ELECTRIC HAND TOOL WITH IMPROVED DUST DISPOSAL

The present invention relates to an electric tool, comprising: a housing; a movable attachment which extends at least partially outside the housing for the purpose of acting on a workpiece during operation; a drive for the attachment disposed in the housing; an airflow generator connected to the drive; and a discharge channel with a container and a filter associated therewith for collecting residues released during action of the attachment on the workpiece .

Such tools are generally known. The distance between the motor and the attachment is here usually kept as short as possible. Air with residues therein is drawn in through the action of the airflow generator, in general a fan. The discharge channel then runs from this fan to a container for containing the residues from which the air can escape through a filter. As a result of providing the filter the residues remain behind in the container.

Such configuration has a number of drawbacks. It is generally the case in the known art that operation takes place with overpressure. The fan propels the airflow with the residues to the container. On the way to the container the airflow and the residues entrained therein tend where possible to leave the channel. Good sealing provisions must therefore be made to prevent the residues, usually of dust- like nature, entering the outside air. It is precisely the intention to prevent this, and to ensure that the residues or dust enter the container.

In a known electric tool based on overpressure it can further be the case that the channels leading to the container may also become clogged when the container becomes

full. In such a case the machine must often be opened in order to empty the channels. Access from outside is very- limited, and a drastic step is therefore necessary to open the machine . In a known electric tool the airflow coming from the container is also utilized to cool the motor. If the container becomes full, this airflow can be obstructed or cease altogether. As a result the motor may become overheated, which can result in damage to the motor, or even irreparable failure of the motor.

The present invention has for its object to obviate or at least alleviate the above stated drawbacks of the prior art, for which purpose an electric tool according to the present invention is distinguished in that the airflow generator is disposed in the discharge channel behind the container and the associated filter in the airflow direction. This in fact brings about a reversal of the configuration of the known art, in accordance with which the airflow is generated on the basis of overpressure, while according to the invention this takes place with underpressure . Because the fan or other embodiment of an airflow generator draws in air in the direction of the container, this is also the case for the residues, usually dust. It is thus possible to ensure, with more certainty and less stringent measures for sealing of the channel, that all residues will enter the container. An improved dust disposal or discharge of residues is thus realized according to the invention.

In a preferred embodiment the electric tool according to the invention has the feature that the discharge channel extends in wholly integrated manner through the housing. This results in a very compact and favourable embodiment without parts and components, which actually belong to the

suction device, being arranged on the housing of the tool. An embodiment of the tool integrated with a suction device is thus realized.

In another specific preferred embodiment the electric tool according to the invention has the feature that the container can be releasably attached to the housing. The channel then preferably remains integrated. The ability to release the container provides the option of also being able to empty the container. This need not have any effect at all on the path or the orientation of the channel .

In another preferred embodiment the electric tool according to the present invention has the feature that the container comprises at least one element from the group comprising a dust bag and a box. It should be noted here that a box, particularly in the case where an underpressure prevails therein, is preferred to a dust bag.

In yet another preferred embodiment the electric tool according to the present invention has the feature that the drive comprises an electric motor with a motor shaft on which the airflow generator is fixedly arranged. The airflow is thus generated with an airflow generator which for instance takes the form of a fan and which can then be arranged fixedly on the motor shaft. Such an embodiment then preferably has the further feature that the attachment is connected via a transmission to the motor shaft. In such an embodiment the driving of the attachment can be adapted to the type of attachment on which the electric tool is based, such as a circular saw, a fretsaw, a hand drill, a sanding machine or belt sander and so on. It is precisely in a configuration with such a transmission and a fan, both connected or coupled to the motor shaft, that it is necessary to provide for integral provision of the discharge channel which runs from the attachment driven with the motor

to the container for the purpose of collecting dust and/or other residues.

In yet another embodiment the electric tool according to the invention has the feature that the airflow generator comprises a fan moulded onto the motor shaft . Now that the motor, the motor shaft and the fan in a possible embodiment of an airflow generator form a functional and structural unit, it is preferably favourable that further modifications to such a unit are unnecessary. In this case the discharge channel, which must then extend along the drive shaft and the fan, must also be designed with extra care. The requirements in respect of the positioning of the discharge channel become even more exacting when an eccentric is also formed on the motor shaft. The tool is then for instance a sanding machine, wherein at least one eccentric is applied. It is particularly when more components are associated with the motor shaft that the inventive value is becomes apparent of the preferably integrated positioning of the discharge channel toward the airflow generator or fan, which is also associated with the motor shaft, with interposing of the container for collecting the residues.

