WO2009071908A1

WO2009071908A1 - Power tool

Info

Publication number: WO2009071908A1
Application number: PCT/GB2008/004026
Authority: WO
Inventors: Michael Edward Best; Martin Roberts-Jones
Original assignee: Impact
Priority date: 2007-12-04
Filing date: 2008-12-04
Publication date: 2009-06-11
Also published as: GB2455322C; GB2455322B; GB0723763D0; GB2455322A

Abstract

A power tool (20), for example for removal of wall paper or barnacles, comprises a housing (5), a driven member (11) for reciprocal movement relative to the housing (5), guide means (l0) to support and guide said driven member (11) when reciprocating relative to the housing (5), electrically powered drive means, and supply means for supply of electrical power to the drive means, said electrically powered drive means comprising a solenoid (6) having a core region and the driven member (11) comprising at least in part a ferrous section whereby energising of the solenoid (6) causes reciprocal movement of the driven member (11) relative to the housing.

Description

POWER TOOL

This invention relates to a power tool and in particular, though not exclusively to a portable electrically powered tool.

For many applications it is necessary or preferable that a tool bit executes a reciprocating linear motion. That motion is readily achievable by the use of a pneumatically or hydraulically powered piston and cylinder drive arrangement, but such power sources generally are noisy and require the provision of a bulky compressor. In consequence the portability and convenience of use, particularly for non-industrial purposes, is very limited.

The use of an electrical power source to drive an electric motor is also well known and examples of electrically operated portable power tools are described in GB 2219958 and GB 2276344. These describe various cam arrangements for converting the rotary motion of an electric motor into reciprocating axial movement of a tool bit. However the cam arrangement and other like devices hitherto proposed, and which are required to be of a robust construction, are relatively bulky and heavy in addition to constituting a significant part of the total manufacturing costs of the power tool.

The present invention seeks to provide a power tool of the kind which facilitates reciprocal movement of a tool bit and in which at least some of the aforedescribed disadvantages of known power tools are mitigated or overcome.

In accordance with one aspect of the present invention a power tool comprises:-

- a housing,

- a driven member for reciprocal movement relative to the housing,

- guide means to support and guide said driven member when reciprocating relative to the housing,

- electrically powered drive means , and - supply means for supply of electrical power to the drive means,

- said electrically powered drive means comprising a solenoid having a core region and the driven member comprising at least in part a ferrous section whereby energising of the solenoid causes reciprocal movement of the driven member relative to the housing.

The driven member may have a tool bit, herein referred to also as a tool head, formed integrally therewith or may comprise an attachment portion to which a tool bit may be selectively secured and from which it may be removed.

The solenoid may define a substantially linear core whereby, in use, the driven member executes linear reciprocal movement. Alternatively the solenoid may define a core which is curved along its length to receive a correspondingly curved driven member whereby, in use, the driven member executes arcuate reciprocal movement.

The power tool preferably comprises also bias means, such as a mechanical spring, which acts between the housing and the driven member to react against the force exerted by the solenoid on the driven member. Thus it will be understood that the present invention more generally provides a power tool in which a tool bit is reciprocated by the action of an electrically powered oscillator. The frequency and stroke length of the resonant spring/mass system may, for example, be determined by selection of the voltage supply to the solenoid, frequency of a multi-vibrator circuit provided to drive the solenoid, or a pulse width modulator (PWM) output variable waveform microprocessor.

The reciprocal movement preferably is in the range 3800 to 5700 cycles per minute (cpm), and more preferably in the range 4000 to 5500 cpm. The frequency may be selected having regard to the intended function of the tool bit. Thus, for example, for a tool bit employed for removal of ceramic tiles, or other relatively hard material, a frequency in the range 4000 to 4500 cpm is preferred. For a tool bit employed for removal of wallpaper, or other relatively soft material, a frequency in the range 5000 to 5500 cpm is preferred. For a tool bit employed for removal of barnacles a frequency in the range 4000 to 4500 cpm is preferred.

For some intended functions of the power tool the aforedescribed reciprocal movement, which may be termed a primary reciprocal movement, may be sufficient for a tool bit to perform effectively. However the present invention further teaches that said primary reciprocal movement may have superimposed thereon a small secondary motion such that, for example, at at least one end region of each stroke of the driven member the tool bit experiences a smaller backwards and/or forwards motion, which may be termed a secondary motion, or secondary chatter.

The extent of the secondary chatter movement preferably is less than 15%, more preferably less than 10% of the stroke length of the primary reciprocal motion.

The stroke length preferably is in the range 1.0 mm to 5 mm, more preferably 1.5 mm to 4.5 mm, and the length of any secondary chatter provided for at the end of the stroke preferably is in the range 0.1 mm to 0.3 mm.

