Type
- Inertial Measurement Unit（IMU）
- Inertial measurement unit (IMU) is used not only for measuring dynamics, posture, and orientation of various movements, but also for measuring position. Tamagawa Seiki manufactures various kinds of products such as MEMS Gyro, Fiber Optic Gyros (FOG) and Inertial Measurement Unit (IMU). Therefore customers can select the sensor for a wide range of applications.
- MEMS Gyro
- Sensor making use of MEMS technology which detects the acceleration by using inertial force (Coriolis force) coming from vibration or rotation.
- Fiber Optic Gyro（FOG）
- Turn the optical fibers like a coil in CW and CCW and input light to both directions. By the interference of the output, the wavelength is changed due to Doppler effect according to the motion (red and blue shift). A gyroscope which detects and outputs the change amount.
- Ring Laser Gyro（RLG）
- Ring Laser Gyroscope (RLG) consists of a ring laser having two independent counter-propagating resonant modes over the same path. The difference in the frequencies is used to detect rotation. It operates on the principle of the Sagnac effect which is also usd for Fiber Optic Gyro (FOG).
Performance / Term
- Angular Velocity
- Change ratio of angle (rotation speed, rotation angle) per unit time.
- Acceleration
- Change ratio of speed per unit time. The gravity is a kind of the acceleration.
- Attitude angle
- The angle between the plane of object and the horizontal ground. Inclination towards front-back is called "pitch" while towards right-left is called "roll".
- Heading angle
- Heading angle is compass direction in which the object's nose is pointed. Without compass direction, it is called "yaw" angle.
- Dynamic Range
- Measurable range of a sensor from minimum to maximum of a motion. The reciprocal of a dynamic range is a scale factor.
- Bias and Drift
- Deviation from ideal center. Difference between output in a stationary state and ideal zero. It is also called zero point bias or offset. It becomes an element of the error (integration error) in case of angle calculation.
- Drift is the indication of bias variation size under the influence of environmental condition such as temperature (rise or fall), power supply variation or vibration. There is also a successive change shifting slowly.
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- Random Walk
- Digitalized value of degree of variation (white noise). It is considered to be the noise which a sensor has.
- Scale Factor
- Ratio of sensor output changed by input. It is also called sensitivity (Sensitivity is distinguished from scale in the IEC standard).
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- Linerity
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Linearity is the property of a mathematical relationship (function) that can be represented as a/A×100 (％) in below graph.
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- Resolution
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The resolution is the minimum input of angular velocity that the gyro can identify. To measure the resolution, input the minute angular velocity to the gyro on the precision rate turntable and see the significant change in the gyro output. In some cases, quantization error is interpreted as resolution.
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- Cross Coupling
- Sensitivity against the detection axis by another axis input. Misalignment which indicates direction accuracy is a kind of the cross coupling.
- Allan Variance
- Plot of quotient when the integrated value of gyro output is divided by integral time. It shows a cluster time (averaging time) in a horizontal axis and an Allan deviation (σ) in a vertical axis. We can read the random walk, bias stability etc. from the plot and also represent the noise component of gyro in a graph.
- Bias instability
- Bias instability is one of indicators of gyroscope which is measured by Alan variance method. The smaller the number, the higher the performance of the gyroscope.
- Calibration
- Calibration is the comparison of measurement values acquired from a device with those of a calibration standard equipment.
- Warm Up
- Warming up operation after turning on the power.
Communication
- RS-232
- RS-232 is a serial port interface standard standardized by the Electronic Industries Alliance (EIA). It is widely used as a communication standard for personal computers and communication devices.
- CAN
- CAN is a communication standard standardized by ISO-11898. Originally used as a communication standard inside automobiles, it is now widely used in the fields of construction machinery, agricultural machinery and factory equipment.
Calculation
- GNSS/INS Hybrid Navigation System
- Compound navigation of GNSS and INS (Inertial Navigation System). Technology for high accuracy and stable navigation. The error estimation of inertial sensor by Kalman filter improves the accuracy.
- Leveling Calculation
- Inertial operating algorithm of MEMS-IMU (IMU consists of MEMS gyros and MEMS accelerometers) made by Tamagawa. It enables a high precision dynamic posture measurement to a low cost (low accuracy) gyro.
※Leveling Calculation vs GNSS/INS/VS
- Inertia calculation
- Calculations are performed only with the built-in gyro and accelerometer without referring to GNSS or external speed. This method can be used only in FOG IMU and RLG in which high-precision gyros are used.
- Inertial Navigation
- A method of calculating the position and direction using only inertial sensor. However, there is a characteristic that the error accumulates and increases when moving a long distance.
- Kalman Filter
- This is a calculation method that improves the accuracy of data by estimating the error for a quantity (position, velocity) that changes over time.
Function
- Offset Cancel
- This function calculates the average value of bias (zero point error) at a certain time. The average value of the bias is offset in the subsequent operations.
- Alignment
- If there is a mounting error or tilt on the IMU installation surface, the tilt is normally output based on the horizontal plane, but when using this function, the installation surface can be set to zero.
- Dead zone(Yaw)
- In order to suppress the yaw angle drift, the Z-axis of angular velocity in the dead zone is converted to zero and is not reflected in the yaw angle calculation.
- Dead Reckoning
- Technology of position measurement with high accuracy even in a tunnel without GPS signal by the compound arithmetic procession of the information from gyro sensor, accelerometer etc.
- Sensor Fusion
- By compounding data from several sensors, improve the measurement reliability of the unit or complement defects of each sensor.
