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AWheel-basedStair-climbingRobotwithaHoppingMechanism 53 Fig. 10. Stroboscopic images of stair climbing 6. Demonstration of step descending Finally, we demonstrate fast and soft descending of steps 0.20 m in height. The hopping mechanism is almost the same as for climbing. However, the degree of difficulty is quite different. As mentioned in Section 3, the soft-landing point is the location at which the velocity in the z-direction of vibration of lower body part, -hMω/m 2 cos(ωt+φ), and that of the parabolic motion of the COM, –g(t-T), are canceled out. Here, although the maximum of the former is hMω/m 2 , the latter becomes a large negative value with time, t, because of descending. In climbing, as the robot lands near the top of the parabolic motion, as shown in Fig. 8, and the descending velocity by parabolic motion is low, there are many parameters, hMω/m 2 cos(ωt+φ), which can cancel out the descending velocity. In contrast, in descending, as the robot lands considerably below the top of the parabolic motion, as the dashed line shows in Fig. 11, and the descending velocity is very high, the parameters, hMω/m 2 cos(ωt+φ), which can cancel it out, decrease dramatically. Thus, we use another technique in descending. Hence, the robot does not jump up, but glides from the step horizontally, starts to vibrate by detaching the reel mechanism while descending, and then lands softly, as the solid line shows in Fig. 11. This method requires posture control at takeoff, but decreases the descending velocity by the parabolic motion on landing and makes the required tread length short. Figure 12 shows the trajectories of two body parts (blue and red lines) and impact accelerations (green and orange lines) during the hopping motion. Here, the parameters are: the reduced mass, M, of 0.74 kg, the mass ratio, m 1 /m 2 , of 2.04, the spring constant, k, of 1,200 N/m, the initial contraction of the spring, h, of 0.11 m, and the horizontal velocity, v x , of 1.0 m/s. The impact acceleration at the moment of landing was approximately 14 G, which was close to that experienced during flight, i.e., almost 10 G. As the impact acceleration under free-fall from the riser height to the step was 77 G, the soft-landing of this robot reduced the impact by 82%. Figure 13 shows stroboscopic images of step descending. The posture at takeoff was controlled by a wheelie. H Top of the parabolic motion Landing point -hMω/m 2 cos(ωt+φ) -g(t-T) Fig. 11. Two methods for descending stairs Fig. 12. Trajectories of the two body parts and impact accelerations during hopping motion ClimbingandWalkingRobots54 Fig. 13. Stroboscopic images of step descending 7. Conclusion We introduced a wheel-based stair-climbing robot with a hopping mechanism for stair- climbing. The robot, consisting of two body parts connected by springs, climbed stairs quickly, softly, and economically by using the vibration of a two-degrees-of-freedom system. In the future, we intend to shorten the required tread length by controlling the wire tension and minimizing the body length to realize a practical stair-climbing robot. AWheel-basedStair-climbingRobotwithaHoppingMechanism 55 Fig. 13. Stroboscopic images of step descending 7. Conclusion We introduced a wheel-based stair-climbing robot with a hopping mechanism for stair- climbing. The robot, consisting of two body parts connected by springs, climbed stairs quickly, softly, and economically by using the vibration of a two-degrees-of-freedom system. In the future, we intend to shorten the required tread length by controlling the wire tension and minimizing the body length to realize a practical stair-climbing robot. 8. References Altendorfer, R.; Moore, E.Z.; Komsuoglu, H.; Buehler, M.; Brown, H.; McMordie, D.; Saranli, U.; Full, R. & Koditschek, D.E. (2001). A Biologically Inspired Hexapod Runner, Autonomous Robots, Vol. 11, (month 2001), pp. 207 – 213 Asai, Y.; Chiba, Y.; Sakaguchi, K.; Sudo, T.; Bushida, N.; Otsuka, H.; Saito, Y. & Kikuchi, K. (2008). Wheel-Based Stair-climbing Robot with Hopping Mechanism - Demonstration of Continuous Stair Climbing Using Vibration-, Journal of Robotics and Mechatronics, Vol. 20, No. 2, Apr. 2008, pp. 221-227 ASIMO OFFICIAL SITE：http://www.honda.co.jp/ASIMO/ Harada, K.; Kajita, S.; Kaneko, K. & Hirukawa, H. (2006). Dynamics and Balance of a Humanoid Robot during Manipulation Tasks, IEEE