Highly performant integrated force sensor
This section deals with the prototyping of a new piezoresistive microforce sensor. An original design taking advantage of both the mechanical and bulk piezoresistive properties of silicon is presented, which enables the easy fabrication of a very small, large-range, high-sensitivity with high integration potential sensor. The sensor is made of two silicon strain gauges for which widespread and known microfabrication processes are used.
The strain gauges present a high gauge factor which allows a good sensitivity of this force sensor. The dimensions of this sensor are 700 μm in length, 100 μm in width and 12 μm in thickness. These dimensions make its use convenient with many microscale applications, notably its integration in a microgripper. The fabricated sensor is calibrated using an industrial force sensor. The design, microfabrication process and performances of the fabricated piezoresistive force sensor are innovative thanks to its resolution of 100 nN and its measurement range of 2 mN. This force sensor also presents a high signal-to-noise ratio, typically 50 dB when a 2 mN force is applied at the tip of the force sensor.
Sensitive multi-DoF microgripper
This force sensor has been integrated with a piezoelectric actuator. Each finger of the microgripper has its own force sensor enabling the measurement of contact force with high accuracy and dynamics. It thus enables to have a highly sensitivie microgripper able to sense forces at the microscale. Below are the picture of the microgripper and its related performances.
A dynamic and non-linear physical model of the microgripper has been investigated and enables to estimate both contact forces and position of the microgripper end-effectors with high accuracy. this models is off great importance for control purpose but also to estimate the unknow characteristics of the component to be manipulated (its position, its stiffness and other mechanical characteristics such as damping).