EP0743275A2 - Method for controlling a multiple telescopic jib and the controlling arrangement for carrying out the method - Google Patents

Abstract

The control device is for the multiple telescopic jib of a loading crane. There are piston-cylinder units (4.1-4.6) between adjacent extenders. The cylinders (6.1-6.6) of these units have lines on both sides connecting them to the preceding and subsequent cylinders. The cylinder of the piston-cylinder unit pivoted to the fixed jib sector is connected on the piston side via an outward line (9.1-9.6) to a pressure source (10) to extend it from its withdrawn position. The piston-side operating pressure of each subsequent unit is reduced. The pressure reduction for the cylinder of a retracted unit is greater relative to that of the preceding unit when the piston rod is extended.

Description

The invention relates to a method for controlling the telescopic extensions of a multiple telescopic boom of a crane or the like, also referred to as thrust pieces, in particular a loading crane, between the adjacent extensions of which a hydraulic piston-cylinder unit is arranged, the cylinder of which is arranged with the the immediately preceding and the immediately following piston-cylinder unit is connected via a line both on the piston side and on the piston rod side, the cylinder of the first piston-cylinder unit articulated to the fixed boom section extending to extend its piston rod its retracted state is acted upon on the piston side by a predetermined working pressure generated by a pressure source, and the piston-side application pressure of each subsequent piston-cylinder unit in its retracted state is reduced to such a value compared to the application pressure of the preceding piston-cylinder unit that each this piston-cylinder units only extends after the previous one.

The invention further relates to a control device for carrying out the aforementioned method for the telescopic extensions of a multiple telescopic boom for a crane or the like, between the adjacent extensions of which a hydraulic piston-cylinder unit is arranged, the cylinder of which is immediately preceding and the immediately following piston-cylinder unit is connected via a line both on the piston side and on the piston rod side, the cylinder of the first piston-cylinder unit articulated to the fixed boom section being connected to the piston side via an extension line, generally via a load holding valve a pressure source is connected, and on the piston rod side with an intake line, and wherein in the piston-side connecting lines between adjacent piston-cylinder units, a biasing valve is arranged, by means of which the piston-side working pressure in the cylinder follows the piston-cylinder unit is to be reduced to a value such that the piston-side working pressure in the preceding cylinder is such that each piston-cylinder unit only extends after the previous one.

In the case of multiple telescopic booms of cranes or the like, a hydraulic piston-cylinder unit is arranged between two adjacent telescopic extensions. by means of which an extension is to be extended from its position retracted into the previous extension or retracted into it from a position extended from the previous extension, the first extension (which is the largest in cross section) adjacent to the relevant extension arm via a piston-cylinder -Unit is connected to the extension arm.

It is desirable to use a sequential control system to ensure that when the extension is extended, the first extension (which is the largest in cross-section) extends next to the extension arm, then only the second extension, etc. and finally the last (smallest in cross-section), and that the sequence when moving in is reversed.

From WO 93/08116 a mechanical path sequence control for the telescopic extensions of a multiple telescopic boom of a loading crane is known, in which at the closed end of the hydraulic cylinder for the subsequent extension in the piston-side connecting line to the previous extension or its piston cylinder -A unit is arranged a shut-off valve which is closed in the retracted state of the following extension, and is opened by a stop arranged on the previous extension when the previous extension has reached its extended end position. If an extension line leading from the pressure oil source to the first piston-cylinder unit is pressurized to extend the retracted telescopic boom, only the first piston-cylinder unit with the first extension connected to it extends until it reaches its final extension position has and thereby opens the shut-off valve to the next piston-cylinder unit by means of a stop, so that now the second piston-cylinder unit is also acted upon by pressure oil on the piston side will and can extend etc.

To retract the extensions, a check valve is connected in parallel to the shut-off valves, which closes when the extensions are extended. If pressure is applied to the retracting line connecting the piston-cylinder units on the piston rod side, pressure oil can initially only - after opening a check valve in a return line leading from the last piston-cylinder unit to the pressure oil source - from the last piston-cylinder unit drain, but not from the other piston-cylinder units, so that the last (outermost) extension is retracted first. If this has reached its retracted end position, a mandrel arranged on the piston of the last (outermost) piston-cylinder unit opens its check valve, bridges the shut-off valve of the last piston-cylinder unit and thus causes hydraulic fluid from the piston-side cylinder space downstream piston-cylinder unit can flow out etc. until all piston-cylinder units and thus all extensions are retracted one after the other from the outside in.

