Proxim RangeLAN2 7920 Instrukcja Użytkownika Pobierz pdf (Strona 44)

• sss.s >> Velocity

• hhh.h >> Heading

• m,t,dd.d,rrrr,aa >> Receiver, Signal and Satellite Status

• CCC >> Checksum

This data string is comma delineated and can therefore be separated into its separate

components using the string tokenizer function in Dynamic C. The needed data from the

GPS card is just the heading portion of the data string that is highlighted in bold above.

Additional data from the GPS card includes in order, a leading time stamp, height,

velocity, heading, receiver status and a final checksum. The data string is 96 bytes long

and this length is used in the software as a method to determine if a valid string has been

received.

3. Navigation

The navigation costate like the GPS/Compass costate waits for an input from the

user before coming out of the sleep state. Upon receipt of a Desired Heading or Location

string (DHeadLoc) from the JAVA application the navigation costate tokenizes the

DHeadLoc string and determines its size and the value of its components. The navigation

costate then calls the navread function which depending on the size of the DHeadLoc

string will either conduct a GPS location calculation or a heading calculation determining

a Course To Steer (CTS) and a difference between the CTS and the current heading. The

difference value is then returned to the navigation costate which depending upon the

values of the difference will turn towards the desired heading. When the desired location

is reached, the robot will automatically stop and signal that it has completed the

navigation costate.

a. Feedback Error Control

The principle of control for a robotic system is straightforward in that we

will employ mechanisms to minimize some error function, figure 17. If we assume that

our goal is to turn the robot to a desired angle

from a current angle

, then the error E

would be given by:

(4)

θθ

=−

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Proxim RangeLAN2 7920 Instrukcja Użytkownika Strona 44