Note: Descriptions are shown in the official language in which they were submitted.
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BACKGROUND OF THE INVENTION
Field of the Invention
This invention relates to torque measurement in a
mechanical device such as a gear speed reducer by sensing the
tangential force of the gears transmitted to one of the
rotating members.
DESCRIPTION OF THE PRIOR ART
All rotating machines such as motors, generators, turbines
and mechanical gear trains or transmissions have one major
function in common; they produce or transmit torque. They all
also absorb some torque which becomes a power loss to the overall
system. The method and apparatus for sensing and measuring
the torque output power and loss have been a continuous challenge
to the engineers in the related field. Most methods for
measuring the torque reauire a modification of the drive train
at some point and a device inserted into it or fastened on it
to measure torque, such as that described in U.S. Patent No.
2,35g,125. The device described in that patent utilizes strain
i gages for both the thrust and torque measurement.-
Another method measuring torque shown in U.S. Patent No. '
3,595,074 consists of a pair of axially spaced plates having
a plurality of flexure plates mounted therebetween wherein one
plate is attached to a rotary machine housing and the other
plate to the drive mechanism. The drive mechanism is supported
by this torque transducer from the housing surface and is mounted
in cantilever fashion at the unsupported ends of the flexure
plates. The reaction or countertorque between the mounting
plates, in proportion to the input or output torque, and the
relative movement of one plate with respect to the other
plate, is measured and hence the torque determined by use of a
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differential transformer, which develops an electrical signal
proportional to the angle through which the end plate is
rotated.
In still another U.S. Patent No. 3,745,819, the axial
thrust developed by tapered roller bearings in response to
radial loads exerted on the rotating member is fed through a
piston adapted to move axially against a pressure chamber to
provide a pressure reading proportional to the radial load
imposed on the rotatable member. This device required an
additional pressurized and sealed mechanism inside the housing
or attached directly to it which has many components in it
and is very expensive to manufacture. Other U.S. patents, such
as No. 2,957,343 shows still another method for measuring torque
as a function of thrust using airIpressure and in U.S. Patent
No. 1,998,450 the thrust is measured by deflecting a spring
which move the plates of an electrical condenser causing a change
in the capacitance which is proportional to the axial movement
of a shaft. Still other methods employ slip rings and require
cutting the shaft and inserting the transducer into the shaft
j 20 member itself to measure the torque of that shaft. Still
another method commercially available employs a Linear Variable
Differential Transformer (LVDT) wherein the core position moves
as a function of the shaft thrust and hence torque output of
the device. Such a unit, however, is very large and requires
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- an extensive modification of the power device.
My invention inserts a transducer into the housing which
supports the shaft bearing and senses the tangential force of a
rotational member. This approach is a much simpler and more
compact package than previous methods and apparatus. As
discussed, many methods have been used to detect the rotary
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motion, separating force, tangential force or axial thrust
of a shaft and translate this to the torque developed by the
- shaft. Although some of the aforementioned patents and methods
were used in conjunction with gear trains and power transmissions,
none of these solved the pro~lem of measuring the torque in a
gear box in the unique way as does my invention.
A gear box and, for that matter, other power transmission
systems, usually operate with a continuous bath of oil available
to the gears when in use. This lubrication is necessary for
translating the high speed and low torque input associated
with such devices into a low speed and high torque output. Such
units are designed to be as small and compact as possible. A
device to measure output torque therefore, must also be small and
compact in size to fit into an existing housing or space, be
low in cost and capabl~ of constant immersion in oil or other
fluids, operate at varying temperatures and contaminated
environments, and have a method of remote readout. This remote
requirement is necessary in many applications of power transmis-
sion and gear reducers since a visual inspection during operation
of the assembly itself is not always possible because of its
location. Also in gear devices, as well as other machinery,
bearings and shafts must maintain their position very accurately
under all conditions of operation to assure proper load of the
power transmitting parts to maintain minimum deflections and
movements often to less than 0.001 inches. This requirement
it easily met with my invention.
This invention solves the problem in gear train devices and
other power transmitting equipment by measuring and monitoring
the torque load directly by measuring the tangential force
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developed at the gears and transmitted to the rotational shaft
member and its housing yet maintaining the accurate alignment
of all parts.
