Artif Life Robotics (2013) 17:400–404 DOI 10.1007/s10015-012-0071-z
ORIGINAL ARTICLE
Study on mobile mechanism of a climbing robot for stair cleaning: a translational locomotion mechanism and turning motion Takahisa Kakudou • Keigo Watanabe Isaku Nagai
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Received: 31 March 2012 / Accepted: 23 October 2012 / Published online: 16 November 2012 Ó ISAROB 2012
Abstract In human living environments, it is often the case that the cleaning area is three-dimensional space such as a high-rise building. An autonomous cleaning robot is proposed so as to move on all floors including stairs in a building. When a robot cleans in three-dimensional space, it needs to turn for direction in addition to climb down stairs. The proposed robot selects movement using legs or wheels depending on stairs or flat surfaces. In this paper, a mobile mechanism and a control method are described for translational locomotion. The translational mechanism is based on using two-wheel-drive type omni-directional mobile mechanism. To recognize a stair using the position-sensitive detector, the robot shifts from translational locomotion to climbing down motion or edge-following motion. It is shown that the proposed robot turns to face a stair with the accuracy of 5°. Keywords
Cleaning robot Climbing robot Stair
1 Introduction Recently, various robots have been developed to support and execute human’s work in various fields. One of such This work was presented in part at the 17th International Symposium on Artificial Life and Robotics, Oita, Japan, January 19–21, 2012. T. Kakudou (&) K. Watanabe I. Nagai Department of Intelligent Mechanical Systems, Graduate School of Natural Sciences and Technology, Okayama University, 3-1-1 Tsushima-naka, Kita-ku, Okayama 700-8530, Japan e-mail:
[email protected] K. Watanabe e-mail:
[email protected] I. Nagai e-mail:
[email protected]
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robots is the autonomous cleaning robot [1]. The automation of cleaning by robots reduces labors and saves energy for a cleaning task, so that there is an increasing need for it in large areas such as stations and airports. In human living environments, it is often the case that the cleaning area is a three-dimensional space such as a highrise building. Considering cleaning in a three-dimensional space, the cleaning area includes the steps of stairs which lead from one level of a building to another. However, many of cleaning robots are not considered to move on places between floors. Tajima et al. [2, 3], have developed a robotic system in which the cleaning robot cooperated with the elevator to clean floors in a high-rise building. However, this system did not consider the cleaning of stairs. As a result, a cleaning robot itself needs the ability to move on stairs for cleaning in a three-dimensional space. Also, the several types of climbing robots using crawlers, wheels and legs were proposed to move on stairs [4–6]. Those robots were developed to move on stairs only for improving transfer performance of them in uneven surfaces and transporting people or objects. Therefore, a climbing robot for cleaning in a three-dimensional space needs to be able to turn itself and keep posture level on the tread board of stairs, as well as moving on stairs. The objective of this study is to develop a climbing robot that can move on all floors including stairs in a building for autonomous cleaning in a three-dimensional space. A climbing robot has been already proposed, where its structure was divided into two mechanisms for climbing down stairs and translational movement [7, 8]. In this paper, a mobile mechanism and a control method are described for translational locomotion. The operational check of the translational mechanism was conducted by facing the robot to the edge of stairs using the position-sensitive detector (PSD).
Artif Life Robotics (2013) 17:400–404
The paper is organized as follows. The concept of the present climbing robot is described in Sect. 2. Section 3 gives the mobile mechanism for translational locomotion. In particular, its mobile mechanism and controller designs are described in detail. The locomotion of the robot on stairs, consisting of cleaning and shifting motion, is explained in Sect. 4. Section 5 presents the way of recognizing a stair using PSDs, together with showing some experimental results. Finally, some conclusions are given in Sect. 6.
2 Concept of climbing robot In this study, a climbing robot which can move on stairs is developed to expand the range of moving for the cleaning robot. The target stair is located in indoor environments and the shape of its step is rectangular. A climbing robot climbs down stairs, because the efficient cleaning is to clean from the upper floor to the lower floor. In addition, a climbing robot for cleaning stairs needs to be able to turn for direction and keep posture level on the tread board of stairs, as well as climb down stairs. Figure 1 shows the proposed climbing robot whose structure is divided into two mechanisms for climbing down stairs and translational locomotion. This robot climbs down each step of stairs by its shape which is a rectangular solid to fit the shape of step. The L-shaped legs which are attached on the both sides of a body are used as a climbing mechanism. The proposed robot climbs down stairs by rotating the body so that the top and bottom sides of the body may be reversed using L-shaped legs with two degrees-of-freedom. Also, the proposed robot turns for direction by a translational locomotion mechanism with omni-directional mobility. A translational locomotion mechanism is discussed in detail in Sect. 3.
