AU7145000A - Guiding accessories for power tools - Google Patents

Description

10550

ORIGINAL

Complete Specification .r 4, Applicant: Applicant's address: Title: Inventor: Inventor's Address: Priority: Avos Developments Limited 99 Sabulite Road, Kelston, Auckland, New Zealand Guiding accessories for power tools Anthony Alfred van Osenbruggen 99 Sabulite Road, Kelston, Auckland, New Zealand Claiming priority from New Zealand patent application No. 500786 dated 3 November 1999 2 Guiding accessories for power tools

FIELD

This invention relates to guides for tools and in particular to guides for setting the operating orientation of freely movable, or hand-held power tools (such as electric drills) in particular with respect to the direction of gravity.

BACKGROUND

There is often a desire to hold a power tool, such as an electric drill, in a particular orientation.

For example, a worker may require that the drill bit is vertical so that the hole to be created in a work surface will be perpendicular to a flat, horizontal surface plane. At other times, there may 1 0 be requirements to make one or more sloping holes within horizontally inclined surfaces, or perpendicular holes within sloping surfaces. It is relatively difficult to achieve precision in this kind of operation by eye, particularly because although an operator can align the drill bit in one o axis, at the same time the drill bit may develop a substantial slope towards or away from the observer in the line of sight. As soon as the operator sets the attitude in one axis, alignment is 15 lost in a perpendicular axis. Some patent documents have been filed concerning means to provide levels or guides for electric drills, and these mostly involve placing a spirit level either on the body of the drill Duperon, US 4546549) or on an external frame (Ashley et al, US 4656749). Some employ a mirror, to be placed on the work, and a sight (MacDonald, US 5246197 and US 5052112). Tools other than electric drills may also require to be held in a certain attitude (not necessarily perpendicular but usually in a fixed relation to horizontal or vertical). For example, these include hand-held circular saws (skill saws) (as in Wolff, US5692310 and US 5887355).

DEFINITIONS

"Attitude" as used herein describes the tilt of the cutting portion of a power tool in relation to the direction of gravity which is towards the center of the Earth, (or in relation to some other frame of reference) and so control of attitude allows a cutting action to be for example, substantially vertical or horizontal or perhaps a specified 20 degrees below horizontal.

"Position" as used herein describes the position of the cutting portion of a power tool in relation to a set of co-ordinates such as latitude, longitude, and altitude or one based on triangulation from nearby reference points. A control of position allows a cutting action to be made at a specified site.

"Orientation" as used herein describes the combination of position and attitude.

A "sDirit level" is a container, generally tubular, including a liquid (originally an alcohol) and a small amount of a gas; the gas forming a bubble, and the container is shaped so that movement of the bubble in relation to datum marks over a slightly outwardly curved surface provides a sensitive indication of the direction of gravity in relation to a mounting of the container.

OBJECT

It is an object of this invention to provide an improved apparatus for placing a moveable tool in a oooo required attitude, position, or orientation, or at least to provide the public with a useful choice.

STATEMENT OF INVENTION In a first broad aspect this invention provides an accessory for a power tool for use at a site, 15 wherein the accessory is capable of being fastened to the power tool by means of an existing accessory handle attachment point and is capable of serving as a handle; the accessory further includes at least one direction sensing means responsive to an orientation of at least one external energy field; the field having a known orientation in relation to the site, the accessory further including at least one display means operatively connected to the direction sensing means and thereby capable of indicating the orientation of the power tool to an operator so that the operator can hold the power tool in a desired attitude prior to or during use.

Alternatively the tool may be a hand-operated cutting tool, a hammering tool, or a marking tool.

Preferably the accessory has the external appearance and function of an accessory handle and is constructed so as to be fastenable to the power tool by means of an existing attachment point provided on the power tool.

Alternatively the accessory has no other function apart from the purpose of indication.

