Traverse systems driven by stepper motors need to get a unique starting position before controlled absolute positioning is possible. This can be realized by mechanical or magnetic switches.

'Trinamic traverse' objects use an optical method. The usable position range of the traverse is divided into a red zone (negative position values) and a blue zone (positive position values). A Tinkerforge color sensor (connected to the payload of the traverse) gives a color signal called the 'position function'. This is the ratio of the blue value B and the red value R. This ratio is small in the red zone and large in the blue zone. At the transition between the red and the blue zone the position function rises steeply. The origin of the traverse is defined as the position where the position function has a certain value (called threshold) between the low values in the red zone and the high values in the blue zone.

When the traverse system is switch on after a period without power the absolute position of the payload is unknown. In this situation a search routine must be executed before the traverse can be used. The search routine finds the origin of the traverse and sets the position to zero. At the start of the search the position function is used to decide in which zone the payload is located. If the payload is in the red zone the traverse moves upwards in safe steps until the blue zone is reached. Then the motion is reversed and the step size decreased to move back to the red zone. In an iterative process the edge between the red and the blue zone is found. In a similar way the iterative search is done if the start position is in the blue zone.

The value of the position function is available in the list of optical functions using the term 'position function'. The call would be 'My traverse (position function)' if the name of the traverse object is 'My traverse'.