U.S. patent application number 14/792882 was filed with the patent office on 2016-04-14 for concentric arc spline rotational spring.
This patent application is currently assigned to Rethink Motion Inc.. The applicant listed for this patent is Rethink Motion Inc.. Invention is credited to Aaron Hulse, Elliott Potter.
Application Number | 20160102724 14/792882 |
Document ID | / |
Family ID | 55655142 |
Filed Date | 2016-04-14 |
United States Patent
Application |
20160102724 |
Kind Code |
A1 |
Potter; Elliott ; et
al. |
April 14, 2016 |
Concentric Arc Spline Rotational Spring
Abstract
A planar torsion spring where the spring comprises a first outer
ring and a second inner ring. The inner ring is positioned within
the first outer ring and possesses a same axis of rotation. The
outer ring is connected to the inner ring with one or more splines.
Each spline extends in one or more concentric arc segments to a
maximum circumference relative to the position of the next
concentric arc between the outer ring and the inner ring. The outer
ring, the inner ring and the spline concentric arcs segments are
positioned in the same plane. At least one spline connects the
outer ring to the inner ring. The spline is positioned in a
plurality of concentric arcs segments and sequentially positioning
each arc to a maximum circumferential length relative to its
position between the outer ring and inner ring.
Inventors: |
Potter; Elliott;
(Friendswood, TX) ; Hulse; Aaron; (League City,
TX) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Rethink Motion Inc. |
Houston |
TX |
US |
|
|
Assignee: |
Rethink Motion Inc.
Houston
TX
|
Family ID: |
55655142 |
Appl. No.: |
14/792882 |
Filed: |
July 7, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
62173498 |
Jun 10, 2015 |
|
|
|
62099191 |
Jan 1, 2015 |
|
|
|
62061815 |
Oct 9, 2014 |
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Current U.S.
Class: |
267/161 ;
29/896.9 |
Current CPC
Class: |
G01B 11/16 20130101;
G01L 5/22 20130101; G01L 3/1407 20130101; F16F 1/027 20130101 |
International
Class: |
F16F 1/02 20060101
F16F001/02 |
Claims
1. A rotational torsion spring comprising: a) an inner ring; b) an
outer ring; c) one or more splines connecting the inner ring with
the outer ring wherein each spline comprises a plurality of
concentric arc segments which store energy when either the inner or
outer ring is rotated in relation to the complementary inner or
outer ring.
2. The rotational torsion spring of claim 1 comprising concentric
arc segments that create an extended spline length wherein spline
stress concentrations are decreased.
3. The rotational torsion spring of claim 2 wherein the extended
spline length creates increased tolerance of the inner ring to
radial misalignment of the outer ring.
4. A planar rotational torsion spring comprising an inner ring
nested within an outer ring and the rotational torsion spring
further comprises at least one spline connecting the outer ring to
the inner ring and the spline forms concentric arc segments between
the outer ring and the inner ring.
5. The planar rotational torsion spring of claim 4 further
comprising the concentric arc segments each encircling at least 90
percent of the length of circumference existing along each arc
segment.
6. The planar rotational torsion spring of claim 5 wherein at least
one concentric arc segment is circumferentially oriented about an
axis of rotation of the inner ring.
7. The planar rotational torsion spring of claim 5 wherein at least
one concentric arc segment is substantially circumferentially
oriented about an axis of rotation of the inner ring.
8. The planar rotational torsion spring of claim 4 comprising a
single spline connecting the outer ring to the inner ring and the
spline forms a plurality of concentric arc segments between the
outer ring and the inner ring and the single spline achieves
deflection of either ring relative to the other ring with higher
stress at the same load of the spring than a planar rotational
torsion spring comprising a plurality of splines.
9. A first planar rotational torsion spring comprising a number of
n splines and achieving deflection of the arc segments with more
stress than a second planar rotation torsion spring of the same
load, material thickness and torsion spring diameter of the first
torsion spring wherein the second torsion spring comprises n+1
splines.
10. A first planar rotational torsion spring comprising a number of
n+1 splines and the first planar rotational torsion spring achieves
a greater stiffness than a second rotational torsion spring
comprising n splines and comprising the same material, material
thickness and torsion spring diameter as the first planar
rotational spring wherein more splines achieve greater stiffness
than a spring with fewer splines.