It is an object of this invention to measure the tangential
force of a rotating member by measuring minute deflection of
an adaptor lnserted between the shaft bearing and its gear
reducer housing. It is also the object of this invention to
detect this deflection by the use of strain gages mounted to
this transducer.
According to the present invention there is provided
an apparatus for detecting and measuring the torque of a
gear speed reducer means having a housing means,a load transmit-
ting rotating shaft means within the housing means, shaft means
having plural bearing means connecting the shaft means to the
- housing means. In the present invention there is provided a
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transducer means located inside the speed reducer housing means
and operatively connected between one of the bearing means
and the housing means. The transducer means has a member
bending in proportion to the tangential force on the rotating
shaft means. The bending member means is positioned in line
with the shaft and the transducer means is connected to the
indicating means so that the tangential force imparted to the
load transmitting shaft means is measured.
In a specific embodiment of the invention strain gage
; elements are mounted to the adaptor and strategically located
on it to sense the radial force developed by the contract between
the gears and pinions and transmitted to the shaft bearing. As
the torque or load increases in a given application, as found
in a gear or speed reducer box, the speed reducer shaft will
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transmit the developed force to the bearings designed to accept
such loading. Normally these beaxings would have a cover plate
in contact with the shaft bearings or a bearing carrier which
prevent axial and/or radial movements of the shafts and maintain
gear alignment. The transducer in this invention may replaces
one of these cover plates and holds the shaft bearing. The
housing is modified so the transducer will fit into the same
relative location to properly align the bearing or depending
on usage, the bearing can be reduced in size and no housing
modification is required. This adaptor or transducer is shown
in a particular location for purpose or describing my invention.
It should be noted that the transducer could be located at any
of a member of bearing locations. If the transducer is
located at the input or output shafts, the electrical connector
would require relocation off-set from the center of the cover
plate. The strain gages mounted on the adapter detect the
minute deflection due to the load and this signal is transmit-
ted to leads connected to an electrical receptacle and brought
out to a connector and cable which will now connect to a visual
indicator or to some type recorder. The strain gages are
connected into a typical bridge circuit which may contain a
strain gage amplifier apparatus, well known in the art and not
discussed here, connected between the gages and the indicator
or recorder.
This type device and method of measurement of torque loads
or tangential forces in power transmission devices is almost
limitless. In other words the size of the gear reducer or
transmission could double in physical siæe and only the
transducer adaptor dimensions would change to match the bearing
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size with a slight change in the strain gage mounting structure
thickness. In most cases even the strain gages used would
not be changed.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a cross-section drawing of a typical gear
reducer box;
Figure 2 shows the mounting of the torque sensing adaptor
to one end of a gear reducer box and the connection to the
recorder means;
Figure 3 is a view of a rotating member and the relative
forces on a double helical pinion and gear;
Figure 4 is a view of a rotating member and the relative
forces on a single helical pinion and gear;
Figure 5 is a cross-section of the adaptor taken along line
5-5 in Figure 2 showing location of the strain gages;
Figure 6 is a view of the adaptor taken along line 6-6 in
Figure 5 and removed from gear reducer box;
Figure 7 is an electrical schematic showing the bridge
network of-the strain gages;
20- Figure 8 is a cross-section taken along line 8-8 in
Figure 2;
Figure 9A is a cross-section of an optional embodiment of
the shaped section taken along line 9-9 in Figure 5 and removed
from the housing;
Figure 9B is a cross-section of an optional embodiment of
the shaped section of Figure 9A;
Figure 9C is a cross-section of an optional embodiment of
the shaped section of Figure 9A, and;
Figure 9D is a cross-section of an optional embodiment of
the shaped section of Figure 9A.
