The effect of shaft misalignment on the accuracy of four types of precision digital shaft angle encoders (219 resolution elements per rotation) was determined using a special test fixture and optical techniques. The encoders and couplings were precisely aligned or misaligned by known amounts. When properly aligned to the shaft whose rotation is to be measured, the encoders exhibit rms errors of less than a single resolution element even when connected through a coupler. When the axes of shaft and encoder transducer are mutually misaligned, the different systems vary as to the amount of corresponding error introduced into the encoder output. In each case, the errors varied in a sinusoidal manner with respect to shaft angle. By the optical method alone, it was not possible to distinguish between errors caused by the associated coupler and those inherent in the encoding transducer itself. A second method of evaluation, utilized a computer to analyze the sum of two identical encoders connected so that one of them turned in a positive direction while the other turned in a negative direction (back-to-back). The large number of measurements per revolution allowed us mathematically to separate out errors due to various causes. The system evaluated by this method showed that the greatest fraction of the errors may be attributed to distortions in the coupler, amounting to the equivalent of several resolution elements. When properly aligned, all systems exhibit excellent accuracy.
A CO2 laser has been designed to provide a relatively simple portable unit that generates coherent light pulses at selected infrared wavelengths. This improved laser was originally designed for the detection of air pollutants. Other applications of this laser would include optical communication and research in infrared transmissive materials. This laser is de-signed for sealed-off operation and high-power repetitive pulsing at selected wavelengths. Earlier systems for pulsing a CO2 laser have employed prisms or gratings within the laser cavity to shift the output from one infrared line to another. However, these systems in addition to being rather cumber-some, and difficult to manipulate, significantly reduce the power output of the laser.
Direct photographic imaging becomes impossible in the wavelength regions beyond about 1.2 microns yet longer wavelengths are rich in information about the world around us. This paper discusses some of the functions that can be performed by infra-red imagery (thermal mapping). It also discusses briefly some of the physical principles affecting the appearance of the results and presents, by reference to several examples of imagery, some representative results obtainable in fire and water polution and in surveying soil conditions. This paper also describes a line-scanning infrared imagery system, based on a cooled, small-area semiconductor detector, that has been developed to answer the need for a relatively simple, lightweight thermal mapping device.
A new, fully automatic exposure control system providing both iris and shutter control is explained herein. The automatic exposure control is through the taking lens without obstructing the optical path during exposure time and works with any system of iris diaphragm, i.e., linear or logarithmic f-stops, etc. The system is independent of lens focal length. The system solves the basic exposure equation and automatically compensates for all parameters including scene brightness variance, camera frame rate, shutter opening, and lens f-stop. The system is dynamic over an equivalent of 10 f-stops or more (depending on the lens used) and works over a wide range of scene brightness levels. A system is truly automatic and requires no attention from the operator once the magazine is installed on the camera. Even filters, when placed on the taking lens, are correctly compensated for Panchromatic film without any adjustments in the automatic exposure control.