With Position Lock Therefor Patents (Class 187/331)
  • Patent number: 11780710
    Abstract: A novel elevator door interlock assembly configured for use in an elevator having a swing door is provided. The elevator door interlock further configured to enable use of the elevator and disable use of the elevator. The novel elevator door interlock including a mounting plate configured for attachment to a surface of a swing door frame. An interlock module is attached to the mounting plate and configured to facilitate locking and unlocking of the swing door. A latch bracket is attached to the swing door and configured for insertion into a cavity formed within the interlock module. The combination of the mounting plate and the interlock module have a maximum thickness of 0.75 inches.
    Type: Grant
    Filed: March 24, 2023
    Date of Patent: October 10, 2023
    Assignee: Atlas Elevator Components, Inc.
    Inventors: Andrew Darnley, III, Susan M. Siegmann, Joseph H. Marshall, Jesse S. Duncan
  • Patent number: 11548759
    Abstract: A system and method for determining an elevator car position uses position markers situated in the elevator shaft and each assigned a discrete car position, first and second detection devices on the elevator car detecting first and second position markers respectively, and an evaluation unit that determines first and second discrete car positions based on the detected first and second position markers respectively. A single interpolation device of the position determining system determines first and second interpolated car positions. The evaluation unit determines first and second car positions based on the first and second discrete car positions and the first and second interpolated car positions respectively. The interpolation device generates an interpolation parameter that characterizes a position of the first detection device relative to the first position marker and determines the first and second interpolated car positions on the basis of the interpolation parameter.
    Type: Grant
    Filed: June 26, 2018
    Date of Patent: January 10, 2023
    Assignee: INVENTIO AG
    Inventors: David Michel, Eric Birrer, Martin Pfister
  • Patent number: 11505433
    Abstract: An access door arrangement of an elevator shaft, wherein at least one elevator car is moving, includes a door lock, whereby in connection with the door lock a reset switch of an inspection mode resetting device is located, whereby the door lock has a lock part movable between a lock position and an open position and whereby the reset switch is integrated in said door lock to be operated by the movement of the movable lock part or a related movable part. This solution allows an easy resetting of the inspection mode of the elevator.
    Type: Grant
    Filed: June 30, 2017
    Date of Patent: November 22, 2022
    Assignee: KONE CORPORATION
    Inventor: Juha-Matti Aitamurto
  • Patent number: 10113347
    Abstract: A sliding door and floor guide assembly including a floor guide and at least one door panel including a pin guide assembly, and a guide shoe. The guide shoe has a curved bottom surface and the rail has a corresponding curved upper surface so that the two surfaces can engage one another. The pin guide assembly includes a spring that exerts a downward force to keep the guide shoe and rail in contact with one another. The guide shoe also includes at least one beveled surface adjacent the region where the guide shoe and rail engage. This beveled surface causes debris on the rail to be moved away from the rail when the door is opened or closed so that the debris does not interfere with the operation of the sliding door.
    Type: Grant
    Filed: March 25, 2016
    Date of Patent: October 30, 2018
    Assignee: ASSA ABLOY ENTRANCE SYSTEMS AB
    Inventor: Jeffrey A. Wolfe
  • Patent number: 9777755
    Abstract: A locking actuator with a collision detection system for a lift is arranged to detect misalignment relative to a locking receptacle and to stop activation of the locking actuator when misalignment is detected.
    Type: Grant
    Filed: April 7, 2015
    Date of Patent: October 3, 2017
    Assignee: ADVANCE LIFTS, INC.
    Inventor: Brian C. Lowe
  • Patent number: 9688515
    Abstract: An elevator car door interlock including a locking assembly, cable assembly, switch assembly, and top mounting assembly. The elevator car door interlock works in combination with flags installed in an elevator's hoistway. A flag is installed in the areas where it is permitted to open the elevator doors. The locking assembly includes an arm that engages the flag. The flag then prevents the arm from reaching its maximum tilt and keeps it in the substantially vertical position. This causes the hook in the locking assembly to remain in the lowered position. The hook in this position allows the cable to freely travel when the elevator doors are attempted to be open. If the elevator is in a locking zone, then there is no flag present and as the door is attempted to be open, a weighted member attached to the bottom of the cable will begin to rise.
