IEEE International Conference on Robotics and Automation

In this paper, we develop an articulated mobile robot that can climb stairs, and also move in narrow spaces and on 3-D terrain. This paper presents two control methods for this robot. The first is a 3-D steering method that is used to adapt the robot to the surrounding terrain. In this method, the robot relaxes its joints, allowing it to adapt to the terrain using its own weight, and then, resumes its motion employing the follow-the-leader method. The second control method is the semi-autonomous stair climbing method. In this method, the robot connects with the treads of the stairs using a body called a connecting part, and then shifts the connecting part from its head to its tail. The robot then uses the sensor information to shift the connecting part with appropriate timing. The robot can climb stairs using this method even if the stairs are steep, and the sizes of the riser and the tread of the stairs are unknown. Experiments are performed to demonstrate the effectiveness of the proposed methods and the developed robot.

Development and Control of Articulated Mobile Robot for Climbing Steep Stairs

This paper suggests a new performance metric for a mobile platform called as a posture variation index (PVI) to evaluate the smoothness of its movement, which is an important factor to predict undesired oscillations or shocks on a mobile platform while traveling on rugged terrain. The PVI consists of the height and pitch angle variations of center of mass of a mobile platform. By using the PVI, the movements of well-known mobile platforms are systematically analyzed. In order to ensure smooth movement as well as high terrainability on rugged terrain, a new mobile platform (RHyMo) is constructed on the basis of the kinematic and quasi-static analyses. The extensive experiments are carried out by using the RHyMo and the Rocker–Bogie platform on the artificial rugged terrain, which verify that in comparison with the Rocker–Bogie platform, the average and maximum height variations of RHyMo are reduced by 12.72% and 5.96%, respectively. Moreover, the average and maximum pitch angle variations of RHyMo are significantly reduced by 65.87% and 60.53%, respectively. The terrainability of RHyMo against a high step and steep stairs is improved with the help of the track mechanism installed in the front linkage.

A New Mobile Platform (RHyMo) for Smooth Movement on Rugged Terrain

A task-space method is presented for the control of a head-raising articulated mobile robot, allowing the trajectory tracking of a tip of a gripper located on the head of the robot in various operations, e.g., picking up an object and rotating a valve. If the robot cannot continue moving because it reaches a joint angle limit, the robot moves away from the joint limit and changes posture by switching the allocation of lifted/grounded wheels. An articulated mobile robot with a gripper that can grasp objects using jamming transition was developed, and experiments were conducted to demonstrate the effectiveness of the proposed controller in operations.

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Task-Space Control of Articulated Mobile Robots With a Soft Gripper for Operations

Snakes can move through almost any terrain. Although their locomotion on flat surfaces using planar gaits is inherently stable, when snakes deform their body out of plane to traverse complex terrain, maintaining stability becomes a challenge. On trees and desert dunes, snakes grip branches or brace against depressed sand for stability. However, how they stably surmount obstacles like boulders too large and smooth to gain such anchor points is less understood. Similarly, snake robots are challenged to stably traverse large, smooth obstacles for search and rescue and building inspection. Our recent study discovered that snakes combine body lateral undulation and cantilevering to stably traverse large steps. Here, we developed a snake robot with this gait and snake-like anisotropic friction and used it as a physical model to understand stability principles. The robot traversed steps as high as a third of its body length rapidly and stably. However, on higher steps, it was more likely to fail due to more frequent rolling and flipping over, which was absent in the snake with a compliant body. Adding body compliance reduced the robot roll instability by statistically improving surface contact, without reducing speed. Besides advancing understanding of snake locomotion, our robot achieved high traversal speed surpassing most previous snake robots and approaching snakes, while maintaining high traversal probability.

Robotic modeling of snake traversing large, smooth obstacles reveals stability benefits of body compliance

One of the important advantages of an active wheeled snake-like robots is that it can access narrow spaces which are inaccessible to other types of robot (such as crawlers, walking robots), since snake-like robots have an elongated, narrow body. Additionally, in areas with rubble, snake-like robots can traverse rough terrain and large obstacles since its body can conform to the terrain’s contours. ‘ACM-R8’ is a new snake-like robot which can climb stairs and reach doorknobs in addition to the features explained above. To fulfill these functions, the design of this robot incorporates several key features: joints with parallel link mechanism, mono-tread wheels with internal structure, force sensors and ‘swing-grousers’ which were developed to improve step climbability. In this paper, the design and control methods are described. Experiments confirmed high mobility on stairs and steps, with the robot succeeding in overcoming a step height of 600 mm, despite the height of the robot being just 300 mm.

