05/204042

04/23/1974

12/02/1971

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400/179

400/489, 199/18

B41J5/10; B41J5/12; B41J5/00; B41J5/30

197/4,9,11,15,19,20,98,99,100,101,102,103,104,180,186R,186A,186B 199/18

1100410		June 1914	Vogel
1753991	Keyboard operator	April 1930	Langford
1842883	Key controlled and power operated machine	January 1932	Swanson
2073115	Typesetting apparatus	March 1937	Mellinger et al.
2318519	Shorthand typewriting machine	May 1943	Palanque
2369807	Keyboard for typewriters or the like	February 1945	Solon

IBM Technical Disclosure Bulletin, "Plastic Keyboard Translator," C.C. Kling, Vol. 4 No. 12, May 1962, pp. 3,4..

Wright Jr., Ernest T.

Blum, Moscovitz, Friedman & Kaplan

What is claimed is

1. A keyboard actuating device for changing a keyboard layout comprising a unitary base member having first and second sides, a first plurality of fluid control means carried by said base member on said first side thereof for manual operation, a second plurality of fluid control means carried by said base member on said second side thereof for operating the keys of a keyboard, said base member, first fluid control means and second fluid control means defining an assembly, and fluid containing passages in said assembly communicating between said first and second fluid control means, said first fluid control means having a normal position extended with respect to said base member, said second fluid control means having a normal position retracted with respet to said base member, each of said first fluid control means being operable to a retracted position with respect to said base member for extending an associated one of said second fluid control means through one of said passages.

2. An actuating device as claimed in claim 1 wherein said base member comprises a plurality of sheets of material fastened together in fluid-tight relationship, said passages in said assembly including grooves in the surface of at least one of said sheets of material, said grooves being closed by another of said sheets of material.

3. An actuating device as claimed in claim 1 wherein at least one of said fluid control means comprises a plurality of pneumatic cells formed as an integral part of a sheet of flexible material.

4. An actuating device as claimed in claim 1 wherein at least one of said fluid control means comprises at least one piston and an associated passage includes means defining a cylinder for slidably receiving said piston.

5. An actuating device as claimed in claim 1 wherein said fluid containing passages are formed as part of said fluid control means.

6. An actuating device as claimed in claim 3 wherein said base member comprises a sheet of material, said passages in said base member including grooves in the surface of said sheet of material, said grooves being closed in fluid tight relationship at least partly by said sheet of flexible material.

7. An actuating device as claimed in claim 2 wherein grooves are provided in the surfaces of at least two sheets of material.

8. An actuating device as claimed in claim 1 wherein the end of a groove in one sheet of material is in communication with the end of a groove in another sheet of material.

9. An actuating device as claimed in claim 3 wherein at least one of said pneumatic cells is in the form of a collapsible bellows.

10. An actuating device as claimed in claim 1 wherein said first and second sides lie in spaced parallel planes.

11. An actuating device as claimed in claim 1 wherein said base member is substantially rigid.

12. An actuating device as claimed in claim 1 wherein said passages in said assembly include grooves in the surfaces of said first and second sides, at least one groove in one side crossing at least one groove in the other side.

13. An actuating device as claimed in claim 1 wherein said assembly has a substantially low profile.

14. An actuating device as claimed in claim 1 wherein said passages in said assembly include grooves in the surfaces of said first and second sides with an end of a groove in one side being in communication with an end of a groove in the other side.

BACKGROUND OF THE INVENTION

Suspicion of faulty design is always justified whenever a machine or an instrument is difficult to learn and operate.

Typewriting is today a time-consuming subject in any educational program on any level. Between two and three full years -- often more -- are needed for the rather low degree of mastery required in this subject.

There are errors on even the most common, simple words when typing is performed on today's typewriter. These errors result from an insufficient keyboard, as a hang-over from last century's layout. This is the only patch-work still preserved in an otherwise modern typewriter. This "universal" keyboard needlessly handicaps a substantial proporation of all ordinary typing. Actually, it uses no genuine home row, but places the typing mostly into an upper row of keys. In overburdens lesser fingers and leaves the left hand to an extent quite unrealized. It forces frequent idling of one hand while the other types entire words. It causes excessive and awkward finger motions that weaken the rhythm, tire the student, and mistreat his record with errors, silently blocking rapid progress.

