EP0653259A1 - Method for setting blind revets and blind rivet nuts and setting apparatus for blind rivets and blind rivet nuts - Google Patents

Abstract

A description is given of a method for setting blind rivets and blind rivet nuts and of a setting apparatus, in which a tensile force is produced during a setting operation with the aid of an electric motor (3). During this process, the rivetting or setting operation is to be monitored without the need for additional mechanical components. For the purpose of monitoring the operation, the input current of the motor (3) is monitored with the aid of a circuit device which has a current-measuring device (8) that monitors the power consumption of the motor and is connected to an evaluation device (10). <IMAGE>

Description

The invention relates to a method for setting blind rivets and blind rivet nuts, in which a tensile force is generated with the help of an electric motor during a setting process, and a setting device for blind rivets and blind rivet nuts with a pulling mechanism driven by an electric motor.

Such a method and such a setting tool are known from DE 41 26 602 A2.

In the following, the term "blind rivets" is also intended to include the "blind rivet nuts" if these are not mentioned separately.

When installing blind rivets, a statement about the quality of the connections made with the blind rivets is desired or even necessary in many cases. In particular, it should be ensured that the blind rivets have been set with the necessary strength. If the tensile force was too low, there is a risk that the rivet connection will not be made with the necessary force has been. If the tensile force was too high, there is a risk that material has been damaged or, in the case of blind rivet nuts, that threads have been damaged.

From EP 0 454 890 A1 it is known to mount a force measuring device in the pulling mechanism of the device in translated devices, such as electrical, hydraulic, pneumatic or hydraulic-pneumatic setting devices, which ensures that the riveting tool works with a predetermined tensile force. The force measuring device can be designed as a strain gauge or as a pressure cell, both of which convert the mechanical tension into an electrical quantity. The setting processes are then evaluated and monitored electrically in each case by comparing the achieved and measured force values with setpoints stored in non-volatile memories. A disadvantage of this arrangement is that the strain gauges or pressure sockets required to record the forces represent additional components which require additional cabling or wiring. To make matters worse, they are arranged on the pull mechanism, that is, in an area that must be dismantled during the daily maintenance of the riveting equipment. This leads to an increased maintenance effort. There is also the risk that the measuring device or the measuring lines are damaged. Furthermore, a number of factors affect the evaluation of the measured values when using a strain gauge, since variables such as diameter, tolerances of the pulling mechanism, fluctuations in the elastic modulus of the materials between different production batches, temperature influences and the like directly influence the measurement result.

US 5 105 719 shows a hydraulic riveting device for positioning a tool that forms a rivet head in a riveting machine. The mold is operated by a hydraulic cylinder. The hydraulic cylinder is connected to a motor via a ball screw drive, which in turn is connected to a controller. The torque generated by the motor and numerical values of the movement and the speed of movement of the motor are fed to the controller. The controller simultaneously controls the hydraulic pressure required to operate the hydraulic cylinder so that the torque generated by the engine remains zero.

Vogel, Johannes: Fundamentals of electrical drive technology with calculation examples, 4th edition, VEB-Verlag Technik, 1989, pp. 254-257 describes DC and three-phase drives powered by converters. Here are several examples of how information can be fed back to a converter or other controller.

EP 0 594 333 A1 describes a device for setting blind rivets, in which the load on the motor is monitored. After the pulling mechanism has reached a certain value, a moderate load must have been reached. If this is not the case, the device is stopped because an error is suspected in this case.

The object of the invention is therefore to achieve a monitoring of the setting processes in electrically operated setting devices without changing the mechanical structure.

This object is achieved in a method of the type mentioned at the outset by selecting a desired current range for the input current depending on the material and dimensions of the blind rivet or the blind rivet nut, and monitoring whether the actual input current reaches a maximum value during the setting process, which is in this target current range.

