Method for controlling punch process noise and apparatus for punching a workpiece

Abstract: A method and apparatus for controlling punch press noise in which the noise level produced is monitored by a detector (48) and the press ram velocity is modified in real time to keep the noise level within preset limits. A time weighted average noise level is also controlled by varying the ram velocity for punching operations over a period of operation to maintain a projected time weighted average within a preset limit.

Description: This invention concerns industrial processes and more particularly metal cutting, such as punching or shearing in which significant noise is generated, creating working environmental problems. Noise level is a function of many variables, i.e., material hardness and thickness, punch size, punch shear, impact velocity, punching velocity, and stripping velocity. Considerable work has been done in this area to alleviate the noise problem in punching operations. See GB-A-2036923 in which a damping device is used to alleviate noise and vibrations in a punch press as an example. It has heretofore been proposed to use a hydrauliccylinder coupled to the ram to drive the punch, with feed back control systems employed to provide precise control over punching velocities. See US-A-4 116 122 for an example of a press using such a control system to improve the quality of the punched part. In US-A-4 823 658, controlled ram speed is described as allowing reduced punching noise. US-A-4 208 935 describes a feed back control over the punch ram to reduce the exit speed of the punch at the end of the punching process to eliminate noise and strain. US-A-5 031 431 and 5 027 631 and GB2186394A (nearest state of the art) describe reducing ram velocities to limit noise in accordance with stored programs which have previously been calculated or empirically determined to keep noise limits within acceptable limits for particular legal limits. In some cases time of shear or ram pressure are relied to correlate with noise level which may or may not hold true in practice. These approaches require extensive and time consuming testing and compilation of data and elaborate computer programs and stored data libraries to carry out, and actual results may vary from calculated noise levels. Stripping noise is not accounted for. In the event that the daily average level of noise exposure is limited by legal authorities or that limits are otherwise desirable as to avoid the need for wearing ear protection, the prior control schemes do not provide any means to insure that allowable time averaged noise levels are not exceeded. In addition, the effects of the operation of nearby machinery or other various factors unique to a particular location are not able to be taken into account. The object of the present invention is to eliminate the need for theoretical studies or extensive laboratory testing and elaborate computer programs, and to provide a means to insure that time averaged noise levels and/or peak level noise are not exceeded. This object has been achieved by the features as indicated in the method claim 1 or in the apparatus claim 2. The present invention comprises a system in which a noise or vibration detector is combined with a press ram control system so that the punching process is controlled in real time to be carried out entirely within desired noise limit parameters, including maximum or peak noise levels or time weighted average noise exposure limits. This combination creates the possibility for a wide variety of control schemes to limit noise while maximizing productivity over a processing period. In a version of the controlled process program, a time weighted average limit of the noise level can be maintained, as by extrapolation of the time weighted average to a period of punch operation, i.e. over one shift, from the sampled punch cycles, and correspondingly adjusting the velocities and cycle frequencies of subsequent punch cycles to limit the time weighted average over a production cycle in the most efficient manner. This control can be integrated with stored program data for particular punching operations to modify the same in accordance with actual results and actual conditions such as noise contributed by operation of surrounding equipment. The invention will now be further described with reference to the drawings wherein Figure 1 is a diagrammatic representation of a system according to an embodiment of the present invention. Figure 2 is a diagrammatic representation of an alternate embodiment of the invention. Referring to Figure 1, the components of a punch press 10 is represented diagrammatically including a hydraulic cylinder 12 mounted on a press frame 14 adapted to drive a ram 15 coupled to a punch 18 carried by an upper turret 19, to drive the punch through a workpiece W and into a matching die 20 carried by a lower turret turned 21. The workpiece W is disposed on a table 22 and driven by a gripper carriage 24 in an X-Y plane to properly position the workpiece for a given punch operation at the location of the ram 15. The hydraulic cylinder 12 is a double acting hydraulic cylinder having an upper chamber 26 above a piston 30 driving the ram 15 down and a lower chamber 23 driving the ram 15 up, when the respective chambers 26, 23 are controllably pressurized or vented by operation of a servo valve 32 communicating with a source of hydraulic fluid under pressure such as a pump 34, and a reservoir 36 containing unpressurized hydraulic fluid. The control system includes a position feedback transducer 38 tracking the position of the ram 15 and supplying an error signal to a servo controller 40 so as to enable a precisely controlled ram velocity to be achieved. Preferably a valve spool position feedback transducer 42 is also used with a valve amplifier 44 to improve the performance of the control system. Such control arrangements are known and are essentially described in the above referenced patents. The sequencing of the punch press operation including turret rotation to select tools, carriage drive to properly locate the workpiece W etc., is carried out under the control of a software program contained in a computer controller 46 in the general manner well known in the art. The ram velocity is desirably controlled to minimize punching noise, but this is done in real time according to the concept of the present invention by utilizing a noise or vibration detector 48 positioned at the station whereat punching is carried out to directly measure noise and generate signals corresponding to the magnitude of the noise level, i.e., the level of noise in real time, and generate signals corresponding thereto. Thus, velocities of the ram 15 during penetration can be limited to reduce noise to maximum permissable levels for any given tool or punch operation, by sampling the noise level actually reached for a given tool or punching operation. If the noise level exceeds a preset level, the velocities for subsequent penetrations can be reduced to low levels minimizing the noise to the extend possible. That is, to velocities on the order of 5 to 12,7 cm (2-5 inches) per second compared with 76 cm (30 inches) per second for normal speed punching. A typical limit is 85 dba, the limit requiring ear protection. A preset time weighted average can also be easily maintained, by extrapolating by calculation the time weighted average that will be reached over a given period, i.e. one work shift, based on the actual readings of sample punching operations and time of the sample. Typically an average of 90 dba for an eight hour shift cannot be exceeded. Thus, if a time weighted average limit as extrapolated will be exceeded, the ram velocities can be correspondingly reduced over the remaining punch press cycles, and/or the frequency of the punch cycles, to reduce the overall number of punch operations for the remaining time of the period. The manner of achieving maximum efficiency in reducing the noise level can be calculated by a suitable program for the computer controller 46. An acoustic dosimeter 50 can be employed in an alternative embodiment shown in Figure 2. Acoustic dosimeters are commercially available which will generate readings of extrapolated time weighted averages over a period of time. The output of such an acoustic dosimeter 50 can be combined by means of software of the computer controller 52 to enable programmed management of the punching operations to be carried out over the period so as to keep the noise level within a preset limit.

