HK1224273B - Method for performing an emergency stop, and a safety arrangement of an elevator - Google Patents

Description

Method for performing an emergency stop of an elevator and safety device thereof

Technical Field

The present invention relates to a technical solution for performing an emergency stop of an elevator.

Background Art

In an emergency stop situation of an elevator, the elevator car is stopped by disconnecting the power supply to the motor of the elevator's hoisting machine and simultaneously connecting, typically two, machinery brakes to brake the traction sheave of the hoisting machine.

Different elevators can be counterweighted for different loads. The elevator load varies from run to run. Therefore, during an emergency stop, the force imbalance changes. This change in force imbalance also causes the elevator car's deceleration to change during an emergency stop. In this case, depending on the situation, the emergency stop may result in excessive or insufficient deceleration of the elevator car.

Purpose of the Invention

One object of the present invention is to disclose a technical solution by which the deceleration can be kept within a desired range during an emergency stop regardless of changes in elevator balance and elevator load. To achieve this object, according to one embodiment of the present invention, a method for performing an emergency stop of an elevator and a safety device for an elevator are disclosed.

An object of the present invention is to prevent a reduction in friction between the traction rope and the traction sheave during an emergency stop.To achieve this object, according to yet another embodiment of the present invention, a method for performing an emergency stop of an elevator is disclosed.

An object of the present invention is to adapt an emergency stop to the operating state of a safety system of an elevator. To achieve this object, according to another embodiment of the present invention, a method for performing an emergency stop of an elevator and a safety device of an elevator are disclosed.

Furthermore, some inventive embodiments and inventive combinations of various embodiments are presented in the descriptive part and in the drawings of the present application.

Summary of the Invention

A method for performing an emergency stop of an elevator, in which method the elevator car is driven to a stop by a motor of a hoisting machine using a given deceleration profile when emergency stop criteria are met.

According to a second aspect, a safety device for an elevator comprises: an elevator car; a traction rope of the elevator car; and a traction machine, the traction machine comprising a motor and a traction sheave, through which the aforementioned traction rope of the elevator car travels. The safety device also comprises: a controller configured to regulate the movement of the elevator car by supplying current to the motor of the traction machine; and a monitoring unit configured to determine the operating state of the elevator and compare the determined operating state with one or more emergency stop criteria. The monitoring unit is configured to form an emergency stop command for the controller when one or more emergency stop criteria are met. The controller comprises a processor for forming a deceleration curve. The controller is configured to drive the elevator car to a stop by the motor of the traction machine using a deceleration curve to be formed in response to the emergency stop command.

When an emergency stop is initiated, the machinery brake of the traction machine is typically engaged to brake the traction sheave. Engaging the brake can result in unnecessarily large deceleration, which can be uncomfortable for passengers and, in the worst case, can cause minor injuries. Particularly in elevators without a counterweight, or with a lighter-than-normal counterweight, for example, for energy conservation reasons, the difference between the minimum and maximum decelerations during an emergency stop when braking with the machinery brake can be unnecessarily large.

The solution presented in this description offers an improvement thereto, since the deceleration is always maintained according to the deceleration curve during an emergency stop, regardless of the balance, load and driving direction of the elevator.

In some embodiments, while the elevator car is driven to a stop by the hoisting machine's motor, a mechanical brake is connected to brake the elevator's hoisting machine's traction sheave. This means that only one mechanical brake is connected to brake the hoisting machine's traction sheave. In this case, both the mechanical brake and the motor brake of the hoisting machine's motor can be used for braking purposes. Furthermore, the need for adjustment and tolerance of the mechanical brake's braking torque is reduced, as variations in the mechanical brake's braking force can be compensated for by the hoisting machine's motor. Braking force can vary, for example, due to environmental conditions and can also vary between different brakes. Therefore, if the mechanical brake is insufficient, braking is also performed by the hoisting machine's motor. On the other hand, if the mechanical brake's braking force, and thus the deceleration of the traction sheave, is excessive, the motor drives counter-braking to maintain deceleration according to a given deceleration curve. This technical solution allows for greater unit-specific variations in braking force between different brakes than before, simplifying the brake's structure. This also improves brake reliability and reduces costs.

