GB2252745A

GB2252745A - Powered tool

Info

Publication number: GB2252745A
Application number: GB9202718A
Authority: GB
Inventors: John Patrick Manning
Original assignee: PALMER ROBERT MAURICE
Current assignee: PALMER ROBERT MAURICE
Priority date: 1991-02-13
Filing date: 1992-02-10
Publication date: 1992-08-19
Anticipated expiration: 2012-02-10
Also published as: EP0499459A2; GB9202718D0; EP0499459A3; GB2252745B

Abstract

A tool in which the operating head is given an improved, controlled linear reciprocatory action includes a cam member (13; 44) and cam follower (32; 40) mounted within a housing (10). Either the cam member or the cam follower is rotated by a drive moans (12) and either the cam follower or the cam member is mounted for linear reciprocatory movement. The cam follower includes a rotary bearing (33; 41, 42) and a spring means (30) is provided to urge the cam member and cam follower out of interengagement. The tool operating head, for example a chisel bit, is given a pulsed and/or reciprocatory action under the read control of the user. The chisel bit is received in a socket 19 of shaft 20 of follower 32, 40. <IMAGE>

Description

2 2. 5 7 7 4 5 Powered Tool The present invention is concerned with tools,

in particular, but not exclusively, of the portable hand-held type. The invention affords the possibility of providing a reciprocating drive to such tools.

While some available power tools, for example rotary drills, have provision for assisting the action of the tool by applying a reciprocatory linear force to the tool bit, there are many, conventionally unpowered, tools for which any linear force is normally applied either by simple manual pressure or with the aid of a hammer or other impacting mans. Such tools include chisels used for cutting wood or masonry. Although many craftsmen prefer to use a hamer when Ynrking with a chisel in the belief that they can thereby better control the cutting action of the tool, the physical effort and skill involved in wielding a hammer, and the risk of injury associated with hammering a metal tool, are serious disadvantages associated with that use.

Many other tools which are not usually subjected to harmering in this way, for example paint scrapers, spades and hoesPwould nonetheless be assisted in their action if a controlled reciprocatory drive could be applied to the working head of the tool. However such a controlled device is not available and tools of this type continue to be used without the benefit of such assistance.

In the few cases where a powered hammering action is applied to a tool, for example in the case of pneumatic road-drills or of hand drills with a hammer bit, the hammer action involves a succession of discrete impacts. That is, the power to be applied to the tool is built up over a short period and then suddenly released, so as to drive the tool in the direction of the workpiece with a sudden surge of power. The resulting hammering action is difficult to control and has little place in the operation of a tool which needs to be used in a controlled manner.

It is an object of the present invention to provide a powered tool in which an improved, controlled linear reciprocatory action is applied to the operating head of the tool in the direction of the %, nrkpiece.

The tool according to the present invention comprises a housing, a cam member and a cam follower munted within the housing along a conmn axis therein for relative axial movement into and out of mutual engagen'ent, said cam me having a surface which, in a direction parallel to said common axis, varies in height around the perin- e-ter of that surface, said can follower ccmprising a rotary bearing for engaging said cam member surface, drive means to rotate one of said cam member and said cam follower about said ccnmn axis, the other of said cam member and cam follower being mounted for linear movement in the direction of said axis, a tool operating head, mounted for linear movement with said linearly movable can member or cam follo%f-.r, and spring means for resiliently urging said cam member and cam follower out of mutual engagement.

The desired controlled linear reciprocatory action is brought about by engagement of the cam follower and the surface of the cam member, as these two cnents are brought into progressive mutual engagenient under increasing pressure of the user upon the housing when the tool is in contact with the workpiece. Initial intermittent contact of the cam follo%.,-er with the high point or points of the cam surface gives rise to a corresponding pulsed axial action of the tool. As the pressure applied to the tool by the user increases, the cam follower follows an increased proportion of the cam surface and the action of the tool approaches progressively a more smooth reciprocatory action.

