3-D force control on the human fingerpad using a magnetic levitation device for fingernail imaging calibration

Abstract

This paper demonstrates fast, accurate, and stable force control in three axes simultaneously when a flat surface is pressed against the human fingerpad. The primary application of this force control is for the automated calibration of a fingernail imaging system, where video images of the human fingernail are used to predict the normal and shear forces that occur when the fingerpad is pressed against a flat surface.The system consists of a six degree-of-freedom magnetic levitation device (MLD), whose flotor has been modified to apply forces to the human fingerpad, which is resting in a passive restraint. The system is capable of taking simultaneous steps in normal force and two axes of shear forces with a settling time of less than 0.2 seconds, and achieves a steady-state error as small as 0.05 N in all three axes. The system is also capable of tracking error of less than 0.2 N when the shear force vector rotates with a frequency of 1 rad/s. This paper also demonstrates the successful tracking of a desired force trajectory in three dimensions for calibrating a fingernail imaging system.

Force prediction by fingernail imaging using active appearance models

“…The data used in this paper was collected in an automated calibration setup similar to that used previously [7]. A hybrid controller (position-force) with feedback linearization is implemented on a Magnetic Levitation Haptic Device (MLHD).…”

5-D force control system for fingernail imaging calibration

“…In previous works, the finger dynamics have been modeled as a linear approximation, since our force range is small. The finger stiffness K f is estimated at 1200N/m and the finger damping b f is estimated at 5 N/(m/s) [3].…”

“…To have the calibration carried out efficiently and automatically, a passive 3-degrees-of-freedom (DOF) force calibration platform was designed in [3], which was composed of a 6-DOF Butterfly Magnetic Levitation Device (Maglev) and a 6-axis ATI Nano 17 force sensor. By using both position and force loop, the device could apply desired calibration Yun Lin and Yu Sun are with the Department of Computer Science and Engineering, University of South Florida.…”

Development of a Finger Pad Force Display for a Hand Haptic Interface

“…The device should be easy to wear and should not obstruct the movement of the hand. Previously developed haptic devices for the finger tips or finger pads [16]- [19] have been problematic in that forces could not be applied to two finger pads of a finger simultaneously because of the size of the device or because the applied forces were insufficient. Therefore, we developed a novel finger pad force display device, as shown in Fig.…”