外文原文--MOBILE ROBOT SYSTEM TO AID THE DAILY LIFE FOR BEDRIDDEN PERSONS

MOBILE ROBOT SYSTEM TO AID THE DAILY LIFE FOR BEDRIDDEN PERSONSTakashi KOMEDA, Hiroaki MATSUOKA, Yasuhiro OGAWA, Mitsuyoshi FUJII, Tateki UCHIDA, Masao MIYAGI, Hiroyuki KOYAMA and Hiroyasu FUNAKUBOSHIBAURA INSTITUTE OF TECHNOLOGY FUKASAKU307, OMIYA, 330, JAPANABSTRACT People who care for bedridden patients have great burdens in mind and body. The number of old-aged people in the population is increasing in Japan, the problem of care for bedridden patients will become an increasingly social problem. We are trying to solve this problem by developing a small mobile robot system for bedridden patients. The purpose of this system is to pick up and to bring a small object putting it somewhere inside the room semi-automatically. This mobile robot consists of a manipulator, visual sensor unit and mobile unit. This system gives information about the surrounding to the patient through the camera and monitor. When the patient directs an target object on the monitor, the system measures a 3-dimensional location of it, and the mobile unit approaches the object and the manipulator picks up and carries it back to the patient. This system is controlled by the image information and also by human through an interface based on images. 1. INTRODUCTION We generally have great burdens in mind and body to help bedridden patients. The population of old aged increasing today, this helping work will become a social problem. We are trying to solve this problem by developing a small mobile robot systeml. The purpose of this system is to bring the target object putting it somewhere inside the room semiautomatic ally. Of course, there are many kinds of works involved in helping bedridden persons, for example changing clothes, giving the medicine and cleaning the bed, etc With this system. however, we think that even if the machine achieves only one type of work instead of a human, the burdens on the helper should decrease in mind and body.2. SYSTEM CONSTRUCTIONFig. 1 shows the overview of the mobile robot. This mobile robot consists of a manipulator, a visual sensor unit and a mobile unit. This system gives information about the surrounding to the patient through the camera and the monitor. When the patient directs a target object on the monitor. the system measures a 3-dimensional location of it. The mobile unit then approaches the target object and the manipulator picks up and carrying it back to the patient. The si7e of the mobile unit is width 600 mm, length 800 mm. height 550 mm, and it has the space to load the controller and batteries. The mobile unit is driven by two DC servo motors and two wheels. Each motor has a pulse encoder for position control. The length of the manipulator is about 1255mm and it has 4 degrees of freedom and a hand. Its weight capacity is about 3 kgf. The actuator of each joint is DC servo motor with a pulse encoder to control its position. A pair of strain gages is put on to the wrist part of the manipulator. The weight of a target object can therefore be measured and used in the feedback loop of the controller.3.VISUAL SENSORThe visual sensor system consists of a CCD camera and an image processor which is controlled by a personal computer. The camera is attached on the wrist part of the manipulator. This design makes it possible to move the camera and manipulator simultaneously. Then, the system gives 0-7803-3280-6/96/%5.00 1996 IEEE - 2789 - surrounding information to the operator through the camera and the monitor. If a target object is directed, it measure a 3- dimensional location of it. The target objects for this mobile robot system arc things for daily using which have different size and shape. It is difficult to treat an image processing to recognize such things and “me its location in real time. To solve this problem, we put things for daily using on a tray which has a cylindrical fixed size grip. This grip is the target object of the visual sensor. Therefore, we can easily measure the size of the target object on the image plane as the number of pixels of the CCD camera, and calculate the distance to the object using a simple formula(Fig.2). The treatment to measure a 3- dimensional distance using the image and a following visual tracking of the target object can be done in real time.Monitor screen No.2 is the image of after O.Ssec of monitor screen No.1. Monitor screen No.1 shows the center and feature points of the target object. Monitor screen No.2 shows that the visual sensor finds new center and feature points by scanning the image. After O.Ssec, the visual sensor will find another new center and feature points.4. VISUAL TRACKINGThe mobile unit is controlled by a personal computer, a control board and motor drivers. The computer calculates the number of drive pulses of each drive motor from the location of the target object, and sends the information to the control board. The control board generates DDA pulse distribution to do the synchronous operation between two motors2. Motor drivers observe the feedback pulse to do the rate control and the position control. However, even if we perfectly control two motors of the