Note: Descriptions are shown in the official language in which they were submitted.
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Method for Monitoring a Lift Installation
The invention relates to a monitoring method of a lift installation according
to the definition
of the introductory part of the independent patent claim.
Conventional lift installations have safety circuits consisting of safety
elements connected
in series. These safety elements monitor, for example, the status of shaft or
cage doors.
Such a safety element can be a contact. An open contact shows that, for
example, a door
is open and a potentially impermissible door state has occurred. If, now, with
the contact
opened an impermissible open state of the door is identified then the safety
circuit is
interrupted. This has the consequence that a drive or brake, which acts on the
travel of a
lift cage, brings the lift cage to a standstill.
A safety system for a lift installation is known from the patent specification
W02005/000727, which comprises a control unit as well as at least one bus
junction and
bus. The bus enables communication between the bus junction and the control
unit. The
bus junction monitors, for example, the state of shaft and cage doors by means
of a safety
element, which is a component of the bus junction. Moreover, the bus junction
consists of
a receiver and a transmitter. In that case the receiver is so designed that it
reads digital
default signals from the control unit, converts these into an analog signal
and thus acts on
the safety element. The transmitter in turn measures, after the safety
element, the analog
signal and converts this into a digital signal. The transmitter makes these
digital data
available to the control unit. These data are either sent by the bus junction
as digital
signals to the control unit or demanded by the control unit by means of
interrogation.
In order that safe operation of the lift installation is guaranteed and the
current state of the
lift installation known digital data has to be exchanged between the control
unit and the
bus junction at short time intervals. This means that the control unit has to
have high
computing capacities in order to be able to evaluate a multiplicity of digital
signals and
items of information. In addition, the bus is strongly loaded by signals,
which are
transmitted between the control and the bus junction, and accordingly has high
data
transmission capacities.
The object of the present invention is thus to provide a monitoring method of
a lift
installation with a reduced data exchange between control unit and bus
junction and with a
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control unit having lower computing capacities.
The object is fulfilled by the invention in accordance with the definition of
the independent
claim.
The monitoring method of a lift installation in accordance with the invention
has a control
unit and at least one bus junction. This bus junction comprises a receiver, a
transmitter
and a safety element. The control unit and bus junction communicate by way of
a bus.
The method executes the following steps:
a digital default signal is transmitted by the control unit to the receiver;
the digital default signal is converted by the receiver into an analog signal;
the safety element is acted on by the receiver with the analog signal;
if the safety element is closed the analog signal is detected by the
transmitter;
for a detected analog signal, a digital signal of the control unit is provided
by the
transmitter; and
on detection of an analog zero signal a digital signal is transmitted by the
transmitter to the
control unit.
The advantage of this monitoring method resides in the small data exchange
between
control unit and bus junction. Since the bus junction when the safety element
is open, thus
when, for example, a shaft door or cage door is open, communicates this
potentially risky
state to the control unit, a constant short-cyclic communication between
control unit and
bus junction is eliminated. As a consequence, use can be made of control units
with
lesser computing capacities as well as buses with smaller data transmission
capacities,
which leads to lower costs.
Advantageously, the digital default signal is transmitted by the control unit
to the receiver
at time intervals. During this time interval the safety element is acted on by
the receiver
with an analog signal corresponding with the preceding digital default signal.
In normal
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operation the digital signal provided by the transmitter is interrogated by
the control unit at
time intervals. These time intervals are preferably selected to be in the
order of magnitude
of 100 seconds.
The advantage of these relatively long default and interrogation time
intervals is a further
relief of the bus between the control unit and the bus junction and a further
reduction of the
signals and data to be processed by the control unit.
Advantageously, on detection of an analog zero signal a digital signal is
spontaneously
transmitted by the transmitter to the control unit. This is the case, for
example, when with
the safety element open an analog zero signal is detected by the transmitter.
By virtue of
the spontaneous transmission of the digital signal, measures are undertaken by
the control
unit in order to bring the lift to a safe operational state.
The advantage of the spontaneous transmission of a digital signal by the
transmitter to the
control unit is based on the fact that the lift can be safety operated
notwithstanding
relatively long default and interrogation intervals.
Advantageously, the monitoring method also includes a test procedure. In this
test
procedure a bus junction is tested by the control unit at time intervals. This
test procedure
is performed by the control unit at least once per day. In that case, the bus
junction is
acted on by the control unit with a digital zero default signal which is
converted by the
receiver into an analog zero signal. Accordingly, the transmitter measures an
analog zero
signal. Thus, in the case of correct functioning a corresponding digital
signal is
spontaneously transmitted by the bus junction to the control unit.
The advantage of this test procedure resides in the simple and reliable
checking of the
functional capability of a bus junction or of the spontaneous transmission
behaviour of the
transmitter. In this test procedure an open safety element is simulated and
the
corresponding spontaneous transmission behaviour of the transmitter provoked.
The
functional capability of the bus junction for normal operation is tested in
every default-
interrogation cycle.
