Background of Study
An inertial measurement unit (IMU) is a combination of electronic sensor that measures specific force of a body, angular rate and sometimes magnetic field. Usually, it is combination of accelerometers and gyroscopes. However, some IMU has additional sensors. Such as magnetometer and barometer.
Navigation technique using IMU is called as inertial navigation. Utilizing gyroscopes and accelerometers to obtain rate of acceleration and rotation, position can be calculated using double integration of accelerometers reading [1]. The advantage of using IMU for inertial navigation is that the external references are not needed because IMU is self-contained [1]. The biggest problem is commercial grade IMU possess large drift and bias error over long period of time.
Agricultural robot is a robot that is capable to perform various agricultural task to replace human labour force. Therefore, it is important for the robot to be able to move in agriculture environment. Compared to human workforce, using mobile robots the cost can be reduce and the profit can be increase [2]. Building a mobile robot that could do all kind of agriculture task can be quite troublesome. As the alternative, only the mobile robot’s base is designed so that additional parts or units can be attached on the robot.
Problem Statement
In agriculture, there are lot of task need to be perform. Relying on the human force, it can be quite difficult sometimes. Human need time to learn and adapt to a new environment. Compared to the mobile robots, it can be program and the quality of work can be maintained and control. Furthermore, it can be duplicate and no additional time required for the robot to learn as technology allow the information to be transferred.
However, for the mobile robots to be able to operate autonomously, a navigation system is a compulsory. Without the navigation system, the operation is limited to manual control. Less monitoring is needed when the mobile robots have the navigation system as it can operate on its own. So, in order for robot to be able to navigate its surrounding, it must be equipped with sensors. Without sensors, the robots can be considered as blind in human’s term and useless. However, most existing robot tends to use combination of sensors for it navigation system. It would require higher cost and more complex to build. For example, global positioning system itself is expensive and it also requires another sensor when signal cannot be received.
For the mobile robot’s base, specific requirement needed to be achieve to allow it to operate in agriculture environment. The main requirement is the mobile robots must be able to move off road and can pass over small obstacles. Next, the mobile robots also need to have space for attachment of additional units or parts and the electronic component must be secured. Majority of existing robots utilized wheel for its locomotion. For natural terrains, legged robot is better compared to wheeled robot because their limbs adaptations on surface irregularities [3]. However, wheeled robot has the advantages such as ease of maintenance, lower cost to build and much simpler control.
Thus, IMU was chosen for the navigation system for the robot as it would reduce the cost and complexity. For the mobile robots, wheel is utilized for its movement.
Objective of the Study
- To develop a navigation system using IMU sensor.
- To develop a robotic platform that is suitable for agriculture task.
- To integrate the navigation system into the robotic platform as a single agricultural robot.
Scope of The Research
- The navigation system is only based on IMU sensor.
- The navigation system able to detect the position of the robot.
- The robotic platform able to operate in agriculture environment such as able to move off road and can pass small obstacles.
- The robotic platform can be combine with units or parts which used in agricultural field.
Project Overview
This project development is separated into 3 segments which are mechanical, electronics and software development. For the mechanical development, it main purpose is to build the structure of the mobile robot. The electronics development purpose is to supply the power and allow data and power exchange between microcontroller and transducers. The software development play role to build the algorithm and coding required for this project and transfer it into the microcontroller.
Mechanical Development
In order to develop the mechanical structure for the mobile robot, the existing agricultural robot is studied via literature review. By comparing the previous agricultural robot build, feature from several project is combine to develop a design for this project mobile robot.
The next step is to sketch the design using computer aided design (CAD) Solidworks 2017 software was used to produce the design required. To simplify the designing process, some of the parts is download through Grab Cad. Whereas for the parts that is not available, custom design of the part is made. Then, full assembly for the mobile robot is done in the Solidworks 2017. This is important to confirm its dimension is accurate before real assembly done to avoid any unmatched design.
There are few matters need to be achieve for design development such are:
- The design is stable and can withstand heavy load
- Secured space for electronic components
- Extra space to attach additional units or parts for various agriculture equipment
Electronics Development
For the electronics development, all required components is listed first. Then, the datasheet for each component is studied to make sure the components is compatible to be used in this project. It is also important to avoid the component from being broken due to overloading.
The next step is to design the circuit connection. With circuit design, the process of assembly and troubleshooting will be much easier. It also works as reference for other peoples. For designing the circuit, Fritzing software is used.
Before actual assembly of the electronics component is done, each components were tested. This to make sure each components are working and save the time for troubleshooting in later stage. The testing is done using simple code from the library available.
Software Development
The algorithm for the navigation system is the essential part in this project. For this project, C language was chosen because microcontroller used is Arduino Mega 2560. In order to develop algorithm for the navigation system, it is important to study the basic working principle of IMU. Since the IMU only provide the acceleration reading of a body, to yield position, double integration is needed.
The next step is to find suitable filter that can be used to remove the bias drift error from the IMU. This is due to commercial grade IMU suffer from large bias drift error over extended period of time. The third step is to combine the algorithm and the filter to produce navigation system for this project.
For the mobile robot movement, simple algorithm is used based on differential drive technique. Lastly, the navigation system will be integrated with the mobile robots. The program then would be tested to find the error in position estimation of the mobile robot by repeating the test several time.
Conclusion
The project IMU based navigation system for agricultural robot is separated into two parts which are Undergraduate Project 1 and Undergraduate Project 2. For the project 1, it focuses on planning and research. Conceptual design and preliminary result also included in this phase. Most of the research for this project is done through literature review on inertial navigation system and agricultural robot design.
For the Undergraduate Project 2, most of the task will be on fabrication of the mobile robot and fully development of the navigation system. Then, the system will be integrated to the mobile robots. Assembled projects will then be tested on field. The result will be collected and analysed in the project discussion.
In conclusion, the most important aspects in developing this project is depended on IMU sensor itself. The navigation system will be depended on the IMU sensor only to determine the position of the mobile robot. Furthermore, this project implementation is also improving the design of agricultural robot. With the existence of this navigation system and agricultural robot, it hoped to be able to reduce work load on agriculture field.