This invention relates to a steadying (i.e., swing stopping)/positioning control device for performing the steadying and positioning of a suspended load in a crane.

The structure of a conventional crane is shown in Fig. 3.

As shown in Fig. 3, a gantry 3 is placed movably across two rails 1 (right and left rails) laid on the ground. Independent travel drive devices 11, 14 are provided for moving the gantry 3 on each rail 1. The travel drive devices 11, 14 are electrically connected to a control device 21, while the control device 21 produces an operation command for each of the travel drive devices 11, 14.

On the gantry 3, a trolley 4 is borne so as to be movable transversely. From the trolley 4, a rope 5 hangs down to suspend a load 6.

When an automatic run is to be made in such a crane, it is necessary to position the suspended load 6 accurately with respect to the traveling direction of the gantry 3, and cause the suspended load 6 to rest at a predetermined position.

For this purpose, the gantry 3 must be positioned at a given target position, and control for steadying the suspended load 6 must be performed simultaneously.

Thus, a control system is provided for receiving feedback on the traveling position and traveling speed of the gantry 3 as well as the swing state of the suspended load, and determining the amount of operation (such as speed command) of the drive devices for the gantry 3.

That is, a traveling position detector 12 and a traveling speed detector 13 are provided for detecting the traveling position x1 and traveling speed x2, respectively, of the gantry 3 on the right rail 1 in Fig. 3. To the suspended load 6, a swing motion detector 17 is attached for detecting swing states, i.e., a swing displacement x5 of the suspended load and a swing speed x6 of the suspended load.

The control device 21 receives inputs of the measured values x1, x2, x5 and x6 by the detectors 12, 13 and 17, as shown in Fig. 4. By control computation, the control device 21 determines the amount of operation of the travel drive devices 11, 14, and carries out control.

In regard to control computation to be performed by the control device 21, it is known that a control system for positioning of the gantry and steadying of the suspended load can be realized by building the gantry and the suspended load into a bogie-pendulum system model as shown in Fig. 5, and constructing an optimum regulator based on this model (reference: "Mechanical System Control" Paragraph 6.2, Furuta Katsuhisa et al., Ohm).

In recent years, cranes have tended to be upsized. Thus, misalignment between the right-hand traveling position and the left-hand traveling position associated with the structural deformation of the gantry 3 may increase. A demand for positioning accuracy in an automatic run is becoming so harsh that the influence of the misalignment between the right and left traveling positions on positioning accuracy cannot be ignored.

A conventional control system drives the right and left drive systems by the same command, and thus is unable to reduce the misalignment between the right and left traveling positions to zero. As a result, the positioning accuracy for the suspended load 6 lowers, posing the grave problem that at the worst, required positioning accuracy cannot be fulfilled.

According to a first aspect of the present invention there is provided a positioning/steadying control system which comprises traveling position detectors and traveling speed detectors for detecting the right and left traveling positions and traveling speeds, respectively, of a crane traveling on two rails across them, right and left independent drive devices, and an arithmetic means for determining the amounts of operation of the right and left drive devices based on the measured values from the detectors as inputs.

In a preferred embodiment the control system is so constructed as to have traveling position detectors and traveling speed detectors for detecting the right and left traveling positions and traveling speeds, respectively, of a crane traveling on two rails across them, and right and left independent drive devices, and to determine the amounts of operation of the right and left drive devices based on the measured values from the detectors as inputs. Thus, the control system can simultaneously perform positioning for the right and left traveling positions, and the steadying of the suspended load.

• Fig. 1 is a schematic view showing the overall construction of a steadying control device in accordance with an embodiment of the present invention;
• Fig. 2 is a block diagram of the steadying control device in accordance with an embodiment of the present invention;
• Fig. 3 is a schematic view showing the overall construction of a conventional steadying control device;
• Fig. 4 is a block diagram of the conventional steadying control device; and
• Fig. 5 is an explanatory drawing showing a model with a gantry and a suspended load.

A suspended load steadying/positioning control device in accordance with an embodiment of the present invention is shown in Figs. 1 and 2. Fig. 1 is a schematic view showing the overall construction of the crane and control system according to the instant embodiment. Fig. 2 is a block diagram of the control device of this embodiment. The same parts as in the aforementioned example are assigned the same numerals and symbols, and explanations for them are omitted.

As shown in Fig. 1, the suspended load steadying/positioning control device of the instant embodiment is equipped with a right-hand traveling position detector 12 and a right-hand traveling speed detector 13 for detecting the traveling position xl and traveling speed x2 of a gantry 4 on a right rail 1 in Fig. 1, and is also equipped with a left-hand traveling position detector 15 and a left-hand traveling speed detector 16 for detecting the traveling position x3 and traveling speed x4 of the gantry 4 on a left rail 1 in the drawing.

