Vol.3 No.4 2011

42/72

Research paper : How car navigation systems have been put into practical use (H. Ikeda et al.)−283−Synthesiology - English edition Vol.3 No.4 (2011) map-matching capacity limits being exceeded. We believed it was necessary to improve the accuracy of the rotation angle sensors. Thus, we explored the ways to reduce production costs of the optical fiber gyro (sample priced at millions of yen) that had been developed at Sumitomo Electric at that time for robots used to work in adverse conditions, and to remodel this gyro into one for the NAVS. Fortunately, we ourselves could produce most parts required for the optical fiber gyro. We mass-produced each part at a low cost and lowered precision to reduce the cost to a level acceptable for NAVS applications. A double digit cost reduction was somehow achieved, and it became possible to install it in the vehicle. The introduction of the optical fiber gyro contributed to improved performance to a level where the NAVS would get lost only once or so per 200 km driving.2) Vibration gyro[7]The GPS became available for NAVS in 1990. Since then, optical fiber gyro-level accuracy has not been highly required for rotation angle sensors. Instead, lower-cost sensors have been in demand. As vibration gyros designed to prevent camera shake emerged on the market, we explored the possibility of using them for NAVS. Vibration gyros designed for cameras were aimed at detecting hand motion, with no consideration given to offset drifts occurring over an extended period of time. We drew up specifications and requested sensor suppliers to develop a vibration gyro for NAVS. It has turned out that Murata Manufacturing Co., Ltd. was able to produce an almost satisfactory gyro sensor, enabling us to replace the optical fiber gyro with a vibration gyro. We did not solely rely on the performance improvement of the vibration gyro itself, but also provided the gyro-handling software with additional functions such as offset drift estimation during driving and estimation of the drift amount by gyro temperature measurement. Because of these software capabilities, the vibration gyro we employed was smaller and less expensive than the optical fiber gyro, yet was five times greater in zero offset.3.2 Development of route calculation and guidance technologiesSince accurate detection of the current location was achieved, there were demands for capabilities to determine the optimal route up to the destination and to guide the vehicle to turn right or left during driving. Route computation algorithms were developed largely in academic laboratories. Prerequisites to route computation were often huge memory and map data storage allowing for fast readout. In contrast, with NAVS it was necessary to quickly compute 500 km routes between Tokyo and Osaka using the base speed of CD-ROM and lowest cost memory. We made route computation fast, spending only 30 seconds, instead of the 30 minutes required by the conventional method.3.3 Development of digital road maps(1) Providing a map databaseMap-matching requires digitized map data, in the configuration of which an intersection and section between intersections are referred to as a node and a link, respectively. Map-matching data contains road connection relations, one-way traffic regulations and other information. Thus, it is far more elaborate data than map data structured solely for display purposes. In Fig. 3, nodes are intersections and curves on roads and come with information such as coordinates, intersection names and connected links. Links are vector data in which nodes are connected by straight lines, containing information such as road attributes and widths.Figure 4 shows an example of actual roads. Roads connecting to an expressway constitute many links that imitate actual curves. Figure 5 shows a displayed map, which contains water systems, building shapes, place names, facility names and other information for readability.Fig. 3 Road configuration data (Courtesy: Sumitomo Electric Industries, Ltd.)informationRoad typeRoad widthIntersection nameXX degreeseast longitudeYY degreesnorth latitudeNodeLinkNode and link structureRegulation informationLink connectionFig. 4 Plotting example of actual roads (Courtesy: Sumitomo Electric Industries, Ltd.)Fig. 5 Example of map data display(Courtesy: Sumitomo Electric Industries, Ltd.)

※このページを正しく表示するにはFlashPlayer9以上が必要です