- SPECIAL REPORTS
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Why is cleaning or overhauling your equipment even necessary? The instrument is used on jobsites where it is exposed to blowing dust and inclement weather. The dust and dirt collect on and inside the instrument, especially around the bearings that have oil or grease exposed. The dirt increases the wear on critical components, reducing accuracy. The lubricants in the instrument dry out and must be replaced to minimize bearing wear. Over time, the instrument optics and electronics can lose adjustment.
Ingenuity Inc. (Sparks, Nev.) typically performs three types of service on an instrument: a complete overhaul, a minor cleaning and adjust-only or optical collimation. When an instrument comes in for service, it is first evaluated. The instrument is checked for any pre-existing problems, and its condition is evaluated to determine the level of service it needs. The amount of dust and dirt on and inside the instrument, the extent of wear on the tangents and bearings, and any repairs that are needed determine what service is to be performed. It is checked for tight or very loose tangents and excess movement in the focus assemblies and telescope bearings. If the instrument is in good condition and has no major problems, a minor cleaning or adjust-only may be all that is needed. On the other hand, if it is extremely dirty, showing signs of wear on the bearings or other critical mechanical assemblies, or requires disassembly for other repairs, it would be recommended for the complete service or complete overhaul.
Minor CleaningThe minor cleaning involves cleaning the tribrach, the tangents, the focus assemblies, the exterior of the instrument, as well as the case and accessories. These assemblies receive the most wear and are the components that have the most exposure to dust and dirt. The tribrach and tangents are removed from the instrument and disassembled. The tribrach level screws and tangent parts are marked during disassembly to ensure matching parts are put back together during reassembly. The fine threads develop individual wear patterns during use and must be matched up during reassembly. If they are not matched up, the wear increases and the threads can even bind. The focus assembly is disassembled and cleaned. This keeps it clean and smooth and ensures your line of sight does not change while focusing the instrument. Even the wrong grease in the telescope tube can cause errors that are not easily traceable. After disassembly, the metal parts are run through an ultrasonic solvent bath and then washed clean. The optics and plastic parts are cleaned by hand so they will not be damaged in the solvent. The clean parts are reassembled with new, wide temperature range lubricants. The reassembled tangents and focus assemblies are put back in the instrument, the tribrach goes on, the exterior is cleaned and the instrument is ready for final collimation.
Complete OverhaulThe complete overhaul is much more involved. After the initial evaluation, the instrument is completely disassembled. Again, many of the parts are marked to assure they are properly matched up when reassembled. On any optical angle reading instruments, the prisms and optical assemblies have their positions marked to make the optical reassembly and adjustment easier. Electronic instrument angle reading systems and the circle positions are marked to make reassembly and adjustment easier. Once the instrument is taken apart, most of the parts go through the ultrasonic solvent bath and washing process.
The remaining optics, circles, electronics and other miscellaneous parts that cannot be immersed are cleaned by hand. During reassembly, some of the moving parts or bearings may need to be refit. Excessive telescope side play is one of the most common problems seen in bearing wear. Critical bearing components are generally precisely ground steel assemblies. Whether free floating or preloaded with pressure, steel bearing side play may ultimately depend on a brass thrust surface. This surface wears and may need to be refit or in some cases replaced. Bearings, even steel, do wear and can allow angle reading optics to shift from the original adjusted position. Realignment in optical instruments is done by adjusting internal prisms and lens assemblies that transmit and focus the image. Electronic angle reading systems are realigned electronically, usually with an oscilloscope and special test box or on/off board computer software. Bearing play is so critical for electronic instruments that troubleshooting and adjustments can only be done with electronic test equipment.
Electronic instruments require adjustment of circuit board components to meet manufacturers' specified waveforms. Electronic total stations may require focus and alignment of the EDM assembly. All the other components, such as compensators and micrometers, are reassembled and adjusted to factory specifications. Since the instrument was completely disassembled, everything must be readjusted. Final collimation and calibration are performed on a collimator system that allows infinity targets to be observed inside the instrument facility.
Which one of these services should your instrument receive? We typically alternate between the two cleaning services. This lets us perform the quicker and less expensive minor clean on the parts of the instrument that need it the most. The next time the instrument is in for service, it may get the complete overhaul. Of course, we evaluate each instrument before starting any work to make sure it gets the service it needs.
How often should your instrument be serviced?That depends on how much use it gets and the conditions to which it is exposed. In our experience, having your instrument serviced once a year is necessary to keep it in good condition. Again, we alternate the services so your instrument gets a complete overhaul about every two to three years.
Often, an instrument doesn't come into the shop until it fails. At this point, service is critical. There are several signs that your instrument is overdue for service. Tangent or tribrach screws that feel loose and turn very easily may have no lubrication left and need to be cleaned and lubricated to avoid further problems. On the other hand, tangent or tribrach screws that are tight may indicate that threads are binding up and need immediate cleaning and lubrication. These problems can be corrected by the minor cleaning. Some symptoms indicate that serious problems are developing. Check your telescope for side play by gently moving it side to side. If there is excessive movement, the bearing lubrication is drying out, or the bearings are worn and the instrument needs to be serviced. Any unusual noise in any of the motions usually indicates excessive dirt. The instrument may display an occasional error message that appears to be unrelated to your current operation. Any of these symptoms indicate the instrument may need a complete overhaul.
Before you balk at the cost of having your instrument serviced, consider a few points. If you let the instrument go too long you might be looking at replacing parts such as bearings or encoders. This means repair bills possibly approaching half of what the instrument is worth. Instrument failure when your crew is under the gun can be costly. The trip to the repair shop and the wait for a rental instrument means downtime, not to mention the damage to your reputation. Finally, our favorite comparison is to that of your vehicle. You wash it occasionally, you get the oil and filter changed several times a year, and you might tune it up every couple of years. If this doesn't happen, the vehicle doesn't go anywhere after a certain point. You know that changing the oil regularly is much cheaper than rebuilding an engine and replacing crankshaft bearings. We'll let you draw the parallels to your total station.