A method and a control system for construction cranes

Abstract

 A control system is provided for construction cranes comprising a crane mast and a swingable working arm. The control system comprises a movable suspension device (72) for suspending a vertically liftable operator lift. An angle measuring device measures an angular deviation of a top portion of the crane mast and provides a control signal to an actuator based on the measured deviation. The actuator is adapted to move the suspension device in response to said control signal along a guide for compensating for the measured deviation. Also provided are an elevating system, a construction crane (10) and a control method.

Description

Technical field

[0001] The present invention relates to a control system for construction cranes of the type comprising a crane mast and a swingable working arm. The present invention also relates to an elevating system for construction cranes, a construction crane and a method of controlling a position of suspension of an operator lift.

Background art

[0002] Construction cranes are commonly used on, for instance, building sites. Such construction cranes comprise a mast or tower rising from the ground. At a top portion of the mast, there is a swingable working arm which may be swung to different working positions in order to lift a load (such as building elements) in one location and release it at another location. The working arm has a load carrying side and a counter ballast side. The working arm may be operated by from a control cabin.

[0003] One type of control cabin is stationary at the top portion of the mast, near the working arm. In order for an operator on the ground to be able to access the control cabin, there may be provided an operator lift which travels vertically along the mast. However, such an operator lift is not allowed to go all the way up to the control cabin, the reason why will be explained in the following. In an unloaded state of the working arm, the weight of the counter ballast will provide a bending moment to the top portion of the mast, thereby bending the top portion of the mast towards the counter ballast side of the working arm. In a fully loaded state the top portion will bend the mast towards the load carrying side. Due to such bending the operator lift cannot, or may not because of less material strength at the top portion of the mast, travel all the way to the control cabin. Therefore, the operator has to step out of the operator lift at a lower level and walk up some stairs the remaining distance.

[0004] WO 91/04220 A1 discloses a control cabin which is movable about the mast to follow the working arm at the swinging of the latter. The movement about the mast is accomplished by means of a ring-shaped track around the mast, along which track the control cabin can travel. The control cabin is not vertically stationary but may travel also up and down along the mast. Thus, an operator does not have to take a separate lift to access the control cabin, but can step into the actual control cabin already at the ground and then travel upwards to an operating position for operating the working arm. While this construction eliminates the problem of the necessity to use a separate lift, just like the stationary cabin type, this type of vertically movable cabins may also be affected by the bending of the top portion of the mast. Such vertically movable cabins are suspended from the top of the mast by means of wires. When the top portion of the mast bends and thus moves in one direction the point of suspension at the top will also move in that direction. Due to the gravitational force, the control cabin will strive to reach the lowest point around the ring-shaped track. This leads to a misalignment between the control cabin and the working arm, which in turn means that the operator will be in a disadvantageous operating position.

Summary of the Invention

[0005] An object of the present invention is to alleviate the drawbacks of the prior art. This and other objects, which will become apparent in the following, are accomplished by a control system, an elevating system, a construction crane and a method as defined by the accompanying claims.

[0006] The present inventive concept is based on the realization that by compensating for a changed point of suspension due to bending of crane mast, the drawbacks of the prior art may be alleviated. In particular, the inventor has realized that constructions cranes of the type having a vertically stationary control cabin with separate lift for accessing the control cabin, as well as construction cranes of the type having a vertically movable control cabin, may benefit from the present inventive concept.

[0007] In connection with the first type, having a control cabin with a separate lift, the lift may be decoupled from the mast and be suspended from a movable suspension device at the top portion of the mast. Any angular deviation of the top portion of the mast will be compensated by moving the suspension device in substantially the opposite direction. The movement of the suspension device will be substantially horizontal. Thus, the lift may travel all the way up to control cabin, regardless of the top portion of the mast being bent or not. Indeed, in some embodiments, the lift may even be without contact with the mast, and merely be suspended from the suspension device, e.g. by means of a gear rack, wires and/or cable, or the like.

[0008] In connection with the second type, having a vertically movable control cabin, the tendency of the control cabin to be at the lowest position around the ring-shaped track due to gravitational force, may be counteracted by moving the suspension device from which the control cabin may be suspended.

