Providing fault-tolerant design for every component is normally not an option.
Associated redundancy brings a number of penalties: increase in weight, size, power consumption, cost, as well as time to design, verify, and test. Therefore, a number of choices have to be examined to determine which components should be fault tolerant: . An example of a component that passes all the tests is a car's occupant restraint system. While we do not normally think of the primary occupant restraint system, it is gravity.
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If the vehicle rolls over or undergoes severe g-forces, then this primary method of occupant restraint may fail. Restraining the occupants during such an accident is absolutely critical to safety, so we pass the first test. Accidents causing occupant ejection were quite common before seat belts , so we pass the second test. The cost of a redundant restraint method like seat belts is quite low, both economically and in terms of weight and space, so we pass the third test.
Therefore, adding seat belts to all vehicles is an excellent idea. Other "supplemental restraint systems", such as airbags , are more expensive and so pass that test by a smaller margin. Another excellent and long-term example of this principle being put into practice is the braking system: whilst the actual brake mechanisms are critical, they are not particularly prone to sudden rather than progressive failure, and are in any case necessarily duplicated to allow even and balanced application of brake force to all wheels.
It would also be prohibitively costly to further double-up the main components and they would add considerable weight. However, the similarly critical systems for actuating the brakes under driver control are inherently less robust, generally using a cable can rust, stretch, jam, snap or hydraulic fluid can leak, boil and develop bubbles, absorb water and thus lose effectiveness.
The cumulatively unlikely combination of total foot brake failure with the need for harsh braking in an emergency will likely result in a collision, but still one at lower speed than would otherwise have been the case. In comparison with the foot pedal activated service brake, the parking brake itself is a less critical item, and unless it is being used as a one-time backup for the footbrake, will not cause immediate danger if it is found to be nonfunctional at the moment of application.
Therefore, no redundancy is built into it per se and it typically uses a cheaper, lighter, but less hardwearing cable actuation system , and it can suffice, if this happens on a hill, to use the footbrake to momentarily hold the vehicle still, before driving off to find a flat piece of road on which to stop. On motorcycles, a similar level of fail-safety is provided by simpler methods; firstly the front and rear brake systems being entirely separate, regardless of their method of activation that can be cable, rod or hydraulic , allowing one to fail entirely whilst leaving the other unaffected.
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Secondly, the rear brake is relatively strong compared to its automotive cousin, even being a powerful disc on sports models, even though the usual intent is for the front system to provide the vast majority of braking force; as the overall vehicle weight is more central, the rear tyre is generally larger and grippier, and the rider can lean back to put more weight on it, therefore allowing more brake force to be applied before the wheel locks up.
On cheaper, slower utility-class machines, even if the front wheel should use a hydraulic disc for extra brake force and easier packaging, the rear will usually be a primitive, somewhat inefficient, but exceptionally robust rod-actuated drum, thanks to the ease of connecting the footpedal to the wheel in this way and, more importantly, the near impossibility of catastrophic failure even if the rest of the machine, like a lot of low-priced bikes after their first few years of use, is on the point of collapse from neglected maintenance.
In addition, fault-tolerant systems are characterized in terms of both planned service outages and unplanned service outages. These are usually measured at the application level and not just at a hardware level.
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The figure of merit is called availability and is expressed as a percentage. For example, a five nines system would statistically provide All implementations of RAID , redundant array of independent disks , except RAID 0, are examples of a fault-tolerant storage device that uses data redundancy. A lockstep fault-tolerant machine uses replicated elements operating in parallel.
At any time, all the replications of each element should be in the same state. The same inputs are provided to each replication , and the same outputs are expected. The outputs of the replications are compared using a voting circuit. A machine with two replications of each element is termed dual modular redundant DMR. The voting circuit can then only detect a mismatch and recovery relies on other methods. A machine with three replications of each element is termed triple modular redundant TMR. The voting circuit can determine which replication is in error when a two-to-one vote is observed.
In this case, the voting circuit can output the correct result, and discard the erroneous version. After this, the internal state of the erroneous replication is assumed to be different from that of the other two, and the voting circuit can switch to a DMR mode. This model can be applied to any larger number of replications. Lockstep fault-tolerant machines are most easily made fully synchronous , with each gate of each replication making the same state transition on the same edge of the clock, and the clocks to the replications being exactly in phase. However, it is possible to build lockstep systems without this requirement.
Bringing the replications into synchrony requires making their internal stored states the same. They can be started from a fixed initial state, such as the reset state. Twenty-one articles described systems demonstrating reasoning capabilities. The systems showed a number of different aspects of reasoning, including recognizing that a problem exists, applying general rules to solve a problem, and developing new rules or conclusions. In the articles from the first five years, the tasks addressed included making underwriting decisions about long-term care insurance, providing customer service for sales and repairs, developing new hypotheses about good conditions for growing crystals and for recovering from medical disability, helping diagnose appliance problems, providing useful analogies for solving problems in physics and in military tactical games, providing answers and explanations to chemistry questions in an advanced high-school test, developing novel atomic models for electron-density maps of proteins, identifying patterns of potentially suspicious facts that could indicate a terrorist plan, resolving problems related to scheduling and project coordination, role-playing with students in a training simulation about how a military officer should handle a car accident with a civilian, and driving a vehicle on different types of road.
In the later articles, the tasks included screening medical articles for inclusion in a systematic research review, processing government forms related to immigration and marriage, solving crossword puzzles, playing Jeopardy, answering questions from museum visitors, analyzing geological landform data to determine age, talking with people about directions and the weather, answering questions with Web searches, driving a vehicle in traffic and on roads with unexpected obstacles, solving problems with directions that contain missing or erroneous information, and using Web sites to find information for carrying out novel tasks.
