Magnetic clutch and brake assembly

A positive acting magnetic clutch and brake assembly characterized by including a movable, magnetic member provided with two sets of detents arranged respectively on its opposing outer surfaces. The member is alternately shiftable into either a brake position, in engagement with a braking post mounted to engage one of the sets of detents, or to a drive position in which a reciprocally mounted mechanical dog is engaged with the other set of detents in a non-slip driving coupling between the magnetic member and a clutch assembly. A reciprocal mounting arrangement for the dog enables the magnetic member to be moved into driving contact with the clutch assembly before the dog becomes positively engaged with any of the detents on the magnetic member.

BACKGROUND OF THE INVENTION 
The invention relates to a magnetic clutch and brake assembly for 
selectively coupling a driven gear to either a power input idler gear, or 
to positively secure the rotatable gear in a braked position. More 
particularly, the invention relates to a clutch and brake assembly that is 
useful in driving and controlling the position of rotatable instrument 
indicating dials such as the decade gear driven indicating pointers 
commonly employed on electrical power measuring meters. 
A wide variety of magnetic clutch and brake mechanisms are generally 
well-known in the prior art. An example of a relatively recently developed 
magnetic clutch and brake mechanism that has been used successfully in 
conjunction with an electric meter dial drive is described in U.S. Pat. 
No. 4,050,020, which issued on Sept. 20, 1977 and is assigned to the 
assignee of the present invention. In fact, the unique features of the 
present invention involve improvements that can readily be made in the 
type of magnetic clutch and brake mechanism disclosed in that earlier 
patent. 
As a consequence of operating experience with the type of magnetic clutch 
and brake assembly disclosed in that patent, it was discovered that many 
electric meter applications demand the provision of the more positive 
driving and braking actions than are provided by that magnetic clutch and 
brake mechanism. The mechanism described in that patent depends solely on 
friction and magnetic coupling between its relatively movable components 
to afford desired clutching and braking functions. Accordingly, the torque 
capability of the device is limited to the holding strength of the 
combined friction and magnetic forces between two sliding clutch surfaces. 
Although under most normally encountered meter operating conditions little 
or no slippage does, in fact, occur between either the clutch or the 
magnetic brake of those mechanisms, field experience has shown that 
undesirable slippage will occur in those few applications where the meter 
is subject to excessive vibration. Of course, when such slippage occurs, 
which the shiftable magnetic member of such a clutch and brake assembly in 
either its driving or braking mode, some error is introduced in the meter 
dial readings. The slippage either reflects relative movement of the 
indicating input gear train, which is not recorded on the movable dials of 
the meter register, or it may represent random error in either an up-scale 
or down-scale movement of the register dial due to random movement induced 
in the dials by vibration and rotation of the dial gear train when it is 
supposed to be held securely in a braked position. In order to avoid such 
undesirable errors in resultant meter readings, it is necessary to improve 
the type of magnetic clutch and brake mechanism described in the foregoing 
patent by incorporating an economically feasible positive driving and 
braking means in it. 
Accordingly, it is a primary object of the present invention to overcome 
the above-noted disadvantages of known types of magnetic clutch and brake 
mechanisms by providing an accurate, and economical to manufacture, clutch 
and brake assembly that is free of such shortcomings. 
Another object of the invention is to provide a magnetic clutch and brake 
assembly that has a positive, high torque drive coupling and brake 
mechanism that prevents more than a predetermined minimum angular degree 
of slippage between a shiftable magnetic member and associated idler gear 
and braking post. 
Yet another object of the invention is to provide an alternative drive 
coupling between a shiftable magnetic member of a magnetic clutch assembly 
that is operable to enable the magnetic member and clutch assembly to 
engage one another in driving relationship without requiring a positive 
drive coupling between the members to be engaged in its positive driving 
relationship. 