An electric tool according to the present invention preferably has the feature that the airflow generator is associated with the motor shaft and is separate from the cooling fan, and wherein the channel is separated from a compartment with the motor therein. Such a configuration has a number of advantages. When a fan is applied to cool the motor and is simultaneously utilized for the purpose of blowing through or suctioning an airflow having therein residues which must be filtered out at any moment from the airflow, it may be that the filter becomes clogged. If the motor is disposed behind the filter in the flow direction,

no cooling air, or insufficient cooling air, reaches the motor. The motor can thus become overheated.

Conversely, when the filter allows passage of micro- residues because it is insufficiently fine, and it is not the intention to allow the filter to become clogged, these micro-residues (dust) reach the motor. If the airflow is then discharged from the housing of the electric tool, micro-residues strongly warmed or heated by the motor leave the housing and are propelled at high speed. A user of the electric tool may thus be injured. It may even be the case here that the micro-residues catch fire in the housing in the vicinity of the motor where the micro-residues are strongly warmed or even heated. If sufficient micro-residue material accumulates at the motor, combustion thereof can take place with all the consequences this entails in respect of the motor or wiring thereof etc . By now keeping the channel separate from the motor, both negative and adverse conditions can be effectively avoided or diminished.

Further preferred embodiments, features and advantages of embodiments of the tool according to the present invention will be elucidated or at least clarified in the following description of several exemplary embodiments, which is formulated on the basis of and with reference to the accompanying drawings, in which the same or similar parts and components are designated with the same reference numerals, and in which:

Fig. 1 shows a schematic view of a drive with attachment and suctioning according to the known art;

Fig. 2 shows a drive with attachment and suctioning according to the present invention;

Fig. 3 shows a specific embodiment of the principle according to the invention illustrated in fig. 2.

Fig. 4 shows another specific exemplary embodiment of the operating principle of fig. 2 ;

Fig. 5 shows a third embodiment of a specific configuration in accordance with the operating principle of fig. 2.

Fig. 1 shows the operating principle of a drive in an electric tool according to the known art . The drive is designated generally with reference numeral 1, while a suction system is designated with reference numeral 2. The drive comprises a motor 3 for the purpose of rotating a motor shaft 4 on which is arranged a cooling fan 5 which also serves to cool motor 3. An attachment 6 is also connected to motor shaft 4, preferably in releasable manner to enable replacement of the attachment. An attachment 6 is for instance a grinding disc, a sanding attachment, a saw for a fretsaw etc.

Suction system 2 is associated with fan 5. An indrawn airflow, designated with arrow A, contains residues which are released when attachment 6 acts on a workpiece . Airflow A is guided into a channel 7 leading to a schematically shown container 8. In the exemplary embodiment shown here the container comprises a filter 9, which holds back the residues. An airflow then leaves outlet 10, where the residues have been filtered out using filter 9. It will be evident that details of the configuration shown here can differ from the reality of a specific embodiment of the known art. Filter 9 can thus form the separation between container 8 and outlet channel 10. Specific reference will be made hereinbelow to a configuration according to the present invention. Such a configuration is shown schematically in fig. 2. Here too an attachment 6 is driven by a motor shaft 4 and, using an airflow generator in the form of a fan 26, an airflow A is

set into motion which has therein residues which are released after attachment 6 has acted on a workpiece (not shown) . A discharge channel 7 here also leads to a container 8 with a filter 9 therein. Disposed in outlet channel 10 is fan 26 which is again also connected to motor shaft 4 associated with motor 3.

Fan 26 thus draws in an airflow without an airflow having to be propelled through container 8 and filter 9 disposed therein. Fan 5 provides only for cooling of motor 3. The channel 7-10 associated with suction can thus be wholly separated from any compartment in a housing having therein the motor 3, as indicated with broken line 27. The two fans 5,26 can on the other hand also be combined.

