EP2149431A1 - Screw device with torque limitation - Google Patents

Abstract

The device has a rotary drive with a torque set point generator adjusting determined power consumption of an electric motor as torque set points relative to torque of the device. An input unit i.e. potentiometer rotary knob, adjusts the points in adjusting stages to select the points such that the drive is disconnected after obtaining the points as a preselected display torque of the drive. A torque limit unit is designed such that two torque difference values between the points are different for partially obtaining a non linear characteristic curve for the stages relative to the points.

Description

The invention relates to a screwdriver with torque limiter according to the preamble of claim 1.

A well-known screwdriver with torque limiter includes a controllable rotary drive with an electric motor and a torque setpoint generator associated therewith with an input unit, in particular as a potentiometer knob. The power consumption of the electric motor during a screwing corresponds linearly proportional to the current tightening torque of the screwing, especially when using a so-called universal motor as a collector motor with brushes and an armature and at least one field. To limit the torque, the torque setpoint generator is used to specify a specific power consumption in accordance with a tightening torque. After this torque setpoint is reached, the electric motor and thus the rotary drive is automatically switched off.

In a concrete embodiment of such a screwdriver ( DE-AS 23 26 027 ), the power consumption of the electric motor and thus a load torque is detected by measuring the voltage drop across a load resistor in the current path of the electric motor and Torque limitation compared with a reference voltage adjustable with a torque setpoint generator.

In a further known embodiment of such a screwing device ( DE 35 00 714 C2 In a phase-angle control, the torque limitation is realized in conjunction with a standstill detection, wherein different adjustable motor operating voltages are specified as torque setpoints and thus as tightening torques.

In addition, rotational position detections are known by a Hall sensor on the engine or by optical scanning of a toothed disc ring on a shaft part, with which a rotation angle follow-up path can be detected. Thus, a combined tightening of the screw is possible such that switches off after a certain set and determined pre-torque of the rotary drive after subsequent execution of a certain set rotational angle follower path.

The torque setpoints can be selected and specified in such power wrenches on the input unit in successive adjustment stages, using as an input unit to a rotary knob of a linear potentiometer is used. The setting levels are given on a ring scale around the rotary knob with ten equal scale intervals and assigned numbers 1 to 10. Based on the setting levels 1 to 10, the potentiometer function results in a linear characteristic with regard to the assigned torque setpoints (see Fig. 3 to the prior art), resulting in a concrete power wrench at the individual Einstellstufen odd and difficult to read for a worker on site associated torque setpoints. These are regularly attached in a torque table as a sticker on a concrete power screwdriver. The following torque table is given as an example: setting stage Torque setpoints (Nm) 1 594 2 933 3 1273 4 1590 5 1925 6 2262 7 2578 8th 2924 9 3259 10 3565

Intermediate values for these torque setting values assigned to the setting stages and anyway odd must be set by a worker on site by interpolated intermediate positions of the rotary knob pointer between marked setting stages. If necessary, the setting levels can be selected digitally via push-buttons, with intermediate positions likewise to be successively selected via push-buttons.

Due to the required interpolation for intermediate values between the setting levels, inaccuracies in large tolerance ranges are practically unavoidable during the adjustment, and, moreover, the operation by a worker is obviously difficult and complicated. Since for many screwing already documentation for the exact execution, in particular with respect to exactly observed tightening torques is required, the above inaccuracies and tolerances inevitably find their correspondence in the documentation, so that thereby Problems may arise between the assembly company and the client when evaluating a screw design.

A particular area of application for such power wrenches is steel construction, for which precise specifications for the tightening torques for certain screwing processes are available with DIN 18 800-7, which must be precisely adhered to. The gradations of the tightening torques for the screw connections (for example M20 to M36) are not linear, so that intermediate settings between the known setting stages of a power wrench with the aforementioned problem are to be set for a worker. Thus, with a required documentation, the exact torque values prescribed in accordance with DIN 18 800-7 can only be obtained in a tolerance window and can not always be exactly determined. This is unsatisfactory when considering such documentation and may lead to larger differences in tolerance to valuation differences, whether a screw has actually been properly performed.

The object of the invention is to develop a screwdriver with torque limiter so that the disadvantages described above are eliminated. This object is achieved with the features of claim 1.

According to claim 1, the torque limiting unit is designed so that at least two torque difference values between each torque setting values assigned to successive setting stages are different, so that at least partially results in a non-linear characteristic for the adjustment stages with respect to associated predetermined torque setpoints.