Preferably an accessory handle is capable of being twisted into a desired rotational attitude with respect to the cutting tool used within the power tool, and then locked into place, so that the accessory handle can (if provided with more than one axis of gravity sensing means) be used to set the tool at a working slope.

Alternatively the accessory handle may be provided with a rotatably lockable level sensing device.

In a related aspect this invention provides an accessory for a power tool for use at a site, •oi* wherein the external energy field is gravity and the direction sensing means comprises at least one spirit level, the level being capable of indicating to an operator the attitude of the power tool, S in at least one tilt axis, in relation to the direction of gravity, so that in use the cutting tool can be operated in a known attitude in relation to the direction of gravity.

In another related aspect this invention provides an accessory for a power tool for use at a site, wherein the direction sensing means comprises a tubular spirit level having a bend causing the level to comprise two parts at substantially 90 degrees; the level being capable of indicating to an operator either of two optional attitudes in relation to the direction of gravity, so that in use the cutting tool can be applied in either of the two attitudes in relation to the direction of gravity.

In a further related aspect this invention provides an accessory for a power tool for use at a site, wherein the external energy field having a known orientation is gravity, an electrical direction sensing means comprises at least one gravity-responsive switching means, the direction sensing means being capable of indicating to a user when the power tool, in relation to the direction of gravity, is in a desired attitude so that in use the cutting tool can be applied in a known attitude in relation to the direction of gravity.

Preferably the readout is visual; alternatively it may be audible.

In a yet further related aspect this invention provides an accessory for a power tool for use at a site, wherein the external energy field having a known orientation is gravity, an electrical direction sensing means comprises at least one transducer means capable of responding to the gravitational attraction of the Earth, the transducer means being connected to indicator means capable of indicating to a user when the power tool, in relation to the direction of gravity, is in a desired attitude so that the cutting tool can be operated in a known attitude in relation to the direction of gravity.

Preferably the readout is proportional; that is, it indicates in some way the extent of a deviation from a desired attitude.

In a still further related aspect this invention provides an accessory for a power tool for use at a site, wherein the external energy field having a known orientation is gravity, an electrical direction sensing means comprises three transducer means each mounted in a mutually 10 perpendicular plane in relation to the other two; each transducer means being capable of responding to the gravitational attraction of the Earth, each transducer means being connected to signal conditioning means and to indicator means capable of indicating to a user when the power tool, in relation to the direction of gravity, is in a desired attitude so that the cutting tool can be operated in a known attitude in relation to the direction of gravity.

o*o* 15 In an even further related aspect this invention provides an accessory for a power tool for use at a site, wherein the accessory includes tilting means capable of tilting the means capable of sensing the direction of gravity to a desired angle in relation to a working axis of the power tool and then capable of holding the sensing means at that angle, so that an offset is conferred upon the indicator means and so that the power tool can be used at any desired tilt in relation to the S: 20 direction of gravity.

In a second broad aspect this invention provides an accessory for a power tool for use at a site, wherein the external energy field having a known orientation comprises electromagnetic radiation radiated from more than one artificial source, and the accessory is capable of determining and indicating the position of the power tool in relation to the more than one artificial source, so that a current position of the power tool can be compared to a desired position and the tool can then be shifted to and used at the desired position.

Preferably the indication of position is relative to a desired position, though optionally it is an absolute indication of position.

In a related aspect this invention provides an accessory for a power tool for use at a site, wherein at least one artificial source comprises an orbiting (GPS) satellite, and the accessory is capable of using GPS signals in order to determine the current position of the power tool, so that the cutting tool can be used at a known position. Preferably a LCD display or the like shows information derived from the GPS signals in a convenient format.

In a further related aspect this invention provides an accessory for a power tool for use at a site, wherein at least one artificial source comprises an orbiting (GPS) satellite, a further artificial source comprises a local transmitter of compatible signals, and the accessory is capable of using the combination of compatible signals in order to determine the current position of the power tool, so that the power tool can be used at a precisely known position.

