A miniature filing machine of the above-named type is primarily intended to be used for precision-tool filing and grinding tasks.

Prior Art Tool machines provided with imbalance bodies are previously known per se.

As an example of such prior art can be cited the tooled machine as described in DE 652 280. This known machine is designed such that the imbalance forces from the tool holder with associated tool are counterbalanced and compensated by the imbalance forces from a pair of laterally disposed mass bodies which are driven in phase opposition to the unit comprising the tool holder and the tool, which unit is movable centrally between these mass bo- dies. Since both the laterally disposed mass bodies and the central tool hol- der unit move in parallel straight motional paths in the longitudinal direction of the machine, no imbalance forces arise in the transverse direction of the machine. There is therefore no need to take any measures to cancel out or counteract imbalance forces in the transverse direction of the machine.

In machines having mechanically controlled stroke length, the acceleration forces from the slide and the tool, plus the frictional resistance against the workpiece, produce axial reaction forces which are absorbed and cause vibration of the machine housing.

Object of the invention The primary object of the present invention is to achieve a miniature filing machine operating with rotary imbalance bodies, in which the imbalance forces generated in the rotation of the imbalance bodies are optimally balan- ced out so that imbalance-related vibrations are as far as possible counterac- ted or prevented from arising in the transverse direction of the slide driving the tool (and hence also of the machine housing).

Apart from preventing disturbing vibrations in the transverse direction of the machine, a further object of the invention is to avoid as far as possible the advent of disturbing axial vibrations in the axial longitudinal direction of the machine housing.

Amongst other objects of the present invention can be mentioned that of achieving a miniature filing machine the machine housing of which is of small transverse dimension, so that the machine is easy to handle and can be used even in tight spaces.

A further object is that the miniature filing machine shall be of simple con- struction so that the machine is reliable.

Yet another object of the invention is to integrate the imbalance bodies di- rectly or indirectly into the drive mechanism of the machine so that the im- balance bodies constitute parts of the drive mechanism.

Account of the invention The above-named objects are achieved according to the invention by the fact that the miniature filing machine of the type specified in the introduction ex- hibits the characteristics specified in the defining clause of Patent Claim 1.

Embodiments of the miniature filing machine according to Patent Claim 1 can additionally exhibit the characteristics specified in Patent Claims 2-12.

The primary distinguishing feature of the miniature filing machine according to the invention is thus that the imbalance bodies, which are set up to be ro- tated synchronously but in opposite rotational directions, are dimensioned such and have such rotationally eccentric centres of gravity (imbalances) that the imbalance forces which are generated in the rotation of the bodies coun- teract and at least largely cancel out one another in the transverse direction of the slide and additionally interact and are added to one another in the lon- gitudinal direction of the slide. The generated imbalance forces are trans- mitted via the bearing members (for example bearing pins) of the imbalance bodies to the holder of the imbalance bodies, which holder, by being joined to or constituting part of the rear part of the slide, produces an oscillating motion of the slide to and fro in the longitudinal direction of the slide and hence of the machine housing.

With the dynamically controlled stroke length, apart from the friction betwe- en slide and machine housing, no reaction forces are transmitted to the ma- chine housing. This also applies to the friction against the workpiece.

One advantage is also that there are no severe shocks if the tool hits against an edge, since it is only the mass of the slide and the tool which is at work and this does not result in any"recoil shock"to the machine housing.

In a first embodiment of the miniature filing machine according to the invention, the rotational axles of the imbalance bodies are mutually pa- rallel and lie in a transverse plane to the holder perpendicular to the longitu- dinal direction of the slide. The holder is in this case expediently configured as a fork-like clamp having mutually separate, parallel side pieces between which the imbalance bodies are arranged rotatably on their rotational axles, the ends of which are in this case supported in the side pieces. The imbalan- ce bodies can either be mounted rotatably on axles secured in the holder or can be fastened to axles the ends of which are mounted rotatably in the hol- der.

In order to prevent rotation of the slide in the machine housing, the fork-like clamp in the rear part of the slide can interact with a guide lug on the inside of the limit wall of the chamber, which guide lug juts into the interspace between the two side pieces of the clamp.

