EP4490091A1 - Door system for a lift car, lift system and method for evacuating a lift car - Google Patents

Abstract

The invention relates to a door system (5) for a lift car (3), comprising: at least one door leaf (6a, 6b) for closing at least a partial region of a car opening (4) of the lift car (3); and a bearing device (10), which is designed to mount the door leaf (6a, 6b) on the lift car (3) so as to be displaceable in the direction of a displacement axis (8) between an open position, in which the door leaf (6a, 6b) releases the partial region, and a closed position, in which the door leaf (6a, 6b) closes the partial region, and additionally so as to be rotatable about a rotation axis (9a, 9b), so that the door leaf (6a, 6b), when it is displaced into the closed position and/or into an intermediate position between the open and the closed position, can be rotated into an emergency open position, in which the car opening (4) is released to such an extent that the lift car (3) can be evacuated via the car opening (4).

Description

DOOR SYSTEM FOR AN ELEVATOR CABIN, ELEVATOR SYSTEM AND METHOD FOR EVACUATING AN ELEVATOR CABIN

The present invention relates to a door system for an elevator car. In addition, the invention relates to an elevator system which includes at least one elevator car equipped with such a door system, and to a method for evacuating an elevator car equipped with such a door system.

An elevator car of an elevator system, as can be used to transport people or goods in buildings, can include a car opening and a sliding door mechanism that opens or closes the car opening to the respective floors of the building by horizontally moving one or more door leaves. In addition to the car opening, the elevator car can have a separate emergency opening through which the elevator car can be evacuated in an emergency.

US 9,284,159 B2 shows an example of a separate side emergency opening that can be closed via a pivoting door.

In versions without such an emergency opening, evacuation can take place via the cabin opening. However, it can happen that in the event of a fault, the elevator car gets stuck at a point in the elevator shaft where the door leaf or the door leaves cannot be pushed open or not far enough, for example because the displacement path is blocked by a support located in the elevator shaft.

There may therefore be a need for an improved door system for an elevator car that allows evacuation via the car opening even if sliding the door panel or panels is not possible for some reason. Furthermore, there may be a need for a corresponding elevator system and a corresponding method for evacuating an elevator car.

These needs can be met with the subject matter of the independent claims. Advantageous embodiments are set out in the dependent claims, the following description and the attached figures.

A first aspect of the invention relates to a door system for an elevator car, which can be moved between several floors in an elevator shaft and at least has a cabin opening. The door system comprises at least one door leaf for closing at least a partial area of the car opening and a storage device which is designed to move the door leaf on the elevator car in the direction of a displacement axis between an opening position in which the door leaf exposes the partial area and a closed position in which the Door leaf closes the partial area, to be displaceable and additionally rotatable about an axis of rotation, so that the door leaf, when it is moved into the closed position and / or into an intermediate position between the opening and the closing position, can be rotated into an emergency opening position in which the The car opening is released to such an extent that the elevator car can be evacuated via the car opening.

This makes it possible, with relatively little design effort, for the car opening to be at least partially opened (and without destructive force) if the displacement path of the door leaf or the door leaves is blocked for some reason, for example because the elevator car is unfavorably at the height of one The carrier passing through the elevator shaft has stopped. This can be, for example, a retaining clip for the guide rail.

A second aspect of the invention relates to an elevator system. The elevator system includes an elevator shaft and at least one elevator car, which can be moved between several floors in the elevator shaft and has at least one car opening. The elevator car includes at least one door system, as described above and below, wherein the door leaf is mounted via the storage device on the elevator car in the direction of the displacement axis between the opening and the closing position and is additionally rotatable about the axis of rotation.

A third aspect of the invention relates to a method for evacuating an elevator car of an elevator system, as described above and below. The method includes at least the following step: if the elevator car is to be evacuated via the car opening and the door leaf is moved into the closed position and/or an intermediate position between the opening and the closed position (and, for example, blocked therein): rotating the door leaf about its axis of rotation into an emergency opening position in which the car opening is released to such an extent that the elevator car can be evacuated via the car opening.

Features of the method can also be features of the door system described above and below and/or the elevator system described above and below and vice versa. Without limiting the scope of the invention in any way, embodiments of the invention may be considered based on the ideas and findings described below.