Hitting wrong keys, a frequent mistake in typing on today's inefficient keyboard, has the most disastrous effect on efficiency, as continuity of rhythmic movements is disrupted. Effecting erasures requires many operations and wastes substantial time.

Continuing ignorance or disregard of motion and time studies as related to today's typewriter keyboard layout is inexcusable, as the benefit of an efficient layout would be great. The change to an efficient keyboard can now be accomplished with a small investment and at a smooth pace.

The Carnegie Foundation assigned Prof. August Dvorak, former director of research of the University of Washington, to do a study on typewriting. The result of his efforts was a simplified typewriter keyboard layout. Prof. Dvorak proved with exhaustive motion study, that a typist's finger tips travel up to 20 miles during a single shift of eight hours on today's typewriter keyboard. But the finger tips on the new, simplified keyboard layout travel only a single mile doing the same job with less effort and less errors.

The keyboard actuator, the object of this invention, will serve as a bridge for accepting the improved keyboard layout, as fear of acquiring skills that can't be utilized on the job is eliminated, because everyone can now own an inexpensive, portable keyboard actuator with an efficient layout that fits on the top of typewriters equipped with today's keyboard layout.

The electronic age puts an additional burden on the computer operator, graphic arts typesetter, etc., by doubling the number of keys on the typewriter-style computer input keyboard. The additional keys are necessary for computer instructions. The entire continuity of typing is disrupted whenever any of the computer-instruction keys is actuated, because of the distant location of these keys: the operator must 1) stop typing; 2) turn eyes from copy to the keyboard; 3) visually lead hand from the letter-key part of the keyboard to the keys for computer instructions that occupy a separate cluster on the outside perimeter of the keyboard; 4) search and select the particular key to be actuated; 5) press the key; 6) visually guide the hand back to the home row of the keyboard; 7) re-direct eyes from keyboard to copy and 8) search for the spot where typing was discontinued.

Computer-input typing is an endless stop-and-go operation, because of the very frequent use of the additional set of keys located out of reach of the fingers which must be visually guided. This mode of typing not only slows down operation, but induces frequent mistakes just like any other distraction. Every one of these keys must be searched for and selected in a maze of some three dozen keys with the speed of a child tapping keys of a typewriter with a single finger.

More keys can be operated with the touch-type method by using the concave arrangement of keys, than on today's typewriter keyboard, because the concave layout brings the finger tips to the immediate vicinity of all keys without a need for reach, as the top of the keys describe exactly the same curve in frontal direction as the fingers turn when the fulcrum of the arc is in the middle joint of the fingers: just a small change in angle in this joint brings the finger tips from the keys of one row to the next. This way up to seven rows of keys can be actuated while the arms remain perfectly still, assuring a more precise operation than typing on today's 4-row keyboard with the stairway-style layout despite the additional keys of the former keyboard. The three additional rows of keys laid out together with the four rows of the letter keys in a double-arcuate fashion can serve the computer instructions. This way both the letter-key part of the typewriter, and also the computer-instruction keys can be comfortably actuated with a 100 percent touch-type method minimizing the error rate while maximizing speed.

Today's computer is capable of a million single tasks in a second. In comparison, man's capacity is only about a half-a-dozen units within the same time interval. Speeding up man's output just a few per cent would benefit efficiency more than if the computer would work twice the speed of a million bits a second, as the ultimate output depends upon the slowest unit of work in the operation.

The bottleneck caused by man's inefficiency in computer keyboard input is best illustrated by the article of the Graphic Arts Magazine of March, 1971: "Many who had been overawed by the productive capacity of the electronic wizard, had come to view it more soberly as they discovered, that the input requirements were more than 100 times greater than the output speed. The decreased need for manpower on the output end concerns us most, because we represent people at that end. Because of this flagrant disparity of speed, untold numbers of computers are currently sitting idle . . . "

The official organ of the British Computer Society sounds similar concern about the mis-match of man to machine: "With the development of sophisticated electronic equipment, the role of man as a machine partner has become extremely critical... This time is rapidly approaching when efficiency of manpower will determine the role of graphic consoles.... Digital input is the critical part of the job, where improvement can be achieved. This means, that the task of the operator must be simplified."

