DE19620782A1 - Screw connection prodn. method by turning screw element using electric driven screwdriver - Google Patents

Abstract

The method involves using an electrical driven motor which is designed so that the torque curve per unit time is detected by an electronic unit. After the rise of the gradient the first redn. of rise is recorded. Following a successive increase of gradient and then following a second redn. of the gradient rise, a switch off of the electrically operated screwdriver (1) results. The switch off is activated at the latest with the beginning of a fall in the gradient. A curve over the time and/or over a rotation angle of the screw connection is determined as a torque curve per unit time. The gradient is determined as a deduction. A screwdriver electronic circuit (5) and a rotational angle measuring system (3) determine the torque per unit time and activate a switch off of the screwdriver with the identifying of a faulty thread.

Description

The invention relates to a method for producing a screw connection according to the upper Concept of claim 1 and a device therefor according to the preamble of the claim 13.

In manual assembly in large series production are used for screwing sheet metal screws or self-tapping screws, especially up to screw sizes M8 preferably battery-operated retail electric screwdriver (cordless screwdriver) used. These Screwdriving tools, usually in the form of pistols, have the following advantages:

• - they do not need a disturbing supply line that hinders the work process,
• - they are easy to use,
• - screwing points that are difficult to reach can be screwed unhindered,
• - There is no risk of damage to sensitive parts from supply lines (e.g. Paint damage to vehicles),
• - The risk of accidents or other people's disabilities caused by the supply line is avoided.

In addition, the use of these tools is widely accepted. The benefits however, there are also some problem points. For example, a con troll the screwing results with regard to screwing time, torque and / or angle and Accordingly, automatic documentation of the tightening result is hardly possible Lich. In addition, the cordless screwdrivers only have one speed for screwing in and Tightening the screw connection specified, resulting in poorer screw results in Compared to electronically controlled electric screwdrivers. A speed reduction when tightening by the worker himself is due to the fast speed with which the screw connection is hardly possible. Add to that this battery So far, screwdrivers have not monitored thread forming or the screwing process have to over-tighten especially with self-tapping or self-tapping To avoid screws.

The last point in particular is problematic because when screwing tapping screws or self-tapping screws in thin sheets with a motor-driven screw mechanism  In practice, it is always seen as over-tightening (pulling out the nut thread) comes from screwdrivers that are not optimally adjusted. But even if the setting is correct it due to the spread of the friction coefficients and the screw geometry as well as the Hole diameter overtighten the screws, or the specified Torques cause the screwdriver to switch off before the screw is screwed in or the thread is formed. In addition, there are several in one production section various screwing operations are carried out, for example sheet metal or Self-tapping screw connections inside the vehicle. If different maximum Torques are required, this leads either to the need to replace the Cordless screwdriver or for an individual torque adjustment. Due to the large number of screw connections with different properties such as Sheet thicknesses, screw-in lengths, materials and surfaces, however, are numerous differently adjusted screwdriver required. Because of the quick screwing in a screw, it is also not possible for the worker to screw a screw through to prevent the screwdriver from being overturned manually, if The torque on the screwdriver is too high. By swapping the This can lead to expensive repair measures due to over-tightened screwdrivers Screws come.

The object of the present invention is to design a screwing method in such a way that one tool different screws and screwdriving cases without re-adjustment can be screwed. The task is also a device as described above is to equip accordingly.

In the method described at the outset, the object is achieved by the features nenden measures of claim 1. With regard to the device, the task at Device described in the introduction solved with the characterizing features of Claim 13.

In the method, a screw connection is made by screwing in a screw element, for example a screw, in particular a sheet metal screw, by means of an electrically driven screwdriver (electric screwdriver), being made by electronics (electronic control) the torque of the screwdriver is monitored. this happens by evaluating the current flowing when driving the screwdriver, which is proportional to the Torque is. According to the invention, the evaluation is carried out in such a way that the electronics the slope of the time course of the torque is detected. After one A certain, predetermined torque curve is switched off by the electronics of the screwdriver, the gradient being the first during a screwdriver operation  an increase, a decrease in the increase, then an increase in the increase or a new increase and then a decrease in the increase or renewed Must have gone uphill. The shutdown can be done immediately with the last Verrin gradient is triggered, the shutdown advantageously takes place at the latest Beginning of a drop in the gradient (negative first derivative). Very advantageous the switch-off takes place when 70% to 10% of the last measured maximum is reached value of the slope and especially when 50% to 20% of this value is reached.