The car opening can be a main opening of the elevator car, via which passengers can enter the elevator car from a floor and/or leave it to a floor during normal operation of the elevator system. The car opening can, for example, be opposite a door opening in a side wall of the elevator shaft if the elevator car regularly stops on a floor. The elevator car can also have a plurality of car openings, for example opposite one another, whereby each car opening can be combined with a door system, as described above and below.

The axis of rotation can, for example, be orthogonal to the displacement axis. For example, the axis of rotation can be a vertical axis in the operational state of the elevator car.

The axis of rotation can, for example, be displaceable together with the door leaf in the direction of the displacement axis (see also below).

The axis of rotation can intersect the displacement axis or be offset laterally, for example horizontally, from the displacement axis. The alignment of the axis of rotation relative to the displacement axis can be constant when the door leaf is displaced between the opening and closing positions. However, it is also conceivable to change the lateral offset of the axis of rotation to the axis of displacement depending on the displacement path of the door leaf.

The door leaf can only be stored so that it can rotate about a single axis of rotation. However, designs are also conceivable in which the door leaf can be mounted so that it can rotate or pivot about two or more than two axes of rotation.

For example, the door leaf can comprise a plurality of displaceable door leaf segments, which can also each be rotatable about their own axis of rotation. Such an embodiment would allow a door leaf that is not completely closed, in particular a door leaf in the middle between the opening and closing positions, to be rotated about its axis of rotation into an emergency opening position. According to one embodiment, the storage device can comprise at least one folding part and at least one sliding part. The sliding part can be mounted on the elevator car in the direction of the displacement axis between the opening and closing positions, wherein the folding part can be mounted on the sliding part so that it can rotate about the axis of rotation, so that the folding part can be displaced together with the sliding part. Furthermore, the door leaf can be attached to the folding part, so that the door leaf can be rotated together with the folding part.

The folding and/or the sliding part can be made in one or more parts, for example in the form of an elongated profile or a strip.

The sliding part can, for example, be designed as a guide shoe for guidance in a corresponding guide rail, which can be arranged above and/or below the cabin opening.

The folding part can be attached to the door leaf as a separate part, for example by screwing and/or welding. The folding part can also be integrated into the door leaf, i.e. that is, both can be different sections of one and the same integrally manufactured component.

According to one embodiment, the folding part can be elongated and can be rotatably connected to the sliding part at its first end. For example, the longitudinal axis of the (elongated) folding part can run horizontally when the elevator car is in an operational state. It is possible for the longitudinal axis of the folding part to run parallel to the displacement axis in a starting position and to form an obtuse, acute or right angle with the displacement axis in the emergency opening position.

Likewise, for example, the sliding part can be elongated and have a longitudinal axis which runs horizontally when the elevator car is in an operational state. The alignment of the longitudinal axis of the sliding part to the displacement axis can be constant or vary when moving between the opening and closing positions. The storage device can therefore be implemented with little design effort. The door system can therefore be easily retrofitted accordingly.

According to one embodiment, the folding part can be rotatably connected to the sliding part via a bearing bolt which partially engages in the folding part and partially in the sliding part. For example, the longitudinal axis of the bearing bolt can lie on the axis of rotation when the door system is assembled. Such storage is robust and enables easy (dis)assembly of the door system. Alternatively or additionally, the folding part can be rotatably mounted via at least one hinge.

According to one embodiment, the folding part can be lockable to the sliding part, with rotation of the folding part about the axis of rotation being prevented in the locked state of the folding part and made possible in the unlocked state of the folding part. This can prevent the folding part, and thus the door leaf, from being unintentionally turned into the emergency opening position.

According to one embodiment, the folding part can be locked to the sliding part via at least one locking bolt, the locking bolt in the locked state partially engaging in the folding part and partially in the sliding part and in the unlocked state not engaging in the folding part, not in the sliding part or neither in the folding part nor in the sliding part. The locking bolt can engage in a corresponding locking receptacle on the folding and/or sliding part, for example in the form of a locking opening. Accordingly, the folding part can be unlocked by moving the locking bolt out of the locking receptacle. Locking and/or unlocking can be done manually and/or automatically.

According to one embodiment, the locking bolt can engage in a second end of the folding part in the locked state. The folding part can, for example, extend over the entire or a large part of the width of the door leaf, whereby “width” can be understood as an extension of the door leaf in the horizontal direction when the elevator car is in an operational state. In other words, the storage and locking bolts - viewed in the horizontal direction or in the direction of the width of the door leaf - can be arranged at opposite ends of the door leaf.

