New Dummy: Replacing One Dummy With Another

Example problem: new 95th %ile dummy replaces old 50th %ile

Here a belted 50th percentile dummy has been replaced (via Include, Replace Include ) by a larger 95th percentile version.

It can be seen that the existing seatbelt (black) now penetrates the chest and the pelvis, so it clearly needs to be refitted.

However if you go directly to the seatbelt fitter and attempt a Fit or an Auto-refit you will get a message something like this:

This has happened because the part sets used to define the belt-to-dummy contact do not exist in the new dummy, and the nodes used to define the path points are also either missing or in totally different locations.

It will be necessary to redefine the parts on the dummy contacted by the belt, and also to move the belt path points back out onto the dummy surface.

Solution part 1: redefine the "dummy" surface

When you first select New Dummy you will see that the " Dummy parts for contacting belt " section will be empty, and the picture of the dummy will be red with the message " No dummy els defined ".

( Note : If your new dummy is sufficiently similar to the old, for example if the relevant part set labels are the same in both, this section may be green and you will not need to redefine the dummy. However this example assumes the worst case with no useful information being carried over. )

Use Add... to select parts or elements of the dummy to be contacted by the belt.

Points to consider when selecting parts for belt-to-dummy contact are:

• You will need to project the belt path onto the surface of the dummy, so it is best to use shells rather than solids. Most dummies are "skinned" with shells to form a continuous outer surface, and it is recommended that the parts of these shells are used. If solid parts are used there is a danger that the "nearest node" to an existing path path may be inside the dummy, especially if - as in this example - the new dummy is larger than the old one and the existing path is partially buried inside it.
  
  
• It is tempting to throw lots of parts into the "dummy" definition, or indeed just to select the whole dummy from the selection menu. However for efficiency and speed of belt form-finding it is best to use the minimum number of parts required to do the job. Typically all you need is a part defining the shoulders and torso, and another part defining the pelvis.

Once you have defined some parts the icon of the dummy should go green:

You can check that you have selected a sensible range of elements using Sketch , and you can change the selection at any time by using Add... and Remove... as required. To start again from scratch use Delete , which will delete all elements in the the "dummy" definition.

Solution part 2: correct the belt path

Initially it is likely that the Belt Path section of this panel will look like this:

• The end nodes of the path, located on the vehicle structure, will probably have survived the replacement of the dummy unchanged. In this example there are nodes at the Retractor ( R ), B-Post slipring ( B ), pelvis slipring ( S ) and end anchorage point ( E ).
  
  
• However all the intermediate points on the belt path have "lost" their associated nodes, since these are either missing or too far away on the new dummy, and have thus reverted to plain path points ( P ) defined only by their coordinates.

In this context having no path points on dummy nodes is considered to be an error. Technically you could still refit the belt in this situation, and you will be allowed to Update dummy & path with errors , but this is not recommended since further manual intervention will be required to fit the belt.

At present most of the intermediate belt points ( P ) are inside the dummy, because the new dummy is larger, and they need to be moved out onto its surface if the belt is to fit over rather than inside the dummy. In addition it is best of the majority of the belt points in the dummy region are defined by nodes on the dummy, rather than just plain points, since that way if the dummy is repositioned its nodes will move, and the path points will move with them.

( Belt fitting after repositioning the dummy will still work if only some path points are defined by nodes. Those in between, defined only by coordinates, will have these coordinates interpolated from the motion of their their neighbouring points that are at nodes. However this process is more likely to be satisfactory if the majority of path points are at nodes. )

Your goal is to achieve a result that looks like the picture on the right in which all path points have found nodes on the "dummy" structure as defined in part 1 above.

Each time you change the definition of the "dummy" the path is scanned automatically to try to find nodes near to each path point, and this panel will be updated accordingly. There are tolerances built into this process and you can perform these checks manually with different tolerances as follows:

The default tolerance for Check path coords is 5mm, and for Find new Nodes is 50mm. These defaults may be changed by the following preferences:

The status of what has been found is reported for nodes, and the ideal is that all points in the path find a node on the "dummy" or the vehicle "structure" and have a green tick against them.

Here is an artifical example in which only dummy structure in the torso region has had parts defined, and the pelvis region has been omitted.

There are 11 path points in total, but only 8 have found nodes: 4 on the dummy and 4 on the vehicle structure. This is marked as "OK" but with the qualification that 3 path points are not on nodes, and these can be seen marked as ( P ) on the path diagram.

In this example this is plainly an error that is easily corrected by adding more "dummy" definition parts, but in other cases it may be acceptable to have isolated path points that are not located at nodes. If you have this situation you will have to examine your structure to determine whether or not the result is acceptable.

If you have trouble identifying where the path points are on the dummy you can use the different views (+XY, etc) to get a better picture.

Also for the duration of the New Dummy process the plot in the graphics window will show the current belt path, labelled with point numbers and node status at each point.

Solution part 3: Update and refit

Once you have defined the dummy and sorted out the belt points you will be able to Update Dummy and Belt Path to save the corrected definition, after which an Auto-refit or possibly a manual Fit will refit the belt.

Here is the example above after an Auto-refit , showing that the belt path has been successfully projected out to the surface of the dummy, fitting round the larger 95th %ile chest.

Possible problems, and how to fix them.

First appearances suggest that the process above has worked first time.

However closer inspection of the end result of this example reveals that the belt is penetrating the upper right hand leg as shown by the close-up here, and this needs to be fixed.

Going into the path editor ( Fit , Define Path ) reveals that the twist of the fitting path in this upper leg region is wrong, resulting in the initial path penetrating the upper leg.

This means that this section of the belt starts off on the "wrong" (inside) surface of the leg and does not pull itself out again.

Using the path editor in Control Twist mode that point #6 is rotated up out of the leg. Once corrected another refit now positions the belt successfully around the dummy.

This is a particular case of the more general problem that moving a belt path from one dummy to another can pose problems that this New Dummy function cannot always solve.

It is a help, but not a panacea - please always check the end result! And be prepared to pay a visit to the belt path editor to adjust the belt path if necessary.