2001 IEEUASME International Conference on Advanced Intelligent Mechatronics Proceedings 8-12 Julv 2001 Como. ltalv

Man-Machine Interface using Steering Wheel and Pedals for a Quadruped Walking Robot

Atsushi Konno, Yusuke Mitsuya, Noriyoshi Kat0 and Masaru Uchiyama

Aftiliation Department of Aeronautics and Space Engineering, Tohoku Universi+y, Aramaki-aza-Aoba 01, Aoba-ku, Sendai 980-8579, JAPAN

E-mail: konnoQspace.mech.tohoku.ac.jp URL: http://wwu.space.mech.tohoku.ac.jp

Abstract- For an easier and natural teleoperation of the quadruped walking robots, a user interface is developed with a steering wheel and an assembly of pedals. In order to change the speed and the direction of the quadruped walk- ing robots according to the operation of the steering wheel and the pedals, an on-line gait transition method is devel- oped. Using this human-machine interface and on-line gait transition, the operator can control the quadruped walk- ing robots almost in the same way as a driver drives a car. A quadruped walking robot named JROB-2 is used in the experiments. As the steering wheel is also equippedwith various control buttons, it is possible to assign various sin- gle command tasks, like stand up and sit down etc., to these buttons and hence control the robot for these tasks without even touching the keyboard or mouse. This paper presents the details of this interface.

I. INTRODUCTION

Over the past few years a considerable number of studies have been made on the control of the quadruped walking robots. Since a fully autonomous robotic system is yet unrealistic, most of the quadruped walking robots must be preprogrammed or operated by human operators.

As for an operator interface for the quadruped walking robots, joysticks have mainly been used so far [l], [2]. How- ever, since a joystick is used in many different modes such as the velocity commanded mode and the position com- manded mode etc., it is ditficult in some cases to imagine the correspondence between the robots movements and the joystick operations.

To make the operation of the quadruped walking robots easier and more natural, a user interface is developed with a steering wheel and an assembly of pedals. An operator can control the quadruped walking robots almost in the same way as one drives a car. The driving interface is standard- ized, therefore it is easier to understand the operations of the robot even for an untrained operator.

In order to follow the velocity and direction commands issued by the operator, an on-line gait transition method is developed. The on-line gait transition from the static to dynamic gait was discussed by Hirose and Yoneda [3]. How- ever, the method discussed in [3] fixes the wave exchange point and changes only the duty factor, consequently, the velocity does not change much.

In the method discussed in this paper, the velocity com- mand for the quadruped walking robot is composed of 1) the stride length, 2) the duty factor and 3) the cycle period.

Therefore, it is possible to have a wide range of velocity. Also, the wave exchange can be done at any moment in a cycle, if the velocity is increased or decreased slowly.

This paper discusses a human-machine interface using the steering wheel and the pedals for a typical quadruped walking robot. A method of the on-line gait transition to fulfill the operators request is also discussed. The discus- sion is concentrated on the locomotion on a flat floor. This paper does not deal with the terrain walking.

11. ON-LINE GAIT TRANSITION The velocity and direction commands for a quadruped

walking robot are given by the configuration of a steer- ing wheel and an accelerator pedal. In order to follow the velocity and direction commands, the appropriate walking patterns are to be generated in the real time. In this sec- tion, a method to change the velocity and direction of a quadruped walking robot is discussed.

A . Changing the Body Velocity The body velocity vb depends upon the stride length S,

the duty factor p and the cycle period T as expressed in eq. (1).

It is obvious from eq. (1) that there are three possible ways to increase the body velocity: (a) increase the stride length S, (b) decrease the duty factor p and (c) decrease the cycle period T. Since the parameters S, ,L? and T are limited by S 5 S,,,,,, 0.5 5 P and Tmin 5 T , respectively, all of these three should change to achieve the maximum body velocity.

The strategy of changing the body velocity proposed in this paper is as follows:

1. The crawl gait (P = 0.75) is applied to the slow walk- ing phase. The stride length S is changed depending upon the body velocity command in this phase. The cycle period T is fixed at an appropriate period Tslw.

2. If the velocity command exceeds Sm,,/O.75Tal,, (when stride reaches the maximum limit), the duty factor p and the cycle period T are decreased to fol- low the velocity command.

