EP0042548B1 - Screwing device with torque detection - Google Patents

Abstract

The screw assembly comprises a drive unit whose output shaft (14) can be connected with a button die to be applied to a screw head. To prevent the casing (10) of the drive unit from rotating, it is fitted with a retainer (24) which is placed against a solid abutment. The retainer (24) has a ring (23) enclosing the output shaft and being connected via a torsionally elastic element (16) with the casing (10). Torsional deformation of the torsionally elastic element (16) is used as a measure for the torque acting on the screw head. (FIG. 1).

Description

The invention relates to a screwing device with torque determination, with a drive device arranged in a housing, the output shaft of which protrudes from the housing, a support leg coupled to the housing via an elastic connecting device and longitudinally movable along a sleeve with a non-circular profile for holding the housing against rotation and with a Device for determining the tightening torque by determining the supporting torque acting on the support foot.

It is known to use screwing devices for tightening screws, which are provided with an electromotive, hydraulic or pneumatic drive. After attaching to a screw to be turned, the drive device is switched on. If the screw is tightened to the required torque, the drive device is automatically displayed or switched off via a torque limiter.

In a known screwing device (DE-A No. 2520250), the housing of the drive device has an extension on which a support leg is longitudinally displaceable but non-rotatably guided. The support foot is formed in two parts and it consists of a tube connected to the neck in a rotationally fixed manner and a housing rotatably mounted on the tube. The arm protruding from the tube acts on a force measuring device fastened to the housing and having a display device. If a force acts on the support foot, the tube is moved in the housing and the relevant force is displayed on the display device. The known screwing device has the disadvantage that the support foot has to be formed in two parts and that both parts of the support foot have to be mounted coaxially to one another. In this case, the torque to be displayed can be falsified by the friction losses in the pivot bearings and by jamming or tilting. Furthermore, the support foot must have a protruding arm to which the force measuring device is attached. This gives the entire device relatively large dimensions in the radial direction, so that the possible uses of the screwing device are limited.

In the case of a screwing machine for fastening railroad tracks (DE-C No. 2637954), the housing is attached to a stationary holder, so that a support foot is not present. A torque measuring device is built into the screw spindle of the screwing machine. This torque measuring device contains a torsionally elastic intermediate part, which is non-rotatably connected to the screw spindle at one end and non-rotatably connected to a drive flange at its other end. With such a device, the torque can only be determined at a standstill because the entire torque measuring device rotates with the screw spindle. Torque measurement is therefore only possible if an upstream slip clutch has triggered. Furthermore, the reading is made more difficult by the fact that after the screw spindle has come to a standstill, the point at which the marking for reading the torque is located must first be found.

In the case of hydraulic or pneumatic power wrenches, there is basically the possibility of measuring the pressure of the working medium in the pressure line leading to the drive device and of using it to determine the torque. However, tests have shown that this pressure is subject to periodic changes over time, so that the pressure evaluation for determining the torque cannot be used without complex additional devices.

The invention has for its object to provide a screw device of the type mentioned, in which the component which triggers the torque limitation is arranged at the output of the screwdriver, that is to say in the immediate vicinity of the screw, and does not require any intervention in the output shaft of the drive device which transmits the screwing force.

To achieve this object it is provided according to the invention that the connecting device is a torsionable part surrounding the output shaft, one end of which is attached to the housing in a rotationally fixed manner and the other end of which engages in a rotationally fixed manner on the sleeve.

In this case, the reaction force acting on the support foot is principally used to determine the torque, but the deformable component is not attached to the support foot itself, but rather coaxially surrounds the output shaft of the power wrench. The torsionally elastic connecting piece is increasingly twisted during the screwing process with increasing screwing torque and actuates the elastic switch when a certain deformation amplitude has been reached. This increases the weight and size of the power wrench only insignificantly. The fact that the torsionally elastic connecting piece surrounds the output shaft or a part of the housing at a small distance allows a favorable adaptation of the shape of the connecting piece to the housing shape, so that the torque limiter does not significantly increase the volume of the power screwdriver.