In addition to the fact that with this path sequence control, the arrangement of the valves is essentially fixed locally, which can possibly lead to constructional difficulties, it is disadvantageous that the piston-cylinder units, which are shut off from the oil pressure before their respective extension, do not have any during operation Can take over security function.

A generic pressure sequence control is known from its own prior public use, in which in each case in the piston-side extension line sections between adjacent piston-cylinder units a biasing valve is arranged, with which the piston-side working pressure in the cylinder of the subsequent piston-cylinder unit compared to the piston-side working pressure of the previous piston-cylinder unit is to be reduced by an amount such that each of these piston-cylinder units only extends after the previous one. In order to achieve a defined sequential control in the order mentioned above, the respective reduction in the pressurization pressure between adjacent piston-cylinder units must be considerable. B. 20%, since a slight pressure reduction of, for example, 3 or 5% would not ensure the desired sequence control.

Although this known pressure sequence control works reliably with a corresponding pressure reduction between adjacent piston-cylinder units and thereby u. a. enables that they can also perform safety functions during operation, it is disadvantageous insofar as the number of extensions is limited due to the gradual reduction of the extension pressure from inside to outside from piston-cylinder unit to piston-cylinder unit . For example, if a working pressure of 280 bar is available on the first piston-cylinder unit and there are four preload valves on five extensions, each of which is set to 70 bar, for example, the last piston-cylinder unit would no longer have any pressure be available.

In order to ensure the desired sequence from the outside to the inside when the extensions are retracted, when pressure is applied to the inlet line, the piston rods of the piston-cylinder units are designed with different sizes of diameter in this known pressure sequence control, so that one can have the same cylinder diameter , As it is regularly chosen for reasons of economy, piston ring surfaces of different sizes (= piston surface minus the piston rod cross-sectional area) are obtained, the piston rod of the first piston-cylinder unit adjacent to the fixed boom section being the largest and the piston rod of the last pistons -Cylinder unit has the smallest diameter (and thus the largest piston ring area with the same cylinder diameter). As a result, the last piston-cylinder unit retracts first due to the greatest working pressure, then the piston-cylinder unit next to it, etc. It is disadvantageous that the number of extensions is limited because the kink resistance of one too small a piston rod diameter is no longer sufficient, as it would have to be provided in multiple telescopic booms, in order to achieve considerable differences in the piston ring surfaces of adjacent piston-cylinder units and thus to ensure the desired retraction order.

The present invention has for its object to provide a generic sequence control method and a generic control device for performing this method while maintaining the advantages of a generic pressure sequence control, which can also be used for multiple telescopic booms with any number of extensions.

The solution to this problem in procedural terms according to the invention is that the pressure reduction generated on the cylinder of a retracted piston-cylinder unit on the piston side compared to the piston side working pressure of the previous piston-cylinder unit is canceled when the piston rod is extended while the task with regard to Control device according to the invention is solved in that the series-connected preload valves are each assigned a by-pass line which is blocked until the relevant piston-cylinder unit is extended and which is to be automatically unlocked when the extended end position is reached.

As will be explained in more detail below, in the sequence control according to the invention, when the extension line is pressurized, all cylinders are immediately pressurized on the piston side, but under different working pressures, which decrease due to the gradual pressure reduction / preload valves provided from the inside out, so that the desired exit order is observed. If the first piston-cylinder unit has reached its extended end position and the pressure reduction from the first to the second piston-cylinder unit is accordingly canceled by activating the corresponding preload valve via the initially blocked by-pass assigned to it, this increases piston-side working pressure in the second piston-cylinder unit and the subsequent piston-cylinder units accordingly, so that there is no longer any restriction on the number of extensions in the method or design according to the invention.

