Rotatable cam limit switch with variable timing and dwell

A rotatable cam limit switch with a switch operating cam mounted directly on a continuously rotating drive shaft and axially shiftable relative to the shaft. The drive shaft is also provided with a "fast thread" for adjustable axial positioning of a timing element in slidable engagement with the cam. Manual axially adjustable yoke elements respectively engage the cam and timing element for establishing preselected switch dwell time and phase relationship between said switch and said shaft.

BACKGROUND OF THE INVENTION 
This invention relates generally to continuously rotating limit switches; 
and, more particularly, to a switch used in connection with machines 
having repetitive cycle of operation, in which use this limit switch 
renders possible the opening and closing of independent circuits at any 
desired angular position, and keeping these circuits open or closed for 
practically any desired angular travel. 
Switches of the present type have a wide application in programming and 
time-sequence operations. They are commonly used on power-presses and 
similar machinery, where a speed change, or even a complete stoppage or 
reversal of the part or all of the machinery, is required of certain 
positions of the main drive. 
Most of the prior art switches comprise juxtaposed adjustable disc-like 
cams mounted on and rotatable with a rotating shaft, the lobe or lobes or 
each cam making contact at various stages of rotation with an independent 
roller-type contact unit. Quite complex and expensive devices have been 
developed through the years for adjusting the angular position and angular 
size of a particular cam lobe. 
Examples of the type of switches involving the field of this invention are 
illustrated in U.S. Pat. No. 2,903,528 granted to E. H. Kuhn assigned to 
the assignee of the present invention and recent developments, such as 
those disclosed in U.S. Pat. Nos. 3,465,269 and 3,721,780 granted to R. V. 
Hendershot and to R. R. Kelly et al, respectively. 
Certain prior art devices which provide both timing and dwell features 
require a plurality of parallel shafts for supporting and adjusting switch 
components. It will be apparent that efforts to minimize the number of 
parts will also minimize the adverse affects of improper alignment between 
the shafts and between the various members, such as cooperating worm 
gears. Also, a reduction of parts reduces costs, friction and free play of 
the cooperating elements comprising the switch assembly. 
The present invention contemplates the achievement of the various functions 
of the prior art, but in a relatively simplified device using a minimum of 
parts, which in turn provide a minimal amount of friction and free play, 
as well as material reduction of cost. 
SUMMARY OF THE INVENTION 
The rotatable cam limit switch of this invention is useful for varying "on" 
and "off" time of an electrical switch or switches and for varying or 
regulating the point in time in which selected operating conditions occur. 
The assembly includes a drive shaft which may be threaded with a so-called 
"fast threaded" portion, or which shaft may support a molded member 
containing the desired thread. A timing adjust sleeve is disposed 
circumjacent to the drive shaft and threadingly engages the threaded 
portion of the drive shaft for axial adjustment relative to the shaft. An 
elongated, generally cylindrical, tubular cam member is provided for 
operating an electric switch or switches responsive to the movement of an 
associated cam follower. The cam member includes a through bore arranged 
to slidably receive the external surface of the timing adjust sleeve. 
Means, such as mating non-circular surfaces, are provided for preventing 
relative rotation between the sleeve and the cam in order to permit the 
cam to rotate concurrently with the sleeve as the shaft rotates. 
Both the timing adjust sleeve and the cam preferably include laterally 
extending yoke members slidably engaging the respective sleeve and cam and 
arranged to be manually, longitudinally moved to adjust the axial position 
of the respective sleeve and cam while the drive shaft is in motion. The 
yoke members further serve to respectively retain the sleeve and cam in 
the desired adjusted position.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
The rotatable cam limit switch of the present invention is indicated 
generally by the numeral 10 and comprises an enclosure or housing 11 which 
supports and protects the entire mechanism. 
The housing 11 is preferably of a die-cast metallic construction defining 
opposed supporting sidewalls 12 and 13 including openings for receiving 
oil-impregnated, sintered bushings 14 and 15 for supporting an input or 
drive shaft 16. The external portion 17 is sealed at its entrance into the 
enclosure 11 with an elastomeric lip-type shaft seal 18. 