3. In order to avoid the saccadic change of the walking patterns, the velocity is increased or decreased in slow steps up to the commanded value.

0-7803-6736-7/01/$10.00 0 2001 IEEE 57

Authorized licensed use limited to: Khajeh Nasir Toosi University of Technology. Downloaded on December 21, 2009 at 05:05 from IEEE Xplore. Restrictions apply.

Fig. 1. Generation of a wave gait.

A method to generate a wave gait is illustrated in Fig. 1. The legs are numbered as shown in Fig. 2.

In Fig. 1, CT represents the number of samples, that is, the cycle period T divided by the sampling time period AT. The index cntlegi is an integer in the range 1 5 cntlegi 5 cT. cntlegi, marked by small circle, denotes where the leg i is in the walking cycle. While cntlegj is less than or equal to PcT, leg i is in the support phase, otherwise leg i is in the swing phase.

The index cntlegl is incremented by 1 after each sampling period. It means that the corresponding small circle shifts one step to right. The indices cntleg2, cntieg3 and cntleg4 are computed as:

(2)

Cntleg3 = Cntlegl + cT( 1 - P) (3) (4)

CT 2

CT cntleg4 = cntleg3 + 2.

cntzeg2 = Cntlegl + -7

Since cntlegi can not exceed cT, therefore if cntlegi becomes greater than cT, i.e. the corresponding small circle moves beyond the right most end, cntlegj is replaced by cntlegi - cT, i.e. the corresponding small circle is again placed at the left most end.

If the minimum difference between cntlegi and cntlegj is greater than or equal to cT(1- p), leg i and leg j can not be in the swing phase simultaneously. Since the difference between cntlegl and ~ntiega, and between cntleg3 and cntleg4 is CT/2, legs 2 and 4 are always in a different phase than legs 1 and 3, respectively.

B. Turning gait This section discusses the construction of a a turning

gait. The curvature center is denoted as Q and lies on the y axis as shown in Fig. 2. The curvature radius is given by the steering command of the steering wheel. The vector from Q to the current footstep of leg i is denoted as ri, while the vector from Q to the home position of leg i is

4" -- Y I -tar

Fig. 2. Concept of the turning gait.

denoted as rqi. Trajectories of the footsteps are planned so that the center of all trajectories will lie at the respective home position. rg represents the vector from Q to the projection of the center of the body 0 on the ground.

Suppose, the direction command changes in the previous period. Since the direction command changes, the trajec- tories of the footsteps should be transferred to a new plan to realize the commanded curvature. Figure 2 shows an example of the transition from a straight gait (Path 1) to a right turning gait (Path 1).

The velocity of leg i at the home position that follow the body velocity command and the direction command is computed as:

(5)

When the leg i comes to the turning point from the s u p port phase to the swing phase, the next landing point is computed in the following manner. Since the period of the support phase is pT, the stride length for leg i should be:

Sqi corresponds to the length of Path 2 in Fig. 2. The landing point TI of the swinging leg i is computed

as:

sine case I case -sine where the angle 8 is computed as:

S O i

(7)

6 takes a negative value for turning right, and a positive for turning left.

When the leg i is in the support phase, the footstep is computed at each sampling period A T depending upon the given body velocity and curvature. The velocity of leg i at the current position that follows the body velocity and the direction commands is given by the computation similar to eq (5) as:

(9)

58

Authorized licensed use limited to: Khajeh Nasir Toosi University of Technology. Downloaded on December 21, 2009 at 05:05 from IEEE Xplore. Restrictions apply.

The footstep position in the next sampling time is given by:

Unlike to the case of the leg swing, A8 assumes a positive value for turning right, and a negative for turning left. It is obvious from eq. (11) that A0 has the same value for all supporting legs.

111. SIMULATION OF THE GAIT TRANSITION

The strategy for gait transition discussed in Section I1 is applied to a quadruped walking robot, JROB-2. In the case of JROB-2, i.e. TITAN-W [4], S,,, is about 0.2 [m], Tmin is about 0.5 [s] and is about 0.9 [m/s] [4]. However, just to be safe, the limits are modified as: S m a , is 0.15 [m], Tmi, 1 [s] and v b , m a , 0.3 [m/s]. Considering these limits, the walking patterns are generated as follows:

1. When 0 5 vb < 0.05 [m/s], the stride length S is changed by the following equation with the tixed values of p = 0.75 and T = 4.0 [s] as:

S = VapT [m].

