U.S. patent number RE30,298 [Application Number 05/863,856] was granted by the patent office on 1980-06-03 for impact sensing detector.
Invention is credited to Michael I. Keller.
United States Patent |
RE30,298 |
Keller |
June 3, 1980 |
Impact sensing detector
Abstract
An impact sensing detector for monitoring the operation of metal
forming impact presses. The detector operates on an analog electric
signal corresponding to the shock wave produced as the press ram
impacts the fixed press platen and workpiece to produce a plurality
of samples of the amplitude of said analog signal. These samples
are digitized and compared against time corresponding standard
samples previously derived from normal press operation. The
detector may also be applied to other working areas of the press
where waveform analysis can detect improper operation in order to
avoid catastrophic failures. Predetermined differences between
compared samples produce warning indicator signals which may be
used to stop the press and also a fault analysis tool to help the
press operator pinpoint the malfunction.
Inventors: |
Keller; Michael I. (Alexandria,
VA) |
Family
ID: |
27050078 |
Appl.
No.: |
05/863,856 |
Filed: |
December 23, 1977 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
Reissue of: |
490503 |
Jul 22, 1974 |
03930248 |
Dec 30, 1975 |
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Current U.S.
Class: |
340/680; 100/99;
340/683; 700/206; 702/182; 702/41 |
Current CPC
Class: |
B30B
15/28 (20130101); G01H 1/00 (20130101); G01P
15/00 (20130101); G01P 15/0891 (20130101) |
Current International
Class: |
B30B
15/28 (20060101); G01P 15/08 (20060101); G01P
15/00 (20060101); G01H 1/00 (20060101); G08B
023/00 () |
Field of
Search: |
;340/501,680,683 ;100/99
;364/475,476 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Trafton; David L.
Attorney, Agent or Firm: Leitner, Palan, Lyman, Martin &
Bernstein
Claims
What is claimed:
1. An apparatus for monitoring the operation of a mechanical press
having relatively movable members including tooling, said members
operating to close upon each other to thereby form a workpiece into
a desired part comprising:
a. means for detecting the shock wave produced as the said members
close upon each other,
b. means for sampling the detected shock wave to produce a
plurality of amplitude samples of said shock wave over time,
c. means for storing each of said samples of the detected shock
wave,
d. means for producing standard samples representing samples of a
shock wave produced when the press is operating normally,
e. means for storing said standard samples,
f. a first arithmetic means for electrically and successively
comparing time-corresponding samples of the detected shock wave and
standard samples to produce signals representing the difference in
amplitude between each set of compared samples,
g. means for storing a plurality of electrical representations of
standard difference signals representing the permissible difference
between each set of compared samples,
h. means for electrically and successively comparing each
difference signal with its corresponding standard difference
signal, and
i. means for producing a warning indicator signal when the value of
at least one of said difference signals is greater than or less
than its corresponding standard difference signal by a
predetermined amount.
2. The apparatus of claim 1 wherein said means for detecting
comprises transducer means for converting said shock wave into a
electric analog,
said means for sampling the detected shock wave and said means for
producing standard samples each includes means for digitizing each
sample and said means for storing samples of the detected shock
wave and standard samples comprises first and second digital memory
means respectively.
3. The apparatus of claim 2 further including:
first gate means, responsive to the output from said digitizing
means, and having an output connected to the input of said first
memory means for applying digitized samples of the press produced
shock wave to said first memory means when enabled,
second gate means, responsive to the output from said digitizing
means, and having an output connected to second memory means for
applying said digitized standard samples to said second memory
means when enabled, and
switch means for selectively enabling either said first gate means
or said second gate means, whereby digitized samples of the press
produced shock wave may be stored in said second memory means when
the press is operating normally to thereby develop the standard
samples against which other shock wave representative samples may
be compared.
4. The apparatus of claim 2 wherein said means for storing said
standard difference signals and said means for comparing each
difference signal with its corresponding standard difference signal
comprises respectively:
a plurality of storage means each storing a standard difference
signal, and a plurality of comparator means, each associated with a
different storage means, for comparing a standard difference signal
with a selected one of said difference signals from said first
arithmetic means to produce a warning indicator signal when said
difference signal is greater than the standard difference with
which it is compared, and
a plurality of AND circuit means selectively enabled to apply each
of said difference signals to a different one of said comparator
means.
