Abstract:
An apparatus and method for monitoring the force severity and impulse energy of a mechanical press for the purpose of accurately predicting operating reliability of a press during its production operation. The method includes continuous or intermittent, automatic or manual monitoring the load during production operation of the press. Apparatus is used to monitor the load which is then communicated to a computational device which computes the impulse energy for one slide stroke of the mechanical press.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application relates to and claims the benefit under 35 U.S.C. §119 of Provisional Application Ser. No. 60/159,818 filed Oct. 15, 1999 by the same inventor. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to press force severity monitoring and, more particularly to utilizing monitored force severity to determine impulse energy for the purpose of determining the effects of any press/die application on the long-term operating reliability of a press during production operation. 
     2. Description of the Related Art 
     Mechanical presses of the type performing stamping and drawing operations employ a conventional construction that includes a frame structure having a crown and a bed portion 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. 
     The press machine applies force to a workpiece so that the stock material acquires the desired formation which corresponds to the die set being utilized. Systems for monitoring press operating reliability assist the press owner in evaluating the severity of certain die/load applications on the reliability of the press being monitored. Conventional monitoring systems include systems which monitor the peak load being developed within certain components of the press machine during a slide stroke of the press. These monitored peak load levels are then compared with historical peak load level measurements or reference peak load levels. 
     Known load monitoring systems include systems which indicate the loads on presses and automatically detect if the load incurred by the force carrying member exceeds a predetermined value or is below a predetermined value. 
     Monitoring the maximum loads 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 the identified range. However, monitoring peak load is not an accurate operating reliability indicator since peak load does not account for multiple load peaks, peak loads which occur more than once during a press cycle, both compressive and tensile loads, multiple compressive or tensile peaks, or impulse energy. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to improve upon the aforementioned method and means of monitoring the operating reliability of a mechanical press, wherein it is desired to monitor the operating reliability of a mechanical press in such a way so as to account for both compressive and tensile loads, multiple peak compressive and tensile loads, and impulse energy. 
     The present invention provides a method and apparatus for monitoring the long-term operating reliability of a mechanical press during its production operation which measures load over time and utilizes impulse energy as a measure of the operating condition of the mechanical press. 
     The invention, in one form thereof, comprises a load sensor which senses compressive and tensile loads and is affixed to a load bearing member of a mechanical press, and a computational device for receiving the load value from the load sensor and computing a measure of the impulse energy for one slide stroke of the running press. The computational device can be, for example, a microprocessor. 
     The invention, in another form thereof, includes a load sensor which senses compressive and tensile loads and is affixed to a load bearing member of the running press, and a computational device for receiving the load value from the load sensor and computing a measure of the impulse energy created by both compressive and tensile forces experienced during one slide stroke of the running press. 
     The invention, in another form thereof, includes a load sensor which senses compressive and tensile loads and is affixed to a load bearing member of a running press, and a computational device for receiving the load value from the load sensor and computing a reference impulse energy value for one slide stroke of the mechanical press. The reference impulse energy value can be, for example, a reference value which corresponds to a slow speed operation of the running press, a reference value which corresponds to a normal production operation of the mechanical press, or a reference value which corresponds to a particular die set which is used with the mechanical press. 
     The invention, in another form thereof, comprises a load sensor which senses compressive and tensile loads and is affixed to a load bearing member of a running press, and a computational device for receiving the load value from the load sensor and storing a reference impulse energy value. The computational device computes the total impulse energy for one slide stroke of the running press, which includes the impulse energy created by both compressive and tensile forces. The computational device also computes a ratio of the total impulse energy for one slide stroke to the reference impulse energy value. 
     The invention, in another form thereof, comprises a load sensor for sensing compressive and tensile loads which is affixed to a load bearing member of the running press and a computational device which computes values of impulse energy for one slide stroke of the mechanical press. The computed value of impulse energy can be, for example, a measure of the impulse energy corresponding to the compressive load sensed by the load sensor, a measure of the impulse energy corresponding to the tensile load sensed by the load sensor, or a total measure of the impulse energy which includes both the impulse energy associated with the compressive load and the tensile load sensed by the load sensor. 
