THE PRESENT INVENTION relates to instrument tuners and more specifically to drum tuners. In general, drum tuners to enable drum nuts to be tightened to a pre-set torque value are known which operate using a ball-and-detent system. A spring which forms part of the tuner may be pre-loaded, and the extent to which the spring is to be preloaded is dictated by the desired torque to which a drum nut is to be tightened. The pre-loaded spring biases the ball into the detent, and the tuner may then be used to tighten the drum nut. Once the pre-set torque has been reached, turning the tuner causes the ball to move from the detent, causing a detectable "click", indicating to the user that the selected torque has been reached. However, this type of drum tuner is prone to over-tightening of drum nuts as in use, it can be difficult to detect the "click" that occurs when the ball has moved from the detent, to indicate that the selected torque has been reached. This may lead to over-tightening of the drum nuts and eventual damage to drums and drum skins. Additionally, tuners which employ a ball-and-detent system are susceptible to wear with use, degrading the accuracy of the tuner.

It is an object of the present invention to alleviate at least some of the difficulties associated with this type of drum tuner. Accordingly, the present invention provides an adjustment device comprising a handle portion that may be grasped by a user, a spindle portion adapted to engage an element to be rotated against a resistive torque, a first magnet arrangement, comprising one or more permanent magnets, attached to the handle portion and a second magnet arrangement, comprising one or more permanent magnets, attached to the spindle portion, wherein there is magnetic attraction between the first and second permanent magnets to form a magnetic coupling, and the handle portion, the spindle portion and the magnetic coupling are arranged so that the first and second magnets are in close proximity to each other, such that when a relative torque below a predetermined torque is applied to the handle portion and the spindle portion, the handle portion and spindle portion will rotate together, due to the magnetic coupling, and when a relative torque greater than the predetermined torque is applied to the handle portion and the spindle portion, the magnetic coupling will be overcome and the handle portion will rotate with respect to the spindle portion.

Preferably, the distance between the first and second magnet arrangements may be increased or decreased.

Conveniently, the adjustment device further comprises an adjustment arrangement configured to increase or decrease the distance between the first and second magnet arrangements.

Advantageously, the adjustment device further comprises a read-out display, the read-out display configured to provide a user with an indication of the distance between the first and second magnets. Preferably, the read-out display is an analogue read-out.

Alternatively, the read-out display is a digital read-out.

Conveniently, the handle portion includes a textured finish on an outer surface. Advantageously, the adjustment arrangement includes a textured finish on an outer surface.

Preferably, rotation of the adjustment arrangement causes the distance between the magnet arrangements to increase or decrease.

Conveniently, the adjustment arrangement includes a screw thread.

Advantageously, the adjustment arrangement further comprises a locking arrangement to prevent operation of the adjustment arrangement to increase or decrease the distance between the first and second magnet arrangements.

Preferably, the adjustment device further comprises a clutch assembly to prevent rotation of the spindle portion with respect to the handle portion.

Conveniently, the spindle portion includes a drive arrangement configured to accommodate a socket.

Alternatively, the spindle portion includes a socket.

Advantageously, the adjustment arrangement is configured to be moveable with respect to the handle portion to increase or decrease the distance between the first and second magnet arrangements. Preferably, the locking arrangement may be moved between a first position in which the adjustment arrangement is substantially prevented from moving with respect to the handle portion and a second position in which the adjustment arrangement may be moved with respect to the handle portion. The embodiments of the present invention will now be described, by way of example only, with reference to the figures, in which: FIGURE 1 shows an example of a drum tuner embodying the present invention; FIGURE 2 shows an exploded view of the drum tuner of figure 1 ;

FIGURE 3 shows a partial view of the tuner of figures 1 and 2; and

FIGURE 4 shows a partial cutaway view of a drum tuner embodying the present invention.

Turning firstly to figure 1 , a drum tuner 1 embodying the present invention is shown. The tuner 1 comprises three main portions, a handle portion 2 that may be grasped by a user to rotate the tuner 1 , an adjustment portion 3 that is housed generally inside the handle portion 2, and a spindle portion 4 which is coupled to the handle and adjustment portions 2, 3.

The handle portion 2 of the tuner 1 is shaped to be easily grasped by a user, and may include a knurled or textured surface, or have a similar effect on the outside surface thereof to aid in gripping. The handle portion 2 houses and generally encloses the adjustment portion 3 which may also have a textured or knurled surface to aid in rotation and grip, and includes a torque read-out display 5 and a locking arrangement 6. Rotation of the torque adjustment portion 3 adjusts the torque setting of the tuner 1 (as will be discussed in more detail below), and the selected torque value is displayed on the torque readout display 5. The torque read-out display 5 may be a simple analogue display, or may be a more complex digital read-out arrangement. The value shown on the torque read-out display 5 may be an indication of the true torque setting of the tuner 1 , in suitable units (for instance Nm), or may be a value not directly indicative of the true torque setting, but a value that may give a user a reference point as to the selected torque value, to aid in easy, rapid and consistent torque selection.

