Suspended load swing displacement detector

Abstract: A swing displacement detector comprises a swing displacement detector 15 for detecting relative displacement xl between a trolley 4 and a suspended load 6 in a crane suspending the suspended load 6 by a rope 5 or the like; a crane upper structure displacement detector 16 for detecting the displacement of a crane upper structure 1 supporting the trolley 4 from the ground surface; and an arithmetic means 17 for receiving as inputs the measured value xl of suspended load displacement by the swing displacement detector 15, and the measured value x2 of crane upper structure displacement by the crane upper structure displacement detector 16, and for correcting the measured value xl of suspended load displacement based on the difference between the measured value xl of suspended load displacement and the measured value x2 of crane upper structure displacement. Thus, the vibrational component of the crane upper structure can be eliminated from the measured value of swing of the suspended load, whereby the swing component of the suspended load can be detected highly accurately.

Description: BACKGROUND OF THE INVENTION This invention relates to a swing displacement detector for measuring the swing displacement of a suspended load in a crane. The structure of a conventional crane is shown in Fig. 3. As shown in Fig. 3, a crane upper structure 1 is supported on the ground via legs 2. Rails 3 are installed on the upper structure 1, and a trolley 4 is borne movably on the rails 3. From the trolley 4, a rope 5 hangs down, and a suspended load 6 is attached to the front end of the rope 5, whereby the suspended load 6 is transported. When an automatic run is to be performed in such a crane, control for steadying (i.e., stopping the swing of) the suspended load is necessary. To carry out the steadying control, it is necessary to measure the relative displacement of the trolley 4 and the suspended load 6 as a feedback signal. To measure this displacement of the suspended load 6, a marker 11 is put on the suspended load 6. This marker 11 is shot with a camera 12 mounted on the trolley 4 vertically downwards. A picture of the marker 11 taken is entered into a suspended load displacement detector 15 which performs image processing of the picture to detect the displacement x1 of the marker 11. With such a crane, a long periodic wave component lasting about 5 to 10 seconds is observed in vibrations of the rope 5 about the position of mounting of the rope 5 on the trolley 4 as a fulcrum. However, the measured value x1 of swing displacement based on the camera 12 mounted on the trolley 4 presents a signal comprising the long periodic wave component, the vibrations of the rope 5, superimposed by a short periodic wave component with a periodic wave component with a period of about 2 seconds, as illustrated in Fig. 4. The reason is as follows: As shown in Fig. 5, the crane upper structure 1 supported by the legs 2 vibrates horizontally owing to a warp of the leg 2 (the vibration is designated as displacement x2). In accordance with the vibrations, the trolley 4 and the camera 12 mounted on the trolley 4 also vibrate in the horizontal direction. Thus, the displacement x2 from the vibrations of the crane upper structure 1 is detected at the same time. Control for steadying of the suspended load 6 is aimed at stopping the long periodic vibrations of the rope 5. Such a short periodic component acts as a disturbance in the feedback signal for control, thus constituting a factor for lowering the control performance. GB-A-2,300,177 discloses a travelling crane having apparatus for preventing load vibration. Vibration prevention is achieved by using values determined for the load's displacement and velocity, the trolley's position and velocity, and the crane body's displacement and velocity. These six values are used in a mathematical expression that provides a trolley velocity command, i.e. a command that makes the trolley move in a fashion to minimise vibration. The load's displacement is measured by a camera that images a marker associated with the load and infers the load's velocity from these measurements. The vibration induced in the crane's body is measured using an acceleration meter: the corresponding velocity and displacement are found using inferential devices comprising an integrator and a filter. Accordingly, the displacement is found indirectly, using two integration operations. SUMMARY OF THE INVENTION According to a preferred embodiment of the present invention there is provided a suspended load swing displacement detector comprising: a swing displacement detector for detecting relative displacement between a trolley and a suspended load in a crane suspending the suspended load by a rope or the like; a crane upper structure displacement detector for detecting the displacement of a crane upper structure supporting the trolley from the ground surface; and an arithmetic means for receiving as inputs the measured value of suspended load displacement by the swing displacement detector and the measured value of crane upper structure displacement by the crane upper structure displacement detector, and for correcting the measured value of suspended load displacement based on the difference between the measured value of suspended load displacement and the measured value of crane upper structure displacement, and wherein the swing displacement detector comprises a camera mounted on the trolley arranged to image a marker put on the load characterised in that the crane upper structure displacement detector comprises a camera attached to the crane upper structure arranged to image a marker fixed on the ground. This embodiment has the upper structure displacement detector for measuring the displacement of the crane upper structure, and based on its measured value, corrects the measured value of the suspended load swing displacement detector. Thus, the detector can eliminate the vibrational component of the crane upper structure from the measured value of swing of the suspended load, thereby detecting the swing component of the suspended load highly accurately. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a structural view of a swing displacement detector in accordance with an embodiment of the present invention; Fig. 2 is an output characteristic view of the swing displacement detector embodying the present invention; Fig. 3 is a structural view showing the outline of a conventional swing displacement detector; Fig. 4 is an output characteristic view of the conventional swing displacement detector; and Fig. 5 is a view showing the manner of vibration of a crane upper structure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A structural view of a swing displacement detector in accordance with an embodiment of the present invention is shown in Fig. 1. The same parts as in the aforementioned earlier technology are assigned the same numerals and symbols, and explanations for them are omitted. As shown in the drawing, a marker 13 is fixed on the ground, and a ground surface marker camera 14 is attached onto a crane upper structure 1. The ground surface marker camera 14 shoots the marker 13, and sends its image signal to an upper structure displacement detector 16. The upper structure displacement detector 16 performs image processing of the signal to determine the displacement of the marker 13, that is, relative displacement between the upper structure 1 and the ground. A suspended load displacement, x1, detected by a suspended load displacement detector 15, and an upper structure displacement, x2, detected by the upper structure displacement detector 17 are each sent to an arithmetic unit 17. The arithmetic unit 17 calculates the difference between the suspended load displacement x1 and the upper structure displacement x2. The measured value x1 of suspended load displacement by the suspended load displacement detector 15 is a value comprising the swing displacement of the suspended load superimposed by the displacement of the upper structure 1, as shown in Fig. 2. The upper structure displacement detector 16, on the other hand, measures the relative displacement between the marker 13 and the upper structure, namely, the vibrational displacement of the upper structure relative to the ground surface. Hence, the difference between the suspended load displacement x1 and the upper structure displacement x2 is sequentially calculated by the arithmetic unit 17, whereby a corrected value, x3, of suspended load displacement unaffected by the vibrations of the upper structure 1 can be obtained as shown in Fig. 2. As described concretely based on the embodiment, the present invention eliminates the vibrational component of the crane upper structure from the measured value of swing of the suspended load. Thus, it can constitute a highly accurate suspended load swing displacement detector even for a crane having a vibrational component in the crane structure.

