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Visual Display for U.C.L.A. Driving Simulator:
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This article first appeared in |
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Written by:
S. F. Hulbert and C. K. Wojcik. Institute of Transportation and
Traffic Engineering University of California, Los Angeles. Document supplied to "..in 70mm - The 70mm Newsletter by Dr. Richard Vetter |
Issue 49 - June 1997 |
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The U.C.L.A. Driving Simulator The U.C.L.A. Driving Simulator has been developed as a research tool in the field of highway safety (Ref.1). The block diagram of this facility is shown in Fig. 1. This simulator is a projection room in which an automobile is driven on steel rollers of a standard chassis dynamometer while the driver views the road scene that is projected onto a curved screen 8.5 ft in radius. The driver also views the road scene behind him by looking through the rear-view mirror at a motion picture projected on a screen placed beyond the rear window of the vehicle. The field of vision of the front view is 150 deg. The projection technique used is a special type of motion picture presentation called Dimension 150, in use under contract with Dimension 150, Inc. There are two variable speed projectors mounted on a turntable in the projection booth (see Fig. 2.). The projectors are manufactured by DeVry, Model MDX-35, modified for selsyn control, and their capacity was increased to 3000 ft of film. This length of film constitutes an average of about 30 minutes of projection time depending on the speed the driver chooses to drive. Since there are two projectors, one can be reloaded while the other is in operation. Hence, the only limitation on time of projection comes from the total length of film (number of reels). Film used for the front-view projection is 35mm colored film. The rear-view projectors are Dumont 16mm, continuous-image projectors, custom built and modified for selsyn control. They are mounted on a fixed base. The speed of the projectors is governed by the speed of the vehicle placed on the chassis dynamometer. To be more specific, one of the steel rollers of the chassis dynamometer drives two synchrogenerators which are interlocked electrically with syncro-motors of the projectors. One of the synchro-generators is interlocked with two synchromotors of the projectors in the projector booth; the second synchro-generator is interlocked with two rear-view projectors. The front view projectors in the projection booth are mounted on turntables which are driven by a dc motor. The voltage input signal to this motor is a product of two voltages; one representing the velocity of the car and taken directly from the tachometer of the chassis dynamometer and the second representing the rotation of the front tires of the vehicle. The latter is measured by resting the front tires on two turn plates that are spring-loaded to simulate the resistance present when making a turn. One of the turn plates is geared to a potentiometer. The voltage signal is proportional to the displacement of this potentiometer. Because motion-picture is a programmed visual presentation technique, a negative voltage signal, representing the steering-wheel displacement during the ride, when the picture was taken (also called compensating steering), is introduced to the system. When this negative signal is equal in magnitude to the signal from the potentiometer (of plus polarity) they cancel out and the input signal to the dc motor is zero and the turntable and the projector remain at rest. When signals do not cancel out, the turntable and projector rotate, causing the picture to move from its center position on the screen and thus simulate a change in the head-way of the vehicle. This method of opposite sign signals is used to force the subject to control the steering wheel as he would in real driving. The heading feedback and the wide range of control of the projection speed eliminate to a large degree, the drawbacks of programmed presentation. When taking pictures of road scenes the camera car must travel at a speed suitable to local traffic conditions, for example 35 mph on a two-lane road and 55 mph on a freeway. The speed of the camera is 24 frames per second and remains constant for all types of driving. Hence the number of frames per unit of distance varies. At 35 mph, the vehicle moves 2.14 ft per frame, i.e., a picture is taken every 2.14 ft; for 55 mph this value is 3.36 ft. Had two films been made these two different speeds and shown, at the simulated speed of the vehicle, say 35 mph, the driver would get an impression of going 35 mph when viewing the picture taken at 35 mph, but when viewing the picture taken at 55 mph he would get an impression of going 55 mph which certainly would be in conflict with the speedometer reading of 35 mph. To eliminate this problem a Vari-Drive unit was installed between the roller of the chassis dynamometer and the synchro-generator. The range of the reduction ratio of this Vari-Drive is 1:2.64. A nomograph for evaluation of viewing velocity is shown in Fig. 3. |
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