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Human Sensitivity In Forced Feedback Systems (07 31 2009 02 28 18)


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This is a paper which got published in SAE Conference proceedings in October 2009.

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Human Sensitivity In Forced Feedback Systems (07 31 2009 02 28 18)

  1. 1. 09CV-0117 Human Sensitivity in Forced Feedback Systems as a Function of Frequency and Amplitude of Steering Wheel Vibrations Nimmagadda, P., Tkacik, P.T., Merrill, Z. A., and Kadire, N. R. The Department of Mechanical Engineering and Engineering Science The University of North Carolina at Charlotte Copyright © 2009 SAE International ABSTRACT carrier, can be much more catastrophic than an ordinary car accident. A typical fully-loaded large A warning system is described as, that improves commercial truck can weigh 80,000 pounds or safety in an over the road truck application by more, while an average passenger automobile warning the driver with steering wheel vibration of weighs approximately 3,000 pounds. While impending roll over. This work focuses on creating statistics show that truck drivers are generally a Haptic feedback and the corresponding driver much more careful on the road than response to a range of frequencies and amplitudes automobile drivers, and thankfully the incidence of of vibration at the steering wheel. The haptic fatal crashes involving trucks and other large feedback system is the endpoint of the entire vehicles has declined in recent years, large truck warning system. An experimental road going crashes still accounted for 5,350 fatalities and system is designed, presented, and tested. The 133,000 injuries in 2001. experimental data reveals information about the response of the human subject to the frequency of The subject of interest in this paper is over-turning steering wheel vibration, while driving a vehicle. accidents and a system to avoid them by providing Data variability is investigated through sampling of an effective warning. Haptic technology refers to a population of drivers. The experimental setup technology that interfaces to the user via the sense probing the amplitude and frequency information is of touch by applying forces, vibrations and/or analyzed. Objective measurement anomalies in the motions to the user. In this case a mechanical data were seen in the subjective tests as well. stimulation is used to warn a driver of a potential Some conclusions are given about the applicability rollover. The system tested is comprised of a of laboratory tests to moving vehicle tests. vibration causing device attached to a steering wheel. The subject of interest is the human INTRODUCTION response to a range of vibration amplitude and frequency. A traffic accident involving a commercial truck, such as an eighteen-wheeler or other large freight
  2. 2. In this system, the vibration causing equipment adaptable system would have had a variable starts the vibration ‘before’ a potential rollover. For eccentricity on a moving eccentric weight. The giving a suitable range of values for the term dilemma was in hitting a driver’s hands and ‘before’ is a project in itself. But here, it is not in the distracting him/her while controlling a moving scope to assess this numerical range but, to vehicle. The solution is shown in figure 3, in which assess the range of frequencies that is apt to be the eccentricity is incorporated into a circular perceived as a warning signal instead of creating flywheel. panic in the driver. EXPERIMENTAL SETUP (VEHICLE) The experimental setup consists of an electronic motor controller, a connecting control wire and a steering wheel mounted motor/shaker system. For reasons of application, it is a mobile system that operates on 12 VDC and runs off of a vehicle “cigarette lighter”. Eccentric hole in flywheel Flywheel Electric motor Figure 2. Image of the steering wheel shaker motor being attached to truck steering wheel. Control Steering wire Wheel Figure 1. Schematic layout of steering wheel shaker experimental system. The Control Wire - has the appropriate connector to the electronic motor controller plus a length of coiled cable that is to be wrapped around a steering wheel column and allows the control wire to wind up and unwind while the steering wheel is turned, (see figure 1). Figure 3. Image of the steering wheel shaker motor The Electric Motor with Clamp – is attached to flywheel with the eccentric hole. the steering wheel with a clamp that allows a wide range of steering wheel sizes. Figure 2 shows it The electronic controller has a collection of controls being attached to a truck steering wheel but it was on its top face. These include: also able to attach to very small steering wheel diameters. • main power, • motor direction, The Flywheel With Eccentric Hole – generates the shaking force on the steering wheel. The • a max speed function, concern for safety with a spinning flywheel was the • engagement of motor braking, determining factor on the design. A more • a variable speed potentiometer.
  3. 3. DB300-0 CD Brush Motor Driver Common (ground) On/Off Maximum speed Forward/Reverse Motor braking s/w no Motor speed s/w no Figure 6. LabView screenshot of motor control program GUI. s/w no s/w no 12 VDC in 2 KΩ potentiometer 0 – 10 VDC power out to shaker motor Figure 4. Shaker motor control wiring diagram. Figure 7. LabView block diagram control and data acquisition program. Figure 5. The motor controller box and both main Figure 5 shows the motor controller. Also shown is power and coiled motor wiring. the arrangement of the coiled motor power wire.
