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Home / About Us / Solutions / Laser Vision System / Del-Tron Solutions
Highly Accurate Linear Slides Help Laser Vision System
Measure Wide Range of Parts to ±0.0004" Tolerances
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Retina Systems, Inc.
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Use of linear slides that provide ±0.0002 accuracy over their entire length makes it possible for a laser vision system to provide ±0.0004 inch accuracy for a wide range of part sizes. The linear slides allow for micrometer adjustment of the laser unit traveling along the slide to quickly accommodate different size parts. These systems are being used to inspect parts on an automated basis with 100% accuracy In the fastener, bearing, automotive, glass and pharmaceutical industries.
Studies supporting automation show that human inspectors can miss as many as 20% of defective parts when operator fatigue sets in. Laser inspection systems, on the other hand, can gage dimensions with much higher accuracy while eliminating inspection errors. Laser inspection systems also are much faster than manual inspection. This non-contact gauging approach is capable of inspecting most applications at speeds as high as parts can be presented for inspection, up to 850 parts per minute.
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Threaded fasteners
For example, threaded fasteners can be inspected for surface problems, missing internal or external threads, damaged threads, or even mixed sizes of threads. The laser beam is scanned in a vertical direction so that it walks down the threads. At the same time a horizontal beam determines the location of the part. The inspection of the peaks and valleys in the thread creates a pulsing return signal that is picked up by the receiver/detector. The signal contains information on the quality and size of the thread. |
As each part reaches the inspection point the detector sends the "part detect" signal to the vision inspection module. Upon receipt of this signal, the vision inspection module actuates the image capture/analysis process. A strobe laser light source is used to illuminate the moving part. A visual image of the part is then captured by a camera aligned to view one specific inspection point in the material handling system.
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Analog signals
A small rectangular element in the camera houses an array of photodiodes whose function is to detect the amount of light reflected from the part to the camera. Each of the photodiodes continuously transmits an analog signal to a vision inspection module that assigns a value of either 0 or 1 to each signal. The vision inspection module then transfers the binary values to digital memory. |
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| The module uses the binary data to perform analytical operations on the captured image such as linear measurement, flaw analysis, and real time image enhancement. The information obtained from these operations is used to make accept/reject decisions. The decisions can be sent out through an RS-232 port to actuate sorting equipment. Retina Systems, Inc., Seymour, Connecticut, is one of the leading manufacturers of high speed, non-contact laser vision inspection systems. Recently, Retina made the decision to add an innovative feature to their inspection systems. This is a micrometer dial and a digital readout that makes it possible for the system to be easily adjusted to measure parts of different sizes. The basic idea was to take machines which had until that point been designed for a single part and make it possible to change them over to handle a wide range of sizes in a few seconds. |
Linear slides
This made it necessary to design into the inspection system a linear slide mechanism with extremely high accuracy to ensure that the laser mechanism does not move back and forth while it is translated by the micrometer dial. Retina Systems design engineers soon faced a serious challenge. The accuracy of the linear slides that they evaluated for the application was not high enough to maintain the quoted accuracy of the inspection system. The back and forth movement of the slide threw the laser out of alignment.
Then, Retina Systems engineers heard about N-series ball slides from Del-Tron, Bethel, Connecticut, that provide accuracy of ±0.0005" per inch of travel and repeatability of 0.0002"', making it possible to meet the critical accuracy requirements of the application. The accuracy figures are measured by comparison of the line of travel to a master straight edge, using a gage or indicator mounted on the slide. The mounting surfaces of the ball slide are machined flat and smooth, and parallel to each other and the line of motion.
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In order to provide even greater accuracy for this critical application Del-Tron engineers offered to add preload to the N-series slides that brings their accuracy up to ±0.0002 inches. Testing by Retina Systems showed that Del-Tron was able to maintain this level of accuracy on a consistent basis despite the fact that the slides cost only $75. |
Retina designed up to six of these slides into a typical systems designed to inspect thread fasteners, making it possible to adjust the lasers that measure over diameter, under diameter, under length, over length, and thread angle of the fasteners. With over 300 of these systems in the field, the slides have shown excellent reliability with not a single failure having been recorded. Del-Tron engineers say that when used at the rated load capacity and moderate speeds, a life of 10 million inches of travel can be expected. The expected life at one half the rated load is 100 million inches. Del-Tron ball slides require exceptionally low levels of maintenance because they are lightly lubricated during assembly, and are self-cleaning in normal service. Additional lubrication is not required, except for applications involving speeds above 1800 inches/min or continuous high loading.
Low friction
The micrometers dials can be rotated very easily because the ball slide assemblies use linear ball bearings to offer extraordinarily low friction. Much more commonly used rotary ball bearings have a higher coefficient of friction because the peripheral track is shorter on the inner race than on the outer race, causing the ball to skid on one or the other. Linear ball bearings run exactly equal distances on the pair of tracks in linear bearings, permitting the balls to run without friction, wear, or skidding at any preload. The typical coefficient of friction for Del-Tron ball slides is 0.003.
These new adjustable vision systems have demonstrated the ability to provide fast and reliable gaging of parts families. In many applications, test times have been reduced by 90% while changeover between parts of different sizes can be accomplished in under a minute. Thanks partly to the use of extremely high-accuracy slides, these laser vision systems are helping hundreds of manufacturers to meet needs for 100% gaging at a very reasonable cost.
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Del-Tron Precision began operations in 1974 supplying original equipment manufacturers with the world’s first commercially available subminiature ball slide. Since then, thousands of Del-Tron ball slides have been incorporated into medical analyzing and testing machines, semiconductor processing equipment, computer peripherals, assembly systems, scientific instruments and many other machines. Del-Tron’s modern corporate campus boasts highly automated computer controlled equipment and final inspection of 100% of all products has been Del-Tron’s policy since its inception. For more information, contact Del-Tron by phone at 800-245-5013, by fax at 203-778-2721 or by email: deltron@deltron.com. |
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