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CAN measuring unit for mobile machines

Micro-electro-mechanical system (Mems) inertial sensors are commonly used for orientation, pose estimation, and tracking. Due to their size and cost, they are used in automotive and industrial applications. Gemac introduces its point of view.

Figure 1: Gemac Motus is a 6 degrees-of-freedom inertial measurement unit with a 3-axis accelerometer and a 3-axis gyroscope (Source: Gemac Chemnitz)

The complete article is published in the March issue of the CAN Newsletter magazine 2022. This is just an excerpt.

With Gemac Motus, a configurable sensor measuring unit was designed for the most varied fields of application to perform 6-axis motion acquisition on mobile machines, such as construction vehicles, agricultural machines, forestry machinery, cranes and hoisting equipment, as well as vessels. The sensor consists of a 3-axis accelerometer measuring the external forces acting on the sensor in all three spatial directions, including gravity. This makes the accelerometer the perfect choice for measuring the orientation or inclination of the device for static cases which means, without the influence of external forces besides gravity. The 3-axis gyroscope allows the measurement of the turn rate as angular velocity around the three sensor axes.

The orientation can also be calculated from the gyroscope data by integrating the turn rate over time. The advantage of the measurements from the gyroscope is that it is not affected by external accelerations, which makes it suitable for dynamic applications. By combining the accelerometer and gyroscope data using a so-called sensor fusion filter, the sensor can provide precise orientation information in static and dynamic applications, making the sensor fusion technology crucial for mobile machines.

Figure 2: Comparison of the integration of gyroscope data by the sensor itself (top) and by an external control unit (bottom). The integrated data processing leads to a lower standard deviation of the signal and thus to more precise data (Source: Gemac Chemnitz)

Integrated calculations for precision

Traditional IMU’s (inertial measurement unit) only provide the raw data for acceleration and angular rate to a controller unit, where further calculations, like integrating the signals, are performed. This brings potential inaccuracies, resulting from signal delays, different time stamps, or rounding of the numbers. Gemac Motus includes calculations in the measurement unit, like, for example, the integration of the angular rate to angle values using internal high precision timestamps. With the internal calculation, the stability of the gyroscope output data can be im-proved essentially (see Figure 2). The already preprocessed data can then be output on the CAN network, thus saving computation time and memory in the controller unit. Besides the acceleration and angular rate in all three directions, Motus provides the output of inclination values in the format of quaternion, Euler angles, or perpendicular angles. Both angle formats can be output with or without sensor fusion, covering both static and dynamic applications.

The CANopen version implements the CiA 301 (version 4.2.0) CANopen application layer and communication profile. The CANopen device profile for inclinometers (CiA 410 version 2.0.0) is supported for the inclinometer function. The output signals can be mapped to up to four TPDOs (Transmit Process Data Objects). The J1939 version provides several standardized Parameter Groups like slope sensor information - Parameter Group Number (PGN) 61481, acceleration sensor (PGN 61485), and angular rate information (PGN 61482). Further, a set of proprietary messages is available, allowing flexible and user-specific mapping of the required output signals.

If you would like to read the full article, you can download it free of charge or you download the entire magazine.


Publish date

CAN Newsletter March 2022