GB2417448A

GB2417448A - Balancing weight system for eccentrically driven tool

Info

Publication number: GB2417448A
Application number: GB0514724A
Authority: GB
Inventors: Joerg Dehde
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2004-07-23
Filing date: 2005-07-18
Publication date: 2006-03-01
Anticipated expiration: 2025-07-18
Also published as: GB2417448B; DE102004035859A1; CN1899765A; CN1899765B; GB0514724D0

Abstract

An eccentric grinding tool (orbital sander or similar) has eccentric shaft 22 on which are mounted fan 32 and axially separated balance weights 10 and 44. The balance weights may be separate from or integrally moulded onto the fan and are non-rotatably mounted on the shaft. Shaft 22 engages non-rotatably with the inner race 40 of a ball or roller bearing. A further balance weight 12 is integral with the inner race. Outer race 42 is non rotatably mounted in grinding plate housing 14, which is covered by a layer of foam rubber and abrasive sheet 20. The grinding tool thus has a first balance weight system mounted on the driveshaft and a second weight system integrated with and adjusted to match, detachable grinding plate 14. The balance weights serve to reduce the transfer of vibrations from the in-use grinding plate to the user of the grinding tool.

Description

24 1 7448 A device having at least two balancing weights

Prior Art

The invention takes as its starting point a device having at least two balancing weights according to the precharacterising clause of Claim 1, a grinding plate according to the precharacterising clause of Claim 7 and a hand-held machine tool according to the precharacterising clause of Claim 8.

It has already been proposed to equip a vibrating grinder with two or more balancing weights for balancing a grinding plate. This can prevent an eccentric vibrating movement of the grinding plate from causing uncomfortable vibrations of the housing when the vibrating grinder is in operation. Two mutually opposing balancing weights arranged in different planes can additionally reduce a dynamic tilting moment which a shaft of the hand-held machine tool can be subject to during operation.

Advantages of the invention The invention takes as its starting point a device having at least two balancing weights for balancing an eccentric tool of a hand-held machine tool, particularly a grinding plate of a vibrating grinder.

It is proposed that a first balancing weight be connected to a shaft of the eccentric tool and a second balancing weight be integrated in the eccentric tool. This enables the mass and position of the balancing weight to be adapted precisely to the balancing tool or to the distribution of its mass, and a housing of the hand-held machine tool to remain at least largely vibration-free during operation, irrespective of the type of insert tools used.

In this connection, any tool which the person skilled in the art would consider useful for following an eccentric path during operation of the hand-held machine tool is classed as an eccentric tool.

The solution according to the invention can be used particularly advantageously for grinding plates of vibrating grinders since such grinding plates are actuated with a comparatively high-frequency vibrating movement which can lead to unpleasant vibrations in the housing of the vibrating grinder. These vibrations can also ultimately shorten the useful life of the vibrating grinder.

In principle, the second balancing weight can be fixedly connected to the eccentric tool or it can be constructed such that it is adjustable. An adjustable balancing weight can be used to counterbalance the device, particularly in vibrating grinders whereof the grinding plates can be equipped with abrasive covers of different weights.

The balancing weight can be constructed for example such that the distribution of the mass of components connected to the drive shaft, particularly components of the eccentric tool and the balancing weights, is not unbalanced, which means that the housing of the hand-held machine tool remains at least substantially vibration-free when the hand-held machine tool is in free operation, i.e. when there is no contact between the eccentric tool and a workpiece. However, constructions of the invention are also feasible in which, with the distribution of the balancing weights, oscillating forces which are transmitted to the housing of the hand-held machine tool from the workpiece by way of the eccentric tool can be at least partially compensated.

In one construction of the invention, it is proposed that the eccentric tool be provided to be eccentrically driven.

An eccentric tool is then particularly provided to be eccentrically driven when a shaft bearing unit is provided for connection to a drive shaft which moves eccentrically.

In this connection, each periodic or quasi-periodic movement, for example an elliptical or cycloidal movement or a movement produced by superimposing two circular movements of a different frequency are classed here as eccentric. The term "provided" is also used to mean "designed" and "equipped" in this connection.

It is furthermore proposed that the eccentric tool be provided to be releasably mounted on the hand-held machine tool. Balancing adapted to a type or weight of the eccentric tool is particularly necessary in exchangeable, releasable eccentric tools for comfortable operation of the hand-held machine tool. As a result of the solution according to the invention, it is possible to avoid a balancing process connected with exchanging the eccentric tool and to achieve a largely vibration-free operation of the electric tool with a plurality of eccentric tools having different centres of gravity and/or weights.

If the eccentric tool is constructed as a grinding plate of a vibrating grinder, an inert mass of the grinding plate can moreover be adapted to the abrasive cover used or to the grain of the grinding paper used. The advantages of the inventive solution here can be used particularly in connection with vibrating grinders having exchangeable grinding plates.