In some embodiments, the movement of the elevator car is measured during an emergency stop. If the deceleration of the elevator car falls below a threshold during the emergency stop, the mechanical brake is applied to brake the traction sheave of the elevator's hoisting machine while the elevator car is driven to a stop by the hoisting machine's motor. In this case, both the mechanical brake and the motor braking of the hoisting machine's motor can be used simultaneously for braking purposes. This solution is particularly advantageous when the required deceleration is so great that the braking force of the hoisting machine's motor would otherwise terminate prematurely.

In some embodiments, a threshold value for limiting the allowed movement of the elevator car is determined, and in addition, if the movement of the elevator car during an emergency stop differs from the allowed movement according to the threshold value by more than the threshold value, a second mechanical brake is connected to brake the traction sheave of the elevator's hoisting machine, and power supply to the motor of the elevator's hoisting machine is disconnected.

In some embodiments, when the speed of the elevator car drops below a threshold during an emergency stop, the machinery brake is engaged and the power supply to the motor of the elevator's hoisting machine is disconnected. This means that the elevator is brought to a safe state at the end of the emergency stop.

In some embodiments, at least two deceleration profiles are formed with different maximum decelerations. In some embodiments, the deceleration profile to be used is selected from the at least two deceleration profiles based on the state of the elevator's safety circuit. In this way, a smaller deceleration can be used in situations where the elevator's safety circuit detects a functional inconsistency that requires an emergency stop but is not particularly critical. This situation includes, for example, an emergency stop to be executed in the middle of the elevator shaft, where, based on the state of the safety circuit, there is sufficient deceleration distance for the reduced deceleration. In addition, a larger deceleration can be used in critical situations where rapid emergency braking is particularly necessary. This situation includes, for example, an emergency stop to be executed near the end area of the elevator shaft or in other situations where the deceleration distance is substantially limited.

In some embodiments, the slip of the hoisting rope of the elevator car on the traction sheave is monitored during an emergency stop, and if the magnitude of the slip exceeds a threshold, the deceleration of the elevator car in the deceleration profile is reduced. This means that when it is detected that the hoisting rope begins to slip on the traction sheave, the braking force of the hoisting machine/deceleration of the traction sheave is reduced so that the slip stops and the static friction between the hoisting rope and the traction sheave is restored, which is greater than the dynamic friction during the slip.

In some embodiments, one or more of the following are used as emergency stop criteria: power outage, opening of the elevator's safety contacts, overspeed of the elevator car, excessive acceleration or deceleration of the elevator car.

In some embodiments, the speed and deceleration of the elevator car are monitored during an emergency stop. If the speed or deceleration of the elevator car deviates from the deceleration curve by more than a given threshold, at least two mechanical brakes are engaged to brake the traction sheave and the power supply to the motor of the traction machine is disconnected. Thus, if an emergency stop by the motor does not proceed as expected, the emergency stop is continued to its end by the mechanical brakes rather than the motor.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 presents a block diagram of a safety device for an elevator according to an embodiment of the present invention.

FIG. 2 presents two different emergency stop curves of the safety device of FIG. 1 .

FIG3 shows the torques of the motor and the mechanical brake of the hoisting machine during an emergency stop.

DETAILED DESCRIPTION

For the sake of clarity, Figures 1 to 3 attempt to present only the features that are necessary for understanding the present invention. Thus, for example, if the presentation of some commonly known components belonging to an elevator is not necessary for understanding the present invention, then these components do not have to be presented in the drawings.

FIG1 presents a safety device for an elevator, in which an elevator car 1 is moved in an elevator hoistway 12 by pulling the elevator car's traction ropes 8 using the traction sheave 5 of the traction machine 2. The elevator car 1 is driven by rotating the traction sheave 5 using the motor in the traction machine 2 and supplying current from the power grid 23 to the motor using a frequency converter 9. The elevator car 1 is also braked by the motor of the traction machine 2 using a motor brake, in which case power is returned to the frequency converter 9, from which power is supplied back to the power grid 23. The motor can be, for example, a permanent magnet synchronous motor, an induction motor, a reluctance motor, or another DC motor. In the elevator of FIG1 , the counterweight 10 is designed to be lighter than usual for energy conservation reasons. Depending on the situation, the weight of the counterweight can be selected for a particular elevator to achieve equilibrium, i.e., equal rope force in the traction ropes 8 on both sides of the traction sheave 5, when approximately 20-40% of the maximum permitted load is loaded into the elevator car.

