In an elevator installation, an elevator car and a counterweight are conventionally supported on and interconnected by traction means. The traction means is driven through engagement with a motor-driven traction sheave to move the car and counterweight in opposing directions along the elevator hoistway. The drive unit, consisting of the motor, an associated brake and the traction sheave, is normally located in the upper end of the elevator hoistway or alternatively in a machine room directly above the hoistway.

Safety of the elevator is monitored and governed by means of a safety circuit or chain containing numerous contacts or sensors. Such a system is disclosed in US 6,446,760. Should one of the safety contacts open or one of the safety sensors indicate an unsafe condition during normal operation of the elevator, a safety relay within the safety circuit transmits a signal to an elevator control which instructs the drive to perform an emergency stop by immediately de-energizing the motor and applying the brake. The elevator cannot be called back into normal operation until the reason for the break in the safety circuit has been investigated and the relevant safety contact/sensor reset. A similar circuit is described in EP-A1 -1864935 but instead of signalling an emergency stop through the control, a drive relay and a brake relay are connected in series to the safety chain so that if one of the safety contacts opens the drive relay and brake relay immediately open to de- energise the drive and release the brake, respectively.

Traditionally, steel cables have been used as traction means. More recently, synthetic cables and belt-like traction means comprising steel or aramid cords of relatively small diameter coated in a synthetic material have been developed. An important aspect of these synthetic traction means is the significant increase in the coefficient of friction they exhibit through engagement with the traction sheave as compared to the traditional steel cables. Due to this increase in relative coefficient of friction, when the brake is applied in an emergency stop for an elevator employing synthetic traction means there is an significant increase in the deceleration of the car which severely degrades passenger comfort and could even result in injury to passengers.

Accordingly, an objective of the present invention is to provide an alternative elevator safety circuit which can be used to decelerate an elevator car during an emergency stop in a more controlled manner. This objective is achieved by an elevator safety circuit comprising a series chain of safety contacts having an input connected to a power source and a first safety relay deriving electrical power from an output of the series chain of safety contacts. A delay circuit is arranged between the output of the series chain of safety contacts and the first safety relay. Hence, if any of the safety contacts open to initiate an emergency stop, any process controlled by the operation of the first safety relay is delayed.

The delay circuit may comprise a diode and a resistor arranged between the output of the series chain of safety contacts and the first safety relay and can further comprise a capacitor in parallel across the resistor and the first safety relay. Accordingly, the amount of delay can be set by selecting an appropriate R-C constant for the delay circuit.

Preferably, the elevator safety circuit further comprises a watchdog timer arranged to selectively bypass the first safety relay. Consequently, the first safety relay can be operated immediately and independently by the watchdog timer without a break in the series chain of safety contacts. The watchdog timer can be arranged in parallel with the first safety relay. Alternatively, the watchdog timer may be arranged in parallel with the capacitor.

The elevator safety circuit can further comprise a second safety relay arranged in parallel with the delay circuit and the first safety relay. Hence, if any of the safety contacts open to initiate an emergency stop, any process controlled by the operation of the second safety relay is immediate.

Alternatively, the second safety relay may be arranged between the output of the series chain of safety contacts and the delay circuit. With this series arrangement, a second diode can be arranged between the output terminal of the series chain of safety contacts and the watchdog timer to ensure that both the first and the second safety relays can be operated immediately by the watchdog timer.

The delay circuit and the first safety relay may be integrated together as a time-delay relay. The time-delay relay can be a normally-open, timed-open relay or a normally- closed, timed-open relay. Preferably, the first safety relay is a brake contact such that if an emergency stop is initiated, the brake is not applied immediately but after a delay. If the brake contact is a time-delay relay, then a second watchdog timer can be arranged in the brake circuit to selectively bypass the coils of the brakes.

Preferably, the second safety relay is a drive relay such that if an emergency stop is initiated, the drive relay immediately informs the elevator drive to either actively control the motor to decelerate the elevator or de-energise the motor.

The invention also provides a method for controlling the motion of an elevator comprising the steps of detecting whether a safety contact opens and operating a first safety relay a predetermined time interval after the opening of the safety contact.

Preferably, the method further comprises the steps of monitoring a drive of the elevator and operating the first safety relay when the drive experiences a software problem, a hardware problem or if the power supply to the drive is outside of permitted tolerances. Accordingly, the first safety relay can be operated independently of the safety contacts.

