US2796966A - Type element driving mechanism - Google Patents

Description

June 25, 1957 Filed Sept. 8, 1953 T. H. TOEPPEN TYPE ELEMENT DRIVING MECHANISM 2 Sheets-Sheet l I IATENTOR. THURSTON H. TOEPPEN June 1957 T. H. TOEPPEN TYPE ELEMENT DRIVING MECHANISM Filed Sept. 8, 195

2 SheetsSheet 2 L VEN TOR.

THURSTON H.TOEPPEN "Hubs ATTORNEY United States Patent TYPE ELEMENT DRIVING MECHANISM Thurston H. Toeppen, Hyde Park, N. Y., assignor to International Business Machines Corporation, New York, N. Y., a corporation of New York Application September 8, 1953, Serial No. 378,724

21 Claims. (Cl. 197-417) This invention relates to typewriters and, more particularly, to an improved type bar actuating and impression control mechanism for a power driven typewriter.

It can be appreciated readily that, in order for a typed page to have the degree of perfection required in modern business, each of the typed characters should have the same color density or color shade regardless of the size of the characters, and regardless of whether it happens to be a lower-case or upper-case character.

It can also be appreciated that, as a matter of preference, the operator may desire to increase or decrease the color density of all characters as a .group, or to vary the penetration of the various type characters into the surface of the work, for example, in paper plate or wax stencil work.

Also in modern business installations, it is frequently necessary for a typist to produce, in one instance, a plurality of carbon copies, whereas in another instance, she may need only a single, original copy. It is well recognized that, other conditions being equal, the greater the number of carbon copies required, the greater the force which must be applied to each type bar in order to produce an impression of adequate color density on the last copy. At the other extreme, a very light striking force is employed to produce the shallow but uniform penetration which is desirable in the preparation of certain types of lithographic plates and wax stencils. In any case, it is desirable to maintain the highest possible degree of uniformity of penetration and/or color density at each impression level throughout a selected range.

To achieve this end, it is an object of this invention to provide an improved type bar actuating mechanism. Another object is to provide a type bar actuating mechanism which supplies not only a high degree of consistency of operation over a long period of useful life with a suflicient range of striking force to accommodate all types of work, but also a convenient means of varying the rorce.

If all type bars strike the work with equal force, the density of impression will vary inversely with the size of the character; that is, the same striking force which causes a large character such as the letter mfto print lightly will, when applied to a small character such as the cause it to print with excessive darkness. The prior art machines of this class have frequently been provided with adjustments which permit the striking force of each type bar to be set at any desired level so that the color density of the character on that type bar will match the color density of some reference character. This type of adjustment will hereinafter be called individual impression control.

In the prior art, it has also been common to provide means for increasing or decreasing the striking force of all type bars as a group by substantially equal amounts, in order to raise or lower the overall level of color density as desired by the operator. This type of adjustment will hereinafter be referred to as group impression control.

In order to demonstrate the need for other requirements of control, it is first necessary to consider how the color densities of large and small characters are differently affected by operation of the group control adjustment.

It has been shown that different striking forces are required in order to produce the same level of color density in characters of different sizes. In conventional machines, the striking forces are increased or decreased by substantially equal amounts as a result of operation of the group control mechanism. Consequently, the color density of the small characters is not changed in the same degree as the large characters. On the contrary, a small character will change color considerably more than a large one. In a typical example of the prior art, the characters m and can be initially adjusted .by means of the individual control so that they print with equal, median color density when the group control is at its central position. However, when the group control is advanced towards its maximum position, the will be much darker and may even be punching holes in the work at a point where the m is only moderately darker than before. On the other hand, when the group control is retracted towards its minimum position, the will be much lighter and may even fail to print at a point where the m is only moderately lighter than at the reference setting. As a result, the color densities of the various characters are uniform only at the reference setting, and go out of balance, or lose uniformity, at the upper and lower ends of the group control scale.

This is a fundamental problem, and has been dealt with in the prior art in two ways. In some cases, the impression range provided by the group control mechanism has been arbitrarily restricted to a rather small amount, so that the color densities of the various sizes of characters do not get conspicuously out of balance; as a result, the usable range is smaller than the desired range. In other cases, the design of the type is modified so as to increase the effective size of the smaller characters and reduce the effective size of the larger characters, thereby minimizing the diiferential between them. The most noticeable result of this approach is the use of abnormally large punctuation marks, and the consequent loss of typographic quality.

These limitations can be overcome .by providing a group control adjusting means which causes a change in the striking force of the type bar to vary in proportion to the area or size of each character involved, and it is a further object .of this invention to provide an improved structure for this purpose. This may be described as control of the rate of change of striking force, and it is hereinafter referred to as gradient control.

Another factor to be considered is the customary practice of placing two characters on the head of each type bar, either of which may be selected by the operator through the use of a shift mechanism of suitable design. The two characters are not ordinarily the same size; in most instances, the upper-case character is somewhat larger, but in many instances, it is smaller. In the prior art, it has usually been convenient to design the mechanism so that the same setting of the individual adjustment which produces a striking force of a certain magnitude for the lowercase character will, when the type bar is shifted, produce a slightly greater striking force, on the average, for the uppercase character on the same type bar. This provision is of benefit in most cases but is a serious handicap in those instances where the upper-case character is smaller than the lower-case character.

