FIELD OF THE DISCLOSURE

The present disclosure relates to floor grinding machines.

BACKGROUND OF THE DISCLOSURE Floor grinding machines for polishing or grinding floor surfaces are already known.

EP 3 463 749 A1 , published by Husqvarna AB on 05.09.201 9, relates to a floor grinding machine for grinding floor surfaces of stone or stone-like material. Such a machine comprises a machine frame, a grinding head, supported by and being ro- tatable relative to the machine frame, a grinding head hood, which defines a space in which the grinding head is rotatable, a hollow and resilient member, arranged in the space, and a pressurized fluid source, operatively connected to the hollow member to supply said pressurized fluid, whereby the hollow member is resiliently expandable upon supply of said fluid. The resilient member is arranged within the space defined by the grinding head hood. The resilient member may comprise an aperture to allow the fluid to escape for cleaning of the inside of the grinding head hood. CN 105196125 A, published by Zhongshan CO LTD on 30.1 2.201 5, relates to a transmission mechanism for a floor grinding machine. The transmission mechanism comprises a lower transmission box and an upper transmission box, a driving gear located in the lower transmission box is connected with transition gears, big planet gears and output gears in a meshed mode from inside to outside in the circumferential direction, the portion, located on the upper transmission box, of a transmission main shaft is connected with a sun gear, the upper portion of each big planet gear is coaxially and synchronously connected with a small planet gear meshed with the sun gear, the small planet gears drive the sun gear to rotate so that the lower transmission box and the upper transmission box can revolve, and moreover the revolution direction is consistent with the input direction of the transmission main shaft and opposite to the output direction of the output gears. As the transmission mechanism is adopted in the floor grinding machine, inertial centrifugal force generated in revolution is effectively balanced, and the floor grinding machine adopting the transmission mechanism operates stably at work; besides, the revolution direction of the upper transmission box and the lower transmission box is opposite to the direction of the output gears to realize cross grinding, the floor grinding machine has the advantages of high efficiency, and the working efficiency is improved.

US 1 928 390 A, published by the American Floor Surfacing Machine Company on 28. 05.1932, relates to a floor surfacing machine of the rotary disc planetary type especially constructed for grinding, rubbing and polishing various kinds of composition floors. The floor surfacing machine comprises a portable support including a relatively stationary depending shaft guide, a perpendicular power-actuated drive shaft mounted for rotation in said guide, a revoluble selflevelling head, a flexible operating connection between said head and shaft, said head being provided with circumferentially spaced marginal bearings, a plurality of duplicate surfacing units having stub shafts mounted for rotation in said bearings, a relatively fixed main pulley connected with said guide and arranged centrally with respect to the axis of revolution of said head, individual supplemental pulleys fixedly attached, to said stub shafts and a flexible tracking belt trained over said pulleys, said belt being substantially diamond-shaped in cross section with one tracking surface engaged with the main pulley and the opposed tracking surface engaged with the supplemental pulleys. The belt-pulley transmission (belt drive) with three pulleys requires a triangular arrangement of the belt between the pulleys and therefore a triangular shape of a surrounding casing. A casing, which houses the belt-pulley transmission, with arms extending from a center radially outwards would therefore not be applicable.

DE 197 29 199 A1 , published by Billmann Gerhard on 1 5.07.1 997, relates to a floor processing machine consisting of a casing on two adjustable wheels, a variable rotary drive with stepped belt pulleys for at least three working disks on radial carrier arms of the counter-operating unit. The working disks are driven at a preset and adjustable angle to the floor. The rotary drive only affects the same-direction rotation of the working disks, not the turning speed, which is controlled by pressure on the reverse side of the toothed belt via an adjustable tensioning device. The belt pulley transmission is not arranged in a housing, in particular not in a housing with at least three arms. WO202/1 206603A1 , published by Husqvarna AB on 14. 10.2021 , relates to an abrasive tool for a floor grinder, wherein the tool extends along a wear direction from a grinding surface to a mounting surface, wherein the abrasive tool comprises at least two sections separated by a surface transversal to the wear direction, where the at least two sections comprise respective abrasive materials associated with different grit sizes, where the section located closer to the grinding surface is associated with a larger grit size compared to the section located closer to the mounting surface. Each tool is held by a respective tool holder and each tool holder is rotatably driven by a respective electric machine. A transmission interconnecting each tool holder is therefore not required.

