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Browse Prior Art Database

Rigid Disk Contaminant Detector

IP.com Disclosure Number: IPCOM000047429D
Original Publication Date: 1983-Nov-01
Included in the Prior Art Database: 2005-Feb-07
Document File: 2 page(s) / 44K

Publishing Venue

IBM

Related People

Taylor, NB: AUTHOR

Abstract

If a laser beam is aimed at a disk so as to form a very small angle with its surface, a small particle on the disk will be seen to reflect a portion of the beam. This article describes a method of detecting and counting the particles on a disk by utilizing a TV camera to pick up the light from the particles. The video signal output from the camera can be used to detect the presence of a particle. The background reflection from the disk is now not as large a factor because only a small portion of the disk is being sensed at one time. This eliminates the problem of background noise. Several characteristics of a TV camera must be taken into account for this system to work properly. The first is that a bright spot can activate several adjacent scan lines. This is taken care of with the circuit of Fig. 1.

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Rigid Disk Contaminant Detector

If a laser beam is aimed at a disk so as to form a very small angle with its surface, a small particle on the disk will be seen to reflect a portion of the beam. This article describes a method of detecting and counting the particles on a disk by utilizing a TV camera to pick up the light from the particles. The video signal output from the camera can be used to detect the presence of a particle. The background reflection from the disk is now not as large a factor because only a small portion of the disk is being sensed at one time. This eliminates the problem of background noise. Several characteristics of a TV camera must be taken into account for this system to work properly. The first is that a bright spot can activate several adjacent scan lines. This is taken care of with the circuit of Fig.
1. A data trigger fires single-shot 1 whose output pulse is about 60% of the horizontal scan time. When single-shot 1 drops, that output fires single-shot 2 whose pulse length is also about 60% of the scan time. These two signals are ORed together to produce a continuous up-level until there are no further data pulses, at which time the output drops. The next factor to be taken into account is the fact that the camera will retain the image even after the data has been scanned off, resulting in multiple counts in some cases. This difficulty is overcome by having the image enter the camera via a mirror driven by a stepper motor. One scan is...