    Type: Grant
    Filed: June 11, 2014
    Date of Patent: June 27, 2017
    Inventors: Ricardo Macareño, Nelson Alonso
  • Patent number: 9045926
    Abstract: A door closer, in particular a hinge door closer, including a locking function or free-swing function, having a door closer housing, an output shaft to be connected to a door, a piston assembly connected to the output shaft and guided in the door closer housing, a closer spring, a piston rod adapted to connect the piston assembly to the closer spring, a hydraulic lock compartment adapted to lock the closer spring, and solenoid control valve, in particular a 3/2-solenoid control valve. A closure damping compartment is formed between the door closer housing and the piston assembly on a side of the piston assembly facing away from the piston rod, and wherein the solenoid control valve controls at least the pressures in the closure damping compartment and in the lock compartment.
    Type: Grant
    Filed: November 30, 2010
    Date of Patent: June 2, 2015
    Assignee: Dorme GmbH + Co. KG
    Inventors: Thomas Salutzki, Volker Bienek
  • Publication number: 20140076670
    Abstract: The elevator has, when the elevator car is in its lowermost access level, no elevator shaft pit or one with absolute minimal depth but complies with regulations with respect to protective spaces against the risk of being crushed. The elevator car is movable in an elevator shaft with shaft doors to several access levels. Maintenance operations can be carried out both on the elevator car or from the interior of the elevator car. Access to the region below the elevator car is possible in that at least the lowermost shaft door is permanently locked, whilst all upper shaft doors can have emergency unlocking means. The at least lowermost shaft door is thus permanently locked, with the exception of the state in which the elevator car is in a stopped state, or is stopped, opposite it. The required permanent protective space consists of the entire interior of the elevator car.
    Type: Application
    Filed: March 21, 2012
    Publication date: March 20, 2014
    Applicant: INVENTIO AG
    Inventor: Markus Henseler
  • Publication number: 20130333983
    Abstract: Landings or car doors for lifts are provided which include a frame which defines the perimeter of an access aperture of the door, the frame comprising a pair of uprights and a pair of crossbeams, the crossbeams respectively comprising an upper horizontal sliding guide and a lower horizontal sliding guide, at least two reciprocally sliding panels to open and close the access aperture of the door. Advantageously, sliding devices and closure devices may be directly attached to each panel so that the panels are self-supporting, wherein the sliding devices couple with the sliding guides of the crossbeams to permit and guide the opening and closing movements of the panels and the closure devices are suitable to block and release the panels. Methods for mounting doors are also provided.
    Type: Application
    Filed: February 28, 2011
    Publication date: December 19, 2013
    Applicant: SEMATIC S.p.A.
    Inventor: Roberto Zappa
  • Publication number: 20130292212
    Abstract: Control system for disengaging a safety lock of a lift floor door, comprising: a linear actuation unit; at least one plate in elastically deformable material; at least one actuation cable between said actuation unit and said plate; said actuation unit, said plate and said actuation cable being associated with the lift cabin, in which the actuation cable induces a deformed configuration of said plate, and the plate in deformed configuration disengages said safety lock so as to allow the floor door to open.
    Type: Application
    Filed: July 10, 2013
    Publication date: November 7, 2013
    Applicant: KONE CORPORATION
    Inventor: Gabriel FIERRI
  • Publication number: 20130199876
    Abstract: The present invention concerns a wind power installation working gallery comprising a working platform and a railing arranged on the working platform, wherein the railing can be closed off by means of a closure element and the closure element is arranged in a transfer region to a lift. The invention concerns in particular a wind power installation having a locking device with a locking mechanism for receiving a first locking element and a second locking element, wherein the first locking element is connected to the lift and the second locking element is connected to the closure element, and the locking mechanism is adapted to release one of the two locking elements by means of the locking of the respective other locking element relative to the locking device. The invention further concerns a locking device, a lift and a wind power installation.
    Type: Application
    Filed: June 20, 2011
    Publication date: August 8, 2013
    Applicant: WOBBEN PROPERTIES GMBH
    Inventor: Johann Muller
  • Publication number: 20110180353
    Abstract: An electromechanically actuated safety lock mechanism particularly suited for elevator hall doors, dumb waiters, and similar lift mechanisms and other applications. A door lock and switch comprises a fixed contact member that is attached to a movable door and a movable locking mechanism attached to a door jamb or second moving door. The locking mechanism may comprise, an involute gear and star wheel, a pawl constrained by a torsion spring and an electromechanical means of actuating same.