In a still further related aspect this invention provides an accessory for a power tool for use at a site, wherein the accessory includes means capable of determining and indicating the direction of gravity as previously described in this section, in addition to determining and indicating the current position of the power tool as previously described in this section, so that the power tool S. 15 can be used at a known position and at a known attitude.

**S

A particular power tool for which this accessory may be used as a handle or the like is a post hole borer, so that GPS satellite technology, optionally enhanced with a local transmitter, may be employed in order to determine placement of one or more holes in a landscape.

In a yet further related aspect this invention provides an accessory for a power tool for use at a 20 site, wherein the accessory further includes tool enabling means capable of inhibiting operation of the tool unless the tool is in a desired orientation.

In a third broad aspect this invention provides an accessory for a power tool for use at a site, wherein the method includes the steps of selecting more than one beacon in order to define a co-ordinate system in three dimensions, creating a list of tasks to be carried out with the power tool at selected positions in relation to the co-ordinate system, and moving the power tool to each position in turn and operating the tool at that position, so that no physical laying out of positions over the site is required.

Optionally, the accessory is also provided with means capable of displaying the attitude of the tool so that the tool may be operated in a desired attitude.

One preferred electrical gravity-sensitive transduction means is a mercury switch having at least one pair of contacts arranged at a low part of a preferably sealed cavity containing mercury.

Preferably the internal geometry of the cavity is arranged to provide for a desirable degree of accuracy. More preferably a series connected array of switches provides for greater control of the attitude.

Another preferred electrical gravity-sensitive transduction means involves a magnetically sensitive switching means mounted in a predetermined relation to a magnetic, eccentric, pivoted weight.

Yet another preferred electrical gravity-sensitive transduction means includes means to interrupt ooooo an optical beam at certain orientations by the movement of an eccentrically mounted, pivoted weight.

ooo.

Optionally damping of the movement of any gravity-responsive object may be used; for example damping by interaction with a viscous fluid or damping by induced eddy currents.

*Soo*: Alternatively, damping may be provided for using electronic signal-processing means such as a low-pass filter.

PREFERRED EMBODIMENT The descriptions of the invention to be provided herein are given purely by way of example and are not to be taken in any way as limiting the scope or extent of the invention.

DRAWINGS

Fig 1: shows one version of an attachable handle including means (a spirit level) to determine a horizontal state or attitude.

Fig 2: shows another version of an attachable handle including means to determine a horizontal state in two axes.

Fig 3: shows another version of an attachable handle including means to determine a horizontal state, or a vertical state.

Fig 4: shows how a handle according to the invention can be fitted to an electric drill.

Fig 5: shows one way to connect standard mercury switches to emulate a circular spirit level like that shown in Fig 3.

Fig 6: shows a circuit to provide power to a motor when the apparatus is held in the correct attitude.

1 0 Fig 7: shows a design for a single-tubed spirit level capable of showing either a horizontal state, or a vertical state.

••go Fig 8: shows a simplified electrical circuit including a gravity sensor and a display that can mimic the appearance of a spirit level.

Fig 9: shows a design for a single tubed spirit level adapted for use on a handle that can be 15 attached to a power tool.

Fig 10: shows a design for an accessory dual-orientation spirit level adapted to be clipped onto a depth gauge of a drill handle.

Fig 11: shows a simplified "square" design of a spirit level tube intended as an alternative to the circular level 905 of fig 9.

Fig 12: shows principles for using GPS satellites or the like, together with a local reference transmitter, to permit an orientation-indicating power tool including a GPS receiver to be placed and oriented accurately about a site. Attitude indication is also, optionally, provided.

Fig 13: shows principles for using silicon accelerometer modules and conditioning means in order to indicate tilt of a power tool.

The "problem to be solved" might be stated as that it is difficult to hold a power tool during use by hand in a reasonably accurate orientation, for example so that a drill bit will create vertical holes at required positions.