     The invention, in another form thereof, comprises a load sensor for sensing compressive and tensile loads which is affixed to a load bearing member of a running press and a computational device for computing impulse energy values for one slide stroke of the running press. The impulse energy values computed by the computational device may be, for example, the impulse energy corresponding to the compressive load sensed by the load sensor, the impulse energy corresponding to the tensile load sensed by the load sensor, or the total impulse energy corresponding to both the compressive load and tensile load sensed by the load sensor for one slide stroke. In this form, the computational device may also be utilized for computing reference impulse energy values, including reference impulse energy values corresponding to normal production operation, slow speed operation, or a particular die set used with the running press. The computational device may further be used to compute a ratio of monitored impulse energy to a reference impulse energy value. The values computed in the computational device may be communicated to, for example, a digital storage device, a modem, a display device, an alert device or a shutoff device. The digital storage may be utilized for compiling histories of impulse energy values and their corresponding ratios to a reference impulse energy value. A modem may be used for communicating impulse energy values and/or their relation to a reference impulse energy value to a remote location. The display device may display monitored impulse energy and/or the ratio of the monitored impulse energy to a reference value so that service personnel may determine how features such as press speed, shut height and the die setup alter the operational condition of the running press. The alert device and the shutoff device will produce an alert signal and discontinue press operation, respectively, if the impulse energy value and/or the ratio of impulse energy value to a reference impulse energy value exceeds a predetermined measure. 
     The invention, in another form thereof, comprises a method of monitoring the reliability condition of a running press by monitoring the impulse energy of the running press and comparing the monitored impulse energy of the running press to a reference impulse energy value. 
     The invention, in another form thereof, comprises a method of monitoring the impulse energy of a running press. This method includes the steps of: placing a load sensor on a load bearing member of the running press, providing a computational device, communicating the load sensed by the load sensor to the computational device, plotting the sensed load value versus time and computing a value of impulse energy for one slide stroke of the running press using the sensed load value versus time curve. 
     The invention, in another form thereof, comprises a method of monitoring the reliability condition of a running press. This method includes the steps of: placing a load sensor on a load bearing member of the running press, providing a computational device, communicating the load sensed by the load sensor to the computational device, computing the absolute value of the sensed load values, plotting the absolute values of the sensed load values versus time and computing the area under the sensed load value versus time curve. 
     The invention, in another form thereof, comprises a method of monitoring the reliability condition of a running press. This method includes the steps of: monitoring the impulse energy of the running press. In this form, the step of monitoring the impulse energy of the running press includes: placing a load sensor on a load bearing member of the running press, providing a computational device, communicating the load sensed by the load sensor to the computational device, plotting sensed load values versus time, and computing a value of impulse energy for one slide stroke of the running press using the sensed load value versus time curve. In this form, the step of computing the value of impulse energy for one slide stroke of the running press comprises, for example, computing a value of tensile impulse energy, computing a value of compressive impulse energy or computing a total value of impulse energy for one slide stroke of the running press. The step of computing a value of tensile impulse energy includes: plotting the sensed tensile load versus time and computing the area under the sensed tensile load versus time curve. In this form, the step of computing a value of compressive impulse energy comprises: computing the absolute value of the sensed compressive load values, plotting the absolute values of the sensed compressive load values versus time, and computing the area under the sensed compressive load value versus time curve. The step of computing a total value of impulse energy for one slide stroke of the running press includes: computing the absolute value of the sensed load values, plotting the absolute values of the sensed load values versus time and computing the area under the sensed load value versus time curve. 
     The invention, in another form thereof, comprises a method of monitoring the reliability condition of a running press. This method includes the steps of: monitoring the impulse energy of the running press, determining a reference impulse energy value and computing a ratio of the monitored impulse energy for one slide stroke of the running press to the reference impulse energy for one slide stroke of the running press. The step of determining a reference impulse energy value includes: establishing a reference impulse energy value which corresponds, for example, to a slow speed operation of the running press, to a normal production operation of the running press, or to a particular die set used with the running press. 
     An advantage of the present invention is that monitoring of impulse energy provides a reliable indicator of mechanical press operating reliability. 
     Another advantage of the present invention is that multiple peaks in loads which occur during a pressing operation may be accounted for in determining the operating reliability of a mechanical press. 
     Another advantage of the present invention is that both compressive and tensile loads can be accounted for in determining the operating reliability of a mechanical press. 
