U.S. patent number 3,831,729 [Application Number 05/322,298] was granted by the patent office on 1974-08-27 for solenoid having increased throw capability.
This patent grant is currently assigned to Centronics Data Computer Corp.. Invention is credited to Robert Howard.
United States Patent |
3,831,729 |
Howard |
August 27, 1974 |
SOLENOID HAVING INCREASED THROW CAPABILITY
Abstract
A solenoid for actuating a print wire normally biased against
the impact direction by novel spiral spring means. Energization of
the solenoid coil rapidly moves the print wire in the impact
direction against the bias of the spring. Release of the energy
supplied to the solenoid coil causes very rapid return of the print
wire to the non-printing (i.e., quiescent) position. The novel
spiral spring structure experiences a substantially linear spring
force upon deflection and provides significantly increased
deflection as compared with conventional structures to allow for
substantially rapid initial acceleration of the print wire in the
impact direction while providing for rapid return of the print wire
to the quiescent condition. The mounting of said spring reduces
bouncing on overshooting.
Inventors: |
Howard; Robert (Roslyn,
NY) |
Assignee: |
Centronics Data Computer Corp.
(Hudson, NH)
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Family
ID: |
26898439 |
Appl.
No.: |
05/322,298 |
Filed: |
January 10, 1973 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
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203230 |
Nov 30, 1971 |
|
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Current U.S.
Class: |
400/124.17;
335/274 |
Current CPC
Class: |
H02K
33/02 (20130101); H01F 7/13 (20130101); F16F
1/326 (20130101); B41J 2/285 (20130101); H01F
7/1607 (20130101); B41J 9/38 (20130101) |
Current International
Class: |
B41J
2/285 (20060101); B41J 2/27 (20060101); B41J
9/38 (20060101); B41J 9/00 (20060101); H01F
7/08 (20060101); H01F 7/13 (20060101); H01F
7/16 (20060101); H02K 33/02 (20060101); F16F
1/02 (20060101); F16F 1/32 (20060101); H02K
33/00 (20060101); B41j 003/10 () |
Field of
Search: |
;197/1 ;335/274,258
;101/93C ;251/129,139,141 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Pulfrey; Robert E.
Assistant Examiner: Rader; R. T.
Attorney, Agent or Firm: Ostrolenk, Faber, Gerb &
Soffen
Parent Case Text
This application is a continuation-in-part of U.S. Pat. Application
Ser. No. 203,230 filed 30 Nov. 1971 by Robert Howard entitled
"Improved Solenoid Having Increased Throw Capacity" and assigned to
the assignee of the present case, which application has been
abandoned.
Claims
What is claimed is:
1. A solenoid assembly comprising:
a housing;
an elongated substantially cylindrical stem having an axial opening
of small diameter extending the length of said stem;
said stem being secured to the forward end of said housing;
an annular shaped coil positioned within said housing and
surrounding a portion of said stem;
a closure cap threadedly engaging the rearward end of said
housing;
an armature positioned within said housing and along the axis of
said housing, at least the forward portion of said armature
extending to a position relative to said coil; whereby said
armature is activated and moved by the magnetic field generated by
the coil when energized;
a slender elongated wire positioned within the axial opening of
said stem and having its forward end extending beyond the forward
end of said stem and its rearward end secured to the forward end of
said armature;
circular shaped spring means having a circular outer periphery and
having its central portion joined to the rearward portion of said
armature;
said housing having an annular shoulder engaging the periphery of
said spring means;
said spring means being formed of a resilient metallic sheet and
having a pair of spiral shaped slots encircling said central
portion and interleaving one another;
each of said spiral shaped slots having an inner end portion near
said central portion and an outer end portion near said spring
outer periphery and encircling said central portion at least
once.
2. The solenoid assembly of claim 1 wherein the inner ends of said
slots lie on opposite sides of said central portion.
3. The solenoid assembly of claim 2 wherein the inner ends of said
slots lie along a common diameter of said spring.
4. The solenoid assembly of claim 1 wherein the outer ends of said
slots lie on opposite sides of said central portion.
5. The solenoid assembly of claim 4 wherein the outer ends of said
slots lie along a common diameter of said spring.