5. The apparatus of claim 4 wherein said AND circuit means includes
delay means, responsive to a clock signal for successively applying
said clock signal to different ones of said AND circuit means
whereby only certain of said AND circuit means is enabled in
coincidence with the generation of each of said difference
signals.
6. The apparatus of claim 5 further including a plurality of
indicator means each associated with a different one of said
comparator means for providing human sense recognizable signals
when its corresponding comparator means produces a warning
indicator signal.
7. The apparatus of claim 2 wherein said means for comparing said
difference signals with predetermined difference standard signals
comprises:
a plurality of storage means each storing a difference standard
signal,
a second arithmetic means responsive to said difference signals
from said first arithmetic means and said difference standard
signals for producing a warning indicator signal when the received
difference signal is greater than the received difference standard
signal, and
means for applying a predetermined one of said difference standard
signals to said second arithmetic means in coincidence with each of
said difference signals.
8. The apparatus of claim 7 wherein said means for applying
predetermined difference standard signals to said second arithmetic
means comprises, delay means responsive to a clock signal, for
successively reading out predetermined difference standard signals
from said storage means in time coincidence with the entry of said
difference signals into said second arithmetic means.
9. The apparatus of claim 8 further including a plurality of
indicator means for producing a human sense recognizable signal in
response to warning indicator signals, a plurality of AND circuits
each associated with a different one of said indicator means, and
means coupling each of said AND circuits to said delay means to
enable a different one of said AND circuits in response to the
reading out of each of said difference standard signals.
10. A method of analyzing the shock waves produced by an impact
press to develop warning indicator signals of press and/or its
tooling malfunctions, comprising the steps of:
a. detecting each shock wave produced and converting said each
shock wave into an electric analog signal,
b. sampling said electric analog signal to produce a time phased
series of amplitude samples,
c. producing a standard electric analog signal which corresponds to
the press produced shock wave when operating normally,
d. sampling said standard signal to produce a time based series of
amplitude samples of said standard signal,
e. comparing each amplitude sample of said detected analog signal
with its time corresponding standard sample to produce a series of
difference signals,
f. determining, experimentally, a plurality of difference standard
signals each corresponding to the maximum allowable value of a
different one of said plurality of difference signals,
g. comparing said difference standard signals with their
corresponding difference signals, and
h. generating a warning indicator signal each time a difference
signal is greater than its corresponding difference standard
signal.
11. The method of claim 10 further including the steps of:
providing a plurality of indicator devices capable of producing
human sense recognizable signals, each of said indicator devices
being responsive to a different one of said warning indicator
signals. .Iadd. 12. Apparatus for monitoring the operation of a
press having relatively moveable members, said members operating to
close upon each other to thereby form a workpiece comprising:
a. transducer means for generating an electrical signal in response
to a mechanical shock wave developed as the relatively moveable
members close upon each other
b. filter means, responsive to said transducer generated electrical
signal for eliminating selected frequencies from said electrical
signal
c. means for producing a monitored shock wave function derived from
said filtered transducer generated electrical signal
d. means for producing a standard function representative of said
monitored shock wave function as it would appear when the press is
operating normally
e. means for comparing said monitored shock wave function and said
standard function, and
f. means for producing a warning indicator signal in response to
predetermined differences between said monitored shock wave
function and said standard function. .Iaddend..Iadd. 13. Apparatus
as claimed in claim 12 wherein said filter means comprises a low
pass filter. .Iaddend. .Iadd. 14. Apparatus as claimed in claim 12
wherein said filter means includes a band limiting filter.
.Iaddend..Iadd. 15. Apparatus for monitoring the operation of a
press having relatively moveable members, said members operating to
close upon each other to thereby form a workpiece comprising:
a. transducer means for generating an electrical signal in response
to a mechanical shock wave developed as the relatively moveable
members close upon each other
b. filter means responsive to said transducer generated electrical
signal for eliminating selected frequencies from said electrical
signal
c. means for producing a monitored shock wave function derived from
said filtered transducer generated electrical signal, said
monitored shock wave function being a function of the amplitude of
said transducer generated electrical signal and the time during
which the said transducer generated electrical signal persists
d. means for producing a standard function representative of said
monitored shock wave function as it would appear when the press is
operating normally
e. means for comparing said monitored shock wave function and said
standard function, and
f. means for producing a warning indicator signal in response to
predetermined differences between said monitored shock wave
function and said standard function. .Iaddend. .Iadd. 16. Apparatus
as claimed in claim 15 wherein said filter means comprises a low
pass filter. .Iaddend..Iadd. 17. Apparatus as claimed in claim 15
wherein said filter means includes a band limiting filter.
