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Robot Systems

reader pic Robots are comprised of several systems working together as a whole. The type of job the robot does dictates what system elements it needs. The general categories of robot systems are:
Controller

The controller is the robot's brain and controls the robot's movements. It's usually a computer of some type which is used to store information about the robot and the work environment and to store and execute programs which operate the robot. The control system contains programs, data algorithms, logic analysis and various other processing activities which enable the robot to perform.

controller pic

The picture above is an AARM Motion control system. AARM stands for Advanced Architecture Robot and Machine Motion and it's a commercial product from American Robot for industrial machine motion control. Industrial controllers are either non-servos, point-to-point servos or continuous path servos. A non-servo robot usually moves parts from one area to another and is called a "pick and place" robot. The non-servo robot motion is started by the controller and stopped by a mechanical stop switch. The stop switch sends a signal back to the controller which starts the next motion. A point-to-point servo moves to exact points so only the stops in the path are programmed. A continous path servo is appropriate when a robot must proceed on a specified path in a smooth, constant motion.

More sophisticated robots have more sophisticated control systems. The brain of the Mars Sojourner rover was made of two electronics boards that were interconnected to each other with Flex cables. One board was called the "CPU" board and the other the "Power" board and each contained items responsible for power generation, power conditioning, power distribution and control, analog and digital I/O control and processing, computing (i.e., the CPU), and data storage (i.e., memory). The control boards for Sojourner are shown below. For more info, visit Rover Control and Navigation at JPL.

Sojourner control board pic

Mobile robots can operate by remote control or autonomously. A remote control robot receives instructions from a human operator. In a direct remote control situation, the robot relays information to the operator about the remote environment and the operator then sends the robot instructions based on the information received. This sequence can occur immediately (real-time) or with a time delay. Autonomous robots are programmed to understand their environment and take independent action based on the knowledge they posess. Some autonomous robots are able to "learn" from their past encounters. This means they can identify a situation, process actions which have produced successful/unsuccessful results and modify their behavior to optimize success. This activity takes place in the robot controller.


Body

The body of a robot is related to the job it must perform. Industrial robots often take the shape of a bodyless arm since it's job requires it to remain stationary relative to its task. Space robots have many different body shapes such as a sphere, a platform with wheels or legs, or a ballon, depending on it's job. The free-flying rover, Sprint Aercam is a sphere to minimize damage if it were to bump into the shuttle or an astronaut. Some planetary rovers have solar platforms driven by wheels to traverse terrestrial environments. Aerobot bodies are balloons that will float through the atmosphere of other worlds collecting data. When evaluating what body type is right for a robot, remember that form follows function.

aercam pic sojourner pic aerobot pic


Mobility

How do robots move? It all depends on the job they have to do and the environment they operate in.

In the Water: RoboTuna AUV Conventional unmanned, submersible robots are used in science and industry throughout the oceans of the world. You probably saw the Jason AUV at work when pictures of the Titanic discovery were broadcast. To get around, automated underwater vehicles (AUV's) use propellers and rudders to control their direction of travel. One area of research suggests that an underwater robot like RoboTuna could propel itself as a fish does using it's natural undulatory motion. It's thought that robots that move like fish would be quieter, more maneuverable and more energy efficient.

On Land: Land based rovers can move around on legs, tracks or wheels. Dante II is Dante II a frame walking robot that is able to descend into volcano craters by rapelling down the crater. Dante has eight legs; four legs on each of two frames. The frames are separated by a track along which the frames slide relative to each other. In most cases Dante II has at least one frame (four legs) touching the ground. An example of a track driven robot is Pioneer, a robot developed to Pioneer Pic clear rubble, make maps and acquire samples at the Chornobyl Nuclear Reactor site. Pioneer is track-driven like a small bulldozer which makes it suitable for driving over and through rubble. The wide track footprint gives good stability and platform capacity to deploy payloads.

