Patent Description:
The <CIT> discloses the preamble of claim <NUM>. The <CIT> discloses an elevator brake having a brake drive circuit which is connected via a rectifier to AC mains to provide a DC link. A galvanically separating link component being connected to the DC link has a secondary side connected to a brake circuit comprising at least one brake coil of the elevator brake and at least one rectifying element, whereby in the primary side of the link component a first semiconductor switch is connected which is controlled by the control device of the elevator. The <CIT> discloses a brake controller having a brake coil earth fault detection.

It is object of the invention to provide an earth fault detection of the brake circuit for such type of elevator, which is economical and easy to install.

The object is solved with an elevator according to claim <NUM>. Preferred embodiments of the invention are subject-matter of the dependent claims. Preferred embodiments of the invention are also described in the specification as well as in the drawings.

According to the invention, in the primary side of the galvanically separating link element, particularly of the DC/DC converter, a first semiconductor switch is connected which is controlled by a control device of the elevator which could also be a safety device of the elevator. Preferably, this first semiconductor switch is PWM modulated. In the brake circuit, a second semiconductor switch is connected, particularly in series with the brake coil, which is also controlled by the control device of the elevator. Furthermore, according to the invention, an earth fault indication circuit is connected between the brake circuit and earth, which earth fault indication circuit comprises an emitting or transmitting part of a galvanically isolating transmission element, particularly an LED of an opto-coupler. Anyway, also a DC/DC converter or transformer and the like may be used as galvanically isolating transmission element. The galvanically isolating transmission element has its receiving part connected to an earth fault transmission circuit which is connected to the control device of the elevator. whereby the control device is configured to control the first and/or second semiconductor switch depending on the signal of the earth fault transmission circuit.

Hereinafter for the sake of clarity, the invention is described via the use of a DC/DC converter as preferred embodiment of a galvanically separating link element and with an opto-coupler as preferred embodiment of a galvanically isolating transmission element, although these examples should not be limiting the invention.

Furthermore, the control device might preferably be configured to terminate the current drive of the elevator car in case an earth fault is indicated to the control device via the earth fault transmission circuit. Preferably in this case the control device receives the input signal of a location sensor of the elevator car for example a door zone sensor, and is configured to terminate the current drive only after the car has arrived at the landing zone and the car doors have been opened. Via this measure, the passengers are not trapped in the car. Preferably, in this case the control device is configured to prevent a restart of the elevator by switching off the semiconductor switches Q1 and Q2. Via this measure, a soft manner of taking the elevator out of service is provided as an earth fault is not such a severe fault which necessitates an immediate standstill of the elevator car independent of its position in the elevator shaft, risking the trapping of passengers. By prohibiting a further travel of the elevator car after it has stopped the car can be put out of service until the problem is solved. Thus, it is possible to release all passengers so that any emergency ride or passenger rescue action is not necessary which could be the case when the semiconductor switches would be switched off immediately after finding an earth fault and on the other hand it is ensured that the further use of the faulty elevator does not lead to dangerous situations.

Principally it would be sufficient to switch only one of the semiconductor switches off. Anyway, a higher degree of safety is provided if both semiconductor switches are switched off. In this case, preferably, the control device is configured to switch off the first semiconductor switch before the second semiconductor switch. Via this measure, the first semiconductor switch which is preferably a PWM controlled semiconductor switch for providing the alternating current for the DC/DC converter cuts off the alternating current of the DC/DC converter allowing inductive current of the brake coil/circuit to discharge through the transformer secondary. This causes the inductive brake coil/circuit current to freewheel causing slow and noiseless engagement/gripping of the brake. When the second semiconductor switch would be shut down before the first semiconductor switch, the inductive brake coil/circuit current is discharged to a varistor, engaging/gripping the brake faster. first semiconductor switch, the inductive brake coil/circuit current is discharged faster, resulting faster engagement/gripping of the brake.