According to a preferred embodiment, in a sequence control according to the invention there is no longer any restriction on the number of extensions with regard to the measures taken for the retracting movement, and at the same time to achieve the considerable economic advantage of being able to work with piston-cylinder units of the same design provided that the cylinder of the last (outermost) piston-cylinder unit on the piston rod side is connected directly to the tank via an inlet line unlocked when extending, that in A preload valve is arranged on the piston rod-side connecting lines between adjacent piston-cylinder units, by means of which the piston rod-side working pressure in the cylinder of the inwardly following piston-cylinder unit compared to the piston rod-side working pressure of the previous piston-cylinder unit to such a value It is to be reduced that each piston-cylinder unit only retracts after the piston-cylinder unit that precedes the outside, and that the bypass valves connected in series are each assigned a by-pass line that is blocked until the relevant piston Cylinder unit is retracted and must be unlocked automatically when the retracted end position is reached. In this embodiment, essentially the same measures are provided for the retraction as for the extension, the prestressing valves provided with a by-pass line and assigned to the cylinder of a piston-cylinder unit on the piston side and on the piston rod side being formed separately or else can form a structural unit.

A variant for the retraction control, in which the cylinder of the last piston-cylinder unit is also connected to the pressure source on the piston rod side via an inlet line that is blocked when extending, consists in the fact that in the piston rod-side connecting lines between each adjacent piston-cylinder unit there is a check valve is arranged, by means of which this line to the inwardly following piston-cylinder unit is blocked until the outwardly preceding piston-cylinder unit has reached its end-of-travel position.

Further preferred embodiments of the present invention are described in the subclaims.

Fig. 1

eine schematisierte Seitenansicht eines Mehrfach-Teleskopauslegers mit sechs Ausschüben und den diesen zugeordneten Kolben-Zylinder-Einheiten;

Fig. 2

ein Schaltschema einer ersten Ausführungsform einer erfindungsgemäßen Steuereinrichtung;

Fig. 3

ein Schaltschema einer Variante einer erfindungsgemäßen Steuereinrichtung;

Fig. 4

eine andere Darstellung des Schaltschemas gemäß Fig. 3; und

Fig. 5

ein Schaltschema für eine weitere Variante einer erfindungsgemäßen Steuereinrichtung.

The invention is explained below using exemplary embodiments with reference to a drawing. It shows:

Fig. 1

a schematic side view of a multiple telescopic boom with six extensions and the associated piston-cylinder units;

Fig. 2

a circuit diagram of a first embodiment of a control device according to the invention;

Fig. 3

a circuit diagram of a variant of a control device according to the invention;

Fig. 4

another representation of the circuit diagram of FIG. 3; and

Fig. 5

a circuit diagram for a further variant of a control device according to the invention.

1 shows a schematic side view of a multiple telescopic boom, generally designated 1, with six extensions 2.1 to 2.6 in the fully extended state. In the fully retracted state, the last (outermost) extension 2.6 has moved into the previous extension 2.5, this into the previous extension 2.4 u.s.f. and the first extension 2.1 into the hollow boom section 3 of an articulated arm or the like, which is therefore stationary with regard to the direction of extension or retraction.

A piston-cylinder unit 4 is assigned to each extension 2. The piston-cylinder unit assigned to the first extension 2.1 4.1 is articulated with its piston rod 5.1 on the boom section 3 and attached with its cylinder 6.1 via a flange 7.1 to the outer end of the extension 2.1. Of the piston-cylinder unit 4.2 assigned to the extension 2.2, only the piston rod 5.2 can be seen in FIG. 1, since its cylinder 6.2 lies behind the cylinder 6.1, the cylinder 6.2 on the flange 7.1 and the outer end of the piston rod 5.2 on an outer end of the extension 2.2 attached flange 7.2 is attached.

The cylinder 6.3 of the piston-cylinder unit 4.3, also fastened to the flange 7.2, for the next extension 2.3 is located behind the piston rod 5.2. Its piston rod 5.3 is attached to a flange 7.3 fastened to the outer end of the extension 2.3, to which in turn the cylinder 6.4 of the piston-cylinder unit 4.4 for the next extension 2.4 is also attached, the piston rod 5.4 of which is attached to one at the end of the next extension 2.4 attached flange 7.4 is articulated, and so on. Such (or similar) arrangement of the piston-cylinder units 4 is made in order to be able to arrange and accommodate them in a suitable manner, since a piston-cylinder unit 4 is arranged in each case between adjacent extensions 2 must be, and the piston-cylinder units must not only be arranged in a suitable manner in the extended position shown, but also in the retracted position of the boom section 3, in which the flanges 7.1-7.6 are directly adjacent to each other. As has already been explained above, the telescopic boom 1 should be controlled so that when entering from the position shown in FIG. 1, the last (outermost) extension 2.6 first moves into the inward extension 2.5, then the (extension 2.6 containing) extension 2.5 in the previous ones Extension 2.4 etc.

