The present invention relates to a driver tool and a method of using the same and is concerned particularly with a tool and method for driving fixtures into threaded engagement.

It is often necessary to drive a threaded fixture, such as a screw or a bolt, into engagement with another article or substrate to a predetermined maximum tightness, i.e., to apply a limit to the torque with which the threaded article is driven. Tools exist in which the maximum torque can be pre-set, either mechanically, for example using a spring or "broken arm" device, or electronically for example by measuring the electrical resistance of a strain gauge bridge attached to a load cell. As the screw or bolt tightens with continued engagement, the torque required to continue turning it increases. Once the maximum pre-set torque is reached, the turning force is disengaged so that the fixture cannot damage the article or substrate.

However, in certain applications, such as when the space for working the fixture is tight, the physical size of the tool can be an impediment. Another problem with previously considered tools is the inaccuracy of the measurement. For example, in applications such as the installation of an implant into a bone site, only small tightening forces must be used, and the pre-load, i.e., the maximum torque with which the fixture is to be tightened against the bone site, may be of such a small value that previously considered tools lack the capability of a sufficiently accurate measurement. If a preload is too little it can result in loosening of the fixture. If the preload is too great, it can cause damage of the bone site and/or failure of the fixture.

Embodiments of the present invention aim to provide a driver tool for driving a fixture, and a method of operating such a tool, in which at least some of the aforementioned disadvantages of the prior art are at least partly addressed.

The present invention is defined in the attached independent claims, to which reference should now be made. Further, preferred features may be found in the sub-claims appended thereto .

According to one aspect of the present invention, there is provided a driver tool for rotatably driving a threaded fixture into an engagement, the driver tool comprising a torque limiter to limit the torque with which the fixture may be driven rotatably by the tool. The torque limiter may be mechanical and may comprise a ratchet.

Preferably, the driver tool comprises first and second engageable/engaged parts.

The tool may comprise first and second parts arranged to engage one another through complementary torque transmitting profiles and wherein the complementary profiles comprise the torque limiter.

The first and second parts are preferably arranged so that when the second part is rotated in a first direction, the cooperation of the profiles limits the torque transmitted to the first part. The first and second parts may be arranged so that when the second part is rotated in a second direction, the cooperation of the profiles does not limit the torque transmitted to the first part.

The tool preferably has one or more resilient connecting portions for connecting the first and second parts, and preferably when a maximum desired torque is reached during rotation of the second part in the first direction, the or each connecting portion resiliently deflects to substantially prevent further transmission of torque.

Preferably, continued rotation of the second part causes the or each connecting portion to return to a substantially undeflected configuration preferably producing an audible indication .

The first part of the tool may comprise attachment means to attach to the threaded fixture. More preferably, the attachment means comprise a press-fit attachment. The second part of the tool may engage with the first part of the tool so that an internal profile of the second part is in contact with a portion of an external side/profile of the first part. The second part may be rotatable about an axis. Rotation of the second part when engaged with the first part may transmit a torque to the first part of the tool. Rotation of the second part of the tool may cause the first part of the tool to rotate about a substantially aligned axis. This rotation may be limited by a torque limiter. The second part of the tool may have a profile such that rotation in a first direction transmits a substantially limited torque to the first part of the tool. The profile of the second part of the tool may have a profile such that rotation in a second, opposed direction transmits a torque that is not substantially limited.

Preferably, the internal profile of the second part of the driver tool comprises at least one cam. More preferably, the internal profile of the second part of the driver tool comprises at least two cams. Even more preferably, the internal profile of the second part of the driver tool comprises at least four cams.

Preferably, the internal profile of the second part of the driver tool comprises at least one cam edge. More preferably, the internal profile of the second part of the driver tool comprises at least two cam edges. Even more preferably, the internal profile of the second part of the driver tool comprises at least four cam edges.

The tool may comprise a sensor arranged in use to sense the stiffness of the fixture as it is being driven.

The tool may include an excitation device arranged in use to excite vibration of the fixture. The sensor preferably includes a detector device arranged in use to detect vibration of the fixture.