Preferably, the safety device is connected with a location sensor of the elevator car and the control device is configured to switch off the first and/or second semiconductor switch only after the location sensor senses the elevator having arrived at a door zone. The location sensor is preferably a door zone sensor of the elevator.

In a preferred embodiment of the invention, the earth fault indication circuit comprises a diode in series with the transmitting part of the opto-coupler which transmitting part is also preferably an LED. Opto-couplers are cheap isolating components which do not require separate power supplies to work as digital isolators or operational amplifiers would. Also, opto-coupler provides galvanic isolation. Also, in this case, the processor reading the earth fault LED information is in different potential, (DC-link), than earth. If the brake control processor would be connected to earth potential (PELV), then there would be no need for opto-coupler at all.

An earth fault could alternatively also be detected by replacing an opto-coupler with a resistor divider circuit and by measuring the voltage in that circuit. Fault current would cause a voltage that can be sensed and considered as earth fault. This voltage sensing could be digital or analog.

In a preferred embodiment of the invention, the earth fault indication circuit comprises a resistor in series with the transmitting part of the opto-coupler which resistor has a higher resistance than the brake coil. The earth fault indication circuit should only act as an indicator of an earth fault and should not draw the brake circuit to ground. Thus, a resistor with a preferably higher resistance than the brake coil is used whereby the resistance of the resistor is preferably at least <NUM> times, preferably at least <NUM> times as high as the resistance of the brake coil. In practice, preferably a value between <NUM> kΩ, more preferably <NUM> kΩ and <NUM> kΩ is used for the resistor which allows enough current flow to operate the transmitting part of the opto-coupler but which also delimits the current flow to values not harming any components in the earth fault indication circuit and still isolating the brake circuit against earth. This earth fault detection circuit works only when DC/DC converter provides a voltage to secondary-side and when the transistor Q2 is open. Thus, the easiest way to detect the earth fault is at start before transistor Q2 is closed or at stop before transistor Q2 is opened. However, due to the high inductance and slowness of the brake itself, earth fault could be detected also during run by opening transistor Q2 for very short period of time (<<NUM>) during which earth fault LED would be lit if there was an earth fault.

Preferably, the first semiconductor switch is a PWM controlled transistor, which is configured to be controlled to generate the necessary intermitting (AC like) voltage for the DC/DC converter to work, which DC/DC converter is regularly a transformer.

Preferably, a varistor is used for clamping brake coil voltage and dropping the brake faster in case transistor Q2 is opened. In normal stops, DC/DC converter is switched off and Q2 is kept closed for short period to allow inductive current to decay through the transformer secondary.

This causes brake coil current to freewheel causing slow and noiseless dropping of the brake pads. So varistor is used to engage/grip the brake faster.

Preferably, the rectifying element comprises at least one diode connected in series with the brake coil as well as one capacitor connected parallel to the brake coil. This is the most simple and effective way to provide a DC voltage in the brake circuit for the brake coil. The ripple in the DC voltage is thereby reduced with the capacitor.

The present invention also relates to a method for handling an earth fault in the brake circuit of an elevator and a use of an elevator according to the above-mentioned specification. According to the invention, in case an earth fault is indicated in the brake circuit, the control device waits with the switching off of the semiconductor switches in the first and secondary side of the DC/DC converter until a location sensor of the elevator indicates that the elevator car has arrived, preferably until it has stopped in a door zone. This method provides a soft handling of a brake circuit earth fault in a way that a current elevator ride is allowed to arrive at the next landing before the semiconductor switches are turned off to keep the elevator car immovable at the door zone. Via this measure, the elevator operation can be made smoother as no emergency rides or the release of trapped passengers in the car have to be provided in case an earth fault is detected in the brake circuit.

Preferably, the control device is configured to prevent a re-start of the elevator after having received an earth fault signal from the earth fault transmission circuit. Via this measure, the elevator can be kept out of service until the earth fault problem is solved. This enhances the safety of the elevator system.

The invention also relates to a method for operating an elevator in an earth fault condition of the brake circuit using an elevator according to the above specifications. According to the inventive method after having received an earth fault signal from the earth fault transmission circuit the control device drives the elevator car to the next landing, so that the passengers are able to leave the car.

