Excalibur, a Three-axis Force Display

In haptic simulation, a force feedback device is combined with a digital representation of a virtual world to create a kinesthetically immersive experience. The force feedback device, or haptic display, is usually a robotic manipulator with which a human operator interacts physically, usually through a handle, stylus, finger-pad or some other form of customized interface. Modeling of the haptic display is often overlooked when building a haptic simulation. Understanding the dynamic behavior of the device is critical in assessing the stability and performance of the overall system as well as in the construction of the digital simulation. This paper describes some of the special modeling requirements for haptic displays. A dynamic model for Excalibur, a new three-axis force display, is developed in a two step process. First an analytical model is constructed based on measured values and basic principals. Then the model is tuned using the results of vibrational testing to achieve a close match between the modal behavior of the theoretical and real systems. Numerical and experimental results are presented for representative points in the device’s workspace.