[PV Robot Front Line] Cleaner Robot by Sinfonia Technology (page 2)
Washes panel surfaces using water, brush, wiper
Fig. 7: Cleaning route examples. The robot has the capability to automatically come down to the lowest point of the panels and wait for a refill if it runs out of water or power halfway. (source: Sinfonia Technology)
Non-slip shoe sole material applied for work in the rain
The company sticked to the idea of cleaning panels with water. Some existing solar panel cleaner robots blow off the dust with air, but this method does not always sufficiently remove the dust. When water is used, on the other hand, most robots are externally supplied with water through a hose, etc.
Embedded with a built-in water tank, the "Resola" requires no incidental work using hoses and pipes. While the prototype 1 discharges water forward from the front of the robot, the mass-produced model delivers water by drops from under the body.
"We decided to make an improvement, finding out that water sometimes does not fall on the panel if it is discharged forward from the front and is then blown away by wind," Sinfonia Technology said.
Nakamura said, "What we paid the most attention to was workers' safety." The Resola can easily slip as it moves along wet sloping panels. Should the 20kg body slide down the panels toward a worker, the person could get injured. Accordingly, the quality of the material used in the crawler (the rubber belt on the drive wheels) that touches the panels becomes important.
Sinfonia Technology secured safe operation on panels sloping up to 20° by looking for a rubber material that hardly slips, adopting the rubber and the pattern used for the soles of shoes that prevent slipping even in rain (Fig. 9).
The "slip" issue in operation on a sloping surface could slightly affect the robot's straight drive and rotation. The Resola can calculate the amount of travel based on the number of crawler rotations and information gained from the built-in gyroscope. Even if it appears to be running stably, however, the crawlers are, in fact, slipping little by little, and, in many cases, the route tends to slightly curve downward. The robot is programmed to rotate 90°. However, in practice, it deviates slightly.
Image recognition drives cleaner run along panel 'lines'
Based on these circumstances, the route should be corrected by coordinating the information acquired through multiple sensors mounted on the robot. The Resola features an infrared CCD camera (on its front side), which allows the robot to detect the "lines" of panels through image processing, run straight by following the guidelines and correct the route when it starts to deviate (Fig. 10).
The "lines" are the two to four electrodes (bus bar electrodes) between and in cells (power generating elements). The Resola is not compatible with thin-film-type solar panels because they have no such "lines." With an inclination sensor built in, the robot detects and corrects the body's inclination with this sensor when rotating 90° at the end of the panel. In addition, it features an ultrasonic sensor on each corner of the body as the last measure to stop without falling from the edge of an array. This sensor is also used to detect the width of space between panels.
"Unexpectedly, it took a long time to program the CCD camera to accurately detect the support lines in various circumstances," Nakamura said.
While repeating test operations at different sites and times, it became difficult to detect the "lines" with the panel surface easily reflecting sunshine due to the sun's direction or the robot detecting the reflection of a building near the panels as "lines." Sinfonia Technology said it overcame these challenges by improving the image recognition software technology.