SIMULATION: Transactions of The Society for Modeling and Simulation International

doi: 10.1177/003754976901200311pmid: N/A

Poux, Jim

doi: 10.1177/003754976901200301pmid: N/A

Rieman, Frank C.

doi: 10.1177/003754976901200302pmid: N/A

Manley, Ivan

doi: 10.1177/003754976901200303pmid: N/A

Balas, Leo F.

doi: 10.1177/003754976901200304pmid: N/A

Wilson, John W.

doi: 10.1177/003754976901200305pmid: N/A

The utility of a four-gimbal system for positioning two reference frames with respect to each other without gim bal lock has long been recognized. As early as 1954 such a system to isolate an inertial platform was proposed by Arnold and Schlesinger1 . However, the exact law for driving the fourth angle has been a question. The situa tion had not improved through 1962 where, in Reference 2, "gimbal flip" (an instantaneous rotation of 180 de grees in two axes, similar to the three-axis gimbal be havior at gimbal lock) appears as an inherent part of the fourth angle's driving law. Clearly this behavior is not desirable for platform isolation or visual display systems used for vehicle motion cues in simulation.This paper describes developments made at Langley (NASA) in the last several years. A driving law for the fourth angle is developed for two different four-gimbal systems. The first is similar to the gimbal systems de scribed in References 1 and 2 and has advantages in design and implementation for platform isolation. The second is specifically designed to minimize occlusion in visual display systems3.In each system, the fourth angle driving law is a direct consequence of maximizing the angle between the two axes causing the singularity. Thus, a necessary differ ential constraint is found to maintain a nonsingular solu tion. A sufficiency condition for a nonsingular solution is also found. The second four-gimbal system that mini mizes occlusion has the interesting result that the maxi mum angle between the singularity-forming axes is not always 90 degrees.

Gutz, Steven

doi: 10.1177/003754976901200306pmid: N/A

Nilsen, R.N.

doi: 10.1177/003754976901200307pmid: N/A

This paper discusses various hybrid applications of a variable transport lag. A specific example, the simulation of a thermally controlled environment, is presented. In it the transport lag is due to the delay caused by having to move a mass of heated air by pump from the heating element into the environment. Various forms of heater control and delay function are presented and their effects on the system are described.Experimental results for various forms of heater con trol and transport lag variation are presented along with a discussion of the problems involved with this type of simulation. Finally, remarks as to possible methods of improvement and extensions are made.

Abraham, R.G.; Collins, M.W.; Heiser, R.; Mutafelija, B.

doi: 10.1177/003754976901200308pmid: N/A

Glickman, Myron

doi: 10.1177/003754976901200309pmid: N/A

Control system analysts are frequently called upon to include a hydraulic servo actuator as part of the loop in a complex closed-loop system simulation. This article presents a general description of several common types of hydraulic servo actuators and several methods for inclusion of the effects of load on the simulation of the actuator in the control loop. These methods are pre sented in block diagram form and are suitable for inclu sion in a larger simulation loop. The block diagrams themselves may be somewhat condensed and modified before inclusion in a larger simulation, but are presented here with all the details shown explicitly for clarity.