Traditional optical systems are made of an optical profile projector, which enlarges the view of the part and of the tool, and a diffusive screen on which the image can be viewed and directly measured: no cameras are used and no images can be stored and analyzed, of course.
This traditional approach imposes several problems to the user and makes all the process very slow because many steps are necessary to set up the machine:

1. a profile must be defined
2. a 1:25 scale contact paper drawing must be prepared
3. the contact paper drawing must be aligned inside the projector
4. the optical system magnification must be tuned to fit the drawing model

"Old style" profile projection optical system.

In addition to a slow process, many factors negatively effect the system measurement accuracy and efficiency:

• Low image resolution
• Low image brightness
• The system cannot be calibrated
• Maximum verifiable diameter is 250 mm
• Maximum verifiable profile width is 20 mm
• The lighting source is an halogen lamp: the lifetime is short, light output is low and the energy consumption is low
• Contact paper is subject to dilation caused by humidity and incandescent lamp heat
• Parallax error and optical distortion make the wheel edge position uncertain

In order to overcome all of these problems, a machine vision system, including a Telecentric Lens and a collimated LED light source have been developed by the joint efforts of Cafro and Opto Engineering.
The Green LED light projected by the collimated source crosses the place where the wheels are positioned and is collected by a telecentric lens. This system provide much higher optical efficiency and a much more stable light source output than incandescent, lamps previously used; also, the illumination evenness is almost perfect allowing a correct determination of the edges shape.
Moreover, the combination of a collimated source and a telecentric lens, yields an optical system with very high resolution, low distortion and field depth; all of these features make it possible a very accurate determination of the part edges and. The measurement is stable and independent from the wheel consumption, due to telecentricity and high field depth.

Optical layout of the device. A telecentric lens is facing a collimated source: only parallel "telecentric" rays are collected to enhance field depth and cancel parallax errors.

A Firewire digital camera, 1/2" VXGA is used to capture the image which is analyzed by means of Matrox Imaging Libraries combined with NI Labview development environment.

An operator using the device to tune the machining process and measure the diamond rinding wheel and the tool.

The machine vision system makes the machining process much more accurate and faster. The profile drawing can be edited by means of any CAD software and imported, stored and modified by the application in order to yield the reference model for the user.
By means of an optical linear encoder and precise translation mechanics the maximum width of the profile can be up to 120 mm, while the maximum diameter reaches 750 mm; in fact the software makes it possible to assemble different views of the part thus providing an overall view and dimensional evaluation of the object.
This is also made possible by the telecentric lens which eliminates any parallax error which would effect the measurement accuracy and a correct combination of different image portions.
In addition to these tecnical features, the system can be verified, calibrated and can be easily adapted to different machines or production lines.

The software interprets the image in terms of the the loaded profile model.