6. The solenoid assembly of claim 1 wherein said spring is formed
from a sheet of spring steel.
7. The solenoid assembly of claim 1 wherein said spring is adapted
to exert a rearwardly directed force on said armature to normally
hold said print wire in the non-impact position when said solenoid
coil is deenergized, said coil being adapted to overcome the
rearward directed force of said spring when energized to rapidly
move said print wire toward the impact position, and thereby flex
said spring to cause said print wire to return rapidly to the
non-impact position when said coil is deenergized; said spring
being adapted to engage said closure cap in returning to the
non-impact position, which closure cap eliminates bounce.
8. The solenoid assembly of claim 1 wherein each of said spiral
slots represents an Archimedian spiral.
9. The solenoid assembly of claim 1 wherein each of said spiral
shaped slots represents an involute of a line.
10. A solenoid assembly comprising:
a hollow substantially cylindrical housing;
an elongated substantially cylindrical stem having an axial opening
of small diameter extending the length of said stem;
said stem being secured to the forward end of said housing;
an annular shaped coil positioned within said housing and
surrounding a portion of said stem;
a closure cap threadedly engaging the rearward end of said
housing;
an armature positioned within said housing and along the axis of
said housing, at least the forward position of said armature
extending to a position relative to said coil; whereby said
armature is activated and moved by the magnetic field generated by
the coil when energized;
a slender elongated wire positioned within the axial opening of
said stem and having its forward end extending beyond the forward
end of said stem and its rearward end secured to the forward end of
said armature;
circular shaped spring means having its central portion joined to
the rearward portion of said armature;
said housing having an annular shoulder engaging the periphery of
said spring means;
said spring means being formed of a resilient metallic sheet and
comprising an inner ring and a concentric outer ring;
a pair of spiral-shaped spring portions each encircling the inner
ring at least once and having their inner ends adjacent the inner
ring being integrally joined to said inner ring and having their
outer ends adjacent said outer ring being integrally joined to the
outer ring.
11. The assembly of claim 10 whereby the outer ends of said
spiral-shaped spring portions are diametrically opposite one
another.
12. The assembly of claim 10 wherein the inner ends of said
spiral-shaped spring portions are diametrically opposite one
another.
13. The assembly of claim 10 wherein the free ends of the outer
extremities of said spiral-shaped spring portions are transversely
aligned to their spiral portions, whereby forming an integral
joining section between said spiral-shaped portions and said outer
ring to significantly reduce torsional stresses during deflection
of the spring means.
14. The assembly of claim 10 wherein the free ends of the inner
ends of said spiral-shaped portions are transversely aligned to
their spring spiral-shaped portions, thereby forming an integral
joining section between said spring spiral portion and said inner
ring to significantly reduce torsional stresses during deflection
of the spring means.
Description
The present invention relates to solenoid assemblies and more
particularly to a novel solenoid assembly especially advantageous
for use in dot matrix impact printers and the like due to its
capability of providing rapid acceleration in the impact direction
and rapid return to its normal position preparatory to subsequent
energization and further providing increased throw as compared with
conventional designs.
BACKGROUND OF THE INVENTION
Solenoid assemblies of the general category described herein are
extremely advantageous for use in high speed dot matrix printers of
the impact type such as, for example, that described in U.S. Pat.
No. 3,703,949 issued Nov. 28, 1971 to Robert Howard entitled "High
Speed Printer" and assigned to the assignee of the present case.
