APPARATUS AND METHOD FOR CONVERTING ROTARY TO HARMONIC RECIPROCATING MOTION
United States Patent 3706238
As a web or the like passes around a driven roll, a member (e.g., a tractor pin or punch) rotatably carried by the roll at a preselected nominal distance from the roll axis is reciprocated with substantially harmonic motion in a generally radial direction toward and away from said axis by a pendulum-like mechanism having an oscillation frequency that increases as the angular velocity of the roll and hence centrifugal force on the member increases. The mechanism comprises an oscillatory element having an eccentric mass center or center of oscillation that at the midpoint of the member's reciprocation stroke is farthest from the roll axis. A cam follower preferably couples the element to a stationary cam that encircles the roll and has a follower-receiving groove of a configuration that ensures synchronization of the element so that it will oscillate at a fundamental natural frequency through one or more complete cycles during each successive revolution of the roll despite frictional drag. Driving force exerted by the oscillatory element on the member thus desirably increases as the angular velocity of the roll increases, whereas the load on the cam remains substantially negligible irrespective of angular velocity. This enables operation at very high rotational (and hence reciprocating) speeds that produce centrifugal forces significantly exceeding those possible with prior art arrangements.
US Patent References:
Centrifugal force compensating mechanism
Merwin et al. - January 1950 - 2494483
APPARATUS FOR PRODUCING STRANDED CABLE
Schillebeeckx - December 1970 - 3546872
Centrifugal force compensating mechanism
Merwin et al. - January 1950 - 2494483
APPARATUS FOR PRODUCING STRANDED CABLE
Schillebeeckx - December 1970 - 3546872
Application Number:
05/194081
Publication Date:
12/19/1972
Filing Date:
10/28/1971
View Patent Images:
Export Citation:
Assignee:
International Business Machines Corporation (Armonk, NY)
Primary Class:
Other Classes:
74/37, 226/72
International Classes:
F16F15/26; F16F15/22; B65H79/00
Field of Search:
74/573,574,37,33,29 57/66.5 226/72 123/43C,44E
Primary Examiner:
Kaufman, Milton
Assistant Examiner:
Shoemaker F. D.
Claims:
What is claimed is
1. Apparatus for substantially counterbalancing the effects of centrifugal force on a member that is concurrently rotated and reciprocated relative to an axis of rotation, characterized by
2. Apparatus according to claim 1, further characterized by the provision of
3. Apparatus according to claim 1, wherein
4. Apparatus for converting rotary motion into substantially harmonic reciprocating motion, comprising
5. Apparatus according to claim 4, wherein the mass center of oscillation of said actuating means is farthest from said axis when the member is at the midpoint of its reciprocation stroke, and the axis of oscillation is always at right angles to said axis of rotation.
6. Apparatus according to claim 4, wherein said means for rotating said member includes means for disposing said member to reciprocate in a path obliquely intersecting said axis of rotation.
7. Apparatus according to claim 4, wherein
8. Apparatus according to claim 4, wherein
9. Apparatus according to claim 8, including
10. Method of substantially counterbalancing the effects of centrifugal force on a member while it is concurrently being rotated and reciprocated relative to an axis of rotation, comprising the steps of
1. Apparatus for substantially counterbalancing the effects of centrifugal force on a member that is concurrently rotated and reciprocated relative to an axis of rotation, characterized by
2. Apparatus according to claim 1, further characterized by the provision of
3. Apparatus according to claim 1, wherein
4. Apparatus for converting rotary motion into substantially harmonic reciprocating motion, comprising
5. Apparatus according to claim 4, wherein the mass center of oscillation of said actuating means is farthest from said axis when the member is at the midpoint of its reciprocation stroke, and the axis of oscillation is always at right angles to said axis of rotation.
6. Apparatus according to claim 4, wherein said means for rotating said member includes means for disposing said member to reciprocate in a path obliquely intersecting said axis of rotation.
