GB2075886A - A hand torque tool with torque measuring element - Google Patents

Abstract

A compressed air screwing tool has the driving torque measured by the deformation of a front housing portion 4 produced by the reaction torque. At least one strain gauge 17 is mounted on the front housing portion 4 in the region 16 which is narrowed to form a neck. The measured values can serve for the digital indication of the screwing torque by means of measuring amplifiers. The housing portion 4 has a front screwthread 10 for receiving a tool head 8, and a rear screwthread 5 for fixing to other housing parts. <IMAGE>

Description

SPECIFICATION A hand machine tool State ofthe art The invention originates from a motor driven hand machine tool according to the preamble to the main claim. Such a hand machine tool is described in German OS 2442 260 (R. 2278). The principle employed with this hand machine tool - in this case it is, for example, applied to a drilling machine operates satisfactorily and has in the meantime passed its practical examination. Of course, this principle may also be used with screwing tools driven by compressed air and which are controlled electronically to an increasing extent. In this way, the possibility is provided enabling the screwing operation to be displayed and documented by means of desired and actual value indications.Now, as is known, the obtaining of an optimal accurately observed pre-stressing force with screw connections through precisely controlled screwing motors in modern machine construction has quite generally become more and more important. This applies especially to screw connections which can be essentially in the form of safety screw connections.

The object of the present improvement is to apply the principle described in the said German OS 2442 260 to a compressed air screwing tool optimally designed for that purpose.

Advantages of the invention The hand machine tool in accordance with the invention comprising the characterising features of the main claim provides the possibility of measuring the torque in a compressed airscrewing tool during the tightening operation. This measured value can then be transmitted to a computer for example which uses it continuously for controlling the screwing operation.

Advantageous further developments and improvements of the hand machine tool set forth in the main claim are made possible by the features set forth in the sub-claims. It is especially advantageous that the invention may also be applied to earlier compressed air screwing tools, which, arising out of their housing design, are not suitable therefor by means of the claimed housing attachment. In so doing, one portion of the housing of the earlier compressed air screwing tool is replaced by a housing portion narrowing in the form of a neck and receiving the tool head and which, in the vicinity of its forward fixing screw-thread, has a region of reduced cross-section with respect to the neck-like housing portion and on the preferably cylindrical outer surface of which the measuring element is mounted.

Drawing Embodiments of the invention are illustrated in the drawing and are described in detail in the following specification. Figure 1 shows a screwing tool driven by compressed air and which is suitable for reception in a clamping device, Figure 2 shows a screwing tool suitable for manual operation and Figure 3 shows a housing attachment for a screwing tool.

Description ofthe embodiments In the following, "front" means the direction towards the workpiece to be treated, "back" means the direction towards the compressed air supply.

The compressed air screwing tool illustrated in the drawing has a housing 1 which is made up of a valve housing 2 arranged at its rear end, a substantially cylindrical motor housing 3 and a housing portion 4 arranged at its front end and narrowing to form a neck. The valve housing 2 and the motor housing 3 are rigidly connected to one another. A compressed air motor (not illustrated in the drawing) designed as a known vane motor and an epicyclic gear driven by the motor are arranged in the motor housing 3. A known coupling for the screwing tool is accommodated in the front housing portion 4. This front housing portion 4 accommodating the coupling is screwed to the motor housing portion 3 by a screw-thread 5 (see Figure 3) arranged at its rear end.

A pipeline 6 through which the compressed air is supplied to the screwing tool for driving the motor, leads into the rear end of the gear housing 2.

Furthermore, a suspension loop 7 is also fixed to the valve housing 2.

Apart from the coupling already referred to, the front housing portion 4 also accommodates a tool head which carries a screwing tool - in this case a screwdriver blade 8. The blade 8 projects from the front end of the front housing portion 4. At its front end 9, the housing portion 4 carries a coaxial fixing screw-thread 10 which is bounded at its rear end by an abutment flange 11. A sleeve-like clamping portion 12 is screwed onto the fixing screw-thread 10 and on its inside it has a shoulder 13 which engages the abutment flange 11 on the front housing portion 4. On its outside, the clamping portion 12 has a cylindrical clamping surface 14. The screwing tool can be rigidly clamped at the said clamping surface in a device 15 shown in dotted lines in Figure 1.

Directly behind the abutment flange 11, the front housing portion 4 has a region 16 of cylindrical tubular cross-section. The cross-section in the region 16 is reduced with respect to the cross-section of the remaining housing portion 4 in order to provide a zone which is easily elastically deformable. Two measuring elements 17 designed as strain gauges and displaced with respect to each other by an angle of 90" are arranged on the cylindrical outer surface in the region 16. In the embodiment illustrated in Figure 1 - as can be seen from the drawing - the region 16 is only slightly longer than the axial length of the measuring elements 17.Moreover, the region 16togetherwith the measuring elements 17 lie in the direct vicinity of the abutment flange 11; the measuring elements 17 are overlapped by the clamping piece 12 and are thus protected against undesired damage. Connecting cables 18which lead to the measuring element are brought out between the housing 4 of the screwing tool and the clamping part 12 overlapping it. In the rear region of the screwing tool, more precisely at the motor housing 3, the connecting cable 18 is fixed by means of a clamping strip 19.