.Iaddend.
Description
BACKGROUND OF THE INVENTION
1. Field of Invention
The invention is in the field of impact sensing detectors for use
in metal forming impact presses and more particularly detectors
which detect irregular operation of the press tooling with respect
to a workpiece.
2. Description of the Prior Art
Metal forming impact presses are used to operate on strips of
metal, termed herein the workpiece, so as to form the workpiece
into desired parts such as contacts for electrical connectors. The
tooling with which these presses are equipped provide the means for
cutting, bending, forming, etc. the basic workpiece into the
desired part, be it a contact or any other of an almost infinite
number of different parts.
Press operation is constantly, semi-automatically monitored to
detect and react to sensed malfunctions. Presses must be observed
to assure that the parts produced conform to standards and also to
assure that minor malfunctions do not go undetected leading to
catastrophic machine or tooling failure. Such catastrophic failures
are extremely costly in that machine or tooling repair or
replacement is expensive. Further, machine downtime reduces the
manufacturer's output.
For these reasons, workers in the art have expended much time and
effort in attempts to develop reliable automatic devices to detect
machine malfunctions and particularly with respect to devices which
will produce early indicators of improper operation leading to
serious malfunctions. Such indicators permit the machine operator
to take corrective action before the severe malfunction actually
occurs, thus preventing expensive repairs and long machine
downtime.
An example of an impact press malfunction detector is described in
U.S. Pat. No. 3,444,390 to Breidenbach et al. issued May 13, 1969.
Breidenback et al. teach the basic concept that irregular operation
of the tooling on a workpiece in a press can be detected by
detecting the peak amplitude of the shock developed as the press
dies contact the workpiece. The detecting mechanism comprises a
suitable transducer such as a piezoelectric transducer which
converts shock induced vibrations, that is the shock wave, into an
electrical output correlatable to the shock.
Breidenback et al. recognized that, in the prior art, the shock
analysis technique is limited to comparatively simple shock waves
due to the confusion of signals which results when the nature of
the shock forces become complex. They indicate that signal
confusion is a particular problem in presses in which press tooling
is caused to perform multiple functions, such as cutting and
drawing all in one stroke. The solution set forth therein is to
threshold compare a peak shock amplitude as represented by the peak
voltage amplitude produced by the piezoelectric transducer to an
adjustable sensitivity level of a latching amplifier after the
piezoelectric resonant frequency has been filtered out.
While such an approach may work well to detect catastrophic press
failures, it fails to give indications of minor malfunctions which
may lead to more severe trouble. The present invention is an
improvement over the Breidenbach et al. press impact sensor and
operates to develop several warning indicator signals unrelated to
peak voltages which may be used to automatically stop the press and
give the press operator an analysis tool whereby he may pinpoint
the malfunction.
SUMMARY OF THE INVENTION
The invention provides an improved impact sensing detector for use
with metal forming impact presses. The impact sensing detector of
the present invention receives the transducer produced analog
electric signal which correlates to the press produced complex
shock wave and converts it into a time based series of digitized
amplitude samples. Each sample is then compared to a time
corresponding standard amplitude sample previously developed by
monitoring a shock wave produced during normal manufacturing press
operation. It has been determined that different press malfunctions
cause different waveform variations detectable by comparing a
multiplicity of amplitude samples of each shock wave with its time
corresponding standard samples. The difference between compared
samples are indicators of malfunction and when at least one of said
indicators exceeds a predetermined programmed difference it becomes
a warning indicator signal which may be used to stop the press. The
warning indicator signal may also be applied to an operator
monitored control panel which includes indicators to inform the
operator of the probable location of the malfunction. Through
experimentation with a press performing specific tooling
operations, predetermined differences between corresponding samples
of the amplitude of the shock wave and the standard will signify
the probable location of malfunctioning portions of the press being
studied or its tooling.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 represents a conventional press in combination with the
impact sensing detector with this invention;
FIG. 2 is a block diagram of one embodiment of the impact sensing
detector of the invention;
FIGS. 3a through 3c represent hypothetical waveforms useful in
explaining the operating of the impact sensing detector;
FIG. 4 is a block diagram of one embodiment of the difference
program circuitry of the impact sensing detector; and
FIG. 5 is a block diagram of a second embodiment of the difference
program circuitry of the impact sensing detector.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring now to the drawings, FIG. 1 depicts a conventional press
assembly 1 having a fixed platen 2 fitted with a die 4 and a ram
assembly 3 fitted with die 6. The ram assembly 3 is connected to an
electrically controlled clutch/brake assembly 8 driven by motor
10.