Every typist moves his hands and arms more or less during typing, despite the warning of the most authoritative books on this subject. On page 111 of "Philosophy and Psychology of Teaching Typewriting," Prof. A. R. Russon and S. J. Wanous write: "An important aid in typewriting is the centering of the action in the fingers and the consequent avoiding of action in the hands or the arms." The purpose of this warning is obvious: the probability of losing the area orientation of finger tips with respect to the location of keys increases with the extent of arm motions, as the fulcrum of movement slips from the knuckle joints to the elbow and shoulder joints.

The arm movements during typing are inevitable on today's typewriter keyboard except for people with very long fingers. The majority of persons with average, but especially with short fingers, must move their arms whenever they want to reach the top row of keys. The double-arcuate layout of the keys, an object of this invention, eliminates the arm reaches to the keys entirely: a slight turn of 20 degrees in the middle joints of the fingers brings the finger tips from one transverse key-row to the next one, because the key tops in this invention are arranged in the same curve as the human fingers move, using the middle joints of the fingers as the fulcrum. Only depressing of the key is necessary after the slight change of the finger angle is accomplished. There is no actual arm movement necessary, as the finger tips are always in a very close relation with the key tops, both following exactly the same curve. The shortest distance between the two keys is an arc in this instance.

Besides typewriters, there are numerous devices like "Linotype" machines, data processing equipment, pianos and the like that are keyboard controlled with a plurality of keys being provided for operating the particular apparatus.

SUMMARY OF THE INVENTION

Generally speaking, in accordance with the invention, keyboard actuators are disclosed which allow for improved keyboard layouts. One embodiment discloses a keyboard actuator which can be mounted on a typewriter having a standard keyboard layout so as to completely revise the layout. Actuating members utilize fluid pressure to transmit the actuation on the actuator to the keyboard. With such an arrangement a keyboard with a fixed layout can be operated with a keyboard actuator that has an entirely different layout without physically modifying the business machine. The standard typewriter keyboard layout can be used instantly just by lifting the keyboard actuator from the typewriter keyboard.

In another embodiment, the actuating elements may be positioned in an arcuate plane to place the actuators in positions more easily accessible to the operator's fingers to thereby reduce fatigue and minimize mistakes. Means may also be provided for supporting the operator's hand in a desired position to further minimize errors.

Accordingly, it is the object of this invention to provide an improved keyboard.

Another object of this invention is to provide an improved keyboard actuator in which the manually operable actuating elements are positioned for improved digital accessibility.

A further object of the invention is to provide an improved keyboard actuator which reduces fatigue and increases accuracy of the operator.

Still another object of the invention is to provide an improved keyboard actuator having means for locating and supporting the hand of the operator.

Still other objects and advantages of the invention will in part be obvious and will in part be apparent from the specification and drawing.

The invention accordingly comprises the features of construction, combinations of elements, and arrangement of parts which will be exemplified in the constructions hereinafter set forth, and the scope of the invention will be indicated in the claims.

BRIEF DESCRIPTION OF THE DRAWING

For a fuller understanding of the invention, reference is had to the following description taken in connection with the accompanying drawing, in which:

FIG. 1 is a perspective, exploded view of a keyboard adapter constructed in accordance with a preferred embodiment of the instant invention shown in position for mounting in operative engagement with the standard keyboard of a typewriter;

FIG. 2 is a partial sectional view of the keyboard adapter of FIG. 1 in operative engagement with a typewriter key;

FIG. 3 is a partial sectional view of an alternate construction of the FIG. 2 mechanism;

FIG. 4 is a partial cross sectional view of another embodiment of a keyboard actuator; and

FIG. 5 is a partial cross sectional view of a further embodiment of a keyboard actuator.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to FIGS. 1 and 2, a typewriter indicated generally at 11 is an example of a typical type of keyboard operated machine. The typewriter 11 includes a keyboard plate 12 through which extends a plurality of keys 13, each key actuating a key lever 14 located within the typewriter housing. Mounting blocks 15 for the keyboard actuator 16 are carried by the keyboard plate 12.

The keyboard actuator is indicated generally at 16 and, in the embodiment of FIGS. 1 and 2, consists of a laminate of five individual sheets or plates. First sheet 17 is provided with a plurality of apertures 18 with a flexible bellows 19 being carried by the first sheet 17 in communication with a respective aperture 18. Second sheet 21 carries a plurality of grooves 22 of predetermined configuration in communication with a respective one of apertures 18 on the top side of second sheet 21 and exposed at the bottom surface of second sheet 21. A third sheet 23 underlies second sheet 21 and is provided with a plurality of apertures 24 for communicating with respective grooves 22. Except where an aperture 24 communicates with a groove 22, the exposed portions of grooves 22 are otherwise sealed by third sheet 23.

