WO2006056966A1

WO2006056966A1 - Angle grinder

Info

Publication number: WO2006056966A1
Application number: PCT/IB2005/053943
Authority: WO
Inventors: Steen Mandsfelt Eriksen
Original assignee: Steen Mandsfelt Eriksen
Priority date: 2004-11-29
Filing date: 2005-11-29
Publication date: 2006-06-01

Abstract

Angle grinder (1) of the kind which comprises a housing (2), a drive motor (8) mounted in the housing, a first bevel gear (9) driven by the drive motor, a second bevel gear (10) mounted on a shaft journaled in the housing and meshing with the first bevel gear, an output shaft (6) for mounting a disc (7), such as a cutting or tool, and where a transmission (11) is arranged between the shaft of the second bevel gear and the output shaft. In this way, the angle grinder's cutting depth can be increased with respect to the prior art.

Description

Angle Grinder

The present invention relates to angle grinder of that kind which comprises a housing having a back part and a front part, a drive motor mounted in the housing, a first bevel gear driven by the drive motor and defining a first rotational axis, a second bevel gear defining another rotational axis forming an angle with the first rotational axis, whereby the second bevel gear is mounted on a shaft rotatively mounted in the housing and meshing with the first bevel gear, an output shaft for mounting a tool, a transmission arranged between the shaft of the second bevel gear and the output shaft, and at least one handle for providing a reaction torque to the torque produced by the angle grinder during operation, whereby the at least one handle is forming an angle with the first rotational axis .

The term angle grinder is, in this connection, used for a machine, which could be arranged for operating tools like e.g. cutting discs, grinding discs, saw blades, sanding discs or wire brushes.

Angle grinders of this kind are well known and used in many different applications. Two examples of common use of angle grinders are cutting a metal pipe and grinding a groove into a brick wall.

Two patent documents that describe angle grinders of this type are US 6,386,961 and US 6,632,128. Both documents show angle grinders with gear systems similar to the kind mentioned in the introductory paragraph. These types of gear systems are very common in angle grinders since they serve two purposes at the same time. The first is to reduce the speed and increase the torque of the output shaft. The second is to arrange the output shaft at an angle to the motor shaft. However, a large problem with the angle grinders of the type mentioned above is that the diameter of the second bevel gear needs to be larger than the diameter of the first bevel gear in order to decrease the speed and increase the torque. This means that this diameter limits the distance between the edges of, for example, a tool connected to the output shaft and the housing of the angle grinder. This limits the cutting depth of the angle grinder. This is further complicated since making the second bevel gear smaller would result in higher output shaft speeds and lower torques. This would require a larger and more powerful motor. Therefore, this type of gear system requires a compromise between cutting depth and motor size.

It is well known that an angle grinder produces large torques that makes it difficult to hold the angle grinder properly. Therefore most angle grinders are arranged with a handle that can be screwed into the housing of the angle grinder. See figure 1 of US 6,632,128, part number 16, for an example of such a handle. However, the fact that the handle can be removed from the housing means that many people loose the handle when it is separated from the angle grinder. Furthermore, it is time consuming to remove the handle or change the side on which it is mounted.

From the U.S. patent No. 5,407,381 is known an angle grinder having a handle with a pivotal bow which can be folded out to function as a handle for during operation providing a reaction torque to the torque acting upon the tool of the angle grinder. Said bow is however somewhat short and therefore only capable of providing smaller reaction torques. Moreover, the bow is placed far from the tool resulting in the angle grinder being difficult to control during operation.

US patent No. 2003/0000716 Al discloses an angle grinder which is provided with a bevel gear driven by a drive motor and a second bevel gear meshing with the first bevel gear. A transmission is arranged between the shaft of the second bevel gear and the output shaft for mounting the tool which is placed in such a way that the plane of the tool is flush with the rotational axis of the first bevel gear in order to obtain a tilting moment-free operation of the angle grinder. The transmission is placed in an extension arm of the housing of the angle grinder. This extension arm reduces the working depth of the tool substantially since it is placed at the same side of the transmission as the second bevel gear.

A problem with angle grinders known in the state of the art is that they typically provide no way of controlling the depth of the cut. For example, an angle grinder is often used to cut a groove in a brick wall for installing new electrical cabling. However with current angle grinders, it is not possible to control how deep the groove will be.

A first aspect of the current invention is to provide an angle grinder of the kind mentioned in the introductory paragraph, which has an increased cutting depth.

