###### Abstract  
In recent years, Automated Guided Vehicles (AGVs) have been playing an increasingly important role in producing industry and infrastructure and will soon arrive to other areas of human life such as the transportation of goods and people. However, several challenges still aggravate the operation of AGVs, which limit the amount of implementation. One major challenge is the realization of reliable sensors that can capture the different aspects of the state of an AGV as well as its surroundings. One promising approach towards more reliable sensors is the supplementary application of virtual sensors, which are able to generate virtual measurements by using other sources of information such as actuator states and already existing sensors together with appropriate mathematical models. The focus of the research described in this paper is the design of virtual sensors determining forces and torques acting on an AGV. The proposed novel approach is using a quadratic boundedness approach, which makes it possible to include bounded disturbances acting on the AGV. One major advantage of the presented approach is that the use of complex tire models can be avoided. Information from acceleration and yaw rate sensors is processed in order to realize reliable virtual force and torque sensors. The resulting force and torque information can be used for several diagnostic purposes such as fault detection or fault prevention. The presented approach is explained and verified on the basis of an innovative design of an AGV. This innovative design addresses another major challenge for AGVs, which is the limited maneuvering possibilities of many AGV designs. The innovative design allows nearly unlimited maneuvering possibilities but requires reliable sensor data. The application of the approach in the AGV resulted in the insight that the generated estimates are consistent with the longitudinal forces and torques obtained by a proven reference model.  
Keywords:fault diagnosis; observers; automated guided vehicles; input estimation; force balance +
Footnote †: journal: Applied Soft  
tasks such as good loading and unloading and only fixed guiding technology such as magnetic guidance or optical guidance are used [2]. One main problem can be the hardware design [2]. AGVs with conventional steering systems such as classical Ackermann steering exhibit limited maneuvering capability and can thus not use the movement areas efficiently. Another main problem is the high cost of sensors in AGVs and the fact that sensor data filtering, sensor data plausibility assessment and sensor fusion are no trivial tasks. In real AGV operation, some parameters such as slip, exact wheel diameter and mass are changed during the operation caused by uneven load distribution or manufacturing imperfection and loading of goods [4]. These conditions aggravate the gathering of reliable sensor data. Further problems can arise from a less than sufficient flexibility, availability and reliability of current AGV designs. The main objective of the presented research is to develop approaches for optimized virtual sensor design and, through this, to more efficient, flexible and reliable AGVs. The presented research combines two main approaches to address these causes: the innovative AGV design, which is described in this paper, allows unlimited maneuvering capabilities and the virtual diagnostic sensor design enhances reliable sensor information without additional expenditures.