In the case of an electric motor, the current drawn is directly a measure of the torque given off by the motor, which is also referred to as torque. The relationship between the delivered torque and the input current does not necessarily have to be linear. For example, it can also be square. In any case, an input current is assigned to every moment and vice versa. The motor usually drives the pulling mechanism via a gearbox with a known transmission ratio, so that the torque given off by the motor can be converted into a pulling force relatively easily. The tensile force that develops during the setting process, in particular the maximum value of the tensile force, allows a conclusion to be drawn about the quality of the riveted joint. Since the transmission ratio between engine and traction device does not change, the tractive force does not have to be determined directly. It is sufficient to know the moment that occurred when the blind rivet was set. This moment can also be represented by the input current. Losses that occur in the setting tool due to friction, for example, are negligible in most cases. In cases where they reach significant sizes in relation to the setting force, they can be taken into account accordingly. The evaluation of the current consumption is relatively easy. In most of the electrically operated setting tools for blind rivets there is already a regulating and control electronics, which only has to be expanded for the purpose of current measurement. So there are no additional mechanical-electrical Measured value acquisition elements, such as pressure cells or strain gauges, are necessary, which represent potential sources of interference. Rather, information that is already present in the device, namely the current profile, is used as a criterion for evaluating the setting process. In principle, the entire current profile can be monitored during the setting process. In principle, only the maximum value from the force-displacement curve, which is described by the current-displacement curve, is important in order to assess whether the setting process went properly or not. In the case of blind rivets, the maximum value occurs when the rivet mandrel breaks. For blind rivet nuts, the maximum value also occurs at the end of the setting process. If the maximum value is not so large that it falls within the target current range, this is a sign of faulty riveting or of an error on the setting tool, which can be caused, for example, by the gripping device of the pulling device being worn and having slipped off the mandrel or, for example a rivet with insufficient setting force was used. If the maximum value is too large, this can be due to increased friction in the setting tool caused by dirt or the choice of the wrong rivet, which may have damaged the parts to be connected. In both cases, corresponding error messages can be issued and the user warned.

The setpoint current range is preferably temperature and / or input voltage compensated. The dependence between the input current and the torque delivered by the motor is temperature-dependent in some cases and / or depending on the input voltage. If, during operation, for example during an 8-hour shift, the motor warms up due to repeated actuation of the motor, temperature compensation can ensure that the temperature increases do not generate false or unnecessary error messages. The same applies to the course of the input voltage, in particular in the case of motors operated by batteries or accumulators, in which the input voltage drops during operation, depending on the state of charge of the battery or the accumulator.

To determine the target current range, it is provided in an advantageous embodiment that the target current range is determined by one or more sample riveting under conditions that are comparable to those of a desired real riveting. This can be accomplished, for example, by taking samples on a sample and measuring the input current required. You can now check the quality of these sample rivets, for example also by means of a destructive material test, and use the determined values of the maximum current to determine a target current range which is used as an evaluation parameter in the following real rivets.

It becomes even easier if the current curve or at least one variable derived from it is stored during the sample riveting, this variable later being used to generate the target current range. In this case, the current profile or the quantity derived therefrom, for example the maximum value, does not first have to be read out, converted and re-entered. Rather, the current flow or the size can be direct can be entered into a memory which will later be used to output the target current range.

The power supply to the motor is preferably interrupted as soon as the input current reaches a predetermined maximum value. Such an operation is particularly advantageous when setting blind rivet nuts. When the predetermined maximum value is reached, it is ensured here that the blind rivet nut is stuck with the necessary force. On the other hand, the maximum value limits the tensile force so that the thread is not damaged.

The possibly current and / or voltage compensated input current profiles or variables derived therefrom from successive setting processes are preferably stored. In many production areas, two or more parts are connected not only via a rivet, but via a large number of rivets. By saving and later evaluating the stored results, one can now make a statement as to whether a sufficient number of riveted joints have been made with the necessary quality. In addition, it is also possible to make a statement about the maintenance requirements of the device by continuously saving the current curves or the derived quantities. If you find, for example, that the maximum values increase continuously, this is a sign of increasing pollution. On the other hand, if it is found that the maximum values repeatedly do not reach the target current range, this is a sign that the pulling mechanism, in particular its gripping mechanism, is worn out.

The input current profiles or the quantities derived therefrom are preferably classified here, only the number of events per class can be saved. This considerably reduces the storage requirements without losing essential information.

The object is achieved in a setting tool of the type mentioned at the outset in that a circuit device is provided which has a current measuring device which monitors the current consumption of the motor and is connected to an evaluation device, the evaluation device having a comparator.

As mentioned above, the current drawn by the motor allows a direct statement about the force exerted by the pulling device, which in turn allows conclusions to be drawn about the quality of the rivet connection or the seat of the blind rivet nut. The evaluation device can display the quality immediately after each setting operation, for example as satisfactory or as unsatisfactory. It can provide information on a malfunction of the setting tool or the need for maintenance or repair. It is therefore not necessary for the input current to be continuously recorded and discretized in terms of numbers or values. One only has to monitor whether the input current reaches a certain threshold or not. If the threshold has been reached, this is a sign that the setting process has proceeded satisfactorily.

The comparator is preferably connected to a threshold value transmitter which outputs one of at least two threshold values which can be preselected from the outside. The threshold values can be selected, for example, as a function of the rivet material used and / or the rivet size. For example, blind rivets made of aluminum require a different pulling force than those made of steel. By being able To select one of several threshold values depending on the blind rivets to be set, the setting tool can be used for a large number of blind rivets.

