Focus Adjustment and Line Alignment Procedures for Tool Microscopes
When using a tool microscope, accurate focusing and aiming are necessary. The measurement error of the same measured object is generally within the range of 1-2 microns. Therefore, only correct focusing and aiming can ensure the accuracy of the measurement results. The correct focusing and alignment (pressure line) methods are introduced as follows:
One Focusing method
1. Firstly, adjust the eyepiece's visual acuity, that is, adjust the clear engraved line image that can be observed in the eyepiece's field of view. If the measurer cannot obtain a clear engraved line image in the eyepiece's field of view, adjust the eyepiece's visual acuity circle to match the measurer's vision, so as to obtain a clear meter line.
2. Move the central microscope with the focusing handwheel to obtain a clear image of the object contour in the eyepiece field of view, and then move the longitudinal and transverse workbenches for alignment. If the measurer's eyes shake up and down, left and right in the eyepiece and no relative movement between the object image and the crosshair is found in the field of view, it indicates that the measured object is correctly imaged on the crosshair, and measurement can be carried out at this time. If there is relative movement between the object image and the reticle, it indicates that the microscope is not focused properly and further careful focusing is needed to make the object image and reticle on the same plane.
II Line pressing method
Line alignment (pressure line) is the process of overlapping the contour edge of the image of the measured object with a meter line, also known as aiming. For a specific tool microscope, the accuracy of the instrument is certain. To achieve high and reliable measurement accuracy, it largely depends on the correct alignment method. There are two alignment methods, one is gap alignment method and the other is overlap alignment method.
1. Gap to line method is suitable for angle measurement. When measuring the angle, if any dotted line of the meter line is placed against one side of the measured angle in the field of view, a narrow gap is maintained between the dotted line of the meter line and the edge of the measured angle. The measurer determines the degree of alignment between the dotted line of the meter line and the edge of the measured object image based on the uniformity of the gap size. If the above alignment method is not used and the method of overlapping with the image edge is directly adopted, it will not only make it difficult for the measurer to align, but also increase the measurement error. At this point, the image of the contour of the tested object in the field of view is not a thin line, but a light and dark contour, and the engraved lines of the meter line have a certain width. If they are overlapped for measurement, it will inevitably result in significant alignment errors, especially when the edges of the measured angle are relatively short, this situation becomes even more severe. Therefore, the gap alignment method should be used for angle measurement.
2. Overlapping alignment method. If the above-mentioned gap alignment method is still used during length measurement, it will increase the length measurement error. The reason is that the gap cannot be measured and is included in the measured length measurement value. Therefore, the overlapping line method is used for length measurement. It is to overlap the dashed line of the meter line exactly with the edge of the contour image, so that half of the dashed line is inside the contour image and the other half is outside the image. When aligning, the center of the dotted line of the meter line should be taken as the reference, and its extension should be used as the reference to obtain accurate measurement results.
