DE102007024627B3 - Method for detecting and controlling the jointing or loosening of a fastener, and device for carrying out the method - Google Patents

Abstract

The The present invention relates to a method and an apparatus for optimized joining of Fastening means, wherein by forming the difference quotients ΔL / Δt or ΔL / Δφ the absolute Location of the fastener or a head arranged thereon relative can be determined for recording.

Description

The The present invention relates to a method of joining or Solve one Fastening means according to claim 1 and a device for carrying out this Method according to claim 8.

Joining process, in particular screwing, are well known in practice. At the usual automated screwing operations put a screw in one for that provided recess screwed a recording. this happens typically with a corresponding tooling device.

For such Devices or methods are also known to be known by way of or depth signals to detect the screw-in depth of the screw and monitor. This is to ensure that the screw only up to a certain screwing depth with a predetermined speed or a predetermined torque is screwed. It is still known the detection of torque over suitable torque sensors or the motor current. This can do that Tightening torque of a screw derived or determined or limited. Also, the detection of the angle of rotation when screwing a screw in itself is known.

From of particular importance in such Einschraubverfahren is the Head rest. Below is the touch of a screw head to understand with the screw receiving receptacle. Reached the screw head during a screwing this support position, so lets screw in the screw just a little further, and that Torque rises quickly. In the prior art, it is therefore required to grasp the screwing depth of the screw to the Detecting the position of the screw head relative to the receptacle predict. For example, a screw with an increased speed be screwed in just before the head rest, in order to subsequently with tightened down at a reduced speed. The speed changeover serves the process optimization. It is due to time reasons to the latest possible Time before a rise in torque. On the other hand must be ensured be that the speed change takes place in time, that not with too high speed over the time of the headrest bolted out and possibly an inadmissible high torque is applied. For this reason it is in the state the technique required, the exact location of the screw head relative to know or to determine for admission.

manufacturing and application-related component tolerances have a disadvantageous effect on the exact position determinations of the screw head - and thus on the joining process out. To take all component tolerances sufficiently into account, It is therefore necessary in practice so far, the speed changeover clearly before reaching the head rest, although this indeed only for the components with the largest error tolerances actually required. Because the speed change therefore usually earlier than actually required is done, unnecessarily long screwed down at reduced speed. This increases disadvantageously the cycle time. It is even conceivable that the component tolerances are so big that the complete screwing process be carried out at a reduced speed got to.

When alternative means for detecting the headrest is in practice a torque monitoring When increasing torque, it is assumed that that the screw has reached the headrest, with the screw already attracts. When using the torque as a criterion for the speed change this would have However, in a not realizable short time happen to the screw connection is not over bolt the target moment out. In addition, screws produce in non-pre-cut threads (self-forming or self-tapping Screws) an irregular and sometimes high torque even before reaching the head rest, so this criterion for speed switching does not make sense is to be used.

In order to the task is to set up a procedure to better determine the To offer head rest of a screw, which overcomes the aforementioned disadvantages. The object is still the provision of a device with the joining process under optimized detection of the headrest is feasible.

The Task is solved by a method according to claim 1 and an apparatus according to claim 8th.

The invention is based on the recognition that a joining or releasing movement of a fastening means relative to a receiving means receiving the fastener can be controlled and controlled particularly safe and accurate, if to a difference quotient ΔL / .DELTA.t or .DELTA.L / Δφ is used. ΔL let it be a path that covers the attachment means relative to the recording. Δt corresponds to the time unit required for this purpose. As an alternative to Δt, Δφ describes a rotation angle unit around which the fastening means rotates about its longitudinal axis while traversing the distance ΔL. By using this difference quotient, the disadvantages known from the prior art can be advantageously overcome and optimum joining movements for ensure each individual joining case individually. In particular, the problem of component tolerances is solved since different dimensions (for example of screws) can be taken into account individually with the aid of the difference quotient during the joining process and do not have to be calculated from the outset.

While at Difference quotient ΔL / Δt a speed and in particular a change the feed rate of the fastener monitored , the difference quotient ΔL / Δφ detects the advance of the fastener dependent on from its rotational movement, in particular therefore a Einschraubwinkels a screw. The advantage of using these difference quotients across from The prior art results essentially as follows:

.DELTA.L / .DELTA.t

One essentially constant value ΔL / Δt a substantially constant feed rate, with the a fastener inserted in a designated receptacle or off this led out becomes. If the fastener encounters an obstacle, so decreases or disappears per unit time Distance, so that the obstacle from monitoring this difference quotient can be recognized immediately. In the example of a screw then the Einschraubdrehzahl can be reduced immediately to the further screwing or the target moment more accurate and safer to drive at a lower speed. On the other hand deliver the the known prior art simple depth signals no reliable Value about it, whether head support is actually achieved at a certain screw-in depth, as screw-in depth and headrest - as described above - due to tolerances not in an exact relationship to stand by each other. While from the prior art so the head rest on the evaluation of the depth signal only "suspected" can through the inventive use of the difference quotient ΔL / Δt (in particular at preferably constant feed rate of the fastener) the headrest can be detected safely and independently of tolerances.