According to one embodiment, the locking bolt can be displaceable, in particular displaceable, between an unlocking position assigned to the unlocked state and a locking position assigned to the locked state. The locking bolt can be coupled to a spring mechanism, which can be designed to apply a restoring force acting in the direction of the locking position to the locking bolt coupled to the spring mechanism. For example, in the operational state of the elevator car, the locking bolt can have a longitudinal axis that is parallel or orthogonal to the longitudinal axis of the bearing bolt and/or to the axis of rotation. However, other orientations of the locking bolt are also possible. The unlocking and the Locking positions can be specified by a corresponding mechanical stop. The restoring force can be a spring force applied via at least one spring. The locking bolt can therefore only be moved from the locking to the unlocking position by overcoming the restoring force. This prevents the folding part from being unlocked unintentionally, for example due to mechanical shocks. The restoring force also causes the locking bolt to move back into the locking position when released, which simplifies locking.

According to one embodiment, the locking bolt can be connectable to an elongated traction means and can be displaced or displaced from the locking to the unlocking position by pulling on the traction means connected to the locking bolt. The traction means can be a flexible, sufficiently tensile means such as a rope or wire. When the door system is assembled, the traction means can be accessible from inside and/or outside the elevator car. For example, the traction means can be suitably protected against unauthorized access during normal operation of the elevator system. Such a locking or actuation mechanism is particularly low-maintenance and takes up little space.

According to one embodiment, the storage device can further comprise a further folding part and a further sliding part. The further sliding part can be slidably storable on the elevator car in the direction of the displacement axis between the opening and closing positions, wherein the further folding part can be rotatable about the axis of rotation on the further sliding part, so that the further folding part can be displaced together with the further sliding part. Furthermore, the door leaf can be fastened at its first end to the folding part and at its second end to the further folding part, so that the door leaf can be rotated together with the folding part and the further folding part. For example, in the operational state of the elevator car - viewed in the vertical direction - the first end can be an upper end of the door leaf and the second end can be a lower end of the door leaf. The door leaf can, for example, rigidly connect the folding parts to one another. For this purpose, the door leaf can be designed to be torsion-resistant. As indicated above, the folding parts can at least partially enclose the door leaf in the horizontal direction. However, it is also possible that at least one of the folding parts additionally surrounds the door leaf at least partially in the vertical direction. For example, the folding parts can also surround the door leaf like a frame. This means that the door leaf can be stored very stably with relatively little design effort. In particular, the sliding part can close at least part of the cabin opening when closed. In particular, the sliding part, as an upper sliding part, can close an upper edge region of the door opening in the emergency opening position, and / or the further sliding part can, as a lower sliding part, close a lower edge region of the door opening in the emergency opening position. The fact that both the upper sliding part and the lower sliding part remain in the emergency opening position has the advantage that the locking bolt attached to it is easily accessible and that the sliding part can be designed to be stable. According to one embodiment, the door system can further comprise at least one further door leaf for closing a further partial area of the cabin opening. Accordingly, the storage device can also be designed to displace the further door leaf on the elevator car in the direction of the displacement axis between an opening position in which the further door leaf exposes the further partial area and a closed position in which the further door leaf closes the further partial area and/or or to rotatably mount another axis of rotation parallel to the axis of rotation. The door leaves can be, for example, a left and a right door leaf, whereby the car opening can be closed when the elevator car is in an operational state by moving the door leaves towards one another in opposite directions, or can be released by moving the door leaves in opposite directions be moved away from each other. It is also possible for both door leaves to be displaceable in the same direction from the same side of the cabin opening and/or towards the same side of the cabin opening. This embodiment makes it possible, for example, for more than one door leaf to be turned into the emergency opening position. This reduces the risk that the cabin opening cannot be opened wide enough in the event of an evacuation.

The door leaves can, for example, be rotatable independently of one another about their axes of rotation.

According to one embodiment, the door leaf can first be unlocked by unlocking the folding part and then rotated into the emergency opening position. The fact that the door leaf must first be unlocked prevents the door leaf from being accidentally opened during normal operation of the elevator system.

