WO2008026200A2

WO2008026200A2 - An adaptor for a torque transducer

Info

Publication number: WO2008026200A2
Application number: PCT/IL2007/001036
Authority: WO
Inventors: Lior Naim; Menachem Schwartz
Original assignee: Rafael Advanced Defense Systems Ltd.
Priority date: 2006-08-31
Filing date: 2007-08-20
Publication date: 2008-03-06
Also published as: IL177832A0; WO2008026200A3; IL177832A

Abstract

The present invention is an adaptor (10) for a torque transducer operable in conjunction with a torque tester The adaptor of the invention comprises an outer sleeve member (5) coupleable with a torque tool, an inner sleeve member (15) coupleable with a torque transducer, and a breakable locking element (25) secured to both the outer sleeve member and the inner sleeve member When the to applies a torque greater than an allowable limit the locking element is adapted to break whereby to decouple the tool from the transducer.

Description

ANADAPTOR FORATORQUE TRANSDUCER

Field of the Invention

The present invention relates to the field of torque tools. More particularly, the invention relates to a device for preventing the overloading of a torque transducer.

Background of the Invention

Torque testers are well known devices to test and calibrate torque tools, such as torque wrenches, screw fasteners, torque multipliers, and electrode wrenches. Torque tools will not function as intended when not calibrated.

Torque testers comprise one or more torque transducers for measuring the torque applied by the torque tools and means for displaying the measured torque to a user. Each torque transducer operates according to different principles. In some transducers, the twist of the rotating axle of a torque tool is measured, while in other transducers, the shearing stress in the axle is measured.

Torque transducers are prone to irreversible damage when being overloaded. In addition to the damage of the transducers, which are expensive, costing $500-$2500, the torque tester is put out of service and the testing of other torque tools cannot be carried out until a new transducer is obtained and installed. Consequently, the user testing a torque tool must be careful that the selected transducer is of a suitable size or capacity to handle the maximum torque applied by the tool. Many torque transducers, for example the transducers disclosed in US 4,763,532 and US 6,909,951, are provided with overload protection by means which are internal to the transducer, to prevent such damage. 007/001036

- 2 -

However, torque transducers provided with overload protection are also prone to irreversible damage during tool testing or calibration, even when a transducer of a suitable size or capacity is employed. When the torque tester is operating in a so-called initial peak mode whereby the set torque of a ratchet type torque tool, and not the highest torque applied, is detected, the transducer is not protected with respect to an excessive torque which is applied thereto. In the initial peak mode, a sensor, such as a vibration sensor or an acoustic sensor, detects the characteristic click sound during engagement of the ratchet element as the set torque is achieved and subsequently displayed. The torque tool axle generally stops rotating after the set torque is achieved and the applied torque is momentarily reduced. At times, an acoustic sensor does not detect the click sound, and the user will therefore continue to apply the torque, often severely damaging the transducer if the applied peak torque is excessive. Alternatively, a torque overload may be caused by an inherently inaccurate tool, by a malfunction of a spring which is adapted to bias the ratchet element, or by human error. A critical load which causes irreversible damage and burn-out to the transducer usually cannot be anticipated.

Many different types of mechanism are known for limiting an applied torque by employing a member which is broken when the load is excessive, for example US 4,947,972, US 5,419,745, US 6,068,452, and US 6,637,287. None of these torque limiters operate in conjunction with a torque tester, and therefore the breakable members are not manufactured with a sufficient level of precision needed by torque testers to ensure structural integrity when the applied torque is below a predetermined value and to ensure breakage when the applied torque is greater than a predetermined value. Furthermore, these torque limiters are located within the torque generating apparatus.

It is an object of the present invention to provide a device that prevents a torque transducer of a torque tester from being overloaded and consequently damaged, particularly during the initial peak mode of the torque tester. It is an additional object of the present invention to provide a torque transducer of a torque tester with overload protection by means of a device that is external thereto.

It is an additional object of the present invention to provide a device for preventing the overloading of any commercially available torque transducer.