7. Apparatus according to claim 4, wherein
8. Apparatus according to claim 4, wherein
9. Apparatus according to claim 8, including
10. Method of substantially counterbalancing the effects of centrifugal force on a member while it is concurrently being rotated and reciprocated relative to an axis of rotation, comprising the steps of
Description:
This invention relates to apparatus and methods for converting rotary motion into harmonic reciprocating motion, and relates more particularly to apparatus and methods wherein a work member that is rotated by a shaft or roll is concurrently reciprocated by a pendulum-type mechanism that, by the centrifugal force resulting from rotation of the shaft, is caused to oscillate at a fundamental natural frequency that is synchronized with each revolution of the shaft.
BACKGROUND OF THE INVENTION
Various forms of apparatus have heretofore been proposed to convert rotary to reciprocating motion. In some types of such apparatus, a rotating shaft or roll is operatively connected to a member that is caused to reciprocate relative to and generally transversely of the axis of rotation. Since the rotating reciprocated member is subject to centrifugal force which varies with the distance of the member from the axis of rotation, the member as it reciprocates is subjected to a progressively increasing force during its outbound stroke and a progressively decreasing force during its return stroke toward the axis. Also, since centrifugal force varies as the square of the rotational speed, drastic increases in centrifugal force occur at progressively higher speeds. As centrifugal force increases, heavy loads are imposed on the cam or other elements that are driving the member; these loads are, of course, heaviest during transition from the outbound to the inbound stroke.
Accordingly, some efforts have been made to offset or counteract the effects of these variations in centrifugal force on a member that is concurrently being reciprocated and rotated. In balancing automobile crankshafts, where a plurality of reciprocating members are involved, some move toward the shaft axis as others move away from it, and all are circumferentially spaced in counterbalancing pairs and driven with harmonic reciprocating motion. Counterbalancing is thus relatively easily achieved when a plurality of work elements operate sequentially.
Counterbalancing is more difficult when there is only one rotating reciprocated work member or when all of a plurality of rotating reciprocated work members must operate to conclude their power stroke simultaneously (rather than sequentially). For example, in U.S. Pat. No. 2,494,483, a hollow rotating drum operatively carries a cable-guiding distributor (a single work member) that is reciprocated transversely of the axis of the drum at a constant speed corresponding to the helical pitch of a double-threaded screw (a cam) so that cable will be spooled onto a reel uniformly in successive layers of equal thickness, as is common in fishing reel take-up mechanisms. As the distributor moves rectilinearly leftward, for example, across the axis of the drum, it acts through a sprocket chain to drive clockwise a corresponding degree the sprocket wheel of a centrifugal force compensating mechanism; this tends to offset, to an increasing degree, the effect of the increasing centrifugal force developed as the distributor approaches the left end of its stroke. With this arrangement, operating speeds must be slow because the speed changes abruptly at the end of each stroke, causing a rapid deceleration from constant speed in the leftward direction to zero, then rapid acceleration followed by constant speed in a rightward direction; and conversely.
These various approaches thus counteract, in varying degree, the effect of centrifugal force on a rotating reciprocated member. However, there is a need for a relatively inexpensive yet effective apparatus and method for substantially perfectly counterbalancing the effects of centrifugal force, over a wide range of rotational speeds, on a single rotating work member (or simultaneously actuated plurality of work members) while it is being reciprocated substantially with harmonic motion, to permit operation at very high rotational and reciprocation speeds with minimal load and wear on the parts that reciprocate such member.
SUMMARY OF THE INVENTION
Toward this end, and according to the invention, applicant has found that these objectives can be achieved by an improved apparatus and method which, insofar as is known, have never heretofore been proposed. According to the invention, the work member, while being rotated, is reciprocated by a pendulum-type means that is oscillated at a fundamental natural frequency by the centrifugal force acting on said member, said frequency being synchronized with each revolution of the work member so that the work member will complete a integral number of full reciprocation strokes with substantially harmonic motion during each complete revolution of the work member about its axis of rotation.
Other objects and advantages will become apparent from the following more detailed description of the invention and from the accompanying drawings, wherein:
FIG. 1 is an elevational sectional view of an apparatus embodying the invention and including a rotating forms feed pin reciprocated with substantially harmonic motion by a weighted gear oscillated at a fundamental natural frequency by centrifugal force;
FIG. 2 is a schematic elevational view of a mathematical model of the apparatus of FIG. 1, showing the pertinent parameters for applicable design equations; and
FIG. 3 is an elevational sectional view of a punch apparatus constructed according to a variation of the invention.