The microprocessor is adapted to be connected to a frequency converter 9, which calculates a speed reference for the elevator car, i.e. a target value for the speed of the elevator car 1. The frequency converter 9 measures the rotation speed of the traction sheave 5 using a pulse encoder 11 and adjusts the speed of the traction sheave 5 towards the speed reference by regulating the current of the motor of the traction machine 2, thereby regulating the speed of the elevator car 1.

The hoisting machine also includes two electromagnetic mechanical brakes 4. The mechanical brakes 4 are kept disconnected by supplying power to the electromagnets of the mechanical brakes 4 using a brake control circuit 18, and the mechanical brakes 4 are connected to mechanically brake the traction sheave 5 of the hoisting machine by disconnecting the power supplied to the electromagnets of the mechanical brakes 4. If an emergency stop of the elevator car 1 is performed by connecting the two mechanical brakes 4 while the elevator car is moving, the deceleration of the elevator car 1 may be excessive depending on the situation (i.e., depending on the load, position, driving direction, and speed of the elevator car). Excessive deceleration can cause discomfort to passengers and, in the worst case, can result in minor injuries. For this reason, in the safety device of the elevator according to FIG. 1 , an emergency stop is implemented in the manner described below.

The safety device of FIG1 includes forced-opening safety contacts 7a and 7b, which are positioned to monitor the safety of selected points in the elevator. Safety contacts 7a and 7b monitor, for example, the position and locking of the doors of the elevator shaft 12. Furthermore, other monitoring functions include the permissible movement limits of the elevator car 1 in the elevator shaft 12, the operation of the elevator's speed governor, the position of the elevator car door, the status of the end buffers of the elevator shaft, the temporary service space to be formed in the elevator shaft, and the status of the safety mechanism to be activated by the speed governor. Opening of the safety contacts indicates that the safety of the monitored point has been compromised.

The safety device also includes an electronic safety controller 6. The elevator's safety contacts 7a and 7b are connected to the electronic safety controller 6, which is configured to read the status of the safety contacts 7a and 7b. Between the safety controller 6 and the frequency converter 9 is a data transmission bus 13, via which the safety controller 6 regularly receives information about the speed of the traction sheave 5 of the traction machine. The data transmission bus 13 is implemented via a running cable extending to the elevator car 1. The safety controller 6 receives measurement data from the acceleration sensor 15 and door zone sensor 14 of the elevator car 1 via the data transmission bus 13. This measurement data indicates the position of the elevator car 1 at the location of the hoistway door of the elevator hoistway 12, as well as information about the floor on which the elevator car 1 is located.

The safety controller 6 also includes undervoltage monitoring of the power grid 23 , via which the safety controller 6 receives information about power outages that have occurred in the power grid 23 .

The safety controller 6 includes a relay output for a safety signal 16. If necessary, the safety controller 6 disconnects the safety signal 16 by opening the contacts of a safety relay within the safety controller 6 to bring the elevator to a safe state. When the safety signal 16 is disconnected, the machinery brake 4 engages to brake the traction sheave 5 of the traction machine, and the current supply to the motor of the traction machine 2 stops. The safety controller 6, together with the aforementioned monitoring circuit, disconnection circuit, and measurement circuit connected to the safety controller 6, forms the elevator's safety circuit.

The safety controller 6 compares the information read from the safety contacts 7a, 7b, the undervoltage monitoring information, the speed information of the traction sheave 5 of the traction machine, the measurement information of the acceleration sensor 15, and the information read from the door zone sensor 14 with the emergency stop criteria stored in the memory of the safety controller 6. When one or more of the emergency stop criteria are met, the safety controller 6 forms an emergency stop command and sends the emergency stop command to the frequency converter 9 via the data transmission bus 13.

The various functional deviations detected by the safety circuit have their own emergency stop criteria. The criticality of the emergency stop situation depends on the emergency stop criteria, and the safety controller 9 includes in the emergency stop command information about which emergency stop criteria are relevant at a specific moment.

After receiving the emergency stop command, the frequency converter 9 immediately initiates the emergency stop. The frequency converter 9 drives the elevator car 1 to a stop using the motor of the hoisting machine 2 using a predetermined deceleration profile to perform the emergency stop. It should be noted that the safety controller 6 does not disconnect the safety signal 16 associated with the emergency stop; in this case, an emergency stop is possible using the torque of the motor. The described solution ensures that the desired deceleration is always maintained during an emergency stop, regardless of the elevator's balance, load, and driving direction.

