BACKGROUND OF THE INVENTION [0001] The invention relates to a ladder arrangement comprising: at least one fixed ladder part including a plurality of steps having a predetermined step distribution; and at least one movable ladder part including a plurality of steps having a substantially same step distribution as the fixed ladder part, and which movable ladder part is arranged movably relative to the fixed ladder part; and wherein the fixed ladder part and the movabie ladder part are in succes¬ sion in such manner that the ladder parts are partly overlapping. [0002] The invention further relates to a person lifter comprising: a carriage; a movable beam; a first beam part connected to the carriage by means of a first articulation and movable relative to the first articulation, and the first part having a fixed length; a second beam part connected to an outer¬ most end of the first beam part by means of a second articulation, the second part being extendable and retractable; and a ladder arrangement comprising a first ladder arranged on the first beam part and a second ladder arranged on the second beam part, the first ladder and the second ladder comprising a plu¬ rality of steps having a predetermined step distribution, the first ladder compris¬ ing at least one fixed ladder part and at least one movable ladder part, the lad¬ der parts being arranged in succession and partly overlapping relative to each other. [0003] The invention still further relates to a method of using a per¬ son lifter provided with ladders, the person lifter comprising at least a carriage, a movable beam and a ladder arrangement, the ladder arrangement compris¬ ing a movable ladder part and a fixed ladder part arranged in succession and partly overlapping relative to each other; the method comprising: moving the beam for driving the outermost end of the beam into the desired position, and placing steps of the movable ladder part and the fixed ladder part substantially at the same point in the overlapping portion of the ladder parts. [0004] Fire-fighting vehicles and corresponding rescue vehicles typically comprise a person lifter provided with ladders in a manner enabling climbing into a person cage or the like at the outermost end of the person lifter. The beam comprised by the person lifter can usually be extended and short¬ ened, whereby the length of the ladders has to be able to change correspond- ingly. Accordingly, the ladders are typically arranged partly overlapping, and they are able to glide relative to each other when the beam is being moved. In order to enable climbing along the ladders, the steps of the ladders should be substantially at the same point in the overlapping portion. Accordingly, the steps have to be placed in position by changing the length of the beam. In this case, the position of the outermost end of the beam naturally changes and the entire beam has to be repositioned for getting the person cage into the original position. Consequently, the problem is the complex and slow use of the person lifter.

BRIEF DESCRIPTION OF THE INVENTION [0005] The object of the present invention is to provide a new and improved ladder arrangement and a person lifter, and, furthermore, a method of using a person lifter provided with ladders. [0006] The ladder arrangement of the invention is characterized in that the ladder arrangement comprises at least one actuator connected to the movable ladder part, the actuator being arranged to move the movable ladder part relative to the fixed ladder part; that the ladder arrangement comprises a control device for controlling the actuator in a manner allowing the steps of the movable ladder part to be arranged substantially at the same point with the steps of the fixed ladder part in the overlapping portion of the ladder parts; and that an outermost end of the ladder arrangement is arranged to remain sub¬ stantially immobile when the actuator is being used. [0007] The person lifter of the invention is characterized in that the first ladder and the second ladder are interconnected by means of a third ar¬ ticulation; that the third articulation is fastened to the second beam part such that the third articulation is located at a distance from the second articulation, whereby an angle between the first ladder and the carriage is always smaller than an angle between the first beam part and the carriage; and that the first ladder comprises at least one actuator for positioning the movable ladder part relative to the fixed ladder part such that the steps in the overlapping portion of the ladder parts can be positioned substantially at the same point by moving the movable part; and that an outermost end of the ladder arrangement is ar¬ ranged to remain substantially immobile when the actuator is being used. [0008] The method of the invention is characterized by moving the movable ladder part by means of at least one actuator relative to the fixed lad- der part for placing the steps substantially at the same point in the overlapping portion of the ladder parts; and keeping the beam and an outermost end of the ladder arrangement substantially immobile when the actuator is being used. [0009] The essential idea of the invention is that the ladder ar¬ rangement comprises one or more actuators arranged to move the movable portion comprised by the ladders in a manner allowing the steps of the over¬ lapping ladder portions to be positioned substantially at the same point. The upper end of the ladder arrangement is arranged to remain in position when the steps are position in place by means of the actuator. [0010] An advantage of the invention is that the steps of the over¬ lapping ladder parts can be placed at the same point without having to move the beam. This allows the person cage to be driven to the desired position and to be kept in place in this position during the setting of the steps. The actuator moves the movable portion of the ladders, but does not affect the upper end of the ladder arrangement. Accordingly, the invention speeds up and simplifies the driving in place of the person cage, which is a very important issue at least in rescue operations. [0011] The essential idea of an embodiment of the invention is that movement of the beam is prevented when the movable ladder part is being moved by means of the actuator. [0012] The essential idea of an embodiment of the invention is that the actuator is arranged to operate both as a transfer device and as a locking device of the movable ladder part. This way, several separate devices are not required for the transfer and locking. [0013] The essential idea of an embodiment of the invention is that the pressure medium-operated actuator, such as a hydraulic cylinder, for ex¬ ample, is arranged to move the movable ladder part. [0014] The essential idea of an embodiment of the invention is that the outermost part of the ladder arrangement, i.e. the upper end, is fastened immobile to the upper part of the beam. The mounting of the upper part of the ladder arrangement thus receives part of the load of the ladders. The actuator may be arranged to move the lowest portion of the ladder arrangement. Alter¬ natively or in addition, some movable ladder part between the lowest ladder part and the immobile uppermost ladder part can be moved. [0015] The essential idea of an embodiment of the invention is that the outermost part, i.e. the upper end, of the ladder arrangement is fastened immobile to the upper part of the beam, and the lower part of the ladder ar¬ rangement is fastened immobile to the carriage of the lifter or to a correspond¬ ing support point. This being so, the actuator is arranged to move a movable ladder part between the ends of the ladder arrangement for placing the steps in position. [0016] The essential idea of an embodiment of the invention is that the person lifter is arranged on a movable carriage, which is a rescue vehicle. [0017] The essential idea of an embodiment of the invention is that the ladder arrangement comprises at least one sensor arranged to monitor the position of the steps in the overlapping portion of the ladder parts. [0018] The essential idea of an embodiment of the invention is that the ladder arrangement comprises at least one control unit arranged to control the actuator and to drive the movable ladder part automatically in such a man¬ ner that the steps in the overlapping portion are substantially at the same point.