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DESCRIPTION OF PREFERRED EMBODIMENTS
Referring to Figure 1 in the drawings, a typical gear
reducer assembly 10 is shown in cross-section with the input
shaft 12 passing through the cover 14 and mounted in housing
16 on bearings 18 with a double helical pinion gear 20 an
integral part of the shaft 12. Gear 20 meshes with the double
helical gear 22 which can be keyed to or be an integral part
of intermediate shaft 24 and supported by a bearing 26 at one
end and a bearing 28 mounted inside bearing carrier 30 which
10 is also the transducer adaptor of the embodiment. The inter-
mediate pinion gear 32 is usually an integral part of intermediate
shaft 24. This pinion 32 meshes with the double helical main
drive gear 34 keyed to main drive shaft 36 by key 38 and
supported by bearings 40 mounted in housing 16. Cover plates
42 and 44 hold bearings 40 in place and locate the gearing in
the housing. Cover plates 46 and 48 are mounted to housing 16
adjacent to shafts 24 and 12, to seal the housing. Bearing
seals 50 and 52 seal the respective bearings to prevent loss of
lubrication of the gear box and prevent dust or other contaminents
20 from entering.
Figure 3 shows the intermediate shaft 24, with its gears
and bearings attached, removed from the gear box to show the
relative forces which act upon it. TFg is the tangential force
developed which is proportional to the torque transmitted by
the gear when driven through shaft 12 and gear 20 when in normal
operation. A separating force SFg is also developed which is
proportional to the torque transmitted by the respective shaft.
Each shaft will have a different torque developed by it and
therefore the tangential forces are only equal at a given mesh
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set of gears. The tangential force is transmitted to gear 22
and shaft 24 and is noted as TFg in Figure 3. Another tangential
force TFP is also developed on the pinion gear 32 of shaft 24.
Both of these forces now are in the same direction and are
vectorially additive. The separating forces SFg and SFp are
a function of the respective tangential forces and are vectored
toward each other. The net force is very small compared to the
tangential force. The combined tangential force is counteracted
through the bearings attached to the shaft 24 and supported in
the housing. In my invention, one of the bearings, in this
case bearing 28, is mounted in a combination bearing carrier
transducer 30 with strain gauges attached, which if properly
located, can detect the tensional and compressive forces in the
carrier transducer 30 caused by the tangential forces TFg and
TFp. In Figure 1 the tangential force is perpendicular to the
paper and the stress on the strain gauges on the bearing carrier
may be in either tension or compression depending on the direction
of rotation of the unit.
Figure 4 shows the relative forces on a single helical
gear and because of the type of gearing it is, an additional
force is developed which is an axial force (AFp) parallel to
the axis of the shaft, in this case shaft 24; but these also
are vectorially additive and counteract each other but a net
force may still exist. The tangential forces, however, are
normally both in the same direction and therefore my invention
', would detect such a force.
!' Figures 5, 6 and 8 show the construction of the bearing
carrier transducer 30 which consists of a flange 56 having an
electrical connector 54 affixed thereon and bolts 58 holding
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the adaptor 30 piloted by diameter 62 in bore 64 to housing 16.
Annulus 60 having outside diameter 66 and bore 68 form a cup-like
part with inside surface 70 and outside surface 72. Bore
74 provides clearance for the end of shaft 24. Ribs 76 and 80
form a shaped structure connecting flange 56 to the cup-like
structure at surface 72. These rib like members are machined
to the proper width so they will deflect a certain amount for a
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given load.
Diameter 82 is machined slightly smaller than diameter 66
10 to facilitate mounting of the strain gages without interference.
Surfaces 84 and 86 are accurately machined to be equidistant
from the centerline of the axis of pilot diameter 62. ~rcuate
~;~ surface 74 complete the rib or shaped structure 76 and 80. The
strain gages 90, 92, 94 and 96 could be mounted to the arcuate
surface 82 depending on the radius of the surface. The preferred
~i embodiment will have flats 102 and 104 interrupting surface 82
such as shown in Figure 9A which provide a surface on which the
gages may be mounted. The gage are affixed to these surfaces,
102 and 104, with an adhesive type material and electrically
20 connected into a standard Wheatstone bridge circuit, well known
in the art as shown in Figure 7.
Other embodiments of the shaped structure are shown in
Figures 9A, 9B, 9C and 9D. In Figure 9A the ribs or shaped
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` structure 76 and 80 are shown having a saw cut 77 and 81 which
; intersect arcuate surface 74' to allow increased deflection
` and sensitivity of the transducer. Figure 9B shows the shaped
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structure as a plurality of rib members having a clearance hoie
75 for passage of the wires from the connector to the gages.
