Requirements, preferences, and constraints

Requirements

• The robot should at least inspect or clean every window one time, regardless of the dirtiness of the window. In other words, windows that are not dirty should be inspected at least once. This is a very reasonable requirement, because people who hire a window washing company expect that they will do every window.
• The window cleaning robot is not allowed to leave stripes due to the dripping of water or incomplete horizontal movements.
• For window washing companies, speed in terms of surface area cleaned per unit of time is of major importance. The higher the speed with which the windows can be cleaned, the more profit that can be made. The goal is to reach a speed of 71 m^2 / hr, which is the mean of three popular commercially available window cleaning robots that are considered (see Appendix \ref{app: table robots appendix}). This seems an acceptable requirement for the model.
• The water consumption is another important aspect, since this has an impact on the speed of the cleaning process and also has a minor impact on the total cost of the cleaning job. All current window cleaning robots of the here considered size do not have a water supply or tank, but use detergent instead. The innovative part of the model is therefore that a water supply is included. This is similar to real window washers, because they also do not use detergent solely. The requirement for the water consumption is based on a bigger window cleaning robot (GEKKO Facade Robot \cite{gekko facade robot}) which has a water consumption of approximately 1 L / min. Because this bigger robot has a size of around 4 times the size of the considered cleaning robots, a requirement of 0.25 L / min seems suitable.
• Energy consumption is the last relevant aspect, since this has an impact on the total cost of the cleaning job. The requirement for the energy consumption is also determined by averaging over the considered window cleaning robots: 73.5 W (see Appendix \ref{app: table robots appendix}).

Preferences

• The window should be made as clean as possible.
• Speed in terms of surface area cleaned per unit should be as high as possible.
• Water consumption should be as low as possible, since it is better for the environment than conventional detergents.
• Energy consumption should be as low as possible.

Constraints

• The robot should be able to clean windows with a dimensions between 0.5 x 0.5 m and 4.0 x 4.0 m. In this range the most common windows will be covered.