The techniques and instrument designs developed for continuously recording tiltmeters and strainmeters are reviewed. Consideration is given to short-base and long-base tiltmeters as well as to rod, wire, laser and borehole hydraulic strainmeters. Since a good design is difficult to achieve, it is necessary to select the goals an instrument must meet and be prepared to compromise on others. The importance of comparison tests is demonstrated, and it is concluded that good results cannot be gotten at low cost or without careful attention to details.

Strainmeters and tiltmeters

Lasers can now be regarded as practical and economic tools with unique properties which have been utilized effectively in several applications in industry. Major applications of the laser are in thermal processes and measurements. Large amounts of concentrated energy allow microdrilling, welding, cutting, and fracturing to be simply effected in even the hardest materials. The coherence properties provide ideal sources for alignment instruments and interferometers for accurate length measurement. This paper describes these applications and their typical capabilities. Future developments and their potential are discussed, with the conclusion that the laser will be increasingly used in the manufacturing environment.

Lasers in industry

A process and system for survey alignment along a straight line in which a columnated laser beam is projected along the line to be aligned from adjacent its starting point to a target plate at an end point thereon, the laser beam being diffracted intermediate such points, and preferably adjacent the starting point, by means of at least one set of two closely spaced parallel edges passing entirely through the beam at an angle, preferably perpendicular, to the beam axis, the spacing of the edges of such set being substantially less than the thickness of the beam. The result of the diffraction is a linear diffraction pattern of beam images tapering with increasing distance from the beam axis to eventually approximate a linelike thinness. The thin images at the opposite ends of this pattern define a straight line which passes through the beam axis independently of the position of the set of edges within the beam and thus locates the beam axis in one direction. Preferably two such sets of edges are provided, arranged in angular, preferably perpendicular, relation so as to locate the beam axis in two directions. The sets of edges may be constituted by a tensioned filament or a line inscribed on a transparent plate.

Process and device for the survey alignment with a laser beam

In this paper a laser straightness measurement system is proposed. Using the characteristics of travelling straight and parallel, a new diode laser system utilizing optical fiber and modulation techniques was developed. This optically aligned beam is used to establish a reference line for the straightness measurement of any mechanical system. A four-quadrant photo detector was used to receive the laser beam. A phase sensitive detecting technique was adopted to process the opto-electrical signals from the detector. A single board microcomputer employing an 8098 processor was developed to conduct all data acquisition and signal processing. The influence from disturbing lights, circuit drift and beam drift can be removed from the system. The system was calibrated using an HP5528 laser interferometer. Results showed good accuracy of 0.3 μm within the range of ±100 μm and pointing stability of 0.3 μm at a 1 m distance was obtained. Two practical testing examples are carried out on a CMM and a grinding machine, respectively. Repeatability of both tests was found within 0.5 μm. This low-cost system has been successfully applied to the straightness measurement of a precision CMM.

A laser straightness measurement system using optical fiber and modulation techniques

Binary phase square spiral zone plates (BPSSZPs), a special type of binary phase vortex lenses, are introduced to generate focused optical vortices showing square symmetry. The numerical solution and fabrication method, as well as the experimental results are given. Different from conventional vortex lenses, these BPSSZPs produce focused vortices with small topological charge following a modulo-4 transmutation rule. In addition, the central diffracted image rotates in the vicinity of the focal plane. These interesting properties suggest that BPSSZPs might become key components for many potential applications such as optical image processing and quantum computation.

Square optical vortices generated by binary spiral zone plates

A system of large rectangular Fresnel lenses has been used in the laser alignment system for the SLAC two-mile accelerator. The alignment system consists of a He–Ne laser light source, a photoelectric detector, and the lenses, one of which is located at each of 297 points which are to be aligned. Each lens has the proper focal length to focus the laser to a point image at the detector. When the alignment at a certain point is to be checked, the image from that lens is scanned by the detector. The image is found to be displaced from its normal position by an amount equal to the product of the position error and the magnification of the lens. The alignment sensitivity is ±0.0025 mm. The targets are enclosed in a 60-cm diam evacuated light pipe to avoid atmospheric disturbances.

K. R. Trigger

Papers

Precision Alignment Using a System of Large Rectangular Fresnel Lenses