The excitation device is preferably arranged in use to excite the fixture electronically into vibration, more preferably into vibration across a range of frequencies. The detector device is preferably arranged to determine a frequency of vibration of the fixture, more preferably to determine a resonant frequency of vibration of the fixture.

The excitation device and/or the detector device may comprise one or more electrically conductive coils. The tool is preferably provided with an amplifier for amplifying a signal detected by the detection device. The tool preferably includes an electronic processor arranged in use to determine a stiffness level of the fixture during driving.

According to a further aspect of the present invention, there is provided, in combination, a threaded fixture and a driver tool for rotatably driving the fixture into an engagement, the tool being arranged in use to sense the stiffness of the fixture as it is being driven, and wherein the fixture comprises a ferromagnetic component that is susceptible to excitation by the tool.

The tool may be according to any statement herein.

In a preferred arrangement, the fixture has a threaded portion at a distal end thereof for engagement with an engagement site in use. The ferromagnetic component may be at a proximal end of the fixture.

The ferromagnetic component may be detachable from the fixture . According to a further aspect of the present invention, there is provided a method of rotatably driving a threaded fixture into an engagement, the method comprising measuring the stiffness of the fixture during driving.

According to another aspect of the present invention, there is provided a method for rotatably driving a threaded fixture into an engagement, the method comprising limiting the torque with which the threaded fixture is driven. The threaded fixture may be rotatably driven by a driving tool. The driving tool may be substantially prevented from rotating the threaded fixture once a predetermined torque has been reached. The predetermined torque limit may be in the range of 4-6 Ncm. More preferably, the predetermined torque limit may be 5 Ncm. The driver tool may be counter rotated to remove the threaded fixture from the engagement.

The method may include exciting vibration of the fixture. The method preferably includes detecting vibration of the fixture, more preferably detecting resonant vibration.

Preferably the method includes electronically exciting the fixture into vibration, more preferably into vibration across a range of frequencies. The method may include determining a frequency of vibration of the fixture, more preferably determining a resonant frequency of vibration of the fixture.

The method preferably comprises determining a stiffness level of the fixture during driving. The tool and/or method described herein may be used in the engagement of a fixture with a bone site, more preferably with a socket in a bone site, for example for attaching a fixture such as a peg into a dental implant, as might be required to assess the stability of the implant.

The invention may include any combination of the features or limitations referred to herein, except such a combination of features as are mutually exclusive, or mutually inconsistent .

A preferred embodiment of the present invention will now be described, by way of example only, with reference to the accompanying diagrammatic drawings, in which:

Figure 1 shows schematically a driver tool and fixture according to an embodiment of the present invention in a disengaged configuration;

Figure 2 shows the fixture of Figure 1 in an enlarged end view;

Figure 3 shows the driver tool and fixture of Figure 1 in an engaged configuration;

Figure 4 shows schematically an electronic circuit of the driver tool of Figures 1-3. Figure 5 shows schematically a two-part driver tool according to a second embodiment of the present invention in a perspective view;

Figure 6 shows schematically a part of the driver tool of Figure 5, in plan view; and

Figure 7 is an end view of the driver tool of Figure 5 in a connected configuration.

Turning to Figure 1, this shows generally at 100 a driver tool and fixture 200 for attaching to a bone site represented generally at B. The tool comprises a handle portion 110 and a socket part 120 for engaging the fixture 200. The fixture 200 has a threaded portion 210 for penetrating the bone B, a cylindrical shaft portion 220 and a hexagonal head 230 for mechanical engagement with the socket 120. A cylindrical ferromagnetic portion 240 is mounted on the hexagonal head.

Inside the handle portion 110 is a torque-limiter/latch device which in this example is mechanical, in the form of a ratchet, and represented schematically at 112. Embedded within the socket wall are electromagnetic excitation and detection circuitry represented schematically at 130 and 140, respectively.

Figure 2 shows the head 230 and ferromagnetic portion 240 in enlarged plan view. Figure 3 shows the driver tool 100 and threaded fixture 200 in engagement. The hexagonal head 230 of the fixture has been fully received in the socket 120 of the tool.