BRIEF DESCRIPTION OF THE FIGURES [0019] The invention will be described in more detail in the accom¬ panying drawings, wherein Figure 1 is a schematic side view of a person lifter according to the invention with the beam lifted to its uppermost position, Figure 2 schematically shows the person lifter shown in Figure 1 with the beam lifted to a horizontal position, Figure 3 schematically shows the person lifter shown in Figure 1 with the beam directed downwards, Figure 4 schematically shows the structure of a ladder arrangement according to the invention, Figure 5 schematically shows the principle of a second ladder ar¬ rangement according to the invention, and Figure 6 schematically shows still another ladder arrangement. [0020] For the sake of clarity, the figures show some embodiments of the invention in a simplified manner. Like parts are denoted with the same reference numerals.

DETAILED DESCRIPTION OF SOME EMBODIMENTS [0021] The person lifter shown in Figure 1 comprises a carriage 1 , which can be a movable carriage, such as a fire-fighting vehicle or another rescue vehicle. A beam 2 is arranged on the carriage 1 , the beam being mov- able in a manner enabling the driving of a person cage 3 or the like at the out¬ ermost end of the beam to the desired place. The beam 2 may comprise a first part 2a and a second part 2b. The first beam part 2a may be connected by means of a first articulation 4 or the like to the carriage 1 in a manner allowing the beam 2 to be rotated in direction A. The outermost end of the first part 2a is provided with a second articulation 5 or the like, and the second beam part 2b, connected thereto, can be rotated in direction B relative to the first part 2a. The length of the first part 2a may be fixed. The second beam part 2b, in turn, may be telescopically extendable and retractable, enabling the movement of the person cage 3 by lengthening and shortening the length of the second part 2b and by rotating the beam parts 2a and 2b relative to the articulations 4 and 5. [0022] The person lifter also comprises a ladder arrangement 6 in a manner allowing climbing from the carriage 1 along the ladders to the person cage 3 and back. On the other hand, the beam 2 does not necessarily have to comprise a person cage 3, but it may be provided with some other means, such as a fire-extinguishing medium nozzle. The ladder arrangement 6 may be arranged on the side of one flank of the beam 2, as is illustrated in Figures 1 to 3. The ladder arrangement may comprise a first ladder 6a arranged in the first beam part 2a and a second ladder 6b arranged in the second beam part 2b. The first ladder 6a and the second ladder 6b may be interconnected by means of a third articulation 7. The articulation between the ladders 6a, 6b may be fastened to the second beam part 2b, at a distance from the articulation 5 be¬ tween the beam parts 2a, 2b. Accordingly, the articulations 5 and 7 are located at different points. This being so, the angle between the first ladder 6a and the carriage 1 is always smaller than the angle between the first beam part 2a and the carriage 1 , as can be seen in Figures 1 to 3. This substantially facilitates and speeds up climbing in the ladders. When the beam 2 is moved to different positions, the distance changes between the lower end of the first ladder 6a and the articulation 7. The first ladder 6a comprises at least two ladder parts arranged movable relative to each other. The ladder parts may be arranged to glide telescopically relative to each other, whereby the ladder parts enable a change in the length of the first ladder 6a when the beam 2 is moved. [0023] Figure 4 shows a structure of the ladder arrangement 6 ac¬ cording to the invention in a strongly simplified manner. The ladders comprise at least one movable ladder part 8 and at least one fixed ladder part 9. The ladder parts comprise steps 8a and 9a having substantially the same step dis- tribution T. The ladder parts 8 and 9 are arranged in succession and they may be interconnected with suitable support members in a manner allowing the movable ladder part 8 to be moved longitudinally relative to the fixed ladder part 9. The ladder parts 8 and 9 are superimposed in an overlapping portion 10. The movable ladder part 8 can be moved longitudinally S by means of one or more actuators 11 , which may be connected directly or by means of suitable power transmission members to act on the movable ladder part 8. The actuator 11 may be a hydraulic or pneumatic cylinder. Alternatively, the actuator 11 may be a pressure medium driven motor arranged to act on the movable ladder part 8 by means of a toothed bar or the like. Furthermore, the actuator 11 may be an electric motor or any other power unit suitable for moving the ladder part 8. The actuator 11 may operate both as a transfer device and as a locking de¬ vice. The upper end 30 of the ladder arrangement 6 may be fastened to the beam 2 in a fastening portion 31. The fastening portion 31 may be arranged in the vicinity of the person cage 3 at the upper end of the beam 2, enabling easy transfer from the ladder into the