Transaction on Robotics, 2006, vol. 22, no. 3, pp. 568-575. Hirose, S.; Sensu, T. & Aoki, S. (1992). The TAQT Carrier: A Practical Terrain-Adaptive Quadru-Track Carrier Robot, Proceedings of IEEE/RSJ International conference on Intelligent Robots and Systems, July 1992, pp. 2068-2073, Tokyo Kikuchi, K.; Sakaguchi, K.; Sudo, T.; Bushida, N.; Chiba, Y. & Asai, Y. (2008). A study on wheel-based stair-climbing robot with hopping mechanism, MECHANICAL SYSTEMS AND SIGNAL PROCESSING (MSSP), Aug. 2008, Vol. 22, Issue 6, 1316- 1326, ELSEVIER Matsumoto, O.; Kajita, S.; Saigo, M. & Tani, K; (1999). Biped-type leg-wheeled robot, Advanced Robotics, 13(3), Oct. 1999, pp.235-236. Nakajima, S.; Nakano, E.; & Takahashi, T.; (2007). Motion Control Technique for Practical Use of a Leg-Wheel Robot on Unknown Outdoor Rough Terrains, Proceedings of IEEE/RSJ International conference on Intelligent Robots and Systems, vol.1, (Month 2004), pp. 1353-1358 Sakaguchi, K.; Sudo, S.; Bushida, N.; Chiba, Y.; Asai, Y. & Kikuchi, K. (2007). Wheel-Based Stair-climbing Robot with Hopping Mechanism -Fast Stair-climbing and Soft- landing by Vibration of 2-DOF system-, Journal of Robotics and Mechatronics, Vol. 19, No. 3, Jun. 2007, pp. 258-263 Sugahara, Y.; Carbone, G.; Hashimoto, K.; Ceccarelli, M.; Lim, H. & Takanishi, A. (2007). Experimental Stiffness Measurement of WL-16RII Biped Walking Vehicle during Walking Operation, Journal of Robotics and Mechatronics, Vol. 19, No. 3, Jun. 2007, pp. 272-280 Yim, M. H.; Homans, S. B. & Roufas, K. D. (2001). Climbing with snake-like robots, IFAC Workshop on Mobile Robot Technology, Korea, May 2001, pp. 21-22, Jejudo. Yoshida, T.; Koyanagi, E.; Tadokoro, E.; Yoshida, K.; Nagatani, K.; Ohno, K.; Tsubouchi, T.; Maeyama, S.; Noda, I.; Takizawa, O. & Hada, Y. (2007). A High Mobility 6-Crawler Mobile Robot “Kenaf”, Proceedings of 4th International Workshop on Synthetic Simulation and Robotics to Mitigate Earthquake Disaster (SRMED2007), July, 2007, p. 38, Atlanta ClimbingandWalkingRobots56 MotionControlofaFour-wheel-drive OmnidirectionalWheelchairwithHighStepClimbingCapability 57 MotionControlofaFour-wheel-driveOmnidirectionalWheelchairwith HighStepClimbingCapability MasayoshiWada X Motion Control of a Four-wheel-drive Omnidirectional Wheelchair with High Step Climbing Capability Masayoshi Wada Dept. of Mechanical Systems Engineering Tokyo University of Agriculture and Technology Japan 1. Introduction In recent years, aging problem has been arising to be among the most serious social issues world wide, especially in some European and Asian countries, involving Japan. It is reported in Japan that the population of over 65 years old would reach 30,000,000 in 2012 and grow over 30% of total population in 2025[1]. Electric wheelchairs, personal mobiles, scooters are currently commercially available not only for handicapped persons but also for elderly. However, such a rapid grow of aging populations suggest that requirements for electric mobile systems will soon increase dramatically for supporting mobility and activity of elderly people and reducing labor of care-givers. However, those mobile systems do not have enough functionalities and capabilities for moving around existing environments including step, rough terrain, slopes, gaps, floor irregularities as well as insufficient traction powers and maneuverability in crowded areas. Promotion of barrier-free environments will be required for a large number of users of wheelchairs and other electric mobile systems however, re-constructing of the existing facilities could not be a feasible solution because of the limitations in economy and time. For overcoming the problem, to improve the mobility of the electric mobile systems to adapt to existing environments could be one solution. For this objective, we propose a new type of wheelchair, four-wheel-drive (4WD) omnidirectional system, with enhanced step climb capability together with high maneuverability. In this chapter, omnidirectional control of a wheelchair with 4WD mechanism would be mainly discussed. The mobile systems realizing holonomic and omnidirectional motion is one of the important research area in mobile robots. It provide flexibility and high maneuverability to motion planners and human drivers. The holonomic and omnidirectional mobile capability is very convenient for human drivers since they do not have to understand drive mechanisms and its configuration at all. A human only commands the direction and velocity of motion he/her wants to perform since a holonomic and omnidirectional mechanism can start to move in any direction with any configuration of the mechanism such as directions of wheels. 