In the prior art, it has also been the practice to change the customary arrangement of the keyboardiin order to reduce the number of such instances to a minimum, but the conditions still represent a substantial limitation espe cially where freedom of choice in the keyboard arrangement is a significant consideration. In such instances, the practice has been to set the individual adjustment at some compromise position with respect to the requirements of the two characters involved, so that neither character has its optimum color density at the reference setting, one usually being too light and the other too dark, unless the relative importance of the two characters happens to be such that one or the other is exclusively favored.

This limitation can be overcome completely by, and it is a further object of this invention to provide an improved structure for, incorporating additional provi sions to supply a separate and independent set of individual and gradient control elements so that one set of control elements is operative in the upper-case condition only, and the other set operative in the lower-case condition only. When this is done, it then becomes practical to locate any character in any desired position without sacrifice of quality.

It is a still further object of this invention to provide anirnproved type bar actuating mechanism having a convenient externally adjustable individual control for regulating the striking force of the type bar in order to vary the color density of the printed Work.

It is a still further object of this invention to provide an improved arrangement of impression controls which are independently adjustable to determine the striking force of each type bar and are movable simultaneously to vary the striking force of all type bars as a group.

Still another object is to provide an improved mechanism which is adjustable to vary the striking force of each type bar in proportion to the area of the character typed.

Another object is to provide an improved mechanism which is adjustable to subject a type bar to different controls when typing upper and lower case characters.

It is a still further object of this invention to provide an improved construction in which the control elements for effecting a uniform color density of type bar imprint, or for effecting any other desired distribution of type bar striking forces, can be pre-assembled and pre-adjusted so as to reduce the cost of typewriter construction and adjustment. 7 p g It is yet another object of this invention to provide an improved power driven typewriter with a substantially wider usable range of uniform print density than has heretofore been available, and in which any character can be placed anywhere on the keyboard without sacrifice of quality. 7

Other objects of the invention will be pointed out in the following description and claims and illustrated in the accompanying drawings, which disclose, by way of example, the principle of the invention and the best mode, which has been contemplated, of applying that principle.

Briefly, this invention relates to an improved type bar actuating mechanism wherein the initial power impulse from a cam action is approximately equal for all type bars, but wherein a motion multiplying leverage shift takes place at a certain stage of the cam action to control the resulting extent of power driven lift of the type bar and its complementary free flight distance, thereby to effect a controlled striking force for each type bar, which striking force may be regulated to be proportional to the size of the type character and the class of work to be done.

In the drawings:

Fig. 1 is a side elevational view of an individual type bar and the mechanism utilized for its actuation.

Fig. 2 is a perspective view ofa cam support bar which is used to position control cams-whichregulate the extent of power drive during a print stroke.

Fig. 3 is a side elevation of a variety of control cams mounted on the cam support bar.

Referring to the drawing and more particularly to Fig. 1, a type bar 1 having the conventional upper and lower case type faces 2' is shown mounted for rotation about a pivot wire 3 and for engagement with a platen 4. The lower or lever arm 5 of the type bar 1 is connected through a link 6 to an actuating mechanism 7 which, in turn, is driven by a switch controlled continuously rotating power roll 3. A key bar or key lever 9 is operable to place the mechanism 7 in driven relation with the power roll 8 to effect a pull on link 6 and the subsequent rotation of the type bar 1 for a print stroke.

While the above and the following descriptions relate generally to only one type bar and its associated mechanism, it is to be understood that the same structure applies to all the type bars in a typewriter.

The actuating mechanism 7 comprises a cam lever or rockable member 10, a trip plate 11, a power cam or cam element 12, a control lever or portion 13 and suitable inter-connecting structure.

Cam lever 10 is mounted for angular motion about a pivot 14. Ascam lever 10 rotates clockwise, its outer arm 15, which is interconnected through link 6 to lever arm 5, exerts a pull on type bar 1 torotate it counterclockwise about pivot wire 3 toward platen 4; A retarding spring 16 maintains cam lever 10 normally in its rest position shown in Fig. l, and restores the cam lever 10 to its rest position after each type bar print stroke.

In order to effect the clockwise movement of cam lever 10 about its supporting pivot 14, power cam 12, which has a serrated peripheral or actuating surface 17, is mounted on a stub shaft 18, supported by control lever 13. An end of shaft 18 extends across an adjacent edge of cam lever 10 to provide a bearing surface whereby, when power roll 8 pushes on the serrated surface 17 of cam 12, shaft 18 simultaneously pushes on cam lever 10 to rotate it clockwise about its pivot 14.

Control lever 13 is mounted for rotation in a plane parallel to cam lever 10; Specifically, control lever 13 is rotatably mounted on a spindle or pivot 19 carried by cam lever 10. Then since shaft 18 is carried by control lever 13, and since an end of shaft 18 initially bears against an edge of cam lever 10, control lever 13 and cam lever 10' initially tend to rotate as a unit about pivot wire 14.