Preferably, in this case after having driven the car to the landing a restart of the car is prevented. Via this measure it is ensured that the elevator stays out of service until the earth fault problem is solved. Preferably in case of an earth fault signal a maintenance signal can be issued to a remote maintenance centre for the elevator, so that immediately measures can be taken to solve the earth fault problem.

It is clear for the skilled person that the above-mentioned embodiments can be combined with each other arbitrarily.

It is further clear for the skilled person that single components mentioned in the invention can be provided as a single component or as a multitude of components. Furthermore, the control device may be or may comprise a safety device of the elevator. The safety device may for example be integrated with the control device or it may be a separate part from the control device of the elevator. The elevator may be a stand-alone elevator or an elevator being part of an elevator system, e.g. an elevator group or multi-group.

According to a preferred inventive method which is performed during a stop of the elevator car following steps are performed:.

In an alternative inventive method which is performed during movement of the elevator car following steps are performed:.

Following terms are used as synonyms: control device - safety device; galvanically isolating transmission element - opto-coupler; galvanically separating link element - DC/DC converter; emitting - transmitting; sensing - receiving;
The invention is hereinafter described by way of an example in connection with the enclosed drawing. In this drawing, <FIG> shows a schematic diagram of an elevator having an earth fault detection in the brake circuit.

<FIG> shows the schematic diagram of a brake drive <NUM> of the elevator brake, which brake drive <NUM> is connected to the two terminals DC+, DC- of a DC link which is part of a frequency converter of an elevator motor drive, whereby the DC link is provided between a rectifier bridge and an inverter bridge. The rectifier bridge is connected with AC mains and the inverter bridge is connected with the elevator motor, eventually via switches or contactors.

According to the invention, the brake drive <NUM> comprises a DC/DC converter <NUM> which is connected via a first semiconductor switch Q1 of the brake drive with the terminals DC+, DC-of the DC link. The secondary side of the DC/DC converter <NUM> forms part of a brake circuit <NUM> of the brake drive <NUM>. The secondary part of the DC/DC converter <NUM> is thus connected to a brake coil <NUM> of the elevator brake via a rectifying diode <NUM> and a second semiconductor switch Q2. Parallel to the brake coil <NUM>, a smoothing capacitor <NUM> as well as varistor <NUM> in series with a second diode <NUM> is connected, whereby the smoothing capacitor <NUM> reduces the DC voltage ripple in the brake circuit <NUM> which is formed by all the above-mentioned components connected with the secondary side of the DC/DC converter <NUM>. The varistor <NUM> is used for clamping the brake coil voltage and dropping the brake faster in case transistor Q2 is opened. In normal stops, DC/DC converter is switched off and Q2 is kept closed for short period to allow inductive current to decay through the transformer secondary. This causes brake coil current to freewheel causing slow and noiseless dropping of the brake pads. Furthermore, an earth fault indicator circuit <NUM> is connected between the brake circuit <NUM> and earth whereby the earth fault indicator circuit comprises an LED <NUM> as the transmitting part of an opto-coupler <NUM> in series with a resistor <NUM>. The resistor has a resistance higher than that of the brake coil <NUM>, preferably at least by a factor <NUM>, preferably at least by a factor <NUM>, so that the value is preferably in a range of <NUM> kΩ to <NUM> kΩ. Thus, the brake circuit is sufficiently isolated against earth. The receiving or sensing part <NUM> of the opto-coupler <NUM> forms an earth fault transmission circuit <NUM>, which is connected to the control device <NUM>. The control device <NUM> may be or may comprise or maybe connected to a safety device <NUM> of the elevator. The control device <NUM> is further connected to the control gates of both semiconductor switches Q1 and Q2 which semiconductor switches may preferably be transistors. The control device <NUM> is further connected with a location sensor <NUM> of the elevator car, for example a door zone sensor, so that the control device <NUM> or safety device <NUM> gets information when an elevator car arrives or stops in a door zone. The invention works as follows:.

