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

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 106 is obtained. A repeatability under 7.8 mu N and a trueness under 15 mu N have been experimentally measured. Finally, the method can be applied to other specifications and applications in terms of range.