Dextrous robot arm
The ESA Dextrous robot Arm (DexArm) project is engaged in the design and development of a robot arm comparable in size, force capabilities and dexterity to a human arm, suitable for space applications.
The first programme to make use of DexArm is Eurobot, a three arm robot complementary in capability to a human being engaged in Extra-Vehicular Activity (EVA). Eurobot will be used for extra-vehicular operations on the International Space Station, for example: moving along the space station structure using standard EVA interfaces, execution of, or provision of support to, routine EVA tasks, and replacement of Orbital Replacement Units (ORUs).
One set of design constraints for DexArm results from it having to withstand the harsh environment of space. Beyond these requirements however, the main challenges for the development team came with the minimisation of resource usage.
To achieve this goal, ESA has encouraged the use of innovative approaches and technologies to drastically reduce mass, volume and power consumption while providing adequate performance in terms of both torque/force capability and positioning accuracy and repeatability.
The DexArm project is being implemented in three phases. The first two phases focused on system requirements, arm architecture and the design and development of a prototype joint for the arm.
Two designs of joint have been produced. The two prototypes made use of different components and had different architectural implementations. During testing, they both exhibited remarkable performance. However, only one prototype was selected for continued development.
The third phase, currently ongoing, is the development of an engineering model of DexArm. The prototype joint selected for continued development has been re-designed in order to integrate changes deemed necessary to improve the already good performance and further reduce resource usage.
The re-engineered prototype has then been used as a basic component for the design of the robot arm.
The prototype joint is a truly complex mechatronic device. It integrates all the mechanical, electronics and computing elements needed to achieve high precision/high torque rotary motion. The joint is composed of:
A comparative analysis of the performance in dexterity, cable passing, folding capabilities and human arm similarity was carried out on selected basic robot architectures featuring different geometric arrangements of seven joints.
The architecture that showed best results made use of roll joints alternating with pitch joints having an asymmetrical movement range.
Based on this architecture, which only tells how joints are disposed in space, robot limbs were designed. Robot limbs must accommodate sets of very contradicting requirements. On one hand they must be very stiff (to allow high robot precision) on the other hand they must be very lightweight. Also they need to maintain a given joint position very firmly, yet allow the joints to move freely throughout their design range.
DexArm development is ongoing. Although the final result is not yet available, there is high confidence that DexArm will meet the requirements of the EuroBot application. Furthermore, its architecture and basic components are sufficiently flexible and powerful to be re-used for other space applications.
The following papers can be downloaded via the ASTRA proceedings link at the right of this page:
Last update: 2 February 2011