Optical Comparators

How internal edge detection works.

Light from the objective lens (main optical comparator lens) exits the back of the lens and passes through a “hot” mirror. This mirror reflects the infrared light and some visible light and lets most of the visible light pass through to form an image on the optical comparator screen. The light reflected by the hot mirror is directed up to a small mirror located inside the top of the comparator. From there it is directed down and onto a fiber optic cable located in the left front section of the optical comparator. In effect the fiber optic cable sees in infrared light anything that passes over the center cross lines of the screen. You will see the image on the screen in visible light.

As the edge of the part you are measuring passes over the cross lines located in the center of the screen the edge sensor (if turned on) will detect that the cross line area has moved from light to dark and will enter a point on the readout. Then as you continue moving the part the sensor will detect that the cross-hair area has changed from dark to light and enter another point.

By using internal edge detection you can speed up the inspection process and achieve greater accuracy of measured parts by eliminating some of the human error associated with lining up the part on the cross lines by eye.

Before doing any work on electric parts of optical comparator make sure that power is off or power cord is disconnected.

Optical comparator profile lamp

To change the optical comparator lamp first use the two thumbscrews located on top of the lamp house to remove the lamp house cover. Remove the bulb by grasping and pulling the bulb directly up. Remove the new optical comparator replacement bulb from its box, and slide the new bulb in place. Switch main power on, remove the objective lens, and set lamp intensity to low. Verify that the lamp filament projected on the optical comparator screen is centered over the cross-hairs. Re-seat lamp and or adjust holder if required.

If the glass lamp is accidentally marked, remove the marks immediately by swabbing with methanol. The optical comparator profile lamp operates at a high temperature and any finger marks will be “burned” into the surface of the quartz reducing the output and life of the lamp.

Optical comparator surface illumination lamp

To change the surface illumination lamp first remove the lamp house cover.

To remove the bulb, grasp and rotate the bulb ejection wire to eject bulb. Remove the new replacement bulb from its box, flip the bulb ejector wire down and slide the new bulb in place. Switch main power on and set optical comparator surface illumination lamp intensity to low. Verify that the projected illumination is centered on the end of the fiber optic cable. Re-seat lamp and or adjust holder ( by bending face ) if required.

Same caution steps apply to optical comparator surface illumination lamp as to profile lamp.

Surface Illumination

Optical comparators illumination of surface features on solid objects is achieved through the use of high intensity fiber optic light guides. These guides are adjustable and can be extended by pulling on the cable ends protruding from either side of the lens mounts. They may be secured in place with the clamping screws on the side of each of the guide blocks.

For the brightest reflected image, place the light guides as close as possible to the face of the component to be inspected. Where components have a directional surface finish, e.g. ground faces, the surface texture should be placed at right angles to the table, this will give the brightest reflected image on the screen.

As the fiber optic cable is a “cold light” source, the heat radiated to the component under test is minimal.

Manual Table Adjustment

The X axis of the stage has a quick release for coarse motion. This feature should not be used to move the stage during a measuring routine. Also, when the quick release is engaged, the control knob of the X axis is disabled.

To engage the quick release, rotate the lever to the furthest position to the right. To re-engage the control knob rotate the lever to the furthest left position.

Stage Helix Adjustment

The top plate of the optical comparator stage has a helix adjustment, which allows the top plate of the stage to be rotated. To do this the 2 locking clamps located beneath the stage must first be loosened. The stage plate can now be rotated ±15 degrees. The helix indicator shows the amount of rotation in 5’ increments. Once the desired helix is adjusted tighten the locking clamps to hold this position.
To restore the helix to the zero (0) position, loosen the locking clamp rotate the helix adjustment to zero.

Vertical Stage Adjustment

Vertical adjustment of the optical comparator work stage is by means of the large hand wheel on the left below the work stage knee.

Screen Angular Measurement

The electronic venire protractor screen, consists of a frosted glass screen divided into four equal quadrants by precision cross lines. The screen is rotated by means of a small hand wheel on the right of the screen. The standard electronic venire protractor can then be used to determine angles with 1 minute resolution.

Electronic Rotary Protractor

16H optical comparators are equipped with a digital electronic rotary screen protractor. These compact units display the current rotary position of the screen and utilizes non-volatile memory to permanently store the calibration data regardless of power loss. Optical comparators display rotary position in either degrees and minutes or degrees and 1/100 of a degree.