[0009] According to a first aspect of the inventive concept, there is provided a control system for construction cranes comprising a crane mast and a swingable working arm. The control system comprises
a movable suspension device for suspending from a top portion of the crane mast a vertically liftable operator lift,
a guide for guiding the movement of the suspension device, the guide being adapted to be mounted at the top portion of the crane mast for providing a linear guiding direction which is substantially parallel to a longitudinal axis of the working arm of the crane,
an actuator for actuating the movement of the suspension device along the guide, and
an angle measuring device for measuring an angular deviation of the top portion of the crane mast relative to a longitudinal axis of a major portion of the crane mast, the angle measuring device being adapted to provide a control signal to the actuator based on the measured deviation,
wherein the actuator is adapted to move the suspension device in response to said control signal to a position along the guide for compensating for the measured deviation.

[0010] In at least some embodiments, the suspension devices may be displaced by rolling means or by sliding means. For instance, it may be rolled or slid by one or more pushing and/or pulling rods. In some embodiments the suspension device may be displaced by means of a rotating spindle extending from the actuator. In other embodiments the suspension device may be moved by means of pistons actuating on the suspension device. In further embodiments in the suspension device may comprise an internal motor for actuating the movement along the guide. In other embodiments, an external motor is provided, suitably in said actuator. The suspension device may have mutually cooperating means with the guide, such as track in the guide and rolling or sliding means on the suspension device, or vice versa. According to at least one example embodiment, the suspension device is movable by means of roller elements, wheels, or gears.

[0011] The actuator may be a separate part which is operatively connected to the suspension device or it may be integrated with the suspension device and move along with the suspension device.

[0012] The control signal may be any type of signal which gives information related to the angular deviation. For instance, it may provide a value of the deviation, which the actuator or a control unit in the actuator transforms into a displacement value representing the distance that the suspension device should be displaced along the guide. The angle measuring device may comprise a control unit which calculates the displacement distance for the suspension device. The control signal may have varying values, e.g. between a lowest voltage, such as -10V and a highest voltage, such as +10V, wherein a negative value corresponds to movement of the suspension device in one direction along the guide, and a positive signal corresponds to the movement of the suspension device in an opposite direction, wherein the absolute magnitude could represent the movement distance, the end values representing the maximum allowable displacement of the suspension device in the respective direction along the guide. The control signal may have varying frequency for indicating different displacements, etc. Any other type of control signals for affecting the movement of the suspension device is also conceivable.

[0013] While various devices may be provided for direct or indirect measurement of the angular deviation of the top portion of the crane mast, according to at least one exemplary embodiment, the angle measuring device comprises an inclinometer. The inclinometer may, for instance, be a mechanical inclinometer or a digital inclinometer, as long as the angle measuring device can be adapted to provide a control signal to the actuator based on the measured angular deviation.

[0014] According to at least one exemplary embodiment, the guide comprises a bar along which the suspension device is movable. The bar may be adapted to extend in parallel with the longitudinal axis of the working arm of the crane.

[0015] According to at least one exemplary embodiment, the actuator is mounted on the bar. Thus, the actuator may, suitably, be mechanically connected to the suspension device by means of a drive part, for instance by means of a spindle, rod, piston or other force transmitting members for moving the suspension device.

[0016] According to at least one exemplary embodiment, the actuator comprises a control signal receiving part and a mechanical drive part adapted to be in engagement with the suspension device, wherein the drive part is adapted to move the suspension device based on the control signal received by the control signal receiving part. In other embodiments, rather than or in addition to a mechanical engagement with the suspension device, the actuator is electronically connected to the suspension device. In such embodiments, the actuator may send a drive signal to the suspension device either via wire or wireless. Furthermore, in some embodiments, the communication between the actuator and the angle measuring device may be via wire or wireless.

[0017] According to at least one exemplary embodiment, the guide is supported by at least one spacer element adapted to be connected to and extend away from the crane mast so as to provide a space between the guide and the crane mast. Suitably, two spacer elements may be provided, forming two respective connection locations for the guide. The spacer element may suitably extend substantially horizontally from the mast, i.e. substantially perpendicularly to the longitudinal axis of the major portion of the mast.

[0018] According to at least one exemplary embodiment, the linear movement of the suspension device is limited to the width of the top portion of the crane mast. According to at least one exemplary embodiment, suspension device is adapted to move along the guide a distance which is shorter than the width of the top portion of the crane mast.