11. The planar rotational torsion spring of claim 4 wherein the
concentric arc segments form an extended load path.
12. The planar rotational torsion spring of claim 4 wherein the
extended spline length created from the concentric shape decreases
stress concentration in the spline.
13. A planar rotational torsion spring comprising an inner ring
nested within an outer ring and the rotational torsion spring
further comprises a plurality of splines wherein each spline
comprises multiple arc segments wherein one arc segment of a first
spline is fixed to the outer diameter of the inner ring and a
different arc segment of the first spline is attached to the inner
diameter of the outer ring.
14. The planar rotational torsion spring of claim 13 wherein each
of the plurality of splines comprise a plurality of circumferential
arc segments.
15. The planar rotational torsion spring of claim 14 wherein the
arc segments are joined by curved segments and the arc segments are
attached to the inner and outer rings by L shaped structures where
the circumferential arc segments turn approximately 50 degrees into
the inner or outer ring
16. The rotational torsion spring of claim 4 comprises a spring
achieving a preselected stiffness with a computed spline thickness
and known spring constant.
17. The rotational torsion spring of claim 4 wherein the design is
selected based upon desired stiffness and strength and known spring
constant.
18. A planar rotational torsion spring comprising an inner ring
nested within an outer ring wherein the rotational torsion spring
further comprises at least one spline connecting the outer ring to
the inner ring and a spline forms concentric arc segments between
the outer ring and the inner ring.
19. A planar torsion spring wherein the spring comprises a first
outer ring, a second inner ring which is positioned within the
first outer ring and possessing a same axis of rotation, the first
outer ring connected to the second inner ring with one or more
splines each extended in one or more concentric arcs to a maximum
circumference relative to the position of the concentric arc
between the first outer ring and the second inner ring and
positioning the first outer ring, the second inner ring and the
spline concentric arcs in the same plane.
20. A method of constructing a planar torsion spring wherein the
spring comprises fabricating a first outer ring, fabricating a
second inner ring which is positioned within the first outer ring
and possessing a same axis of rotation, further connecting the
first outer ring to the second inner ring with one or more splines,
extending the spline in a plurality of concentric arcs,
sequentially positioning each arc to a maximum circumferential
length relative to its position between the first outer ring and
second inner ring, fabricating the spline with the maximum number
concentric arcs between the inner circumference of the first outer
ring and the outer circumference of the second inner ring and
positioning the first outer ring, the second inner ring and the
concentric arcs of the spline in the same plane.
Description
RELATED APPLICATIONS
[0001] This Disclosure claims priority to Provisional Application
entitled "Elastic Torque Sensor for Planar Torsion Spring" filed
Oct. 9, 2014 as application Ser. No. 62/061,815. This application
also claims priority to Provisional application entitled
"Concentric Arc Spline Rotational Spring" filed Jan. 1, 2015 as
application Ser. No. 62/099,191. These provisional applications are
incorporated by reference herein in their entirety. This
application claims priority to and incorporates by reference herein
provisional application Ser. No. 62/173,498 entitled "Elastic
Torque Sensor for Planar Torsion Spring filed Jun. 10, 2015. This
application claims priority to and incorporates by reference herein
nonprovisional application Ser. No. 14/691,702 entitled Series
Elastic Motorized Exercise Machine filed Apr. 21, 2015
FIELD OF USE
[0002] This disclosure pertains to the field of planar torsion
springs.
BACKGROUND OF DISCLOSURE
[0003] Rotational torsion springs that work by storing energy with
torsion or twisting; that is, a flexible elastic object that stores
mechanical energy when it is twisted. When the rotational torsion
spring (hereinafter "torsion spring") is twisted, it exerts a force
(torque) in the opposite direction, proportional to the amount
(angle) the torsion spring is twisted. Torsion springs are known in
the industry. However use is being adapted to new applications and
optimal material shapes, dimensions and designs are frequently
created on a trial and error basis.
SUMMARY OF DISCLOSURE
[0004] A torsion spring is a type of spring that stores mechanical
energy when a twisting force (torsion) is applied. These include
torsion bars where the torsion is resisted by shear stresses, and
spiral torsion springs wherein the torsion is resisted by bending
stresses about the axis of their curvature.