The frequency converter 9 selects the deceleration rate to be used from at least two different alternatives based on the emergency stop criteria. FIG2 presents two optional deceleration curves 3a and 3b. In the deceleration curve 3a with a smaller deceleration rate, the maximum deceleration rate is preferably approximately 100 s, while in the deceleration curve 3b with a larger deceleration rate, the maximum deceleration rate is preferably approximately 100 s. In situations where an emergency stop is required due to a functional inconsistency in the emergency stop criteria but is not particularly critical, the frequency converter 9 uses the deceleration curve 3a with a smaller deceleration rate. This situation is, for example, an emergency stop to be performed in the middle of the elevator shaft, where, based on the information received from the safety contacts 7a, 7b and the door zone sensor 14, there is sufficient deceleration distance for the reduced deceleration rate. In critical situations where a particularly rapid emergency braking is required due to a functional inconsistency in the emergency stop criteria, the frequency converter 9 uses the deceleration curve 3b with a larger deceleration rate. This situation is, for example, an emergency brake to be performed near the end of the elevator shaft 12, or another situation where the deceleration distance is substantially limited based on the information received from the safety contacts 7a, 7b and the door zone sensor 14. There may also be multiple deceleration profiles with different maximum deceleration rates.

The calculation of the deceleration curves 3a, 3b can be performed using the same microprocessor as the calculation of the speed reference; in a further developed embodiment, the frequency converter 9 comprises a separate microprocessor for calculating the deceleration curves 3a, 3b, in which case an emergency stop to be performed using the deceleration curves 3a, 3b is also possible when the processor calculating the speed reference fails.

The brake control circuit 18 is also configured to supply current to the electromagnet of the machinery brake 4 under the control of the frequency converter 9 so that the machinery brakes can be disconnected and connected independently of each other at a time.

During an emergency stop, the frequency converter 9 uses an encoder 11 to measure the rotational speed of the traction sheave 5 and attempts to adjust the measured speed to the deceleration profiles 3a and 3b by adjusting the current of the motor of the traction machine 2. In this case, if the deceleration of the traction sheave 5 is insufficient within the permitted range (the motor's torque ends prematurely), the frequency converter 9 also connects the second mechanical brake 4 to brake the traction sheave 5 while the frequency converter 9 continues to adjust the traction sheave's speed using the motor. This situation is presented in more detail in Figure 3. During the emergency stop of Figure 3, the frequency converter 9 simultaneously uses one of the mechanical brakes 4 and the motor brake of the motor of the traction machine 2 for braking during the emergency stop. If the braking torque 21 of the mechanical brake 4 is temporarily less than the required total torque 22 (the mechanical brake is insufficient for braking), the frequency converter 9 additionally uses the torque 20 of the motor of the traction machine 2 for braking. On the other hand, if the braking torque 21 applied by the machinery brake 4 and, therefore, the deceleration of the traction sheave 5 is temporarily too great, the frequency converter 9 drives the motor against the brake 4 in the opposite direction using the torque 20, so that the total torque 22 and, therefore, the deceleration of the traction sheave 5 / elevator car 1 is maintained according to the deceleration profiles 3a, 3b. This means, therefore, that the variation in the braking force of the machinery brake 4 is compensated by the motor of the traction machine 2, and in this case, the deceleration profiles 3a, 3b required for applying the total torque 22 are achieved.

The combined use of the motor and the machinery brake 4 in emergency braking described above is advantageous in particular when the deceleration required by the deceleration curves 3a, 3b is so great that the braking force of the motor of the traction machine alone might otherwise end prematurely.

By means of the technical solution, it is also possible to allow larger, unit-specific variations of the braking force between different brakes 4, in which case the need for manual adjustment of the brakes 4 is eliminated and the structure of the brakes 4 can be simplified.

