GB2293011A

GB2293011A - Screwing device with ultrasound-controlled tightening of screw-connection

Info

Publication number: GB2293011A
Application number: GB9517239A
Authority: GB
Inventors: Michael Habele
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1994-09-06
Filing date: 1995-08-23
Publication date: 1996-03-13
Anticipated expiration: 2015-08-23
Also published as: DE4431675B4; GB2293011B; SE9503053L; GB9517239D0; DE4431675A1; SE510355C2; SE9503053D0

Description

- 1 2293011 Screwincr device for the ultrasound-controlled tichteninc of

screw- connections

Prior art

The invention is based on a screwing device of the generic type of Claim 1. A screwing device of this type is already known (DE 42 31 429 Cl), said screwing device being provided with =cans for the electric activation of a vibration body arranged on a screw-connection and for acknowledging measuring signals. The voltage in supplied to the vibration body via a resilient contact pin which is accommodated in a screwing tool, the circuit is being closed via a screwing tool itself, a rotary drive shaft and via housing parts of the screwing device. In the event of defective contact in this earth line, for example in the region of the electric contact surfaces between screwing tool and screw- connection, and due to external disturbances to the earth line, for example caused by electromagnetic vibrations, the ultrasound measuring of the tightening torque, and thus the screwing accuracy of the screwing device, may be adversely affected.

Advantages of the invention In contrast, the screwing device according to the invention and having the characterizing features of Claim 1 has the advantage that disruptive influences on the measurement result can be reduced and thus a higher screwing accuracy can be achieved. Furthermore, a reliable earth contact in even ensured, upon attachment of the screwing tool, if the edges of the screwing tool and screw head do not coincide precisely and it is thus not possible to position the screwing tool correctly on the screwing head. Even in this case, a reliable earth 2 contact is achieved via the earth conductor, with the result that the screwing torque can be established simply by starting the screwing device, without the screwing drive having to be activated beforehand for the purpose of aligning the edges.

By virtue of the measures outlined in the subclaims, advantageous refinements and improvements of the screwing device specified in Claim 1 are possible.

Drawing An exemplary embodiment of the invention is represented in the drawing and explained in more detail in the following description. The single figure shows a longitudinal section through the screwing-tool part of a screwing device defined according to the invention.

is Description of-the exemplary embodiment

In the drawing, 10 designates a front, screwingtool part of a screwing device. The screwing device 10 is provided with a rotary drive shaft 11 which can be driven in rotation by means of a drive motor (not shown in any more detail). Provided at that end of the rotary drive shaft 11 which is represented in Figure 1 is a screwingtool receiving means 12 for a screwing tool 13 which serves for tightening a screw-connection. By way of example, all that is shown of the screw-donnection is a screw 14. However, the screwing device 10 may likewise be attached to a nut of the screw-connection. The screwing tool 13 is designed, for example, with a receiving opening 15 which is designed an a hexagonal socket and is intended for a hexagonal screw head 16 of the screw 14.

Located on the end side of the screw head 16 is a vibration body 19, which is vibration- coupled to the screw 14. The vibration body 19 is, for example, a piezoelectric crystal which, with corresponding electric excitation, produces high-frequency acoustic vibrations and conducts the same into the screw- connection. Conversely, the piezoelectric crystal receives echo vibrations from the screw- connection and converts these into associated echo signals. By comparing excitation signals and echo signals in a schematically represented evaluation device 17, conclusions can be made, in a known manner, an to the voltage state in the screw-connection and, consequently, an to the current screwing torque.

The screwing device 10 in provided with means 20 which are connected to the evaluation device 17 and are intended for activating the vibration body 19 and acknow ledging the echo signals. The means 20 comprise a trans mission element 21 which extends axially, predominantly within the rotary drive shaft 11, in an axial bore 18. At its screwing-tool end, the transmission element 21 in designed in two parts with an axially telescopically is displaceable contact pin 22 which can be forced In the direction of the screw 14 by a spring. The transmission element 21 in correspondingly pad in a hollow cylindrical manner, with the result that the contact pin 22 can spring in axially. Provided at the free tip of the transmission element 21 and/or of the contact pin 22 thereof in a contact surface 24 which serves to activate the vibration body 19, f itted on the and side of the screw head 16, and thus comes to bear on the screwing tool 13 when the latter in positioned on the screw 14.

The circuit to the vibration body 19 in closed via an earth conductor 25. The earth connection by way of the earth conductor 25 takes place via the screw head 16, the vibration body 19 being located on the surface thereof. The earth conductor 25 in designed approximately in the form of a sleeve and encloses the transmission element 21 concentrically in the front part of the screwing device 10. in this arrangement, the transmission element 21 and the earth conductor 25 are electrically insulated from one another by an insulator 26 and, in the region of the contact pin 22, by a gap.

The earth conductor 25 can be displaced axially in a resilient manner, an can the contact pin 22. For this purpose, it in forced axially forwards by a spring element 27. When the screwing tool 13 in attached to the screw 14, the free end side 28 of the earth conductor 25 makes contact with the electrically conductive screw head 16 at a radial distance from the vibration body 19.