US 2010/0267316 A1 , published by Groupe Russotti Inc. on 21 .10.201 0, relates to a grinding apparatus for grinding a surface, the grinding apparatus includes a plurality of satellites, a carrier for supporting the plurality of satellites, a plurality of primary gears rotatably mounted within the carrier and disposed about a motor output, a static gear which is fixed with respect to the motor and co-axial with the motor output, and a plurality of secondary gears which each rotate with one of the primary gears. The primary gears rotate the satellites with respect to the carrier and the secondary gears rotate the carrier around the static gear. The static gear is a ring gear surrounding the primary and secondary gears. The carrier, which supports the satellite and the static gear, needs to have therefore a circular shape.

US 4030 251 A, published by Boettcher William on 21 .06.1 977, relates to a marginal floor brush spacedly surrounding the rim of a chambered sanding machine base. The brush meets the floor and confines wood dust developed by a rotary sanding unit in the base. The dust is drawn from under the brush by a vacuum unit in the machine. A cover, which covers the base all around, has a circular cylindrical shape.

5 SUMMARY OF THE DISCLOSURE

Floor grinding machines for polishing or grinding floor surfaces are known and typically used for either producing an even or polished floor surface, or for the purpose of renovating floor surfaces which have deteriorated due to e.g. wear, or which have been damaged. Floor grinding machines are therefore typically0 equipped with grinding elements in the form of bonded abrasives. As another option, floor grinding machines may be equipped with cutting elements, adapted for example for removing glue, paint, lacquer or other surface treatments from a floor surface.

Depending on the base material of the floor and the desired surface finish and structure, the floor can be either wet grinded or dry grinded. The floor grinding machine therefore has to be versatile for both applications. The achievable grinding results do not only depend on the grinding elements and the operating parameters of the machine, but also on an efficient removal of the grinding dust, especially when dry grinding. An effective dust and/or fluid removal prevents the0 grinding elements from clogging with dust and therefore prolong not only the life span of the grinding element but also improve the achievable surface finish. In addition, the effective removal of dust from the grinding area lowers the dust exposure of the user.

As can be seen for example in CN 1051 961 25B, the known floor grinding ma¬

5 chines usually comprise a transmission for transferring the power from the electric motor to the individual grinding heads, which transmission is usually housed in a circular shaped rotational symmetric housing. Usually the known floor grinding machines comprise transmissions with a belt or gearing and rotational symmetric housing, which is usually bell shaped. The known bell shaped transmission hous¬0 ings fully cover the grinding area. This makes it particularly difficult to efficiently remove the dust and fluid from the grinding area. In addition, the known rotational symmetric housings are comparatively bulky and heavy. The bell shaped housings cause a high moment of inertia, which requires a more stable and therefore also heavier overall structure and therefore in consequence leads to a higher total weight of the floor grinding machine.

As can be seen in EP 3 463 749 A1 the air ducting of the known existing grinding head covers mainly draw off to the dust only at the rear of the grinding head cover in an upwards manner. To be able to remove dust with this locally limited suction effect, strong and therefore oversized vacuum cleaners are necessary. In0 addition, it has shown to be particularly difficult to also efficiently remove the excessive fluid within the floor grinding process with the known air routing within the known grinding head covers. The present floor grinding machine comprises an electric motor which extends along an axis of rotation and which is interconnected to a grinding unit. The axis of rotation is thereby usually arranged essentially perpendicular to the grinding surface. Good results can be achieved when the floor grinding machine has a modular

5 setup. The floor grinding machine can comprise a chassis for moving the thereto interconnectable grinding assembly a floor. This allows that the machine can be disassembled in essentially two parts, which is beneficial for lowering the weight for the transport. The grinding assembly is therefore preferably detachably interconnected to the chassis for example via a connector. The connector can be realized0 by a bolt or a quick clamp device. In a preferred variation the grinding assembly comprises a grinding unit and thereto attached grinding disks, which grinding unit is arranged between the electric motor and the grinding area. The grinding assembly may comprise a mount for interconnecting the grinding assembly to the chassis. Typically, the grinding assembly is interconnected to the chassis via the connector to the mount in a swiveling manner. This allows that the grinding assembly can compensate unevenness of the floor.

