METHOD FOR CONTROLLING AN ELEVATOR

A method includes commanding a brake controller to open a machinery brake, measuring the brake current of the machinery brake, and when the measured brake current does not meet or exceed a predetermined threshold value within a predetermined time period, then generating a signal indicating failure of the machinery brake and cancelling the elevator run sequence, else executing the elevator run sequence.

FIELD

The invention relates to a method for controlling an elevator.

BACKGROUND

An elevator may comprise a car, a shaft, hoisting machinery, ropes, and a counterweight. A separate or an integrated car frame may surround the car.

The hoisting machinery may be positioned in the shaft. The hoisting machinery may comprise a drive, an electric motor, a traction sheave, and a machinery brake. The hoisting machinery may move the car upwards and downwards in the shaft. The machinery brake may stop the rotation of the traction sheave and thereby the movement of the elevator car.

The car frame may be connected by the ropes via the traction sheave to the counterweight. The car frame may further be supported with gliding means at guide rails extending in the vertical direction in the shaft. The guide rails may be attached with fastening brackets to the side wall structures in the shaft. The gliding means keep the car in position in the horizontal plane when the car moves upwards and downwards in the shaft. The counterweight may be supported in a corresponding way on guide rails that are attached to the wall structure of the shaft.

The car may transport people and/or goods between the landings in the building. The shaft may be formed so that the wall structure is formed of solid walls or so that the wall structure is formed of an open steel structure.

The machinery brake may be formed of at least one electromechanical brake which is used as a safety device to apply braking force to the traction sheave or the rotating axis of the hoisting machinery in order to stop the movement of the hoisting machinery and thereby also of the elevator car. A machinery brake comprises normally two separate electromechanical brakes. The brakes have to be dimensioned to stop and hold an elevator car with nominal load standstill in the elevator shaft. Additionally, they may also be used in rescue situations and also in emergency braking situations to stop the elevator car if an operational fault occurs, e.g. an overspeed situation of the elevator car. Further, they are used to protect the passengers from unintended car movement at the landing and to provide safe operating environment for the servicemen inside the elevator shaft. It is thus necessary to ensure that the brakes are operating correctly. For example, if the brakes do not open correctly, the brake pad may drag against the traction sheave during the run of the elevator car. This may cause accelerated wear of the brake pad and the brake surface, which may further lead to degradation of the braking force.

Correct opening of the brake may be monitored with a sensor, such as a brake switch, which changes its state when the brake opens. Brake switches may, however, be expensive, unreliable and sometimes difficult to fit into the brakes.

Sometimes the brake switch does not notice that the brake has not opened completely. This means that a brake dragging situation may continue for a longer period, causing problems such as momentary interruptions in the use of the elevator.

The electromagnetic brake may comprise a frame part and an armature part being movably attached to the frame part. Spring means may be arranged to operate between the frame part and the armature part in order to push the armature part away from the frame part when the machinery brake is activated. A brake shoe acting on a brake surface may be attached to the armature part. The brake shoe is pushed against the brake surface when the machinery brake is activated. Electromagnet means may further be arranged in the frame part. The magnetic field of the electromagnet means pulls the armature part against the force of the spring means towards the frame part. The machinery brake is deactivated i.e. the brake shoe is drawn away from the brake surface when the electromagnet is deactivated.

SUMMARY

An object of the invention is an improved method for controlling an elevator.

The method for controlling an elevator according to the invention is defined in claim1.

The method for testing an elevator machinery brake is defined in claim9.

The method for controlling an elevator provided with a machinery brake and a machinery brake controller controlling the machinery brake, the method comprising

a first step in which the brake controller is commanded to open the machinery brake,

a second step in which the brake current of the machinery brake is measured, wherein

a third step in which, if the measured brake current does not meet or exceed a predetermined threshold value within a predetermined time period, then a signal indicating failure of the machinery brake is generated and the elevator run sequence is cancelled, else the next step in the elevator run sequence is executed.

According to an embodiment, alternatively or additionally, the third step includes: if the measured brake current does not meet or exceed a predetermined threshold value within a predetermined time period, then a signal indicating failure of the machinery brake is generated and the elevator run sequence is cancelled, else, (immediately) when the measured brake current meets or exceeds the predetermined threshold value, the next step in the elevator run sequence is executed. This means that the run sequence software can proceed immediately to the next step in the run sequence, there is no need to wait for the predetermined time period to expire. The advantage with such a solution is a faster elevator start.

The method provides an improvement in the brake control sequence. The brake current in the brake is tested in order to verify that the brake can open normally. Upon issuing the brake open command, the brake current may be measured for each brake separately. Presence of the brake current provide a prerequisite for the opening function of the brake.