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Development of snake-like robot ACM-R8 with large and mono-tread wheel

Generally, wheel mechanisms are inferior to a tracked or walking mechanism in terms of step climbability or traversability in rough terrain; however, they are superior in terms of energy efficiency, structural simplicity, and carrying capacity. This paper proposes a new wheel mechanism, the swing-grouser wheel, which can climb high steps (especially in low friction environments) and has high energy efficiency. In addition, the swing-grouser wheel can climb regardless of the body inclination. Its merits are compared to the results of prior studies. Furthermore, the performance of the swing-grouser wheel was confirmed using a real device experiment and a 2D physics simulation, and improved using a full search of the parameters of the swing-grouser wheel. As a result, one improved parameter resulted in climbing at over 68% of the wheel diameter in a low friction environment; additionally, the energy efficiency was better than that of the previous model.

Study of swing-grouser wheel: A wheel for climbing high steps, even in low friction environment

The vehicle using omnidirectional wheels has ability to move in all directions without changing the body direction unlike a normal four wheel drive vehicle. However most of omnidirectional vehicle are designed for using only on flat ground. In this paper, we propose a new type of omnidirectional wheel, “Spiral Mecanum Wheel”, which enables vehicle climb the step. This new wheel consists of spiral beams and many small rollers, and these small rollers are arranged along the spiral beams. When the vehicle with this spiral Mecanum Wheels moves in normal direction, the edge of the spiral moves to cover the step from above. We have performed the experiments using Spiral Mecanum Wheel and showing the wheel works very well. As a result, in the experiment using single Spiral Mecanum Wheel, this Spiral Mecanum Wheel climbed the step about 83% of the wheel diameter in normal direction motion. The vehicle with Spiral Mecnaum Wheel climbed the step about 37% of the wheel diameter in tangential direction motion and 59% in normal direction.

Spiral Mecanum Wheel achieving omnidirectional locomotion in step-climbing

The crank wheel mechanism, consisting of a wheel mechanism and parallel links connected to each wheel, achieved high mobility and efficiency because it has both wheels and legs in a simple structure. However, each prior model of crank wheel mechanism has had shortcomings such as mass oscillation or fragile structure. In this paper, we propose a novel crank wheel mechanism, the “Eccentric Crank Rover”(ECR), which is an enhanced crank wheel mechanism with eccentric wheels. The eccentric wheels increase the under-body clearance, and change the body trajectory from straight to trochoid curve, which has the same shape as the crank legs but opposite phase trajectory. Thus, the body itself acts as a “second” crank leg. We experimentally confirmed higher step climbability, larger clearance, and lower cost of transport than other models such as normal wheel model, eccentric wheel model, and crank wheel model without eccentric wheel.

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Eccentric Crank Rover: A novel crank wheel mechanism with eccentric wheels

Snake-like robot which has active joints and thruster mechanisms has been proven to have its high mobility on narrow and rough terrain because of its slim and long trunk. However, larger space than its slim trunk is necessary for snakelike robot to turn. Thus, in order to improve the mobility of snake-like robot, turning method which makes turning radius smaller is needed. In this paper, a new turning method for snake-like robot which has both pitch and yaw joints, and thruster mechanism in each module is proposed. In this method, both pitch and yaw joints are bent to their limits, and take advantage of steep bent area which are not used normally. This new method was applied to an active snake-like robot ACM-R8, and experimented in physics simulations and hardware experiments. As a result of these experiments, it was confirmed that the new method made the turning radius smaller.

/pdf/turning-method-that-minimizes-turning-radius-for-snake-like-35sbycp2zx.pdf

Hirotaka Komura

Papers

Development of snake-like robot ACM-R8 with large and mono-tread wheel

Study of swing-grouser wheel: A wheel for climbing high steps, even in low friction environment

Spiral Mecanum Wheel achieving omnidirectional locomotion in step-climbing

Eccentric Crank Rover: A novel crank wheel mechanism with eccentric wheels

Turning method that minimizes turning radius for snake-like robot with active joints and active wheels