Such switch assemblies applied in tools are for instance known from US 2,263, 136 and EP 1 125 698. The American patent shows a tool with a dual control member.

The control members are coupled mechanically to a switch mechanism. In EP 1 125 698 a switch is operated with a first control member arranged on the fixed body of the tool. A second control member is arranged on a separate handle which can be coupled to the tool. When the handle is coupled to the tool, the first switch mechanism also becomes operable by means of the second control member.

A need has however been found to exist for a further improved switch assembly which can be operated from different positions on the electric tool. According to au first aspect, an improved operation is the intended purpose. According to a second aspect, an increased safety is aimed for.

The present invention meets such a need in that the switched-on mode can be deactivatd with the first and the second control member. A circuit is hereby provided which can be placed in a switched-on mode, but wherein two control members are available to interrupt this mode. The safety of machines on which such circuits are applied is hereby increased.

According to another aspect, the switch assembly comprises a release means, optionally formed by the locking

means, for releasing the first switch mechanism from a switched-on mode, which mechanism can be operated at least by the first and the second control member.

As a result of these measures it becomes possible to operate the switch mechanism with two different control members, wherein the control members can be arranged at a different position on the tool.

In such a situation it is attractive that the first and the second control member can both be locked in the position in which the first switch mechanism is switched on.

A structurally inexpensive embodiment is created when the first and the second control member are both arranged on the same component connected mechanically to the first switch assembly.

The construction is further simplified when the component is supported for sliding movement in its lengthwise direction.

Instead of a sliding movement as applied above, it is likewise possible to have the control member perform a different movement, such as a tilting movement. The choice here depends of course on the type of movement with which the switch can be operated, the relative position between the control members and the switch, and ergonomic considerations for operation of the switch.

It is possible in principle to embody such a switch assembly with two separate switches, each of which can be operated by their own control member. In such a situation the invention provides the measure that the switch assembly comprises a second switch mechanism, that the second control member is adapted to operate the second switch mechanism, and that the first and the second switch mechanism are electrically connected to each other.

The switch mechanisms can herein be formed by mechanisms which, once they have been placed in the switched-on position, will maintain this until they are actively returned to their original position, although it is equally possible for the switches to be formed by switches which are only in switched-on mode when pressure is maintained on the control member.

The different types of switch require a different type of circuit. It is however also possible that the first switch mechanism can be electrically operated, and that the first and the second control member are each formed by a push button for electrical operation of the first switch mechanism. The first switch mechanism herein fulfils a relay function.

As stated above, both switch mechanisms can be embodied to perform an on/off function. In some tools it is attractive if at least one of the switch elements can perform a regulating function, so that the rotation speed and/or the torque of the tool can be controlled.

Only one of these elements need here be embodied as such, and the other switching element can retain its on/off function.

In the above discussed embodiments there is mention in one embodiment of two or more switch mechanisms.

It is however cheaper to make use of a single switch mechanism. The present invention provides for this purpose the measure that the first switch mechanism can be operated mechanically and that the first and the second control member are both coupled mechanically to the first switch mechanism.

The invention relates not only to a switch assembly according to the invention but also to an electric tool provided with such a switch assembly.

It is then attractive for the component in which the switch can be operated to extend parallel to a wall of the housing of the hand tool.

A specific application of the dual control switch according to the present invention is obtained when the tool is adapted to be held with at least a first and a second mutually differing position of a hand, and that the position of the control members is chosen so as to be operable in each of the positions of the holding hand without removing the holding hand from the tool.

A more specific application is obtained when the tool is adapted to enable handling only by the holding hand in the first position of the holding hand, and to be held by two hands in the second position of the holding hand.

The advantages of the invention become particularly manifest when the tool is formed by a right- angle grinder.

The present invention will be elucidated hereinbelow with reference to the accompanying figures, in which: Figure 1 shows a circuit diagram of a first embodiment; Figure 2 shows a circuit diagram of a second embodiment, wherein three switches are arranged instead of two switches; Figure 3 shows a circuit diagram of a third embodiment; Figure 4 is a schematic cross-sectional view of a construction of a fourth embodiment of the present invention; Figure 5 shows a cross-section of a right-angle grinder wherein a switch assembly according to the fourth embodiment of the present invention is applied ;

Figure 6 is a detail view in a first position of the switch unit shown in figure 5; Figure 7 shows a view corresponding with figure 6 in a second position; and Figure 8 is a cross-sectional view of a fifth embodiment.

As already stated in the preamble, it is possible to switch the electric motor arranged in the tool by means of two switches, which are of course arranged at different locations in the housing of the tool. Figures 1-3 show embodiments in which the invention is not incorporated, but in which the invention can however be applied.

The circuit shown in figure 1 comprises two two- way switches 1, 2 and an electric motor 3. Switches 1,2 and electric motor 3 are connected in series. The motor is switched on or off by operating either of the switches.

