US3546439A - Magnetic cam reset positioner - Google Patents

Description

United States Patent [72] Inventors Howard J. Sampson Deep River;

Thomas W. Rogerson, Old Lyme, Connecticut April 30, 1969 Dec. 8, 1970 Com-ac Corporation New York, New York a corporation of New York [21] AppLNo. [22] Filed [45] Patented [73] Assignee [54] MAGNETIC CAM RESET POSITIONER 3,122,315 2/1964 Krebsdzio Primary Examiner-Richard B. Wilkinson Assistant Examiner-Stanley A. Wal Attorney-Charlton M. Lewis ABSTRACT: 1n a counting wheel that is resettable to zero by means of a heart-shaped cam, the cam is shifted away from dead center position before engagement by the cam follower by mounting cooperating magnetic elements, one on the wheel and the other in suitable rotational relation to the path of movement of the cam follower, to produce a torque on the wheel when it is in dead center position. The cam follower and its support structure may form the second magnetic element. By providing a third magnetic element cooperating with one of the antidead-center elements, the wheel can be held in zero position while the reset mechanism is returned to normal idle condition.

j This invention has to do with apparatus for resetting a gcounter wheel or similar mechanism to zero position by mechanismincludingaresetcam.

Reset cams are ordinarily mounted directly on the wheel and are of general heartform, with a sharp peak opposite to the dwell portion of the cam. To reset the cam and counter wheel to zero position, a manual or other control is operated to disconnect the normal drive train and move a cam follower radially toward the cam, normally engaging the ramp surface on one side or the other of the cam peak and sliding along that surface to the cam dwell point. The cam is thereby zeroed by rotation in one direction or the other, depending upon the ramp surface engaged.

Such reset mechanisms have the disadvantage that the cam follower may occasionally engage the cam directly at its peak, producing a dead center condition which disables fiirther reset cam away from dead center position before the cam is engaged. In many counting devices of the described type only the fi 't counter wheel requires such antidead-center mecha 'sm, since the other wheels are driven stepwise and do not sto with the cam at dead center position.

In ac ordance with a further aspect of the invention, a third magnetic element is provided, mounted in position to cooperate with one of the above described magnetic elements action. Many proposals havebeen made for overcoming that difficulty, often involving complex mechanisms for mechanically prying the cam away from dead center position.

The present invention provides a simple and economical means for reliably avoiding dead center engagement of the cam and cam follower in a reset mechanism of the described type. That is accomplished without any additional moving parts and without requiring any special precautions in operation of the reset mechanism.

In accordance with the present invention, the reset cam is shifted away from dead center position by magnetic force generated by cooperation of two magnetic elements. One of those elements is typically a permanent magnet, the other an armature structure of magnetically permeable material. One of the elements is mounted in fixed rotational relation to the cam. The other element is mounted in'such relation to the path of movement of the cam follower as to produce a force on the first element when the cam is in dead center position.

The second magnetic element may be fixedly mounted on the frame of the mechanism. The elements are then designed so that the force between them cannot override the normal mechanism for driving the counter wheel, but is sufficient to shift the cam away from dead center position as soon as that drive mechanism is disconnected upon operation of the reset control. x A

In preferred fonn of the invention; the second magnetic element is mounted for movement with the cam follower. In normal idle position of the reset mechanism the two magnetic elements are then radially spaced and are essentially inoperative. Upon operation of the reset control, the magnetic elements are brought into operating relation in time to shift the cam away from dead center position before the follower can engage the cam. With that arrangement, the interaction between the two magnetic elements may be made as strong as desired without interfering with"v normal operation of the counter, since the magnetic action is normally disabled. The system is therefore particularly suitable for use in mechanisms in which the counter wheel is frictionally driven, for example, and is not disconnected from its normal drive during reset.

