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Encyclopedia Britannica - Main :: TUM-VAN |
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TYPEWRITER , a writing machine which produces characters resembling those of ordinary letterpress; the term is also applied to the operator who works such machines. In 1714 a British patent was granted to Henry Mill, who claimed that he had brought his invention to perfection at great pains and expense, for " An Artificial Machine or Method for the Impressing or Transcribing Letters, Singly or Progressively one after another as in Writing, whereby all Writing whatever may be Engrossed in Paper or Parchment so Neat and Exact as not to be distinguished from Print "; but beyond the title the patent gives no indication of the nature or construction of the machine. In America a patent for a " typographer " was obtained by William A. Burt in 1829, but the records of it were destroyed by a fire at Washington in 1836. The " typo-graphic machine or pen " patented by X. Progrin, of Marseilles, in 1833, was on the type-bar principle, and at the York
horizontal
the required type was over the printing point. The Great Exhibition of 1851 contained a machine patented by Pierre Foucault, of Paris, in 1849, in which a series of rods with type at their ends could be pushed down to emboss paper at the printing point to which they were arranged radially; and there was in addition the " typograph " of William Hughes, which was also intended for embossing, though it was subsequently modified to give an impression through carbon paper. Between 1847 and 1856 Alfred E. Beach in America, and between 1855 and 186o Sir Charles Wheatstone in England, constructed several typewriters, and in 1857 Dr S. W. Francis, of New York
Pratt
hammer
capital and small letters.The great majority of modern typewriters are worked from a keyboard; the few that are not, known as index machines, will be disregarded here, for although they are much less expensive in first cost than the others, they scarcely come into competition as practical instruments, on account of their slowness. Key-board machines fall into two classes, according as the types which make the impressions are (a) carried at the end of levers or type-bars which strike the paper when the keys are depressed, or (b) are arranged round the circumference of a wheel, or segment, which is rotated by the action of the keys until the corresponding type is brought opposite the printing point. The former of these arrangements is the more common. Another point of difference is in the inking device; in some cases, the type is inked by means of an ink-pad before being brought down on the paper to make the impression, but more frequently an inked ribbon is drawn
502 for two or more characters. For example, in the former class there is one key for the capital A and another for the small a, the keys being arranged in two banks corresponding to the upper and lower cases of a printer's type-case; in the latter, one key is capable of striking both the small and the capital letter, and it does one or other according as a subsidiary key is or is not brought into simultaneous use with it. In type-bar machines designed on this plan, each bar carries two or more letters (cf. fig. 1). This form of keyboard is also applied to type-wheel machines.Though there are numberless differences in detail, all type- writers, apart from the index machines, bear a general resem-blance to each other in their me- chanical arrangements. The really essential operations may be reduced to two; the machine must print a letter when a key is struck, and it must have a device by which the paper may be moved a short distance to the left with each stroke in order that the letters may be printed separately, not one on top of the other. Of the many subsidiary appliances that are fitted a bell to warn the operator that he is approaching the end of a line, a lock to prevent the machine from working after the end of the line has been passed, attachments for facilitating insertion of fresh paper, corrections, and tabulation, &c.some are certainly of advan- tage, but others are more useful to the manufacturer in drawing up his advertisements than to the expert operator, whose first care often is to disconnect them from " visible writing," which is some- times put forward as a recommendation of extraordinary importance; doubtless the novice who is learning the keyboard finds a natural satisfaction in being able to see at a glance that he has struck the key he was aiming at, but to the practised operator it is not a matter of great moment whether the writing is always in view or whether it is only to be seen by moving the carriage, for he should as little need to test the accuracy of his performance by constant inspec- tion as the piano-player needs to look at the notes to discover whether he has struck the right ones. The one important desid- eratum, without which no type- writer can produce work of satisfactory appearance, is ac- curacy of alignment. For the attainment of this the use of type-bars has given wide scope to the ingenuity of inventors, who have been confronted with the problem of making a system of levers at once strong, rigid Machine. them on bearings which are steady and adjustable for wear in conditions where space is much restricted. In the Oliver machine the type-bar is of the form shown in fig. r, to secure stiffness and a double bearing. In the Bar-Lock, the type-bars are arranged three in one hanger, so that each has a bearingthree times as wide as would be possible in the same space if each had a hanger to itself (fig. 2) ; in addition the wear of the pivots can be taken up by the screws seen on the right of the bearings, and as a further P precaution each type-bar is locked at the printing point by falling between a pair of conical pins, which centre it exactly in the required place. In the Yost and the Empire the type-bars pass through guides. The centre guide of the former is shown at G in fig. 3, the type being just about to strike the paper. Pressure on one of the keys works the lever and pushes up the FIG. 3 Central connecting-rod C, when the type leaves Guide and Type-bar of the ink-pad P and passes through the Yost Machine. guide, which is slightly bevelled so as to guide it exactly to the printing point. In the Smith Premier the shafts upon which the type- bars swing are mounted tangentially on the ring (fig. 4), so that long supporting bearings are obtained, while the shortness of the type-bars themselves renders it possible to make them very stiff. The rocking-shaft mechan- ism a (fig. 5), by which the power is transmitted from the keys to the type-bars, admits of each key having the same leverage and tends to uniformity of touch . This last quality is also aimed at by inter-posing an intermediate parallel bar between the key levers and the type-bar, as in the New Century Caligraph. In the Dens-more the friction of the movements is minimized by the employment of ball bearings for the type-bar pivots. Electrical type-writers, in which the depression of a key does not 1 work a type-bar directly, but merely closes a circuit that energizes an electro-magnet, have been sug- FIG, 5.-Rocking-shaft Mechanism of gested as a means of Smith Premier. obtaining uniformity of I, Key with stem. 2, Rocking shaft. touch combined with ease3, Connectingrod. 4. TYPe;bar, and rapidity, but have not as yet displaced the A and B, Conical bearings, If, in. apart. ordinary machines to any extent. One special form of typewriter, the Elliott-Fisher, is designed to write in a book such as a ledger. One leaf is clamped between the platen and an open frame which holds the paper smoothly. The operative parts slide on this frame, and move up and down the page so as to space the lines properly, the keyboard, with the type-bars, ribbon, &c., travelling step by step across the page. An adding device may be combined with this machine. Machine. End of Article: TYPEWRITER If you wish, you can link directly to this article.
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