In operation, a workpiece (not shown) to be formed into parts, is
fed between the dies 4, 6 with ram 3 in its raised position. The
ram is then caused to move downwards at high velocity impacting the
workpiece resting on die 4 to complete the desired operation. Dies
4, 6 may take any of very many different shapes. In multiple
function tooling, dies 4, 6 have several different cooperating
areas to accomplish several operations. For example, the dies may
include cooperating areas which independently perform a cutting
operation, a bending operation and a crimping operation during each
press cycle. In such a press, a portion of a continuous workpiece
would initially be placed under the cutting area of dies 4, 6 with
the first press stroke cutting this portion into an outline of the
desired part. Thereafter, as the workpiece is fed further through
the press 1, a second portion of the workpiece is positioned in the
cutting area of the dies while retaining the previously, partially
cut portion in the bending area. Thus, upon a second press stroke,
as the die 6 on ram 3 strikes the workpiece resting over die 4, the
previously cut portion of the workpiece is bent to shape, while the
second portion is cut into the outline of a desired part. The
process is continuous, with each press stroke operating to cause
several different operations, although during each stroke a
particular portion of the workpiece is experiencing only one
operation. To those working in the art this is known as progressive
die stamping.
It should thus become apparent to those skilled in the art that
each time the die 6 on ram 3 impacts the workpiece, a shock wave is
produced and that the nature of the shock is complex. The shock may
be detected and converted into an electric analog signal by means
of a transducer 12, such as a piezoelectric transducer, suitably
mounted on press 1. An example of a suitable transducer mounting
arrangement is described in the aforementioned Breidenbach et al.
patent. This does not preclude the application of a multiplicity of
transducers in a single press.
This electric analog signal is applied to the impact sensing
detector 14 of the present invention. As will be more fully
explained with reference to FIG. 2, when a malfunction occurs, a
warning indicator signal is generated on an output line 18 to stop
the press and provide a signal to control panel 16. When a
multiplicity of transducers are used, an equal number of detectors
would be employed, one being associated with each transducer.
FIG. 2 illustrates the details of one embodiment of the detector 14
of the present invention. The output of transducer 12 is applied to
low pass filter circuitry 22 which functions to substantially
eliminate the high frequency portion of the signal generated by
transducer 12, this high frequency component being attributable to
the resonant frequency characteristic of the transducer element
itself. Thus, the output of circuitry 22 represents the complex low
frequency amplitude variation produced by the operation of the
press, tooling, and workpiece.
The filtered analog signal is amplified in amplifier 24 and
thereafter applied to a time gated analog sampler 26 wherein the
shock induced electric analog signal is converted into periodic,
very narrow amplitude samples which are applied to the
analog-digital converter 28. Converter 28 operates to convert each
amplitude sample into a digital word. Each word is applied to
register 30 and from there it is transferred to either memory 36 or
38 depending upon whether AND gate 32 or 34 enabled through the
operation of switch 40 connected to source 42. The aforementioned
sequence is initiated by triggering a system clock 100 on the basis
of an exceeded threshold (leading edge of the waveform).
