[PV Robot Front Line] Panel Inspection Robot by Atox

Inspection services based on 'robot management' expertise

2014/06/20 13:05
Kenji Kaneko, Nikkei BP CleanTech Institute

A solar panel inspection robot "PV module inspection robot (Fig 1)" is being developed by Atox Co Ltd, with the cooperation of Nagaoka University of Technology, the National Institute of Advanced Industrial Science and Technology (AIST) and Togami Electric Manufacturing Co Ltd. Atox (Chuo-ku, Tokyo) is engaged in the maintenance of nuclear power plants and provides services related to radioactive materials. The robot is scheduled to be put into practical use within the next fiscal year at the earliest.

Development takes place at the laboratory (Energy Engineering Laboratory) of Noboru Yamada, associate professor at Nagaoka University of Technology.

Lifted up by disk, turned 90 degrees

A PV panel sheet is installed at an angle of 30° in the Yamada laboratory. In late May, I observed a demonstration run of the PV module inspection robot using this panel (Fig 2). The robot weighs 10 kg. It is lifted up and installed on a corner of the panel by a student in charge of the research. The main unit of the robot is 48cm x 39cm in size, but it looks bigger when it is placed on the panel.

When instructions are transmitted from a laptop PC, the crawlers (rubber belts around front/rear drive wheels) turn and the robot moves slowly in a transverse direction. When the robot reaches the edge of the panel, it stops and the main unit is lifted up slightly and turned 90° (Fig 3). Then, it comes down on the panel and starts moving in a longitudinal direction.

Turning technology known in robot contests

The following three targets were set for the development. (1) The robot does not slip when it is put on 30° solar panels. (2) The robot can move across gaps between panels (modules). (3) The computer judges the running route for autonomous travel. The three targets were realized by the prototype unit used for the demonstration run.

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Images are recognized by a CCD camera for running, and, according to the explanation, the robot can move over the gap between the panels on its own if the gap is less than 10cm. It can run on panels angled up to 30° if the surface condition (cleanliness) is good. According to the explanation, the friction force of the incorporated rubber was measured, and the contact area of the crawler that prevents the 10kg main unit from slipping was calculated. However, the friction force declines in rainy weather, making it impossible to run.

The most characteristic part of the running method is the turning technique that lifts up the main unit. In vehicles equipped with crawlers such as tanks and heavy machinery, directions are normally changed by an "ultra-pivotal brake turn," where crawlers on both sides are turned in directions opposite to each other. This turning method, however, features high load on the road surface. If the ultra-pivotal brake turn method is incorporated in the robot that travels on solar panels, the glass surface could be scratched.

Because of this reason, a turning mechanism that lifts up and turns the entire unit was incorporated in the center of the main body (Fig 4). A disk that is attached by rubber and about 25cm in diameter is pressed against the glass surface, and the main unit is lifted up and turned 90°, preventing the glass surface from being scratched by the crawlers (Fig 5).

"This kind of turning method is frequently used in models introduced at robot contests," Yamada said.

Travels along vertical, horizontal lines of panel

The robot can travel on its own on the panel surface because the model number and cell layout information of the panel to be inspected are stored in advance as an "address" and the current position in the address is obtained by processing the images of the CCD camera. The camera recognizes lattice patterns on the panel surface and judges the vertical lines and the horizontal lines by image processing.

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The "lattices" represent 2 to 4 electrode wires (bus bar electrodes) that exist in boundaries between cells (power generation element) or in cells. The vertical lines are support lines for straight travel, and the support line angle is corrected to zero after the start of turning. Meanwhile, the horizontal lines are used to estimate the position of the current cell against the original position, which is estimated based on the number of vertical lines the robot has crossed.

The prototype inspection robot cannot be used on thin-film panels made of CIS or amorphous (non-crystalline) silicon or back-contact-type crystalline silicon panels because these panels do not have bus bar electrode wires on the surface.

Mapping soundness of conductivity of each cell

The "cell line checker," faulty module identification equipment manufactured by Togami Electric MFG Co Ltd, is mounted on the front area of the robot to check for abnormalities in panels. The inspection sensor is mounted on an arm and can be moved to an arbitrary cell position (Fig 6). The inspection system is also used by Kazuhiko Kato at AIST, and the system has already been used for actual conductivity inspections.

A transmitter is installed in advance in the array connection terminal box, and a minor signal current is flowed in to receive the induction field generated in the module by the sensor. The wiring condition is obtained from the receiving sensitivity, and the conductivity of each cell is evaluated and mapped in three levels: "conductivity," "to be observed" and "no conductivity."

According to the explanation, inspection methods other than the conductivity inspection method are planned to be developed in the future and mounted on the robot to realize a variety of inspection methods. Also, currently, communication with the laptop PC is done via a cable, but the cable will be eliminated to realize wireless communication. At the same time, the system will be improved by downsizing and weight reduction.