Design and optimization of force feedback interfaces

There are many fields in which humans cannot intervene directly because the environment is hostile or inaccessible on their scale. To intervene in such environments, we need to use robots that are advantageously remote-controlled. The most effective way of controlling them is to use force feedback master arms.

Similar devices are used to interact with simulated virtual reality environments. Digital mock-ups, which are increasingly replacing physical prototypes in the design of new products and systems, can be used to simulate the assembly of a complex system, to detect and correct errors at a very early stage in the design cycle, or to design a real virtual factory aimed at optimizing workstation ergonomics and productivity. However, effective use of this technology requires appropriate methods and peripherals. In this context, force feedback interfaces are particularly interesting. They can be used to control the movements of certain objects in the virtual scene, enabling the user to feel the forces applied to these objects when they collide with their environment, as in the real world. We'll refer to these as "haptic interfaces" rather than master arms.

In both cases, we're dealing with more or less complex polyarticulated mechanical structures equipped with sensors and actuators - in other words, real robots. However, force feedback interfaces are very different from industrial robots, which are generally position-controlled to follow repetitive trajectories independently of external disturbances, in a controlled environment from which humans are excluded. In contrast, force feedback interfaces are manipulated by a user, and must therefore offer a high level of safety and security. They must also be highly effort-sensitive and dynamic, so as to be able to follow all the operator's gestures and restore the slightest effort applied to the remote robot or the user's avatar in virtual reality, whether these interfaces are fitted with a simple handle or have a more complex architecture, as on arm or hand exoskeletons.

These performance and safety constraints require compliance with a number of criteria, and the implementation of appropriate technological solutions. This article presents these criteria and their common values, then introduces robotic modeling and dimensioning tools for designing interfaces that meet these requirements. Their application will be illustrated by several examples.