High strength magnet-pole piece assembly tool

Apparatus for assembling a pair of high strength magnets and the common pole piece into a unit for use in a disk drive includes a bed with a channel in which the magnets can slide or translate, and a stop centrally located in the channel to prevent execessive impact between the magnets as they slide under the force of mutual attraction toward each other. A recess in the bottom of the channel below the stop is adapted to receive the pole piece, and the attractive force between the pole piece and the magnets firmly attaches the magnets to the pole piece in the desired location after they have been properly positioned with respect to the pole piece by interaction of the stop and channel walls with the magnets. After the magnets have attached themselves to the pole piece, the assembly can be handled without shifting the magnets on the pole piece to allow further manufacturing processes, say baking in an oven where glue on the surface of the magnets or pole piece can be melted to mechanically bond the assembly together.

BACKGROUND/INFORMATION DISCLOSURE STATEMENT 
It is now the usual case that the small transducers on disk memory units 
employing rigid disks are carried by an arm which is rotatably mounted to 
the deck which holds the disk spindle itself. The arm is positioned by a 
powerful permanent magnet motor which rotates the arm to position the 
transducer on the disk at the desired radius. The motors are typically 
designed with extremely high torque so that actuation, i.e. movement from 
one radius to another, of the arm occurs as quickly as possible. 
High torque requires high strength magnets. The magnets are usually made 
from a boron rare earth metal (such as samarium or neodymium) alloy and 
have extremely high flux generating capability. When fully magnetized, 
they are so powerful that a normal person cannot manually restrain the 
magnets from slamming onto the pole piece which mechanically supports 
them, or into each other, with such force that the magnet itself is 
shattered by the impact, causing pieces to fly dangerously around the area 
and damage the magnet beyond use. And if a person is unlucky enough to get 
a finger between such a magnet and any ferrous object, serious injury is 
possible. 
In one particular actuator motor design, a pair of such magnets are coated 
with a thermosetting glue and then mounted in required, spaced-apart 
positions, on a common surface of a pole piece. The magnetic attraction 
between the magnets and the pole piece allows the magnet-pole piece 
assembly to be transported without shifting of the magnets on the pole 
piece to an oven for baking to mechanically bond the magnets to the pole 
piece. 
Two magnet pairs are used to define between them a flux carrying gap in 
which the coil of the actuator motor moves in response to current passed 
through it. The coil is attached to the transducer arm, and in this way 
the arm is rotated to place the transducers at the desired radius. 
A serious problem, alluded to above, is how one attaches and properly 
positions the magnets on the pole pieces without risking one's limbs or 
damaging the magnets. Once they have attached themselves to the pole 
piece, if they are not positioned properly, it is remarkably difficult to 
reposition them before baking. While repositioning can be done manually, 
or even with a tool, when thousands of these assemblies are needed for a 
production run, it is simplest to assure that the magnets are attached 
accurately at the very beginning. 
There appears to be very little in the literature which addresses these 
problems. There are a number of patents which deal with various aspects of 
assembling conventional rotary electric motors. Among these, roughly in 
the order of their relevance, are U.S. Pat. Nos. 4,586,244; 4,608,752; 
4,644,640; 4,126,933; and 4,443,934. 
BRIEF DESCRIPTION OF THE INVENTION 
My apparatus for positioning the magnets on the pole piece takes advantage 
of the fact that each of the magnets used in the actuator design discussed 
above have two pairs of exterior corners, each pair of which defines a 
line intersecting them. The two lines so defined are approximately 
parallel to each other with a predetermined spacing from each other. 
The positioning apparatus includes a non-magnetic bed having a channel 
formed of a pair of opposed and facing interior walls and a floor between 
the walls. The walls are spaced from each other a distance slightly 
greater than the spacing between the magnets' pair of parallel lines so as 
to allow each magnet to slide within the channel with each pair of corners 
defining one of the lines adjacent an interior wall, and permitting only a 
predetermined rotation of a magnet within the channel. There is a recess 
adapted to receive the pole piece, centrally located in the channel floor 
with the surface of the pole piece on which the magnets are to be 
positioned approximately flush with the channel floor. The recess is 
positioned to receive the pole piece so as to create the predetermined 
spatial relationship between each magnet and the pole piece as the magnets 
slide toward each other in the channel and over the pole piece. 
