Remote Touchscreen-Controlled Defense Turret Senior Design Documentation Courtney Mann, Brad Clymer, Szu-yu Huang Group 11
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User InterfaceBuilding the Window consists of six functions, outlined below with their corresponding input variables.Function: CreateTrackbar Parameters: trackbarname, string winname, value, count, onChange, userdata trackbarname: Name of the created trackbar. winname: Name of the window which will be used as a parent of the created trackbar. value: The optional pointer to an integer variable, whose value will reflect the position of the slider. Upon creation, the slider position is defined by this variable. count The maximal position of the slider. The minimal position is always 0. onChange Pointer to the function to be called every time the slider changes position. This function should be prototyped as void Foo(int,void*); , where the first parameter is the trackbar position and the second parameter is the user data (see the next parameter). If the callback is NULL pointer, then no callbacks is called, but only value is updated userdata The user data that is passed as-is to the callback; it can be used to handle trackbar events without using global variables Function: getTrackbarPos Parameters: trackbarname, winname Trackbarname Name of the trackbar. winname Name of the window which is the parent of the trackbar. Function: imShow Parameters: winname, image winname Name of window image Image to be shown Function: namedWindow Parameters: name, flags name Name of the window in the window caption that may be used as a window identifier. flags Flags of the window. The only supported flag is CV_WINDOW_AUTOSIZE . If this is set, the window size is automatically adjusted to fit the displayed image (see imshow ), and the user can not change the window size manually. Function: setTrackbarPos Parameters: trackbarname, winname, pos, trackbarname and winname are as above. pos Sets the trackbar position. Function: waitkKey Parameters: delay delay Delay in milliseconds. 0 is the special value that means “forever”
Motor controllers, for both pan motor and tilt motor, receive the coordinates of a chosen target, which is analyzed and transformed from analog to digital data by the Arduino using function analogWrite(). In order to have smooth movement on the motors, the group is going to implement a multichannel PID controller to eliminate as much error as possible before the signals are sent from the user interface to the motor driver. A closed loop PID controller has better control of the servo system to improve transient response time, reduce the steady state error, and reduce the sensitivity to the load parameter (inertia). Improving transient response time implies that the bandwidth has to be increased. The faster the response time is, the quicker the system will settle. Steady state error indicates the accuracy of the servo system. Load parameters represent the tolerance of fluctuation in both input and output parameters. Servo control can be broken into two fundamental classes, command tracking and the disturbance rejection characteristics of the system. The servo control system can be seen in Figure 10. User Command Arduino Servo Control PID Controller Analog Data Digital Data Servo Drivers
Attitude Servos Figure : Servo Control System Command tracking is that, when the coordinates of a designated target are fed into the system control module, the servo control addresses how smooth the movement of a motor is and how accurately the user commands are followed. This part of the servo control is referred as “Feedforward control”. This can be interpreted as what internal commands are needed for the user’s motion commands to be followed without any error. Disturbances can be the torque disturbances on the motor shaft or false motor parameters estimations used in the feedforward control. Disturbance rejection characteristics address the prediction of the needed internal commands for zero following error. Disturbance rejection control reacts to unknown disturbances and modeling errors. A combination of both feedforward control and disturbance rejection control provides the best overall performance. After errors have been filtered out by PID controller, signals corresponding to the designated target will be fed into the motor drivers. These two motor drivers have the exact same two functions, amplification and calculation of the cycle rate. In order for motors to move, the voltage fed from the PID to the motors must be increased to meet their operating voltage. Cycle rate determines how long motors remain at their positions. Motors will position themselves back to their center position after a firing command has been received and executed. That is, when the user interface send a firing command to laser pointer driver, it also stops updating the coordinates of designated targets to Arduino (No voltage will be applied to motor drivers, therefore, motors orientate themselves back to center points.) The compensator block diagram is shown in Figure 11. Coordination of designated targets ∑ PID Controller 1/dt Position Feedback Servo Drivers
Feedback Interface C’(t)
C(t) - r(t) + e(t)
r(t) = Reference Input e(t) = Calculated Error c(t) = Position Command c’(t) = Rate Command Figure : Compensator Block Diagram Rate Command =  (4)
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