Sensors

It was assumed that the design of the components of the agents' architecture (sensors, actuators and processors) has already been defined and all that remains is to develop an agent program. But success in creating real robots is no less dependent on how well the sensors and actuators are designed that are suitable for the task.

Sensors are nothing more than an interface between robots and the environment in which they operate, providing the transmission of perceptual results. Passive sensors , such as video cameras, in the full sense of the word function as an observer of the environment - they intercept signals generated by other sources of signals in the environment. Active sensors , such as locators, send energy on Wednesday. Their action is based on the fact that part of the radiated energy is reflected and re-enters the sensor. As a rule, active sensors provide more information than passive ones, but at the expense of increasing the energy consumption from the power source; Another disadvantage is that with the simultaneous use of multiple active sensors, interference may occur. In general, sensors (active and passive) can be divided into three types, depending on whether they register distances to objects, form media images, or monitor the characteristics of the robot itself.

Most mobile robots use rangefinders , which are sensors that measure the distance to nearby objects. One of the widely used types of such sensors is an audio locator , also known as an ultrasonic transducer. Sound locators emit directional sound waves that are reflected from objects, and part of this sound enters the sensor again. At the same time, the arrival time and the intensity of such a return signal carry information about the distance to the nearest objects. For autonomous underwater vehicles, the technology of underwater sonars is mainly used, and on earth sound locators are mainly used to prevent collisions only in the immediate vicinity, since these sensors are characterized by a limited angular resolution. Other devices that are alternative to sound locators include radar (mainly used in aircraft) and lasers. Laser rangefinder is shown in the figure.

A typical example of a sensor and its practical application: laser range finder (distance sensor) SICK LMS - a widely used sensor for mobile robots (a); distance measurement results obtained using a horizontally mounted distance sensor, designed on a two-dimensional map of the medium (b)

Some distance sensors are designed to measure very short or very long distances. Short distance measurement sensors include ^ tactile sensors, such as contact bars, contact panels, and sensor covers. At the other end of the spectrum is the global positioning system (Global Positioning System — GPS), which measures the distance to satellites emitting impulse signals. Currently, more than two dozen satellites are in orbit, each of which transmits signals at two different frequencies. GPS receivers determine the distance to these satellites by analyzing the phase shift values. Then, performing triangulation of signals from several satellites, GPS receivers determine their absolute coordinates on Earth with an accuracy of several meters. In differential GPS systems , a second ground receiver with known coordinates is used, so that, under ideal conditions, the accuracy of measuring the coordinates to a millimeter is ensured. Unfortunately, GPS systems do not work indoors or under water.

The second important class of sensors are image sensors - video cameras, which allow to obtain images of the environment, as well as to simulate and determine the characteristics of the environment using computer vision methods. In robotics, stereoscopic vision is particularly important because it allows you to get information about the depth; nevertheless, the future of this direction is under threat, since the development of new active technologies for obtaining spatial images is being successfully implemented.

The third important class includes proprioceptive sensors that inform the robot about its own condition. To measure the exact configuration of a robotic joint, electric motors that drive it often are equipped with shaft angle encoders , which allow even small increments of the angle of rotation of the motor shaft to be detected. In robot manipulators, shaft angle encoders are able to provide accurate information for any period of time. In mobile robots, decoders of the angle of rotation of the shaft, which transmit data on the number of wheel revolutions, can be used for odometry - measurement of the distance traveled. Unfortunately, the wheels often move and slip, so the odometry results are accurate only for very short distances. Another reason for errors in determining the position are external forces, such as currents, affecting autonomous underwater vehicles, and winds, knocking off automatic aircraft. This situation can be improved by using inertial sensors , such as gyroscopes, but even they, used without other additional means, do not make it possible to eliminate the inevitable accumulation of errors in determining the position of the robot.

Other important aspects of the condition of the robot are monitored using sensors.

force and torque sensors . These sensors cannot be dispensed with if robots are designed to work with fragile objects or objects whose exact shape and location are unknown. Imagine that a robotic manipulator with a maximum compression force of one ton spins an electric light bulb into a cartridge. It is very difficult to prevent such a situation, that the robot will put too much effort and crush the light bulb. But force sensors allow the robot to feel how tightly it holds the light bulb, and torque sensors - to determine with what force it turns it. Good sensors make it possible to measure forces in three directions of transport and three directions of rotation.