A particularly convenient and economical form of the present invention may be applied to a counter mechanism having several adjacent coaxial counter wheels each of which is molded integrally with its drive gear and reset cam, the reset cam followers'being carried by reset arms that are yoked together and mounted for simultaneous radial movement. A small permanent magnet may be molded directly in each counter wheel to which the invention is to be applied, radially outward of the reset cam and slightly offset from the cam point, with the magnetic poles parallel to the wheel axis. The armature, or second magnetic element, for each wheel may then comprise the two regular reset arms that are on opposite sides of the wheel. In practice, no change is usually required in those arms, beyond forming them and their supporting yoke structure of magnetically penneable material. During reset operation the arms and yoke complete a magnetic circuit between the poles of each magnet, producing efiicient cooperation between magnet and armature for shifting the when the counter wheel is in zero position, producing a yielding force tending to retain the wheel in that zero position. Such retaining action prevents accidental deflection of the counter wheel from zero by vibration or other action during "the brief period after the cam has been released by the cam follower and before the normal drive mechanism has been recoupled to the counter wheel. A yielding force sufficient for that purpose can still be small enough to avoid affecting normal drive of the counter.

A full understanding of the invention and of its further objects and advantages will be had from the following description of certain illustrative manners in which it may be carried out. The particulars of that description, and of the accompanying drawings which form a part of it, are intended only'as illustration and not as a limitation upon the scope of the invention.

In the drawings:

FIG. 1 is a transverse schematic section of an illustrative form of the invention, taken on the line l1 of FIG. 2;

FIG. 2 is a schematic'section partly on the line 2-2 and partly on the line 2A-2A of FIG. 1;

- FIG. 3 is a schematic section corresponding to FIG. 1 and showing the reset mechanism partially operated;

FIG. 4 is a section similar to FIG. 3 and showing the mechanism fully operated;

FIG. 5 is a fragmentary'section on line 5-5 of FIG. 2; and

FIG. 6 is a schematic section illustrating amodification.

A support frame of generally U-form is indicated at 10, with the base 11 and the two parallel legs 12 and 13. The main shaft 14 is fixedly mounted on those legs and carries the freely rotatable first counter wheel 15 and a plurality of additional counter wheels, of which several are shown at 16. Each counter wheel carries on its circumference numerals only one of which is visible through the window 17 in the housing indicated at 27. The wheels are typically formed of molded plastic with the respective integral drive gears 18 and 19 and the reset cams 20 and 21. Those cams are of conventional heart form with pointed peak 22, dwell region 24, and two oppositely oblique ramp surfaces 26 interconnecting the peak and dwell regions symmetrically on opposite sides of the cam (FIG. 3). During normal operation of the counter mechanism, first counter wheel 15 is driven'via the drive pinion 30, the remainder of the drive mechanism being omitted from the drawings for clarity of illustration. Pinion 30 is mounted on the shaft 33 and normally engages gear 18. Second counter wheel 16 is driven from wheel 15 via the transfer pinion 32 (FIG. 5), which normally engages gear 19. Transfer pinion 32 is actuated from first counter wheel 15 by a Geneva formation of conventional type schematically indicated at 34 (FIG. 2), which causes second wheel 16 to advance one step for each complete revolution of wheel 15, bringing the next numeral to window 17. Successive counter wheels are similarly driven from wheel 16.

The reset mechanism, as conventionally shown, comprises an assembly 40 of reset arms 41, 42 etc., rendered mutually rigid by the longitudinal structural member 44, and mounted for swingingmqygmghtas a unit about the shafi 45. Arms 41 and 42 carry at their ends'tl'i'e" cam follower formations 46 which swing along parallel paths 48 and are adapted to engage and operate the respectiveheart shaped cams 20, 21. Arm as sembly 40 may be operated in any suitable manner, as by depressing the manual button 50, which is slidably mounted on the frame bracket 52 and engages one of the arms 41, 42 to cause the arm assembly to swing counterclockwise as seen in FIG. 1. Operation of arm assembly 40 also serves to disengage 3 drive pinion 30 and transfer pinions 32 from their respective gear couplings'with the counter wheels. As shown, the com-v mon pinion shaft 33 is carried on auxiliary arms 48 of the reset arm assembly, so that it is moved downward away from wheel shaft 14 in-response toreset operation, as shown clearly by Comparison of FIGS. 1, 3 and 4." The parts are so dimensioned that the pinions are disengaged before cam followers 46 engage their respective reset carns20 and 21.

The reset mechanism'is normally maintainedin idle conditidn, as shown in FIG. 1, by .one or more springs 60 which yildably urge pinion shaft 33 toward main shaft 14. Asshown best in F lG. 5, each transfer pinion 32 carries a square hub 35 which is engaged by one, of the springs 60. Adjacent hub faces coirespond to countenwheel positions with adjacent numerals at window 17. During reset operation, while the transfer pinions are free from gears 19, springs 60 thus maintain the pinions in proper rotational position to insure direct reengagement with the gear after the latter has been reset. Prompt rengagement of drive pinion 30 with gear 18 of the first oo'iinter wheel is typicallyinsured by utilizing relatively fine teeth on those gears. Since main drive pinion -30istypically driven continuously, there, is a, possibility that thereset operation'will be initiated at .a moment when the point of cam 20 is directly on the path ,48, of cam follower 46.