  4. 4. The yellow wire at the bottom is the main power tricky venture. All tests were done at low speeds wire plugged into the 12 VDC “cigarette lighter” and on the UNC Charlotte campus (light traffic outlet. This eccentric hole flywheel was used for all areas). moving vehicle tests. The motor controller was small enough to fit easily into a moving vehicle without issues. For additional control, a LabView program was incorporated into the system that allowed exact voltage control of the motor, (see figure 7.). This bypassed the potentiometer of figure 4 and provided the voltage directly. An accelerometer was mounted to the shaker and provided the frequency response at these voltages. Figure 6 shows a screenshot with the round voltage control dial on the left and the frequency spectrum plot, data file, and amplitude vs. time plots. Figure 8 shows the connections between the Figure 9. Vehicle test with accelerometer on components of the experimental setup. steering wheel shaker. Figure 8. Flow Diagram of the Experimental setup. Figure 10. Moving tests with vehicle underway. EXPERIMENTAL TESTS (VEHICLE) The most significant feature of the moving tests The experiments in the vehicle were done both was the large vibration required to overcome the stationary and with the vehicle moving. natural vibration levels found on a truck. Whereas on the stationary tests we recorded “not In figure 9, the small box ahead of the controller is noticeable”, “very weak”, and “weak” vibrations; in the charge amp for the accelerometer and the the moving tests, there was no “very weak” level. small box to the rear of the controller is the That is, it was either “weak” or “not noticeable” with National Instruments I/O interface. These all fit on nothing in between. the center console of the truck. EXPERIMENTAL SETUP (LABORATORY) In figure 10, it was found that while driving a vehicle with multiple wires connected to the The laboratory based experimental setup is as steering wheel, despite great efforts to keep them shown in the Figure 9. It consists of gaming from knotting up in the steering wheel, this was a steering wheel with the vibration causing
  5. 5. equipment with a accelerometer installed on it. It The shaker system mounted easily and allowed a also has the motor controller, the NI-USB 6008 wide range of subjects. Since it wasn’t particularly DAQ card, the Kistler dc charge amplifier and the heavy, it could also be transported to a variety of LabView installed Laptop. locations. The accelerometer output is given as an input to The polar moment of inertia and the diameter of the coupler (charge amplifier) which then amplifies the game console steering wheel is considerably the signal and outputs it through the USB lower than for a actual vehicle steering wheel, (see connector to the Labview software. The Labview figure 9 and 10). This had two major effects. First, program is also used to control the speed of the the steering wheel did not have the ‘normal’ feel of motor by controlling the voltage input to the motor a steering wheel in a vehicle. It felt like what it through the NI-DAQ USB 6008 device. was, a game console steering wheel. Second, since the inertia was lower, the ratio of inertias between the laboratory based steering wheel and the shaker eccentric was such that the vibrations were stronger, (see figure 12). This was considered a positive effect as the eccentric wheel proved to supply a weak vibration signal in the truck. At the game console, the amplitude of vibration seemed more appropriate for this experiment. Figure 11. Steering Wheel Shaker Laboratory setup Figure 13. Driver’s view of laboratory based experiment. Figure 12. Close up of lab based experiment. RESULTS The laboratory based system used a popular video Tests were performed in three conditions; the game steering wheel console clamped to a table. laboratory tests, the stationary vehicle tests, and tests in a moving vehicle.
  6. 6. Figure 14 shows the relationship between the weight was sensitive to the truck steering system. voltage to the motor and the fundamental It appeared that at some motor speeds, the resonance or motor speed. As would be assumed, eccentric appeared to be out of phase with the the Natural Frequency, or First Harmonic of the shaker system and a vibrational damping occurred. system is tied to the rotational speed of the At other motor speeds, these two would resonate eccentric weight. together and add to the amplitude. What is most significant about the plots is the relationship of the test methods to motor speed. That is, between the lab test and the stationary steering wheel test, at the same motor voltage, the lab test spins much faster and resonates at a higher frequency. The frequency or speed difference grows with motor voltage. It was felt that this was logical as the lower inertia of the lab steering wheel allowed for it to ‘ring’ at a higher frequency and thus the motor rotated faster as well. Curiously, in the mobile tests for the same conditions this trend reversed and the large truck steering wheel then allowed the motor to turn faster. This counter-intuitive result may have been a result of the power steering of the truck while moving or an interaction of vibrational frequencies Figure 15. Accelerometer Natural Frequency that naturally permeate the steering system. vibration amplitude versus motor voltage during the stationary truck test. It was also possible to drive the truck and sense the additive effect and damping effect at these different eccentric motor speeds. That is, as the motor voltage increased and the motor speed increased, the vibration would get larger, then subside, and then at a higher spedd, re-excite and vibrate even more. Figure 14. Natural Frequency (Hz) of the three test systems as a function of motor voltage. Figure 15 revealed a vibrational pattern that could be sensed by the driver during the driving test. The amplitude values plotted are selected from the vibration of the accelerometer on the shaker system at the natural frequency. This revealed that the harmonic resonance of the motor eccentric Figure 16. Data plot of the response of the subjects vs the voltage input to the motor for laboratory test
