EP3342506B1 - Force gradient evaluation - Google Patents

Description

The present invention relates to a blind riveting method and a portable blind riveting device for carrying it out.

State of the art

Blind riveting processes are used to connect at least two components (joining partners). A blind riveting process is characterized by the fact that the components to be connected need to be pre-punched. A rivet is pressed into the hole and then the rivet mandrel is acted upon until it breaks off. Then the riveting process is finished.

Riveting devices of all kinds are known, but in industrial applications it is desirable to monitor each individual connection step, especially in order to meet the high quality requirements for the riveted connections.

From the DE 10 2013 112 363 A1 A blind rivet setting method is known in which at least, among other things, the force gradient is monitored in order to detect a break in the rivet mandrel and to be able to bring the pulling mechanism back into the starting position at an early stage.

Disclosure of the invention

According to the invention, a blind riveting method and a blind riveting device are proposed. Advantageous refinements are the subject of the subclaims and the following description.

A method according to the invention is defined in claim 1 and is used to connect at least two components using a blind riveting device. A portable blind riveting device with integrated control is used. This control is intended for self-sufficient device control, i.e. it can take over complex control processes for the blind riveting device without the need for a higher-level external blind rivet control, in particular quality monitoring processes and documentation processes, as well as measured value evaluations regarding individual device components. An integrated pulling mechanism is also provided for pulling on a mandrel of a blind rivet. The pulling mechanism is subjected to a force specified by the control, which is transmitted to the mandrel, with a force gradient being determined by the control at least temporarily, preferably continuously, during the pulling process. This can be a temporal gradient, i.e. force per time, and/or a local gradient, i.e. force per path.

In blind riveting processes, a force as a function of the position or path of the pulling mechanism can be used to assess the quality of the blind riveting process. For example, it can be examined whether the force curve is within certain limit values, for example a so-called envelope curve. If the yield point of the rivet mandrel is reached (elongation of the rivet mandrel), then it is shortly before it breaks off, and the gradient also drops. If the force gradient is now monitored by the control (continuously or according to predeterminable time periods), changes in the rivet mandrel can be recorded particularly advantageously and in a very simple manner and an impending tear-off process can be recognized and thus influenced.

According to the invention, particularly in industrial applications, it is possible to monitor each individual connection step in order to meet the high quality requirements for the riveted connections.

Preferably, the force gradient is determined during at least a selected time and/or distance range during the riveting process. This makes it possible, for example, to select the time or distance ranges in which experience shows that demolition is to be expected. This means that monitoring of the entire blind riveting process is not necessary.

Alternatively, it is also preferred if the force gradient is determined over the entire period of time or over the entire path of the rivet mandrel. This makes it more likely that the break point will be detected exactly, especially if, for example, a break occurs at an unusual position or at an unusual time.

The force gradient is advantageously determined by means of a time- or distance-dependent scanning. With time-dependent scanning, the force can be recorded at a certain frequency, for example, so that the gradient can be determined. With path-dependent scanning, the force can be recorded, for example, after every certain distance has been covered by the pulling mechanism, for example every 5 µm. With path-dependent scanning, for example, a low feed rate can be taken into account insofar as only a small amount of data is generated. For time-dependent sampling, for example, attention should be paid to a suitable frequency, for example 50 or 100 kHz, so that the amount of data is not too large, but a gradient can still be recorded with sufficient precision and thus a break can be detected.

The control carries out an action using the determined force gradient and in particular influences the pulling speed and/or pulling force. This is done depending on at least one gradient parameter and one train speed parameter. The gradient parameter particularly preferably defines a force gradient drop from which the action is carried out if a force gradient drop determined by the controller reaches the gradient parameter.