The new and unique way in which the current invention fulfils the above-mentioned aspects is that the tool is mounted on the opposite side of the transmission than the second bevel gear.

Another aspect of the current invention is to provide an angle grinder of the kind mentioned in the introductory paragraph, which is easier to handle and safer to use than previously known.

The special position of the tool implies that a relatively large torque acts upon the angle grinder during operation. The angle grinder is therefore equipped with at least one handle arranged in such a way that it easily is able to provide the necessary reaction torque. The at least one handle is, in a preferred embodiment of the invention, mounted on the housing about a pivot axis placed at least at a distance from the back part of the housing, thereby obtaining that the handle is always available to the operator and also obtains a suitable length.

The operator obtains a very good and safe control with the angle grinder during operation when the pivot axis of the at least one handle is placed at the front part of the housing and the pivot axis is extending at least mainly parallel to the second rotational axis.

The at least one handle can, according to the invention, be pivotally mounted on the housing about a locking mechanism adapted to lock the handle in positions between a first - and second position, whereby it is advantageously obtained that the operator is able to handle the angle grinder easily and safely during operation.

The housing and the at least one handle can, according to the invention, moreover be arranged such that the handle, at least partly, fits into at least one recess in the housing in the first position of the handle, which in this way is not in the way for an operator wanting to operate the angle grinder without using the handle.

The transmission could take the form of two spur gears. The first spur gear could be connected to the output shaft and the other spur gear connected to the second bevel gear. This would be a relatively inexpensive and robust embodiment. The transmission could also comprise a belt transmission, for example a toothed belt. This could be advantageous in that a belt drive transmission produces less noise than a gear transmission. To increase the safety of the angle grinder, at least one switch could be arranged so that it is triggered when the at least one handle is in its first position. When the switch is triggered, the drive motor could be arranged to stop or slow down. The angle grinder produces high torques at high speeds. When the handles are folded in, the user has less control over the angle grinder. Therefore, automatically reducing the speed or stopping the motor when the handles are folded in protects the user from loosing control of the angle grinder.

The invention will be explained in greater detail below where further advantageous features and exemplary embodiments are described with reference to the drawings, in which

Fig. 1 is a schematic representation seen in perspective of an angle grinder according to the invention with a part of the housing removed,

Fig. 2 shows the same angle grinder from another angle, this time with the complete housing shown and with one handle half extended, and

Fig. 3 shows the same as fig. 2 but with both handles extended.

Figures 1, 2, and 3 show an embodiment 1 of an angle grinder according to the invention. The angle grinder 1 comprises mainly a housing 2, a safety cover 3, two handles 4, a transmission 5 with an output shaft 6, a tool 7, and an electrical motor 8.

The tool 7 is detachably connected to the output shaft 6 using conventional means such as a threaded nut (not shown) .

The electrical motor 8 drives the output shaft 6 via the transmission 5. The transmission is comprised of a first bevel gear 9, a second bevel gear 10 and a belt drive transmission 11. The first bevel gear 9 is connected directly to the motor 8. The first bevel gear 9 is smaller than the second bevel gear 10 in order to decrease the speed of the output shaft and increase the torque with respect to the output of the motor. Furthermore, the bevel gears allow the output shaft to be arranged at a right angle to the motor. A fan 12 connected to the motor cools the motor down.

The belt drive transmission 11 arranged between the shaft of the second bevel gear and the output shaft allows the axis of the output shaft to be offset from the axis of the second bevel gear. Due to this offset, the distance between the output shaft and the edge of the housing can be reduced. This increases the cutting depth of the angle grinder. In this particular embodiment, the belt drive comprises a toothed belt.

The two handles 4 are pivotally connected to the housing 2. This allows the handles to be folded into the housing when they are not in use and folded out when they are in use.

Figure 1 shows the two handles in their first position, that is to say completely folded into the housing. Figure 2 shows one handle half folded out, and figure 3 shows the two handles in their second position, that is to say completely folded out.

In this embodiment the handles are arranged about pivot axes, which are mainly perpendicular to the centre axis of the housing. The user can choose if he/she wants to use no handles, only one handle, or both handles. This makes the angle grinder very flexible.

