SE467243B - PROCEDURES FOR SUPERVISION OF AN ELECTRONICALLY CONTROLLED SCREW DRIVER - Google Patents

Description

15 20 25 30 35 467 243 2 control interval. The known systems therefore require a large effort for safety control (system control) in the control electronics in order for emerging faults to be determined and indicated as quickly as possible.

The object of the invention is to provide a method for monitoring screwdrivers, by means of which, with high operational reliability, manual testing of the control electronics ("master" screw connection) and testing of the sensors can largely be dispensed with and system control can be reduced to a minimum.

This object is solved by the procedure set out in claim 1.

The additional control signal introduced according to the invention expands the hitherto two-dimensional acceptance window delimited by the given limit values into an acceptance cube, so that the position of the end point of the extraction curve is tested in three dimensions. In order for a screw connection to be accepted as correct, all comparison results must show that both the sensor signals and the control signal are between the associated limit values. If only one of the tested signals is outside the associated band which is limited by the ndnimi and nmximi values, there is a system error, which without much effort by electronic means can be determined and indicated by an evaluative logic device.

Since both the sensor signals and the control signal can be produced as a function of the screwing process, there is also a direct connection between the control signal and the output signals of the sensors. Based on this connection, by comparing the control signal with the sensor signals, the function of the sensors can be monitored directly, while conversely the control signal resp. The sensor for this is monitored with the sensor signals. 'Thanks to the introduced control signal, therefore, both a test of the sensor signals and their associated electronic equipment and, conversely, a test of the control signal and its associated electronic equipment is possible. Since the present system error can be determined immediately and unconditionally by the method according to the invention, the manual, cumbersome counter-measurement can be done by means of rotating torque recorders or the use of expensive and complicated measuring and adjusting workpieces for countermeasuring 31/10 15 20 25 30 35 467 245 completely dispensed with. During each screwing operation, the system again tests that the function is faultless. Continuous monitoring is thus ensured.

A simple embodiment is obtained if the control electronics and their input signals generating the sensors are doubled.

The input signals of the additional control electronics are then (directly) independent of the signals of the other control electronics, whereby the output signals of both control electronics are processed in a superior central logic device. Based on the output signals, the central logic device can unambiguously determine whether both systems are working correctly and whether, in the event of system malfunction, there is a correct or incorrect screw connection or whether there is a system fault in one of the two control electronics.

In a simple embodiment of the method according to the invention, three quantities are connected, namely the output signals of the sensors and a control signal, in such a way that the individual conditions can be determined immediately and unconditionally. For this purpose, a parameter for the screwdriver motor is advantageously used as a control signal, whereby in the case where the screwdriver is driven by an electric motor, this parameter is advantageously constituted by the working current. If this is not possible, the output signal from a control torque sensor can also be used as a parameter or control signal. The indication of a system error is advantageously done optically by activating, for example, an LED, a light bulb or a similar means. In the case of fully automatic screwdrivers, which are not continuously monitored by one person, it is advisable to allow the indication of a system fault to be made by acoustic means. The acoustic means may be arranged independently or in addition to optical indicating means.

As a suitable further development of the invention, it is transmitted in one plane determined by two signals of the limit values associated with the signals delimited by the acceptance window on the entire set curve for a "master" screw connection. This setpoint curve describes a curve sequence occurring under optimal screwdriving conditions for a "master" screw connection. By transferring the associated acceptance window at each point of this set-up curve, an acceptance area is created around the curve. In the case of a later drawn screw joint, the curve course for this can be tested at any point on the curve or continuously. If the curve for a screwing process goes, this is determined immediately, and the screwing process is interrupted, whereby the error is indicated outside the acceptance range, optically or acoustically.

Similarly, there is a possibility for continuous monitoring of the screwing process in a system defined by three signals. The three signals define a space coordinate system, in which an acceptance cube can be displayed with the minimum and maximum values associated with the signals. If this acceptance cube, in accordance with what has been stated above, is transmitted at each point on the setpoint curve for a "master" screw connection, a three-dimensional acceptance channel is obtained. In the case of each denar drawn screw joint, the curve for the screw-tightening process must be within this acceptance channel in order for the screw-tightening process to be able to end correctly.

