EP0316519A1 - Method for measuring and correcting the ram adjustment of high-speed punching presses, and circuit for carrying out the method - Google Patents

Abstract

The rams employed here serve for the cutting, punching, bending and/or stamping of semifinished products or the like having high tolerance requirements. The ram should be adjusted as a function of the number of strokes and the actual value in each case for the depth of immersion of the ram is measured. For this purpose, use is made of a detector head (4) which has a plurality of induction loops and is guided with the ram stroke along a permanent magnet strip (1) which in its longitudinal extent is divided into a large number of alternating North-South poles. The induced voltage characteristic is taken off for each predetermined unit of displacement length via cosine and sine functions of the induction loops, and the amplitudes of the two functions are measured and evaluated at the turning point, to be precise in such a way that one of the amplitudes or the maximum neighbouring the amplitude measured at the turning point serves as reference voltage and the other amplitude gives the measured value. …<IMAGE>…

Description

The invention relates to a method according to the preamble of claim 1 and to a circuit for performing such a method.

It is known in high-speed lifting presses that the depth of immersion of the upper tool in an associated lower tool increases with increasing working speed, as a result of which the tolerance requirements placed on the press for cutting and punching operations, as well as for bending and embossing work, are significantly shifted and negatively influenced. But not only the semi-finished products or the like to be produced suffer from the ram adjustment, the tools are also subject to increased wear as a result of which frequent downtimes and increased tool costs cannot be avoided.

A circuit arrangement by means of which the actual value immersion depth of such a tappet is determined by inductive measurement and with which a corresponding actual / target value comparison is then possible in order to carry out the required correction is known from DE-PS 27 31 084. There, the tappet adjustment at stroke rates of over 600 strokes per minute is corrected by means of a motor which acts via a gear train with a high reduction ratio on a pin bearing adjusting element, by means of which the tappet opposes its drive member is adjustable, wherein the immersion depth can be changed, that is, corrected in the desired manner. Instead of the current actual value measurement of the immersion depth, this known circuit can also be used to make a correction via a program stored in a memory, and depending on the number of strokes corresponding to this program, monostable flip-flops are supplied with control signals which in turn control the correction motor according to the signal information.

Another known circuit arrangement for an actuator of a plunger adjustment (DE-PS 2833829) uses at least one limit switch for detecting the immersion depth, which is adjustably attached to the press frame in the action of the plunger and whose signal output is connected to the set input of a first flip-flop, the signal output is in turn coupled back to a reset input of a further flip-flop by means of a branch line via a switching stage which determines the size of an adjustment step, a set input of a further flip-flop having a switch activated when the cutting press is interrupted and a reset input of the latter flip-flop is connected to a further switch which is activated when the plunger has reached a lowermost position relative to its drive element, which it must not fall short of depending on the tool.

The two known circuit arrangements have the advantage that the ram adjustment is possible during the operation of the press, on the other hand however, the main disadvantage that these are very complex circuit arrangements, with a correspondingly high outlay on costs for both the hardware and the software side.

The present invention uses this known prior art and it is based on the object of providing a method and a circuit arrangement of the generic type and designing such that the plunger immersion depth measurements and the corrections which can be carried out with them are carried out with the least possible susceptibility to malfunction and with a manageably low outlay on equipment becomes possible.

This object is achieved according to the invention by the features specified in the characterizing part of claim 1.

Advantageous further developments and refinements, in particular also for the formation of the circuit for carrying out the method, result from the subclaims.

The present task solution advantageously enables the increasingly precise tools of the type of interest here to be able to adapt to the higher quality requirements, even with an increased stroke rate of the presses. Special parts in the electrical and electronics industry can therefore be manufactured with very tight tolerances regardless of the stroke speed, specifically for stroke speeds that can be, for example, 2000 strokes per minute. The measuring system used is robust enough to withstand the harsh environmental conditions prevailing for such press operations without that this affects its high measuring accuracy. The implementation of the method with the associated circuit arrangement is simple, in particular also for the operator of the press, whereby restrictions on the tool installation space, in contrast to the prior art, are practically completely eliminated. It is also not necessary in the present solution to the problem to have to make readjustments, or to have to carry out special mechanical adjustments and thus time-consuming work on the press itself.

