13-11-2012, 04:23 PM
Mechatronics design of response enhancement of Stewart fine tuning platform for the square kilometer array
Mechatronics design.pdf (Size: 287.15 KB / Downloads: 28)
Abstract
For the rapid response requirement of the trajectory tracking of the next generation large
radio telescope-square kilometer array (SKA), a mechatronics design strategy using homogeneous
electrorheological (ER) damper to enhance the response of Stewart fine tuning
platform is proposed in this paper. The viscosity-variable homogeneous ER damper is directly
attached on the ram of the linear actuator to tune the additional damping of the actuator
controlled system, so that the large gain coefficient can be used to enhance the response of
Stewart fine tuning platform. The position PD controller design methodology is proposed
based on this mechatronics strategy using conventional pole assignment technique, and the
relationship between the ER damping coefficient and the bandwidth of linear actuator control
system is presented. The simulation results have verified the effectiveness of this mechatronics
design strategy, the designed controlled actuator system based on this mechatronics strategy
has large gain coefficient and favorable performance over the conventional designed one,
which have laid a solid base for the engineering implementation of the SKA.
Introduction
Radio astronomy is part of the science of astronomy and can in fact be considered
as a science of its own. Radio astronomy has been crucial in discovering phenomena
such as quasars, pulsars, gravitational lenses, superluminal motion and the cosmic
microwave background. Throughout the development of astronomy, steps in the
enlargement of knowledge have always followed technical improvement in the instrumentation
used. This is especially true for radio astronomy, which has, in the
comparably few years of its existence, contributed enormously to our understanding
of the universe, partly through confirmation of postulates made earlier, e.g. the 21
cm Hydrogen line, interstellar chemistry, and the cosmic background radiation, but
to major part also through unexpected detections and the ones we expect to make in
the future, require highly sophisticated instrumentation and signal processing.
Radio astronomy has increasingly threatened the limiting factor of sensitivity.
Receiver development is already so advanced that an order of magnitude sensitivity
increase cannot be achieved by lowering the receiver noise temperature, because the
system noise temperature is already mainly determined by the antenna temperature.
Improved receiver stability to enable longer integration times is also not considered
as help. The only option is another quantum step in collecting area [1].
Model of PD control linear actuator
The designed Stewart fine tuning platform consists of a base, a moving platform
and six electrical linear actuators. The base and the moving platform are connected with these actuators, and the actuators shorten or extend its length to achieve the
desired trajectory of the moving platform [7,13]. The electrical linear actuator is
selected as a high efficient and zero backlash one, which consisting of a dc servomotor,
a gear reduction unit and a spiracon roller screw [13,14], and the encoder
attached on the shaft of the motor to realize the semi-closed-loop position control. If
the decentralized control strategy is adopted to realize the tracking control of
Stewart fine tuning platform, then the diagram of one component of PD control
actuator is shown in Fig. 2.
Conclusions
In order to improve the bandwidth of Stewart fine tuning platform to meet the
requirement of rapid response and high precision tracking for the SKA, a mechatronics
strategy to realize the additional damping coefficient of the actuator system
using ER damper is proposed in this paper. The viscosity-variable damper is developed,
and it can be directly attached on the ram of the actuator to tune the additionally
obtained damping. Based on this mechatronics strategy, a novel PD
position controller design method is developed using pole assignment technique. The
performance comparison of the mechatronics designed controller with the conventional
PD controller is carried out.