The twistable (torsionally elastic) part can be a piece of pipe which is held at one end by the housing, while the other end is twisted by the support foot. The torsion rotation between the two ends of the pipe section is used here as a measure of the torque applied. Strain gauges can also be attached to the pipe section, which determine the deformation of the pipe section and are connected to an electrical evaluation circuit.

The torsional elasticity of the connecting device can easily be brought to the required level by the shape and size of slots or other openings which are provided on the connecting device. The connecting device is usually made of steel or another material with the required elasticity. This means that even high torques at small torsion angles can be determined with great accuracy.

The torque can be determined in such a way that when a certain limit value of the torque is reached, a switch is actuated, which switches off the drive device. Another possibility is to carry out a continuous measurement and display of the respective torque, the operator switching off the device when the torque has reached a certain size.

If, by means of the torque determination, only a switching operation is to be carried out when a limit value is reached, the invention and the pipe section can carry a switching part for actuating an electrical switch in an advantageous embodiment. The switch and the switching part are mounted on the tube piece offset in the axial direction to one another and the switching part acts on the switch via an arm. Because both the switching part and the switch are attached to the pipe section, an exact, defined attachment of the twistable connecting device to the housing of the screwing device is not necessary. On the other hand, such a defined attachment is required if the switching part is fastened to the torsionally flexible connecting device, the switch is fastened to the housing, or vice versa. The attachment of both parts to the pipe section means that the pipe section can be attached to the housing relatively loosely, so that it adjusts itself freely under load and is not subjected to any additional clamping forces. A loose coupling of the pipe section to the housing with the possibility of free adjustment in the event of a load is required for accurate measurements.

In an expedient development of the invention, it is provided that the switching part closes the switch in the unloaded state, and that the coupling between the switching part and the switch is interrupted when the predetermined torsion angle is reached. The switch thus has the function of a normally closed contact, that is to say a contact which is normally closed and which is opened to switch off the drive device. If the switch malfunctions, the drive device is switched off in this way.

In a preferred embodiment of the invention, a spring moving the arm in the direction of the switch is provided, and a stop limiting the movement of the arm and lifting the arm from the switch is connected in a substantially rotationally fixed manner to the housing or the housing-side end of the torsionally elastic connecting piece.

Although the support foot causes the creation of a torsional moment on the torsionally elastic connecting device, it is not itself part of the device for torque limitation. Its shape and dimensions are not included in the measurement result or the switching point. In order to be able to replace the support foot, the connecting device has a tooth profile at its end, on which a ring of the support foot is guided so as to be longitudinally displaceable and non-rotatable.

The invention is based on the idea of determining the torque by measuring a torsion movement that is as pure as possible. In order to prevent the torsionally elastic connecting device from being additionally subjected to bending forces which could falsify the measurement result, the end of the connecting device is mounted on a cylindrical extension of the housing.

According to a second variant of the invention, it is provided that the connecting device, as a twistable part, has an essentially radial measuring flange, which is connected at its inner end in a rotationally fixed manner to the sleeve and at its outer end in a rotationally fixed manner but longitudinally displaceably connected to the housing.

It is important that the measuring flange is not rigidly clamped at both ends, but that at least one end is longitudinally displaceable relative to the housing of the screw device. This prevents transverse forces and bending stresses from being transmitted from the support foot to the measuring flange, which would falsify the measurement result. The measuring flange must be able to adjust freely in the axial direction at least at one end - but preferably at both ends. Strain gauges can be attached to one of the two end faces of the measuring flange, which measure the torsional deformation of the measuring flange and display it on a display device.

Two exemplary embodiments of the invention are explained in more detail below with reference to the figures.

