Nintendo's Wii originally used a three-axis (X, Y, Z) accelerometer, and later added a gyroscope. "Nintendo has long known that it is not enough to have a three-axis accelerometer. It was just that there were no consumer electronics gyroscopes available on the market until Invensense introduced the first MEMS gyroscope for consumer electronics." Invensense Mobile Products Lin Shanghong, director of system engineering, said. This situation also happened to Apple CEO Steve Jobs. At the launch of the iPhone 4 in June 2010, Steve Jobs personally demonstrated the gyroscope's innovative application for detecting the horizontal rotation of objects—a solution that was not possible based on other motion sensors alone. Therefore, by understanding the working principle of the gyroscope, we can appreciate the Nintendo and Apple's hope for the gyroscope, and also help domestic consumer electronics terminal manufacturers to skillfully apply the device to achieve a variety of innovative applications.
The gyroscope can be a useful complement to the accelerometer and electronic compass. When the three-axis gyroscope plus the three-axis acceleration sensor forms a six-axis motion sensor, basically all forms of motion can be detected, including parameters such as speed, direction, and displacement. "The movement of the object is nothing more than six kinds, the displacement of the three directions of X, Y and Z and the rotation of the three directions of X, Y and Z. These six movement modes constitute the complete movement of the object." Invensense mobile product business Vice President Jiang Zhengyao said. If an electronic compass is added to the six-axis motion sensor, the absolute position can be corrected while detecting the motion trajectory, achieving perfect object motion trajectory tracking. Therefore, the future development and application of the gyroscope is closely related to the acceleration sensor and the electronic compass.
The acceleration sensor is equivalent to a spring system with a weight in the middle, and springs are supported on all sides. When placed flat on the table, some springs are stretched and some are flattened. When changing, different springs are compressed differently to detect forces in different directions. Typical applications include horizontal and vertical switching of the phone/camera picture.
The electronic compass mainly detects geomagnetism. The common electronic compass is based primarily on the Hall effect. However, the geomagnetic environment is not perfect. For example, the geomagnetic south pole does not necessarily refer to the same north on different surfaces of the earth; at different latitudes of the earth, the angle between the geomagnetic direction and the horizontal direction is different. Therefore, the electronic compass can only refer to a general direction and then corrected. In addition, electronic compasses are also susceptible to interference from magnetic fields such as metals, speakers, and antennas. Especially when applied to mobile phones, you need to be careful to choose a suitable location on the PCB.
The gyroscope detects the angular velocity. Based on the principle of Coriolis force: When an object moves linearly in the coordinate system, assuming that the coordinate system makes a rotation, the object will feel a vertical force and vertical acceleration during the rotation. "The formation of the typhoon is based on this principle. The rotation of the earth drives the atmosphere to rotate. If the atmosphere is rotated by a tangential force, it is easy to form a typhoon. The direction of the typhoon in the northern and southern hemispheres is different." Lin Shanghong uses an image. The metaphor explains the principle of Coriolis force. It is much more complicated to implement this principle in a MEMS device to make a gyroscope. "First use MEMS as a vibration system to generate a linear motion V through a fast and stable vibration. When the plane of V has a rotating topology, the direction of the Coriolis force can be detected. Angular velocity. The angular velocity of the X, Y, and Z axes is detected by vibrations in different directions, and the interference of gravity can be removed by stable oscillation," Lin Shanghong explained.
Figure 2: Simulation diagram of the working principle of MEMS gyroscope
“Acceleration sensors and electronic compasses use the Earth as a reference for direction detection. Acceleration sensors detect the difference between the object and the angle of gravity. The electronic compass detects the difference between the object and the north angle. If the center of the earth and the north are detected, The three axes are fixed. However, the acceleration sensor does not detect gravity, and all the forces in all directions are detected. The magnetic field detected by the electronic compass is disturbed by other magnetic fields. Therefore, there are many deficiencies in detecting the motion of the object. The reference object of the gyroscope is itself, so it can detect the process of changing the position of the object. If the object is flat, it is enough to use the accelerometer or electronic compass. Through the above principle, we can Several sensors are used together, such as correcting each other for accuracy, or completely detecting the direction and trajectory of the object together," Lin Shanghong said.
Table 1: Overview and analysis of common sensor usage
Gyro opens consumer electronics innovation applications
The emergence of gyroscopes has given room for a large application of consumer electronics. For example, in terms of device input, after the keyboard, mouse, and touch screen, the gyroscope brings us gesture input. Because of its high precision, it can even realize electronic signature. For example, let the smart phone become smarter. : In addition to mobile Internet access and fast processing of data, you can also “see and seeâ€, know where your host is, what your interests are, and provide corresponding services. In addition to the above, there are many application areas that are worth exploring. Lin Shanghong recommended the following innovative application methods for reference.