DESCRIPTION--FIG. 1
As illustrated in this figure, the apparatus embodying the invention comprises a drive shaft 10 rotated at constant angular velocity by suitable means (not shown). Encircling shaft 10 and disposed side by side are a ring 11 and a cam 12. The ring is secured by a key 13 for rotation with the shaft. The cam is mounted on a bearing 14 and held stationary by means including a screw 15 that connects the cam to a shaft-encircling yoke 16 having a depending portion that is slidable along a guide rod 17. Collars 18,19 cooperate with a spacer ring 20 to retain the ring and cam at preselected fixed positions along shaft 10.
Ring 11 has a rectangular slot 21 extending generally radially inward from its outer periphery. Inset in this slot are complementary portions (only the rear one shown) of a rectangular housing 22. This housing provides complementary half portions of a bore 23 for a retractable tractor feed pin 24; a dish-shaped opening 25 for receiving an oscillatable gear 26 mounted on a shaft 27 having its axis at right angles to the axis of shaft 10; and a cam follower 28 including a laterally projecting pin 29 that rides in a cam groove 30 in the inner radial face of cam 12.
Rack teeth 31 formed in one side of pin 24 mesh with teeth 32 on gear 26 to convert rotary motion of the gear into reciprocating axial movement of the pin. Gear 26 is oscillated, in the manner hereinafter to be described, and has a pendulum-like weight 33 of calculated mass disposed to provide a preselected radius of oscillation r (see FIG. 2). This weight is so located that its mass center of oscillation is farthest from the axis of shaft 10 when pin 24 is located at the midpoint of its reciprocation stroke. Rack teeth 34 formed along one side of follower 28 mesh with the teeth 32 of oscillatory gear 26.
OPERATION--FIG. 1
In operation, as shaft 10 starts to rotate, cam 12 through follower 28 will rotate gear 26 to one limit of its preselected oscillatory amplitude to initiate its pendulum-like oscillation; whereupon centrifugal force will cause weight 33 to maintain the gear oscillating with said preselected amplitude but at a frequency that increases as the angular velocity of the shaft increases. The mass center and the radius of oscillation are calculated in the manner presently to be described to cause gear 26 to oscillate at a fundamental natural frequency synchronized with the angular velocity of pin 24 so the pin will complete an integral number of substantially harmonic reciprocations per revolution of the shaft 10. However, cam 12 and follower 28 are provided to positively ensure that such synchronization will be maintained despite any frictional drag; this result is achieved by the harmonic-ensuring configuration of cam groove 30.
It should be noted that the driving power for reciprocating pin 24 is provided primarily and almost exclusively by the centrifugal-force-induced oscillation of gear 26; that cam 12 and follower 28 provide essentially negligible driving power; and that the load on the cam and follower is therefore negligible and does not vary substantially over a wide range of different constant angular velocities of the shaft or even during relatively low rates of acceleration or deceleration to a different velocity. The improved apparatus herein disclosed thus desirably enables the shaft to rotate at very high speeds that would create unacceptable cam and follower loads in conventional apparatus because centrifugal force on the rotating reciprocated member (in this case pin 24) increases as the square of the angular velocity of the rotating means (shaft 10) as well as directly proportional to the distance of the rotating reciprocated member from the axis of rotation.
DESCRIPTION--FIG. 2
To minimize the load on cam 12 and follower 28, and achieve the desirable results heretofore described, it is essential that centrifugal force cause gear 26 to oscillate at a fundamental natural frequency that is so synchronized with the angular velocity of the shaft that pin 24 will complete an integral number of substantially harmonic reciprocations during each complete revolution of the shaft and hence of the pin.
Where one harmonic reciprocation per revolution is desired, this requirement can be achieved by designing the gear 26, pin 24 and follower 28 to satisfy the following condition:
and
m 1 R 1 = m 2 R 2
where, as shown in FIG. 2,
m and I are the mass and inertia of gear 26;
r is one-half the pitch diameter of gear 26;
r is the radius of oscillation of gear 26;
m 1 and m 2 are the masses of pin 24 and follower 28, respectively;
R is the radial distance from the axis of rotation (axis of shaft 10) to the rotational axis of gear 26 (axis of shaft 27);
R 1 and R 2 are the radial distances from the axis of rotation (axis of shaft 10) to the mass centers of pin 24 and follower 28, respectively.