The spindle portion 4 includes a drive arrangement 7 at its free end which may be shaped so as to fit a standard square-drive type socket, or may be shaped to form a proprietary interface with sockets or the like that are specific to particular drums. Alternatively, the drive arrangement 7 may comprise an integral socket, spanner or alien key type arrangement. Figure 2 shows an exploded view of the drum tuner 1 of figure 1 . For ease of understanding, the three separate portions - the handle portion 2, the adjustment assembly 3 and the spindle assembly 4 of the tuner 1 - are separated from one another. As can be seen, the adjustment portion 3 includes a locking arrangement, which takes the form of a locking plunger 6. The locking plunger 6 includes an elongate portion 9, and will be discussed in more detail later. The elongate portion 9 is located generally within and passes through the main part of the adjustment portion 3. The locking arrangement 6 need not necessarily be a locking plunger 6 with an elongate portion 9, but may take any suitable form to enable adjustment of the torque setting of the tuner 1 , discussed in more detail later.

Further, the handle portion 2 has an internal thread 12 which may be screwed onto an external thread 13 formed on a lower portion of the adjustment portion 3. Rotation of the adjustment portion 3 causes the external thread 13 of the adjustment portion 3 to advance into, or retract from, the internal thread 12 inside the handle portion 2, resulting axial movement of the adjustment portion 3 with respect to the handle portion 2 of the tuner 1 . As can be seen in figure 3, the distal end of the adjustment portion 3 of the tuner 1 makes contact with the topmost portion 10 of the spindle portion 4. By virtue of the contact between the distal end of the adjustment portion 3 and the topmost portion 10 of the spindle portion 4, the axial movement of the adjuster 6 causes complementary axial movement of the spindle portion 4 with respect to the handle and adjustment portions 2, 3 of the tuner 1 .

Turning now to figure 4, the internal parts of the locking plunger 6 can be seen. The elongate portion 9 passes into and is generally enclosed by the adjustment portion 3. The locking plunger 6 is biased, by a spring assembly 21 towards a first position, in which the plunger 6 is generally protruding from the handle portion 2 (as shown in figures 3 and 4). In the first position, the handle portion 2 and the adjustment portion 3 may not move relative to one another. This is discussed in more detail below. The plunger 6 may be moved into a second position, in which the plunger 6 is pushed into a recess provided on the top of the adjustment portion 3.. In the second position, the handle portion 2 and the adjustment portion 3 may move relative to one another, also discussed in more detail below. The elongate portion 9 has a tapered section 22 and a non-tapered section 23.

Preferably, the movement of the locking plunger 6 from the first position to the second position is in a direction which is generally aligned with the axis about which the spindle portion 8 rotates. When the plunger 6 is in the first position, the non-tapered section 23 of the elongate portion 9 bears against the proximal end of a locking pin 24, retaining the locking pin 24 in an engaged position. The locking pin 24 passes through the wall of the adjustment portion 3 and the distal end of the locking pin 24 engages with grooves (not shown) in the inner wall of the handle portion 2, preventing the adjustment portion 3 from rotating with respect to the handle portion 2. When the locking pin 24 is in the engaged position, both the handle and adjustment portions 2, 3 may be co-operatively rotated.

When the locking plunger 6 is in the second position, the tapered section 22 of the elongate portion 9 bears against the proximal end of the locking pin 24, allowing the locking pin 24 to move into a released position. The locking pin 24 does not engage with the grooves in the inner wall of the handle portion 2, and allows the adjustment portion 3 to rotate with respect to the handle portion 2. As discussed above, rotation of the adjustment portion 3 with respect to the handle portion 2 causes the adjustment portion 3 to advance into, or retract from, the handle portion 2. The adjustment portion 3 is affixed to the spindle portion 4 by way of a bearing 26 and a screw 27, but any suitable system may be used so that the spindle portion 4 may rotate freely with respect to the adjustment portion 3. As the adjustment portion 3 is advanced into or withdrawn from the handle portion 2, the spindle portion 4 is moved axially along with the adjustment portion 3.

The axial movement of the adjustment and spindle portions 3, 4 affects the distance between the handle portion 2 and the spindle portion 4.

Figure 5 shows a partial view of the drum tuner 1 , including the adjustment portion 3, the handle portion 2 and the external thread 13 of the adjustment portion 3. The external thread 13 engaged with the internal thread 12 of the handle portion 2. As discussed above, the plunger 6 is biased, under spring tension, into the first position.