A tape applied to a metal band and magnetized at certain high-precision intervals serves as a measuring ruler, while the sensor head is characterized by four coils that are fed with a carrier frequency, the voltage induced in the coils being fed to the function evaluation by the relative movement between the metal band and the sensor . Because the coil arrangement in the detector head supplies two sine voltages offset by ninety degrees, a directional detection of the relative movement between the metal strip and the sensor head and thus between the ram movement and the press frame can be predefined in a simple manner. The evaluation of the inductive and thus non-contact measurement method is particularly simple in that first a rough path measurement is carried out by generating counting pulses at the zero crossings of the sine / cosine functions and that the amplitude value is stored at the reversal points for the two functions and this for the exact ones Measurement is evaluated.

For retrofitting a press, the Relativbe serve movement between the sensor head and permanent magnetic head equally as for the evaluation of their automatic operation, tei the possible existing deviation is first measured and displayed and after measurement of the deviation the machine is stopped, if the measurement proves a correction necessary, which in turn is then carried out automatically.

The present procedure is to be described in more detail with reference to the accompanying drawings, which also include an advantageous circuit arrangement for carrying out the present method.

• Fig. 1 Einzelne Teile der Vorrichtung zur Durchführung des Verfahrens in perspektivischer Wiedergabe,
• Fig. 2 eine Funktionsdarstellung der am Umkehrpunkt des Stößels gemessenen Amplituden zur Verdeutlichung des vorliegenden Verfahrens und
• Fig. 3 einen beispielsweisen Schaltungs­aufbau zur Durchführung dieses Verfahrens.

Show it:

• 1 individual parts of the device for performing the method in perspective,
• Fig. 2 is a functional representation of the amplitudes measured at the reversal point of the ram to illustrate the present method and
• Fig. 3 shows an exemplary circuit structure for performing this method.

An advantageous embodiment of the device for carrying out the method according to the invention for measuring and correcting the ram adjustment in high-speed lifting presses is shown in perspective in FIG. 1 with regard to the individual parts required for this. Block 3 takes the magnetic ruler 1, which is characterized by alternating magnetic poles (cf. also FIG. 3) that alternate every two millimeters in length and are applied to a suitable metal strip. The block 3 is firmly attached to the machine frame of the press, for which the receiving channel is used. It is also possible to fix the block 3 not on the static press part but on the moving tool part.

The sensor head 4 consists essentially of a detector 2, in which four coils are accommodated, which are acted upon with a suitable carrier frequency. The relative movement between the fixed tool half of the press and the moving tool half, i.e. the plunger, corresponds to the relative movement between the magnetic ruler 1 and the sensor head 4, the detector 2 being moved close to the magnetic ruler and parallel to it in the double arrow direction shown. The contactless length measurement of the distance thus traveled along the north-south pole arrangement, which changes every two millimeters at a distance between the magnetic ruler 1 and detector 2 of 0.1 to a maximum of 0.5 mm, influences the amplitude of the carrier frequency and thus modulates the carrier frequency in the Coils of the detector head 4 AC voltages, the respective course of which corresponds to sine functions, but which are offset by 90 degrees to one another, since the distances between the individual coils are matched to the distances between the alternating north-south pole arrangements in the ruler. The Voltage profiles picked up by the detector 2 in the scanning head 4 are fed via a line 6 to the plunger immersion depth measurement unit 7 and processed there in a manner to be described later.

A coupling piece 8 makes it possible to separate the sensor head, which in the exemplary embodiment is movably attached to the ram, from the processing and display unit 7 and to install it independently at a suitable location within the press or next to it.

