1. Outline

Japanese agriculture has encountered “a critically increasing number of farmers giving up farming” because of their aging. Under such a circumstance, a consolidation and upscale of farmlands per responsible farmer has been accelerated. In order for the responsible farmers to address a shortage of labor, an improvement in work efficiency, and laborsaving, the responsible farmers started a transition to the smart agriculture utilizing ICT which could be a next-generation agriculture.
A combine harvester (hereinafter, simply referred to as “combine”) is an agricultural machine which simultaneously performs harvesting and threshing of grain, such as rice and wheat. However, since an expert skill is required for operating the combine, the responsible farmers have demanded a development of a combine which allows anybody including an unskilled person to “easily harvest the grain without waste” by “a simple operation.” In order to meet the demand, a combine with an automatic driving assist function utilizing RTK-GNSS was developed (Figure 1). With this combine, although a worker needs to board on the combine for monitoring work and safety, since the harvest work can be done with hands free in which a driving operation of the combine is not necessary, it can allow the unskilled persons to utilize this combine. In addition, the skilled workers are unleashed from the harvest work which is high in labor load, thereby incredibly reducing their labor.

Figure 1. WRH1200A: Combine with Automatic Driving Assist Function

2. Developing Technology

2.1 Automatic Generating Technology of Field Map
Based on a traveling trace when harvesting along the inside of a field ridge by a manual drive (calculated from the position and direction of RTK-GNSS), and an accurate traveling trace obtained from work information for determining whether the combine is currently harvesting or not, the center of gravity of the field is calculated. Next, a straight line approximation of the traveling trace is performed using the least-squares method to determine a field outline (a trace separated from the center of gravity) and an inside, non-harvested area (a trace close to the center of gravity), and a field map is generated automatically (Figure 2).

Figure 2. Automatic Generation of Field Map

2.2 Optimal Route Calculation Technology
A lattice-like travelable lines which take a swath of the combine into consideration were prepared on the basis of each side of the non-harvested area, and an algorithm is established for automatically and sequentially determining an efficient traveling line so that redundant traveling distance is reduced to the minimum by using the swath, a turning radius, and a vehicle size, as parameters.
Moreover, a harvest weight per unit area is measured using a yield sensor for measuring the weight of a grain storage tank, and a harvestable traveling distance until the tank reaches “full” is estimated. The algorithm then determines whether another trip is possible on the basis of a discharge position at which the grain is to be discharged, and moves the combine to the discharge position at the optimal timing.

2.3 Automatic Driving Control Technology
From the highly-precise positional and directional information obtained from a built-in RTK-GNSS unit of an Inertial Measurement Unit (IMU), a positional deviation and a directional deviation from a target course are calculated, and a steering control is performed so that each deviation becomes the minimum (Figure 3).
Since the turning performance of the combine is greatly influenced also by a change in the lateral weight balance due to the hardness of the field and the weight of the grain storage tank, by adding to this technology an auto gain function which detects overs and shorts in an amount of a steering instruction every turn and fluctuates the amount of instruction, the condition adaptable range is extended.

Figure 3. Steering Control

3. Postscript
It is the very first combine in the industry which has the automatic driving assist function utilizing the RTK-GNSS. This combine solves the problem of the responsible farmers without expert skills, and contributes to the laborsaving of the responsible farmers. Since it is able to shorten their working hours about 10% by the optimal route calculation function, the resulting surplus time can be reassigned to the business expansion.
We are now sure that this combine will become an aid of the restoration of the Japanese agriculture which bears food security, by introducing the automatic driving assist combine into the agricultural market to promote the smart agriculture.

(reference)
* Published: Collected papers of Japan Society of Mechanical Engineers, 77-777, Volume A (2012-12), Page 1234

Ten Okuyama*1
Tetsuya Nakajima*2
Takashi Nakabayashi*2
Shu Yoshida*2
Tadahiro Ishikawa*2

*1 Regular member, KUBOTA CORP. (1-2-47, Shikitsu-higashi, Naniwa-ku, Osaka-shi, 556-8601)
*2 Non-member, KUBOTA CORP. (1-2-47, Shikitsu-higashi, Naniwa-ku, Osaka-shi, 556-8601)