The laser accelerometer is a particular type of accelerometer family, used when it is necessary to carry out extremely precise measurements that cannot be obtained with other types of instruments. The operating principle is based on the physical principle that acceleration is a derivative of speed over time. In this device, a laser interferometer measures instant by instant the movement of the moving object, a computer connected to it performs the second derivative with respect to time, thus directly obtaining the acceleration value.
A laser accelerometer comprises a frame having three orthogonal input axes and multiple proof masses, each proof mass having a predetermined blanking surface. A flexible beam supports each proof mass. The flexible beam permits movement of the proof mass on the input axis. A laser light source provides a light ray. The laser source is characterized to have a transverse field characteristic having a central null intensity region. A mirror transmits a ray of light to a detector. The detector is positioned to be centered on the light ray and responds to the transmitted light ray intensity to provide an intensity signal. The intensity signal is characterized to have a magnitude related to the intensity of the transmitted light ray.
The proof mass blanking surface is centrally positioned within and normal to the light ray null intensity region to provide increased blanking of the light ray in response to transverse movement of the mass on the input axis. The proof mass deflects the flexible beam and moves the blanking surface in a direction transverse to the light ray to partially blank the light beam in response to acceleration in the direction of the input axis. Control responds to the intensity signal to apply a restoring force to restore the proof mass to a central position and provides an output signal proportional to the restoring force.
The problems with these devices are that they are expensive, slightly bulky, they require the interferometer to be mounted on the ground (or on a place to be considered fixed), and the laser must be pointed continuously towards the moving object.