The French Région Pays de la Loire project RobEcolo:
Design and Control of Wooden Robots
Objectives of the RobEcolo project
Why a project on the design of an industrial wooden robot? You may believe that this idea is crazy? However, this idea comes from the actual context of climate change. The Climate Change Mitigation (CCM) has become a priority in Europe. To deal with this huge challenge, the European Council adopted new environmental targets for EU in 2008, the so-called “20-20-20 targets”, in which the first two targets are:
- To reduce emissions of Greenhouse Gases by 20% by 2020, and
- To increase energy efficiency to save 20% energy consumption by 2020 (40% and 27 % by 2030, resp.).
Such targets cannot be achieved without the collaboration of Governments and Industry. However, with the financial crisis, Industry is faced with its survival with respect to (wrt) the low cost countries. Thus, Industry must (i) innovate, (ii) robotize its processes to avoid relocation / reinforce the reshoring trend.
In 2014, the robot world operational stock was about 1,500,000 units A recent study shows that at least 6.107 kWh of energy is consumed per year to operate the robots while at least 1,500,000 T of raw materials (whose stock on Earth is limited and whose extraction / processing is polluting) have been used to build them. For the manufacturing of the robot worldwide stock, the equivalent of 11,000,000 T of CO2 has been released in the atmosphere. So, the use of current robots goes against CCM.
The main objective of RobEcolo is to propose innovative design methodologies leading to new robots with a drastically reduced EI (in terms of Greenhouse Gas emission during the robot manufacturing phase).
We usually believe that the environmental impact of a machine is mainly due to its use, and not due to its design / manufacture. However, a recent study  performed in order to characterize the environmental impact of an industrial robot has shown that more that 60 % of the greenhouse gas emitted during the total life cycle of this machine were emitted during the manufacturing / design phase (Fig. 1 - this ratio does not take into account the industrial process for which the robot is used).
Fig. 1. Environmental impact of a Kuka KR 270 robot during its total life cycle (manufacturing + use during 12 years) / Energy consummed during the use phase (data from ).
Fig. 2. Greenhouse gas emitted for the production of several materials (equivalence measured in kg of CO2 – data taken in ).
Up to now, the designer of an industrial robot does not consider the environmental impact when designing a robot. Thus, he uses usual materials (aluminum / iron alloys, carbon composites) which are extremely polluting (Fig. 2). The idea of RobEcolo is to design a wooden industrial robot, as wood has a negative environmental impact. The use of wood for designing machines is not a new idea. Wood was used in the past for designing machines (e.g. the Jacquard loom in the 19th century, or most of the airplanes before World War II) but was progressively replaced by metallic (and later the carbon composite) materials. However it is still used for the design of buildings due to its high payload-to-weight ratio and its low cost. Nowadays, designing machines with wood is limited to mock-ups (Fig. 3), prototyping (Fig. 4) or entertainment (Fig. 5). It is also used in machines in which wooden elements do not impact the accuracy, e.g. chassis of cars (cf. Morgan car manufacturer).
Fig. 3. Wooden mock-up of a walking robot .
(a) Prototype of the Stanford OpenArm robot .
(b) The Willow-Garage PR1 robot .
Fig. 4. Examples of robot prototypes made with wood: for these robots, wood was used as a prototyping purpose (due to its low cost) or on parts that were not used to ensure the structural stiffness and overall accuracy.
Fig. 6. The elephant (animatronics) of the Machines de L'Isle Museum of Nantes.
Fig. 7. Prototype of an industrial parallel robot in which one link has been replaced by a wooden element.
Thus, wood is never used in critical parts ensuring accuracy of machines. The reason is given below. A recent attempt to introduce wood in industrial robot manufacture was presented in  (Fig. 7). The results showed that the approach was valid enough to compete with usual materials. However, this study missed two crucial issues: The wood performance / dimensions will vary with the atmospheric conditions / external solicitations and with the conditions they have grown; thus, new robot design issues appear: How to be sure that the design process is robust wrt wood variability, i.e. that a robot made with wood can be accurate, stiff, etc., even if wood properties vary? Moreover, at equal stiffness, most of wood types are heavier than carbon: How to the lower energy consumption associated with moving the robot? Robotic companies do not trust in wood. How prove them that wood are good materials for robot design? The goal of RobEcolo is to show that industrial wooden robots could be a good alternative to metallic industrial robots, despite these two aforementioned issues.
Within RobEcolo, we are going to prove that it is possible to design a wooden industrial robot which has performance (in terms of accuracy and stiffness) equivalent to those of standard industrial robot. The challenge is to design a robot (with a size similar to the SCARA TP80 FastPicker of Staübli, with repeatability lower than 500 µm and a deformation under a payload of 1 kg lower than 500 µm), and this even is the wood properties / dimensions vary.
To reach these goals, we are going to develop robust design algorithms that will take into account the variability of the wood performance and that will allow the definition of robot architectures for which the impact of this variability is minimal. For using these algorithms, it will be necessary to define models for the characterization of the robot deformations, models which do not exist for wooden robots and which must be created. Moreover, in order to ensure the accuracy even of the dimensions of the wooden links may vary with the atmospheric conditions, we are going to use sensor-based controllers. The sensors involved in these controllers will observe elements of the robots as close as possible from the end-effector. The use of these sensors may impact the robot performance, and we will take into account this potential impact at the beginning of the design phase. Finally, all theoretical results will be obtained on a prototype of wooden robot that will be designed during the project.
 Fizians Environnement "Eco-design of two types of robots: KUKA 270 and IRSbot-2", 2014.
 T. Laurent et al., “Eco-conception: Vers un Robot en Bois” (in French), Technologie, 168, 2010.
 A. Roennau et al. “Design and Kinematics of a Biologically-Inspired Leg for a Six-Legged Walking Machine,” Int. Conf. Biomed. Rob. & Biomech, 2010.