4 ClimbingandWalkingRobots58 This characteristics is vary suitable for wheelchairs and personal mobiles which is used for daily life for maneuvering crowded area at home. In the following sections, a new type of omnidirectional system is proposed which realizes the holonomic and omnidirectional capability together with high mobility on irregular terrains or steps. 2. Conventional Omnidirectional Systems For Wheelchairs A standard wheelchair cannot move sideways. It needs a complex series of movements resembling parallel automobile parking when a wheelchair user wants to move sideways. A lot of omnidirectional drive systems were developed and applied to electric wheelchairs to enhance standard wheelchair maneuverability by enabling them to move sideways without changing the chair orientation. In Fig. 1, an omnidirectional wheelchair with Mechanum wheels [2] uses barrel-shaped rollers on the large wheel's rim inclining the direction of passive rolling 45 degrees from the main wheel shaft and enabling the wheel to slide in the direction of rolling. The standard four-Mechanum-wheel configuration assumes a car-like layout. The inclination of rollers on the Mechanum wheel causes the contact point to vary relative to the main wheel, resulting in energy loss due to conflictions in motion among the four wheels. Because four-point contact is essential, a suspension mechanism is definitely needed to ensure 3-degrees-of-freedom (3DOF) movement. Fig.2 shows an omnidirectinal wheelchair with ball wheel mechanisms developed at MIT [3]. Each ball wheel is driven by an individual motor which provides active traction force in a specific direction while perpendicular to the active direction. With this drive system, the point of contact of a wheel is stable relative to the wheelchair body that enables accurate motion control and smooth movements with no vibration. Fig. 1. Omnidirectional wheelchair with Mechanum wheels [2] Fig. 2. Ball wheel omnidirectional wheelchair [3] MotionControlofaFour-wheel-drive OmnidirectionalWheelchairwithHighStepClimbingCapability 59 This characteristics is vary suitable for wheelchairs and personal mobiles which is used for daily life for maneuvering crowded area at home. In the following sections, a new type of omnidirectional system is proposed which realizes the holonomic and omnidirectional capability together with high mobility on irregular terrains or steps. 2. Conventional Omnidirectional Systems For Wheelchairs A standard wheelchair cannot move sideways. It needs a complex series of movements resembling parallel automobile parking when a wheelchair user wants to move sideways. A lot of omnidirectional drive systems were developed and applied to electric wheelchairs to enhance standard wheelchair maneuverability by enabling them to move sideways without changing the chair orientation. In Fig. 1, an omnidirectional wheelchair with Mechanum wheels [2] uses barrel-shaped rollers on the large wheel's rim inclining the direction of passive rolling 45 degrees from the main wheel shaft and enabling the wheel to slide in the direction of rolling. The standard four-Mechanum-wheel configuration assumes a car-like layout. The inclination of rollers on the Mechanum wheel causes the contact point to vary relative to the main wheel, resulting in energy loss due to conflictions in motion among the four wheels. Because four-point contact is essential, a suspension mechanism is definitely needed to ensure 3-degrees-of-freedom (3DOF) movement. Fig.2 shows an omnidirectinal wheelchair with ball wheel mechanisms developed at MIT [3]. Each ball wheel is driven by an individual motor which provides active traction force in a specific direction while perpendicular to the active direction. With this drive system, the point of contact of a wheel is stable relative to the wheelchair body that enables accurate motion control and smooth movements with no vibration. Fig. 1. Omnidirectional wheelchair with Mechanum wheels [2] Fig. 2. Ball wheel omnidirectional wheelchair [3] The other omnidirectional mechanism is VUTON crawler[4] which consists of many cylindrical free rollers. Since VUTON mechanism allows the multiple rollers to touch the ground simultaneously, heavy load can be applied on the platform. All of the above omnidirectional systems need one motor to drive one wheel mechanism therefore four motors are needed to drive a four-wheeled wheelchair, while a wheelchair has three degrees of freedoms (DOF) on the floor. Thus, it involves 1 DOF redundancy in actuation which causes conflictions in motion among the four wheels. 