What is a Gyroscope Sensor?

11 September 2020

8587

A gyroscope is a device used to sense and maintain direction, designed based on the theory of indestructible angular momentum. The gyroscope sensor is a simple and easy-to-use positioning and control system based on free space movement and gestures.

The gyroscope sensor is a simple and easy-to-use positioning and control system based on free space movement and gestures. Flick the mouse on an imaginary plane, the cursor on the screen will follow it, and you can draw circles around the links and click buttons. When you are speaking or leaving the table, these operations can be easily achieved. The gyroscope sensor was originally applied to the helicopter model and has been widely used in mobile and portable devices such as mobile phones (iPhone's three-axis gyroscope technology).

Catalog

Ⅰ Working principle

A gyroscope sensor is a device used to sense and maintain direction, designed based on the theory of indestructible angular momentum. Once the gyroscope starts to rotate, due to the angular momentum of the wheel, the gyroscope has a tendency to resist changes in direction. The principle of a gyroscope is that the direction pointed by the axis of rotation of a rotating object will not change when it is not affected by external forces. People use it to keep their direction based on this principle. Then use a variety of methods to read the direction indicated by the axis, and automatically transmit the data signal to the control system. We actually use this principle when riding bicycles. The faster the wheel turns, the less likely it is to fall because the axle has a force to keep it level. A modern gyroscope sensor can accurately determine the position of moving objects. It is an inertial navigation instrument widely used in modern aviation, navigation, aerospace, and defense industries. The main part of the traditional inertial gyroscope is a mechanical gyroscope, and the mechanical gyroscope has high requirements on the process structure. The basic idea of modern fiber-optic gyroscopes was put forward in the 1970s. After the 1980s, fiber optic gyroscopes have developed very rapidly, and laser resonant gyroscopes have also made great progress. The fiber optic gyroscope has a compact structure, high sensitivity, and reliable operation. Fiber optic gyroscopes have completely replaced mechanical traditional gyroscopes in many fields and become a key component in modern navigation instruments. In addition to the ring laser gyroscope, the development of fiber optic gyroscopes at the same time.

Ⅱ Basic parts of the gyroscope sensor

When analyzing the motion of a gyro approximately from a mechanical point of view, it can be regarded as a rigid body. There is a directional fulcrum on the rigid body, and the gyroscope can rotate with three degrees of freedom around this fulcrum, so the motion of the gyro is a rigid body that moves around a fixed point. More precisely, a flywheel rotor that rotates at a high speed around an axis of symmetry is called a gyroscope. The gyroscope is installed on the framing device so that the rotation axis of the gyroscope has the freedom of angular rotation. The whole of this device is called a gyroscope.

The basic components of the gyroscope sensor are:

(1) Gyro rotor (synchronous motor, hysteresis motor, three-phase AC motor, etc. are often used to make the gyro rotor rotate at a high speed around the rotation axis, and its speed is approximately constant);

(2) The inner and outer frame (or inner and outer ring, it is the structure that enables the spinning axis of the gyro to obtain the required degree of freedom of angular rotation);

(3) Accessories (refers to torque motors, signal sensors, etc.).

Two important characteristics of gyroscope sensors

characteristics of gyroscope sensors

Gyroscopes have two very important basic characteristics: one is a fixed axis, and the other is precession. Both of these characteristics are based on the principle of conservation of angular momentum.

Fixed axis

When the gyro rotor rotates at high speed, without any external torque acting on the gyroscope, the direction of the gyroscope's rotation axis in the inertial space remains stable, that is, pointing to a fixed direction; at the same time, it resists the power of any change in the rotor axis. This physical phenomenon is called the fixed axis or stability of the gyroscope.

Its stability changes with the following physical quantities:

(1) The greater the moment of inertia of the rotor, the better the stability;

(2) The greater the rotor angular velocity, the better the stability.

The so-called "moment of inertia" is a physical quantity that describes the inertia of a rigid body in rotation. When the same moment is applied to two different rigid bodies rotating around a fixed axis, the angular velocities obtained by them are generally different. A rigid body with a large moment of inertia obtains a small angular velocity, that is, maintaining the inertia of the original rotating state. Conversely, the angular velocity of a rigid body with a small moment of inertia is large, that is, the inertia of the original rotating state is small.

Precession

When the rotor rotates at a high speed, if the external torque acts on the outer ring axis, the gyroscope will rotate around the inner ring axis; if the external torque acts on the inner ring axis, the gyroscope will rotate around the outer ring axis. The direction of the rotational angular velocity and the direction of the external torque are perpendicular to each other. This characteristic is called the precession of the gyroscope.

