US 3642109 A
A device which increases the tension of transmission belts in response to a decrease in belt tension caused by belt wear, elongation, etc. The belts are carried on a movable pulley and a pivotal cam moves the pulley to increase the tension in the belt.
Description (OCR text may contain errors)
[ 1 Feb. 15, 1972 United States Patent Cappotto et al.
 BELT TENSION DEVICE 197/17 Cappotto.................................197/17  Inventors: Samuel D. Cappotto, Syracuse; Herrick R. Barkdonwmw Diamond, Homer; Aaron C. Zeamer, Groton, all of N.Y.
 Assignee: SCM Corporation Primary Examiner-Robert E. Pulfrey Assistant Examiner-Stephen C. Pellegrino AttorneyMilton M. Wolson, Carlos Nieves and Harvey Zeller A device which increases the tension of transmission belts in Jan. 19, 1970  Filed:
 Appl. No.:
ABSTRACT response to a decrease in belt tension caused by belt wear, elongation, etc. The belts are carried on a movable pulley and a pivotal cam moves the pulley to increase the tension in the belt.
.197/17, 74/242.ll .B41j 23/08, Fl6h 7/l2 197/17; 74/242.1l
[52} US.  Int. Cl.
 Field of References Cited UNITED STATES PATENTS 5 Claims, 4 Drawing Figures PATENTEBFEBISIQIZ 33542109 SHEETIUFZ n (1) m SAMUEL .CAPPOTTO HERRICK R. DIAMOND AARON C. ZEAMER ATTORNEY mcmmm 15 Ian 3.642.109
SHEET 2 OF 2 INVENTOR. SAMUEL D. CAPPOTTO HERRICK R. DIAMOND AARON C-ZEAMER BY ,GMLIGM AT TORN EY BELT TENSION DEVICE This invention relates to power drive systems and specifically such systems wherein the power is transmitted by a belt and pulley arrangement.
In a typical arrangement a first pulley is secured to a rotative power source, for rotation therewith. An endless belt in the form of a loop connects the first pulley with a second pulley secured to an output shaft so that power is transmitted from the power source to the output shaft.
An electric typewriter is an example of a device in which a variation of this power drive system is utilized. (Although in the following discussion a typewriter will be used for illustration purposes; it is within the scope of the present invention to use the disclosed invention in various other machines and apparatus).
In an electric typewriter, a motor is utilized to rotate a power roll for driving a typebar against an inked ribbon, which causes an impression to be formed on a paper positioned to the rear of the ribbon. The power is transmitted from the motor to the power roll by a first endless belt in the form of a loop which is positioned around a pulley secured to the motor and also around an idler pulley so that the motor acting through the first endless belt rotates the idler pulley. The purpose of the idler pulley will be discussed in a following paragraph. A second endless belt in the form of a loop is positioned around an inner diameter of the idler pulley and also around another pulley secured to the power roll so that the power roll is rotated by the idler pulley which in turn is rotated by the motor.
It is well known that in typewriters such as described above a decrease in belt tension is a common cause of irregular, nonuniform type impression. A decrease in belt tension may occur from various reasons, such as belt wear and belt elongation due to stretching.
A prior art approach to solving the problem of decreased belt tension has been to position the transmission belts around a spring-biased intermittent moveable idler pulley. The force of the spring moves the idler pulley and the attached belts in a direction to increase the tension in the belts, in response to a decrease in the belt tension.
In an approach such as this, the spring must exert a constant force on the idler pulley to maintain a unifonn type impression. However, in this prior art approach as the spring exerts a force on the idler pulley; the pulley is moved toward the spring and thereby the length of the spring is reduced. Since the length of the spring is reduced, the force it exerts on the idler pulley is lessened, and thus the force available to increase the belt tension is lessened, causing the resulting type impression to be nonuniform and unsatisfactory.
it is therefore an object of the present invention to provide a novel belt-tensioning device for use in apparatus having power drive systems which utilizes a spring and cam arrangement to exert a substantially constant force on a belt-carrying pulley.