A linear course over time can also be a different time dependent size, such as the angle of rotation of the screw spindle or Screw connection (also indirectly via a screw drive) can be detected. Control technically particularly simple, the gradient is recorded as a derivative that the slope of the Reproduces gradients in each point. The reductions can accordingly can advantageously be detected as the second derivative (inflection point) of the gradient. To small ones To iron out fluctuations in the torque curve, the recorded values Advantageously performed via a low-pass filter to avoid malfunctions. The low pass file ter is matched to a conventional screwdriver process and can be a soft, for example be filter.

Depending on the screwdriving insert, the degree of reduction in the first increase in the gradient can be can be specified. For example, it can be specified that a small ne shoulder in the torque curve to meet the first three criteria of the gradient history is sufficient. It can be used, for example, for thread-forming screws Sheet metal also be set to reduce the first increase (second criterion) must include a decrease in the torque curve.

According to the invention, the torque curve or individual values thereof, such as Max. Thread forming torque, final torque reached, from which conclusions can be drawn the screw connection with regard to the thread formation and also the nut thread formation can be drawn, stored in a memory. The filed Values can be evaluated immediately or later to release the counterpart standes, whereby the method according to the invention in particular in a band assembly is used advantageously. A variety of screwdrivers can also be used with a centra len unit can be networked, this networking online, for example by IR-Über transmission or by reading stored screwdriver values on the central unit can be done.  

If different switch-off criteria are desired, switching can be advantageous The values are changed by changing appropriately prepared screwdriver bits.

If desired, the screwdriver can be advantageous in the method according to the invention also to a conventional screwdriver, possibly with torque detection and -Shutdown are switched, preferably also when using the invention According to the method, a torque cut-off can be activated, so that even when Errei high torque, the screwdriver is switched off. This can happen with for example, be used advantageously when very high thread forming Torque values can occur which increase the risk of the screwing element turning off bring (the screw) with it. With such a shutdown can then at this Screw connection either screw elements with a smaller diameter (A lower Torque when thread forming) or reinforced screws will. The interruption of the power transmission when a predetermined rotation is reached For example, a mechanical clutch can, for example, in particular also done via the electronics by measuring the screwdriver current.

In a further preferred embodiment, before the switch-off point is reached Screwdriver reduces the speed of the screwdriver so that towards the end of the screw connection the screw connection is screwed in more slowly. This will result in better setting behavior the screw connection and / or a more precise determination of the switch-off point.

Self-tapping and / or thread-forming are advantageous when screwing Screw elements screwed in. The screw connection is also advantageously done by hand operated screwdrivers, in particular cordless screwdrivers. Other preferred measures are described below for the device.

The electric screwdriver belonging to the invention has means, in particular electronics or electronic circuit that when screwing a screw element, for example a Screw and in particular a self-tapping and / or thread-forming screw be, an effective torque by evaluating one when driving the electric screwdriver determine flowing current. According to the invention, these agents record a time Torque curve and loosening a shutdown of the electric screwdriver after one determined gradient course during a screwing process. This predetermined Gradient course has the following criteria:

• Gradient increase,
• - reducing this increase,
• Increase in the gradient or increase in the gradient again,  
• - decrease in increase or increase again.

The gradient itself or its evaluation is advantageously carried out using a low-pass filter, so that Glitches or small fluctuations are not registered. The reduction of Increase is advantageously determined via the second derivative of the torque curve, the extent of this reduction is advantageously determined as a criterion. So at for example, a certain time and / or a rotation for the first reduction as a criterion angle of the screw element and / or a degree of change in the slope be determined. If this is not the case, an error message is either issued ben or the reduction is not recognized as such. The extent of change in the stei supply can be advantageous in the first reduction of the increase as a decrease in the Torque and at the second reduction as a value up to the maximum value of the Torque can be selected.

In addition, the electric screwdriver, which is advantageous as a handheld screwdriver and in particular is designed as a cordless screwdriver, other features, such as a speed reduction before triggering the shutdown or a mechanical torque limit contain. These individual configurations have already been described above in the method.

The invention is described below using an exemplary embodiment and two drawings gene described in more detail.

Show it

Fig. 1 shows a schematic electric screwdriver with a control unit; and

Fig. 2 shows a torque curve according to the invention.