Many robots use wheels for locomotion. One of the first US roving vehicles used for space exploration went to the moon on Apollo 15 (July 30, 1971) and was driven by astronauts David R. Scott Lunar
Rover and James B. Irwin. Two other Lunar Roving Vehicles (LRV) also went to the moon on Apollo 16 and 17. These rovers were battery powered and had radios and antenna's just like the Mars Pathfinder rover Sojourner. But unlike Sojourner, these rovers were designed to seat two astronauts and be driven like a dune buggy.

The Sojourner rover's wheels and suspension use a rocker-bogie system that is unique in that it does not use springs. Rather, its joints rotate and conform to the contour of the ground, which helps it traverse rocky, uneven surfaces. Six-wheeled vehicles can overcome obstacles three times larger than those crossable by four-wheeled vehicles. For example, Sojourner wheels one side of Sojourner could tip as much as 45 degrees as it climbed over a rock without tipping over. The wheels are 13 centimeters (5 inches) in diameter and made of aluminum. Stainless steel treads and cleats on the wheels provide traction and each wheel can move up and down independently of all the others.

In the Air/Space: Robots that operate in the air use engines and thrusters to get around. One example is the Cassini, an orbiter on it's way to Saturn. Cassini engines Movement and positioning is accomplished by either firing small thrusters or by applying a force to speed up or slow down one or more of three "reaction wheels." The thrusters and reaction wheels orient the spacecraft in three axes which are maintained with great precision. The propulsion system carries approximately 3000 kilograms (6600 lbs) of propellant that is used by the main rocket engine to change the spacecraft's velocity, and hence its course. A total velocity change of over 2000 meters per second (6560 ft/s) is possible. In addition, Cassini will be propelled on its way by two "gravity assist" flybys of Venus, one each of Earth and Jupiter, and three dozen of Saturn's moon Titan. These planetary flybys will provide twenty times the propulsion provided by the main engine.

Deep Space 1 is an experimental spacecraft of the future sent into deep ion engine space to analyze comets and demonstrate new technologies in space. One of it's new technologies is a solar electric (ion) propulsion engine that provides about 10 times the specific impulse of chemical propulsion. The ion engine works by giving an electrical charge, or ionizing, a gas called xenon. The xenon is electrically accelerated to the speed of about 30 km/second. When the xenon ions are emitted at such a high speed as exhaust from the spacecraft, they push the spacecraft in the opposite direction. The ion propulsion system requires a source of energy and for DS1 the energy comes from electrical power generated by it's solar arrays.


Power

Power for industrial robots can be electric, pneumatic or hydraulic. Electric motors are efficient, require little maintenance, and aren't very noisy. Pneumatic robots use compressed air and come in a wide variety of hydraulic sizes. A pneumatic robot requires another source of energy such as electricity, propane or gasoline to provide the compressed air. Hydraulic robots use oil under pressure and generally perform heavy duty jobs. This power type is noisy, large and heavier than the other power sources. A hydraulic robot also needs another source of energy to move the fluids through its components. Pneumatic and hydraulic robots require maintenance of the tubes, fittings and hoses that connect the components and distribute the energy.

Two important sources of electric power for mobile robots are solar cells and batteries. There are lots of types of batteries like carbon-zinc, lithium-ion, Lithium-Ion Battery pic lead-acid, nickel-cadmium, nickel-hydrogen, silver zinc and alkaline to name a few. Battery power is measured in amp-hours which is the current (amp) multiplied by the time in hours that current is flowing from the battery. For example, a two amp hour battery can supply 2 amps of current for one hour. Solar cells make electrical power from sunlight. If you hook enough solar cells together in a solar panel you can generate enough power to run a robot. Solar cells are also used as a power source to recharge batteries.

RTG pic Deep space probes must use alternate power sources because beyond Mars existing solar arrays would have to be so large as to be infeasible. The lifespan of batteries is exceeded at these distances also. Power for deep space probes is traditionally generated by radioisotope thermoelectric generators or RTGs, which use heat from the natural decay of plutonium to generate direct current electricity. RTGs have been used on 25 space missions including Cassini, Galileo, and Ulysses.


