Overview The top loader is a mobile crane that is used to move containers in a yard. It is commonly used for moving containers on and off trucks in a given yard block. Whereas a [GantryCrane](RTG.html)is better equipped to handle digging and restacking, a top loader is more mobile and can move more easily between blocks that are not aligned end-to-end. Properties  Determine Moves - This dropdown box determines how the top loader's movement is calculated. Options include: - "Based on Time Per Move" - The top loader's movements are separated into two categories: unstacking and stacking. Each of these categories is assigned a different expression for calculating the move time. When the top loader moves, it calculates the movement time based on the appropriate category and then splits its movements across the calculated time. - "Based on Time Per Move plus Speed to Bay" - This is similar to the previous option except that the travel speed is separated out. In this case, the travel is done based on a speed value while the remaining movement is done based on the unstacking and stacking expressions. - "Based on Top Loader Speeds" - All of the top loader's movements are handled separately and are based upon speed values assigned by the user and actual distances represented in the model. Stacking Travel Time - This value is the time it takes to move a container from a truck and place it in the yard block. Unstacking Travel Time- This value is the time it takes to remove a container from the yard block and place it on a truck. This value is only associated with the target container. If digging is required, that time is handled in the "Digging" section below. Move Per Hour Conversion Tool- This widget is a tool for converting moves per hour into minutes per move. Most modelers think about yard equipment in terms of moves per hour, but the model requires values in terms of minutes per move. Using this tool, you can easily integrate the correct values into the expressions above. Speeds - These values are the various speeds of the top loader. Each movement is handled separately. If the acceleration or deceleration are 0, then the top loader will instantly move at top speed or stop completely without any acceleration or deceleration time. Time and length units are determined by the [Model Units window](Model_Units.html). Digging- If the top loader has to dig for a container (because other containers are stacked on top of the target container), these values are used to calculate how much time it takes to reach the target container. If the "Search for least number of containers to displace" box is checked, the Top Loader can start digging either from the front or back of the yard block depending on which will be the fastest. There are two options for calculating dig time. Each option uses the "Dig Time" expression in a different way: - "Based on Time Per Displaced Container (no real digging)" - The dig time is evaluated for every container that has to be moved out of the way, including the entire stack(s) in front of the container and any containers on top. The top loader doesn't actually move any containers. Instead, it waits the calculated amount of time and then FlexTerm swaps the target container to the top of the stack, and the top loader moves it from the top. - "Based on Time Per Unstacked Container (no real digging)" - The dig time refers to an average time to dig through containers and is evaluated only once for the entire digging operation. The top loader waits the calculated amount of time and then FlexTerm swaps the target container to the top of the stack, and the top loader moves it from the top. Note: The top loader does not have an option for real digging because it is not optimized for digging and should rarely be used in a situation requiring digging. Truck Travel Time- During an unstack operation, the top loader picks up a container, backs out of the block, waits for a truck to move in front of it, and then loads the container on to the truck. Similarly during a stack operation, the top loader removes the container from a truck, waits for the truck to move out of the way, and then carries the container to the block. Although the Top Loader's movement time is calculated for this entire batch of tasks, part of the time is actually used by the truck. In order for the top loader to accommodate the time required for the truck to move, the "Truck Travel Time" value is used to specify how long the truck's movement will take. After the stacking/unstacking time is calculated, this value is subtracted from that time and the resulting time is the movement time of the top loader. Even though the top loader assumes the truck is going to take this designated amount of time for its travel, that may not be the case. The truck may be slower or faster and, therefore, cause the overall operation time to increase or decrease. If the "Force defined truck travel time in stack and unstack times" checkbox is checked, the truck will be forced to travel in exactly the amount of time given by the "Truck Travel Time."