In addition, the control should ensure that when extending, only the first extension 2.1 extends from the boom section 3, only then the second extension 2.2 from the extension 2.1 and the like.

2 shows a circuit diagram for a control device which ensures a corresponding sequential control for the extension, FIG. 2 showing an intermediate state in which the three piston-cylinder units 4.1-4.3 have already been extended and have reached their extended end position, while the following piston-cylinder units 4.4-4.6 (and thus their extensions 2.4-2.6) are still retracted.

From Fig. 2 it can be seen that the cylinder 6.1 of the first piston-cylinder unit 4.1 on the piston side is connected via an extension line 9.1 provided with a load-holding valve 8 to a pressure source 10, so that the cylinder 6.1 takes the extension 2.1 out of it Extends (not shown) inserted position when the extension line 9 is pressurized. Since adjacent piston-cylinder units 4 are each connected, inter alia, on the piston side to an extension line 9.n, namely the cylinder 6.1 with the cylinder 6.2 via a line 9.2, the cylinder 6.2 with the cylinder 6.3 via a line 9.3 etc., all cylinders become 6 is pressurized when the line section 9.1 leading from the pressure source 10 to the first piston-cylinder unit 4.1 is pressurized. However, the piston-side working pressure in the individual cylinders gradually decreases from the first piston-cylinder unit 4.1 to the last piston-cylinder unit 4.6, because the piston-cylinder units on the piston side connecting line sections 9.2, 9.3 etc., a preload valve 11 is connected which reduces the working pressure in the subsequent cylinder 6 compared to the working pressure in the preceding cylinder 6 on the piston side, reference being made at this point to the fact that the preload valves of the piston-cylinder Units 4.2-4.5 are each assigned a by-pass 12, which is closed when the assigned piston-cylinder unit is not yet fully extended, as is still the case in FIG. 2 with respect to the by-pass lines 12.4 and 12.5 is, and which is opened upon reaching the extended end position of the respective piston-cylinder unit 4 with the activation of the associated bias valve 11.

If the telescopic boom 1 is initially in a fully retracted state and pressure is exerted on the extension line 9.1, only the cylinder 6.1 moves with the first extension 2.1 relative to its piston rod 5.1, although the other cylinders 6.2 etc. are also pressurized become, since the working pressure generated by the pressure source 10 in the cylinder 6.1 is greater than in the cylinder 6.2 due to the preload valve 11.2 upstream of the cylinder 6.2 and the working pressure prevailing there is in turn appreciably greater than in the cylinder 6.3 downstream, etc. If, for example, the piston-side working pressure in the first cylinder 6.1 is 200 bar and the preload valves 11 reduce the working pressure in the following cylinder by 50 bar, for example, the working pressure in the second cylinder 6.2 is only 150 bar, in the third cylinder 6.3 only 100 bar and so on.

However, this pressure state only exists as long as the first piston-cylinder unit 4.1 has not yet reached its extended end position. If this is the case, then the preload valve 11.2 assigned to the second piston-cylinder unit 4.2 is activated via its by-pass 12.2, so that essentially the pressure generated by the pressure source 10 can now set in its cylinder 6.2 and the piston-side pressure changes to the pressure downstream Piston-cylinder units 4.3-4.6 increased accordingly.

This is particularly clear in FIG. 2 using the example of the piston-cylinder units 4.3 and 4.4, the piston-cylinder unit 4.3 already being fully extended and the piston-cylinder unit 4.4 still being fully retracted. It can be seen that the preload valve 11.3 assigned to the piston-cylinder unit 4.3 is already activated via the assigned by-pass 12.3 (and there is also an activation towards the inside), so that the piston-cylinder units 4.3 and 4.4 piston-side connecting line 9.4 is essentially directed to the pressure generated by the pressure source 10, so that the biasing valve 11.4 no longer has the working pressure of z. B. is only 50 bar, but - if you neglect the pressure losses - essentially the pressure generated by pressure source 10, so that the pressure applied to the outward piston-cylinder units increases accordingly and accordingly due to the successive Activation of the preload valves 11, any number of piston-cylinder units 4 or extensions 2 can be provided.