A still further object of the invention is to provide a magnetic braking 
assembly with a positive brake means that mechanically prevents more than 
a predetermined degree of angular rotation of a shiftable magnetic member 
after it is moved to its braked position even when the mechanism is 
subjected to substantial mechanical vibration. 
Additional objects and advantages of the invention will be apparent to 
those skilled in the art from the description of it presented herein 
considered in conjunction with the accompanying drawings. 
SUMMARY OF THE INVENTION 
In one preferred embodiment of the invention a magnetic clutch and brake 
assembly is provided with a shiftable magnetic member that is selectively 
movable, responsive to energization of an associated solenoid coil, 
between a brake post and an input idler gear. The shiftable magnetic 
member is provided with first and second sets of detents that cooperate, 
respectively, with the brake post and a reciprocally mounted dog 
positioned in driving relationship on the idler gear. Both the brake post 
and reciprocally mounted dog are made of magnetic metal that is attracted 
to the shiftable magnetic member thereby to cause these components of the 
assembly to be magnetically pulled into one of the associated sets of 
detents when the shiftable magnetic member rotates sufficiently to align 
them with the detents. The dog is positioned in a slot formed in the idler 
gear assembly and restricted in its axial movement between an idler gear 
core member and a collar provided for this purpose on a shaft supporting 
the dog. Within this restricted range of movement the collar is 
retractable to enable the magnetic member of the assembly to contact the 
core portion of the idler clutch assembly in driving relationship without 
requiring the dog to be aligned with, or positioned in positive driving 
engagement with, one of the detents in the shiftable magnetic member. The 
slot for positioning the dog is made narrow enough to keep its axial teeth 
aligned with the shaft on which it is mounted so that the teeth will drop 
into the detents on the magnetic member as they become aligned with the 
teeth.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
The preferred embodiment of the invention is particularly suitable for 
application with a time-of-day meter register and associated register 
control means of the kind fully described in the above-mentioned U.S. Pat. 
No. 4,050,020. Accordingly, the description of the invention presented 
here will be limited to its characteristic features, because reference to 
that prior art patent may be made by any reader desiring a more thorough 
explanation of the type of meter environment and associated clutch and 
brake control circuitry that is suitable for such an application of the 
invention. Referring now to FIG. 1 of the drawing, there is shown a 
magnetic clutch and brake assembly 1 that is constructed in accordance 
with the invention. The assembly is mounted, in a manner that will be more 
fully explained below, between two frame plates 2 and 3 of an electric 
meter register, which may be of any suitable conventional form. As is more 
fully explained in the above-mentioned patent, the register plate 2 also 
supports a series of meter indicating dials that are driven in normal 
fashion by a decade gear train, the input gear of which is positioned in 
continuous meshing engagement with a gear portion 4A of magnetic member 4 
in the clutch and brake assembly 1. Such dials and their associated decade 
gear train are not illustrated in FIG. 1 because it is only necessary to 
an understanding of the present invention to recognize that the decade 
gear train has an input rotatable gear that is continually meshed with the 
integral gear wheel 4a formed on the magnetic member 4. Although the meter 
dial pointers, associated decade gear train and input rotatable gear are 
not illustrated in FIG. 1, such components are fully shown and described 
in the above-referenced patent if the reader wishes to gain more 
familiarity with such mechanisms. In the interest of completeness, the 
disclosure of U.S. Pat. No. 4,050,020 is included herein by reference 
thereto. 
As shown in FIG. 1, a shaft 5, which in this embodiment is formed of a 
non-magnetic material such as brass is rotatably mounted in a pair of 
metal bearings 6 and 7 that are staked, respectively, into the meter frame 
plates 2 and 3. Axial movement of the shaft 5 relative to the plates 2 and 
3 is restricted within a desired tolerance by the collars and shoulders 
shown on the shaft. 
