U.S. patent number 3,699,296 [Application Number 05/145,652] was granted by the patent office on 1972-10-17 for catastrophically buckling compression column switch and actuator.
This patent grant is currently assigned to International Business Machines Corporation. Invention is credited to Richard H. Harris.
United States Patent |
3,699,296 |
Harris |
October 17, 1972 |
CATASTROPHICALLY BUCKLING COMPRESSION COLUMN SWITCH AND
ACTUATOR
Abstract
A snap-action switch and actuator are disclosed in which a
resilient columnar compression member is axially loaded to the
point of catastrophic buckling. In one embodiment, the column
serves as both an electrical conductor and a contact. In this
embodiment, it buckles into contact with another conductive member
to complete a circuit. Alternatively, the buckled column may
actuate a piezoelectric, optical, or other signal producing means
to produce signals used for switching or to close other
contacts.
Inventors: |
Harris; Richard H. (Raleigh,
NC) |
Assignee: |
International Business Machines
Corporation (Armonk, NY)
|
Family
ID: |
22514002 |
Appl.
No.: |
05/145,652 |
Filed: |
May 21, 1971 |
Current U.S.
Class: |
200/453; 200/181;
200/276.1; 200/276 |
Current CPC
Class: |
H01H
1/242 (20130101); H01H 2235/012 (20130101) |
Current International
Class: |
H01H
1/12 (20060101); H01H 1/24 (20060101); H01h
013/28 () |
Field of
Search: |
;200/166BA,67DB,67DA,159R,181,67A |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Schaefer; Robert K.
Assistant Examiner: Vanderhye; Robert A.
Claims
What is claimed is:
1. An actuating mechanism for initiating operation of electrical
contacting apparatus, which actuating mechanism comprises:
a columnar member;
end mounting means for mounting the ends of said columnar
member;
at least one end of said columnar member being pivotally mounted by
one of said end mounting means; and
means for axially loading said columnar member in compression to
catastrophically buckle said columnar member with at least one end
thereof pivoting on its said mounting means and with the buckled
portion of said columnar member moving laterally with respect to
the ends thereof to initiate the operation of associated electrical
contacting apparatus.
2. An electrical switch mechanism, as in claim 1, further
comprising:
first electrical contact initiating means for contacting said
columnar member prior to the application of said catastrophically
buckling axial load; and
second electrical contact initiating means disposed laterally
adjacent said columnar member for contacting the buckled portion of
said columnar member when said member is catastrophically
buckled.
3. An electrical switch mechanism, as described in claim 2,
wherein:
said resilient columnar member is electrically conductive;
said first electrical contact initiating means for contacting said
columnar member prior to the application of said catastrophically
buckling axial load is an electrically conductive contact; and
said second electrical contact initiating means disposed laterally
adjacent said columnar member for contacting the buckled portion of
said columnar member when said member is catastrophically buckled
is an electrically conductive contact.
4. An electrical switch mechanism as described in claim 3,
wherein:
said mechanism includes guide means for guiding the buckling
columnar member into contact with said second contact initiating
means.
5. A self-restoring electrical switch mechanism as described in
claim 2, wherein:
said movable end mounting means is resiliently biased against
movement in compression of said columnar member by said columnar
member.
6. A self-restoring electrical switch mechanism as described in
claim 5, wherein:
said resilient columnar member is electrically conductive; and
said first and second electrical contact initiating means are
electrically conductive.
7. An electrical switch mechanism as described in claim 5, wherein
said mechanism includes guide means for guiding the buckling
columnar member into contact with said second contact initiating
means.
8. An electrical switch mechanism as described in claim 7,
wherein:
said resilient columnar member is electrically conductive; and
said first and second electrical contact initiating means are
electrically conductive.
9. An actuating mechanism for initiating operation of electrical
contacting apparatus, which actuating mechanism comprises:
a resilient columnar member;
end mounting means for mounting the ends of said columnar
member;
one of said end mounting means being freely disposed to move
axially with respect to the longitudinal axis of said columnar
member;
at least one end of said columnar member being pivotally mounted by
one of said end mounting means; and
means for axially loading said columnar member in compression, said
means for axially loading said columnar member acting upon said
movable end mount, with said axial load being of sufficient
magnitude to buckle said columnar member catastrophically with at
least one end thereof pivoting on its said mounting means and with
the buckled portion of said columnar member moving laterally with
respect to the ends thereof to initiate the operation of associated
electrical contacting apparatus.