Memories 36 and 38 may be identical. Memory 36, termed herein the
store for samples of the standard waveform, stores the digital
samples derived from the shock wave developed during a single
impact of a normal press operation. Memory 38, which is termed the
store for samples of the monitored shock wave, stores the digital
samples derived from the monitored shock wave which occurs while
the press is being monitored for warning indicators of press and/or
tooling malfunction. At any one time, memory 38 stores samples
derived from a single shock wave. After these samples are compared
with time corresponding standard samples, they are dumped to make
room for samples derived from the next shock wave produced upon the
next ram stroke.
The comparisons of corresponding samples is carried out in
arithmetic unit 44, which in the preferred embodiment is selected
to produce a digital word representing the absolute value of the
arithmetic difference between the amplitude of the sample stored in
memory 38 and the amplitude of its corresponding sample in memory
36. Of course, arithmetic unit 44 may be selected to develop the
actual arithmetic difference between corresponding samples.
Through experimentation with the monitored press, one learns that
predetermined differences between certain samples provide
indications of different malfunctions. These predetermined
differences are used to cause the generation of warning indicator
signals on line 18 through the operation of the difference programs
circuitry 46, explained in detail with reference to FIG. 4. The
warning indicator signals on line 18 trigger latching amplifier 50
to energize relay coil K.sub.1 with cooperating normally closed
switch K.sub.1A. When coil K.sub.1 is energized, switch K.sub.1A
opens to de-energize the press via the electrically controlled
clutch/brake assembly 8.
The operation of the impact sensing detector 14 will now be
explained in greater detail. It should be noted at this point that
the detector can be applied in multiplicity on a given press to
function in a similar manner on band liited portions of a shock
waveform. It should be further noted at this point that each
element of the detector 14 is conventional and does not, by itself,
form a portion of this invention.
With the press operating normally, switch 40 is placed in position
A to enable AND gate 32. The press produced shock wave is detected
by transducer 12 to develop on electric analog signal
representative of the normal manufacturing operation shock wave.
FIG. 3a is a hypothetical representation of the waveform which
would appear at the input of sampler 26 when the press is operating
normally. The output of the sampler 26, a series of short duration
pulses of individually varying amplitude corresponding to the
analog input, as illustrated in FIG. 3b, is applied to the
analog-digital converter 28 wherein each sample is converted into a
digital word and successively applied to word locations 36.sub.1
through 36.sub.1 of memory 36 through gate 32. It should be
understood by those skilled in the art that gate 32 represents
several gates, one associated with each stage of register 30.
The first digitized sample t.sub.1 is initially stored in word
location 36.sub.n. As the second digitized sample t.sub.2 is
entered into memory 36, the sample t.sub.1 stored in location
36.sub.n is shifted into word location 36.sub.n-1 to make room for
the second digitized sample t.sub.2 which is now stored in location
36.sub.n. This process continues until all digitized samples of the
standard waveform are stored in memory 36 with the first sample
t.sub.1 so stored being located in word location 36.sub.1.
With samples of the standard wave form digitized and stored in
memory 36, the detector 14 is now ready to monitor the shock waves
produced by the press 1 during its manufacturing operation. To
accomplish this, the operator causes switch 40 to assume position B
thereby disabling gate 32 while enabling gate 34. As with gate 32,
gate 34 represents a plurality of gates, one associated with each
stage of register 30.
The manufacturing operation shock wave sensed by transducer 12 are
converted into digitized samples in the manner previously described
with respect to the formation of the digitized samples of standard
waveform. However, during the manufacturing operation monitoring
phase, the digitized samples of the shock wave are stored in memory
38. The operation of memory 38 corresponds to the operation of
memory 36. With reference to FIG. 3c, which illustrates the samples
of the transducer produced signal during press or tooling
malfunction, the first sample, t.sub.1 ' of the monitored shock
wave is stored in word location 38.sub.1 while the last sample
t.sub.n ' is stored in word location 38.sub.n. It should thus
become apparent to those skilled in the art that corresponding word
location in memories 36 and 38 store time corresponding samples of
the standard and the electric analog signal representing the
monitored shock wave. Thus, time corresponding samples t.sub.1 and
t.sub.1 ' are stored in corresponding word locations 36.sub.1 and
38.sub.1.
Time corresponding samples are now successively gated into the
arithmetic unit 44 which generates, in this preferred embodiment, a
digital word corresponding to the absolute value of the arithmetic
difference between the standard sample and the sample of the
monitored shock wave as represented by the electric analog signal.