The invention is based on the fact that an indication of a correct brake opening function is received as soon as the brake current is observed in the brake. It is thus not necessary to wait until the brake opens physically in order to establish that the brake functions correctly, it is enough that the brake current in the brake coil is detected.

The method makes it possible to verify, at the beginning of the elevator run or alternatively during monitoring of the condition of the machinery brake, that the machinery brake opens correctly and the risk of brake dragging is reduced, which brake dragging might cause malfunction of the machinery brake.

The method may thus be applied to test a correct opening of the brake during normal elevator operation as well as during a specific brake test sequence.

DETAILED DESCRIPTION

FIG. 1shows a side view of an elevator.

The elevator may comprise a car10, an elevator shaft20, hoisting machinery30, ropes42, and a counterweight41. A separate or an integrated car frame11may surround the car10.

The hoisting machinery30may be positioned in the shaft20. The hoisting machinery may comprise a drive31, an electric motor32, a traction sheave33, and a machinery brake100. The hoisting machinery30may move the car10in a vertical direction Z upwards and downwards in the vertically extending elevator shaft20. The machinery brake100may stop the rotation of the traction sheave33and thereby the movement of the elevator car10.

The car frame11may be connected by the ropes42via the traction sheave33to the counterweight41. The car frame11may further be supported with gliding means27at guide rails25extending in the vertical direction in the shaft20. The gliding means27may comprise rolls rolling on the guide rails25or gliding shoes gliding on the guide rails25when the car10is moving upwards and downwards in the elevator shaft20. The guide rails25may be attached with fastening brackets26to the side wall structures21in the elevator shaft20. The gliding means27keep the car10in position in the horizontal plane when the car10moves upwards and downwards in the elevator shaft20. The counterweight41may be supported in a corresponding way on guide rails that are attached to the wall structure21of the shaft20.

The car10may transport people and/or goods between the landings in the building. The elevator shaft20may be formed so that the wall structure21is formed of solid walls or so that the wall structure21is formed of an open steel structure.

FIG. 2shows a cross sectional view of the elevator machinery brake.

The elevator machinery brake100may comprise a frame part50and an armature part60.

The frame part50may be fixedly attached to a stationary frame construction of the hoisting machinery30. The armature part60may be movably supported on the frame part50. The movable support should allow movement of the armature part60in relation to the frame part50. The movable support should further transfer the brake torque from the armature part60to the frame part50. Brake torque occurs when the brake shoe5comes into contact with the breaking surface6of a rotating part of the hoisting machinery to brake the motion of the hoisting machinery30. The armature part60may thus be kept in a position parallel to the frame part50during movement of the armature part60in relation to the frame part50. The armature part60may move in a first direction S1and in an opposite second direction S2in relation to the frame part50.

The movable support may be realized with support pins90passing between the armature part60and the frame part50. The support pins90may be formed of bolts. The bolts may have a head91and a body92extending outwards from the head91. The body92of the bolt90may be formed of a first body portion extending outwards from the head91and a second body portion having a smaller diameter. The second body portion92of the bolt90may be provided with an outer threading mating with an inner threading in a corresponding blind bore in the frame part50.

The frame part50may comprise a first surface51and a second opposite surface52. The armature part60may also comprise a first surface61and a second opposite surface62. The first surface51of the frame part50may face against the first surface61of the armature part60. The first surface51of the frame part50and the first surface61of the armature part60may be substantially planar.

The frame part50may further comprise a first central bore57positioned in a middle portion of the frame part50. The first central bore57may extend through the frame part50from the first surface51to the second surface52of the frame part50. The first central bore57may be formed of three consecutive bore portions. Each of the bore portions may have a circular cross-section. The diameter of the first central bore57may decrease stepwise in the direction from the first surface51towards the second surface52of the frame part50. The bore portion with the smallest diameter at the second end52of the frame part50may be provided with a threading57C.

The armature part60may further comprise a second central bore67positioned in the middle portion of the armature part60. The second central bore67extends through the armature part60from the first surface61to the second surface62of the armature part60. The second central bore67in the armature part60may be concentric with the first central bore57in the frame part50. The second central bore67in the armature part60may be formed of two consecutive bore portions having a circular cross-section with a different diameter.

The elevator machinery brake100may further comprise spring means70arranged between the frame part50and the armature part60.