It is an additional object of the present invention to provide a torque tester with a breakable member that is manufactured with a sufficient level of precision to ensure structural integrity when the applied torque is below a predetermined value and to ensure breakage when the applied torque is greater than a predetermined value.

Other objects and advantages of the invention will become apparent as the description proceeds.

Summary of the Invention

The present invention provides an adaptor for a torque transducer operable in conjunction with a torque tester, comprising an outer sleeve member coupleable with a torque tool, an inner sleeve member couple able with a torque transducer, and a breakable locking element secured to both said outer sleeve member and said inner sleeve member, wherein said locking element is adapted to break whereby to decouple said tool from said transducer when a torque applied by said tool is greater than an allowable limit.

Preferably, the inner sleeve member comprises a base element and a head element which is connected to, and smaller than, said base element, said base element being formed with a socket in which a male connecting means of the transducer is received. The outer sleeve member is preferably formed with a socket in which the head element of the inner sleeve member is received, the locking element being introducible within aligned apertures, e.g. diametrically opposite apertures, formed within the head element of the inner sleeve member and within the outer sleeve member to allow a tool axle, the outer sleeve member, the inner sleeve member, and the connecting means of the transducer to rotate in unison when the torque applied by the tool is less than the allowable limit.

In one aspect, the base element and head element of the inner sleeve member and the outer sleeve member are tubular.

The locking element preferably has a head and a rod introducible into the aligned apertures, said rod being formed with two regions of reduced thickness. The thickness of the rod at the regions of reduced thickness is suitably selected to ensure that the locking element will be sheared at a predetermined stress level corresponding to the allowable limit of the transducer. The length of the rod is greater than the largest dimension of the base element of the outer sleeve member and the distance between the two regions of reduced thickness is substantially equal to the largest dimension of the head element of the inner sleeve member.

The locking element is preferably made from stainless steel 416T. In order to decouple the tool from the transducer when a torque applied by said tool is greater than an allowable limit, the locking element will shear at an applied torque of greater than approximately 659 kg-mm when its rod diameter is 6.35 mm and its rod thickness is 0.91 mm at the regions of reduced thickness and at an applied torque of greater than approximately 3916 kg-mm when its rod diameter is 6.35 mm and its rod thickness is 2.2 mm at the regions of reduced thickness. The hardness of the outer sleeve member and of the inner sleeve member is preferably greater than that of locking element, to prevent damage to the inner and outer sleeve members when the allowable limit of the transducer is exceeded and the locking element is sheared. The hardness of the outer sleeve member and of the inner sleeve member ranges from 50 to 55 HRC, and the hardness of the locking element ranges from 21 to 34 HRC.

The present invention is also directed to a torque tester which comprises at least one torque transducer, to at least one of which is coupled the aforementioned adaptor.

Brief Description of the Drawings

In the drawings:

- Fig. 1 is a perspective view of an adaptor for a torque transducer, according to one embodiment of the present invention;

- Fig. 2 is a photograph of a commercially available toque transducer;

- Fig. 3 is a photograph of the engageable inner and outer sleeve members;

- Fig. 4 is a photograph of the adaptor of Fig. 1 coupled to the transducer of Fig. 2;

- Fig. 5 is a side view of the a locking element; and

- Fig. 6 is a vertical cross sectional view cut along plane A-A of Fig. 1.

Detailed Description of Preferred Embodiments

The present invention is a novel adaptor that is adapted to decouple a torque tool from a torque transducer of a torque tester when the applied torque exceeds the allowable limit of the transducer. For brevity, the torque tool to be tested and calibrated, torque transducer, and torque tester will be referred to hereinafter as "tool", "transducer", and "tester", respectively.

Fig. 1 illustrates a perspective view of one embodiment of the adapter of the present invention, which is designated by the numeral 10. Adaptor 10 comprises outer sleeve member 5, inner sleeve member 15, and breakable locking element 25, e.g. a locking pin, which is secured to both outer sleeve member 5 and inner sleeve member 15. Inner sleeve member 15 is engageable with the Allen head 12 of transducer 13 shown in Fig. 2, and Allen head 7 of outer sleeve member 5 is engageable with a suitably sized socket of a tool to be tested (not shown). During a calibration operation whereby adaptor 10 is engaged with the tool and with Allen head 12 of transducer 13, adaptor rotates in unison with the tool while the applied torque is displayed. When the applied torque is greater the allowable limit, locking element 25 breaks and inner sleeve member 15 is decoupled from outer sleeve member 5, so that further rotation of outer sleeve member 5 will not transmit torque to inner sleeve member 15.