Sensors

Sensors are the perceptual system of a robot and measure physical quantities like contact, distance, light, sound, strain, rotation, magnetism, smell, temperature, inclination, pressure, or altitude. Sensors provide the raw information or signals that must be processed through the robot's computer brain to provide meaningful information. Robots are equipped with sensors so they can have an understanding of their surrounding environment and make changes in their behavior based on the information they have gathered.

Sensors can permit a robot to have an adequate field of view, a range of detection and the ability to detect objects while operating in real or near-real time within it's power and size limits. Additionally, a robot might have an acoustic sensor to detect sound, motion or location, infrared sensors to detect heat sources, contact sensors, tactile sensors to give a sense of touch, or optical/vision sensors. For most any environmental situation, a robot can be equipped with an appropriate sensor. A robot can also monitor itself with sensors.

nomad pic The Big Signal robot NOMAD uses sensing instruments like a camera, a spectrometer and a metal-detector. The high resolution video camera can identify dark objects (rocks, meterorites) against the white background of the Antarctic snow. The variations in color and shade allow the robot to tell the difference between dark grey rocks and shadows. Nomad uses a laser range finder to measure the distance to objects and a metal detector to help determine the composition of the objects if finds.

Very complex robots like Cassini have full sets of sensing equipment much like human senses. It's skeleton must be light and sturdy, able to withstand extreme temperatures and monitor those temperatures. Cassini determines it's location by using three hemisperical resonant gyroscopes or HRG's which measures quartz crystal vibrations. The eyes of Cassini are the Imaging Science Subsystem (ISS) which can take pictures in the visible range, the near-ultraviolet and near-infrared ranges of the electromagnetic spectrum.


Tools

As working machines, robots have defined job duties and carry all the tools they need to accomplish their tasks onboard their bodies. Many robots carry their tools at the end of a manipulator. The manipulator contains a series of segments, jointed or sliding relative to one another for the purpose of moving objects. The manipulator includes the arm, wrist and end-effector. An end-effector is a tool or gripping mechanism attached to the end of a robot arm to accomplish some task. It often encompasses a motor or a driven mechanical device. An end-effector can be a sensor, a gripping device, a paint gun, a drill, an arc welding device, etc. There are many examples of robot tools that you will discover as you examine the literature associated with this site. To get you going, two good examples are listed below.

Tools are unique to the task the robot must perform. aerogel pic The goal of the robot mission Stardust is to capture both cometary samples and interstellar dust. The trick is to capture the high velocity comet and dust particles without physically changing them. Scientists developed aerogel, a silicon-based solid with a porous, sponge-like structure in which 99.8 percent of the volume is empty space. When a particle hits the aerogel, it buries itself in the material, creating a carrot-shaped track up to 200 times its own length. This slows it down and brings the sample to a relatively gradual stop. Since aerogel is mostly transparent - with a distinctive smoky blue cast - scientists will use these tracks to find the tiny particles.

Robonaut has one of the many ground breaking dexterous robot hands developed over the past two decades. These hand devices make it possible for a robot manipulator to grasp and manipulate objects that robonaut hand pic are not designed to be robotically compatible. While several grippers have been designed for space use and some even tested in space, no dexterous robotic hand has been flown in Extra Vehicular Activity (EVA) conditions. The Robonaut Hand is one of the first under development for space EVA use and the closest in size and capability to a suited astronaut's hand. The Robonaut Hand has a total of fourteen degrees of freedom. It consists of a forearm which houses the motors and drive electronics, a two degree of freedom wrist, and a five finger, twelve degree of freedom hand. The forearm, which measures four inches in diameter at its base and is approximately eight inches long, houses all fourteen motors, 12 separate circuit boards, and all of the wiring for the hand.

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