Components
Power source
At present mostly (lead-acid)
batteries are used as a power source. Many different types of batteries can be used as a power source for robots. They range from lead acid batteries which are safe and have relatively long shelf lives but are rather heavy to silver cadmium batteries that are much smaller in volume and are currently much more expensive. Designing a battery powered robot needs to take into account factors such as safety, cycle lifetime and weight. Generators, often some type of internal combustion engine, can also be used. However, such designs are often mechanically complex and need fuel, require heat dissipation and are relatively heavy. A tether connecting the robot to a power supply would remove the power supply from the robot entirely. This has the advantage of saving weight and space by moving all power generation and storage components elsewhere. However, this design does come with the drawback of constantly having a cable connected to the robot, which can be difficult to manage.
Potential power sources could be:
- pneumatic (compressed gases)
- hydraulics (liquids)
- flywheel energy storage
- organic garbage (through anaerobic digestion)
- faeces (human, animal); may be interesting in a military context as faeces of small combat groups may be reused for the energy requirements of the robot assistant (see DEKA's project Slingshot Stirling engine on how the system would operate)
Actuation
Actuators are like the "
muscles" of a robot, the parts which convert
stored energy into movement. By far the most popular actuators are electric motors that spin a wheel or gear, and linear actuators that control industrial robots in factories. But there are some recent advances in alternative types of actuators, powered by electricity, chemicals, or compressed air.
Electric motors
Main article:
Electric motorThe vast majority of robots use electric motors, often brushed and brushless DC motors in portable robots or AC motors in industrial robots and
CNC machines. These motors are often preferred in systems with lighter loads, and where the predominant form of motion is rotational.
Linear actuators
Various types of linear actuators move in and out instead of by spinning, and often have quicker direction changes, particularly when very large forces are needed such as with industrial robotics. They are typically powered by compressed air (
pneumatic actuator) or an oil (
hydraulic actuator).
Series elastic actuators
A
spring can be designed as part of the motor actuator, to allow improved force control. It has been used in various robots, particularly walking
humanoid robots.
Air muscles
Pneumatic artificial muscles, also known as air muscles, are special tubes that contract (typically up to 40%) when air is forced inside them. They have been used for some robot applications.
Muscle wire
Muscle wire, also known as Shape Memory Alloy, Nitinol or Flexinol Wire, is a material that contracts slightly (typically under 5%) when electricity runs through it. They have been used for some small robot applications.
Electroactive polymers
EAPs or EPAMs are a new plastic material that can contract substantially (up to 380% activation strain) from electricity, and have been used in facial muscles and arms of humanoid robots,
and to allow new robots to float, fly, swim or walk.
Piezo motors
Recent alternatives to DC motors are
piezo motors or
ultrasonic motors. These work on a fundamentally different principle, whereby tiny
piezoceramic elements, vibrating many thousands of times per second, cause linear or rotary motion. There are different mechanisms of operation; one type uses the vibration of the piezo elements to walk the motor in a circle or a straight line.
Another type uses the piezo elements to cause a nut to vibrate and drive a screw. The advantages of these motors are
nanometer resolution, speed, and available force for their size.
These motors are already available commercially, and being used on some robots.
Elastic nanotubes
Elastic nanotubes are a promising artificial muscle technology in early-stage experimental development. The absence of defects in
carbon nanotubes enables these filaments to deform elastically by several percent, with energy storage levels of perhaps 10
J/cm
3 for metal nanotubes. Human biceps could be replaced with an 8 mm diameter wire of this material. Such compact "muscle" might allow future robots to outrun and outjump humans.
Sensing
Sensors allow robots to receive information about a certain measurement of the environment, or internal components. This is essential for robots to perform their tasks, and act upon any changes in the environment to calculate the appropriate response. They are used for various forms of measurements, to give the robots warnings about safety or malfunctions, and to provide real time information of the task it is performing.
Touch
Current
robotic and
prosthetic hands receive far less
tactile information than the human hand. Recent research has developed a tactile sensor array that mimics the mechanical properties and touch receptors of human fingertips.
The sensor array is constructed as a rigid core surrounded by conductive fluid contained by an elastomeric skin. Electrodes are mounted on the surface of the rigid core and are connected to an impedance-measuring device within the core. When the artificial skin touches an object the fluid path around the electrodes is deformed, producing impedance changes that map the forces received from the object. The researchers expect that an important function of such artificial fingertips will be adjusting robotic grip on held objects.
Scientists from several
European countries and
Israel developed a
prosthetic hand in 2009, called SmartHand, which functions like a real one—allowing patients to write with it, type on a
keyboard, play piano and perform other fine movements. The prosthesis has sensors which enable the patient to sense real feeling in its fingertips.
Vision
Computer vision is the science and technology of machines that see. As a scientific discipline, computer vision is concerned with the theory behind artificial systems that extract information from images. The image data can take many forms, such as video sequences and views from cameras.
In most practical computer vision applications, the computers are pre-programmed to solve a particular task, but methods based on learning are now becoming increasingly common.
Computer vision systems rely on image sensors which detect electromagnetic radiation which is typically in the form of either
visible light or
infra-red light. The sensors are designed using
solid-state physics. The process by which light propagates and reflects off surfaces is explained using
optics. Sophisticated image sensors even require
quantum mechanics to provide a complete understanding of the image formation process. Robots can also be equipped with multiple vision sensors to be better able to compute the sense of depth in the environment. Like human eyes, robots' "eyes" must also be able to focus on a particular area of interest, and also adjust to variations in light intensities.
There is a subfield within computer vision where artificial systems are designed to mimic the processing and behavior of
biological systems, at different levels of complexity. Also, some of the learning-based methods developed within computer vision have their background in biology.
Other
Other common forms of sensing in robotics use
LIDAR,
RADAR and
SONAR.
Manipulation
Robots need to manipulate objects; pick up, modify, destroy, or otherwise have an effect. Thus the "hands" of a robot are often referred to as
end effectors,
while the "arm" is referred to as a
manipulator.
Most robot arms have replaceable effectors, each allowing them to perform some small range of tasks. Some have a fixed manipulator which cannot be replaced, while a few have one very general purpose manipulator, for example a humanoid hand.
For the definitive guide to all forms of robot end-effectors, their design, and usage consult the book "Robot Grippers".
Mechanical grippers
One of the most common effectors is the gripper. In its simplest manifestation it consists of just two fingers which can open and close to pick up and let go of a range of small objects. Fingers can for example be made of a chain with a metal wire run through it.
Hands that resemble and work more like a human hand include the
Shadow Hand, the
Robonaut hand,
... Hands that are of a mid-level complexity include ie the Delft hand, ...
Mechanical grippers can in come in various types, including friction and encompassing jaws. Friction jaws use all the force of the gripper to hold the object in place using friction. Encompassing jaws cradle the object in place, using less friction.
Vacuum grippers
Vacuum grippers are very simple astrictive
devices, but can hold very large loads provided the
prehension surface is smooth enough to ensure suction.
Pick and place robots for electronic components and for large objects like car windscreens, often use very simple vacuum grippers.
General purpose effectors
Some advanced robots are beginning to use fully humanoid hands, like the Shadow Hand, MANUS,
and the
Schunk hand.
These highly dexterous manipulators, with as many as 20
degrees of freedom and hundreds of tactile sensors.
Development history