Thus the nature of the driving force applied to the tool at the nrkpiece is variable in a controlled manner under the control of the user of the tool. The detailed form of the eventual reciprocatory action is set by the profile of the cam surface and the frequency of the reciprocation can be varied by varying the speed of rotation of the rotated cnent.

The housing is preferably generally cylindrical in shape and preferably tapers somewhat towards the tool operating head. It may conveniently be made in trin parts, joined together along the length of the tool so as to permit ready assembly and optionally subsequent dismantling for imintenance purposes. The housing parts may be imde in metal or mculded in a plastics material.

The cam member is mounted within the housing along a ccirmDn axis with the cam follower. Conveniently that axis is coaxial with that of the housing. The cam surface which controls the re"-iprocation of the tool head faces in a direction parallel to that axis. Thus the cam member may be generally disc-shaped and then the cam surface is one of the faces of the disc. Whatever the form, of the cam meinber, the cam surface varies in a continuous manner around at least the perimeter of the surface. The cam profile may be repeated at least once around the periphery of the cam surface or one cycle of the cam profile my correspond to one complete circuit of the surface.

In a preferred form of the present invention, the cam surface comprises one or more flat surfaces inclined at an angle of less than 90 degrees to the common axis of the cam nr and cam follower. Preferably the angle of inclination of the surface(s) to the perpendicular to that axis lies within the range frcm 2.5 to 15-degrees, more preferably of the order of 6 to 7 degrees.

-I The cam follower incorporates a rotary bearing for engaging the surface of the cam member. By means of this interengagen-ent, the relative rotary movement of the cam me and cam follower is converted into the desired relative axial movement of these two ccimponents, with the minimum loss of power attributable to friction between them. The bearing may be mounted with its axis coaxial with that of the cam me or may be inclined to that latter axis. An advantage of such an inclined bearing is that it may be of larger diameter than the interior diameter of the housing and may thus rotate at a lower speed. However that advantage must be weighed against the disadvantage that the load on the bearing is off-set as a result.

In general, it is preferred that there are at least two points of contact of the cam follower with the cam surface, disposed symmetrically about the ccmion axis of the two components. In that case, the can profile should be multiplied a corresponding number of times around the can surface.

The relative rotary moveinent of the cam member and cam follower may be achieved by rotation of either of these two ccmponents. That is, either the cam member may be rotated and the cam follower be mounted for linear movement towards and away from the cam surface, or the cam follower may be rotated and the cam me be mounted for linear movement towards and away fran the cam follower. The rotation of whichever ccrnponent is rotated is effected by drive mans. Preferably the drive means takes the form of an electric motor contained within the housing. The motor may be poed frcm the electricity mains supply but in a preferred form of the invention, one or more batteries are disposed within the housing to drive the motor. It is especially preferred that the battery or batteries be rechargeable. Thus the powered tool according to the invention may be not only portable but also completely self-contained..

Spring means are provided for resiliently urging the cam manber and cam follower out of mutual engagen-ent. Thereby, these two cnents only engage each other when the user applies pressure to the housing in order to apply the operating head of the tool to the workpiece. This pressure by the tool user overcomes that of the spring means and the cam follower and cam surface will progressively engage each other as the pressure applied is increased. Thus the initial interengagement, as described above, will comprise an intermittent regular contact between the cam follower and the high point or points of the cam surface. Progressively increasing pressure progressively increases the extent of interengagEment of the cam follower with the cam surface. If the dimensions and structure of the tool permit, then the cam follower may eventually remain in engagenent with the cam surface throughout the cycle of relative rotation of these components. However, in one preferred form of the present invention, a stop is provided within the housing to limit the extent of this interengagement, such that the engagement remains intermittent and the action of the tool operating head remains pulsed rather than smoothly reciprocal.

The spring means preferably ccuprises one or more ccmpression springs, which conveniently may be disposed bet,,qeen the interior of the housing and the linearly-movable corrponent, forexaTiple the cam follower.