    Type: Application
    Filed: January 27, 2010
    Publication date: July 28, 2011
    Inventor: Tim Askins
  • Publication number: 20110114423
    Abstract: A safety system for an elevator has a bar mounted on a landing door, the bar being adapted to extend into a passageway of the landing door, and a holding member adapted to prevent the bar from extending into the passageway of the landing door when a car door is positioned correctly behind the landing door. The bar is adapted to extend into the passageway when the landing door is opened and when the holding member does not prevent the bar from extending into the passageway of the landing door.
    Type: Application
    Filed: November 18, 2009
    Publication date: May 19, 2011
    Applicant: Inventio AG
    Inventor: Mario Y. Ogava
  • Patent number: 7823699
    Abstract: An electromagnetic door lock assembly (30) includes a first portion (32) supported relative to hoistway doors (22) and a second portion (34) supported for movement with an elevator car (24). The first and second portions cooperate so that electromagnetic interaction between them unlocks a set of hoistway doors (22) for access to the car (24), for example. In disclosed embodiments, a first portion (32) of the actuator has at least one stationary electromagnetic portion (36A, 36B) and at least one moveable portion (38). The second portion (34) that moves with the car (24) includes at least one stationary electromagnetic portion (44). Magnetic interaction between the first and second portions (32, 34) causes selected movement of the moveable portion (38) for selectively locking or unlocking the doors (22).
    Type: Grant
    Filed: July 6, 2004
    Date of Patent: November 2, 2010
    Assignee: Otis Elevator Company
    Inventors: Jacek F. Gieras, Pei-Yuan Peng, Bryan Robert Siewert, Muhidin A. Lelic, Gary Copsey
  • Patent number: 7650971
    Abstract: The invention relates to a safety lock (1) for an elevator landing door detecting intrusion of a person in the shaft through the landing door, activating a bistable switch (21) through its spindle lever (11) putting the elevator into safe operation when the landing door is opened by turning the corresponding key, it being impossible to reset the switch (21) manually from the inside of the shaft, which comprises a device (17) fixing the lock in the open position with the door open, that is released when the door is closed such that the switch (21) can be reset by turning the lock (1) in the closing direction of the door in which the key is turned in the opposite direction to the opening direction, the switch (21) being reset mechanically by a mechanical means connected to the spindle lever (11).
    Type: Grant
    Filed: February 3, 2005
    Date of Patent: January 26, 2010
    Assignee: Otis Elevator Company
    Inventors: David Pillin, Sébastien Fougeron, Gérard Sirigu
  • Patent number: 7549516
    Abstract: An elevator door interlock incorporates cast parts thereby drastically reducing the number of parts required for assembly. Other elements are also incorporated to further reduce complexity in manufacturing, servicing, and configuration.
    Type: Grant
    Filed: February 11, 2005
    Date of Patent: June 23, 2009
    Assignee: Honeywell International Inc.
    Inventors: Gary W Eisenhower, Jr., David E Falcon, Michael T. Bunyer, Jeffrey S Hall, Richard A Bear
  • Publication number: 20080271959
    Abstract: An electromagnetic door lock assembly (30) includes a first portion (32) supported relative to hoistway doors (22) and a second portion (34) supported for movement with an elevator car (24). The first and second portions cooperate so that electromagnetic interaction between them unlocks a set of hoistway doors (22) for access to the car (24), for example. In disclosed embodiments, a first portion (32) of the actuator has at least one stationary electromagnetic portion (36A, 36B) and at least one moveable portion (38). The second portion (34) that moves with the car (24) includes at least one stationary electromagnetic portion (44). Magnetic interaction between the first and second portions (32, 34) causes selected movement of the moveable portion (38) for selectively locking or unlocking the doors (22).
    Type: Application
    Filed: July 6, 2004
    Publication date: November 6, 2008
    Inventors: Jacek F. Gieras, Pei-Yuan Peng, Bryan Robert Siewert, Muhidin A. Lelic, Gary Copsey
  • Patent number: 7413058
    Abstract: An active slide (10) for doors of lifts' cabins, comprising a linearly developing blade, vertically oriented, featuring respective ends folded according to the same angle, connected in an articulated manner with a carriage (12) connected to a driving engine by means of a cogged belt (14) and a lever (16) through elastic means (20), said slide cooperating with a balancing hook (18) and an unlock lever (22); the unlock lever (22) is operatively connected to electrically activating means (24) provided with a cam (26) or the like for striking the free end of the lever itself.
