Feasibility study of using line tracer robot under disaster situation

Transcription

1 Feasibility study of using line tracer robot under disaster situation Hyung Ki Kim* a, Gi Sang Choi a, Gi Heung Choi b a Dept. of Electrical & Computer Engineering, Univ. of Seoul Siripdae-gil 13, Dondaemun-gu, Seoul, Korea, Mechanical Systems Engineering, b Hansung Univ., 389 Samsung-dong3-ga, Seongbuk-gu, Seoul, Korea ABSTRACT Line tracer robots are widely accepted in various industry for the purpose of moving objects. In this study feasibility of using line tracer robots under disaster situation is studied as the line tracing capability may be useful in case of disaster. A small scale line tracer robot is designed, implemented, and tested under disaster situation. Specifically, the MCU based robot hardware including sensor, encoder, motor, and power supply is designed and implemented. Also, the software for receiving sensor signal, for driving motor and for implementing line searching algorithm is designed. The devised robot detects the guide line using 6 infrared optical sensors and can adjust the direction of motion with the front steering servo motor according to the sensor signal. In driving test, the robot showed reliable performance both on the straight and curved paths having obstacles under limited visibility condition as in disaster situation. Keywords: disaster, limited visibility, line tracer robot, infrared sensor 1. INTRODUCTION In recent years, there have been numerous studies on rescue robots working under disaster situation such as fire or earthquake, as well as construction robots, exploring robots for investigating polluted area, and on guide robots [1]. Attempt to perform all the different kinds of rescuing tasks with a universal robot is not practical, because task requirements in rescue activities under disaster conditions are different from the task requirements that robots are usually assigned. Then, it is necessary to contrive a special robot system that can perform rescuing tasks effectively under disaster condition [2]. J. Burke et al. have performed a number of studies on field robotics in unstructured environments. J. Burke et al. have conducted a series of studies of robots for military and search and rescue operations [3]. J. Burke et al. have examined methods for evaluation of robot use, and also have investigated the methodology for robot-use in field applications [4]. In this study, a line tracer robot based on Motorola HCS12_T-Board was designed. The robot can be used for rescuing purpose when the visibility is limited in case of disaster. In order to maximize the visibility in smoke situation, infrared sensor fitted with the light concentrating lenses is adopted. Also, flexible steering algorithm based on infrared sensor is used. Experiments were done to study the way of safely moving the robot in the presence of obstacles under limited visibility condition due to smoke or under complete blackout condition due to power failure. 2. DESIGN AND IMPLEMENTATION The line tracer robot is composed of infrared sensors with concentrating lens for path recognition, a servo motor for steering and four driving wheels using a body of RC car. The DC motor for driving is located at the rear of the body [5]. It is powered by a DC source that exerts an output of 7.2volts. The robot is 40cm in length and 30cm in height. Table 1. shows the electronic components used for the robot. Table 1. Electronic components for the robot 16 MHz crystal clock, up to 25 MHz bus clock using PLL analog input potentiometer Memory: 256KB Flash, 4KB EEPROM, 12KB RAM up to 85 free general-purpose I/Os 16-Bit Timer (Input Capture/Output Compare) around the MCU, arrangement compatible with Motorola EVB 16-channel 10-bit A/D-Converter PWM (Pulse Width Modulator) *khk139@uos.ac.kr; phone ICMIT 2007: Mechatronics, MEMS, and Smart Materials, edited by Minoru Sasaki, Gisang Choi Sang, Zushu Li, Ryojun Ikeura, Hyungki Kim, Fangzheng Xue, Proc. of SPIE Vol. 6794, , (2007) X/07/$18 doi: / Proc. of SPIE Vol

2 As the main processor a HCS12-T-Board based on MS9S12DG256 microcontroller unit is used. It also has 256KB flash memory, 4KB EEPROM, 12KB RAM, and 2 10bit A/D Converter modules built in it, and has been successfully applied to electronic control of passenger vehicles. In order to regulate the input voltage, LM2940(1A Low Dropout Regulator) was used as the power supply unit. It can supply the input voltage exactly at 5 Volts even in case the input voltage goes well below 7 Volts. Fig. 1 shows the infrared sensor assembly for line tracing. The reflected infrared light is concentrated by the lenses and received by the light emitting infrared sensor. Fig. 1. Infrared sensor assembly Table 2 The specification of the OPE5T85 infrared emitting diode used on this study. Rise time Beam angle Wavelength 25 ns 8 degrees 850 nm As the beam angle is just 8 degrees, 10 of them were employed to cover wider angle. The 10 light emitting sensors were controlled using 2 Darlington Arrays ULN2803 as in Fig. 2, and they are made switched on and off by the MCU at the rate of 1kHz. For filtering infrared signal only, the high pass filter in Fig.3 was adopted. As the output voltage from the sensor is very low, a resistor (47kOhm) was added in series with the sensor A Fig. 2. circuit for light emitting sensors Proc. of SPIE Vol

