Motion measurement method and apparatus applied to large multi-paddle wave simulation system

Patent metadata

Field	Value
Publication number	US-10488194-B2
Application number	US-201716308999-A
Country	US
Kind code	B2
Filing date	Sep 11, 2017
Priority date	Mar 17, 2017
Publication date	Nov 26, 2019
Grant date	Nov 26, 2019

Abstract

The present invention belongs to the technical field of image measurement, and provides a motion measurement method and apparatus applied to a large multi-paddle wave simulation system. When the motion of the wave maker is measured, firstly site images are collected by the cameras; the mark point on each wave making paddle in the image processing boards is identified; and a central position is computed. Then, the central position is contrasted with the initial position to calculate displacement of the image plane and convert the displacement into the displacement on a physical space in combination with calibration parameters. Next, data is transmitted to the computer through the EtherCAT network, and coded identification is conducted on the data. Finally, comparative analysis is conducted on a measured value and a target value of the motion of the wave making paddle in the computer, thereby obtaining motion information of the wave maker. In the present invention, when the motion of the wave maker is measured, the problems of difficult target recognition and unstable motion tracking caused by nonuniform illumination in the experiment site as well as the problems of great time consumption of an image analysis algorithm and low efficiency of data transmission of multiple camera systems are fully considered.

First claim

The invention claimed is:

1. A motion measurement apparatus applied to a large multi-paddle wave simulation system, the motion measurement apparatus comprising a computer, cameras, infrared light supplementing apparatuses, round fluorescent mark points and EtherCAT image processing circuit boards, wherein the cameras are infrared enhanced industrial cameras with fixed focus lenses, and the quantity of the cameras is determined by a measurement range; the quantity of the infrared light supplementing apparatuses is determined by the needs of imaging conditions; and the quantity of the EtherCAT image processing boards is consistent with the quantity of the cameras;
the motion measurement apparatus adopts a data acquisition structure based on EtherCAT network; the computer is used as a master station of the EtherCAT network; the cameras are arranged above a wave making system; under the condition of satisfying the requirement for measurement precision, a field of view covers all wave making paddles; when a single camera cannot cover a measured region, a manner that a plurality of cameras are operated jointly is adopted; each camera is connected with each EtherCAT image processing board through a Camera Link interface as a slave station of the EtherCAT network; a Trig interface of each EtherCAT image processing board is mutually connected together; the first EtherCAT image processing board is connected with the computer through a RJ45 network interface; the EtherCAT image processing board of each camera is mutually connected together through the RJ45 network interface; the infrared light supplementing apparatuses are put at one side of the cameras for illuminating the site; the quantity of the infrared light supplementing apparatuses is selected according to the site imaging quality; and the round fluorescent mark points are pasted or smeared on connecting paddles of the wave making paddles.

2. The motion measurement apparatus according to claim 1 , wherein the infrared light supplementing apparatuses are 850 nm infrared light supplementing lamps.

3. A motion measurement method applied to a large multi-paddle wave simulation system, comprising the following steps:
step A: installing the cameras directly above the wave maker; selecting the quantity of the cameras according to measurement precision, camera resolution and the measurement range; connecting the EtherCAT image processing boards mutually and then connecting with the computer to form a data acquisition structure based on EtherCAT network; fixing the round fluorescent mark points to the connecting paddles above the wave making paddles; arranging four auxiliary identification points in a 4-neighborhood arrangement manner, i.e., along the axial operation direction of the wave making paddles at places which allow the same distance from the top, the bottom, the left and the right of the mark points; adjusting the positions of the cameras so that the arrangement directions of the mark points are consistent with the row and column directions of a shot image; disposing the cameras to be an external triggering mode through the EtherCAT image processing boards; and unifying trigger signals by the EtherCAT image processing boards through the Trig interface while sending consistent synchronous trigger acquisition signals to respective cameras;
step B: performing system calibration during first operation when the arrangement of the cameras is completed; shooting an image respectively in an initial position and a maximum stroke position of the wave making paddles; conducting image binarization and round target extraction on the connected images by the EtherCAT image processing boards; establishing a lookup table for motion image information of each wave making paddle; recording a ratio of a physical distance of a motion stroke of the wave making paddle to an image plane distance, wherein N is the quantity of the wave making paddles on an image plane; simultaneously recording a motion range of the mark points as well as image coordinates at a starting point and a terminal point of a moving track of a center mark point; numbering each wave making paddle on the image plane in an order from left to right, and storing the calibration information in storage spaces of the image processing boards according to the numbers;
step C: conducting image acquisition for the site of the current time; collecting image data in the EtherCAT image processing boards by FPGA into a storage unit; then, conducting data processing on the images in the storage regions by DSP on the EtherCAT image processing boards; firstly, extracting all the mark points within the motion range of each wave making paddle; then distinguishing each extraction point on a motion section line of the center mark point recorded in a calibration process; considering the point as a correct mark point only when an adjacent point exists respectively on the top, bottom, left and right of the current point; next, subtracting the recorded initial position from the coordinate of the mark point, thereby obtaining image displacement of motion of the wave making paddle; subsequently multiplying the value by K i to obtain a physical displacement value; obtaining displacement information of each wave making paddle on each image after completing image analysis of each wave making paddle; and finally, constructing a sub-message by the EtherCAT image processing boards for the motion information of the wave making paddles in the images in a manner of ‘numbers & displacement’, and feeding back the sub-message to the computer through the EtherCAT network;
step D: extracting, by the computer, messages transmitted by image processing cards; and renumbering the data in the messages according to the numbers of the slave station so that the number of the push paddle motion information of each wave maker is unique and each wave maker is successively arranged in accordance with a spatial position relationship;
step E: analyzing the displacement information of the wave making paddle by the computer: arranging the displacement data of each wave making paddle in the order of the numbers to form a measurement data curve; and meanwhile, calculating a difference value between a measured data curve and a target data curve at the current time, counting a maximum difference value and a mean difference value and drawing an error curve for operation of each wave making paddle for facilitating an experimenter in detecting the control precision of the wave maker;
step F: repeating step C to step E until the measurement of wave making motion is ended.

Assignees

• Univ Dalian Tech

Inventors

• Du Hai
• Meng Juan
• Li Muguo

Classifications

• G01M10/00

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