If the curve for a screwing process at any point goes outside the acceptance channel, this is determined, whereby the screwing process is interrupted and the error is indicated.

To simplify the procedure with respect to the acceptance area or the acceptance channel can. one may connect a function table for linearization of the setpoint curve for a "master" screw connection.

Through this further development of the procedure, the monitoring can take place continuously during the entire screwdriving process.

In most cases, however, it is sufficient that in fixed given points or planes in the two-resp. the three-dimensional system examines the curve of a screwing process and tests it with respect to the associated acceptance range. If the curve leaves the acceptance range at any of these points, the screwing process is interrupted as incorrect, indicating at the same time any existing system fault.

The method according to the invention can be carried out in a particularly simple manner using a microprocessor which, on the basis of the given limit values, tests the screw connection and the system and makes any faults which can be detected.

In order that in the method according to the invention the input of the limit values or the input of the cut-off criteria 10 15 20 25 30 35 467 243 5 is to be facilitated, these are stored under marking for the corresponding screwdriving process in a memory, from which they are called at the beginning of or during the screwdriving process individual treatment units. Conveniently, the limit values and the cut-off criteria can be determined by performing a "master" screw connection and preferably automatically entered into the memory.

Further features of the invention appear from the claims, the description and the drawings.

Advantageous embodiments are shown in the accompanying drawings and are described in more detail below with reference to these.

Fig. 1 shows a Screwdriver made in accordance with the invention with associated electronic equipment; Fig. 2 is a block diagram of the screwdriver of Fig. 1; Fig. 3 is a torque / rotation angle diagram with different curves; Fig. 4 shows a working current / rotation angle diagram with different curves; Fig. 5 shows the diagrams of Figs. 3 and 4 plotted in a space coordinate system; Fig. 6 is a representation according to Fig. 5 with a drawn acceptance channel.

The screwdriver S schematically shown in Fig. 1 serves to tighten screws 41 in screw joints V. Connected to the screwdriver S are a torque sensor MD, a rotation angle sensor VV and a control rotation angle sensor WK, which emit their output signals to an electronics E. Via a line Depending on the output signals, the electronics device E controls the screwdriver S driven in the exemplary embodiment shown by an electric motor, whereby a working variable for the drive motor, in the exemplary embodiment shown the motor working current, is treated as an additional control signal. The electronic element E activates depending on the output signals from the sensors resp. of the control signal an indicator A according to given criteria.

Furthermore, with the aid of a monitor B, the linearity curve for the electronics can be examined or, for example, the torque / rotation angle curve can be displayed.

In connection with the block diagram in Fig. 2, the construction of the electronic device E and its mode of operation will now be described in brief. The electronic device essentially consists of a control circuit MK, which processes the output signals from the sensors MD and W, and a control circuit KK, which processes the control signal emitted by the control angle sensor WK and the control signal derived from the working current of the electric motor EM.

In the sub-block denoted by S 'in Fig. 2, the screwdriver is represented essentially by its electric motor EM and the sensors WK, MD and W connected to the screwdriver are shown

Depending on the receiver design, the torque sensor MD is supplied with direct current, a carrier frequency signal, a direct voltage signal or with alternating or three-phase current. In the unloaded state, the sensor MD outputs a zero output signal to a reconnected amplifier 16. The distortion of the sensor MD which occurs during the screwing process due to the mechanical interconnection with the screwdriver results in a change of the output signal proportional to the torque. The change of the output signal amplified in the amplifier 16 is used for controlling a switched-on, adjustable window discriminator 17. By means of potentiometers 19 and 20, the window discriminator 17 is set to limit values which correspond to a minimum resp. a maximum torque, here denoted Mmin and Mmax. The window discriminator 17 compares the output signal from the torque sensor with the given limit values and signals via three lines to a memory 18 if the output signal is greater than M, less than Mmin or lies between the limit values.

Memory: X18 is connected to a logic circuit 34, so that the comparison results can be further processed.

