The way humans and artificially intelligent machines interact is undergoing a dramatic change. This change becomes particularly apparent in domains where humans and machines collaboratively work on joint tasks or objects in teams, such as in industrial assembly or disassembly processes. While there is intensive research work on human–machine collaboration in different research disciplines, systematic and interdisciplinary approaches towards engineering systems that consist of or comprise human–machine teams are still rare. In this paper, we review and analyze the state of the art, and derive and discuss core requirements and concepts by means of an illustrating scenario. In terms of methods, we focus on how reciprocal trust between humans and intelligent machines is defined, built, measured, and maintained from a systems engineering and planning perspective in literature. Based on our analysis, we propose and outline three important areas of future research on engineering and operating human–machine teams for trusted collaboration. For each area, we describe exemplary research opportunities.

The state-of-the-art technique for optical vibration analysis of macroscopic structures is laser-Doppler vibrometry in which a single-laser beam measures the motion in the beam direction. Thus, three laser beams are necessary to investigate three-dimensional (3-D) motions. The laser spots can be separated on macroscopic specimens with scattering surfaces to prevent optical crosstalk between the measurement beams, but such separation is impossible for a microscopic scatter point. We demonstrate a solution for this problem: an optical 3-D vibrometer microscope with a single-impinging laser beam, which collects scattered light from at least three directions. We prove that it is possible to realize a small laser focus of $<3.5-μm$ diameter on a proper scatter point such as an etch hole of a microelectromechanical-systems device to obtain real-time, 3-D vibration measurements with megahertz vibration bandwidth and picometer amplitude resolution. A first measurement of operational-deflection shapes is presented.

The intensity of the reflected measuring beam is greatly reduced for laser-Doppler vibrometer (LDV) measurements on rough surfaces since a considerable part of the light is scattered and cannot reach the photodetector (laser speckle effect). The low intensity of the reflected laser beam leads to a so-called signal dropout, which manifests as noise peaks in the demodulated velocity signal. In such cases, no light reaches the detector at a specific time and, therefore, no signal can be detected. Consequently, the overall quality of the signal decreases significantly. In the literature, first attempts and a practical implementation to reduce this effect by signal diversity can be found. In this article, a practical implementation with four measuring heads of a Multipoint Vibrometer (MPV) and an evaluation and optimization of an algorithm from the literature is presented. The limitations of the algorithm, which combines velocity signals, are shown by evaluating our measurements. We present a modified algorithm, which generates a combined detector signal from the raw signals of the individual channels, reducing the mean noise level in our measurement by more than 10 dB. By comparing the results of our new algorithm with the algorithms of the state-of-the-art, we can show an improvement of the noise reduction with our approach.

An important feature of a heterodyne laser Doppler vibrometer (LDV) is the possibility of measuring an optical path length oscillation at a frequency f at a choosable frequency f_het ± f, at which the photo-electric measurement shows an optical quantum noise that is significantly greater than the detector dark noise. The full-squeezed light enhancement of a heterodyne LDV’s signal-to-noise ratio has not been achieved so far. Here we use a sideband spectrum that is squeezed around f_het = 40 MHz and demonstrate the squeezing-enhanced measurement of an optical path length vibration at f = 1 MHz of about 3.5 dB while fully maintaining the signal power. The proof of principle we provide will enable the realization of ultra-precise LDVs over an extended signal bandwidth for probes or environments that require low intensities.

Scanning laser–Doppler vibrometry (SLDV) can localize and visualize damages in mechanical structures. In order to enable scanning, it is necessary to repeat the vibration. Therefore, this technique is not suited to detect emerging hazards in working machinery that change the vibration behavior. A common technique for such cases is monitoring the vibration excited by machine operation with accelerometers. This technique requires mechanical coupling between sensors and the measurement object, which influences the high-frequency vibration responses. However, in the low-frequency range, local damages do not shift resonances or distort operational deflection shapes (ODS) significantly. These alterations in the vibration behavior are tiny and hard to detect. This paper shows that multipoint laservibrometry (MPV) with laser excitation can measure these effects efficiently, and it further demonstrates that damages influence ODSs at frequencies above 20 kHz much stronger than at frequencies below 20 kHz. In addition, ODS-based damage indices are discussed; these are highly sensitive to minute visible changes of the ODSs. In order to enhance the sensitivity of hazard detection, the response vector assurance criterion value is computed and evaluated during operation. The capabilities and limitations of the methodology on the example of a cantilever with manually emerging damage are demonstrated.

Vibrations in large structures such as buildings, dams, cranes, plants, drilling platforms, bridges, and wind turbines are often difficult to measure because, among other reasons, it is challenging or even impossible to attach suitable vibration sensors to all the positions/locations of interest. Optical, noncontact measurements from the ground, conversely, are only possible for the visibly accessible parts and often require long measurement distances or unfavorable viewing angles from the ground due to the vertical extent of the location of interest on the large structure. Employing noncontact vibration measurement methods from or via an unmanned aerial vehicle (UAV) is preferable for many applications and is, therefore, becoming an increasingly interesting research topic around the world. This paper reviews the current state of the art for measuring and analyzing vibration in large structures with laser-Doppler vibrometry (LDVy) supported by unmanned aerial systems (UASs)—which employ one or more UAVs and associated ground-based control equipment—and related topics, including excitation as well as data collection, transfer, processing, and interpretation. The review includes a brief overview of vibration-determined damage detection in large mechanical and civil structures, associated nondestructive testing (NDT) sensor technologies including in particular LDVy, UAV technology, and other NDT measurements supported by UASs with a focus on LDVy as the preferred vibration sensor technology. Ultimately, following the presentation of the state of the art, we discuss some of the currently foreseen challenges for implementing LDVy with UASs for operational stability analysis of large structures and the currently addressed and possible future research topics required to maximize the benefit of this exciting system integration opportunity.