A Polyimide Film-Based Simple Force Plate for Measuring the Body Mass of Tiny Insects

Abstract

Insects exhibit excellent maneuvers such as running and flying despite their small bodies; therefore, their locomotion mechanism is expected to provide a design guideline for micromachines. Numerical simulations have been performed to elucidate this mechanism, whereby it is important to develop a model that is physically identical to the target insect’s parts to reproduce kinematic dynamics. In particular, in flight, the shape and mass of wings, which flap at high frequencies, are significant parameters. However, small insects such as fruit flies have small, thin, and light wings; thus, their mass cannot be easily measured. In this study, we proposed a high-resolution and simple force plate to measure the mass of each part of a tiny insect. The device consists of a circular plate supported by flat spiral springs made of polyimide film, and a laser displacement meter that detects the displacement of the center of the plate. The simple plate fabrication process requires only a couple of minutes. A fabricated force plate with a sub-N/m spring constant achieved a resolution of less than 2 µg. As a demonstration, the wing mass of the fruit flies was measured. The experimental results suggest that the wings accounted for approximately 0.4% of the body mass.

Thin Glass Micro Force Plate Supported by Planar Spiral Springs for Measuring Minute Forces

“…Compared with previous polyimide force plates of the same size and with a similar spiral structure [ 18 ], the fabricated glass force plate had a higher resonant frequency, although the force resolution was the same. This is because the glass wafer was thinner than the polyimide film (100 μm), thereby resulting in a lighter weight.…”

“…To develop a force plate suitable for measuring tiny insects, such as fruit flies, the required dimensions, force resolution, and resonant frequency were determined, similarly to in a previous study [ 18 ]. The body of a fruit fly is approximately 3-mm-long, and a plate diameter of 10 mm was assigned to ensure that the plate was sufficiently large to accommodate a fruit fly.…”

“…Although this type of force plate is sufficiently sensitive, its development requires a complex microelectromechanical system (MEMS) process or minute and complex manual assembly, and a fragile structure owing to the concentrated strain. Another measurement principle configures the system as a force plate using a mechanical structure and external displacement meter [ 17 , 18 , 19 ]. Although the measurement system is complex, the force plate element has no electrical components, which simplifies the fabrication process.…”

“…Recently, laser processing has been widely used in microfabrication [ 22 , 23 ]. A previous study developed a force plate using a 100-µm-thick polyimide film [ 18 ], and the device achieved a resolution of less than 0.02 µN, thereby demonstrating its suitability for measuring the body weight and mass of each body part of a fruit fly. However, despite its easy handling and unbreakable characteristics, polyimide is unsuitable for long-length measurements owing to its viscoelastic properties, which cause gradual deformation after a large load is applied.…”

MEMS highly sensitive and large-area force plate for total ground reaction force measurement of running ant

“…Recently, force plates using different measurement principles have been developed for fruit flies. These plates consist of a plate structure supported by mechanical springs and a laser displacement sensor [21][22][23]. The plate has a sufficiently large area to measure the total GRF while the fly is walking.…”