In this paper, we study the perception of stiffness while pressing and pinching virtual springs. These exploration events are highly relevant for telerobotics, but their influence on stiffness perception is largely unexplored. Our study contributes to the understanding of the limits of stiffness perception for human-robot interactions. According to our experiments, mean Weber fraction values between 0:134 and 0:166 are obtained for a reference stiffness value of 200 N/m. Our results also show that the differential sensitivity for stiffness is not significantly affected by the actual exploration event. To test the constancy of the extracted Weber fraction values five further reference stiffness values are evaluated suggesting a constant stiffness sensitivity value in the range of stiffness between 135 and 390 N/m.

1. On the Discrimination of Stiffness during
Pressing and Pinching of Virtual Springs
Chair of Media Technology
Technische Universität München
IEEE International Symposium on Haptic Audio-Visual Environments
and Games, Dallas, TX
11 October 2014
Giulia Paggetti
giuliapaggetti@gmail.com
Burak Cizmeci
burak.cizmeci@tum.de
Eckehard Steinbach
eckehard.steinbach@tum.de
Cem Dillioglugil
cem.dillioglugil@gmail.com

2. Technische Universität München
Chair of Media Technology
Teleoperation with perceptual coding
force
position/velocity
transparency stability
Network
operator
teleoperator
force
position/velocity
Ferrel and Sheridan, “Supervisory Control of Remote Manipulation„ IEEE Spectrum, 1967
Hinterseer et al. “Perception-based data reduction and transmission of haptic data in TPTA systems„ IEEE Trans. on Signal
Proc., 2008
11 October 2014 Burak Cizmeci: Discrimination of Stiffness during Pressing and Pinching Events 2

3. Technische Universität München
Chair of Media Technology
3
Model-mediated teleoperation
operator teleoperator
sensors
Model
Estimator
transparency stability
Local
Model parameters
force force
Rendering
Network
position/velocity position/velocity
 Model Parameters
o Object shapes
o Object movement
o Material properties: stiffness, damping and friction
P. Mitra and G. Niemeyer, “Model mediated telemanipulation”, International Journal of Robotics Research, 2008
11 October 2014 Burak Cizmeci: Discrimination of Stiffness during Pressing and Pinching Events

4. Technische Universität München
Chair of Media Technology
Overview
• Introduction to stiffness perception
• Experimental conditions and procedure
• Exp. 1: Pressing vs. Pinching
• Exp. 2: WFs for various references
• Conclusion & Future Work
Burak Cizmeci: Discrimination of Stiffness during Pressing and Pinching Events 4
11 October 2014

5. Chair of Media Technology
Introduction to stiffness perception
Technische Universität München
 Discriminating stiffness
Burak Cizmeci: Discrimination of Stiffness during Pressing and Pinching Events 5
Non-deformable
surface
Deformable
surface
11 October 2014
by pressing by pinching with haptic devices
Perception with direct contact Perception with tools

6. Chair of Media Technology
Stiffness perception with haptic devices
Technische Universität München
Challenges to utilize previously determined perceptual thresholds:
 A wide array of applied methodologies and technologies [1,2,3,4]
□ From custom-designed to commercial haptic devices
□ Different stiffness ranges
□ Different test conditions from real and virtual scenes to augmented reality
 A broad range of stiffness thresholds from 0.036 [3] to 0.30 [1]
[1] M.K. O'Malley and M. Goldfarb. “The implications of surface stiffness for size identification and perceived surface hardness in
haptic interfaces”, ICRA 2002
[2]S. Yamakawa, H. Fujimoto, S. Manabe, and Y. Kobayashi “The necessary conditions of the scaling ratio in master-slave systems
based on human difference limen of force sense” IEEE Trans. On Systems, Man and Cybernetics, 2005.
[3] N. Gurari, K.J. Kuchenbecker, and A.M. Okamura. “Stiness discrimination with visual and proprioceptive cues”, EuroHaptics 2009
[4] M. Kuschel, M. Di Luca, M. Buss, and R. L. Klatzky, “Combination and integration in the perception of visual-haptic compliance
information”, IEEE Trans. on Haptics, 2010
11 October 2014 Burak Cizmeci: Discrimination of Stiffness during Pressing and Pinching Events 6

7. Technische Universität München
Chair of Media Technology
Research questions
1. Does the exploration event make any difference?
□ Experiment 1: Detection of WFs for pressing and pinching with
respect to a reference stiffness 200 N/m
2. Is there any influence of the reference‘s stiffness on the
differential sensitivity for stiffness?
□ Experiment 2: Detection of WFs for pinching with respect to
reference stiffnesses 50, 135, 220, 305 and 390 N/m
11 October 2014 Burak Cizmeci: Discrimination of Stiffness during Pressing and Pinching Events 7

