Embedded inertial sensor for tracking projectile impact on granular media

Abstract

Due to the opacity of most granular materials, it is often desirable to have three dimensional (3D) particle tracking techniques beyond optical imaging to explore granular dynamics. Using inertial measurement units (IMU) embedded in a projectile, we obtain the trajectory of projectile impacting on a granular medium under microgravity using tri-axial acceleration and angular velocity data. In addition to the standard algorithm for reconstruction, we emphasize solutions to various sources of error to determine projectile trajectory accurately.

Challenges in `seeing' through particulate materials

“…Since the pioneer use of accelerometers in tracing projectile motion inside a granular medium [83], there have been substantial progresses in developing more robust and accurate tracking algorithm for the detection of tracer position and velocity in both translation and rotational degrees of freedoms by means of sensor fusion (see, e.g., [84]). As IMU sensors become more and more widely used in consumable products, they become more compact, easier for integration and data transmission, and more readily available.…”

“…For more specific challenges associated with individual steps described above, interested readers may refer to a recent article [84]. In the future, the development of sensing technology allows more information, such as local humidity and temperature, force applied on the surface, magnetic field, to be collected as 'smart' particles going through the sample.…”

Challenges of 'imaging' particulate materials in three dimensions

“…Along with the development of MEMS (micro-electromechanical systems) technologies, sensors such as IMU (inertial measurement units) capable of measuring angular velocity, acceleration, magnetic fields, and other properties can be encapsulated in a microchip with a typical size of a few millimeters for convenient integration into the peripheral circuit with a micro-controller. Since the pioneer use of accelerometers in tracing projectile motion inside a granular medium [101], there have been substantial progresses in developing more robust and accurate tracking algorithms for the detection of tracer position and velocity in both translation and rotational degrees of freedoms by means of sensor fusion (see, e.g., [102]). As IMU sensors become more and more widely used in consumer products, they become more compact, easier for system integration and data transmission, and more readily available.…”

“…Step-by-step coordinate transformation into a fixed laboratory frame is necessary as the moving target may rotate while traveling. For a successful reconstruction, accurate synchronization of accelerometer and gyroscope during the sampling process, removing drifting of the sensor output, as well as an appropriate selection of sampling rate need to be carefully considered [102].…”

“…During this process, error arising from background noise, drift of the raw signal, as well as uncertainty from coordinate transformation, will accumulate. It is recommended to use techniques such as a combination of forward and backward integration to reduce accumulated error [102].…”