.DELTA.L / Δφ

This difference quotient covers a distance traveled per angle of rotation of the fastening means, which is also a typical application for a screw. A constant difference quotient ΔL / Δφ here again means a constant feed or return stroke speed of the fastening means. However, if, for example, a screw reaches the receptacle (head rest) with its head, then the screw does not return an additional travel ΔL in the case of a further (possibly minimal) rotational movement, so that the quotient ΔL / Δφ falls sharply or drops to zero. By monitoring the difference quotient ΔL / Δφ, in contrast to the prior art, the head support can also be reliably detected without tolerances, and this quotient offers a further advantage:
Since in a trouble-free screwing the path portion .DELTA.L is in a fixed ratio to the rotational angle .DELTA..PHI., It is also advantageously possible to work with different or arbitrarily running rotational speeds during the screwing-in operation, without influencing the difference quotient .DELTA.L / .DELTA..phi. Only when reaching the head rest of this relationship is disturbed, so that in particular a changeover of the screwing speed can be made by appropriate evaluation. By contrast, until reaching the head rest, it can be screwed in at an increased speed, thus speeding up and optimizing the process.

Compared to the prior art, the use of the difference quotient ΔL / Δφ is also characterized by being clearly superior to torque monitoring. It is known from the prior art to detect the headrest by an increase in the screwing torque (torque sensor or motor current). In fact, however, the headrest usually does not occur simultaneously with the increase in torque, but already before. The reason lies in a certain thread clearance between the internal thread of the receptacle and the external thread of the screw. When screwing the screw is typically on the screw head facing flanks of the internal thread and slides on this along the screwing in the depth. After reaching the head restraint, the screw first rotates by a certain angular share before the thread flanks of the internal thread of the receptacle facing away from the screw head are contacted by the screw thread. Only then does the actual tension between the screw head and the thread flanks arise with the consequent increase in torque. The monitoring of the screwing determined so not the actual head rest, but only the incoming tension state, the time of the head restion occurs. In the prior art, which closes from the increase in torque on the head restraint, therefore, the reduction of the A screw speed is inevitably with increasing torque and - depending on the absolute speed - may be too late not to screw beyond the target torque. By contrast, the detection of the head support according to the invention with the aid of the difference quotient ΔL / Δφ allows the changeover tion of the speed even before a significant tightening torque of the screw ever occurs. This ensures consistent and good manufacturing quality over the previously known method.

Of the Difference quotient ΔL / Δφ triggers beyond that Yet another problem of the prior art, in which Help of torque monitoring closed on the headrest. In stiff threads or self-forming or self-tapping screws, the torque varies sometimes considerably and can at overcrowding of a set limit value erroneously signal the headrest, although this is not given. By the invention reference the distance ΔL to the angle of rotation Δφ and its monitoring this error is safely excluded.

A simplest embodiment the method according to the invention for joining or releasing one Fastener, relative to an associated receptacle, looks at it prior to that, the fastener along a longitudinal axis via a path in the receptacle is introduced or removed from this. It should be compared to the Prior art, the control of the joining or release movement of the fastener relative to the recording using the difference quotient ΔL / Δt or ΔL / Δφ. As already mentioned, describes Δt the time unit or Δφ the rotation angle unit of around its longitudinal axis twisted fastener, during which the fastener covers the distance .DELTA.L relative to the recording.

To a preferred embodiment of the Procedure, the fastener is one with a thread provided screw, which for joining is screwed into the receptacle. This happens with at least one - preferably constant - speed. The use of a constant speed advantageously allows the alternatively use of the difference quotient ΔL / Δφ or also ΔL / Δt, since the latter at constant Speed up to the head rest also gives a constant value. For the Difference quotient ΔL / Δφ, this restriction applies Reason of temporal independence the distance ΔL from the rotation angle Δφ advantageously not anyway.

Even though the use of the prescribed difference quotient in general for joining methods can be used to advantage There is a particularly advantageous embodiment is a screw to use as a fastener with a head whose extension perpendicular to the longitudinal axis the screw is larger as the outer diameter of the screw thread. This results when screwing mandatory a headrest whose detection using the prescribed procedures is particularly easy and advantageous possible.