• Fig. 1 eine Teil-Draufsicht einer ersten Ausführungsform des Kraftschraubers, teilweise aufgeschnitten,
• Fig. 2 einen Längsschnitt durch den Kraftschrauber nach Fig. 1,
• Fig. 3 einen Schnitt entlang der Linie Ill-IIl von Fig.1,
• Fig. 4 einen Schnitt entlang der Linie IV-IV von Fig. 3,
• Fig. 5 eine perspektivische Ansicht des drehelastischen Verbindungsstückes mit schematischer Darstellung des Schalters und des Schaltteiles bei dem Kraftschrauber nach Fig. 1,
• Fig. 6 eine Seitenansicht einer zweiten Ausführungsform des Kraftschraubers, teilweise geschnitten, und
• Fig. 7 eine schematische Darstellung der elektrischen Auswerteschaltung für den Kraftschrauber der Fig. 6.

Show it:

• 1 is a partial plan view of a first embodiment of the power wrench, partially cut away,
• 2 shows a longitudinal section through the power wrench according to FIG. 1,
• 3 shows a section along the line III-II1 from FIG. 1,
• 4 shows a section along the line IV-IV of FIG. 3,
• 5 is a perspective view of the torsionally flexible connector with a schematic representation of the switch and the switching part in the power wrench according to FIG. 1,
• Fig. 6 is a side view of a second embodiment of the power wrench, partially sectioned, and
• 7 is a schematic representation of the electrical evaluation circuit for the power wrench of FIG. 6.

The power screwdriver shown in FIGS. 1-5 has a drive device 11 accommodated in a housing 10, which, for example, consists of a hydraulic motor can exist. For reasons of clarity, the drive device 11 is only indicated in FIG. 2, but is not shown in more detail in the rest. The housing 10 is essentially cylindrical and has at its front end an axially projecting hollow projection 12 with a reduced diameter through which the output shaft 13 of the drive device 11 projects. At the outer end of the drive shaft 13 there is a square 14 for attaching a key nut or the like.

The pipe section 16 is fastened to an annular flange 15 which runs around the housing 10 with an annular flange 17. The torsionally flexible pipe section 16 consists of the cage shown in FIG. 5. A cylindrical section 18 adjoins the ring flange 17, the cylinder wall of which is interrupted by numerous parallel longitudinal slots 19. The slots 19 each continue a short distance in an inward end wall 20. A sleeve 21 projects from the end wall 20 and has a toothing 22 or longitudinal splines. As can be seen from Fig. 2, the sleeve 21 is mounted on the neck 12 of the housing 10, while the twistable part 18 of the pipe section 16 encloses the end of the housing with the formation of a small annular space. The pipe section 16 thus essentially adapts to the contour of the part of the housing 10 which it encloses.

A ring 23 is slid onto the toothing 22 on the front sleeve 21 of the pipe section 16 and has an internal toothing that fits into the toothing 22. The ring 23 is part of the support foot 24, which has an arm projecting obliquely forward, which can be attached to a fixed abutment in order to prevent rotation of the housing 10.

To protect the torsionally elastic region 18 of the pipe section 16, a protective cap 26 is provided which engages over the ring flanges 15 and 17 and the area 18 of the pipe section and is fastened to the housing 10. The protective cap 26 has no significance for the function of the device.

On the cylindrical part 18 of the pipe section 16, an L-shaped block 27 is fastened in the vicinity of the ring flange 17, one leg 28 of which runs parallel to the ring flange 17 and is fastened to the torsionally elastic part 18 in the immediate vicinity of the ring flange 17. The other leg 29 of the block 27 projects freely forward and covers the part 18.

A radially projecting switching element 30 in the form of a pin is fastened to the end wall 20 of the pipe section 16. The switching element 30 projects through an elongated hole 31 of an arm 32 running approximately axially parallel to the connecting piece 16, the other end of which actuates an electrical switch 33 which is fixedly attached to the block 27. The arm 32 is pressed in the direction of the switch 33 by a spring 34 supported in the block 27.