Fig. 3 shows a specific embodiment of the operating principle as illustrated schematically in fig. 2. Fig. 3 shows a sanding machine 11. The sanding machine comprises a sanding attachment 12 having passages 13 therein for carrying therethrough an airflow having therein residues 14 from the operation with sanding attachment 12 as possible embodiment of an attachment 6. The airflow in openings 13 contains residue 14 and channel 7 leads from openings 13 to container 8 which is associated with a filter 9. Residues 14 are removed from the airflow at filter 9 and an airflow without residues then moves to fan 26 arranged on motor shaft 4. Fan 26 thus draws in and discharges the airflow laterally or otherwise from housing 15 of sanding machine 11. The residues remain behind in container 8 in front of filter 9.

The motor is here enclosed between bearings 16 and motor shaft 4 protrudes through lower bearings 16 toward fans 5 and 26 and an eccentric mechanism 17 for the purpose of causing a sanding attachment 12 to make a desired movement when motor 3 is set into operation.

It is noted that the passages and channels for generating airflows and entraining residues can be wholly realized within the limitations of an existing sanding machine without an open connection to the space with motor 3 therein. A partition wall 19 provides herefor and forms a realization of the separation along broken line 27 in fig. 2. The channels and openings and passages for the airflows can therefore be implemented and integrated with minimal modifications in respect of a known sanding machine, because these channels, passages and openings take an integrated form in sanding machine 11.

The embodiment of a sanding machine 18 in fig. 4 differs from sanding machine 11 in fig. 3 in that fan 26 for generating the desired airflow for entraining residues 14 forms a unit with a fan 5 which serves substantially only for the purpose of cooling electric motor 3. The combined fan 5,26 is thus arranged with the motor itself between bearings 16, wherein only an eccentric mechanism 17 is further arranged under the lower bearing 16 in the view of fig. 4. Fan 26 laterally discharges the airflow drawn in via container 8 with a filter 12 so that there is once again no open connection to the motor compartment .

Fig. 5 shows another embodiment of an electric tool designed in accordance with the present invention. Fig. 5 shows a belt sander 20 wherein attachment 6 is therefore designed as circulating sanding belt 21 which is trained around rollers 22 and driven therearound, since motor 3 is connected to at least one of the rollers. Arranged in known manner between rollers 22 is a tensioning mechanism which can be activated and deactivated in order to exchange sanding belt 21. Electric motor 3 is connected via a motor shaft 4 to a wheel 23 which is associated via a transmission (not shown) with at least one of the rollers 22, wherein a

cord runs round wheel 23 and a driven roller 24 for the purpose of transmitting the circulating movement of wheel 23 onto roller 22. Debris or grinding dust as embodiment of residue is here flung upward in rearward direction during the rotating movement of sanding belt in the direction of arrow B. The residue thus enters container 8 almost of its own accord via inlet 23 thereof. Outlet 24 of container 8 is covered with a filter 9, from which a channel 10 runs to a fan 26 arranged on motor shaft 4 between electric motor 3 and drive wheel 23. After having residues 14 removed by means of filter 9, an airflow reaches fan 26 via discharge channel 10 and is subsequently discharged laterally from housing 25 of the belt sander and/or used to cool the electric motor. Fan 26 is however preferably applied to cool the motor, so that due to partition 19 the airflow remains separate of the cooling of motor 3.

Now that diverse embodiments of the present invention have thus been described with reference to the accompanying drawings, many alternative embodiments and options will occur to the skilled person, all lying within the definitions of the scope of protection as stated in the claims, at least to the extent that such alternative and additional embodiments do not depart from the letter or spirit of these claims. It is in any case asserted that the present application is in no way limited to that specifically described or shown, but only by the limits of the scope of the definitions given in the claims. The principles of the present invention could therefore also be applied in other electric tools, such as fretsaws, handheld drills, battery-powered drills, right-angle grinders and so on. The subject matter of the present application is thus not limited to sanding machines or belt sanders. Of specific

importance however is the feature that the channels from and to the container are integrated into the housing of a tool, this having very advantageous effects in respect of space requirement therefor without having to create space for such channels and passages outside the limitations of a usual housing.

Containers 8 are designed in each case as releasable boxes, although use can also be made of a dust bag with a filter at the outlet thereof. Eccentric mechanisms can be realized in ways other than the two of figures 3 and 4, and belt sanders can also be realized with dispositions of the components and/or other tensioning mechanisms other than those shown in fig. 5. It will be apparent that many additional and alternative embodiments of the present invention are possible without departing from the scope of the invention as defined in the claims.