US2548835A - Telegraph key - Google Patents

Description

April l0, 1951 H. J. H. wAssELl.

TELEGRAPH KEY Filed Nov. l, 1946 EEE y I uNvENToR ATTORNEY Patented Apr. 10, 1951 TELEGRAPH KEY Harold Joseph Hughes Wassell, Danbury, England, assignor, .by mesne assignments, to Radio Corporation of America, New York, N. Y., a corporation of Delaware Application November 1, 1946, Serial No. 707,174 In Great Britain June 20, 1946 2 Claims. l

This invention relates to telegraph keys of the up and down type and has for its main object the provision of improved telegraph keys of this type of good feel or touch capable of use by skilled telegraphers for high speed accurate telegraphy with a minimum of fatigue and in which adjustment may be readily and accurately made by each individual operator to suit his own tastes.

Although a very large number of different `forms of up and down telegraph key have been used hitherto, there has been little or no attempt to ascertain and analyze the various fundamental operations in the process of hand keying, with the result that (in general) keys have been unnecessarily large and many of them have been far from satisfactory as .regards feeL and there is a long felt need for a small neat key which is capable of comfortable use at high speed by a skilled telegrapher and which shall vbe capable of rapid adjustment to suit his individual requirements. This need is especially urgent as regards keys for use in shipboard wireless telegraphy.

The quality and feel of a key depends, of

course, on its construction; but, owing to the Vagari-es of taste of dilferent telegraphers, it is impossible to produce a key which (without adjustment) will be equally pleasing to all operators. provid-e an improved key Whose construction is such that the feel or touch is good (as cornpared to known keys) and which provides a range of easily attained adjustments such as will enable said key to be adjusted to satisfy any skilled telegrapher.

According to the main feature of this invention, a telegraph key of the type referred to comprises means (including a handle vassociated with an indicator) for adjusting the return spring force of the key, and independent means (including a second handle and associated indicator) for adjusting the gap or play of the key. Preferably each said handle is a knob marked with indicator numbers or other indicia and is arranged to give the full range of its adjustment in approximately one rotation. With this arrangement a telegrapher, who has once experimentally adjusted his key to what he regards as the best adjustment, has only to note the indicia for these adjustments to be able to recover them instantly even if lost; for example, by dierent settings made by a preceding telegraph Watc keeper of different tastes.

Other important constructional features of the The present invention, therefore, seeks to invention are based upon a careful research into and analysis of the factors which arise in hand keying and (which has resulted, as will be seen later) in the provision 'of improved key constructions which satisfy, to a higher degree than hitherto, the onerous requirements of a comfortable key for high speed use.

The following sequence of operations takes place in manual keying:

1. The pressure of the -spring is overcome.

2. The mass of the -moving member is vaccelerated, the movement being essentially along the are of a circle.

3. The energy of the moving mass is dissipated as the forward Contact or stop is reached.

4. The mass of the moving member is accelerated in the reverse direction. This is mainly effected by the force of the return .spring though, in the case of some 'telegraphers the operator may provide a substantial amount of return force.

5. The energy of the moving mass is dissipated as the back contact is reached.

Now for high speed keying, `the keying cycle is quite short and, if the signalling is to be good, the transit time must be small relative to the half keying cycle. At thirty-five words per minute, the half keying cycle is about 1/28 of a second and the requirement as to transit time may be taken as .being not more than about 1/10 of the dot time i. e., about 1/280 of a second. Three factors are available for reducing transit time; namely (a) increasing .the force onthe key, (b) reducing the mass of the moving 'memben and (c) reducing the gap. Of these it is obvious that the force cannot be increased far, since this will involve rapid fatigue yof the `operator so that consideration of small transit time leads to the appreciation of the desirability of reducing the mass and (so far as is consistent with the .delicacy of touch of the telegrapher and the obtaining of clean contact make and break) reducing the gap. k

Another important factor which must be considered, especially as regards what happens when the key reaches its stops (items 3 and 5' of the foregoing sequence), is that of transverse vibrations in the key itself, The existence of such vibrations is a prime cause of bad feel in many known keys, though the fact has'not hitherto been appreciated. f Such vibrations tend. to cause .confusion to the telegrapher, especially if the natural period of the key for transverse vibrations is near the period of keymovement, as with many known keys it is. It is important therefore that this natural period shall be small in relation to the transit time-which again involves small mass and, so far as other considerations allow, a small length of key. A yet further reason for keeping the key mass small is that the amplitude of the vibrations is proportional to the weight per unit length of the key and to the fourth power of the length.