The invention is herein described by way of specific examples with reference to the accompanying drawings of which:

FIG. 1 is a schematic of an elevator safety circuit according to a first embodiment of the present invention;

FIG. 2 is a schematic of an elevator safety circuit according to a second embodiment of the present invention:

FIG. 3 depicts graphical representations of the control signal to, and the associated response of, the watchdog relay employed in the circuits shown in FIGS. 1 and 2:

FIG. 4 is a schematic of an elevator safety circuit according to a third embodiment of the present invention:

FIG. 5 illustrates a typical time-delay relay for use in the circuit of FIG. 4; and

FIG. 6 depicts graphical representations of the coil power to, and the associated response of, the time-delay relay of FIG. 5.

A first elevator safety circuit 1 according to the invention is shown in FIG. 1 wherein an electrical power supply PS is connected to an input terminal T1 of a series chain of safety contacts S1-Sn. The contacts S1-Sn monitor various conditions of the elevator and remain closed in normal operation. For example, contact S1 could be a landing door contact which will remain closed so long as that particular landing door is closed. If the landing door is opened without the concurrent attendance of the elevator car at that particular landing, indicating a possibly hazardous condition, the contact S1 will open and thereby break the safety chain 1 initiating an emergency stop which will be discussed in more detail below.

A drive relay 3 is connected between the output terminal T2 of the series chain of safety contacts S1-Sn and a common reference point 0V. The common reference point is hereinafter referred to a gound and is considered to have zero voltage.

Power is also supplied by the output terminal T2 through a delay circuit 13 to a brake contactor 7. The delay circuit 13 comprises a diode D1 , a resistor R and a capacitor C. The diode D1 and the resistor R are arranged in series between the output terminal T2 and an input terminal T4 to the brake contactor 7 whereby the diode D1 is biased to permit current flow in that particular direction and the capacitor C is arranged between ground 0V and the junction T3 of the first diode D1 and the resistor R.

Accordingly, in normal operation, with all safety contacts S1-Sn closed on the series chain, current flows from the power supply PS through the series chain S1-Sn and through the respective coils of the drive relay 3 and the brake contactor 7 maintaining both in their closed positions. Furthermore, the current flow will also charge the capacitor C of the delay circuit 13. With the drive relay 3 in its closed position the elevator drive 5 continues to control the motor 11 to raise and lower an elevator car in accordance with passenger requests received by the elevator controller. Similarly, with the brake contactor 7 closed, current flows through the brake circuit 19 to electromagnetically hold the elevator brakes 9 open against the biasing force of conventional brake springs.

If, however, an emergency situation is detected and one of the safety contacts S1-Sn opens, the circuit 1 is interrupted and current no longer flows through the coil of drive relay 3. Accordingly, the drive relay 3 immediately opens signalling to the drive 7 that an emergency stop is required whereupon the drive 7 actively controls the motor 11 to immediately decelerate the elevator. Alternatively, the drive relay 3 can be arranged to de- energise the motor 11. Meanwhile, although no current flows through the diode D1 , the charged capacitor C of the delay circuit 13 will discharge through the resistor R to maintain current flow through the coil of the brake contactor 7. Accordingly, the brake contactor 7 will continue to close the brake circuit 19 and the brakes 9 will remain open or de-active until the capacitor C has discharged sufficiently. Hence, although the safety circuit 1 has been interrupted, the brakes 9 will not be applied immediately but will instead be delayed for a certain time period determined by the R-C constant employed in the delay circuit 13. Hence, the invention provides a two phase emergency stop sequence comprising a first phase wherein the drive 5 immediately controls the motor 1 1 to decelerate the elevator in a controlled manner and a subsequent second phase wherein the brakes 9 are applied.

The elevator safety circuit 1 also contains a watchdog timer 15 connected in parallel across the brake contactor 7 i.e. between the terminal T4 and ground 0V. Alternatively, the watchdog timer 15 could be connected in parallel across the capacitor C of the delay circuit 13 as illustrated in the embodiment of FIG. 2. The watchdog timer 15 receives a signal DS from the drive 5. Under normal operating conditions, this signal DS is continuously sequenced on and off as depicted in FIG. 3 and the watchdog timer 15 remains open. If the drive 5 experiences a software or hardware problem or if the power supply to the drive 5 is outside of permitted tolerances, as in the case of a power disruption, the signal DS from the drive 5 stops cycling and after a short time period Δί1 the watchdog timer 15 times out and closes. Should this happen, the safety circuit 1 discharges through the watchdog timer 15 so that the drive relay 3 and the brake contactor 7 immediately open as in the prior art.

