Painting Robots par Leonel Moura
http://www.lxxl.pt
Vous pouvez commenter ce robot ou venir en discuter sur le forum des robots et de la robotique à cette adresse:
http://www.robot-passion.com
Des robots autonomes dotés d’une intelligence rudimentaire créent des peintures fondées sur l’aléatoire et la stigmergie.
Description et caractéristiques (en anglais) :
The basic architecture of each robot (mbot) contains three components: The sensors, the controller and the actuators. The sensors receive signals from the environment, which are processed by the microcontroller in order to command the actuators, mechanical devices that produce conditional motion.
The sensors are of two kinds: those that receive the signal from the key environmental variable chosen, which is colour, and those that perceive the proximity of obstacles.
In regard to ‘colour’ sensors, there are two RGB sensors in each robot, directed to the floor.
Each sensor is composed by one LED (Light Emmiting Diode) for each colour. In this case, since at the end of the process it is required to discriminate “bright†from “dark†colours, a fourth LED was added, directed to White. The function of each LED is to measure the intensity of reflected light. Given that a surface of a certain colour reflects more intensively the light of the same colour, each LED captures ‘only’ (in practice, ‘mainly’) the colour it is directed to. For each cycle of the sensor, the four LEDs are fired sequentially and an integration of the correspondent intensity values provides the RGB (and White) evaluation of the surface covered by the sensor. Since there are two sensors of this kind, a new integration is needed before the signal is transmitted to the processor.
In regard to proximity sensors, there are four of them, located in the robot’s front. They consist of an IR emitter/receptor that produces a signal which is proportional to the distance from a white wall. Hence, the bounding barriers of the terrarium where robots evolve must be white, as well as robots’ enclosing boxes.
Since solar light may interfere with the sensors, robots should function in a small intensity artificial light environment. The range of distances perceived by this type of sensors is 1 to 15 cm.
The controller is an on-board PIC 16F8Â76 from Microchip, which reads signals from sensors, processes them according to a program, and transmits the result to the actuators. The program is uploaded into the chip, prior to each run, through the serial interface of a PC. This program is developed based on the PC graphic interface, consisting of a flowchart where test blocks for sensors and actuators are combined according to a certain sequence, that can obviously be changed whenever wanted. Each test block compares a given variable with a previously defined parameter and executes an “IF…THEN†rule. After compilation, the program is uploaded to the robot via the PC serial interface.
The actuators consist of two servomotors producing movement by differential traction based on velocity control and one servomotor for manipulating the two pens that execute the action of painting. The latter is commanded by a signal analogous to the one sent to traction motors but, in this case, an angular position control is used. The function of this actuator is to raise or drop each pen, according to the signal provided by the controller.
The chassis consists of an oval 20 x 15 cm platform, moved by 3 wheels and carrying two marking-pens. Each robot is 12.5 cm tall, weights 750 grs and their life-time endowed with 8 AA type batteries is approximately 4 hours.
In regard to the programming interface, it contains a special module, called RANDOM, that allows initialising the process. This function generates an uniformly distributed random number and compares it with the threshold inputted as a control parameter. If the random number exceeds the threshold one pen is dropped and the robot paints a coloured trace whose length depends on another control parameter.
Once a robot ‘sees’ a trace of a given binary colour (“dark†or “brightâ€), the pen of the same range of colour is dropped and, consequently, that colour is accentuated. Also, the movement actuator reacts to colour in the following manner: when a colour is perceived by both RGB sensors, the robot goes ahead; when a colour is perceived by one of them, the robot turns towards the direction where that colour comes from.
Prior to launching any collective experiment, the following procedure is performed:
– Parameterisation of the control program in the graphic interface with the same values, compilation and transmission for each robot
– Calibration of all sensors of each robot in the programming interface
– Provision of fresh batteries for each robot
robot-painting-robot.jpg
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