The drive mechanism of the imbalance bodies is preferably disposed in the rear part, opposite to the slide, of the machine housing, which latter prefera- bly has a rotationally symmetric configuration. The drive mechanism can expediently be a pneumatic device comprising at least one compressed-air nozzle for generating a propellant-air jet, the kinetic energy of which is used to rotate one of the imbalance members. The propellant-air jet is preferably directed tangentially to the periphery of the imbalance body in question, which in this case is provided at the periphery with projections, for example in the form of teeth or cogs, which herein act as turbine wheel pistons if the imbalance body is compared with a turbine wheel.

The synchronous driving of the imbalance bodies is most simply achieved by these being in driving engagement one with the other, preferably by the pro- jections (the teeth or cogs) at the peripheries of the imbalance bodies being in mutual engagement like the cogs of interacting gearwheels.

When the drive mechanism is a pneumatic device, the same preferably comprises a separate compressed-air nozzle for each imbalance body. Alternative types of drive mechanisms can also be envisaged. Such a possibility involves the imbalance bodies being realized as preferably per- manently magnetized rotors which are driven and synchronized by electronic means.

When the two imbalance bodies are mounted side by side in a common transverse plane to the slide and machine housing respectively, the imbalan- ces of the two imbalance bodies-i. e. for each imbalance body the displa- cement of its centre of gravity in relation to its centre of rotation-are thus arranged such that in each rotation position of the imbalance bodies they are directed in the same directions in the longitudinal direction of the miniature filing machine and slide but are always mutually directed directly towards or away from each other in the transverse direction of the machine and slide, i. e. transversely to the longitudinal axis of the machine.

The two imbalance bodies do not necessarily have to be arranged alongside each other in the transverse direction of the slide or machine housing but can alternatively be arranged in line with each other in the longitudinal direction of the slide or machine housing.

In such an alternative main embodiment of the miniature filing machine according to Claim 1, the imbalance bodies can thus be arranged such that their rotational axles are parallel with each other and lie in a longitudinal plane to their holder, which longitudinal plane lies parallel with the longitu- dinal direction of the slide or machine housing.

The holder of the imbalance bodies can in this case expediently be configu- red as an oblong, preferably uniformly thick block having an elongated, continuous opening, which opening then extends in the longitudinal direc-

tion of the block and in which opening the imbalance bodies are arranged rotatably on their rotational axles. The ends of the rotational axles are herein received in the block on opposite sides of its elongated opening.

In order to prevent the block, which supports the imbalance bodies and is joined to the rear part of the slide located inside the housing chamber, from being allowed to rotate in the chamber during operation, the block is pre- ferably mounted non-rotatably in the machine housing. In a simple embodi- ment which ensures this, the end section of the block at that end of the block opposite to the slide is received in a correspondingly configured recess in the limit wall present there of the housing chamber. The simple principle for achieving a holder received non-rotatably in the housing chamber is to pro- vide the holder with a section of non-circular cross section which is mounted in axially displaceable arrangement in an opening or a barrel of correspond- ing non-circular cross section in the end wall of the chamber.

The drive mechanism of the imbalance bodies is expediently disposed in the rear part, opposite to the slide, of the machine housing, which latter is pre- ferably rotationally symmetric. As in the first main embodiment of the miniature filing machine according to the invention, which embodiment has already been described above, the drive mechanism can in the realization in- volving"tandem-mounted"imbalance bodies expediently be a pneumatic device comprising a compressed-air nozzle for generating a propellant-air jet preferably directed tangentially to the periphery of the rear imbalance body in the chamber. The imbalance body is herein provided along its periphery with projections acting as small turbine pistons. These projections are pre- ferably teeth or cogs which stand in rotational driving engagement with a corresponding set of projections on the periphery of the front imbalance body in the chamber. The air-jet driving of the rear imbalance body thereby brings about a counter-directed rotation of the front imbalance body.

The compressed air which is injected into the chamber by means of the compressed-air nozzle must naturally also be able to flow out from the chamber. This is most simply effected by a waste-air duct being configured in the drive mechanism or a wall section connected thereto, which waste-air duct leads from the inside of the house chamber to the exterior of the machi- ne housing.

For the two main embodiments of the miniature filing machine according to the invention, the respective holder of the imbalance bodies expediently has its axial motion in the chamber limited by elastic, end-position-forming stop members. These stop members can quite simply be spring members mounted in recesses in the limit walls of the chamber directly opposite adjacent end faces of the holder at the front and rear end respectively of the same.