One of the striking aspects of the reasoning systems was their ability to produce high levels of performance. For example, the systems were able to make insurance underwriting decisions about easy cases and provide guidance to underwriters about more difficult ones, produce novel hypotheses about growing crystals that were sufficiently promising to merit further investigation, substantially improved the ability of call center representatives to diagnose appliance problems, achieved scores on a chemistry exam comparable to the mean score of advanced high-school students, produced initial atomic models for proteins that substantially reduced the time needed for experts to develop refined models, substituted for medical researchers in screening articles for inclusion in a systematic research review, solved crossword puzzles at an expert level, played Jeopardy at an expert level, and analyzed geological landform data at an expert level.
However, common-sense reasoning has historically been more difficult for IT systems to demonstrate. The articles from the first five years were consistent with the historical contrast, showing high levels of reasoning within narrow areas of specialized expertise but no evidence of the broad and more flexible reasoning that is typical of human common sense. But during the later period, there were examples of systems that used information from the Web to reason across a broad range of areas.
Vision capabilities. Twenty-two articles described systems demonstrating vision capabilities. These include systems that recognized objects and different features of those objects, including their position in space. In the articles from the early years, the tasks of the systems included locating a soccer ball and other soccer players, identifying cars and their movements in a video of a traffic intersection, finding the registration booth and several rooms at a conference, identifying drivable surfaces and obstacles for an autonomous car, determining the location of a ping-pong ball, guiding autonomous vehicles to move shipping containers, identifying people and obstacles in a crowded museum, locating pallets in a factory, recognizing objects in cluttered environments, guiding a robot to grasp irregularly shaped objects such as lettuce, and identifying vehicles on a road to provide driver assistance.
In the later articles, the tasks included recognizing chess pieces by location, rapidly identifying types of fish, recognizing the presence of nearby people, identifying the movements of other vehicles for an autonomous car, locating and grasping objects in a cluttered environment, moving around a cluttered environment without collisions, learning to play ball-and-cup, playing a game that involved building towers of blocks, navigating public streets and avoiding obstacles to collect trash, identifying people and locating drinks and laundry in an apartment, and using Web sites to find visual information for carrying out novel tasks such as making pancakes from a package mix.
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All of the systems involved identifying various—and diverse—objects, and they all also involved recognizing features of the identified objects, particularly their location and movement. Movement capabilities. Seventeen articles described systems demonstrating movement capabilities. These included systems that involved spatial orientation, coordination, movement control, and body equilibrium.
Many of the systems integrated movement capabilities with capabilities in one or more of the other three general areas of capability. In the early articles, the tasks of the systems included walking, kicking a ball, passing a ball between two robots, moving down a hallway, following a map to locate a meeting room in a hotel, using an elevator, driving a car in the desert, playing ping-pong, autonomously moving shipping containers, navigating around people and pursuing objects in a crowded museum, moving pallets autonomously in a factory, and grasping irregularly shaped objects such as lettuce.
In the later articles, the tasks included moving chess pieces, driving a car in traffic, grasping objects in a cluttered environment, moving around a cluttered environment without collisions, learning to play ball-and-cup, playing a game that involved building towers of blocks, navigating public streets and avoiding obstacles to collect trash, retrieving and delivering drinks and laundry in an apartment, and using the Web to figure out how to make pancakes from a package mix. With these examples of IT and robotics capabilities, we can then look at the skills required in different occupations to see how they compare.
To make this comparison, the study used the U. The feature set includes ratings for a number of ability scales that are related to the four general areas of capability discussed above. The study used these anchoring tasks to provide concrete descriptions of the different levels of capability required for different jobs throughout the economy. To focus on the big picture, the study grouped together all of the different abilities into two cluster ratings: one focused on language and reasoning, and the other focused on vision and movement.
For each occupation, the highest rating across the different abilities was used as the rating for each of the two clusters. The table omits level 7 on the rating scale because there are so few jobs that require that level of skill. So a crucial question for assessing the likely impact of IT and robotics capabilities on work over the next few decades is how those capabilities compare with this middle level of ability on the rating scale for workers. The nation has already seen some replacement of sales jobs with technology in the extensive use of the Web for retail, along with the use of self checkout in stores.
Currently, the level of interaction provided by such sales-related technology is low, but the research systems show capabilities that would allow more helpful interactions. Some of the research systems specifically provided interactions related to customer service, as well as related tasks such as answering questions from museum visitors or giving people directions.
tekhmann.com/media/lucie/1994-citas-en.php Some of the reasoning systems provided underlying analytic capabilities that could extend the kinds of transactions that can be carried out without a person, including processing government forms, using Web sites to find information, making insurance underwriting decisions, or diagnosing appliance problems. It is possible to imagine how the ease and range of interaction and the depth of analysis of sales-related computer systems can be steadily extended over time to add many functions of current sales occupations.
Future systems will be able to use regular language with customers to understand what they are looking for and to suggest possible solutions. The middle section of Table 3 includes the large number of occupational groups involving both a medium level of language and reasoning skills and a medium level of vision and movement. The language and reasoning skills for many of these jobs are similar to those for the sales occupations just discussed. It is easy to imagine, for example, that the interaction and analysis that will make it possible to extend the capabilities of sales-related computer systems will also be applicable to the capabilities of administrative systems, where there is often an interaction with an internal customer.
As a contrast, it is useful to consider one of the occupational groups in the middle section that involves an extensive role for vision and movement.