In accordance with the present invention the rotary position of first counter wheel is}shi fted out of such dead center position immediately followingrelease of pinion 30 from gear 1:8."That is accomplished by mounting the permanent magnet in counter wheel 15 and by providing armature means for cooperating with that'magnet to exert a torqueon .the wheel urging it away from dead center position. In the present embodiment, that armature'structure comprises the reset arms 41 and 4 2. .Thosearms andeithertheir connecting yoke 44 or supportingshaft'45 are fo'rmed of magnetically permeable material. In idle condition of the reset mechanism those arms are withdrawn radiallyoutwar'd of magnet 70, and exert only negligible force on the magnet.

the zone of magnet 70 and are closely spaced from opposite ends of the magnet. When the cam is in dead center position, as shown in solid lines .in-. FIG. 3, magnet 70 .is partially overlappedby theends 'of the armature arms, which with their sup-, porting structure providea. substantially closed magnetic circuit for the magnetic lines of force of themagnet. However, since the magnet is thenoffset circumferentially from the arms, it is drawn towardali'g'nmentwith the armature structure. With suitable design, even amagnet'of negligible mass compared to the entirewheel can be madeto produce sufficient force to turn thecounterwheel reliably, bringing cam 20.

toan oblique position, such as that shownin dashed lines in. FIG. 3, with cam point. 22 out of the path ,48 of cam follower.

46. That action occurs promptly after release of .the gear drive and before the cam follower can engage the cam. Further movementofarm'flthcn causes cam follower 46 to engage ramp surface 26. of the cam ,resetting wheel. 15 to zero positionas shown in FIG. 4. Each of the other reset arms similarly resetsits counter wheel to zero.

In accordance witha further aspect of the invention, magnet70 is made to perform the additional function of effective;

ly locking counter wheel 15. in zero position during the short interval between release, of v the reset cam as follower 46 is withdrawn. and reengagementof drive. pinion30 just before.

thereset mechanisnireturns to idle position. Such locking is acc'fompiishedin the present embodiment of the inventionby providing an arrnatureg8 0, which is typically mounted in fixed ppfsfition, as on the frarne. bracket 82. Armature 80 is preferably of U-form, withtwo arms that spac'edly embrace the outer portion of, counter wheel 15,:at the angular position of magnet 70 when the wheel is. in zero position (FIG, 4). The restrainingforce exeitedupon the counter wheel by cooperatio iiofmagnet 'm and armature 80, is sufficient to prevent ac;

:cid'entaldisplacement of the wheelduringitsbrief period of release, but is insufficient toprevent normal wheel drive via Upon initiation .of reset 'operationarms 40. are swung into I,

pinion 30. A particular feature of the present system is the dual function of magnet 70, which acts'both to shift the wheel away fromdead center position and to prevent accidental shifting of .the wheel away from zero position.

It is sometimes preferredto form the entire reset arm assembly .or its equivalent of plastic or of some metal that is not magnetically permeable. Suitable armature structure, typically similar toarmature 80, may .then be mounted onthe reset arms formovement withthem; or fixedly mounted closely adjacent-those arms, thus operating essentially in the manner. already described. Alternatively, such an arm-attire may be fixedly mounted at anyconvenient angular relatior rtomain shaft 14, as'shown schematicallyat a in FIG. 6, with a magnet mounted in the wheel in position to partially over! lap the armature when the wheel is-in dead center position. With that arrangement, the wheel may also be'restrained-in zero position byproviding another. magnet 92 in the wheel in such angular position as-to be aligned with armature 80a when the wheel is zeroed. In that case, two magnetic elements in the wheel cooperate with a single magneticelement in fixed rotational position, whereas in the system of FIGS. 1 to 5 a single magnetic element in the wheel cooperated with angula'rly spaced armature structures 40 and 80.