3. Four-Wheel-Drive (4WD) Mechanism To give a high mobile capability to a wheelchair, we introduce a four-wheel-drive (4WD) mechanism to our omnidirectional mobile system. At first, the original 4WD design is simply mentioned. The 4WD drive system was invented in 1989 [5] for enhancing the traction and step climbing capability of the differential drive systems which schematic is illustrated in Fig.3. This 4WD mechanism has recently applied to a product design by a Japanese company [6]. The wheelchair equips four wheels, two omni-wheels in front and two normal tires in rear. A normal wheel and an omni-wheel, mounted on the same side of the chair, are interconnected by a chain or a belt transmission to rotate in unison with a drive motor. A common motor is installed to drive normal and omni wheel pair via synchro-drive transmission on each side of the mechanism. Then two motors provide deferent velocity on each side witch presents differential drive motion of 4WD mechanism. Thus all four wheels on 4WD can provide traction forces. Since the center of rotation shifts backward, when it turns about a steady point on the floor, it requires large space when the wheelchair is controlled in the standard differential drive manner. The offset distance between drive wheels and a center of a chair makes the maneuverability of the wheelchair worse. Fig. 3. Original 4WD synchronized transmission 4. Powered-caster Omnidirectional Control We apply powered-caster control to 4WD mechanism to give an omnidirectional mobile capability to a wheelchair with 4WD. In this section, The powered-caster omnidirectional control for the original single type configuration[7] is breafly mentioned followed by the control of 4WD mechanism in the next section. ClimbingandWalkingRobots60 4.1 Powered-caster Mechanism Fig.4 shows a top view of a powered-caster. The original design of the powered-caster is a single wheel type in which normal wheel is off-centered from steering shaft. The wheel shaft and the steering shaft of the powered-caster is driven by independent motors. When only the wheel shaft is rotated by the motor, the caster moves in forward direction which is denoted as w x in Fig.4. When only the steering shaft is rotated by an another motor, the mechanism rotates about the point of contact which is also shown in the figure. By this motion of rotation, the steering shaft moves in lateral in w y at the instant which is tangential of the circle which center is at the point of contact with the radius is s, the caster-offset. These velocity vectors are independently controlled and directing right angle for each other. To generate a velocity V in the direction at the center of the steering shaft, the wheel and the steering shaft rotations, w and s , are derived by the following kinematics. w w s w y x ss rr cos 1 sin 1 sin 1 cos 1 (1) where s and r are the caster offset and the wheel radius respectively. Thus shaft rotations are determined by a function of , the relative angle between the desired direction and the wheel mechanism. Fig. 4. Velocity control of a powered-caster 4.2 Omnidirectional Mobile Robot with Powered-casters Figure 5 shows a schematic overview of an omnidirectional mobile robot with two powered- casters. The robot with a pair of powered-casters is controlled by four electric motors which involves one redundant DOF in actuation. For this class of omnidirectional robots, the powered-caster provides an active traction force in an arbitrary direction for propelling the robot. To coordinate the multiple powered-casters, motors on a powered-caster are controlled based on the velocity based robot model. MotionControlofaFour-wheel-drive OmnidirectionalWheelchairwithHighStepClimbingCapability 61 4.1 Powered-caster Mechanism Fig.4 shows a top view of a powered-caster. The original design of the powered-caster is a single wheel type in which normal wheel is off-centered from steering shaft. The wheel shaft and the steering shaft of the powered-caster is driven by independent motors. When only