ES2552434T3 - Procedure to block the operating position of a boom, personnel lift and lifting cylinder - Google Patents

Abstract

A method for blocking an operating position of a boom, comprising raising the boom (3) by means of at least one lifting cylinder (8) by extending and retracting the length of the lifting cylinder (8), in the that the piston rod (13) of the lift cylinder piston (8) moves relative to the cylinder body (14); and raising the boom (3) to an operative position (A) and preventing, by means of at least one locking device (17), that the at least one lifting cylinder is retracted in the return direction; using the blocking device (17) provided with a first blocking member (10) and a second blocking member (15), in which a relative movement between them takes place in the longitudinal direction of the lifting cylinder (8) , when the lifting cylinder (8) is extended or retracted in the released position of the locking device (17); and preventing the relative longitudinal movement between the blocking members (10, 15) at least in the return direction of the lifting cylinder, when the blocking device (17) is in the blocking position; characterized by providing the first blocking member (10) and the second blocking member (15) with a rotationally non-symmetrical, coincident shape, in the longitudinal direction of the lifting cylinder (8); and selecting the operation of the locking device (17) between a released position and a blocking position by changing the respective positions of the locking members (10, 15) around the longitudinal axis of the lifting cylinder (8), in which the Rotationally non-symmetrical shapes of the blocking members (10, 15) thus occupy a matching or non-coincident position, respectively; disposing a first tubular locking member (10) around the lifting cylinder (8) and moving it together with the piston rod (13) relative to the cylinder body (14); retaining the second locking member (15) immovably on the outermost end part of the body (14) of the cylinder; and rotating the first locking member (10) around its longitudinal axis relative to the second locking member (15), thereby allowing the selection of the released position or the locked position.

Description

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DESCRIPTION

Procedure to block the operating position of a boom, personnel lift and lifting cylinder

Background of the invention

The invention relates to a method for locking a pen in a desired operating position. To block the boom, a lift cylinder used to lift the boom is mechanically locked to prevent the cylinder from retracting. At least one of the boom lift cylinders is provided with a locking device for blocking.

The invention further relates to a personnel lift and a boom lift cylinder. The field of the invention is described in more detail in the preambles of the independent claims of the application.

Personnel elevators are used, for example, in firefighting and rescue operations, as well as in building construction and various maintenance tasks. A personnel lift comprises a boom that is raised from a transport position to an upright position by means of one or more lifting cylinders. If the boom is long, a lifting cylinder of relatively large dimensions must also be provided. In that case, a hydraulic lift cylinder also has large volume fluid spaces. Although the compressibility of the fluid is small, a long lift cylinder has flexibility due to its large volumes of fluid. It should also be noted that, because the lifting cylinder is at the lower end of a long boom, even a small flexibility in the lifting cylinder causes large movements in the upper part of the long boom. Such flexibility significantly hinders the positioning of the pen. To solve this problem, a locking device designed to the cylinder body of the lifting cylinder has been designed to mechanically block the piston rod. A prior art locking device wedges the piston rod to block it immovably. A disadvantage of this solution is that the wedge members are pressed with an extremely large force against the piston rod, which can damage the surface of the rod and, in this way, can cause leaks in the lifting cylinder. Document JP-10026104-A describes a hydraulic cylinder provided with a transverse locking device, JP-S5337281-A describes a cylinder provided with a locking bearing disposed within the cylinder in connection with a cylinder piston and document CN -201195678-Y describes a lifting jack.

Brief Description of the Invention

An object of the invention is to provide a novel and improved method for blocking the operating position of a boom, a personnel lift and, in addition, a novel and improved lifting cylinder.

The process of the invention is characterized by the features characterized by the independent claim of the

process.

The personnel lift of the invention is characterized by the features characterized by the first independent claim of the apparatus.

The lifting cylinder of the invention is characterized by the features characterized by the second independent claim of the apparatus.

