A mobile robot is a software-controlled computer that uses sensors and other technologies to define and interact with its surroundings. Mobile robots work by combining artificial intelligence (AI) with physical robotic elements like wheels, tracks, and legs. Mobile robotics is one of the fastest expanding industries in current times. The reasons for such exponential success rates are their abilities to substitute humans in fields such as surveillance, planetary exploration, industrial automation, rescue operations, petrochemical applications, and construction to name a few among a lot of others.
A Mobile robot can move autonomously, which means without the external human assistance, the robot itself can determine the required course of actions for performing a specific task, the robot is able to achieve this using perception systems. The robot also needs a control system also called a “cognition unit”, using which it can coordinate with all the sub-systems in the robot.
The basics of mobile robots
The basics of mobile robotics include the fields of:
The locomotion problems are solved by understanding the mechanics, kinematics, dynamics and control theory.
The perception consists of the areas of signal analysis and specialized fields such as computer vision and sensor technologies.
It is responsible for analyzing the input data from the sensors and taking the corresponding actions to achieve the objectives of the mobile robot.
This system requires knowledge from various different fields to work at its best, the fields include algorithms, information theory, and artificial intelligence.
Classifications of mobile robots:
According to the locomotion systems of the mobile robots they can be categorized into the following major groups:
- Stationary robot
- Water-based mobile robots
- Air-based mobile robots
- Land-based mobile robots
- Wheeled mobile robot (WMR)
- Walking mobile robot
- Tracked slip locomotion
Stationary robots are fixed robots. Many examples of stationary robots are manipulators and industrial robots. These robots are capable of not only handling the objects in the industrial area but they are also used for painting, assembling, welding machining. Stationary robots move in fixed and known areas. They cannot move in the unknown area.
Grasping robots make up a major part of the stationary robots, such devices have long been known to help humans to handle tasks. A broad overview can be found in Carlos et al.
Water-based mobile robots:
Water-based robots are designed only for moving in the water area. These robots work in underwater and on the water where a man cannot go. Ocean-One is an example of water-based robots.
Air-based/ AIV robots:
These robots are capable of working in the air. These are programmed to balance themselves in air without human interaction and this idea is inspired by plans in the air. The best example of these robots is done.
Land-based robots are categorized as followed:
Wheeled Mobile robots:
Wheels are one of the most important robot locomotion mechanisms, and autonomous intelligent vehicles (AIVs) are part of a complex mobile robotics research area that relies on concepts such as pattern recognition and signal – image processing. They’ll play a major role in transportation, storage, and distribution.
When the robot travels on smooth, non-rugged terrain, the use of wheels is simpler than using treads or legs, and is easier to design, create, and program. They seem to be much cheaper than their legged counterparts too. Wheel regulation is less complicated and in contrast with other methods, they inflict less wear and tear on the surface as they drive-in. Another advantage is that in terms of balance problems, they do not pose any great difficulties, as the robot normally comes in contact with a wall. The biggest downside of wheels is that they are not very effective at rolling over obstacles like rough hills, hard surfaces, or low-friction areas.
There are four types of base wheel:
- Standard fixed wheel: These are traditional one-degree (DOF) plates, revolving around the touchpoint.
- Castor wheel: It has two DOFs and an offset steering joint to turn around.
- Swedish plate: It has three DOFs, revolving around the wheel rim, the touchpoint, and the rollers.
- Ball or spherical wheel: It is technically complex to implement.
A number of wheels and types of wheels are more important for the kinematics and the dynamics of robots.
Single wheeled robots are unicycle robots, they are inherently unstable. Two-wheeled-robots can be more stable than one-wheeled. Three-wheeled is considered a guaranteed balanced robot. One actuator controls its two wheels and one wheel is for steering. Four-wheeled robots are more stable and easier to control. With the increase of wheels we can make more stable but complexity increases. There are also spherical wheels used for motion in robots but they are more complex. They can turn their direction more easily.
Walking mobile robot:
These robots are equipped with legs like human or animal legs. Walking robots are more expensive and more complex making balance but the can easily walk on a rough track with better stability and control. Wheeled robots required the plan surface to move. In these robots stability is the main issue. In these robots, stability is controlled with geometric sensors and control algorithms.
