Three sensors
①Acceleration sensor
An accelerometer measures acceleration in various directions in space. It utilizes the inertia of a "gravity block." As the sensor moves, this "gravity block" exerts pressure in the X, Y, and Z directions (forward, backward, left, right, up, and down). A piezoelectric crystal converts this pressure into an electrical signal. As the motion changes, the pressure varies in each direction, and the electrical signal changes accordingly, thus determining the direction and magnitude of the phone's acceleration. For example, if you suddenly push the phone forward, the sensor knows you are accelerating forward.
② Gyroscope
A gyroscope is a device used to measure angles and maintain orientation. In games such as flight games, sports games, and first-person shooters, it can fully monitor the player's hand displacement, thereby achieving various game operation effects. The image below shows a basic mechanical gyroscope model. The golden rotor in the center remains unaffected by inertia during the device's movement, while the three surrounding "steel rings" change position as the device's orientation changes, thus detecting the device's current rotational state.
Actually, the gyroscopes in our mobile phones and other electronic products don't look like this. Like accelerometers, they are also microelectronic components that utilize the Coriolis force. The motion of a continuously vibrating oscillator in a rotating system changes the circuit state, causing changes in relevant electrical parameters, thereby reflecting motion such as left-right tilt, forward-backward tilt, and left-right sway.
What is the Coriolis force? Imagine an athlete at point O in the center of a counter-clockwise rotating disk (point O is stationary). The athlete wants to pass a basketball to another athlete at point A on the edge. After the athlete shoots the ball along the straight line OA, the athlete at point A will find the basketball deflects to the right and eventually lands at point A'. With the rotating disk as the frame of reference, the basketball appears to be subjected to a force to the right, causing it to deflect. This force is called the Coriolis force.
③ Electronic compass (geomagnetic sensor, geomagnetometer)
Accelerometers and gyroscopes can generally describe the complete motion state of a device. However, with prolonged movement, cumulative deviations can occur, making it impossible to accurately describe the motion posture, such as the control screen tilting. Electronic compasses (geomagnetic sensors) measure the Earth's magnetic field and use absolute pointing functionality to correct and compensate for these cumulative deviations, thereby correcting the direction, angle, force, and speed of human movement.
Triaxial sensor
① Three-axis gyroscope
A three-axis gyroscope simultaneously measures position, trajectory, and acceleration in six directions. A single-axis gyroscope can only measure two directions, meaning a system would need three gyroscopes, while a single three-axis gyroscope can replace three single-axis gyroscopes.
Advantages: Three-axis gyroscopes are small in size, light in weight, simple in structure, reliable, more sensitive, and more accurate.
② Triaxial accelerometer
A triaxial accelerometer works based on the fundamental principle of acceleration. Acceleration is a spatial vector; to accurately understand the motion of an object, its components on all three coordinate axes must be measured. Furthermore, when the direction of the object's motion is unknown beforehand, only a triaxial accelerometer can detect the acceleration signal. Since a triaxial accelerometer is also based on the principle of gravity, it can achieve tilt angles of ±90 degrees or 0-360 degrees on both axes. After calibration, its accuracy is higher than that of a dual-axis accelerometer measuring angles greater than 60 degrees.
Advantages: The advantage of a triaxial accelerometer is that it can detect acceleration signals when the direction of an object's motion is unknown beforehand. Three-dimensional accelerometers are small in size and lightweight, can measure spatial acceleration, and can comprehensively and accurately reflect the motion properties of objects.
③ Triaxial magnetometer
Triaxial magnetometers, also known as electronic compasses, are widely used in drones, smartwatches, and navigation devices. For detecting changes in object motion, the triaxial magnetometer plays a crucial role in providing absolute pointing, ensuring stable flight, assisted navigation, and other diverse functions. Therefore, the reliability of the triaxial magnetometer is the cornerstone of the stable operation of these devices.
six-axis sensor
A six-axis sensor typically refers to a three-axis gyroscope plus a three-axis accelerometer.
Nine-axis sensor
A nine-axis sensor typically refers to a three-axis gyroscope + a three-axis accelerometer + a three-axis magnetometer. There are also six-axis accelerometers + three-axis gyroscopes, and six-axis gyroscopes + three-axis accelerometers.
A nine-axis sensor is actually a combination of three sensors: a 3-axis accelerometer, a 3-axis gyroscope, and a 3-axis electronic compass (geomagnetic sensor). These three components have different functions but work together to form a motion sensing and tracking element commonly used in electronic products such as mobile phones, tablets, and game consoles, applied to interactive control in various software and games.
Nine-axis sensors, as integrated sensor modules, reduce circuit board space and overall footprint, making them more suitable for use in lightweight and portable electronic devices and wearable products. The accuracy of integrated sensor data depends not only on the precision of the device itself but also on post-assembly correction and the appropriate algorithms for different applications. Suitable algorithms can fuse data from multiple sensors, compensating for the limitations of individual sensors in calculating accurate position and orientation, thereby achieving high-precision motion detection.