If during the tightening process the given maximum value for the torque is exceeded, the logic circuit 34 immediately emits via a line 43 a switch-off signal to a motor controller 3, whereupon the electric motor EM is stopped.

The rotation angle sensor W is supplied from a supply voltage device (not shown). When rotating the screwdriver spindle S "(Fig. 1), the pulses proportional to the angle of rotation emit to a counter 31 with an integrated digital-to-analog converter. A trigger signal which in the embodiment shown is emitted on a line 27 of the window discriminator 17 upon reaching a threshold moment MS releases the counter 31. si. 10 15 20 25 30 35 467 243 7 The threshold moment is set in the window discriminator 17 by means of a potentiometer 26. The angle of rotation undergone during the tightening process after reaching the threshold moment MS lies after the release of the counter 31 at the entrance to a first in the form of a proportional analog voltage.

The amplified signal is used to control a switched-off window discriminator 22. The limit values for the "window", ie. the minimum permissible value and the maximum permissible value at the angle of rotation, the Wmin window discriminator 22 by means of potentiometers 24 and 25.

The limit values set on the window discriminator 22 and Wmax 1 are triggered during the tightening process by the amplifier's output voltage and compared with the output signal from the rotation angle sensor, W. On three parallel output lines the comparison results are supplied to a memory 23, which in turn makes these values available. for the logic circuit 34.

The window discriminator 22 signals on different lines to the memory the following states: "The output signal from the angle sensor W greater than the maximum permissible rotation angle Wmax", "the output signal less than the minimum permissible rotation angle Wmin" and "the output signal between given limit values".

If the maximum permissible angle of rotation Wmax is exceeded during the tightening process, the logic circuit 34 will directly act on the motor control device 3 via the line 43 to stop the electric motor, whereby the tightening process is thus interrupted.

The torque / rotation angle diagram shown in Fig. 3 corresponds to the measuring circuit MK. The limit values Wmin set by the potentiometers 24 and 25 in the window discriminator and the Wmax natural 22 define the acceptance window FMK in the X-direction, while the torque limit values set by the potentiometers 19 and 20 in the discriminator 17 define the acceptance window in the FM range. . The logic circuit 34 can now test whether, at the moment of turning off the screwdriver, the end point of the torque / rotation angle curve I (Fig. 3) is within the acceptance window FMK. If this is the case, the screw connection is correct, unless there is a system fault.

The control circuit designated KK in Fig. 2 processes two control signals, which are independent of the output signals from the sensors MD and W but change depending on the screwing process. The working current supplied via the motor control device 3 to the electric motor EM is determined by means of an interconnected current measuring device 4. This current measuring device is designed in such a way that no falsification of the measurement or motor control occurs. With an increase in the torque delivered by the electric motor, a possible proportional increase in the working current arises. This change results in a varying output signal from the current measuring device 4, which signal is amplified in an amplifier 5 and is used for controlling a subsequent window discriminator 6. By means of potentiometers 8 and 9, the limit values corresponding to the permissible torques Mmax and Mmin are set for Imax and Imin. The window discriminator 6, in the same way as the window discriminators 17 and 22 already described, signals an "exceeding" of the maximum permissible working current ", an" undershot of the maximum permissible working current "and" the operating current between given limit values "to a memory 7, which makes the information available to a logic circuit 15. If during the tightening process the maximum permissible working current is exceeded, the logic circuit 15 will act via a line 42 directly on the motor controller 3 to stop the electric motor.

The processing of the signal from the control angle sensor WK takes place in the same way as the already described processing of the signal from the angle sensor W. When the threshold value MS is reached, the window discriminator 17 releases via the line 27 a counter 32 with integrated digital analog converter, the output of which is fed to an window discriminator. ll.

This signals in the same way as the window discriminator 22 on different lines to a memory 12 whether the limit values set near the potentiometers 13 and 14 have been exceeded or exceeded or whether the output signal from the control angle sensor WK is between the limit values. The memory 12 makes this information available to the logic circuit 15, which, when the maximum permissible control rotation angle WKmax is exceeded, acts on the motor controller 3 via the line 42 and stops the electric motor.