The invention is clarified and further described in detail in the following by
way of several
exemplifying embodiments and three figures, in which:
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Fig. 1 shows a schematic view of a safety system according to the invention;
Fig. 2 shows a schematic view of a second form of embodiment of a safety
system
according to the invention; and
Fig. 3 shows a schematic view of a third form of embodiment of a safety system
according to the invention.
The present monitoring method is particularly suitable for lift installations,
as was
described in the introduction. Fig. 1 shows a form of embodiment of a safety
system 10
according to the invention which is technically adapted to perform the
monitoring method.
The safety system 10 has a control unit 11 and at least one bus junction 13.
The
communication between the control unit 11 and the bus junction 13 takes place
by way of
a bus 12. Data can thus be sent in both directions between the bus junction 13
and the
control unit 11 by way of the bus. The bus junction 13 itself consists of a
receiver 14, a
transmitter 15 and a safety element 16. The receiver 14 and the transmitter
15,
respectively, are each so designed that the former receives default signals
from the control
unit 11 and the latter provides status data as signals of the control unit 11.
The control unit 11, the bus 12 and the at least one bus junction 13 form a
bus system.
Within this bus system each bus junction 13 has an individual, unique address.
The
establishing of a communication between the control 11 and a bus junction 13
takes place
by way of this address.
The control unit 11 sends digital default signals to the receiver 14 by way of
the bus 12.
The control unit in that case addresses a specific bus junction 13 and
communicates the
default signal to its receiver 14. The receiver 14 receives this default
signal and generates
an analog signal which corresponds with the default signal and which acts on
the safety
element 16. The action of the analog signal is symbolised by the arrow 16.1.
The analog
signal can be a defined voltage, current strength or frequency.
The safety element 16 shows the state of a safety-relevant element. Thus, the
safety
element 16 finds use as, for example, a door contact, lock contact, buffer
contact, flap
contact, sensor, actuator, travel switch or emergency stop switch. The safety
element 16
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is in that case so designed that a closed safety element 16 represents a safe
state and an
open safety element 16 represents a potentially risky state of a lift
installation.
When the safety element 16 is closed the transmitter 15 behind the safety
element 16
measures the arriving analog signal. This measuring process is represented by
the arrow
16.2. After the measurement, the transmitter 15 converts the measured analog
signal into
a digital signal. Finally, the transmitter 15 prepares the digital signal for
the control unit 11.
In normal operation the control unit 11 transmits a current, voltage or
frequency value
default signal to a selective bus junction 13 by means of statement of the
address of the
bus junction 13 and a current, voltage or frequency value in digital form.
This default
signal is repeated at specific time intervals, i.e. the control unit 11
transmits a new current,
voltage or frequency value to the bus junction 13. The new value preferably
differs from
the preceding value. Within such a time interval the receiver generates,
according to the
default signal, a specific analog signal. If the safety element is closed the
transmitter 15
measures this analog signal and prepares the measured value as a digital
signal. At the
cyclic rate of the above-mentioned time interval the control unit 11 addresses
the
transmitter 15 of the bus junction 13 and by way of a reading function obtains
the data of
the current, voltage or frequency value prepared as a digital signal .
The time intervals between such default-interrogation cycles are in principle
freely settable
and primarily depend on the reliability of the bus junction components. For
preference
these time intervals last for several seconds. In the case of high
reliability, time intervals of
100 seconds or longer can also be set.
The control unit 11 performs this method with all bus junctions 13 of the
series and checks
the resonance thereof, i.e. the default signals and the digital signals
provided by the
respective transmitters 15 are compared by the control unit 11. If the default
signals
correspond with the prepared digital signals, the control unit recognises that
the receiver
14 and the transmitter 15 function correctly.
A fault current, a fault voltage or a fault frequency is present if the
transmitter 15 measures
a current of 0 mA, a voltage of 0 mV or a frequency of 0 Hz. This corresponds
with the
state of an open safety element, thus, for example, an open cage or shaft
door. If now, for
example, a fault current is measured by the transmitter 15, the transmitter 15
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spontaneously sends the transmitted value to the control unit 11. Thanks to
the unique
address of the bus junction 13 the control unit 11 is capable of precisely
localising the
fault. The control unit 11 optionally resorts to measures in order to
eliminate the fault or to
transfer the lift to a safe operating mode. These operating modes comprise,
inter alia,
maintenance of a residual capability of the lift in a safe travel range of the
lift cage, the
evacuation of trapped passengers, an emergency stop or, ultimately, the
warning of
maintenance and service personnel to free trapped passengers and/or eliminate
a fault not
able to be removed by the control unit.
The safe operation of a bus junction 13 primarily depends on the functional
capability of
the receiver 14 and transmitter 15. Since the receiver 14 and the transmitter
15 are
already tested in normal operation in each default-interrogation cycle with
respect to the
functional capability thereof, the bus junction 13 needs a separate test in
order to check
the spontaneous transmission behaviour of the transmitter 15 on occurrence of
a fault.
