The most common commercial solutions to inspect through holes, narrow gaps or pipes are the videoscopes. There are multiple types depending on the field of application or the underlying technology. Endoscope is a medical apparatus referred commonly to the inspection of the human body. Borescope is an optical device consisting of a rigid or flexible tube with an eyepiece on one end, an objective lens on the other linked together by a relay optical system in between. The optical system in some instances is surrounded by optical fibres used for illumination of the remote object. Videoscopes are an advanced type of borescope that houses a very small CCD chip embedded into the tip of the scope. The video image is relayed from the distal tip and focusable lens assembly back to the display via internal wiring.
Fibrescopes are videoscopes made with fibreoptics where each fibre constitutes a unique pixel. They do not present the same visual quality as their CCD or CMOS counterparts and their ability to bend is more reduced.
Most of the videoscopes are very thin, allowing the inspection of even the smaller pipes. They usually have an articulated head with one or two degrees of freedom which allow the change of direction and the navigation of junctions. The articulation of the head is operated typically with pneumatic pressure or electronically via shape memory allows as shown in Figure 2. On the later method, a couple of wires control each degree of freedom by the contraction of one and compression of the other and viceversa. There are also other methods for articulating the borescopes as the power as the direct articulation by the thumb, power assisted, servo articulation, direct geared articulation, and multi-articulation. With the motor driven articulation, one does not feel articulation and if the unit is not centered before removing it from an inspection, the user risks damaging the articulation cables or motors (which are very expensive to repair). The cons are that, with a four-way knob system, the user typically needs a scope holder or must hold the scope in one hand while articulating with the other. With the lever type, one has the best of both, since the user can hold the scope and operate the articulation easily with one finger, still have a feel for the movement and reduce the risk of damaging the articulation cable or motor. This is because the unit can be centered once one removes his or her finger from the lever . However, a 2 dof articulation should be enough to navigate inside most pipes.
The inspection length varies significantly between different videoscopes models and manufacturers and could constitute one of the best options for in-pipe inspection. The main drawback of these devices is that they are usually manually inserted and thus, the inspection length could be limited by the friction caused by the pipe and the number of bends.
Some videoscopes are able to mount different set of tooling for remote manipulation such as retrieving small objects, capturing magnetic elements, etc.
Olympus has developed a propulsion system called MPP04-01 Airgun (Figure 3) to push and pull Eddy current based probes. It features a grooved design to reduce pushing force in tube end and to improve durability. It is ideal for steam condensers, coolers, and heat exchangers.