Behind the precise hovering of UAVs and the smooth cornering of autonomous vehicle, there is a crucial core processor - Inertial Measurement Unit (IMU). Its accuracy directly determines the accuracy of smart devices perceiving their own posture. A high-precision IMU, whichexcellentPerformance cannot be separated from the most critical process in the production process: factory calibration. As the demand for IMU calibration enters the era of micro radians, the piezoelectric nano rotating table becomes an ideal partner for calibration scenarios with its unique technological advantages.

Inertial Measurement Unit is a sensor device used to measure the motion state of an object. IMU typically consists of an accelerometer and a gyroscope, with the accelerometer used to measure the linear acceleration of an object in three orthogonal directions. Gyroscopes are used to measure the angular velocity of objects around three orthogonal axes. By processing these acceleration and angular velocity data, IMU can calculate the attitude, velocity, and position information of the object.

IMU has the characteristics of high update frequency and high calculation accuracy in a short time. It does not rely on external signals and can work independently in indoor, underground, underwater and other GPS signal constrained environments. Therefore, it is widely used in aerospace, unmanned aerial vehicles, autonomous vehicle, robots, intelligent wear and many other fields.

The accelerometer and gyroscope integrated inside the IMU measure linear acceleration and angular velocity, respectively. Due to some factors, there may be slight deviations in the actual output data: errors caused by installation, non-linear errors in scale factors, or measurement direction deviations caused by misalignment between axes. The essence of calibration is to establish an error model through precise testing, compensate and correct these systematic errors, and ensure that the IMU output data is closer to real motion.

Error Model Diagram

Accelerators usually rely on gravity constant calibration: the direction of gravity vector is fixed. By placing the IMU in different postures and collecting the output values of the accelerometer at various positions, comparing the deviation between the theoretical value and the measured value, the zero bias and scale factor errors of the accelerometer can be calculated, and the accelerometer calibration can be completed.

Dynamic calibration is performed while the IMU is in motion, commonly using a rotating or swinging platform for calibration. The principle of IMU dynamic calibration is to clarify the input values and observe the output values for comparison. Provide a known, constant, and accurate physical quantity (such as a specific angle and angular velocity) for the IMU, use a stable constant angular velocity, combine it with the angular velocity input provided by the turntable, change the IMU attitude, analyze the sensor output differences, calculate all error parameter models, and correct dynamic measurement errors.

IMU factory calibration is not a simple rotation test, but a systematic test of equipment and processes. Its core requirements focus on the following aspects:

The accuracy of sensors has advanced to a more precise level, so the calibration equipment needs to achieve micro arc level attitude adjustment. Traditional turntables are susceptible to mechanical clearances and friction, making it difficult to meet the calibration requirements of high-end IMUs for installation errors and scale factors.

Calibration not only requires measuring static errors, but also verifying sensor performance through dynamic angular velocity testing. This requires the turntable to be able to quickly switch postures, and the motion process should be stable without shaking, avoiding the introduction of additional errors.

When IMU needs to work stably in some extreme environments, calibration also needs to be carried out synchronously with full temperature testing. The equipment needs to be compact in size and not affected by temperature changes.

The piezoelectric nano rotating platform is driven by the inverse piezoelectric effect of piezoelectric ceramics, and the input voltage causes the material to undergo nanoscale deformation. Its nanoscale resolution, frictionless nature, and ultra fast response speed meet the requirements of IMU calibration.

The piezoelectric nano rotating table can generate and stabilize extremely small angular steps (such as micro radians) to accurately calibrate the nonlinear errors of sensors.

Piezoelectric driving has millisecond level response speed and the advantages of being non-magnetic and frictionless. This allows the rotary table to perform extremely smooth, shake free low-speed rotation and scanning, making it an ideal input source for testing sensors. It can help to more clearly separate the dynamic errors of IMU and perform targeted compensation.

By combining multiple piezoelectric products such as piezoelectric nanorotation stage and piezoelectric nanopositioning stage into a multi axis system, a multi degree of freedom precision motion platform can be constructed, which can quickly and accurately adjust the IMU to any theoretical posture required for the calibration process. Its extremely high repeatability positioning accuracy ensures consistency in each calibration, fundamentally guaranteeing the uniformity and reliability of the performance of IMU products at the factory.

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