[0019] Although the guide may be stationary relative to the crane mast and the actuator is adapted to move the suspension device along the stationary guide, in at least some embodiments the guide may be movable relative to the crane mast. Thus, according to at least one exemplary embodiment, the actuator is adapted to move the guide instead of or in addition to only moving the suspension device.

[0020] According to at least one exemplary embodiment, the actuator is adapted to move the suspension device by tilting the guide, thereby causing the suspension device to move along the guide due to gravity. Thus, if top portion is bent towards the load carrying side of the working arm the guide may be tilted in one direction to compensate for the bending (for instance lifting one end of the guide), while if the top portion is bending towards the counter ballast side the guide may be tilted in the opposite direction (for instance by lowering said one end of the guide or by lifting the other end of the guide).

[0021] According to at least one exemplary embodiment, the guide comprises a concave portion along which the suspension device is movable, wherein the suspension device, due to gravity, is promoted to move to a vertically lowest position along said concave portion. Since the position of said concave portion will vary depending on the degree of tilting of the guide, the suspension device will follow accordingly to the lowest position.

[0022] The suspension device may be provided with any common suspension means for wires, cables etc., for keeping a lift or control cabin suspended. According to at least one exemplary embodiment the suspension device is provided with a rack holding means for holding a rack part of a gear rack. Suitably, a pinion part of the gear rack may be connected to an operator lift, such as a control cabin or a separate lift for accessing a control cabin.

[0023] According to a second aspect of the present inventive concept, there is provided an elevating system for construction cranes. The elevating system comprises an operator lift. The system also comprises elongate suspension means extending from the suspension device of a control system according the first aspect and being connected to the operator lift for moving the lift vertically along the crane mast. An operator lift may, for instance, be a separate lift for accessing a vertically stationary control cabin or it may, for instance, be a vertically movable control cabin.

[0024] According to at least one exemplary embodiment, said elongated suspension means comprises a gear rack, the gear rack comprising a rack part and a pinion part, wherein the rack part is connected to the suspension device and the pinion part is connected to the operator lift. The pinion part may move vertically upwards and downwards along the rack part, thereby causing the operator lift to travel in the vertical direction.

[0025] According to at least one exemplary embodiment, said elongate suspension means is pivotally connected to the movable suspension device. In case of a gear rack, the rack part may maintain its vertical suspension (similarly to a pendulum which due to gravity would strive to extend vertically from its position of suspension).

[0026] The working arm of a construction crane has a load carrying side and a counter ballast side. If the top portion of the mast is inclined towards the load carrying side, the suspension device and thus the position of the suspension of the operator lift is moved towards the counter ballast side.

[0027] If the top portion of the mast is inclined towards the counter ballast side, the suspension device, and thus the position of the suspension of the operator lift, is moved to towards the load carrying side.

[0028] In some embodiments, said elongated suspension means comprises at least one wire or cable.

[0029] In some embodiments, the elongated suspension means comprises a combination of a gear rack and at least one wire or cable.

[0030] According to at least one exemplary embodiment, said operator lift is a control cabin from which an operator controls the operation of the working arm, wherein the control cabin is movable around the circumference of the mast, suitably along at least one annular track. Thus, by means of the present inventive concept, due to the compensating movement of the suspension device the control cabin may be aligned with the working arm of the crane, despite any angular deviation of the top portion of the crane. The operator will have a satisfactory line of sight, without having to turn his/her neck or assume other inconvenient working positions.

[0031] In at least some embodiments, the control cabin is connected to a pinion part of a gear rack and the suspension device is connected to a rack part of the gear rack. The rack part is, suitably, pivotally mounted to the suspension device. When the actuator moves the suspension device to compensate for an angular deviation of the top portion of the mast, the rack part will also move and maintain its vertical extension without any inclination. The rack part will, in turn affect the position of the cooperating pinion part, which in turn will affect the position of the control cabin around the annular track around the crane mast.

[0032] According to at least one exemplary embodiment, said operator lift is adapted to be lifted to the top portion of the crane for enabling an operator to access a control cabin which is stationary relative to the working arm of the crane. In some embodiments, a lift motor may be arranged on the lift. In other embodiments, a lift motor may be arranged on the suspension device. In the latter case, the motor may suitably be moved together with the suspension device along the guide.

[0033] According to a third aspect of the present inventive concept a construction crane is provided. It comprises a controls system according to the first aspect and an elevating system according to the second aspect.