In case the brake circuit <NUM> has an earth fault which is indicated by the broken lines 34a, 34b, and the semiconductor switch Q2 is controlled off (not to conduct), this immediately leads to a current flow in the earth fault indication circuit <NUM> which leads to an emission of the LED <NUM> of the opto-coupler <NUM>. Via the receiving part <NUM> of the opto-coupler <NUM>, the control or safety device activates a delay circuit <NUM> which is connected to the input of the location sensor and of the earth fault transmission circuit in a kind of AND link so that only when also the location sensor indicates that the elevator car has stopped, is stopping or has arrived at a door zone, the safety device <NUM> or control device <NUM> is allowed to shut down the first semiconductor switch Q1 and/or the second semiconductor switch Q2. Preferably, the control device <NUM>/safety device <NUM> has a succession circuit <NUM> which leads in case of the shutting down of the brake circuit first to the shutting down of the first semiconductor switch Q1 and only afterwards of the second semiconductor switch Q2. This leads to the shutting down of the DC/DC converter in such a way that the brake is engaged/gripped slowly and silently.

The presence of an earth fault in the brake circuit <NUM> can be monitored before an elevator travel by controlling the first semiconductor switch Q1 to power the brake circuit <NUM> while the second semiconductor switch Q2 is off. In another embodiment, the presence of an earth fault can be monitored after an elevator travel by controlling the second semiconductor switch Q2 off while still powering the brake circuit <NUM> by controlling the first semiconductor switch Q1. Also, in another embodiment the presence of an earth fault can be monitored during the elevator travel by controlling the second semiconductor switch Q2 off and then back on. The period when the second semiconductor switch Q2 is off is less than the time required for the brake to engage/grip, preferably less than <NUM> milliseconds. (This depends on the inertia/mass of the brake system. ) Hence, this can be performed during the elevator travel.

The invention thus allows a very reliable and simple mechanism of detecting an earth fault in the brake circuit as well as to provide the necessary measures to take the elevator smoothly out of service, preferably after having driven the elevator car to a nearby door zone.

In a preferred embodiment, the safety device could indicate to the control device <NUM> of the elevator to drive the elevator car to the next landing in travelling direction so as to reduce the length of the elevator travel after having detected the earth fault in the brake circuit.

Claim 1:
Elevator comprising an elevator motor driving at least one elevator car in a hoisting path, which elevator motor is driven via a frequency converter controlled by a control device (<NUM>) of the elevator, the frequency converter comprising a rectifier bridge and an inverter bridge and a DC link (DC+, DC-) in between, the elevator further comprises at least one elevator brake acting on a brake element rotating with the rotor of the elevator motor, which elevator brake is driven via a brake drive (<NUM>) which is connected to the DC link (DC+, DC-) of the frequency converter, whereby the brake drive comprises a galvanically separating link component (<NUM>) having a primary side connected to the DC link (DC+, DC-) and a secondary side connected to a brake circuit (<NUM>) comprising at least one brake coil (<NUM>) of the elevator brake and at least one rectifying element (<NUM>, <NUM>),
whereby in the primary side of the link component (<NUM>) a first semiconductor switch (Q1) is connected which is controlled by the control device (<NUM>) of the elevator, and whereby in the brake circuit (<NUM>) a second semiconductor switch (Q2) is connected which is also controlled by the control device (<NUM>) of the elevator, characterized in that an earth fault indication circuit (<NUM>) is connected between the brake circuit (<NUM>) and earth, and which earth fault indication circuit (<NUM>) comprises an transmitting part (<NUM>) of an galvanically isolating transmission element (<NUM>), which transmission element (<NUM>) has its receiving part (<NUM>) connected to an earth fault transmission circuit (<NUM>) connected to the control device (<NUM>) of the elevator, wherein the control device (<NUM>) is configured to control the first and/or second semiconductor switch (Q1, Q2) depending on the signal of the earth fault transmission circuit (<NUM>).