The present invention relates to a method and a device for providing oscillation damping in a hydraulically operated crane. In particular, the invention relates to a crane having a loading tool attached to a slewable boom.
Such cranes are generally occurring, for example, in the forestry business for the loading of timber. It is in that connection, a generally familiar fact that it is difficult for the operator to bring the loading tool quickly and securely into an exact position for engagement with the cargo to be lifted.
This problem is obviated or at least brought down to a minimum by means of the present invention, as defined in method claim 1 and in apparatus claim 4.
In the method according to the invention, the hydraulic regulation of the boom embraces an operator-independent pressure detection provided for a rotator link belonging to the working tool and intended for the counteraction of undesired oscillations of the loading tool.
The pressure detection is advantageously effected on a hydraulic slew device arranged for the slewable boom and produces pressure information that is fed into a break means that, in the rotator link between the loading tool and the outer end of the boom, damps the oscillatory motion of the loading tool.
Preferably, the oscillation damping is effected by the break means acting against at least one joint of the rotator link.
By a device according to the invention, a rotator link belonging to the loading tool has a hydraulically actuated brake mechanism, the regulation of which is operator-independently pressure sensed for the counteraction of undesired oscillations of the loading tool.
Preferably, the brake mechanism is formed with a hydraulically actuated brake, which, via a line, is coupled to a hydraulic slew device arranged for the slewable boom for the receipt of pressure information.
The rotator link is preferably double jointed and at least one of the joints thereof is formed with the hydraulically actuated brake mechanism.
The brake mechanism advantageously embraces a piston/cylinder device where the cylinder is coupled to one joint of the rotator link, the one joined to the loading tool. The piston rod projecting into the cylinder is coupled to the other joint of the rotator link, the one joined to the boom of the crane.
The pressure detection is preferably effected on a hydraulic slew device - arranged for the turning of the slewable boom - for the receipt of pressure information from the same.
This pressure information from the hydraulic slew device arranged for the slewing of the boom is conveyed to the chamber in the cylinder of the break means via an axially extending channel in the piston rod projecting into the cylinder.
The pressure information is extracted from the hydraulic slew device, drive motor, of the boom in the hydraulic chamber of which pressure variations are produced upon the slewing of the boom. A pressure detecting system is coupled to the hydraulic chamber of the drive motor for the transfer of the pressure information to the piston/cylinder device of the break means in the rotator link of the loading tool.
Advantageously, the pressure-sensing system embraces a shuttle valve connected to the hydraulic chamber of the drive motor in order to, via a pressure-indicating line, forward the occurring pressure present during the shewing of the boom to the cylinder in the break means of the loading tool. The shuttle valve allows braking upon both acceleration and retardation of the slew motion of the boom.
The invention furthermore relates to a crane that comprises a device for damping oscillations in accordance with what has been mentioned above.
The invention will be explained more in detail below in connection with an embodiment that shown in the appended drawings and depicted in connection with a known crane for forestry use, wherein
The oscillation damping according to the present invention, which is operator-independent, automatic and self-locking, will be exemplified in an application of a crane 1 known per se, as shown in
In the operation of the boom 2, the slew device 6 is thus brought to slew the same for adjustment into a position where the cargo to be lifted is placed. A certain technique is required of the operator conducting the crane in order to get the grip 3 into the correct position. Even if it is known to form the rotator 4 with a brake mechanism having oscillation dampers, the grip 3 will still obtain an undesired oscillation.
In order to obviate or at least quickly bring down this undesired oscillation to a minimum, the present invention embraces an operator-independent pressure detection in the hydraulically driven slew device 6. In that connection, a pressure indication or pressure information is obtained that is fed to an oscillation damping rotator link 14 belonging to the rotator 4.
The principle for the invention will be described in more detail in the following, reference being made to
Thus, the crane is equipped with a hydraulic slew device 6 that can slew the crane boom both clockwise and counter clockwise. The hydraulics of the slew device 6 may be made as any hydraulic drive motor having hydraulic pressure chambers, but in the embodiment described herein, it embraces four actuator cylinders 11A, 11B, 12A, 12B, the pistons of which drive a gearwheel D for the slewing of the boom to the right or the left depending on the position of an operator-actuated actuator valve V. The actuator valve V has three positions: L, 0 and R for the connection of the slew device 6 to a hydraulic source S. In the intermediate position 0, the slew device 6 is locked while the positions L and R feed the cylinders 11A, 11 B, 12A, 12B of the slew device 6 from the hydraulic source S for the slewing of the boom to the left and to the right, respectively.
The rotator link 14 known per se embraces a brake mechanism 16, 18. Furthermore, in this embodiment, the rotator link 14 is double jointed 5, 19, where at least one of the joints is actuatable by a brake function. In the embodiment shown here, the brake mechanism 16, 18 of the rotator link 14 embraces a piston/cylinder device interconnected between the two joints 5, 19. The piston rod 16 is then joined to the joint 5 directed perpendicular to the plane of the drawing while the cylinder 18 is coupled to the joint 19 extending in the plane of the drawing.
For the provision of the operator-independent function counteracting undesired oscillations, the piston rod 16 according to the invention is provided with a channel 17, which mouths in a chamber 20 formed by the cylinder 18. The channel 17 is connected to a shuttle valve 10 via the line 9. By the two entrances thereof, the shuttle valve 10 is joined to the slew device 6 for the output of the pressure that prevails in the hydraulics thereof in the slewing of the boom of the crane. The shuttle valve 10 supplies said hydraulic pressure to the rotator link 14 and the piston/cylinder device 16, 18 arranged therein. The shuttle valve 10 allows braking upon both acceleration and retardation of the slew motion of the boom.
When slewing of the boom of the crane is desired, the actuator valve V, which is spring-loaded so as to normally assume the middle position 0, is brought into one of the outer positions, for example into L, for the slewing of the boom to the left. In that connection, the cylinder 11 B is pressurized from the hydraulic source S, while the cylinder 12B is pressure-relieved. On the cylinder 11 B as well as on the cylinder 12A, a pressure is then obtained (a pressure change, pressure increase, pressure pulse) that, via the shuttle valve 10 and the line 9, is supplied to the piston/cylinder device 16, 18 of the rotator link 14. By the pressure change arisen thereby in the chamber 20 of the cylinder 18, in the embodiment shown herein, the piston/cylinder device 16, 18 is pressed apart against the respective joint 5 and 19, so that brake action is provided on these joints and thereby the desired oscillation damping. The same conditions occur when operating the slew device 6 in the right direction.
By the fact that the pressure detection is carried out automatically in the slew device 6 and is forwarded to the rotator link 14 via the shuttle valve 10, there is obtained an operator-independent damping oscillation function for the boom of the crane and the working tools thereof.
Even if the invention and the function thereof here has been exemplified in connection with a known embodiment of the slew device 6 and a known embodiment of the rotator link 14, a person skilled in the art appreciates that the invention also is applicable in other embodiments. Accordingly, the slew device may equally well be hydraulic components of another embodiment where pressure detection may take place, and the rotator link may be designed differently with pressure action by, for example, drum brakes or disc brakes.
Therefore, the present invention must not be considered limited to the above-mentioned designs, but its principle, as defined in the subsequent claims, is applicable in different embodiments.
This list of references cited by the applicant is for the reader's convenience only. It does not form part of the European patent document. Even though great care has been taken in compiling the references, errors or omissions cannot be excluded and the EPO disclaims all liability in this regard.