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~ The ribs 76', 76" and 80' and 80" make up the shaped structure
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~ the strain gages 90", 92", 94" and 96" mounted thereupon. Figure
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and 104' with strain gages 90', 92', 94' and 96' mounted there-
upon. Hole 55' is similar to diameter 78 of Figure 6 and is
the opening to allow to lead wires from the gages to be brought
, out to the connector via the cross hole 57'.
;~ Another embodiment of the shaped section is shown in
Figure 9D wherein the shaped member is a square section having
sides 101, 102", 103 and 104". The strain gages 90", 92", 94"
^ 10 and 96" are mounted on surfaces 102" and 104". Hole 55" and
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cross hole 57" are the passages for the wires from the strain
gages to the connector with hole 55" being similar to diameter
78 shown in Figure 6. It is obvious to one skilled in the art
that the shaped structure previously described could have many
different cross sections configurations depending on the parti-
cular sensitivity desired and available mounting space. ~lso
the least expensive method of manufacturing the transducer would
also dictate the shape of this section.
The number of strain gages can vary from one to any reason-
able number that can be conveniently mounted. In case only
one strain gage is used, it would require three passive precision
resistors in the other legs of the bridge circuit shown in
Figure 7. Usually a minimum of four strain gages would be used.
The gages are standard commercially available gages such as
manufacture~ by ~licro-Measurements Company.
Since these gages operate either in tension or compressionj
there is no restriction on mounting them on the shaped structure
except they should be positioned to properly sense compression
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the surface so they are perpendicular to the resultant tangential
; force ~TFp and TFg) with the grids positioned in the direction
of the axis of the shaft. Although only four strain gages are
shown, additional gages may be used if properly spaced and
connected. The gages should be mounted as close to flange 56
as possible to give maximum sensitivity. In this embodiment
only the tangential force is considered and measured. It is
obvious that the transducer assembly 30 could be rotated 90
- and the separating force detected and measured. The preferred
embodiment uses tangential force because this force is usually
much larger than the separating force and a more accurate method.
; If the ratio of the tangential force to separating force is
10:1, the sensitivity of the device for measuring the large
force is much better.
, When the gages are connected in the bridge circuit as
shown in Figure 7, gages 1 and 2 must be connected in the circuit
to detect the same type of stress and gages 3 and 4 similarly
connected. Therefore, gages 1 and 2 must be elements 90 and
; 92 shown in Figure 6 and gages 3 and 4 must be elements 94 and
96. A voltage and ground connection is made across two junctions
as shown in Figure 7 and the output signals are sensed at terminals
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A and B for subse~uent connection to a measurement means. Bore
78 in flange 56 of Figure 5 provides access for the circuit
leads to be connected from connector 54 to gages 90, 92, 94 and
96. Indicator 88 is shown in Figure 2 to be connected via cable
98 to output connector 54. The connector 54 is a hermetically
sealed connector and is sealed by gasket 100 to flange 56 as
shown in Figure 5.
Bearing 28 is shown in Figure 5 mounted on diameter 25 of
shaft 24 and held in place by snap ring 27. The outside diameter
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of bearing 28 is a slip fit into diameter 68 of adaptor 30. The
construction shown here is for a typical ball bearing application
and it is obvious that other type bearings could be used and
the relative construction would vary slightly. Clearance is
shown between surface 70 and the end of bearing 28 to allow for
lateral or axial movement of the shaft to allow the gear to
self-align. It is possible for this clearance to be non-existant
if the bearing is pressed into contact with surface 70. This
would be acceptable and not affect the unit. The clearance
between diameter 66 and bore 64 is controlled and selected to
have a specific clearance between the elements. This predeter-
mined clearance provides a built-in overload protection since
the adaptor ribs 76 or 80 (depending upon direction) can only
deflect a specified distance before diameter 66 contacts bore 64.
No further deflection will occur and no damage can occur to the
transducer or gages giving longer life to the elements. This
clearance is therefore subject to the load application and
the maximum overload allowed.
