- Research Article
- Open Access
Energy-efficient narrow wall climbing of six-legged robot
© The Author(s) 2018
- Received: 23 April 2018
- Accepted: 7 September 2018
- Published: 24 September 2018
In this paper, we propose two gait strategies for a limb mechanism robot, called ASTERISK, to move on narrow spaces. Specifically, we describe two types of locomotion, namely, vertical-body climbing gait and horizontal-body climbing gait, that the robot uses to climb on two parallel walls. The proposed strategies are verified through both simulations and experiments on an actual robot. Moreover, to reduce power consumption during locomotion, we employ a power efficiency model based on the pose of the robot and its limbs. The simulation and experimental results confirm the effectiveness of proposed gait strategies.
- Limb mechanism
- Narrow space
- 3D locomotion
Forthcoming robots are expected to assist humans in hazardous areas to perform tasks such as the maintenance and inspection of plants, disaster response, construction operations, and demining [1, 2]. Hence, such robots will be used in a various scenarios including structured or unstructured environments, flat or rough terrain, indoor or outdoor, and narrow spaces. Recently, wheel-based and crawler robots have been widely used given their high-mobility mechanisms . A wheel-based robot generally has limitations in locomotion over rough terrain. A crawler robot has no such limitation, however, its mechanism has another problem in stability when applied in different types of terrain. On the other hand, legged robots have been proposed as a general solution for any type of terrain [4–6]. In fact, legs allow the robot to flexibly select the contact points for locomotion, thus becoming suitable even for irregular terrain.
In this paper, we propose new gait strategies for locomotion in narrow spaces, particularly for climbing. In addition, we introduce a model to reduce power consumption when applying the strategies. This paper is organized as follows. In “Limb mechanism robot ASTERISK” section, we detail the limb mechanism robot ASTERISK. Then, we propose the gait strategies in “Proposed gait strategies” section. In “Evaluation of gait strategies” section, initial simulation and experimental results are presented. From these results, we propose a power efficiency model in “Power efficiency model” section, whose evaluation is presented in “Power efficiency evaluation” section. Finally, our conclusions are drawn in “Conclusion” section.
As mentioned above, the limb mechanism robot called ASTERISK has 6 limbs that can be used for either locomotion or manipulation. The ASTERISK limbs are radially attached to the body at even intervals, as shown in Fig. 1. This arrangement allows homogenous mobility and omnidirectional manipulation.
Static model between parallel walls
Gait strategies to climb on parallel walls
Static model of gait strategies
Gravitational acceleration (m/s2)
Coefficient of static friction between limb and wall
Vertical motion per cycle (m)
Cycle duration (s)
Experiments with real robot
After verifying the feasibility of both gait strategies in simulations, we implemented them on an real environment using the ASTERISK robot. The applicable parameters were the same as those for the simulation (Table 1). In addition, the two walls consisted of acrylic boards, and the limb tips were made of silicon rubber to increase friction. In the experiments, we manually set the robot near the ground and between the walls as its initial starting position.
The coordinate values are expressed with respect to the robot coordinate system, and the red lines represent the best trajectories of the support limbs. The position and posture on these trajectories satisfy (13). To guarantee stability, we omitted the area between −30 and 30 mm along the y axis from the analysis.
In this paper, we propose two new gait strategies for the limb mechanism robot ASTERISK to climb on parallel walls. Both strategies, vertical-body climbing gait and horizontal-body climbing gait, consider two swing limbs and four support limbs. For vertical-body climbing gait, the body of the robot remains upright, whereas for horizontal-body climbing gait, the body of the robot remains horizontal, i.e., parallel to the ground. We verified the feasibility of the proposed gait strategies through simulations and real robot experiments. In addition, we evaluated a power efficiency model that may prevent servo failures. This model also improved the position and posture of the robot limbs, and reduced the total torque during climbing.
As future work, we aim to improve the robot stability during motion using the proposed strategies. In addition, ASTERISK will be tested for a climbing task within an in-pipe environment.
KO contributed concepts and drafted the manuscript. TT carried out the main experiment of this study. KK support the design of experiment and revised the manuscripts. TA, YM, MK, MH contributed concepts and revised the manuscript. All authors read and approved the final manuscript.
The authors declare that they have no competing interests.
Availability of data and materials
The datasets during and/or analysed during the current study av ailable from the corresponding author on reasonable request.
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