It is preferred here that an engine temperature meter and / or an engine voltage meter are provided, which are connected to the threshold value transmitter, the threshold value transmitter changing the preselectable threshold value depending on the engine temperature and / or engine input voltage. Only the threshold value for a specific temperature and / or voltage state of the motor is therefore specified. If the temperature or the input voltage changes, the threshold value is adjusted accordingly. For this purpose, the threshold value transmitter can, for example, have stored the characteristic relationships between the moment, the input current, the temperature and the input voltage in the form of curves or tables.

The threshold value transmitter preferably has a memory device in which various threshold values are stored. Each threshold value can correspond to a specific combination of material and size of the blind rivets.

It is particularly preferred here that the storage device is connected to a reading device which has a peak current meter, a buffer for storing a plurality of peak current values and a computing device for determining an average value and / or a tolerance band from the stored peak current values. This enables the threshold value required for the corresponding rivet connection to be determined in a simple manner during sample riveting, which threshold value can optionally be stored in the storage device with a predetermined tolerance band. Of the The value determined in this way can be called up and used later when a similar riveted joint is to be restored.

The comparator is advantageously designed as a window comparator. In this case, two threshold values or a pair of threshold values are necessary to form a window. The window represents the target current range. The maximum value of the current determined during the setting process must lie in this window. If it is too small, the setting process did not run with the necessary force. If it is too large, the setting tool is either dirty or damaged or the wrong rivet has been used.

A position sensor for the pulling mechanism is preferably provided, which is connected to the evaluation device. With the aid of the position sensor, the current profile can be determined at characteristic points, or the position sensor can be used to determine whether or not a predetermined current value has been reached within a certain range of motion.

In a preferred embodiment, the position sensor is designed as a limit switch. One can monitor here in a very simple manner whether the necessary current maximum has occurred in the course of the setting process, that is to say before the end position has been reached.

The invention is described below with reference to a preferred embodiment. Herein shows the only figure
is a schematic representation of a circuit arrangement of a setting tool.

A setting tool for blind rivets or blind rivet nuts has a schematically illustrated pulling mechanism 1, which is driven by an electric motor 3 via a gear 2.

The electric motor 3 is powered by a voltage source 4 when an operating switch 5 is closed by an operator.

A first switch 6 and a second switch 7 are arranged in series between the voltage source 4 and the motor 3, the function of which is explained below. Furthermore, a current measuring device 8 is arranged in the connection between motor 3 and voltage source 4. In the simplest case, this can be designed as a current-voltage converter. However, it is also possible for the current measuring device 8 to contain an analog / digital converter which provides the current values digitally.

The current measuring device is connected via a changeover switch 9 to an input of a window comparator 10. The window comparator is connected via a compensation device 11 to a setpoint memory 12, which in turn can be controlled via a keyboard 13.

The motor 3 has a temperature sensor 14 and a voltmeter 15, which are connected to the compensation device, as indicated by the lines T and U.

The window comparator 10 is connected to the second switch 7. The switch 7 opens in response to a signal from the window comparator 10.

In its end position, the pulling mechanism 1 closes a limit switch 16, which in turn closes the first switch 6 opens and emits a corresponding signal to the window comparator 10.

A display device 17 and a result memory 18, to which a classification device 19 can be connected upstream, are connected to the window comparator 10.

The other output of the changeover switch 9, which is not connected to the window comparator 10, is connected to a buffer store 20 which is connected to the setpoint value store 12 via a computing device 21.

The arrangement works as follows:
Using the keyboard 13, a setpoint value pair is selected from the setpoint value memory 12, depending on the size and the material of the blind rivet or the blind rivet nut to be set. This setpoint pair can have been previously entered via the keyboard 13. However, it is also possible to read this setpoint value pair, which defines a setpoint current range, into the setpoint value memory 12 in that the switch 9 is switched to the position shown in dashed lines in one or more sample rivets and the one measured during riveting with the aid of the current measuring device 8 Current course of the motor 3 is stored in the buffer 20. In many cases it will also suffice to store the maximum value of the current in the buffer store 20. The computing device 21 forms the target current range from the values determined during sample riveting, ie it sets the upper and lower limits of the target current range for a specific type of rivet. This target current range is then stored in the target value memory at a position which was previously selected using the keyboard 13. There are for determining the target current range a variety of ways. For example, the computing device 21 can form the mean value from the values stored in the buffer. From this mean value, the upper or lower limit of the target current range is then created by adding or subtracting a tolerance value. The tolerance range can also be determined by evaluating the scatter during sample riveting.

The pair of values read from the setpoint memory 12, which defines the setpoint current range, is fed to the compensation device 11. The compensation device 11 converts the setpoints as a function of the motor temperature T and the motor voltage U, so that the window comparator 10 is supplied with threshold values which correspond to a current range in which the necessary tractive force is also present at the temperature T prevailing in the motor and the current motor voltage U. is exerted on the blind rivet or the blind rivet nut.