The activation means 13 are arranged in the circuit diagram according to FIG. 2 as mechanical means, but they can also be of an electrical or hydraulic type, for example.

In order to bring about a retraction in the reverse order in the sequence control according to FIG. 2, the arrangement has been made in the same way as in the above-described prior art, which is obviously used previously. The diameter of the piston rods 5 decreases from the first piston-cylinder unit 4.1 to the last piston-cylinder unit 4.6, so that the piston ring area 14.6 of the last piston-cylinder unit 6.5 is larger than the piston ring area 14.5, the latter again larger than the piston ring area 14.4 of the piston-cylinder unit 4.4, etc., which follows inwards and the piston ring area 14.1 of the first piston-cylinder unit 4.1 is therefore the smallest. Since all cylinders 6 (and therefore their pistons as well) have the same diameter in the usual way, the piston ring surface 14.6 of the last piston-cylinder unit 4.6 is thus subjected to the greatest force when from the pressure source 10 via the inlet line 15.1 via the Load-holding valve 8 pressure is given to the control device, the piston-cylinder units 4 connected in series also on the piston rod side, in each case via an inlet line section 15.2 or 15.3, and so on are connected to the following piston-cylinder unit.

2 also limits the number of extensions, because the difference in size of the piston ring surfaces 14 of adjacent piston-cylinder units 4 must be considerable in order to actually implement the desired sequence control when retracting, and Since the piston rods cannot be made arbitrarily thin for reasons of buckling safety - although this restriction is not as strong as in the non-activated pressure sequence control with regard to the extension - Fig. 3 also shows a variant in a circuit diagram in which this restriction also does not more is given. Rather you can in this configuration, in a highly advantageous manner, all the piston-cylinder units 4 are of the same design, that is to say not only have the same cylinder diameter but also the same piston rod diameter.

In the configuration according to FIG. 3, the arrangement with regard to the extension corresponds to the configuration according to FIG. 2. The same or equivalent parts are provided with the same reference numerals, with FIG. 3 again showing a state in which the first three piston-cylinder units 4.1-4.3 are (already) extended, while the last three piston-cylinder units 4.4-4.6 are (still) retracted.

The inlet line 15, which is led from the pressure source 10 via the load holding valve 8 to the piston-cylinder units 4 and which is pressurized to retract the extended extensions 2 or their piston-cylinder units 4, is not in this embodiment to the first piston-cylinder unit 4.1, but to the last piston-cylinder unit 4.6, so that its cylinder 6.6 in the fully extended state (not shown) (like this in FIG. 3 with respect to the piston-cylinder units 4.1. -4.3 is shown), pressure is applied to the piston rod side via a line section 15.6 and is the first to enter. This is achieved in that the same arrangement has been made in the entry line branch as with respect to the exit arrangement. It is namely in the inlet line sections 15.n, which connect two adjacent piston-cylinder units 4 each on the piston rod side, each a biasing valve 11 ', each of which - except for the biasing valve 11'.1, which in the piston rod side Connection line 15.1 between the first piston-cylinder unit 4.1 and the second piston-cylinder unit 4.2 is arranged - a by-pass 12 'is assigned, so that when retracting, basically the same results - but in reverse order - as when extending:

If the inlet line 15 is pressurized, the last piston-cylinder unit 4.6 moves in first because the greatest working pressure is applied to it on the piston rod side, while the working pressure of the piston-cylinder unit 4.5 following inwards through the preload valve 11 ' .5 is reduced, the piston rod-side working pressure in the subsequent cylinder is further reduced, etc. If, however, a piston-cylinder unit that precedes the outside is now completely retracted, the inward biasing valve 11 'is activated via the by-pass 12' assigned to it, as in FIG. 3 between the piston-cylinder units 4.4 and 4.3 becomes clear. If one assumes that the piston-cylinder unit 4.4 has just been retracted so that its preload valve 11'.4 has just been activated by means of an activation means 13 'via its by-pass 12'.4, this is due to the inside the following piston-cylinder unit 4.3 on the piston rod side only the working pressure reduced by its preload valve 11'.3, while the outward preload valves 11 'are all activated and the piston rod-side working pressure on the inward following piston-cylinder units 4 due to the each intermediate, not yet released bias valves 11 'gradually decreases.