The stroke length of the machine is determined by the weight of the slide inclusive of tool in relation to the weight and displacement in the centre of gravity of the imbalance bodies. Apart from the friction forces acting upon the slide and the tool, the stroke length is not affected when the rotation speed is changed. By giving the slide and the imbalance bodies a well balan- ced weight, which will not be too low, the stroke length is also kept suffici- ently constant in normally occurring filing and polishing tasks.

Brief description of the figures The invention will now further be described and explained with reference to some embodiments shown in the appended figures, in which: Fig. 1 shows an axial longitudinal section through a first embodiment of a miniature filing machine according to the invention; Fig. 2 shows an axial longitudinal section, along the section line 2-2 in Fig.

1, through the miniature filing machine in Fig. 1;

Fig. 3 shows a diagrammatic representation of the rotation positions for the imbalance bodies of the machine in Figs 1-2 in respect of the angular positions 0°, 90°, 180° and 270° of a rotation turn; Fig. 4 shows an axial longitudinal section through a second embodiment of a miniature filing machine according to the invention; Fig. 5 shows a partial longitudinal section, along the sectional line 5-5 in Fig. 4, through the miniature filing machine in Fig. 4; and Fig. 6 shows finally a cross section through the machine in Figs 4-5, along the section line 6-6 in Fig. 5.

Preferred illustrative embodiments Figs 1-2 show a first embodiment of a miniature filing machine according to the present invention. The machine has a rotationally symmetric machine housing 10 having a cylindrical rear part 12 and a front part 14 which tapers conically in the forward direction (to the right in Figs 1-2). In a chamber 16 in the housing part 12 and a thereto connecting barrel 18 in the housing part 14 there is mounted in axially movable arrangement a slide 20, which is dis- placeable to and fro in the housing 10. The slide 20 comprises firstly a cy- lindrical rod 22, which extends through the barrel 18, and secondly a holder 24 situated in the chamber 16 and fixed in the rear end of the rod. The front part of the rod 22, which front part projects from the housing 10, forms with its front section 26 a tool fixture for a tool 28, in this case a file, which can be used for precision-tool filing and polishing tasks.

The holder 24 supports a pair of imbalance bodies 30,32, which are mounted rotatably in the holder. The holder has the form of a fork-like clamp having parallel side pieces 23,25 between which the imbalance bodies are arranged rotatably on their rotational axles, the ends of which are received in the side pieces. By"imbalance body"is meant in this context a rotatable body, the centre of gravity of which is displaced a little way from the centre of rotation

of the body. As can be seen from Figs 1-2, the imbalance property inherent to the bodies 30,32 has been achieved by virtue of the left halves (viewed in Fig. 1) of the bodies being thicker (see Fig. 2) than their right halves. At the periphery, each imbalance body is provided with radial projections 34 con- figured as teeth or cogs. The imbalance bodies are mounted and mutually placed in the holder 24 such that, as a result of the projections 34, they are in driving engagement one with the other like interacting gearwheels. Rotation of the one imbalance body thereby produces a synchronous but oppositely directed rotation of the other imbalance body.

The rotational driving of the imbalance bodies 30,32 is achieved pneumati- cally by means of a compressed-air-fed drive mechanism 36 in the rear half of the housing part 12. The pneumatic drive mechanism 36 comprises a housing body 38 having a central pressure distribution chamber 40 from which ducts 41,43 having tubular compressed-air nozzles 42,44 extend to and emerge in the chamber 16. The chamber 40 is fed compressed air via a line 46 and a nipple 48. The nozzles 42,44 direct compressed-air jets tan- gentially to the cogs 34 on the peripheries of the imbalance bodies. The cogs act in this case as turbine pistons, the motions of which set the imbalance bodies rotating. In this case there is therefore a separate compressed-air noz- zle for each imbalance body, but since the imbalance bodies are in geared driving engagement one with the other it is actually sufficient for only the one imbalance body to be provided with compressed-air driving. The com- pressed air blown via the nozzles 42,44 into the chamber 16 in the form of propellant-air jets is allowed to flow out from the chamber through an axial waste-air duct 50 through the housing body 38, as is shown in Fig. 2.

In order to prevent the slide 20 from rotating in the chamber 16 and barrel 18, the holder 24 is arranged non-rotatably in the chamber 16. This is achieved by the housing body 38 being provided with a forward-directed

guide lug 52, which juts in between the side pieces 23,25 of the clamp- like holder 24.