This allows a worker in conjunction with the easily and accurately selectable Einstellstufen predetermined, repeatedly occurring torque setpoints Select and specify a non-linear characteristic comfortably and simply as well as exactly and exactly documented. Problems with respect to a tolerance-sensitive attitude and corresponding documentation no longer occur.

The input unit for a worker can consist of a rotary knob with an associated graduated ring scale for an analog setting in a conventional manner or optionally be constructed digitally with buttons and associated LEDs and / or a digital display.

A particularly preferred field of use of a screwing device according to the invention is the steel construction, in particular the steel construction, where prestressed high-strength screw connections are used with a share of about 90%, which are to be executed according to the provisions of DIN 18 800-7. In claim 2, the standardized screw M20 to M36 in six stages with the binding assigned tightening torques for the "torque method" specified (in the DIN 18 800-7 further included screw M12 and M16 require only relatively low tightening torques, which are carried out regularly by hand are and for the screwdriving device according to the invention is practically not used as a power wrench with its high performance potential). In the "torque method", the screwdriving process is carried out in one operation until the set tightening torque has been reached and the rotary drive is switched off.

For example, the torque difference values between the second setting stage corresponding to M22 and the third setting stage corresponding to M24 having a difference of 150 Nm are substantially smaller than the torque difference values between the third setting stage corresponding to M24 and the fourth setting stage corresponding to M27 having a difference of 450 Nm there is a significant nonlinearity of the associated Characteristic results, which causes the previous adjustment and documentation problems in a linear characteristic according to the prior art.

Further and as an alternative to the above "torque method", a "combined method" is standardized in DIN 18 800-7, in which the screwing is carried out torque-dependent up to a pre-set torque and then the rotary drive is rotated further by a predetermined further rotation angle. The screwdriving apparatus according to the invention can also be used for this combined method, in which case the corresponding setting torques are assigned to the six setting stages and associated set further rotation angles are detected until the rotary drive is switched off via a rotation angle sensor. As a rotation angle sensor, a Hall sensor on the electric motor or an optically scannable toothed disk ring can be used on a shaft part in a conventional manner.

The screwdriver according to claim 4 may be designed so that the tightening torques are fixed for both the "torque method" and for the "combined method" and are preferably easily selectable with a distinctive addition of a worker.

In a particularly preferred embodiment according to claim 5, the screwdriving device is an angle wrench with an angle gear, which builds much lower in comparison with the usual elongated design with axially oriented rotary drive and gearbox. Since there are often cramped conditions in steel construction, especially in steel construction at the screwing, such an angle screwdriver in conjunction with the above normalized torque settings is a particularly well suited to the specific application tailored screwdriver.

The proposed in claim 6 synchronous motor in the rotary drive is particularly well suited for the inventive measure for the realization of a non-linear characteristic.

According to claim 7, a known per se documentation system can be connected as an option to the screwdriver, which performs time-shifted from screwing transmitted from the screwing at the same time or with stored data for screwing an evaluation and documentation.

Basically, it is possible according to claim 9 with appropriate design of the input unit, for example as a potentiometer knob to select torque intermediate setpoints between the setpoint levels permanently assigned torque setpoints.

Reference to a drawing, the invention is explained in detail.

Fig. 1

eine nicht lineare Drehmomentkennlinie für Drehmoment-Sollwerte, welche sechs Einstellstufen zugeordnet sind;

Fig. 2

eine Darstellung eines Winkelschraubers und

Fig. 3

eine lineare Kennlinie über zehn Einstellstufen nach dem Stand der Technik.

Show it:

Fig. 1

a non-linear torque characteristic for torque setpoints associated with six adjustment stages;

Fig. 2

a representation of an angle wrench and

Fig. 3

a linear characteristic over ten adjustment levels according to the prior art.

In Fig. 3 is a concrete torque characteristic according to the prior art shown with ten adjustment stages, in which the torque difference values between each two adjustment stages according to the specific measurement protocol all about at 340 Nm, resulting in the (almost) linear characteristic curve usual in the prior art. The values in the two lower lines are indicated in a torque table on the associated power screwdriver as a sticker. A M30 screw connection must be made in accordance with DIN 18 800-7 in the "torque method" with a tightening torque of 1,650 Nm. From a worker is thus in the present gradation of the prior art, the fourth stage with an associated tightening torque of 1590 Nm, which is then to correct the desired value 1,650 Nm, by adjusting the setting with a potentiometer knob after the characteristic above is proceeded. Such an adjustment correction is in any case costly for a local worker and a possible source of error. Likewise, an inaccurate setting leads to a correspondingly inaccurate torque shutdown of the screwdriver with correspondingly unsatisfactory documentation subject to tolerances. Corresponding settings are given for 800 Nm and 2,800 Nm for M24 and M36.

