crawler crane

Abstract

Crawler crane comprising a pair of crawler tracks (6), a boom (10) which can be raised and lowered by means of a cylinder (33) and is rotatable about a vertical axis by means of a motor (31), wherein the crawler crane further comprises a rotation sensor (46) which is suitable for detecting a rotation angle of the boom (10) measured with respect to a direction of travel of the crawler tracks, and a pair of pressure sensors (44) which are suitable for detecting the differential pressure of the cylinder (33), wherein the crawler crane is further configured to only permit the rotation of the boom (10) if the differential pressure across the cylinder (33) detected by the sensors (44) is less than a predetermined maximum value which is dependent on the detected rotation angle of the boom (10).

Description

Field of the InventionThe present invention relates to a crawler crane.The invention has been developed, without being limited thereto, in particular with regard to a caterpillar compaction crane.Background ArtKnown are caterpillar cranes for so-called pick and carry, i.e. cranes which are suitable for lifting and transferring loads depending on the requirements. There are cranes of different sizes, from larger and bulky, but powerful, to smaller, which are particularly wending but unsuitable for very heavy loads.A problem of known cranes and in particular of compact cranes is that, since they are relatively light and do not have stabilizers, they tend to tilt when attempting to lift heavy loads laterally of the crane. To prevent tilting, the crane is normally positioned so that the weight to be lifted is behind the can, the boom of the crane extending within an extremely small allowable angle. This strategy makes it possible to prevent tilting, but limits it.SUMMARY OF THE INVENTIONAn object of the invention is to solve the problems of the prior art. A further object is to provide a crane with a particularly large working angle. It is therefore desirable to provide a crane that enables loads to be lifted with a boom extending within a large allowable angle. Another object is to produce an efficient device. It is also intended to provide a compact crane. A further object is to provide a cost-effective, simple, reliable and safe crane in use.These and other objects are achieved with a crawler crane having the features set forth in the following claims.Brief Description of the DrawingsFurther features and advantages will become apparent from the following detailed description of a preferred embodiment of the invention with reference to the accompanying purely exemplary and non-limiting drawings, in which:FIG. 1 is an overall side view of the crane,FIG. 2 is a circuit diagram of the hydraulic circuit of the crane; andFIG. 3 is a top view of the crane with working angles.DETAILED DESCRIPTIONReferring now to the drawings, a crawler crane 2 includes a structure 4 equipped with a pair of crawlers 6 (one of which is seen in FIG. 1 ) for traveling. A revolving crane 8 is mounted above the superstructure 4 and is rotatable about a vertical axis via a slewing gear 7. The crane 8 comprises a boom 10 with telescopic beds 12. The caterpillar crane 2 further comprises a control stand 9 with levers to enable an operator to operate the crane.FIG. 2 shows the hydraulic circuit diagram of the hydraulic installation 20 for operating the crane. In the figure, symbols according to the standard ISO 1219-1:2012 are used. The solid lines indicate conduits for a fluid, the solid points indicate connections between the conduits. The fluid is typically an oil.The hydraulic installation 20 comprises an engine 22, preferably an electric motor, which is supplied, for example, by a rechargeable battery. The motor 22 controls a pump 24, preferably a hydraulic pump with a constant volume flow. The pump 24 takes out a fluid from a reservoir tank 26 and sends it to a directional control valve 28.The directional control valve 28 comprises a plurality of sections for supplying different working units which control different movements of the track crane 2. It may for example comprise all or some of the following sections: a section 30 for controlling a motor 31 allowing the crane 8 to rotate on the slewing gear 7, a section 32 for supplying a cylinder 33 for raising and lowering the boom 10 of the crane, a section 34 for supplying a pair of cylinders 35 for controlling the telescopic blades 12 of the boom 10 of the crane, a section 36 for controlling a unit 37 for operating a winch. The cylinders are preferably double acting cylinders.It will also be noted that each section has two outputs A and B, commonly referred to as forward and reverse flow, but the fluid may flow in either direction (from A to B or from B to A in the drawings) depending on the movement demanded. Section 32 directs fluid to, for example, cylinder 33 through exit B to raise boom 10 and through exit A to lower it.The directional control valve 28 further supplies a pair of cylinders 40 for changing the distance between the crawler tracks 6. In the diagram shown, section 30 alternately supplies motor 31 allowing the crane 8 to rotate and cylinders 40 allowing the distance between tracks 6 to be changed. A shuttle valve 42 makes it possible to divert the flow coming from the directional control valve 28 to one or the other working unit. Since there is never the need to lift the boom 6 while changing the distance between the crawlers, this configuration makes it possible to optimize the circulation. A variant in which the two working units 31, 40 are supplied by different sections of the directional valve 28 is of course not to be excluded. Quite generally, different configurations are possible, with a different number of sections for the directional valve and / or with another unit, which is controlled by one or more of the sections, for a crane of more or less complex or in any case variable configuration with regard to the permitted movements.A pair of pressure sensors 44 are disposed between the cylinder 33 performing the lifting of the boom 10 and the corresponding section 32. The two sensors are arranged at forward and reverse flow between section 32 and cylinder 33, respectively. The comparison between the two detected values makes it possible to detect the differential pressure of the cylinder 33, i.e., the pressure difference between the fluid in the two chambers of the cylinder 33.A rotation sensor 46 is provided on the motor 31 for detecting the instantaneous rotation angle at which the boom 10 is located with respect to the body 4. The rotation angle to be recognized in FIG. 3 is defined as the angle between the projection of the boom on a horizontal plane and a traveling direction of the crawler belts; it is set to be 0° when the boom 10 is oriented parallel to the direction of the crawler belts 6.Another crawler sensor, which is not visible in the figures, is provided to detect the distance between the crawlers 6.The crawler crane 2 further comprises a computer configured such that the crane 8 can operate in both directions at an angle between 0° and 90° when it meets certain preset criteria, resulting in a total operating angle of 180°.The software receives the distance between the crawlers 6 detected by the crawler sensor, the differential pressure of the cylinder 33 detected by the sensors 44, and the angular position of the crane 8 detected by the rotation sensor 46, and uses these data to check whether or not the crane meets the safety criteria for allowing its rotation or travel.The computer compares the distance between the tracks detected by the track sensor with a preset threshold. The threshold value is preferably set to the maximum distance, i.e. to the distance at which the stability of the crane is the greatest. For this purpose, the sensor may be a sensor that transmits an electric on / off signal depending on whether the crawler tracks are at the largest distance or not.When the distance between the crawlers is less than the preset threshold, the turning of the crane 8 is prohibited. The boom 10 is thus supported in axis with the direction in which the crawler belts extend. In this position, the crawler crane 2 can still move if necessary. This may be useful when a load must be conveyed through a narrow opening.On the other hand, when the distance between the crawlers is equal to or larger than the preset threshold, the angular position is detected via the sensor 46. If it is less than a first predetermined angle α, the so-called pick and carry is permitted, i.e., it is possible to operate the crawler belts 6 when the boom 10 is carrying a load as long as the boom remains within the predetermined angle α. The angle α can be, for example, between 20° and 30° and is preferably 25°.On the other hand, when the boom 10 is disposed at an angle larger than the predetermined angle α, the operation of the crawler belts is always prohibited. However, it is permissible to raise and lower loads while crawler belts are stationary by rotating the boom 10 by an angle larger than α, provided that the differential pressure on the cylinder 33 detected by the sensors 44 remains below a predetermined maximum value depending on the angular position. If it is lower, it is permissible to rotate the boom 10 further, otherwise not. The maximum values of the differential pressure change with the angular position of the crane and are predetermined so as to guarantee that the risk of tilting is prevented in view of the specific characteristics of the crawler crane 2 such as weight and size of the platform.The software thus uses a pre-filled correspondence table with permissible maximum values of the differential pressure for each angular interval of the boom 10 to be compared with the values measured by the sensor 44. Each interval may be more or less large according to the desired precision. Optionally, instead of a maximum allowable value correspondence table for respective rotational angle intervals of the boom 10, a formula for real-time calculation of the maximum allowable value of the differential pressure depending on the angle detected by the sensor 46 may be provided.The crawler crane 2 configured in this way can thus lift and transfer loads without moving even if the boom is arranged at an angle between α and β, wherein β is preferably 90° or in each case lies between 70° and 90°. The crane is thus operationally reliable overall, when viewed in both rotational directions, at an angle of 2*β, i.e. up to 180°, with suitably limited load.Obviously, without departing from the principle of the invention, embodiments and details of embodiment may differ substantially from those described and illustrated without thereby departing from the scope of the invention. Purely by way of example, it cannot be ruled out that, in certain crane models, no sensor is required which measures the distance between the caterpillar tracks, for example because the caterpillar tracks are not movable.References included in the specificationThis list of documents cited by the applicant has been produced in an automated manner and is only included for the better information of the reader. The list is not part of the German patent application or utility model application. The DPMA does not take any adhesion for any faults or omissions.Cited Non-Patent LiteratureISO 1219-1:2012