    Type: Grant
    Filed: November 3, 2005
    Date of Patent: August 19, 2008
    Assignee: Sematic Italia S.p.A.
    Inventor: Roberto Zappa
  • Patent number: 7398862
    Abstract: A door locking system for a freight or passenger elevator or goods lift installation having vertically spaced landings served by a vertically movable car, the landings and car each being protected by associated horizontal slide doors, a mechanical interlock device at each landing that prevents a landing door from opening without the presence of the car in registration with the landing, a door lock on the car for normally preventing the car door from opening when the car is out of registration with any landing, the interlock device being arranged to mechanically enable the door lock to release the car door to open when the car is in registration with a landing.
    Type: Grant
    Filed: June 2, 2006
    Date of Patent: July 15, 2008
    Assignee: The Peelle Company Ltd.
    Inventor: Zygmunt Dziwak
  • Patent number: 7264089
    Abstract: A system and method for installing an elevator door hatchway opening. The system comprises a steel square comprising a top piece, a bottom piece and left and right jambs, a door buck that is bolted to the steel square and at least one exterior hatchway door that is installed on a center portion of the steel square. The steel square is attached by at least one swing lock hinge to at least one elevator shaft way bracket while the steel square is angled outside of an elevator shaft way.
    Type: Grant
    Filed: July 22, 2005
    Date of Patent: September 4, 2007
    Inventor: Michael Sergi
  • Publication number: 20040079593
    Abstract: A door coupler provided with coupling elements actuated by means of a linkage so as to engage a counter element provided on the landing door and a locking hook that has a closed position and a released position. The release of the locking hook from the closed position to the released position is allowed when the coupling element meets the counter element. The locking hook and the coupling elements are disposed at a distance from each other.
    Type: Application
    Filed: September 22, 2003
    Publication date: April 29, 2004
    Inventors: Franz Josef Karner, Franz Mittermayr, Rupert Oberleitner
  • Patent number: 6659514
    Abstract: An electromechanical interlock for a swinging elevator door is disclosed. The interlock comprises a pivotal hook member that may be attached to a swinging elevator door. The hook has a beak end and may pivot between a locked and an unlocked position. Disposed on the beak end is an electrical conductor. When the interlock is in the locked position, the beak end engages a lug and the conductor contacts electrical contacts to complete an electrical circuit. A solenoid pivots the hook from a locked position to an unlocked position. The electromechanical interlock may be adapted for use with sliding elevator doors as well as swinging doors.
    Type: Grant
    Filed: May 4, 2001
    Date of Patent: December 9, 2003
    Assignee: Thyssen Elevator Capital Corp.
    Inventor: Patrick M. Bass
  • Publication number: 20030178259
    Abstract: A goods hoist having an elevator cage with controlled access arranged to move between a lower station and an upper station by a fluid pressure operated ram associated with a hoist mechanism located at the lower station and supported adjacent the upper station; the controlled access prevents access unless the cage is located at a predetermined location via safety interlocks.
    Type: Application
    Filed: March 25, 2002
    Publication date: September 25, 2003
    Inventor: Russell Peter Henderson
  • Patent number: 6591946
    Abstract: A door locking system for retrofit installation on an automatic sliding two-panel door of an elevator car prohibits opening and closing of the door from the interior of the car when between two floors. The door locking system includes a hook retainer mounted on one side of the door opening. A locking pawl is mounted to a panel of the door on the opposite side of the opening for selectably engaging the hook retainer. A cable is coupled to a drive mechanism and to the locking pawl for disengaging the locking pawl from the hook retainer when at a floor stop. A flexible cable housing slidably retains the cable and defines a path length between the drive mechanism and the locking pawl. A path length adjuster mechanism is connected between two sections of the cable housing for manually adjusting the path length. A hold-down is mounted to the door to retain the cable housing in close proximity to the door while permitting movement parallel with the door in response to adjustment of the path length.