In a preferred variation, the grinding assembly comprises the electric motor, the grinding unit and an interconnected grinding head cover. For a simple construction, the grinding unit can be directly flange-mounted to the electric motor. For trans¬0 ferring the power from the electric motor to the grinding disks, a transmission interconnects an input shaft to several output shafts. Preferably the transmission is arranged within a housing whereby the input shaft is arranged in the center of the housing and the output shafts are arranged in arms of the housing. Typically, the housing comprises at least three arms, whereby an output shaft is arranged at a distal end of each of the at least three arms. Good results can be achieved when the housing is arranged rotational with respect to the axis of rotation. In a preferred variation the housing rotates with 60 up 1 50 rounds per minute, preferably with

5 about 90 to 100 rounds per minute. In a preferred variation the electric motor is mounted in a torque-proof manner and the housing rotates with respect to the electric motor.

Typically, at least one grinding disk can be interconnected to each arm of the housing. Besides the rotation of the housing with respect to the electric motor, the0 grinding disks itself usually rotate with respect to the housing. The grinding disks are interconnected to the input shaft by the transmission. For a compensation of the occurring torque, the grinding disks typically rotate in a reverse manner with respect to the housing, which housing itself rotates with respect to the electric motor. For transferring the power from the electric motor to the grinding disks, the transmission usually comprises gearing and/or a belt. Good results can be achieved when the grinding disks rotate with about 500 to 2000 rounds per minute, preferably 1000 to 1 200 rounds per minute. In a preferred variation the transmission ratio between the input shaft and the output shafts is between 5: 1 and 1 5: 1 , preferably about 1 1 .5: 1 . A transmission ratio of about 1 1 .5: 1 leads to a good ratio0 between rounds per minute and torque at the grinding disks and therefore favorable grinding results.

In a preferred variation, the transmission can comprise a planetary transmission which comprises a first (upper) and a second (lower) transmission level. The upper transmission level usually faces the electric motor and the lower transmission level faces the grinding disks. To achieve a comparatively small and dense setup of the planetary transmission, the size of the gears as well as the size of the module is designed as small as possible. Good results can be achieved when the sun gear of

5 the first transmission level comprises 65 - 75 gears. The planetary gears of the first transmission level, which revolve around the sun gear of the first transmission level, typically comprises 1 1 - 1 5 teeth. The sun gear of the upper transmission level is usually mounted in a torque-proof manner with respect to the housing of the grinding assembly, whereby the planetary gears of the upper transmission level revolve0 around the sun gear of the upper transmission level. In a preferred variation the planetary gears of the upper transmission level and the planetary gears of the lower transmission level are interconnected to each other in a torsionally rigid connection, such that the housing and the thereto interconnected grinding disks revolve around the axis of rotation.

The sun gear of the second transmission level is usually interconnected to the input shaft and transmits the power to the output shafts via the planetary gears of the second transmission level. The sun gear of the second transmission level, which is interconnected to the input shaft, typically comprises 1 1 - 1 5 teeth. To achieve a small diameter of the sun gear of the lower transmission level, the module is typi¬0 cally 1 .5. To prevent that the planetary gears of the second transmission, which revolve all around the sun gear of the second transmission level, come in touch with each other, the planetary gears typically comprise 65 - 75 teeth. Typically, the di- ameter of the gears of the output shafts is smaller than the diameter of the planetary gears of the second transmission level. Good results can be achieved when the ratio between the planetary gears of the second transmission level and the gears of output shafts is essentially 2: 1 . This allows that the arms of the housing rejuvenate

5 in an outward direction.

Good results can be achieved when the shape of the arms follows the outer contour of the gearing and/or the belt. This allows for a space saving design of the housing. Furthermore, such a shape of the arms improves the lubrication of the bearings and the gears in comparison to a rotational symmetric housing where the lubricant is0 transported to the outer wall due to the centrifugal force and away from the bearings and gears. Essentially straight and rejuvenating arms can be achieved, when the input shaft is interconnected to the respective output shaft via at least one planetary gear, whereby the sun gear is interconnected to the input shaft. The planetary gear of each of the arms and the thereto connected respective output shaft are arranged in a line.