10. An electrical switch mechanism, as described in claim 9,
wherein:
said resilient columnar member is electrically conductive;
said associated electrical contacting apparatus is an electrically
conductive contact means disposed laterally adjacent said columnar
member; and
when the columnar member buckles catastrophically, the buckled
portion of said columnar member moves laterally with respect to the
ends thereof to electrically contact said electrical contact means,
thereby completing an electrical circuit.
11. A self-restoring actuating mechanism for initiating operation
of electrical contacting apparatus as described in claim 9,
wherein:
said axially movable end mounting means is resiliently biased
against movement in compression of said columnar member by said
columnar member.
12. A self-restoring contact actuating mechanism as described in
claim 11, wherein:
said associated electrical contacting apparatus contacted by said
columnar member when said member is catastrophically buckled is a
piezoelectric means for producing electrical signals; and
said piezoelectric means is further connected to an electric
circuit completing device responsive to electrical signals produced
by said piezoelectric means for closing electrical contacts.
13. A self-restoring contact actuating mechanism as described in
claim 11, wherein:
said associated electrical contacting apparatus contacted by said
columnar member when said member is catastrophically buckled is a
capacitive electric means for producing electrical signals; and
said capacitive electric means is further connected to an electric
circuit completing device responsive to electrical signals produced
by said capacitive electric means for closing contacts.
14. A self-restoring contact actuating mechanism as described in
claim 15, wherein:
said columnar member is an electrically conductive compression
spring;
and the lateral movement of the buckled portion of said columnar
member during catastrophic buckling thereof moves the buckled
portion into both physical and electrical contact with associated
electrical contacting apparatus.
15. A self-restoring contact actuating mechanism as described in
claim 11, further including:
guide means for guiding buckling columnar member into contact with
said associated electrical contacting apparatus.
Description
BACKGROUND
1. Field of the Invention
This invention relates to electrical switching apparatus in general
and in particular to the mechanism for actuating or driving
electrical switch contacts or electrical signal generating means
for producing electrical switching signals.
2. Prior Art
It has been known in the prior art to use a resilient spring means
as an electrical contact member which performs the dual functions
of forming electrical connection and of exerting a biasing force to
return the actuating member to its unactuated position upon the
release of the actuating force. However, these prior art devices
did not provide the quick snap-action necessary to unambiguously
define the switch make condition; i.e., they do not provide a fixed
point in the actuator travel position at which the operator is
certain that he has completed contact. The snap-action feature is a
desirable addition to electrical switches in general, as has been
known in the prior art, because it provides the operator with a
definitely identifiable switch make point. As stated, while prior
art devices have provided the dual functions of forming electrical
connection and of providing a restoring force by using a spring
member, these devices have not provided both the desirable
snap-action and the restoring force by using a spring member, and
they have not utilized such simple, reliable construction to
achieve long life and low cost.
Similarly, while many prior art devices have provided "contact
hysteresis," in that once contact is made, it is maintained until
after the actuator is restored some distance above the make point,
these prior devices have been relatively complex and expensive to
build. The contact hysteresis effect is desirable to ensure that
the contacts will remain made and not be accidently opened by the
operator. (The lack of hysteresis allows contact bounce to occur
that is dependent upon actuator velocity and small changes in
actuator direction resulting in unpredictable ambient vibrations.)
Also, it is desirable to provide a resilient "key feel," of a
sudden snap followed by increasing resistance to actuator travel
beyond the point of make. It is also desirable to prevent erroneous
switching caused by insufficient contact duration. While prior art
devices have provided contact hysteresis and the desirable force
buildup and overtravel for "key feel," they have not provided these
features in a simple, reliable snap-action switch, nor have they
utilized a spring member as both a snap actuator and as biasing and
restoring means.
OBJECTS
In light of the foregoing desired features, it is an object of this
invention to provide an improved switch and an improved switch
actuator having an unambiguous "make-point" provided by an improved
snap-action member.
It is also an object of this invention to isolate the making of
electrical contact from the operator's control once he has
depressed an actuator beyond a fixed amount, in an improved and
simpler way.
It is further an object of this invention to provide an improved
switch actuating mechanism having contact hysteresis and good key
feel which is simpler, more reliable, and less costly than those
known in the prior art.