The magnets are initially positioned at the channel ends, preferrably in 
keepers, so that there is no likelihood that the magnets will be 
prematurely attracted toward each other. A magnet pusher at each end of 
the channel simultaneously slides the magnets placed at the ends of the 
channel toward each other until mutual magnetic attraction between them 
pulls them toward each other. A stop is located in the channel above the 
pole piece recess at least partially closing the channel. The mutual 
magnetic attraction pulls the magnets into contact with the stop at a 
point where interaction between the magnets and the stop and channel wall 
causes the magnets to rotationally and translationally position themselves 
on the pole piece in the predetermined spatial relationship. The force of 
the magnetic attraction between the magnets and the pole piece serves to 
maintain the magnets in the predetermined spatial relationship on the pole 
piece. The stop cushions the impact between the magnets so that no damage 
occurs to the parts involved. 
It is preferred that the stop comprise a member protruding into the channel 
above and approximately centered on the recess which receives the pole 
piece. In a preferred embodiment the member is slidably mounted in the bed 
with a tip within the channel. The member's tip has a bevel facing each 
end of the channel. A spring urges the member into the channel. When the 
magnet strikes the bevel, it creates a camming action which forces the 
member's tip out of the channel allowing the magnets to further shift 
under their mutual attraction force into their preferred position on the 
pole piece. The camming of the member's tip serves to decelerate the 
magnets at a rate slow enough to prevent harm to them. 
It is convenient to use a ferrous keeper for the magnet in which the magnet 
is magnetized, thereby avoiding the necessity of handling the magnet by 
itself. 
It is preferred that a cover be placed on the channel so that when the 
magnets position themselves, there is no possibility of them jumping out 
of the channel and possibly causing injury to a worker or damaging 
themselves. 
Accordingly, one purpose of this invention is to allow an assembly 
comprising high strength magnets and a pole piece to be assembled without 
causing damage to the parts involved or to the operator. 
A second purpose of the invention is to allow such an assembly to be 
consistently assembled with the magnets correctly positioned on the pole 
piece. 
Yet another purpose is to allow untrained manufacturing personnel to 
assemble the magnet assembly. 
A further purpose is to allow both magnets of such a dual magnet assembly 
to be simultaneously positioned on the pole piece, thereby speeding the 
assembly process.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
In FIG. 1 the magnet 10 shown therein can be seen to have a block form with 
a pair of substantially flat sides 17 (of which only an edge is shown) and 
18, thereby defining a uniform thickness of the block. Magnet 10 has a 
first pair of exterior corners 11, 12 defining a line 15 intersecting or 
mutually tangent to corners 11, 12, and a second pair of corners 13, 14 
having a second line 16 intersecting or mutually tangent to corners 13, 
14. Lines 15 and 16 are approximately parallel to each other in the plane 
of either side of magnet 10. The magnetization is oriented such that the 
two flat surfaces 17 (only an edge of which is shown) and 18 comprise the 
poles. 
Magnet 10 may be made of any high flux generating, high remanence magnetic 
material. One preferred material, formed into the desired shape by 
sintering, is a recently developed compound comprising approximately 27% 
neodymium, 1% boron, and 72% iron, all by weight. Should such material be 
formed into a magnet 10 such as is shown in FIG. 1 comprising a block 
approximately 0.25 in. (1 cm.) thick with each side 17, 18 having an area 
of approximtely 1.8 sq. in., its attractive force when the flux path is 
efficiently closed is upwards of 70 lbs. (30 kg.) on a flat steel surface. 
Such a magnet can generate 35 kilolines per sq. in. or more of magnetic 
flux. Accordingly, it can be seen that these magnets are definitely not 
toys, and can easily do substantial damage to any surface to which they 
are attracted, unless restrained. Any human body part such as a finger, 
which is caught between such a magnet and a metal surface to which it is 
attracted can be severely injured if the magnet 10 is not restrained. 