Quite apart from the fact that the bias valves 11 'with their by-pass 12' - just like the bias valves 11 with their by-pass 12 in the extension branch - each form a unit, the corresponding units 11.n and 12.n and 11'.n and 12'.n of a piston-cylinder unit 4 form a structural unit, as is indicated in FIG. 3 by a dash-dotted line.

FIG. 4 shows the circuit arrangement according to FIG. 3 with simultaneous assignment to the representation according to FIG. 1 in a different representation for the purpose of further clarification, but all piston-cylinder units in accordance with FIG. 1 being fully extended.

5 shows a further variant of a sequence control according to the invention in a representation as a switching arrangement, which corresponds to the extension control with the configurations according to FIGS. 2 and 3 and with regard to the configuration of the piston-cylinder units 4 with the configuration according to FIG. 3. Furthermore, it also corresponds to the control system according to FIG. 3 insofar as the inlet line 15 is led from the pressure source 10 to the last piston-cylinder unit 4.6. It differs from the embodiment according to FIG. 3 essentially in that in the adjacent piston-cylinder units 4 inlet line sections 15n connecting the piston rod side there is not a bias valve 11 'provided with a by-pass 12' (and accordingly unlockable) , but a shut-off valve 16, which is blocked in the not yet retracted state of the piston-cylinder unit 4 that precedes the outside and is only opened when the preceding piston-cylinder unit has reached its end-of-travel position. In this embodiment, too, which - as stated - essentially corresponds in terms of arrangement or circuitry with the configurations according to FIGS. 2 and 3, the same piston-cylinder units 4 can therefore be used for all extensions 2. Are all extensions 2 extended? and are to be retracted, pressure is applied from the pressure source 10 via the inlet line 15 on the piston rod side to the last piston-cylinder unit 4.6, the valve 16.5, which is the last piston-cylinder unit 4.6 with the piston cylinder following inwards - Unit 4.5 connects on the piston rod side, is locked. In the retracted end position of the last piston-cylinder unit 4.6, the valve 16.5 is switched to passage by means of the release means 13 ', so that the piston-cylinder unit 4.5 following inwards can now be retracted and so on

It should be added that both the preload valves 11 and 11 'and the shut-off valves 16 are each assigned a check valve 17 which is blocked in the normal operational flow direction and connected in parallel.

REFERENCE SIGN LIST

1 Multiple telescopic boom 1 2nd Extensions 2nd 3rd Boom section 3rd 4th Piston-cylinder unit 4th 5 Piston rod 5 6 cylinder 6 7 flange 7 8th Load holding valve 8th 9 Exit line 9 10th Pressure source 10th 11, 11 ' Preload valve 11 12, 12 ' Bypass 12th 13, 13 ' Activation means 13 14 Piston ring surface 14 15 Entry line 15 16 Shut-off valve 16 17th check valve 17th

Claims (14)