The control signals from the control circuit KK determine a working current / control angle plane, in which the limit values I 1. , wK. , wK mln mln maX the control signals for the working current resp. the control angle max 'delimits an acceptance window FKK. If at the end of a screwdriving process is within the acceptance window FKK, ie. if the I-WK curve ends in this acceptance window, the screw connection has sufficient prestressing force, provided that a system fault does not exist.

The logic circuits 15 and 34 signal the results to a central logic device 2, which in turn tests whether the screw connection has been made in accordance with the given parameters or not and whether a system fault exists in the control circuit or in the measuring circuit resp. in sub-block S '. In principle, it can be assumed that if there is a correspondence between the output signals from the logic circuits 15 and 34 to the central logic device 2, there is no system error with a probability that is limited to safety. The central logic device 2 can therefore, on the basis of the results signaled to it from the logic circuits 15 and 34, immediately determine whether the screw connection can be described as correct with regard to the given parameters.

The screwing process is started by a signal from an input circuit 1 to the central logic device 2. The starting signal can be triggered in the input circuit manually or by other electronic means. Via a line 28, upon receipt of the start signal, the central logic device 2 will empty the memories 7, 12, 18 and 23 and reset the measuring circuit and the control circuit. Thereafter, the central logic device 2 starts via a line 44 the motor control device 3, which immediately connects the drive motor EM, whereby the screwdriver initiates its rotational movement. the head 40 (Fig. 1) the torque M and the working current I.

If the screwdriver has been fitted to the screw 41, the rotation signal increases if the output signal from the rotation sensor MD exceeds the threshold value MS preset with the potentiometer 26, the counters 31 and 32 are released by the window discriminator 17 via the line 27, so that the rotation angle measurement can take place. If the screwing process takes place according to the known yield strength-controlled tightening method, upon reaching a certain determined coupling gradient, which is calculated by the output signal from the torque sensor MD and the angle sensor W, the electric motor will be stopped, so that the screwing process is terminated. The switch-off moment 12, 18 and 23 is evaluated by the logic circuits 15 and 34, the outputs of which present information: in the memories 7, is made available to the central logic device 2. If the outputs from the logic circuits 15 and 34 are equal and if the outputs from the sensors and the control signals from the control circuit are in their associated acceptance windows FKK and FMK (see Figs. 2 and 3), by activating a lamp 30 a "correct" will, however, the output signals and the control signals are indicated for the screw connection. If outside the associated acceptance windows, by activating a lamp 45 it will be indicated that the screw connection is incorrect. If the output signals from the logic circuits 15 and 34 are different, a system error will be indicated by activating a lamp 29. When indicating a system error, the insignificant (Fig. 3) window FKK (Fig. 4) is not reached. If the lamp 29 is lit, the user knows that there is a system fault in the system itself about the acceptance window FMK or the acceptance, namely either in the measuring circuit MK, the control circuit KK or in the sub-block S '(fig. 2).

Thus, with the method according to the invention, a plurality of errors can be determined: If, for example, the torque sensor MD is disturbed so that it emits an excessive output signal, or if the electronic equipment connected to the torque sensor works incorrectly, the measurement may indicate that the torque is greater than it actually is. applied torque. After the switch-off, the end point of the MW curve I (Fig. 3) is admittedly in the acceptance window FMK, so that the measuring circuit MK signals that the screw connection is correct, even though the torque actually applied to the screw connection is lower and therefore 1 , »Incorrect, but this is stated by the control circuit KK. It actually applied, namely a workflow that is less than Im. follows the curve V in the I-WK diagram in Fig. 4, so the end-too-low torque corresponds to low and therefore the point of this curve is outside the acceptance window FKK, whereby the logic circuits 15 and 34 emit different signals to the central logic device 2, thereby finding that system error exists. 10 15 20 25 30 35 467 243 ll The same applies if, for example, the current measuring device 4 works incorrectly. Due to the lateral positioning of the measuring and control circuits, which work with mutually independent signals, both the measuring circuit and the control circuit can be monitored with regard to fault-free function. If, for example, the control angle sensor WK is defective or the connected electronic equipment is faulty, in the MW plane in Fig. 3 the acceptance window FMK can be achieved (curve I), but in the I-WK plane in Fig. 4 the acceptance window cannot be achieved ( curve III). The central logic element 2 determines that the results from the logic circuits 15 and 34 are different and indicates a system error by activating the lamp 29.