The tool operating head, for example a chisel or hoe blade, may be fixedly secured to the linearly-movable component, in which case the tool is dedicated to a given activity using that fixed operating head. Howeever, it is preferred to provide a chuck or other form of socket into which a tool bit may be removably and interchangeably securable; the chuck or other socket may conveniently be directly linked to the linearly-movable ccniponent, for example the cam follower. Thus, by way of excmple, a range of chisel bits may be made available and/or one or more chisel bits may be interchangeable with, say, a paint scraper or wallpaper scraper bit.

As indicated above, the invention nay be applied to tools of a wide range of kinds and functions. Thus the tool may be a wood or masonry chisel or may have a haiffner bit. It may be a scraper for paint or wallpaper or for the remval of textured plaster surfaces or of barnacles. It may be a file or may have an operating head specifically for fettling castings of aluminium or another metal or alloy. The tool may be adapted for chasing out mortar between bricks. In another form, it has proved to be highly effective in removing putty frcm window frames, using a chisel bit. It may further be used for horticultural purposes such as hoeing, forking 10 and digging.

The inventon will now be further described with reference to the accarpanying drawings, which illustrate, by way of example only, three preferred embodiments of the tool according to the present invention and Wherein:- Fig. 1 is a vertical sectional view of the operating parts of a first anbodin-K-nt of the tool; Fig. 2 is a corresponding view of a second embodiment of the tool; and Fig. 3 is a corresponding view of a third embodiment of the tool.

The tool illustrated in Fig. 1 comprises a housing 10 formed in t%m longitudinal halves, of which only one is visible in the drawing. The housing is essentially cylindrical in shape and tapers towards a flat end 11.

zk Secured axially within the housing 10 is a rechargeable DC electric motor, which drives, via reduction gears, a can member 13 mounted upon its output shaft 12.

The cam irr 13 is of a stepped, generally cylindrical structure and the cam surface in this embodiment is a plane surface 14, inclined at a shallow angle (about 7 degrees) across the axis of rotation of the member 13. Thus, as the cam member rotates, the foremost point 15 on the cam surface follows a circular path around the axis of rotation.

Also retained within the housing 10 is a cam follower 32, which carries a single rotary bearing 33 and, by running upon the cam surface 14, converts the rotary motion of the cam member 13 into the desired linear motion of the cam follower. The cam follower 32 is mounted in a bearing 23 and is free to move axially by a short distance but cannot rotate.

An operating tool bit such as a chisel bit (not shown) is received in a socket 19 in the shaft 20 of the cam follower 32 and is retained in place by a collar 21 and screw 22. The tool bit therefore moves linearly with the cam follower. A ccmipression spring 30 disposed between the end face 11 of the housing 10 and the collar 21 urges the cam follower 32 out of contact with the cam surface 14 until the spring pressure is overcame by pressure applied by the tool user when the tool engages a workpiece. The spring 30 is enclosed by a rubber sealing boot 31.

In use of the tool, the cam member 13 is rotated at a predetermined speed determined by the rate of rotation of the electric motor shaft 12. Provision may be made for varying that speed electrically, for example via a rheostat, to enable the rate of repetitive linear movement of the tool bit to be varied in turn.

Since the cam follower 32 and carn member 13 are maintained out of mutual contact until the tool is applied to a workpiece, the tool bit remains stationary, even when the motor is running, until the tool is required to be used. When the tool is withdrawn from the workpiece, the tool bit stops again. The nature.of the movement of the tool bit is determined by the extent to which the bearing 33 and cam is surface 14 are interengaged and may be varied progressively from a pulsed action to smooth reciprocation. The frequency of the action is determined by the motor speed.

The tool shown in Fig. 2 is similar to that of Fig. 1 except in bn important respects. Firstly, the cam follower 40 carries two bearings 41 and 42, set at diagonally opposite points of the cam follower. The surface 43 of the cam member 44 has a peripheral profile which comprises two inclined cams in series. The bearings 41, 42 are thus at identical "levels" on the respective cams at any given moment and the resulting linear thrust is in balance across the diameter of the cam follower.