• a) Einschrauben der Schraube in die Aufnahme mit einer Einschraubdrehzahl,
• b) Wiederholte oder permanente Ermittlung des Differenzenquotienten ΔL/Δt oder ΔL/Δφ, und
• c) Bestimmung der Kopfauflage durch Überwachung des Differenzenquotienten ΔL/Δt oder ΔL/Δφ auf eine Wertänderung.

In order to determine the support (head support) of the screw head on a contact surface of the receptacle, the following method steps are provided according to the invention:

• a) screwing the screw into the receptacle with a screw-in speed,
• b) Repeated or permanent determination of the difference quotient ΔL / Δt or ΔL / Δφ, and
• c) Determining the head support by monitoring the difference quotient ΔL / Δt or ΔL / Δφ on a value change.

According to feature c) the difference quotient should be monitored for a value change to close on the head rest. The determination of the difference quotient can be cyclical or essentially permanent, so that changes of the difference quotient are immediately recognizable also in the millisecond range. Of course you can the determination of the difference quotient by suitable limit values or tolerances are matched to the respective joining process, which by specifying suitable parameters, for example in a Control unit, can be realized.

In continuation of the inventive process sequence, the Einschraubdrehzahl adapted according to the invention detected headrest - and in particular be reduced. Thus, the process meets the requirements, a temporally optimized joining process to offer, and to work each with optimum Einschraubdrehzahl. In particular, the adjustment of the screw-in speed after reaching the headrest can be done so fast (if necessary in fractions of a second), that the tightening torque described above when tightening the screw only occurs when the adjusted speed is already set or is given. As already described, this ensures that that the screw connection does not take place at an unsuitably high speed and for example, the target moment is exceeded.

Next the surveillance on reaching the headrest is the inventive method also for process monitoring significant. Thus, upon reaching a (largely arbitrary) screw-off criterion using the history or the current value of the difference quotient the status of the tightening state or process is determined and monitored become.

If, for example, a screw with a certain target torque is to be tightened, it can be monitored with the aid of the difference quotient whether the feed rate of the When the target torque was reached (and thus at shutdown), the screw was zero, ie the head rest actually existed. Only then, for example, a desired bias in the screw can be applied. This can largely be ruled out that a stiff screw, which has reached its target moment before head support, as a good fitting (IO) is classified. Such a case occurs, for example, when self-tapping screws, the diameter of the predrilled hole is too small or dirty, which can not be excluded for manufacturing reasons.

As a general rule let yourself Use the difference quotient to determine if a screw for example, makes an advance per rotation angle, so screwed further will or not, so stands or stuck. Also can be recognize it (if necessary also in connection with a depth measurement), whether a determined moment results from the headrest or for other reasons (for example, stiff Screw, other blockage).

• a) Antriebsmittel zum Fügen oder Lösen des Befestigungsmittels in seiner Längsrichtung entlang eines Weges in die Aufnahme oder aus dieser heraus,
• b) eine Steuereinheit zur Steuerung der Antriebsmittel,
• c) Sensormittel zur Erfassung einer vom Befestigungsmittel relativ zur Aufnahme zurückgelegten Wegstrecke ΔL, und
• d) Sensormittel zur Erfassung der Zeit Δt, während derer das Befestigungsmittel die Wegstrecke ΔL zurücklegt und/oder Sensormittel zur Erfassung des Drehwinkels Δφ, um welche sich das Befestigungsmittel während der zurücklegten Wegstrecke ΔL um seine Längsachse dreht.

A device according to the invention, which is particularly suitable for carrying out the method according to the invention, should accordingly have:

• a) drive means for joining or releasing the fastener in its longitudinal direction along a path in the receptacle or out of this,
• b) a control unit for controlling the drive means,
• c) sensor means for detecting a distance traveled by the fastening means relative to the recording distance .DELTA.L, and
• d) sensor means for detecting the time .DELTA.t, during which the fastening means travels the distance .DELTA.L and / or sensor means for detecting the rotational angle .DELTA..phi., around which the fastener rotates about its longitudinal axis during the distance traveled .DELTA.L.

According to the invention Control unit thereby formed to form the difference quotient ΔL / .DELTA.t or .DELTA.L / Δφ, whereby the above-described advantages over the prior art feasible are.

It It goes without saying that the specialist has suitable sensor means to provide the individual values (ΔL, Δt, Δφ) by the difference quotient to build.

Further advantageous embodiments emerge from the dependent claims.

following the invention will be explained in more detail with reference to a figure example.

there shows:

1 a schematic representation of individual measured values over time, and

2 an application of the method for a screw.

In 1 is a schematic representation of the course of typical sizes of a Verschraubungsverfahrens over time to recognize. The time axis t covers the range of largely trouble-free screwing a screw in the associated recording on the moment of the headrest (t _K ) addition, to the moment of torque increase due to the tension.