It willbe. evident without specific illustration that per: manent magnets may be incorporated in the structures that have been described as armatures, supplementing or replacing.

the magnetization of the'elements that have been described as permanent magnets. Also, magnetization maybe derived or, -supplementedbyelectromagnets to any, extent desired. How- 'ever, an important advantage ofthe invention is the fact that the desiredfunctions can be performed reliably by extremely portion connected byopposit ely oblique ramp portions, a cam follower having a normal position spaced from the cam and actuatable to move along a: path thatis generally radial with respect to the axis to normally'engage a ramp portion of the cam and rotate the same to reach said dwell portion, therebyresetting the wheel to zero position, and a reset control for ac-.

tuating, the cam follower, the cam having a dead center posi-.

tion in which the cam follower engages the cam atthe peak portion thereof, disabling furthepcamtfollower movement;

first magnetic means mountedin fixed angular relation to the. :cam, second magnetic means mounted in definite angular;

relation to the cam follower path such that, upon operation of the reset control when the cam is in dead center position, the

firstand second magnetic means cooperate to rotate the cam away fromdeadcenter position before the cam followerengages cam.

2. The combination defined ,in claim 1, and in which one of j said magnetic means is a permanent magnet and the other magnetic means is a magnetically permeable armature.

3. The combination defined in claim 1, and in which said second magnetic means is mounted for movement with the. cam follower in position to be essentially isolated magnetically fromthe first magnetic means in normal position of the cam follower. and to interact magnetically with the first magnetic means as thecam follower moves .alongits path and before the.

cam follower engages the 4. The combination defined in claim 1, and in which:

the first magnetic means comprises a permanent bar magnet mountedzon the wheel offset from the axis and parallei thereto;

the. second magnetic means comprises two magnetically-v coupled arms' of magnetically permeable .material mounted for generally radial movement of respective arm portions adjacent opposite axial faces of the wheel; and the cam follower beingimounted onone of said arms.

a reset mechanism for a counter.

5. The combination defined in claim 1, and in which said mechanism includes drive means normally coupled to the wheel and releasable in response to operation of the reset control to permit resetting the wheel to zero position, said second magnetic means being fixedly mounted in position to cooperate with the first magnetic means whenever the cam is in dead center position to exert a yielding torque on the wheel tending to move the same away, from said dead center position, said torque being insufficient to override the normal operation of the drive means, and being sufficient to move the cam away from dead'center position upon release of the drive means.

6. The combination defined in claim 1, and in which said mechanism includes drive means normally coupled to the wheel and releasable in response to operation of the reset con trol to permit resetting the wheel to zero position, said combination including also third magnetic means mounted generally on the opposite side of the axis from one of said first and second magnetic means in position to cooperate magnetically with the other of said first and second magnetic means to exert a holding torque tending tolock the wheel in zero position during continued release of the drive means after disengagement of the cam follower means, said torque being insufficient to override the normal operation of the drive means.

7. In combination with a resetmechanism for a first counter wheel that is rotatable about an axis and has a zero position, said mechanism including a first reset cam rotationally fixed with respect to the wheel on one side thereof and having a peak portion ,and a dwell portion connected by oppositely I having a zero position and with a second reset cam positioned between the wheels and rotationally fixed to the second wheel, the wheels extending radially beyond the cams, cam followers for the respective cams mounted on respective arms carried by a common support, the support having a normal position with the cam followers radially spaced from the cams, and being actuatable to move the arms inward along generally radial paths on opposite sides of the first wheel to cause the cam followers to normally engage ramp portions of the respective cams and rotate the same to return the wheels to their zero positions, drive means normally coupled to the wheels for driving the same and releasable to permit resetting of the wheels to zero position, and a reset control for actuating the support and releasing the drive means, at least the first cam having a dead center position in which its cam follower engages the peak portion of the cam, disabling further cam follower movement; a permanent magnet mounted fixedly on the first wheel parallel to the axis and radially outward of the cams in such position that in said dead center position of the first cam the magnet is circumferentially offset from the paths of the cam follower arms, the cam follower arms and at least a portion of the support comprising magnetically permeable material and forming a magnetic armature of U-form, said actuation of the support causing said armature to cooperate with the magnet to form a magnetic circuit tending to align the magnet between the arms as the latter move along said path, thereby exerting on the wheel a torque sufficient to move the cam away from dead center position before the cam follower oblique ramp portions, there being a second counter wheel engages the rotatable about the axis on the other side of the first wheel and

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