The front panel of the device 7 contains a text display for the operator, a numerical display for the measured values obtained, as well as control buttons for different functions and a key selector switch for the possible operating modes. The possible operating modes consist in converting the press, in which parts of the device are set to a certain stroke and thus to a defined ram position, which is about the same as the respective tool change. Another mode of operation under the term "automatic" means that the device automatically orients itself to the new plunger position after the conversion has been carried out, it being possible for the device to measure a certain deviation, and the press then stops first if the deviation exceeds a tolerance limit - or falls below and then makes the necessary correction itself. In another operating mode "bypass / stroke", the device outputs are inactive; The current stroke is displayed, whereby this operating mode lies outside the actual operation of the device.

Finally, a mode of operation called "ventilation" is provided, which is used to travel a path for the ram in the upward direction that was defined during commissioning, that is to say to separate the two tool halves for test purposes.

The contactless, sliding movement of the scanning head 4 along the magnetic ruler 1 initially leads to a rough path measurement by generating counting pulses at the zero crossings of the sine curve in that one pulse results per millimeter of path. The amplitude values are recorded or stored at the reversal points of the voltage curve, and the counting impulses thus given are used to roughly determine the path of a specific stroke quantity. The anologic sinus amplitude measured at the reversal point of the movement of the plunger (see also FIG. 2 in this regard) then gives the exact value via the known arc-sinus function link or, as described in more detail below, it is possible to determine this in this way , in this connection it should also be mentioned that the offset coil arrangement in the detector head and the resulting offset of the voltage profiles by 90 degrees also enable direction detection of the plunger movement.

The plunger immersion depth is fundamentally continuously or variably adjustable, the respective plunger deviation being measured with increasing stroke frequency and the increase in immersion depth being measured by this increasing frequency while the press is running and this is then stopped when a set tolerance limit is either reached is exceeded or undershot upwards or downwards. The deviation that has occurred is corrected during the downtime of the press, for which purpose the press is switched from the "continuous operation" mode to "setup", that is to say discontinuous operation. After the correction that has become necessary is taken into account, the press then operates again until the set tolerance range is left again or until the press may need to be set up again.

The use of the scanning head 4 in conjunction with the magnetic ruler 1 in the embodiment shown in FIG. 1 (with the actual press omitted) is particularly advantageous in so far as the corrections which can be predetermined thereby are independent of the actual tool, that is to say the plunger and the like. as well as the fixed press half, ie that wear of the individual tool parts does not impair the measuring process, as is the case, for example, with the ram correction using the known limit switches. The sine / cosine curve in the coils within the sensor head 4, which are offset by one millimeter from one another in the exemplary embodiment, is shown in FIG. 2 at the reversal point of the up-down movement of a plunger. For the measurement of the reversal point, it is ultimately of no interest how many sine or cosine periods are traversed to the reversal point of the ram; the only thing of interest for the measurement of the reversal point is the last maximum of the sine or cosine function before the reversal point or the amplitude of the functions directly at the reversal point. One of these values is used for the evaluation as a reference voltage and the last one in each case voltage value occurring at the reversal point as a measured value. As can be seen from FIG. 2, the reversal point practically represents a mirror plane for both the sine and the cosine function, which exactly defines the measured value and the reference value for the evaluation electronics and, in the exemplary embodiment, a deviation from the desired immersion depth with an accuracy of up to 1 / 100 millimeters.

Fig. 3 shows a block circuit diagram of a circuit which enables the aforementioned functions. Thereafter, the scanning head 4, which is guided past the magnetic ruler at a distance, outputs, via the detector 2 consisting of four coils, which are fed via an oscillator 10 with a suitable carrier frequency, the signals which are modulated by the relative movement between the detector 2 and the magnetic ruler 1 in the form of the aforementioned sine waves. respectively. Cosine signals each directly to an associated low-pass filter 12, 13 or via the digital analog converter 11, 14 to the other low-pass filter 13, 12. Each of the low-pass filters 12, 13 is on the output side with the two peak value memories 15, 17 and 21, 22, one Rectifiers 19 and 43, respectively, and a converter 20, 24 are connected in the manner given in the functional representation.

