Regulator control of a short-radius centrifuge and subjective responses to head movements in a rotating environment

Abstract

Artificial gravity is made through the centripetal force from a rotating chair or short-radius centrifuge. It is a very promising countermeasure, as it alone should remove all the adverse effects of microgravity. In order to effectively use artificial gravity as a long-duration space flight countermeasure, the effects of artificial gravity on the human body must be investigated. If artificial gravity is created by use of a short-radius centrifuge, the high angular velocity required, about 23 rpm, causes unexpected and illusory body motions when making head turns. My work in artificial gravity consisted of two parts, a study that investigated the vestibular response to head movements during centrifugation and regulator feedback control of the centrifuge. This experiment studied the perceived illusory body sensations and heart rate changes induced by head movements in both the yaw and pitch planes while supine during centrifugation. Yaw right, yaw left, and pitch head movements yielded successively significantly higher heart rate than baseline. Results show that 68% of subjects in the yaw plane and 48% of subjects in the pitch plane experienced illusory body tilt as predicted by a model of the vestibular system while 13% in yaw and 40% in pitch experienced body tilt in the opposite direction from the predicted model. Pitch head movements yielded significantly higher magnitude and duration of illusory tilt. These side effects are serious and will need to be controlled if short-radius centrifugation is to be a successful countermeasure. Regulator feedback control has been implemented on the centrifuge with both an optical encoder and an accelerometer. Tachometer development, automatic control, and classical PID control theory was used to develop the gain and integrator time constants, which lead to K=1.5 and Ti=1 sec. This results in an improved steady state error by 99.8% and a more accurate response of the centrifuge by 5.7% for the accelerometer and 52% for the encoder feedback system from the open loop system.