In a basic form, one version of this invention can be considered as a modified form of an "ISO" standard handle which comprises a cylindrical handle having a stud with a standard screw thread protruding axially from one end. This fits a wide range of power tools of various types and from various manufacturers in the United States, Germany, Japan, and so on. If a variety of S. 10 screw threads exist, it is trivial to provide adapters. The handle has been modified so that it can become an accessory for a power tool wherein the accessory includes means capable of indicating the attitude and perhaps also the position of the machine to which it is attached, with relation to gravity and/or a co-ordinate system.

Use of a standardised accessory has the advantage that the invention can be purchased at a 15 later date that the main tool, and perhaps from a different supply line. It can be used in turn with any one of a range of power tools that an operator may possess.

We prefer that the accessory handle is fastenable to the power tool by means of an existing attachment point which is perpendicular to the drive axis the axis about which the drill is turned, the nail is hammered, or the saw blade is turned. (Fig 4 shows an electric drill 400 having such 20 an attachment point, at 401). Then, provision of a level-sensing device capable only of sensing whether the length axis of the handle is level provides a first but useful step in assisting with tool orientation. The user can use the "handle-level" to set an orientation in one axis, and look at the tool from the side to set an orientation in a perpendicular axis. The actual level-sensing means may be a spirit level but may also be some other form of transducer such as a gravity-sensitive electrical device, for instance a mercury switch.

NON-ELECTRICAL INFORMATION 1. SPIRIT LEVELS In Fig 1, a handle 100 includes a shaft that may be gripped during use (102) and a stud 105 compatible with a range of different brands of power tool. A spirit level 101, having a slightly convexly curved interior containing a sealed-in liquid and a bubble 103 is provided with graduations such that when the bubble is midway between the marks the tube, and presumably the device holding the tube, is level. The setting circle or threaded washer 106 may be used to lock the stud in place and set the level uppermost when the power tool is in use.

The vibration during use of the power tool can be considerable in some circumstances. We have found that as long as the user can "set up" his or her body to hold the tool in the correct attitude before starting work, it can be held reasonably correctly for a period. Ideally, the level indicator is independent of vibration and the use of viscous damping within spirit levels, or other forms of damping (such as electronic circuits that have long time constants) can help to provide continuous indication of attitude. See Fig 13 and the related description.

A second degree of orientation may be provided if the handle is also provided with a second level, at right angles to the first, as shown in Fig 2, where 202 is the second spirit level. This might physically be constructed entirely within the handle, or a shaped unattached end might contain a tubular level-sensing structure. (The might be small and may not need to affect the 15 external outlines of the handle). The handle is then capable of indicating a level state in two planes. There are from time to time occasions when a tool is required to be operated at a predetermined slope. Then, if the handle can be locked into position on the tool so that the cross arm of the T is perpendicular to that slope, the operator can know that the tool is at a certain sloped orientation. Preferably a graduated scale and locking means is provided upon the accessory handle, so that the slope of the tool can be set without reference to external levels, protractors, or the like. Fig 9 develops this version with a handle 901 having a lengthwise oriented tube 902 as described previously, and in addition a large disk 904 which is provided with an at least partly circumferential spirit level 905 having the usual bubble 906 and graduated markings. Threaded collar 903 provides for adjustment of the disk 904 so that the circumferential level can indicate a vertical (or a horizontal) attitude. (We have not shown protective means for this tube which is otherwise vulnerable to damage).

Fig 3 shows the use of two radially symmetrical spirit levels 301 and 303 to indicate the attitude of the handle 300.