There are three factors influencing the size of precession:

(1) The greater the external force, the greater the angular velocity of precession;

(2) The greater the moment of inertia of the rotor, the smaller the angular velocity of precession;

(3) The greater the angular velocity of the rotor, the smaller the angular velocity of precession.

Ⅲ Classification of the gyroscope sensor

According to the degree of freedom of the rotor rotation, it is divided into two degrees of freedom gyroscopes (also called three degrees of freedom gyroscopes) and single degrees of freedom gyroscopes (also called two degrees of freedom gyroscopes). The former is used to determine the attitude angle of the aircraft, and the latter is used to determine the attitude angular velocity, so it is often called a single degree of freedom gyroscope.

However, it is usually classified according to the supporting method used in the gyroscope sensor:

1. Ball-bearing free gyroscope

It is a classic gyroscope. The use of ball bearing support is the earliest and most widely used support method. The ball bearings rely on direct contact, the friction torque is large, the accuracy of the gyroscope is not high, the drift rate is a few degrees per hour, but the work is reliable, and it is still used in occasions where the accuracy is not required.

A free-rotor gyroscope (dual-degree-of-freedom gyroscope) can measure two attitude angles by the angle sensing elements of the inner ring shaft and the outer ring shaft.

2. Liquid float gyroscope

It is also known as float top. The inner frame (inner ring) and the rotor form a sealed spherical or cylindrical float assembly. The rotor rotates at a high speed in the float assembly, and the float assembly and the shell are filled with the float to generate the required buoyancy and damping. The one whose buoyancy is equal to the weight of the float assembly is called a full floating top; the one whose buoyancy is less than the weight of the float assembly is called a semi-floating top.

Due to the use of buoyancy support, the friction torque is reduced, and the accuracy of the gyroscope is high, but there is still friction because it cannot be positioned. In order to make up for this shortcoming, magnetic levitation is usually added on the basis of liquid levitation, that is, the floating liquid bears the weight of the float assembly, and the thrust formed by the magnetic field makes the float assembly suspend in the center position.

Modern high-precision single-degree-of-freedom liquid-floating gyroscopes are often three-floating gyroscopes that use liquid float, maglev, and dynamic pressure air float. This type of gyroscope has higher accuracy than ball bearing gyroscopes, with a drift rate of 0.01 degree/hour. However, liquid floating gyroscopes require higher processing accuracy, strict assembly, and precise temperature control, so the cost is higher.

3. Electrostatic gyroscope

It is also known as an electric floating top. Evenly distributed high-voltage electrodes are arranged around the metal spherical hollow rotor to form an electrostatic field on the rotor and use electrostatic force to support the high-speed rotating rotor. This method belongs to the spherical support, the rotor can not only rotate around the rotation axis, but also can rotate in any direction perpendicular to the rotation axis, so it belongs to the free rotor gyroscope type.

The electrostatic field has only suction, the closer the rotor is to the electrode, the greater the suction, which makes the rotor in an unstable state. Using a set of supporting circuits to change the force of the rotor can keep the rotor in the center position. The electrostatic gyroscope adopts non-contact support and there is no friction, so the accuracy is very high, and the drift rate is as low as 10-10 degrees/hour. It cannot withstand large shocks and vibrations. Its disadvantage is that the structure and manufacturing process is complex, and the cost is relatively high.

4. Flexible gyroscope

A gyroscope with a rotor mounted on an elastic support device. Dynamically tuned flexible gyroscopes are widely used in flexible gyroscopes. It is composed of an inner flexible rod, outer flexible rod, balance ring, rotor, driveshaft, and motor.

It relies on the dynamic reaction moment (gyro moment) generated during the torsion motion of the balance ring to balance the elastic moment generated by the flexible rod support so that the rotor becomes an unconstrained free rotor. This balance is tuning.

The flexible gyroscope is an inertial element that developed rapidly in the 1960s. Because of its simple structure, high accuracy (similar to liquid floating gyroscopes), and low cost, it has been widely used in aircraft and missiles.

5. Laser gyroscope

Its structural principle is completely different from the above several gyroscopes. The laser gyroscope is actually a ring laser, without a high-speed rotating mechanical rotor, but it uses laser technology to measure the angular velocity of an object relative to inertial space and has the function of a rate gyroscope.