DESCRIPTION--FIG. 3
In the apparatus constructed according to this variation of the invention, the rotating reciprocated member is a punch 100 that is reciprocated in a path obliquely intersecting the axis of rotation of a hollow shaft 101. The punch has a generally triangular cross section providing two V-shaped intersecting sides that adjacent their inner ends are partially relieved to define a V-shaped cutting edge 102. Springs 103 nested in an element 104 act, through a plate 105, on the rear face 106 of punch 100 to maintain the V-shaped sides in slidable surface contact with corresponding mating surfaces of a die 107. This provides a zero clearance cutting action that assures a very clean shear cut and longer wear life of the punch as cutting edge 102 cuts a V-shaped notch to remove a triangular chip C from one edge of a web 108. This cutting is done as web 108 advances partially wrapped around a cylindrical surface 109 of element 104; it being noted that element 104 is secured by suitable means (not shown) to shaft 101 for rotation thereby and that the hollow shaft is connected to a vacuum source (not shown) to duct away the chips C.
As illustrated, a cable 110 passes around a drive pulley 111 and idler pulleys 112,113. Cable 110 is suitably connected to punch 100, drive pulley 111 and a cam follower 114. Pulley 111 has a pendulum-like weight 115 of calculated mass disposed to provide a preselected radius of oscillation. As with weight 33, weight 115 is so located that its mass center of oscillation is farthest from the axis of shaft 101 when punch 100 is at the midpoint of its reciprocation stroke. Cam follower 114 has a laterally projecting pin 116 that rides in a cam groove 117 in the inner radial face of a stationary cam 118 that is suitably anchored and disposed in encircling relation about the rotating shaft 101.
In operation, as shaft 101 starts to rotate, cam 118 through follower 114 will rotate pulley 111 to one limit of its preselected oscillatory amplitude to initiate its pendulum-like oscillation. Thereafter, centrifugal force will cause weight 115 to maintain drive pulley 111 oscillating with said preselected amplitude but at a frequency that increases as the angular velocity of shaft 101 increases. The mass and radius of oscillation of weighted pulley 111 are calculated to cause the pulley to oscillate at a fundamental natural frequency synchronized with the angular velocity of punch 100 so the punch will complete an integral number of substantially harmonic reciprocations per revolution of shaft 101. As in the earlier embodiment, cam 118 and follower 114 are provided merely to positively ensure that such synchronization will be maintained despite frictional drag; this is achieved by pin 116 riding in the harmonic ensuring configured groove 117.
It should be noted that all of the advantages previously described in connection with the embodiment of FIG. 1 are achieved with the apparatus of FIG. 3. The two idlers 112,113 are required because the punch 100 reciprocates in a path which is oblique, whereas follower pin 116 moves radially in and out as it rides in groove 117. If the punch 100 were replaced with a rotating reciprocated element that reciprocated in a truly radial path, idler 113 could be eliminated; in such case, cable 110 would merely be connected to drive pulley 111 and wrapped around idler pulley 112. In either event, the use of cable and pulleys provides a relatively friction-free means of translating oscillation of weighted pulley 111 into reciprocation of a work member, such as punch 100.
The foregoing and other changes may be made without departing from the spirit and teachings of the invention. In actual test of a feasibility model employing one drive pulley (like 111) but only one idler pulley (like 112), it was found that the oscillating eccentric drive pulley could compensate for the inertia load on a rotating reciprocated member, thus establishing the validity of the analytically derived formula described in connection with FIG. 2.
Note that the motion of the oscillating drive mechanism 26 or 111 will approach pure harmonic only if angle θ (the angular displacement of the mass center of said mechanism, see FIG. 2) is less than 21/2°. The term "substantially harmonic," as used herein, is therefore intended to embrace structures where θ may exceed 21/2°. However, θ preferably does not exceed 30°; if it does, the configuration of cam groove 30 or 117 should be mathematically calculated to match the large pendulum oscillations in order to avoid undesirable loads on the corresponding cam and follower.