Fig 11 shows a substantially rectangular tube 1100 (though with outwardly extending arcuate limbs eg 1103 which may be preferred over the circular tube 905 of Fig 9. Generally, a handle of the type of 901 is provided with a lock nut so that it can be tightened in a preferred orientation and for example if the intention is to drill holes at say 20 degrees inclination in the purlins of a roof, the lock nut can be adjusted so that the level indicates "level" when the attached drill is at an offset of 20 degrees from horizontal. In a conventional short tube, one means for damping movement of the bubble is that if it occupies most of the cross section of the tube, fluid flow is restricted behind the bubble. In a complete ring tube, a narrowed portion of the tube at 1102 in Fig 11) may be helpful.

Fig 7 shows a composite design for a liquid bubble spirit level 705, and the same when mounted on a handle 701. In this design an L-shaped tube 705 is provided with both a horizontal and a vertical portion and a bubble 706 is shown between graduations on the short limb of the tube, when at the same time there will not be a bubble between the graduations adjacent to 705. The handle 7001 shows a concentric end display configuration 702, attached oooo to an elongated limb 703 as another variation of this composite design. A preferred variation of this L-shaped tube is to provide a circular level indicator (eg 1003 in Fig 10) attached to a slightly arcuate tube 1004. In fact Fig 10 shows (by way of non-limiting example) a combination indicator fitted with clips 1005, 1005') capable of attaching the indicator in a correct orientation to a depth gauge 1001 of a standard handle 1000 intended for attachment to a drill or other hand-held power tool. This accessory level is then capable of indicating the correct alignment of the depth gauge and hence the entire power tool. Whether the interior of the level comprises a single 20 continuous cavity having a single bubble, or whether there are separate cavities for the circular and the elongated indicator is optional.

Those accessory handles (or the like) that provide "on-tool lighting means" may also be provided with means to specifically illuminate the fluid-filled level itself, such as a fibre optics conductor between an existing lamp and a level indicator, or a separate lamp.

ELECTRICAL ATTITUDE-SENSING INFORMATION 1. ON/OFF An electrical interface to a level-sensing device offers some advantages and may be provided quite conveniently especially if the power tool is a battery-operated one (or is capable of being controlled by a battery-powered circuit). It may be provided with, or as part of, an accessory handle that already is fitted with electrical devices such as battery storage, workplace illumination or the like.

Advantages of the electrical interface include making the correct attitude more obvious such as by means of coloured lights or the like, and even allows for controlling the power tool so that its cutting tool cannot function unless it happens to be in the correct attitude. Audible indications tend to be less useful in view of the noise that power tools typically make.

An example solution to electrical control is illustrated in Figs 5 and 6. Mercury switches are made for level-sensitive control purposes. A single switch (such as 503) of the type available in our laboratory is in the "ON" state for almost half a solid circle; that is the mercury globule is in contact with the internal electrodes if the wire leads are pointing down. However, connecting several switches in series and in a physical arrangement such that they are all "ON" together in only a limited range of attitudes overcomes that problem. Fig 5 shows at 500 an elevation view of three switches 501 502, and 503 each separated by 120 degrees (in a plan view) and with their axes diverging, according to this invention. Fig 6 employs a set 500 of attitude-sensitive switches in a circuit for a battery-powered motorised tool. The battery is 601; the motor is 602.

A bypass switch 603 is provided in case the tool is to be used in some attitude other than vertical, and a further switch 604 ensures that the tool is off when not in use. Mercury switches provide a relatively robust but relatively coarse control of tool attitude.

ELECTRICAL ATTITUDE-SENSING INFORMATION 2. PROPORTIONAL 4OI*** If an electronic level sensor system is to be used, it is preferably proportional; that is, it indicates in some way the amount of a deviation from a desired attitude. In other words, rather than 20 having a"yes/no" display using for example mercury switches, the invention will provide a series of lamps, or a coded brightness, or a colour change, to show the operator how far to change the attitude of the tool is so that he or she can shift it by a controlled amount.

