Infrared cone guided docking, circuit tests

The last few weeks have brought significant progress towards a prototype unit, and especially towards the elements of a prototype we plan to display at TAROS.

We've already produced V-REP simulations displaying our remarkably elegant solution for infrared cone guided docking, a target docking port shines an IR led from its centre, this infrared LED is placed within a conical black plastic shield which restricts its cone of light to a known angle away from the normal to the docking port. The IR light is detected by phototransistors around the rim of an approaching docking port. By judging which phototransistors are illuminated by the LED, and comparing the light intensity on each, the approaching port can guide itself down to the last few cm, at which point the geometry of the spikes and pits around the port give a perfect alignment as the ports push together.

A screen capture from a V-REP simulation of two robots docking using an infrared cone. The robot on the right drive randomly until it enters the cone of IR light, then moves so as to keep its array of phototransistors (top-most one of four visible and highlighted wih red flashes) within the other robots's infrared cone cast by the LED (highlighted with purple flashes). After docking the two modules drive together.

Many robots are fitted with infrared sensors for proximity detection, ranging and communication. Often the infrared LEDs present are just held on or off and the level detected by an analog sensor. However by modulating the infrared we can fit filtering circuits to our phototransistor sensors and use a mixture of high and low pass stages to clean out any background light sources, for example daylight or incandescent bulbs. With this background filtered out we can apply a gain with an amplifier, then feed our cleaned up and amplified waveform to our microcontroller's ADC. Crucially, unlike the kind of digital receivers you find in televisions and other IR remote controlled devices, we can get a power level for the modulated signal.

Oscilloscope trace of a received modulated signal, processed in a high pass amplifier before being sent to the microntroller for further analysis.

Right now we've got the necessary circuitry for an approaching docking port to navigate its way to a target docking port from up to approximately 40 cm away. We're using standard infrared receiver to decode robot and docking port ID numbers from the infared LED's signal at greater ranges and let approaching ports know which docking port they are approaching.

We're hoping to achieve some further increase in range by optimising components, then we should have a nice little demo of two docking ports, their IR guidance and their genderless connection mechanism to display alongside our poster.