Abstract Details

Name: Amaresh Mandal
Affiliation: Manipal Institute Of Technology,Manipal
Conference ID: ASI2017_1400
Title : A Programmable System on Chip (PSoC) based Controller for the PSMT Segment Support Actuators
Authors and Co-Authors : Prasanna Deshmukh,Indian Institute of Astrophysics,Bangalore. Padmakar Parihar,Indian Institute of Astrophysics,Bangalore.
Abstract Type : Poster
Abstract Category : Instrumentation and Techniques
Abstract : The primary mirror of any Segmented Mirror Telescope (SMT) is made of a large number of small mirror segments placed side by side to form the large monolithic surface. The most crucial task for any SMT is to maintain alignment of these mirror segments against external disturbances like wind, gravity, temperature and structural vibrations. This is achieved by using three position actuators per segment working at few-nanometer scale range. We have designed and developed a segment support actuator for the Prototype Segmented Mirror Telescope (PSMT) which is being developed at Indian Institute of Astrophysics, Bangalore. PSMT will have seven mirror segments and each segment will be supported and driven by three soft actuators. Every actuator has a dedicated local controller. The major challenges in designing actuator controller are: it should provide a few nanometer position accuracy in presence of all kind of disturbances, should facilitate servo update rate up to several KHz and should synchronously operate all 21 actuators commanded by the global controller through Ethernet or CAN network. These challenges are met by developing a mechanically robust actuator operated by a precision local controller. The electronics of local actuator controller has been developed around PSoC (Programmable System on Chip) hardware. PSoC 5LP chip is chosen because of its versatility, low cost, and ease of design. It supports the design of both analog and digital component on a single chip along with ARM Cortex M3 processor. PSoC gives design flexibility by offering Universal Digital Blocks (UDB) along with the built-in configurable ADC, DAC, filters and communication modules. The basic implementation of the local controller on PSoC has been completed and it has several modules such as Encoder interface, Position loop, Offloading loop, Signal filtering, Communication interfaces etc. In addition to the controller, separate customized driver boards which primarily provide needed power to several motors used in the actuator has also been designed and developed. The local control system of each actuator uses PID algorithm to maintain its position to the desired set point is provided by the global controller via CAN network. For the best performance, the PID gains are determined experimentally using relay tuning method. An extensive experimentation has been carried out to test the performance of actuator combined with the controller. In this paper, we present the design, implementation and some of the laboratory test results.