The rotary drive shaft 11 and the screwing tool 13 are connected in a rotationally fixed manner via a polygonal profile 30 in the region of the screwing-tool receiving means 12. The screwing-tool receiving means 12 is designed as an polygonal insert 31, and a correspond ing polygonal socket 32 is provided on the screwing tool 13. In the example given, the polygonal profile 30 is formed by a square profile. An annular groove 33 is located approximately centrally in the screwing-tool receiving means 12. Two connecting bodies 34 engage radially into the annular groove 33. The connecting is bodies 34 are each arranged in mutually opposite bores 35 which pass radially through the wall of the screwing tool 13 in the region of the polygonal prof ile 30. The con necting bodies 34 are designed in the form of pins and are rounded off on their side 36 engaging into the annular groove 33. Upon engagement of the connecting bodies 34 into the annular groove 33, the screwing tool 13 in axially fixed in a positively locking manner on the screwing-tool receiving means 12. Radially on the out side, the connecting bodies 34 are overlapped by a securing element 37 and retained in their connection position. in this arrangement, the securing element 37 is designed in the form of a ring, e.g. as an O-ring. The pin-like connecting bodies 34 have play within the bores 35, with the result that, after the securing element 37 has been removed, they can be displaced radially out wards, the connecting bodies coming out of engagement with the annular groove 33, with the result that the screwing tool 13 can be removed from the rotary drive shaft 11. Provided on the outer circumference of the screwing tool 13, in the region of the bores 35, is an encircling groove 38 in which the securing element 37 is arranged. Provision is made for play between the bore 35 and the securing element 37, with the result that the screwing tool 13 can butt axially against the end side of the rotary drive shaft 11.

By virtue of the resilient disPlaccability of contact pin 22 and earth conductor 25, disturbanceinsensitive activation of the vibration body 19 and acknowledgement of the echo signals during the screwingin operation are possible. In order not to have to advance the screwing device 10 constantly, the screwing device 10 is attached to the screw-connection such that the screw head 16 In located relatively far down the receiving opening 15 of the screwing tool 13, at most an far an a stop 39 which In formed by the insulator 26 axially in front of the receiving means 12. For reasons of protection, the contact pin 22 of the transmission element 21 and the earth conductor 25 do not project is axially beyond the screwing tool 13 when said screwing tool 13 Is removed from the screw head 16. In order also to be able to activate the vibration body 19 when the screwing tool 13 Is not positioned fully on the screw head 16, an axial, circular clearance 40 formed, for example, by an encircling incision in provided on the and side directed towards the screw 14, said clearance 40 having a greater diameter than the width across the corners of the screw head 16. Consequently, even when the edges of the receiving opening 15 and screw head 16 do not coincide, the screw 16 can penetrate into the screwing tool 13 to such an extent that satisfactory electric contact in ensured. In this case, in order to position the screwing tool 13 fully, the edges have to be made to coincide by rotating by means of the screwing drive. When the screwing tool 13 is fully positioned on the screw head, the screw head 16 then moves axially forwards within the receiving opening during the screwing operation, the advancing contact pin 22 and earth conductor 25 ensuring uninterrupted activation of the vibration body 19.

Claims

Claims

Screwing device for the ultrasound-controlled tightening of a screw-connection, which screwing device (10) exhibits a screwing tool (13) for exerting a screw ing torque on the screw-connection and is provided with means (17, 20) for the electric activation of a vibration body (19), which is vibration-coupled to the screw connection, and for signal acknowledgement, which means (20) comprise an electrically conductive transmission element (21) for transmitting electric signals to the vibration body (19) and with the acknowledgement of echo signals, and further comprise an earth connection, is characterized in that the earth connection in formed by an earth conductor (25) which is electrically insulated with respect to the transmission element (21) and, at least in the case where the screwing device (10) in withdrawn from the screw-connection, with respect to the screwing tool (13).
2. Screwing device according to Claim 1, charac terized in that the screwing tool (13) has an axial through-passage opening (15, 32) in which the earth conductor (25) is arranged.
3. Screwing device according to Claim 2, charac terized in that the earth conductor (25) is designed in the form of a sleeve and encloses the transmission element (21) concentrically such that it makes electrical contact with the screw- connection, when the screwing tool (13) is positioned thereon, at a radial distance from the vibration body (19).
4. Screwing device according to Claim 3, charac terized in that the earth conductor (25) makes contact with the screwing device (10) in the region of the end surface of a screw head (16) of a screw (14).

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5. Screwing device according to one of the preceding claims, characterized in that the earth conductor (25) is forced, by a spring element (27), in the direction of the screw-connection and can be displaced axially counter to the prestressing of the spring element (27).
6. Screwing device according to Claim 5, characterized in that the sleevelike earth conductor (25) with the transmission element (21) acc=modated therein in an insulated manner in guided in an axial bore (18) of a rotary drive shaft (11).
7. Screwing device according to one of the preceding claims, characterized in that the front section (22) of the transmission element (21) and of the earth conductor (25) in arranged in a front region, designed as a receiving opening (15) for a screw head (16), of the throughpassage opening (15, 32).
S.. Screwing device according to Claim 7, characterized in that the screwing tool (13) is provided, on its front end side, with an axial, encircling clearance (40) which has a greater diameter than the width across the corners of the associated screw head (16).
9. A screw device substantially as herein described is with reference to the accompanying drawing.