Traversing hoists – Methods
Reexamination Certificate
2001-06-15
2003-08-05
Brahan, Thomas J. (Department: 3652)
Traversing hoists
Methods
C212S273000, C294S081400
Reexamination Certificate
active
06601718
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention concerns a process for orienting the load in cranes in which the load supported by cables is turned by a specified absolute angle using rotating gear between cable and load.
In order to assure efficient material flow, most cranes are equipped with a special load-lifting member on the lower block of the load cable depending upon the goods that are to be transported. For example, a container spreader serves as a load-lifting member for containers. When an asymmetrical object is to be transported, orientation of the load at the destination point is necessary. Orientation means that the load at the destination point is rotated by a specified angle. For this purpose, a rotating gear is built into the load-lifting member, between the cable hanging point and the gripping device for the load.
If such rotating gear is actuated, then a too rapid rotation of the load will result in rotary oscillation, which an experienced crane operator can damp with a proper counter-move of the rotating gear. However, how rapidly he can compensate for such torsional oscillation depends upon the experience and the skill of each crane operator. For example, in the case of corresponding wind loading, a corresponding torsional oscillation may be induced from outside. These overlaid torsion oscillations are very difficult for the crane operator to compensate for.
Already known are processes for the suppression of swinging oscillation in cranes.
Thus, DE 127 80 79 describes a device for the automatic suppression of the swinging of a hanging load by means of a cable that is attached to a cable attachment point that is movable in the horizontal plane, by moving the cable attachment point in at least one horizontal coordinate in which the speed of the cable attachment point in the horizontal plane is controlled by a regulating circuit, depending on a value derived from the deflection angle of the load cable against the final vertical line.
DE 20 22 745 shows an arrangement for the suppression of swinging oscillations of a load that is hung on the cat of a crane by means of a cable, whose drive is equipped with a rotating device and a travel regulating device, with a regulating device that, taking into account the oscillation period, accelerates the cat during a first part of the path traveled by the cat and, during the last part of this path, delays it in such a way that the movement of the cat and the oscillation of the load at the destination point become equal to zero.
From DE 321 04 50, a device on lifting equipment was made known for the automatic control of the movement of the load-bearing member, with a slowing of the swinging that occurs on acceleration or braking of the load hanging from it, during an acceleration and/or braking interval. The basic idea is based on simple mathematical swinging. The cat and load mass is not included for calculating the movement. Coulomb and friction of the cat or bridge drives proportional to speed are not considered.
In order to transport a load body as rapidly as possible from its location to its destination, DE 322 83 02 suggests that the rotational speed of the drive motor of the running cat be controlled by a computer in such a manner that the running cat and the load carrier are operated at the same speed steady-state travel and the damping of swing is achieved in the shortest time. The computer known from DE 322 83 02 works on a computer program to solve the differential equations that apply to the undamped two-mass oscillation system formed by the running cat and the load body, where the coulomb and speed-proportional friction of the cat or bridge drive are not considered.
In the process that became known from DE 37 10 492, the speed between the destinations on the way is chosen in such a manner that after passing through half the total path between starting point and destination, the effective swing is always equal to zero.
The process that became known from DE 39 33 527 for damping of load swing oscillations includes a normal speed-position regulation.
DE 691 19 913 discusses a process to control the setting of a swing load in which, in a first regulating circuit, the difference between the theoretical and the actual position othe load is portrayed. This is derived, multiplied by a correction factor, and added to the theoretical position of the movable carrier. In a second regulating circuit, the theoretical position of the movable carrier is compared with the actual position, multiplied by a constant, and added to the theoretical speed of the movable carrier.
DE 44 02 563 covers a process for the regulation of electrical drives for lifting equipment with a load hanging from a cable, which generates the desired progress of the speed of the crane cat on the basis of the equations describing the dynamics, and feeds it to a speed and current regulator. Furthermore, the computer device can be expanded by a position regulator for the load.
The regulating processes that became known from DE 127 80 79, DE 393 35 27 and DE 691 19 913 need the cable angle sensor for load swing damping. In the expanded embodiment according to DE 44 02 563, this sensor is also necessary. Since the cable angle sensor causes substantial costs, it is advantageous if the load swing can be compensated for even without this sensor.
The process of DE 44 02 563 in the basic version also requires at least the cat speed. Also, in DE 20 22 745, multiple sensors are necessary for load-swing damping. Thus, in DE 20 22 745, at least an RPM and position measurement of the crane cat must be done.
Also, DE 37 10 492 needs at least the cat or bridge position as an additional sensor.
As an alternative to this process, another approach suggests, as became known, for example, from DE 32 10 450 and DE 322 83 02, solving the differential equations on which the system is based and, on this basis, determining a strategy for the system in order to suppress load swings where, in the case of DE 32 10 450, the cable length, and in the case of DE 322 83 02, the cable length and load mass, are measured. In these systems, however, the friction effects of static friction that are negligible in the crane system and friction proportional to speed are not taken into account. Even DE 44 02 563 does not consider friction and damping terms.
In the previously unpublished DE 199 20 431, by the Applicants of this invention, a process was achieved for load swing damping on cranes, with a control algorithm that is based on the fundamental idea that not only the function of the desired load position as a function of time is to be generated as a control value, but also the function for the desired load speed, desired load acceleration, desired load jerk and the derivation of the desired load jerk, and, in a pre-control block, fed to the crane system weighted in such a manner that the resulting overall system of crane dynamics and pre-control is correct as to speed, acceleration, jerk and the derivation of the jerk. As minimum input values for this older priority, but not published, process, the cable length and the load mass are needed.
None of the previously known processes addresses the set of problems of torsion oscillations upon actuation of the rotating gear, mentioned at the beginning.
SUMMARY OF THE INVENTION
The problem to be solved by this invention is, therefore, to create a process for orienting the load on cranes in which the load supported by cables is turned a specified absolute angle using rotating angle using rotating gears with which a load can be turned to a defined angular position without giving rise to torsion oscillations and with which, possibly, externally caused torsion oscillations can be effectively damped.
According to the invention, the problem is solved using a process with the combination of a regulation for the rotating gear suppressing torsional oscillations of the load, where, as input values, the absolute rotational angular speed and the angular position of the rotating gear are measured and fed back to the setting input. Here, a regulation of the rotationa
Aschemann Harald
Hofer Ebberhard Paul
Lahres Stefan
Sawodny Oliver
Brahan Thomas J.
Dilworth & Barrese LLP.
Sawodny Oliver
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