Control lever 13 is provided with a finger 20 which is displaced from spindle 19 at someconvenient distance. Finger 20 is positioned for engagement with the peripheral surface of a certain control stop or cam 21 in such a manner that when finger 20 engages the surface of control stop 21, further rotation of the control lever 13 about pivot 14 as a unit with cam lever 10 is blocked. This'engagement terminates the first stage of the driving cycle, during which the rise motion of power cam 12 has been applied directly to earn lever 10 through shaft 18. Thereafter, if the rise of cam 12 continues to urge shaft 18 away from the power roll, the point of engagement between finger 20 and stop 21 (hereinafter called check point A) becomes a new center of rotation for control lever 13. As soon as control lever 13 begins to rotate about check point A, it exerts a torque on cam lever 10 through spindle 19, to rotate cam lever 10 about its pivot wire 14. When thecenter of rotation of control lever 13 shifts from pivot 14 to check point A, the surface of cam lever 10 which had been in direct contact with shaft 18 becomes separated therefrom since cam lever 10 will move at a greater angular velocity after check point A has been reached. The amount of increase in angular velocity is a function of the inverse ratio of the radial distance between pivot 14 and spindle 19, to the radial distance between pivot 14 and shaft 18. In terms of its ultimate geometrical effect one unit of rise of power cam 12 has about twice as much effect on the type bar rise during the second driving stage as-during the first stage. The manner in which the relationship between the two driving stages is varied to control the striking force of the type bar will be described subsequently, v

Conditioning of actuating mechanism! Key lever 9 is mounted for pivotal movement about an arbor or fulcrum wire 22 in response to a pressure applied to a key button 23. The outer end of key bar 9 is supported in a guide comb 24 which is provided with individual springs 25 for restoring key bar 9 to its rest position (Fig. 1) after it has been depressed for a type bar print stroke.

Key bar 9 has an abutment or lug 26 and a ledge 27 positioned for engagement with actuating mechanism 7. More specifically, trip latch 11 which is mounted for pivotal movement about a stud 28, carried by cam lever 10, is provided with an ear 29 which, in its rest position, is held closely adjacent lug 26 by means of a restoring spring 30. Restoring spring 30 interconnects car 31 on cam lever 10 and car 31' on trip plate 11.

Trip lever 11 is provided remotely from stud 28 with an actuating surface 32, against which the abutting surface 33 of cam 12 is normally held by a cam restoring spring 34, which interconnects cam 12 with an ear 34' carried by cam lever 10.

With this structure, depression of key bar 9 permits lug 26 to act on shoulder 29 to pivot trip plate 11 about stud 28 whereupon actuating surface 32 pushes on abutting surface 33 of cam 12 to rotate the latter clockwise about its supporting shaft 18 until the serrated surface 17 comes into engagement with continuously rotating power roll 8.

The structure of actuating mechanism 7 is such that after a complete print stroke, which has heretofore been alluded to, spring 34 will have brought cam 12 back into its rest position (Fig. 1). The abutting surface 33 will then be in engagement with actuating surface 32 of the trip latch, but if key lever 9 is still depressed, then ear 29 will not return to its original position under lug 26. Instead, ear 29 will stop against ledge 27, whereupon pivot 28 moves forward in slot 35 extending spring 30 in the process. In this condition, lug 26 cannot act on ear 29 to rotate trip latch 11, consequently a second print stroke of that particular type bar cannot take place so long as the key bar is held depressed. Upon release of the key bar 9, however, the restoring spring 30 pulls trip latch 11 upwardly to the left until it is again positioned for contact with lug 26, whereupon subsequent depression of the key bar 9 will condition actuating mechanism 7 for another type bar print stroke.

Impression control Referring again to actuating mechanism 7, it has been pointed out that it not only rotates type bar 1 for a print stroke, but also, in combination with stop 21, controls the striking force with which type bar 1 contacts the platen.

In all cases, the type bar is driven positively up to some desired point, through the operation of the mechanism which has been described, after which cam surface 17 is separated from power roll 8 so that the type bar rise cycle is completed by means of the momentum which has been imparted to the moving parts, especially the head of the type bar.

The operation of the impression control mechanism can best be appreciated by considering in some detail the three basic stages of type bar rise which are involved: (1) direct cam drive, (2) indirect cam drive, (3) free flight. Of these, the first two accelerate the type bar to a height and velocity which are determined by the geometry and dynamic characteristics of the system; the third stage serves to fill in the remaining distance, during which the type bar velocity is reduced by the operation of retarding spring 16 and frictional forces. The total excursion of the type bar is the same in all cases, and consequently, the extent and duration of the third stage is, therefore, the complement of the first two stages.

In the mechanism here described, the final striking force of the type bar is determined by the duration of the first stage of the action which in turn controls the subsequent stages. During the first stage, as previously described, cam lever 10 and control lever 13 rotate as a unit about pivot 14 until finger 20 contacts stop 21 at check point A. As a result of this motion, type bar 1 is lifted by an amount which is directly proportional to the initial clearance between finger 20 and stop 21.

It also has been shown that during the second stage of operation, any further rise of cam surface 17 produces an amplified motion of cam lever 10, so that an additional rise of the type bar then takes place, which is substantially greater for each remaining unit of rise of power cam surface 17.