The spring means70may be fitted at least partly in the frame part50. The spring means70may be supported within the first central bore57with a guide pin53e.g. a pin bolt extending from the second surface52of the frame part50through the first central bore57into the spring means70. The guide pin53may comprise a head54and a body55with a threaded portion55A and a pin portion55B. The diameter of the threaded portion55A of the guide pin53may be greater compared to the diameter of the pin portion55B of the guide pin53. The threaded portion55A may be threaded in the threading57C in the first central bore57at the second surface52of the frame part50.

A support plate56e.g. a washer may be arranged on the pin portion55B of the guide pin53so that the support plate56abuts against a step between the pin portion55B and the threaded portion55A of the guide pin53. The spring means70may surround the guide pin53at least partly. A first end of the spring means70may be supported on the support plate56. A second opposite end of the spring means70may be supported on the first surface61of the armature part60. The compression of the spring means70may be regulated with the pin bolt53.

The first central bore57in the frame part50may receive the guide pin53, the support plate56and the spring means70. The second central bore67in the armature part60may receive at least an outer end of the pin portion55B of the guide pin53. An outer end of the pin portion55B of the guide pin53may thus move in the first direction S1and in the second direction S2in the second central bore67in the armature part60when the armature part60moves in the first direction S1and in the second direction S2in relation to the frame part50. The guide pin53forms thus a guide for the spring means70acting between the frame part50and the armature part60.

The spring means70is pushing the armature part60in the first direction S1away from the frame part50. The spring means70will thus activate the machinery brake100in a situation in which the armature part60is free to move in the first direction S1.

The frame part50may further comprise a ring recess58receiving an electromagnet80. The ring recess58may have the form of a ring extending from the first surface of the frame part50into the frame part50. The ring recess58may be concentric with the first bore57in the frame part50. The ring recess58may accommodate a coil for magnetizing the electromagnet80. The electromagnet80may move the armature part60in the second direction S2against the force of the spring means70towards the frame part50. The electromagnet80will thus move the armature part60against the force of the spring means70in the second direction S2. The machinery brake100will be deactivated when the electromagnet means80is activated.

At least a middle portion of the frame part50i.e. the portion within the coil may be of a ferromagnetic material e.g. of iron forming a core for the coil. A current flowing in the coil magnetises the core of the frame part50. Magnetization of the core of the frame part50will pull the armature part60towards the frame part50. The core concentrates the magnetic flux produced by the current flowing in the coil.

The armature part60may be made of a ferromagnetic material e.g. of iron. The armature part60will thus be attracted to the core50when a current flows in the coil in the electromagnet means80in the frame part50.

The armature part60may be attached to a brake shoe5. The brake shoe5may act on a rotating brake surface provided on a rotating part of the hoisting machinery30. The brake shoe5and the brake surface on the rotating part of the hoisting machinery30may be planar or curved. The brake could be e.g. a drum brake or a disc brake.

A machinery brake controller200may control the machinery brake100i.e. the electromagnet80in the machinery brake100. The controller200may control the current supplied to the coil in the electromagnet80.

The machinery brake operates in the following way:

The machinery brake controller200keeps the electromagnet means80in an activated state i.e. keeps the current supply to the electromagnet means80switched on when the elevator is operated in a normal state. The armature part60is thus pulled towards the frame part50, whereby the brake shoe5is at a distance from the brake surface6. The hoisting machinery30may thus operate normally.

The machinery brake controller200disconnects the current supply to the electromagnet80i.e. deactivates the electromagnet80, when the elevator car10is to be stopped. Deactivation of the electromagnet80is realized by disconnecting the current flowing through the coil in the electromagnet80so that the magnetic field keeping the armature part60pulled towards the frame part50is disconnected. The spring means70will thus push the armature part60away from the frame part50, whereby the brake shoe5will be pushed against the brake surface6. The rotation of the traction sheave33will thus be stopped, whereby also the car10is stopped.

FIG. 3shows a side view of an elevator machinery brake system.

The car10is hanging on a first side of the traction sheave33and the counterweight41is hanging on an opposite second side of the traction sheave. The hoisting ropes42pass from the car10over the traction sheave33and to the counterweight41. The traction sheave33is driven by the electric motor32which may be formed of a permanently magnetized synchronous electric motor. The machinery brake100comprises two electromagnetic brakes110,120acting on the traction sheave33. The electromagnetic brakes110,120are controlled by a machinery brake controller200. The elevator and the electric motor32of the elevator is controlled by a main controller300.

There are at least three different options to realize the invention.

A first option would be to determine the proper function of the two brakes100one at a time. One common current sensor401could be used this first option in order to measure the current supplied to the brakes100from the machinery brake controller200.