Such a configuration, just as the other configurations according to the present invention, can likewise be applied to three switches. Such a circuit is shown in figure 2. A bipolar two-way switch 4 is here added to the two two-way switches 1,2. It is here also possible to switch motor 3 on or off by operating any of the switches.

Figure 3 shows a circuit wherein the electric motor 3 is connected in series to make contacts 5 of a relay 6. Relay 6 can be operated by means of two push- buttons 7,8 connected in parallel. It will be apparent that a greater number of push-buttons can be applied instead of two push-buttons.

A significant difference between the circuits of figures 1 and 2 on the one hand and that of figure 3 on the other is the fact that in the circuit of figure 3 only one switch (relay 5,6) is available which is adapted to switch

the actual motor current. Push-buttons 7,8 function here as control members.

As shown in figure 3, it is also possible to make use of a mechanical operation of a single switch instead of electric control members 7,8. Such a configuration is shown in figure 4.

Use is once again made here of a single switch 10, which can be operated by means of a lever 11. Lever 11 is connected to a slide member 12 which is urged to the left by means of a spring 13, whereby switch 10 is normally switched off at all times. By pushing switch block 12 to the right counter to the spring pressure of spring 13, lever 11 moves switch 10 to its switched-on mode.

Slide member 12 extends over a large distance.

This slide member can hereby be operated at two different locations, so that it in fact forms two control members.

On the right-hand side the slide member is provided with a hook 14 which is connected pivotally to the slide member and which can be hooked behind a protrusion 15 forming part of switch housing 16. Slide member 12 can hereby be locked in its right-hand position. Hook 14 is part of the locking means.

This construction has the further advantage that the mode of the switches is visible. In addition, when the first switch is in the off position, the second switch will also always indicate the off-mode. No confusion can therefore result.

For the purpose of release use can be made of a control member 17 which releases the hook 14 relative to protrusion 15, so that slide member 12 can be moved once again to the left. In order to also enable release of hook 14 from the other operating position, control member 17 is

connected to a second control member 18 by means of a lever 19.

Direct operation herein takes place from both operating positions by moving slide member 12 to the right.

The tool can be switched off/released irrespective of which control member activated the locked position.

The release of hook 14 takes place directly by means of control member 17 and indirectly, via lever 19, by means of control member 18.

Figure 5 shows a right-angle grinder 20 in which a motor 21 is arranged which is mounted on a shaft 22. This latter is mounted by means of bearings 23 in housing 24 of right-angle grinder 20. At one of its ends the shaft 22 is provided with a bevel gear 25 which is in engagement with a second bevel gear 26 which is fixed to a shaft 27 to which a grinding stone can be attached. Shaft 27 is mounted in housing 24 by means of bearings 28.

Present for operation of the motor is a switch mechanism 29 which can be operated by means of a protrusion 31 fixed to a slidable switch member 30.

The construction hereof is shown more clearly in figures 6 and 7. Switch 29 can be operated by sliding control member 30 in the direction of arrows 32 in figure 6. Both arrows 32 moreover indicate the positions of the locations at which control member 30 can be operated.

The switch member is provided on its forward end with a tiltably mounted hook 33 which can hook round a protrusion 34 fixed to housing 24. A draw spring 35 is tensioned between hook 33 and housing 24 to urge the hook 33 to the locking position.

The consequence hereof is that, when control member 30 is moved to the position furthest to the right in the drawings, which is shown in figure 7, control member 30

is locked in this position, wherein switch mechanism 29 is switched on and the tool is activated.

For the purpose of release use is made of release elements 36,37 respectively which are arranged on control member 30 and which are each arranged tiltably relative to control member 30.

When release element 37, which is formed integrally with hook 33, is depressed in the direction of arrow 39, hook 33 is released, so that the control member returns to its original position. A direct operation of the locking element thus takes place here.

Conversely, when release element 36 is depressed in the direction of arrow 39, wherein the associated movement is transmitted via lever 38, an indirect operation takes place.

As a result of these measures it is possible to activate and deactivate the switch 29 at two different positions. This is important in the present case because the grinder in question can be held in two different ways.

In a first way of holding, the grinder is held with only one hand, wherein use is made of the position furthest to the right in figures 6 and 7. It is also possible to hold the grinder with two hands, wherein one hand is placed in a position such that it can operate the control member in the position furthest to the left.

Figure 8 shows a cross-section of a hand tool which can be operated from two sides of the housing. The tool can hereby be used by right and left-handed users.

The tool comprises a housing 45 in which a switch 41 is arranged. Mounted on the switch is a T-shaped lever 42 with which the switch can be operated. The lever comprises for this purpose two distal ends 43,44 respectively, each of which protrude through an opening 46,

47 respectively arranged in housing 45. Using these distal ends 43,44 the switch can be operated between the switched-off position drawn in full lines in the figure and the switched-on position of switch 41 drawn with broken lines. An embodiment is thus obtained which can be used by both left and right-handers, and which makes use of a different configuration of the switch assembly.

It will be apparent that numerous variations can be made to the shown construction, for instance by application in different tools.