Right Click Options at Basic Path Points

View on point changes the current view to look at this point

All except the first also imply some change of scale, bringing you to a "natural" distance from the belt.

A minor digression: Using Cut Sections in conjunction with belt fitting.

It can be useful to use PRIMER 's Cut Section capability combined with View on point when trying to get a good view for fitting a belt to tight geometry. From version 18 onwards the cut section panel can be undocked to become "floating", making it possible to use both it and belt fitting concurrently, with both sets of controls accessible and active.

One problem with using both tools concurrently is that the mouse can only be active for one thing at once: either manipulating the belt or dragging the cut section. The "ownership" of the mouse can be switched between the operations in two ways:

Using the main "tabs" buttons. Normally the "tabs" area selects which panel is at the top of the docked lower right hand side of the user interface, but when a panel is floating, which will be the case of an undocked cut-section panel, the next panel - in this case seatbelt fitting - is visible at the top of the docked area. Clicking on the relevant tab with make that panel the "owner of the mouse".

Using the "mouse control" buttons at the top of the respective windows Another way of controlling "ownership" mouse is via the and buttons at the top left of candidate panels, as shown here. If the symbol is then it is the current owner, here the cut section panel; if the symbol is then it could potentially own the mouse, but does not do so at present.

Reset... resets the selected attributes of this point to their status when the path editor was first started

NOTE!! "Reset" is not the same as "unset" below. Reset goes back to pre-edited state , Unset unsets totally.

Unset... totally unsets or resets to default state the selected projection, path curvature, twist and skew

NOTE!! "Unset" is not the same as "reset" above. Reset goes back to pre-edited state , Unset unsets totally.

Tweak path... allows fine adjust of path orientation and shape

There is further explanation of each of these below.

Tweak path: Reverse radial. Useful when you are using the "path curvature" method to define the outwards direction vector and you need the projection of the path to be on the other side of the basic path point.

Tweak path: Reverse in-plane. Useful if the path has got twisted and you want to correct this.

Note : If this happens you may find that when you fix point N you find the problem has moved on to point N+1, with the result that you end up working your way down the belt fixing a succession of points. This can result in the belt definition becoming quite complex (internally) making it difficult to edit, and it is often the case the the best approach is to unset the twist at all points and to start again.

The reason for this is that the belt fitter tries to keep twist consistent between adjacent points, so when two adjacent points have very different natural twist - more than 90 degrees in effect - it is forced to choose between [allow belt to twist more than 90 degrees] and [swap the sign at this point to give less twist]. It doesn't always get it right, and particular if you go back and move a point then a decision which was right previously may now be wrong.

This process works from path point 1 working forwards, so if the belt gets sufficiently muddled due to extensive editing then if it is usually best to unset twist at all points and start again from end #1.

Tweak path: Curl angle. "Curls" the belt so that it is no longer flat, giving it some guidance when passing through curved structure.

Here is a situation where the belt is "edge on" to some structure, and during fitting it might decide to turn downwards instead of upwards, giving the wrong shape.

Here the belt path has been "curled" by 60 degrees, giving it an initial shape which will make it much more likely to fit correctly in the curved child seat wing.

A curl angle is applied using the following rules:

• A +ve curl direction moves both edges of the belt "outwards", that is in the +ve radial direction. Using a -ve angle will curl it "inwards".
• The curl angle is defined in degrees, and sets the amount by which each half of the belt, either side of the centreline, will move outwards in total.
• Values can be in the range 0 to +/-180 degrees. However an angle >90 will not result in the belt "curling in on itself", rather the sides will become parallel and progressively more of the belt will curl round.
• Curl is applied at a point and its effect tapers linearly to the curl angle at adjacent points.

Another side-effect of applying a curl angle to a belt is that it supersedes the overall "curve angle" of the belt at that point, effectively making the belt path less stiff in transverse bending at this point.

Properties: adds detail to the belt path

This capability is identical to the properties popup in the basic path editor, it allows you to set path point attributes by clicking on the path point itself rather than by having to identify its point number and then navigating to the relevant editor row. This is described fully in Adding detail to the basic path above, so only a summary is given here.

