Kolibri HIGHSPEED - High Speed Resolution Sensor

Kolibri Highspeed is a 3D sensor based on fringe projection technique, which allows the measurement of industrial products within the production line process. In the continuous measurement process a measurement velocity of 8.9 megapixel per second with a measuring point density of 20 μm can be reached. The certainty on the surface to be tested reaches about 5 μm. his precision was achieved through the application of a newly developed algorithm, exploiting the geometrical properties and the epipolar geometry of measuring objects, as well as a parallelization on the processor level.

The measurement of wet soldering paste is used in the quality control of the production of conductor boards. Together with a medium-sized business for test engineering in the electronics industry, a sensor based on fringe projection technique was developed at the Fraunhofer Institute of Applied Optics and Precision Engineering. It allows the measurement of conductor boards within the production line process. The measurement of the height and volume of the soldering paste according to the substrate is realized by the sensor. The sensor consists of a fringe projector and two high resolution cameras (Fig. 1) and was integrated into the inspection system for the conductor board. It is arranged approximately perpendicular over the horizontally aligned conductor boards. For realization of different measuring positions, it is moved by a mechanical moving system on two horizontal axes. One measuring position covers a 50 mm × 40 mm area of the conductor board by projection and observation. The sensor is moved by the guide system in approximately 140 ms to the next position, where a new section of the conductor board can be analyzed.

Depending on the size of the conductor board, between eight and 20 measuring positions can be realized. During movement, the sensor is exposed to very high accelerations, which places special demands on the mechanical resistance. The mechanical solidity of the sensor is attained by using a construction consisting of carbon, on which the sensor components were bolt and glued.

The surface of a conductor board to be analyzed is very inhomogeneous. The soldering paste, which is only applied to metallic surfaces, reflects the projecting light mostly diffusely, which is pre-condition for a specific sensor measurement accuracy. By contrast, the conductor board substrate has mostly both reflecting and translucent surfaces. This leads to systematic and random measurement errors. These errors are eliminated by choosing an angle of incidence of the projecting light such that the occurring reflection will no longer be projected on the camera images. The systematic error, which appears because of the penetration of the projecting light into the conductor board surface, is compensated by correction values which are determined experimentally. Figure 2 shows a conductor board and the measurement result. In contrast to previously developed systems, strict reduction of the picture recording time and accelerated computing had to be reached in order to achieve the requested testing velocity. This was realized by implementation of a series of new algorithms. The phase determination algorithm was expanded for any phase steps. The eight- and the six-phase algorithm, respectively, are used in the system.

By using epipolar geometry, the number of images per sequence was set to the half. The unwrapping of the phase values, which was previously realized by the Gray code, is now carried out by a special new algorithm with utilization of the geometrical features of the measuring objects (low height expansion of the measurement volume), thereby attaining a further reduction of the image sequence length. Projection and image recording by the high resolution cameras with 5 megapixels are done at a 15 Hz image frame rate. The local measurement resolution is 20 μm (average pixel distance in object space). The analysis of the extreme amounts of data required before the level-corrected height mapping of the soldering paste in the requested velocity is achieved, is effected by parallelization of 16 computing and analysis processes.

Using the developed sensor, the measurement of the soldering paste with an inspection velocity up to 35 cm/s was realized. This equals a measurement velocity of 8.9 megapixels/s. The cycle time for one measuring position is 0.563 s. The measuring uncertainty of the system is < 8 μm.

Measurement principle

• Contactless optical 3D metrology
• Simultaneous fringe projection and image acquisition based on stereo vision
• Time-optimised computation of phase values and 3D coordinates using known system geometry parameters

System Parameters

• Measurement point pitch: 20 μm
• 2 cameras: 5 megapixels each
• Single measurement field: 40 mm x 50 mm
• Measurement uncertainty: 5 μm – 10 μm

Permanent measurement cycle

• Duty cycle: 0.56 s
• Measurement velocity: 35 cm²/s
• 8,9 megapixels/s

• Highly precise inline inspection of industrial products
• Permanent measurement cycle of large objects in short dutyt
• Preparation of measurement with respect to the specifications for effective evaluation and processing
• Implementation of sensors into automated inspection systems
• Possibility of remote diagnostic and automated recalibration