A more preferred electrical gravity-sensitive transduction means involves a magnetically sensitive switching means (such as a Hall effect switch or sensor) mounted in a predetermined relation to a magnetic, eccentric, pivoted weight so that the sensor output indicates when the transducer is in the correct orientation. Several such Hall effect transducers could give a proportional indication in several mutually perpendicular axes. The pivoting means could include some form of damping so that the weight does not swing to and fro, nor responds unduly to vibration.

Yet another preferred electrical gravity-sensitive transduction means includes an optical beam interrupted at desired orientations by an eccentric, pivoted weight. Fig 8 shows at 800 the exterior view of a handle fitted with a proportionally indicating light-emitting diode array 801 (with one lamp 802 illuminated). The diagrammatic circuit below shows how this may be made. A paired infra-red transmitter and receiver forms a pair of optical beams 808, 809 (passing through the plane of the paper). A light-absorbing interrupter 805 comprises a centrally pivotally mounted disk having an eccentric weight 806 and a notch 807. Damping may be provided by support within a viscous fluid or damping by inducing eddy currents, or by vanes in air. The device is designed to indicate a vertical attitude when the notch allows equal amounts of light to flow in each beam, so minimising effects of temperature sensitivity, battery voltage, etc. An amplifier 803 comprises an interface between the gravity transducer 804 and a level-displaying bar graph 006• array 801. For prototyping simplicity a complete unit including an analogue to digital converter and drive logic for an array of LEDs, such as the TSM 3914 /TSM3915 is preferred.

0@*S ELECTRICAL ATTITUDE-SENSING INFORMATION 3. SOLID-STATE 15 An improved electronic gravity sensor can be constructed with silicon micro-fabricated devices.

For example, Analog Devices, Inc (Norwood, MA, USA) produce a suitable family of accelerometers having bandwidths from DC to 100 Hz. The ADXL150 EM-3 device is a tri-axial evaluation module including three type ADXL150 accelerometers that is capable, with suitable resolving circuitry, of indicating the direction of the centre of the earth to within one degree.

Vibration during use of the power tool, which might totally interfere with readings from previously described kinds of level sensors can be either averaged out, or, if over a certain level, can be rejected using either analogue electronic circuits that have amplitude clipping and suitably long time constants or using digital signal-processing means to provide a continuous indication of attitude. A preferred resilient mounting of the evaluation module should protect the sensors from damage by very high impulses. Fig 13 shows a block diagram 1300 of a prototype circuit using an ADXL150 EM-3 module (1301) which requires a 5 volt supply, and has three analogue output leads. The block diagram includes a "set" button (1305) for loading and holding (remembering) a certain tilt, and providing an indication of the current tilt (relative to the desired tilt) at an array of LEDs (1307). Module 1302 imposes excessive-amplitude clipping on the X, Y, and Z signals, and imposes suitably long time constants on the "surviving" signals. For example any impulse corresponding to an impulse of over about 2x g in either direction should be rejected. A time constant of about 0.5 seconds should be appropriate. Module 1303 sums the signals with "desired tilt" or offsets from the button-equipped module 1305. This button can be pressed briefly while the tool is at a desired tilt, to load an offset into the electronics when any attitude other than true vertical is to be used. Module 1304 converts three-axis tilt information into currents driving an X/Y array of LEDs in a display module 1306, located at a convenient place for viewing on the accessory handle for the power tool. The operator is required to keep the central LED lit during use of the tool for accurate aiming, and in this example illustration a small tilt to the left is being requested. The difference in tilt between the central LED and the adjacent ring of LEDs may be 0.5 degree; between the next two, 5 degrees, and so on. Otherwise, any of the display formats previously described may be suitable options for use with this example. A switch activated only when the central LED is on could be used to enforce the requirement of using the power tool only when it is in the correct attitude.

It will be appreciated that a small microprocessor having say three analogue input ports and a number of LED-capable output ports (or means to drive an LCD display) and internal memory for executable code provides a convenient digital solution to the above signal processing and 15 display needs.