To detect the swing state of a suspended load 6, a swing motion detector 17 is mounted on the suspended load 6 to detect a swing displacement x5 and swing speed x6 of the suspended load 6 in the traveling direction by use of an accelerometer or the like.

The control device 21 receives inputs of detection signals x1, x2, x3, x4, x5 and x6 from the detectors 12, 13, i5, 16 and 17, computes the amounts of optimum operation necessary for returning to zero the entered motion state amounts, i.e., the right and left traveling positions and traveling speeds, the swing displacement and swing speed of the suspended load, and issues control command signals to the right and left travel drive devices 11, 14.

As shown in Fig. 2, an optimum steadying gain K is separately precalculated and preset in the control device 21. The control device 21 has a control arithmetic portion 22 which, based on this optimum gain K, computes the amounts of optimum operation in response to the right and left traveling positions and traveling speeds, the swing displacement and swing speed of the suspended load 6 that have been entered from the detectors 12, 13, 15, 16 and 17, and performs optimum steadying/positioning control by the right and left travel drive devices 11, 14.

The foregoing suspended load steadying/positioning control device concerned with the instant embodiment performs optimum steadying/positioning control by the following concrete processing steps (1) to (3):

• (1) The detectors 12, 13, 15, 16 and 17 detect the traveling positions and traveling speeds of the right and left drive devices, as well as the motion state amount of the suspended load 6, and issues these data to the control device 21.
• (2) Then, based on these motion state amounts, the optimum control portion 22 calculates speed commands ul, u2 for the right and left drive devices 11, 14 according to the computation of optimum steadying control using the following Numeric Expression 1:$$\text{u = Kx}$$ where u represents an operation amount vector to be described below, ul represents a speed command for the right-hand drive device 11, and u2 represents a speed command for the left-hand drive device 14. That is, the following Numeric Expression 2 holds:$$\text{u = [}\mathit{\text{u}}\text{1}\mathit{\text{u}}{\text{2]}}^{\text{T}}$$ In the Numeric Expression 1, x represents a state amount vector to be described below. Its elements are, in order of arrangement from left to right, a right-hand traveling position x1 and a right-hand traveling speed x2, a left-hand traveling position x3 and a left-hand traveling speed x4, a swing displacement x5 and a swing speed x6 of the suspended load. That is, the following Numeric Expression 3 holds:$$\text{x=[}\mathit{\text{x}}\text{1}\mathit{\text{x}}\text{2}\mathit{\text{x}}\text{3}\mathit{\text{x}}\text{4}\mathit{\text{x}}\text{5}\mathit{\text{x}}{\text{6]}}^{\text{T}}$$
  Further, K represents a constants matrix with 2 rows and 6 columns shown below.
  The above constants matrix K is an optimum gain determined by the following procedure:
  • (a) From motion equations formulated for the right and left travel drive devices 11, 14, gantry 3, rope 5 and suspended load 6, a state equation (Numeric Expression 5) as indicated below, is derived. This state equation is a linear differential equation expressing the vibrations of the suspended load 6 as a spring-mass system.$$\frac{\mathit{\text{d}}}{\mathit{\text{dt}}}\text{x=Ax+Bu}$$ where u and x represent the aforementioned operation amount vector and state amount vector, respectively, A represents a transition matrix with 6 rows and 6 columns, and B represents a drive matrix with 6 rows and 2 columns.
  • (b) For the above state equation (Numeric Expression 5), the optimum gain K of Numeric Expression 7 that minimizes an evaluation function J of Numeric Expression 6 below is sought. where Q and R represent weighting matrices with 6 rows and 6 columns and 2 rows and 2 columns, respectively.$$\text{u=Kx}$$
    By so minimizing the evaluation function J, the optimum gain K is found which rapidly reduces all elements of the state amount to zero with the smallest possible operation amount u.
• (3) Based on the optimum gain K obtained by the above-described computation, the optimum control portion 22 determines optimum operation amounts adapted to the motion state amounts and the run state by the detectors 12, 13, 15, 16 and 17, and issues the optimal operation amounts as control command signals for the right and left drive devices 11, 14.

Such optimum control can eliminate the misalignment between the right and left traveling positions, achieve the steadying of the suspended load, and ensure highly accurate positioning of the suspended load.

As described based on the embodiment, the present invention has traveling position detectors and traveling speed detectors for detecting the right and left traveling positions and traveling speeds, respectively, of a crane traveling on two rails across them, and right and left independent drive systems, and computes the amounts of operation of the drive devices by means of an optimum regulator. Thus, the invention permits the accurate positioning of a suspended load even in a crane having structural deformation.