Elevator having a safety chain with a series connection of safety switch arrangements

Abstract

An elevator has a safety controller to which several safety switch arrangements are connected. The safety controller is configured to cause the stop of the elevator motor and the activation of the motor brakes. A comparator is provided in the safety controller for the determination of the status of the safety chain. The comparator is connected with a memory for storing at least one resistor reference value, which comparator is configured to output a safety chain status signal in dependence of comparison of a measured resistance value with the resistor reference value. Each of said safety switch arrangements includes at least one first resistor and a safety switch which are connected in series. The value of the first resistor is different in at least some safety switch arrangements, preferably in all safety switch arrangements. Each safety switch arrangement includes at least a second resistor connected in parallel with the safety switch, which second resistor has a higher value than the first resistor. The detection of a short circuit as well as of the opening of a safety switch arrangement are allowed.

Claims

1. An elevator, comprising: a safety controller to which several safety switch arrangements are connected, which safety controller is configured to cause the stop of the elevator motor and the activation of the motor brakes; and a comparator provided in the safety controller for the determination of the status of the safety chain, which comparator is connected with a memory for storing at least one resistor reference value, which comparator is configured to output a safety chain status signal in dependence of comparison of a measured resistance value with the resistor reference value, wherein each of said safety switch arrangements comprises at least one first resistor and a safety switch which are connected in series, wherein the value of the first resistor is different in at least some safety switch arrangements, and wherein each safety switch arrangement comprises at least a second resistor connected in parallel with the safety switch, which second resistor has a higher value than the first resistor, wherein a measuring tool includes a bridging resistor connected to pins, wherein the pins are connected with taps on both sides of one of said safety switches.

2. The elevator according to claim 1, wherein the safety controller is connected to a safety chain comprising a series connection of the safety switch arrangements.

3. The elevator according to claim 1, wherein the comparator is connected to the safety chain via an analogue digital converter.

4. The elevator according to claim 1, wherein the at least one resistor reference value is an allowed range of resistor values for the safety chain.

5. The elevator according to claim 1, wherein the second resistor is connected in series with the first resistor.

6. The elevator according to claim 1, wherein the stored reference value comprises a lower reference value and a higher reference value.

7. The elevator according to claim 1, wherein the bridging resistor is electrically connected to the comparator to indicate an allowed safety chain status.

8. The elevator according to claim 1, wherein the safety controller is part of the elevator control.

9. The elevator according to claim 1, wherein the first resistor is directly connected to the safety switch of the safety switch arrangement.

10. A method for checking the safety status of an elevator using a safety chain with a series connection of safety switch arrangements, wherein each safety switch arrangement comprises a series connection of a safety switch with at least a first resistor, in which method the resulting resistance value of the complete safety chain is measured and a second resistor connected in parallel with the safety switch, wherein at least one safety switch arrangement in the safety chain is assumed to be short circuited if the measured resulting resistance value is by a first threshold value below the sum of the values of the first resistors in the safety chain, wherein at least one safety switch arrangement in the safety chain is assumed as being open if the resulting resistance value is by a second threshold value above the sum of the first resistor values in the safety chain, wherein different values of the first resistors are used in the safety switch arrangements, wherein by measuring, via a measuring tool, the resulting resistance value of the safety chain, it is determined which of the safety switch arrangements is short circuited, wherein a short circuit is measured by bridging the safety switch of a safety switch arrangement with a bridging resistor of the measuring tool having a value lower than the second threshold value, and wherein the bridging resistor is connected to pins, wherein the pins are connected with taps on both sides of one of said safety switches.

11. The elevator according to claim 1, wherein the value of the first resistor is different in all safety switch arrangements.

12. The elevator according to claim 2, wherein the comparator is connected to the safety chain via an analogue digital converter.

13. The elevator according to claim 2, wherein the at least one resistor reference value is an allowed range of resistor values for the safety chain.

14. The elevator according to claim 3, wherein the at least one resistor reference value is an allowed range of resistor values for the safety chain.

15. The elevator according to claim 2, wherein the second resistor is connected in series with the first resistor.

16. The elevator according to claim 3, wherein the second resistor is connected in series with the first resistor.

17. The elevator according to claim 4, wherein the second resistor is connected in series with the first resistor.

18. The elevator according to claim 2, wherein the stored reference value comprises a lower reference value and a higher reference value.

19. The elevator according to claim 3, wherein the stored reference value comprises a lower reference value and a higher reference value.

Description

BRIEF DESCRIPTION OF THE DRAWING

(1) FIG. 1 shows a schematic diagram of the safety relevant parts of an elevator.