     Another advantage of the present invention is that additional force severity activity which is due to multiple load peaks of either compressive or tensile loads can be accounted for in determining the operating reliability of a mechanical press. 
     A further advantage of the present invention is that impulse energy can be used to create a relative application severity reference signal which does not relate to actual peak load level. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     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: 
     FIG. 1 is a schematic representation of an embodiment of the impulse energy monitoring apparatus; 
     FIG. 2 is an elevational of a typical press which is the subject of impulse energy monitoring; and 
     FIG. 3 is a graphical representation of load versus time measurements for different press applications. 
     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 
     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 the bed  20  are uprights  26  which support a crown  28 . Above crown  28  and attached thereto is a press motor  34 . A slide  30  is operatively connected so that during operation press motor  34  causes slide  30  to reciprocate in rectilinear fashion toward and away from the 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 the shop floor  52  by means of shock absorbing pads  54 . 
     FIG. 1 illustrates one embodiment of the invention wherein a computational device  12  receives sensed load values from load sensors  10 . Computational device  12  is communicatively connected to digital storage device  14 , modem  16 , display  18 , press alert signal  40  and press shutoff signal  42 . Modem  16  may be connected to global computer networks, such as the internet, or another device may be substituted for modem  16 , such as a NIC for direct connection to a computer network. Alternatively, other local or wide area network connection devices may be utilized. Data storage such as envisioned in data storage device  14  may be conducted either locally or remotely. 
     During press operation, load sensors  10  continually monitor and communicate load values to computational device  12 . Computational device  12  receives load values from load sensors  10  and plots monitored load values versus time. FIG. 3 graphically depicts four load versus time curves for different press applications. As depicted in FIG. 3, different press applications may have the same peak compressive load (L 1 ) and yet have very different impulse energy values. FIG. 3 a  depicts a press application in which the peak compressive load (L 1 ) is experienced three times during a slide stroke L 1 , L 1 ′, L 1 ″. The press application depicted by FIG. 3 a  also displays significant, but not identical, tensile loads which are measured during a press slide stroke. FIGS. 3 a - 3   d  depict press applications which have very different impulse energy values and yet have the same peak load value (L 1 ). Computational device  12  computes the area under the load versus time curve to determine the impulse energy for one slide stroke of the running press. Computational device  12  also computes and stores a reference impulse energy value. Computational device  12  transmits impulse energy information to digital storage device  14 , modem  16 , and/or display  18 . 
     In one preferred embodiment, computational device  12  computes a reference impulse energy value which corresponds to a normal production operation of the running press. Computational device  12  then continually computes a ratio of measured impulse energy for one slide stroke of a mechanical press to the reference impulse energy which corresponds to a normal production operation of the running press. Device  12  could also compute a ratio to a set of force severity levels developed via correlation to empirical damage levels. This would create an equivalency to vibration severity levels, particularly creating a predetermined level based upon empirical data that showed a correspondence between force severity levels and a general level of damage that is going to occur. Computational device  12  may also communicate this ratio to digital storage device  14 , modem  16 , and display unit  18  as well as to a press alert signal  40  or a press shutoff signal  42 . 
     During press operation, display  18  is visually checked by the operator or production manager to determine whether the impulse energy is acceptable. Alert signal  40  may be connected to a visual or audible alarm to warn the operator when the impulse energy has reached a predetermined level. Press shutoff signal  42  may be used to shut off press  22  when the impulse energy of the press  22  reaches a predetermined level. 
     The system may organize and compare compressive and tensile readings and warnings separately. The system may also compare the normal tensile and/or compressive inputs to that of a normal reference for a die when the die is being run or operated. Additionally, comparisons may be made by comparing the measurements to a general force severity level based on an empirical correlation of damage to a predetermined level of impact or impulse. 
     The system may also monitor variations in measured load or impulse from an initial setting or variation from the beginning the initial running of the system (e.g., measuring startup loads or impact versus mid-day, end-of-day, or other timed measurements). Such initial values for comparison may automatically or manually loaded in the system. The system may trip or sound an alarm when either an impulse limit and/or a peak load limit is exceeded or alternatively below a set minimum. 
     Digital storage device  14  stores historical data for the press being monitored so that press operating reliability may be accurately predicted. Additionally, modem  16  may communicate impulse energy values to a remote location. 
     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.