Optical Detection of Impact Contact Times with a Beam Deflection Probe

Abstract

We present an optical detection technique, called the beam deflection probe, to accurately measure contact times of normal-incidence impacts of steel and sapphire spheres with a transparent glass block. It exploits the deformation of the area that is in a mechanical touch during the rebound. The deformation of the surface acts as a dynamic contact mirror. When illuminated by a laser beam, total internal reflection takes place at the contact mirror, the beam is deflected from it, and its angular deflection history is monitored by a quadrant photodiode. A simple threshold-level data processing of the photodiode signals is used to determine the impact duration. It is shown that the shape of the signal is highly dependent on the location of the impact relative to the center of the laser-beam illuminated area while the determination of the contact time does not depend on the impact position. Using an automated ball release mechanism, the contact time of low-velocity impacts was measured for various ball diameters and approach velocities conforming to the Hertz contact theory. The proposed optical detection of contact times supplements the existing measurement techniques and represents the only alternative to the piezoelectric detection when contact times are to be measured on the microsecond scale.

Dynamics of contact electrification

“…Despite the small mass of the sphere of 10 mg, the peak force exceeds 4 N for the first contact. Scaled according to the radius of the spheres, our data also agree with data observed using a wire attached to the sphere to drive an electric current during contact ( 23 , 24 ) or by optical techniques ( 25 ).…”

Simplified detection of cavitation threshold in control valves

“…2) depending on the pressure drop in the control valve. The next optical method is the laser beam deflection probe (BDP) that linearly converts the light power into the output voltage with a single silicon photodiode [16]. When the laser beam traveling through the liquid inside the valve gets obscured by the cavitation structure (bubble, vapor cloud), the output voltage from the photodiode is reduced proportionally to the transmitted amount of light.…”

Non-contact ultrasonic inspection by Gas-Coupled Laser Acoustic Detection (GCLAD)

“…Optimization of the tools made these techniques usable even on not perfectly smooth or reflective surfaces 21 , 22 , finding applications in numerous industrial fields. Alongside these techniques and tools, there are less established technologies like the Optical Beam Deflection (OBD) 23 , where a laser probe beam is incident on the surface of the piece with a certain angle. The laser beam is reflected from the surface at an angle that depends on the shape of the surface itself, altered by the passage of the ultrasonic wave.…”