A suitably compact solenoid coil 8 is mounted in spaced relationship to the 
input gear for the decade dial gear train (not shown). Conventional 
mounting means such as welding or metal screws are used to secure the 
housing of the solenoid coil to a third frame plate 9 of the meter 
register with which the clutch and brake assembly 1 is associated. In 
order to operate the clutch and brake assembly 1 of the invention to move 
the magnetic member between the brake post 15 and the idler gear assembly 
10, means (not shown) for selectively energizing the solenoid are 
connected to coil 8 to enable it to be energized with direct current to 
produce magnetic flux fields of either a forward or a reverse polarity 
through the center of the coil. A suitable control circuit and solenoid 
energizing means to afford this desired function is described in the 
above-referenced U.S. Pat. No. 4,050,020. Such means for selectively 
energizing the solenoid coil 8 are operable to move the magnetic member 4 
between a braked position and a clutch engaging position thereby to 
alternately brake the input rotatable gear for the decade dial gear train 
or to couple it in driving relationship to an idler clutch gear 10A that 
forms part of a clutch idler gear assembly 10, which also includes a core 
member 10B on which the gear 10A is staked. The core member 10B is formed 
of magnetizable metal, such as soft iron, so that it is continuously 
biased toward the magnetic member 4 by the flux produced by the permanent 
magnet material of that member. 
The core member 10B is further characterized by having an axial slot 11 
formed in the end thereof that is closest to the magnetic member 4 when 
the component parts are assembled on shaft 5. An end view of the slot 11 
is shown in FIG. 5, while one side of the slot 11 is shown in FIGS. 1 and 
2. 
To afford the positive clutching objective of the invention, a dog 12 is 
mounted between the magnetic member 4 and the clutch idler gear assembly 
10, as shown in FIGS. 1, 2 and 5. In this form of the invention the dog 12 
is formed of magnetizable metal such as steel so that it is responsive to 
the magnetic field produced by the magnetic member 4 and is continuously 
biased toward the magnetic member 4 for the purpose that will be more 
fully described below. As is more clearly shown in FIG. 6, the dog 12 
comprises an annulus 12A and a tooth portion comprising two teeth 12B and 
12C that are narrower than the slot 11 in the core portion 10B of the 
clutch gear assembly 10. The annulus 12A is slidably mounted around the 
shaft 5 for reciprocal movement relative to the shaft, and the tooth 
portion (12B, 12C) of the dog is positioned within the axial slot 11 of 
the clutch gear assembly core member 10B. Movement of the annulus 12A away 
from the core member 10B is restricted by a collar 5A on the shaft 5. 
Otherwise, the annulus 12A of dog 12 is free to slide axially between the 
collar 5A and the core member 10B sufficiently to enable the teeth 12B and 
12C to be completely retracted within the slot 11 so that the core member 
10B can be moved into driving contact with the magnetic member 4 without 
requiring the teeth portion of the dog 12 to be positioned in positive 
driving relationship with the detents (described more fully below) in the 
magnetic member 4. In order to keep the dog 12 from being twisted in the 
slot 11, the teeth 12B and 12C of the tooth portion of the dog are made to 
have longitudinal axes substantially greater in length than the width of 
the slot 11. 
The clutch idler gear assembly 10 is rotatably mounted on the shaft 5 and 
is limited in axial movement by engagement on one end with a shoulder on 
the shaft 5 as seen in FIG. 1, while being limited in movement in an axial 
direction at the other end by the bushing 7. Thus, although the assembly 
10 can move axially within this restricted range of movement, it is 
prevented, by engagement with the shoulder on the shaft 5 from following 
the magnetic chamber 4 to which it is attracted by the magnetic flux 
produced by the member 4. 
Pursuant to the invention, a first set of detents 13 and a second set of 
detents 14 are formed, respectively, on opposite ends of the magnetic 
member 4. Some of these detents are shown in the cross-sectional views of 
FIGS. 1 and 2, but can be more fully seen in FIGS. 3 and 4. Each of the 
sets of detents 13 and 14, respectively, comprise a series of angularly 
spaced recesses that are formed in otherwise generally flat areas of the 
end surfaces of the magnetic member 4 thereby to form circular patterns of 
recesses on the end surfaces. In this embodiment of the invention, the 
first and second sets of detents (13 and 14) are formed by molding the 
respective recesses into the magnetic material of magnetic member 4. Of 
course, in alternative embodiments the recesses may be suitably formed by 
machining or otherwise mounting projections or other wall means on the end 
portions of the magnetic member 4 to afford the positive braking and 
clutching functions that will be more fully explained below. 
