Technical Field

The present invention relates to an electronically- operated riveting machine, usable in particular for the clamping of threaded elements onto a metal sheet or a similar surface for the assembly of components.

Background Art

It has long been known that special tools have been used to tighten threaded elements conventionally used for the assembly of components by deformation on metal sheets or the like.

A first type of riveting machine of known type consists of a purely mechanical tool that can be operated manually.

Pneumatically-operated riveting machines have long been used to make the rivets tightening operations easier, faster and repeatable in series.

In particular, these pneuma tic riveting machines allow selecting the traction force to be applied to the rivet, a force that can vary significantly depending on the size and material of the rivet and on the element to be clamped (e.g., between 200 kg and 4000 kg).

Once the traction force has been selected, the pneumatic riveting machines allow the automatic tightening of the rivet by simply pressing on a special trigger.

In order to select the optimum traction force, the operator relies on their own experience and on known machining data, which can be found in specific tables and referred to the specific rivet. If necessary, the operator carries out a series of tests to determine the correct force for the tightening of the specific rivet.

In particular, the force to be applied can be set by adjusting a special air discharge valve.

Pneumatic riveting machines are however generally not easy to use.

In fact, the presence of the compressed air pipe, necessarily present on the pneumatic riveting machines, makes these difficult to use in different environments and situations of use.

To overcome such a problem, the use is known of electronically-operated riveting machines.

In addition to the improved handling thereof, the presence of an electronic actuator allows for a better control of the machining process and operational safety.

As with pneumatic riveting machines, electronic riveting machines also allow the preliminary adjustment of the pulling force. The adjustment is affected by the type of rivet and by the thickness of the part on which the machining is carried out, but also by the temperature and machining tolerances of the rivets themselves.

Also with reference to electronic riveting machines, the optimal force is determined by the operator by means of special reference tables and, if necessary, after a series of tests.

Specifically, the traction force value to be applied to the rivet can be set by means of a special potentiometer or by means of a dedicated menu on a display. All types of riveting machines of known type do however have some limitations.

In fact, the selection and setting of the optimal traction force is carried out manually by the operator and is based on data determined a priori and on the operator’s own experience. Therefore, the selected force may not actually correspond to the optimal one, with direct consequences on the quality of the machining.

In addition, the manual selection of the optimal force may require the execution of a series of clamping tests, resulting in loss of time that could be spent in the actual machining.

Description of the Invention

The main aim of the present invention is to devise an electronically- operated riveting machine that allows quickly and effectively adjusting the optimal traction force to be applied to the rivets.

Another object of the present invention is to devise an electronically- operated riveting machine which allows overcoming the aforementioned drawbacks of the prior art in a simple, rational, easy, effective to use and cost effective solution. The aforementioned objects are achieved by the present electronically- operated riveting machine according to claim 1.

Brief Description of the Drawings

Other characteristics and advantages of the present invention will be more evident from the description of a preferred, but not exclusive, embodiment of an electronically-operated riveting machine, illustrated as an indication, but not limited to, in the attached tables of drawings in which:

Figure 1 is a general diagram of a riveting machine according to the invention; Figure 2 is a block diagram that illustrates the operation of the riveting machine according to the invention;

Figure 3 is a graph that illustrates the operation of the riveting machine according to the invention.

Embodiments of the Invention

With particular reference to these figures, reference numeral 1 globally indicates an electronically-operated riveting machine, which can be used, e.g., for the clamping of threaded elements onto a metal sheet or a similar surface for the assembly of components.

The riveting machine 1 comprises at least one pulling element 2, supported by a tool-holder head, which can be operated for the traction of rivets, and actuating means 3 which are operatively connected to the pulling element 2 and adapted to actuate the pulling element itself between an initial tightening position and a final tightening position.

According to a possible embodiment, described in detail below, the riveting machine 1 is made up of an electronic riveting machine and the actuating means 3 are made up of an electric motor. In this case, the riveting machine 1 comprises a rechargeable battery 4 connected to the electric motor 3.

Different embodiments cannot however be ruled out.

For example, the riveting machine 1 may be made up of an electronically- operated pneumatic riveting machine.

Advantageously, the electronic riveting machine 1 comprises an automatic setting system 5 of the traction force applied by the actuating means 3.

In particular, the system 5 according to the invention allows improving the functionality and the correctness of the machining in the electronic riveting machines, making a setting of the optimal pulling force in a completely automatic manner and in real time.

The operating principle of the system 5 is based on the measurement and analysis in real time and during machining of the traction force applied by the riveting machine on a locking element to be clamped.

The system 5 according to the invention comprises at least one processing and control unit 6 operatively connected to the actuating means 3.

The system 5 also comprises direct or indirect measuring means 7, adapted to measure the traction force applied by the actuating means 3.

In particular, the measuring means 7 may be made up of the pressure gauge conventionally present on the riveting machines of known type or of a dedicated device.

For example, the measuring means 7 may be made up of at least one load cell operatively associated with the pulling element 2.

Depending on a further possible embodiment, in particular in the event of the riveting machine 1 being of the electronic type, the measuring means 7 may be made up of a unit of measurement of the current consumption of the electric motor 3.

Advantageously, the processing and control unit 6 is configured to calculate a value of final tightening force depending on the value of the traction force applied by the actuating means 3, measured in real time by the measuring means

7.