The grinding unit usually comprises a housing with at least three arms extending from a center of the housing radially outward. In comparison to a conventional housing which is rotationally symmetric and essentially bell shaped, such an essentially star shaped housing allows a better suction of the grinding dust and fluid as it0 does not fully cover the grinding area. Furthermore, the star shaped housing is lighter and causes a lower moment of inertia compared to a bell shaped housing. Another advantage of the essentially star shaped housing is that it creates an air flow similar to a fan which is beneficial for the dust removal. By the rotation of the housing the arms essentially function as fan blades which convey the dust away from the center. For a smooth rotation of the grinding disks, the arms are typically arranged at the housing in manner, such that in a circumferential direction they are equally spaced apart from each other. In case of three arms the arms are displaced

5 by essentially 1 20° with respect to the axis of rotation. Depending on the size of the grinding machine and the size of the grinding disks, also four or more arms are possible.

The housing is typically designed as an essentially single-pieced housing which is limited by a cover plate and bearing covers. This leads to a comparatively easy de¬0 sign which is structurally rigid, easy to manufacture and comparatively lightweight. Preferably the housing is made by casting from a lightweight material such as aluminum or magnesium. For an easy assembly, both transmission levels are preferably arranged in one common housing. This is especially beneficial for the lubrication of the transmission and the heat dissipation. Typically, the first and the second transmission level are assembled in the housing with all the bearings and the housing is then limited by a cover plate.

Good grinding results can be achieved when the floor grinding machine comprises a grinding head cover for housing the transmission and/or the grinding disks. The grinding head cover prevents the dust and/or fluid from spreading in the surround¬0 ing room. Additionally, the grinding head cover directs the air flow of the suction unit for an efficient removal of the dust and/or fluid. In a preferred variation the grinding head cover is essentially bell shaped. The grinding head cover preferably comprises a tapered end, which is interconnected to the grinding assembly. Depending on the geometry and the state of wear of the grinding disks, the distance along the axis of rotation between the transmission and the floor may vary. To prevent the occurrence of a gap between the grinding head cover and the floor, which would cause dust and/or fluid leaking into the surrounding room, the grinding head cover can be mounted in a floating manner such that the sealing element is constantly in contact with the floor. Good results can therefore be achieved, when the grinding head cover is movably interconnected to the grinding assembly. In a preferred variation the grinding assembly comprises a housing which is arranged between the electric motor and the grinding unit. The housing can be made by either deep drawing or as a plastic or composite component. In a preferred variation the housing has a polygonal outer contour. This allows that the grinding head cover can be interconnected to the housing in a floating and non-rotating manner. Therefore, the grinding head cover can have an opening with a polygonal contour that essentially corresponds to the outer shape of the housing.

Opposite to the tapered end, the grinding head cover comprises a widened end which is interconnected to the floor. For a favorable sealing effect between the grinding head cover and the floor, the grinding head cover can comprise a sealing element, for example in form of a brush hem. Good results can be achieved when the sealing element is arranged at the grinding head cover in a circumferential direction with respect to the axis of rotation. In a preferred variation the sealing element is arranged along an outer edge of the grinding head cover completely circumferential. For the removal of the grinding dust and/or the fluid from within the inside of the grinding head cover, the grinding head cover can comprise a suction port which is designed for the removal of grinding dust and/or the fluid. The inside of the grinding head cover is thereby to be understood as the side facing the grinding disks and the outside is defined as the side facing the surrounding room. In a preferred variation the suction port is interconnected to a suction channel which is arranged at least partially circumferential with respect to the axis of rotation within the grinding head cover. To focus the directed flow of air and locally increase the suction effect, the cross section of the suction channel has to be relatively small. Therefore, the flow of air is directed by a guiding plate which is arranged within the grinding head cover. The guiding plate is preferably bent and follows the contour of the grinding head cover such that a gap is formed between the guiding plate and the grinding head cover. Good results can be achieved by locally focusing the suction effect of an interconnected suction unit, such as a vacuum cleaner, by a sickle-shaped guide plate. The sickle-shaped guiding plate can be arranged within the grinding head cover, wherein the lower end facing the floor ends where the sealing element starts. In a preferred variation the suction channel is defined by a leading edge and a trailing edge whereby the trailing edge is defined by the outer wall of the grinding head cover and the leading edge of the suction channel is defined by the sickle-shaped guide plate. The sickle-shaped guiding plate can be interconnected to the grinding head cover by mechanical connection means like rivets or screws. To achieve a uniform suction effect along the whole suction channel, the thereto connected tubular suction channels rejuvenates. Preferably the tubular suction channels narrow starting from the suction port towards the distal ends. This ensures a uniform suction effect along the whole suction channel even at its distal ends.