The electric screwdriver 1 shown in Fig. 1 is composed of an electric motor 2, a Drehwinkelmeßvorrichtung 3, a screwdriver spindle 4, an electronic circuit 5 and a battery block 6. In addition, there is a stationary control unit 7 , which is connected to the cordless screwdriver 1 wirelessly 8 , for example via infrared light. The rotary angle measuring device can, for example, be optoelectronic. The screwdriver 4 is powered by the electric motor 2 and is driven by the battery block 6 , the following screwing process taking place in a controlled manner via the electronic circuit 5 in conjunction with the angle of rotation measuring device 3 . After switching on the cordless screwdriver via a hand switch (not shown), the electric motor 2 rotates a screw (not shown) at high speed (approx. 300-900 rpm) during the screwing-in phase in order to produce the screw connection. While screwing in, the torque on the screwdriver 4 is determined in the electronic circuit. At the same time, the angle of rotation (via the angle of rotation measuring device 3 ) and / or the screwing time is also recorded. Towards the end of the tightening phase of the screw connection, the electronic circuit 5 automatically reduces the speed of the electric motor 2 (to approximately 50-300 rpm, in particular 50-100 rpm) in order to achieve a more precise shutdown, as a result of which the screw connection is set reduced and fluctuations in the coefficient of friction of the screw connection are kept to a minimum. In the electronic circuit 5 , the recorded screw values are also stored in a memory module with regard to torque and angle of rotation and passed on to a stationary control unit for evaluation.

In the case of a strip assembly, such screw values are advantageously transmitted to the stationary control unit 7 from which the receipt of a correct screw connection can be determined. After receiving the corresponding screwdriver values, the stationary control unit 7 then releases the object for further transport through the belt and / or a warning signal (acoustically and / or visually) with regard to the correct and / or incorrect number and / or quality of the screw connections.

During the tightening phase of the screw connection, the diagram shown in FIG. 2 is recorded and evaluated in the electronic circuit 5 . The integrated screwdriver electronics 5 recognizes and differentiates the joining or thread forming torque 9 from the tightening torque 10 . This ensures that the screw connection is carried out correctly even when the screwing moments 9 are greater than the switch-off or tear-off moments 10 . In the case of pure torque detection, the screwdriver would either already break off the screw connection during the joining process 9 or overtighten the screw. The electronic circuit 5 recognizes the joining moment 9 as an increase 11 in the torque M, a decrease 12 in the increase 11 and a decrease 13 in the torque M. The reduction can optionally be detected, so that a shoulder is also recognized as the joining moment 9 . The joining moment 9 is thus recognized independently of the torque M, so that problem screw connections 14 with a particularly high torque M are also processed. If necessary, a particularly high torque can be specified here as a switch-off torque for securing, for example, the screw element against twisting. After the reduction 13 of the torque during thread forming 9 , the electronic circuit 5 detects a renewed increase 15 and a reduction 16 of this renewed increase 15 . In the reduction 16 there is also the beginning of the nut thread deformation 17 . Through this automatic recognition of the beginning of the nut thread deformation 17 of the wrench 1 can also be without predetermined Drehmomentabschaltwerte off in time 18, so that here too Problemverschrau exercises 19 in which the nut thread is mized DEFOR even at a low torque, detected and are screwed.

The detection of the torque in the electronic circuit 5 takes place via the angle of rotation α, which, for a known screw length, can also contain, for example, additional switch-off moments for further securing the screwing process. A shutdown can also take place here on the basis of a predetermined number of revolutions of the screw, measured in part from a characteristic point in the torque curve, such as the turning points, the maximum or minimum. The reduction of the screwdriver speed towards the end of tightening 10 can also take place, for example, by determining the turning point in this area (transition from renewed increase 15 to reduction 16 ).

This method or the screwdriver works largely independently of the screw size and from the screwdriving case and thus switches automatically at maximum or at one given torque curve.