In order to perform the positive braking desired for the invention, a brake 
post 15 is mounted on the meter frame plate 2 in cooperating relationship 
with the first set of detents 13 for positively braking the magnetic 
member 4 when it is moved to position a portion of the brake post 15 
within a detent of the first set of detents 13. In this form of the 
invention, the brake post 15 is made of magnetizable metal such as soft 
cast iron and is slidably mounted within the bore 16A of a bushing 16 
which is fixedly positioned in the meter register face plate 2. The 
maximum outward limit of movement of the brake post 15 relative to the 
bushing 16 and frame member 2 is determined by a collar 15A or other 
suitable conventional limit stop means mounted thereon, while the inner 
range of movement of the brake post 15 is limited either by its contact 
with the magnetic member 4 or by an indicating pin 15B striking the end of 
a slot in which it is rotatably mounted. Due to the magnetic flux produced 
by the magnetic member 4, it will be understood that the brake post 15 is 
continuously biased toward the magnetic member. Consequently, when the 
magnetic member 4 is moved toward its braked position, as shown in FIG. 1, 
the brake post 15 will be pulled toward either a seated position within 
one of the detents of the first set of detents 13 or on one of the lands 
13A. If the initial contact between the brake post and the magnetic member 
4 causes the brake post to rest on one of the lands 13A (see FIG. 3) 
between the detents, and the magnetic member 4 is subsequently rotated due 
to vibration or other causes, the brake post 15 will be magnetically 
pulled into its lodged, recessed position in one of the detents 13 thereby 
to positively brake the magentic member and prevent any further rotation 
of it relative to the frame member 2. Thus, a primary objective of the 
invention is afforded. 
The second set of detents 14 located on the opposite end of the magnetic 
member 4 is arranged to cooperate with the dog 12 to provide the positive 
clutch operation desired for the invention. Specifically, the dog 12 is 
operable, responsive to the magnetic member 4 being moved by the action of 
solenoid 8 against the idler clutch assembly 10, to enter at least one of 
the detents in the second set of detents 14 thereby to provide a positive 
driving coupling between the magnetic member 4 and the clutch idler gear 
assembly. More specifically, because the slot 11 is formed to slidably 
receive the dog 12 and restrict its angular movement to an angle smaller 
than the arcuate extent of one of the detents in the second set of detents 
14, the angular rotation of the magnetic member 4, and of the continuously 
meshed rotatable gear driving the decade gear train of the associated 
meter dial, is limited to this small angular movement once the teeth 12B 
and 12C of the dog 12 have become seated in the second set of detents 14. 
Of course, such positive clutching action is essential only if vibration or 
other forces tend to cause relative movement between the clutch idler gear 
assembly 10 and the magnetic member 4. Greater movement can occur with the 
present invention only during the limited area of travel during which the 
teeth 12B and 12C of the dog 12 are positioned on the lands 14A (see FIG. 
4) between the detents 14. Such positioning of the dog 12 can occur, as 
briefly explained above, due to the novel mounting arrangement for the 
dog, which allows it to be completely retracted within the slot 11 in the 
core member 10B when the magnetic member 4 is moved against the core 
member. Because of the magnetic attraction between the magnetic member 4 
and the magnetizable metal of the dog 12, there exists means for 
continuously biasing the dog toward the magnetic member 4 thereby causing 
it to seat the tooth portions (12B and 12C) of the dog in a detent (or 
detents) in the second set of detents 14 in response to the magnetic 
member 4 being moved against the core member 10B and rotated sufficiently 
to align the tooth portion of the dog with one of the detents. As 
indicated above, due to the fact that the shaft 5 is made of non-magnetic 
material, it does not interfere with the magnetic means for continuously 
biasing the dog 12 with the force of the magnetic flux on it produced by 
the magnetic member 4 pursuant to the invention. 