carriage. When steps are being set by means of the actuator 11 , the position of the person cage 3 and the position of the upper end 30 of the ladders remain unchanged, and thus their position does not have to be reset later. [0024] The ladder arrangement 6 comprises one or more sensors 12 for monitoring the mutual position of the steps 8a and 9a in the overlapping portion 10. Monitoring information can be transmitted from the sensor 12 to a control device 13 comprised by the ladder arrangement 6, the control device, in turn, being arranged to directly control the actuator 11 or a valve 14 or a corresponding adjustment member acting on the actuator 11. When the beam 6 is driven to the desired place and position, the steps 8a and 9a in the over¬ lapping portion 10 may be at different points relative each other. This is illus¬ trated by a step 15 shown with a dashed line. In order to get the steps in the overlapping portion to substantially the same point relative to each other, the movable ladder part 8 should be moved with the actuator 11 either upwards U or downwards V in such a manner that the steps 8a and 9a take the position shown by a solid line in Figure 4. The control device 13 may be arranged to control the actuator 11 automatically to set the steps 8a and 9a at the same point. The sensor 12 indicates to the control device 13 when the steps 8a and 9a are at the same point. Alternatively, the actuator 11 is operated manually, for instance by controlling the actuator in a first direction or a second direction by means of push buttons 16 for transferring the ladder part 8. An indicator 17, such as a indicator lamp or a sound signal, for example, can be provided in connection with the control device 13 for indicating to the user when the steps 8a and 9a are correctly in the overlapping portion 10. [0025] Figure 5 further shows an embodiment for adjusting the movable part 8 of the ladder 6b. The actuator 11 may be arranged to move the third articulation 7 in direction S, enabling movement of the movable ladder part 8 relative to the fixed ladder part 9 in a manner allowing the steps in the overlapping portion of the ladder parts 8 and 9 to be arranged at substantially the same point. Figure 5 further shows that the third articulation 7 is closer by distance X to the outermost end of the beam 2 as compared with the second articulation 5. This being so, angle C between the first ladder 6a and the car¬ riage 1 is always smaller than angle D between the first beam part 2a and the carriage 1. This allows the angle of ascent of the ladder part 6a to be rendered smaller, which naturally facilitates and speeds up climbing in the ladders. [0026] Let it be mentioned that, in the same way as the first ladder 6a, the second ladder 6b shown in Figures 1 to 3 and 5 may comprise a mov¬ able part and a fixed part and one or more actuators 11 for setting the steps 8a and 9a of the ladder parts substantially at the same point in the overlapping portion. [0027] The ladder arrangement shown in Figure 6 comprises a lower first ladder 6a and an upper second ladder 6b. The lower end of the first ladder 6a may be fastened to the carriage 1 of the person lifter by means of a fastening point 20. The outermost end 30, i.e. upper end, of the second ladder 6b may, in turn, be fastened to the upper end of the beam 2 by means of a fas¬ tening point 31. The second ladder 6b may comprise a turning part 22, which may be rotationally connected by means of an articulation 23 to a movable por¬ tion 24 in the second ladder 6b. The turning part 22 may further be connected by means of the articulation 7 to a movable portion 25 in the first ladder 6a. The actuator 11 , which is not shown in Figure 6 by way of clarity, may be ar¬ ranged to turn the turning part 22 in direction E, whereby the movable ladder parts 24, 25 move. The steps can then be set in place by turning the turning part 22. The lower part of the first ladder 6a may comprise a fixed ladder por¬ tion 26, which may be connected to the carriage 1 by means of an articulation 27. Furthermore, the outermost end of the second ladder 6b may comprise a fixed ladder portion 28. In both ladders 6a, 6b, the movable ladder parts and the fixed ladder parts are arranged to glide telescopically relative to each other, which is illustrated by transverse lines 29 marked in Figure 6. [0028] The ladder arrangement according to the invention can be applied to other kinds of beams than those shown in the figures. The beam may comprise a plurality of extendable and retractable beam parts articulated to each other or having a fixed length. Furthermore, the ladders may comprise a plurality of movable portions and, correspondingly, one or more fixed por¬ tions. [0029] The characteristics described in the present application can also be applied separately and, on the other hand, other combinations than those shown in the figures by way of example can be constructed from the characteristics. [0030] The drawings and the related description are only intended to illustrate the idea of the invention. The details of the invention may vary within the scope of the claims.