The printer described therein is capable of forming characters or
other symbols by selectively impacting one or more of the slender
print wires against an inking ribbon so as to print "dots" upon the
surface of the paper document. Since printing speed is of the
essence in such devices, it becomes quite important to provide an
apparatus for rapidly impacting the print wires and rapidly
returning the print wires to the rest position. The printing speed
in the above-mentioned printing apparatus is of the order of 50 to
165 characters per second depending on the gap in the solenoid
which could be from 0.015 to 0.018. To obtain such speeds, it is
important to provide solenoid assemblies which are capable of
moving the slender print wires from the rest position to the impact
position and to return the print wires to the rest position within
a time interval of the order of 1 to 3 milliseconds while at the
same time providing an impact of sufficient force to print a
clearly legible dot upon the paper document or other printing
surface. Whereas solenoid assemblies of the type described in the
above-mentioned copending application discloses such a solenoid
assembly which provides an extremely long useful operating life, it
has been found that certain applications require solenoid
assemblies having the capability of moving a print wire over a
significantly greater distance (i.e., "throw") than has heretofore
been attainable. For example, with solenoid assemblies of the type
described in the above-identified copending application, the print
wires are caused to move a distance of the order of 0.115 inch
between the rest position and the impact position. There exists a
number of applications in which a significantly increased "throw"
(i.e., total linear movement) of the solenoid print wire is
required. In such applications it has been found that the spring
element described in the aforementioned copending application is
incapable of providing such an increased throw since deflection
beyond its present capabilities causes either the spring to deflect
beyond its elastic limit whereby a permanent deformation takes
place and the spring member is no longer capable of resuming its
normal undeflected condition or its fatigue failure limit is
exceeded and fracturing occurs.
BRIEF DESCRIPTION OF THE INVENTION
The present invention is characterized by providing a solenoid
assembly which incorporates a novel spring element employed to
achieve the characteristics described hereinabove. The solenoid
assembly of the present invention comprises a case for housing the
coil and armature. A stem portion threadedly engages the forward
end of the housing and is provided with an axially aligned
elongated opening for receiving and reciprocally mounting a slender
elongated print wire. The rearward end of the print wire is fixedly
secured to the solenoid armature at the forward end of the
armature. The rearward end of the armature is fixedly secured to a
spring member of the "spiral" type at its central portion. The
peripheral portion of the spring rests against an annular-shaped
spacer which abuts a shoulder provided therefor within the solenoid
housing. The rearward portion of the armature assembly abuts the
projection of a cap member which threadedly engages and seals the
rearward end of the housing. The cap member is adjustable to
regulate the amount of stress or tension (i.e., preloading) imposed
upon the spring member and also provides for "half cycle" snubbing
as anti-bounce device. A tubular wire guide is positioned within
the solenoid assembly stem portion and is appropriately lubricated
so as to reduce wearing of the reciprocating print wire extending
therethrough.
The "spiral" spring means is formed from a flat sheet of
prehardened tempered spring steel or any other suitable material
exhibiting similar characteristics. The spring has a centrally
located hub portion for joinder with the rearward end of the
armature. The spring may be compared with an elongated leaf spring
which has been constructed in the form of a tight spiral with the
entire length of the leaf spring lying within an imaginary plane.
The particular spiral design employed may be either an Acrhimedean
spiral or an involute of a line wherein separate interleaving
spirals are cut or otherwise formed within the flat spring steel
disc. This provides for a relatively long active "beam" over which
the deflection stresses can be absorbed.
The spring maintains the slender print wire of its solenoid in the
quiescent condition when the solenoid coil is deenergized. Upon
energization of the solenoid coil, the electromagnetic field urges
the armature toward the forward end of the solenoid assembly. This
force overcomes the spring constant of the spring member to deflect
the center portion of the spring member secured to the armature
relative to the outer periphery which rests against the
aforementioned shoulder. The spring constant of the spring is
substantially linear with increasing deflection over the entire
range which is substantially increased by as much as 3 to 5 times
the throw of conventional solenoid assemblies. This spring design
permits significantly increased throw of the solenoid print wire
without causing the spring member to be deflected beyond its
elastic limit while at the same time providing a spring structure
having an extremely long useful operating life.
OBJECTS OF THE INVENTION
It is therefore one object of the present invention to provide a
novel solenoid assembly for use in high speed dot matrix printers
of the impact type having an increased throw as compared with
conventional structures.
Another object of the present invention is to provide a novel
spring member of the leaf spring type in the form of a circular
disc member having spiral grooves cut therein, which is extremely
advantageous for use in printers of the dot matrix type.
BRIEF DESCRIPTION OF THE FIGURES
These, as well as other objects of the present invention, will
become apparent when reading the accompanying description and
drawings in which:
FIG. 1 is a sectional view of a solenoid assembly designed in
accordance with the principles of the present invention;
FIG. 2 is a plan view of a solenoid spring designed in accordance
with the principles of the present invention;
FIG. 2a is a plot showing the force versus deflection
characteristics of the springs of FIGS. 2 and 3;
FIG. 3 is a plan view showing another spring design embodying the
principles of the present invention; and
FIG. 4 shows another alternative embodiment of the present
invention.
