Drives and Controls Magazine
19.9mm-tall robot cuts generator inspections to 6 days
Published:  28 February, 2017

Mitsubishi Electric has developed a 19.9mm-tall robot that can inspect electricity generators by passing through the narrow gap between the rotor and stator. By eliminating the need to remove the rotor for inspections, it cuts the time taken for these inspections – which typically happen once every four years – from around 34 days, to just six days.

Because of its accuracy, Mitsubishi says that the robot will also allow inspections can be carried out less frequently and help operators to avoid stocking parts they may not need. As well as reducing inspection costs, it says that the device will improve both the reliability and availability of power generators.

Existing inspection robots are typically about 30mm high and are thus unable to pass through the narrow gap between the rotor and stator in about a third of Mitsubishi's generators. The new robot incorporates a proprietary propulsion mechanism comprising a crawler belt and flat plate to achieve its 19.9mm height. It can inspect any of Mitsubishi's mid-sized or large generators.

Vibrations from the propulsion system are said to be low, allowing accurate data to be collected from the generator. The tests performed include assessments of the stator wedge tightness, visual examinations, and core insulation inspections.

The robot incorporates a cam-based mechanism that taps the stator to determine how tightly its wedges are installed. This system delivers a force that is said to be 10 times higher than a conventional mechanism. The tapping test uses vibration analysis to detect five levels of stator wedge tightness – compared to the three levels detected by a conventional inspection device.

Mitsubishi’s generator inspection robot squeezes into the narrow gap between the rotor and stator

Mitsubishi has three patents pending in Japan and elsewhere for aspects of the inspection robot, including one for the propulsion mechanism and two for detecting the tightness of the stator wedges.

•  ABB has an even thinner (8.5mm) inspection robot that specialises in visual inspections.