Figure 1
This paper deals with the plan for the design of a closed loop system position control device. The system allows for a particular rotational position to be located and to be continually monitored. The system allows for a resistance feedback signal to be utilized in controlling the rotational position of a shaft.
The purpose of a position control system is to report the location of a rotational object and compare it to the desired position. A system of this nature requires an automatic control system that can sense and react quickly to any variances in desired locale. By continually adjusting the mechanical components of the system, the stability of the system is ensured.
For our specific application, the potentiometer interprets the position of our system based on its desired location. A resulting voltage signal is compared to the signal that corresponds to the desired reference signal. A difference in this voltage is then acted upon by a controller and the position is then corrected.
Figure 1
The Plant 
Figure 2 and a DC motor
Figure 3
is connected to a gear box which generates a torque. The potentiometer 
Figure 4 measures the angular position
with respect to the frame of the system and transforms corresponding
angular position into a voltage.
After putting both the motor and plant together and combining
like terms, the transfer function 
Figure 5
was found. The summing junction 
Figure 7
could be either a common opamp 
Figure 6,
or could be controlled through software. The model for the controller 
Figure 8 will have a proportional gain
for the input signal to the motor. Block diagram of the system
is shown in 
Figure 9. Using Mason's rule
and a signal flow graph 
Figure 10, a
closed loop transfer function for the system was found 
Figure 11.
Note Figure 12 was omitted.
The Diagram of the System Model and Connected Controller 
Figure 13
is a proposed system setup to test the described position controller.
(All of the computational & graphical results have been omitted to save space.)
A reference voltage input of 1.5 volts, equal to 3.14 radians, produced a plant output of 3.10 radians. The corresponding steady-state error is equal to 1.27 percent. These calculations are a result of computer simulation on MATLAB version 3.5 (student version) and Boeing Computer Services EASY5x.
Figiola, Richard S. and Beasly, Donald E.,"Theory and Design for Mechanical Measurement", John Wiley & Sons, Clemson, South Carolina, 1991
Nise, Norman S. "Control Systems Engineering", The Benjamin/Cummings Publishing Company, Redwood City, California, 1992
The Math Works Inc.,"The Student Edition of MATLAB", Prentice Hall, Englewood Cliffs, NJ, 1992
Boeing Computer Services, Easy5x, "Engineering Analysis System", Workstation Version User's Guide, Seattle, Washington, 1991