This paper presents a complete design methodology for a multi-axis resonant force sensor. The proposed device has been designed to be useable in a context of physical interaction between robots and humans. The proposed solution allows the three force components and the three torque components to be measured simultaneously and can be inserted into an interface handle or a robot end-effector. The information on wrench can then be used to detect and control interactions for cooperative tasks between humans and robots. In the context of sensors for robotic co-manipulation, it is imperative to guarantee not only a certain level of performance (accuracy, dynamics, size) but also to guarantee certain non-functional specifications associated with safety, measurement redundancy or functional integration of the sensor into its environment. The consideration of all these design specifications, both functional and non-functional, led to the principles and technologies used to develop this sensor. Multi-axis resonant sensors have excellent performance and safety characteristics, two key elements for collaborative robotics, but the literature review did not reveal any significant previous work in this area. Thus, this paper proposes an original sensor based on a breakthrough technology in the crucial field of multi-axis force sensors. The performances obtained on our prototype are already close to the performances of the best existing 6-axis industrial sensors, which suggests very good prospects for this new technology. In addition, and compared to alternative technologies, resonance technology offers new possibilities in terms of sensor fault detection, thus improving the intrinsic safety of these devices.