Alimak develops and manufactures vertical transport solutions for both the construction andthe industrial sector. The majority of the elevators that the company is producing are climbingup- and downwards along a pinion rack. The lift cage travels between different landings, andthe cage door should for safety reasons not be possible to open while the elevator is operating.To solve this problem Alimak has developed a door interlock, but the shape of the interlockhas resulted in a problem where there is occurring an undesirable torque in some of thecomponents of the mechanism.The purpose of this thesis was to present one or more concepts on how the door interlockcould be reconstructed. The main goal was that the produced concepts would be shaped insuch way that the torque either would be reduced or eliminated. Besides the main goal therewere two secondary goals, the generated concepts should be lighter than, and use fewercomponents than, the existing interlock.By using the software Creo three concepts were generated. They were compared with eachother by using a decision matrix, and the one with the best potential to fulfill the goalstogether with the highest results from the decision matrix were picked out for furtherprocessing. After processing a final concept were obtained. The concept were not exposed tothe undesired torque, hade a weight of approximately 3,7 kg less than the existing interlockingmechanism and had less components.The project has not treated any economical or manufacturing factors which results in thatthere still is a lot of work to be done if Alimak chooses to implement the interlock on their devices.