S ranges from 0 [m] to 0.15 [m]. 2. When 0.05 [m/s] 5 v b < 0.3 [m/s], the duty factor p

and the cycle period T are changed by the following equations with a fixed value of S = 0.15 [m],

p ranges from 0.75 to 0.5, while T ranges from 4.0 [SI 3. When 0.3 [m/s] 5 v b , the base velocity is k e d at

to 1.0 [SI.

v b = 0.3 [m/s]. In this case, p is 0.5, T is 1 [SI and S is 0.15 [m].

In order to examine the validity of the gait transition al- gorithm described above, preliminary simulations are per- formed. The body velocity command v b is increased by 0.01 [m/s] in each cycle from an initial value of 0.01 [m/s] to the maximum of 0.3 [m/s], and is plotted in Fig. 3 (a). The duty factor ,B and the cycle period T can be changed at any moment in a gait. However, in order to show the change of the gait clearly, v b is changed only at the begin- ning of each cycle.

The profiles of v b vs. s, v b vs. p, and v b vs. T are plotted in Figs. 3 (b), (c), and (d), respectively.

The change of gait due to v b is plotted in Fig. 4. 1 to 4 on the vertical axes are the leg numbers. The solid lines indicate the periods of the support phase. As V., increases, p and T decrease as shown in Fig. 4.

Gait tramition phase

0 0.05 0.1 0.15 0.2 0.25 0.3 Body velocity V, [ d s ]

(b) vb Vs. s

0 0.05 0.1 0.15 0.2 0.25 0.3 Body velocity Vb [ d s ]

IV. QUADRUPED WALKING ROBOT JROB-2 This section describes the testbed JROB-2. JROB-2

is a research platform having an embedded PC, sensors, and batteries integrated on the quadruped walking robot TITAN-W [4], developed at Tokyo Institute of Technol- ogy. Since JROB-2 is equipped with a PC and batteries, it is a self-sustaining system. JROB-2 is connected to the network via radio ethernet communication. The details of JROB-2 are described in the following subsections.

A . System Configuration TITAN-VlU is a commercially available quadruped walk-

ing robot. However, since TITAN-VU does not own any computers, batteries and sensors, the users need to inte- grate these items by themselves according to their will. In order to standardize the control system of TITAN-VU, JROB-2 was developed with the collaboration of Tohoku University, University of Tsukuba and Kyoto University.

The hardware of JROB-2 consists of five subsystems: the quadruped mechanism TITAN-VU, a computer, mo- tor drivers, a robot head and a power supply. The power supply subsystem includes batteries and DC-DC converters and is located between the posterior legs and the anterior legs, while a computer and the motor drivers are placed in the upper part of TITAN-VU. CAD model and dimensions of JROB-2 are illustrated in Fig. 5, while a photograph of JROB-2 is shown in Fig. 6 . The typical weights of differ- ent constituent parts are presented in Table I. The control system of JROB-2 is illustrated in Fig. 7.

B. Electronic Devices Motor drivers, a PC, a hard disk, a video transmitter, a

video field multiplexing device [5], batteries, DC-DC con-

59

Authorized licensed use limited to: Khajeh Nasir Toosi University of Technology. Downloaded on December 21, 2009 at 05:05 from IEEE Xplore. Restrictions apply.

8 4 . 7 5 8 4 . 7 4 8 4 . 7 2 8 4 . 7 8 4 . 6 8 84.66 8 4 . 6 4 8 4 . 6 2 84.6 84.58 B=O.56 8=0.54 8 4 . 5 2 8 4 . 5

Leg 4

Leg 3

Leg 2

Leg 1

20 30 40 M TI^ [SI

Fig. 4. Simulation results.

.-.... ,,:& $qy ..:.., .

Fig. 8. Binocular robotic head.

TABLE I1 INTERFACE USING SW-FFW.

Interface device Command Steering wheel Steering Accelerator pedal Acceleration or deceleration Brake pedal Button A Start servo Button B Stop servo Button C Button X Sit down Button Y Stand up

Stop and move to home position

Change direction (forward c+ backward)

(a) Steering wheel and pedals

Fig. 9.