Each difference output is applied to the difference program
circuitry 46 where it is compared with a programmed difference
standard. As previously noted, these difference standards are
determined by experimentation and electronically retained.
An example of the difference standards program circuitry 46 is
illustrated in FIG. 4. The circuitry includes AND gates 60.sub.1
through 60.sub.n, each of which receives the digitized difference
output from arithmetic unit 44. Each of these gates represents a
plurality of gates, each receiving one bit of the digitized
difference output. The outputs from gates 60.sub.1 through 60.sub.n
are applied as one input to respective comparators 62.sub.1 through
62.sub.n. A second input to each of these comparators is a digital
word corresponding to a difference standard stored in respective
registers 64.sub.1 through 64.sub.n. The outputs from the
comparators are applied, via the OR gate 21, to line 18 to trigger
latching amplifier 50 when a warning indicator signal is detected
by any one or more of the comparators.
In operation, the samples stored in word locations 36.sub.1 and
38.sub.1 are compared in arithmetic unit 44 and the difference
between these samples applied to comparator 62.sub.1 through gate
60.sub.1. At this point in time, gates 60.sub.2 through 60.sub.n
are disabled by the operation of delay unit 70. The delay unit 70
operates to successively enable gates 60.sub.1 through 60.sub.n so
that comparators 62.sub.1 through 62.sub.n receive only the
difference output corresponding to the difference between the
signals stored in word locations 36.sub.1, 38.sub.1 through
36.sub.n, 38.sub.n respectively.
The delay 70 operates in the following manner. After a transducer
produced electric analog signal has been sampled, digitized, stored
in memory 38 and compared with the standard stored in memory 36, a
clock pulse is applied to AND gate 72 which has been enabled by the
output of the single shot 76. The single shot 76 is triggered by
the signals on line 63, said signals corresponding to the
difference outputs produced upon a comparison of the samples stored
in word location 36.sub.n with the sample stored in word location
38.sub.n. Thus, the clock pulse enters delay unit 70 and appears on
line d.sub.1 in time coincidence with the difference output from
arithmetic unit 44 produced by comparing the sample t.sub.1 of the
standard with the sample t.sub.1 ' of the monitored shock wave. As
sample t.sub.2 ' of the standard is compared with sample t.sub.2 '
of the monitored shock, the clock pulse appears on line d.sub.2 to
enable gate 60.sub.2, thereby permitting the difference output to
enter comparator 62.sub.2. Any additional clock pulses appearing at
the input of gate 72 are prevented from entering delay unit 70
since when these clock pulses are generated, the single shot pulse
has decayed and gate 72 is disabled. Thus, comparator 62.sub.1
receives only the difference signal corresponding to the difference
between sample t.sub.1 and sample t.sub.1 ', while comparator
62.sub.2 ' receives only the difference signal corresponding to the
difference between sample t.sub.2 and sample t.sub.2 ' and so
on.
As previously explained, the second input to each comparator is a
difference standard stored in a corresponding register 64.sub.1
through 64.sub.n. Whenever the arithmetic difference from the
arithmetic unit is equal to or greater than the difference
standard, a warning indicator signal is generated at the comparator
output. The result of each comparison may also be coupled to a
respective warning lamp 17, or other suitable indicator such as a
buzzer, on control panel 16. Each lamp 17 may be labeled with a
description 19 of the probable location of the malfunction which
caused the lamp to be energized. The warning indicator signal is
applied to the latching amplifier 50 via the OR gate 21 and line 18
and simultaneously to one of the lamps 17 of the control panel 16
as described.
For purposes of illustration, it will be assumed that an
investigation of the operation of a particular tooling, workpiece,
and press using the detector system of the present invention has
led to an independent determination that when sample t.sub.2 is
greater than sample t.sub.2 ' by at least voltage V.sub.1, the
velocity of the ram on contact with the workpiece was below that
required to make an acceptable part. Thus, register 64.sub.2 would
be programmed to store the value V.sub.1 and when a warning
indicator signal is generated by comparator 62.sub.2, a lamp 17
labeled "ram velocity" would light, informing the operator that
there was a probable malfunction relating to the ram velocity. This
would be particularly useful in blanking and cupping presses in
which the two operations take place in rapid succession on a single
stroke.