It will be recognized that the dog 12 may be formed to have one or a 
plurality of teeth in its tooth portion. In this embodiment of the 
invention two teeth 12B and 12C are provided at diametrically opposing 
points extending from one planar side of the annulus 12A of the dog. The 
detents in the second set of detents 14 on the magnetic member 4 are 
arranged in diametrically opposite pairs to receive therein either or both 
of the teeth 12B and 12C on the dog 12. In alternative embodiments, it 
should be recognized that a dog structure may be successfully employed 
pursuant to the invention even though its teeth are not diametrically 
aligned, because a single tooth becoming lodged in a cooperating recess 
will provide a positive driving torque for the clutch assembly. 
Similarly, it will be apparent that various forms of magnetic members can 
be used to develop a suitable magnetic member 4 for various embodiments of 
the invention. However, as shown in the drawings, in this form of the 
invention the magnetic member 4 comprises a generally cylindrical 
permanent magnet that is formed of pressed powdered magnetic material 
having a gear 4A formed integrally around its perimeter and having the 
first and second sets of detents 13 and 14 molded into opposite ends of 
the cylinder. Of course, a separately formed gear wheel could be used and 
assembled with a magnetic core portion to make the magnetic member 4, if 
desired, in some adaptations of the invention. 
From the foregoing description of the invention it should be noted that 
FIG. 1 illustrates the component parts of the invention with the shiftable 
magnetic member 4 in its braked or positively stopped position. In this 
position the brake post 15 is seated within one of the detents of the 
first set of detents 13 on the magnetic member 4 and the teeth 12B and 12C 
of the clutch dog 12 are disengaged from the detents 14 in the other end 
of the shiftable magnetic member, being retained against the magnetic 
attraction of member 4 by the collar 5A on shaft 5. It will also be 
understood that when energization of the solenoid coil 8 has driven the 
magnetic member 4 to this brake position this action served to drive the 
brake post 15 outward relative to the bushing 16 in which it is slidably 
and rotatably mounted. That outward movement causes the brake post 15 to 
rotate and thereby turn an indicating pointer 15B, positioned in a helical 
slot in bushing 16, so that an operator looking at the face of the meter 
register plate 2A, and the pointer 15B, can readily ascertain the braked 
condition of the clutch and brake assembly. This indicating function is 
more fully described in the above-mentioned U.S. patent. 
FIG. 2 of the drawing shows the shiftable magnetic member 4 in its 
positively engaged driving relationship to which it is driven by 
energizing the solenoid coil 8 in a reverse direction to attract the 
magnetic member 4 into contact with the core member 10B of the clutch 
idler gear assembly 10. The teeth 12B and 12C of the shiftable clutch dog 
12 are seated respectively in either or both detents of the second set of 
detents 14, but these teeth may have initially rested on the lands 14A 
between the detents when the magnetic member 4 was first driven into 
contact with the core member 10B. If that were the case, a clutching 
action for the assembly would have been affected due to the frictional and 
magnetic forces existing between the soft iron of core member 10B and the 
permanent magnet material of magnetic member 4. However, if relative 
rotation subsequently occurs between these two members the teeth 12B and 
12C of the dog will be attracted into the detents 14 by the continuous 
magnetic biasing force exerted on the dog 12 by the magnetic member 4, 
thereby to prevent further relative movement and provide a positive 
clutching action between the magnetic member 4 and the idler gear assembly 
10 pursuant to the invention. 
From the foregoing description of the invention it will be apparent that 
further modifications and alternative embodiments of it may be made 
without departing from its teaching; accordingly, it is our intention to 
encompass within the following claims the true spirit and scope of the 
invention.