In the same manner that the frequency of reciprocal movement of the driven member may be pre-selected or varied in use in accordance with the intended function of a tool bit, the stroke length of the reciprocal movement and the length of any secondary chatter movement similarly may be pre-selected or varied. Thus, for example, for a tool bit employed for removal of ceramic tiles or removal of barnacles the stroke length preferably is in the range 3.5 mm to 4.5 mm, more preferably 4mm, and the secondary chatter at the two ends of the stroke preferably is 0.2 mm. For a tool employed for removal of wallpaper the stroke length preferably is in the range 1.8 mm to 2.8 mm, more preferably 2.3 mm, and the secondary chatter movement at the ends of each stroke preferably is 0.2 mm. The power tool may comprise means to control one or more of the frequency, stroke length and chatter length independently or one or more of said perameters may be pre-set. Control means may be provided automatically to vary one parameter in a manner related to selection of another parameter. Thus if the frequency is varied there may automatically be a variation of stroke length and/or secondary chatter.

The power tool may of a cordless type powered internally by a replaceable and/or rechargeable battery. In the case of a rechargeable battery, an induction charging coil may be provided within the housing, particularly if the tool is to be sealed against ingress of water, so that the battery may be recharged in situ without any requirement to provide an access point and related risk of leakage. Alternatively the tool may be externally powered by a cable which extends into the housing.

The present invention further provides a power tool in combination with a tool bit selectively removable from the power tool.

One 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 is a perspective view of a portable hand power tool in accordance with the present invention;

Figure 2 is a view similar to that of Figure 1 with part of the housing removed;

Figure 3 is a longitudinal sectional view of the power tool of Figure 1 , and

Figure 4 is an exploded perspective view of part of the tool as shown in Figure 3. An electrically powered and portable hand tool 20 comprises a cast aluminium housing 5, an external knuckle guard 4, a protective nose cone 2 and a nose piece 3.

Provided within the housing 5 is a power source 21 comprising a lithium ion battery pack 7 and an induction charging coil 9 which enables the battery to be charged from an external charger via the wall of the housing.

Also provided within the housing 5 is an electro magnet coil, shown as solenoid 6, which is excitable by the battery 7 acting via a control printed circuit board (PCB) 8 and pressure switch 22. The PCB 8 comprises a highspeed switching facility which determines the frequency of excitation of the solenoid. That frequency may be pre-selected or control means may be provided to enable that frequency to be varied.

A driven member in the form of a steel shaft 11 , of two part construction, extends through the core of the solenoid 6. One end, an inner end 23, is provided with a flange 24 and a recoil spring 12 is provided between the flange and an end of the solenoid.

The other, outward end 25 of the shaft 11 has an attachment zone 26, comprising for example a detent 27 (see Figure 2) or other means known per se, whereby a tool blade 1 may be attached to and removed from the end 25 of the driven shaft. Alternatively the tool bit may be secured in any other manner known per se, for example as described in the aforementioned GB 2276344. The protective nose cone2 fits over the detent or other means by which the tool blade 1 is secured to the shaft 11.

The portion of the shaft between the ends 24,25 extends through a guide chassis 10, comprising oilite guide bearings which restrain the shaft against lateral movement but allow it to reciprocate freely in the axial direction of the solenoid core at a frequency corresponding to the frequency of excitation of the solenoid. In operation of the power tool the cone 2 and the nose piece 3 reciprocate in unison with the shaft 11.

In the aforedescribed embodiment the length of reciprocating axial movement of the shaft, i.e. the stroke length, is determined by the power applied to the solenoid, but in an alternative construction, not illustrated, the stroke length may be limited by mechanical stops.

To provide for secondary chatter movement the drive shaft 11 is of a two-part construction comprising a main part 28 which extends through the solenoid to the end flange 24 and an outer end portion 29 which is able to reciprocate axially relative to the main portion 28. The portion 29 is of a square tubular section profile and two opposite faces are provided with longitudinally extending slots 30 each of which, in the assembled condition, is occupied by a pin 31 secured to the end region of the main shaft portion 28. The length of the slot is selected to result in the desired degree of chatter movement such that, in use, the tool is able to execute a secondary harmonic motion. In this embodiment the slot has a length 0.2 mm greater than the diameter of the pin 31 thereby to provide for secondary chatter of a 0.2 mm stroke length.

