U.S. patent application number 11/046961 was filed with the patent office on 2005-06-16 for displacement based dynamic load monitor.
Invention is credited to Broek, Titus, Schoch, Daniel A..
Application Number | 20050131651 11/046961 |
Document ID | / |
Family ID | 34277995 |
Filed Date | 2005-06-16 |
United States Patent
Application |
20050131651 |
Kind Code |
A1 |
Schoch, Daniel A. ; et
al. |
June 16, 2005 |
Displacement based dynamic load monitor
Abstract
An apparatus and method for monitoring the force severity of a
mechanical press without utilizing a contact force sensor. The
method continually computes values of dynamic deflection for the
press being monitored and utilizes these values to compute load on
the press at any point in time.
Inventors: |
Schoch, Daniel A.; (Minster,
OH) ; Broek, Titus; (Sidney, OH) |
Correspondence
Address: |
RANDALL J. KNUTH P.C.
4921 DESOTO DRIVE
FORT WAYNE
IN
46815
US
|
Family ID: |
34277995 |
Appl. No.: |
11/046961 |
Filed: |
January 31, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11046961 |
Jan 31, 2005 |
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09678183 |
Oct 2, 2000 |
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6868351 |
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60160170 |
Oct 19, 1999 |
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Current U.S.
Class: |
702/71 |
Current CPC
Class: |
B30B 15/0094
20130101 |
Class at
Publication: |
702/071 |
International
Class: |
G01R 013/00 |
Claims
1-15. (canceled)
16. A method of monitoring load on a mechanical press having a
slide, said method comprising the steps of: determining a value of
dynamic deflection, using a no-load press motion characteristic;
determining a value of static stiffness for the press being
monitored; calculating load on the press at any point of the slide
stroke, using the value of dynamic deflection for the relevant
point of the slide stroke and the value of static stiffness.
17. The method of claim 16, wherein said step of determining a
value of dynamic deflection comprises the steps of: generating a
theoretical no load value of slide displacement; generating an
actual load value of slide displacement corresponding in time to
the theoretical no load value of slide displacement; computing a
difference between the theoretical no load value and the actual
load value of slide displacement; and establishing the difference
between the theoretical no load value and the actual load value of
slide displacement as the value of dynamic deflection.
18. The method of claim 16, further comprising the steps of:
determining a plurality of values of dynamic deflection at
increments of the entire slide stroke; and calculating a plurality
of load values corresponding to the plurality of dynamic deflection
values.
19. The method of claim 18, further comprising the steps of:
generating a plot of load vs. time for a slide stroke of the
press.
20-26. (canceled)
27. A method for use with a press machine having a slide, said
method comprising the steps of: generating a signal indicative of
slide displacement under a press no-load condition for said press
machine; generating a signal indicative of slide displacement under
a press load condition for said press machine; and comparing the
no-load slide displacement signal and the load slide displacement
signal.
28. The method as recited in claim 27, wherein the comparison step
further includes the step of: generating at least one measure of
press machine activity, using the no-load slide displacement signal
and the load slide displacement signal.
29. The method as recited in claim 28, wherein the at least one
measure of press machine activity being indicative of at least one
of press machine behavior, response, and performance.
30. The method as recited in claim 27, wherein generation of the
no-load slide displacement signal includes generating a theoretical
no-load valuation of slide displacement.
31. The method as recited in claim 27, wherein the step of
generating the load slide displacement signal further includes the
step of: non-contactable monitoring of slide displacement.
32. The method as recited in claim 31, wherein the monitoring step
further includes the step of: collecting slide displacement data
with at least one non-contacting sensor.
33. The method as recited in claim 27, wherein the comparison step
further includes the step of: generating a differential valuation
between the no-load slide displacement signal and the load slide
displacement signal.
34. The method as recited in claim 27, wherein the comparison step
further includes the step of: generating a measure of dynamic
deflection.
35. The method as recited in claim 27, wherein the press load
condition involves deployment of a tooling die configuration in the
press machine, and the press no-load condition involves
non-deployment of the tooling die configuration in the press
machine.