In a preferred variation the distance between the leading and the trailing edge is in

5 the range of 5 mm - 20 mm. Good results can be achieved when the suction channel has an essentially rectangular diameter between the leading and the trailing edge in a cross section with respect to the axis of rotation. This ensures that no additional operation is necessary for removing grinding dust and/or fluid from the floor after the actual grinding process. Therefore, the suction effect needs to be0 focused and locally strong. The grinding dust and/or fluid is typically carried away from the center of the housing towards the wall and/or sealing element of the grinding disk by the rotation of the arms. The grinding dust and/or fluid is transported out of the grinding head cover through the suction channel and the thereto interconnected suction port. The suction port is preferably essentially funnel-5 shaped and merges into tubular suction channels. Good results can be achieved when a V-shaped guiding plate is arranged within the suction channel which is configured to direct and concentrate the air flow such that the suction effect is enhanced. In a preferred variation the suction port merges into two essentially tubular suction channels which merge into the suction channel. To further increase the suc¬0 tion effect in the suction channel, the diameter of the tubular suction channels rejuvenates from a proximal end adjacent to the suction port, to a distal end which merges into the suction channel. To not reduce the space for the grinding disks within the grinding head cover, the two essentially tubular suction channels are preferably arranged at the outside of the bell shaped grinding head cover.

To be able to supply fluid for wet grinding the floor, the floor grinding machine can comprise at least one fluid line which is arranged at the outside of the grinding head

5 cover. The advantage of arranging the fluid line on the outside, facing the surrounding room, is that the accumulation of dust between the inner wall of the grinding head cover and the fluid line is prevented. Furthermore, it ensures that the inside of the grinding head cover can be cleaned more easily. To be able to supply the fluid to the grinding area in a directed manner, the fluid line may comprise0 thereto interconnected fluid outlets. These fluid outlets are preferably designed as nozzles. In a preferred variation the at least one fluid line is releasably interconnected to a fluid source such that the at least one fluid line and thereto interconnected fluid outlets are flushable for cleaning. This ensures that the fluid outlets, in particular the nozzles of the fluid outlets, can be easily cleaned by flushing or by blowing the dust particles out or through. The fluid source is usually designed as a water tank which is interconnected to the chassis. The fluid line may be connected to the fluid source by a plug-in or a snap connection. This ensures that the fluid line can be disassembled toolless onsite.

It is to be understood that both the foregoing general description and the following0 detailed description present embodiments, and are intended to provide an overview or framework for understanding the nature and character of the disclosure. The accompanying drawings are included to provide a further understanding, and are incorporated into and constitute a part of this specification. The drawings illustrate various embodiments, and together with the description serve to explain the principles and operation of the concepts disclosed.

The grinding head cover described herein above should be considered a separate

5 inventive concept, which may be subject of one or several divisional patent applications.