An electronic relay 25 switches the analog output signal information of the modules 19 and 23 to digital commands and leads these digital signals alternately to a peak value memory 28, which is followed by an analog measured value memory 29, corresponding to the analog measured value memories 16, 18, 26 and 27 are connected to the outputs of the peak value memories 15, 17, 21 and 22. Thus, for an out Evaluation of the signals obtained by the amplitude values of the coils of the detector 2 as path information, the demodulated associated direct voltage components, which are superimposed on the alternating voltage components, can be used by measuring the positive and negative peak values and digitizing these measured values for a computer-controlled correction. For this purpose, the integrated switching logic 30, which bwz with the converters 20. 24 is connected, controlled by them in such a way that, in synchronism with the zero crossings of the sine and cosine signals, first the memory pulses for the analog measured value memories 16, 18, 26 and 27 and 29 and then the reset pulses for the peak value memories 15, 17, 21, 22nd or 28 are specified or generated. The outputs of the analog measured value memories 16, 18, 26, 27 and 29 are at the inputs of a multiplexer 31, the output information of which is amplified by an impedance converter 22 and can be fed to the memory logic 34 via the analog digital converter 33. By means of the multiplexer 31 which can be switched by the computer and whose outputs feed an analog-digital converter as described above, the computer logic thus has access to each individual peak value which is supplied via the individual peak value memories. Half the difference between the peak values corresponds to the DC voltage offset, which is output with the correct sign at the respective digital / analog converter and subtracted at the signal input. After the correction has taken place, the digital-analog converter signal (14, 11) on the output side passes through the low-pass filters 13, 12 in order to suppress the demodulated carrier frequency components (sine / cosine). The rectified signals are output in the manner described above from the rectifiers 19, 23 to the changeover switch 25, which, controlled by the logic circuit 30, switches through the signal which is clearly marked with the last maximum at the point of reversal, to the downstream peak value memory, while at the same time via the logic circuit 30, according to the reversal of direction indicated at the point of reversal, the voltage maximum is stored in the associated measured value memory.

By normalizing the reverse voltage to the associated peak value and then evaluating it using the arc-sine function, the distance in the exemplary embodiment is interpolated within a millimeter to within a hundredth of a millimeter.

The measurement of the values added to one millimeter in each case is carried out by the computer 34 by enumerating the zero crossings of the sine and cosine signals. The zero crossings are processed via the logic circuit in the memory 34. According to the functional diagram, the logic memory 34 is also connected to the display and operating part 35 and, of course, the inputs and outputs 36.

Claims (6)

1. Method for measuring and correcting the ram adjustment in high-speed lifting presses, which consist of a lower tool and a relatively movable upper tool or ram for cutting, punching, bending and / or stamping semi-finished products or the like with high tolerance requirements, in which the ram is to be readjusted as a function of the number of strokes and the actual value of the immersion depth of the plunger is measured and compared with the desired immersion depth, characterized in that a detector head having a plurality of induction loops is guided with the plunger stroke along a permanent magnet strip known per se, which is divided in its longitudinal extent into a multiplicity of alternating north-south poles, the induced voltage curve being tapped via cosine and sine functions of the induction loops for each predetermined path length unit, and the amplitudes of both functions being measured and evaluated at the point of reversal ground in such a way that one of the amplitudes or the maximum adjacent to the amplitude measured at the reversal point serves as a reference voltage and the other amplitude specifies the measured value. 2. The method according to claim 1, characterized in that either the detector head and / or the permanent magnet strip or the like is movable relative to the fixed tool. 3. The method according to claim 1 and 2, characterized in that the sensor head is moved close to the magnetic ruler and parallel to it. 4. The method according to claim 1 to 3, characterized in that the plunger immersion depth is measured continuously variable during the run of the lifting press, and that the plunger correction is carried out while the press is at a standstill after exceeding or falling below a set tolerance limit. 5. Circuit for performing the method according to claims 1 to 4, characterized in that a counting pulse for a rough path measurement is given at the zero crossing of each of the sine functions given via the detector coils. 6. Circuit for performing the method according to at least one of claims 1 to 4, characterized in that the measured amplitude values of an arc-sine function linkage are subjected to the reversal point of the movement of the plunger.

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