[0034] According to a fourth aspect of the present inventive concept, there is provided a method of controlling a position of suspension of an operator lift suspended from a movable suspension device located at a top portion of a crane mast of a construction crane. The construction crane comprising a working arm with a load carrying side and a counter ballast side, the method comprising:

measuring an angular deviation of the top portion of the crane mast relative to a longitudinal axis of a major portion of the crane mast,

moving said suspension device, based on the measured deviation, in a direction which is substantially parallel to a longitudinal axis of the working arm of the crane, wherein

if the top portion of the mast is inclined towards the load carrying side, the suspension device, and thus the position of suspension of the operator lift, is moved towards the counter ballast side, and

if the top portion of the mast is inclined towards the counter ballast side, the suspension device, and thus the position of suspension of the operator lift, is moved towards the load carrying side.

Brief description of the drawings

[0035] 

Fig. 1 illustrates a construction crane according to at least one exemplary embodiment of the inventive concept.

Fig. 2 schematically illustrates a control system according to at least one exemplary embodiment of the inventive concept.

Fig. 3 is a top view of an operator lift which may be incorporated in an elevating system according to at least one exemplary embodiment of the inventive concept.

Detailed description of the drawings

[0036] Fig. 1 illustrates a construction crane 10, in the form of a tower crane. It has an unmovable mast 12. A working arm 14 is mounted at the top portion of the crane mast 12. It is swingable in a horizontal plane. It has a load carrying side 15 for lifting objects from one place to another and a counter ballast side 16 functioning as a counterweight.

[0037] An operator lift is vertically movable along the mast. In the present example, it is illustrated as a control cabin 18 which is movable around the mast 12, suitably along an annular track. However, in other embodiments the operator lift may be a separate lift for accessing a vertically stationary control cabin at the top portion of the crane mast.

[0038] In the present exemplary embodiment, the control cabin 18 is mounted on a carriage 20 which is movable up and down the mast. The control cabin 18 is suspended from the top portion 21 of the crane mast 12 by means of elongated suspension means 40 extending from a suspension device 72 which is movable along a guide portion (see Fig. 2). The elongated suspension means 40 may, for instance, be a gear rack, a wire or cable, or a combination thereof. They may suitably be mounted at a location 42 of the crane as indicated in Fig. 1.

[0039] Fig. 2 schematically illustrates a control system 70 according to at least one exemplary embodiment of the inventive concept. It may, for instance, be a control system for the crane 10 illustrated in Fig. 1. In particular, Fig. 2 is a schematic top view, wherein the crane is seen from above.

[0040] The working arm has a load carrying side 15 and a counter ballast side 16. A suspension device 72 is movable in parallel with the working arm and its longitudinal axis. The suspension device 72 is mounted on a guide 74 which extends in parallel with the longitudinal axis of the working arm. Said guide 74 may be a bar which is distanced from the mast 12 by means of at least one spacer element extending outwardly from the mast. In the present example two spacer elements 76 are provided.

[0041] An actuator 78 is provided on a prolongated portion 80 of the guide 74. Thus, in this example the bar comprises both an actuator holding portion and a guide portion. The actuator 78 controls the displacement of the suspension device 72 along the guide 74 by means of any suitable drive means 82, such as a spindle, rod, piston etc. The suspension device 72 may, for instance, be provided with at least one roller element, wheel or other mechanism for moving the suspension device 72 in response to the force transmitted by the drive means 82. Such roller element, wheel or other mechanism may suitably travel in a defined path in said guide 74, such as a linear track or groove along said guide 74. As explained under the heading Summary of the Invention, instead of, or in addition to, moving the suspension device along a guide which is stationary relative to the crane mast, in at least some embodiments the actuator could be adapted to displace the actual guide, which in turn would lead to a displacement of the suspension device along the guide. For instance, the guide may be tilted, whereby gravity causes the suspension device to move. A curved or concave portion of the guide would provide a variable lowest position which would vary with the degree of tilting, and the suspension device would strive to reach said lowest position when the degree of tilting changes.

[0042] In the present example, said guide 74 protrudes horizontally beyond at least one of the spacer elements 76, and the actuator 78 is located on such a protruding or prolongated portion 80 of said guide 74. However, other configurations and placements of the actuator 78 are conceivable.