According to the invention, the train speed parameter defines a train speed change from which the action is carried out if a train speed change determined by the controller reaches the train speed parameter. By means of the control, it is possible to weaken the strong mechanical jerk that occurs with less innovative solutions when the rivet mandrel is torn off, because this jerk causes vibrations on the worker's wrist and on the device mechanics and can therefore contribute to premature wear. Advantageously, the control system detects a mandrel break ahead of time by means of the force gradient. Preferably, the control returns the pulling mechanism to a mechanical starting position at the latest when the mandrel break is detected, in particular before it is reached a mechanical end position. If the pulling mechanism is moved back to its mechanical starting position before reaching its mechanical end position, this saves process time because more riveting processes can now be carried out in the same time. It also saves electrical energy and protects the energy supply, e.g. battery, of the portable blind riveting tool.

In a further embodiment of the invention, the force gradient is preferably also used to detect a device defect and/or a problem in the blind rivet connection produced. Using the control, it is possible, for example, to detect wear-related changes in the train mechanics early and to initiate preventive maintenance work or to detect connections that do not conform to the specification very early in the process. The defect is preferably detected by comparing the force gradient with at least one force gradient threshold value stored in the controller. This makes it possible to define and communicate (even several) maintenance thresholds.

Such threshold values can be selected, for example, based on test or empirical values. A defect can then be detected if the gradient (in terms of magnitude) exceeds the threshold value. It can be taken into account that, for example, a defect can only be assumed from a certain value of the gradient. It is also understood that such threshold values are material-dependent and can therefore, for example, be specified or set each time the riveting device is used again, that is, can be specified by a user. In addition to the type of material, the thickness of the components to be connected can also be relevant. It is also conceivable that a distinction is made between different types of defects and/or defects in different components, for example a component and the rivet, by using different threshold values.

It is also conceivable that a detected defect is displayed on display means, for example a display. This means that a defect can be identified quickly and the corresponding components or rivet can be sorted out. An acoustic signal that indicates the detection of a defect is also conceivable. The blind riveting device is therefore preferably also provided in order to implement such signaling.

Particularly preferably, the force gradient is linked to an associated riveting process and stored in the blind riveting device, in particular even if a defect or connection error has been detected.

This makes it possible to document the riveting process and its quality (“logbook function”). For example, defects can be easily found or explained later in this way. In addition, such documentation is often required for industrial applications. It can also be useful to only carry out the linking and saving if a defect has been detected. This avoids unnecessary generation of data. In this way, it is also possible to determine the total number of defects that occur during a certain period of time, which makes it possible, for example, to draw conclusions about the quality of the components or rivets used. Using the control, it is therefore possible to document prevailing boundary conditions during the connection process. Using the control, it is also possible to document problems that occur during the connection process.

It is also advantageous if, in addition to the force gradient, a further method and/or a further quality parameter is determined for a quality assessment of a connection produced by means of an associated blind riveting process. The method or the quality parameter can be, for example, a force-distance or a force-time curve. In this way, a quality assessment of the entire blind riveting process can be carried out, which in particular also allows an assessment of other or additional factors of the blind riveting process in addition to the detection of the tear. In addition, redundant evaluation criteria are also possible in this way, at least in part. Two redundant evaluation criteria are often even required for reasons of process reliability. In addition, one can then take advantage of the fact that the force has to be recorded anyway for the force gradient.

With regard to the claimed portable blind riveting device, reference is made at this point to the above statements on the method according to the invention in order to avoid repetition.

A control program according to the invention is set up, in particular in terms of programming, to carry out a method according to one of the preceding claims when it is executed on the control of the blind riveting device.

The implementation of the method in the form of a computer program is also advantageous because this causes particularly low costs, especially if an executing control device is used for additional tasks and is therefore available anyway. Suitable data carriers for providing the computer program are, in particular, magnetic, optical and electrical memories, such as hard drives, flash memories, EEPROMs, DVDs, etc. It is also possible to download a program via computer networks (Internet, intranet, etc.).

Further advantages and refinements of the invention result from the description and the accompanying drawing.

It is understood that the features mentioned above and those to be explained below can be used not only in the combination specified in each case, but also in other combinations or alone, without departing from the scope of the present invention.

The invention is shown schematically in the drawing using an exemplary embodiment and is described in detail below with reference to the drawing.