In this separate test an open safety element 16 is simulated. The control unit
11 simulates
the open safety element 16 in that a default signal of 0 mA, 0 mV or 0 Hz is
passed to a
specific bus junction 13. A zero default test is thus concerned in that case.
In the case of
fault-free functioning of the bus junction 13 the bus junction 13 or the
transmitter 15 thereof
must spontaneously report to the control unit 11. This test guarantees that
every opening
of a safety element 16 leads to a spontaneous transmission of a digital signal
of the bus
junction 13 to the control unit 11.
This test is carried out repeatedly in time for each bus junction 13. Since
during this test
the control unit 11 cannot recognise any real data about the state of the
safety element 16
of a tested bus junction 13 the test time is kept as short as possible and the
test is carried
out only as often as necessary. The test time is in that case largely
dependent on the
speed of data transmission by way of the bus 12 and usually amounts to 50 to
100
milliseconds. The frequency of the zero default test is oriented primarily to
the reliability of
the transmitter 15 used. The more reliable the transmitter 15, the less
frequently does this
have to be tested so that a safe operation of the lift can be guaranteed.
As a rule the zero default test is carried out at least once per day. However,
this test can
also be repeated in the order of magnitude of minutes or hours.
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Fig. 2 shows a second form of embodiment of the safety system 10 according to
the
invention. By contrast to the safety system 10 of Fig. I the safety element 16
is of
redundant design. Each bus junction 13 thus has at least two safety elements
16.a, 16.b,
16.n. In Fig. 2, for example, three safety elements 16.a, 16.b, 16.n monitor
the state of a
safety-relevant element of the lift. In that case each safety element 16.a,
16.b, 16.n
preferably lies at a separate output 16.1.a, 16.1.b, 16.1.n of the receiver
14, which acts on
the safety elements 16.1, 16.b, 16.n in accordance with the default signal of
the control
unit 11 by an analog signal. These signals can have the same or different
values. In the
case of closed contacts 16.a, 16.b, 16.n the transmitter 15 measures the
arriving analog
signal at each of separate inputs 16.2.a, 16.2.b, 16.2.n. In normal operation
the
transmitter 15 makes available the measured analog values as digital signals
of the control
unit 11, which regularly interrogates the bus junctions 13. If an analog zero
signal is
measured at an input 16.2.1, 16.2.b, 16.2.n, the transmitter 15 spontaneously
reports this
to the control unit 11.
The advantage of this form of embodiment is that it is also possible to make
use of more
advantageous, but not secure, safety elements 16.a, 16.b, 16.n. A safe status
monitoring
of the lift is guaranteed by the redundant design thereof.
A third form of embodiment of the safety system 10 according to the invention
is shown in
Fig. 3. In this form of embodiment the states of several safety-relevant
elements of the lift
are detected by means of a bus junction 13. Each state of a safety-relevant
element is
detected by a safety element 16.d, 16.e, 16.m. The combining of the safety
elements
16.d, 16.e, 16.m in a bus junction 13 is preferably realised when the safety-
relevant
elements to be monitored lie physically close to one another, such as, for
example, upper
adjacent shaft doors or the cage door and an alarm button mounted on the lift
cage.
The control unit 11 preferably sends, for each safety element 16.d, 16.e,
16.m, different
default signals to the receiver. The receiver 14 converts the default signals
into a
corresponding analog signal and acts on the respective safety element 16.d,
16.e, 16.n by
way of a separate output 16.1.d, 16.1.e, 16.1.m. If the safety elements 16.d,
16.e, 16.m
are closed the transmitter 15 measures, for each safety element, the arriving
analog signal
at a separate input 16.2.d, 16.2.e, 16.2.m. Here, too, in normal operation of
the transmitter
the measured analog values are provided as digital signals of the control unit
11, which
regularly interrogates the bus junctions 13. The transmitter 15 preferably
also provides
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information about at which input 16.2.d, 16.2.e, 16.2.m the analog signal was
measured. If
an analog zero signal is measured at an input 16.2.d, 16.2.e, 16.2.m, the
fault source can
be uniquely localised thanks to the separate inputs 16.2.d, 16.2.e, 16.2.m.
The advantage of this form of embodiment is the smaller number of bus
junctions 13
required and the costs saving thereby achievable.
The examples illustrated in Figs. 2 and 3 can also be combined. Thus, bus
junctions 13
can be designed in such a manner that the state of several safety-relevant
elements of the
lift is detected by a respective redundant safety element 16.
The bus junctions 13 described in Figs. 2 and 3 are tested not only in normal
operation in
each default-interrogation cycle for the resonance thereof, but also by means
of a zero
default signal. This test is preferably carried out separately for each safety
element 16.a,
16.b, 16.n; 16.b, 16.e, 16.m. The functional capability of all outputs of the
receiver 14 and
all inputs of the transmitter 15 are thus individually tested together.
