2023 ASEE Annual Conference & Exposition

We are developing a suite of tools and techniques utilizing optical measurements for teaching a variety of upper-level engineering and physics topics. These designs are intended to be inexpensive and accessible for non-experts. Here we report progress on two tools: a digital holography apparatus for measuring mechanical strain at the micron-level, and a diode laser-based feedback controls system. The holography apparatus has been used once to date for teaching a junior/senior undergraduate mechanical measurements laboratory, while the laser power system will be used in the next semester to teach principles of feedback control systems to electrical and mechanical engineering students. In this paper, we present the designs of the tools and preliminary results from teaching engineering labs and projects with these tools. These tools benefit students by providing a novel alternative to traditional engineering lab apparatus, the opportunity to explore high-precision measurements in a standard undergraduate lab setting, and a starting point for future projects to add new features in the context of project-based learning.
We use digital holography for imaging the mechanical deformation of a loaded beam. Our prior work characterized the deformation and related it back to the material’s Young’s modulus; however, that approach suffers from an unclear boundary condition, given that the results typically fell in between the two extremes of rigidly clamped and simply supported boundaries. By measuring with different clamping and loading conditions (i.e. one side clamped, end-loaded vs. center-loaded) we have characterized the boundary condition with greater accuracy, and now can extract a Young’s modulus from this setup that is accurate to within 25%.
The goal of the laser feedback controls lab is for students to create a feedback loop that stabilizes the laser power to a constant level. The apparatus uses a printed circuit board and some 3D printed mounts to provide the students with a powered laser, a conditioned photodiode signal that is proportional to laser power, and an area into which various optical filters can be inserted to rapidly adjust the laser power, useful for testing the feedback response of the students’ control algorithm. Either digital or analog control signals are compatible with the hardware; we plan to have students use primarily analog control methods because they mostly closely match the theoretical framework (i.e. Laplace transforms) that is taught in this course. We anticipate teaching with the laser-photodiode system presented side-by-side with the more traditional servo motor system. It is anticipated that having a second physical system to deepen knowledge and develop new intuition will be of benefit to the students’ learning outcomes.
This work is supported by the NSF Division of Undergraduate Education.