36. The method as recited in claim 27, further includes the step
of: determining a value of load on said press machine, using the
slide displacement signal comparison.
37. The method as recited in claim 27, further includes the steps
of: generating a signal indicative of dynamic deflection, using the
slide displacement signal comparison; and determining a signal
indicative of load on said press machine, using the dynamic
deflection signal.
38. The method as recited in claim 37, further includes the step
of: repeatedly performing the dynamic deflection signal generation
and load signal determination during a press operation.
39. The method as recited in claim 37, further includes the step
of: providing an indication of press machine load as a function of
a variable.
40. The method as recited in claim 39, wherein the variable
includes at least one of crank angle and time.
41. A method for monitoring operation of a press machine having a
slide, said method comprising the steps of: providing a signal
indicative of a no-load press machine motion characteristic; and
determining a load on said press machine, using the signal
indicative of a no-load press machine motion characteristic.
42. The method as recited in claim 41, wherein the providing step
further includes the step of: generating a signal indicative of
slide displacement under a press no-load condition for said press
machine.
43. The method as recited in claim 42, further includes the step
of: generating a signal indicative of slide displacement under a
press load condition for said press machine.
44. The method as recited in claim 43, wherein the determining step
further includes the step of: generating a differential comparison
between the no-load slide displacement signal and the load slide
displacement signal.
45. The method as recited in claim 41, wherein the no-load press
machine motion characteristic including an indication of no-load
slide displacement.
46. The method as recited in claim 41, further includes the step
of: iteratively performing the signal providing step and load
determination step over a selectable duration of slide travel.
47. A method for use with a press machine having a slide, said
method comprising the steps of: determining an indication of
dynamic deflection pertaining to said press machine, the dynamic
deflection being based at least in part on a no-load press machine
motion valuation; and determining a load on said press machine,
using the determination of dynamic deflection.
48. The method as recited in claim 47, wherein the determination of
dynamic deflection further includes the steps of: generating a
signal indicative of slide displacement under a press no-load
condition for said press machine; generating a signal indicative of
slide displacement under a press load condition for said press
machine; and generating a differential comparison between the
no-load slide displacement signal and the load slide displacement
signal.
49. A system for use with a press machine having a slide, said
system comprising: a first assembly to generate a signal indicative
of slide displacement for said press machine under a press no-load
condition; a second assembly to generate a signal indicative of
slide displacement for said press machine under a press load
condition; and a computing device coupled to said first assembly
and said second assembly, said computing device being configured to
operably compare the no-load slide displacement signal and the load
slide displacement signal.
50. The system as recited in claim 49, wherein said second assembly
includes at least one sensor disposed in non-contacting
relationship to said slide.
51. The system as recited in claim 49, wherein said computing
device being configured further to generate a differential
comparison between the no-load slide displacement signal and the
load slide displacement signal.
52. The system as recited in claim 49, wherein said computing
device being configured further to generate an indication of
dynamic deflection based on the comparison.
53. The system as recited in claim 49, wherein said computing
device being configured further to generate an indication of load
on said press machine based on the comparison.
54. A system for use with a press machine having a slide, said
system comprising: means for providing a signal indicative of a
no-load press machine motion characteristic; and means for
determining a load on said press machine, using the signal
indicative of a no-load press machine motion characteristic.
55. The system as recited in claim 54, wherein said providing means
further includes: means for generating a signal indicative of slide
displacement under a press no-load condition for said press
machine.
56. The system as recited in claim 55, further includes: means for
generating a signal indicative of slide displacement under a press
load condition for said press machine.
57. The system as recited in claim 56, wherein said determining
means further includes: means for generating a differential
comparison between the no-load slide displacement signal and the
load slide displacement signal.
58. An apparatus for operable use with a press machine, said
apparatus comprising: a first no-load press machine
motion-indicating signal generator; a second load-related press
machine motion-indicating signal generator; and a comparator,
operably coupled to said first signal generator and said second
signal generator.
59. The apparatus as recited in claim 58, further includes: a load
calculator, operably coupled to said comparator.
