title: Customization, control, and characterization of a commercial haptic device for high-fidelity rendering of weak forces.
abstract: BACKGROUND
  The emergence of commercial haptic devices offers new research opportunities to enhance our understanding of the human sensory-motor system. Yet, commercial device capabilities have limitations which need to be addressed. This paper describes the customization of a commercial force feedback device for displaying forces with a precision that exceeds the human force perception threshold.
  
  
  METHODS
  The device was outfitted with a multi-axis force sensor and closed-loop controlled to improve its transparency. Additionally, two force sensing resistors were attached to the device to measure grip force. Force errors were modeled in the frequency- and time-domain to identify contributions from the mass, viscous friction, and Coulomb friction during open- and closed-loop control. The effect of user interaction on system stability was assessed in the context of a user study which aimed to measure force perceptual thresholds.
  
  
  RESULTS
  Findings based on 15 participants demonstrate that the system maintains stability when rendering forces ranging from 0-0.20 N, with an average maximum absolute force error of 0.041 ± 0.013 N. Modeling the force errors revealed that Coulomb friction and inertia were the main contributors to force distortions during respectively slow and fast motions.
  
  
  METHODS
  Existing commercial force feedback devices cannot render forces with the required precision for certain testing scenarios. Building on existing robotics work, this paper shows how a device can be customized to make it reliable for studying the perception of weak forces.
  
  
  CONCLUSIONS
  The customized and closed-loop controlled device is suitable for measuring force perceptual thresholds.
authors.affiliation: Robotics, Brain and Cognitive Sciences, Istituto Italiano di Tecnologia, Via Morego, 30, Genoa 16163, Italy. Electronic address: netta.gurari@iit.it.
authors.forename: Netta
authors.initials: N
authors.lastname: Gurari
authors.affiliation: Robotics, Brain and Cognitive Sciences, Istituto Italiano di Tecnologia, Via Morego, 30, Genoa 16163, Italy. Electronic address: gabriel.baud-bovy@iit.it.
authors.forename: Gabriel
authors.initials: G
authors.lastname: Baud-Bovy
mesh_terms: D000465:Algorithms; D002138:Calibration; D055615:Electrical Equipment and Supplies; D004867:Equipment Design; D005246:Feedback; D017276:Friction; D018737:Hand Strength; D006801:Humans; D010812:Physical Stimulation; D055698:Touch Perception; D014584:User-Computer Interface; D014783:Viscosity
keywords: Force feedback device; Force perception; Grip force measurement; Haptics; Stability; Transparency