SUMMARY
This invention achieves the foregoing objects by utilizing the
catastrophic buckling phenomenon exhibited by a resilient columnar
member under axial load to provide the snap action desired. The
catastrophic buckling of the columnar member provides contact
hysteresis and a desirable key feel as will be further described
herein. To allow for catastrophic buckling of the columnar member,
at least one end of the column is mounted to allow a degree of
freedom in the end constraint which permits the column to change
rapidly from a higher energy load condition to a lower energy load
condition. In one embodiment, the columnar member is utilized as an
electrical conductor which buckles into contact with a cooperating
electrical conductor to complete a circuit. Alternatively, the
buckling columnar member is used to actuate electrical signal
producing devices to control switching functions
electronically.
In the drawings:
FIGS. 1a through 1c illustrate an embodiment of the invention which
utilizes a helical compression spring as the columnar buckling
contact member and as a key biasing or restoring means.
FIGS. 2a and 2b illustrate another embodiment of the invention in
which the columnar contact member makes contact with cooperating
contact members to complete circuits in both its unbuckled
(normally closed contact) and in its buckled condition (normally
open contact).
FIG. 3 illustrates a force-displacement diagram of a typical
embodiment of this invention and shows how key force builds up to a
peak followed by a catastrophic buckling or snap action and a later
increase of force to produce greater key travel, and it shows the
delayed release or contact break point upon the release of the
actuator.
FIG. 4 illustrates how lateral deflection of a columnar member
having large eccentricity is a function of axial deflection.
FIG. 5 illustrates another embodiment of the invention in which the
buckled knee of the columnar member actuates a signal
generator.
FIGS. 6a and 6b show a more detailed view of the embodiment shown
in FIG. 1 which illustrates one type of end mounting which permits
catastrophic buckling of the columnar member.
An important aspect of this invention lies in the use of a
bucklable columnar member to provide the desired snap action and
hysteresis. Therefore, some columnar member must be provided which
can be loaded to the point of catastrophic buckling. The column
need be of no particular material to satisfy this criteria; but, in
general, thicker cross-sections and stronger materials produce
columns of a given length which buckle catastrophically at higher
loads than a column of the same length but of smaller cross-section
or one of more easily strained material. Similarly, it is
well-known that column length is a vital factor in determining the
buckling point or load. Any good mechanical engineering handbook
will contain longer discussions of column buckling and can easily
be resorted to by those unfamiliar with these considerations of
length, cross-section, etc. to design a column which will buckle at
any desired load.
Since the buckling column provides the actuating element in this
invention, it is obvious that if only one-time operation is
desired, the column can be made of relatively less elastic and,
therefore, fracturable or easily ruptured material, or the
dimensions of the column may be adjusted to ensure that
catastrophic buckling will also fracture the column. However, for
most purposes, a reusable, and, therefore, a necessarily more
resilient and elastic column is desired. Therefore, I have
described embodiments in which the column is designed not to
fracture when it catastrophically buckles.
As shown in FIGS. 1a through 1c, a preferred embodiment of my
invention as used in an electrical switch can be constructed as
follows. Resilient columnar buckling member 14 is disposed between
mounting means 12 and 18. In FIG. 1a, buckling member 14 is shown
in its extended, (It is actually partly compressed to give an
initial 25 grams preload to the actuator) or unactuated, unloaded
state. To provide a means for axially loading the column, axial
loading end cap 10 is shown as being slidably disposed within
conductive sleeve 16, but many other types of support for this cap
could be utilized, or the cap could be replaced with a pivoted
lever or plunger or any other suitable load applying mechanism. As
shown, buckling member 14 is supplied with electric current through
end mounting 18 which is insulated from conductive sleeve 16 by
insulator 20. Also, as shown, current source 22 is connected
between sleeve 16 and mounting means 18, but in its unbuckled
condition, buckling member 14 does not contact sleeve 16 and,
hence, a circuit is not complete. Some means must be provided for
insulating the opposite end of buckling member 14 from electrical
contact with sleeve 16. In the present embodiment, this is
accomplished by making end cap 10 of electrically non-conductive
material, but suitable sleeve insulators could also be used.
FIG. 1b shows buckling member 14 partially deflected under the
influence of load L applied to end cap 10. Increasing load L will
increase the deflection of buckling member 14, until, as shown in
FIG. 1c, buckling member 14 reaches its critical or catastrophic
buckling position. At this point, either one or both ends of member
14 pivot about a point on the periphery of the end surface of the
member where it touches the end mounting means 12 or 18 and lateral
deflection of member 14 increases rapidly, bringing member 14 into
contact with sleeve 16 and completing an electric circuit. However,
once member 14 is in its buckled condition, the release of load L
on end cap 10 will not immediately cause member 14 to break contact
with sleeve 16, since a lesser load L is necessary to maintain
member 14 in its buckled condition than was necessary to cause it
to buckle initially. Thus, some upward travel of end cap 10 must
take place in order for buckled member 14 to return to an
unbuckled, and non-contacting position. This phenomenon provides a
hysteresis effect and is particularly useful in electric switches
as pointed out earlier.