As regards the measuring elements 17 designed in this case as strain gauges, it is a question of electrical resistors which change their value in accordance with the mechanical stress acting on them. With.the screwing tool clamped (rigidly) in the device 15 the driving torque acting thereon is equal to the reaction torque at the rotary tool 8 acting on the elements to be screwed. This reaction torque then produces an elastic deformation of the region 16 of the housing portion 4. The deformation is - as already mentioned - measured by the measuring elements 17 as a variation in resistance. By means of a known amplifier, the measured values produced can serve for the digital indication of the screwing torque and also be used continuously for controlling the screwing operation.

The described measuring device may also be used for the data recording of the variation and the switching off accuracy of a screwing tool provided with a mechanical disconnecting coupling during its manufacture.

A second embodiment of a screwing tool likewise driven by a compressed air motor is illustrated in Figure 2. This second embodiment differs from the first embodiment basically by the fact that this screwing tool provided with a handle is held by an operator. Moreover, the housing portions 2 and 3 correspond to those of the first embodiment. With this second embodiment, a front housing portion 24 is fixed to the front end of the motor housing 3. As with the first embodiment, the housing portion 24 carries a screw-thread 5. Once again, the front housing portion 24 illustrated in Figure 3to a larger scale, serves for the reception of a coupling not illustrated in the drawing and a tool head.Two spanner surfaces 25 are applied to the front housing portion 24 substantially in the centre of its axial length and with the aid of which the said housing portion can be rigidly screwed to the motor housing 3. Moreover, a fixing screwthread 10 which is bounded at its rear end by an abutment flange 11, is arranged at the front end of the housing 24. Moreover, a region 26 of reduced cross-section and thus more easily elastically deformable, is located directly behind the abutment flange 11. This region 26, the axial length of which is certainly longer than with the first embodiment, corresponds completely as regards its function to the region 16 of the first embodiment.In this embodiment, four measuring elements 27 displaced with respect to each other by 90" and which are likewise formed as strain gauges as in the first embodiment, are arranged on the cylindrical outer surface of the front housing portion 24 in the region 26. In this case too, the connecting cables 18 to the measuring elements are once again fixed to the motor housing 3 by a clamping strip 19.

In this embodiment, a tubular outer housing 28 which overlaps the measuring elements 27, the front housing portion 24 and a portion of the motor housing 3, is screwed onto the fixing screw-thread 10. On its outside, this outer housing 28 has a contoured gripping surface 29.

This embodiment does not differ in function from the first embodiment. However, since the region 26 is of longer axial length than the region 16 of the first embodiment, it may be deformed at lowertorques.

Thus, this second embodiment is better for use with the lower torques occurring in manual operation.

The indication or the data processing of the obtained measured values is no different from the first embodiment.

The screwing tools illustrated in Figures 1 and 2 are basically designed for torque measurement in accordance with the invention. However, screwing tools with a housing of some other construction - as is illustrated for example in Appln. No. 2050511 A can also be modified for torque measurement in accordance with the invention with the aid of the housing attachment. For that purpose, the front housing portion used therein is exchanged for the housing portion 24 illustrated in Figure 3 which is then offered as a separate component. Moreover, a clamping part 12 or an outer housing 28 can be selectively screwed onto its fixing screwthread 10.

Claims (9)

1. A motor driven hand machine tool on the housing of which is arranged a measuring element especially designed as a strain gauge, which measures the torque applied by the driving motor through the deformation of the housing of the hand machine tool produced by the reaction torque, according to Patent (Patent Application P 2442 260) characterised in that the hand machine tool is a screwing tool driven by compressed air, the housing of which has a coaxial fixing screw-thread at its front end receiving a tool head carrying the screwing tool screwdriver blade or socket - especially in the form of a narrow neck and that the measuring element is arranged on the outside of the housing preferably in the direct vicinity of the fixing screwthread - viewed in an axial direction.

2. A hand machine tool according to claim 1 characterised in that the front housing portion has a region of reduced cross-section, especially cylindrically tubular, in which the measuring element is arranged.

3. A hand machine tool according to claim 1 or 2 characterised in that a sleeve-like clamping part which overlaps the measuring element and has a particularly cylindrical clamping surface on its outside, is screwed onto the fixing screwthread.

4. A hand machine tool according to claim 1 or 2 characterised in that a tubular outer housing which overlaps the measuring element and the housing of the screwing tool and has an especially contoured gripping surface on its outside, is screwed onto the fixing screw-thread.

5. A hand machine tool according to claim 3 or 4 characterised in that the connecting cables to the measuring elements are brought out beyond the housing between the housing ofthe screwing tool and the clamping part overlapping it.

6. A hand machine tool according to claim 5 characterised in that the connecting cables are fixed to the housing by means of a clamping strip.

7. A housing attachment for a screwing tool driven by compressed air, preferably for use in multiple spindle screwing tools according to one of the preceding claims, characterised by a housing portion receiving the tool head and narrowing to form a neck and which has a region in the vicinity of its front fixing screwthread with a cross-section reduced with respect to the neck-like housing portion and on the preferably cylindrical outer surface of which is mounted the measuring element and by a holding portion (clamping part or outer housing) which can be screwed onto the fixing screw-thread.

8. A hand machine tool substantially as herein described with reference to Figure 1, Figure 2, Figures 1 and 3 or Figures 2 and 3 of the accompany ing drawings.

9. A housing attachment for a machine tool substantially as herein described with reference to Figure 3 of the accompanying drawings.