A threaded bolt 35 runs parallel to the switch 33, the fine thread of which passes through a transverse bore of a screw 36 extending at right angles to the threaded bolt 35. By turning the screw 36, the position of the screw bolt 35 can be changed relative to the arm 32, so that a calibration of the torque limit is possible by turning the screw 36. The switch-off torque is set by turning the screw bolt 35 on a rotary knob 37. The rotary knob 37 is supported on the transverse screw 36 with a spring 38, so that the adjustment takes place without play. By turning the knob 37, the screw 35 is advanced or withdrawn. The shutdown torque is thus set. There is a scale on the button 37 on which the set cut-off torque can be read.

• Wird von der Antriebseinrichtung 11 die Ausgangswelle 13 gedreht, dann wird auf den (nicht dargestellten) Schraubenkopf ein Drehmoment ausgeübt. Der Stützfuss 24 hält über das Verbindungsstück 16 das Gehäuse 10 fest. Bei grösser werdendem Drehmoment wird das drehelastische Rohrstück 16 zunehmend auf Torsion beansprucht, d.h., seine vordere Stirnseite 20 verdreht sich relativ zu dem Stirnflansch 17. Der Block 27 verändert dabei seine Lage jedoch nicht, weil er an dem rückwärtigen Ende des Rohrstückes 16 befestigt ist. Dadurch behalten auch das Schaltteil 30 und der Gewindebolzen 35 ihre Position bei. Zunächst beginnt das Schaltteil 30 in dem Langloch 31 zu wandern. Sobald das Langloch 31 durchlaufen ist, nimmt das Schaltteil 30 den Arm 32 mit, bis dieser gegen das vordere Ende des Gewindebolzens 35 stösst. Der Arm 32 wird dann um das vordere Ende des Gewindebolzens 35 herum verschwenkt, so dass sein eines Ende von dem Schalter 33 abhebt, der nun nicht mehr gedrückt gehalten wird und somit öffnet. Der Schalter 33 bewirkt über eine Elektronikschaltung die Betätigung eines Magnetventils, das die Antriebseinrichtung 11 abschaltet.

The switching device works as follows:

• If the drive shaft 11 rotates the output shaft 13, then a torque is exerted on the screw head (not shown). The support foot 24 holds the housing 10 in place via the connecting piece 16. As the torque increases, the torsionally flexible pipe section 16 is increasingly subjected to torsion, ie its front end face 20 rotates relative to the end flange 17. The block 27 does not change its position, however, because it is attached to the rear end of the pipe section 16. As a result, the switching part 30 and the threaded bolt 35 also retain their position. First, the switching part 30 begins to wander in the elongated hole 31. As soon as the elongated hole 31 has passed through, the switching part 30 takes the arm 32 with it until it abuts the front end of the threaded bolt 35. The arm 32 is then pivoted around the front end of the threaded bolt 35 so that its one end lifts off the switch 33, which is now no longer held down and thus opens. The switch 33 effects the actuation of a solenoid valve, which switches off the drive device 11, via an electronic circuit.

The torsionally elastic pipe section 16 is fastened at one end with its ring flange 17 to the ring flange 15 of the housing 10. For this purpose, the two ring flanges have screw holes 40. The diameter of the screw holes 40 is, however, considerably larger than the diameter of the screws inserted through them, which are supported on the ring flange 17 with washers (not shown). The screws are also not fully tightened, so that the ring flange 17 can freely adjust relative to the ring flange 15. In this way, additional material stresses are avoided and it is achieved that the cylindrical part 18 of the connecting piece 16 is subjected to a pure torsional stress.

In the embodiment of FIG. 6, those parts which correspond in structure and function to the corresponding parts of the first embodiment are provided with the same reference numerals.