The structure and work of the laser gyroscope are: a triangular cavity is made of a material with a very small thermal expansion coefficient. Three mirrors are installed at each vertex of the cavity to form a closed optical path. The cavity is evacuated, filled with helium-neon gas, and equipped with electrodes to form a laser generator.

The laser generator generates two laser beams directed at opposite directions. When the ring laser is in a static state, the optical path of the two laser beams is the same, so the frequency is the same. The difference between the two frequencies (frequency difference) is zero, and the interference fringe is zero.

When the ring laser rotates around the axis perpendicular to the plane of the closed optical path, the light length of the light that is consistent with the direction of rotation is extended, the wavelength increases, and the frequency decreases; the other light is the opposite, so there is a frequency difference, forming interference fringes.

The number of interference fringes per unit time is proportional to the rotational angular velocity. The drift rate of the laser gyroscope is as low as 0.1 to 0.01 degrees/hour, and it has high reliability and is not affected by linear acceleration. It has been applied in the inertial navigation of aircraft and is a new type of gyroscope with great development prospects.

6. MEMS gyroscope

It is a silicon microelectromechanical gyroscope. Most MEMS gyroscopes rely on the alternating Coriolis force caused by mutually orthogonal vibration and rotation. MEMS (Micro-Electro-Mechanical Systems) refers to a complete micro-electro-mechanical system that integrates mechanical elements, micro-sensors, micro-actuators, signal processing and control circuits, interface circuits, communications, and power supplies.

The MEMS gyroscope uses the Coriolis theorem to convert the angular velocity of a rotating object into a direct-current voltage signal proportional to the angular velocity. Its core components are mass-produced through doping technology, photolithography technology, corrosion technology, LIGA technology, and packaging technology.

MEMS gyroscope

 Main features of the MEMS gyroscope sensor

(1) Small size and lightweight, its side length is less than 1mm, and the weight of the device core is only 1.2mg.

(2) Low cost.

(3) The reliability is good, the working life is more than 100,000 hours, and it can withstand the impact of 1000g.

(4) Large measuring range.

Ⅳ Application of gyroscope sensor

1. Gyroscope sensor in aviation flight

Due to the high-tech development of various electronic equipment and computer control, most modern aircraft designs are statically unstable. Electronic equipment and computers must be used to assist in the control to achieve good flight control.

It is more difficult to control this kind of aircraft solely relying on the pilot's fingers. Although the aircraft can still fly, it will fluctuate to varying degrees and is always in an unstable flight state. Sometimes the center of gravity setting is not accurate, and a slight difference will make the flight of the aircraft unstable.

There are various turbulences in the air, which will also make the flight of the aircraft unstable. At this time, use the gyroscope to increase the stability, and the aircraft will always fly smoothly, making it easier for the pilot to control the aircraft and making various actions more standard.

The most obvious thing that the gyroscope makes the pilot feel is when landing, and it is the landing of the plane that needs the gyroscope the most. Because the landing aircraft is slower and near the stall point, it is more likely to be affected by the wind and cause the wings to shake up and down. At this time, you must constantly use your fingers to adjust the aircraft's attitude to keep it level and gradually drop the altitude. Many novice pilots sometimes make too much correction, the plane will produce greater shaking, it is easy to enter a stall and cause landing failure.

However, if the gyroscope is turned on to increase the stability, because the sensor of the gyroscope is very sensitive, the wing is slightly pressed down, and the gyroscope immediately sends a command to hit the ailerons to make the aircraft level. This process happens so quickly that it may have been corrected by the gyroscope without seeing the wing depression. So you will see that the aircraft is always very stable, keeping the level unchanged and gradually descending altitude, which is of great help to the pilot.

2. Gyroscope sensor in-car navigation equipment

In-vehicle navigation is to determine the target after receiving the GPS satellite signal, and then plan the route according to the database of the navigation software, and then conduct the navigation. Because GPS requires the on-board navigation system to work within the direct line of sight of the synchronous satellite, tunnels, bridges, or high-rise buildings will block the direct line of sight, making the navigation system unable to work.

Furthermore, the navigation system uses the laws of triangle and geometry to calculate the position of the car, so the car must be under the sight of three synchronous satellites at the same time to determine the position. The more synchronous satellites in the direct line of sight of the navigation system, the more accurate the positioning.

In response to this problem, some navigation manufacturers have found a solution, and the mystery of achieving precise navigation lies in a small thing-a gyroscope.

When the gyroscope is applied to car navigation, it greatly improves the accuracy of navigation. Its functions are reflected in

(1) The gyroscope can continue to play the role of navigation and correct the problem of inaccurate GPS positioning when the GPS signal is not good.