Method for controlling the telescopic extensions (2) of a multiple telescopic boom (1) of a crane or the like, in particular a loading crane, between the adjacent extensions (2) of which a hydraulic piston-cylinder unit (4) is arranged, whose cylinder (6) with the preceding and the following piston-cylinder unit (4) both on the piston side and on the piston rod side Connected via a line (9 or 15), the cylinder (6) of the first piston-cylinder unit (4.1) articulated on the fixed boom section (3) for extending from its retracted state on the piston side with a pressure source (10 ) generated, the specified working pressure is applied, and the piston-side pressure of each subsequent piston-cylinder unit (4.2, 4.3, ...) in its retracted state compared to the pressure of the previous piston-cylinder unit (4.1. or 4.2., 4.3, ...) is reduced to such a value that each of these piston-cylinder units (4.2, 4.3, ...) only extends after the previous one, characterized in that the piston (2) of a retracted piston Cylinder unit (4) on the piston-side pressure reduction compared to the piston-side working pressure of the previous piston-cylinder unit (4) is canceled when the piston rod (5) is extended. A method according to claim 1, characterized in that the pressure reduction of a piston-cylinder unit (4) remains canceled until all piston-cylinder units (4) are extended. Method according to claim 1 or 2, characterized in that the cylinder (6) of the last piston-cylinder unit (4.6) in the extended state is acted upon directly on the piston rod side with the predetermined working pressure generated by the pressure source (10). Method according to claim 3, characterized in that the pressure on the piston rod side of each piston-cylinder unit (4.5, 4.4, ...) following inwards, in the extended state, compared to the pressure of the piston-cylinder unit (4.6 or 4.5 or 4.4 ...) reduced to such a value is that each of these piston-cylinder units (4.5, 4.4, ...) only moves in after the previous one. A method according to claim 4, characterized in that the pressure reduction on the piston rod side of the extended piston-cylinder unit (4) compared to the piston rod side working pressure of the previous piston-cylinder unit (4) is canceled when the piston rod (5) is retracted. Method according to Claim 3, characterized in that the connection on the piston rod side of each piston-cylinder unit (4) to the piston-cylinder unit (4) following inwards is blocked until the respectively preceding piston-cylinder unit (4) has reached its entry end position. Method according to one or more of the preceding claims, characterized in that the application pressure between two adjacent piston-cylinder units (4) is in each case reduced by at least about 20%. Control device for the telescopic extensions (2) of a multiple telescopic boom (1) for a crane or the like, in particular a loading crane, between the adjacent extensions (2.1-2.6) of which a hydraulic piston-cylinder unit (4) is arranged whose cylinder (6) is connected to the preceding and the following piston-cylinder unit (4) both on the piston side and on the piston rod side via a line (9 or 15), the cylinder (6.1) connecting to the fixed boom section (3) articulated first piston-cylinder unit (4.1) on the piston side via an extension line (9) is connected to a pressure source (10) and on the piston rod side with an inlet line (15), and in each case a biasing valve (11) is arranged in the piston-side connecting lines (9.n) between adjacent piston-cylinder units (4), by means of which the piston-side working pressure in the cylinder (6) of the subsequent piston-cylinder Unit (4) compared to the piston-side working pressure in the preceding cylinder (6) is to be reduced to such a value that each piston-cylinder unit only extends after the previous one, for carrying out the method according to one or more of the preceding claims, characterized that the series-connected preload valves (11) are each assigned a by-pass line (12), which is blocked until the piston-cylinder unit (4) in question is extended, and which automatically reaches the extended end position can be unlocked. Control device according to claim 8, characterized in that the by-pass line (12) and the bias valve (11) each form a switchable structural unit which is designed such that the bias valve (11) is effective when the by-pass valve Line (12) is blocked and vice versa. Control device according to claim 8 or 9, characterized in that the cylinder (6.6) of the last piston-cylinder unit (4.6) on the piston rod side is connected directly to the pressure source (10) via an inlet line (15) which is blocked during extension. Control device according to claim 10, characterized in that a biasing valve (11 ') is arranged in the connecting rod-side connecting lines (15.n) between adjacent piston-cylinder units (4), by means of which the piston rod-side working pressure in the cylinder (6) piston-cylinder unit (4) following inwards in relation to the piston rod-side working pressure the piston-cylinder unit (4) preceding to the outside is to be reduced to such a value that each piston-cylinder unit only moves in after the one preceding to the outside; and that the series-connected preload valves 11 'are each assigned a by-pass line (12') which is blocked until the relevant piston-cylinder unit (4) is retracted and which automatically reaches the retracted end position can be unlocked. Control device according to claim 11, characterized in that the biasing valves (11), each assigned to the cylinder (6) of a piston-cylinder unit (4) on the piston side and on the piston rod side and provided with a by-pass line (12) or (12 ') ) or (11 ') are designed as a structural unit. Control device according to Claim 10, characterized in that a shut-off valve (16) is arranged in the connecting rod-side connecting lines (15.n) between adjacent piston-cylinder units (4), by means of which these lines (15.n) are blocked until the piston-cylinder unit (4) preceding to the outside has reached its end-of-travel position. Control device according to one or more of claims 8 to 13, characterized in that the pre-load valves (11) or (11 ') or the shut-off valves (16) are each assigned an activation means (13) or (13') by means of which they must be activated in the extended or retracted end position of the relevant piston-cylinder unit (4).

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