The input or drive shaft 16 is provided for at least a portion thereof with 
a "fast thread" or "fast traverse" portion 20 which can be integral with 
the shaft, or can be a thermoplastic molding pressed on and locked to the 
shaft, or it can be a formed metal tube, pressed on or locked to the 
shaft. 
A timing adjust sleeve 21 comprising a metallic tubular member defining a 
hexagonal outer surface (see FIG. 3) with a bore containing 
thread-engaging means, such as a pin 22 forced into a transverse opening 
in the sleeve 21, or may take the form of "fast thread" machined 
internally of the bore of the sleeve 21 (not shown) for engagement with 
the threaded portion 20. One form of "fast thread" which may be used has 
1.80 inches pitch for every 360.degree., i.e., the sleeve will traverse 
1.8 inches between centers of each spiral convolution. 
The operating cam 23 is tubular and includes a bore having an internal 
hexagonal shape to permit a slip-fit over the timing adjust sleeve 21. 
Thus, the cam is free to slide longitudinally relative to the sleeve 21 
and arranged to rotate therewith. It should be noted that although the 
external surface of the sleeve 21 and the internal surface of the cam 23 
are shown in their best mode as hexagonal, actually any contour permitting 
relative slidable motion between the parts, and yet retaining a 
non-rotational relationship between the parts, will work satisfactorily. 
For instance, although not shown, the external surface of the sleeve 21 
may be provided with at least one longitudinal groove arranged to slidably 
receive an inwardly extending tang portion on the external surface of the 
cam 23; or the groove or grooves may be formed internally of the bore of 
the cam 23 and engage an upright pin or flanged tongue on the sleeve, if 
so desired. 
The operating cam 23 may be a glass-reinforced, self-lubricating 
thermoplastic molding, or it may be of a sintered metal compression 
molding. The external surface of the cam 23 is similar to the surface 
described in the cam of U.S. Pat. No. 3,465,269 issued to Hendershot. That 
is, as illustrated in FIGS. 1 and 3, the cam 23 is formed as a generally 
cylindrical member having a cylindrical body portion 24 providing an 
elongated raised node or land portion 25 formed integrally with body 
portion 24. Land portion 25 projects outwardly of the circumference of the 
body portion 24 with its exterior defining a cylindrical segment providing 
a raised camming surface; the lesser diametered exterior surface of body 
portion 24 also constituting a cylindrical segment forming a depressed 
camming surface 29. The raised cam surface of portion 25 is uniform in 
diameter and triangular in shape. If represented in a developed plane, 
portion 25 would appear as right triangular surface, the base of the 
right-hand end of the cam 23 and the hypotenuse of which comprises an 
elongated riser 26 extending spirally around the cylindrical body portion 
24. The leg of such triangular surface also constitutes a linear riser, 
indicated at 27 which extends generally parallel to the lengthwise axis of 
the cam 23. In a similar fashion, the cylindrical exterior of the body 
portion 24 not occupied by raised land portion 25, constitutes a depressed 
cam surface 28, bounded by the two riser portions 26 and 27 and the 
left-hand end of the cam as seen in FIG. 1. In general, it may be stated 
that the cam 23 constitutes a more or less cylindrical member having a 
spiral riser extending between a depressed cylindrical surface segment and 
a raised cylindrical surface segment thereof with such surface segments if 
developed in a plane, being configured generally as triangular. 