60. An apparatus for operable use with a press machine having a
slide, said apparatus comprising: a first no-load slide
displacement value generator; a second load-related slide
displacement value generator; and a comparator, operably coupled to
said first value generator and said second value generator.
61. The apparatus as recited in claim 60, further includes: a load
calculator, operably coupled to said comparator.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates generally to an apparatus and
method for monitoring press force severity and press load.
Specifically, the present invention relates to a method and
apparatus for monitoring dynamic press load without the use of a
contact force sensor.
[0003] 2. Description of the Related Art
[0004] Mechanical presses of the type performing stamping and
drawing operations employ a conventional construction which
includes a frame structure having a crown and a bed and which
supports a slide in a manner enabling reciprocating movement toward
and away from the bed. These press machines are widely used for a
variety of workpiece operations employing a large selection of die
sets with the press machine varying considerably in size and
available tonnage depending upon its intended use.
[0005] A press applies force to a workpiece so that the workpiece
(i.e. stock material) acquires the desired geometry corresponding
to the die set being utilized. Systems for monitoring press
operating reliability assist the press owner in evaluating the
impact of certain die/load applications on the reliability of the
press being monitored. Conventional monitoring systems include
systems which utilize contact load sensors to monitor the peak load
being developed within certain components of the press machine
during a slide stroke of the press. Known methods of monitoring
peak loads utilize an electrical resistance or piezoresistive
strain gage or other transducer which is mounted on the press and
which voltage change due to resistive change indirectly measures a
value of applied load. Monitoring load exerted on load bearing
members during a slide stroke of a mechanical press allows press
and die applications to be adjusted when monitored peak load values
are outside an acceptable range.
[0006] What is needed in the art is an apparatus and method to
compute the load on a press without utilizing a contacting load
sensor.
SUMMARY OF THE INVENTION
[0007] The present invention provides a method and apparatus for
the identification of dynamic load on a mechanical press which does
not require a contact load sensor.
[0008] More specifically, the method and apparatus of the present
invention continually computes a theoretical no load slide
displacement curve while also creating an actual slide displacement
curve during a load condition of the mechanical press. The
apparatus and method of the current invention then employs a curve
matching technique to superimpose these two curves so that values
of dynamic deflection at different points in the slide path may be
computed. Values of dynamic deflection are then utilized in
conjunction with a constant corresponding to the static stiffness
of the press to calculate load on the press.
[0009] The invention, in one form thereof, comprises a method of
generating a theoretical slide displacement curve for a mechanical
press. This method includes the steps of: providing an equation
that can be utilized to calculate slide displacement as a function
of press speed and which includes variables to account for press
parameters which effect slide displacement; providing a
computational device; determining the speed of the press;
determining the aforementioned equation variables; communicating
the equation, the speed of the press and the equation variables to
the computational device; calculating the theoretical distance
above bottom dead center for each increment of a slide stroke; and
plotting the calculated distance above bottom dead center values
vs. time. The step of determining the equation variables can
further include the steps of: determining the appropriate variable
corresponding to the press drive mechanism of the mechanical press,
determining the appropriate variable corresponding to the
connecting rod length of the mechanical press, determining the
appropriate variable corresponding to the stroke length of the
mechanical press, and determining the appropriate variable
corresponding to the bearing size of the mechanical press.
[0010] The invention, in another form thereof, comprises a speed
sensor for sensing a value of press speed, input means for
inputting a plurality of variables corresponding to characteristics
of the monitored press, computer storage means for storing an
equation which can be used for generating the theoretical slide
displacement curve, and a computer processor means for generating
the theoretical slide displacement curve. In this form of the
invention, the computer processor means are communicatively
connected to the sensor means, the input means and the storage
means. The equation utilizes the plurality of variables
corresponding to characteristics of the press and the value of
press speed to generate the theoretical slide displacement curve.
The plurality of variables input via the input means can include a
value of connecting rod length, a value of stroke length, a value
of drive type, and a value of bearing size.