Character description

• Figure 1 shows a force-position curve during a blind riveting process.
• Figure 2 shows a portable blind rivet setting device according to the invention.

Detailed description of the drawing

In Figure 1 an exemplary force-position curve is shown in a blind riveting process. In particular, a first gradient region 103, an evaluation zone 104 of the force F and a descending second gradient region 105 are shown.

A force F is plotted against a position or a path s in mm, within which the evaluation zone 104 falls. F(s) in kN indicates a curve of a force F that is exerted on the rivet mandrel to remove it, as a function of the position s of the pulling mechanism during removal. It should be noted that only a relative position s, i.e. the path traveled by the train mechanics, is relevant here.

It can be seen from the curve F(s) that an irregularity in the form of a drop in force occurs shortly before the break. Before that, the force changes from a positive slope to a negative slope relative to the distance s. dF can therefore be used to describe the decrease in force F during a path section ds. This means that there is a (local) gradient dF/ds here. The control takes over the determination of this gradient 103 and the comparison with a threshold value and thus coordinates the behavior of the device mechanics shortly before and/or during and/or after the demolition. It goes without saying that the gradient can be determined not only as a distance-dependent but also as a time-dependent manner. In order to implement the idea according to the invention, the drop 105 of the gradient is recognized by means of a computer program that can be executed on the controller and which carries out the claimed method.

In Figure 2 A hand tool 100 according to the invention is now shown roughly schematically in a preferred embodiment. By way of example, the hand tool 100 is designed as a battery-operated hand tool 100. The hand tool 100 has the following essential components: tool control 101 and pull mechanism 102. In addition, the following can be provided: protocol memory, data memory, energy interface for arranging a battery or a power connection, energy supply in the form of a battery, on/off switch, output for receiving a connecting means for Connecting components/workpieces, operating unit (display/keyboard). All of these components are preferably at least partially encompassed by a common housing.

This hand tool is preferably designed as a portable battery-powered blind riveting device. The tool control 101 is provided as an integrated, self-sufficient control that is set up to carry out a method according to the invention.

Reference symbol list

Motorized hand tool 100 Tool control 101 Train mechanics 102 gradient 103 Evaluation zone 104 Falling gradient 105

Claims (9)

1. Method for connecting at least two components by means of a handheld tool designed as a portable blind riveting device (100) with an integrated controller (101), provided for the autonomous device control, and with an integrated pulling mechanism (102), provided for pulling on a mandrel of a blind rivet, wherein the pulling mechanism (102) is subjected to a force which is predefined by the controller (101) and which is transmitted to the mandrel, characterized in that a force gradient and a pulling rate change are determined at least at times during the pulling process by the controller (101), wherein starting from a defined pulling rate change the controller (101) influences the pulling mechanism (102) on the basis of the force gradient, thereby weakening a mechanical jerk that occurs when the riveting mandrel breaks off.
2. Method according to Claim 1, wherein the controller (101) recognizes a mandrel break-off by means of the force gradient.
3. Method according to Claim 2, wherein the controller (101), upon recognizing the mandrel break-off, returns the pulling mechanism (102) to a mechanical starting position, in particular before reaching a mechanical end position.
4. Method according to any of the preceding claims, wherein the force gradient is also used for recognizing a defect with regard to the device and/or the blind riveting connection produced.
5. Method according to Claim 4, wherein the defect is recognized on the basis of a comparison of the force gradient with at least one force gradient threshold value stored in the controller (101).
6. Method according to any of the preceding claims, wherein the force gradient is linked with an associated riveting process and is stored, in particular even if a defect or connection fault has been recognized.
7. Portable blind riveting device (100), in particular rechargeable battery-powered blind riveting device, with an integrated pulling mechanism (102) for pulling on a mandrel of a blind rivet and with an integrated autonomous controller (101), which is configured to carry out a method according to any of the preceding claims.
8. Control program which causes the blind riveting device (100) with the autonomous blind riveting controller (101) according to Claim 7 to carry out a method according to any of the preceding claims.
9. Machine-readable storage medium with a control program according to Claim 8 stored thereon.

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