FIG. 2 shows two of the magnets 10 of FIG. 1 in a preferred position on a 
pole piece 20 for use in a particular type of disk drive actuator. Side 
17, shown only on edge, has a coating of a thermosetting glue by which the 
magnets 10 are permanently attached to the pole piece 20. A thin coating 
of the glue is placed on sides 17 and 18 before the magnets 10 are 
positioned on the pole piece 20, and the attractive force of the magnets 
10 is more than sufficient to hold them in proper positions on pole piece 
20 given reasonably careful handling. After the magnets 10 have been 
positioned on pole piece 20, the assembly is baked to set the glue and 
mechanically attach the magnets 10 to the pole piece 20. A spacer 21 aids 
in defining the preferred position of magnets 10 on pole piece 20. 
As mentioned above, the magnets 10 are magnetized so that sides 17 and 18 
are the poles. They are oriented magnetically on pole piece 20 so that the 
flat side 17 or 18 of one magnet 10 on pole piece 20 having a north pole 
is coplanar with a side of the other magnet having a south pole. 
Therefore, there is mutual magnetic attraction between the two magnets 10 
carried on pole piece 20 when assembled correctly. More to the point for 
the operation of the invention to be described, these magnets have mutual 
attraction for each other when still several centimeters apart because of 
the needed magnetic orientation with respect to each other. 
As mentioned earlier, handling these magnets requires great caution. 
Accordingly, is is preferred to carry them after they have been magnetized 
in the keepers 32, 33 shown in FIGS. 3a and 3b respectively until they 
have been positioned on the pole piece 20. Keepers 32, 33 are made of a 
magnetically soft iron to which the magnets 10 are strongly attracted. 
Each keeper 32, 33 has a slot 30 slightly wider that the thickness of the 
magnets 10 and which cuts entirely through keepers 32, 33 so as to 
intersect three sides thereof as shown. Slots 30 are of a size allowing 
the magnets 10 to be positioned within them in a preferred spatial 
orientation shown with the second pair of corners 13, 14 near the outside 
of the slot 30, and the first pair of corners 11, 12 adjacent the bottom 
of the slot. The magnets 10 are positioned in their keepers 32, 33 before 
they are magnetized, and are magnetized in the keepers. After 
magnetization, the keepers conduct most of the flux from magnets 10 
through themselves and prevent these magnets from attracting themselves 
unexpectedly to ferrous surfaces. At the same time, the magnetic 
attraction between the keepers and their magnets is so strong that the 
magnets will typically not shift within the slot. This is a useful 
characteristic, since the orientation of the magnet 10 is important when 
attaching it to pole piece 20, and if the orientation of magnet 10 is not 
easily changed in its keeper, a predetermined position of the keeper 
predetermines the position of the magnet as well. 
The apparatus of FIG. 4 is used for correctly positioning a pair of magnets 
10 on a pole piece 20 without running the risk of damage to the parts or 
harm to anyone. The preferred embodiment comprises a sub-base 44 carrying 
four posts 46 on which the remainder of the device is supported. A base 49 
is supported on the ends of posts 46 in spaced apart relationship with 
sub-base 44. The base has a channel in which the actual attachment of the 
magnets 10 to a pole piece 20 occurs. 
Two brackets 48 are attached to opposite sides of base 49, which brackets 
support a pair of compressed air driven magnet pushers, generally 42, each 
of which have a cylinder-piston unit 40 and a non-magnetic anvil 43 at the 
operating end of the piston. Each anvil 43 has a small bevel 70 on its 
contact surface which can be seen better in FIGS. 5 and 6. The bevel is 
chosen to properly orient the magnets 10 as they exit their keepers 32, 
33. Each anvil 43 is approximately aligned with channel 50 so that as a 
pusher 42 is actuated, anvil 43 can enter the adjacent end of channel 50. 
Magnet pushers 42 are actuated by compressed air supplied by hose 71 and 
controlled by a valve 72. Opening valve 72 causes cylinder-piston units 40 
to drive anvils 43 toward each other simultaneously. A conventional spring 
in or double action capacity of the units 40 returns the anvils 43 to 
their retracted position shown in FIG. 4 when the valve 72 is closed. 
Between the end of each anvil 43 when it is in its retracted position as 
shown in FIG. 4 there is a space in which a keeper 32 or 33 may be 
temporarily placed on a rest with its slot aligned with the adjacent 
retracted anvil 43. The height of each anvil 43 is less than the width of 
the slot 30 (dimension .times.in FIG. 3), so that an anvil 43 may enter 
its adjacent slot 30 when the pusher 42 is actuated. The rests supporting 
keepers 32, 33 may be simply surfaces of bed 49. 
