Page 418 - Mechatronics for Safety, Security and Dependability in a New Era

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depending on the direction of the tilt (Reid & Grant (1991)). To reproduce transient accelerations, the
platform is linearly moved in the same acceleration direction and come back when the acceleration is
continuous or vanishes (Seigler & Kemeny (2001)). The implementation of this technique depends on
the mechatronics and the architecture of the motion platform (Kheddar & Garrec (2002)). However,
designers proposed architectures by seeking as often as possible to supply the driver with stimuli that
are as close to those existing in actual situations. The most sophisticated ones bring into play hybrid
architectures (X-Y, 6 axis + yaw) and their costs reach up to 100M$ (e.g. the NADS, USA). These
simulators seek to simulate all possible driving situations. They are, however, not always able to
accurately reproduce braking manoeuvres.

Another approach is possible; it is founded on the design of part-tasks simulators, intended for certain
studies or applications (e.g. a particular driving task study) (Seigler & Kemeny (2001)). For these
simulators, and concerning movement restitution, the goal is to produce a "sufficient illusion" in order
to make possible the achievement of the task. By "sufficient illusion", we mean an illusion that allows
the driver to carry out the task by using the same strategies as those he/she would have employed in an
actual situation. This is essential to guarantee transferability of results acquired on a simulator to real
situations. We designed a driving simulator whose objective is the study of "normal" driving situations
(e.g. outside of sliding or harsh braking situations). We will focus on the most common driving
situation: car following or queuing driving. Our objective is not to render acceleration in a realistic
physical way, but rather to study the minimal inertial effect from which the subject extracts the
necessary information to carry out the driving task in a manner comparable to a real driving situation.
To do this, we have designed a motion platform equipped with two degrees of freedom. This makes it
possible to animate the simulator's cab with a longitudinal movement, on the one hand, and with a
weak pitch movement from the driver's seat or a weak tilt of the back of this seat, on the other hand.

PLATFORM DESCRIPTION

Figure 1: The driving simulator: CAD model of the motion platform and seat (left), overview (right)

The overall system is considered as two independent mechanically linked systems: the rotating driving
seat and the longitudinal motion platform (fig 1). Each of them is driven by a single actuator. The
motion platform undergoes translation motions according to one direction (front and back) which
correspond to driver's acceleration and deceleration. The overall system's design allows having a
simple linear model of the motion. The motion base supports the cabin consisting of the seat, the
vehicle board and the driver. Because the rotations of the seat are low in amplitude, its induced inertia
is negligible comparing to the total mass of the cabin's set. The linear motion of the cabin's set is made
thanks to a ball screw/nut transmission mechanism driven by a DC actuator. The technological design
was made in order to reduce, even eliminate, mechanical flaws such as backlash, mechanical play,