[0011] The invention, in another form thereof, comprises a method
of monitoring performance parameters for a mechanical or hydraulic
press. This method includes the steps of: generating a theoretical
no load slide displacement curve, generating an actual slide
displacement curve during a load condition of the press,
determining the contact point on the actual slide displacement
curve which corresponds to the slide contacting the stock material,
establishing a start point on the slide downstroke between top dead
center and the contact point, establishing an end point on the
slide upstroke between top dead center and the contact point,
identifying the points on the theoretical slide displacement curve
corresponding to the start point and the end point, identifying the
points on the actual slide displacement curve corresponding to the
start point and the end point, superimposing the identified start
points on the theoretical and actual slide displacement curves, and
superimposing the identified end points on the theoretical and
actual slide displacement curves. In this form of the invention,
the step of generating a theoretical no load slide displacement
curve may further comprise the steps of: providing an equation that
can be utilized to calculate slide displacement as a function of
press speed which equation includes variables corresponding to
press drive mechanism, connecting rod length, stroke length and
bearing size; determining the speed of the press; determining the
appropriate variable corresponding to the press drive mechanism of
the mechanical press; determining the appropriate variable
corresponding to the connecting rod length of the mechanical press;
determining the appropriate variable corresponding to the stroke
length of the mechanical press; determining the appropriate
variable corresponding to the bearing size of the press; providing
a computational device; communicating the equation, the speed of
the press and the equation variables to the computational device;
calculating the theoretical distance above bottom dead center for
each time increment of a slide stroke; and plotting the calculated
distance above bottom dead center values for each time increment
vs. time. The step of generating an actual slide displacement curve
during a load condition of the press can be accomplished by
monitoring the displacement of the slide of the press with either a
contact or a non-contact displacement sensor and plotting the
monitored slide displacement vs. crank angle or time. A first
inflection point corresponds to the point at which the slide
contacts the stock material (i.e. the contact point).
[0012] The invention, in another form thereof, comprises a method
of monitoring performance parameters for a mechanical press. This
method includes the steps of: generating a theoretical no load
slide displacement curve, generating an actual slide displacement
curve during a load condition of the press, determining the contact
point on the actual slide displacement curve which corresponds to
the slide contacting the stock material, establishing a start point
on the slide downstroke between top dead center and the contact
point, establishing an end point on the slide upstroke between top
dead center and the contact point, identifying the points on the
theoretical slide displacement curve corresponding to the start
point and the end point, identifying the points on the actual slide
displacement curve corresponding to the start point and the end
point, superimposing the identified start points on the theoretical
and actual slide displacement curves, and superimposing the
identified end points on the theoretical and actual slide
displacement curves. In this form of the invention, the method of
monitoring performance parameters for a mechanical press further
comprises the steps of: calculating the distance between the
theoretical slide displacement curve and the actual slide
displacement curve at a plurality of increments on the slide
upstroke between the contact point and the end point, calculating
the sum of the distances between the theoretical slide displacement
curve and the actual slide displacement curve at each increment,
shifting the actual slide displacement curve, calculating the sum
of the distances between the theoretical slide displacement curve
and the actual slide displacement curve at each increment, and
repeating the shifting and calculating steps until the sum of the
distances between the theoretical slide displacement curve and the
actual slide displacement curve at each increment reaches a minimum
value.
[0013] The invention, in another form thereof, comprises a method
of monitoring performance parameters for a mechanical press. This
method includes the steps of: generating a theoretical no load
slide displacement curve, generating an actual slide displacement
curve during a load condition of the press, determining the contact
point on the actual slide displacement curve which corresponds to
the slide contacting the stock material, establishing a start point
on the slide downstroke between top dead center and the contact
point, establishing an end point on the slide upstroke between top
dead center and the contact point, identifying the points on the
theoretical slide displacement curve corresponding to the start
point and the end point, identifying the points on the actual slide
displacement curve corresponding to the start point and the end
point, superimposing the identified start points on the theoretical
and actual slide displacement curves, and superimposing the
identified end points on the theoretical and actual slide
displacement curves. In this form of the invention, the method of
monitoring performance parameters for a mechanical press further
comprises the steps of: determining a value of dynamic deflection,
determining the value of static stiffness for the press being
monitored, providing a computational device, communicating the
value of dynamic deflection and the value of static stiffness to
the computational device, and calculating load on the press at any
point in time by multiplying the value of dynamic deflection by the
value of static stiffness. The step of determining a value of
dynamic deflection includes measuring the distance along the
ordinate between the theoretical no load slide displacement curve
and the actual slide displacement curve to determine a difference
in displacement between these two curves. After a value of dynamic
deflection is determined, this value of dynamic deflection may be
utilized to calculate load on the press for any time increment of a
slide stroke. The calculated load for individual time increments
may then be plotted vs. time to establish a load curve for an
entire pressing cycle of the press.
