuit.
A disconnection of the energy supply to the winding of the motor w hile the motor is in stop state is reached
by inhibiting the power semiconductors. A s semiconductors under c ertain circumstances can break down, or
because of electromagnetic interferences it is possible, that they switch on, the behavior of a shutdown drive,
must be considered ,if such an error appears.
The break down or the „random“ switching on of a single or of several power semiconductors at the same DC-
link potential does not lead to a uncontrolled starting, because there no current flow is achieved. Once when
an additional power semiconductor is connected to another DC-link potential, c urrent can flow through the
motor. If, thereby the DC link is directly short-circuited, the fuses at the input to the converter are tripped.
The motor will not start.
If, due to this error, the DC-link is connected to a winding of the motor, in the motor a magnetic field can be
build up. At an asynchronous motor, the occuring static magnetic fi eld does not lead to a sudden movement
of the inductor.
If a permanently-excited synchronous motor is connected, the inductor will move into a notch position. The
angular movement, which thereby is made is dependent of the inductor’s position and the number of pole
pairs of the motor. It amounts to maximum 180°/number of pole pairs. Then the flowing current effectuates
Instrution Manual b maXX ® BM3400 27
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