High speed reciprocal electromagnetic actuator with cancelled retarding-flux

An electromagnetic actuator is provided by a single armature plunger that reciprocally shuttles between two magnetic paths provided by a pair of coils. Undesired retarding-flux is cancelled in overlapping linkage paths through the plunger, yielding increased net magnetic force in the intended direction of movement and faster plunger operation. When either coil is energized, a primary flux path is created around that coil through the plunger, and a secondary flux path is created around both coils through the plunger. The primary path attracts the plunger to close a magnetic air gap. The secondary path holds the plunger in place. Current to the ON coil is also supplied through a limiting resistor to the OFF coil to generate reverse polarity flux in the latter cancelling secondary flux from the ON coil.

BACKGROUND AND SUMMARY 
The invention relates to an electromagnetic actuator having a single 
armature plunger that reciprocally shuttles between two magnetic paths. 
The invention affords optimal utilization of the magnetic circuit, 
including cancellation of undesired retarding-flux in overlapping linkage 
paths, resulting in increased net magnetic force and faster plunger 
operation. 
In one desirable aspect of the invention, non-magnetic spacers may be 
eliminated. The nonmagnetic spacers may otherwise be needed for producing 
reluctance to control the ratio between two magnetic flux path forces. 
This control is necessary to insure that the dominant magnetic force is in 
the intended direction of plunger movement. 
Another desirable aspect of the invention is its three-wire control 
capability, eliminating the need for two dedicated wires for each magnetic 
path. 
A pair of coils are energizable to create magnetic fluxes having portions 
of their linkage paths in common, including through the plunger. When 
either coil is energized, a primary flux path is created around that coil 
through the plunger, and a secondary flux path is created around both 
coils through the plunger. The primary flux attracts the plunger to close 
a first gap, and the secondary flux attracts the plunger in the opposite 
direction to maintain a second gap closed. 
In accordance with the preferred embodiment of the invention, current to 
the energized coil is also supplied through a current limiting resistor to 
the other coil to generate reverse polarity flux around the latter 
opposing the noted secondary flux in cancelling relation. This reduces or 
eliminates the retarding-flux in the closed gap and enables the plunger to 
rapidly move under the influence of the noted primary flux in the open 
gap.