While the invention has been illustrated as embodied in a retractable pin feed apparatus and in web punching apparatus, it will be apparent that the invention may be employed to control other rotating members that are reciprocated with harmonic motion for performing a desired work operation. Accordingly, the scope of the invention is to be limited only as specified in the claims.
BACKGROUND OF THE INVENTION
Various forms of apparatus have heretofore been proposed to convert rotary to reciprocating motion. In some types of such apparatus, a rotating shaft or roll is operatively connected to a member that is caused to reciprocate relative to and generally transversely of the axis of rotation. Since the rotating reciprocated member is subject to centrifugal force which varies with the distance of the member from the axis of rotation, the member as it reciprocates is subjected to a progressively increasing force during its outbound stroke and a progressively decreasing force during its return stroke toward the axis. Also, since centrifugal force varies as the square of the rotational speed, drastic increases in centrifugal force occur at progressively higher speeds. As centrifugal force increases, heavy loads are imposed on the cam or other elements that are driving the member; these loads are, of course, heaviest during transition from the outbound to the inbound stroke.
Accordingly, some efforts have been made to offset or counteract the effects of these variations in centrifugal force on a member that is concurrently being reciprocated and rotated. In balancing automobile crankshafts, where a plurality of reciprocating members are involved, some move toward the shaft axis as others move away from it, and all are circumferentially spaced in counterbalancing pairs and driven with harmonic reciprocating motion. Counterbalancing is thus relatively easily achieved when a plurality of work elements operate sequentially.
Counterbalancing is more difficult when there is only one rotating reciprocated work member or when all of a plurality of rotating reciprocated work members must operate to conclude their power stroke simultaneously (rather than sequentially). For example, in U.S. Pat. No. 2,494,483, a hollow rotating drum operatively carries a cable-guiding distributor (a single work member) that is reciprocated transversely of the axis of the drum at a constant speed corresponding to the helical pitch of a double-threaded screw (a cam) so that cable will be spooled onto a reel uniformly in successive layers of equal thickness, as is common in fishing reel take-up mechanisms. As the distributor moves rectilinearly leftward, for example, across the axis of the drum, it acts through a sprocket chain to drive clockwise a corresponding degree the sprocket wheel of a centrifugal force compensating mechanism; this tends to offset, to an increasing degree, the effect of the increasing centrifugal force developed as the distributor approaches the left end of its stroke. With this arrangement, operating speeds must be slow because the speed changes abruptly at the end of each stroke, causing a rapid deceleration from constant speed in the leftward direction to zero, then rapid acceleration followed by constant speed in a rightward direction; and conversely.
These various approaches thus counteract, in varying degree, the effect of centrifugal force on a rotating reciprocated member. However, there is a need for a relatively inexpensive yet effective apparatus and method for substantially perfectly counterbalancing the effects of centrifugal force, over a wide range of rotational speeds, on a single rotating work member (or simultaneously actuated plurality of work members) while it is being reciprocated substantially with harmonic motion, to permit operation at very high rotational and reciprocation speeds with minimal load and wear on the parts that reciprocate such member.
SUMMARY OF THE INVENTION
Toward this end, and according to the invention, applicant has found that these objectives can be achieved by an improved apparatus and method which, insofar as is known, have never heretofore been proposed. According to the invention, the work member, while being rotated, is reciprocated by a pendulum-type means that is oscillated at a fundamental natural frequency by the centrifugal force acting on said member, said frequency being synchronized with each revolution of the work member so that the work member will complete a integral number of full reciprocation strokes with substantially harmonic motion during each complete revolution of the work member about its axis of rotation.
Other objects and advantages will become apparent from the following more detailed description of the invention and from the accompanying drawings, wherein:
FIG. 1 is an elevational sectional view of an apparatus embodying the invention and including a rotating forms feed pin reciprocated with substantially harmonic motion by a weighted gear oscillated at a fundamental natural frequency by centrifugal force;
FIG. 2 is a schematic elevational view of a mathematical model of the apparatus of FIG. 1, showing the pertinent parameters for applicable design equations; and
FIG. 3 is an elevational sectional view of a punch apparatus constructed according to a variation of the invention.