  7. 7. ‘moderate’. That is, at the accelerometer dip in amplitude (figure 15), there was a corresponding change in the opinion from ‘strong’ to ‘moderate’. At higher voltages and motor speeds, the vibration continued as expected to rise and the trends in vibration amplitudes and respondants opinions returned to the stronger vibration levels. In table 1, the values corresponding to the four catagories of responses are the medians of motor voltage. For example, as can be seen in Figure 16, the median motor voltage for moderate is 1.2 V. It is observed that the ratio is around 0.66, which implies that lab test produces the similar human response at 0.66 times the motor voltage of a stationary on-vehicle test. Figure 17. Data plot of the response of the subjects vs input to the motor during a stationary truck test CONCLUSION Human Lab A warning system is described as the one that response test On vehicle Ratio improves the safety in an over the road truck application by warning the driver with steering Very Weak (V) 0.5 0.8 0.63 wheel vibration of impending roll over. This work focuses on the driver response to a range of Weak (V) 0.8 1.1 0.73 frequencies and amplitudes at the steering wheel. It does not depend on, but is in collaboration with a Moderate (V) 1.2 1.8 0.67 (heavy truck) trailer rollover sensor. Strong (V) 1.8 2.9 0.62 An experimental road going system, a stationary vehicle test and a laboratory based steering wheel Table 1. Center Voltage for each response and the shaker are designed, presented, and tested. The ratio experimental data reveals information about the sensitivity of the human driver as a function of During testing, the respondant was told to describe steering wheel shake frequency and amplitude. the vibration. The descriptive terms were defined to the respondant prior to testing. “Moderate” was On the stationary tests we recorded “not defined as a vibration that was not so strong as to noticeable”, “very weak”, and “weak” vibrations; in cause a sense of panic but not too weak that it the moving tests, there was no “very weak” level. couldn’t be felt at all. “Very Strong” was described That is, it was either “weak” or “not noticeable” with as a vibration that might startle the respondant nothing in between. when driving a vehicle. “Weak” and “Strong” were intermediate levels and “Unnoticeable” was Data variability was investigated through sampling described as just that. “Very Weak” was defined of a population of drivers, and found to be in sync as a vibration as the edge of perception. with the anomalies in the vibration measured. The experimental setup probing the amplitude and When reviewing figure 15, it was noticed that the frequency information was analyzed. For this resonance was present in the desktop tests as system, it was found that there was a correlation well. It is noticed that the truck test vibration at 1.5 between the laboratory test and the stationary volts has a dip in the amplitude of vibration, see vehicle test. Comparing the median motor voltage figure 15. In figure 16, at 1.5 volts, the percentage between the two tests showed that there was a of respondants gave a subjective opinion that also 0.66 ratio of shaker motor voltage to the human showed an increase from ‘strong’ back to response between the tests.
  8. 8. In summary, it has been determined that the and Dr. Peter Tkacik is an Assistant Professor of laboratory based steering wheel shaker test can Mechanical Engineering and Engineering Science provide stationary on-vehicle test results by using a in the Lee College of Engineering of the University 0.66 correction factor on the motor voltage. of North Carolina at Charlotte. They can be Therefore, on-vehicle tests may be simulated in the reached for Mr. laboratory using this correction. Nimmagadda, for Mr. Kadire, and for Dr. Tkacik. Additionally, ACKNOWLEDGMENTS Dr. Tkacik can be reached at (704) 687-8114. The authors want to acknowledge the support for equipment and resources donated by the Mechanical Engineering and Engineering Science Department of UNC at Charlotte. Also the help extended by many of the friends and colleagues. REFERENCES 1. Giacomin, J., Fustes, F., “Subjective equivalence of steering wheel vibration and sound”, International Journal of Industrial Ergonomics, 35 (2005) 517-526. 2. Mandayam A. Srinivasan, Ki-Uk Kyung “Perceptual and Bio mechanical Frequency Response of Human Skin: Implication for design of Tactile Displays”,IEEE First Joint Eurohaptics Conference and symposium on Haptic Interfaces for Virtual Environment and Teleoperator Systems, 0-7695-2310-2/05. 3. Roberts J.R, Jones R., et al,Evaluation of vibrotactile sensations in the ‘feel’ of a golf shot, Elsevier Science ‘Journal of Sound and Vibration’ 285 (2005) 303 – 319. 4. Anthony J Champagne, “Correlations of Electric power Steering Vibration to Subjective Ratings”, SAE 2000 World Congress, Human Factors in 200: Driving, Lighting, Seating Comfort, and Harmony in Vehicle Systems (SP- 1539). 5. Cebon D, “Heavy Vehicle Vibration – a case th study.” Proc.9 IAVSD symposium on The Dynamics of Vehicles on Roads and on Tracks., Linkoping, Sweets and Zeitlinger, 1985. 6. 7. Lamri Nehaoua, Hakim Mohellebi et al,“Design and Control of a Small-Clearance Driving Simulator” IEEE Transactions on Vehicular technology, Vol.57, No.2, March 2008. CONTACT Prajwal Nimmagadda and Nishanth Reddy Kadire are working on their Masters of Science degrees