The frequency converter 9 also monitors the slippage of the traction rope 8 on the traction sheave 5 during an emergency stop. The frequency converter 9 compares the measurement information being received from the acceleration sensor 15 with the measurement information of the traction sheave 5 being received from the encoder 11, and if the measurement data differ from each other by more than a permitted difference, the frequency converter infers that the gripping force has weakened and the traction rope 8 has begun to slip on the traction sheave 5. Because the friction of the traction rope 8 on the traction sheave 5 decreases during the slippage, the frequency converter 9 temporarily reduces the deceleration in the deceleration curves 3a, 3b so that the slippage stops and the friction returns to the initial level.

The safety controller 6 monitors the speed and deceleration of the elevator car 1 during an emergency stop. Threshold values for the permitted speed and deceleration of the elevator car are recorded in the memory of the safety controller 6. If the speed or deceleration of the elevator car 1 differs from the deceleration curves 3a, 3b by more than the threshold value recorded in the memory, the safety controller 6 disconnects the safety signal 16, in which case the power supply to the motor of the traction machine 2 is stopped, the two machinery brakes 4 are engaged to brake the traction sheave 5, and the emergency stop is continued to the end by the machinery brakes 4 without motor braking.

At the end of emergency braking, when the speed of the traction sheave 5 / elevator car 1 has decreased below a certain threshold, most preferably below 0.2 m/s, the safety controller 6 brings the elevator to a safe state by disconnecting the safety signal 16. In this case, the power supply to the motor of the traction machine 2 is stopped and the machinery brake 4 is engaged to brake the traction sheave 5.

In some further developed embodiments, the operating voltage of the safety controller 6 and the remaining voltage of the safety circuits are stored in a battery to prevent power outages. Furthermore, the operating voltage of the microprocessor of the frequency converter 9 and other control circuits is set from the frequency converter's intermediate circuit. In this case, the braking energy of the motor of the traction machine 2 can be used to supply the operating voltage of the aforementioned microprocessor/control circuits. This means that emergency braking using the motor of the traction machine 2 is also possible during a power outage in the power grid 23, as described above.

In some further developed embodiments, the software of the frequency converter 9 is configured to independently initiate an emergency stop procedure in certain situations as described, without receiving a separate command from the safety controller 6. The frequency converter 9 can thus include overspeed monitoring and undervoltage monitoring, in which case the frequency converter 9 can initiate an emergency stop, for example due to an overspeed of the traction sheave 5 or the elevator car 1 or due to an acceleration or deceleration of the traction sheave 5 or the elevator car 1 that differs from the normal situation, or on the other hand due to a power interruption that has occurred in the power grid 23.

In FIG1 , the frequency converter 9 and the contactor 17 of the main circuit of the machinery brake 4 are controlled by a safety signal 16. The control can also be implemented in other ways; the safety signal 16 can, for example, be connected to control the electronics of the frequency converter 9 and the brake control circuit 18 so that when the safety signal 16 is disconnected, the transmission of control pulses to the IGBT transistors of the frequency converter 9 and to the MOSFET transistors of the brake control circuit 18 stops, in which case the power supply to the motor of the traction machine 2 stops and both machinery brakes 4 are engaged to brake the traction sheave 5.

The invention has been described above by means of some examples of its embodiments. It is obvious to a person skilled in the art that the invention is not limited only to the embodiments described above, but that many other applications are possible within the scope of the inventive concept defined by the claims.

Claims (16)