A second option would be to determine the proper function of the two brakes110,120simultaneously based on the magnitude of the brake current. One common current sensor401could also be used in this second option in order to measure the brake current supplied to the brakes110,120from the machinery brake controller200. The current sensor401must, however, be more accurate in this second option compared to the current sensor401in the first option. This is due to the fact that the current sensor must be able to indicate the difference between the current of one brake and the common current of two brakes.

A third option would be to determine the proper function of the two brakes110,120simultaneously based on the brake current supplied to each brake. Two current sensor402,403are needed in this third option in order to measure the current supplied to each of the two brakes110,120from the machinery brake controller200.

There are several factors affecting the brake current in a machinery brake:

The brake type,

The number of active brake coils,

The temperature of the brake coil,

The line voltage supplied by the elevator control,

The manufacturing tolerances and/or variances of the brake coil.

It is therefore difficult to define a predetermined value for the brake current that would indicate that both brakes are active.

Most of these factors can, however, be eliminated by measuring the actual brake current at every installation at a moment when it is known that both brakes are open. The factors that can be eliminate are at least:

The brake type,

The line voltage supplied by the elevator control,

The manufacturing tolerances and/or variances of the brake coil.

The current limit should be set high enough so that the current level of a single brake is not enough to exceed that limit. In case of dual brakes, both brakes should be of similar type, whereby it is safe to assume that the total brake current is divided equally between the two brakes. The current limit could thus be set in the range of 60 to 75% of the reference total current of the two brakes. This means that when the measured current, in a situation in which both brakes are active, is equal or over the current limit, then both brakes are open, else at least one brake is not open.

One of the best moments to measure the reference total brake current is lift setup drive start due to the fact that:

Setup must be done before the elevator is taken into use,

Both brake coils need to be operative for a successful setup,

There must be somebody present,

Measuring a brake current reference during setup does not add any additional steps to the commissioning process.

In addition to automatic current measurement a possibility of manual current measurement may also be provided in the system. Manual current measurement is needed when maintenance work of the machinery brake e.g. replacing of the brakes is done. A new current measurement is needed after this.

Measurement of the reference brake current must take place at exactly the same moment, in relation to the brake open command, as the later current measurements are done.

Measuring the reference brake current still leaves the problem relating to the variation in the brake current due to variations in the temperature of the brake coil unsolved. The resistance of the brake coil increases as the temperature of the brake coil increases, whereby the brake current decreases. This means that if the brake current limit is set too high, the lift start would unnecessarily fail when the brake coils are hot.

The generic formula for the resistance as a function of the temperature is as follows:

where

R=Conductor resistance at temperature T,

α=Temperature coefficient of the resistance for the conductor material,

T=Conductor temperature in degrees Celsius

Tref=Reference temperature at which the temperature coefficient α of the conductor material is specified.

The temperature coefficient α for some common materials that may be used in machinery brakes are listed below:

Assuming that the brake current is measured at 20 degrees Celsius and the temperature of the brake varies in the interval −10 degrees Celsius to +120 degrees Celsius, then the brake coil resistance relative to the brake coil resistance at the measurement time is (assuming further that the brake coil is of copper):

The (total) brake current relative to the current at the measurement time is thus (the inverse value of the previous relationship due to the Ohm's law U=R*I):

Assuming further that the brake current in a single brake is 50% of the total brake current we end up with the following relationships:

Setting the current limit to 65% of the measured reference current should eliminate the problems relating to the temperature variations. This current limit should eliminate false alarms with hot brakes. This current limit should on the other hand ensure that failure of one brake with cold brakes at low temperatures is detected with clear margin.

The reference current may be measured always at setup start and/or the user may trigger current measurement manually e.g. by setting a parameter value, whereby the current would be measured at next start. The current may be measured 300 ms after the brake open command is given. The current should always be measured regardless of the brake controller type. The measured current value may be stored in a parameter table. The limit value of the current learned at setup when the lift is standing may be shown in a read only mode through a parameter user interface. The measured current value for a specific start may be shown in the user interface when the lift moves.

The brake current needed to open the brake is specific for each brake type and provided by the brake manufacturer. The limit or threshold of the brake current may be set by default to 65% of the measured current value. The limit-% may be adjustable e.g. in the range of 60 to 80%. The brake current is checked 300 ms after the open commands are given i.e. at the same moment when the brake current is measured. If the brake current at start does not meet or exceed the limit, the start fails. The measured brake current meets or exceeds the predetermined threshold value when the measure current is equal to or greater than the predetermined threshold value.

In case any component affecting the brake current is changed e.g. the brake controller or the actual brake, then the brake current measurement must be repeated. In case of false detections and/or failure due to a single brake fault, the user can either adjust the limit with a parameter or repeat brake current measurement at a different brake temperature.