According to one idea, at least one of the boom lift cylinders comprises a locking device provided with at least one first locking member and at least one second locking member that are independent of the basic structure of the lifting cylinder. The first locking member is an elongated part arranged to move with the piston rod and in relation to the cylinder body and a second locking member fixed thereto. The locking device further comprises means for coupling the first and second locking members to be immovable relative to each other in the longitudinal direction at least in the return direction of the lifting cylinder. In the released position of the locking device, the lifting cylinder can be extended and retracted freely. The basic idea of the blockage is that, when viewed in the longitudinal direction of the lifting cylinder, the blocking members are provided with rotationally shaped, non-symmetrical shapes or surfaces, and still coincident and, therefore, the rotation of the members of Locking one relative to the other allows the selection of a locked position and a released position. The lock reflects the rotation positions and the compatibility of the locking members relative to each other in the longitudinal direction of the lifting cylinder.

An advantage of this is that the blocking forces caused by the operation of the blocking device act

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on the blocking members, which are independent of the basic structure of the lifting cylinder and, therefore, the blocking does not damage the lifting cylinder in any way. For example, the blockage does not cause forces that could damage the piston rod and its sealing surfaces. In addition, the locking device is strong and both its structure and operation are simple.

According to one embodiment, the first blocking member and the second blocking member are locked relative to each other in a blocking manner in at least one predetermined blocking position. The shape lock is firm and allows the pen to be locked accurately in a predetermined position. In addition, the shape lock can have a simple structure.

According to one embodiment, the first locking member is a tubular piece, and the second locking piece is arranged to act on the first tubular locking member. The first tubular locking member is arranged to surround the piston rod of the lifting cylinder, thereby protecting the piston rod from damage. The tubular locking member may have an outer surface that is waterproof and has no openings and, therefore, is capable of protecting the piston rod also from impurities.

According to one embodiment, the first locking member is a tubular piece with a rectangular, preferably square cross section. This embodiment facilitates the manufacturing of the locking device.

According to one embodiment, the first locking member is a tubular piece with a waterproof outer shell.

In addition, the upper end of the tubular locking member is sealed with sealing members. This prevents the entry of impurities, dust and water, such as water used in firefighting, to the blocking device from above. In some cases, the lower end may also be sealed, the blocking device also being protected against impurity entry from below. On the other hand, the lower end may be open, so that a ventilated structure without moisture due to condensation is provided, for example, which is formed inside.

According to one embodiment, the first locking member serves as a safety lock and a protection for the piston rod of the lifting cylinder.

According to one embodiment, the first locking member is arranged to support the structure of the lifting cylinder, which is a characteristic that can be taken into account during the design of the structural parts of the lifting cylinder.

According to one embodiment, the first tubular locking member is disposed around the lifting cylinder and moves together with the piston rod relative to the cylinder body. The second locking member is immovably disposed on the outermost end part of the cylinder body. The first blocking member and the second blocking member have rotationally non-symmetrical, matching shapes, when viewed in the longitudinal direction of the lifting cylinder. The first tubular locking member may be rotated about its longitudinal axis with respect to the second blocking member to select a released position or a locked position.

According to one embodiment, there are two adjacent lifting cylinders associated with the boom, in which both cylinders are provided with a first tubular locking member with a common rotating device provided therebetween. The rotating device allows the first locking members of the adjacent lifting cylinders to be rotated to select the released position and the locking position of the lifting cylinders.

According to one embodiment, the locking device only blocks the return movement of the lifting cylinder.

According to one embodiment, the locking device blocks the lifting cylinder in both directions, that is, in the return direction and in the impact direction.

According to one embodiment, one or more detection members, such as sensors, are provided in association with the blocking device to allow detection of the blocking state and of the released position of the blocking device. The personnel lift has a control unit that can comprise a control strategy to prevent normal use of the boom until the locked position is detected. This embodiment improves security. When in operation, the boom is always secured by a mechanical locking device as a precaution against hose breakage and other damage.

