Piezoresistive cantilever force-clamp system

Abstract

We present a microelectromechanical device-based tool, namely, a force-clamp system that sets or "clamps" the scaled force and can apply designed loading profiles (e.g., constant, sinusoidal) of a desired magnitude. The system implements a piezoresistive cantilever as a force sensor and the builtin capacitive sensor of a piezoelectric actuator as a displacement sensor, such that sample indentation depth can be directly calculated from the force and displacement signals. A programmable realtime controller operating at 100 kHz feedback calculates the driving voltage of the actuator. The system has two distinct modes: a force-clamp mode that controls the force applied to a sample and a displacement-clamp mode that controls the moving distance of the actuator. We demonstrate that the system has a large dynamic range (sub-nN up to tens of μN force and nm up to tens of μm displacement) in both air and water, and excellent dynamic response (fast response time, <2 ms and large bandwidth, 1 Hz up to 1 kHz). In addition, the system has been specifically designed to be integrated with other instruments such as a microscope with patch-clamp electronics. We demonstrate the capabilities of the system by using it to calibrate the stiffness and sensitivity of an electrostatic actuator and to measure the mechanics of a living, freely moving Caenorhabditis elegans nematode.

The Tactile Receptive Fields of Freely Moving Caenorhabditis elegans Nematodes

“…The force clamp module manages communication with the RTOS/FPGA for the force clamp 16 . The data management module records image processing and stage movement data generated in the HAWK software as well as experimental parameters and stimulus profile data from the force clamp module; it saves data to the hard disk in real time.…”

“…For tracking and targeting, we built on systems reported by Leifer et al 8 and Stirman et al 26 , who implemented real-time tracking for delivering optical stimuli to user-defined body segments ( Figure 1). For mechanical stimulus delivery, we relied on our previous system consisting of a custom, self-sensing, cantilever force probe [18][19][20] integrated into a closed loop control system 16 . HAWK introduces the ability to automatically measure and classify behavioral responses.…”

“…In this way, animals were in the same locomotion state prior to stimulation, independent of the target stimulus position. We used a the real time, closed loop force clamp system to apply a step force profile vertically onto the animal, and maintain the desired force for 100 or 150 ms 16 .…”

“…Using a microfluidic device, McClanahan, et al recently demonstrated a microfluidics-based behavioral touch assay which locally compressed the worms using a pressurized membrane at the top of the channels automatically classifies behavioral response types (pause, reversal, speed-up, and null responses). Central to the function of HAWK are two key, custom innovations: 1) a custom-force sensing cantilever that acts as the stimulator [15][16][17] and 2) an optical system to track and target the animal. The detailed design, fabrication and signal conditioning of these silicon, piezeoresistive cantilevers were previously reported [18][19][20] .…”

Micro-Domain Force Estimation Using Hall-Effect Sensors for a Magnetic Microrobotic Station

“…Thus, the applied force from the environment to microrobot is needed to be measured and then transfered to the human operator's hand. Many methods for measuring force from the micro-Newton to milli-Newton range have been developed, such as atomic force microscopes (6) , microscales, piezoresistive cantilevers (7) - (12) and capacitive force sensors (13) . These force measurement systems have been employed in the research field of microsystem and microassembely, as well as biomedical/ biological research.…”