带有自锁式关节的农业六足机器人能耗优化模型及验证

六足机器人具有成为丘陵山区未来重要农业装备的潜力,但高能耗是其实际应用的技术瓶颈。普通机器人关节无自锁特性导致其在静立时也需耗能以克服重力,而如果让关节自锁以保证静立时不耗能,则运动能耗又将大幅提高。为此,该文以机器人在运动及静立过程中的综合能耗最少为目标,给出带部分自锁式关节的六足机器人设计方案,提出其能耗优化模型：引入经试验验证的关节正反向驱动力矩传递效率差异来修正现有模型缺陷,基于地面力学修正现有约束条件,针对自锁式关节不同配置给出对应的目标函数。以模型给出的能耗极小值为评定依据,对自锁式关节进行优化配置。试验及仿真结果表明：所提出的能耗优化模型比现有模型更准确,能进一步降低运动能耗40%以上;对特定构型的六足机器人,不使用自锁式关节时静立功耗超过38 W,所有关节均可自锁时运动能耗比前者高3倍以上;在应用该文优化模型和最优关节配置方案后,既可保证静立能耗为0,又可保证运动能耗与不使用自锁式关节时基本相当：完成30°下坡、平路、30°上坡行走时,运动能耗仅分别高出14.2%、16.3%、45.5%。该文提出的能耗优化模型可为带有自锁式关节的农业六足机器人设计和能耗优化提供理论支持。

Energy consumption optimization model of agricultural hexapod robot with self-locking joints

Abstract: Hexapod robot has the potential to be an important agricultural equipment in hilly areas in the future, but its feature of high energy consumption has become a technical bottleneck in practical application. Energy self-sufficiency may be within our reach if the robot is driven by electric motors and can be charged by solar energy, but this type of robot often has no self-locking joints, which leads to certain energy consumption against gravity even when they stand still; although the joint brake mechanism may be helpful, but shortcomings like energy penalty and lack of compact in mechanism that come with it will appear. If the joints are self-locking to ensure no energy consumption when the robot stands still, then the energy consumption when moving will increase dramatically. Based on the above problems, to minimize overall energy consumption of the robot when it''s moving or long-time standing still, a hexapod robot design with optimal disposition of self-locking joints was given, the energy consumption optimization model was also built only considering that the robot had a specific motion which avoided a non-deterministic polynomial hard problem, and thus the model just needed to optimize the energy consumption instantaneously. A defect of such an existing optimization model based on the torque distribution algorithm was corrected by introducing the difference of torque transmission efficiencies of robot joints in forward and reverse drive; in order to adapt the compacted soil ground in hilly areas, the constraints of the existing model which were suitable for the rigid environment were modified based on terrain mechanics. For different self-locking joints configurations, there would be different energy consumption optimization models, and their corresponding objective functions were given separately; this allowed energy consumption comparison of different configurations being conducted based on the minimum values of objective functions from different optimization models, and then the self-locking joints must be positioned properly and used as few as possible in the optimal configuration. In order to validate the optimization models and the effect of optimal disposition of self-locking joints, an experiment and optimization simulations were carried out. Torque transmission efficiencies of a self-locking worm joint in forward and reverse drive were tested in the experiment. The test data agreed with the ones obtained from the theoretical formula, which proved the correctness for the model to introduce the difference of torque transmission efficiency and the accurateness of the model compared with the existing one. Optimization results of the model proposed in this paper were contrasted with that of the existing one through Matlab and Adams co-simulation. Comparison results show that: joint torques as the optimum solution obtained from the optimization model of this paper have fewer chances to do negative work when robot is moving, which is better in accord with the "gravitationally decoupled actuation" and "coupled drive" concepts, and thus the total energy consumption of robot can be further reduced by more than 40% compared with the existing model. For a given robot configuration, the power consumption is more than 38 W when standing still if the robot has no self-locking joints, and the energy consumption when moving is 3 times higher than the former one if all the joints are self-locking; only when applying the optimization model and the optimal joints disposition, the robot can not only stand still with no energy consumption but also consume energy basically at the same level as the former one when moving, and the energy consumption of the robot is only 14.2%, 45.5% and 16.3% higher than that with no self-locking joints when walking downhill, uphill along a 30° ramp and level, respectively. The energy consumption optimization model proposed in the paper provides theoretical supports for the design and optimization of agricultural hexapod robot with self-locking joints.