It, therefore, follows that if the total rise of cam surface 17 is utilized, such rise through suitable mechanism hereinafter described may be divided in any desired proportion between the first stage of operation and the second stage, and that the point of division is a function of the initial clearance between finger 20 and stop 21. This relationship will be clearer if two extreme cases are considered involving very large and very small clearances, as follows:

If this clearance (finger 20 to stop 21) is sufiicient to absorb the entire rise of cam surface 17, then the entire power-driven rise of the type bar is provided by the first-- stage condition, and none by the second stage. In this case, the type bar may be power driven to a minimum point as indicated schematically in Fig. 1 by the lower case letter a.

If, on the other hand, the initial clearance is reduced to zero, the first-stage condition is also reduced to zero, and the entire rise of the type bar is then produced by the amplified leverage of the second stage of operation. Consequently, the type bar rises much farther under power, toward the point indicated by the letter d.

By suitable choice of initial clearance, the division point between the first and second stages can be set wherever desired, so that the type bar can be driven to any desired intermediate level, such as those indicated in Fig. 1 by 5b,, c,

In any case, the time duration for the rise of cam surface 17 is substantially the same, because .the same cam surface or cycle is employed and the power roll surface speed is constant. However, it should be noted that the operation as described above takes into account only the geometry of the mechanical elements. Under actual operating conditions the masses and spring characteristics of the parts, in conjunction with the particular rotational speed of power roll 8, significantly influence the response of the mechanism, but do not change the basic pattern, in which the type bar tends to follow the cam action, as described, until the power driven portion of the cycle is complete. At this point, the driving force of the cam drops off, but the acceleration which has already been given to the type bar continues to carry it onward toward the platen. As the type bar goes into the third stage of its flight, cam 12 is lifted clear of the power roll and is snapped back into its rest position by spring 34. Also, for convenience in description, it has been assumed that the full rise of the power cam surface 17 is employed dur'mg the first and second stages of operation. In practice this not always the case, since the actual point of disconnection is determined by a complex combination of dynamic factors which may sometimes result in the cam being lifted off the power roll before its maximum lift has been delivered.

As a result of the sequence of events indicated above, the type bar is raised through stages 1 and 2 by means of the power derived from the rise of cam surface 17. At the close of stage 2, the type bar has achieved a certain height and velocity. From then on, it can only decelerate. The deceleration stage also supplements the control mechanisms of the first two stages in determining the final striking force of the type bar, because a type bar which is operating with a high power cut-off point will have a short deceleration distance and a-very heavy striking force, whereas the same type bar when operating with a low power cut-off point will have a long deceleration' distance which will tend tofurther reduce the final striking; force.

Individual control From the foregoing; it is evident that the final striking force of the type bar is basically determined; by the initial clearance existing between finger 2t) and stop 21, and that the striking force increases as the clearance decreases'and vice versa. It is, therefore, possible to pro duce any desired striking force for each type bar within the design limtis of the machineif' suitable means of establishing and varying the clearance are provided for each type bar. v

The final object is then twofold: (l) to compensate for those conditions which may tend to limit the range or degrade the quality of impression in work being done, (2) to permit the operator to select an impression level suited to the character of the work being done. These objects can be achieved by suitable design of the, adjustable cam stops 21 and the rotatable bar 36 on which they are mounted.

With a control cam 21 having a slope of constantly increasing radius such as that shown in Fig. 1, it follows that since the height to which a type bar is driven under power is inversely proportional to the at rest clearance between finger 20 and the surface of control cam 21, the striking force for any type bar is controlled byvarying the point of control cant 21 which engages finger 20.

In order to provide for the ready adjustment of earns 21, each cam is formed of a resilient material and in an arc of slightly greater than 180. The cam is provided with a number of radially inwardly extending fingers 21a which support the cam surface and which frictionally grip and hold the stop to the control bar. Control bar 36, in turn, has a plurality of transverse peripheral grooves 37 (see Fig. 2) which are arranged to position a control cam in alignment with each of the fingers 20 respectively. With this structure of the cam 21 and grooves 37, the cam can be rotated so that any point on its periphery, for example, points a through d (Fig. 1) can be aligned for contact with the finger 20. One of the fingers 21a of control cam 21 has a serrated surface or detent 21 which hooks into one of a plurality of longitudinal grooves 36' in bar 36.

With the construction of the parts described, it can be seen that the force with which a type head hits the platen is selectively variable for each key. That is, with reference to Fig. 1, it is possible to cut off the power stroke of the print character at a point a, for example, by setting control cam 21 so that point a engages finger 20.

.Likewise,-it is possible to cut otf the power stroke of' the print character In at the point at by setting control cam 21 so that point d engages finger 29. It follows that this improved type bar control permits the regnilation of the striking force for each type bar, and consequently, the level of color density or shade of each type character can be individually controlled by placing detent 21 in any one of the longitudinal grooves 36.

Group control While the above described individual control construction provides for selective control of uniform color density for each typed character under one set of conditions, it has been pointed out that the typist may wish to raise or lower the striking force of all the type characters as a group so that a greater force will be available for printing a plurality of carbon copies than that which she would use to print a single carbon copy or for preparing a plate or stencil which may require a very light impression. To efiect this group control, it is simply necessary to provide for the rotation of thecontrol cam support shaft 36 so as to increase or decrease the distance between all; of the. fingers 20 and. allot the control cams 21, at one time.