For the above reasons it is preferred, in carrying out the present invention, to make the key of aluminum or an aluminum alloy rather than of the more usual brass. Another advantage of aluminum lies in its greater deadness; i. e., the quality by which any vibrations set up are quickly damped out. The factor of deadness may be numerically indicated by the inverse of the specic acoustic resistance (the density of the material multiplied by the velocity of sound therein) which, for aluminum may be taken as 138x104 grams/sec. cm?, whereas for copper the figure is 316x104 and for steel 390x104.

For reasons corresponding to those underlying the selection of a natural period of transverse vibration well below the transit time, the natural period of oscillation of the key considered as a pendulum should lie well outside any transit time occurring in keying. The longest transit time likely to occur in practice is about 0.2 of a second (this corresponds to a keying speed of six words per minute) and the natural period of the key should be long compared to this.

The location of the stops or contacts and of the knob and bearings is of importance. When the key is operated the blow at impact (when the key reaches the stop) is applied to the compound pendulum constituted by the key. Itis, therefore, important; that the blow shall be struck as nearly as possible at the center of percussion of the key, otherwise complex Vibrations will be set up at the key pivots. The center of percussion of a key is not, in practice, very well defined but may, in practice, be regarded as lying within a fairly small area whose position depends upon the key design as a whole.

As regards comfortable movement of the hand in keying, experiment indicates that a radial distance of or 6" from pivot to knob probably gives the most comfortable arc of movement. This consideration alone leads to a large and cumbersome key but in practice, if the gap is kept small, a comfortable action can be obtained, in an up and down key, with a radius of about 3".

As regards construction as distinct from adjustment, the present invention is based upon a consideration of the factors set forth in the above analysis and provides an improved key of small size, neat and durable construction, and good feel in which the foregoing desiderata are achieved to a substantially fuller extent than hitherto.

According to an important feature of this invention, a telegraph key comprises a rigid key bar of not less than 21/2 inches long from bearing to knob and so dimensioned and constructed that its'natural frequency of transverse vibration is at least 1000 cycles per second and is preferably above- 4000 cycles per second.

Preferably the key bar is pivoted near one end and the up and down contacts or stops are arranged near the other end of the key bar with the knob between them, one being nearer the pivot than the knob and the other being further away.

Preferably, also, the key bar is of aluminum or aluminum alloy.

The invention is illustrated in the accompanying drawings which show a preferred form of key. Fig. 1 is an underneath plan view; Fig. 2 is a side view with the cover in position but showing the main parts of the key in dotted lines; Fig. 3 is a plan view of the key bar showing the knife edge pivots, spring and knob; Fig. 4 is a detail side View showing the gap adjustment; `Fig. 5 is an enlarged section showing the contact arrangement under the knob, and Fig. 6 is a schematic elevation showing the relative positions of the pivot, the return spring, the knob and the up and down stops or contacts. The dimensions can be ascertained from the drawings since Figs. 1 to 4 are all to the same scale which is indicated in usual fashion.

Referring to the drawings, the key therein shown comprises a rigid key bar i made of aluminum and pivotally mounted near one end by means of knife edges 2 arranged as shown at right angles to the length of the key bar. Spring return pressure is obtained by means of a coiled spring 3 whose end 4 hooks into a loop 5 mounted about half way along on the top of the key bar as shown. The spring 3 provides an upward return force which can be adjusted by the external knob G. As will be seen from Fig. l, the anchored end l of the spring 3 is fitted into a collar 8 which has a pin 9 which can engage any of a ring of holes in the side wall of the base I0. By pushing in the knob 6, the pin 9 can be brought clear of the side wall of the base whereupon rotation of the knob will adjust the tension of the spring. When the desired return force is obtained, the knob 6 is pulled out and the pin 9 engaged in the nearest hole to maintain the adjustment. The design is such that a full range of adjustment is given by one revolution of the knob 6 which is engraved with numbers which thus serve to indicate the spring adjustment.

At the knob end, the key bar has an upstanding screwed stem il on which is screwed a collar l2 with upstanding pins i3 adapted to engage in any opposite pair of holes i4 in a ring of holes provided in a knurled skirt I5 having a ring of numbers engraved thereon as shown in broken lines in Fig. 3. The skirt I5 is separate from the knob IE and has a clearance (not shown) with respect to the stem Hy on which the said knob is screwed.