Element length: varying the local element length from point N to point N+1

Here is an example of meshing a belt explicitly through a buckle. No slipring is defined here, instead a 2d mesh of shells will be continuous through the slot and form-finding will pull it tight. It is clear from the left hand image that the belt element length (here 7mm) is much too coarse to give a good fit around such detailed geometry, and moreover during analysis elements this coarse will "ratchet" their way through the buckle, like pulling a bicycle chain round a sharp corner.

Original situation with a constant 7mm element length along the entire belt mesh.

Revised geometry using a "local" 1mm element length through the buckle.

Here are the results of fitting the two meshes above.

Coarse mesh works - sort of - but it is easy to see that it would be unsatisfactory

This looks massively better and will allow the belt to pass more smoothly through the buckle.

Local Friction: varying the local belt fitter contact friction from point N to point N+1

This example demonstrates problems that can occur when the friction at a buckle, or similar geometry, is too low. In real life the belt material would scrunch up in the corner, but the belt fitter cannot do that because it has to try to maintain a reasonable initial element shape. As a consequence the "irresistible force" of the belt tightening meets the "immovable object" of the belt elements' determination to keep a reasonable shape, and things can go wrong.

Here the incoming path (red) and the outgoing (green) are not symmetrically aligned with the buckle, resulting in a tendency to pull to the left as drawn here when form-finding.

During fitting the belt (correctly) gets pulled to the left causing bunching up in that corner, and sometimes the contact at the edge of the belt will will "punch through" into the structure.

Increasing the friction coefficient from its default of 0.2 in this belt to 1.0 in the region where it passes through the buckle solves the problem

Understanding the friction model used in belt fitting.

The belt fitter does not use a FE model of the belt, rather it is geometrical; the form-finding operation used to pull the belt onto the structure is similarly geometrical - no force is involved.

Conventional coulomb friction resists sideways shear force by applying a resistive force based on some factor times the normal force, but if no force is involved in the calculation is this not possible. So the friction model used in the belt fitter is a compromise that is a simple factor on the tendency to move sideways, ranging from

For most typical belts a value of around 0.2 - 0.3 gives a reasonable approximation to the resistance of a belt being dragged across clothing and structure, however it can be useful to increase the value to 1.0 locally to make it "stick like glue" in situations such as this.

Remember that friction only applies when the belt is in contact with something, material "in free air" will not be affected.

Same belt refitted with a local friction coefficient of 1.0 in the buckle region

Sticky points serve as an additional option for centring path points in slots. The central belt path points can now ‘stick’ or adhere when they come into contact with the structure. This feature allows the belt’s outer edges to fit properly while the belt’s central path remains close to the initial contact point.

When the friction is set to 1.0, the entire belt would adhere to the slipring, leading to unwanted distortions and preventing it from twisting correctly. Sticky points, on the other hand, only adhere the centre row of belt points, acting more like a pin joint. This allows the outer sections of the belt to fit properly, making it more suitable for fitting a belt in a fully meshed slipring slot.

The ‘#Sticky pts’ value represents the number of points along the centre of the belt, between the current and next path point, that will adhere to the structure. In the image below, 6 sticky points were inserted between the two path points around the slipring. 

Belt stiffness: Add additional belt stiffness using beams from point N to point N+1.

This option permits increasing the belt stiffness automatically by creating a number of transverse beam elements between point N to N+1. The user needs to provide the part id to be used for all the beam elements. Users can give the part id directly in the popup text box shown to the right.

Or click on Select..., which will open another menu shown on the right where Pick, Select, etc. operations can be used for selecting the part.

Once generate is pressed in 3.Mesh-> tab, PRIMER will generate the number of beam elements according to the belt mesh using the part id given.

Delete point: deletes the selected base path point.

There is no sub-menu for this, the point is simply deleted. This is the same as changing the editor mode to "delete" and deleting the point there.