8. Chair of Media Technology
Experimental conditions
 Haptic Device: Force Dimension Sigma 7
 Interacting object: Accordion shaped elastic cubes with non
Technische Universität München
deformable surface rendered with linear model (F=kx).
11 October 2014 Burak Cizmeci: Discrimination of Stiffness during Pressing and Pinching Events 8

9. Technische Universität München
Chair of Media Technology
Experimental procedure
 1-up 4-down adaptive double staircase detection is applied.
 2-IFC (interval forced choice) procedure:
□ 500 ms pause between each stimuli
□ 1600 ms pause between each trial
□ After the second interval, the subject inputs his/her answer
□ A break of 30 sec after 20 trials
□ 5 min break in the middle
 Training session with 40 trials
H. Levitt, “Transformed up-down methods in psychoacoustics” , The Journal of Acoustical society of America, 1971
Burak Cizmeci: Discrimination of Stiffness during Pressing and Pinching Events 9
11 October 2014

10. Chair of Media Technology
Experiment 1: Pressing vs. Pinching
Technische Universität München
 Reference stiffness value 200 N/m compared with harder and softer
stimuli
 10 male and 4 female (7 subjects per group), aged between 22 and 30
Group Pressing
Starting stiffness value
Pinching
Starting stiffness value
202.5 N/m (below threshold) 202.5 N/m (below threshold)
262.5 N/m (above threshold) 262.5 N/m (above threshold)
197.5 N/m (below threshold) 197.5 N/m (below threshold)
137.5 N/m (above threshold) 137.5 N/m (above threshold)
Group A
above reference
Group B
below reference
11 October 2014 Burak Cizmeci: Discrimination of Stiffness during Pressing and Pinching Events 10

11. Technische Universität München
Chair of Media Technology
Experiment 1: Results
Groups Pressing
(WF±σ)
Pinching
(WF±σ)
Group A 0.147±0.047 0.166±0.032
Group B 0.134±0.032 0.143±0.041
11
ANOVA factors F(1,12) p-value significant
pressing vs. pinching 1.93 0.19 No
above vs. below reference 0.97 0.34 No
Interaction between event
0.28 0.60 No
and group
11 October 2014 Burak Cizmeci: Discrimination of Stiffness during Pressing and Pinching Events

12. Chair of Media Technology
Technische Universität München
Experiment 2 : WFs for various references
 Pinch the object using the gripper fingers
 Reference stiffness values 50, 135, 220, 305, 390 N/m compared
with harder and softer stimuli
 13 new participants (5 female) aged between 23 and 28
Reference Starting point
above threshold
Starting point
below threshold
50 N/m 47.5 N/m 7.5 N/m
135 N/m 132.5 N/m 92.5 N/m
220 N/m 217.5 N/m 177.5 N/m
305 N/m 302.5 N/m 242.5 N/m
390 N/m 387.5 N/m 287.5 N/m
Burak Cizmeci: Discrimination of Stiffness during Pressing and Pinching Events 12
11 October 2014

13. Technische Universität München
Chair of Media Technology
Experiment 2 : Results
Reference 50 N/m 135 N/m 220 N/m 305 N/m 390 N/m
WF±σ 0.281±0.127 0.151±0.05 0.143±0.032 0.127±0.038 0.132±0.034
 Significant difference is detected between softest reference 50 N/m
and the other reference values. F(4,48)=15.94, p=0
 No statistical difference between 135, 220, 305 and 390 N/m
Burak Cizmeci: Discrimination of Stiffness during Pressing and Pinching Events 13
11 October 2014

14. Technische Universität München
Chair of Media Technology
Conclusion
 We studied stiffness perception of virtual springs
 We analyzed two events: pressing and pinching
 Observation 1:
□ No significant difference between pressing and pinching
 Observation 2:
□ No statistical perceptual difference between stimuli (135 – 390 N/m) for
pinching
11 October 2014 Burak Cizmeci: Discrimination of Stiffness during Pressing and Pinching Events 14

15. Technische Universität München
Chair of Media Technology
Future Work
15
• Further investigation for the stiffness range (50 - 135 N/m )
 Perform experiments on deformable surface compliant objects
 Perform experiments on incongruent visual-haptic information
o Under delay conditions
 Validation of results on a real physical interaction
 Usage of these thresholds in stiffness data reduction for model-mediated
teleoperation
11 October 2014 Burak Cizmeci: Discrimination of Stiffness during Pressing and Pinching Events

16. Technische Universität München
Chair of Media Technology
Thank you for your attention!
11 October 2014 Burak Cizmeci: Discrimination of Stiffness during Pressing and Pinching Events 16