In Fig. 1 on the other hand, the torque characteristic with six setting stages for a power wrench according to the invention with a preferred use in steel construction is shown, which is tailored to the requirements of DIN 18 800-7 and designed:

The standardized settings M20, M22, M24, M27, M30 and M36 are sequentially assigned to the six setting stages, which in turn correspond to the standardized tightening torques 450 Nm, 650 Nm, 800 Nm, 1,250 Nm, 1,650 Nm and 2,800 Nm. This information is expediently attached in a corresponding torque table as a sticker on the power screwdriver. At the input unit can thus easily be seen and selected for a worker easily the individual adjustment stages each with the associated normalized fitting or there are immediately for Verschählungsmaße M20 to M36 indicated and selected. This ensures a comfortable handling without input errors at the screwing and the power wrench switches off exactly at the specified in DIN 18 800-7 tightening torque according to the assignment to the setting, so that a correspondingly accurate documentation is obtained.

In Fig. 2 a screwdriving device is shown as a power wrench 1 in the embodiment as an angle wrench, in which in a first housing part 2, a rotary drive and a torque limiting unit are included together with a torque sensor and a rotation angle sensor. The electronics required for this purpose are accommodated in a lower housing part as electronics box 3. On the upper cylindrical housing part, the input unit 4 is rear side mounted together with buttons for a digital Einstellstufenanwahl and a digital display. Including the housing 2 is followed by a handle 5 with an on-off switch 6. The power wrench assembly is angled by 90 ° by means of an angular gear 7 for a total of low construction, on the output side, a receiving part 8 is detachably mounted for a screw head. Furthermore, the torque arm 9 required for power screwdrivers is mounted on the transmission side.

Such a trained power wrench 1 is due to its low height in connection with the input design to Fig. 1 precisely adapted to the needs of steel construction and ideally suited for its use there.

Claims (8)

Screwdriver with torque limiter - With a controllable rotary drive with an electric motor and a rotary torque setpoint generator associated therewith, with which a certain detected power consumption of the electric motor according to an associated torque of the screwdriver is set as a torque setpoint, - Wherein the torque setpoint generator on an input unit (4) in at least three successive adjustment stages for selecting a each setting level associated and increasing from setting to setting stage torque setpoint is adjustable, so that in a screwing after reaching a set Torque setpoint switches off as a preselected tightening torque of the rotary drive, characterized in that the torque limiting is designed so that at least two torque difference values between each successive adjustment stages associated torque setpoints are different, so that at least partially results in a non-linear characteristic for the adjustment stages with respect to associated predetermined torque setpoints. Screwdriver according to claim 1, characterized in that in successive adjustable by an operator Einstellstufen, preferably in six successive adjustment stages, the respective torque setpoints are specified according to the tightening torques according to DIN 18 800-7 for the "torque method": setting stage screw tightening 1 M20 450 Nm 2 M22 650 Nm 3 M24 800 Nm 4 M27 1,250 Nm 5 M30 1,650 Nm 6 M36 2,800 Nm Screwdriving apparatus according to claim 1, characterized in that in successive setting stages, preferably in six successive setting stages, the respective torque setpoints corresponding to the prestressing moments according to DIN 18 800-7 are assigned to the "combined method", setting stage screw tightening 1 M20 340 Nm 2 M22 490 Nm 3 M24 600 Nm 4 M27 940 Nm 5 M30 1,240 Nm 6 M36 2,100 Nm and, - That subsequently to the Voranziehmoment control of the rotary drive is further rotated controlled by a further rotation angle for the screw connection of 45 ° to 90 ° according to DIN 18 800-7 via a rotation angle sensor. Screwdriving apparatus according to claim 3, characterized in that the adjustment stages for the "combined process" with the associated Voranziehmomenten are set up as additional adjustment stages to the setting stages for the "torque control process". Screwdriver according to claim 1 to 4, characterized in that the screwing tool is an angle wrench (1) with bevel gear (7). Screwdriver according to one of claims 1 to 5, characterized in that a controllable synchronous motor is used in the rotary drive. Screwdriver device according to one of claims 1 to 6, characterized in that the screwdriver is a per se known documentation system for documentation of a screwing is connectable. Screwdriving device according to one of claims 1 to 7, characterized in that intermediate torque setpoint values between the setpoint values permanently assigned torque setpoint values can be selected by means of the input unit.

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