Game
High-speed games such as golf, badminton and swords can be achieved with gyroscopes. These games have to detect very fast waves, which is a big challenge for current accelerometers. “When Tiger Woods swings, the club head reaches 180km/s in 0.2s, which is equivalent to an instantaneous acceleration of 11 gravitational accelerations. Now the range of accelerometers for consumer electronics is not so large. If you use the gyroscope, you can accurately detect this fast swing. When you swing, the angular velocity of the club head is about 1,800°/s, which is equivalent to 5~6 turns of 1s. This is within the range of gyroscope angular velocity detection, so it can be very Good simulation of the real scene of this game." Lin Shanghong said.
Another type of game, such as a shooting game, requires the device to remain motionless, and then fine-tuned to shoot. This type of game requires high precision and low interference, and existing acceleration sensors cannot meet this requirement. Lin Shanghong said, "We assume that the error angle of the shooting game is ±5°. After conversion to the acceleration sensor, cos5° is equivalent to a gravity acceleration of 3~4‰. The accuracy of the existing acceleration sensor does not reach this magnitude. The method is aimed at shooting. The gyroscope can detect very small hand shake, and the interference is very low. It is only about 0.05° when it is held for 10s without moving, which is very suitable for this kind of aiming game."
2. Human machine interface
In the field of human-machine interface, gyroscopes can also be very innovative. As early as two or three years ago, Logitech added gyroscopes and accelerometers to its mouse to implement the function of the indicator (laser pen). Now, through gyroscopes, gesture input can be implemented on consumer electronics, such as writing in the air, or controlling the function of the device by shaking, oscillating, etc. The detection of angular velocity of the gyroscope is very precise, and even biometrics such as signature recognition can be realized. Therefore, the application of E Cash can be realized by using a gesture to check credit cards and checks. "Another benefit of gesture control is that it saves power for consumer electronics. When you rely on gestures to control certain functions, you don't need to turn on the screen backlight. For example, call Dad and hold a mobile phone to write a 'D' in the air. The mobile phone automatically dials to the dad without having to light up the screen for dialing. This way can greatly save the power consumption of the screen backlight." Lin Shanghong added.
3. Positioning function
Gyroscopes can be used to complement GPS and electronic compasses. For example, in a tunnel or parking lot, the GPS will lose the signal. At this time, the gyroscope can assist the blind area navigation according to the direction and speed of the car movement. On the three-dimensional road such as the overpass, the GPS cannot identify which layer the car is on, and the gyroscope is By detecting the action of the car's uphill slope, the car is estimated to be on the first floor according to the speed. If the blind spot navigation function is realized by the acceleration sensor, it is necessary to remove the gravity acceleration first, measure the linear acceleration, and then calculate the track trajectory of the car according to the vehicle speed, which is complicated to calculate; if the electronic compass is used to realize the blind spot navigation, it is prone to drift. It is necessary to correct the "8" shape of the navigator to identify and remove the magnetic flux. This corrective action is inconvenient for the driver, but if used in conjunction with the gyroscope, the electronic compass can be quickly corrected in a small range of displacement.
In addition to car navigation, pedestrian blind spot navigation can also be achieved through gyroscopes. However, Lin Shanghong pointed out that pedestrian blind spot navigation is more difficult than car blind spot navigation, because the car's operation is relatively simple, and the data measured by pedestrians when they place the device in different positions are very different, such as the waist and leg detection. The signal beats differently and requires sensor filtering. The realization of blind spot navigation for pedestrians is a huge project and is currently under discussion.
4. Image anti-shake
There are currently two implementations, one is EIS (electronic anti-shake) and the other is OIS (optical anti-shake). The gyroscope has been widely used in the EIS, and the hand shake is detected by the two-axis gyroscope, and several repeated photographs are quickly performed, and then the image in the photograph taken before and after the vibration is cut off. If used in conjunction with an electronic compass, it is also possible to correct the absolute position. “The use of gyroscopes to achieve anti-shake has many advantages, such as accuracy, which makes the quality of the image superposition better; the gyroscope detects the vibration of the camera itself, which can be separated from the vibration of the object to avoid misoperation; Cooperate with other sensors, etc." Lin Shanghong pointed out. Jiang Zhengyao said that the image anti-shake function will soon be applied to mobile phones. “When the gyroscope is used in the game console, only 6% of the accuracy is enough, and the accuracy of the mobile phone is much higher. Invensense now has 1% precision products for mobile phones, and will be implemented in the first half of 2011. The mobile phone with image anti-shake technology is available," he said. When the mobile phone realizes the EIS with the gyroscope, it is very helpful for the videophone function. Because the amount of data is large when the image is shaken, the amount of data will be greatly reduced after the gyroscope is anti-shake, and the wireless bandwidth can be saved and the frame width can be improved to optimize the clarity and smoothness of the video.
In addition, pedometer applications can be implemented, as well as applications that combine the motion of the device with the real scene through the camera.
Table 2: Application of sensors in consumer electronics
docking station for macbook air,docking station for laptop,docking station usb c,USB C HUB,thunderbolt 3 usb type c hub
Shenzhen Konchang Electronic Technology Co.,Ltd , https://www.konchang.com