The mechanical structure is necessary for mobile robots to be controlled to do tasks. There are different pillars of a robot control system: cognition, perceptions, processing, and action. The perception system makes robot informed about the environment and make a relationship between environment and robot. In second. This information is processed and sends to the actuator in the form of appropriate commands which will move robot mechanically. When all information and commands are processed and the position of the robot is known, the cognition system plans to make a path for the robot to achieve its objective. The Control system must make a decision on the basis of information from sensors and actuators. In fact, the control system of a mobile robot is responsible for all tasks, it decides that where to move, on the basis of input data.
Cognition model represents the relation of robot, environment, and way of interaction, and other hand computer vision and pattern recognition are used for tracking and mapping algorithms to build a map. Artificial intelligence and Motion detection are also used for interaction. For example, a planner is responsible for movement without any collision.
Eventually, motion planning and other artificial intelligence algorithms might be used to determine how the robot should interact. For starters, a planner may decide how to attain a task without colliding with obstacles, falling over, and so on. in the future, artificial intelligence is called to play a significant role in the handling of all the knowledge collected by the robot and send instructions to the robot. Robots show nonlinear dynamics. Nonlinear control techniques take advantage of the system’s knowledge and/or parameters in order to reproduce its behavior. Nonlinear control, estimation, and observation lead to complex algorithms.
It is vital that an autonomous mobile robot gains knowledge about its working environment and about itself. This is achieved by means of sensors and thereafter relevant information is extracted from the measurements of those sensors. Using sensors allows robot positioning and localization tasks to be performed. They are used for Mapping and displaying. These are also very useful in many robotic applications, such as object recognition. In speech recognition systems, the latest developments of sensors and artificial intelligence are used, which are very important for reproducing human capabilities.
Types of sensors:
There are many types of sensors used in mobile robots. We can classify them on the basis of their working.
- Passive sensors
- Proprioceptive sensors
Passive sensors measure ambient energy entering the sensor, such as microphones, temperature measurements, and Charge Coupled Device (CCD) or CMOS cameras. Active sensors radiate energy into the environment and measure the reaction. Active sensors radiate energy into the environment and measure the reaction. They can handle more regulated interactions with the work environment, producing better efficiency, while they can suffer from interference with their own and external signals.
Proprioceptive sensors read internal values for the robot, such as engine speed, wheel load, joint angles, battery voltage, etc. Exteroceptive sensors obtain information from the robot’s surroundings, such as distances, the strength of light, and the amplitude of the sound.
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Different types of sensors are the following:
- Tactical Sensors: They are designed to sense objects with or without direct touch at a small distance, and are used to detect physical contact or proximity. Normally, they can sense forces and can reveal an object’s exact location, allowing the robot to control the end-effector’s position and grasping force. Tactile sensors can detect heat variations, too.
- Force Torque Sensors: The robot uses a torque force sensor to determine what force the robot is applying. With this device, it is possible to perform various robot tasks such as assembly, hand guide, teaching, and force limitation.
- Encoder: Encoders are used for analog sensors to convert or translate information.
- Ultrasonic sensors: it is a sound-based sensor and used for distance.
- Sonar: this sensor is used on water and on land. It is used for object detection.
- Active beacons: this sensor is a system of two kinds of the beacon. Trilateration and triangulation.
- Accelerometers: it is a device to measure acceleration. They are used in humanoid robots.
- Gyroscopes: for measurement of angular velocity and orientation, we use Gyroscopes.
- Laser range finder: In this sensor, a laser beam fired and distance of objects is calculated by speed of light
- Vision-based sensors: These process data from any modality and produce an image using the electromagnetic spectrum. CCD and CMOS are the two current technologies for creating vision sensors
- Color tracking sensors: it detects the color in the surrounding.
- Proximity sensors: it measures the force of contact in the environment.
- Depth sensors: for object detection, we use the depth sensors. In which an IR sensor and infrared sensor is used.
In general, robotics, and mobile robotics in particular, will continue their evolution over the next few years. Cognitive architecture, artificial intelligence, speech communication, and affective human-robot interaction will increasingly be integrated into the design of robots. In certain uses, such as defense and military defense, Surveillance, risky jobs and traveling in unsafe areas, space exploration, etc.