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Form deviation, decenter and tilt: detecting three relevant errors in one measuring run

2019-01-18 | Products | Reilly, Karin
Optical and tactile tracing possibilities
MarForm MFU 200 Aspheric 3D

To ensure precise quality inspection of optical lenses, Mahr offers the MarForm MFU 200 Aspheric 3D – a measurement system in which Mahr has cleverly combined tactile and optical measurement techniques. In addition to the measurement of surface geometries, the relations between the front and back side as well as the lens edge can be determined.

For the exact examination of the quality of an optical lens, it is often necessary to not only measure the surface geometries, but to also determine the relationship between the front and back of the lens as well as to the lens edge. In order to be able to realize these requirements in optical production, Mahr offers a measuring method for the fast and comprehensive measurement and evaluation of the form and position of optical surfaces.

Fully automatic measurement for error detection

Through the combination of tactile and optical measurement techniques, an optical axis of an aspheric surface, for example, detects the position of the mechanical axis of the lens edge and determines the tilt of the backside towards this axis. Mahr has united the various optical and tactile probe systems in the high-precision reference form measuring machine MarForm MFU 200 Aspheric 3D. With only one fully automatic measurement, the measuring system detects the three most common errors in optical production: form deviation, decenter and tilt*. Operation is quick and simple thanks to semi-automatic measuring without the input of drawing data, and the optional automatic teach-in function of the measuring locations.


Mask for simplified data entry 

 

Complete measurement in just one clamping

The optical surface is measured without contact using the IPS 15 optical sensor. The edge and the back of the optical element can be measured with a tactile probe. Both systems (optical and tactile) are combined in one probe arm unit on the probe system of the MarForm MFU 200 Aspheric 3D measuring system. A wide selection of stylus arms allows for further combinations of different styli in one stylus unit. This makes it possible to measure all sides of an optical element (e.g., an aspheric) in one clamping and using the automatic switching between the optical and tactile tracing elements.

This measuring method has the advantage that the polished optical surface does not undergo mechanical tracing, but is measured only optically and thus without contact. The slightly rough lens edge is detected quickly and accurately with the tactile probe.

     
                       a                                                           b                                                            c

Different tracing methods of the aspheric surface: optically with different angles (a and b) and tactile tracing of the edge

 

Reproducible measuring results independent of external influences

Depending on the design of the optical element, various features and relevant dimensions can be determined:

  • Single surface centration error of the edge geometry to the optical axis
  • Angle and angular position of the edge geometry to the optical axis
  • Tilt angle and angular position of the backside to the optical axis

The technology used by Mahr also detects non-systematic deviations which, for example, arise due to external influences or the movement of the machine itself. The measuring system is always aware of exactly where the probe element is located. In combination with a highly dynamic digital control, this also benefits the positioning accuracy of the system. Thus, an extremely high reproducibility can be achieved even under changing conditions.

         
Form deviation of the surface in the direction of the standard according to ISO 10110-5 and mapping of a centering error

        
Cylindricity / decentering of the collar and tilting of the base geometry to the aspherical axis (spindle)

*using a licensed asphericon GmbH patent

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