GB2423492A

GB2423492A - Angular gear for a hand-held machine tool

Info

Publication number: GB2423492A
Application number: GB0611129A
Authority: GB
Inventors: Steffen Wuensch
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2003-12-22
Filing date: 2004-12-21
Publication date: 2006-08-30
Anticipated expiration: 2024-12-21
Also published as: GB2423492B; GB0611129D0

Abstract

A hand-held grinding tool comprises a housing 12, a motor 24 and an angular gear 37 located in the housing, and a grinding plate 30 on one side of the housing. The angular gear comprises a pin 36 eccentrically mounted on a drive shaft 32 of the motor and the outer ring 40 of a roller bearing 42 arranged with its axis of rotation parallel to the plane of the grinding plate. The eccentric pin is located in a slot 38 on the outer ring which is reciprocated about its axis of rotation as the eccentric pin rotates. A cam 46 is mounted on the outer ring, is offset by 90 degrees from the slot and engages with an opening 48 in the plate. Rotation of the drive shaft is transformed via pivoting motion of the outer ring into linear reciprocation of the opening in the plate. Use of an eccentric coupling 49 between the plate and housing enables the plate to perform an orbital motion.

Description

Hand-held machine tool The present invention relates to hand-held machine

tools.

EP 0 244 465 discloses a hand-held machine tool in which the rotational motion of its drive motor is converted into a vibrating rotational motion of its driven spindle. Here, the grinding tool, for example a grinding wheel, coupled to the driven spindle executes the vibrating rotational motion synchronously with the driven shaft. This motion is executed at a particular frequency and with a particular rotational travel back and forth which results in safe and precise handling of the machine and reliable and accurate control when guiding the tool. A motor-generated linear motion can not be imparted to the tool here.

According to the present invention there is provided a hand-held machine tool comprising a housing with an underside, a tool movably disposed at the underside of the housing and arranged to be motor-driven via an angular gear, the angular gear having an eccentric for driving a pivot lever back and forth about a pivot axis, and coupling means engaged between the tool and the housing to guide vibrating motion of the tool.

The tool can be a grinding tool for carrying an abrasive sheet.

A type of motion which can be used particularly effectively for grinding or shaving can be imparted to the tool when the coupling means comprises an eccentric, arranged between the tool and the housing. The coupling means can be engaged in a counter-opening of the housing and can engage in an engagement opening of the tool. The eccentric is conveniently arranged to convert vibrating motion of the grinding tool, or other tool, particularly into an orbital motion.

In the case of linearly driven tools, their direction of motion is particularly stable when the coupling means comprises a cam, which may engage an elongated groove in the tool, and stabilise the vibrating motion of the tool.

A particularly versatile hand-held tool can be produced when the coupling means can generate an orbital motion and also serve as a linear guide, particularly when locked against rotation.

In a particular embodiment of the invention the angular gear which converts a rotating motion into a back-and-forth motion includes a pivot lever with a motion-transmitting part mounted such that it is pivotable about a pivot axis parallel to a virtual workpiece surface, the pivotal motion of the moLiorl-transmitting part being convertible into a linear back-and-forth motion of the tool.

The pivot lever may have a downwardly angled lever arm that can be conveniently coupled with form fit to the tool.

More particularly the pivot lever of the angular gear can be formed by a ring which is mounted such that it is pivotable about its centre axis and whereof the circumference can be coupled in motion-transmitting manner to a driving eccentric at one point and in force- transmitting manner to tool which is drivable back and forth at another point, particularly a point which is offset through 9Q0 with respect to the first point.

A linear tool drive using few components can be produced with the ring is arranged vertically in the housing, its plane extending parallel to the feed direction of the hand- held machine tool. An especially simple mounting of the ring can be realised if the outer ring of a rolling bearing serves as the ring.

A compact and robust angular gear can be produced with a form fit both between the ring and the tool and between the ring and a driving eccentric. More especially that part of the ring which is offset downwards through 900 can carry a cam which fits in an engagement opening of the tool.

The invention is explained in more detail below with reference to an exemplary embodiment and the associated drawing, which shows: Fig. 1 a lateral partial longitudinal section through the hand-held machine tool; Fig. 2 a cross-section through the hand-held machine tool according to Fig. 1; Fig. 3 a horizontal partial longitudinal section according to Fig. 1; and Fig. 4 a three-dimensional illustration of the angular gear of the hand-held machine tool; Fig. 5 a view from below of a grinding wheel of the hand-held machine tool; Fig. 6 a view from below of an abrasive sheet of the hand-held machine tool; Fig. 7 a view from below of a further grinding wheel of the hand-held machine tool.

