Balancing arm for a Robotic Waiter

Sammanfattning: This project focuses on balancing a drinking glass, to be able to transport it without the contents being spilled. It is designed with the aim of replacing a waiter in a restaurant or bar environment, but the technology itself could well be applied on mobile cup holders in cars or boats for instance. The core of the project is to study how and if it is possible to create a platform capable of balancing a drinking glass when exposed to different acceleration forces. This report describes one way of constructing this cup holder, with explanations of how the hardware has been designed and put together as well as how the software was written to make the components work together. The objective was to tilt the platform so that the acceleration resultant always was aligned with the z-axis of the sensor. The balancing part was divided in two separate systems, each controlling one rotation around two perpendicular axes. The rotation was controlled by two DCmotors, which counter forces that occur when the prototype is tilted and accelerated in different directions. To measure these movements, an IMU sensor containing both an accelerometer and a gyroscope was used. This sensor was placed in the center of rotation to increase sensor accuracy. To relate the input signal from the sensor to the output signal to the motors, a PIDcontroller was used. It was studied whether mathematical modelling or experimental testing provided the best method to determine the parameter values for this PID-controller. To test the performance, data about acceleration and relative angle to the acceleration resultant was gathered. This showed how high accelerations the system could handle, to evaluate if the system could be used in a restaurant or a bar environment. It also showed how much the platform was tilting in relation to the acceleration resultant, which determines if the liquid would stay in the glass. Additionally, a survey was created to gather opinions regarding robots in a restaurant or bar environment. The implementation is deemed possible and the survey showed that there is a great interest for this product. A clear majority answered that they would be attracted to a restaurant or a bar with robotic waiters. The study of three different ways to apply the derivative part of the PIDcontroller concludes that the use of the gyroscope was the best for this application, despite its inability to react on acceleration from linear motion. Experimental testing proved most time efficient to determine the parameter values for the PID-controller, but the non-linearized mathematical model of the system that is presented could well serve as a foundation to further improve this controller.