Optical Comparators

First free the two scale wires that run to the digital readout and coil them up and secure with a rubber band or wire twist tie.

Move the stage to the extreme left and right to enable removal of the four stage mounting screws.

Open the two lead screw quick releases and lift the stage off of the comparator holding it horizontal. CAUTION: If it is tilted it will slide quickly to one side or front to back and might fall or get damaged.

Take note: If there are any shims or washers under the stage at the mounting location. If shims or washers are present they will have to be replaced the same way they are located now.

Place the new stage on the comparator and then remove the shipping locks. CAUTION: If you tilt the stage during installation it will slide to the side and will damage the teeth in the quick release that engages the lead screw or will damage the stage.

Secure the stage to the optical comparator with the four mounting screws. Leave three of the screws loose and one just snug so that the stage can pivot around it. Turn the screen so that the vernier scale is at 0 or the screen pointer indicates that the horizontal line is set to its horizontal position. Place a pointer on the optical comparator stage so that it appears on the screen along the horizontal line. Now using the lowest magnification lens move the stage left and right using the quick release. If the pointer does not follow the screen horizontal line twist the stage so that the left and right stage travel matches the horizontal line. Then tighten all stage mounting screws and re-attach the scale cables.

Use the locking hardware removed from the new optical comparator stage to lock the old stage for return shipping.

Optical comparators can be very complex machines. However every optical comparator has similar design features and follows the same working principles. Optical comparators are used to magnify inspected part and cast its shadow onto a screen with chart to check for imperfections. Every optical comparator has a light source, which emits light beam. That light beam travels through prism and projects the shadow of inspected part. The shadow is then reflected through series of mirrors and finally ends up on chart screen. The operator can then compare the part against preset chart. Optical comparators have multiple lenses available, with different magnification steps. Zoom options vary from 5X to 500X. Screen sizes are also available in different sizes, from 10” to astonishing 80”. Combining screen size with optical zoom operator can inspect really big parts for really small anomalies. Another features found in modern optical comparators are digital readouts. These can vary from very simple, 1 or 2 axes digital readouts to more complicated 3 axes, programmable readouts, with geometric displays. More sophisticated digital readouts feature serial or parallel interfaces to interact with personal computers. In the nearest future those readouts can be expected to be equipped with more modern ports, such as usb, firewire and possibly Ethernet or lightpeak. Digital readouts with computer connection interfaces allow to transfer inspection results and to further export to CAD applications to manipulate extracted data.

Last important element found in optical comparators is stage. Optical comparator stages can be fully motorized or manual. Stages allow adjusting the position of inspected part. Inspected elements mounted on stage are resistant to external vibration providing more accurate results.

To summarize, the principle of optical comparator is to magnify inspected part. Basic elements found in most, if not every optical comparator are:

• Light source
• Mirrors
• Screen with chart ring
• Stage, motorized or manual
• Digital readout