The machinery brake100in the figure shows two independent brakes110,120. The two brakes110,120may be commanded to open simultaneously at the beginning of a new elevator run sequence, and commanded to open alternatively in connection with a brake test sequence. A machinery brake with two independent brakes110,120is common in most countries e.g. in Europe and in China. However, in some countries as e.g. in the USA, machinery brakes with one main brake and one separate emergency brake is commonly used. In a normal elevator run, only the main brake is used. The emergency brake is only used in emergency situations. The invention may be used in an elevator with a machinery brake comprising only one main brake as well as in an elevator with a machinery brake comprising two independent brakes110,120.

FIG. 4shows a first flow diagram of a bake test.

The first flow diagram of the brake test shown in this figure may be used in connection with the normal drive of the elevator. The machinery brake comprises two brakes A and B.

Step501comprises issuing a command to start a new sequence to run to the destination floor. The command to start a new run sequence may be issued on a basis of a service request, which may be received from a call input device of an elevator.

Step502comprises issuing a command to the brake controller200to open brake A. Opening of brake A is achieved by leading a brake current to the coil in brake A.

Step503comprises measuring the brake current and if a break current meeting or exceeding a predetermined threshold within a predetermined time period is detected, then brake A is considered to work properly.

Step504comprises, if the answer in step503is no, i.e. if the measured brake current does not meet or exceed a predetermined threshold within a predetermined time period, then issuing a command to deactivate the brakes A and B, aborting the run and issuing a fault code.

Step505comprises, if the answer in step503is yes, i.e. if the measured brake current meets or exceeds a predetermined threshold within a predetermined time period, then issuing a command to the brake controller200to close brake A. Closing of brake A is achieved by cutting the brake current to the coil in brake A.

Step506comprises issuing a command to the brake controller200to open brake B. Opening of brake B is achieved by leading a brake current to the coil in brake B. A command to start raising the ramp torque is also issued.

Step507comprises measuring the brake current and if a break current meeting or exceeding a predetermined threshold within a predetermined time period is detected, then brake B is considered to work properly. If the answer is no, i.e. if the measured brake current does not meet or exceed a predetermined threshold within a predetermined timer period, then step504is executed i.e. a command to deactivate the brakes A and B is issued, the run is aborted and a fault code is issued.

Step508comprises, if the answer in step507is yes, i.e. if the measured brake current meets or exceeds a predetermined threshold within a predetermined timer period, then issuing a command to the brake controller200to open brake A. Opening of brake A is achieved by leading a brake current to the coil in brake A. The speed reference is also released in step508, whereby the car10starts to move.

FIG. 5shows a second flow diagram of a brake test.

The second flow diagram of the brake test shown in this figure may be used in a special automatic or manual brake test run. The machinery brake comprises two brakes A and B.

Step601comprises issuing a command to run an automatic or manual brake test run.

Step602comprises issuing a command to the brake controller200to open only one of the brakes brake A, B. Opening of a brake A, B is achieved by leading a brake current to the coil in the brake A, B to be opened. The other brake A, B i.e. the brake to be tested is left closed.

Step603comprises measuring the brake current in the brake A, B that was commanded to open in step602.

Step604comprises measuring movement of the elevator. This movement of the elevator may be measured or detected simultaneously as the measurement of the brake current is done in step603. This movement may be detected e.g. from the rotation of the hoisting motor and/or from the movement of the car in the shaft.

Step605comprises, if a brake current meeting or exceeding a predetermined threshold within a predetermined time period is detected in step603and if no movement of the elevator is detected in step604, then the brake that was commanded to open is closed and the brake to be tested has passed the brake test successfully.

Step606comprises, if the measured brake current does not meet or exceed the predetermined threshold within a predetermined time period in step603or if movement of the elevator is detected in step604, then brakes A and B are commanded off i.e. the brakes A and B are closed, the run is aborted and a fault code is issued.

(Test steps602-606are repeated for both brakes A and B by turns).

Step607comprises repeating the automatic brake test as soon as possible and if three consecutive tests failed, then further runs are prevented. Step607is only applicable for the automatic brake test.

The use of the invention is not limited to the elevator disclosed in the figures. The invention can be used in any type of elevator e.g. an elevator comprising a machine room or lacking a machine room, an elevator comprising a counterweight or lacking a counterweight. The counterweight could be positioned on either side wall or on both side walls or on the back wall of the elevator shaft. The drive, the motor, the traction sheave, and the machine brake could be positioned in a machine room or somewhere in the elevator shaft. The car guide rails could be positioned on opposite side walls of the shaft or on a back wall of the shaft in a so called ruck-sack elevator.