Research Of Ultrasonic Three Dimensional Coordinate Measuring System

Three-dimensional coordinate measurement is an important technology inmodern machinery and instrument industries. Up to now there are kinds ofthree-dimensional coordinate measurement systems, such as coordinate measuringmachines, laser tracker systems, digital photography systems, theodolites, etc. Buttheses systems are costly, and have relatively poor scalability. This thesis makesresearch on a measuring system for large dimension measurements based onultrasonic sensors. To implement a three-dimensional coordinate measurementsystem with low cost, good scalability, and strong applicability, this thesis hasfinished the following tasks.Firstly，this thesis describes the methods of ultrasonic distance measurement andcoordinate measurement commonly used both at home and abroad. Then athree-dimensional coordinate measuring method is proposed, which uses ultrasonicsensors to realize three-dimensional coordinate measurement of objects. Spatialthree-dimensional coordinate measurement is realized through a scheme of onetransmitter and multiple receivers. The algorithm of ultrasonic distance measurementbased on the peak method and cross-correlation method is proposed. Then the modelof three-dimensional coordinate estimation based on the least square method andGauss-Newton iterative method is established.Secondly, hardware circuit based on ultrasonic sensors is designed for thesystem, including transmitter and receiver circuits, A/D conversion circuit,temperature compensation circuit, serial port transmitting circuit and the powersupply circuit. And the experimental device based on orifice plate is designed forsystem testing.Then the core control part of the entire system is completed using the Veriloglanguage and modular design method based on FPGA, which includes the A/Dacquisition module, the frequency demultiplication module, the peak method andcross-correlation method module, least-squares minimization estimation and Gauss-Newton iterative estimation modules, and the serial port transmitting module.The measurement of the transmitter’s three-dimensional coordinate is achieved.Finally, the system is tested, and the accuracy of estimation result is analyzed.The main errors which affect the ranging accuracy and coordinate estimationaccuracy are compensated, such as temperature, ranging distance, transceiver angle,and hardware delay. Experimental results show that coordinate estimation accuracycan be controlled to within16mm after error compensation.The ultrasonic three-dimensional coordinate measurement system has low cost,and is easy to build, operate and expand with its distributed structure. For profilemeasurement and volume measurement of large-scale objects, it can meet therequirements of accuracy in many cases, and has a promising prospect.