Figure 4 is a schematic representation of the circuitry in the driver tool 100 which acts as a sensor to determine the stiffness of the fixture. The tool includes an excitation device 130 including an oscillator, for exciting vibration of the ferromagnetic part 240 of the fixture, and a detector 140 including an amplifier, for detecting vibration of the part 240. Excitation coils EC and detection coils DC are embedded in the socket wall and are connected respectively to the excitation device 130 and detector 140.

The detector 140 is connected to an analogue-to-digital converter (ADC) 150 which in turn is connected to a microprocessor 160. A display 170 is connected to the microprocessor .

The oscillator in the excitation device is able to expose the ferromagnetic part 240 to an electromagnetic excitation signal of varying frequency which causes the fixture 200 to vibrate. This vibration is picked up by the detection coils DC, and the signal is amplified before being converted by ADC 150. The microprocessor 160 monitors the signal. When the natural resonant frequency of the fixture is reached, the amplitude of its vibration will increase greatly. However, the natural resonance frequency will depend on the stiffness of the fixture 200 which itself will vary as the fixture becomes embedded in the bone site B. the resonant frequency can be correlated to the degree of attachment, stiffness or preload of the fixture to the bone site. From a reference lookup table (not shown) , the microprocessor is able to determine when the required stiffness - and hence degree of tightness - of the fixture is reached. A value for, or related to, the stiffness is displayed on the display 170 as is (optionally) an indication that a user-selectable maximum tightness/stability has been reached.

Using the apparatus described above, the stiffness of the threaded fixture may be determined as it is being installed/tightened, thus permitting real-time, accurate monitoring of the degree of tightness/preload .

The torque limiting device 112 may be activated and/or regulated in response to the measured stiffness.

The excitation and detection coils may be positioned radially around the socket and may be physically separate to one another, or may overlay one another. Alternatively, the same coils may be alternately used to excite and to detect the vibration of the ferromagnet, and thus the fixture, using appropriate switching (not shown) . In an alternative arrangement (not shown) , the coils may be incorporated into a separate probe that is connected to the driver tool, optionally wirelessly, and may be held close to the fixture while the latter is being driven.

The driver 100 alone, or the driver together with the ferromagnet 240, can be a removable part that is detached from the fixture once the fixture has been tightened to the required degree. Alternatively, in an embodiment not shown,

1U the fixture 200, the ferromagnet 240 and the driver 100 may comprise a single component.

The driver 100 may be substantially made of a non-ferrous metal, or else of plastic or ceramic material. The handle part 110 may be integral with the socket part 120 or may be connectable to it, for example by a keying configuration. The threaded distal end 210 of the fixture may have one of a number of profiles for tightening the fixture to the bone site .

In use, a fixture is inserted into the socket part of the tool and the user selects the maximum tightness/preload that is to be applied to the fixture. The handle is then turned, to drive the fixture into the bone site. As the handle is turned, the tool measures the stiffness of the fixture. When the fixture tightens in its location, its stiffness increases and when the predetermined stiffness is reached the display indicates this to the user either graphically or numerically. The user may then withdraw the tool, leaving the fixture safely engaged with the site at an appropriate tightness/preload .

Although the example given above is of a tool with a fixture for securing to a bone site, for example as part of a dental implant, the tool can be used with other fixtures, such as but not limited to screws, bolts and nuts, where accurate determination of tightness is needed and overtightening must be prevented. Turning to Figure 5, this shows, generally at 1000, a two- part driver tool according to a second embodiment of the present invention. The tool 1000 comprises first and second parts 1100 and 1200 which are shown separated in the drawing, but which are joined in a push fit as will be described below. The first part 1100 has a head portion 1110 for engaging with a threaded fixture (200) as described above with reference to Figures 1-4. The second part 1200 is a finger wheel which is used to impart a torque, or turning force, to the first part, and hence to the fixture, during its installation.

