Holographic scanning systems have been used for years in point-of-sale bar code scanners and other low resolution applications. These simple scanning systems could not successfully provide the accuracy and precision required to measure, inspect and control the production of today's high tech optical fibers, medical extrusions and electrical cables. A new class of instruments for the precision measurement of industrial processes has been created by the development of systems with a unique combination of holographic optical elements that can compensate for the wavelength drift in laser diodes, the application of proprietary post-processing algorithms, and the advancements in replication methods to fabricate low cost holographic scanning discs. These systems have improved upon the performance of traditional polygon mirror scanners. This paper presents the optical configuration and design features that have been incorporated into a holographic scanning inspection system that provides higher productivity, increased product quality and lower production costs for many manufacturers.
Holographic-based scanning systems have been used for years in the high resolution prepress markets where monochromatic lasers are generally utilized. However, until recently, due to the dispersive properties of holographic optical elements (HOEs), along with the high cost associated with recording 'master' HOEs, holographic scanners have not been able to penetrate major scanning markets such as the laser printer and digital copier markets, low to mid-range imagesetter markets, and the non-contact inspection scanner market. Each of these markets has developed cost effective laser diode based solutions using conventional scanning approaches such as polygon/f-theta lens combinations. In order to penetrate these markets, holographic-based systems must exhibit low cost and immunity to wavelength shifts associated with laser diodes. This paper describes recent developments in the design of holographic scanners in which multiple HOEs, each possessing optical power, are used in conjunction with one curved mirror to passively correct focal plane position errors and spot size changes caused by the wavelength instability of laser diodes. This paper also describes recent advancements in low cost production of high quality HOEs and curved mirrors. Together these developments allow holographic scanners to be economically competitive alternatives to conventional devices in every segment of the laser scanning industry.
An injection molding process development has been conducted to demonstrate the feasibility of manufacturing, by injection molding, mirrors with sufficient surface accuracy for utilization in laser printers and mechanical stiffness for ease of assembly.
Holographix, Inc. has developed a family of holographic laser scanning systems for printing applications. These systems have been designed to significantly reduce production costs without compromising print quality. Holographix has been awarded several patents on its designs and licenses its technology to OEMs. The optical designs for these systems, developed with Optical Research Associates (ORAR), range from `low-end' laser scanners for 300 dpi and 600 dpi desktop printers to prepress scanners with 1200 dpi and greater resolution. The designs are well corrected for linearity and line bow. Unique features of these designs are telecentricity at the focal plane and the achromatic correction for both cross-scan and in-scan errors due to wavelength variations. The achromatization capability allows the use of laser diode sources for a major cost savings and telecentricity improves in-use performance. This paper briefly describes the concept of holographic laser scanning and key features of the optical designs.
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