A particularly robust constructive design having an advantageously shielded balancing weight can be achieved if the second balancing weight is arranged between a shaft bearing unit and an abrasive-cover holding face of the grinding plate.

A secure releasable connection between the balancing weight and the shaft can be achieved if the second balancing weight is non-rotatably connected to the shaft by way of a shaft bearing unit so that the shaft bearing unit transmits the torque from the shaft to the balancing weight. A part of the shaft bearing unit which is mounted on the eccentric tool can play the role of the connecting component here, for example an inner bearing ring of the shaft bearing unit, which can be particularly advantageously constructed as a slide bearing, a ball bearing or a rolling bearing.

If the device comprises at least one first balancing weight which is connected to a shaft of the hand-held machine tool, a fixed balance which is adapted to a standard type of eccentric tool can be advantageously integrated in fixed manner in the hand-held machine tool so that the balancing weight integrated in the insertable eccentric tool is a corrective balancing weight which corrects the balance relative to the standard type and can therefore be constructed more simply and more economically. That type of eccentric tool which is produced or used on the largest scale is particularly advantageously selected as the standard type. The second balancing weight can be advantageously integrally formed on a fan wheel of the hand-held machine tool here to reduce the number of components.

The invention furthermore takes as its starting point a grinding plate which is provided to be releasably mounted on a vibrating grinder.

It is proposed that the grinding plate comprise an integrated corrective balancing weight for compensating a centrifugal force. As a result, the grinding plate can particularly also be used in connection with vibrating grinders which have a fixed basic balance adapted to another grinding plate type. It is advantageously possible to retrofit a vibrating grinder with a grinding plate according to the invention.

The invention furthermore takes as its starting point a hand-held machine tool, particularly a vibrating grinder, which comprises at least one exchangeable eccentric tool and at least two balancing weights.

It is proposed that a first balancing weight be connected to a shaft of the hand-held machine tool and that a second balancing weight be at least partially integrated in the eccentric tool. The advantages of the inventive solution can be used particularly in connection with hand-held machine tools which comprise a full set of different types of eccentric tool if the different types of eccentric tool each comprise balancing weights which are adapted to a specific distribution of the mass of the grinding plate used.

Drawing Further advantages are revealed in the following description of the drawing. The drawing shows an exemplary embodiment of the invention. The drawing, the description and the claims contain numerous features in combination.

The person skilled in the art will also expediently consider the features individually and combine them in further useful ways.

The drawing shows: Fig. 1 a vibrating grinder with an insert tool; Fig. 2 a shaft of the vibrating grinder with a fan wheel and a grinding plate and also with three balancing weights; and Fig. 3 the shaft and a detail of the grinding plate from Figures 1 and 2.

Description of the exemplary embodiments

Figure 1 shows a hand-held machine tool 16 which is constructed as a vibrating grinder and has an eccentric tool constructed as an exchangeable grinding plate 14. The hand-held machine tool 16 furthermore has a dust-collecting container 24, an on/off switch 26 arranged on a handle element and a power supply cable 28 with a mains plug (not illustrated here). A further handle element 30 enables the operator to exert pressure comfortably on a workpiece.

Arranged in a housing of the hand-held machine tool 16 is an electric motor (not illustrated here), which begins to operate when the mains plug is plugged in and the on/off switch 26 is switched on, and which has a motor shaft which is in direct operative communication with a shaft 22 (Figure 2) of the hand-held machine tool 16.

The grinding plate 14 has a flat basic shape and is provided to be equipped with an exchangeable abrasive cover, for example with corundum paper, on a side opposite the housing of the hand-held machine tool 16. However, constructions of the invention in which the grinding plate 14 is equipped with a permanent abrasive cover are also feasible.

Figure 2 shows a detail of an eccentric device of the hand- held machine tool 16 with a fan wheel 32 and the shaft 22.

A first balancing weight 10 is constructed in one piece with a third balancing weight 44 opposite the first balancing weight 10 and is fixedly connected to the fan wheel 32 or integrated in the fan wheel 32. To compensate a dynamic tilting moment, the third balancing weight 44 is offset axially in the direction of the body of the hand- held machine tool 16 relative to the shaft 22.

The shaft 22 has a flattened portion on a free end, by means of which it can be pushed into a corresponding cutout in a shaft bearing unit 18 connected to the grinding plate 14 during assembly to produce a non-rotatable and releasable connection, a rotary position of the shaft 22 relative to a bearing ring 40 of the shaft bearing unit 18 being fixed by the flattened portion.

During assembly, the grinding plate 14 is moreover connected to the body of the hand-held machine tool 16 by way of a releasable quick-change clamping connection and by means of flexible vibrating-spring legs. The vibrating- spring legs enable a restricted movability of the grinding plate 14 in directions which are located in the plane extending from the grinding plate 14, whilst the connection in the direction extending perpendicularly to the plane is rigid. The quick-change clamping connection enables the grinding plate 14 to be released from the body of the hand held machine tool 16 without the use of tools and with only a few movements.