DETAILED DESCRIPTION 
Electromagnetic actuator means 2 includes a housing 4 having a pair of 
coaxial coils 6 and 8 energizable through terminals T1, T2 and T3 to 
create magnetic flux. Magnetically permeable yoke 10 directs the flux 
paths of the coils. An armature plunger 12 reciprocally shuttles between 
left and right positions. 
Coils 6 and 8 are mounted on an insulating bobbin 14 having an axial 
passage for guiding the reciprocal left-right movement of plunger 12. Yoke 
10 is an E-shaped member having first and second outer legs 10a and 10b 
and a center leg 10c. The yoke further includes left and right 
magnetically permeable insets 16 and 18 screwed into outer legs 10a and 
10b. Insets 16 and 18 have axial bores 16a and 18a therethrough for 
guiding axial reciprocal movement of extension shafts 12a and 12b secured 
to plunger 12 in threaded relation. Inner inset edge 16b provides a 
shoulder stop for limiting leftward axial movement of plunger 12. Inner 
inset edge 18b provides a right shoulder stop for limiting rightward axial 
movement of plunger 12. 
When plunger 12 is in the leftward position shown in FIG. 1, energization 
of right coil 8 creates a primary flux path extending around right coil 8 
through plunger 12 attracting the latter to a rightward position to close 
axial magnetic air gap 20. Energization of right coil 8 also creates a 
secondary path around both coils through the plunger attracting the latter 
in the opposite direction to its leftward position against shoulder stop 
16b. The primary flux path extends around energized coil 8 through yoke 
means 10 and plunger 12, specifically through right outer yoke leg 10b, 
through inset 18, through axial gap 20 between shoulder stop 18b and the 
right edge 12c of the plunger, through plunger 12, through a radial gap 22 
across bobbin 14 between plunger 12 and center yoke leg 10c, through 
center yoke leg 10c and back to right outer yoke leg 10b to complete the 
primary loop. The secondary path, created when right coil 8 is energized, 
extends around both coils 6 and 8, specifically through right outer yoke 
leg 10b, through inset 18, through axial gap 20, through plunger 12, 
through shoulder stop and inset 16, through left outer yoke leg 10a, and 
back to right outer yoke leg 10b to complete the secondary loop. The 
structure is symmetric, and the above description likewise applies when 
coil 6 is energized and plunger 12 is in its rightward position with gap 
20 closed. 
When either coil is energized, the primary and secondary flux forces urge 
opposite directions of movement of the plunger. One path must always 
overpower the other, regardless of which coil is energized, if there is to 
be reciprocal movement of the plunger in an intended direction of 
movement. 
In the present invention the ratio of the permeances of the magnetic paths 
is controlled by circuit means such that one path always overpowers the 
other, to insure plunger movement in either direction. Circuit means are 
provided responsive to energization of either one of the coils to generate 
flux in the other coil opposing the noted secondary path flux. This 
reduces the net flux holding the plunger in place, and affords faster 
plunger movement responsive to the primary flux in the open magnetic air 
gap for example gap 20. In the preferred embodiment, the coils are 
connected in reverse polarity, for example by winding the coils in 
opposite polarity directions around the bobbin. A first terminal T1 is 
provided for energizing coil 6, a second terminal T2 is provided for 
energizing coil 8, and a current limiting resistor 24 is connected between 
terminals T1 and T2 for applying reduced current to coil 8 from T1 and for 
applying reduced current to coil 6 from T2. A common return for both 
terminals is provided at T3. 
With plunger 12 in its leftward position in FIG. 1, energization of coil 8 
at terminal T2 creates the above noted primary and secondary flux path 
forces. Current from terminal T2 also flows through resistor 24 to left 
coil 6 to energize the latter in reduced reverse polarity relation to 
decrease or cancel the retarding secondary flux otherwise holding plunger 
12 in place in its leftward position against shoulder stop 16b. This 
reduction or cancellation of retarding-flux enables faster movement of 
plunger 12 to its rightward position in response to the primary flux in 
the open magnetic air gap 20. The same considerations apply for reverse 
direction movement of plunger 12 in response to energization of coil 6 at 
terminal T1. 
The ratio of the permeances of the primary and secondary paths may be 
controlled in other manners, for example as taught in copending 
application Ser. No. 406,614, filed Aug. 9, 1982. A pair of 
reluctance-producing nonmagnetic spacer washers may be provided adjacent 
each respective shoulder stop 16b and 18b to afford an axial gap between 
each yoke edge 16b and 18b and plunger 12 in its left and right positions. 
The ratio of the primary and secondary path permeances is controlled by 
the ratio of the axial width of the respective nonmagnetic spacer and the 
radial width of gap 22. This ratio of widths is controlled such that the 
primary path flux force always overcomes the secondary path flux force. 
The present invention not only insures that the primary flux path force 
always overcomes the secondary flus path force, but additionally cancels 
the retarding secondary flux force to thus increase the net magnetic force 
on the plunger in the other direction to close the magnetic air gap. 
Nonmagnetic spacers may of course be used if desired. 
Extension shafts 12a and 12b are provided to perform a designated task, 
such as closing or opening electric contacts, a hydraulic circuit, or 
various other given functions. The shafts need not be identical, as shown 
at enlarged shaft 12b further including an integral hex nut near its end. 
Armature shuttle plunger 12 is thus reciprocal in housing 4 between left 
and right positions respectively closing and opening first and second gaps 
between plunger 12 and yoke 10 at inset shoulder stop 16b and 18b. Plunger 
12 is in overlapping flux paths in each of its left and right positions. 
Energization of the right coil 8 creates a primary flux around the latter 
attracting the plunger to its rightward position to close right gap 20 and 
open a left gap between the left edge of plunger 12 and left shoulder stop 
16b. Energization of right coil 8 also creates a secondary flux around 
both coils attracting plunger 12 to remain in its leftward position with 
the left gap closed and the right gap 20 open. Energization of left coil 6 
creates a primary flux around the latter attracting plunger 12 to its 
leftward position to close the left gap and open the right gap 20, and 
creates a secondary flux around both coils attracting plunger 12 to remain 
in its rightward position with right gap 20 closed and the left gap open. 
It is recognized that various modifications are possible within the scope 
of the appended claims.