With the method according to the invention, one can not only ascertain a system error as such on the basis of the available signals, but one can also locate the erroneous area more accurately. If, for example, in a screwdriving process the I / WK curve runs as the curve V in Fig. 4 and the MW curve runs as the curve I in Fig. 3, it can be immediately read from the comparison results signaled to logic circuits 15 and 34 that the working current at the stroke time was' outside the given limit values, and thus that the system error occurs in this area. Similarly, errors in the other areas can be found.

By producing two signals in one plane (see Figs. 3 and 4), a diagram is obtained for each case, in which a setpoint curve representing a correct screwing process can be introduced (see curves I and II in Figs. 3 and 4). . In such a diagram, the minimum and maximum values associated with the represented signals in each case delimit an acceptance window (FMK, FKK).

Thus, the representation of the outputs from the sensors MD and W leads to the diagram in Fig. 3, where the corresponding x 'Mmin' Wmax 'Wmin the acceptance window FMK, in the center of which the end point of it is correctly located. the minimum and maximum values Mma delimit the screwdriving process representing the curve I The same applies to the representation in Fig. 4.

Already. with three signals, a space coordinate system according to Fig. 5 can be settled. In this space coordinate system, the measured quantities M and W and the control signal I are connected.

In the I-W plane, which corresponds to the representation in Fig. 4, the acceptance window FKK lies, while the acceptance window FMK shown in Fig. 3 lies in the M-W plane of the space coordinate system. The two acceptance windows form in the room an acceptance cube AKK.

The curves representing a correct screwing process (I na I and II in Figs. 3 and 4), transferred to the space coordinate system in Fig. 5, give a space curve, the end point of which lies in the acceptance cube AKK. If in a screwing process the space curve is outside acceptance cube, the screw connection does not have the predetermined values, incorrectly.

If now, as a further development of the method according to which it is marked as the finding, the acceptance window delimited in a plane, for example the acceptance window FMK in Fig. 3, is transferred at each point on curve I, an acceptance area AKB is obtained (Fig. 3), within which every other curve for a screw course must be in order to ensure a correct screw connection within the tolerance range. By establishing the acceptance area AKB according to Fig. 3, it is possible that during the entire screwing process at each point on the curve I, ie. at each point in the screwing process, test whether the signals are within the respective associated acceptance ranges. If the acceptance range delimited by the preset or given limit values is exceeded, the screwdriving process is interrupted and the error is indicated.

This further development of the method according to the invention is possible also in a space coordinate system defined by three signals, as shown in Fig. 5. By transmitting the acceptance cube AKK at each point on the space curve representing a correct screw connection, a three-dimensional acceptance channel AK is established, within which the space curve must lie in order for the screw connection corresponding to the curve to be designated as correct. If the space curve leaves the acceptance channel * in one of the three directions, this is determined immediately on the basis of one of the comparison results, and the screwing process is thereby interrupted, at the same time as an error indication occurs.

By establishing the acceptance area AKB resp. the acceptance AK, a continuous monitoring can take place during the entire screw-drawing process, whereby higher safety can be achieved. Usually, however, it is sufficient to perform an interval test of the position of the curve in the plane resp. in space in relation to the acceptance area AKB resp. the acceptance channel AK, i.e. to carry out an examination at specific, given points resp. in definite, given planes.

In order for the insert when transferring the acceptance window resp. the acceptance cube on the optimal set curve for the screw connection should be as small as possible, the curves are preferably linearized by connecting a function table.

The method according to the invention can advantageously be carried out using a microprocessor, to which the output signals from the sensors and the preselected limit values for the individual signals are applied. By means of a microprocessor, it is also easy to carry out a continuous test of the screw-drawing process without this requiring an increased input of equipment.