The output shaft 13 of the screw device is surrounded by a sleeve 21 which has a longitudinal toothing 22. The ring 23 of the support foot 24 is loosely pushed onto this sleeve. At the end of the sleeve 21 abutting against the front end wall 50 of the housing 10 there is a further set of teeth 51 with longitudinal teeth. The internal toothing of a measuring flange 52 engages in this toothing 51 and runs parallel to the end wall 50 and is movable in the axial direction. The measuring flange 52 is bent backwards at its outer edge 53 and has an inner toothing 54 at its outer end which engages in an outer toothing 55 of the end wall 50. In this way, the measuring flange 52 can adjust freely in the axial direction relative to the end wall 50 of the housing 10 and relative to the sleeve 21, but the sleeve 21 is coupled to the housing 10 in a rotationally elastic manner. Since the end flange 52 is torsionally elastic, it deforms when torque is transmitted. On the side of the end flange 52 facing the end wall 50 there are dimming measuring strips 56 which, according to FIG. 7, are connected together in a known manner to form a bridge circuit 57. The bridge circuit 57 has feed lines 58 and signal lines 59, which are connected to a control device 60. The control unit 60 has a display device 61 and an adjustment button 62 for the cut-off torque. An electrical switch 63 located in the control device 60 switches off the drive device for the screwing device when the output voltage of the bridge circuit 57 on the signal lines 59 exceeds the limit value set on the button 62.

Due to the fact that the measuring flange 52 according to FIG. 6 only transmits torsional forces, but no transverse forces and bending stresses, it is excellently suited for the torque detection. The sleeve 21 loosely surrounds the output shaft 13 which rotates in it. The sleeve 21 has no fixed connection to the housing 10. It is only prevented by holding means (not shown) from falling off the output shaft 13 (according to FIG. 6 to the right). The rotational coupling of the sleeve 21 to the housing 10 takes place via the twistable measuring flange 52.

Claims (12)

1. Screwing device with torque detection, with a drive mechanism (11) arranged in an outer casing (10) and the output shaft (13) of which projects from the casing, a support leg (24) for holding the housing fast against rotation, attached to the housing through an elastic coupling device (16), and movable lengthwise along a cylindrical shell (21) with non-circular section shape, and with facilities for determining the screwing moment by ascertaining the bracing moment acting on the support leg, characterized in that the coupling device (16) is a twistable component surrounding the output shaft (13) and whereof one end is fixed rotationallyfast on the casing (10) and the other hand is engaged rotationally fast on the cylindrical shell.

2. Screwing device according to claim 1, characterized in that the twistable component is a tubular member (16).

3. Screwing device according to claim 2, characterized in that the tubular member (16) has longitudinal slots (19).

4. Screwing device according to claim 2 or 3, characterized in that the tubular member (16) supports a switching component (30) for actuating an electric switch (33) in that the switch (33) and the switching component (30) are applied to the tubular member (16) shifted relative to one another in the axial direction, and in that the switching component (30) acts upon the switch (33) through an arm (32).

5. Screwing device according to claim 4, characterized in that the switching component (30) in the unloaded condition closes the switch (33), and in that, when the prescribed angle of torque is -attained, the coupling between switching component and switch is released.

6. Screwing device according to claim 4, characterized in that a spring (34) is provided which moves the arm (32) in the direction towards the switch (33), and in that a stop (35) limiting the movement of the arm (32) and retracting the arm from the switch (33) is connected essentially fast against turning with the casing (10).

7. Screwing device according to claim 1, characterized in that there is attached to the casing a switch which is actuated by a switching component fastened to the coupling device.

8. Screwing device according to any one of claims 2 to 7, characterized in that the tubular member piece (16) encloses the casing (10) over part of its length.

9. Screwing device according to any one of claims 2 to 8, characterized in that the end of the tubular member (16) is supported on a cylindrical extension (12) of the casing (10).

10. Screwing device according to any one of claims 2 to 9, characterized in that the tubular member (16) is secured by a front flange (17) to the casing (10), and in that there extend through the front flange (17) bolts which permit independent adjustment of the front flange (17) relative to the casing (10).

11. Screwing device according to claim 1, characterized in that the coupling device as a twistable component has an essentially radial orifice assembly (52) which at its end is connected fast against rotation with the cylindrical shell (21) and at its outer end is connected fast against rotation but longitudinally displaceable with the casing (10).

12. Screwing device according to claim 1 or 11, characterized in that the twistable component bears at least one strain gauge (56) which is connected with an electric evaluation circuit (60).

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