According to one embodiment, the door leaf can be pivoted into the elevator car when turning into the emergency opening position. This means that the door leaf can largely protrude into the elevator car in the emergency opening position. This can be an advantage in narrow elevator shafts. Additionally or alternatively, the door leaf can be expanded by one vertical axis can be rotated as the axis of rotation. Accordingly, the door leaf or the door leaves can be mounted so as to be displaceable in the direction of a horizontal axis as the displacement axis.

Preferably, only one individual door leaf can be turned into the emergency opening position. In the case of telescopic sliding doors with several telescopically moving door leaves, only the front door leaf can preferably be rotated into the emergency opening position. This is quite enough to evacuate passengers from the cabin.

Advantageous embodiments of the invention are further explained below with reference to the accompanying drawings, whereby neither the drawings nor the explanations are to be construed as limiting the invention in any way.

Fig. 1 shows an elevator system according to an embodiment of the invention from above.

Fig. 2 shows an elevator car of the elevator system from Fig. 1 from vom.

The figures are only schematic and not to scale. The same reference numerals designate the same or identical features in the various drawings.

Fig. 1 shows a top view of an elevator system 1 with an elevator shaft 2, which connects several floors of a building. An elevator car 3 that can be moved between floors is arranged in the elevator shaft 2. The elevator car 3 has a car opening 4, which can be closed by means of a door system 5.

In this example, the door system 5 comprises a first door leaf 6a and a second door leaf 6b, which are in opposite directions along a horizontal displacement axis 8, each between an opening position in which the cabin opening 4 is released by both door leaves 6a, 6b, and a closed position, in which the cabin opening 4 is closed by both door leaves 6a, 6b, are slidably mounted.

In addition, the first door leaf 6a is rotatably mounted about a vertical first axis of rotation 9a and the second door leaf 6b about a vertical second axis of rotation 9b, in such a way that each door leaf 6a, 6b, when in the closed position and / or in an intermediate position between the Opening and closing positions are blocked, for example due to a carrier running in the elevator shaft 2, can be rotated in an emergency into an emergency opening position in which the cabin opening 4 is released to such an extent that people can leave the elevator cabin 3 via the cabin opening 4.

For example, the cabin opening 4 in the emergency opening position of one or both door leaves 6a, 6b can have a width of at least 20 cm, preferably at least 35 cm or at least 50 cm. For this purpose, the door leaf 6a, 6b can be rotatable, for example, by at least 20°, preferably by at least 40°, at least 60° or at least 80°, about the axis of rotation 9a or 9b.

The rotation axes 9a, 9b can intersect the displacement axis 8, as shown here. Alternatively, one or both axes of rotation 9a, 9b can be offset horizontally from the displacement axis 8.

Each door leaf 6a, 6b can, for example, be pivoted at least partially into the elevator car 3 by rotating about its axis of rotation 9a or 9b.

Fig. 1 shows the two door leaves 6a, 6b in the closed position, with the opening and emergency opening positions of the door leaves 6a, 6b being indicated by dashed lines.

Fig. 2 shows a front view of the elevator car 3 with details of a storage device 10, via which the two door leaves 6a, 6b are mounted on the elevator car 3 so that they can be moved and rotated.

In this example, the storage device 10 comprises for each door leaf 6a, 6b an upper folding part 11 and a lower folding part 12 as well as an upper sliding part 13 and a lower sliding part 14. The upper sliding parts 13 can each be above the cabin opening 4 and the lower sliding parts 14 each be mounted on the elevator car 3 below the car opening 4 along the displacement axis 8 between the opening and the closing position.

For example, the sliding parts 13, 14 can be designed as guide shoes, which can be guided by corresponding guide rails on the elevator car 3.

Each upper folding part 11 is, on the one hand, rotatably mounted on one of the upper sliding parts 13 about the axis of rotation 9a or 9b and, on the other hand, is attached to an upper end of one of the two door leaves 6a, 6b. Analogously, each lower folding part 12 is, on the one hand, rotatably mounted on one of the lower sliding parts 14 about the axis of rotation 9a or 9b and, on the other hand, is attached to a lower end of one of the two door leaves 6a, 6b.

The door leaves 6a, 6b are thus rotatable together with the respective folding parts 11, 12 about the respective axis of rotation 9a, 9b, the upper folding parts 11 being displaceable together with the respective upper sliding part 13 and the lower folding parts 12 being displaceable together with the respective lower sliding part 14 .

