Tech Chat | What is attitude sensor and how does it work?

Attitude sensor is a common sensor that applied in various systems to provide attitude data of the system. Our SAgro100 auto-steering system has also applied attitude sensors to obtain tractor attitude & heading data.

In previous blog, we have introduced the angle sensor that can provide the tractor steering data for some complex terrains, such as slopes, hills, mountains, etc. However, due to its installation difficulty and compatibility limit, users prefer attitude sensor better. So today we will introduce what the attitude sensor is and how it works.

1. Working Principle

The attitude sensor is a device used to detect the attitude of an object. It can measure the angle, direction and position of the object in space, determine the attitude of the object through the data fusion algorithm, and output the calibrated angular velocity, acceleration, magnetic data, etc. The motion attitude measurement is carried out through the sensor data algorithm based on the quaternion, and the zero-drift three-dimensional attitude data represented by the quaternion, Euler angle, etc. are output in real time. Attitude sensors are widely used in many fields, such as aerospace, robotics, automobiles, medical equipment and so on.

The working principle of the attitude sensor can be divided into two types: one is a sensor based on an inertial measurement unit (IMU), and the other is a sensor based on a magnetometer and an accelerometer.

1.1 IMU-based attitude sensor

An IMU-based attitude sensor usually consists of a gyroscope and an accelerometer. Gyroscopes can measure the angular velocity of an object rotating around three axes (X, Y, Z axes), while accelerometers can measure the acceleration of an object along three axes. By processing the gyroscope and accelerometer measurements, the pose of the object can be determined.

The working principle of IMU is based on Newton's first law and second law. Newton's first law states that if an object is not acted upon by an external force, it maintains its original state, that is, it moves in a straight line with a uniform velocity or remains at rest. Based on this law, the accelerometer can be used to measure the acceleration of gravity experienced by the object to determine the position of the object. Newton's second law states that the acceleration of an object is proportional to the magnitude and direction of the force on the object and inversely proportional to the mass of the object. Based on this law, the gyroscope can be used to measure the angular velocity of the object around the three axes to determine the direction of the object.

1.2 Magnetometer-based attitude sensor

Attitude sensors based on magnetometers and accelerometers measure the orientation and position of objects in the Earth's magnetic field. A magnetometer measures the effect of the Earth's magnetic field on an object, while an accelerometer measures the acceleration due to gravity experienced by an object. By processing the magnetometer and accelerometer measurements, the orientation and position of an object within the Earth's magnetic field can be determined.

The accuracy and stability of the attitude sensor are important factors affecting its performance. In order to improve the accuracy and stability of the attitude sensor, a variety of techniques can be used, such as Kalman filtering, adaptive filtering, digital filtering, and so on.
In practical applications, the attitude sensor can be used in combination with other sensors, such as GPS, laser range finder, etc., to improve the accuracy of its positioning and navigation. The application range of attitude sensors is getting wider and wider, and there is still a lot of room for development in the future.

The attitude sensor in our SAgro100 system is of the IMU-based type. It is called gyroscope in software. In fact, it includes a gyroscope and an accelerometer.

2. Applications

Attitude sensors are widely used in aircraft, drones, smartphones, VR/AR, attitude trackers, and human motion equipment, which require low-cost, high-dynamic 3D attitude measurement. 

Among them, for aircraft and UAVs, the attitude sensor is an important component to ensure their smooth flight.

In VR/AR glasses and posture trackers, the posture sensor can be used to detect the user's head posture, so as to achieve a more natural interactive experience. In addition, attitude sensors can also be applied to some sports medical equipment, such as smart bracelets and pedometers, to record user's exercise information.

3. Installation

In SAgro100 autosteer kit, the attitude sensor is installed on the tractor body to measure its attitude data, and the angle sensor is installed on the front wheel to measure the attitude information of the wheels. These two attitude information play an important role in vehicle navigation. After internal algorithm processing, the vehicle's motion information is obtained, and combined with the dual-antenna positioning and orientation technology, it guides the vehicle to drive more accurately according to the set trajectory.

Installation of attitude sensor on ordinary MFWD tractors:

Fix the Gyroscope horizontally in the tractor cab and connect it with the gyroscope cable. The direction of the Gyroscopes should be perpendicular to the forward direction of the tractor. NOTE: The gyroscope is best mounted near or under the seat as there is less vibration.

Installation of attitude sensor on ordinary MFWD tractors:

Due to the particularity of this type of tractor, it is difficult to install angle sensors on the wheels. Instead, articulated tractors use Gyroscopes for tractor orientation data. The Gyroscopes should be mounted in a flat location on the front half of the tractor.

4. Upgrade

Due to the compatibility and installation difficulty, our users prefer attitude sensors rather than angle sensors, in our future agricultural auto-steering kits, the angle sensor will be completely replaced by the attitude sensor. 

The updated dual-gyro mode of our autosteer systems will provide both ease of installation and accuracy in complex environments and low speeds.

Learn more about SAgro100 automated steering system.
https://www.singularxyz.com/SAgro100_Automated_Steering_System.html