Mass estimation considering stiffness and fabrication of period measurement device in mass measurement using velocity-feedback relay control

Abstract

A mass measurement system with a relay feedback of velocity has been developed to achieve measurement without gravity. In this system, mass is estimated from the periods of oscillation in the relay-feedback system. Originally, the velocity of the object was solely fed back, which caused the orbit of the object to drift easily. A restoring force compensation by a spring was introduced to avoid such drift. However, a slight drift still occurs in spite of the restoring force element. A new estimation formula has been derived which can estimate mass regardless of the position of the closed orbit. An analytical study on this formula shows that mass is overestimated when the restoring force is neglected in the estimation. Several experimental results show that the estimated mass is slightly larger than the actual value even though the new formula is used in estimation. In the measurement, the periods of oscillation are measured with a digital oscilloscope. A delay in the period measurement is expected to cause such overestimation. To reduce the error due to delay in measuring periods, a new device for rapid period measurement is developed, which uses the edge detecting function of a micro-computer. It is experimentally demonstrated that the measurement error is reduced by the developed measurement device.