An alternative elevator safety circuit V according to the invention is illustrated in FIG. 2. The circuit V essentially contains the same components as in the previous embodiment but in this case the drive relay 3 and the brake contactor 7 are arranged in series between the output terminal T2 of the series chain of safety contacts S1-Sn and ground 0V. Again, the circuit V provides a two phase emergency stop sequence comprising a first phase wherein the drive 5 immediately controls the motor 1 1 to decelerate the elevator in a controlled manner and a subsequent second phase wherein the brakes 9 are applied.

In the present embodiment, it is not sufficient for the watchdog timer 15 to bypass just the brake contactor 7 as in the previous embodiment, since power would still flow through the drive relay 3 if there is a malfunction with the drive 5. Instead, a second diode D2 is inserted between the output terminal T2 and the watchdog timer 15 to drain the circuit V and ensure that both the drive relay 3 and the brake contact 7 are opened immediately if there is a drive fault.

A further embodiment of the invention is shown on FIG. 4. In this circuit 1 " the delay circuit 13 and brake contactor 7 of FIG. 1 are replaced by a time-delay relay 17. In the present example the relay 17 is a normally-open, timed-open relay NOTO as depicted in FIG. 5 having the switching characteristics illustrated in FIG. 6.

In normal operation, with all safety contacts S1-Sn closed on the series chain, current flows from the power supply PS through the series chain S1-Sn and through the respective coils of the drive relay 3 and the time-delay relay 17 maintaining both in their closed positions. With the time-delay relay 17 closed, current flows through the brake circuit 19 to electromagnetically hold the elevator brakes 9 open against the biasing force of conventional brake springs.

If an emergency situation is detected and one of the safety contacts S1-Sn opens, the circuit 1 " is interrupted and current no longer flows through the coils of drive relay 3 or the time-delay relay 17. Accordingly, the drive relay 3 immediately opens signalling to the drive 7 that an emergency stop is required whereupon the drive 7 actively controls the motor 1 1 to immediately decelerate the elevator. On the other hand, as illustrated in FIG. 6 the time-delay relay 17 remains closed for a predetermined time period A 2 after its coil has been de-energised and accordingly the time-delay relay 17 will continue to close the brake circuit and the brakes 9 will remain open or de-active during the predetermined time period At2. Hence, although the circuit 1 " has been interrupted, the brakes 9 will not be applied immediately but will instead be delayed for a certain time period A 2. Again, this embodiment provides a two phase emergency stop sequence comprising a first phase wherein the drive 5 immediately controls the motor 1 1 to decelerate the elevator in a controlled manner and a subsequent second phase wherein the brakes 9 are applied.

As in this first embodiment shown in FIG. 1 , the elevator safety circuit V" contains a first watchdog timer 15 connected in parallel across the time-delay relay 17. As previously described, the first watchdog timer 15 receives a signal DS from the drive 5. Under normal operating conditions, this signal DS is continuously sequenced on and off as depicted in FIG. 3 and the first watchdog timer 15 remains open. If the drive 5 experiences a software or hardware problem or if the power supply to the drive 5 is outside of permitted tolerances, as in the case of a power disruption, the signal DS from the drive 5 stops cycling and after a short time period Δί1 the first watchdog timer 15 times out and closes. Should this happen, the safety circuit V" discharges through the first watchdog timer 15 so that the drive relay 3 immediately opens. However, in this embodiment, even though the safety circuit V" discharges through the first watchdog timer 15, by its very nature, the time-delay relay 17 will not open immediately but will instead be delayed for a certain time period At2. To overcome this problem, a second watchdog timer 15' is installed in the brake circuit 19 to permit current to bypass the coils of the brakes 9 if the signal DS from the drive 5 stops cycling. Accordingly, both the drive 5 and the brakes 9 are notified simultaneously if there is a drive fault by the first and the second watchdog timers, respectively.

The skilled person will readily appreciate that the invention as defined in the following claims is not limited to the examples described hereinbefore. For example, instead of mounting the brake sets 12,14 within the drive unit as depicted in FIG.1 , they could be mounted on the car so as to frictionally engage the guide rails to bring the car to a halt. Furthermore, although the two safety relays have been specifically described as being operative with respect to the brake and the drive, they can just as easily be used to control other functions within the elevator.

Although the present invention is has been developed, in particular, for use in conjunction with synthetic traction means, it can equally be applied to any elevator to reduce the deceleration of an elevator car during an emergency stop and thereby improve passenger comfort.