BRIEF DESCRIPTION OF THE DRAWINGS

The herein described invention will be more fully understood from the detailed description given herein below and the accompanying drawings which should not be0 considered limiting to the invention described in the appended claims. The drawings are showing:

Fig. 1 a perspective view from the front and above on a first variation of the floor grinding machine;

Fig. 2 an exploded perspective view from the front and below on the grinding assembly of the floor grinding machine according to Figure 1 ;

Fig. 3 an exploded perspective view from the front and above on the grinding unit of the grinding assembly according to Figure 2;

Fig. 4 a top view from below on the lower transmission level of the grinding unit according to Figure 3; 0 Fig. 5 a top view from above on the grinding assembly of the floor grinding machine according to Figure 1 with mounted grinding head cover; Fig. 6 a lateral view of the grinding head cover according to Figure 5 with a partial cut out;

Fig. 7 a lateral sectional view of the grinding head cover according to Figure 5;

Fig. 8 a detail view of the grinding head cover according to Figure 7 ;

5 Fig. 9 a sectional top view from below on the grinding head cover according to Figure 7.

DESCRIPTION OF THE EMBODIMENTS

Reference will now be made in detail to certain embodiments, examples of which0 are illustrated in the accompanying drawings, in which some, but not all features are shown. Indeed, embodiments disclosed herein may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will satisfy applicable legal requirements. Whenever possible, like reference numbers will be used to refer to like components or parts.

Figure 1 shows a perspective view from the front and above on a first variation the floor grinding machine 1 . Figure 2 shows an exploded perspective view from the front and below on the grinding assembly 26 of the floor grinding machine 1 . Figure 3 shows an exploded perspective view from the front and above on the grinding0 unit 3 of the grinding assembly 26. Figure 4 shows a top view from below on the lower transmission level 13 of the grinding unit 3. Figure 5 shows a top view from above on the grinding assembly 26 of the floor grinding machine 1 with mounted grinding head cover 1 5. Figure 6 shows a lateral view of the grinding head cover 1 5 with a partial cut out. Figure 7 shows a lateral sectional view of the grinding head cover 1 5, Figure 8 shows a detail view of the grinding head cover 1 5 and Figure 9 shows a sectional top view from below on the grinding head cover 1 5.

Figure 1 shows the modular set-up of the floor grinding machine. The chassis 25 for moving the floor grinding machine 1 on a floor is interconnected to the grinding assembly 26, which comprises the electric motor 2 and the grinding unit 3. The shown grinding assembly 26 is detachably interconnected to the chassis 25 via a connector 27. As can be also seen, the grinding head cover 1 5 is movably interconnected to the grinding assembly 26. The shown connector 27 can be realized by a bolt or a quick clamp device. The shown variation of the floor grinding machine 1 also comprises a fluid line 22 which is arranged at the outside of the grinding head cover 1 5, facing the surrounding room. The advantage of arranging the fluid line 22 on the outside is that the accumulation of dust between the inner wall of the grinding head cover 1 5 and the fluid line 22 is prevented. Furthermore, it ensures that the inside of the grinding head cover 1 5 can be cleaned more easily. To be able to supply the fluid to the grinding area in a directed manner, the shown fluid line 22 comprises thereto interconnected fluid outlets 23 designed as nozzles. The shown fluid line 22 is releasably interconnected to a fluid source 24 such that the fluid line 22 and thereto interconnected fluid outlets 23 are flushable for cleaning. As can be best seen in Figure 2, the shown variation of the grinding assembly 26 comprises an electric motor 2 which extends along the axis of rotation x and which is interconnected to a grinding unit 3. A housing 37 is arranged between the electric motor 2 and the grinding unit 3. The housing 37 may comprise a mount 38 for

5 interconnecting the grinding assembly 26 to the chassis 25. The grinding unit 3 comprises a housing 4 with at least three arms 5 extending from a center 6 of the housing 4 radially outward and in circumferential direction equally spaced apart from each other. The housing 4 of the shown variation is arranged rotational with respect to the axis of rotation x and each arm 5 of the housing 4 comprises at its0 outer end an output shaft 9, configured for mounting a grinding disk. The grinding disk is interconnected to the input shaft 8 by the transmission 7.

