Improvement of strain gauges micro-forces measurement using Kalman optimal filtering

Abstract

Manipulation of small components and assembly of Microsystems require force measurement. In the microworld (the world of very small components), signal/noise ratio is very low due to the weak amplitude of the signals. To be used in feedback control or in a micromanipulation system, a force sensor must allow static and dynamic measurements. In this paper, we present a micro-force measurement system based on the use of strain gauges and a Kalman optimal filter. Using a model of the measurement system and a statistical description of the noise, the optimal filter allows filtering the noise without loss of dynamic measurement. The performances of the measurement system are improved and fast force variations can be measured.

Noise characterization in millimeter sized micromanipulation systems

“…Moreover the resonance frequency of millimeter sized micromanipulation systems is most of time below 1KHz. For instance, in references [7], [25] and [29], the resonance of the microgrippers are 700Hz, 600Hz and 200Hz respectively.…”

“…In that sense, numerous micromanipulation systems (notably microgrippers) based on actuators with high positioning accuracy and good deformation/force ratio can be found in the literature [4] [5] [6]. The size of end effectors can vary from few micrometers [4] up to several tens of millimeters [7] [8]. While micrometric structures are suitable for high resolution positioning, millimeter ones have the advantage of offering large displacements.…”

“…In most cases, noise and vibrations are the main factors reducing the performances of micromanipulation systems for both actuation [9] [10] [11] and sensing [12] [13] leading to a low repeatability and a loss of accuracy. Moreover, when end effectors are used as sensors, vibrations are reflected in the sensor output as a measurement noise reducing significantly the sensing resolution [7] [14]. Undesired vibrations are partially caused by random motions of particles within materials known as thermal fluctuations leading to the thermal noise, and also by external perturbations coming from the surrounding environment reflecting the so called environmental noise.…”

“…Moreover, the noise has to be considered differently according to the dimensions of the micromanipulation system. Taking into account physical origins of noises is usually not addressed in conventional studies dealing with noise and vibration rejection in microrobotics [7] [20] [23] [24]. A better understanding about this will allow a more efficient controller design by an accurate modeling of the noisy process leading to the improvement of achievable closed loop performances.…”

An Overview on Gripping Force Measurement at the Micro and Nano-Scales Using Two-Fingered Microrobotic Systems

“…The resistance variation of the strain gauge is measured. Taking into account the strain gauge deformation and the stiffness of the sensing finger, the gripping force is deduced [26]. The main advantage of strain gauges is that they allow the measurement of high amplitude (in the order of milli-Newtons) forces, but it has a limit in terms of miniaturization 3 .…”