In order to further simplify the implementation of the method according to the invention, it is suitable to store the limit values associated with the individual signals (outputs from the sensors, the control signals) and the desired switch-off criterion in a memory, from which they are retrieved by the individual processors. units. Likewise, the limit values and cut-off criteria stored in a memory for each occasion can be called up at the beginning of a corresponding screwing process and entered into the individual units.

As a further development of the method according to the invention, it is also advantageous to determine the permissible limit values by performing a "master" screw connection, whereby these values can be stored in the memory automatically.

The determination of any system errors possible with the method according to the invention can, in addition to the example shown in Fig. 2, be performed with two independently operating control electronics, which signal their results to, for example, the indirectly dependent signals central control electronics. thus, are compared with each other to determine any existing system faults, after which the signals identified as fault-free signals are further processed to determine whether the screw connection is correct. Applied to the embodiment according to Fig. 2, in this embodiment the output signal from the torque sensor MD would thus be directly compared with the output signal from the current measuring device 4, which emits a signal proportional to the operating current of the electric motor EM.

Since the working current / torque curve of the electric motor EM is known, by comparing the two output signals with each other, a conclusion regarding a system fault can be drawn immediately. Because the rotation angle sensors W and WK are identical, if a system error can be detected directly if the output signals are different.

The setting of the limit values in the individual window discriminators can advantageously be done by means of mechanically preset sensors, which by means of a button press or by means of a switch switch on the corresponding units.

In order to increase the functional safety of the procedure, it is appropriate to make the equipment digital. .u w

Claims (10)

10 15 20 25 30 35 467 243 15 Patent claims Method for monitoring an electronically controlled screwdriver, which is connected to a torque sensor and an angle sensor, the outputs of which are supplied to an electronic control device which monitors the screwing process and in accordance with given switching criteria switches off the screwdriver and compares the sensor sensors and maximum values and depending on the comparison result make the quality of the screw connection determinable, characterized in that at least one additional control signal varying with the screwing process is generated, which is independent of the sensors' (MD, W) output signals and that at least in the screwdriver (S) switch-off moment also the control signal a given minimum and maximum value, whereby for a comparison with each other all comparison results for a screwing process are logically linked and deviation of a signal from the associated band, determined by the associated minimum and maximum values, by means of the means (2) for logical comparison and a system error is indicated. Method according to claim 1, characterized in that a further second control electronics (MK) independent of said control electronics (MK) is used, which are supplied with control signals independent of said outputs of said sensors, namely a torque dependent and a rotation angle dependent control signal, and att. from the control electronics (KK, MK) is processed in a superior central logic device (2). Method according to Claim 1 or 2, characterized in that a parameter for the screwdriver's motor is used as the control signal. Method according to Claim 3, characterized in that in the case where the screwdriver is driven by an electric motor, its working current is used as a parameter. Method according to Claim 1 or 2, characterized in that the output signal from a control angle sensor (WK) is used as a parameter. Method according to Claim 1 or 2, characterized in that the output signal from a control torque sensor is used as a parameter. Method according to one of Claims 1 to 6, characterized in that a system error is marked by means of an optical indicator. Method according to one of Claims 1 to 6, characterized in that a system fault is indicated acoustically. Method according to one of Claims 1 to 8, characterized in that the acceptance window (FMK, FKK) delimited by the minimum and maximum values in a diagram described by one of two related signals (Fig. 2, Fig. 3) corresponds to the one in this diagram, when performing a "master" screw connection through the setpoint curve (I, II), is transmitted at each point of this setpoint curve and that in a subsequent screwdriving process a deviation from the acceptance zone (AKB) thus established at some point, any, on the curve is indicated and the screwing process is interrupted. Method according to one of Claims 1 to 8, characterized in that the space coordinate system defined in one of three signals is represented by the minimum and maximum values (AKK) associated with the signals corresponding to that in this space coordinate system when performing a "master". the screw-through curve should be transmitted at each point of this curve and that in a subsequent screw-drawing process deviation from the acceptance channel thus obtained at any point, at any point, on the curve is indicated and the screw-drawing process is interrupted. m;