Troubleshooting of Common Faults in Biological Microscope
1. Troubleshooting of common faults
1. Self-slip of the lens barrel: This is one of the frequent failures of biological microscopes. The solution for the microscope with the sleeve structure can be divided into two steps.
Step 1: Hold the two coarse adjustment handwheels with both hands, and tighten them relatively firmly. See if the problem can be solved. If the problem cannot be solved, use a special double-column wrench to unscrew a coarse adjustment handwheel and add a piece of friction plate. If it is too thick, replace it with a thinner slice. The rotation of the hand wheel is effortless, the lens barrel moves up and down easily, and does not slide down by itself. The friction sheet can be punched out with a puncher from waste photographic film and a soft plastic sheet less than 1 mm thick.
Step 2: Check the meshing state of the gear on the coarse adjustment handwheel shaft and the rack on the lens barrel. The up and down movement of the lens barrel is accomplished by the gear driving the rack. Theoretically speaking, the optimal meshing state of the gear and the rack is that the index line of the rack is tangent to the index circle of the gear. In this state, the gear rotates easily and the wear on the rack is minimal? Now there is a wrong way to add a spacer behind the rack so that the rack presses the gear tightly to prevent the lens barrel from sliding down. At this time, the index line of the rack intersects the index circle of the gear, and the tooth tips of the gear and the rack are tightly against the roots of each other. When the gears rotate, there will be severe grinding against each other. Since the rack is made of copper material, the gear is made of steel material. Therefore, the mutual grinding will damage the teeth on the rack, and a lot of copper scrap will be produced on the gear and the rack. Eventually the rack will wear out so badly that it cannot be used. Therefore, you must not use the rack to prevent the lens barrel from sliding down. Solving the problem of the lens barrel sliding down by itself can only be achieved by increasing the friction between the coarse adjustment hand wheel and the eccentric shaft sleeve. But there is one exception, that is, the index line of the rack is far away from the index circle of the gear. At this time, when the coarse adjustment handwheel is turned, the phenomenon of idling and slipping will also occur, which will affect the up and down movement of the lens barrel. If this is done by adjusting the eccentric shaft sleeve of the coarse adjustment handwheel, the meshing distance between the gear and the rack cannot be adjusted. It can only be solved by adding an appropriate sheet behind the rack. The standard for adjusting the meshing distance between the gear and the rack by adding shims is: it is not difficult to turn the coarse adjustment handwheel, but it does not run idly.
After adjusting the distance, add some neutral grease between the gear and the rack. Just let the lens barrel move up and down a few times. Finally, the two compression screws on the eccentric shaft sleeve must be tightened. Otherwise, when the coarse adjustment handwheel is turned, the eccentric shaft sleeve may rotate accordingly, and the rack is stuck, so that the mirror cannot move up and down. At this time, if the force of turning the coarse adjustment handwheel is too large, the rack and eccentric shaft sleeve may be damaged. After tightening the compression screw, if it is found that the eccentric shaft sleeve still rotates. This is because the thread of the screw hole of the compression screw has not been improved. Because the manufacturer changes the thread by machine, there are often one or two threads that have not been changed in place. At this time, even if the compression screw cannot be screwed in place, the eccentric bushing will not be pressed tightly. If such a fault is found, the problem can be solved as long as the thread of the screw hole is tapped with an M3 tap. I used this method to completely solve the problem of eccentric shaft sleeve rotation of 30 biological microscopes in our school.
After completing the above steps one by one, the problem of the lens barrel sliding down by itself is basically completely solved.
2. The positioning failure of the shutter: This may be caused by the fixing screw of the shutter being too loose, and the positioning marbles escaping from the positioning hole. Just put the marble back into the positioning hole and tighten the fixing screw. If it is difficult for the light shield to rotate after tightening, it is necessary to add a washer between the light shield and the stage. After the thickness of the washer is tightened with the screw, the shutter can rotate easily, the positioning marbles will not escape, and the positioning of the shutter is correct.
3. Difficulty in rotating the objective lens converter or failure in positioning: Difficulty in rotating the converter may be due to too tight fixing screws. Makes turning difficult and can damage parts. If it is too loose, the bearing marbles inside will fall off the track and squeeze together, which also makes it difficult to rotate; in addition, the marbles are likely to escape to the outside, and the diameter of the marbles is only one millimeter, so it is easy to lose. The tightness of the fixing screws shall be subject to the fact that the converter can be rotated easily and there is no looseness in the vertical direction. After adjusting the fixing screw, the locking screw should be locked immediately. Otherwise, after the converter turns, problems will occur again.
The positioning failure of the converter may sometimes be caused by the fracture or elastic deformation of the positioning pin. Generally, it only needs to be replaced once.
4. The lens of the eyepiece and objective lens is polluted or mildewed: After a period of use of most microscopes, the outside of the lens will be stained or mildewed. Especially the high-magnification objective lens 40X is very easy to be polluted by sugar solution when doing the experiment of "Observation of plasmolysis and recovery of plant cells". Mildew will occur if the lens is contaminated and not cleaned in time. The way to deal with it is to use a clean and soft silk cloth dipped in warm water to wash away pollutants such as sugar solution, then dry it with a dry silk cloth, then use long-fiber absorbent cotton dipped in some lens cleaning solution to clean it, and finally blow dry it with a blower. It should be noted that the cleaning solution must not penetrate into the inside of the objective lens. Because in order to achieve the required magnification, the lenses of the high-magnification objective lens need to be glued together tightly. Is the glue transparent and very violent? Once this layer of glue is dissolved by solvents such as alcohol and ether, when the light passes through the two lenses, the optical path will change. The observation effect will be greatly affected. Therefore, do not let solvents such as alcohol and ether penetrate into the interior of the objective lens during cleaning. ?
5. The frame and mirror hips cannot be fixed when they are tilted: this is caused by the loosening of the connecting screws between the frame and the base. Use a special double-head wrench or use needle-nosed pliers to clamp the two holes of the double-eye nut and tighten it firmly. If the problem is not solved after tightening, it is necessary to add an appropriate gasket to the nut to solve it.
If the lenses inside the eyepiece and objective lens are polluted or mildewed, they must be disassembled and cleaned. The eyepiece can be directly unscrewed and removed for cleaning. However, the structure of the objective lens is more complicated, and the stacking of the lenses and the distance between the lenses have very strict requirements, and the precision is also high. The manufacturer is calibrated and positioned during assembly. Therefore, after being disassembled and cleaned, it must be assembled strictly as it is.
The lenses of biological microscopes are all made of precision-processed optical glass sheets. In order to increase the light transmittance, a thin light-transmitting film needs to be coated on both sides of the optical glass sheets. In this way, the light transmittance can reach 97%-98%. The surface of this layer of light-transmitting film is very flat and smooth, and it is very rough? Once the surface of the light-transmitting film is scratched and left traces, its light transmittance will be greatly affected. Observation becomes blurry. Therefore, when wiping the lens, be sure to wipe it gently with a clean soft silk cloth or a clean brush. If you wipe it with lens cleaning paper, wipe it gently to avoid damage to the light-transmitting film.
