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This article examines the design and specifications of unit LAM-6 for noncontact determination of the dimensions of semifinished and finished hydraulic-turbine vanes. The unit was developed on the basis of a method which employs acoustooptic locating to measure distances.In certain sectors of industry such as power engineering, it is necessary to check the shape and dimensions of the finished product, as well as the shape and dimensions of the semifinished product at different stages of the production process. Such checking requires universal measuring instruments which provide information that is not only accurate but is in a form in which it can be analyzed on a computer.The All-Russian Scientific Research Institute of Physico-Optical Measurements has worked with the Institute of Physico-Engineering Studies to develop and make portable compact unit LAM-6 for noncontact determination of the geometric dimensions of semifmished and finished hydraulic-turbine vanes. The unit continues the LAM series of instruments that operate by the method of acoustooptic locating, which is based on determination of the coordinates of points of an object by measuring the time of propagation of an acoustic signal created in air when a pulse of laser radiation acts on the surface being measured [1][2][3].The main specifications of the LAM-6 are shown in Table 1. The unit is built in the form of individual portable blocks and can easily be transported to permanent facilities. The unit makes it possible to determine the coordinates of points of the surface of a finished vane or the semifmished product and compare the measurements with a mathematical model of the vane. The functional model of the unit consists of the following: measurement-layout block (MLB); preliminary data analysis block; portable pulsed laser; notebook computer. The measurement-layout block is an acoustooptic distance gage mounted on a rotating head equipped with a counter to record angles corresponding to direction at the point on the surface whose coordinates are being measured.Thus, determination of the coordinates of points of the surface of a vane entails measurement of the distance to a point of the surface and two angles (spherical coordinate system). The technique of acoustooptic distance determination used in the unit involves the laser excitation of a sound wave in air (at the interface with the surface) and determination of distances by measuring the time interval between the moment a short (I 0 -8 sec) laser pulse reaches the object and the moment the acoustic pulse reaches the microphone of the measurement system. The acoustic pulse is created by effects associated with the interaction between the pulsed laser radiation and the surface of the material of the vane. In particular, the pulse is created by a combination of heat generation, laser cleaning of the surface (the removal of layers of an oxide and contaminants from the surface), and optical breakdown on the microscopic scale. The measurement-layout block includes the following: rotating head with...

A description is given of an automatic apparatus for measuring the dimensions of objects of complex geometrical shape using an optoacoustic ranging method. The results are given of measuring the dimensions of a test object, a steam-turbine blade, and a shoemaker's last. An accuracy of better than ++_ 50 #m was achieved.Means of measuring the dimensions of bodies of complex geometrical shape are at present being used more and more in various branches of the national economy. The principal branches in which such devices are employed are automobile engineering (bodywork and its components), aircraft engineering (streamlined components, cabin glazing), the shoemaking industry (lasts), orthopedics (prosthetic and orthotic devices), power engineering (turbine blades), tool production (dies), computer production (dies), restoration work (replicas), design.The authors have developed and manufactured an apparatus designed to measure objects such as steam-turbine blades. The principal requirements imposed on the apparatus during its development were as follows: the measurements must be made automatically and without mechanical contact with the object, maximum overall dimensions of the investigated components of 1000 x 100 x 100 mm, weight below 40 kg, time to measure one component less than 5 rain, measurement accuracy better than +0.1 rnm.In creating such an apparatus the authors had to correctly choose a noncontacting method for measuring the dimensions. Only two methods were considered as having the specified measurement accuracy. These were either to use different versions of the photoelectric method [I] or to use the optoacoustic ranging method [2,3]. It is well known that the photoelectric methods, based on analyzing light beams scattered by the surface of the object, are characterized by high accuracy (an error of _< 5 t~m) with a short time required to obtain the results. However, serious disadvantages include a small working range of measurement (1-10 ram), a complex electronic processing circuit, and also an absence of Russian-made measurement heads operating in accordance with this principle.The optoacoustic ranging method consists of recording acoustic pulses in air which arise when laser radiation interacts with a surface, and measuring the time intervals required for the sound to propagate from the object to a microphone. This method provides the specified accuracy and has a working distance range of 10-1000 mm. Since the processing electronic circuit is quite simple and the measuring part is capable of being made in practically any laboratory, the authors decided on the optoacoustic ranging method when they were ~eveloping the apparatus.The kinematic scheme of the interchangeable component and measuring part was dictated by the measured object and was conventional (rotation and vertical motion of the object, movement of the measuring part of the apparatus in a horizontal plane). The radiation source generating the acoustic pulses took the form of a laser of 1.06 t~m wavelength, pulse duration 10 -8 sec, and...