The folding parts 11, 12 can, for example, be screwed and/or welded to the respective door leaf 6a, 6b. The folding parts 11, 12 can also be designed as correspondingly shaped sections of the respective door leaf 6a, 6b.

The folding parts 11, 12 and/or the sliding parts 13, 14 can be designed, for example, as elongated profiles, angles or strips.

In the example shown in FIG. 2, the folding parts 11, 12 each extend over the entire width of the respective door leaf 6a, 6b. The folding parts 11, 12 can also only partially extend in the width direction and/or at least partially in the height direction of the door leaves 6a, 6b, for example in order to form a frame around the respective door leaf 6a, 6b.

Each folding part 11, 12 can, for example, be rotatably mounted about the axis of rotation 9a or 9b at its first end (here adjacent to a side edge of the cabin opening 4) via a bearing bolt 15, which extends from the folding part 11, 12 into the adjacent sliding part 13 or 14 .

In addition, each folding part 11, 12 can be locked at its second end, which is opposite the first end in the horizontal direction, via a locking bolt 16 on the respective sliding part 13 or 14.

Fig. 2 shows the locking bolt 16 of each door leaf 6a, 6b in the locked state, in which the locking bolt 16 engages both in the respective folding part 11, 12 and in the respective sliding part 13, 14 and thus allows rotation of the respective folding part 11, 12, i.e . H. the respective door leaf 6a, 6b is prevented from moving into the emergency opening position.

For example, each locking bolt 16 can be vertically between one

Unlocking position in which the locking bolt 16 is completely out of the respective position Folding part 11, 12 is moved out, and a locking position in which the locking bolt 16 partially engages in the respective folding part 11, 12, can be slidably mounted.

In addition, the locking bolt 16 can be coupled to a spring mechanism 17, which applies a restoring force acting in the direction of the locking position to the locking bolt 16.

Each locking bolt 16 can optionally be connected to an elongated traction means 18, for example a rope or wire, wherein the locking bolt 16 can be moved into the unlocking position by pulling on the traction means 18.

As shown by way of example in FIG. 2, the two locking bolts 16 of the same door leaf 6a and 6b can be connected to different ends of the same traction means 18. By pulling on the traction means 18, both locking bolts 16 can be moved into the unlocking position at the same time (when the traction means 18 is released, the locking bolts 16 move back into the locking position on their own due to the restoring force).

Alternatively, the position of the storage bolts 15 can be swapped with the position of the locking bolts 16.

Finally, it should be noted that terms such as “comprising”, “comprising”, etc. do not exclude other parts or steps and indefinite articles such as “a” or “an” do not exclude a plurality. It is further noted that features or steps described with reference to one of the above embodiments may also be used in combination with features or steps described with reference to other of the above embodiments. Reference symbols in the claims are not to be viewed as a limitation.