At the left-hand end of the cam 23, as viewed in FIG. 1, there is provided 
a kerf or annular groove 30 which receives and cooperates with the outer 
ends of a bifurcated arm portion 31 of a shifting yoke member 32. The yoke 
portion 32 is internally threaded to receive the threaded portion of the 
dwell adjust shaft 35. The shaft 35 is headed at the right-hand end, as 
viewed in FIG. 1, to provide a tamper-proof style of hexagonal socket 36 
for manual adjustment with a special mating wrench (not shown). For 
instance, the socket 36 of the preferred embodiment includes an upstanding 
pin 37 which will provide interference means for preventing the entrance 
of the usual "Allen" style wrench. The adjustment wrench (not shown) is of 
hardened steel including a reentrant hole for receiving the pin 37. Thus, 
only the "setup man" or other authorized personnel having the special 
wrench would be free to make the adjustment. It is within the province of 
the present invention, however, to provide plastic manually operated 
adjustment knobs (not shown), or other means of manual adjustment, such as 
knurling the ends of the shaft, if so desired. 
As viewed in FIG. 1, it will be noted that the timing adjust sleeve 21 also 
includes a kerf or annular groove 40 for receiving the bifurcated arm 
portion 41 of the yoke 42. The yoke 42 is internally threaded to receive 
the threaded portion of the timing adjust shaft 43. The shaft 43 is 
terminated at its right end, as viewed in FIG. 1, in the same manner as 
the shaft 35. That is, this shaft also includes a hex socket portion 44 
with an upstanding pin 45 for manual adjustment of the shaft 43. The yokes 
32 and 42 each include laterally extending pointer arm portions 46 and 47, 
respectively. 
It will be observed from FIGS. 1 and 2 that the housing or enclosure 11 
includes at its upper surface, as viewed in FIG. 1, spaced openings for 
receiving dwell position and timing position scale means 48 and 49, 
respectively. It will be further observed from FIG. 2 that the distal ends 
of the respective pointer portions 46 and 47 may be viewed through the 
scales 48 and 49, respectively, to indicate the position of the cam 23 and 
the timing adjust sleeve 21. The scale assemblies 48 and 49 each consist 
of metal, plastic or glass printed scales and a glass or protective 
window. The pointer arm portions 46 and 47, in conjunction with the scales 
48 and 49, serve as a setting index for the timing and dwell of the 
subject device. 
The enclosure or housing 11 is cast to provide internal raised embossments 
51 and 52 which are tapped to provide two conduit entrances 53 and 54. A 
removable front bearing plate 55 is die cast to provide bushing seats 56 
and 57 for supporting the timing adjust shaft and the dwell adjust shaft, 
respectively. 
Any of the several types of switch modules may be used for operation by the 
rotating cam 23. For instance, a precision switch having a moment arm for 
supporting a cam at one end and actuating a switch operator at its 
opposite end, similar to that shown in the Hendershot U.S. Pat. No. 
3,465,269 may be used. However, the present invention contemplates the use 
of a snap action, double toggle, electric switch indicated generally by 
the numeral 60, and of the type shown and described in U.S. Pat. No. 
2,791,656, issued to William F. Dehn and Roy E. Wilson, for "Contact 
Actuating Quick Action Switch" and assigned to the assignee of the present 
invention. Only so much of the structure and operation of the switch 60 
will be described as is necessary for an understanding of the present 
invention, and attention is drawn to the Dehn et al patent for a full 
description of the switch. 
The toggle switch comprises an insulating molded housing 61 defining a 
central cavity 62 within which there is disposed a reciprocally movable 
carrier 63. The carrier 63 has depending supporting abutments 64 at each 
end and a spring seat 65 extending downwardly from the carrier 63 to 
retain the upper end of a biasing switch spring 66 held in place within a 
recess of the housing 61. The carrier 63 is normally urged upwardly to a 
position as shown in FIG. 1 by the switch spring 66 and upper travel of 
the carrier 63 is limited by stops formed in the housing 61 and that 
engage the upper surface of the plunger 67. 
