成果報告書詳細
管理番号20160000000596
タイトル*平成27年度中間年報 次世代ロボット中核技術開発 革新的ロボット要素技術分野 小型油圧駆動系と燃料電池・電池ハイブリッド電源によるフィールドアクチュエーション技術
公開日2016/7/22
報告書年度2015 - 2015
委託先名国立大学法人東京大学
プロジェクト番号P15009
部署名ロボット・AI部
和文要約
英文要約(1) Evaluation of Maximum Force of EHA Actuators for Hydra
Maximum force of single pump EHAs are 1500N. We evaluated maximum force of redundant pump EHAs. They are designed to produce 3000N. To safely measure the force, we measured maximum differential pressure acting on cylinders instead of direct force measurement. From the test, we observed equivalent maximum force of 1750N, which is 58% of design value. In the same test, single pump EHA produced almost 1500N, which implies there is an effect of absolute pressure acting on pumps that increase internal leakage. In the test, we observed communication failure between FPGA that control power transistors, and MCU that handles position control. The detailed evaluation revealed that the noise contamination was the cause.
(2) Evaluation of Switching Characteristics of Hybrid Power System
By using an Electronics Power-Load Equipment, we made experimental evaluation of the dynamic characteristics of the hybrid power system consisting of a Fuel-cell battery and the Lithium-ion battery. Due to the specified difference of the voltages of the two kinds of batteries, there is a drop of voltage when the external power load increases and the Fuel-cell battery switches to the Lithium-ion battery. The dynamics response of switching was high enough not to make an influence on the control performance of the robot movements. However, the voltage drop itself would need further study. It is useful to design the hybrid power system to have the minimum voltage difference as long as the passive hybrid system confirms its stable performance. This will be a design principle of the passive-hybrid power system for the field robotics systems.
(3) Thermal Characteristics and Design of Electronics Circuit
In previous research, we studied effect of heat development in the pumps on output force of EHAs. Liquid cooling was introduced in EHA pumps to significantly reduce the effect of the heat that is generated by internal leakage. Motor drivers are another source of heat in actuator system. SiC hybrid IGBTs are used in our motor drivers, which generates heat proportional to forward voltage and drain current. Robots require large maximum voltage rating of power devices due to large EMF voltage generated by regeneration of motors. Large voltage rating leads to large power loss in Si based power devices. Temperature of power devices must be monitored to prevent damage of motor drivers. We monitored temperature of IGBT while EHAs are producing large force. Tests were performed with different cooling condition of the power device. When a redundant pump EHA is producing 1500N and single pump EHA is producing 1000N, temperature increased from 40deg to 90 deg in 37 seconds in case of no cooling. In case of heat sink with force convection, temperature increased from 45deg to 90 seconds in 40 seconds. No large difference in temperature was observed between different cooling condition, which implies necessity of larger heat sink or larger heat transfer. Since motor drivers are mounted on robots, it is unrealistic to use large heat sinks. We are developing and testing liquid cooling of motor driver power devices. From evaluation above, we came to a conclusion that motor drivers with larger power capacity are necessary in developing actuation system with high reliability. This year, we focused on design of a next generation motor driver with the following features.
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