ASAE Conference Proceeding
This is not a peer-reviewed article.
Automated Rice Transplanter with GPS and FOG
Y. Nagasaka, N. Umeda, Y. Kanetai National Agriculture Research Center, Japan
Pp. 190-195 in Automation Technology for Off-Road Equipment (ATOE) Proceedings of the 26-27 July 2002 Conference (Chicago, Illinois, USA), ed. Qin Zhang ,Pub. date 6 July 2002 . ASAE Pub #701P0509
The authors developed an automated 6-row rice transplanter. It has RTKGPS to locate precise position, FOG sensors to measures direction and actuators to control steering, engine throttle, clutch, brake and so on. RTKGPS has 3cm precision at 10Hz data output rate and FOG sensors are issued to restore the inclination of the vehicle. Main computer synchronizes RTKGPS position data with FOG data then it corrects the position error caused by the vehicle inclination. All actuators are controlled by a programmable logic controller (PLC). All control data is sent form main computer to PLC through RS232C.
The drift of the FOG sensor was corrected by the using position data. To eliminate the influence of the drift, first, the deviation from the desired path calculated by the yaw angle and vehicle speed was compared with the deviation calculated by GPS data. Then the drift of the heading angle was calculated. The influence of the FOG drift can be eliminated, the authors can correct the FOG drift and the initial error of heading angle and can make long time operation continuously.
The experiment was conducted 4 days after puddling. The deviation from the desired straight path was less than 10cm at 0.8m/s of travel velocity. During the rice transplanter went forward and back in a 30m*100m square field 5 times, we obtained satisfactory results.KEYWORDS. Automated operation, Paddy fields, Rice transplanter, RTKGPS, FOG
The objective of this study is to develop an automated operating system in paddy fields. The goal of this research is that one operator controls multiple machines and makes a highly efficient operation. In Japan, operating area for one farmer is going to increase, but it is not enough consolidated. Probably they are dispersed. It is necessary to develop an automated operation technology that one operator drives multiple machine at several dispersed fields. It is possible when operators use automated control system.
The authors developed an automated rice transplanter and made a 6-row automated rice transplanting operation (2000). In this study, the authors modified this rice transplanter to make more precise operation. RTKGPS and FOG sensors are not replaced but a vehicle control unit is replaced. A programmable logic controller (PLC) is used to make a precise actuator. Control. All data is sent with digital signal.
Materials and Methods
Sensors and Actuators
The authors modified a 6-row rice transplanter. Figure 1 shows the modification of the rice transplanter for control by a computer whose CPU is 486 compatible 66 MHz. Figure 2 shows the automated rice transplanting system. An RTKGPS with a 3 cm precision at 10 Hz data output was used to locate the position of the rice transplanter. For the communication between the reference station and the rover station, wireless radio modems were used. The baud rate was set at 9,600 bps. A FOG sensor was used to measure the yaw angle, and an inclination-measuring apparatus comprised of 3 FOG sensors and 3 accelerometers was used to measure the roll and the pitch angles. The GPS position data, the yaw, the roll and the pitch angle data were transferred to a computer through RS232C interface. The sampling rate was 10 Hz for GPS, 20Hz for the yaw angle, 25Hz for the roll and pitch angle. The main computer corrected the position data influenced by the vehicle inclination and calculated the control parameters, then sent them to a PLC (Programmable Logic Controller) through parallel output port every 100miliseconds.
Figure1 Automated Rice Transplanter
The PLC received control parameters from main computer through parallel input unit, then control actuators. Figure 3 shows the actuators to control the levers, pedals and so on. All actuators are connected to relays, so the moving direction and speed could be controlled with pulse width from PLC. The steering angle was sensed with an absolute rotary encoder and it was controlled by DC-motor. The clutch and brakes positions were sensed with proximity sensors and they were controlled by electrical linear cylinders. The positions of transplanting instruments control lever, of engine throttle and of HST lever were measured with absolute rotary encoders and they were controlled by electrical linear cylinders. The PLC control loop was 2miliseconds.
(1) Correction of the inclination
When a rice transplanter travels in a paddy field, unevenness of the ground cause roll and pitch angles of about 3 degrees. In this system, the GPS antenna is fixed on the rice transplanter. The GPS data indicate the position of the top of the GPS antenna. Assuming the antenna height is 2 m, the horizontal distance between the top of the antenna and the bottom is 10.5 cm when the roll angle is 3 degrees. To determine the precise position of the ground surface point under the GPS antenna, the influence of the roll and pitch angles must be corrected.
Figure 4 shows the method of correction of the inclination. Assuming the presence of space coordinates xyz on the rice transplanter and plane coordinates XY on which the rice transplanter travels, the straight desired path, y=kX+C was derived on XY . In this Figure it is assumed that the top of the GPS antenna corresponds to P(p1,q1,h1) , the roll angle is ? , the pitch angle is f , the yaw angle is ? and the GPS antenna height is h . The ground surface point under the GPS antenna P’ is expressed as follows:
In the above equation, the yaw angle k’ is expressed by the following equation.