the wheel shaft is rotated by the motor, the caster moves in forward direction which is denoted as w x in Fig.4. When only the steering shaft is rotated by an another motor, the mechanism rotates about the point of contact which is also shown in the figure. By this motion of rotation, the steering shaft moves in lateral in w y at the instant which is tangential of the circle which center is at the point of contact with the radius is s, the caster-offset. These velocity vectors are independently controlled and directing right angle for each other. To generate a velocity V in the direction at the center of the steering shaft, the wheel and the steering shaft rotations, w and s , are derived by the following kinematics. w w s w y x ss rr cos 1 sin 1 sin 1 cos 1 (1) where s and r are the caster offset and the wheel radius respectively. Thus shaft rotations are determined by a function of , the relative angle between the desired direction and the wheel mechanism. Fig. 4. Velocity control of a powered-caster 4.2 Omnidirectional Mobile Robot with Powered-casters Figure 5 shows a schematic overview of an omnidirectional mobile robot with two powered- casters. The robot with a pair of powered-casters is controlled by four electric motors which involves one redundant DOF in actuation. For this class of omnidirectional robots, the powered-caster provides an active traction force in an arbitrary direction for propelling the robot. To coordinate the multiple powered-casters, motors on a powered-caster are controlled based on the velocity based robot model. The inverse kinematics of two-wheeled mobile robot is represented as (2) which represents a relationship between the commanded robot velocity in 3DOF[ v x , v y , v ] and a A wheel velocity [ a x , a y ] and a B wheel velocity[ b x , b y ]. v v v v W v W v W v W b b a a y x y x y x sin10 cos01 sin10 cos01 2 2 2 2 (2) Fig. 5. A two-wheeled omnidirectional robot 5. Omnidirectional Control of 4WD Mobile system In our project, it is a goal to develop an omnidirectional wheelchair with high mobility and maneuverability in a single design which can be used in multiple environments including outdoor and indoor. To enable a wheelchair to move in any direction instantaneously, omnidirectional control method, called "powered-caster control" which was introduced in previous section, is extended and applied to the 4WD mechanism [7]. Fig.6 shows a schematic of the 4WD omnidirectional wheelchair. The wheelchair has two omniwheels in front and standard pneumatic tires in rear which form 4WD configuration. A pair of an omniwheel and a pneumatic tire mounted on the same side of the wheelchair are connected by belt transmission for rotating unison and driven by a common motor which configuration is completely identical to the original 4WD system shown in Fig.3. In our design, an additional third motor is mounted on the conventional 4WD platform for rotating a chair about the vertical axis which is also illustrated in Fig.6. Those three motors including two wheel motors and the chair rotation motor enable the wheelchair to realize independent 3DOF omnidirectional motion by a coordinated motion control [8],[9]. ClimbingandWalkingRobots62 To achieve coordinated control for omnidirectional motion of a chair, the powered-caster omnidirectional control for a twin-caster configuration has been applied to the 4WD system. Fig.7 illustrates a schematic top view of a 4WD mechanism. In Fig.7, it is found that rear two drive wheels and center axis form a twin-caster configuration, i.e. parallel two wheels are located on the off-centered position which midpoint is distant from vertical steering axis, which is emphasized by thick lines in the Fig.7 and a vehicle with a twin caster drive mechanism is shown in Fig.8. The powered-caster omnidirectional control enables the caster mechanism to emulate the caster motion by actuating wheel and steering axes. Fig. 6. A 4WD omnidirectional wheelchair Fig. 7. Omnidirectional vehicle with 4WD mechanism Fig. 8. Omnidirectional vehicle with a twin-caster [...]