D. Driving Interface Various steering wheels and pedal assemblies are avail-

able for PC games. In this work, Microsofts Sidewinder Force Feedback Wheel (hereinafter SW-FFW) set is used as the interface device (see Fig. 9).

As SW-FFW is equipped with various control buttons, as shown in Fig. 9 (a), many single command tasks can be assigned to these buttons. The task assignments for these buttons are presented in Table 11. This assignment makes it possible to control the robot without even touching the keyboard or mouse. SW-FFW is connected to a PC which constructs man-machine interface (see Fig. 7). The PC scans the buttons, and reads the angle of the steering wheel, the accelerator, and the break.

The accelerator increases/decreases the body velocity command vb. In order to avoid a saccadic change in the ve- locity, 6 is increased/decreased in the steps of 0.005 [m/s] in each sampling period up to the commanded velocity.

The angle of the steering wheel corresponds to the cur- vature radius. The minimum curvature radius is set as 0.5 [m]. When the wheel is in the neutral position, the curva- ture radius is set at infinity.

The commands for the body velocity and the curvature radius are sent to JROB-2 via wireless LAN.

V. OPERATION WITH THE PROPOSED MAN-MACHINE

A sequence of the proposed operation for JROB-2 using steering wheel and pedals based man-machine interface is presented in Fig. 11. Monitoring the scene captured by

INTERFACE SETUP

(b) Operation

Cockpit.

Fig. 10. Control programs.

the robotic head, the operator gives the robot velocity and direction commands with the steering wheel and the pedals. Figure 11 shows a sequence of walk forward and turning left operations.

The captured images for turning right operation (not for the same operation) on the steering wheel are shown in Fig. 12. Cameras are fixed in this experiment, however, more useful operations can be realized with their motions.

VI. CONCLUSION This paper addresses a method to operate a quadruped

walking robot with a steering wheel and an assembly of pedals. An on-line gait transition to follow the operators commands for velocity and direction is also discussed. Us- ing the developed user-interface, the operator can control a quadruped walking robot with an case like that of driving a car. Since this interface is easy to understand even for an untrained or new operator, it can be adopted as a standard interface for general mobile robots.

Though the developed interface can not always exploit the full abilities of the quadruped walking robot, such as a side step, yet it is possible to easily add this feature utilizing the various buttons available with the wheel.

Acknowledgments This research has been partly supported by the Grant-in-

Aid for Scientific Research of the Ministry of Education of Japan (No. 12750199), and partly by OMRON corporation (No. 991011).

61

Authorized licensed use limited to: Khajeh Nasir Toosi University of Technology. Downloaded on December 21, 2009 at 05:05 from IEEE Xplore. Restrictions apply.

(4 (4 (f Fig. 11. Operation of the quadruped walking robot using steering wheel and pedals.

(4 Fig. 12. Operation for right turn.

REFERENCES vehicle, Journal of the Robotics Society of Japan, vol. 9, no. 3, pp. 267-275, 1991 (In Japanese).

[I] Dennis R. Pugh, Eric A. Kbble, Vincent J. Vohnout, [4] Keisuke ARIKAWA and Shigeo HIROSE, Development of quadruped walking robot TITm-W[, in pmc. of 1996 IEEE Int. Workshop on Intelligent Robots and systems (IROS 96), 1996, pp. 208-214.

[2] Joseph S. Byrd and Kevin R DeVries, A six-legged telerobot for [5) Yoshlo Matsutmoto, Tomohiro Shibata, Katsuhiro Sakai, Masayuki Inaba, and Hirochika Inoue, Real-time color stereo vision system for a mobile robot based on field multiplexing, in Pmc. of 1997 IEEE Int. Conf. on Robotics and Automation ( I c m 971, 1997, PP. 1934-1939.

Thomas E. Bihari, and Thomas M. Walliser, Technical descrip tion of the adaptive suspension vehicle , The International Jour- nal of Robotics Research, vol. 9, no. 2, pp. 24-42, 1990.

nuclear applications development, The International Journal of Robotaes Research, vol. 9, no. 2, pp. 43-52, 1990.

[3] shigeo mom and K~ yonda, UD,,,,-~ & static fusion con- trol and continuous trajectory generation of quadruped walking

62

Authorized licensed use limited to: Khajeh Nasir Toosi University of Technology. Downloaded on December 21, 2009 at 05:05 from IEEE Xplore. Restrictions apply.