DETAILED DESCRIPTION OF THE FIGURES
The solenoid assembly 10, shown best in FIG. 1, is comprised of a
cylindrical shaped case 11 which is also described in detail in
U.S. Pat. 3,690,431 issued Sept. 12, 1972 to Robert Howard entitled
"Print Head Assembly Containing Solenoids" and assigned to the
assignee of the present case (see FIG. 1a thereof) which is
incorporated herein by reference thereto. The case is a hollow
cylindrical member provided with a recessed shoulder 11a spaced
inwardly from its right-hand end. The right-hand end is threaded at
11c for receiving an adjustable threaded closing cap 23. The
forward end of casing 11 is further provided with a slot 11e
through which the leads 17a and 17b of the solenoid extend so as to
couple the solenoid to the peripheral driving circuitry, not shown
herein for purposes of simplicity.
Case 11 receives a stem member 12 having a threaded portion 12a
threadedly engaging a tapped mounting hole provided in a print head
assembly such as, for example, that described in copending U.S.
Pat. application Ser. No. 179,457 filed Sept. 10, 1971 by Robert
Howard entitled "Printer Head Assembly" and assigned to the
assignee of the present application. Lock nut 13 threadedly engages
threaded portion 12a to firmly secure the solenoid assembly to the
print head assembly in a manner shown in detail in the
above-mentioned copending application.
The stem is provided with a circular-shaped flange portion 12b
which is received within the forward end of case 11 whereby the
right-hand peripheral edge of flange 12b may nominally abut against
shoulder 11a. The rearward most portion 12c of stem 12 has a
diameter which is less than both flange 12b and threaded portion
12a with the extreme right-hand end portion 12b being of still
further reduced diameter so as to form a shoulder 12e positioned
between sections 12c and 12d.
Stem 12 is provided with an axially aligned opening which is
comprised of portion 12f of a first diameter and portion 12g of
slightly enlarged diameter extending therethrough. The extreme
left-hand end portion 12h is tapered to form a conical entrance
portion to facilitate the insertion of a hollow tubular elongated
wire guide 14 which is positioned within opening portion 12g so
that its right-hand end abuts against shoulder 12j positioned
between portions 12f and 12g of the axially aligned opening. The
wire guide is preferably force-fitted within opening 12g so as to
experience no linear movement relative to stem 12 when the solenoid
is operating. The interior of wire guide 14 is preferably coated
with a suitable lubricant to reduce friction losses and wearing of
print wire 15 which is mounted for reciprocating movement
therethrough.
A solenoid core member 16 having a tubular shaped portion 16a, and
an outwardly extending flange portion 16b, is telescoped upon the
right-hand end of stem 12 whereby the left-hand end of hollow
cylindrical portion 16a abuts against shoulder 12e in the manner
shown. The hollow cylindrical portion 16a is preferably
force-fitted upon the right-hand portion 12d of stem 12. The
flanges 12b and 16b, the stem portion 12c, the tubular portion 16a
and the interior surface of case 11 define a hollow interior space
which is provided for receiving the solenoid coil 17 whose turns or
windings are wound about stem portion 12c and tubular portion 16a
with the axial length of the windings being defined and physically
limited by flanges 12b and 16b. The two end terminals of solenoid
coil 17 are wound so as to extend to slot 11e provided in case 11.
The coil end terminals 17a and 17b are shown as extending outwardly
through slot 11e. A predetermined length of each of the leads 17a
and 17b is mounted with an associated insulating sleeve 17c and
17d, respectively.
As was described hereinabove, the slender elongated print wire 15
is slidably received by the interior of wire guide 14 and extends
still further to the right so as to be slidably received by the
portion 12f of the stem axial opening and to protrude therebeyond
by a predetermined distance. The right-hand end portion 15a of
print wire 15 is mounted within an axially aligned opening 18a
provided within the solenoid armature 18. Armature 18 is
substantially cylindrical in shape and is further provided with a
right-hand portion of reduced diameter relative to the main body
portion, forming an annular shoulder. The right-hand portion of
armature 18 is further provided with an axially aligned opening for
receiving a fastening member to secure the armature to spring
member 19. Aforementioned U.S. Pat. No. 3,690,431 shows a detailed
view of the armature member in FIG. 1b thereof.
