Miniaturized light projectors, called pico projectors among experts, are used as optical 3D sensors for industrial metrology. They inspect the 3D
structure of cutting-tools, e.g., or measure the interior decor surfaces of cars.

Today it is possible to watch movies on cell phones. Texas Instruments miniaturized the multimedia projectors in such a way that Samsung engineers were able to integrate them in mobile phones. The first cell phones with integrated pico projectors are already available for purchase. With this technology, customers can use the mobile devices for far more than just watching films. They can play self-made video sequences or present power point presentations using any wall or surface they want to. This shows how the communication technology pushes the miniaturization of systems to improve the performance parameters. This has become a demand also for optical 3D sensors in measurement and inspection systems. Only if small optical 3D sensors are made available, which provide easy handling at reliable accuracy and attractive pricing, optical 3D metrology will be able to acquire the position in technical applications that it has long been attributed to.
Since more than 10 years, measurement engineers successfully employ digital projection systems based on the DLP technology (Digital Light Processing) from Texas Instruments in optical 3D sensor applications. Thus it was a natural step for the company to integrate the miniaturized pico DLP projectors, so far marketed in connection with mobile phones, also in mea-surement and inspection systems.

Advantages of Pico Projectors
DLP projectors have quite a number of advantages compared to other technologies in measurement applications. Compared to the LCD based systems, light has not to be polarized which results in superior efficiency. The fill factor, the small distances between the micro mirrors at currently around 10x10 µm results in a homogenous image. Furthermore the images show a high linearity due to the digital pulse width modulation of the light. The high switching speed allows the 3D video acquisition in real time. All these advantages, originally developed for multi-media beamer or print system applications, are now applied to the new DLP based pico projectors as well. These projectors have exterior dimensions of approx. 70x50x15mm and are weighing about 50g. They can be connected to a PC via analog or digital interfaces, and can be operated just like conventional multi media projectors.
To make use of the projector as an optical 3D sensor it has to be connected to and synchronized with one or more acquisition cameras. For this task Texas Instruments developed a special circuit board, offered under the name Beagle Board, based on TI's OMAP3530.
This platform had originally been designed for small and energy saving systems such as smart phones and hand-held consoles. It comprises an ARM Cortex A8, a signal- as well as OpenGL-compatible 2D/3D graphics processor, and runs on Linux. Peripheral devices can be connected via USB. The HDMI connection between Beagle board und pico projector can transmit image data as well as control signals, allowing the setting of the projector's brightness and gamma parameters directly from the board. However, the required connection with the Beagle Board leads to a high entry barrier for digital light projection applications with the pico projector.

Getting Over the Barrier with System Solution
Aiming at quick and efficient usability of the DLP pico projector's full potential, GFMesstechnik has developed the Pico DevKit, a turn-key solution for the easy adoption of optical 3D sensor technology as well as other applications of digital light projection. The scope of delivery for the Pico DevKit comprises the DLP pico projector, the Beagle board and necessary wiring, and can simply be connected to a standard PC via USB. The projector has been optimized for metrology applications by an especially modified firmware. The Pico DevKit provides programming interfaces for LabView as well as for Visual Studio and synchronizes external devices like cameras with additional trigger signals. The developer of digital optical light projection systems gets with the Pico DevKit a versatile tool, enabling him to implement applications without major additional development effort.

Hand-held Measuring Devices
The picture above shows as one implementation example the hand guided optical 3D in-vivo skin measurement system PrimosPico for the acquisition and evaluation of human skin structure, wrinkles, wounds and scars, being used in cosmetic as well as dermatological studies world wide. Other applications realized with DLP pico projection in optical metrology, are 3D sensors for the integration in measuring machines, devices for the 3D measurement of body parts and faces, as well as hand-held sensors for industrial metrology, e.g. for the mea-surement of interior decor surfaces of cars, or for measurements on cutting tools.