Position control of the mirror figure control actuator for the Keck Observatory ten meter primary mirror.

摘要

Each of the 108 hydraulic actuators on the Keck ten meter primary mirror lengthens or shortens under electronic control in steps of about four nanometers. The starts and stops of longer moves are profiled to help prevent the stimulation of mirror system mechanical resonances by abrupt actuator length changes. At the move endpoint, the actuator is kept still to prevent the pumping of periodic energy into these resonances. Endpoint stiffness is maintained by electronic feedback. The combined power dissipation of the actuator and its local control system is constrained by the need to minimize heat generation in the vicinity of the mirror. In this paper, we discuss observed stictional and other mechanical phenomena associated with a very short bi-directional actuator length changes and trace the impact of the various constraints on actuator controller design and implementation. We present some results of tests with an actuator controller driving an actuator which in turn drives a displacement sensor. The units under test are production devices to be used in the Keck primary mirror active figure control. 2 refs., 6 figs.