Actively servoed multi-axis microforce sensors

This paper presents design, fabrication, and calibration results of MEMS-based two-axis capacitive force sensors capable of resolving forces up to 490μN with a resolution of 0.01μN in x, and up to 900μN with a resolution of 0.24μN in y in the passive mode. Electrostatic microactuators are integrated to enable the force sensors to operate in an actively servoed mode, in which system stiffness is modulated using force compensation, greatly increasing force measurement dynamic ranges. When the microforce sensor is actively servoed, an externally applied force is balanced by the electrostatic forces generated by the electrostatic microactuators within the sensor. The movable parts of the sensor are maintained in the equilibrium position, making the system a regulator system. The force measurement is obtained by interpreting the actuation voltages. Probes of different shapes are integrated with the sensors for micromanipulation. Other types of end-effectors, such as microgrippers and microneedles for different micromanipulation tasks can be integrated by modifying the fabrication sequence. The current application of the force sensors is for providing real-time force feedback during microrobotic cell manipulation.