Delays in Admittance-Controlled Haptic Devices Make Simulated Masses Feel Heavier

PLoS One. 2015 Sep 11;10(9):e0138023. doi: 10.1371/journal.pone.0138023. eCollection 2015.

Abstract

In an admittance-controlled haptic device, input forces are used to calculate the movement of the device. Although developers try to minimize delays, there will always be delays between the applied force and the corresponding movement in such systems, which might affect what the user of the device perceives. In this experiment we tested whether these delays in a haptic human-robot interaction influence the perception of mass. In the experiment an admittance-controlled manipulator was used to simulate various masses. In a staircase design subjects had to decide which of two virtual masses was heavier after gently pushing them leftward with the right hand in mid-air (no friction, no gravity). The manipulator responded as quickly as possible or with an additional delay (25 or 50 ms) to the forces exerted by the subject on the handle of the haptic device. The perceived mass was ~10% larger for a delay of 25 ms and ~20% larger for a delay of 50 ms. Based on these results, we estimated that the delays that are present in nowadays admittance-controlled haptic devices (up to 20ms) will give an increase in perceived mass which is smaller than the Weber fraction for mass (~10% for inertial mass). Additional analyses showed that the subjects' decision on mass when the perceptual differences were small did not correlate with intuitive variables such as force, velocity or a combination of these, nor with any other measured variable, suggesting that subjects did not have a consistent strategy during guessing or used other sources of information, for example the efference copy of their pushes.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Biomechanical Phenomena
  • Electrical Equipment and Supplies
  • Female
  • Hand / physiology*
  • Humans
  • Male
  • User-Computer Interface
  • Weight Perception / physiology*

Grant support

This research is supported by the Dutch Technology Foundation STW, which is part of the Netherlands Organization for Scientific Research (NWO) and partly funded by the Ministry of Economic Affairs, Agriculture and Innovation. STW grant 12160. Moog B.V. provided support in the form of salaries for author PL, but did not have any additional role in the study design, data collection and analysis, decision to publish, or preparation of the manuscript. The specific roles of this author are articulated in the ‘author contributions’ section.