[0005] This Disclosure pertains to a rotational torsion spring
comprising an inner ring positioned concentrically with an outer
ring. The inner ring can be termed the input side of the torsion
spring. The outer ring can be termed the output side of the torsion
spring. The outer ring has a larger radius than the inner ring.
Both rings share the same axis of rotation. The inner ring and the
outer ring are connected with splines positioned between the inner
ring and the outer ring. In a preferred embodiment, of the splines
is configured with long arc segments. The long arc segments extend
approximately parallel to the circumference of the inner and outer
rings.
[0006] The disclosure illustrates a torsion spring comprising
concentric arc splines connecting the inner ring and outer ring of
the torsion spring. Each spline comprises a serpentine component
that extends from the inner ring to an outer ring. The serpentine
shape of each spline is preferably identical. Each spline is
attached to the inner ring and outer ring by each spline forming an
L shaped segments at its juncture with each ring.
[0007] Each of the splines has a depth dimension. For example, the
depth is the dimension of a steel plate from which the spline may
be cut. The depth is a dimension parallel to the center
longitudinal axis of the inner and outer rings.
[0008] Each of the splines has a thickness. This is the dimension
of the spline relative to the plane to the rotational spring. This
can be also termed the spline thickness or width of the concentric
arc. The geometry of the torsion spring subject of this disclosure
allows the reduction of spline thickness for a specified torsion
spring load. For example the spline subject of this disclosure may
be less thick (thinner) than the spline disclosed in provisional
application 62/061,815 which is incorporated by reference in its
entirety. It will be appreciated that the spline thickness may vary
depending upon its position relative the inner or outer rotational
ring, etc.
[0009] The spline depth may also vary. The depth may be less than
the depth of the concentric inner or outer ring.
SUMMARY OF DRAWINGS
[0010] The patent or application file contains at least one drawing
executed in color. Copies of this patent or patent application
publication with color drawings will be provided by the Office upon
request and payment of the necessary fee.
[0011] The accompanying drawings, which are incorporated in and
constitute a part of the specification, illustrate preferred
embodiments of the invention. These drawings, together with the
general description of the invention given above and the detailed
description of the preferred embodiments given below, serve to
explain the principles of the invention.
[0012] FIG. 1 illustrates a previous design of a planar torsional
spring comprising two splines connecting the output side and the
input side of the spring. Limited annular or concentric arc
segments are illustrated.
[0013] FIG. 2a illustrates one design of a planar torsion spring
taught by the disclosure comprising three splines with expanded
concentric arc construction. FIG. 2a is a top view. The dimensions
of spline thickness and spline depth are clearly illustrated. FIG.
2b illustrates a side view. The depth of the spline is clearly
viable. It will be appreciated that each spline concentric arc has
the same or similar axis of rotation. This is the axis of rotation
of the inner ring and the outer ring or is based upon this axis of
rotation.
[0014] FIG. 3 illustrates the locations and amounts of stress
experienced by the rotational torsion spring subject of this
disclosure. The Figure illustrates the stress analysis. The highly
stressed portions of the structure are illustrated in red. The
movement of the splines is exaggerated.
[0015] FIG. 4 illustrates the location and amounts of stress
experienced by the rotational torsion spring of a two spline
rotational torsion spring. Again, the areas of the torsion spring
subject of high stress are illustrated in red. The red areas of
FIGS. 3 and 4 have different amounts of stress associated with
them. FIG. 3 has less stress magnitude than FIG. 4 even though they
have the same load applied and design stiffness.
[0016] FIGS. 5a and 5b illustrate a comparison of an inner and
outer ring where FIG. 5b shows the rings to be misaligned and do
not share the longitudinal axis of orientation.
DETAILED DESCRIPTION OF DISCLOSURE
[0017] The planar torsion spring comprises an inner ring nested
within a larger diameter outer ring. The rings are joined together
by one or more splines. The splines can form elongated concentric
arcs (hereinafter "concentric arc segments") surrounding the inner
ring. The design of the spline can be opposite the design of a
wheel spoke radiating directly between an outer rim and inner hub.