In particular, according to a preferred but not exclusive embodiment, the processing and control unit 6 is configured to perform at least the following steps described below and illustrated in the block diagram in Figure 2.

First, the processing and control unit 6 controls a first step 100 of start of tightening.

Specifically, the processing and control unit 6 activates the actuating means 3 to start moving the pulling element 2.

Then, the actuating means 3 are brought to a set traction speed.

By way of example, if we examine Figure 3, in particular the first stretch of the curve relating to the motor speed, the acceleration can be noted of the actuating means and the stretch at the set constant speed.

Specifically, the processing and control unit 6 controls the acceleration of the actuating means 3 until the set traction speed is achieved (steps 110 and 120). Advantageously, the processing and control unit 6 controls the measurement in real time by means of the measuring means 7 of the value of the traction force applied by the actuating means 3.

It is useful to compare the traction force applied by the actuating means 3 with a maximum force value, followed by an error message in the event of the applied traction force exceeding the maximum force value (steps 130 and 140).

In fact, during all the tightening phases it is also necessary to check that the traction force gradually achieved does not exceed the maximum force value established for the electronic riveting machine 1 , otherwise parts of the riveting machine itself will be damaged.

Advantageously, the processing and control unit 6 processes in real time the traction force value applied by the actuating means 3 (step 150), in order to determine a reference force value calculated by an appropriate algorithm (step 180).

In practice, therefore, once the set traction speed (or initial tightening speed) has been achieved, the processing of the measured traction force values begins. Processing continues until a precise threshold value calculated by a special algorithm is detected.

By way of example, in Figure 3 three waveforms are shown that represent the variation in time (in milliseconds) of the speed (graph Gl), of the traction force (graph G2) and of the position (graph G3), respectively, of the pulling element

2.

For the correct measurement, the pulling speed must be constant. In fact, in such conditions the necessary traction force has a trend like that illustrated in Figure 3, i.e. it grows with negative second derivative.

In particular, the function G2 expressing the waveform is concave up to the maximum deformation of the rivet. Specifically, the maximum deformation does not occur at a precise stroke value, as it also depends on the thickness of the material on which it is applied.

The maximum deformation occurs at the point where the slope of the traction force becomes maximum.

Taking specifically into consideration the example in Figure 3, it is possible to verify the following:

- a little inversion of the force at about 500 milliseconds indicates the moment at which the pulling element 2 begins the deformation thereof;

- at 700 milliseconds the tightening force is about 800Kg;

- subsequently, from 1350 milliseconds the traction force increases rapidly from 1250Kg.

This is where the rapid increase in the driving force begins. This is where the pulling element 2 is most deformed, is completely crushed on the support and, as a result, its resistance to deformation increases. From this point on, the deformation becomes excessive and could lead, in extreme cases, to the abnormal deformation of the pulling element 2.

According to a preferred embodiment, the processing in real time of the traction force value (steps 150 and 180) comprises at least the following steps:

storing a plurality of measured values of traction force;

selecting a first set of initial values out of the stored values of traction force; calculating an average start traction value as the average of the first set of initial values;

selecting a second set of final values out of the stored values of traction force;

calculating an average end pulling value as the average of the second set of initial values;

comparing the average end pulling value with the average start pulling value multiplied by a predefined constant (preferably 2.5);

when the average end pulling value exceeds the average start pulling value multiplied by the predefined constant, set the actual value of traction force as reference force value.

According to a possible embodiment, the stored values of traction force are the last 100 measured values of traction force, the first set of initial values comprises the first 70 values out of the stored values of traction force, while the second set of final values comprises the last 10 values out of the stored values of traction force.

Moreover, still with reference to this preferred embodiment, the default constant value is 2.5.

During processing, it is useful to compare the traction force applied by the actuating means 3 with a maximum value of force and to indicate an error message in the event of the applied traction force exceeds the maximum value of force.

The processing and control unit 6 calculates a value of final tightening force depending on the point of maximum increase variation (step 200).

Therefore, the point of maximum increase variation represents the reference force value for determining the final pulling force.

In particular, the calculation of the value of the final tightening force consists in increasing the reference force value at the point of maximum increase variation by a preset default percentage.

Preferably, this default percentage is comprised between 5% and 25% of the reference force value at the point of maximum increase variation.

Therefore, the tightening check must therefore identify the point of maximum deformation and allow inserting a percentage increase relative to the corresponding traction force in order to finish tightening correctly. This percentage, which can be comprised between 5 and 25% of the traction force achieved at the point in the inflection, allows finishing the tightening without abnormally over-deforming the rivet.

Subsequently, the processing and control unit 6 reduces the traction speed of the actuating means 3 until the final tightening force value has been reached (step 190).

During speed reduction, the traction force applied by the actuating means 3 is usefully compared with the final tightening force value (step 210).

Finally, the processing and control unit 6 carries out the end of tightening after achieving the final tightening force value (step 220). In practice, this end of tightening comprises the operations required to unscrew the rivet from the tie rod of the pulling element.

It has in practice been found that the described invention achieves the intended objects.

In particular, the electronically-operated riveting machine, according to the invention, allows automatically adjusting the optimal traction force to be applied to the rivets.