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# 40

FOG -Fibre-optic gyroscopes

§1 Gyroscopes of various types have been around for many years. There are many types of gyroscopes (gyros) available today. Most familiar for many people is the spinning (1) mass gyro, similar to a spinning top (2) which you may have played with as a child. However, because of the moving parts, spinning mass devices have some drawbacks related to wear, maintenance and start-up time. In recent years, mechanical gyros have begun to be replaced by new types of gyros based on optical technologies.

§2 One of the most exciting developments in gyroscopes is the recent commercialization of the fibre optic gyro (FOG). In order to determine the rate of rotation, the output from a light source is split into two beams which simultaneously traverse a circular path in opposite directions. If the FOG is not rotating, then both beams will traverse exactly the same distance and, when re-combined, they will be exactly in phase and will give maximum intensity at an optical detector. If the FOG is rotating, the split/recombine (3) point will move in space during the time that the light beams (4) are travelling along the optical path. When the beams are recombined, they will no longer be in phase and the relative phase shift can be detected as a decrease in intensity at the detector. This phase shift is proportional to the rotation rate.

§3 The FOG has many advantages for robotic applications. It is a lightweight device and can be packaged in a number of ways to fit within available space constraints. The FOG is a solid state device with no moving parts. Consequently it is inherently a very high reliability sensor.

§4 The FOG consists of two separate subsystems, the optical subassembly and the signal processing and control electronics. The two are usually co-located. The subassemblies are relatively small and recent FOG designs have included both optics and electronics in a package similar in size to a cigarette pack. Low power consumption is also appreciated by robot manufacturers.

§5 Several FOG manufacturers have developed product lines which span (5) a wide variety of application requirements. This is possible since the basic FOG design can be upgraded, primarily through adjusting the fibre length and the addition of more sophisticated electronics and software.

Michael Reunert and Bob Yoshida - Sensor Review

Vocabulary notes:

1. to spin = to rotate
2. a spinning top : une toupie
3. to split = to cut into two
4. a (light) beam) : un rayon (de lumière)
5. to span : (ici) englober

UNDERSTANDING THE TEXT

1 Read the first sentence of each paragraph and decide whether the text probably is about … (answer Yes or No)

• conventional gyroscopes, which have been in existence for a long time ;
• new kinds of gyroscopes ; " their positive points ;
• their negative points ;
• the kind of machines required to manufacture a FOG ;
• the applications of FOGs ;
• a description of the parts of a FOG.

2 Pick up the compound nouns and adjectives in paragraphs 3 and 4.

3 Contracted adverb clauses (=formes elliptiques)

a/ Pick up one in para 3 and recast it as a full phrase.
b/ Recast as a contracted adverb clause: "When the beams are recombined, they will no longer be in phase".

4 Answer the questions.

§1

• Are gyroscopes a recent invention ?
• What kind of gyro do many people know ?
• Name the three drawbacks of spinning wheel gyro ?
• What is the cause of these drawbacks ?
• Do today's gyros still use the spinning wheel technology ?

§2

• What is the basic principle of a FOG ?
• What happens to the light beam when the FOG is not rotating ?
• What happens to the light beam when the FOG is rotating ?
• The split / recombine point moves in space. What does this prove ?
• Explain the relationship between this move and the path of the light beam
• What happens when the two beams are recombined ? How is rotation finally detected

§3and 4

• List the advantages mentioned
• What have several manufacturers done?
• What is the use of adjusting the fibre length ?
• Mention another way to upgrade a FOG.

§5

• What information are we given about the range of applications ?
• " What makes this possible ? Mention the two ways to upgrade FOGs.

5 What is a gyroscope ? How does it function ? What can be its applications ? (Use the information of the text.)

LANGUAGE STUDY

1 How to express consequence:
Use the drawbacks mentioned in paragraph 1 and recast them with : thus causing / resulting in / so that as in the following example: There are mechanical parts, resulting in problems of wear.

2 Fill in each blank with preposition from the list ( or Ø):
in - like - into - of - for - to.

• A conventional gyro resembles …. a spinning top (= it is similar … a spinning top = it looks … a spinning top.)
• A gyro can be used … determine rotation speed. " It can also be used … stabilisation and guidance of all kinds of vehicles.
• The principle of the FOG consists … splitting a light source … two beams.
• The appliance consists … two separate subsystems.

3 Oral exercise

Go back to the advantages listed in paragraphs 3 and 4 and explain why you believe each of them is a positive point. Use phrases such as : this allows me/ people/ engineers to (do) - this has the benefit of + ING - this makes it possible to, or other phrases studied in exercise 1.

4 Writing exercise

a. Turn the following notes into complete sentences.

• 1. (article?) gyroscopes (to be) devices measuring rotation.
• 2. The first gyroscope for vehicles (to demonstrate / passive) by Sperry in 1900.
• 3. Since this time, there (to be /mind the tense!) gyros of various types.
• 4. Today, they (to use/ passive) in (much / many ?) navigational systems.
• 5. They also (to develop / passive /present perfect); the aim : to improve vehicle dynamic systems,
• 6. for instance (article?) smart suspensions.

b. Improve your first draft.

• Sentence 1 : Recast "measuring" with a relative clause.
• Sentence 3 : Introduce a linkword expressing contrast.
• Sentence 4 : Introduce a link word to add a new idea. Sentence 5 Join the two parts of the sentence with a link word expressing aim / purpose.
• Sentence 6 : Use another phrase for introducing examples.

5 Translation exercise.
Read the following passage :
FOGs are being used in stabilization systems. An example involves a Japanese manufacturer of small, remote-controlled helicopters used for precision spraying of agricultural chemicals. Without gyros, the helicopter became unstable and was difficult to control.. As a result of installing a FOG, the operation of the helicopter was greatly simplified, operator training time has been reduced and the system is currently meeting with commercial success.

• a. Pick up the conjugated verbs in each sentence: What are the tenses ( particularly in sentence 1) ?
• b. Pick up the compound nouns and adjectives Sentence 1 : a noun - sentence 2: a noun and an adjective - sentence 4 : a noun
• c. Vocabulary: current(ly) is a 'faux ami' (a word looking like a French one but with a different meaning)
• c. Make out the -ING forms which may be:
  • part of the progressive form;
  • an (ordinary) noun;
  • a gerund (= nom verbal) necessary after a preposition.
• d. Translate this text into French.

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