Another object of the present invention is to provide a belttensioning device, for use in typewriters and similar machines wherein a uniform type impression is desired.
Another object of the present invention is to provide a novel belt-tensioning device wherein a spring-biased cam moves an idler pulley to increase the tension in the belts carried on the idler pulley in response to a decrease in belt tension caused by belt wear, elongation, etc., so that the belts are maintained at a constant uniform tension.
These and other objects of this invention will become more fully apparent by reference to the appended claims and as the following detailed description proceeds in reference to the accompanying drawing wherein:
FIG. 1 is a front perspective view of an electric typewriter including the belt-tensioning device of the present invention;
HO. 2 is a partial side elevation showing the belt-tensioning device wherein the cam is shown in its initial position.
FIG. 3 is a partial side elevation showing the belt-tensioning device wherein the cam is shown in an intermediate position.
FIG. 4 is a partial side elevation showing the belt-tensioning device wherein the cam is shown in its final position.
Referring now to the drawings in detail and particularly to FIG. 1, wherein is illustrated a typewriter 10 including a belttensioning device 12.
The typewriter 10 comprises a motor 18 mounted on a backframe (not illustrated). A pulley 17 is mounted on an output shaft 16, of motor 18 for rotation therewith. An endless belt 20 in the form of a loop is wrapped around pulley l7 and a large diameter portion 22 of variable pitch idler pulley 24. ldler pulley 24 is mounted on a pulley shaft 25 for vertical and rearward movement in side frame 10. Thus it is seen that power from motor 18 acting through pulley l7 and belt 20 causes rotation of idler pulley 24.
A second endless belt 26 in the form of a loop is wrapped around the inner diameter 28 of idler pulley 24 and around a pulley 30 which carries a power roll 32. Rotation of the inner diameter 28 of idler pulley 24 is transmitted to power roll 32 by means of transmission belt 26. Power roll 32 is carried on a A shaft 34 which is mounted in a typewriter side frame 14.
The power roll 32 drives typebar 34 through a known key action system 36 to cause printing. The illustrated key action is described in detail in US. Pat. Re. No. 25,01 1, reissued July. 18, 1961 to J. P. Barkdoll. From the description in this patent,-
it is understood that the speed of power roll 32 affects the impression of the typebar 34 and as is well known in the typewriter art in order to maintain a uniform type impression a constant power roll speed should be maintained.
One means employed in the disclosed device for maintaining the belts 20 and 26 at constant tension, is a conventional impression control member 36. One end 35 of impression control member 36 is attached by means of a spring 38 to side frame extension 40. The other end of impression control lever 36 is mounted on pulley shaft 25. An upward projecting tabv42 mounted on impression control lever 36 carries a cam follower stud 44. An impression control knob 46, which is manually operated, is attached to side frame 14 by means of a small stub shaft 48. The impression control knob 46 has an in terior cam hub 50. As is understood from the drawing, spring 38 urges cam follower stud 44 into engagement with interior cam hub. The configuration of cam hub 50 is such that rotation of impression control knob 46 in a clockwise direction urges cam follower stud 44 and therefore impression control lever 36 rearwardly. Movement of impression control lever 36 rearwardly increases the speed of power roll 32 in a known manner. What has heretofore been described is a conventional impression control mechanism whereby an operator by manually rotating impression control knob 46 may control the type impression by increasing (or decreasing) the speed of the power roll 32. The impression control lever 36 is not required to be'used in conjunction with the belt-tensioning device of the present invention, next described.
A follower member 52 is pivotally mounted on impression control lever 36 about pin 54. A cam 56, carried on cam shaft 57 mounted in typewriter side frame 14, having a cam lobe portion 58 and an arm portion 60 is biased clockwise by a spring 62 against the lower surface of an extension 64 of follower member 52. The spring 62 is attached to a crossmember 65 secured to side frame 14. An adjustable tab portion 66 of follower member 52 engages an upper surface 68 of impression control lever 36 so that follower member 52 and impression control lever 36 form a rigid connection in the sense that upward movement of follower member 52 will cause upward movement of impression control lever 36. By this arrangement of parts it is seen that cam 58 exerts a force on the lower surface of extension 64 which causes follower member 52, impression control lever 36 and idler pulley to 24 to move upwardly to increase the tension in belts 20 and 26.