A fourth sheet 25 carries a plurality of grooves 26 exposed on the top side thereof and sealed by third sheet 23 except where a groove 26 communicates with an aperture 24. One the bottom side of fourth sheet 25, the groove 26 communicates through the bottom surface of fourth sheet 25. A fifth sheet 27 underlies fourth sheet 25 and is provided with apertures 28 with each aperture 28 communicating with a groove 26. Depending from fifth sheet 27 are a plurality of flexible bellows 29 whose interiors communicate with apertures 28. As best seen in FIG. 2, in normal position, bellows 29 is collapsed while bellows 19 is expanded.

Bellows 29 is in engagement with key 13 of the typewriter keyboard. Depression of flexible bellows 19 causes fluid transfer through the keyboard actuator 16 by means of the aforesaid grooves 22, 26 and apertures 18, 24, 28 to flexible bellows 29 to thereby expand the flexible bellows 29 and depress key 13 to the phantom line position shown in FIG. 2. Such depression of the key 13 actuates the typewriter 11. When bellows 19 is released, the assembly will return to the FIG. 2 position.

By proper selection of the configurations of grooves 22 and 26 and the locations of apertures 18, 24, 28 all the keys 13 on typewriter 11 may be effectively repositioned to change the keyboard layout to any desired layout. Thus, if it is desired to change the keyboard layout of an existing business machine, it is merely necessary to mount thereto a keyboard actuator 16 in which the flexible bellows 19 are in the desired positions and are connected, through the fluid passages, to the flexible bellows 29 which are in contact with the keys 13 of the business machine.

An alternate arrangement of a keyboard actuator is shown in FIG. 3. The actuator is indicated generally at 31 and is composed of an intermediate plate 32, an upper plate 33 and a lower plate 34. A passage 35 in the intermediate plate 32 includes spaced walls 36 with the spaced walls 36 and walls of the passage 35 defining a pair of spaced cylinders in which are mounted plungers 37 and 38. Plunger 37 has a piston-like end 39 and plunger 38 has a piston-like end 41, such ends 39, 41 riding in the cylinders defined by the walls of passage 35 and spaced walls 36. A spring 42 acting between lower plate 34 and plunger 37 biases the plunger 37 to the upward position.

Actuator 31 may be mounted on the keyboard of any keyboard operated machine with the number of pairs of plungers 37, 38 being equal to the number of keys 13 on the keyboard. One key 13 is shown in FIG. 3 with plunger 38 in operative engagement with the key 13. Manual depression of plunger 37 causes a compression of fluid in passage 35 thereby applying fluid pressure to the piston-like end 41 of plunger 38 to thereby advance plunger 38 against key 13 to effect operation of key 13. The normal return biasing of key 13 as well as the return biasing of plunger 37 by means of spring 42 will cause plungers 37 and 38 to return to the normal position as shown in FIG. 3 when manual depression of plunger 37 is released.

By preselected placement of passages 35 and plungers 37 and 38, a keyboard layout may be redesigned to any preselected layout.

The above described embodiments disclose two forms of keyboard actuators 16, 31 utilizing fluid pressure for transfer of motion. In one embodiment, depression of an expanded bellows 19 causes expansion of a compressed bellows 29. In the other embodiment, depression of a plunger 37 riding in a cylinder causes a second plunger 38 riding in a second cylinder to be advanced. Any combination of the above two actuator forms can be employed on the same actuator. In both embodiments, the operative elements are inter-connected in fluid-tight relationship. By utilizing fluid transfer as the means for transferring motion, any desired keyboard layout can be utilized as no complex mechanical transfer linkages are required. The embodiment of FIGS. 1 and 2 has considerable versatility and is especially suitable for repositioning a layout of a large number of keys in a keyboard.

The above described embodiments disclose a keyboard actuator 16, 31 having its operating elements or plungers 29, 38 in a single plane in the same manner that the keys 13 of the keyboard generally lie in a single plane. However, it has been found that a large error rate and much of the fatigue experienced by keyboard operators results from the stairway-style keyboard layout common to keyboard machines. The provision of a hand guide in combination with an arcuate arrangement of the finger engagement surfaces of bellows can minimize accidental finger displacement.