Brief Description of the Figures

Some embodiments of the invention will be described in more detail with reference to the accompanying drawings, in which

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Figure 1 is a schematic view of a personnel lift with its boom raised to the operative position and its extended telescopic boom parts;

Figure 2 is a schematic view of a personnel lift with its boom in transport position supported by a chassis;

Figure 3 is a schematic view of a pen of the invention in the transport position;

Figure 4 is a schematic view of the pen of Figure 3 raised in its operative position;

Figure 5 is a schematic view of a detail of a locking device in its locked position and its released position; Y

Figure 6 is a schematic view, seen from the longitudinal direction of the lift cylinder, of the released position and the locked position of the locking device in the arrangement of Figure 4.

For the sake of clarity, some embodiments of the invention have been simplified in the Figures. Similar parts are designated with similar reference numbers.

Detailed description of some embodiments of the invention

Figure 1 shows a personnel lift 1 comprising a chassis 2 provided with a boom 3. The chassis 2 can be a mobile chassis, such as a vehicle or a trailer. The chassis 2 can be provided with a pivoting frame 4 to which the lower end of the pen 3 is fixed by means of a first joint 5. The upper end of the pen 3 can be provided with a basket 6 for people that houses one or More people to be elevated. The basket 6 for people may also be provided with tools, such as the equipment necessary for spraying the fire extinguishing medium. The pen 3 may comprise only one pen section or two or more articulated pen sections. The pen 3 in Figure 1 comprises a first pen section 3a and a second pen section 3b, with a second joint 7 between them. The lower part of the first pen section 3a is fixed to the pivoting frame 4 by means of a first joint 5 to allow it to be raised and lowered relative to the joint 5. By pivoting the pivoting frame 4, the pen 3 can be moved in a lateral direction. The second boom section 3b can be raised and lowered relative to a second joint 7. In Figure 1, in reference number 3b 'designates the second boom section raised in the upper position. The length of the first boom section 3a and the second boom section 3b can be changed telescopically, allowing the boom 3 to be retracted to the transport position B shown in Figure 2 and extended to a desired length. in operative situation A. As shown in Figure 1, the personnel lift can be powerful. As the number of high-rise buildings increases, personnel elevators used in rescue operations, in particular, must allow increasing heights to be reached. The range can be up to 100 meters. Figure 2 shows the boom 3 of the personnel lift driven to the transport position on the chassis 2.

Figures 1 and 2 further show a lifting cylinder 8 with its lower end fixed to the pivoting frame 4 and its upper end to a retaining lug 9, or similar element, located at a distance from the lower end of the first section 3a of pen. The lifting cylinder 8 can be a hydraulic cylinder. A single lifting cylinder 8 may be sufficient to lift the boom 3 from a transport position B to an operative position A, although typically two, three or even more lifting cylinders are used. The lifting cylinder 8 has a long stroke to allow the first boom section 3a to be raised to an almost vertical operating position A. In addition, the lifting cylinder 8 is sized to allow the large boom 3 to be moved in a controlled manner to raise and lower it. Because the force created with the lifting cylinder 8 is high and its stroke is long, the lifting cylinder has a large volume of fluid. Consequently, hydraulic flexibility can occur in the lifting cylinder, which the present application intends to prevent by means of a mechanical locking device described herein. For the sake of clarity, the locking device is not shown in Figures 1 and 2, but different embodiments are presented below with reference to Figures 3 to 6.

For the sake of clarity, Figure 3 shows only the first pen section 3a, which is in a substantially horizontal transport position B. Therefore, the lifting cylinders 8, for example two, are driven to their most retracted position, in which the piston rod is almost entirely inside the cylinder body. As shown in the Figure, the outermost end of at least one lifting cylinder 8 has, attached thereto, a first locking member 10 which can be an elongated tubular piece capable of moving with the piston rod and which is slide over the cylinder body. When the lifting cylinder 8 is in the retracted position, the first tubular locking member 10 can cover the lifting cylinder 8 substantially completely. The first end of the lifting cylinder 8, that is, its lower end, is fixed to the

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pivoting frame 4 by means of a first coupling element 11 and its second end, that is, the upper end, is fixed to the fixing lug 9 on the boom by means of a second coupling member 12, as indicated in Figure 3, the pivoting frame 4 can be pivoted in the direction of the arrow C around a vertical joint, and the lifting cylinder 8 can be extended and retracted in the linear direction D to raise and lower the pen part 3a in the direction G in relation to the joint 5.