The contacts whose general arrangement is best shown in the schematic Fig. 6 include a fixed bottom contact il carried by a strip i3 from' the base l0 (or a member attached thereto) and cooperating with a, contact i9 on the end of a strip 20 held by a screw 2i to the key bar i. The key bar I consists of two parts, la and ib, each of L section, held together at about the center of its length by rivets 22. The contact i9 is carried by the upper L section la. The other pair of contacts comprises a fixed contact 23 carried from the base plate I0 (or a member xed thereto) and a cooperating moving contact 24 on a strip 25 held by a screw 2t to the lower L section l b. The screwed stem H has a squared head 2l which is between the parts la, ib, the said stem passing through a hole in the section Ea. Floating distance rods 28, 20 pass through holes in the part l a and in the head 21 being diagonally positioned with respect to the said head. It will be seen that, by screwing down the collar i2 on the stem Il, so that the bottom of said collar presses on the tops of the distance rods 28, 29, the part Ib may be forced away from the part Ia at the knob end (against the natural spring of these parts), thus increasing the distance the key can move between a position in which contacts I1, I9 touch and a position in which contacts 23, 24 can touch.

This is so because contact I9 is carried by part Ia and contact 24 by part Ib, parts Ia and Ib being forced apart as collar I2 is screwed down.

The screwing down of the collar I2 is effected by the numerically engraved skirt I5. In practice, the knob I6 is slacked back or removed, the skirt I disengaged from the `pins I3 and the collar I2 unscrewed until a minimum gap, which can just be felt, is achieved. The skirt is then v engaged on the pins I3 so that one end of the circular scale of engraved numbers thereon comes opposite an index mark (not shown) on the cover 30 of the key. The knob I5 is then screwed down on to the skirt I5. By screwing down the skirt I5 from this position, the gap may be increased as desired, the positions of adjustment being indicated by the numbers on the skirt. The skirt I5 may be formed with a pointer or step (not shown) cooperating with a stop (not shown) on the cover so as to limit the gap adjustment to one revolution of the skirt, the design being such that this one revolution gives all the range of gap adjustment likely to be required.

The cover is held in position in any convenient way; e. g., by a bolt (not shown) having an external knurled knob 3! and passing through a hole 32 in the key bar into a retaining nut member or screwed hole on the base.

The various devices marked A are Condenser and other elements of an electrical lter provided to minimize sparking at the key contacts and consequent shock excitation of nearby radio apparatus. These elements, which are conveniently housed under the key cover 30, forrn no part of the present invention and need not be described herein. It will be noted, incidentally, that the key is practically totally enclosed and since the cover and base are of metal it is very well screened electrically.

The following are the leading particulars of an experimental key constructed and dimensioned as shown in the accompanying drawings:

Total weight, 1 pound, 3 ounces.

Weight of key bar (excluding pivot bar and knife edges), 2 ounces Length between pivot and knob, 3% inches Natural period of key bar regarded as pendulum,

0.57 second Natural frequency of key bar-transverse vibrations, 4200 cycles per second.

What is claimed is: 1. A telegraph key comprising a pivoted key bar formed from two longitudinal L section parts joined together to provide a single member, a return spring linked to said bar, said spring exerting an upward return force thereon, a spring tension adjustment member ooacting with said spring and provided with indicia for indicating the spring tension, two xed and two movable contacts controllable by said key, each of the two movable contacts being carried by a corresponding one of the longitudinal parts of said key bar and each being disposed adjacent a corresponding one of said xed contacts, and means associated with said longitudinal parts of said key bar for adjustably forcing apart the L section parts to adjust the spacing between the xed and movable contacts, said spring acting to urge said key bar in a direction to cause one of said movable contacts to engage its associated ixed Contact. k

2. A telegraph key, comprising a pivoted key bar, a knob mounted on said key bar, a skirt interposed between said key bar and said knob, said skirt being provided with indicia for indicating the contact spacing and being separable from and capable of being locked in an adjusted position of said knob, a return spring mechanically coupled to said bar, said spring exerting an upward return force thereon, a spring tension adjustment member coacting with said spring and provided with indicia for indicating the spring tension, two fixed and two movable contacts controllable by said key, the two movable contacts both being carried by said key bar and each thereof being ldisposed adjacent an associated fixed contact, and adjustable means coupled to said skirt and adjustable by said knob for changing the spacing between at least one of the fixed and its associated movable contact, said spring acting to urge said key bar in a direction to cause one of said movable contacts to engage its associated fixed contact.

HAROLD JOSEPH HUGHES WASSELL.

REFERENCES CITED The following references are of record in the` Number Name Date 329,399 Leggo Oct. 27, 1885 509,964 Steiner Dec. 5, 1893 568,103 Runkle Sept. 22, 1896 824,031 Kitsee June 19, 1906 1,589,709 Lowenstein June 22, 1926 2,290,982 Mayorquin July 28, 1942 FOREIGN PATENTS Number Country Date 115,787 Great Britain May 23, 1918

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