The shaft 22 is mounted such that it is rotatable about an axis of rotation 34 which is offset parallel through an eccentricity 38 in relation to an axis of symmetry 36 (Figure 3) . Figure 3 shows the grinding plate 14 in the condition in which it is mounted on the body of the hand-held machine tool 16, whereby the shaft 22 engages in the cutout in the inner bearing ring 40.

The shaft bearing unit 18 is constructed as a rolling bearing with the inner bearing ring 40, whereof the inside face forms the corresponding cutout, and with an outer bearing ring 42 which is non-rotatably connected to a body of the grinding plate 14, which is constructed as a plastics injection moulded part. The shaft bearing unit 18 is arranged offset relative to a centre of gravity of the grinding plate 14.

Mounted on an edge of the inner bearing ring 40 which is remote from the housing of the hand-held machine tool 16, there is a second balancing weight 12 which is adapted to a weight of the grinding plate 14 and which, shielded from below from an outside area by a cellular-rubber-coated grinding-cover holding face 20 of the grinding plate 14, can rotate relative to the body of the grinding plate 14 by means of the inner bearing ring. The second balancing weight 12 is thus arranged between the shaft bearing unit 18 and the abrasive-cover holding face 20. The grinding plate 14 is constructed with two layers to generate an intermediate space for receiving the second rotating balancing weight 12. The second balancing weight 12 is non- rotatably connected to the shaft 22 by way of the shaft bearing unit 18 or by way of the inner bearing ring 40 of the shaft bearing unit 18.

The abrasive-cover holding face 20 is equipped with a layer of cellular rubber, which is approximately 2 mm thick.

If the shaft rotates 22, the free end of the shaft 22 engaging in the inner bearing ring 40 displaces the grinding plate 14 along a circular path which extends in the plane of the grinding plate 14 and of which the radius of 3 mm results directly from the eccentricity 38 of the shaft 22. The eccentric tool constructed as a grinding plate 14 is thus driven eccentrically.

The grinding plate 14 is part of an assortment of grinding plates 14 of varying weight and size, which are each equipped with a second balancing weight 12 adapted to the weight and size of the corresponding grinding plate 14.

Only one standard grinding plate (not illustrated here) in the range, which is produced on the largest scale, is completely balanced by the first balancing weight 10 and does not have a second balancing weight 12. The balancing weights 12 of the other types of grinding plate 14 are corrective balancing weights which are provided to compensate an imbalance difference between the standard grinding plate and the respective grinding plate 14.

List of reference numerals Balancing weight 12 Balancing weight 14 Eccentric tool 16 Hand-held grinding machine 18 Shaft bearing unit Abrasive-cover holding face 22 Shaft 24 Dust-collecting container 26 On/Off switch 28 Power supply cable Handle element 32 Fan wheel 34 Axis of rotation 36 Axis of symmetry 38 Eccentricity Bearing ring 42 Bearing ring 44 Balancing weight

Claims

Claims 1. A device having at least two balancing weights (10, 12, 44) for

balancing an eccentric tool (14) of a hand-held machine tool (16), particularly a grinding plate of a vibrating grinder, characterized in that a first balancing weight (10) is connected to a shaft (22) of the eccentric tool (14) and a second balancing weight (12) is integrated in the eccentric tool (14).
2. A device according to Claim 1, characterized in that the eccentric tool (14) is provided to be eccentrically driven.
3. A device according to one of the preceding claims, characterized in that the eccentric tool (14) is provided to be releasably mounted on the hand-held machine tool (16).
4. A device according to one of the preceding claims, characterized in that the eccentric tool (14) is constructed as a grinding plate of a vibrating grinder.
5. A device according to Claim 4, characterized in that the second balancing weight (12) is arranged between a shaft bearing unit (18) and an abrasive-cover holding face (20) of the grinding plate (14).
6. A device according to one of the preceding claims, characterized in that the second balancing weight (12) is non-rotatably connected to the shaft (22) by way of a shaft bearing unit (18).
7. A grinding plate (14) which is provided to be releasably mounted on a vibrating grinder (16), characterized by an integrated corrective balancing weight (12) for compensating a centrifugal force.
8. A hand-held machine tool (16), particularly a vibrating grinder having at least one exchangeable eccentric tool (14) and having at least two balancing weights (10, 12), characterized in that a first balancing weight (10) is connected to a shaft (22) of the hand-held machine tool (16) and in that a second balancing weight (12) is at least partially integrated in the eccentric tool (14).
9. A balancing device for an eccentric tool substantially as herein described with reference to the accompanying drawings.
10. A grinding plate substantially as herein described with reference to the accompanying drawings.
11. A hand-held machine tool substantially as herein described with reference to the accompanying drawings.