Between the keepers 32, 33 (when inserted on their respective rests on base 
49) and on base 49 there is arranged a bed 73 on which there is a channel, 
generally 50, whose bottom or floor 61 may be defined by the upper surface 
of bed 73. It is probably helpful to refer to FIG. 5 from time to time 
during this explanation to better visualize the arrangement of the channel 
50 on bed 73. The floor of channel 50 is accurately aligned with and 
adjacent to the lower surface of each keeper's slot 30. The purpose of 
this is to provide a continuous path for a magnet 10 carried in a keeper 
32 or 33 into channel 50. The edges of bed 73 also serves to prevent the 
keepers 32, 33 from being moved by magnet pushers 42 when they are 
actuated. 
One side of channel 50 is defined by edge 54 of a rear guide block 57; the 
other is defined by edge 55 of front guide block 59. Guide blocks 57 and 
59 may be integral with bed 73, or may be removable and held in place on 
bed 73 by pins or machine screws, not shown. It is preferred that edge 55 
of front guide block 59 have a slight central depression or relief 60 
which has the effect of widening channel 50 slightly in its central 
length. The relief 60 is of an amount which allows the magnets 10 as they 
approach their positions to rotate slightly into the preferred angular 
positions. 
There is in the floor 61 of channel 50, midway from its ends, a recess 62 
whose shape corresponds to that of the pole piece 20 such that the pole 
piece is held without the possibility of it translating or rotating in the 
plane of the floor 61, and yet allowing the pole piece to be easily 
inserted and removed from this recess 62. The bottom of the recess 
supports the pole piece so that the surface of the pole piece 20 to which 
the magnets 10 are to be fastened when in the recess 62, is approximately 
flush with or slightly below the floor 61 of the channel 50. The bottom of 
recess 62 may simply be a part of the upper surface of base 49. The bed 73 
may be lifted by a lifter mechanism, generally 41 in FIG. 4, which presses 
upwards on the bottom surface of bed 73 to make access to the magnet 
assembly easy. An alternative to this is to remove the magnet assembly 
from the top of the recess 62. Another alternative is to make the entire 
bottom of the recess 62 removable, so that the magnet assembly may be 
removed through the bottom of bed 73. 
A magnet stop member 52 is located in the front guide block 59, and is 
adapted to slide from a first position, shown in FIGS. 4, 5, and 6, to a 
retracted position where its tip 58 is almost completely withdrawn from 
the channel 50. The magnets 10 are then free to attract themselves to a 
position as close to each other as the non-magnetic spacer 21 will allow. 
Magnet stop member 52 is normally held with tip 58 protruding into channel 
50 by spring 51, spring 51 having a relatively low deflection force 
allowing tip 58 to be withdrawn easily from channel 50. Tip 58 has a slot 
75 aligned with the centerline of stop 52 to accomodate the end of spacer 
21. 
Stop member 52 is shown in greater detail in FIG. 7. It is preferrably made 
of Nylon (reg. trademark) or some other low friction non-magnetic 
material. Stop member 52 has a cross piece 76 which allows tip 58 to 
protrude only a preselected amount into channel 50, thereby only partially 
closing it. Spring 51 fits into slot 77 to thereby transmit its force to 
member 52 and urge its tip 58 fully into its preferred position in channel 
50. 