It will be appreciated the spoke will extend from the inner hub in
a radially straight direction to the outer rim. It will be
appreciated that the elongated concentric arc (serpentine) shape of
the splines of the Applicant's design permits the greater
deflection of the spline with lower stress. The Applicant's design
achieves this improvement by the longer load path formed of the
elongated design of the concentric arc segments of each spline. It
will be further appreciated that the spline can be deflected or
deformed by the rotation of one ring relative to the other ring.
With fewer splines, each spline can be designed longer to achieve a
wider range of stiffness, but a lower maximum achievable stiffness.
With fewer splines, each spline can be designed to have a longer
extended path between the inner ring and the outer ring. The
thickness of the spline may be varied through the elongated length.
The depth of the spline may also be varied
[0018] The Applicant discloses that incorporating more splines
connecting the inner and outer rings allows a narrower range of
achievable stiffness, but a higher maximum stiffness. There can be
as few as 1 spline, and the practical upper limit of splines is
dictated by the overall diameter of the spring. This disclosure
teaches that fewer splines allows a broader range of stiffness,
while a greater number of splines narrows the range of stiffness
but increases the total stiffness of the spring. Further, this
application claims priority to Nonprovisional application Ser. No.
14/691,702 entitled "Series Elastic Motorized Exercise Machine"
filed Apr. 21, 2015 and which is incorporated in its entirety by
reference herein.
[0019] FIG. 1 illustrates an example of a planar torsion spring
100. It will be appreciated that the flat spring lies in the plane
of the page. The planar torsion spring has an axis of rotation 140.
The axis of rotation is parallel to the longitudinal axis of the
spring. The axis of rotation is parallel to the depth 135 of the
planar torsion spring. This axis of rotation is shared with the
outer ring 110 (the output side) and the inner ring 120 (the input
side).
[0020] It will be appreciated that the axis of rotation of the
torsion spring may be shared with the axis of rotation of other
components of an apparatus utilizing the torsion spring. Such an
apparatus can be the Series Elastic Motorized Exercise Machine.
[0021] The planar torsion spring illustrated in FIG. 1 illustrates
a design utilizing two splines 130. As shown, the splines connect
the input side 120 with the output side 110. Each spline comprises
a single arc segment. The width of the arc segment has a distinct
width apparently unrelated to the relationship of the arc to the
varying circumference existing between the outer ring and inner
ring. This design is distinct from the design illustrated in the
Applicant's disclosure.
[0022] This disclosure pertains to a novel planar torsion spring.
An example of the planar torsion spring of the Applicants'
disclosure is shown in FIG. 2. The spring comprises a planar
surface. This plane extends along the x and y axis. The spring has
a radius in the x and y axis. The spring comprises an outer ring
110 (the output side) and an inner ring 120 (the input side). The
output side is concentric about the input side. The input side and
output side share the same axis of rotation 140. The axis of
rotation is parallel to the longitudinal axis of the spring. The
depth 135 of the spring is also parallel to the longitudinal axis.
The axis of rotation and longitudinal axis are in the z
direction.
[0023] The planar torsion spring can be described as an inner ring
positioned within the concentric ring of an outer portion ring. The
inner and outer rings are connected by one or more splines. The
splines comprise multiple concentric arc segments positioned in a
serpentine pattern between the inner circumference of the outer
ring and the outer circumference of the inner ring. The Applicant's
design illustrated in FIG. 2a achieves maximum extension of each
spline relative to the circumference between the first outer ring
(output side) and the circumference of the second inner ring (input
side) and each spline has the maximum number of concentric arc
segment splines between the inner circumference of the first outer
ring and the outer circumference of the second inner ring. The
maximum length of a spline and the number of concentric arc
segments may be impacted by the number of spines.
[0024] Another definition of the disclosure would be a method for a
planar torsion spring wherein the spring comprises fabricating a
first outer ring, fabricating a second inner ring which is
positioned within the first outer ring and possessing a same axis
of orientation, further connecting the first outer ring with the
second inner ring with one or more splines and extending the spline
to a maximum length relative to the circumference between the first
outer ring and second inner ring, fabricating the spline with the
maximum number concentric arc segments between the inner
circumference of the first outer ring and the outer circumference
of the second inner ring and positioning the first outer ring, the
second inner ring and the spline in the same plane.