Secondly, the bearing 23 is extended somewhat to provide a stop 45, which by abutting the collar 21 when the cam follower has moved about halfway into full engagement with the cam surface 43, prevents the cam follower from becaming fully engaged with that surface. In this way, while increasing pressure on the workpiece increases the extent of engagement, the action will remain a pulsed action and will not progress to the stage wherein a smooth reciprocating action of the tool bit is reached.

Referring now to Fig. 3 of the accompanying drawings, the third embodiment, shown therein, of the power tool according to the present invention corresponds in many ways to that shown in Fig. 2 but the mounting of the cam follower 40 and cam member 44 has been reversed. That is, the cam follower 40 is mounted on the motor drive shaft 12 for rotation therewith, while the cam mr 44 is mounted on the shaft 20 for linear movement in the bearing 23. In other respects, the illustrated tool resembles that of Fig. 2 and in use the method of operation and the operating benefits are the same.

As will readily be understood, the form of the power tool according to the present invention is such that the user is able to apply a Yellcontrolled pulsed or smooth reciprocating action to a tool bit applied to a workpiece, such as has not been possible with prior comparable tools. The disadvantages and risks associated with manual hanwring and with hamwrpowered tools are greatly reduced or eliminated.

Claims

CIAIMS

A powered tool ccoprising a housing, a cam mie and a cam follower mounted within the housing along a conmn axis therein for relative axial movement into and out of mutual engagement, said cam me having a surface which, in a direction parallel to said conmn axis, varies in height around the perimeter of that surface, said cam follower ccmprising a rotary bearing for engaging said cam we surface, drive mans to rotate one of said cam member and said cam follower about said ccmwn axis, the other of said cam member and cam followT---r being mounted for linear movement in the direction of said axis, a tool operating head, mounted for linear movement with said linearly movable cam me or cam follower, and spring means for resiliently urging said cam member and cam follower out of mutual engagement.
2. A tool as claimed in claim 1, wherein the housing is generally cylindrical.
3. A tool as claimed in either of the preceding claims, wherein the cam member is generally disc-shaped and the cam surface is one of the faces of the disc.
4. A tool as claimed in any of the preceding claims, wherein the drive means is an electric motor within the housing.
5. A tool as claimed in claim 4, wherein the electric motor is powered by one or more batteries disposed within the housing.
6. A tool as claimed in any of the preceding claims, wherein the cam surface comprises one or more flat surfaces inclined at an angle of less than 90 degrees to the common axis of the cam manber and cam follower.
7. A tool as claimed in claim 6, wherein the angle of inclination of the surface(s) to the perpendicular to said ccmwn axis lies within the range from 2.5 to 15 degrees.
8. A tool as claimed in claim 7, wherein said angle is of the order of 6 to 7 degrees.
9. A tool as claimed in any of the preceding claims, where-in the cam profile is repeated at least once around the can surface.
10. A tool as claimed in any of the preceding claims, wherein the cam follo wer contacts the cam surface at at least two points, disposed symmetrically about the ccarmn axis of the can member and can follower.
11. A tool as claimed in any of the preceding claims, having a stop within the housing to limit the extent of mutual engagEnent of the cam rnE and cam follcwer.
12. A tool as claimed in any of the preceding claims, wherein the drive mans rotates the cam manber and the cam follower is mounted for said linear axial movemnt.
13. A tool as claimed in any of the preceding claims, having a chuck or other form of socket into which a tool operating head in the form of a tool bit is removably secured.
14. A powered tool, substantially as hereinbefore described with reference to, and as illustrated in, Fig. 1 of the accampanying drawings.
15. A powered tool, substantially as hereinbefore described with reference to, and as illustrated in, Fig. 2 of the acccrnpanying drawings.
16. A powered tool, substantially as hereinbefore described with reference to, and as illustrated in, Fig. 3 of the accompanying drawings.