It will be observed that the plunger 67 has been modified from that shown 
in the aforementioned Dehn et al U.S. Pat. No. 2,791,656. That is, the 
plunger 67 is adapted to receive a tubular retainer 68 extending 
thereabove. The tubular retainer 68 is preferably of a hardened metal 
material and contains at least one hardened steel ball, and preferably two 
steel balls 69 resting on a hardened steel wear plate 70. The retainer 68 
is slightly pinched, crimped or otherwise provided with means for loosely 
retaining the uppermost ball 69 within the bore of the tubular retainer 
68. This is not necessary to complete the invention, but does serve to 
minimize frustration in assembly caused by the balls dropping out of the 
retainer as the cam 23 and the uppermost ball 69 are positioned relative 
to one another. It will be further understood that the preferred 
embodiment includes the two cooperating balls for minimizing friction, but 
that, in certain instances, it may be desirable to provide only one ball. 
It will be apparent that the balls 69 seated in the retainer 68 provide a 
direct acting cam follower which rises and falls with respect to the 
operating areas of the cam 23 to provide a means of actuating the switch 
60 through operation of the plunger 67. 
A thin resilient leaf spring 71 is inserted between the abutments 64 of the 
carrier of the carrier 63. The leaf spring 71 is of a length slightly 
greater than the distance between the abutments 64. Upon inserting the 
leaf spring 71, the abutments 64 are deflected slightly outwardly and the 
resilient leaf spring 71 is placed under compression and stressed beyond 
the point where bending occurs to assume a bowed configuration. Portions 
of the leaf spring 71 are cut away to form a pair of movable contact 
blades 72. The movable contact blades 72 are formed as a unitary whole 
with the leaf spring 71 and each is deflectable at its free end which 
mounts a movable contact 73. 
A pair of upper fixed contacts 75 is disposed above the leaf spring 71 and 
a pair of lower fixed contacts 76 is disposed below the leaf spring 71. 
Contact terminals are provided to mount each of the stationary contacts 75 
and 76. 
In the absence of force exerted on the top of the plunger 67, the leaf 
spring 71 will be bowed downwardly (not shown) under the urging of the 
switch spring 66 and the movable contacts 73 will bear against the lower 
fixed contact 76 with the contact blades 72 deflected to provide contact 
force. When a downward force is applied to the top of the plunger 67, due 
to contact between the upper ball 69 and the raised node 25 as shown in 
FIG. 1, the plunger and carrier 63 will be urged to the lower position and 
in opposition to the urging of the switch spring 66. In this position, the 
leaf spring 71, as shown, will be bowed upwardly and the movable contacts 
73 will press upon the upper fixed contacts 75 with the contact blades 72 
deflected to provide contact force. 
From the foregoing description of the cooperating elements of the present 
invention, it will be observed that manual rotational adjustment of the 
socket 36 and attendant rotation of its related dwell adjust shaft 35 will 
cause corresponding axial shifting of the cam 23 with respect to the 
stationary cam following roller or ball 69 on the switch 60, to thereby 
effectively alter the extent of the raised land surface or node 25 on the 
cam 23 as it is engaged by the upper ball 69. 
Thus, considering the position of the upper ball 69 of the switch 60 to be 
initiated by depression of the switch plunger 67 from its position shown 
in FIGS. 1 and 2, the duration of switch "on" time can be regulated or 
variably adjusted according to the axial positioning of the cam 23 along 
sleeve 21. This function of axially shifting the cam 23 is reflected on 
the scale 48 as previously mentioned. It will be noted, for example, that 
in the position of the ball 69 and cam 23, shown in FIG. 1, the balls 69 
are engaged with an uninterrupted end portion of the uniform cylindrical 
exterior surface of the cylindrical body portion 24 of the cam 23. Thus, 
the "on" time at that relative position between the cam and cam follower 
is zero, as reflected on the scale 48 and the related pointer arm 46 (see 
FIG. 2). Conversely, shifting of the cam means to the left, as viewed in 
FIG. 1, so that the uppermost ball 69 is in engagement with the 
uninterrupted depressed cylindrical surface portion 29 at the left-hand 
end of the cam 23, will produce 100% switch "on" time. Variations, of 
course, will be determined by the relative position between the ball 69 
and the cam 23. 