3 Mobile mechanism for translational locomotion It is assumed that the cleaning robot is used in an indoor environment that is flat such as wooden floor or tile floor.
Fig. 1 Outline of climbing robot for cleaning stairs
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The robot performs translational locomotion using wheels that have high transfer efficiency. However, the robot may be limited in motion by its corners colliding with the wall and the riser of stairs when turning around, because the shape of the proposed robot is a rectangular solid as shown in previous sections. So omni-directional mobility is adopted to move and turn around keeping a posture. For some of omni-directional mobile mechanisms with wheels, there are mechanisms with omni-wheel, mecanum wheels, etc. Also this mechanism is attached to the top and bottom of the robot, because the robot climbs down stairs by rotating the body so that the upper and lower sides of body may be reversed. To reduce the robot weight, it is desirable to use the fewest possible actuators. Therefore, the mobile mechanism for translational mobility used an omni-directional mobile mechanism with two-wheel-drive system in this study. 3.1 Mobile mechanism design Figure 2 shows the proposed mechanism for translating on stair treads. The size of the mechanism is as follows: the width is 400 mm, the length is 250 mm, and the ground clearance is 20 mm. Its mechanism consists of four ballcasters and two driving wheels that are attached on a circular plate with a joint. Then, its mechanism is equipped with PSDs and encoders as shown in Fig. 3. The PSD as the range sensor is used for the robot to recognize stairs. Two PSDs are attached on both ends in the front side of the mobile mechanism for translational locomotion. If the origin is set at the rotational axis, the positions of PSD 1 and PSD 2 are xpsd ; ypsd and xpsd ; ypsd in an x–y coordinate, respectively. On the other hand, the encoders are used to control the velocity of the robot or measure the angle of the circular plate. 3.2 Controller design Cleaning robots keep the quality of cleaning constant by controlling the velocity of the robot. The velocity of the
Fig. 2 Overview of translational mechanism
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402 Fig. 3 Design of a variety of sensors a top view, b lateral view
Artif Life Robotics (2013) 17:400–404
PSD 1
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Rotational joint Connected part
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robot is controlled using a PD controller with encoders to measure the rotation of wheels. Figure 4 shows the block diagram of the velocity control. The motors for the wheel can take states such as, normal rotation, reverse rotation, stop and braking by sending the signal from the microcomputer SH7125 through a motor driver.
Circular plate
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Target + value -
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Fig. 4 Block diagram of velocity control
4 Locomotion on stairs The locomotion of the robot on stairs is assumed to consist of two motions, i.e., the cleaning motion and the shifting motion.
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4.1 Cleaning motion The locomotion of commonly marketed cleaning robots is classified into four basic motions such as, parallel, spiral, wall-reflection and wall-following motions. The parallel motion is one of the more suitable motions for cleaning stairs, because the shape of step is a rectangular form that makes a path planning easy to make for cleaning. In the cleaning motion based on such parallel motion, the robot repeats straight going and 90° turn, keeping the posture as shown in Fig. 5a.
(b) Fig. 5 Translational locomotion on stairs a parallel motion to clean stairs, b turning motion to face stairs
4.2 Shifting motion 4.3 Kinematic model motion When the robot shifts from translational locomotion to climbing down motion or edge-following motion that moves to clean along the edge of stairs, it might fall down stairs due to its posture. Some ball-casters of the robot fall down stair by design when the posture of the robot is inclined at more than 10° over the edge of stairs. Also it is difficult for the robot to stop when the robot once starts falling in descent stair. Therefore, the robot turns to face the edge of stair whenever stairs are recognized as shown in Fig. 5b.
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The kinematic model of the mechanism for translational locomotion is given by 2 3 2r 3 r x_ 2 sin hc 2 sin hc _ 4 y_ 5 ¼ 4 r cos hc r cos hc 5 hR ð1Þ 2 2 h_ L r r h_ 2d 2d where x and y are the position coordinates of the robot, hc is the rotated angle of a circular plate, hR and hL are the
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Start angle
vout
v
vin O psd
Rout
Rin
Edge Exceeded angle
Shortened angle Fig. 7 Experimental condition
Fig. 6 Kinematic model of turning motion
Table 1 Posture angles Start angle (°)
rotational angles for the right and left wheels, r is the wheel radius, and 2d is the distance between wheels.