The position of extension 64 of follower member 52 with respect to cam 56 may be varied by changing the position of adjustable tab portion 66 of follower member 52 with respect to the upper surface 68 of impression control lever 36. For example bending adjustable tab portion rearwardly on upper surface 68 of impression control lever 36 will cause extension 64 of follower member 52 to pivot downwardly on cam 56 whereby cam 56 will assume a more flattened position. This feature is especially important as it permits the initial position of cam 56 to be readily adjusted so as to take advantage of its full cam range.
From the foregoing description and with particular reference to FIG. 1, it will be observed that as the tension in belt and/or belt 26 is decreased due to wear, etc., the force which extension 64 of follower 52 exerts on cam 56 will also be lessened. This will permit spring-biased cam 56 to move extension 64 of follower 52 upwardly, which as discussed previously will raise idler pulley 24 to increase the belt tension. In the present device, the increase in belt tension in response to a decrease in belt tension occurs so rapidly that for all practical purposes the belt system may be considered to be maintained at a uniform tension.
FIG. 2 represents the belt-tensioning device in its initial position prior to any decrease in belt tension. It is noted that in this position spring 62 is at its greatest length and will exert its greatest force on cam lobe 58 of cam 56.
As the tension in 20 or 26 decreases the cam 56 and spring 62 assumes various intermediate positions; one of which is illustrated in FIG. 3. In this position the length of spring 62 and therefore the force exerted by spring 62 will be less than the length and force of spring 62 when it is in the position illustrated in FIG. 1.
It is desired however that the force exerted by the springbiased cam 56 on the extension 64 of follower 52 remain substantially constant for any position of spring 62 and cam 56 to insure a uniform type impression. The cam 56 is therefore designed so that the effective lever arm of the cam 56 acting on extension 64 of follower 52 increases as the force of spring 62 decreases whereby the force of cam 56 on extension 64 of follower 52 remains substantially constant for any position of spring 62 and cam 56. FIG. 4 illustrates the belt-tensioning device in its final position wherein cam 56 is in its final position. Cam 56 is prevented from further movement by its engagement with stop 70 located at the lower rear portion offollower 52.
Thus it is seen that in any given cam position, the output force of cam 56 decrease remains substantially constant even though the force exerted by the spring 62 which acts on cam 56 decreases. This results in an improved belt-tensioning device wherein the belt tension is maintained at a constant uniform tension to provide a substantially uniform type 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 ofthe following claims.
What is claimed is:
1. In an electric typewriter having a power drive system including a power source, a first belt connecting said power source to a moveable pulley, an impression control lever connected to said pulley by means of a shaft, a second belt connecting said pulley to an output shaft, said pulley being moveable to increase the tension in said first and second belt and a device which moves the pulley in response to a decrease in belt tension, said device comprising:
a. a follower member pivotally supported on said impression control lever in such a manner that movement of the follower member causes the impression control lever and pulley to be moved.
b. a pivotal cam mounted on the typewriter, and
c. means connected to the cam and responsive to a decrease in belt tension of either the first belt or the second belt or both the first and the second belt for pivoting the cam against the surface of the follower member to cause movement of the follower member and pulley. 2. In an apparatus as set forth in claim 1 whereln the means responsive to a decrease in belt tension for pivoting the cam comprises a spring attached at one end to the cam and at the other end to a typewriter frame member.
3. In an apparatus as set forth in claim 2 wherein the effective lever arm of the cam against the surface of the follower member increases as the force of the spring attached to the cam decreases.
4. In an apparatus as set forth in claim 2 wherein the cam comprises a cam lobe portion which engages the surface of the follower member, and an arm portion to which the spring is attached.
5. In an apparatus as set forth in claim 1 wherein means are provided on said follower means to vary the position of said follower means with respect to the cam.