Evaluation of Deadband Effect in Steer- by-wire Force Feedback System by Using Driving Simulator Nuksit Noomwongs a and Sunhapos Chantranuwathana b

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1 Applied Mechanics and Materials Submitted: ISSN: , Vol. 619, pp Accepted: doi: / Online: Trans Tech Publications, Switzerland Evaluation of Deadband Effect in Steer- by-wire Force Feedback System by Using Driving Simulator Nuksit Noomwongs a and Sunhapos Chantranuwathana b Department of Mechanical Engineering, Chulalongkorn University, Bangkok, Thailand, a Nuksit.N@eng.chula.ac.th, b Supavut.C@chula.ac.th Keywords: Driving Simulator; Steer-By-Wire (SBW); Deadband; Steering Force Feedback Model. Abstract. This paper presents an evaluation of dead band in force feedback which affects on driving precision with Steer-by-Wire System by using Driving Simulator. Dead band is considered as a zero zone of a relation between Force feedback torque and hand wheel angle. Experimental was designed to focus on dead band size from 0 to ±10 degrees of Force feedback model. The result has shown that the driver has the best driving precision with dead band size of ±4 to ±6 degrees. Introduction By-Wire technology is used widely in automotive application nowadays such as Drive-by-Wire in acceleration system and Steer-by-Wire (SBW) in steering system. Steering feel or steering force feedback is considered to be the 2 nd rank importance for driving after the vision feedback [1]. When SBW is used, it gives the freedom to feedback the desired force (torque) to the driver which can improve the driving and handling performance [2]. The evaluation of the steering force feedback model is carried out by Driving Simulator with the designed track geometry [3]. The track geometry consists of straight and curve line. And the evaluation of force feedback model is considered by using error of vehicle position from the center line of the track [4]. Deadband or dead spot on the force feedback model has influence on the stability of the vehicle especially at high speed driving because dead band can be a low-pass filter to cut off small amplitude and high frequency input from the steering wheel [5]. The effect of dead band on the driving precision is not yet studied in the previous literatures. Therefore, the dead band is added into the force feedback model and evaluated by using Driving Simulator in this paper. Development of Driving Simulator In this research, Driving Simulator (DS) is used for testing and evaluating force feedback in Steer-by-Wire system because of its flexibility, repeatability and safety. Driving Simulator consists of two main parts which are hardware and software part as illustrated in Fig. 1. Hardware part consists of steering wheel system for obtaining the steering input from the driver. Steering angle input is measured by multi-turn potentiometer and the voltage signal is converted and input to the software part by LabVIEW program. Brushless servo motor is used for generating force feedback to the driver. Force Feedback control and setting is carried out in LabVIEW program. Inertia mass which represents the inertia of typical passenger car steering system is installed onto the parallel shaft connected to the steering shaft by 1:1 pulley and belt as shown in Fig. 2. Vehicle and environment model (for display) is in the software part of Driving Simulator. There are two main programs in the software of the Driving Simulator. LabVIEW for converting between analog and digital signal as well as controlling the force feedback in the servo motor mounted on the steering shaft. Another program is Unity program which is generally used in computer game development. There are graphic and physic engines in Unity program. Graphic engine is used for the display of Driving Simulator while physic engine is used for the vehicle model. Steering input from driver will be sent to Unity program from LabVIEW program via TCP/UDP. Output from Unity program is shown on the display. All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of Trans Tech Publications, (ID: , Pennsylvania State University, University Park, USA-10/05/16,16:28:35)

2 Applied Mechanics and Materials Vol Figure 1 Schematic diagram of Driving Simulator used in this research. Figure 2 Driving simulator used in this research. Experiments Experiments are carried out by 10 drivers with license. Speed of vehicle is controlled not to over than 100 km/h. Layout of test track and overview of display in shown in Fig.3. Test track has 5 meter width and consists of two of 150 meter straight line and two 75 meter radius curvature. Figure 3 Layout of test track and display from unity program in driving simulator. Force feedback model used in the experiment is shown in Fig. 4. The model is adapted from simplified Dahl s model. Slope of graph is varied in two values which are 1.5 N-m/rad and 2.5

3 290 Mechanical and Electrical Technology VI N-m/rad [2]. Dead band is added onto the simplified Dahl s model and varied from zero to ±10 degree as shown in Fig.4. Test drivers will be explained about experiment process before beginning the experiment and asked to drive at the middle of the track. Each driver is allowed for free run for practicing the driving and get used to the system. After that, parameters which are slope of torque to steering angle and dead band will be randomly varied. Each of experiment parameter conditions is carried out 2 times. Figure 4 Force feedback model used in the experiment. Results are in term of error from the center line of the track. The error in the straight line portion is calculated by (1) Figure 5 Error from centerline (a) straight line (b) corner. While the error at the corner as shown in Fig. 5 is calculated by 0 0 (2) When E is error, is radius of curvature and is coordinate of vehicle in X and Y direction respectively 0 and 0 is X and Y coordinate of center of curvature of the corner respectively Results Errors from center line of the track calculated by Eq. 1 and 2 are represented in the Fig. 6 and 7 as error average and standard deviation of each parameter conditions. From the results, it shows that trend of error average for both two value of torque-steering angle slope are almost same with varied of dead band. Average Error is decreasing from zero dead band to ±4 degree dead band and then looks constant during ±4 to ±6 degree and then increasing after that. Standard deviation of error graph also shows the same trend as average error. When compare between different torque-steering angle slope, it found that there is no major differences.

4 Applied Mechanics and Materials Vol Figure 6 Relation between average error and deadband width. Conclusions Figure 7 Relation between standard deviation of error and deadband width. In this research, Driving Simulator for evaluating Steer-by-Wire force feedback was developed based on LabVIEW and Unity program. Force feedback model which modified from Dahl s model by adding dead band is proposed and evaluated by experiment on Driving Simulator. Error of vehicle position from center line of the track is used for evaluated the model. From the results, it shows that dead band in the range of ±4 to ±6 degree gives the lowest average error from the centerline of the track. And the change in value of torque doesn t affect much on the driving precision. References [1] Gordon, D. A. in: Experimental Isolation Driver Visual Input, Public Road, vol. 33 (1996), p [2] Toffin, D., Reymond, G., Kemeny, A., and Droulez, J. in: Influence of Steering Wheel Torque Feedback in a Dynamic Driving Simulator. DSC North America 2003 (October 2003). [3] Liu, A., and Chang, S. in: Force Feedback in a Stationary Driving Simulator, Nissan Basic Cambridge Research (1995). [4] Mourant, R. R., and Sadhu, P. in: Evaluation of Force feedback steering in a fixed base Driving Simulator, Proceeding of the Human Factors and Ergonomics Society 46 th Annual Meeting (2002). [5] Susan G. Hill Jason S. Metcalfe, and Kaleb McDowell. In: The Use of a Steering Shaping Function to Improve Human Performance in By-Wire Vehicle, Army Research Laboratory (2008).

5 Mechanical and Electrical Technology VI / Evaluation of Deadband Effect in Steer-by-Wire Force Feedback System by Using Driving Simulator /