The embodiment shown in the figures has locking mechanisms 13 arranged at each pivot point. Each locking arrangement 13 is in the form of two pivot tabs 14 arranged on each side of the handle. The tabs 14 pivot about screws 15 when the user pushes the tabs inward towards the housing. The arrow in figure 2 shows this. When a tab is pushed inwards towards the housing, a cross-shaped slot 16 formed in the tab disengages with an elongated protrusion 17 formed on the handle. When both tabs are pushed inwards and the cross-shaped slots on both tabs disengage with protrusions on the handle, the handle can be pivoted. When the cross-shaped slots are aligned with the elongated protrusions again, the tabs click into place again, thereby locking the handle in position.

In the current embodiment, the handle can be locked in one of two positions, either all the way out or all the way in. However, this is only one embodiment out of many other possible forms of locking arrangement.

In other locking arrangements the handles could be locked in many different positions. For example, the locking mechanism could consist of a screw that is tightened to lock the mechanism and loosened to adjust the mechanism.

Each handle 4 forms, in an advantageously embodiment, an angle between 60° and 120°, preferably between 75° and 105° and especially about 90° with the first rotational axis in the second position.

The housing 2 is formed with two recesses 18, each corresponding to the shape of the handles 4. In this way, when the handles are folded in towards the housing, the handles fit into the recesses. In this way, the handles do not protrude from the housing when they are not in use.

As a safety feature, each recess is arranged with a contact switch 19. When the handle is folded into the recess, the contact switch is triggered. Upon triggering this contact switch, the speed of the drive motor can be reduced or even stopped. This feature can be engaged or disabled by the user.

Via an adjustment knob (not shown) , the speed of the angle grinder can also be manually adjusted by the user.

In a more advanced version, a switch could be arranged which has more triggering positions. In this way, the speed could be adjusted as the handle is put into different positions.

In the above discussion, the power was supplied to the drive motor 8 via an electrical cable. It should be obvious to the person skilled in the art that a battery could be used instead in order to make the angle grinder portable. Furthermore, in the above discussion, the drive motor 8 was an electric motor, however it should be obvious to the person skilled in the art that other forms of motors, such as a pneumatic motor, could also be used.

Claims

Claims :

1. An angle grinder of that kind which comprises - a housing (2) having a back part and a front part, a drive motor (8) mounted in the housing, a first bevel gear (9) driven by the drive motor and defining a first rotational axis, a second bevel gear (10) defining another rotational axis forming an angle with the first rotational axis, whereby said second bevel gear is mounted on a shaft rotatively mounted in the housing and meshing with the first bevel gear (9), an output shaft (6) for mounting a tool (7), - a transmission (11) arranged between the shaft of the second bevel gear (10) and the output shaft (6) , and at least one handle (4) for providing a reaction torque to the torque produced by the angle grinder during operation, whereby the at least one handle

(4) is forming an angle with the first rotational axis, characterized in comprising that the tool (7) is mounted on the opposite side of the transmission (11) than the second bevel gear (10) .

2. An angle grinder according to claim 1, characterized in that the at least one handle (4) is pivotally mounted on the housing (2) about a pivot axis placed at least at a distance from the back part of the housing (2) .

3. An angle grinder according to claim 1 or 2, characterized in that the pivot axis of the at least one handle (4) is placed at the front part of the housing (2) .

4. An angle grinder according to claim 1, 2 or 3, characterized in that the pivot axis of the at least one handle (4) is extending at least mainly parallel to the second rotational axis.

5. An angle grinder according to any of the claims 1 - 4, characterized in that the at least one handle (4) is pivotally mounted on the housing (2) about a locking mechanism (13) adapted to lock the handle in positions between a first - and second position.

6. An angle grinder (1) according to claim 5, characterized in that the housing (2) and the at least one handle (4) are arranged such that the at least one handle (4), at least partly, fits into at least one recess (18) in the housing in the first position of the handle (4) .

7. An angle grinder according to claim 5 or 6, characterized in that the at least one handle (4) forms an angle of between 60° and 120°, preferably between 75° and 105° and especially about 90° with the first rotational axis in the second position of the handle (4) .

8. An angle grinder according to any of the claims 1 - 7, characterized in that said transmission (11) comprises a belt transmission (11) .

9. An angle grinder according to any of the claims 1 - 8, characterized in that said transmission comprises two spur gears.

10. An angle grinder according to any of the claims 1 - 9, characterized in that said angle grinder further comprises at least one switch (19) which is triggered when the at least one handle (4) is in its' first position.

11. An angle grinder according to claim 10, characterized in that the drive motor (8) stops or slows down when said contact switch (19) is triggered.