3 ..I J >>PAP5 Fig. 3. light sensor circuit with the high pass filter HITEC HS-925MGH servo motor was used as the steering drive for the robot. As the servo motor can consume up to 400mA of current momentarily, an independent power supply unit for the motor was needed. As the stable power source, LM1117-ADJ adjustable voltage regulator was adopted. It can supply the input voltage between 1.25 to 10 V. Fig. 4. Steering mechanism of the robot using the servo motor The resistance of the motor was measured as 0.5 ohm. If the 9V of Ni-Cd battery is applied to this motor, the maximum current would be 18A. Therefore, four MC33886 motor drives which have the maximum current output of 5A were connected in parallel to produce 20A of output current. Fig. 5 shows the single connection of MC33886 motor drive with the motor. As the starting current of the motor is rated at 66.13A, the motor current has to be limited electronically. Limiting the starting current is possible with the active current limiting function of MC33886, and stable start up can be achieved. Fig. 5. connection of motor drive MC33886 and the DC motor. A rotary encoder with the resolution of 500 pulses/rev. was attached to the drive shaft to measure the angular velocity of the wheel.. Fig. 6. Encoder circuit Proc. of SPIE Vol

4 Fig. 6 shows the encoder circuit. The outputs of the encoder were not directly connected to the MCU, but positive and negative directions are counted using the phase difference between the two outputs of the encoder. In addition, the resolution can be doubled by 2 times subdividing the encoder output using exclusive-or gate. 3. SOFTWARE DESIGN 10 infrared sensors were used for line searching. They were read at the rate of 10 khz using the timer and the ADC function of the MCU. The resolution of the ADC was 10 bits. In order to increase the resolution the output of the encoder was 4 times subdivided by using exclusive or gate, and also by counting both the rising and the falling edges of input pulse accumulator. The difference between normalized outputs from the left and right infrared sensors was used as the measure of the deviation of the direction of motion from the centerline as in (1). Position = normalized output of the left infrared sensor normalized output of the right infrared sensor (1) A Position ot intrared sensor Fig. 7. Traverse position detection The stream of square pulses containing steering command was sent to the servo motor at the rate of 500 Hz. The servo motor was driven with 16 bit PWM. The speed of the left wheel a, the center of the robot b, and the right wheel c, can be computed using the relationship in (2)-(4). where w, r, are wheel thread, turning radius, and rotational speed, respectively [6]. w a r (2) 2 b r (3) w c r (4) 2 The DC motor was driven by PWM driver and the duty ratio of the PWM was determined using the PID control algorithm. Tuning of the PID controller was done by trial and error. The light emitting infrared sensor was installed to direct 45 degrees downwards. It enables the robot to preview the centerline, but the strength of the reflected light is significantly weakened as the traveling distance is longer. The light collecting lens was effective in compensating the weak reflected light. The lens, infrared sensor assembly was designed according to the formula defining the relationship between the distance from the lens to the object, and the distance from the lens to the sensor, and the focal length of the lens as in (5) (5) f where,, and f are the distance from the lens to the object, the distance from the lens to the sensor, and the focal length of the lens, respectively. The lenses assembly was designed to rotate horizontally to provide wider view. This feature helps the robot to find the guide line even in case the robot lost the track and placed away from the centerline. Proc. of SPIE Vol

5 4. EXPERIMENT sensor value white ground black line density of smoke(visibility) Fig. 8. sensor values by a density of smoke An experiment is done to check the infrared sensors under a limited visibility such as a fire and blackout. Fig 8 shows sensor output depending on the smoke density. Clearly, the difference in strength between the light reflected from black line and the light reflected from white background gets smaller with the higher smoke density. It suggests that the robot can find the centerline, and normal line tracing is possible when the density of smoke is not high position position density of smoke(3) normal normal density of smoke(5) the distance the distance Fig. 9. An ability of traveling by a density of smoke Fig 9 compares the deviation of the robot from the centerline under the normal condition and the smoke condition. Apparently, the deviation becomes larger with the thicker smoke. Also, delay in the response is inevitable with the smoke. Proc. of SPIE Vol

6 Fig. 10. steering simulation of servo motor Fig 10 shows that the steering angle of servo motor as velocity is simulated using arctangent. Also this data is used for traveling in actually. 5. CONCLUSION In this study a line tracer robot for hazardous environment is designed and implemented. It is shown that the stability and performance of software is as important as the hardware in implementing such a robot. The scanning lenses of the infrared sensor was effective in providing wider angle of view, and the developed robot with the scanning infrared sensors was able to trace the line even under limited visibility condition in disaster situation. It can be used to rescue people in case of disaster as well as in moving various objects under limited visibility condition. REFERENCES 1. Chung, K. M, Shin, H.C, Jeong, S.H and Kim, S.H, "A study on the Crossingover Capability of Mobile Mechanisms with passive joints", Seminar of Ground Weapon system, Vol.12, pp.1, Satoshi Tadokoro, "Robotics and AI for Emergency Response Problems in Large Scale Disaster", Journal of HWRS- ERC, vol.2(2), pp.46-53, Burke J., Murphy R., Coovert M., and Riddle D., "Moonlight in Miami:A Field Study of Human-Robot Interaction in the Context of an Urban Search and Rescue Disaster Response Training Exercise", Human-Computer Interaction, Vol.19, pp , Burke J., and Murphy R., "Human-Robot Interaction in USAR Technical Search: Two Heads are Better Than One", in Proceedings of the 13 th IEEE/ROMAN, pp , C.M. Kim, H.C. Moon, S.G. Kim,and J.H. Kim, "Obstacle Avoidance and Lane Recognition for the Directional Control of Unmanned Vehicle", Proceeding of ICCAS2002, pp , JOHN J. CRAIG, Introduction to ROBOTICS, Addison-Wesley Pub co., Boston, Proc. of SPIE Vol