Metrology Fixtures: Advantages & Disadvantages

Fixed Position Measurement Fixtures versus Rotational Position Measurement Fixtures

In this article, I aim to detail some of the advantages and disadvantages associated with two types of metrology fixtures.

When you are tasked with measuring features of a product from different angles you have the following options:

Fixed Position and Rotational Position, Measurement Fixtures.

The first option is through the use of multiple Fixed Position Fixtures that capture the correct orientation of the product as required. The alternative is to have one fixture that secures the product while rotating to various angles, thus, allowing for the features be measured without the need to remove and reposition the part.

Whether you choose the Fixed Position or the Rotational Position Fixtures, either can be designed and manufactured to accommodate single or multiple stations. The number of stations will largely depend on the quantity of parts that you wish to measure and the available size of your Co-ordinate Measuring Machine or Vision Measuring Machine table.

Let us now consider the advantages and disadvantages for both fixture types:

Fixed Position Measurement Fixtures

  • Part to part positions can be closer; therefore, this yields maximum number of parts for a given area.
  • Overall fixture heights (“Z” Dimension) are lower to the machine table, this is a benefit where the measuring machines Z-axis travel is a constraint.
  • Loading, unloading and reloading of the same parts, is time consuming and can lead to damage or distortion of the parts, which will ultimately lead to dimensional failures.
  • Requires a separate fixture per orientation.

Rotational Position Measurement Fixtures

  • Lower capital expenditure required with this type of fixture compared to Fixed Position Fixtures, which require multiples to achieve the same result.
  • Less time and costs involved in qualifying this type of fixture.
  • Fixture setup times greatly reduced over having multiple Fixed Position Fixtures.
  • Routine run times are generally faster.
  • Load and unload the part only once, less human intervention.
  • Part rotation about 2 Axis is possible, allowing for the parts to be viewed and measured from all angles.
  • Weight ratio of the rotational type as compared to fixed type is greater.
  • The Y Axis row spacing is larger than that of the fixed type, in order to accommodate the rotation of the rows.

Consideration should be given to providing a loading / unloading station when dealing with sensitive components. With this additional piece of bespoke equipment, components are transferred from a moulding machine to the loading station without been handled.

So why not benefit from a Rotational Position Fixture on your next project when the components specification requires that measurement be taken from different directions.