The top graph shows the torque curve. Evident is a slightly fluctuating torque to a substantially constant value. The variations can result, for example, from inaccuracies in the thread or ovality. The torque maintains this largely constant value until the screw head reaches the receptacle (head rest t _K ). Until the actual bracing occurs, the torque also retains its previous value over time t _K and increases steeply only upon entry of the actual bracing.

in the underneath graph is shown the angle of rotation, the over here the time has been applied and - at constant screwing speed - one idealized linear increase reflects.

The Screw depth L shown below runs (again at as constant assumed Einschraubdrehzahl) linearly increasing until the moment the headrest t. From then on, the screw does not go any further back, because the headrest blocks this.

Finally, in the bottom diagram, the difference quotient ΔL / Δφ or ΔL / Δt is shown. The course ΔL / Δt can be seen directly from the diagram above. The difference quotient remains constant as long as the depth of engagement increases in the same way as the time. If this ratio changes from t _K , the quotient ΔL / Δt changes substantially to zero. In conjunction with the diagrams for the angle of rotation, the depth of engagement L, the course of the difference quotient ΔL / Δφ, which also remains constant until the point in time t _K and decreases with reaching this headrest, is also obtained.

This change in the difference quotient ΔL / Δφ or ΔL / Δt can be used according to the invention for detecting the head support and overcomes the disadvantages described above State of the art.

2 shows a schematic representation of a possible application of the method according to the invention. In this case, a screw S is to be screwed into a receptacle A, wherein the screw S has a head K at its upper end. The screw S is to be screwed about its longitudinal axis Z with a rotation angle, wherein it covers a path L in the direction Z. By detecting path portions .DELTA.L in connection with rotational angle sections .DELTA..phi. Or time intervals .DELTA.L, the moment of the head support, that is, when the head K is seated on the upwardly facing support surface of the receptacle A, can be inventively determined and used to optimize such a joining process.

Claims (9)

Method for joining or releasing a fastener (S) relative to an associated one Receptacle (A), wherein the fastening means (S) along its longitudinal axis (Z) about a path (L) is introduced into or removed from the receptacle (A), in which the control of the joining or release movement of Fastener (S) relative to the receptacle (A) is under use of the differential quotient ΔL / Δt or ΔL / Δφ, where Δt one to detecting time unit and or Δφ is a rotational angle unit to be detected the around its longitudinal axis (Z) is twisted fastener (S), during those the fastening means (S) relative to a distance to be detected .DELTA.L returned for admission (A). Method according to claim 1, characterized in that that the fastener is a threaded screw (S) is which to join in the receptacle (A) with at least one preferably constant Speed (s) is screwed. Method according to the preceding claim, characterized in that the screw has a head (K) whose Extension perpendicular to the direction (Z) is greater than the outer thread diameter. Method according to the preceding claim for determination the support of the screw head (K) on a contact surface of Image (A), characterized by the following process steps: a) Screw the screw (S) into the receptacle with a screwing speed (N) b) Repeated or permanent determination of the difference quotient ΔL / Δt or ΔL / Δφ c) Determining the head support by monitoring the difference quotient ΔL / Δt or ΔL / Δφ on a value change. Method according to the preceding claim, characterized in that the screwing speed (s) is approximately constant and the determination of the headrest is done by monitoring of the difference quotient ΔL / Δt to one Value change. Method according to one of the two preceding claims, characterized characterized in that the screwing speed (s) after detected Edition of the screw head (K) adapted, in particular reduced, becomes. Method according to one of the three preceding claims, characterized characterized in that the course and / or the absolute value of Difference quotient ΔL / Δt or ΔL / Δφ for evaluation the bolted state is used, in particular by checking Reaching the head rest when entering any shutdown criterion. Device for joining or release a fastening means (S) relative to an associated receptacle (A), in particular for implementation the method according to any one of the preceding claims, comprising a) drive means for joining or release the fastening means (S) in its longitudinal direction (Z) along a Way (L) in the receptacle (A) or out of this, legs Control unit for controlling the drive means, c) sensor means for detecting one of the fastening means (S) relative to the receptacle (A) traveled Distance ΔL, d) Sensor means for detecting the time .DELTA.t, during which the fastening means (S) covers the distance ΔL and / or Sensor means for detecting the angle of rotation Δφ, around which the fastening means (S) during the laid back Distance ΔL to its longitudinal axis (Z) turns, e) wherein the control unit for forming the difference quotient .DELTA.L / .DELTA.t or .DELTA.L / Δφ formed is. Device according to the preceding claim, characterized characterized in that the control unit for determining the edition of the head (K) of a fastener designed as a screw (S) a contact surface recording (A) by monitoring of the difference quotient ΔL / Δt or ΔL / Δφ to one value change is trained