Control electronics for an adaptive secondary mirror

The recent concept of an adaptive secondary mirror controlled by a large number of force actuators has been explored through the realization of a thirty actuators prototype. The design and implementation of the local position control electronics and real time software is presented. Both centralized and de-centralized control approaches are considered, and for the experimental implementation the de-centralized solution is adopted. The design is based on a digital approach. Mirror actuators are controlled by an array of DSPs. Each DSP controls two actuators: the position measurement are obtained from capacitive sensors co-located with the actuators and a local closed loop position control is implemented on the DSP to drive the voice coils. In the prototype unit, a bi- direcitonal fast serial line is used to exchange data with the wavefront computer. The communication link can be used to download program code and data to the DSPs thus allowing the greatest flexibility in the definition of algorithms and working parameters. The same link is used during mirror operation to issue position commands to the deformable mirror and to get back diagnostic data.