It is also preferrable that the tip 58 have a bevel on eaoh side facing 
generally toward one end of channel 50 so that the bevels on tip 58 will 
be the contact points for magnets 10 on stop member 52 as they near the 
end of their range of motion. If the bevel angle is chosen correctly for 
the material from which the magnet stop 52, front guide block 74, and 
magnets 10 are made, as well as the weight and strength of the magnets 10, 
and the deflection force of spring 51 is only a few ounces, the force of 
the magnets' mutual attraction pressing magnets 10 against the bevels will 
create a camming force on stop member 52 causing it to automatically 
retract and position the magnets 10 on pole piece 20 in their 
predetermined spatial relationship. At the same time, the camming creates 
a smooth deceleration of the magnets 10 preventing damaging impact between 
the magnets. For a guide block 59 and magnet stop 52 both made of Nylon 
with smoothly finished rubbing surfaces and magnets 10 as described in 
conjunction with FIG. 1, a bevel angle of 8 -9 degrees from the magnet 
stop's centerline will assure that magnet stop 52 will retract 
automatically from channel 50 when magnets 10 strike the bevels on its tip 
58. All this occurs without any damage to the magnets 10. 
To assure that the magnets track accurately in the channel 50, I prefer to 
close the mouth of channel 50 with a cover 45 which may merely rest on the 
guide blocks 57 and 59 with locating pins (not shown) preventing its 
lateral movement during use. Cover 45 can be thus easily removed to allow 
insertion of each pole piece 20. 
One uses this apparatus to form a magnet assembly by initially placing a 
pole piece 20 in recess 56, and placing the cover 45 in the position shown 
in FIG. 4. Two magnet keepers 32, 33 are prepared with a magnetized magnet 
10 positioned in each with its pair of corners 13 and -4 approximately 
aligned with the outside corners of slots 30 as shown in FIG. 3. The 
keepers 32, 33 are positioned in the apparatus as shown in Fig. 4 between 
the anvils 43 and the channel 50. Valve 72 is then opened and compressed 
air flows in tube 71 to cylinder-piston units 40, which causes the anvils 
43 to press against the magnets 10 in their keepers 32, 33. The magnets 
are forced out of the keepers 32, 33 and into the channel 50 until they 
are sufficiently close to begin mutually attracting each other. 
In FIG. 6, outline 10a of a magnet 10 shows a first intermediate position 
of a magnet as it slides in channel 50 toward magnet stop tip 58. Outlines 
10b and 10c show further intermediate positions of a magnet 10 in the slot 
as it slides toward tip 58. Outline 10d shows a last intermediate position 
where magnet 10 has contacted tip 58 and stop 52 is about to start sliding 
in the direction of the adjacent arrow to allow maget 10 to reach its 
final position. It should be realized that a second magnet 10 is being 
simultaneously pushed from keeper 33 into channel 50 so that the two 
magnets slide simultaneously toward stop member 52. It is quite important 
that the magnets arrive at the stop 52 at nearly the same time to prevent 
damage to it. This can be accomplished by using cylinder-piston units 50 
whose stroke velocities are identical. To accomplish this I prefer to use 
double-acting cylinders for which speed can be controlled with a flow 
control valve in each exhaust chamber outlet of cylinder-piston units 50. 
The attractive force between the two magnets when both press against the 
adjacent bevels on tip 58 is sufficient to overcome the force of spring 51 
and cam stop member 52 into its retracted position with its tip 58 
withdrawn from channel 50. The natural resilience of spacer 21 and stop 52 
and the relatively gradual deceleration of magnets 10 as they cam stop 52 
from channel 50 serves to allow magnets 10 to reach their predetermined 
positions on pole piece 20 without the excessive impact between them which 
may cause them to be damaged. 
The width of channel 50, i.e. the spacing between guide block edges 54 and 
55 should be greater than the spacing between lines 15 and 16 in FIG. 1, 
but only slightly so, so that there is no possibility that a magnet 10 can 
rotate from approximately the desired angular orientation while sliding in 
channel 50. The magnets, under the influence of correctly spaced edges 54 
and 55, properly shaped relief 60 and spacer 21, and properly designed 
stop member 52, and the magnets' mutual attraction, will consistently 
slide into their preferred orientation on pole piece 20. 
Once the magnets 10 have reached their desired position, cover 45 can be 
removed and the lifter assembly 41 activated to allow access to the magnet 
assembly. At the same time, the pushers 42 are retracting anvils 43 so 
that the keepers 32, 33 in the apparatus can be replaced with others which 
have magnets in their slots 30. The lifter mechanism 41 is deactivated and 
a new pole piece placed in recess 62. The apparatus is then ready, with 
the replacement of cover 45, to position another pair of magnets 10 on the 
new pole piece. 
There are a number of variations which the above invention can have, 
depending on the shape of the magnets and pole pieces to be assembled and 
the magnets' strength. I wish to cover all of these variations in the 
claims which follow.