When the GPS signal is not good, the gyroscope can continue to perform precise navigation based on the known position, direction, and speed, which is also the basic principle of inertial navigation technology. It can also correct the problem of excessive positioning deviation when the GPS signal is not good.

(2) The gyroscope can provide more sensitive and accurate direction and speed than GPS

GPS cannot detect the speed and direction of the car immediately. It can only be measured after a certain distance. Therefore, when your car changes its direction in a non-navigation situation, navigation will not be possible. Recognize the steering of your car, and it turns out to be the wrong direction. The gyroscope can detect the instant direction and speed change so that the navigation software can modify the navigation route in time.

(3) The gyroscope can recognize more sensitively and accurately when getting on the overpass

The accuracy of civilian GPS cannot identify whether an overpass is on or off, but the gyroscope can detect whether the car has moved upward, allowing the navigation software to modify the navigation route in time. Relying on the signal navigation of GPS satellites and the inertial navigation of the gyroscope, the navigation accuracy is effectively improved. Even after the GPS signal is lost, the system can continue to navigate through autonomous calculations and provide accurate driving instructions to the owner.

3. Gyroscope sensor in UAV Flight Control System

The flight control system of the UAV is one of its most important components, and the stable control of the attitude is an effective method for the UAV to perform various tasks smoothly. In the current actual manufacturing and application of UAVs, some UAV products are based on three-axis gyroscopes and inclination sensors to form a full attitude stabilization control system.

UAV

UAV attitude stabilization control belongs to internal loop control, which includes attitude maintenance and control, speed control, and other modes. The inner loop control is based on the three-axis gyroscope and inclination sensor to obtain the flight attitude of the UAV, and through the control of the elevator and rudder, the flight attitude is stabilized and controlled.

The angular velocity information measured by the gyroscope is used as feedback control for stabilization, which makes the aircraft maneuver more "dumb" so that the tilt angle sensor is used to measure the aircraft roll and pitch angles. Then the angular rate information measured by the gyroscope and the attitude angle measured by the inclination sensor is subjected to the strap-down calculation to obtain the fused attitude information. This more complex strapdown algorithm can greatly improve the accuracy of the attitude.

4. Gyroscope sensor in the field of photography/photographing

When we take a video or take a photo, have we ever seen each other? Through a device to ensure that your "camera" is fixed in the same position, no matter how your hands are skewed or your body shakes, it can keep the phone relatively stable. We all know that only when the mobile phone or camera is relatively "stable" can we take beautiful pictures or videos. The core secret that can keep the "stabilizer" always stable is the "acceleration and gyroscope" sensor.

Why is it said that the "acceleration and gyroscope" sensor is the core secret of the selfie artifact? Because the core of the camera stabilizer is to detect the posture of the "camera", and then control the motor connected to the "camera" to do corresponding actions in real-time according to the change of the posture of the "camera". As long as the motor is controlled fast enough, the "camera" can be guaranteed that it can always stabilize in a fixed position. Regardless of whether your hand is shaking from side to side or up and down, your "camera" will be immobile under the control of the steady shooting artifact, thus taking stable pictures and images.

The overall frame of the stabilizer is shown in the figure below, and the orange part is the working part of the acceleration and gyroscope sensor.

the overall frame of the stabilizer

It feeds back the posture of the "camera equipment" to the central MCU processing unit. The central MCU unit controls the motor to perform corresponding actions according to the detected posture and movement of the "camera equipment". The action of the motor keeps the "camera equipment" stable. In this way, the photos taken will be clearer and the recorded video will be more stable.

5. Gyroscope sensor in the smartphone

Gyroscope sensor in the smartphone

The use of the gyroscope is the nearest to our mobile phone. The application of the gyroscope in the mobile phone is mainly reflected in the following aspects:

(1) Navigation.

(2) It can be used in conjunction with the camera on the mobile phone.

(3) Sensors for various games.

(4) Can be used as an input device.

(5) It is also the most promising and application scope in the future.

Ⅴ Development trend of the latest technology of gyroscope sensor

At present, the gyroscope technology is changing from the traditional mechanical rotor gyroscope to the new type of gyroscope represented by the optical gyroscope. The following briefly introduces several new gyroscope technologies that are at the forefront of the technical field, hoping to help readers broaden their horizons and understand the latest development of gyroscope technology.