An important aspect of the invention as embodied in FIG. 1 is that
the end mount 12 and/or 18 must allow some pivotal deflection of
member 14 about a point on its periphery at one or both ends
thereof in order to permit the catastrophic buckling to take place.
Exactly how this pivoting is accomplished will be discussed further
below. Of course, one end mounting means, such as mounting 18, must
resist axial forces applied at the opposite end of member 14 in
order for the build up of stress to take place which leads to
catastrophic buckling. While member 14 is shown to be a helical
compression spring in FIG. 1, other resilient columnar members,
such as thin wires or thin flat plates, might be similarly
utilized.
Another embodiment of the invention is shown in FIGS. 2a and 2b in
which the conductive sleeve 16 of FIG. 1 is replaced with two
conductive strips 30 and 32. As shown in FIG. 2a, strip 30 is in
contact with columnar member 24 when the columnar member is in its
unbuckled condition (although it is partially deflected). If
external wires were added, a circuit would thus be completed
between conductive member 30 and buckling member 24 until such time
as member 24 is deflected or buckled far enough to break contact
with conductive member 30. As shown, member 30 biases the
deflection of member 24 in a predetermined or preferred direction.
And, as shown in FIG. 2b, the buckling of member 24 is further
constrained by guide members 28 so that it can buckle only into
contact with member 32. However, it is obvious that guide members
28 could be eliminated if contact 32 were enlarged to surround the
columnar member as shown in FIGS. 1a-1c. In this configuration, the
invention exhibits both normally closed and normally opened contact
points.
As shown in FIG. 2a, and in FIGS. 6a & 6b, end mount 36 in cap
26 restrains a portion of the periphery of buckling member 24
during catastrophic buckling, so that buckling member 24 can pivot
about the restraint point. However, end mount 36 could easily be
made with a pivoting ball base to permit holding the entire
periphery of the end of member 24, but still providing a means
thereby to allow member 24 to pivot.
FIG. 3 shows a schematic plot of how the force on the end of the
buckling member varies with the amount of displacement of the end.
This figure is useful in defining the phenomenon, which, for this
specification and claims, is called catastrophic buckling. As can
be seen, the force required to deflect the columnar member begins
at some pre-load point as shown at point 40 and increases linearly
to a point 42 just prior to catastrophic buckling then drops
sharply at the point 43, where catastrophic buckling occurs, to
point 44. It then rises more rapidly as the buckled column is
further deflected by additional movement of the end cap after the
columnar member contacts the sidewall or other contact. In this
condition, electrical contacts would be closed. Continued
depression is followed by an extremely steep rise in force 45 when
the column is completely buckled or the end cap is bottomed out. On
the release of force on the end of the columnar member, the
columnar member remains buckled until the force falls substantially
below that necessary to originally cause buckling, as shown by the
arrows on the force-travel diagram. "Switch Break" would occur at
point 46 when the catastrophic buckling condition is relieved.
FIG. 4 graphically illustrates the amount of laterial deflection of
the columnar member as a function of axial deflection of one end
thereof. As can be seen, lateral deflection of the columnar member
increases gradually with increasing axial deflection of one end of
the columnar member until a critical point 50 is reached at which
catastrophic buckling occurs and lateral deflection increases very
rapidly with only a slight increase in axial deflection. If the
buckling "knee" of the columnar member then reaches a stop member,
such as a contact member, as shown at point 52, additional lateral
deflection is stopped as indicated on the diagram. Axial deflection
may be increased at this point, but on release, the deflection path
is the same as shown at 54, until catastrophic buckling is relieved
at 56.
FIG. 5 illustrates another embodiment of the invention in which the
buckled columnar member actuates a piezoelectric or other signal
generator to provide an electric signal pulse useful for actuating
electronic switching devices. By way of example, the impact
produced when the rapidly buckling columnar member 24 hits the
device 25, which for the moment will be considered to be a
piezoelectric device, causes a voltage signal to be produced on
leads 27. This signal will die as contact pressure between buckled
member 24 and the piezoelectric device 25 stabilizes, but a new
pulse is produced upon the release of pressure.