In Figure 4, the pen part 3a has been raised to the operative position A, where it points directly upwards or diagonally upwards at a desired angle. In that case, the lifting cylinders 8 can be driven to their other extreme positions with the piston rods 13 pushed out of the bodies 14 of the cylinders. When inside the first tubular locking member 10, the piston rods 13 are not visible, but, for the sake of clarity, Figure 4 shows the piston rod of the right side lifting cylinder with a broken line. The first tubular locking member 10 has its upper part fixed to the outermost end of the piston rod 13 and, therefore, moves with the piston rod 13 and relative to the body 14 of the cylinder. The first locking member 10 and the cylinder body 14 have suitable guide surfaces therebetween to allow the first locking member 10 to slide over the cylinder body 14 when the length of the lifting cylinder 8 is changed. The upper part of the body 14 of the cylinder is further provided with a second locking member 15 which can comprise a rotationally non-symmetrical outer shape, for example, a substantially square shape. The second locking member 15 may be immovably fixed to the body 14 of the cylinder. The cross-section of the inner surface of the first tubular locking member 10 may have a rotationally non-symmetrical shape that corresponds to the outer shape of the second locking member 15. Alternatively, the lower part of the first blocking member 10 is provided with a separate piece fixed to the tubular part and provided in a manner that corresponds to the outer shape of the second blocking member 15. In addition, the first locking member 10 is arranged to rotate around its longitudinal axis, in the direction E, a predetermined limited angle by means of a rotating device 16. The rotating device 16 may be a hydraulic cylinder, for example, coupled between the first locking members 10 of two adjacent lifting cylinders 8, which allows both locking members 10 to rotate simultaneously, albeit in opposite directions. When the boom is raised to the operative position A, the first blocking member 10 can be rotated from the released position to the blocking position, thereby forming a shape lock between the blocking members 10 and 15, and the first blocking member 10 is no longer able to extend over the second blocking member 15. This provides a firm mechanical block between the blocking members 10 and 15 belonging to the blocking device 17, in which the blockage prevents the retraction of the lifting cylinder 8 and the lowering of the boom. In this way, the locking device 17 forms a safety lock, which prevents an involuntary lowering of the boom due to failures and damages, for example. When the boom must be lowered, the lifting cylinder 8 can be extended slightly to reduce friction between the locking members 10 and 15. Then, the first locking member 10 can be turned back to the release position so that it is set to a position coincident with the second locking member 15. In this way, the first blocking member 10 is able to move again beyond the second blocking member 15 towards the lower end of the lifting cylinder 8.

The length of the first blocking member 10 and the position of the second blocking member 15 select such that when they are in the blocking position, the distance L between the clamping members 11 and 12 of the lifting cylinder 8 coincides with the position A desired operation of part 3a of the pen. It is also possible to arrange two or more operating positions for part 3a of the boom. Figure 4 shows, with broken lines, alternative blocking members 15a belonging to the blocking device 17, in which the blocking members are located at a distance from the blocking members 15 at the top of the tube 14 of the cylinder. This allows the lifting cylinder 8 to be locked to a second alternative length with the locking members 15a. Obviously, the coupling to the blocking position in the second blocking position cannot be based on the rotation of the first blocking member 10, but the operation of the blocking members 15a can be based on some other blocking principle.