mobile unit using the feedback pulse, the mobile unit docs not always move exactly because of the difference of the diameter of each drive wheel and the road surface condition. Therefore, we use the visual tracking method to solve this problem. This mobile robot has an image information from CCD camera, and this information renews every 0.5 second. When the mobile unit approaches the target object, the computer calculate the position of the target object on the monitor every 0.5 second. If the position shifts from the center of the monitor, the mobile unit is controlled to change the direction to catch it in the center. This method is able to keep the object in the center of the monitor continuously(Fig.3). The method was confirmed by measure the relation between the center of the target object on the monitor and the angle of mobile robot. Fig.4 shows one of the results when the mobile robot has approached about 1800 mm. This result shows that the center of the target object positioned about 360 pixel point (full pixel is 512) when the mobile robot starts action to approach to the target, and is caught the center of the monitor (256 pixel point) when the mobile robot run about 750 mm. The method is able to keep the center within 5 pixels during 750 mm to 1800 mm running and enough precision for this mobile robot.5. CONTROLLER AND INTERFACEOur mobile robot can bring the target from the undecided position inside the room semi-automatically. However, if the operator wants a specific target, he must communicate with the robot through the computer. For example, if the target is at the right side of the robot, he must point out the arrow on the monitor by the mouse cursor to turn the robot to find the target on the monitor. In addition, he must teach the robot which is the target. Furthermore, this robot is used by the operator who is not professional about robots, and is handicapped.We have therefore developed an interface system between the robot and the operator based on following conceptions. (1) Easy and simple. The operator can control the robot easily like as radio-controlled car and also this input method must be simple.(2) Safety High space is not necessary, and for the softy tic robot can interrupt the movement every time tic robot or operator recognizes a dangerous motion. This robot has the small camera which is attached on the wrist part of manipulator, the operator can recognize the direction of the end cofactor and the sconce through the monitor. But, it is not sufficient to control tic robot with surrounding information through the camera, the operator also necks information about status of the robot. For example if the position of the robot reaches the upper limit of its working space, it is impossible to move the robot even if the operator directs to move UP.Under the configuration of Multi CPU, each task compensate robot motion, and the operator can choose cash task as an object according to his necessity. With this system. the operator can simply choose the robot motion task as an edict from existing several tasks (Fig. 7). These tasks are not always in active, hut always on standby to get the command from the operator. This means that if the operator finds it necessary, he can interrupt the motion to execute another tasks which can escape from a dangerous path.It is also necessary to compensate the safety when the robot finds a danger while the movement, this means not the operator but the robot can recognize the danger. In our system, a pair of strain gages is placed on the wrist part of the manipulator, the robot can measure the load at the wrist part using these strain gages, and rccogni7c the danger when excessiveness force arise at this part. Using the time slice method, we can interrupt the robot motion without influence when robot recognize a danger. This means that this system watches a danger both operator and robot.6. CONCLUSIONS(1)We have developed the mobile robot system which consists of a manipulator, a mobile unit and a visual sensor, and is controlled by image information. (2)We have developed a visual tracking method to correct the motion direction, it is simple way, high response and good accuracy to use this system.(3)We have developed the interface system between our mobile robot and the operator. This interface can observe each task of robot motions and show the graphical motion using the real status information. We tried to check functions of this system, it was simple and easy to operate the robot and also we confirmed that it is useful for safety, In future, we will improve this system more interactive and try to apply to the obstacle avoidance.ACKNOWLEDGMENT We wish to thank the Welfare Equipment Development Center of Japan for support this project.REFERENCES 1. T.Komcda etc. “ Mobile robot system to aid the daily life of bedridden persons in the private house”, Proceedings of 2nd European Conference on Advancement Rehabilitation Technology, 24.4( 1993) 2. T.Komeda etc. I Mobile robot system to aid the daily life of bedridden persons in the private house(2nd report)”, Proceedings of 3rd European Conference on Advancement Rehabilitation Technology, pp.179-181(1995)