[0014] The invention, in another form thereof, comprises a method
of monitoring load on a mechanical press without using a contact
load sensor. This method includes the steps of: determining a value
of dynamic deflection, determining the value of static stiffness
for the press being monitored, providing a computational device,
communicating the value of dynamic deflection and the value of
static stiffness to the computational device, and calculating load
on the press at any point in time by multiplying the value of
dynamic deflection by the value of static stiffness. The step of
determining a value of dynamic deflection can further include the
steps of: generating a theoretical no load value of slide
displacement, generating an actual load value of slide displacement
corresponding to the theoretical no load value of slide
displacement, computing the difference between the theoretical no
load value and the actual load value of slide displacement, and
establishing the difference between the theoretical no load value
and the actual load value of slide displacement as the value of
dynamic deflection.
[0015] The invention, in another form thereof, comprises a method
of monitoring load on a mechanical press without using a contact
load sensor. This method includes the steps of: determining a value
of dynamic deflection, determining the value of static stiffness
for the press being monitored, providing a computational device,
communicating the value of dynamic deflection and the value of
static stiffness to the computational device, and calculating load
on the press at any point in time by multiplying the value of
dynamic deflection by the value of static stiffness. The method of
monitoring load on a mechanical press without using a contact load
sensor in this embodiment of the current invention further
comprises the steps of: determining a plurality of values of
dynamic deflection at increments of the entire slide stroke,
calculating a plurality of load values corresponding to the
plurality of dynamic deflection values, and generating a plot of
load vs. time for a slide stroke of the press.
[0016] The invention, in another form thereof, comprises a speed
sensor for sensing a value of press speed, input means for
inputting a plurality of variables corresponding to characteristics
of the press, storage means for storing an equation which can be
used for generating a theoretical slide displacement curve, a
computational device for generating a theoretical slide
displacement curve, and a non-contact displacement sensor for
sensing slide displacement during an actual load condition of the
press. The equation stored in the storage means utilizes a
plurality of variables corresponding to characteristics of the
press and the value of press speed sensed by the sensor means to
generate a theoretical slide displacement curve. The computational
device is communicatively connected to the sensor means, the input
means and the storage means so that the computational device may
utilize the equation and its variables to generate a theoretical
slide displacement curve. The computational device may further be
utilized to plot sensed slide displacement from the non-contact
displacement sensor vs. a count quantity. The computational device
may further be utilized to match an actual load slide displacement
curve generated by plotting the output of the non-contact
displacement sensor for a slide stroke to the theoretical slide
displacement curve. In an effort to match the theoretical slide
displacement curve and the actual applied load displacement curve,
the computational device can be utilized to determine the contact
point on the actual slide displacement curve which corresponds to
the slide contacting the stock material. The computational device
may further be utilized to establish a start point and an end point
on the slide downstroke between top dead center and the contact
point and the slide upstroke between top dead center and the
contact point, respectively. The computational device may then be
utilized to identify the start point and the end point on both the
theoretical slide displacement curve and on the actual slide
displacement curve and to superimpose the identified start points
and end points so that the theoretical and actual slide
displacement curves can be compared to obtain indicators of press
performance. In this form of the invention, the computational
device may be, for example, a microprocessor. The count quantity
against which the slide displacement is plotted can be, for
example, a measure of time or crank angle.