Figure 5 shows the lifting cylinder 8 in the locked position and in the released position. The left lifting cylinder 8 has been locked in the operative position by rotating the first locking member 10 belonging to the locking device 17 in the direction E relative to the second locking member 15, which is fixedly held , to the upper part of the body 14 of the cylinder. The first blocking member 10 may comprise an elongated tube part 10a which may have a flat end piece 10b, known as a slide ("coulisse"), at its lower end. The end piece 10b is provided with an opening 10c, whose shape substantially corresponds to the shape of the outer surface of the second locking member 15. This allows the first locking member 10 to be rotated about its longitudinal axis to a released position, in which the opening 10c and the second member Lock 15 fit together, and to a lock position, in which the end surfaces of the end piece 10b and the second lock member 15 are against each other.The shape of the inner side of the cross section of the part

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The tube 10a can substantially correspond to the shape of the second locking member 15 to allow it to rest on the second locking member 15 when the tube part 10a has slipped over the body 14 of the cylinder. In addition, the lower end of the first locking member 10 may be provided with a guide sleeve 10d or a similar guide surface that may be fixed to the outer surface of the cylinder body 14 by means of sliding parts 10e or similar guide pieces. The guide sleeve 10d and its guide pieces 10e can retain the first parallel locking member 10 with respect to the longitudinal axis of the lifting cylinder 8 after the lifting cylinder 8 has been extended and the end piece 10b has moved above the second locking piece 15. This ensures that the locking members 10 and 15 are parallel with respect to the longitudinal axis of the lifting cylinder 8 and one of them can penetrate the other when the locking device 17 has been turned to the released position. The second locking member 15 may be a flat piece with a rotationally non-symmetrical outer surface having a substantially square shape, for example.

In Figure 5, the right locking device 17 is in the released position and the first locking member 10 has slid over the cylinder body 14 because the lifting cylinder 8 has been retracted. As can be seen in the Figure, the sliding parts 10e rest against the cylinder body 14 and keep the first parallel locking member 10 with respect to the longitudinal axis of the lifting cylinder 8. The sliding parts 10e may be of a suitable sliding bearing material, such as a plastic suitable for this purpose.

Figure 6 shows the operation of the locking device 17 as seen in the direction of the piston rod of the lifting cylinder. The blocking devices 17a and 17b of the adjacent lifting cylinders are operated with the same rotating device 16, whose linear movement D is transmitted by means of the lugs 18 to a rotational movement of the first locking member 10. When the rotating device 16 is retracted, the opening in the end piece 10a of the first locking member 10 and the second locking member 15 fit together, the locking devices 17a and 17b being in the released position. When the rotating device 16 is extended, the lugs 18 'move outward to the position shown with a broken line and the blocking member 10 rotates to the first blocking position. Also, the rightmost partial Figure shows a locking device 17c in the locked position. In that case, the second locking member 15 and the end piece 10b are interleaved and movement into the piston rod is prevented.

Unlike Figures 3 to 6, it is also possible to arrange the second locking member 15 to rotate relative to the first blocking member 10. The second locking member 15 may be rotated relative to the body 14 of the cylinder by means of a suitable rotating motor, for example, or by means of some other actuator. In addition, it is possible to rotate the cylinder body 14 with a suitable actuator, which allows the second locking member 15 to rotate relative to the first locking member 10. In some cases it is also possible to rotate both locking members 10 and 15 around the longitudinal axis of the lifting cylinder 8. In other words, this is a matter of the position of the blocking members 10 and 15 relative to each other and the compatibility of their forms. This allows the selection of the released position and the shape lock position of the lifting cylinder 8.

One point to note is that the arrangement of the lifting cylinder 8 may be the opposite of that shown in the previous Figures, that is, the piston rod 13 may be below and the body 14 of the cylinder above. This aspect is not essential for the operation of the lifting cylinder 8 and the locking device 17. The first locking member 10 is coupled to the piston rod 13 and arranged to move relative to the body 14 of the cylinder when the lifting cylinder 8 is extended or retracted.

