Psychophysical Model of Motorcycle Handlebar Vibration

1
Psychophysical Model of Motorcycle Handlebar
Vibration

• Investigators Prof. George Chiu, Prof. Hong
  Tan
• Students Ali Israr, James Mynderes
• Haptics Interface Research Laboratory
• Herrick Laboratories
• Purdue University, USA

2
Objectives

• Review existing literature on human response to
  vibrations transmitted through the hand.
• Develop a base-line function of human perception
  for motorcycle handlebar vibrations along one
  axis.
• Establish the psychophysical model relating
  physical measurements of vibrations to human
  assessment of perceived vibration levels.
• Make recommendations on handlebar mount design
  parameters for improved rider comfort.

3
Background

• Total perceived acceleration can be calculated
  by
• ISO defined functions
• Critical Band model of Makous et al. (1995)
• ISO weighted function
• Critical band model of Makous et al. (1995)
  implies that - the total perceived energy is
  equal to the sum of the energy of individual
  frequency components above the detection
  threshold curve.
• The base-line frequency function is the detection
  threshold frequency curve in ISO and
  psychophysical methods.

4
Experimental Methods

• Participants Ten participants (5 male and 5
  female, age 22-44 average 27 years) were used in
  two psychophysical experiments.
• Exp. 1 Detection Threshold Experiment
• 10 test frequencies 20, 30, 75, 100, 150, 170,
  200, 230, 260, and 300 Hz.
• Two-interval forced-choice (2IFC), one-up
  two-down adaptive method.
• Threshold value converged to 70.7 percentile
  point to the true value.
• Each participant was tested accumulatively for 2
  hours on different days.
• Exp. 2 Subjective Magnitude Experiment
• 15 test stimulus at different speeds and
  gear-levels were provided by Polaris.
• Each stimulus was randomly presented twice in
  each session.
• Participant rated vibrations to numbers between
  0-100.
• Four sessions were completed for one participant
  in one day.
• Data was normalized for each session and
  participant.
• All experiments were done in closed environment
  with participant sitting in riding posture. Pink
  noise was used through headphones to mask
  surrounding and actuator noise.

5
Experimental Setup

• Test rig A 2005 Victory Vegas motorcycle frame.
• Motran AFX-70NS linear Inertial Force Actuator
  (IFA) powered by a QSC two-channel 70 W audio
  amplifier.
• A PCB 356B18 triaxial accelerometer with PCB
  480E09 ICP signal conditioner (1x to 100x gain).
• One axis feedback control was provided by a
  dSPACE ACE1104 rapid prototyping kit.
• SigLab Dynamic Signal and System Analyzer was
  used for data acquisition.
• Cardboard screen is placed in front of the
  participant to visually partition hand
  vibrations.
• Two LEDs were mounted on the screen in front of
  the participant to indicate experimental steps.
• Foot pedals were used for subject response and
  response recording was done through parallel port
  of a desktop.

6
Results Detection Threshold Experiment

• A typical Stair case function (below).
• Threshold level against test frequencies (right).

NOTE Threshold levels were similar to the
threshold levels derived from the data in
psychophysical literature.
7
Results Subjective Magnitude Experiment

• A psychophysical Model

8
Summary Conclusion

• Recommendations were made on handlebar mount
  design parameters for improved rider comfort.
• Low frequency vibrations (lt50 Hz) had a much
  larger effect on perceived vibration intensity
  than high-frequency vibrations.
• Psychophysical detection threshold was a better
  measure of the baseline function for the human
  perception.
• It is possible to predict the perceived vibration
  intensity from the measured vibration spectrum
  using the psychophysical model.
• Future studies
• Determining thresholds, or baseline functions,
  for two dimensional vibrations and access
  perceived intensity.
• Similar Experiments on design of seat and
  footrest vibrations.