From the foregoing it will be understood that the present invention avoids the need to use a cam or similar drive train mechanism which is necessary to convert rotary motion of an electric motor into reciprocating movement of a tool bit and, by the use of an electro-magnet drive, also avoids the need for an hydraulic or pneumatic power source. The resulting construction is believed to provide a significant reduction in manufacturing costs and reduce the number of moving parts such that it is possible to provide a more robust and reliable product. Internal friction also is reduced and hence, particularly in the case of a battery operated tool, more efficient use of the battery power is achieved, leading to an improvement in the period for which the battery is able to operate the tool effectively.

MBGBDE2

Claims

Claims:

1. A power tool comprising :-

- a housing,

- a driven member for reciprocal movement relative to the housing,

- electrically powered drive means , and

- supply means for supply of electrical power to the drive means,

2. A power tool according to claim 1 wherein the frequency of said reciprocal movement is in the range 3,800 to 5,700 cycles per minute.

3. A power tool according to claim 2 wherein said frequency is in the range 4,000 to 5,500 cycles per minute.

4. A power tool according to claim 3 wherein said frequency is in the range 4,000 to 4,500 cycles per minute.

5. A power tool according to claim 3 wherein said frequency is in the range 5,000 to 5,500 cycles per minute.

6. A power tool according to any one of the preceding claims wherein the stroke length of the reciprocal movement is in the range 1.0 mm to 5 mm.

7. A power tool according to claim 6 wherein said stroke length is in the range 1.5 mm to 4.5 mm.

8. A power tool according to any one of the preceding claims wherein at at least one end of each stroke of said reciprocal movement the driven member provides for a smaller secondary movement of the driven member or a tool secured thereto.

9. A power tool according to claim 8 wherein said secondary movement comprises a secondary harmonic motion.

10. A power tool according to claim 8 or claim 9 wherein said secondary movement has a stroke length less than 15% of the stroke length of said reciprocal movement.

11. A power tool according to claim 10 wherein said stroke length of the secondary movement is less than 10% of the stroke length of said reciprocal movement.

12. A power tool according to any one of claims 8 to 11 wherein the stroke length of the secondary movement is in the range 0.1 mm to 0.3 mm.

13. A power tool according to any one of the preceding claims wherein the solenoid defines a substantially linear core whereby, in use, the driven member executes linear reciprocal movement.

14. A power tool according to any one claims 1 to 12 wherein the solenoid defines a core which is curved along the length of the core whereby, in use, the driven member executes arcuate reciprocal movement.

15. A power tool according to any one of the preceding claims wherein bias means acts between the housing and driven member to react against force exerted by the solenoid on the driven member.

16. A power tool according to any one of the preceding claims wherein the frequency of reciprocal movement of the driven member may be varied in use of the tool.

17. A power tool according to any one of the preceding claims wherein the stroke length of reciprocal movement of the driven member may be varied in use of the tool.

18. A power tool according to any one of the preceding claims wherein at at least one end of each stroke of said reciprocal movement the driven member provides for a smaller secondary movement of the driven member or a tool secured thereto and the stroke length of said secondary movement of the driven member may be varied in use of the tool.

19. A power tool according to any one of the preceding claims wherein at least one of the frequency of reciprocal movement of the driven member, stoke length of reciprocal movement of the driven member and stroke length of any secondary movement of the driven member is non variable.

20. A power tool according to any one of the preceding claims and comprising control means whereby one or more of the parameters of frequency of reciprocal movement of the driven member, stoke length of reciprocal movement of the driven member and stroke length of any secondary movement of the driven member may be controlled independently of one or more of the other of said parameters.

21. A power tool according to any one of the preceding claims and comprising control means whereby one or more of the parameters of frequency of reciprocal movement of the driven member, stoke length of reciprocal movement of the driven member and stroke length of any secondary movement of the driven member is varied automatically in a manner related to a user inputted variation of one or more other of said parameters.

22. A power tool according to any one of the preceding claims wherein said tool is powered internally.

23. A power tool according to claim 22 wherein the housing contains a rechargeable battery and an induction charging coil for use in recharging the battery.

24. A power tool according to any one of the preceding claims wherein the driven member has a tool head formed integrally therewith.

25. A power tool according to any one of claims 1 to 23 wherein the driven member comprises an attachment portion to which a tool head may be selectively secured.

26. A power tool according to claim 1 and substantially as hereinbefore described.

27. A power tool according to claim 8 when dependent on claim 4 wherein the stroke length of the reciprocal movement is 4 mm and the stroke length of the secondary movement is 0.2 mm.

28. A power tool according to claim 8 when dependent on claim 5 wherein the stroke length of the reciprocal movement is 2.3 mm and the stroke length of the secondary movement is 0.2 mm.

29. A power tool according to any one of the preceding claims in combination with a tool head selectively removable from the power tool.

MBGBCL1