ELECTRICAL POSITION INFORMATION The initial concept of an accessory for a power tool comprising a tilt-indicating device can be extended to make use of the Global Positioning Satellite (GPS) system or the like, to provide a tool locator device capable of locating the position (perhaps using GPS-type principles) and 20 attitude (using tilt/level sensors as previously described in this specification) sufficiently accurately for constructional purposes on a site. Standard "domestic" GPS used to have an intentionally limited accuracy. There are several ways to increase accuracy considerably, such as the use of a local, fixed GPS transmitter to provide an approximately 1 mm accuracy over a kilometer or so. Fig 12 shows a construction site 1200, provided with a fixed local GPS transmitter 1205 as well as one or more nearby GPS satellites 1204, 1204A. A power tool 1202 is fitted with a GPS receiving means 1203 and an operator-compatible liquid-crystal display 1201 (or 1306 fig 13) which would preferably indicate co-ordinates relative to a "next desired position" rather than absolute altitude, longitude, and altitude. Indicators may be graphical such as the arrow on the display 1201 and in that case an internal microprocessor interfaced to the GPS receiver may be used to handle sequences of operations and indicate where to move the tool to for the next operation. The power tool would include its own means for determining attitude relative to gravity. A compass or other means of determining the direction faced by the machine tool may also be required. As a result, the shaping or cutting tool bit 1206 may be located in three-dimensional space and in attitude to a useful degree of accuracy. Note that the "GPS" system has been used herein as an illustration. Alternative location systems, such as a time-synchronised set of several local transmitters like 1205, or microwave, optical, or sonic systems may be used. The power tool may transmit a pulse to a set of spaced-apart receivers; a computer may compute the current position, and a separate receiver on the power tool may then be used to provide an indication to the operator. Advantages of this system include that even a large construction site may be laid out precisely in a "numerically controlled" way. Foundations as well as subsequent attachments can be placed accurately. This approach has a particular advantage where it is difficult to define a point at which an operation is to occur by normal measurement or triangulation, perhaps because of intervening structures or non-rectilinear S constructions.

S* ELECTRICAL POSITION INFORMATION 2. POST HOLES.

Mechanical post hole borers are used on farms for placing fence posts, on building sites to make building foundations, and the like. Using the invention in or as a handle of a post hole borer allows GPS satellite technology or developments (as described above) to accurately place a series of holes in a landscape, and perhaps supersede normal surveying as a process for establishment of fence and boundary lines. Minor mechanical adaptation of the attachment of the handle to the body of the machine may be required, because strains are greater.

VARIATIONS

An accessory handle has been used by way of example as a foundation for installing this invention. Another example described use of an existing (or accessory) depth gauge.

Alternatively, an existing battery case may be used, or the mechanism may be built into a power tool at the time of manufacture. The mechanism may be otherwise attached to the tool.

The invention could be provided in combination with a hand tool, such as a hand-operated drill, or a brace and bit, or perhaps an adze or a plane for use in boatbuilding. The invention may be used with a marking device.

16 Finally, it must be reiterated that the scope of this invention is not limited to the specific preferred embodiments as set forth in the accompanying claims.

Claims (10)