1. A method for performing an emergency stop on an elevator, wherein... - When the emergency stop criteria are met, the elevator car (1) is driven to a stop by the motor of the traction machine (2) using the given deceleration curves (3a, 3b). Its features are, - Form at least two deceleration curves (3a, 3b) with different maximum decelerations, and - Select the deceleration curve to be used from the at least two deceleration curves (3a, 3b) based on the state of the elevator's safety circuit (6, 7a, 7b). 2. The method according to claim 1, characterized in that: - While the elevator car is driven to a stop by the motor of the traction machine, a mechanical brake (4) is connected to brake the traction sheave (5) of the traction machine of the elevator. 3. The method according to claim 1 or 2, characterized in that: -Measure the movement of the elevator car (1) during an emergency stop. 4. The method according to claim 2, characterized in that: -Measure the deceleration of the traction sheave (5), If the deceleration of the traction sheave is too large, the brake is driven to resist the motor so as to maintain the deceleration of the traction sheave (5) according to the given deceleration curves (3a, 3b). 5. The method according to claim 4, characterized in that: - Determine the threshold for limiting the permissible movement of the elevator car; - Additionally, if the movement of the elevator car (1) during an emergency stop differs from the allowed movement by more than the threshold, a second mechanical brake (4) is engaged to brake the traction sheave (5) of the elevator's traction machine, and the power supply to the motor of the elevator's traction machine (2) is disconnected. 6. The method according to any one of claims 2, 4 and 5, characterized in that: - Monitor the slippage of the traction rope (8) on the traction sheave (5) during emergency stops; - If the sliding amplitude exceeds the threshold, the deceleration of the elevator car in the deceleration curves (3a, 3b) is reduced. 7. The method according to any one of claims 1, 2, 4 and 5, characterized in that the emergency stop criterion is one or more of the following: - Power outage; - The safety contacts (7a, 7b) of the elevator are disconnected; - The elevator car (1) overspeed; - Excessive acceleration or deceleration of the elevator car (1). 8. A safety device for an elevator, the safety device comprising: Elevator car (1); The traction rope (8) of the elevator car; The traction machine (2) includes a motor and a traction sheave (5), and the traction rope (8) of the elevator car travels via the motor and the traction sheave (5); A controller (9) configured to regulate the movement of the elevator car (1) by supplying current to the motor of the traction machine (2). The safety device is characterized in that it includes a monitoring unit (6), which is configured to determine the operating state of the elevator and compare the determined operating state with one or more emergency stop criteria, and the monitoring unit (6) is configured to generate an emergency stop command for the controller (9) when one or more emergency stop criteria are met. The emergency stop command includes a description of the status of the safety circuits (6, 7a, 7b); Furthermore, the controller (9) includes a processor for generating deceleration curves (3a, 3b); Furthermore, the controller (9) is configured to generate at least two deceleration curves (3a, 3b) with different maximum decelerations; Furthermore, the controller (9) is configured to select from the deceleration curves (3a, 3b) the deceleration curve to be used during the emergency stop based on the emergency stop command; Furthermore, the controller (9) is configured to drive the elevator car (1) to a stop via the motor of the traction machine (2) using the deceleration curves (3a, 3b) to be formed in response to an emergency stop command. 9. The safety device according to claim 8, wherein the monitoring unit (6) is configured to determine the state of the safety circuit (6, 7a, 7b) of the elevator. 10. The safety device according to claim 8, characterized in that the traction machine (2) includes two mechanical brakes (4) for braking the traction sheave (5) of the traction machine, and the controller (9) is configured to connect only one of the mechanical brakes (4) to brake the traction sheave (5) of the traction machine of the elevator while the elevator car is driven to a stop by the motor of the traction machine (2). 11. The safety device according to any one of claims 8-10, wherein the controller (9) is configured to determine the deceleration of the elevator car (1). 12. The safety device according to claim 11, wherein the controller (9) is configured to engage a mechanical brake (4) to brake the traction sheave (5) of the traction machine of the elevator if the deceleration of the elevator car (1) drops below a threshold during the emergency stop. 13. The safety device according to any one of claims 8-10 and 12, characterized in that the monitoring unit (6) is configured to determine the speed of the elevator car (1) when the speed of the elevator car (1) drops below a threshold during an emergency stop, connect the mechanical brake (4) and disconnect the power supply to the motor of the traction machine (2) of the elevator. 14. The safety device according to any one of claims 8-10 and 12, characterized in that the controller (9) is configured to Determine the deceleration of the traction sheave (5), and The motor is driven to resist the brake so that if the determined deceleration of the traction sheave is too large, the deceleration of the traction sheave (5) is maintained according to the given deceleration curves (3a, 3b). 15. The safety device according to any one of claims 10 and 12, characterized in that a threshold for limiting the permissible movement of the elevator car is recorded in the memory of the monitoring unit (6); Furthermore, the monitoring unit (6) is configured to: if the movement of the elevator car (1) during an emergency stop differs from the allowed movement by more than the threshold used to limit the allowed movement of the elevator car, also connect a second mechanical brake (4) to brake the traction sheave (5) of the elevator's traction machine and disconnect the power supply to the motor of the elevator's traction machine (2). 16. The safety device according to any one of claims 8-10 and 12, characterized in that the emergency stop criterion is one or more of the following: - Power outage; - The safety contacts (7a, 7b) of the elevator are disconnected; -The elevator car was overspeeding; - Excessive acceleration or deceleration of the elevator car.