A laser range finding apparatus comprises a pulse laser (11), a light deflecting device, a photodetector arrangement (22) having an opto-electronic photodetector (23) and also an electronic control and evaluation system (10) in which a sensing signal representative for the range of an object is determined in accordance with the pulse transit time method from the time between the transmission and reception of a light pulse taking account of the speed of light. The electronic control and evaluation system (10) includes means for measuring the total electrical charge which has flowed via the photodetector (23) during the reception of a light pulse and/or for the measurement of the pulse width of the received light pulse. The compensation takes place as a result of the transit time measurement errors which arise as a result of the signal dynamics in dependence on the measured electrical charge or pulse width on the basis of respective correction values which were determined by the electronic control and evaluation system with respect to charges or pulse widths and pulse transit times, which were measured with respect to at least one reference object (86) having different reflectivities and arranged at a defined range from the light deflecting device (15).

Circular reference features such as drilled holes are located in an area of a part such as a cylinder head, the surface of which is laser scanned to obtain scan data. The scan data provides height values of the part. Differences in height values are used to determine the points on scan lines which are boundary points of the circular holes. A first algorithm is used to estimate the contour and radius of each hole. A second algorithm provides a correction factor for the radius of each hole. The circular reference features are used for registering the part relative to a reference datum. Methods are provided that allow the accurate determination of the location of such reference features to within 0.01 mm. (0.0004 in.) from the scan data. The method may be utilized to create modified scan data to machine the part. The method may be utilized iteratively from different views of the part to obtain data which represents the part. Also, the method may be utilized iteratively on similar parts to detect minor differences between the parts.

Reference or analytic features such as intake and exhaust valves and valve guides are located in an area of a workpiece or part such as a cylinder head, the surface of which is laser scanned to obtain laser scan data. The scan data provides a fine grid of height (Z) values of the part. The part is scanned along lines with constant x or constant y. The method uses a graphical interface and least squares techniques to determine a reference plane for the desired analytic feature. Image processing techniques are then used to extract the desired feature and its boundary. Finally, techniques are used to calculate the precise dimensions of the analytic feature.

An optical instrument (10), such as a stability monitor or a target range finder, uses an unstabilized laser (12) to project a composite optical signal of coherent light having two naturally occurring longitudinal mode components. A beamsplitter (24) divides the signal into a reference beam (26) which is directed toward one photodetector (28) and a transmitted beam (42) which illuminates and is reflected from a distant target (44) onto a second photodetector (52) optically isolated from the first photodetector. Both photodetectors are operated on the square law principle to provide electrical signals modulated at a frequency equal to the separation between the frequencies of the two longitudinal mode components of the optical signal projected by the laser (12). Slight movement of the target may be detected and measured by electrically monitoring the phase difference between the two signals provided by the photodetectors and the range of the target measured with the aid of microprocessor (132) by changing the separation between the longitudinal modes by shifting the length of the resonator cavity in an iterative series of increments.

A target has leading and trailing edges which are boundaries between a retroreflector and a non-retroreflector. The target is used in target determining apparatus for distance, width, azimuth, gauging, profiling, object detection, and particular target identification. A laser light source scans along a scanning path across the target. The retroreflector reflects light back toward the scanning means where it is received in a photoreceptor to determine the angles of the target edges. The distance to the target and the width are inversely proportional to the length of time that the light beam scans across the target. The laser light also scans across a reference point and the length of time between this reference point and the reflection from the target is directly proportional to the azimuthal position of the target relative to the reference. Further, the target may include a plurality of reflective and non-reflective strips transverse to the scanning path to establish binary indicia on the target. This results in a series of pulses from the photoreceptor as the beam scans the width of the target. This information is then decoded to determine the binary indicia and hence identify that particular target. The foregoing abstract is merely a resume of one general application, is not a complete discussion of all principles of operation or applications, and is not to be construed as a limitation on the scope of the claimed subject matter.