This project aims at developing a flexible manipulator for picking. Fruit or vegetable picking requires a compliant and dexterous grip to guarantee the integrity of the object as well as a flexible carrying structure to be able to navigate between the branches without damaging them. The objective is to develop a continuous proboscis robot, without joints and operated by remote motors and cables, like the tendons in a human hand. The project is divided into 3 main issues well known in the field of robotics, namely design, modeling and control. These 3 aspects are actually very intertwined for this kind of complex systems. A good design with a good integration of actuators and sensors facilitates enormously the control by means of an adequate modeling which answers at the same time to a certain realism and an efficiency of calculation.
The context
In the context of the fight against global warming and unprecedented technological convergence (digital, artificial intelligence, etc.), agriculture must reinvent itself to produce better, while respecting the environment and human health. Agricultural robotics is one of the levers of this transformation. It is a promising solution for meeting the environmental and health challenges currently facing France and all other developed countries. The urgency of climate change will require an ever greater reduction in the use of inputs (pesticides, water, etc.) and fossil fuels. In addition, the agricultural sector suffers from a lack of attractiveness and a negative image among many young people (rurality, repetitive tasks, exhaustion, economic difficulties, isolation, etc.). Digitization and robotization will enhance the value of this profession and relieve farmers of repetitive and tiring tasks such as weeding, carrying, picking and regular crop maintenance.
The objectives
The major scientific objective is to be able to respond to the three issues of design, modeling and control, in a simultaneous and integrated approach, sometimes called co-design (hardware and software).
The targeted robot is similar to a trunk, about one meter long and able to reach several stable configurations in a continuous way. It is made of a flexible material, without joints, and operated by cables. A solution with 3 segments and 6 cables is today tested for the seizure of object in little constrained environment. In a second step, increasing the number of segments and cables will increase the kinematic redundancy of the trunk, which will allow to optimize the grip and/or to avoid possible obstacles in the environment.
A deformable body has by definition an infinite number of parameters. This constitutes a first difficulty in the mathematical characterization of this kind of system. The control of this type of model can be solved by an optimal control approach which consists in minimizing a cost criterion under constraints. These constraints represent the geometrical and elasto-mechanical conditions of the system. The scientific difficulty would be to incorporate a nonlinear deformation model in large displacement with a management of unilateral contacts (robot-object and robot-robot self-collision). Several avenues are being studied: 1) Use of SOFA software, 2) POD model reduction, 3) Cosserat and MPC model.
The control would still require the development of estimation modules such as:
- estimation of the robot state,
- perception of the environment, identification and localization of the object,
- and robot-object contact localization.
The results
The expected results for the project are to have :
- A working prototype with 6 torque-controlled motors;
- A control of the horn configuration;
- A stable grip of an axisymmetric object;
- An implementation of exteroceptive sensors for the real time estimation of the configuration of the proboscis.
Partnerships and collaborations
The members of the Roboterrium – Equipex Tirrex network are partners in the project.