A solenoid spring 19 is mounted upon armature 18 so that its
central opening (to be more fully described in connection with
FIGS. 2 and 3) receives the reduced diameter portion of armature 18
and rests against the aforementioned annular shoulder. A stress
relief washer 20 is positioned upon spring 19 so that its central
opening receives the reduced diameter portion of armature 18. A
fastening member 21 has a shaft portion (not shown) passing through
the openings in washer 20, spring 19 and armature opening 18d so as
to firmly secure washer 20 and spring 19 to the right-hand end of
armature 18 with a minimum of stress concentration applied to the
center section of the spring.
Spring member 19 has a substantially circular-shaped outer
periphery, as will be described in detail hereinbelow. A
ring-shaped spacer member 22 has its left-hand surface bearing
against shoulder 11b of solenoid case 11 and has its right-hand
surface bearing against the periphery of spring 19. The spacer 22,
spring 19 and armature 18 are maintained in position within case 11
by means of cap 23 which is provided with a threaded portion 23a
which threadedly engages tapped portion 23b whose left-hand surface
bears against the head of fastener 21. An axially aligned opening
23c is provided for adjusting the preloading of spring 19 in a
manner to be more fully described. A linear groove 23d is provided
in the left-hand surface of cap 23 to facilitate insertion of an
adjusting tool such as, for example, a screwdriver head. By
rotating cap 23 within casing 11, the amount of preloading of
spring 19 may be easily and accurately controlled.
As is directed in detail in aforementioned U.S. Pat. No. 3,690,431
the various components of the solenoid assembly are adjustable so
as to facilitate fine adjustment thereof. Once the spring has been
appropriately preloaded by the rotation of end cap 23 within the
solenoid assembly, an epoxy 25 may be deposited in the region shown
in FIG. 1 to rigidly maintain cap 23 in the desired position. From
the foregoing, it can be seen that the initial assembly of the
solenoid can be performed in a simple, straightforward fashion,
since relatively little concern need be given at the time of
initial assembly to the final adjustment thereof. The final and
accurate adjustment of the solenoid assembly may then be performed,
at which time epoxy is deposited at the forward and rearward
portions of the housing in the manner shown in FIG. 1 to retain the
components in their desired alignment. For example, the amount of
preloading exerted upon spring member 19 may be measured by the
insertion of a probe (not shown) through axial opening 23C. After
precise adjustment of the preloading, the epoxy may be deposited at
the position 25 as shown in FIG. 1.
FIG. 2 is a detailed plan view of one preferred embodiment of
spring 19 shown in FIG. 1 which is comprised of a central portion
19a having a central opening 19b for receiving the reduced diameter
portion of armature 18. As was mentioned hereinabove, spring member
19 is preferably formed from a flat sheet of spring steel so as to
have a circular periphery 19c. In addition thereto, a pair of
spirals 19d and 19e are cut or otherwise formed within the
disc-shaped spring member with the spirals defining an involute of
a line. The inner ends 19f and 19g of the spirals 19d and 19e,
respectively, can be seen to lie opposite one another along a
diameter D.sub.1 of the disc-shaped spring. The outer ends 19h and
19j of spirals 19d and 19e, respectively, also lie opposite one
another and along a diameter D.sub.2 of the disc. It can be seen
that the region between the two separately generated involutes
constitutes an elongated leaf spring wound in a right spiral
fashion. The characteristics of this design cause the spring member
19, even though it is of a spiral design, to function in a manner
substantially similar to that in which an elongated straight leaf
spring functions. FIG. 2a shows the spring characteristics of
spring 19 wherein spring deflection d is plotted along the X-axis,
while spring force f.sub.s is plotted along the Y-axis. The slope C
relates deflection to spring force. From the point of zero
deflection (i.e., with the spring in its normal undeflected state)
the spring which is preloaded follows a constant spring rate slope.