Description of the exemplary embodiment

Fig. 1 shows the lateral sectional view of a battery- powered vibrating grinder 10 which has a flat, narrow, box- shaped housing 12. This serves as a handle, where the hand of the operator should be placed on the upper side 11 of the housing 12 such that the front 14 of the housing points in the feed direction and a control button 16 seated in the front 14 of the housing 12 is within comfortable reach of the hand. An electrical on and off switch 17 inside the housing 12 can be operated by this control button 16.

Arranged on the rear 18 of the housing 12, extending parallel to the upper side 11, there are two insertion openings 20 for two batteries 22 of which the ends which are not illustrated in more detail project slightly out of the rear. Arranged inside the housing 12, there is an electric motor 24, particularly a d.c. motor, which is supported in a chassis 26 which is coupled at the bottom to a grinding wheel 30 by way of a resilient supporting ring 28, said d.c. motor engaging in the grinding plate 31 of said grinding wheel 20 such that it cannot escape.

Projecting out of the motor 24 to the right, as seen in the viewing direction, there is a motor shaft 32 on which a first eccentric 34 is held in torsion-resistant manner, an eccentric pin 36, which forms a novel angular gear 37 together with a rolling bearing 42 which is at least partially rotatably mounted in the chassis 26, being seated on the free end of said eccentric 34. To this end, the eccentric pin 36 engages in a transverse groove 38 of an outer ring 40 of the rolling bearing 42 so that the outer ring 40 can be driven vibrating upwards and downwards through a small angle of rotation with respect to the inner ring 41.

The inner ring 41 is connected to the chassis 26 by way of a bearing axle 44 such that it is fixed to the housing.

Seated on the outer ring 40, there is cam 46 which points downwards as seen in the viewing direction and engages in an engagement opening 48 in the grinding plate 31 or in an elongated strip 29 mechanically reinforcing this latter.

The engagement opening 48 can be constructed as a circular bore so that the cam 46 vibrating back and forth in a clockwise and anti-clockwise direction as seen in the viewing direction carries the grinding wheel 30 towards the front 14 and rear 18 in linearly driven manner.

Positioned on the left towards the rear 18 as seen in the viewing direction, there is arranged a second eccentric 49 having a masscompensating means 50 which projects upwards into an engagement opening 55 incorporated in the housing by means of an upper journal 51 and downwards into a further engagement opening 54 either in the grinding plate 31 or in the elongated strip 29 by means of its eccentric journal 52. This eccentric 49 forms a passive eccentric drive of the battery-powered grinder 10 in that, excited by the back-and-forth motion of the grinding wheel 30, it imparts an orbital motion to its rear region.

The grinding wheel 30 carries a resilient abrasive pad on its grinding plate 31 of hard resilient material, said abrasive pad 35 having a touchand-close fastening 58 on its underside, to which the velour reverse side of an abrasive sheet 56 can be fastened in adherent manner.

Fig. 2 shows a cross-section through the battery-powered vibrating grinder 10, which clearly shows the parallel arrangement of the batteries 22 next to one another and parallel to the upper side 11 of the housing 12, and moreover the arrangement of the motor 24 extending parallel to the batteries and the grinding wheel 30. It can also be seen that the supporting ring 28 is guided along the longitudinal sides within the housing 12 and serves as a means for resiliently suspending the grinding wheel 30 with respect to the chassis 26. It can furthermore be seen that, arranged on the upper side of the resilient, fixed grinding plate 31 of the grinding wheel 30, there is an elongated strip 29 which serves for force-transmission and for reinforcing the grinding wheel 30 and in which the eccentric pin 36 of the first eccentric 34 or the eccentric journal 52 of the second eccentric 49 engages in force- transmitting manner.

In a horizontal longitudinal section according to Fig. 1, Fig. 3 shows that the housing 12 of the battery-powered vibrating grinder 10 is constructed as an elongated narrow box which receives inside it the motor 24, which is aligned parallel to the longitudinal axis and the grinding wheel and sets the outer ring 40 of the rolling bearing 42 in rotational vibration by way of the eccentric 34, said rolling bearing 42 for its part engaging with its cam 46 in the engagement opening 48 of the elongated strip 29.

The arrangement of the bearing axle 44 of the rolling bearing 42 and its supporting position on the chassis 26 is also clear. It is furthermore possible to see that the outer ring 40 of the rolling bearing 42 contains the transverse groove 38 in which the eccentric pin 36 of the first eccentric 34 engages such that its circular motion is converted into a linear forward and backward motion of the outer ring 40.

In the region of the rear 18 of the housing 12, it is possible to see the second eccentric 49 which engages with its eccentric journal 52 in the engagement opening 54 in the elongated strip 29 of the grinding plate 31.

The passive vibrating drive formed by the second eccentric 49 for the grinding wheel 30 is triggered by the back-and- forth motion of the grinding wheel 30 as a result of being driven by the first eccentric 34. Here, the grinding wheel acts as a connecting rod and the second eccentric 49 acts as a crankshaft. The interaction between both types of motion is mutually matched in constructive manner so that a particular linear travel of the grinding wheel 30 effects a particular rotational travel of the eccentric 50 and therefore a defined orbital motion of the grinding wheel 30.