... Fig 18 Variable center of rotation (b) Spin turn about the back position 70 Climbing and Walking Robots 7 .3 Task example The holonomic and omnidirectional mobile systems are easy to maneuver because 3D command in X- and Y- directions and rotation are directory commanded and an operator does not have to consider the wheel motions and its configurations To demonstrate maneuverability, a task example was... consists of two separated body segments, where front and rear segment can slide linearly up and down in order to negotiate a large height difference of front and rear landing points on the stairs Stair Climbing Robots and High-grip Crawler 75 Fig 3 YANBO -3, which also equipped with manipulability Fig 4 Slope climbing (left) and Stair climbing (right) of YANBO -3 Authors have also been developed quadruped with... Figure 10 and show its high mobility 78 Climbing and Walking Robots And we have another maneuver to realize the leg-wheel hybrid locomotion YANBO-2 and YANBO -3, mentioned above, have 3- DOF ankle joint with eternity rotatable circle shaped sole Therefore using these characteristics, both YANBO-2 and YANBO -3 can establish leg and wheel hybrid locomotion manoeuvres (Ota et al., 2002; Ota et al., 20 03) , as... quadruped walking robot with minimum actuatedDOF for walking motion (Yoneda et al., 2001a; Yoneda & Ota, 20 03; Yoneda, 2007) Taking lightweight advantages with small number of actuators that is three motors are used in Hypeion-1 and 5 motors are used in Hyperion-2, a wall climbing robot “Hyperion-1SP” and “Hyperion-2SP” was developed Wall climbing motion and ceiling walking motion of 76 Climbing and Walking. .. Robots and Systems (IROS2007), pp 1196-1202 Stair Climbing Robots and High-grip Crawler 73 5 X Stair Climbing Robots and High-grip Crawler 1)Kan 1)Chiba Yoneda, 1)Yusuke Ota and 2)Shigeo Hirose Institute of Technology, 2)Tokyo Institute of Technology Japan 1 Introduction Stair climbing is one of the most attractive performance of mobile robot for both legged and wheeled (e.g Stoeter et al., 2002; Murphy,... Robotics and Automation (ICRA2000), pp 1 531 -1 538 [9] M Wada (2007), Omnidirectional and Holonomic Mobile Platform with Four-WheelDrive Mechanism for Wheelchairs, JSME Journal of Robotics and Mechatronics, Vol 19, No 3, pp 264-271 [10] M Wada (2007), Holonomic and Omnidirectional Wheelchairs with synchronized 4WD Mechanism, Proceedings of the 2007 IEEE/RSJ International Conference on Intelligent Robots and. .. to realize a 3DOF angular velocity commands xv , y v and v by independent speed controllers 66 Climbing and Walking Robots for omnidirectional movements Thus, holonomic 3DOF motion can be realized by the proposed mechanism This class of omnidirectional mobility, so called “holonomic mobility”, is very effective to realize the high maneuverability of wheelchairs by an easy and simple operation... generate each frame 6-DOF motion that is necessary and sufficient DOF to lead walking and tasking motion Moreover, in order to acquire higher step adaptabilities to move stairs, one more actuator was attached for extending a leg and keeping frame balance during stair climbing Fig 9 ParaWalker-II, walking and task performing twin-frame mobile system, and its stair climbing motion to extend one leg 2.4 Leg-wheel... incline slopes and appropriate manipulate motions Then total DOF increases to eight, however, the number of actuators are still much less than other biped structure robot, like humanoid (Yoneda & Ota, 20 03) 74 Climbing and Walking Robots Fig 1 YANBO-1, Stair climbing motion Fig 2 YANBO-2, Step climbing motion 2.2 Quadruped Authors also have been developing various kinds of quadruped walking robot (Hirose... style of Leg-Wheel Hybrid locomotion in YANBO -3, wheeled locomotion (upper) and wheeled and leg mixture locomotion (lower) Stair Climbing Robots and High-grip Crawler 79 3 Advantages of Crawler type Vehicles in practical use Through from above mentioned various types of researches, we believe one of the realistic solution which the robots should support and help human tasks in our daily lives is to . of rotation Climbing and Walking Robots7 0 7 .3 Task example The holonomic and omnidirectional mobile systems are easy to maneuver because 3D command in X- and Y- directions and rotation are. realize a 3DOF angular velocity commands v x , v y and v by independent speed controllers Climbing and Walking Robots6 6 for omnidirectional movements. Thus, holonomic 3DOF motion. MotionControlofaFour-wheel-drive OmnidirectionalWheelchairwithHighStep Climbing Capability 71 7 .3 Task example The holonomic and omnidirectional mobile systems are easy to maneuver because 3D command in X- and Y- directions and rotation are directory commanded
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