One or more sensors 30 may be provided in association with the blocking device 17 to allow detection of the blocking position and the released position of the blocking device 17. This detection data can be transmitted to one or more personnel elevator control units 31. The control unit 31 can prevent movement and normal use of the pen until the data of a detected lock has been received. This embodiment is illustrated in Figure 4.

The upper end of the first tubular locking member 10 may be provided with sealing members 32. Because the structure of the first blocking member 10 is a sealed Waterproof flange at the upper end, the entry of dirt and water into the lifting cylinder 8 can be effectively prevented. This is advantageous in rescue operations, in particular, since it allows the freezing of the cylinder 8 due to the water used for extinction. The lower end of the first blocking member 10 may be vented, that is, the lower end may be open 33 and may comprise a gap or openings to allow impurities that have entered the blocking member 10 and the water that has entered or it has condensed in its interior leave the structure. This improves the strength and reliability of the construction.

An additional point to consider is that it is possible to arrange a first locking member 10 that is moved with a separate actuator, in which case the blocking member is actuated to the locked position by means of an actuator after the cylinder The lift has been actuated to its predetermined position where the lock must take place. The actuator for moving the first locking member may be a medium pressure cylinder or motor 5, for example.

In some cases, the features described in the present application may be applied as such, regardless of other features. On the other hand, the features described in the present application can be combined, when necessary, to provide different combinations.

The drawings and related specification are only intended to illustrate the idea of the invention. The details of the invention may vary within the scope of the claims.

Claims (7)