Low stress springs of this design having high length to deflection
ratios have proven highly successful for use in solenoids where the
length of travel reaches a maximum of 0.085 inch whereas springs of
aforementioned U.S. Pat. No. 3,690,431 have been found to reach
their elastic limit and to become permanently deformed after
deviation distances of the order of 0.015 inch.
The positioning of the cap 23 with respect to the neutral position
of the spring 19 (preloading in direction of forward stroke)
prohibits reverse bending hence eliminates bounce, i.e.,: rearward
kinetic energy is dissipated in impacting the cap 23. The cap's
absorbtion characteristics are enhanced by the selection of a
suitable plastic material.
FIG. 3 shows a modified spring member 19' having a central portion
19a' provided with a central opening 19b' for receiving the
fastening member which joins it to armature 18.
The spring member is provided with a circular periphery 19c' and is
further provided with two spiral-shaped slots 19d' and 19e' whose
inner ends 19f' and 19g' respectively, lie along a first diameter
D.sub.1 ' and whose outer ends 19h' and 19j' lie opposite one
another along a diameter D.sub.2 '. The spiral shaped elongated
slots 19d' and 19e' are of slightly greater width W' than the width
W of the spiral-shaped slots provided in the spring 19 of FIG. 2.
The spirals 19d' and 19e' of FIG. 2 represent curves lying in a
plane which are generated by a point moving away from or toward a
fixed point at a constant rate while the radius vector from the
fixed point rotates at a constant rate. Such a spiral is known is
an Archimedean spiral. As was the case with the spring member 19 of
FIG. 2 the pair of spiral-shaped slots 19d' and 19e' can be said to
define an elongated leaf type spring which is wound in a tight
spiral manner so that the entire leaf spring lies within a plane.
The characteristics of the spring force for the spring 19' of FIG.
3 are substantially similar to those shown in FIG. 2a.
In one preferred embodiment of the present invention, the print
wires are moved a distance of the order of 0.075 inch from the rest
position to the impact position. Relationship of force plotted
against deflection distance is a similar linear relationship as
compared with the logarithmic relationship obtained from the spring
design of the spring shown in FIG. 2 of the aforementioned U.S.
Pat. No. 3,690,431. The linear spring force characteristic greatly
simplifies the determination of the required driving force provided
by the solenoid coil 17 while the design further provides a greatly
increased amount of deflection without causing the spring to be
deflected beyond its elastic limit. Thus, the spring 19 (or 19')
provides a substantially linear relationship between spring force
and deflection distance over the entire "throw" of the print wire
15.
When the solenoid coil is deenergized (i.e. when impact against a
paper document has occurred) the magnitude of the spring force is
substantially at its maximum value, thereby placing the print wire
exclusively under the control of spring 19. The force imposed upon
the armature by spring 19 at this time causes a rapid return of the
armature toward the rest position.
FIG. 4 shows an alternative arrangement for the spring of FIG. 3,
for example, wherein cutout portions 19k and 19l have been provided
behind the end portions 19j' and 19h' of the slots formed in the
spring to relieve the torsional stresses which are developed at
points 20a and 20b, respectively. Likewise, slots 20c and 20d are
provided adjacent the inner extremities 19g' and 19f' of the slot
19 to relieve the torsional stresses that would otherwise be
developed at points 20e and 20f. The spring of FIG. 4 is therefore
comprised of a continuous outer ring R and a continuous inner ring
R'. The spiral spring portions 32 and 33 have their outward
extremities coupled to outer ring R by radially aligned integral
joining portions 20a and 20b which are transversely aligned to the
spiral spring portions, and have their inner extremities joined to
ring R' by radially aligned integral joining portions 20e and 20f
which are transversely aligned to the spiral spring portions. This
structure significantly improves the useful operating life of the
spring by markedly reducing torsional stresses which are otherwise
present at the inner and outer extremities of the spiral spring
portions.
It can therefore be seen that the foregoing invention provides a
novel spring design enabling substantially increased throw for a
slender print wire not heretofore attainable in conventional
solenoid driving assemblies.
Although there has been described a preferred embodiment of this
novel invention, many variations and modifications will now be
apparent to those skilled in the art. Therefore, this invention is
to be limited, not by the specific disclosure herein, but only by
the appending claims.
* * * * *