DETAILED DESCRIPTION OF THE INVENTION

(2) The FIG. 1 shows a safety controller 10 connected to an elevator control 12 which is in functional connection with an elevator motor 14 as well as the motor brakes 16. The safety controller 10 comprises a safety chain 18 with a series connection of five safety switch arrangements 20, 22, 24, 26, 28. The safety chain 18 is connected to an analog-digital-converter (ADC) 30 which is connected to a comparator 32 having an internal memory 34.

(3) The FIGURE also shows a measuring tool 50 which is explained in detail hereinafter. Each of the safety switch arrangements 20-28 consists of a safety switch 36 connected in series with a first resistor 38. In the safety switch arrangement 20, 22, 24, 26, 28, furthermore, a second resistor 40 is connected in parallel to the safety switch 36, but in series to the first resistor 38. On both sides of the safety switch are taps 39 which can be connected to pins 42 of the measuring tool. These pins 42 are connected by a bridging resistor 44. This measuring tool 50 further comprises a body 46 to which the pins 42 and the bridging resistor 44 are mounted. during the measurement of the safety switch 36 of a safety switch arrangement 20, 22, 24, 26, 28 the pins 42 of the measuring tool 50 are connected to the tabs 39 thereof. In this connection, it has to be mentioned that the construction of each safety switch arrangement is identical to that shown in connection with safety switch arrangement 20. These safety switch arrangements are arranged in the elevator at different locations as e.g. landing door contacts, car door contacts, shaft pit working arrangement, over-speed protection, etc.

(4) The function of the inventive safety controller is as follows: In normal operation, all safety switches are closed which enables the elevator motor to work and the motor brakes to open. In this status the resulting resistance value of the safety chain 18 is the sum of the values of the first resistor of each safety switch arrangement 20, 22, 24, 26, 28. When the elevator car stops at a floor and the car door and landing door are open, two of said safety switch arrangements are open which initiates the safety controller to issue a signal to the elevator control 12 to keep the motor 14 stopped and to keep the brakes 16 in grip. This status check is performed via an ADC which provides the resulting resistance value of the safety chain 18 as a digital value to the digital comparator 32. The comparator 32 compares the resulting resistance value with reference values stored in the internal memory 34. In this connection, it has to be carried out that the memory can also be placed at a different location, e.g. somewhere at the safety controller 10 or within the elevator control 12. For the derivation of the status signal by the comparator, two threshold values are defined. A first threshold value is provided if the resulting resistance value is lower than the sum of the first resistance values. If said first threshold value is exceeded, one of the safety switch arrangements 20-28 is deemed short circuited. This means that for the corresponding safety switch arrangement a zero value is measured instead of the first resistance value. This leads to a reduction of the measured resulting resistance value by the value of one first resistor. Accordingly, the first threshold value has to be a little bit lower than the first resistor value to reliably indicate a short circuit.

(5) If, on the other hand, a safety switch 36 is open, then the comparator 32 measures for said safety switch arrangement the series connection of the first resistor 38 and the second resistor 40. The second resistor 40 which is connected in parallel to the safety switch has preferably a value which is essentially higher than that of the first resistor 38. For example, the first resistor 38 may have a value of about 100, whereas the second resistor 40 may have a value of about 1 k.

(6) For a proper detection of an open safety switch, the second threshold value should therefore be lower than the second resistor value, i.e. lower than 1 k in this example.

(7) Accordingly, the inventive safety controller is able to provide a proper signalling of a short circuit status as well as an open switch status of a safety switch arrangement.

(8) The bridging resistor 44 of the measuring tool 50 has a value lower than the second resistor value, e.g. 500. If the function of the safety switches in the safety switch arrangements are measured, the pins 42 are connected to the taps 39 of each safety switch arrangement and the safety switch 36 is opened. In case of a proper opening function, the resulting resistance value should increase by the value of the bridging resistor, in the present case 500. This increase of the resistor value indicates the proper function of the safety switch. If the resistance value is unchanged then the safety switch is short circuited. In this case the elevator has to be put out of use and the short circuited safety switch arrangement should be replaced.

(9) It shall be clear for the skilled person that the number of safety switch arrangements connected to the safety controller 10 is dependent on the size and the components of the elevator. It is further clear for the skilled person that the safety controller 10 may be an integral part of the elevator control 12 or that the safety controller 10 may directly activate the brake 16 and stop the elevator motor 14. The safety switch arrangements 20 to 28 could also be connected to the safety controller otherwise than via a series connection, e.g. via separate ports.

(10) The invention may be varied within the scope of the appended patent claims.