[0025] The advantages of this construction include increased
strength and flexure of the spring.
[0026] The above state definitions are now combined with the planar
rotational spring diagramed in FIG. 2. Connecting the outer ring
(output side) with the inner ring (input side) are splines 130.
Three splines are illustrated. Each spline follows a serpentine
path from the outer circumference of the inner ring to the inside
circumference of the outer ring. The spline architecture includes a
plurality of annular segments 131. In the illustration, each spline
has three annular segments. Each segment comprises an arc of
approximately 120.degree.. Each annular segment is attached by a
curved section of the spline 132. The curved sections reverse
direction of the annular segments of the spline. Each spline
attaches to the input and output sides by an L shaped protrusion
133 extending from the output or input side and immediately turning
to form an annular segment.
[0027] It will be appreciated that there may be more than three
annular segments. This could be achieved by making the thickness
134 of the spline narrower. This change in geometry may require the
depth 135 of the spline of the torsion spring to be increased. It
could also be achieved by making the diameter of the planar torsion
spring larger.
[0028] The advantages of this construction, i.e., three splines
constructed of three annular segments attached by curved segments
and attached to the inner and outer rings by L shaped structures as
illustrated in FIG. 2, increased strength and flexure of the
spring. Each curved section 132 and L shaped structure 133 acts as
a flexure point.
[0029] An additional advantage is that the input side can be
deflected from the output side by an increased angle. It will be
appreciated that the drawing illustrates the spring at an
equilibrium state. If the output side is subjected to force, the
spring will flex. When flexed, the output side of the spring may
rotate while the input side stays in the same position. The
increased flexure of the spring allows increased angle of rotation
or deflection of the output side relative to the input side without
permanent deformation of the spring.
[0030] In another embodiment, not shown, is one or more splines
comprising a winding configuration about the other or winding about
the input side.
[0031] Continuing the discussion/comparison of the novel 3 spline
design described above and illustrated in FIG. 3 and the 2 spline
configuration illustrated in FIG. 4, the stress analysis for both
spring designs is illustrated. These two springs have the same
stiffness and strength, but the novel spring design subject of this
disclosure (FIG. 3) can be manufactured from more standard, less
expensive alloy. The lower stress of the spring depicted in FIG. 3
is evidenced by the small portions of the spring that exhibit a red
color and lower overall magnitude of force represented by the red
color.
[0032] The geometry of the 3 spline torsion spring subject of FIG.
3 was made by the inventors. One advantage of the inventors'
geometry is that each spline has a greater load path. It will be
appreciated that the greater load path allows more deflection given
a material and a lower amount of stress. concentration leading to a
greater achievable stiffness range before overload.
[0033] Given a desired stiffness, the general geometry of the
design reduces the stress in the material, resulting in a stronger
spring than the design illustrated in FIG. 1.
[0034] The color drawings FIGS. 3 and 4 shows the areas
experiencing stress (red). The magnitude of the area in red shows
the amount of stress. It is important to note that the springs of
FIGS. 3 and 4 were subjected to the same torque and stiffness but
the splines of FIG. 3 shows greater strength due to geometry (less
stress). FIG. 3 illustrates smaller areas of stress concentration
and lower overall stress. It will be appreciated that the degree of
distortion of the splines is exaggerated in FIG. 3 (and FIG. 4).
Also the stress scale delineated on FIG. 3 and FIG. 4 is different.
FIG. 4 has a higher scale of stress. FIG. 3 shows up to 6.454e8
N/m.sup.2 In contrast; FIG. 4 illustrates 7.241 e8 N/m.sup.2. It
will be appreciated that if the spline is exposed to excessive
force, the structure of the spline can break or be permanently
deformed. The splines may also be subject of hysteresis wherein the
shape of the spline is temporary deformed after bending due to
torque.
[0035] It will be appreciated that the spring geometry includes the
depth 135 of the splines, as well as the spline thickness 134 and
spline load path (illustrated as 131, 132, 133 and 134). The
geometry and material selection determine the spring stiffness. For
example the planar torsion spring illustrated in FIG. 3 and
comprised of standard steel alloys e.g., 17-4PH stainless steel can
achieve the same stiffness and strength of the spring illustrated
in FIG. 4 comprised of more expensive or more difficult to work
with such as custom 465 stainless steel or maraging steel. Also,
the spring illustrated in FIG. 3 can achieve a wider range of
spring stiffness than the design in FIG. 4.