1. 3. An accessory for a power tool as claimed in claim 2, characterised in that the direction sensing means comprises a tubular spirit level having a bend causing the level to comprise two parts at substantially 90 degrees; the level being capable of indicating to an operator either of two optional attitudes in relation to the direction of gravity, so that in use the power tool can be operated in either of the two attitudes in relation to the direction of gravity.
2. 4. An accessory for a power tool as claimed in claim 2, characterised in that the external energy field having a known orientation is gravity, an electrical direction sensing means comprises at least one gravity-responsive switching means, the direction sensing means being capable of indicating to a user when the power tool, in relation to the direction of gravity, is in a desired attitude so that in use the power tool can be operated in a known attitude in relation to the direction of gravity. 18 An accessory for a power tool as claimed in claim 2, characterised in that the external energy field having a known orientation is gravity, an electrical direction sensing means comprises at least one transducer means capable of responding to the gravitational attraction of the Earth, the transducer means being connected to indicator means capable of indicating to a user when the power tool, in relation to the direction of gravity, is in a desired attitude so that the power tool can be operated in a known attitude in relation to the direction of gravity.
3. 6. An accessory for a power tool as claimed in claim 2, characterised in that the external energy field having a known orientation is gravity, an electrical direction sensing means comprises three transducer means each mounted in a mutually perpendicular plane in relation to the other two; each transducer means being capable of responding to the gravitational attraction of the Earth, each transducer means being connected to signal S°conditioning means and to indicator means capable of indicating to a user when the power tool, in relation to the direction of gravity, is in a desired attitude so that the power tool can be operated in a known attitude in relation to the direction of gravity.
4. 7. An accessory for a power tool as claimed in any one of claim 2 to claim 6, characterised in that the accessory includes tilting means capable of tilting the means capable of sensing the direction of gravity to a desired angle in relation to a working axis of the power tool and then capable of holding the sensing means at that angle, so that an offset is conferred upon the indicator means and so that the power tool can be used at any desired tilt in relation to the direction of gravity.
5. 8. An accessory for a power tool as claimed in claim 1, characterised in that the external energy field having a known orientation comprises electromagnetic radiation radiated from more than one artificial source, and the accessory is capable of determining and indicating the position of the power tool in relation to the more than one artificial source, so that a current position of the power tool can be compared to a desired position and the tool can then be shifted to and used at the desired position.
6. 9. An accessory for a power tool as claimed in claim 8, characterised in that at least one artificial source comprises an orbiting (GPS) satellite, and the accessory is capable of using GPS signals and displaying information derived therefrom in order to determine the current position of the power tool, so that the power tool can be operated at a known position. An accessory for a power tool as claimed in claim 9, characterised in that at least one artificial source comprises an orbiting (GPS) satellite, a further artificial source comprises a local transmitter of compatible signals, and the accessory is capable of using the combination of compatible signals in order to determine the current position of the power 10 tool, so that the power tool can be used at a precisely known position.
7. 11. An accessory for a power tool as claimed in claim 9, characterised in that the invention is particularly adapted for use as a handle of a post hole borer so that GPS satellite technology or the like may be employed in order to determine placement of one or more holes in a landscape.
8. 12. An accessory for a power tool as claimed in any one of claims 8, 9, 10, or 11, characterised in that the accessory includes means capable of determining and indicating the direction of gravity as claimed in any one of claims 2 to 6, in addition to determining and indicating the current position of the power tool as claimed in any one of claims 8, 9, 10, or 11, so that the power tool can be operated at a known position and in a known attitude.
9. 13. An accessory for a power tool as claimed in any previous claim, characterised in that the accessory further includes tool enabling means capable of inhibiting operation of the tool unless the tool is in a desired orientation.
10. 14. A method for using, at a site, a power tool equipped with an accessory capable of determining the position of the power tool (as claimed in any of claims 8 to 11), characterised in that the method includes the steps of selecting more than one beacon in order to define a co-ordinate system in three dimensions, creating a list of tasks to be carried out with the power tool at selected positions in relation to the co-ordinate system, and moving the power tool to each position in turn and operating the tool at that position, so that no physical laying out of positions over the site is required. A method as claimed in claim 13 for using, at a site, a power tool equipped with an accessory capable of determining the position of the power tool (as claimed in any of claims 8 to 11) wherein the accessory is also provided with means (as claimed in any of claims 2 to 6) capable of displaying the attitude of the tool so that the tool may be operated in an intended attitude at an intended position. il i .g. Dated this 3rd day of November 2000 Avos Developments Limited By their Patent Attorneys LESICAR PERRIN el•.il a. oo. o* o O