The Scanner

The scanner is the heart of the tunnelling microscope, controlling the x, y and z motion of the tip relative to the sample. The requirements that the scanner must 

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IP formats up to 35x43 cm can be handled automatically in full daylight. If an exposed cassette is inserted in the scanner the following actions are performed ... 

Typically the throughput amounted 30-50 images/hour for a pixel matrix of 2000x2500. The scanner was controlled by a PC with menu oriented software. Important parameters such as pixel size and PMT amplification could be adjusted easily. 

The P-scan System 4 can be configured in many ways, dependent on the application. Figure 1 shows a basic system configuration. The P-scan processor (PSP-4) controls the scanner and the water pump. Scarmer operation on site is performed from the remote control unit, as an alternative to the control from the computer. The PSP-4 also includes the ultrasonic system. 

In order to support the scanners, a special scanner driver utility for configuration and operation of the scanners is included in the system. Figure 6 shows the scanner control window on the PC display together with the remote scanner control unit, from where the same functions can be controlled. 

To meet the demand for flexibility the basic electronic components of the scanner system are build as individual modules (Master, Link, Driver and Motor Modules) containing control-and communication electronics. The modules connect through external cables. 

The Master Module (Figure 2, a) controls both the communications in the local network and the communieation between the network and the base station (a Scanner Master Controller or a FORCE Institute PSP-3 or PSP-4 ultrasonic acquisition unit). The communication between the base station and computer (PC with Windows 95 or Unix-workstation) containing the scanner control software runs on a standard ethemet connection. 

Up to 20 modules can be connected to the network without the need for extra cable between the base station and the scanner is needed. 

For produetion eontrol of small diameter nozzle welds a magnetic wheel scarmer has been build (Figure 4). One standard motor module drives the magnetic wheel and one standard motor module drives the Y-module slide. The two motors are connected to the Master Module. The scanner is controlled from a FORCE Institute PSP-3 ultrasonic acquisition unit with build-in scarmer controller. 

Fig. 2 shows the CFRP-sandwich specimen and the transducer mounted on the scanner. Fig. 23 presents a C-scan of the specimen as first interesting result. Only the defects visible from the outside are indicated. The distance between transducer and specimen was smaller than the focal length, so that the angle of incidence at the edge of the sound beam converts the longitudinal waves to Rayleigh-waves in the specimen. These waves provide a very sharp image of the surface. This method opens the possibility for a non-contact acoustic microscope. 

The system also consists of a LCD-screen located nere the object to be scanned. This screen is a slave to the one on the acqusition computer and consequently shows the same image. The purpose of this screen is to help the scanner technician to acheive a full coverage of the area to be scanned. 

The scanner has been constructed in modules which, for future applications, makes it easy to increase the length of the scanner for inspection of larger blades, by adding further modules to the system. In co-operation with LM Glasfiber and RIS0 it was decided to construct the first scatmer for inspection of blades with a length of max. 21m. In order to be able to scan primarily the bonded areas from the root to the tip of the rotor blade, a so-called X-unit module was constructed. The movement from the root to the tip of the blade was controlled by the P-scan system. 

Since it was required by LM Glasfiber that the scanner should be able to inspect joints between the shells and the iimer beams on each side and also the joints between the shells on the leading and trailing edge of the rotor blades, the X-Unit module was designed with three different set-ups for the Y-modules, which perform the movement of the probes transverse the length of the blade. The three different set-ups of the Y-modules are ... 

The coin-tap test is a widely used teclinique on thin filament winded beams for detection of disbonded and delaminated areas. However, since the sensitivity of this teclinique depends not only on the operator but also on the thickness of the inspected component, the coin-tap testing technique is most sensitive to defects positioned near the surface of the laminate. Therefore, it was decided to constructed a new scaimer for automated ultrasonic inspection of filament winded beams. A complete test rig illustrated in figure 6 was constructed in order to reduce the scanning time. While the beam rotates the probe is moved from one end to the other of the beam. When the scarming is complete it is saved on diskette and can then be evaluated on a PC. The scanner is controlled by the P-scan system, which enables the results to be presented in three dimensions (Top, Side and End view). 

Consumer Products. Laser-based products have emerged from the laboratories and become familiar products used by many millions of people in everyday circumstances. Examples include the supermarket scaimer, the laser printer, and the compact disk. The supermarket scanner has become a familiar fixture at the point of sale in stores. The beam from a laser is scaimed across the bar-code marking that identifies a product, and the pattern of varying reflected light intensity is detected and interpreted by a computer to identify the product. Then the information is printed on the sales sHp. The use of the scanner can speed checkout from places like supermarkets. The scanners have usually been helium—neon lasers, but visible semiconductor lasers may take an impact in this appHcation. 

In its most common mode of operation, STM employs a piezoelectric transducer to scan the tip across the sample (Figure 2a). A feedback loop operates on the scanner to maintain a constant separation between the tip and the sample. Monitoring the position of the scanner provides a precise measurement of the tip s position in three dimensions. The precision of the piezoelectric scanning elements, together with the exponential dependence of A upon c/means that STM is able to provide images of individual atoms. 

High pressure xenon lamps are also employed in some TLC scanners (e.g. the scanner of Schoeffel and that of Farrand). They produce higher intensity radiation than do hydrogen or tungsten lamps. The maximum intensity of the radiation emitted lies between k = 500 and 700 nm. In addition to the continuum there are also weak emission lines below k = 495 nm (Fig. 14). The intensity of the radiation drops appreciably below k = 300 nm and the emission zone, which is stable for higher wavelengths, begins to move [43]. 

The scanners commercially available today operate on the basis of the optical train illustrated in Figure 22. 

WEB A bar code scanner in a grocery store is a He-Ne laser with a wavelength of 633 nm. If 12 kj of energy is given off while the scanner is reading bar codes, how many photons are emitted ... 

Some hospitals are using a bar code scanner in the administration of unit dose drugs. To use this system, a bar code is placed on the patient s hospital identification band when the patient is admitted to the hospital. The bar codes, along with bar codes on the drug unit dose packages, are used to identify the patient and to record and charge routine and PRN dm. The scanner also keeps an ongoing inventory of controlled substances, which eliminates the need for narcotic counts at the end of each shift. 

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