As shown in Fig. 3, inner sleeve member 15 has a larger diameter tubular base element 14 and a smaller diameter tubular head element 16, which is connected to, and concentric with, base element 14. Base element 14 has a socket which is engageable with the Allen head of the transducer. Head element 16 is bored with two sets of diametrically opposed apertures 18 arranged such that each adjacent aperture is separated by an angular distance of approximately 90 degrees. Outer sleeve member 5 has a base element 24 having essentially the same diameter as base element 14 of inner sleeve member 15, and an Allen head 27 engageable with the tool. Base element 24 is formed with a socket 26 having a recess of substantially the same diameter as head element 16 of inner sleeve member 15, and is bored with two sets of diametrically opposite apertures 28 arranged such that each adjacent aperture is separated by an angular distance of approximately 90 degrees. Accordingly, head element 16 of inner sleeve member 15 can be received in socket 26 of outer sleeve member 5, and each set of apertures 28 bored within inner sleeve member 15 can be aligned with each set of apertures 18 bored within outer sleeve member 5. When a set of apertures 18 is aligned with a set of apertures 1036

- 7 -

28, the locking element is introduced into the aligned apertures in order to secure inner sleeve member 15 to outer sleeve member 5.

It will be appreciated that outer sleeve member 5 and inner sleeve member 15 may be shaped in any other desired fashion, such as with a rectangular base member, head element, and socket, although a tubular configuration will usually be preferable due to the lower moment of inertia.

Fig. 4 illustrates a portion of tester 45 as adaptor 10 is coupled to transducer 13.

A side view of locking element 25 is illustrated in Fig. 5. Locking element 25 has a head 31 and a rod 32, e.g. a cylindrical rod, formed with two regions 34 and 35 of reduced thickness. The diameter d of rod 32 at the regions of reduced thickness is selected to ensure that locking element 25 will be sheared at a predetermined stress level, which corresponds to the allowable limit of the transducer and which will be described hereinafter. The length L of rod 32 is greater than the diameter of base element 24 of outer sleeve member 5. The distance D between regions 34 and 35 of reduced thickness is substantially equal to the diameter of head element 16 of inner sleeve member 15. Locking element 25 is preferably made from stainless steel 416T, due to its resistance to rust and corrosion, its heat treatment, relatively high ultimate shear strength of approximately 60 kg/mm², and good machinability, although other materials including other types of stainless steel may be used as well.

As shown in Fig. 6, locking element 25 is precisely dimensioned so that when head 31 contacts the periphery of base element 24 of outer sleeve member 5, regions 34 and 35 of reduced thickness are located at the two interfaces between head element 16 of inner sleeve member 15 and base element 24 of outer sleeve member 5. The hardness of outer sleeve member 5 and inner sleeve member 15 is preferably greater than that of locking element 25, to prevent the abrasion and possible irreversible damage to the outer and inner sleeve members when locking element 25 is sheared, following the application of an excessive torque by the tool to the transducer. For example, the hardness of locking element 25 ranges from 21-34 HRC and the hardness of outer sleeve member 5 and inner sleeve member 15 ranges from 50-55 HRC. Thus, when the torque applied by the tool exceeds the allowable limit of the transducer, locking element 25 is sheared at regions 34 and 35. Locking element 25 is therefore broken into three distinct portions to ensure that the outer sleeve member will no longer be coupled to the inner sleeve member, to avoid irreversible damage to the transducer. To continue the calibration operation, another relatively inexpensive locking element 25 can be introduced into aligned apertures of the adaptor. The adaptor of the present invention therefore reduces costly damage to a transducer and avoids heretofore unavoidable downtime to a tester, which further increases financial losses to a workplace that requires the use of a large number of tools.

