LAMI:The EPFL Vision Sphere

The LAMI
Laboratoire de Microinformatique
Microprocessor and Interface Lab

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The EPFL Vision Sphere

Nowadays, robotics designers need to embark vision sensors : vision is the richer sense for controlling a robot. We, the Biovision & Robotics Group, are interested not only in integrating a vision platform on the Koala (©K-TEAM), which already implies small size and power efficiency, but also in mimicking fast moves of the human eye. After studying the current state of the art, we have not found such a system.

The EPFL Vision Sphere was then conceived by an undergraduate student, Sébastien Menot, in a semester project ended in February 1997. The solution was chosen in order to lower the inertial mass. The principle is closed to your computer mouse : in a mouse, you have a ball supported by two encoder wheels, one support wheel and the mouse pad, in the EPFL Vision Sphere, you have a sphere supported by two motor wheels (Maxon motors, i.e. the two black sticks in the front view) and two ball bearings (the small white cylinders). Moreover, two semi-circular rails (see below) that cross beside the sphere give the exact orientation of the camera. Two incremental optical encoder (HP Encoders, the two big black cylinders in the front view).

View from Beside

The system obtains some mechanical performances close to the human eye (speed, aperture). Here are the characteristics :

Maximum size of the prototype : 170 mm x 170 mm
Sphere diameter : 60 mm,
Weight of the sphere with the camera : 90 g,
2 degrees of freedom (pan & tilt) with similar features :

Aperture+/- 45 ^o (solid angle of 90^o).
Measured Maximum Acceleration : 40.000 ^o/s²
Measured Maximum Speed : 600^o/s

Position resolution in pan and tilt : 0.25^o.

The precise control in position has been the subject of an other semester project in collaboration with the Institute of Automatic Control of the EPFL ended in June 1997. Using a robust pole positionning method (RST), a control algorithm has been implemented on a Motorola 68336 based board (EXT336 ©K-TEAM). The typical power consumption of the whole system is around 0.5 A under 12 V DC and the peak around 1.0 A. This system can be remote controlled in position via a serial link with speeds up to 38'400bits/s.

A picture shot from the Vision Sphere

Inside the sphere, we placed a low cost CCD camera from Marshal Electronics, Inc. (V-1210). The camera outputs a 640x480 NTSC composite image (interlaced). We have chosen the wider lens : 110^o(H) x 83^o (V). You can see on the right an example of a grabbed image, where you can note an important distortion. We have first used this platform in stand alone to design original image processing algorithm. We grab images on Sun Ultra 1 Creator station equipped with a SunVideo board and control the position of the camera with a serial link.

For the embedded processing on the Koala, an image processing board Shyriu II has been designed by Jean-Marc Kohler in another semester project ended in February 1998. The ancillary board (left on the image) does the video acquistion (Cirrus Logic PX4072) and preprocesses the image with a programable logical array (Flex 8000). This preprocessing can be reprogrammed from the main board. The main board (right on the image) is based on an IBM PowerPC 403 GCX microcontroller (66 MHz Internal Bus Clock and 33MHz External Bus Clock).

The major follow-up of this project is the EPFL Stereo platform.