Vision-Based Microforce Measurement With a Large Range-to-Resolution Ratio Using a Twin-Scale Pattern

Abstract

Force sensors are often required in order to work at the microscale, but existing ones rarely meet all expectations, particularly in terms of resolution, range, accuracy, or integration potential. This paper presents a novel microforce measurement method by vision, based on a twin-scale pattern fixed on a compliant structure. This approach enabled subpixelic measurement of position by the use of a micromachined pattern based on the Vernier principle. This method also presents flexibility, insensitivity to electronic noise, fast operating time, and ease of calibration. The major contribution consists in the large range-to-resolution ratio of the measurement system. With an experimental range of 50 mN and a resolution below 50 nN, a range-to-resolution ratio of 10 6 is obtained. A repeatability under 7.8 μN and a trueness under 15 μN have been experimentally measured. Finally, the method can be applied to other specifications and applications in terms of range.Index Terms-Microforce sensor, range-to-resolution ratio, twin scale, vision.

Transverse compressive properties of natural fibers determined using micro mechatronic systems and 2D full-field measurements

“…When an external force is applied to the tip of the sensor (Fig. 1), a relative displacement is induced between two parts in the middle; (2) two periodic patterns sputtered onto these two parts; (3) a vision microscope to track the relative motions of the patterns and a Fourier-based transform enables to estimate the relative displacement between the two parts [5,6]. Based on this principle, it is then possible to estimate the external force applied to the sensor (knowing the stiffness previously calibrated).…”

2D visual micro-position measurement based on intertwined twin-scale patterns

“…We previously presented a displacement measurement method based on pattern [13], [14]. Despite a high performance level, this method is limited to one-direction measurement.…”

“…This method was already applied to displacement measurement along one direction in a previous work [13]. We also applied it to the measurement of a force through the use of a compliant structure [14]. Experiments showed a 5 nm error for a range of 168 µm and real-time processing.…”

Pattern-based vision for microrobotic manipulators calibration and servoing

“…From the knowledge of the stiffness between the shuttle and the base plate, we derive the forces applied to the shuttle from the measurement of its displacements. The stiffness is measured from the different frequencies of free oscillations with and without an additional known mass [9].…”

“…Recently, we proposed a concept based on a twin-scale pattern with two different periods that allows a large range-toresolution ratio and a fast operating time [7], [8], [9]. In this paper, we presents some recent results on nanometric position and microforce measurement using this twin-scale method.…”