Claims: A method of controlling the noise levels produced by the operations of a program controlled punch press (10) having a ram (15) driven through workpiece (W) at a work station to punch a hole therein, a program control (46) causing a series of punching operations to be carried out in said punch press (10) over a timed period of operation thereof with a programmed ram velocity, the method comprising the step of: positioning a noise detector (48) adjacent the punch station, and monitoring therewith the actual noise level at said noise detector (48) produced by a sampled punching operation in said programmed operation in real time; characterized by projecting a time weighted average noise level which will be produced over said time period of operation of said punch press (10) from said noise levels detected in said monitoring step, and reprogramming said control program in real time to vary the programmed ram velocity and/or the frequency of the punch operations for subsequent programmed punching operations during said time period of operation so as to maintain said time weighted average noise level within preset limits. A metal cutting apparatus for cutting a workpiece by a shearing action, for conducting the method of claim 1, comprising: a press (10) including a press frame (14); a table (22) supporting said workpiece (W) within said press frame (14); press ram means (15) adapted to engage a tool means (18) for advancing said ram (15) to drive said tool (18) through said workpiece (W) at a work station; said ram actuating means including a double acting hydraulic cylinder (12) defining upper and lower pressure chambers (26, 23), said ram (15) connected with a piston (30) to be driven therewith; a source (34) of hydraulic fluid under pressure pressurized and valve means (32) for selectively communicating a variable pressure hydraulic fluid to said pressure chambers (26, 23) from said source (34) to control the velocity of said ram (15), said valve means (32) responsive to command signals to control the communication of said pressure chambers (26, 23) with said pressure source (34) and a reservoir (36) to achieve a command velocity of said ram (15); program controller means (46) for generating command signals transmitted to servo valve operator means (40); and detector means (48) positioned to detect noise occurring at said work station caused by said ram (15) driving said tool (18) through said workpiece (W) and generating signals corresponding to the level of said noise; said program controller means (46) receiving said signals from said detector means (48) and modifying said command signals transmitted to said valve operator means (40) if said detector means signals correspond to noise levels exceeding preset limits, characterized by a feed back signal generator means (38) associated with said hydraulic cylinder (12) producing position feed back signals corresponding to the actual position of said ram (15), said servo valve operator means (40) responsive to said position feed back signals to maintain said command velocity;, said detector means (48) comprising an acoustic dosimeter generating signals corresponding to the projected time weighted average sound levels over a period of operation of said apparatus, and wherein said controller means (46) modifies said command signals over the course of said period to maintain said projected time weighted average noise level within preset limits.

Inventors: HUNTER JAMES R, SCHORN GERARD, HUNTER, JAMES R., SCHORN, GERARD
Applicants: MURATA MACHINERY LTD, MURATA MACHINERY LTD.
Application year: 1992
Main classification: B21D28
IPC codes: B30B15, B21D28