Referring to FIG. 4, an acutator 51 in which the operating bellows are located in a curved plane is depicted. The actuator, indicated generally at 51 is of the five sheet construction similar to that described in connection with FIG. 2. The third, fourth and fifth sheets 23, 25 and 27 respectively are generally similar to the third, fourth and fifth sheets 23, 25 and 27 respectively of the FIG. 2 embodiment. However, second sheet 52 has a planar bottom surface and an arcuate top surface with the arcuate top surface of second sheet 52 being covered by arcuate first sheet 53. A plurality of flexible bellows 54 are carried by first sheet 53 and communicate through grooves and apertures 60 with flexible bellows 29 carried by the fifth sheet 27.

A hand rest and alignment guide 55 is carried by second sheet 52. A mounting member 56 is also secured to second sheet 52. A tube 57 has one end mounted in the mounting member 56 by means of a ball joint 58. A rod 59 is slidably mounted in tube 57 with its position being adjustable through set screw 61. The upper end of rod 59 carries a hand rest 62 on which the hand 63 of the operator may rest. The fingers of the operator are shown positioned above the flexible bellows 54. By swiveling of tube 57 through ball joint 58 and by height adjustment of hand rest 62, the position of hand rest 62 may be located to permit all flexible bellows 54 to be reached by the fingers of the operator's hand 63 without moving the forearms, no matter how long or short his fingers are. As shown in FIG. 4, the small finger of the left hand has one of the flexible bellows 54 in depressed condition. The small finger controls all of the flexible bellows 54 in the disclosed row with the other fingers controlling flexible bellows 54 in adjacent rows. With the hand resting on hand rest 62, the operator can reach all key tops from row to row just by bending his fingers in the middle joint without changing the position of the hand 63 and arm. The hand rest 62 acts as a guide or area locator for the hand 63 with respect to the keys or bellows 54 of the keyboard, increasing accuracy. It is understood that the hand rest 62 extends along the entire length of the keyboard actuator 51, supporting both hands.

A flexible feeler 64 may be carried by first sheet 53 to provide means for the operator to "feel" the position of his fingers with respect to the rows of bellows 54. Feeler 64 may be formed of a sheet of flexible plastic material extending transversely of the disclosed row of bellows 54 with the sheet being cut to define individual fingers 64' which may be deflected so as not to prevent ready access to the bellows 54 furthest from hand rest 55.

A further form of actuator is shown in FIG. 5 and is generally indicated at 65. For simplicity, only the first 67 and second 66 sheets have been indicated. The second sheet or plate is identified as 66 and the first sheet 67 is formed integrally with flexible bellows 71 through 75 and 81 through 85. The bellows 71-75 and 81-85 communicate with remote locations through passages 86 and/or grooves 87. In contrast with FIG. 4 where grooves 60 defining fluid containing passages are in lower plate 51, the grooves 87 in FIG. 5 are formed in the flexible upper plate 67.

Actuator 65 discloses a completely new configuration in which the bellows 71-75 on the left hand side would be controlled by the operator's left hand and the bellows 81-85 on the right hand side would be controlled by the operator's right hand. Behind each of the disclosed bellows 71-75 and 81-85 would be rows of additional bellows. Bellows 71 is operated by the small finger of the left hand, bellows 72 is operated by the ring finger of the left hnd, bellows 73 is operated by the middle finger of the left hand, bellows 74 and 75 are operated by the index finger of the left hand. The effective height of a bellows 71-75 in its uncompressed condition is different with respect to adjacent bellows 71-75 to accommodate the different finger lengths on the fingers of each hand. Finger engagement surfaces 88 of bellows 71-75 and 81-85 designated to be activated by shorter fingers are located on a concave arc having a smaller diameter than the bellows 71-75 and 81-85 to be depressed by longer fingers, because short fingers describe a smaller arc, using the middle-phalanx joint as its fulcrum. This multi-level curved layout brings the finger engagement surfaces 88 of the bellows 71-75 and 81-85 to the immediate vicinity of shorter fingers, compensating for the difference with the longer fingers. This mode of operating is comfortable for all fingers. In contrast, the long fingers must be forcibly held higher whenever the short fingers are in action on today's flat typewriter keyboard layout, to avoid accidental actuation. While the bellows 71 through 75 lie in a general plane inclined to one side of the vertical and the bellows 81 through 85 lie in a general plane inclined to the other side of the vertical, the plane including the finger engagement surfaces 88 of the bellows on each side is generally curved. In such manner, the fingers of the operator in a normal rest position are automatically juxtaposed in comfortable relationship to the bellows 71-75 and 81-85 which they operate.