[0043] An angle measuring device 84, here in the form of an inclinometer, is provided at the top portion 21 (see Fig. 1) of the crane mast. The angle measuring 84 device is adapted to measure the angular deviation of the top portion of the crane mast 12 relative to a longitudinal axis of a major portion of the crane mast 12. Said longitudinal axis is perpendicular to the plane of the drawing figure, and would normally be the vertical (perpendicular to the plane of the horizon).

[0044] In an unloaded state of the working arm 14, the weight of the counter ballast side 16 exerts a moment on the top portion 21 of the mast 12, causing it to bend from the longitudinal axis of the major portion of the crane mast 12 (i.e. a portion below the top portion 21 which is not subjected to bending) in a direction toward the counter ballast side 16. In a loaded state of the working arm 14, depending on the load carried by the working arm on the load carrying side 15 the top portion 21 of the crane mast 12 may instead bend towards the load carrying side 15.

[0045] The angle measuring device 84 is adapted to provide a control signal to the actuator 78 based on the measured deviation of the top portion 21 of the crane mast 12, wherein the actuator 78 moves the suspension 72 device in response to the control signal to compensate for the measured deviation.

[0046] By moving the suspension device 72, the position of the operator lift, (here in the form of control cabin 18) suspended from the suspension device 72 will also be affected. As has been previously mentioned, the present inventive concept may be implemented with different types of operator lifts, for instance lifts that are separate from vertically stationary control cabins, or operator lifts in the form of vertically movable control cabins. Fig. 3 is an illustration of the latter.

[0047] Fig. 3 is a top view of an operator lift which may be incorporated in an elevating system according to at least one exemplary embodiment of the inventive concept, wherein the operator lift is in the form of a vertically movable control cabin 18.

[0048] The control cabin 18 is mounted to a carriage 20 which is engaged with the mast 12. In this exemplary embodiment the carriage 20 extends around all four vertical sides of the mast 12. The carriage 20 is provided with a number of supporting wheels 22 which bear against the vertical beam of the framework of the mast 12. The support wheels 22 are distributed between the upper edge and the lower edge of the carriage, in order to take up loads due to torque/moment. The carriage 20 has a box-like shape, for example, with closed sides.

[0049] The control cabin 18, in which the operator may sit, may have any suitable common design. The carriage is provided with at least one annular track, herein as an upper raceway 24. The carriage 20 may, suitably, also be provided with a lower raceway at the lower portion of the carriage 20. Such raceways may be provided with guide grooves 28 for pivotable wheels 30 which are arranged on beams at the control cabin 18. By means of these wheels 30, the control cabin 18 may move along the raceway 24, causing the control cabin 18 to be rotated around the mast 12 of the crane.

[0050] Without the inventive control system, the control cabin 18 might, due to bending of the top portion 21 of the crane mast 12, roll away from the desired rotational position to a displaced rotational position around the raceway 24 (resulting in impaired overview of the working site for the operator). However, the inventive control system 70 provides the compensating movement of the movable suspension device 72 along the guide 74, which in turn will maintain the control cabin 18 in the desired rotational position and counteract the unwanted displacement.

[0051] In the exemplary illustration, the rotational position of the control cabin 18 relative to the mast 12 is controlled by means of a toothed belt 32 which is laid over the raceway 24. The teeth 33 of the belt 32 engage with control devices in a motor 34 on the roof of the control cabin 18, on the one hand, and to guides 36 on raceway 24, on the other hand.

[0052] The control cabin 18 may be suspended from a suspension device 72 movable along the guide 74, such as illustrated in Fig. 2. The suspension device 72 and the guide 74 are suitably arranged at location 42 at the top portion of the mast.

[0053] An elongated suspension means 40 may extend from the suspension device 72 to an engagement location at the control cabin 38. For instance, the elongate suspension means 40 may be in the form of a gear rack with cooperating rack part and pinion part, as exemplified above.

[0054] In other embodiments, a block (not shown) may be fixed to the suspension device 72 and may be stored on a cable which is engaged with a wheel, pulley or other suitable elements disposed on the roof of the control cabin 18.