DESCRIPTION--FIG. 1
As illustrated in this figure, the apparatus embodying the invention comprises a drive shaft 10 rotated at constant angular velocity by suitable means (not shown). Encircling shaft 10 and disposed side by side are a ring 11 and a cam 12. The ring is secured by a key 13 for rotation with the shaft. The cam is mounted on a bearing 14 and held stationary by means including a screw 15 that connects the cam to a shaft-encircling yoke 16 having a depending portion that is slidable along a guide rod 17. Collars 18,19 cooperate with a spacer ring 20 to retain the ring and cam at preselected fixed positions along shaft 10.
Ring 11 has a rectangular slot 21 extending generally radially inward from its outer periphery. Inset in this slot are complementary portions (only the rear one shown) of a rectangular housing 22. This housing provides complementary half portions of a bore 23 for a retractable tractor feed pin 24; a dish-shaped opening 25 for receiving an oscillatable gear 26 mounted on a shaft 27 having its axis at right angles to the axis of shaft 10; and a cam follower 28 including a laterally projecting pin 29 that rides in a cam groove 30 in the inner radial face of cam 12.
Rack teeth 31 formed in one side of pin 24 mesh with teeth 32 on gear 26 to convert rotary motion of the gear into reciprocating axial movement of the pin. Gear 26 is oscillated, in the manner hereinafter to be described, and has a pendulum-like weight 33 of calculated mass disposed to provide a preselected radius of oscillation r (see FIG. 2). This weight is so located that its mass center of oscillation is farthest from the axis of shaft 10 when pin 24 is located at the midpoint of its reciprocation stroke. Rack teeth 34 formed along one side of follower 28 mesh with the teeth 32 of oscillatory gear 26.
OPERATION--FIG. 1
In operation, as shaft 10 starts to rotate, cam 12 through follower 28 will rotate gear 26 to one limit of its preselected oscillatory amplitude to initiate its pendulum-like oscillation; whereupon centrifugal force will cause weight 33 to maintain the gear oscillating with said preselected amplitude but at a frequency that increases as the angular velocity of the shaft increases. The mass center and the radius of oscillation are calculated in the manner presently to be described to cause gear 26 to oscillate at a fundamental natural frequency synchronized with the angular velocity of pin 24 so the pin will complete an integral number of substantially harmonic reciprocations per revolution of the shaft 10. However, cam 12 and follower 28 are provided to positively ensure that such synchronization will be maintained despite any frictional drag; this result is achieved by the harmonic-ensuring configuration of cam groove 30.
It should be noted that the driving power for reciprocating pin 24 is provided primarily and almost exclusively by the centrifugal-force-induced oscillation of gear 26; that cam 12 and follower 28 provide essentially negligible driving power; and that the load on the cam and follower is therefore negligible and does not vary substantially over a wide range of different constant angular velocities of the shaft or even during relatively low rates of acceleration or deceleration to a different velocity. The improved apparatus herein disclosed thus desirably enables the shaft to rotate at very high speeds that would create unacceptable cam and follower loads in conventional apparatus because centrifugal force on the rotating reciprocated member (in this case pin 24) increases as the square of the angular velocity of the rotating means (shaft 10) as well as directly proportional to the distance of the rotating reciprocated member from the axis of rotation.
DESCRIPTION--FIG. 2
To minimize the load on cam 12 and follower 28, and achieve the desirable results heretofore described, it is essential that centrifugal force cause gear 26 to oscillate at a fundamental natural frequency that is so synchronized with the angular velocity of the shaft that pin 24 will complete an integral number of substantially harmonic reciprocations during each complete revolution of the shaft and hence of the pin.
Where one harmonic reciprocation per revolution is desired, this requirement can be achieved by designing the gear 26, pin 24 and follower 28 to satisfy the following condition:
and
m 1 R 1 = m 2 R 2
where, as shown in FIG. 2,
m and I are the mass and inertia of gear 26;
r is one-half the pitch diameter of gear 26;
r is the radius of oscillation of gear 26;
m 1 and m 2 are the masses of pin 24 and follower 28, respectively;
R is the radial distance from the axis of rotation (axis of shaft 10) to the rotational axis of gear 26 (axis of shaft 27);
R 1 and R 2 are the radial distances from the axis of rotation (axis of shaft 10) to the mass centers of pin 24 and follower 28, respectively.