[0017] The invention, in another form thereof, comprises a speed
sensor for sensing the speed of a mechanical press, a non-contact
displacement sensor for sensing slide displacement during an actual
load condition of the press, input means for inputting a plurality
of variables corresponding to characteristics of the press, and a
computational device for computing a value of load on the press at
any point of the slide stroke. The computational device is
communicatively connected to the speed sensor, the non-contact
displacement sensor and the input means. The computational device
is utilized to compute a theoretical no load value of slide
displacement and to compute a value of dynamic deflection by
computing the difference between the theoretical no load value and
the corresponding actual load value of slide displacement sensed
during an actual load condition of the press. The computational
device then multiplies the thusly determined value of dynamic
deflection by the value of static stiffness for the mechanical
press to determine a value of load on the press at a point of the
slide stroke. The input means may be utilized for inputting
variables including: a value of static stiffness corresponding to
the press being monitored; an equation for generating theoretical
slide displacement values which includes variables corresponding to
press drive mechanism, connecting rod length, stroke length and
bearing size; a value of connecting rod length; a value of stroke
length; a value of drive type; and a value of bearing size.
[0018] An advantage of the present invention is the ability to
accurately match a theoretical no load slide displacement curve for
a mechanical press with an actual applied load slide displacement
curve for a mechanical press. Another advantage of the present
invention is the ability to compute load on a mechanical press
without utilizing a contact load sensor.
[0019] A further advantage of the present invention is the ability
to graph load as a function of time so that it may be utilized to
monitor the operational condition of a mechanical press.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] The above-mentioned and other features and advantages of
this invention, and the manner of attaining them, will become more
apparent and the invention will be better understood by reference
to the following description of an embodiment of the invention
taken in conjunction with the accompanying drawings, wherein:
[0021] FIG. 1 is a schematic representation of an embodiment of the
load computing apparatus;
[0022] FIG. 2 is an elevational view of a typical press which is
the subject of load monitoring;
[0023] FIG. 3 is a graphical representation of load vs. time
measurements for different press applications;
[0024] FIG. 4 is a graphical representation of an actual slide
displacement curve and a theoretical no load slide displacement
curve;
[0025] FIG. 5A is a graphical representation of a theoretical no
load slide displacement curve superimposed with an actual slide
displacement curve and a corresponding force curve representing a
graph of the load experienced during a slide stroke of a mechanical
press; and
[0026] FIG. 5B is a graphical representation of a theoretical no
load slide displacement curve superimposed with an actual slide
displacement curve.
[0027] Corresponding reference characters indicate corresponding
parts throughout the several views. The exemplification set out
herein illustrates one preferred embodiment of the invention, in
one form, and such exemplification is not to be construed as
limiting the scope of the invention in any manner.
DETAILED DESCRIPTION OF THE INVENTION
[0028] Referring now to the drawings and particularly to FIG. 2,
there is depicted a typical press 22 having a bed 20 with a bolster
24. Attached vertically to bed 20 are uprights 26 which support
crown 28. Above crown 28 and attached thereto is press motor 34.
Slide 30 is operatively connected so that during operation, press
motor 34 causes slide 30 to reciprocate in rectilinear fashion
toward and away from bed 20. Tooling 32 is operatively connected to
slide 30. Leg members 50 are formed as an extension of bed 20 and
are generally mounted to shop floor 52 by means of shock absorbing
pads 54. Generally, the present invention utilizes a computational
device to continually compute a theoretical no load slide
displacement curve as well as to continually plot an actual slide
displacement curve. The computational device is further used to
employ a curve matching technique to match these two curves so that
operational parameters of a mechanical press may be determined.
Particularly, this information is utilized to compute a value of
load on the press.
[0029] FIG. 1 illustrates one embodiment of the invention wherein a
computational device 12 receives sensed position values from
non-contact displacement sensor 14. Non-contact displacement sensor
14 can be, for example, a hall effect sensor. Computational device
12 further receives a value of press speed (spm) from speed sensor
16. Storage means 18 stores an equation which includes variables
corresponding to press parameters which effect slide displacement
such as possibly including the speed of the press and variables
associated with the geometry of the press. Storage means 18 is
communicatively connected to computational device 12. Input means
10 are utilized to input press parameters corresponding to the
geometry of the press and may additionally be utilized to input the
equation for determining a theoretical slide displacement curve.
