Design & evaluation of spherical washout algorithm for Desdemona simulator

In co-operation with TNO Human Factors, AMST Systemtechnik developed an advanced simulator motion system based on a 6 Degrees-of-Freedom (DoFs) centrifuge design. The simulator cabin is suspended in a freely rotating gimbal system (3 DoFs, >360°) which, as a whole, can move vertically along a heave axis (1 DoF, ±1m) and horizontally along a linear arm (1 DoF, ±4m). To provide sustained centripetal acceleration (1 DoF, 0-3g), the linear arm can spin around a central yaw axis. Unique about Desdemona’s 6 DoFs motion capabilities is that it can combine onset cueing along the x, y and z-axis (like a hexapod simulator) with sustained acceleration cueing up to 3g (like a Dynamic Flight Simulator). In addition, unusual attitudes and large attitude changes can be simulated one-to-one. Desdemona was developed as a spatial disorientation training and research simulator with applications in flight simulation, driving simulation and astronaut training. TNO is responsible for the motion cueing algorithms. Since the Desdemona simulator can move and rotate along three orthogonal axes, a classical washout scheme can be applied to transform vehicle (e.g.: aircraft) motion into simulator motion cues. However, for Desdemona this approach has a number of disadvantages:
- The motion space actually used for simulation would be limited to a relatively small circular segment of about 90° (R=4m) in which a rectangular area can be fitted (the remaining segment of 270° is not used).
- The possibility to use centripetal acceleration to simulate sustained specific force would not be used, since sustained cues are simulated by tilting the pilot with respect to gravity in the classical washout algorithm.
- The classical washout algorithm is based on simulator kinematics in a Cartesian Frame-of-Reference while the kinematic design of Desdemona is spherical.
To make better use of the circular motion space of Desdemona a dedicated washout algorithm was developed, called: Spherical Washout Filter. Instead of directly high-pass filtering the x- and y-component of the specific forces, these components are first transformed to radial and tangential acceleration after which the radius, the cabin yaw angle and the central yaw rate are high-pass filtered. The spherical washout algorithm significantly enlarges the motion space, since the simulator moves back towards a certain base radius and not towards a fixed neutral point in space as is the case in conventional hexapod simulation. In addition, sustained specific forces can be simulated using a combination of tilt and centripetal acceleration.