Since the resultant required shear force F to shear rod 32 is dependent upon the required torque MR, and distance D between regions 34 and 35 of reduced thickness is the moment arm upon which MR acts,

F = MR / D (Equation 1).

It therefore follows that the ultimate shear strength τ of rod 32, or its maximum shear stress prior to being sheared, is τ = F /A (Equation 2), where A is the sheared area, or the area of rod 32 at regions 34 and 35 of reduced thickness. After substituting the equivalent of F and A, x = (4 MR) / (π d² D) (Equation 3).

The relationship between the theoretical maximum rod diameter dTHBOR at the regions of reduced thickness and the required torque MR for causing shearing of the rod is therefore dTHEOR = [(4 MR)/ Π X D]⁰-⁵ (Equation 4). Example 1

A test was conducted to determine the maximum rod diameter at the regions of reduced thickness for the TT-50I transducer manufactured by Stutevant Richmont, USA having an allowable applied torque limit of 635 kg-mm. Due to the size of the transducer, the diameter of the head element of the inner sleeve member was 14 mm. The locking element was made from stainless steel 416T having a rod diameter of 6.35 mm. The maximum shear stress prior to the fracturing of the locking element rod was found to 60 kg/mm². By use of Equation 4, the theoretical maximum rod diameter at the regions of reduced thickness was therefore found to be 0.98 mm.

Three locking elements were produced having a rod diameter of 0.98 mm at the regions of reduced thickness. Each locking element was secured to an outer sleeve member and inner sleeve member of an adaptor in engagement with the transducer. A tool was coupled to the adaptor, and the minimum torque need to shear the locking element at the regions of reduced thickness was determined. Table I below tabulates the test values of the minimum torque MT needed to shear the locking element at the regions of reduced thickness d, in comparison with the required maximum torque MR and with the maximum permissible torque Mp specified by the manufacturer of the transducer. The required maximum torque MR is a chosen value which is included within the permissible range of the transducer, i.e. less than Mp.

Table I

The test value MT for each locking element was found to be greater than MR. Since the test values MT were also greater than the maximum permissible torque Mp, a correction to the theoretical rod diameter d of 0.98 mm at the regions of reduced thickness was necessary in order to reduce the test value

MT.

To determine the corrected rod diameter dcoRR at the regions of reduced thickness, a variation of Equation 4 led to the following proportion:

(d²coRR / d²THEOR) = (MR / MT-AVG) (Equation 5), where MT-AVG is the average of the three test values MT. After substituting the values for MR and MT-AVG, the corrected rod diameter dcoRR was found to be 0.91 mm.

Two locking elements were then produced having a rod diameter of 0.91 mm at the regions of reduced thickness. Each locking element was secured to an outer sleeve member and inner sleeve member of an adaptor in engagement with the transducer. A tool was coupled to the adaptor, and the minimum torque need to shear the locking element at the regions of reduced thickness was determined. Table II below tabulates the test values of the minimum torque MT needed to shear the locking element at the regions of reduced thickness d, in comparison with the maximum permissible torque Mp specified by the manufacturer of the transducer.

Table II

- li ¬

lt may be concluded therefore that a locking element made from stainless steel 416T having a rod thickness of 0.91 mm at the regions of reduced thickness will shear at an average applied torque of 659 kg-mm.

Example 2

A test was conducted to determine the maximum rod diameter at the regions of reduced thickness for the TT-300I transducer manufactured by Stutevant Richmont, USA having an allowable applied torque limit of 3637 kg-mm. Due to the size of the transducer, the diameter of the head element of the inner sleeve member was 16 mm. The locking element was made from stainless steel 416T having a rod diameter of 6.35 mm. The maximum shear stress prior to the fracturing of the locking element rod was found to 60 kg/mm². By use of Equation 4, the theoretical maximum rod diameter at the regions of reduced thickness was therefore found to be 2.2 mm.

