Similarly, the computation of the inverse kinematic model is easier than the computation of the direct kinematic model. The explicit formulation of the direct geometric model is usually more complicated since it can have up to 40 solutions. It is shown that the closed-form solution of the inverse geometric model is straightforward for a six degree-of-freedom parallel robot. This chapter deals with the geometric and kinematic modeling of such robots. This concept is currently used in designing new generations of high speed machine tools.
Recently, these kind of structures have attracted considerable interest in various manufacturing applications due to their inherent characteristics, as compared with those of serial robots, which include high structural rigidity and better dynamic performances.
Since then, they have been used in other applications requiring manipulation of heavy loads with high accelerations such as vehicle driving simulators or the riding simulator developed for the French National Riding School. Parallel architectures were originally proposed in the context of tire-testing machines and flight simulators. W Khalil, E Dombre, in Modeling, Identification and Control of Robots, 2002 8.1 Introduction As G-loads are typical of high-performance fighter aircraft, the following section describes the use of simulators in military aviation. While vibrations occurring during suborbital flights may still be achieved by a hexapod platform, depending on the characteristics (frequency, magnitude, direction), this definitely does not apply for the reproduction of sustained accelerations, or G-loads. However, the suborbital flight parameters outlined above exceed this motion envelope. These motion parameters can be adequately reproduced by a Level D motion platform.
Looking at the flight envelope, transport aircraft normally operate at low angular rates within ± 30 degrees angle of bank, pitch attitudes of 5–15 degrees nose up, and without significant G-loads. Courtesy: 2016 National Aerospace Centre (NLR), Amsterdam, The Netherlands.įull-flight simulators are widely used for recurrent training and proficiency checks of airline pilots, and are even qualified for the entire conversion training to a new aircraft (“type rating”), which proves that today's simulator technology offers good operational fidelity for transport aircraft.
The Generic Research Aircraft Cockpit Environment, representative of a hexapod-type full flight simulator.
This technique, known as “tilt coordination,” makes use of the perceptual ambiguity between body tilt and translation, and shows that the limited motion space of a simulator can sometimes be surpassed when knowledge of human motion perception is taken into account.įig. Also, a commonly applied technique to produce a sensation of forward acceleration during takeoff is to tilt the simulator cabin backward ( Groen and Bles, 2004). In addition to these motion cues representing “maneuver motion,” certification also requires the generation of some special motion effects to simulate “disturbance motion” (e.g., tail strikes, engine failure, turbulence).
This way, only transient, or “onset cues” are being reproduced, which are associated with changes in aircraft motion (e.g., pitching up, or rolling into a turn).
Motion-driving algorithms in the simulator's software convert the equations of aircraft motion into platform motions, filtering out large displacements, which would drive the platform into its limits and cause noticeable false cues ( Nahon and Reid, 1990). The commonly used motion platform consists of six linear actuators (hence the name “hexapod”), which move synergistically to produce angular excursions up to ± 30 degrees, and linear displacements of about 6.5 ft/2 m ( Fig. The most advanced full-flight simulator approved for pilot training is classified as Level D by the FAA (2007) (or Type VII by ICAO (2015)), and requires a six degrees-of-freedom motion platform.
These range from fixed-base procedure trainers, comprising a generic cockpit, to full-flight simulators, comprising a type-specific cockpit operating on a motion platform to give the pilot the “feel” of flying. Depending on the training objectives, different categories of flight simulators are approved for commercial pilot training.