RPS Alignment

The Reference Point System (RPS) Alignment is a technique developed by Volkswagen and has now become the Automotive Industry Standard for inspection.

This is probably the most versatile alignment technique. It will primarily use geometric features and can be used to create an alignment very similar to a plane line point, or best fit on points. It can also be used with surface points and can be used like a free form fit. Uniquely it can also use a combination of geometric and Surface Points.

As with all methods, a decision needs to be made on which Geometric Elements will determine the alignment.

In this example we are using the Geometric Model. The CAD file for this part is Geometric Model.odx.

We will create the alignment using two circles and the plane that was created whilst probing Circle 1.

Circle 1

Plane 1 (along this face) Circle 2

The first step is to probe the required geometry.

You can see here that the probed circles and planes are ‘floating in space’ in relation to the part.

Circle 2

Plane 1

Circle 1

As the part is aligned, you will see the probed geometry marry to the part.

Move up the levels until Geometric Group 1 is Closed.

From the Alignments Sub-Menu icon , in the Element Toolbar:

Choose the RPS Alignment button .

The RPS Alignment dialogue box appears and prompts the user to define the items for the alignment.

The items used for alignment, are selected via the Pull Down Menu.

Once an item is chosen, other items can be added using the icon.

The plane is defaulted as Lock Position and you cannot choose which axis you want to lock - this comes from the plane orientation.

Circle 1 and Circle 2 are selected and will be aligned using the centres of these circles.

Nominal values for the X, Y and Z coordinates are displayed. If the coordinates are greyed out, they will not be used in the alignment.

You can use a ‘whole’ feature as the first feature in an RPS alignment.

While the centre of a feature allows you to only consider the position of a point, the ‘whole’ feature allows the use of the feature’s orientation.

Here we are using Plane 1 as our first feature.

Plane 1 is locked on the Y axis due to the orientation of its normal found whilst probing.

Circle 1 is used to lock the X axis.

This now means that the centre of Circle 1 has now been aligned to the nominal value for X, in this case -30.000.

It is however free to move along or rotate around the Y and Z axis.

As you can see below, Circle 1 can move backwards and forwards along the Y axis and up and down the Z axis. It cannot move along the X axis.

Y

Z

Circle 1

The movement is allowed, as the centre of Circle 1 is only aligned in the X axis.

It also needs locking in the Z axis. This will move the probed geometry to X and Z nominal values for the centre of Circle 1, X -30.000 and Z 55.000.

There is now only movement available in the Y axis.

We do not need to lock Circle 1 in the Y axis, as it is locked by Plane 1.

This is due to Plane 1 being locked in position.

The first feature has two choices that allow the locking of it. Lock Position and Lock Direction.

Lock Position fixes the orientation of the plane and the location.

Lock Direction fixes the orientation of the plane but the position is free to move along the axis. Two rotational axes are locked.

Y

Plane 1

Circle 1

Now we have the centre of Circle 1 locked in X and Z by aligning it to the CAD nominals. It is locked on Y due to the centre being on Plane 1.

At present only Circle 1 and Plane 1 are aligned. We now need to align Circle 2.

Circle 2 is already aligned in X and Y, we need only to align Z.

This is due to relationship between Circle 1 and Circle 2.

PowerINSPECT knows that Circle 2 is on Plane 1. It also knows the distance between the centre’s of Circle 1 and Circle 2 along the X axis.

All that is required to align the part to the CAD is the nominal for Z (75.000)

As you can see the part is now aligned

Circle 1

Plane 1

Circle 2

Now there is no freedom of movement for any of the 3 features used in the alignment.

The probed features now aligned, cannot move in any axes independent of the part.

PowerINSPECT has aligned the probed positions to the CAD nominals, satisfying X, Y and Z coordinates.

If you lock all axes on Circle 1 and Circle 2 centre’s the alignment will be successful, however it will be overconstrained.

An over constrained alignment cannot be created perfectly. Some best fitting will occur.

Overconstrained alignments are often used in the automotive and aerospace industries.

Examples of RPS Alignment Inspection drawings

Дата добавления: 2015-11-16