This paper will address the market requirements for laser scanning components and subsystems in information-handling systems from the points of view of the anticipated market growth and the types of scanners that will be utilized. Recent market studies by the author's firm have indicated that shipments of laser-based products in these applications will grow from $15 million in 1974 (end-equipment value) to several hundred million in 1980, stimulating both the market and need for innovation in laser scanning subsystems. Major equipment categories include POS scanners, facsimile, COM, laser platemakers, memories and special laser recorders, etc. Forces affecting the market rate of development for some of these equipments are examined. A measure of the market value for optical subsystems shipped in these equipments during the years 1975 - 1979 is given.
Recent advances in the area of facsimile communication have increased transmitting speed significantlyi, One reason for this is the development of fast, economical laser-based scanning systems' I. The design of such a system is very complicated, being dependent upon scanning speed and method, scanning device used, optical layout, facsimile machine geometry, modulation scheme, and cost. This paper describes a computer-aided design rationale for a laser-based galvanometer scanning system. System configuration, design goals, and methodology are presented. Design curves are given which allow for future scanning system design.
Some general principles are presented for determining likely applications for laser scanning in the printing industry. The special requirements of imagery in this field are discussed. Stress is laid on cost/ effectiveness and the systems approach. The implications of these ideas for scanner design are developed. Three examples are given of production systems which follow these principles.
A flat bed laser plate-maker system is being developed for Dow Jones and Company, publishers of the Wall Street Journal, to scan paste-ups and proofs and to reproduce the scanned information remotely on film or plates. Throughput of about one minute per plate is achieved. Presently, the fastest and most advanced way for producing newspaper printing plates is by preparing paste-ups and photographing each fully assembled page. Moreover, when transmission to a remote location is needed, telefax or more simply, "fax" transmission is used. Now, a flat bed laser plate-making system can eliminate the initial photographic step, improve the operational steps and, at the same time, speed up the whole process. In the laser system, the paste-up is scanned directly (without the photographic step) by a recently demonstrated flat field scanning system. Photomultiplier tubes change the reflected laser energy to an electrical signal which is digitized and transmitted to a second laser system, much like the first, where a second laser beam exposes a sensitive sheet of film or a coated plate to form the received image with great detail and quality. Most of the data processing takes place in digital domain. Scanning, transmission and recording take place in less time than is presently needed for fax operation alone.
A replication process can be used to produce multiple copies of high quality scanners with significantly less effort than required to make originals by the traditional methods. The replication process eliminates the requirement for grinding and polishing. Single facet flat scanner mirror surfaces can be replicated on cast and ribbed aluminum substrates. Non-traditional materials such as alumina and beryllia ceramics with high stiffness-to-weight ratios are practical scanner substrates. Polygon scanners are fabricated in split molds with all facets replicated simultaneously. Pyramidal scanners are made in one-piece molds yielding angular tolerances of better than 5 arc seconds. A 23-faceted replicated internal scanner that yields an x-y raster scan is shown and described. A scanner that uses an array of roof prisms to provide a truely linear scan is also described as a practical replication.
Development in laser,coatings, logic, etc. has expanded the use of optical scanners. The first part summarizes the general laws of physics that a designer has to cope with and gives references for additional information. The second part reviews what can be expected from general purpose commercial equipment, and the last section describes special purpose scanners of recent design.
Optical scanners in current use can be divided neatly into two basic families: devices with no moving mirror such as cathode ray tubes and electro- and acousto-optics, and electro-mechanical devices. This paper is limited to the latter group. Discussed are the five generic types, the attributes and limitations of each, ancillary equipment such as drives and control circuits and, in a general way, the suitability of each for various applications. X-Y scanning is covered. Because of the current interest in bar code scanning both laser and white light bar code systems are presented in some detail to illustrate the optical and electronic elements of systems incorporating electro-mechanical scan-ners. Throughout this paper, references to scan angle mean the angular motion of the mirror, not that of the reflected beam. Beam motion is double the mirror scan angle.
There is a growing requirement for optical beam steering devices which will provide extreme amplitude and frequency stability over a wide range of environmental conditions. This paper is a description of such a device, which has been developed using fundamental vibration theory and state of the art electronic design techniques.
Without compensation, moving-coil mirror galvanometers make acceptable repetitive saw-tooth light beam scanners at frequencies up to 10% of their natural frequencies. With the electronic compensation described here, that range can be extended to 30% of their natural frequency.
Techniques have been developed to extend the accuracy and repeatibility of X-Y beam deflection systems. Absolute beam placements of ± 5pm over 100mm (+ 1/20,000) with precisions of + 2.5μm (+ 1/40,000) have been demonstrated at speeds far beyond the limitation imposed by an optimum servo control. A comparison is made of scanning times at various precisions; results indicate that high accuracy and precision can be attained without materially sacrificing system speed. Basic to the operation of the deflection apparatus is an optical position monitoring capability and a unique control philosophy that drives the deflectors in open loop mode. Distortion is compensated by the position monitor and the control logic, so that beam placement has a guaranteed absolute accuracy in the deflection plane. Limitations of the present apparatus will be discussed, as well as possible extensions of precision and accuracy.