OPERATION
A power transmission such as the gear reducer or speed
reducer assembly 10, shown in Figure 1, is driven by a prime
mover through shaft 12 and ultimately converts a high speed and
low torque input to the,output shaft 36 as a low speed and high
torque output. As the sp~eed reducer shaft 36 picks up the load,
it is transmitted back through the reducer system through the
double helical or herringbone gear 34 to the pinion gear 32
on the intermediate shaft 24 which also has gear 22 affixed
thereto. Gear 22 transmits the load to pinion gear 20 on shaft
12 which is ultimately picked up by the prime mover. As stated
earlier any of the bearings in the system could be mounted in an
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1~883~5
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adaptor 30, such as shown in Figure 1 for the application of my
invention. For purpose of this disclosure, the transducer
adaptor 30 is shown operating in conjunction with the intermediate
shaft 24 and its bearing 28. The inner race of bearing 28 is
affixedly held to shaft 24 by snap ring 27 best seen in Figure
5. The outer race of bearing 28 is a slip fit into bore 68 of
adaptor 30. This fit allows the shaft and bearing assembly a
slight movement when initially assembled so as to seek its
running position when first assembled. The adaptor,30 with the
strain gage and connector attached are affixed to the housing
16 by a convenient means such as bolts 58 with pilot diameter
62 accurately locating the adaptor 30 to the housing 16. Uhder
load conditions, regardless of the direction of rotation of the
gear reducer, the ribs 76 and 80 will act as a cantilever under '
load and deflect in proportion to the tangential force on the -'
gears. This force will cause the strain gages 90, 92, 94 and
96 to respond to the bending load caused by the compressive
strain on one rib surface and a tensile strain on the other rib
surface. With the proper voltage applied as shown in Figure
7, signals at terminals A and B will be proportional to the -
tangential force applied to the gears. This signal at terminals
A and B will be communicated through the connection from the
strain gages to connector 54, through cable 98 to the indicator '' '
88 shown in Figure 2. The Wheatstone bridge network is well
known in the art and additional discussion is not needed except
to reiterate that any number of gages may be used and if less
than four are used in a given circuit, then precision resistors
must be substituted in order for the bridge to function properly.
A strain gage amplifier may also be used to amplify the signal
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883~5
depending upon the relative values and sensitivity of the
measuring means. This aspect of Wheatstone bridges and amplifiers
are also well known in the art and additional discussion is
unwarranted.
If a given load were to increase beyond the safe working
limits of its design, my invention will prevent damage to the
adaptor and the strain gages by the surface 66 of annulus 60
contacting bore 64 and preventing further deflection of the rib
sections. The indicator 88 or its associated circuitry would
normally have limit switches in it to sense overloads and
operate in conjunction with the reducer so the system could be
shut down to prevent subsequent damage to personnel or machinery.
The strain gages are always connected so that gages in
compression and the gages in tension are in opposite legs of
the bridge. Since the ~ages work equally well whether in
tension or compression the direction of deflection of the rib
members make the unit bi-directional and no changes are required
to compensate for direction of rotation shaft for proper
functioning or operation of my invention.
The gages are shown mounted on flat surfaces 102 and 104.
They would work equally well on an arcuate surface depending
on the diameter of a given surface. The preferred embodiment
would have flats machined as shown in Figure 6 for the best
mounting of the strain gages, The gages are also encapsullated
in a material which will protect them from the environment
within the gear reducer which is a heavy oil to lubricate all
the gears in such a device. Other protection can be provided
depending on the fluid or environment the adaptor is exposed to.
; In summary my invention is a bearing carrier or adaptor
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modified to have oriented shaped members capable of deflecting
when a force is applied and with strain gages attached to these
members which will sense the tangential force produced in one
of the shafts in the assembly which is proportional to the torque
transmitted through the unit. This deflection is transmitted
to a recorder or similar device where it ismonitored or connected
to electrical circuit elements for controlling the system or
acting in the event of an overload to the system.
This invention has been described with a preference given
to certain embodiments. One skilled in this art will see
modifications upon reading and understanding this specification
and it is my intention to include all such modifications insofar
as they come within the scope of these appended claims.
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