Consider the sketch of an electromechanical system in Fig.1 below. It gives a payload such as camera or a laser marker a single motional degree of freedom - namely, rotation around the vertical axis. The mechanical configuration is such that two motors are used to exert torque on the payload. The payload is directly attached to a voice coil motor with a limited angular range. This, in turn, is seated on a stage that is rotated by a classical DC motor via a transmission gear (belt). This, in turn, is placed on a base that is exposed to disturbing rotational motion (driven manually in our case but it emulates unwanted motion of a carrier such as a car or aircraft - obviously, the current system is just a 1D simplification of such inertial stabilization system).


Figure 1.: mechanical configuration for a dual stage system.

The control goal for the system is to keep the inertial angular rate of the payload at a given value, irrespectively of the disturbing motion of the base. The classical task is to stabilized the orientation of the payload even in presence of some rotational motion of the carrier. Another task is to reorient the payload to a new direction.

The control inputs are:

  • voltage on the voice coil motor
  • voltage on the DC rotary motor (with a belt gear)

The disturbance input is:

  • angular rate of the base (carrier). Treat it as an unmeasurable disturbance, even though it can be estimated with the help an incremental optical encoders measuring position of the base with respect to the stationary part (desk in the lab).

The measurements are:

  • inertial angular rate of the payload around the vertical axis (measured by MEMS Coriolis sensor of an inertial angular rate)
  • angle between the inner and middle stages (measured by a magnetic incremental encoder)

A real benchmark system is in the lab run by the lecturer and is pictured in Fig.2.


Figure 2. Laboratory system demonstrating the functionality of a dual stage inertially stabilized system. Restricted to one axis.

A video demonstrating the functionality is

A mathematical model and physical parameters can be found in the paper:

  • M. Rezac and Z. Hurak. Structured MIMO H∞ Design for Dual-Stage Inertial Stabilization: Case Study for HIFOO and Hinfstruct Solvers. Mechatronics, Elsevier, Vol.23, Iss.8, December, 2013, pp: 1084–1093. DOI: http://dx.doi.org/10.1016/j.mechatronics.2013.08.003.

Your goal is to think about the right configuration for satisfaction of the inertial stabilization and directional repointing and apply some classical control design techniques (lead, lag, PI, PID) and some more advanced (LQ, LQG, Hinf, structured Hinf, mu-synthesis, ...).

Matlab file(s) implementing the model and some design procedure can be downloaded from MatlabCentral. You can perhaps start your design by reproducing our own design. And then add some more designs of your own.

Last modified: Tuesday, 14 April 2020, 1:19 PM