The above described detector system has many advantages over prior
art impact sensing detectors. The detector of the present invention
has the ability to detect and analyze an entire shock wave, rather
than only its peak, and permits monitoring of a sequence of
operations that can be taking place in the press. The apparatus of
this invention which monitors the difference between time
corresponding samples of a standard and a monitored shock wave
permits programming to detect any level of difference that is a
meaningful factor in a successful operation for longevity of the
tooling and press. Costly repairs and downtime may be averted by
proper operation of the difference program to thereby detect
deviations that are symptomatic of an ultimate catastrophic machine
or tooling failure.
A second embodiment of the difference program circuitry 46 is
illustrated in FIG. 5. As compared to the FIG. 4 embodiment, the
difference program circuitry of FIG. 5 uses fewer elements. More
specifically, the several AND circuits 60.sub.1 through 60.sub.n,
the several comparators 62.sub.1 through 62.sub.n and OR gate 21
are replaced by a single arithmetic unit 80 and AND gates 82.sub.1
through 82.sub.n. Since each of the circuits 60.sub.1 through
60.sub.n represents several AND circuits, the embodiment of FIG. 5
not only eliminates the several comparators but also reduces the
number of AND circuits required.
The circuitry of FIG. 5 operates in the following manner. The
output from the arithmetic unit 44 represents the absolute value of
the difference between a monitored sample and its time
corresponding standard sample. In the FIG. 5 embodiment, this
output is denoted as D. The D output is applied to one input of a
second arithmetic unit 80. A second input to the arithmetic unit 80
is the difference standard, denoted in FIG. 5 as S and stored in
the memory 86. Memory 86 replaces the several difference standard
registers 64.sub.1 through 64.sub.n used in the FIG. 4 embodiment.
Each of the word locations 86.sub.1 through 86.sub.n of the memory
86 stores a different difference standard S.
As arithmetic unit 44 sequentially compares the samples stored in
memories 36 and 38, delay 84 clocks out corresponding difference
standards. This delay may be identical to delay 70. Thus, as the
samples stored in word locations 36.sub.1 and 38.sub.1 are compared
in the arithmetic unit 44, and the results D applied to arithmetic
unit 80, line d.sub.1 of the delay 84 generates a clocking signal
causing the difference standard stored in word location 86.sub.1 to
enter the arithmetic unit 80. Arithmetic unit 80 operates to
provide an output in the form of a logic high whenever the
difference signal D from arithmetic unit 44 is equal to greater
than the difference standard S with which it has been compared. A
logic high at the output of the arithmetic unit 80 causes latching
amplifier 50 to activate relay coil K.sub.1 whereby the press is
stopped.
The AND gates 82.sub.1 through 82.sub.n are provided to key the
lamps 17 on the control panel 16 to specific comparisons. That is,
when line d.sub.1 is at a logic high, only gate 82.sub.1 is enabled
and thus if a warning indicator signal is realized as a result of
the comparison of the monitored sample stored in word location
38.sub.1 with the standard sample in word location 36.sub.1, only
the lamp associated with the label "bending" lights. As the
monitored samples in word locations 38.sub.2 etc., are sequentially
compared with their corresponding standard samples stores in word
locations 36.sub.2 etc., gates 82.sub.2 through 82.sub.n are
sequentially enabled while the difference standards stored in
locations 86.sub.2 through 86.sub.n are sequentially applied to the
arithmetic unit 80.
The above described detector system as relates to tooling and
workpiece can be applied as a fault detector in other workpiece
working areas of a press. For example, the workpiece is generally
mechanically advanced by cooperating, powder driven, geared pinch
rollers which must reliably advance the workpiece prior to the
impact of the ram. Failure to properly advance the workpiece can
result in catastrophic failure of tooling and/or machine. Various
techniques have been attempted to monitor the completion of the
feeding portion of the machine cycle, but it has not been possible
to detect slippage of the pinch rollers during any portion of the
feed cycle. Such detection can be performed by the detector
disclosed herein by detecting and processing the waveform generated
by the power driven feed mechanism and workpiece being transferred,
thereby sensing a misfeed before the tooling and workpiece are
impacted.
* * * * *