The effect of the above-described construction is that the imbalance forces (centrifugal forces) generated in the rotation of the imbalance bodies 30,32 counteract and cancel out one another in the transverse direction of the slide 20, i. e. perpendicular to the centre line A (as shown in diagrammatic repre- sentation in respect of the angular positions 0° and 180° in Fig. 3), whereas they interact and are added to one another in the longitudinal direction of the slide along the centre line A (as shown in respect of the angular positions 90° and 270° in Fig. 3). The imbalance forces are transmitted from the bo- dies 30,32 to their holder 24, which is thereby set in an oscillating to and fro motion inside the chamber 16 and which hence, in turn, transmits a corre- sponding to-and-fro-running drive motion to the slide rod 22 (and conse- quently also to the tool fixture 26). For location of the slide 20 in the ma- chine housing 10, the motion of the slide holder 24 in its axial direction is limited by a pair of end position springs 54 and 56 mounted in blind holes 58 and 60 in the end walls in the end walls 62 and 64 respectively of the cham- ber 16. The springs 54,56, which do not reach contact with the end faces 55,57 of the holder 24, have the sole task of locating the holder 24, and hence the slide 20, in the chamber 16 so as thereby to prevent the holder from banging against the machine housing in the motional end positions of the slide.

In the above-described embodiment having the rotational axles of the imbal- ance bodies lying side by side in a transverse plane to the slide and on oppo- site sides of the centre line of the slide, those transverse forces which would otherwise give rise to transversal vibrations in the miniature filing machine are optimally balanced out.

Conducted tests have shown however that an alternative realization having the imbalance bodies placed in tandem one behind the other in a longitudinal plane to the slide and the machine, for example hav- ing the rotational axles of the bodies situated on the centre line of the slide, also gives rise to no perceptible vibrations in the machine. Such a tandem realization offers certain constructional advantages and means, moreover, that the external diameter of the machine housing can be minimized.

A second embodiment of a miniature filing machine according to the present invention having imbalance bodies placed in tandem is now described with reference to Figs 4,5 and 6. The miniature filing machine has in this case a cylindrical machine housing 66 comprising a rear part 68 and a front part 70.

In the front part there is a chamber 72 and a thereto connecting barrel 74 for the slide 76 mounted in axially movable arrangement. That part of the slide situated inside the chamber 72 constitutes a holder 82 for the imbalance bodies 78 and 80. The holder 82 has the form of an oblong, uniformly thick block having an elongated opening 84, in which opening the imbalance bodies realized as gearwheels with eccentrically placed circular imbalance weights 86a and 86b are arranged rotatably on their rotational axles, the ends of which are secured in the block 82. The holder 82 is arranged non- rotatably in the chamber 72 by virtue of the fact that the rear end section 88 of the holder is received in a recess 90 of rectangular cross section in the front end of a housing body 92 over which the housing parts 68,70 are con- nected to each other.

In this realization also, the drive mechanism of the miniature filing machine comprises a pneumatic nozzle device which in this case however only has one compressed-air nozzle 94, the propellant-air jet of which is directed tan- gentially to the cogs 96 of the imbalance body 78. The compressed air is supplied to the nozzle 94 through an axial duct 97 configured in the housing body 92 and emanating from a supply air chamber 98 in the housing body.

Compressed air is supplied to the chamber 98 via a central duct 100 in a nipple 102 screwed in the housing body. The air blown into the chamber 72 flows out from the chamber via a waste-air duct 104, an annular gap 106 and axial channels 108 in the rear part 110 of the nipple 102.

For location of the slide 76 in the machine housing 66, the holder 82 of the slide is axially movable to a limited extent between a pair of end position springs 112 and 114 acting as end position stops. The spring 112 is mounted between the bottom of a blind hole 116 in the chamber wall 111 of the housing body 92 and the rear end face 118 of the holder end section 88, and the spring 114 is mounted between an annular shoulder 120 around the mouth of the slide barrel 74 in the end wall 119 of the chamber 72 and the front end face 122 of the holder 82.

Finally, Fig. 6 shows how the imbalance body 80 is mounted in the holder 82. The imbalance body 80, which comprises the gearwheel 124 and the im- balance weight 86b secured therein by its axial hub bush section 126, is mounted by means of needle bearings 128 on the bearing axle 130 secured in the holder 82.