Claims: A suspended load swing displacement detector for a crane with a trolley (4) suspending a load (6) by a rope (5) or the like, said suspended load swing displacement detector comprising: a swing displacement detector (15) for detecting relative displacement (x1) between the trolley (4) and the suspended load (6); a crane upper structure displacement detector (16) for detecting the displacement of a crane upper structure (1) supporting the trolley (4) from the ground surface; and an arithmetic means (17) for receiving as inputs the measured value (x1) of suspended load displacement by the swing displacement detector (15) and the measured value (x2) of crane upper structure displacement by the crane upper structure displacement detector(16), and for correcting the measured value (x1) of suspended load displacement based on the difference between the measured value (x1) of suspended load displacement and the measured value (x2) of crane upper structure displacement, and wherein the swing displacement detector (15) comprises a camera (12) mounted on the trolley (4) arranged to image a marker (11) put on the load (6), characterised in that the crane upper structure displacement detector (16) comprises a camera (14) attached to the crane upper structure (1) arranged to image a marker (13) fixed on the ground.

Inventors: HOSHINA HIROMITSU, KOUNO SUSUMU, TOYOHARA TAKASHI, HOSHINA, HIROMITSU, KOUNO, SUSUMU, TOYOHARA, TAKASHI, Hoshina, Hiromitsu, Mitsubishi Heavy Ind., Ltd., Kouno, Susumu, Mitsubishi Heavy Ind., Ltd., Toyohara, Takashi, Mitsubishi Heavy Ind., Ltd.
Applicants: MITSUBISHI HEAVY IND LTD, MITSUBISHI HEAVY INDUSTRIES, LTD.
Application year: 1997
Main classification: B66C13
IPC codes: B66C13