The present invention relates to a hoisting boom assembly, whose frame and actuators are to be coupled to a mobile working machine and which comprised an upright column or the like supported by the frame and at least partially rotatable around a vertical axis by means of a rotary actuator, a second boom having its first section pivotably journalled in a vertical plane, a horizontal shift mechanism and a horizontal shift actuator for shifting the free end of the second boom in a horizontal direction, the horizontal shift mechanism being adapted to act between a first boom and the sections of the second boom so that the horizontal shift mechanism can be operated between the sections of the second boom independently of the position of the first boom; the first boom being fitted between the upright column or the like and the second boom and having its first end pivotally mounted on the upright column or the like, preferably on the top section thereof, and having its second end pivotally mounted on the second boom; and an actuator fitted between the upright column or the like and the first boom for pivoting the first boom in vertical plane relative to the upright column or a like.
When manipulating the hoisting boom assembly, the operating range of the second boom is defined so that in a first extreme position of the second boom the longitudinal direction of its second section is substantially parallel to the longitudinal direction of its first section, the second section serving as an extension or a jib for the first section and, in a second extreme position of the second boom, the longitudinal direction of its second section is substantially opposite to the longitudinal direction of the first section, the second section being thus preferably tangential to the first section. A particular object of the present invention is a hoisting boom assembly suitable for for example, use in drilling operations in addition to being used with a loading harvester.
In the past, a loading harvester has been generally fitted with a hoisting boom assembly provided with two booms, a lifting boom and a carrier boom. When this type of hoisting boom assembly is operated to carry a load in the direction of a crane, it is necessary to operate both the lifting and the carrier boom. This results in a complicated operation of the hoisting boom assembly. In order to achieve a major operating range or reach, the carrier boom generally comprises a telescopic boom. However, this results in a heavy overall hoisting boom assembly, and particularly the passage of a pressure medium or hydraulic fluid to the end of a boom assembly is technically difficult to carry out.
In order to eliminate the above drawbacks, for example, the SE Publication 383 991 discloses hoisting boom assemblies operating in such a manner that a single actuator, especially a hydraulically operated cylinder-piston aggregate, is used to produce a linear movement a horizontal direction. In the prior known hoisting boom assemblies, this boom arrangement is journalled directly to an upright column which is in turn coupled with the body of a mobile working machine, such as a tractor. A drawback of this structure is, however, that the boom assembly is very long and has a high center of gravity. A high center of gravity results from the fact that the upright column must be sufficiently long in order that the hoisting boom assembly can be pivoted to lie above the operator's cabin in a transporting position.
The Applicant's Finnish Patent No. 82826, entitled "Hoisting boom assembly", discloses a solution which is further developed relative to the prior art hoisting boom constructions, such as those mentioned above. Unlike the other prior art, this patent discloses a hoisting boom assembly, comprising a first boom fitted between an upright column and a second boom and having its first end pivotally mounted on the upright column and its second end pivotally mounted on the second boom, an actuator fitted between the upright column and the first boom for pivoting the first boom in a vertical plane relative to the upright column, and the hoisting boom assembly including a horizontal shift mechanism which is adapted to act between the first boom and the sections of the second boom so that it is possible to operate the horizontal shift mechanism between the sections of the second boom independently from the position of the first boom.
The principal benefits gained by the above solution over the prior art include among other things the following aspects. The vertical shifts of a load carried on the free end of a second section can be effected by pivoting the first boom in a vertical plane. An actuator acting between the upright column and the first boom is sufficient for carrying out this function. The horizontal shifts of a load can be effected with a pivoting movement of the second boom sections in the vertical plane by utilizing a horizontal shift mechanism and a horizontal shift actuator. In practical applications, the hoisting boom assembly will have a low center of gravity particularly for the reason that the assembly includes a first boom, whose pivoting movement in a vertical plane can be used for shifting the center of gravity of the hoisting boom assembly to a position most advantageous in view of operation. Thus the hoisting boom assembly can be laid on top of a mobile working machine, such as a tractor, in a transporting position, whereby the first boom is lifted to an upright position to extend parallel to the upright column. In order to facilitate this, the sections of the second boom are pivoted to lie parallel to and on top of each other in a horizontal direction and, thus, these sections can be laid in the longitudinal direction of a working machine by pivoting the upright column to a position appropriate for this purpose.
A hoisting boom assembly disclosed in the Applicant's above-cited earlier Patent has proved practically useful and, thus, it has achieved a firm foothold on a market for hoist assemblies. Its undeniable advantages over the prior art solutions include the simplicity and reliability of both its construction and application. However, in certain practical situations, for example when carrying a load in a suitably inclined position of a working machine, there has been found a problem that the best controllability of a hoisting boom assembly is not possible in all conditions. Thus, especially with a hoisting boom assembly in its second extreme position, when the first and second section of the second boom are completely pivoted into contact with each other, a result of a load carried by the hoisting boom assembly is that, when manipulating the hoisting boom assembly, the sections of the second boom have a quite substantial traveling speed in situations following or preceding the second extreme position and, thus, the forces acting in the hoisting boom assembly are quite substantial. Thus, the operator of a hoisting boom assembly is required to have professional skill and accuracy for controlling the operation of a hoisting boom assembly so that excessive travelling speeds and abrupt halts are avoided.
The above drawback occurs due to the fact that a first transmission rod included in the horizontal shift mechanism and a horizontal shift actuator included in the horizontal shift mechanism are pivotally mounted at the same point. Thus, in the second extreme position of the second boom, the horizontal shift actuator extends in a direction nearly identical to that of the first and second section of the second boom, whereby an active force produced by the horizontal shift actuator includes a component force directed perpendicularly to the sections of the second boom and having an opening effect, this component force being very small relative to a component force parallel to the sections of a hoisting boom. Thus, the horizontal shift actuator does not function in an ideal fashion, since a force effect produced thereby is unfavorable particularly in the second extreme position of the second boom. Such disposition of a horizontal shift actuator also results in that, depending on the lead carried by the hoisting boom assembly, the travelling speeds of the sections included in the hoisting boom assembly in situations close to the second extreme position vary to a great degree due to the major forces of the horizontal shift actuator. Thus, the function of a hoisting boom assembly must be known in detail in order to relate the operation of a horizontal shift actuator to various loads.