1. Helium-neon ring laser gyroscope

Compared with the traditional mechanical rotor gyroscope, the main advantages are no mechanical rotor, simple structure (less than 20 parts), good anti-vibration performance, fast start-up, high reliability, and digital output.

In addition, some researchers have also proposed to replace the helium-neon gas with a solid gain medium, which can make the gyroscope have a longer working life, lower cost, and simpler manufacturing. This type of gyroscope is also called a solid-state ring laser gyroscope (solid-state RLG).

At present, the inertial navigation system based on the helium-neon ring laser gyroscope has been widely used in aviation and marine navigation, navigation, guidance, and control of strategic missiles, and has become one of the main high-performance gyroscopes.

2. Fiber optic gyroscope

Beginning in the 1960s, the US Naval Research Office hoped to develop a fiber-optic angular velocity sensor with lower cost, simpler manufacturing process, and higher accuracy than helium-neon ring laser gyroscopes, also known as fiber optic gyroscopes.

At present, the most common fiber optic gyroscope is a phase-sensitive fiber optic gyroscope, which measures the phase shift of two counter-propagating beams in a fiber coil and rotates the sensitive carrier to calculate its angular rate.

Therefore, the accuracy of the fiber optic gyroscope mainly depends on the type of fiber used and the photoelectric detection system, and the bias value is generally between 0.001 degrees/hour and 0.0002 degrees/hour. Now, fiber optic gyroscopes have been widely used in torpedoes, tactical missiles, submarines, and spacecraft.

3. Integrated optical gyroscope

With the development of integrated optical circuits, very complex functions can be implemented on a single chip. Integrated ring cavity lasers with a diameter of several millimeters and photoelectric detection circuits can be integrated on the same chip as the sensitive components of the integrated optical gyroscope. It can greatly reduce the quality and size of existing optical gyroscopes, reduce costs and power consumption, better control thermal effects, and increase reliability. Therefore, optical gyroscopes manufactured by integrated optical technology have good development prospects.

At present, extensive research has been carried out around the integrated ring cavity laser, but the key technology has yet to be broken. In addition, cutting-edge technologies including nuclear magnetic resonance and superfluid have also been verified and will also be applied to new gyroscopes in the future.

Ⅵ Frequently asked questions

1. What is a gyroscope sensor in a phone?

Accelerometers in mobile phones are used to detect the orientation of the phone. The gyroscope, or gyro for short, adds an additional dimension to the information supplied by the accelerometer by tracking rotation or twist.

2. What is the difference between accelerometer and gyroscope?

The main difference between the two devices is simple: one can sense rotation, whereas the other cannot. Using the key principles of angular momentum, the gyroscope helps indicate orientation. In comparison, the accelerometer measures linear acceleration based on vibration.

3.  What does a gyroscope measure?

A gyroscope (from Ancient Greek γῦρος gûros, "circle" and σκοπέω skopéō, "to look") is a device used for measuring or maintaining orientation and angular velocity. It is a spinning wheel or disc in which the axis of rotation (spin axis) is free to assume any orientation by itself.

4.  What is gyroscope sensor used for?

Gyro sensors, also known as angular rate sensors or angular velocity sensors, are devices that sense angular velocity. In simple terms, angular velocity is the change in rotational angle per unit of time. Angular velocity is generally expressed in deg/s (degrees per second).

5.  What are the applications of gyroscope?

Gyroscopes are used in compasses and automatic pilots on ships and aircraft, in the steering mechanisms of torpedoes, and in the inertial guidance systems installed in space launch vehicles, ballistic missiles, and orbiting satellites.

6.  What are the types of gyroscope?

There are three basic types of gyroscope:

Rotary (classical) gyroscopes.

Vibrating Structure Gyroscope.

Optical Gyroscopes.

7.  Who invented gyroscope?

Carl Norden

8.  What keeps a gyroscope spinning?

In the absence of external torques a gyroscope will maintain its angular momentum. An external torque applied in the same direction or in a direction opposite to the angular momentum will cause the gyroscope to speed up or slow down.

9.  What is gyroscope effect?

Gyroscopic effect is ability (tendency) of the rotating body to maintain a steady direction of its axis of rotation. The gyroscopes are rotating with respect to the axis of symmetry at high speed.

10.  Is a gyroscope affected by gravity?

Gyroscopes are affected by gravity, as they have mass, but the faster they spin the less gravity has an effect. Ultimately if the spin was fast enough, then the gyroscope would drift into space.

Related Articles:

What is a Radar Sensor?

MAP Sensor: Working, Structure and Types