Similarly, device 25 could be replaced with a capacitive switch
element such as shown in IBM Technical Disclosure Bulletin, Vol. 5,
No. 12, May 1963, p. 22 or Vol. 12, No. 8, January 1970, p.
1166.
Also, it is obvious that the columnar member need not physically
contact a signal generating device if, instead of the above
devices, a photosensitive circuit device is arranged to detect the
buckling of the column. In such a case, device 25 could be replaced
by a suitable light sensitive element. Such devices wherein a
moving object interrupts a light beam to trigger associated
electrical switching means are well known and need no description
to those of ordinary skill in the art, but a variety of
photoelectric trigger circuits are to be found in Markus' Handbook
of Electronic Control Circuits, pp. 191-203, First Edition, 1959,
the McGraw-Hill Book Co., Inc.
FIGS. 6a and 6b show a more detailed view of the end mount 36 of
the type used in FIG. 2a which permits catastrophic buckling of the
columnar member. As can be seen, this mount engages a portion of
the periphery of the end of the columnar member so that the end
surface of the columnar member may pivot in its mount. Many other
types of pivot mechanism could be substituted such as a pivoted
mount instead of a fixed mount in which the column pivots. This
pivoting of the end surface of the columnar member about a point on
its periphery or, as otherwise expressed, a pivoting of the end of
the column with respect to the axis of the column, changes its
deflection energy characteristic to a lower energy mode and permits
the columnar member to remain buckled, even though the buckling
force is later reduced to a point below which buckling would have
originally occurred.
STATEMENT OF OPERATION
The embodiment illustrated in FIGS. 1a-1c can be used to visualize
the operation of the invention. As shown, the end cap 10 may be a
keybutton which is depressed by an operator. As the operator
depresses the keybutton, the columnar member 14 undergoes axial
compression and begins to assume a laterally deformed or curved
shape as shown in FIG. 1b. This curve has two inflection points and
is thus a high-energy deformed shape. As the operator continues to
push on the keybutton, the force necessary for each additional
increment of travel increases as shown in FIG. 3 until a point is
reached at which the column becomes unstable and buckles
catastrophically to a lower energy condition in which the column
has only one inflection point. Its end pivots in mount 12 about a
point on its periphery. This catastrophic buckling of the columnar
member causes the "knee" of the buckled column to come into contact
with conductive sleeve 16, in the embodiment shown, thus completing
a circuit with current source 22. To the operator, this phenomenon
is accompanied by a sudden decrease in the amount of force required
to deflect the keybutton. This is shown in FIG. 3. Continued
depression of the keybutton does not affect the contact made
between buckled columnar member 14 and sleeve 16, but the amount of
force required to deflect the column further does increase as the
remaining portion of the column becomes more highly stressed.
If the operator now releases the force on the keybutton, it will
spring back under the urging influence of the deflected columnar
member; but because of the changed end condition at mount 12 with
relation to the columnar member 14, less force is required to keep
the columnar member in its buckled, contact-forming condition. This
means that contact will be maintained between columnar member 14
and sleeve 16 until the force drops to some point below that at
which original buckling occurred. Such buckling conditions are
described further by Wahl in Mechanical Springs (p. 69), Second
Edition, McGraw-Hill. This is the contact hysteresis effect which
is desired in this type of electrical switch and it also provides a
desirable key feel.
The mode of operation of the embodiments shown in FIGS. 2 and 5 are
similar, except that in FIG. 2, the internal guide members 28 and
the urging of the normally closed contact member 30, guide the
buckling columnar member into a preferred direction of buckling to
insure that contact will be made with normally open contact 34 as
shown in FIG. 2 or to actuate a piezoelectric or other type of
transducer as shown in FIG. 5 to produce an electric signal
indicative of a closed contact condition.
ADVANTAGES
The foregoing description has alluded to some of the advantages of
this invention, but notable among them are the following:
The invention is simpler, more rugged, and more reliable than
switches and their actuator mechanisms known in the prior art and
it is cheaper to construct.
Further, the invention provides an electric switch mechanism with a
desirable contact hysteresis characteristic and a desirable
snap-action without the use of numerous and complicated parts.
Additionally, the invention provides an actuator mechanism which
gives the operator a desirable "key feel" or tactile signal in the
form of reduced operating force to inform the operator when contact
has been made.
While this invention has been particularly shown and described with
reference to a preferred embodiment thereof, it will be understood
by those skilled in the art that various changes in form and detail
may be made therein without departing from the spirit and scope of
the invention.
* * * * *