[0055] In addition to the control system 70, the construction crane may also be provided with another type of signal transmitter. Such other signal transmitter may be arranged on the mounting of the working arm 14 of the crane, which emits a rotation-indicating signal which is representative of the angular rotation of the boom 14. Thus, this is a different signal than the control signal provided by the angle measuring device of the inventive control system. Based on the rotation-indicating signal, the motor 34 is controlled, and the control cabin 18 may be rotated to a position vertically in line with the guide 74 and the suspension device 72. Thus, when the control cabin 18 is not at the top portion 21 of the crane mast 12, or no angular deviation of the top portion 21 is detected by the angle measuring device 84, then the control cabin 18 may move around the mast 12 based on only the rotation-indicating signal. The control cabin 18 will thus automatically follow the rotation of the working 14 arm to the correct rotational position around the mast 12 so that the crane operator has a good overview of the work area. However, if the top portion 21 of the crane 10 bends, then a further compensation may be used based on the control signal provided by the angle measuring device 84.

[0056] The present inventive concept can be used when producing new construction cranes. However, the control system and/or elevating system can also be retro-fitted to already existing cranes.

Claims

1. A control system for construction cranes comprising a crane mast and a swingable working arm, the system comprising:

a movable suspension device for suspending from a top portion of the crane mast a vertically liftable operator lift,

a guide for guiding the movement of the suspension device, the guide being adapted to be mounted at the top portion of the crane mast for providing a linear guiding direction which is substantially parallel to a longitudinal axis of the working arm of the crane,

an actuator for actuating the movement of the suspension device along the guide, and

an angle measuring device for measuring an angular deviation of the top portion of the crane mast relative to a longitudinal axis of a major portion of the crane mast, the angle measuring device being adapted to provide a control signal to the actuator based on the measured deviation,

wherein the actuator is adapted to move the suspension device in response to said control signal to a position along the guide for compensating for the measured deviation.

2. The control system as claimed in claim 1, wherein the guide comprises a bar along which the suspension device is movable.

3. The control system as claimed in claim 2, wherein the actuator is mounted on the bar.

4. The control system as claimed in claim 3, wherein the actuator comprises a control signal receiving part and a mechanical drive part adapted to be in engagement with the suspension device, wherein the drive part is adapted to move the suspension device based on the control signal received by the control signal receiving part.

5. The control system as claimed in any one of claims 1-4, wherein the guide is supported by at least one spacer element adapted to be connected to and extend away from the crane mast so as to provide a space between the guide and the crane mast.

6. The control system as claimed in any one of claims 1-5, wherein the actuator is adapted to move the suspension device by tilting the guide, thereby causing the suspension device to move along the guide due to gravity.

7. The control system as claimed in claim 6, wherein the guide comprises a concave portion along which the suspension device is movable, wherein the suspension device, due to gravity, is promoted to move to a vertically lowest position along said concave portion.

8. An elevating system for construction cranes, comprising:

an operator lift,

elongate suspension means extending from the suspension device of a control system according to any one of claims 1-7 and being connected to the operator lift for moving the lift vertically along the crane mast.

9. The elevating system as claimed in claim 8, wherein said elongated suspension means comprises a gear rack, the gear rack comprising a rack part and a pinion part, wherein the rack part is connected to the suspension device and the pinion part is connected to the operator lift.

10. The elevating system as claimed in any one of claims 8-9, wherein said operator lift is a control cabin from which an operator controls the operation of the working arm, wherein the control cabin is movable around the circumference of the mast, suitably along at least one annular track.

11. The elevating system as claimed in any one of claims 8-9, wherein said operator lift is adapted to be lifted to the top portion of the crane for enabling an operator to access a control cabin which is stationary relative to the working arm of the crane.

12. A construction crane, comprising an elevating system as claimed in any one of claims 8-11 and a control system as claimed in any one of claims 1-7.

13. A method of controlling a position of suspension of an operator lift suspended from a movable suspension device located at a top portion of a crane mast of a construction crane, the construction crane comprising a working arm with a load carrying side and a counter ballast side, the method comprising:

measuring an angular deviation of the top portion of the crane mast relative to a longitudinal axis of a major portion of the crane mast,

moving said suspension device, based on the measured deviation, in a direction which is substantially parallel to a longitudinal axis of the working arm of the crane, wherein

if the top portion of the mast is inclined towards the load carrying side,

the suspension device, and thus the position of suspension of the operator lift, is moved towards the counter ballast side, and

if the top portion of the mast is inclined towards the counter ballast side, the suspension device, and thus the position of suspension of the operator lift, is moved towards the load carrying side.

Drawing