DESCRIPTION--FIG. 3
In the apparatus constructed according to this variation of the invention, the rotating reciprocated member is a punch 100 that is reciprocated in a path obliquely intersecting the axis of rotation of a hollow shaft 101. The punch has a generally triangular cross section providing two V-shaped intersecting sides that adjacent their inner ends are partially relieved to define a V-shaped cutting edge 102. Springs 103 nested in an element 104 act, through a plate 105, on the rear face 106 of punch 100 to maintain the V-shaped sides in slidable surface contact with corresponding mating surfaces of a die 107. This provides a zero clearance cutting action that assures a very clean shear cut and longer wear life of the punch as cutting edge 102 cuts a V-shaped notch to remove a triangular chip C from one edge of a web 108. This cutting is done as web 108 advances partially wrapped around a cylindrical surface 109 of element 104; it being noted that element 104 is secured by suitable means (not shown) to shaft 101 for rotation thereby and that the hollow shaft is connected to a vacuum source (not shown) to duct away the chips C.
As illustrated, a cable 110 passes around a drive pulley 111 and idler pulleys 112,113. Cable 110 is suitably connected to punch 100, drive pulley 111 and a cam follower 114. Pulley 111 has a pendulum-like weight 115 of calculated mass disposed to provide a preselected radius of oscillation. As with weight 33, weight 115 is so located that its mass center of oscillation is farthest from the axis of shaft 101 when punch 100 is at the midpoint of its reciprocation stroke. Cam follower 114 has a laterally projecting pin 116 that rides in a cam groove 117 in the inner radial face of a stationary cam 118 that is suitably anchored and disposed in encircling relation about the rotating shaft 101.
In operation, as shaft 101 starts to rotate, cam 118 through follower 114 will rotate pulley 111 to one limit of its preselected oscillatory amplitude to initiate its pendulum-like oscillation. Thereafter, centrifugal force will cause weight 115 to maintain drive pulley 111 oscillating with said preselected amplitude but at a frequency that increases as the angular velocity of shaft 101 increases. The mass and radius of oscillation of weighted pulley 111 are calculated to cause the pulley to oscillate at a fundamental natural frequency synchronized with the angular velocity of punch 100 so the punch will complete an integral number of substantially harmonic reciprocations per revolution of shaft 101. As in the earlier embodiment, cam 118 and follower 114 are provided merely to positively ensure that such synchronization will be maintained despite frictional drag; this is achieved by pin 116 riding in the harmonic ensuring configured groove 117.
It should be noted that all of the advantages previously described in connection with the embodiment of FIG. 1 are achieved with the apparatus of FIG. 3. The two idlers 112,113 are required because the punch 100 reciprocates in a path which is oblique, whereas follower pin 116 moves radially in and out as it rides in groove 117. If the punch 100 were replaced with a rotating reciprocated element that reciprocated in a truly radial path, idler 113 could be eliminated; in such case, cable 110 would merely be connected to drive pulley 111 and wrapped around idler pulley 112. In either event, the use of cable and pulleys provides a relatively friction-free means of translating oscillation of weighted pulley 111 into reciprocation of a work member, such as punch 100.
The foregoing and other changes may be made without departing from the spirit and teachings of the invention. In actual test of a feasibility model employing one drive pulley (like 111) but only one idler pulley (like 112), it was found that the oscillating eccentric drive pulley could compensate for the inertia load on a rotating reciprocated member, thus establishing the validity of the analytically derived formula described in connection with FIG. 2.
Note that the motion of the oscillating drive mechanism 26 or 111 will approach pure harmonic only if angle θ (the angular displacement of the mass center of said mechanism, see FIG. 2) is less than 21/2°. The term "substantially harmonic," as used herein, is therefore intended to embrace structures where θ may exceed 21/2°. However, θ preferably does not exceed 30°; if it does, the configuration of cam groove 30 or 117 should be mathematically calculated to match the large pendulum oscillations in order to avoid undesirable loads on the corresponding cam and follower.
While the invention has been illustrated as embodied in a retractable pin feed apparatus and in web punching apparatus, it will be apparent that the invention may be employed to control other rotating members that are reciprocated with harmonic motion for performing a desired work operation. Accordingly, the scope of the invention is to be limited only as specified in the claims.