The proximal end of the locking pin 24 is maintained in contact with the tapered section 22 of the plunger 6, and the locking pin 24 is also biased under spring tension. In this position, the distal end of the locking pin 24 is extended beyond the outer diameter of the adjustment portion 3 in order to engage with any one of a number of matching grooves 30 of a splined section 28, which may be cut axially into the top inner diameter of the adjustment portion 3. This, as discussed above, prevents any movement of the adjustment portion 3 relative to the handle portion 2.

The splined section 28 may be a series of equally spaced axial grooves 30 cut to match the end profile of the locking pin 24. The spacing of the grooves 30 is chosen to select the resolution of the tool. In the embodiment shown in figure 5, there are 20 grooves, which divides one revolution of the adjuster into 20 increments. By selecting the pitch of threads 12, 13, one increment may represent an axial movement equal to 1/20th of the pitch of the threads 12, 13. Other configurations of grooves 30 may be used to suit the purpose of the tuner, and a second locking pin (not shown), offset by half a division, may be also be added to double the resolution.

To change the position of the adjustment portion 3 relative to the handle portion 2, the plunger 6 is depressed against spring tension to allow the locking pin 24 to engage with an undercut section 220 of the plunger 6. Due to the locking pin 24 being under spring tension to engage with the tapered section of the plunger 22, the proximal end of the locking pin 24 will take up a new position in the undercut section 220, allowing the distal end of the locking pin 24 to disengage from the splined section 28.

The adjustment portion 3 is then free to turn with respect to the handle portion 2. When the desired adjustment has been made, the plunger 6 may be released and the distal end of the locking pin 24 may again engage with another of the grooves 30 of the splined 28. The axial movement of the adjustment portion 3 relative to the handle section 2 may be a precise value, within machining tolerances, equal to the thread pitch divided by the number of grooves 30 of the splined section 28 passed over. The read-out 5 on the tuner 1 may indicate the relative position of the adjustment arrangement 3 with respect to the handle portion 2.

Returning to figure 2, rotation of the adjustment portion 3 also causes the information displayed on the torque read-out display 5 to change. In the embodiment shown, rotation of the adjustment portion 3 causes the read-out display 5 to move rotationally with respect to the a display portion 1 1 , so that differing numbers are viewable through a "window" on the torque read-out display 5 dependent on the axial position of the spindle portion 4. The display portion 1 1 may be calibrated to give an accurate torque read-out, or to give a range of reference values, as discussed above.

The handle portion 2 terminates, at its lower end, in a cavity 8 having side walls 17 and a top wall 18. The spindle portion 4 has a protruding flange 19 part way along its length. When the tuner 1 is assembled, the flange 19 lies within, and can rotate within, the cavity 8. A surface 20 of the flange is generally planar and faces the top wall 18 of the cavity 8.

A first magnet arrangement 14 is provided on the top wall 18 of the cavity 8. The first magnet arrangement 14 comprises one or more magnets 14 which present portions having an alternating polarity, facing in the direction of the flange 19 of the spindle portion 4. The first magnet arrangement 14 may comprise a single, relatively large sectional magnet 14 which may, for example, be annular in shape. Alternatively, one or more smaller magnets, for instance arranged radially on the top wall 18 of the cavity 8, may be used.

A second magnet arrangement 15 is provided on the surface 20 of the flange 19. The second magnet arrangement 15 comprises one or more magnets 15 which present portions thereof also having of an alternating polarity, facing in the direction of the top wall 8 of the cavity 18. The second magnet arrangement 15 may again comprise a single, relatively large sectional magnet 15 which may, for example, be annular in shape. Alternatively, one or more smaller magnets, for instance arranged radially on the surface 20 of the flange 19, may be used. The first and second magnet arrangements 14, 15 are permanent rare-earth magnets 14, 15, but may in other embodiments be electromagnets or any other suitable type of magnet, dependent upon the use of the tuner 1 . The first and second magnet arrangements 14, 15 are aligned such that the poles of one magnet arrangement 14 are generally aligned with opposing poles of the second magnet arrangement 15. Potentially, the north poles of the first magnet arrangement 14 may be aligned with the south poles of the second magnet arrangement 15. The converse arrangement may also be used, and either orientation will ensure that magnetic attraction forces are present between the first and second magnet arrangements 14, 15, rather than repulsion forces.

The magnet arrangements 14, 15 are also configured such that axial rotation of the handle portion 2 causes similar axial rotation of the spindle portion 4. When the spindle portion 4 is engaged with a braking load, such as a drum nut, the axial rotation of the handle 2 and spindle portions 4 will be linked until the torque required to tighten the drum nut further equals the torque that can be transmitted to the spindle portion 4 from the handle portion 2 through the attractive forces between the magnets 14, 15. Once the drum nut reaches the required, pre-set torque level, the magnetic attraction forces will be overcome by the rotational force applied to the handle portion 2, and the spindle portion 4 will no longer rotate as the handle portion 2 is rotated, but will remain stationary with respect to the handle portion 2.