    Type: Grant
    Filed: October 11, 2001
    Date of Patent: July 15, 2003
    Assignee: Inventio AG
    Inventor: Richard Lauch
  • Patent number: 6474448
    Abstract: A modular lock (10) for elevator doors, in particular for locking and unlocking the floor doors of elevators and hoists, comprises a first fixed plate (12) and a second plate (14) articulated on the same, cooperating with the blades of the car activator and provided with means (52, 62) for striking a contact (48, 56).
    Type: Grant
    Filed: July 17, 2000
    Date of Patent: November 5, 2002
    Assignee: Sematic Italia S.p.A.
    Inventor: Roberto Zappa
  • Patent number: 6446759
    Abstract: A coupling (8) for engaging an elevator car door (16) and a landing door (20) includes a fixed vane (36) and a movable vane (38). The movable vane is positioned by an engagement link (42) in response to movement of the car door (16) and the presence or absence of a corresponding landing door roller (28).
    Type: Grant
    Filed: June 8, 2001
    Date of Patent: September 10, 2002
    Assignee: Otis Elevator Company
    Inventors: Richard E. Kulak, Michael J. Tracey
  • Publication number: 20020029937
    Abstract: A hold block for fastening a structural elevator component, such as a landing door sill, an overhead structure of a landing door opening or a car door sill, to a base. The hold block comprises a fixing element for fixing the hold block to the base and a supporting element, disposed at an angle relative to the fixing element, for attachment of the structural component to the hold block, both of the elements being made of the same continuous plate-like material. In addition, the hold block comprises an adjustment elbow between the fixing element and the supporting element to allow adjustment of the angle between the planes defined by the elements, and a locking element for locking this angle.
    Type: Application
    Filed: May 18, 2001
    Publication date: March 14, 2002
    Inventors: Jouni Kalm, Matti Rasanen
  • Patent number: 6070700
    Abstract: An operating system placed on the cabin door is shown with a continuous line in rest position and with a dotted line in working position. An arrow marked with a (Y) indicates a horizontal movement undertaken by the operating system in the Y-direction and an arrow marked by (X) indicates a horizontal movement undertaken by the operating system in the X-direction. The X/Y movement of the operating system is produced by an actuator and motive mechanics. On a shaft door is placed an operating cam upon which the operating system rests. Operating system sensors measure the distance to the shaft door and the operating cam. An electromagnet of the operating system produces the necessary force for coupling of cabin door to shaft door.
    Type: Grant
    Filed: April 1, 1999
    Date of Patent: June 6, 2000
    Assignee: Inventio AG
    Inventor: Heinz-Dieter Nagel
  • Patent number: 6006866
    Abstract: An elevator is provided with a car and inner and outer doors. The inner door registers with one of the outer doors when the car is disposed within a floor zone. A solenoid on the car has a plunger for blocking the inner door from opening. Power will only be applied to the solenoid to move the plunger to a retracted position to allow the inner door to be fully opened when both the car is disposed within a floor zone and the inner doors are being opened by the main elevator controls. A floor zone sensor is mounted to the car for detecting when the elevator is disposed within one of the floor zones. A door sensor is also mounted to the car for detecting when the inner door is being opened by the main elevator controls. A controller operates the electric solenoid to lift the plunger from the extended position to the retracted position in response to receiving both a door data signal from the door sensor and a floor zone data signal from the floor zone sensor.
    Type: Grant
    Filed: June 17, 1998
    Date of Patent: December 28, 1999
    Assignee: Advanced Microcontrols, Inc.
    Inventors: Gregory L. Horne, Tom J. Harrison
  • Patent number: 5880414
    Abstract: When an elevator is running, the car door 27 is locked in the closed position by a brake shoe 12 which engages the edge of the door hanger 24 in response to a push-type solenoid 19 overcoming the force of a spring. When the door is not closed, a friction brake pad 11 contacts the door hanger surface to hold the door open for passenger boarding or to stop the door in case of failure of door operator power while the door is in motion.