One typical mechanism for effectinga 'groupco'ntrol is shown in Fig. 2- wherein a crank arm 55' is secured for Gradient control At this point, reference'is' made tothe fact that changes in imprint force should be proportional to the areaof the printed character. change in color density, there should be a greater change in the imprint force of a largeletter such as the m thanthe change required for a small character such asthe It has been explained that through the use of the control cams 21 the rate of change in type barlift and-imprint force is controlled by the slope of the cam surf-ace (i. e. the distance'betweenfinger 20 and thesurface of cam 21 is thus controlled). It follows, therefore, that in orderfor the-imprint force change for a large character to be greater than the force change for a small character, a cam of greater slope should be employed for the large characters than that used for the small character. In practice, it has been found desirable to use three or four sets of cams, each having a different slope (see Fig. 3). In this manner, a control cam from one of the sets is chosen for each character soas toeffect a rate of change in imprint force substantially proportional to the area of the character to be printed; This is called gradient-control, because its effects the gradient of the striking force. Gradient control insures that when the typist selects the printing level she desires, regardless of whether it is light, medium 'or heavy, allof the type characters will print with substantially the same degree of color density, regardless of'their size.

Upper and lower case control It has been pointed out that one of the objects of this invention is to provide a uniform density contnol not only individually and collectively, but also for upper and lower case characters. It was mentioned, for example, that while many of the, upper case characters are, larger than the lower case characters, so as to call for a, certain greater impact force than that required for the lower case character, there is not. auniform ratio of character area between upper and lower case characters, and in some cases the ratio. is reversed. Consequently, any force multiplying factor that can be utilized to exert a, general increase in the. print force of the upper case letters would be detrimental to uniform, shade or color density particularly with respect to the characters usually located in the upper case positions on the type bars carrying the Arabic numerals.

It is apparent, therefore, that it is not sufficient to use only one set of control cams 21 to regulate individual control, group control a d gradient control. In this improved arrangement, the structure is such as to provide a uniform pressure of imprint for both upper and lower case characters irrespective of the relative sizes between the upper and lower case positioned characters. This uniform pressure is brought about by providing a second control cam 3'8'('Fig. 2) constructed similarly to control earns 21 for each of the actuating mechanisms 7'. Specifically, for each actuating mechanism 7, a second control cam 38 is positioned immediately adjacent the control cam 21 to permit the finger 20 normally to engage control. cam 21, but atthe time of basket shift-.-that is for upper case printing-the control camshaft 36' is shifted axially For example, to produce an equal-- so as to present the second cam 38 in position for engagement .with the finger of the actuating mechanism 7.

'Fig. 2 shows a preferred method of producing the axial shift in control shaft 20. Specifically, the control shaft 36 is axially movable by an axial pressure produced at its opposite ends. For example, one end 40 has an extension 41 for engagement with a bushing 42 which extends from the side wall of the typewriter. The opposite end 43 includes a notched collar 44 which engages a shaft 45. Shaft 36 is biased by a spring 46, which tends to urge extension 41 into the bushing 42. The construction of the notched collar 44 of the control cam shaft and its mounting shaft 45, is such as to permit rotation of the control cam shaft 36 about its axis while maintaining the bias in spring 46.

In order to control the axial position of shaft 36 and hence, which of the control cams is positioned for engagement with fingers '20, a bellcrank 48 is mounted on a spindle 49 (fixed to the side wall of the typewriter), for rotation in response to axial displacement of a connecting rod 50 which interconnects an arm 51 of the bellcrank 48 with the typewriter basket (not shown). The oppositearm or engaging arm 52 of the bellcrank 48 is provided with a shoulder 53 which is positioned in contact with a ledge 54 on control cam shaft 38. With this structure, when the shift key of the typewriter is depressed to lower the basket in a manner well-known in the art, shaft 50 is moved axially downward to rotate bellcrank 48 counterclockwise whereupon the shoulder 53 pushes on ledge 54 of control shaft 36 and moves it in opposition to the bias of spring 46, whereby the upper case control cam 38 is positioned for engagement with the finger 20 of control lever 13.

An incidental benefit derived from the construction of the shaft 36 and its mounting lies in the fact that all the control cams 21 and 38 can be pre-assembled on the shaft before installation in the typewriter. That is, once a setting for each control cam in a typewriter has been determined, the same setting can be used for any other similar machine in an assembly line. Accordingly, a subassembly may be used to reduce materially the cost of installation which now exists in conventional machines (in existing machines, the type bar drive control had to be set for each type bar after a machine had been assembled).

In summary, to overcome the objections of the past type bar actuating mechanisms, this improved structure has been provided in which the effective power cam rise is nearly the same regardless of the color density or shade of imprint which is to be produced. The initial response of the system is the same for all conditions, but after an optionally variable amount of motion at a basic rate, a leverage shifting factor is introduced which multiplies the amount of type bar motion produced by whatever amount of cam rise still remains. A simple, .but comprehensive combination of adjustments, has been provided which permits complete control of the color densities of all characters on the keyboard at all levels of impression.