The force of attraction between the magnets in the tuner 1 , and therefore the torque value at which the spindle portion 4 will "slip" with respect to the handle portion 2, is changed with the lateral movement of the spindle portion 4 with respect to the handle and adjustment portions 2, 3. As the spindle portion 4 is moved away from the handle and adjustment portions 2, 3 by rotation of the handle portion 3, the distance between the two sets of magnets 14, 15 will increase. Therefore, given that magnetic attraction is inversely proportional to the square of the distance between two magnets, the attraction between the magnets will decrease, and will be approximately a quarter as strong for each doubling of the distance between the magnets 14, 15. Conversely, as the distance between the two sets of magnets 14, 15 is decreased, the attraction between the magnets will increase, with the attraction between the magnets 14, 15 increasing by approximately four times for each halving of the distance therebetween.

This increase and decrease in the magnetic attraction is exploited to allow the tuner 1 to be set to a wide range of torque settings. When the magnets 14, 15 are in close proximity, the torque applied to the tuner 1 which will cause the handle and adjustment portions 2, 3 to "slip" with respect to the spindle portion 4 will be relatively high. Conversely, when the magnets 14, 15 are separated from one another, the torque required to cause the handle and adjustment portions 2, 3 to slip with respect to the spindle portion 4 will be relatively low.

When the handle and adjustment portions 2, 3 slip with respect to the spindle portion 4, the magnets 14, 15 will momentarily be aligned such that the polarities of the magnets 14, 15 are similar, and the magnets 14, 15 will therefore be opposed, not attracted. The locking pin 24, when engaged, ensures that there is no movement of the adjustment portion 3 with respect to the handle portion 2 when slipping occurs, ensuring that the torque setting of the tuner 1 is not altered and therefore the accuracy of the torque setting of the tuner 1 is retained. In general, as it is not desirable to use a set torque setting to unscrew drum nuts, the tuner 1 may further comprise a clutch or ratchet assembly 16 to ensure that when the tuner 1 is turned in a non-tightening direction, the handle and adjustment portions 2, 3 are rotated with the spindle portion 4, regardless of the torque applied, or to ensure that the handle and adjustment portions 2, 3 always rotate with respect to the spindle portion 4 when the tuner 1 is turned in a non-tightening direction, usually anti-clockwise. The embodiment shown in the figures uses a clutch assembly 16, which also prevents a drum nut from being loosened when the first and second magnet arrangements 14, 15 are aligned so as to have common polarity, when the handle portion 2 is rotated with respect to the spindle portion 4. Other embodiments may dispense with the clutch assembly 16.

The clutch assembly 16 may take the form of a known roller and wedge arrangement, or may take any suitable form which would be appreciated by a person skilled in the art.

In use, a user would use the drum tuner 1 to tighten the skin of a drum. The user would determine the required torque setting to which the drum tuner should be pre-set, and would grasp the handle portion 2 and the adjustment portion, depressing the plunger 6, and rotating the adjustment portion 3 with respect to the handle portion 2 to set the tuner 1 to the required torque setting. The torque to which the tuner 1 is set would be read by the user from the display portion 1 1 within the torque read-out display 5. The rotation of the adjustment portion 3 would cause the magnets 14, 15 to move closer or further apart from one another, and when the required torque has been set, the user would release the plunger 6, preventing further rotation of the adjustment portion 3 with respect to the handle portion 2.

The user would then attach the required socket to the distal end of the spindle portion 4 (or if the tuner 1 incorporates a drum nut fitment at the distal end of the spindle 4, would simply use the tuner 1 ) and use the tuner 1 to tighten the drum nuts to the required torque setting. Once the drum nuts are tightened to the required torque setting, the handle and adjustment portions 2, 3 of the tuner 1 would continue to be rotatable, but the spindle portion 4 would not rotate. This "slipping" of the tuner 1 would indicate to the user that the selected torque for the drum nut has been reached.

The user could then repeat this tightening process until the drum is tuned, before removing the socket from the end of the spindle portion 4 (if fitted). This allows the user to tighten all of the drum nuts to the same degree easily and quickly.

It is also envisaged that devices embodying the present invention may be used for tightening or adjusting elements other than drum nuts.

When used in this specification and claims, the terms "comprises" and "comprising" and variations thereof mean that the specified features, steps or integers are included. The terms are not to be interpreted to exclude the presence of other features, steps or components.

The features disclosed in the foregoing description, or the following claims, or the accompanying drawings, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for attaining the disclosed result, as appropriate, may, separately, or in any combination of such features, be utilised for realising the invention in diverse forms thereof.