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A method for blocking an operating position of a pen, comprising raise the boom (3) by means of at least one lifting cylinder (8) by extending and retracting the length of the lifting cylinder (8), in which the rod (13) of the cylinder piston (8) lifting moves relative to the body (14) of the cylinder; Y raising the boom (3) to an operative position (A) and preventing, by means of at least one locking device (17), that the at least one lifting cylinder is retracted in the return direction; using the blocking device (17) provided with a first blocking member (10) and a second blocking member (15), in which a relative movement between them takes place in the longitudinal direction of the lifting cylinder (8) , when the lifting cylinder (8) is extended or retracted in the released position of the locking device (17); Y prevent the relative longitudinal movement between the blocking members (10, 15) at least in the return direction of the lifting cylinder, when the blocking device (17) is in the blocking position; characterized by providing the first blocking member (10) and the second blocking member (15) with a rotationally non-symmetrical, coincident shape, in the longitudinal direction of the lifting cylinder (8); Y select the operation of the locking device (17) between a released position and a blocking position by changing the respective positions of the locking members (10, 15) around the longitudinal axis of the lifting cylinder (8), in which the shapes Rotationally non-symmetrical of the blocking members (10, 15) thus occupy a coincident or non-coincident position, respectively; disposing a first tubular locking member (10) around the lifting cylinder (8) and moving it together with the piston rod (13) relative to the cylinder body (14); retaining the second locking member (15) immovably on the outermost end part of the body (14) of the cylinder; Y rotate the first locking member (10) about its longitudinal axis relative to the second locking member (15), thereby allowing the selection of the released position or the locked position. 2. Personnel elevator comprising: a chassis (2); a pivoting frame (4) arranged to pivot on the chassis (2); a pen (3) with its bottom part coupled to the pivoting frame (4) by means of a horizontal joint (5); at least one lifting cylinder (8) for raising and lowering the boom (3) relative to the horizontal joint (5), in which the lifting cylinder (8) comprises a cylinder body (14) and a rod ( 13) piston, which are arranged to move relative to each other when the lifting cylinder (8) extends or retracts during operation; at least one locking device (17) arranged in relation to at least one lifting cylinder (8), in which the locking device (17) is arranged to mechanically lock the body (14) of the cylinder and the rod (13 ) piston relative to each other so that they are immovable at least in the return direction of the lift cylinder when the boom (3) has been raised to its at least one operating position (A); at least one basket (6) for people arranged at the top of the pen (3); and wherein the locking device (17) comprises at least a first locking member (10) that is arranged to move together with the piston rod (13), but is a separate part thereof and, moreover, at least a second locking member (15) connected to the body (14) of the cylinder, so that when the lifting cylinder is extended or retracted, a relative movement takes place between the first blocking member (10) and the second member (15 ) lock in the longitudinal direction of the cylinder (8) of 5 10 fifteen twenty 25 30 35 40 Four. Five elevation; and wherein the blocking device (17) comprises at least one blocking position, in which the blocking members (10, 15) are immovably locked to each other at least in the return direction of the lifting cylinder, and a released position, in which longitudinal movement between the blocking members (10, 15) is allowed; characterized by that the first blocking member (10) comprises a tubular part (10a) and an end piece (10b) arranged around the lifting cylinder (8) and the first blocking member (10) is arranged to cover, continuously, the piston rod (13) substantially completely; the end piece (10b) comprises a locking opening (10c) having a rotationally non-symmetrical shape; the second locking member (15) is fixed to the outermost end portion of the cylinder body (14) and the shape of the outer surface of the second locking member (15) corresponds substantially to the shape of the opening (10c ) of blocking, so that the second blocking member (15) and the blocking opening (10c) coincide in the direction of the longitudinal axis of the lifting cylinder (8); Y The locking device (17) comprises at least one rotating device (16) that allows the first locking member (10) to be rotated about its longitudinal axis so that in the released position the locking opening (10c) can be positioned so that it coincides with the second blocking member (15) and, on the other hand, in the blocking position, the blocking opening (10c) can be placed in a non-coincident position relative to the second member (15) of blocking. 3. Personnel elevator according to claim 2, characterized in that The boom (3) has two adjacent lifting cylinders (8) coupled thereto, in which both cylinders are provided with a first tubular locking member (10) with a common rotating device (16) disposed therebetween. 4. A lifting cylinder for a boom, comprising: a cylinder body (14) and a piston rod (13), in which the length of the lifting cylinder (8) is arranged so that it extends and retracts during its operation; Y at least one locking device (17) arranged to mechanically lock the body (14) of the cylinder and the piston rod (13) relative to each other so that they are immovable at least in the return direction of the lifting cylinder; and the locking device (17) comprises at least a first locking member (10) that is coupled to the free end of the piston rod (13) and arranged to move together with the piston rod (13) relative to the body ( 14) of the cylinder and at least a second locking member (15) coupled to the body (14) of the cylinder, so that during the operation of the lifting cylinder (8) a relative movement takes place between the first member (10) of locking and the second locking member (15) in the longitudinal direction of the lifting cylinder (8); and wherein the blocking device (17) comprises a blocking position, in which the blocking members (10, 15) are locked together at least in the return direction of the lifting cylinder, and a released position, in which allows relative movement between the blocking members caused by the operation of the lifting cylinder; characterized by that the first blocking member (10) and the second blocking member (15) comprise rotationally non-symmetrical, coincident shapes in the longitudinal direction of the lifting cylinder (8); Y The locking device (17) comprises at least one rotating device (16) which allows the relative positions of the locking members (10, 15) to be rotated relative to the longitudinal axis of the lifting cylinder (8) so that in the position released the rotationally non-symmetrical shapes of the blocking members (10, 15) can be placed to coincide with one another and, on the other hand, in the locked position they can be placed in a non-coincident position; Y The first locking member (10) is a tubular structure arranged around the lifting cylinder (8) and arranged to continuously cover the piston rod (13) substantially completely. 5. Lifting cylinder according to claim 4, characterized in that the rotating device (16) is arranged to act on the first locking member (10); and 5 the second blocking member (15) is fixed. 6. Lifting cylinder according to claim 4 or 5, characterized in that The first blocking member (10) is a tubular structure with a rotationally non-symmetrical cross section. 7. Lifting cylinder according to any one of claims 4 to 6 above, characterized in that 10 the first locking member (10) is a tubular structure, in which its end on the side of the body of The cylinder is provided with an end piece (10a) having a rotationally non-symmetrical locking opening (10c).