The method chosen is a sensor guided feedback program to control the three step motors which operate the sand excavator.  This method is quite similar to concept one in that there is a basic program that controls the operation of the sand excavator, however it is dissimilar in that there are sensors to provide a feedback to the system in order to accurately adapt to changes within the experiment.   The pro’s of the feedback control system is that it can compensate for disturbances and changes in the conditions of the experiment.  The addition of feedback sensors allows for greater control over the system by relaying information back to the microcontroller in order to reduce the possibility of error if there were to be changes in the position of the pressure plates.  The sensors can also allow us to prevent damaging the target sand samples. 

             There are three different sensors that have been considered for use which are whiskers, ultrasonic and light feedback sensors.  The whisker feedback sensors are physical whiskers that when come into contact with a physical obstacle will displace and therefore sends a signal to the microcontroller which can thus be used to readjust the pathway for the sand excavator.    These would be useful for detecting how close the apparatus is to the sides of the pressure plates and the sand box.  The issue of using whisker sensors is that they lack accuracy at times and since they require physical contact, it is an intrusive method of sensing which could disturb the integrity of the experimental data.   

             The ultrasonic feedback sensors produce ultrasonic sound waves that when “bounce” off obstacle walls will provide a measurable frequency which can determine a specific location of the obstacle without having direct contact.  This method is a less intrusive method which in turn does not cause a loss of integrity in the experimental data.  Although being less intrusive, the accuracy of this system can be less than physical sensors since there is no perfectly flat plane that the waves can bounce off of and therefore we get a wide range of frequencies that the system would have to compensate for.  

             The light feedback sensor emits infrared laser which bounces off surfaces with different frequencies dependent on the color of the surface.  This is due to the fact that different colored surfaces absorb different wavelengths of light which will change the frequency of the light that returns to the sensor.  As previously mentioned, this method is a less intrusive method which in turn does not cause a loss of integrity in the experimental data but can also provide a visual aspect which the programmer can anticipate where the system will need to adjust for changes within the experiment.  Since this is a nonintrusive method, there is a degree of inaccuracy since only a range of frequency values is provided by the light sensor and if the two surfaces are too similar, is can be difficult to ascertain the differences between the two surfaces.

 

 

 

 

 

 

 

 

 

 

 

 

Design Concept

High Speed Sand Target Impact Testing

Senior Design 2009-2010 Group #3

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CAD Drawing courtesy of Group 4 2008-2009.