    Type: Grant
    Filed: December 31, 1997
    Date of Patent: March 9, 1999
    Assignee: Otis Elevator Company
    Inventors: Jerome F. Jaminet, Thomas M. Kowalczyk, Frank Guliuzza, Jr., Edward E. Ahigian, Richard E. Kulak, Thomas M. McHugh, Thomas He, Richard E. Peruggi, David W. Barrett
  • Patent number: 5730254
    Abstract: An elevator car door restraint includes a position indicator mounted at the access points at each of the floors, a locking arm pivotally mounted between its ends on a first portion of the car for movement of the first end of the locking arm between an engaged and disengaged position, and for contact by the second end of the locking arm with one of the position indicators. A lock plate mounted on the second portion of the car which moves relative to the first portion of the car when the car door moves includes a contact face which is engageable with the first end of the locking arm when the first end is moved to the engaged position to mechanically restrain the elevator car door from opening. The locking arm is biased by a spring so that the first end of the arm is rotated into engagement position unless the first end is permitted from such rotation by contact of the second end with a position indicator. An integral hoistway interlock for center-parting the hoistway access doors is also provided.
    Type: Grant
    Filed: July 21, 1995
    Date of Patent: March 24, 1998
    Assignee: Vertisys, Inc.
    Inventor: Hai T. Nguyen
  • Patent number: 5669465
    Abstract: An elevator hoistway door lock assembly comprises first and second lock subassemblies. Each lock subassembly has a rotatable latch mounted on a respective door hanger, a first and second catches are mounted on the hoistway for engagement with each respective latch, a first and second cam followers are fastened to the respective latches and movable between a first position in which each latch engages the respective catch in a locked position and a second position in which each latch is disengaged from the respective catch in an unlocked position so that the hoistway doors may be moved to an open position and each pair of electrical contacts for indicating a locked condition of the respective door when the contacts are electrically connected.
    Type: Grant
    Filed: July 28, 1995
    Date of Patent: September 23, 1997
    Assignee: Otis Elevator Company
    Inventors: Richard E. Kulak, Thomas M. McHugh, Edward E. Ahigian, Jerome F. Jaminet, Thomas He, Richard E. Peruggi, Thomas M. Kowalczyk, David W. Barrett
  • Patent number: 5544720
    Abstract: An apparatus for entraining and unlatching an elevator car door and a shaft door includes an electromagnet having a movable armature attached to a first bellows mounted on a wall of the car. An entraining and unlatching cam is attached to a second bellows which is mounted on the car door. The cam has stiffened cam entry surfaces, cam surfaces and front surface. The bellows are connected by a hose as a closed pneumatic system operating with below atmospheric pressure. When the electromagnet is not actuated, an internal compression spring in the second bellows extends the cam into engagement with rollers mounted on a shaft door to splay the rollers thereby unlatching the shaft door and entraining it with the car door. At the same time, the first bellows retracts the armature to unlatch the car door. When the electromagnet is actuated, the armature latches the car door and the second bellows retracts the cam to permit the rollers to fold toward one another thereby latching the shaft door.
    Type: Grant
    Filed: January 26, 1995
    Date of Patent: August 13, 1996
    Assignee: Inventio AG
    Inventor: Peter A. Spiess
  • Patent number: 5507365
    Abstract: The lock is of the type comprising: a housing that can be fastened to the door frame of the landing entrance, a locking bolt for the landing entrance, a bolt-control lever, an exterior lever-operating arm actuated by a cam in the elevator car, an electrical contact indicating the presence of the elevator car, a door pull-away electrical contact, a cable bushing device, and a housing attachment. These components are adaptable to many types of elevators, either by being reversible and/or by adaptation of spare parts supplied and arranged in a stand-by configuration in a recess in the housing.
    Type: Grant
    Filed: October 1, 1993
    Date of Patent: April 16, 1996
    Inventor: Dominique Prudhomme
  • Patent number: 5454447
    Abstract: An elevator hoistway door lock comprises a rod journaled for rotation on a hoistway door. A pin which extends laterally from the rod engages a lip when the rod is rotated into a locked position by means of its own weight, and optionally a spring. The pin clears the lip when the rod is rotated into an unlocked position by means of a retiring cam disposed on the elevator car. The electrical safety switch contacts are interconnected by a rotating contact disposed on the rod, only when the rod is rotated to place the pin in the locked position.
    Type: Grant
    Filed: April 6, 1994
    Date of Patent: October 3, 1995
    Assignee: Otis Elevator Company
    Inventors: Richard E. Kulak, Thomas M. McHugh, Edward E. Ahigian, Jerome F. Jaminet, Thomas He, Richard E. Peruggi, Thomas M. Kowalczyk, David W. Barrett