While there have been shown and described and pointed out the fundamental novel features of the invention as applied to a preferred embodiment, it will be understood that various omissions and substitutions and changes in the form and details of the device illustrated and in its operation may be made by those skilled in the art without departing from the spirit of the invention. It is the intention, therefore, to be limited only as indicated by the scope of the following claims.

What is claimed is:

l. A power mechanism for typewriters and similar office machines comprising power driving means, a type bar, a rockable member mounted to drive said type bar to a printing position, a power unit for operating said rockable member, said power unit having an element ro- 10 tatably engageable with said power driving means for driving engagement with the latter, means for imparting an initial rotational movement to said element to engage it with said power driving means, a pair of adjustable control means positioned for selective engagement with'said power unit to vary respectively the degree of power driven operation of said rockable member, and means for selectively engaging said control means with said power unit.

2. In a power mechanism for typewriters and similar oflice machines comprising, in combination, power driving means, a type bar having a pair of type faces thereon, a shift device for selecting the type face on said type bar to be printed, and a rockable member mounted to drive said type bar to a printing position, a power unit for operating said rockable member, said power unit including an element rotatably engageable with said power driving means for driving engagement with the latter, means for imparting an initial rotational movement to said element to engage it with said power driving means, and a pair of adjustable control means positioned for selective engagement with said power unit in response to the operation of said shift device to vary respectively the degree of power driven operation of said rockable member.

3. In a power mechanism for typewriters and similar office machines comprising in combination, power driving means, a type bar having a pair of type faces thereon, a shift device for selecting the type face on said type bar to be printed, and a rockable member mounted to drive said type bar to a printing position, a power unit for operating said rockable member, said power unit including an element rotatably engageable with said power driving means for driving engagement with the latter, means for imparting an initial rotational movement to said element to engage it with said power driving means, means to restore said element after disengagement from said power driving means, and a pair of adjustable control means positioned for selective engagement with said power unit in response to the operation of said shift device to limit respectively the degree of power driven operation ofsaid rockable member.

4. A power mechanism for typewriters and similar ofiice machines 'comprisnig power driving means, a type bar, a rockable member mounted to drive said type bar to a printing position, a power unit for operating said rockable member having an element rotatably engageable with said power driving means for driving engagement with the latter, means for imparting an initial rotational movement to said element to engage it with said power driving means, means to restore said element after disengagement from said power driving means, and control means positioned for engagement with said power unit to vary the degree of power driven rotation of said rockable member, said control means comprising a control bar having an axis parallel to that of said power driving means and an adjustable control cam positioned on said control bar to partially encircle the same and to have one peripheral point at a time positioned for engagement with said power unit.

5. A power mechanism for typewriters and similar office machines comprising power driving means, a type bar, a rockable member mounted to drive said type bar to a printing position, a power unit for operating said rockable member, said power unit having an element rotatably engageable with said power driving means for driving engagernent with the latter, means for imparting an initial rotational movement to said element to engage it with said power driving means, means to restore said element after disengagement from said power driving means, and control means positioned for engagement with said power unit to vary the degree of power driven operation of said rockable member, said control means comprising a control bar having an axis parallel to that of said power driving means, an adjustable control cam positioned onv said control bar to partially encircle the same and to have one peripheral point at a time positioned for engagement with said power unit, and means for rotating said control be printed, and a rockable member mounted to drive saidtype bar to a printing position, a. power unit for operating said rockable member having an element rotatably engageable with said power roller for driving engagement with the latter, means to impart an initial rotational movement to said elements to engage it with said power roller, and control means positioned for engagement-with said power unit to vary the degree of power driven operation of said rockable member, said control means comprising a control bar having an axis parallel to that of said power roller, a pair of adjustable control cams juxtapositioned on said control bar for selective engagement with saidpower unit, and means interconnecting said control bar and said shift device to axially displace said control bar in response to the, operation of said shift device to select which of said control cams is engageable with said power unit.

7. In a power mechanism for typewriters and similar office machines comprising, in combination, power driving means, a type bar having a pair of type faces thereon, a shift device for selecting the type face: on said'type bar to be printed, and a rockable member mounted to drive said type bar to a printing position, a power unit for operating said rockable member, said power unit having an element rotatably engageable with said power driving means for driving engagement with the latter, means for imparting an initial rotational movement tosaid element to engage it with said power driving means, means to restore said element after disengagement from said power driving means, and control means positioned for engagement with said power unit to vary the degree of power. driven operation of said rockable member, said control means comprising a control bar having an axis parallel to that of said power driving means, a pair of adjustable control cams juxtapositioned on said control bar for se lective engagement with said power unit, means interconnecting said control bar and said shift device to axially displace said control bar in response to the operation: of said shift device to select which of said cams is engageable. with said power unit, and means to rotate said control bar to vary the section of said control cams positioned for contact with saidpower unit.