The actuator 65 of FIG. 5 can either be in the form of an adapter for a standard keyboard machine or can be constructed as an integral part of a machine which is operated as the result of depression of levers in which the multiple bellows 71-75 and 81-85 act as the keys to operate the type bars and escapement. The layout and the configuration of the actuating bellows 71-75 and 81-85 closed in FIG. 5 provides for optimum comfort and minimum fatigue as, in order to operate the bellows 71-75 and 81-85 the hands are held with the palm on a vertically slanted angle that complies with the anatomical structure of the human hand. In order to turn the palm down to the typing position, one of the long bones of the forearm rotates, so that it crosses diagonally over the second forearm bone, requiring extra muscular effort.

The constant and unnecessary use of the muscular energy to hold the hands in an awkward horizontal position contributes to the fatigue of the typist, just like the finger of telegraph operators is often afflicted with cramps when operating on the Morse code machine with the palm in horizontal level. By changing the tapping motions from the vertical to a lateral direction with the palm in substantially vertical plane, the cramps disappear, enhancing the efficiency of the operator at the same time ("A Study of Telegrapher's Cramp," Industrial Fatigue Research Board, Report 43).

While the key tops 88 on FIG. 5 describe an open curve for the fingers of each hand in a transverse, left-to-right direction, the key tops 88 also describe an open arch in a frontal direction, as seen in FIG. 4.

The transverse curve-arrangement of the bellows forming the keys 71-75 and 81-85 in FIG. 5 makes up for the difference in the length of individual fingers; the longer keys 71-75 and 81-85 are assigned for the short fingers to prevent any cramped, unnatural posture of the long fingers whenever the short fingers despress the keys, that is inevitable on today's typewriter keyboard with all keys built to the same height on the same row.

The frontal arch of the key tops shown in FIG. 4 enables the typist to reach all rows of keys of the keyboard just by changing the angle of the finger in the finger's middle joint, contrary to the stairway-style layout of today's keyboard, where the typist must move the hand and the entire arm to reach the top row. The arch of the key tops is smaller for the shorter fingers, as these fingers describe a smaller curve. All above designs are made with consideration to the anatomical measurements of the human fingers, eliminating the need for special, time-consuming finger exercises necessary on today's keyboard that forces the hand to adapt to the rigid layout. The keyboard adaptor instead adapts the structure of the keyboard to the anatomy of the human hand.

The key bars of the first typewriter keyboards were made out of wooden slats, which made necessary a simple and direct type of construction to eliminate bends and complicated structures. For this reason they had to be laid out in a staggered, diagonal cross-pattern, or else they would interfere with each other. This primitive layout is still incorporated in today's keyboard. It fits the right hand, but forces the clumsier left hand in an unnatural position which defies all anatomical realities of the human hand.

The wrist joint of the left hand must make a sharp 40 degree twist toward the left side to conform with the staggered key layout of the keyboard. The action of the hand and fingers is considerably affected by such a distortion of the wrist, because the tendons attached to the bones of the hand and fingers pass under the wrist and continue into the long muscles of the forearm. This way the muscles must overcome the sharp bend of the tendons in the contorted wrist every time a key is activated. Even small amounts of strain when multiplied with every key stroke of the finger cause physical fatigue, that eventually becomes a mental fatigue with resulting errors.

Typing can be made easier by creating two banks of keys in a convergent layout: vertical rows of keys of one bank to be actuated with the left hand has keys arranged in a staggered fashion sloping upward toward the right side, the other bank of keys assigned for the right hand leans toward the left side. This arrangement of keys allows an effortless operation, because the hands and fingers run parallel with the forearm, enabling to exert the most efficient muscle action with the tendons in a perfectly straight line.

It will thus be seen that the objects set forth above, and those made apparent from the preceding description, are efficiently attained and, since certain changes may be made in the above constructions without departing from the spirit and scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawing shall be interpreted as illustrative and not in a limiting sense.

It is also to be understood that the following claims are intended to cover all of the generic and specific features of the invention herein described, and all statements of the scope of the invention which, as a matter of language, might be said to fall therebetween.