In order to prevent a fixed dead centre position of the second eccentric 49, the eccentric 49 can be designed in such a way that it is always in a tilted position from which it is able to change easily into a circular motion as soon as the first eccentric 34 starts to rotate.

However, it can also be expedient to effect a resilient lateral pretensioning of the grinding wheel 30 with respect to the housing 12 so that the rear end of the grinding wheel 30 constantly attempts to pivot laterally with respect to the housing 12 with the result that the eccentric 49 does not remain suspended in a linear dead centre position, but instead continues to rotate laterally and can therefore be actuated by the linear travel.

Instead of an eccentric 49, in the rear region of the battery-powered vibrating grinder 10 a linear pin fixed to the housing can engage in a groove which is arranged as a linear guide in the elongated strip 29 and is provided instead of a circular engagement opening 54 for the eccentric journal 52.

Thus, the grinding wheel 30 is forced into a linear vibrating motion which is guided linearly back and forth - without an additional orbital motion.

As a core piece of the novel angular gear 37, the rolling bearing 42 illustrated as a detail in Fig. 4 shows its outer ring 40 to have an upwardly pointing radially protruding cam 46 and, rotated to the left as seen in the viewing direction, the transverse groove 38 in the outer ring 40 in which the eccentric pin 36 of the first eccentric 34 engages such that its eccentrically circular motion 13 converted into a forward and backward pivotal rotational motion of the outer ring 40 and therefore the cam 46.

On its lower side (as seen in the viewing direction), the outer ring 40 contains a further transverse groove 382 by means of which the rolling bearing 42 can be brought into engagement with another eccentric according to the requirements of the constructive application or which, in the event of wear on the first transverse groove 38, replaces this latter by rotation of the outer ring.

The cam 46 for carrying the grinding wheel 30 is of a crowned construction so that, when engaging in the engagement opening 48, it lies against it with as large a surface area as possible and the amount of wear is minimised.

In one exemplary embodiment (not illustrated) of a novel angular gear of this type, the rolling bearing 42 can also be rotated through 900 about its transverse axis, in which case an axially protruding cam has to be arranged in its outer ring 40 in order to convert the vibrating rotational motion of the outer ring 40 into a linear motion of a part to be carried along with it.

Fig. 5 shows a view from below of a grinding wheel 301 which is constructed in the shape of an iron and on which either a one-piece congruent abrasive sheet or an approximately congruent abrasive sheet composed of a plurality of segments can be placed.

Fig. 6 shows an iron-shaped abrasive sheet 56 which is formed by two segments 561, 562; an equilateral triangle with curved outside edges and an adjoining remaining piece which is separated by a predetermined tear line 563.

Fig. 7 shows a further iron-shaped grinding wheel 302 having through holes 60 arranged on a graduated circle for dust extraction and having a separate rhombic tip segment 313 which can be replaced by similar tip segments, which can be attached by a touch-and-close fastening and form the point of maximum wear on the abrasive sheet and can therefore be replaced more often than the remaining region of the abrasive sheet.

Claims

Cia ims 1. A hand-held machine tool comprising a housing with an

underside, a tool movably disposed at the underside of the housing and arranged to be motor-driven via an angular gear, the angular gear having an eccentric for driving a pivot lever back and forth about a pivot axis, and coupling means engaged between the tool and the housing to guide vibrating motion of the tool.
2. A hand-held machine tool according to claim 1, wherein the coupling means comprises an eccentric.
3. A hand-held machine tool according to claim 1 or 2, wherein the coupling means engages with a counter-opening of the housing.
4. A hand-held machine tool according to claim 1, 2 or 3, wherein the coupling means engages in an engagement opening of the tool.
5. A hand-held machine tool according to claim 2, wherein the eccentric is arranged to convert vibration motion of the grinding tool or other tool into an orbital motion.
6. A hand-held machine tool according to Claim 1, 2 or 3, wherein coupling means engages in an elongated groove of the tool to stabilise the vibrating motion of the tool.
7. A machine tool according to any one of claims 1 to 6, wherein the pivot lever is movable back and forth about a pivot axis and has a lever arm coupled to the tool to transmit a horizontal forward-and_backward motion to the tool.
8. A hand-held machine tool according to Claim 7, wherein the lever arm is coupled with form fit to the tool.
9. A hand-held machine tool according to claim 8, wherein the lever arm is provided with a cam which fits in an engagement opening in the tool.
10. A hand-held machine tool according to Claim 9, wherein the engagement opening is arranged in an elongated strip incorporated in or mounted on the tool.
11. A hand-held machine tool according to any one of claims 1 to 10, wherein the tool is a grinding tool for carrying an abrasive sheet.