8. In a power mechanism for typewriters and similar ofiice machines comprising, in combination, power driving means, a type bar having a pair of type faces thereon, a shift device for selecting the type face on said type bar to be printed, and a rockable member mounted to drive said type bar to a printing position, a power unit for operating :said rockable member, said power unit having an element rotatably engageable with, said power driving means for driving engagement with the latter, means to impart an initial rotational movement to said element to engage it with said power 'driving means, and control means positioned for engagement with said power unitto vary the degree of power driven operation. of said rockable member, said control means comprising. a control bar, a pair of stop means. positioned on said control bar for engagement one, at a time with said power unit, and means interconnecting said shift device and said controlbar to select which of said stop means is engageable with said power unit.

9. In a power mechanism for typewriters and similar office machines comp-rising power driving means, a type bar having a type face thereon, and a. rockable member mounted; to drive said type bar to a printing position, a power unit for operating; said rockable member comprising an, element rotatably engageable withsaid power driving means for driving engagement with the latter,

12 means. to, impart an initial rotational movement to said element to engage it with said power driving means, and control means positioned for engagement with said power unit to-vary the degree, ofi power driven, operation of said rockabilemember, said'control means comprisinga control bar having an axis parallel to that. of said power driving means, and an adjustable control ca m positioned on said control bar to have one point at a time positioned for enrgagement with said power unit, said control cam having a slope rate commensurate with the area of said type face relative to the average area of all the type faces of said typewriter.

10. A power mechanism for typewriters and similar ofiice machinescomprisingpower driving means, a type bar, a rockable member mounted to drive. said type bar to a printing position, and a power unit for operating said rockabie member comprising a control portion pivoted on said rockable member, .a cam element pivoted onsaidv control portion and rotatable through a cycle for driving pivot being in direct driving relation with said rockable member to drive it at one rate until the pivotal movement of said control portion has been blocked, and control means engaged by said controlportion duringrthe. course of the rotation of said cam element by the power driving means to block the pivotal movement of said control portion thereby to vary the extent of direct drive between. said cam element pivot and said rockable member.

11. In a power mechanism for typewriters and similar office machines comprising, in combination, power driving means, a type bar having a pair of type faces thereon, a shift device forselecting the type face on said type to be printed, and a rockable member mounted to drive said type bar to a printing position, a power unit for operating said rockable member comprising a control portion pivoted on said rockable member, a cam element pivoted on said control portion and rotatable for driving relation with said powerdriving means, and control means engaged by said control portion during the course of rotation of said element by the power driving means for .varying the degree of power driven operation of said rockable member,.said control means comprising a control bar, a pair of stop meanspositioned on said control bar for engagement one at a time with said control portion, and means interconnecting-said shift device and said control bar to selectrwhich' of said stop means is engageable with said control portion.

12. In a power mechanism for typewriters and similar ofiice machines comprising power driving means, a type bar having a pair of type faces thereon, a. shift devicev for selecting the. type face on said; type bar to be printed, and a rockable member mounted to drive said type bar to a printing position, a power unitfor operating said rockable member comprising. a control portion pivoted on said rockable member, a cam. element pivoted. onsaid control portion and rotatable for driving relation with said power driving means,.said' cam element pivot being in direct driving relation with said rockable. member to drive it. atv one rate until the. pivotal movement of said control portion has been blocked, and control means engaged by said control portion during the course of the rotation of said element by. the power driving means'to block the pivotal movement of said control portionthereby to vary the extent of direct drive betweensaid cam element pivot and said rockable member, said: control means comprising a control bar, a pair of'stop means positioned on said control bar for engagement one at a time with saidcontrol portion, and means interconnecting said shift deviceand said control bar to select which of said stop means, respectively, is engageable with saidcon-- trol portion.

13. A power mechanism for typewriters and similar ofiice machines comprising a power roller, a typebar, a rockable member mounted to drive said type; bar to: a. printing-position, a power unit for operatingzsaid rockable: member comprising. a, control. portion pivoted: on the.

13 latter, a cam element eccentrically pivoted on said control portion and rotatable through a cycle for driving relation withsaid power roller, means to initially rotate said element until its smallest radius is gripped by said power roller, said cam element pivot being in direct driving relation with saidrockable member to drive it at one rate until the pivotal movement of said control portion has been blocked, and being in indirect driving relation with said rockable member to drive it at a greater rate after the pivotal movement of said control portion has been blocked, and control means positioned for engagement by said control portion to block the pivotal movement of said control portion thereby during the course of the rotation of said element by the power rolller to vary the extent of direct drive between said cam element pivot and said rockable member.

14. A power mechanism for typewriters and similar oflice machines comprising a power roller, a type bar, a rockable member mounted to drive said type bar to a printing position, and a power unit for operating said rockable member comprising a control portion pivoted on said rockable member, a cam element eccentrically pivoted on said control portion and rotatable for driving relation with said power roller, said cam element pivot being in direct driving relation with said rockable member to drive it at one rate until the pivotal movement of said control portion has been blocked, and being in indirect driving relation with said rockable member to drive it at a higher rate after the pivotal movement of said control portion has been blocked, and control means positioned for engagement by said control portion during the course of the rotation of said element by the power roller to block the pivotal movement of said control portion thereby to vary the extent of direct drive between said cam element pivot and said rockable member, said control means comprising a control bar having an axis parallel to that of said power roller, and an adjustable control cam positioned on said control bar to have one section at a time engageable with said control portion.