[0009]

Claims

A crawler crane comprising a pair of crawler belts (6), a boom (10) raisable and lowerable by a cylinder (33) and rotatable about a vertical axis by a motor (31), the crawler crane further comprising a rotation sensor (46) adapted to detect a rotation angle of the boom (10) measured with respect to a traveling direction of the crawler belts, and a pair of pressure sensors (44) adapted to detect the differential pressure of the cylinder (33), the crawler crane further being adapted to allow the rotation of the boom (10) only when the differential pressure on the cylinder (33) detected by the sensors (44) is less than a predetermined maximum value depending on the detected rotation angle of the boom (10).The crawler crane according to the preceding claim, configured so that the crawlers (6) cannot be activated when the detected rotation angle of the boom (10) is greater than a predetermined first angle (α).The track crane according to any one of the preceding claims, wherein the tracks (6) are arranged at a variable distance, further comprising a track sensor for detecting the distance between the tracks (6), wherein the crane is configured such that the tracks (6) cannot be activated when the detected distance between the tracks is less than a predetermined threshold and the detected angle of rotation of the boom (10) is different from 0°.The crawler crane according to any one of the preceding claims, wherein the predetermined maximum value of the differential pressure at the cylinder (33) is calculated in real time based on the detected rotation angle of the boom (10).The crawler crane according to any one of the preceding claims, wherein the predetermined first angle (α) is between 20 and 30°, preferably 25°.The crawler crane according to any one of the preceding claims, wherein rotation that causes the rotation angle of the boom (10) to exceed a predetermined second angle (β) is prohibited.The crawler crane according to the preceding claim, wherein the predetermined second angle (β) is 90°.

Images