The first part is of a plastics material, such as Polyamide and comprises a generally cylindrical body 1120 which carries the head 1110 and a pair of resiliently deformable connecting arms 1130 extending parallel to the longitudinal axis of the body 1120 and away from the head 1110. The connecting arms 1130 are for connecting the first part to the second part, and each arm 1130 has a barb portion 1132 for engaging with the second part, as will be described below. The connecting arms 1130 together provide a broadly circular outer torque transfer profile Pl for mating with the second part.

The second part 1200 comprises a generally cylindrical body 1210 having a knurled outer cylindrical surface to provide a good grip for a user's fingers (not shown) . Inside the body 1210 is a broadly circular inner torque transfer profile P2 that is complementary fit with the outer profile of the first part. Figure 6 shows the second part in plan view and more clearly illustrates the inner torque transfer profile P2 which comprises a circumference C2 interrupted by notch portions N2. Each notch N2 comprises an inclined ramp part R2 and a substantially radial step part S2.

In order to connect the first and second parts, the second part 1200 is pushed axially over the connecting arms 1130 of the first part 1100. As the first and second parts are urged together, the resilient connecting arms 1130 of the first part become deflected towards one another in a radial direction. When the barb portions 1132 pass beyond the inner profile P2 of part 1200, the arms 1130 spring back to their undeflected positions and the first and second parts are connected .

Figure 7 is an end view of the two parts when connected together, looking through the second part 1200 to the first part 1100. The barb portions 1132 can be seen projecting beyond the profile P2 of the second part. Also, the profiles Pl and P2 are mated together.

If rotation of the second part is attempted in a clockwise direction, represented by Arrow Al, the torque is initially transmitted via the ramp portion R2 of profile P2 to profile Pl of the first part to drive the fixture (not shown) into engagement. When a predetermined tightness, i.e. resistance is reached, indicating that the fixture is fully engaged, the ramp portion R2 of profile P2 begins to slide over a corresponding feature Fl in the profile Pl causing the resilient arms to deflect towards one another by a small distance, equal to the depth of the step portion 32. It should be noted that this deflection of the arms is not sufficient to bring the barbs beyond the profile P2 and so does not allow the first and second parts to be separated.

The circumferential portion C2 of the profile P2 then slides over the profile Pl, imparting no torque. As rotation of the second part 1200 continues, eventually profile Pl reaches the step portion S2 of profile Pl and the arms 1130 snap back to their undeflected positions, making an audible "click" as they do so, indicating to the user that maximum tightness has been reached. Further turning of the second part will transmit no torque to the fixture but will merely lead to repeated cycles of deflecting the arms and them springing back with a "click" sound.

The mass and stiffness of the components, especially the arms 1130, and the profiles Pl and P2 are selected carefully to ensure the desired predetermined torque is not exceeded. In the case of a dental post/peg engaging with a threaded socket (not shown) of a dental implant (e.g. in a jaw bone) for example, the maximum torque is in the range 4-6 Ncm, and more preferably 5 Ncm.

In contrast, when the second part 1200 is rotated anticlockwise, in the direction represented by Arrow A2, the step portion 32 of profile P2 engages directly with a complementary step portion 31 of profile Pl and torque is transmitted from the second part to the first, part step to step, without limit (within expected operating ranges) . This enables the fixture to be withdrawn from engagement. Therefore, using complementary profiles for the first and second parts, with ramp portions and step portions, torque may be transmitted from the second part to the first part - and hence to the fixture - in a controlled, limited manner in one direction of turning, and in an unlimited manner in the opposite direction. Overtightening of the fixture is therefore prevented.

This is important to avoid damaging the fixture or the socket or implant or surrounding bone. It is also important to ensure that the fixture is tightened to the correct/standard degree if the fixture is to be used for testing the socket, for example when assessing the stability of the socket/implant .

Whilst endeavouring in the foregoing specification to draw attention to those features of the invention believed to be of particular importance, it should be understood that the applicant claims protection in respect of any patentable feature or combination of features referred to herein, and/or shown in the drawings, whether or not particular emphasis has been placed thereon.