Using Electro Optical Metrology in the Defence Industry

The problem: To offer a method of checking how straight a torpedo tube, and its diameter, to an accuracy of 0.05 mm (0.002 inches) with easy operation. The method should also not require the use of plug gauges, which are awkward to use, or require the ship to be dry docked whilst testing is undertaken.

The solution: The new system utilizes a trolley with a central glass target, which can be moved the length of the torpedo. A micro-alignment telescope, which has pre-set vertical and horizontal displacement coordinates, is used to measure the target straightness and this value is recorded. The diameter of the torpedo is determined at the same time using displacement transducers that are located on arms connected to the measurement head.

A graph of the torpedo’s internal profile is drawn using the data, which can then be compared with a standard template. By comparison it can be determined if the torpedo can pass cleanly through the barrel.

Aligning Gun Barrels

The problem: There are several different ways of checking the straightness of gun barrels. Gun barrels already contain an inherent ‘bend’, which is introduced during the production of the barrel. In addition to this, as a result of gravity over their service period, gun barrels exhibit drooping too. There is a need to measure the ‘bend’ and ‘droop’ of a barrel so it can be compensated for.

The solution: Taylor Hobson has developed an optical system, which is easy to operate and delivers accurate results when checking the straightness of gun and tank barrels. The system uses a telescope with a CCD device. A target or collimator is then mounted in a sledge arrangement and moved along the barrels length. The target should be designed to work with the spiral rifling found in gun barrels.

Micro-Aligning Telescopes to Improve Military Vehicle Performance

The problem: Modern light-armor military vehicles can move at very fast speeds and, as a result of this, it is important that there is good alignment in their drive shaft bearings, and that their suspension rollers are parallel and aligned square to the drive axis.

Bad alignment results in intense wear and unwanted vibrations which, if left unchecked, can result in track damage and breaking of the vehicle. Usually errors are only identified at the test ground, and a lot of dismantling must take place before the issues can be fixed.

The solution: Using a micro-aligning telescope the alignment of the system can be tested early in the manufacturing process. Testing is possible from as soon as the locating bores have been connected to the hull.

Figure 1 shows a method of checking the alignment using a micro-aligning telescope. The drive (between bores B and C) is taken to the two tracks independently via drive shafts which run through bores A, B, C and D. Standard alignment measurement methods are used to ensure that these bores are aligned, and the telescope is located centrally in bore A.

An optical square, located at the end of the telescope, is used to determine a right angle line of sight down the hull’s side. A sighting on a scale is then used to determine the distance between this line and the faces of the track suspension bores.

As different machines machine the hull’s two sides it is of high importance that the measurements from both sides are compared with one another. The two lines of sight must be co-planar if the hull is skewed, this is guaranteed using a Taylor Hobson Talyvel level on the optical square.

Figure 1

Figure 1

Aligning Periscopes

The problem: Periscopes, as the vision system of a submarine, are of extremely high importance. A periscope operating with misaligned bearings must use more motor power to be operated, and this excess power results in more noise generation, which could be detected by potential threats.

Submarine periscopes are approximately 10 meters long with a diameter of 25 centimeters, and they are moved (rotated, raised and lowered) using hydraulic motors that are mounted on bearings in the pressure hull and fin. Bearing alignment is important as misalignment can cause damage to the bearings, distort the periscope or even cause failure of the motors due to increased energy demands.

The solution: Alignment checks should always be carried out in respect to the line central to the bore of the lower bearing, found in pressure hull of the submarine. A Micro Alignment Telescope can be fixed using an adjustable support plate to the fin of the submarine. A target can then be fixed, using an adjustable target holder/spider fixture, to the lower bearing bore and a second target is also mounted. The Alignment Telescope is then focused on both of these targets, and everything else is adjusted to sit on the reference line.

Aligning Weapons on Fighter Aircraft (Harmonization)

The problem: The weapons on a fighter aircraft must be aligned with the aircraft’s longitudinal fuselage datum (LFD) to be effective – this process is called harmonization. Harmonization checks must be carried out following any changes to the nose cone, the display unit, the front windscreen, the radar mainframe or the navigational system.

The solution: The Taylor Hobson Micro Alignment Telescope can be used for harmonization, to achieve this telescopes and collimators (which give a line of sight) are mounted on a sighting frame and alignment-checking jig. The use of machine vision systems, such as CCD or CCTV, to do this removes human error.

During the manufacture of the aircraft the gun mounting points are aligned to the LFD and this alignment can be sued as the datum. An aircraft sighting board is fixed to the aircraft’s front and an alignment jig with attached telescope is fixed to the gun mounts.

A clinometer is then used to check the inclination of the aircraft roll and checking jig. The first step in harmonization is aligning the LFD jig with the ATB (Aircraft Target Board) to give a reliable datum. Once a datum is established the ATB can then be used to align the PDU (Pilots Display Unit) and INU (Internal Navigation Unit).

Aligning the ATB (Aircraft Target Board)

Micro Alignment Telescopes, which are focused to infinity, are fixed to the LFD sighting frame and are then sighted onto a collimator fixed on the adjacent ATB bracket. The assembly of the frame is then modified in azimuth and elevation so that the telescope crosslines center towards the collimator graticules. Any movements following this setting is recorded for error correction.

Checking the Alignment of the INU (Internal Navigational Unit)

A telescope is mounted in the INU sighting jig which is then aligned to the adjacent ATB collimator. Re-shimming is then used to correct any misalignments. The same procedure can be carried out to align the FLIR and PDU.

Similar problems are encountered when harmonizing smaller systems such as handheld antitank guns which have issues with parallelism setting. In these situations the tracer rifle, sighting aid and the missile inside must all be parallel to one another, which can be achieved using autocollimation.

Aligning Helicopter Drive Shafts

The drive shaft and gearbox of a helicopter must be aligned correctly, and this can be achieved using a Taylor Hobson Micro Alignment Telescope and mirror. The Taylor Hobson Telescope can focus from zero to infinity in a straight line, allowing components to be placed square to this line. Firstly, the telescope is placed square to the mirror target:

Following this it is then placed in line with the mirror targets center:

Leveling Missile Platforms

The problem: Many missile systems must have a precise datum for ground equipment before launch can occur.

The solution: Taylor Hobson’s Talyvel electronic level can provide a reference to gravity in two directions, for use in any True centrerline location before launch.

This information has been sourced, reviewed and adapted from materials provided by Taylor Hobson.

For more information on this source, please visit Taylor Hobson.

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