(2) Correction of initial yaw angle offset
It is very difficult to set the vehicle direction paralleled to the traveling direction. FOG sensor cannot sense the azimuth and it has drift. So to sense the initial yaw angle, the deviation from the desired path calculated by the yaw angle and vehicle speed was compared with the deviation calculated by GPS data (Figure 5). Then the offset angle was calculated and the yaw angle was corrected.
The deviation from the desired path measured by RTKGPS is supposed dGPS and the deviation calculated by the yaw angle ?(i) and the vehicle speed v(i) is dGyro . v(i) is measured by GPS. dGyro is estimated as following equation(2). In this equation, n is the time after starting calculation and ts is sampling interval. dGyro is calculated 15 seconds after starting operation .
Then the distance from the starting point is ln , the offset of yaw angle ?offset is calculated as following equation(3). In this equation, it is supposed that dGPS and dGyro are enough smaller than ln .
(1) Straight drive
The desired traveling path was calculated with corner points of the square field measured by RTKGPS before operation. The rice transplanter must be driven along the desired path. The steering is controlled to get back close to the desired path. When it is supposed that the deviation from the target line is d and the yaw angle is y, the aiming steering angle daim is given as the following equation. Kp1 , Kp2 are decided by the vehicle speed.
daim = Kp1d+K p2? (4)
The GPS data quality indicator was monitored while the rice transplanter travels automatically, and if the radio link between GPS base station and GPS rover station is disconnected, the clutch is released and the operation is interrupted.
(2) Turn control
At the headland, the rice transplanter moves forward and backward to turn so as to minimize the headland space. The width of headland is 3.5m. Figure 6 shows the way of turning at the headland. When the rice transplanter reaches the edge of the field, it moves backward 40cm straightly. While the rice transplanter is turning and the yaw angle is less than 160 degrees, only the yaw angle is obtained, the steering angle is kept 40 degrees and one side brake is applied. When the yaw angle becomes more than 160 degrees, the rice transplanter is controlled to get back close to next desired path. If the rice transplanter does not get close the new desired path enough after turning, the steering is controlled to get close to the desired path when it moves to backward.
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Results and discussion
The experiment was conducted 4 days after puddling. Figure 7 shows the path of the GPS antenna, and in this data the influence of the vehicle inclination was corrected. The deviation from the desired straight path was less than 10cm at 0.8m/s of travel speed during the operation. The rice transplanter went for and back in a 20m*100m square field 4 times. As the turning radius of the vehicle at the headland was around 2m, it was easy to get back close to the new desired path after turning.
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Figure 8 shows the path of the GPS antenna, the steering angle and the yaw angle. The steerin g angle changes from – 7degree to 8 degree. The yaw angle changes –3 degree to 3 degree. Because of control method during transplanting operation, the steering angle sometimes changes rapidly when the deviation or the yaw angle become large. It is caused sudden changing of the yaw angle or the deviation from the desired path. GPS data has about 70miliseconds latency and the automated system also has latency depending on such as mechanical delay, the calculation and the data transfer. So the change of the deviation is loosened but the sudden change of the traveling path makes the operation such as spraying or fertilizing more difficult. In paddy fields, because of unevenness of the ground and of the soil condition changing during operation, it is thought that it is difficult to estimate the location and direction of the vehicle with the calculation of the vehicle dynamics. It is necessary to improve the control method to make more precise operation to drive an automated vehicle interspace of crop row for spraying or fertilizing.
In this experiment, conventional mat type rice seedings were used and two persons supplied them to the rice transplanter every two returning operation at the edge of the field. At the headland, it took about 50 seconds to turn and to get back close to new desired path. The operating time is 22minuites per 10a.
When the data communication between RTK base and rover station via radio link was disconnected, the clutch was released and operation was interrupted. Then as soon as the radio link was connected, it started operation again.
In this study, a 6-row automated rice transplanter was developed. RTKGPS receiver was used to locate precise position and FOG sensors were used to measure the direction and the inclination of the vehicle. A main computer corrects the influence of the inclination and calculates the location. All actuators are electrical and they are controlled by a PLC. When the rice transplanter traveled 100m in a paddy field, the deviation from the desired straight path was less than 10cm. The operating time was 22minutes per 10a at the 20m*100m field.
This research is proposed by the Ministry of Agriculture, Forestry and Fisheries of Japan.
Yoshisada NAGASAKA, Ryuji OTANI, Kazuto SHIGETA, Ken TANIWAKI, A Study about an Automated Rice Transplanter with GPS and FOG: ASAE paper#001045,2000