Claims

Expectations 1. Door system (5) for an elevator car (3), wherein the elevator car (3) can be moved in an elevator shaft (2) between several floors and has at least one car opening (4), the door system (5) comprising: at least one door leaf (6a, 6b) for closing at least a portion of the cabin opening (4); and a storage device (10) which is designed to hold the door leaf (6a, 6b) on the elevator car (3) in the direction of a displacement axis (8) between an opening position in which the door leaf (6a, 6b) releases the partial area, and a closed position, in which the door leaf (6a, 6b) closes the partial area, to be displaceable and additionally rotatable about an axis of rotation (9a, 9b), so that the door leaf (6a, 6b), when it is in the closed position and / or in a Intermediate position between the opening and the closing position can be rotated into an emergency opening position in which the car opening (4) is released to such an extent that the elevator car (3) can be evacuated via the car opening (4), the storage device ( 10) comprises at least one folding part (11, 12) and at least one sliding part (13, 14); wherein the sliding part (13, 14) can be mounted on the elevator car (3) in the direction of the displacement axis (8) between the opening and closing positions, the folding part (11, 12) being rotatable about the axis of rotation (9a, 9b). Sliding part (13, 14) can be stored, so that the folding part (11, 12) can be moved together with the sliding part (13, 14), and the door leaf (6a, 6b) can be fastened to the folding part (11, 12), so that the Door leaf (6a, 6b) can be rotated together with the folding part (11, 12). 2. Door system (5) according to claim 1, wherein the folding part (11, 12) is elongated and is rotatably connectable to the sliding part (13, 14) at its first end. 3. Door system (5) according to claim 1 or 2, wherein the folding part (11, 12) is rotatable with the via a bearing bolt (15), which partially engages in the folding part (11, 12) and partially in the sliding part (13, 14). Sliding part (13, 14) can be connected. Door system (5) according to one of claims 1 to 3, wherein the folding part (11, 12) can be locked on the sliding part (13, 14), with a rotation of the folding part (11, 12) about the axis of rotation (9a, 9b) in the locked State of the folding part (11, 12) is prevented and is made possible in the unlocked state of the folding part (11, 12). Door system (5) according to claim 4, wherein the folding part (11, 12) can be locked to the sliding part (13, 14) via at least one locking bolt (16), the locking bolt (16) partially being inserted into the folding part (11, 12) in the locked state. and partially engages in the sliding part (13, 14) and in the unlocked state does not engage in the folding part (11, 12) and/or does not engage in the sliding part (13, 14). Door system (5) according to claim 5 based on claim 2, wherein the locking bolt (16) engages in a second end of the folding part (11, 12) in the locked state. Door system (5) according to claim 5 or 6, wherein the locking bolt (16) is displaceable between an unlocking position associated with the unlocked state and a locking position associated with the locked state; wherein the locking bolt (16) can be coupled to a spring mechanism (17), which is designed to apply a restoring force acting in the direction of the locking position to the locking bolt (16) coupled to the spring mechanism (17). Door system (5) according to claim 7, wherein the locking bolt (16) can be connected to an elongated traction means (18) and can be moved from the locking to the unlocking position by pulling on the traction means (18) connected to the locking bolt (16). Door system (5) according to one of claims 1 to 8, wherein the storage device (10) further comprises a further folding part (12) and a further sliding part (14); wherein the further sliding part (14) on the elevator car (3) can be displaced in the direction of the displacement axis (8) between the opening and closing positions can be stored, the further folding part (12) being rotatable about the axis of rotation (9a, 9b) on the further sliding part (14), so that the further folding part (12) can be moved together with the further sliding part (14), and the door leaf (6a, 6b) can be attached at its first end to the folding part (11) and at its second end to the further folding part (12), so that the door leaf (6a, 6b) together with the folding part (11) and the further folding part (12) is rotatable. Door system (5) according to one of the preceding claims, further comprising: at least one further door leaf (6b) for closing a further partial area of the cabin opening (4); wherein the storage device (10) is further designed to move the further door leaf (6b) on the elevator car (3) in the direction of the displacement axis (8) between an opening position, in which the further door leaf (6b) releases the further partial area, and a closed position , in which the further door leaf (6b) closes the further partial area, can be moved and/or rotatably mounted around a further axis of rotation (9b) parallel to the axis of rotation (9a). Elevator system (1), comprising: an elevator shaft (2); and at least one elevator car (3), which can be moved between several floors in the elevator shaft (2) and has at least one car opening (4); wherein the elevator car (3) comprises at least one door system (5) according to one of the preceding claims, wherein the door leaf (6a, 6b) via the storage device (10) on the elevator car (3) in the direction of the displacement axis (8) between the opening and the closed position is displaceable and additionally rotatable about the axis of rotation (9a, 9b). Method for evacuating an elevator car (3) of an elevator system (1) according to claim 11, wherein the method comprises: if the elevator car (3) is to be evacuated via the car opening (4) and the door leaf (6a, 6b) is in the closed position and / or an intermediate position between the opening and closing positions is shifted: rotating the door leaf (6a, 6b) about its axis of rotation (9a, 9b) into an emergency opening position in which the car opening (4) is released to such an extent that the elevator car (3 ) can be evacuated via the cabin opening (4). A method according to claim 12, wherein the elevator car (3) comprises the door system (5) according to claim 5; wherein the door leaf (6a, 6b) is first unlocked by unlocking the folding part (11, 12) and then rotated into the emergency opening position. Method according to claim 12 or 13, wherein the door leaf (6a, 6b) is pivoted into the elevator car (3) when rotating into the emergency opening position; and/or wherein the door leaf (6a, 6b) is rotated about a vertical axis as the axis of rotation (9a, 9b).