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.

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.