The operating mode can also be selected via the keyboard 13, for example whether blind rivets or blind rivet nuts should be set.

If blind rivet nuts are used, other evaluation criteria are sometimes to be used. Since there is no tearing of a rivet mandrel and therefore no sudden drop in the motor current when setting blind rivet nuts, a maximum current must be defined which must be achieved but not significantly exceeded in order to achieve a setting process of the required quality.

This maximum current is of course also dependent on the blind rivet nut used, i.e. on its size or material. In this case, the window comparator 10 indicates an operation signal the second switch 7 as soon as the lower threshold is reached. The second switch 7 opens and thus interrupts the setting process. Since the interruption occurs exactly at the moment of the highest moment and therefore at the moment of the highest force, it is ensured that the blind rivet nut has been set with sufficient strength. Since the maximum current is limited, tearing of the threads is prevented.

For all setting processes, the limit switch 16 can be used to assist in monitoring the setting process. In the case of blind rivets, the maximum value of the current must have been reached before the limit switch 16 is actuated. With blind rivet nuts, you can set a predefined pulling path, for example by means of adjustable stops. Then the maximum value must be reached almost exactly when the limit switch 16 is actuated. It can then be determined whether or not the current value is in the target current range when the limit switch is actuated.

Various evaluations can be carried out via the result memory 18. On the one hand, statements about the need for maintenance of the setting tool can be made here. If the maximum current values rise over time, this can be attributed to increasing contamination of the device, which requires higher friction and thus an increased effort on the part of the motor. If there are a large number of rivets in which the target current range has not been reached, this indicates wear on the gripping mechanism. In this case, the gripping mechanism slips off the rivet without the rivet being set correctly.

In many cases it is not necessary to save the respective maximum value yourself. You can rather Classify the respective maximum values into different classes via the classification device 19 and only store the number of events per class in order to save storage space. In the simplest case, three classes will suffice, namely a class in which the target current range has not been reached, a class in which the values are in the target current range and a class in which the values are above the target current range.

By refining the division of the target current range into different sub-ranges, the statements can be further specified and statistically evaluated.

Claims (15)

Method for setting blind rivets and blind rivet nuts, in which a tensile force is generated with the help of an electric motor during a setting process, characterized in that a target current range for the input current is selected and monitored depending on the material and dimensions of the blind rivet or the blind rivet nut, whether the actual input current reaches a maximum value during the setting process that lies within this target current range. A method according to claim 1, characterized in that the target current range is temperature and / or input voltage compensated. Method according to claim 1 or 2, characterized in that the target current range is determined by one or more sample riveting under conditions which are comparable to those of a desired real riveting. Method according to Claim 3, characterized in that the current curve or at least one variable derived therefrom is stored during the sample riveting, this variable later being used to generate the target current range. Method according to one of claims 1 to 4, characterized in that the power supply to the motor is interrupted as soon as the input current reaches a predetermined maximum value. Method according to one of claims 1 to 5, characterized in that the optionally current and / or voltage compensated input current profiles or variables derived therefrom from successive setting processes are stored. Method according to Claim 6, characterized in that the input current profiles or the quantities derived therefrom are classified, only the numbers of events per class being stored. Setting tool for blind rivets and blind rivet nuts for carrying out the method according to one of claims 1 to 7 with a pulling mechanism driven by an electric motor, characterized in that a switching device is provided which monitors the current consumption of the motor (3) and with an evaluation device (10 ) connected current measuring device (8), the evaluation device having a comparator (10). Setting tool according to Claim 8, characterized in that the comparator (10) is connected to a threshold value transmitter (11, 12) which outputs one of at least two threshold values which can be preselected from the outside. Setting tool according to Claim 9, characterized in that a motor temperature meter (14) and / or a motor voltage meter (15) are provided which are connected to the threshold value transmitter (11, 12), the threshold value transmitter (11, 12) depending on the preselectable threshold value changed by motor temperature (T) and / or motor input voltage (U). Setting tool according to claim 9 or 10, characterized in that the threshold value transmitter (11, 12) has a memory device (12) in which various threshold values are stored. Setting tool according to Claim 11, characterized in that the storage device (12) is connected to a reading device (20, 21) which has a peak current meter (8, 20), an intermediate store (20) for storing a plurality of peak current values and a computing device (21) for Determination of an average value and / or a tolerance band from the stored peak current values. Setting tool according to one of claims 8 to 12, characterized in that the comparator (10) is designed as a window comparator. Setting tool according to one of claims 8 to 13, characterized in that a position sensor (16) for the pulling mechanism (1) is provided, which is connected to the evaluation device (10). Setting tool according to claim 14, characterized in that the position sensor (16) is designed as a limit switch.

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