| Traditional eddy current detecting apparatus are mainly used in the field of flaw detection, vibration measurement, thickness measurement and so on. Aiming at the problem of visualization of metal block, a set of detecting, imaging and positioning apparatus based on flexible eddy current sensor array has been developed in this article. This apparatus is composed of three parts: signal acquisition and disposal system, image acquisition and combination system, marking and printing system. Compared with traditional eddy current detecting apparatus there are three improvements in this apparatus: The first, we substituted overlapped flexible eddy current sensor array for traditionary coiled eddy current sensor array to detect the block and screw. Image acquisition system was utilized to acquire the surface images of the covering which could be showed together with the position of the block and screw. The function of marking and printing were added in this apparatus, which would print out the centerlines of the screw on the corresponding position of covering. Figure 1 The principle figure of signal sampling system In the signal acquisition and disposal system, overlapped flexible eddy current sensor array is proposed. It substitutes for traditional coiled eddy current sensor array to increase the position accuracy under the premise that the measuring range is guaranteed on one hand, and also to provide convenience to add marking and printing system. The flexible eddy current sensor array is a sensitive coil array in certain regular distribution manufactured in the thin film basis. However, overlapped flexible eddy current sensor array is folding many above same arrays to form the overlapped array according to some regularity. On the base of measuring range of the single layer it may be designed more scalar to enhance the measuring range of sensor; Moreover in order to enhances the detection depth of the sensor, the signal rectifying circuit is presented to revise the non-linear signal entirely. This circuit might make the survey scope 5 times to diameter of the poke under linearity premise precondition. The coil of single-layer overlapped flexible eddy current sensor array coil can be made into many kinds of shapes hence it becomes possible to make holes through the printing system. Its structure is much thinner, and if put printing system above the sensor, it won't take printing system to arrive at the measured object surface. Thus, carrying on marking and printing above the sensor becomes reality. The ADSP21060 chip has been adapted in order to realize the real time signal processing and imaging. There is a high speed data signal acquisition and processing circuit with ideal and flexible data interface in this paper. Although ADSP21060 has serial port itself, it has especial difficulty in the communication with the computer. In this paper a serial communication controller (PC16550D) is used to connect the serial port. PC16550D is the universal asynchronous communication chip made by National Semiconductor Company. To meet the requirement of the communication in real-time processing, PC16550D is used to implement high speed serial interface communication of system. To content the requirement of the communication system in real time processing, we can implement high speed serial interface communication of the system, meanwhile the control ability of system communication interface can be intensified. Fig.2shows the hardware circuit's block diagram of ADSP21060 and PC's communication. Fig.2 The hardware circuit of the communication between ADSP21060 and PC The signal of eddy current sensor has been input to DSP through the measure circuit and the choice switch. The signals will have been filtered and revised after they have been switched by A/D. The signals have become 8 digit data signals by quantifying. There is always high frequency rumble in the primary measure data which obtained from the eddy current sensor. The data must be processed in global threshold value way in DSP. Laplace edge detecting operator to process the data is given in this article. It is different with traditional signal processing methods on eddy current sensor that image-processing algorithm is adopted to deal with the measured data and obtain position and radius information of covered metal screw. In order to realize displaying the covered surface image and the information of metal weld block synchronously, detecting and imaging apparatus has introduced image acquisition and combination system, which gathers image characters on the object using CCD vidicon, then combines the images using characteristic frame of reference method to completely gain the surface information covered by detecting pokes. In addition, processed signal and covered object image are synchronously displayed, hence the operator can intuitionisticly infirm the detected object's position. And also to position the screw holes on the weld block accurately, detectingand imaging apparatus increases the marking and printing system. It is insufficient to guarantee the precise of ±0.2 to hit the bolt aiming at via on the inside surface only depending upon synchronization display, but also upon implementing marking and printing the corresponding screw center position between inside board surface and weld block. To sum up, marking and printing also is one of the sound and direct reasons to use overlapped flexible eddy current sensor array. Fig3 was the structure of detecting equipment, which was composed of pins, permanent magnet stick and electromagnet. While electrified, permanent magnet stick bringing about pins struck ribbon through the Φ2.3mmholes in the sensor array and made marks on the covering. Fig3 the structure of detecting equipment The eddy current detecting, imaging, positioning apparatus designed in this paper, substituted overlapped flexible eddy current sensor array for traditionary coiled eddy current sensor array to detect the block and screw to extend the detecting area and increase the location accuracy. And a CCD camera was utilized to acquire the surface images of the covering. Once the block was detected, the surface image was then could be showed together with the position of the block and screw directly, which made the visual fix more directly and accurately. At last the function of marking and printing were added in this apparatus, after detecting the screw in the block, it could print out the centerlines of the screw on the...
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