15. In a power mechanism for typewriters and similar ofiice machines comprising a power roller, a type bar having a pair of type faces thereon, a shift device for selecting the type face on said type bar to be printed, and a rockable member mounted to drive said type bar to a printing position, a power unit for operating said rockable member comprising a control portion pivoted on said rockable member, a cam element pivoted on said control portion and rotatable through a cycle for driving relation with said power roller, said cam element pivot being in direct driving relation with said rockable member to drive it at one rate until the pivotal movement of said control portion has been blocked, and control means engaged by said control portion during the course of the rotation of said element by the power roller to block the pivotal movement of said control portion thereby to vary the extent of direct drive between said cam element pivot and said rockable member, said control means comprising a control bar having an axis parallel to that of said power roller, a pair of adjustable control cams juxtaposition-ed on said control bar for selective engagement with said control portion, and means interconnecting said control bar and said shift device to axially displace said control bar in response to the operation of said shift devicce to select which of said cams is engageable with said control portion.

16. A power mechanism for typewriters and similar ofiice machines comprising a power roller, a type bar having a pair of type faces thereon, a shift device operable to select the type face on said type bar to be printed, a rockable member mounted to drive said type bar to a printing position, a power unit for operating said rockable member comprising a control portion pivoted on said rockable member, a cam element eccentrically pivoted on said control portion and rotatable through a cycle for driving relation with said power roller, means to initially rotate said element until its smallest radius is gripped by said power roller, said cam element pivot being in direct driving relation with said rockable member to drive it at one rate until the pivotal movement of said control portion has been blocked, and being in indirect driving relation with said rock-able member to drive it at a higher ratefafter the pivotal movement of said control portion has been blocked, and; control means engaged by said control portion during the course of the rotation of said cam element by the power roller to block the pivotal movement of said control portion thereby to vary the extent of direct drive between said cam element pivot and said rockable member, said control means comprising a control bar having an axis parallel to that of said power roller, a pair of adjustable control cams juxtapositioned on said control bar for selective engagement with said control portion, means interconnecting said control bar and said shift device to axially displace said control bar in response to the position of said shift device to select which of said cams is engageable with said control portion, and means to rotate said control bar to vary the section of said earn positioned for contact with said control portion, each of said control cams having a slope rate comensurate with the area of its associated type face on said type bar, relative to the average area of all of the type faces of said typewriter.

17. A power mechanism for typewriters and similar oflice machines comprising a power roller, a type bar, a rockable member mounted to drive said type bar to a printing position, a power unit for operating said rockable member comprising a control portion pivoted on said rockable member, a cam element pivoted on said control portion and rotatable for driving engagement with said power roller thereby .to effect a rotation of said control portion and the rotation of said rockable member, and control means engaged by said control portion during the course of rotation of said element by the power roller for varying the degree of power driven operation [of said rockable member.

18. A power mechanism for typewriters and similar ofiice machines comprising a power roller, a type bar, a rockable member mounted to drive said type bar to a printing position, and a power unit for operating said rockable member comprising a control portion pivoted on said rockable member, a cam element pivoted on said control portion and rotatable for driving engagement with said power roller thereby to effect a rotation of said control portion and the rotation of said rockable member, and control means engaged by said control portion during the course of rotation of said element by the power roller for varying the degree of power driven operation of said rockable member, said control means comprising a control bar having an axis parallel to that of said power roller, and an adjustable control cam positioned on said control bar to partially encircle the same and to have one peripheral portion at a time engageable with said control portion.

19. A power mechanism for typewriters and similar ofiice machines comprising a power roller, a type bar, a rockable member mounted to drive said type bar to a printing position, and a power unit for operating said rockable member comprising a control portion pivoted on said rockable member, a cam element pivoted on said control portion and rotatable for driving engagement with said power roller thereby to effect a rotation of said control portion and the rotation of said rockable member, and control means engaged by said control portion during the course of rotation of said element by the power roller for varying the degree of power driven operation of said rockable member, said control means comprising a control bar having an axis parallel to that of said power roller, an adjustable control cam positioned on said control bar to partially encircle the same and to have one section at a time engageable with said control portion and means to a rockable member mounted to drive said type bar to a printing position, a power unit for operating said rockable member comprising a control portion pivoted on said rockable member, a cam element pivoted on said control portion and rotatable for driving engagement with said power roller thereby to effect a rotation of said control portion and the. rotation of said rockable member, and control means engaged by said control portion during the course of rotation of said element by the power roller for varying the degree of power driven rotation of said rockable member, said control means comprising a control bar having an axis parallel to that of said power roller, a pair of adjustable control cams juxtapositioned on said control bar for selective engagement with said control portion in response to the operation of said shift device, each of said control. cams having a slope rate commensurate with the arealof its associated type face on said type bar relative m the average area of: allthe type faces of said. machine.

- 21.. In a power mechanism for. typewriters and similar oflice. machines, a type element having a pair of type facesthereommeans-driving said type element to print position, shifting means for determining which of said type faces is to be printed, and a'pair of control stops engageable with said type elementdriving means in response to the opera- -tion of said shifting means to control the imprint force of said type faces respectively.

References Citedin the tile of this patent UNITED STATES PATENTS Schulze Feb; 16, 1926

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