Axial movement of the cam 23 will be affected by the manual rotation of the 
hex socket 36, the shaft 35 and the threaded yoke 32 with its bifurcated 
arm portion 31 engaging the annular groove 30 in the cam 23. 
The trim of the cam 23 with respect to the cam follower ball 69 for 
adjustable switch "on" time, as immediately above noted, is effectively 
coupled in the present device to the function of phase shifting the cam 23 
with respect to the rotational movement of the input or drive shaft 16. 
Such phase shifting relationship is brought about by means of the "fast 
threaded" portion 20 at the right-hand end of the shaft 16 as viewed with 
respect to FIG. 1. The timing adjust sleeve 21 with its thread engaging 
means, such as the internally extending pin 22, in engagement with the 
threads of the portion 20 of the shaft 16 will be caused to move in an 
axial direction with respect to the shaft 16 by manual rotation of the 
hexagonal socket 44 of the timing adjust shaft 43. The threaded shaft 43 
engages the threads of the yoke 42, which engages the groove 40 on the 
sleeve 21 by means of its bifurcated arm portion 41. Movement of the 
sleeve 21 with respect to the shaft 16 correspondently causes rotation of 
the cam 23 and consequent phase shifting of the cam 23 with respect to the 
shaft 16. 
By this expedient, the point in time at which either of the riser portions 
26 or 27 of the raised cam surfaces is presented to the cam follower ball 
69 of the switch 60 may be accordingly advanced or retarded. In other 
words, the cam is phase shifted to alter shift operation except, of 
course, for such relative position of the cam follower ball 69 and the cam 
23 as illustrated in FIG. 1, whereat the cam follower ball 69 engages a 
continuous uninterrupted surface of the cam 23. 
From the foregoing description, it will be appreciated that the embodiment 
of the improved rotating cam limit switch described herein provides an 
effective means for controlling operation of an electrical switch means, 
both as to the point in time which a switch may be activated or 
deactivated in regard to a source of fixed cycle of motion applied to the 
input shaft 16. There is also provided an effective means for adjustably 
varying the duration of a given operating condition for the switch means, 
such as the degree of "on" or "off" time, according to the axial position 
of the cam 23 relative to its stationary follower 69. Such adjustments can 
obviously be made during rotational movement of the drive shaft 16. 
As previously stated, the present functions may also be achieved as 
described in the Hendershot U.S. Pat. No. 3,465,269. The present invention 
takes advantage of the functional operation of that device and reduces 
various operating members of that device to their lowest common 
denominator. That is, rather than requiring five parallel shafts including 
continuously rotating shafts and adjustment shafts traversing the cavity 
length of the enclosure or housing 11, the shafts are reduced to three 
components. It will be readily observed that the single-shaft design 
(other than normally stationary adjustment shafts) promotes ease of 
assembly due to lack of critical multiple-shaft alignment problems. In 
addition, the present device eliminates a number of gears requiring great 
care in assembly of both the gears and the shafts to achieve proper 
alignment between members. Improper alignment may result in increased 
operating torque tending to shorten the life of a device. 
Other prior art devices, such as the device described in the E. H. Kuhn 
U.S. Pat. No. 2,903,528, includes a multiplicity of cooperating parts and 
specially machined worm gear members, as well as cam members that are made 
of several pieces rather than combined into one cylindrical device as 
described herein. Similar adjustable rotating cam limit switches are also 
shown in the Cork et al U.S. Pat. No. 3,120,595 and the Hermale U.S. Pat. 
No. 3,483,344, each of which require specially machined parts of 
relatively complex and expensive construction. 
It will be observed that, although a single switch assembly is shown and 
described herein, several of the assemblies may be arranged in 
side-by-side relationship where more than one switch and cam arrangement 
are desired. Each of the operating shafts may be simultaneously rotated by 
means of pulleys or meshing gear arrangements which are not herein shown 
and do not form a part of the present invention. Such arrangements are 
known and understood by those skilled in the art.