Computational device 12 receives input from input means 10,
non-contact displacement sensor 14, speed sensor 16 and storage
means 18 and utilizes this information to continually generate,
during press operation, a theoretical no load slide displacement
curve and an actual slide displacement curve. These two curves are
superimposed one on the other so that a comparison between the
curves may be made to obtain operational parameters corresponding
to the operating state of the press being monitored. Input means 10
may additionally be utilized to input a value of static stiffness
corresponding to the press being monitored. Computational device 12
may utilize this value in conjunction with a value of dynamic
deflection to compute load at any point of the slide stroke of the
press being monitored.
[0030] During press operation, non-contact displacement sensor 14
continually monitors and communicates slide displacement values to
computational device 12. Similarly, speed sensor 16 continually
monitors and communicates press speed values to computational
device 12. Prior to press monitoring, an equation for theoretically
calculating slide displacement as a function of press speed is
input into storage means 18. Prior to monitoring, input means 10
are utilized to enter press variables corresponding to the geometry
of the press as well as a value of static stiffness (K.sub.static)
which has been empirically determined for the press being
monitored.
[0031] Computational device 12 continually utilizes speed values
derived from speed sensor 16 in conjunction with the equation
contained in storage means 18 and the press variables input through
input means 10 to generate a theoretical no load slide displacement
curve. FIG. 4 depicts such a generated theoretical no load slide
displacement curve.
[0032] Computational device 12 continually receives slide
displacement values from non-contact displacement sensor 14 and
plots an actual slide displacement curve. Such an actual slide
displacement curve is depicted in FIG. 4. Computational device 12
continually computes both a theoretical slide displacement curve
and an actual slide displacement curve during operation of the
press being monitored. Computational device 12 then employs a curve
matching technique to superimpose these two curves in an effort to
obtain operational parameters of the press being monitored.
[0033] To match the actual slide displacement curve and the
theoretical no load slide displacement curve, computational device
12 first identifies start point 56 and end point 58 on both of
these curves. Start point 56 is a point on the downstroke and is
chosen as a point on the slide path between contact point 60 (i.e.
where the slide contacts the stock material) and top dead center.
Similarly, end point 58 is chosen as a point on the slide upstroke
between the contact point and top dead center. To superimpose the
actual slide displacement curve and the theoretical no load slide
displacement curve, computational device 12 matches start points 56
and end points 58. After these two points have been matched,
computational device 12 utilizes a fine tuning method which shifts
the actual slide displacement curve until the sum of the
incremental distances between the actual slide displacement curve
and the theoretical no load slide displacement curve above the
contact point on the upstroke of the slide are minimized. FIG. 5B
illustrates curves matched using this method. In this way, a value
of load on the press may be continually computed during press
operation so that a load vs. time curve may be generated.
[0034] FIG. 3 graphically depicts four load vs. time curves for
different press applications. As depicted in FIG. 3, different
press applications may have the same peak compressive load (L1) and
yet have very different impulse energy values. The value of
utilizing impulse energy as an indicator of press performance is
outlined in pending U.S. Provisional Patent Application Ser. No.,
60/159,818 the disclosure of which is herein explicitly
incorporated by reference. Since impulse energy provides a reliable
indicator of press operating condition, it is advantageous that the
current invention can continually compute values of load during
press operation. FIG. 5A graphically depicts a superimposed actual
slide displacement curve with a theoretical no load slide
displacement curve as well as a force vs. slide position curve
generated by the method and apparatus of the current invention.
Computational device 12 may be communicatively connected to a
visual display device, an alert signal, press shutoff signal or a
digital storage device which will store historical data for the
press being monitored. Computational device 12 may further be
connected to a modem or otherwise to a remote source where press
operational condition may be usefully communicated.
[0035] While this invention has been described as having a
preferred design, the present invention can be further modified
within the spirit and scope of this disclosure. This application is
therefore intended to cover any variations, uses, or adaptations of
the invention using its general principles. Further, this
application is intended to cover such departures from the present
disclosure as come within known or customary practice in the art to
which this invention pertains and which fall within the limits of
the appended claims.
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