The robot recognizes stairs by discriminating a difference between the ground clearance and the rise of stairs using a PSD. The PSD outputs the value that converts a distance to an object into DC voltage. When a PSD value is less than or equal to a threshold for discriminating stair and floor, the robot recognizes it as a stair, whereas the robot recognizes it as a floor, respectively. The robot turns to face the edge of stairs using two PSDs. If anyone of PSDs recognizes a stair, the circular plate of the robot is rotated so that a reacted PSD is located on the wheel axis. Next the robot turns in direction, so the other PSD recognizes a stair. Finally, the robot stops if both PSDs recognize stairs. Also, the robot turns as shown in Fig. 6, if the angular velocities of inner and outer wheels have a relationship in their turning radii such as vin Rin ¼ ð2Þ v R out
Trials 1
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Postur angle for step [deg]
5 Stair recognition using PSD
Posture angle (°)
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Start angle [deg] Fig. 8 Average and SD of posture angles
out
where vin and vout are the rotational velocities of the inner and outer wheels, and Rin and Rout are the turning radii of the inner and outer wheels. 5.1 Operational check We had conducted an operational check to verify the accuracy of recognizing stairs using PSDs. The evaluation item is the posture of the robot when it was turned to face stairs at a constant velocity of 150 mm/s from start angles, where the posture angle exceeded from the edge of stairs
was assumed to be positive, whereas one under the edge of stairs was assumed to be negative. Experimental conditions are as follows: start angles were assumed to be 15°, 30°, 45°, 60° and 75° as shown in Fig. 7. A rise is defined as 180 mm in this study. A threshold for recognizing a stair was decided as 80 mm, which is the mid-distance between the rise of step and the ground clearance of the robot. Table 1 shows the posture angles of the robot, in which the robot faced the edge of stairs every start angle. Figure 8 shows the average and standard deviation (SD) of posture angles every start angle.
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5.2 Consideration
References
If the posture of the robot is inclined at more than 10° to the edge of stair, anyone of ball-casters in front side falls down stair. The margin of error in the posture angle is defined as ±5° to shift from translational locomotion to climbing down motion. As a result, the error in the posture angle was within 5°, and the largest value of SD was 1.2° after turning motion to face a stair. A relationship between the angular velocity and the turning radius of the wheel was vin ffi 0:42vout : This performed with an enough accuracy because a relationship of them gave a close agreement with vin ¼ 0:43vout defined by Eq. (2) in ideal condition.
1. Tribelhoron B, Dodds Z (2007) Evaluating the roomba: a low-cost, ubiquitous platform for robotics research and educations. In: Proceedings of the IEEE international conference on robotics and automation, pp 1393–1399 2. Tajima S, Aoyama H, Seki T et al (2004) Development of robotic floor cleaning system for high-rise buildings (in Japanese). J Robotics Soc Jpn 22(5):595–602 3. Aoyama H, Ishimura S, Nishihara I et al. (2009) The development of the cleaning device of the office building cleaning robot (in Japanese). In: Proceedings of the JSME conference on robotics and mechanics, 1P1-B14, pp 1–2 4. Yuan J, Hirose S (2005) Actualization of safe and stable stair climbing and three-dimensional locomotion for wheelchair. In: Proceedings of the IEEE/RSJ international conference on intelligent robots and systems, pp 2391–2396 5. Kashiki T, Koyanagi E, Yoshida T et al (2005) A mobile robot which climbs stairs step by step turning two wheeled arms configuration control system (in Japanese). In: Proceedings of the JSME conference on robotics and mechanics, 1P2-S-019, pp 1–4 6. Hirasawa J (2011) Trial production and analysis of a stair climbing robot that equips only one motor (in Japanese). In: Proceedings of the JSME conference on robotics and mechanics, 2A2-L04, pp 1–2 7. Kakudou T, Nagai I, Watanabe K (2010) A cleaning robot for stairs and the simulation of stair movement. In: Proceedings of the 13th international conference on climbing and walking robots and the support technologies for mobile machines, pp 1306–1313 8. Kakudou T, Watanabe K, Nagai (2011) Study on mobile mechanism for a stair cleaning robot: design of translational locomotion mechanism. In: Proceedings of the 11th international conference on control, automation and systems, pp 1213–1216
6 Conclusion A cleaning robot to climb down stairs has been developed for cleaning a three-dimensional space. In particular, mobile mechanisms and a locomotion control method were proposed for the robot to clean and climb down stairs. The operational check of the robot was conducted for recognizing stairs. In the result, it was confirmed that the proposed robot was able to recognize a stair with an enough accuracy to shift from translational locomotion to climbing down motion. As future work, a function is improved in the level of recognizing a surrounding environment such as walls or balusters in stairs.
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