Three locking elements were produced having a rod diameter of 2.2 mm at the regions of reduced thickness. Each locking element was secured to an outer sleeve member and inner sleeve member of an adaptor in engagement with the transducer. A tool was coupled to the adaptor, and the minimum torque need to shear the locking element at the regions of reduced thickness was determined. Table III below tabulates the test values of the minimum torque MT needed to shear the locking element at the regions of reduced thickness d, in comparison with the required maximum torque MR and with the maximum permissible torque Mp specified by the manufacturer of the transducer. The required maximum torque MR is a chosen value which is included within the permissible range of the transducer, i.e. less than Mp. Table III

The test value MT for each locking element was found to be greater than MR. Since the test values MT were less than the maximum permissible torque Mp, no correction to the theoretical rod diameter d of 2.2 mm at the regions of reduced thickness was necessary.

It may be concluded therefore that a locking element made from stainless steel 416T having a rod thickness of 2.2 mm at the regions of reduced thickness will shear at an average applied torque of 3916 kg-mm.

While some embodiments of the invention have been described by way of illustration, it will be apparent that the invention can be carried out with many modifications, variations and adaptations, and with the use of numerous equivalents or alternative solutions that are within the scope of persons skilled in the art, without departing from the spirit of the invention or exceeding the scope of the claims.

Claims

1. An adaptor for a torque transducer operable in conjunction with a torque tester, comprising an outer sleeve member coupleable with a torque tool, an inner sleeve member coupleable with a torque transducer, and a breakable locking element secured to both said outer sleeve member and said inner sleeve member, wherein said locking element is adapted to break whereby to decouple said tool from said transducer when a torque applied by said tool is greater than an allowable limit.

2. The adaptor according to claim 1, wherein the inner sleeve member comprises a base element and a head element which is connected to, and smaller than, said base element, said base element being formed with a socket in which a male connecting means of the transducer is received.

3. The adaptor according to claim 2, wherein the outer sleeve member is formed with a socket in which the head element of the inner sleeve member is received, the locking element being introducible within aligned apertures formed within the head element of the inner sleeve member and within the outer sleeve member to allow a tool axle, the outer sleeve member, the inner sleeve member, and the connecting means of the transducer to rotate in unison when the torque applied by the tool is less than the allowable limit.

4. The adaptor according to claim 3, wherein the base element and head element of the inner sleeve member and the outer sleeve member are tubular.

5. The adaptor according to claim 3, wherein diametrically opposite apertures are formed within the head element of the inner sleeve member and within the outer sleeve member.

6. The adaptor according to claim 3, wherein the locking element has a head and a rod introducible into the aligned apertures, said rod being formed with two regions of reduced thickness.

7. The adaptor according to claim 6, wherein the thickness of the rod at the regions of reduced thickness is suitably selected to ensure that the locking element will be sheared at a predetermined stress level corresponding to the allowable limit of the transducer.

8. The adaptor according to claim 6, wherein the length of the rod is greater than the largest dimension of the base element of the outer sleeve member.

9. The adaptor according to claim 6, wherein the distance between the two regions of reduced thickness is substantially equal to the largest dimension of the head element of the inner sleeve member.

10. The adaptor according to claim 7, wherein the locking element is made from stainless steel 416T.

11. The adaptor according to claim 10, wherein the locking element is sheared at an applied torque of greater than approximately 659 kg-mm when its rod diameter is 6.35 mm and its rod thickness is 0.91 mm at the regions of reduced thickness.

12. The adaptor according to claim 10, wherein the locking element is sheared at an applied torque of greater than approximately 3916 kg-mm when its rod diameter is 6.35 mm and its rod thickness is 2.2 mm at the regions of reduced thickness.

13. The adaptor according to claim 10, wherein the hardness of the outer sleeve member and of the inner sleeve member is greater than that of locking element.

14. The adaptor according to claim 13, wherein the hardness of the outer sleeve member and of the inner sleeve member ranges from 50 to 55 HRC₅ and the hardness of the locking element ranges from 21 to 34 HRC.

15. A torque tester comprising at least one torque transducer, to at least one of which is coupled an adaptor according to any of claims 1 to 14.

16. An adaptor for a torque transducer, substantially as described and illustrated.

17. A torque tester, substantially as described and illustrated.