With the invention with a handheld screwdriver for thin sheet or plastic screw connections achieved the following:

• - Different screws and screwdriving cases can be done with one tool without having to reset screwed with optimal tight fit;
• - Different speeds (fast screwing in, slow tightening) can occur be given with the success of a tightening time reduction and improvement by more precise switch off,
• - Integrated electronics control and monitor the torque, the angle of rotation and the screwing time,
• - The screwdriver results can be saved and after screwing to a sta Ordinary control unit for evaluation and / or documentation are transmitted,
• - Parameters for various screw connections can be saved in the tool become,
• - Several cordless screwdrivers can be used in a network (monitoring several Cordless screwdriver during assembly, in particular final assembly, the cordless screwdriver  For example, different bits are advantageous for different screws are laid),
• - The two tightening phases, thread forming and final tightening, are separated controlled; a separate torque (current) occurs during thread forming - Evaluation, whereby higher torques can be accepted than in the later one Tightening phase,
• - The detection of the thread forming is done by a comparison of increasing to falling or slightly increasing torque (current),
• - The beginning mother deformation is recognized by forming a Current / angle of rotation quotient or time quotient; the quotient formed is reduced by a predetermined amount of the measured maximum value, the screwdriver stopped.

The invention is advantageously used in automobile construction, advantageously in final assembly and especially when installing dashboards and connected to the body / body those parts.

Claims (19)

1. A method for producing a screw connection by screwing in a screw element by means of an electrically driven screwdriver, an electronics acting on the screwing element when screwing in the torque is determined by evaluating a current flowing when driving the screwdriver, characterized in that the electronics a torque curve over time is recorded as a gradient, that after an increase in the gradient a first decrease in the increase is registered, and that after a subsequent increase in the gradient and a subsequent second decrease in the increase, the screwdriver is switched off. 2. The method according to claim 1, characterized in that the shutdown at the latest is triggered at the beginning of a drop in the gradient (negative first derivative). 3. The method according to claim 1 or 2, characterized in that as a temporal Torque curve is a curve over time and / or over an angle of rotation Screw connection is detected. 4. The method according to any one of the preceding claims, characterized in that the gradient is recorded as a derivative. 5. The method according to any one of the preceding claims, characterized in that the respective reduction is registered from a turning point of the gradient. 6. The method according to any one of the preceding claims, characterized in that screwing in with values of the torque curve over time, if necessary is stored in a memory. 7. The method according to any one of the preceding claims, characterized in that one or more screwdrivers can be networked with a central unit.   8. The method according to any one of the preceding claims, characterized in that different values of the second reduction to trigger the shutdown of the Screwdriver can be specified. 9. The method according to any one of the preceding claims, characterized in that a maximum torque on the screwdriver can be set at the Also achieve a shutdown of the screwdriver, in particular an undersize force transmission to the screw element is triggered. 10. The method according to any one of the preceding claims, characterized in that as a screwdriver, a hand-operated screwdriver, in particular a cordless screwdriver is set. 11. The method according to any one of the preceding claims, characterized in that before switching off the screwdriver triggered by the second reduction in the There is an increase in the screwing element's rotational speed. 12. The method according to any one of the preceding claims, characterized in that screwed a self-tapping and / or thread-forming screw element becomes. 13. Electric screwdriver with means which, when a screwing element is screwed in, determine the torque by evaluating a current flowing when driving the electric screwdriver, characterized in that the means ( 3 , 5 ) detect a temporal torque curve ( FIG. 2) as a gradient, and that the means ( 3 , 5 ) trigger a shutdown ( 18 ) of the electric screwdriver ( 1 ) after they have registered the following gradient course during a screwing-in process:

• Gradient increase ( 11 ),
• - reducing this increase ( 12 ),
• Increase in gradient or increase in gradient again ( 15 ),
• - reducing the increase or increase ( 16 ).

14. Electric screwdriver according to claim 13, characterized in that the means ( 3 , 5 ) trigger the shutdown ( 18 ) of the electric screwdriver ( 1 ) at the latest when a gradient begins to decrease after the decrease in the increase or the renewed increase. 15. Electric screwdriver according to claim 13 or 14, characterized in that the zeitli che torque curve a curve over time and / or over an angle of rotation (α) of the screw element. 16. Electric screwdriver according to one of claims 13 to 15, characterized in that the means ( 3 , 5 ) detect a derivative of the torque curve as a gradient. 17. Electric screwdriver according to one of claims 13 to 16, characterized in that A memory is provided for recording values of the torque in time course. 18. Electric screwdriver according to one of claims 13 to 17, characterized in that this is a handheld screwdriver, in particular a cordless screwdriver. 19. Electric screwdriver according to one of claims 13 to 18, characterized in that it has a speed reduction before triggering the shutdown ( 18 ).