An optical system was developed to provide fast incremental scanning of a backscattered laser velocimeter focus point over a 36-cm distance. The system is used to measure flow velocities at 16 positions along its optical axis and to scan these 16 positions up to 30 times a second. Dwell time at each location is approximately 2 milliseconds. Sample volumes typically are 0.2 mm in diameter by 1.4 cm in length. The optical scanning system consists of a wheel containing plane parallel quartz windows of various thicknesses. The laser velocimeter beams are imaged to a primary focus within the dead airspace of an optical cell. -The beams emerging from the cell pass through the windows of the scanning wheel. The refraction of the beams passing through the windows causes an apparent shift of the focus within the optical cell and hence in the test zone. Light scattered from the secondary focus within the test zone is concurrently collected and reimaged through the same optical path which originally projected the primary focus. The reimaged backscattered light containing the velocity information is then collected and focused onto a photomultiplier detector system to complete the scanned laser velocimeter optical system.
Laser scanning of linear bar codes with random orientation has required the development of multi-dimensional scan generators. Scan patterns of substantial complexity have been generated by single rotating multi-faceted mirrors which had previously been used largely for generating single line repetitive raster scans. Several approaches will be described, including an approach whereby scan vectors generated by the rotating element are reimaged by a second reflection from the element itself.
The scanning of a one dimensional multi-color light intensity distribution by means of the acousto-optic interaction using acoustic surface waves is presented. In the experiment laser sources of different color are used to image a multi-color transparency into the surface region of a LiNbO, surface acoustic wave light modulator. An rf acoustic pulse propagating on the LiNbO surface scans this ithage and diffracts the light. Each color component is then individually detected in the3diffracted light by means of a photodiode. Four different device schemes are compared, being classified by the configuration through which the light and acoustic beams interact. Applications of the system to producing a real-time signal of the Fourier transform of an optical transparency and to electronic focusing by use of chirped acoustic waves are also discussed. Argon and HeNe lasers are used as light sources, and center frequency of the surface acoustic wave varies from 45 to 100 MHz.
The types of motors considered for rotating mirror deflectors are dc, induction, hysteresis synchronous, reluctance and brushless dc. Factors concerning the choice of mlotor are considered. How to estimate windage and friction, calculate time to speed and determine size of llotor are illustrated by examples. Finally, open loop and closed loop speed control systems are discussed.
A map of lenses for laser scanning has been studied. The class of lenses are all flat field and telecentric on the image side. The laser source was not assumed to be a collimated beam. Three of the most promising types have been designed and the construction para-meters are presented. The simplest solution uses a mirror.
Gas bearings are useful for optical scanning systems in a broader sense than is implied by their application as self-lubricated bearings for high speed spinners in aerospace vehicles. Aerostatic bearings extend the scanning geometries and speeds into new areas of use including linear motions and low speeds with extremely high resolution. Pressurized gas bearings are also useful for the manufacture of metal optics and gas bearing parts. Highly accurate surfaces with fine finishes can be machined directly and measured in the process, thereby reducing the cost of subsequent processes such as inspection, lapping, qualifying, and plating. Higher information rates and packing densities can be obtained at much lower scanning velocities, thus reducing heat generation, centrifugal distortion, vibration, and control requirements. An objective of this paper is to develop a perspective for synthesis of laser scanning systems around the truly strong points of pressurized gas bearings.
The design of rotating mirror deflectors should be predicated on cost performance trade-offs. Precision, relatively costly rotating polygons are used for 100 MHz laser recorders but a less precision counterpart can be used in a very cost effective manner for laser supermarket POS scanning systems. Parameters of deflector design are discussed with respect to scanner configuration and how its choice affects cost and scanner accuracy. Limits of speed required, driving power, material selection, types of bearings and available motors are also discussed. Examples of a sophisticated precision air bearing scanner and a low cost simple rotating mirror deflector with a ball bearing motor are presented.
In laser scanning and recording systems, the results obtained with a given lens will be highly dependent upon the width of the incoming beam. Wide variations in resolution, total power and power distribution within the focussed spot result from varying the input beam width. Previous work by researchers in the field identify these interrelationships for specific conditions and applications. This paper provides characteristic curves showing these interrelationships in sufficient detail to provide the system designer with simple design aids. This allows selection of the most suitable parameters for the system under consideration. Further illustrations, and the associated discussions, help to provide a mental picture of the changes that occur about the focussed image plane. Mathematical relationships and references are provided, but are not essential to develop an understanding of the resulting characteristics.
A new method of generating a pixel clock which can achieve fractional pixel registration across the entire film format without the need for precision servo control of the spinner motor is described. This method utilizes an auxiliary laser beam in parallel with the main writing/scanning beam. A description of several classical methods of generating precision pixel clocks for use with laser printers and laser scanners is included. The pixel placement accuracy achievable with each method is discussed along with advantages and limitations of each method. The auxiliary beam of the new method is first diverted from the writing beam just prior to its impinging the film and is then passed through an optical ruling. The modulated auxiliary beam is then collected on a photodetector. The resulting signal from the photodetector is used as a reference signal to which the pixel clock is phase locked. Generating the pixel clock in this manner not only produces accurate line-to-line pixel registration along the line, which is independent of perturbation in the scanner rotation, but also corrects for geometric distortions along the line length caused by the lens system.