[0036] Further, the new spring geometry reduces stress
concentration by distributing the load more predictably and evenly.
This means that the peak stress in the material is less with the
new design given a size and stiffness target. The new spring
geometry (FIG. 3) illustrates a larger load path. It will be
appreciated that the greater load path allows the forces created by
spring deflection to be spread over a greater area, resulting in
smaller and less consequential stress concentrations. Given that
the overall dimensions between the two spring designs are the same,
the new spring design allows the use of more standard alloys to get
the same maximum load rating and stiffness.
[0037] The Applicants' design illustrated in FIG. 3 can also be
modified using a parametric equation where strength and stiffness
are input parameters and dimensions are the equation output. An
example of such an equation is stated below. Utilization of such an
equation allows the Applicants' design to be easily modified to
determine stiffness. Note the equation can be used to select the
spline thickness. It does not select the design pattern or number
of arc segments. This allows designers to very quickly change the
spring stiffness to match their intended application.
SplineThickness=-1e-4*DesiredStiffness.sup.2+0.0577*DesiredStiffness+3.4-
142
DesiredStiffness is in units of Nm/deg SplineThickness is in units
of mm This equation is specifically for an inner ring diameter of
50 mm and an outer ring diameter of 210 mm with a 6.35 mm depth.
The equation maintains the same form for different inner ring and
outer ring diameters as well as different thicknesses, but it will
have different coefficients.
[0038] The concentric serpentine nature of the splines helps to
reduce stress due to radial misalignment of the input and output
axes of rotation due to assembly tolerances. Radial misalignment is
illustrated in FIG. 5a showing a simplified view of two planar
torsion springs. The perspective of the illustration (showing two
end views of torsion springs) is looking down the longitudinal axis
of the torsion spring. The illustration on the left side of FIG. 5a
shows the inner ring and outer ring in proper alignment. The right
side of FIG. 5a illustrates the outer ring 501 of the torsion
spring having a different axis of rotation relative to the inner
ring 502. The left side of FIG. 5b again shows proper alignment.
FIG. 5b shows axial misalignment, where both the outer 503 ring and
inner ring 504 are concentric but in different positions along the
longitudinal axis. In other words, the new design allows for
greater misalignment axially or radially between the inner and
outer rings before stress buildup causes problems. This allows for
cheaper, lower precision manufacturing processes to be used in
making the parts the spring attaches to. It will be appreciated
that the selection of concentric arc segment splines enhances the
tolerance of the torsion spring to misalignment. The tolerance for
axial and radial misalignment allow for wider (easier) mounting
tolerances, which makes manufacturing easier.
[0039] Another variable of the planar torsion spring of the
Applicants' concentric arc segment spline design is that the length
of each arc segment 131 (see FIG. 2) can be varied. Reducing or
expanding the arc length will change the way the spring behaves,
depending on the application. This variation is independent of the
total number of splines. Given a number of splines, longer thinner
concentric arc segments lead to a softer spring overall. The length
of the arc segments is directly tied to the stiffness and strength
of the spring.
[0040] A planar torsion spring comprising concentric arc segments
tolerates radial or axial misalignment with reduced stress compared
to other spring designs. Radial misalignment occurs when the axis
of rotation of the inner ring and outer ring are not identical.
[0041] This specification is to be construed as illustrative only
and is for the purpose of teaching those skilled in the art the
manner of carrying out the disclosure. It is to be understood that
the forms of the disclosure herein shown and described are to be
taken as the presently preferred embodiments. As already stated,
various changes may be made in the shape, size and arrangement of
components or adjustments made in the steps of the method without
departing from the scope of this disclosure. For example,
equivalent elements may be substituted for those illustrated and
described herein and certain features of the disclosure maybe
utilized independently of the use of other features, all as would
be apparent to one skilled in the art after having the benefit of
this description of the disclosure.
[0042] While specific embodiments have been illustrated and
described, numerous modifications are possible without departing
from the spirit of the disclosure, and the scope of protection is
only limited by the scope of the accompanying claims.
* * * * *