Figure 3 shows the gearing 10 which is designed as a planetary transmission 1 1 in the shown variation. The planetary transmission 1 1 is arranged in a housing 4 which in the shown variation is designed as an essentially single-pieced housing 45 which is limited by a cover plate 28 and bearing covers 29 as can be best seen in Figure 2. To seal the housing 4, typically a sealing element 39 is arranged between the housing 4 and the cover plate 28. A single pieced housing 4 leads to a structurally rigid design, which is easy to manufacture and comparatively lightweight. The planetary transmission 1 1 of the shown variation comprises a first 1 2 and second0 1 3 transmission level which are arranged in the common housing 4. This is especially beneficial for the lubrication of the transmission 7 and the heat dissipation. Typically, the first 1 2 and the second 1 3 transmission level are assembled in the housing 4 with all the bearings and sealing elements and the housing 4 is then limited by the cover plate 28. The shown planetary transmission 1 1 comprises an upper transmission level 1 1 which faces the electric motor 2 and a lower transmission level 1 2 which faces the grinding disks. The size of the gears as well as the size of the module of the gears is designed as small as possible. The sun gear 1 21 of the shown first transmission level 1 2 comprises 65 - 75 gears. The planetary gears 1 22 of the shown first transmission level 1 2 revolve around the sun gear 1 21 and comprises 1 1 - 1 5 teeth. In the shown variation the sun gear 1 21 of the first transmission level 1 2 is mounted in a torque-proof manner with respect to the first direction x, whereby the planetary gears 1 22 of the upper transmission level 1 2 revolve around the sun gear 1 21 of the upper transmission level 1 2, thereby causing a rotation of the housing 4 with respect to the axis of rotation x. The planetary gears 1 22 of the upper transmission level 1 2 and the planetary gears 132 of the lower transmission level 13 are interconnected to each other in a torsionally rigid connection, in the shown variation with a feather key 30 such that the housing 4 and the thereto interconnected grinding disks revolve around the axis of rotation x.

Figure 4 shows that the sun gear 1 31 of the second transmission level 1 3 is interconnected to the input shaft 8 and transmits the power to the output shafts 9 via the planetary gears 1 32 of the second transmission level 13. The sun gear 1 31 of the second transmission level 13 comprises 1 1 - 1 5 teeth in the shown variation. To achieve a small diameter of the sun gear 1 31 the module is typically 1 .5. To prevent that the planetary gears 1 32 of the second transmission level 13, which revolve all around the sun gear 131 , come in touch with each other, the planetary gears 1 32 typically comprise 65 - 75 teeth. To achieve a rotor-shaped housing geometry, the arms of the housing, which extend away from the center 6 need to rejuvenate towards the outside. Therefore, the diameter of the gears of the output shafts 9 is smaller than the diameter of the planetary gears 132 of the second transmission

5 level 1 3. In the shown variation the ratio between the planetary gears 1 32 of the second transmission level 1 3 and the gears of output shafts 14 is essentially 2: 1 . The sealing element 39 of the housing 4 follows the contour of the housing 4, wherein the arms 5 of the housing 4 rejuvenate away from the center 6 of the housing 4. 0 Figure 5 and 6 show a top view and a sectional view of the grinding assembly 26 of the floor grinding machine 1 which comprises a grinding head cover 1 5 for housing the transmission 7 and/or the grinding disks. The shown grinding assembly 26 comprises a grinding head cover 1 5 for housing the transmission 7 and/or the grinding disks to prevent the dust and/or fluid from spreading in the surrounding5 room. The shown grinding head cover 1 5 is essentially bell shaped and comprises a tapered end 31 , which is interconnected to the grinding assembly 26. Depending on the geometry and the condition of the grinding disks, the distance along the axis of rotation between the transmission 7 and the floor may vary. To prevent the occurrence of a gap between the grinding head cover 1 5 and the floor, which would0 cause dust and/or fluid leaking into the surrounding room, the shown grinding head cover 1 5 is mounted in a floating manner. To prevent the grinding head cover 1 5 from rotating around the axis of rotation x, the shown tapered end 31 com- prises an opening 32 which has a polygonal outer contour 33. Opposite to the tapered end 31 with respect to the axis of rotation x, the shown grinding head cover 1 5 comprises a widened end 34 which is interconnected to the floor. For a favorable sealing effect between the grinding head cover and the floor, the grinding head cover 1 5 of the shown variation comprises a sealing element 35, for example in form of a brush hem. The shown sealing element 35 is arranged at the grinding head cover 1 5 in a circumferential direction with respect to the axis of rotation x. At least one fluid line 22 is arranged at the outside of the grinding head cover 1 5 and comprises thereto interconnected fluid outlets 23 which can be best seen in Figure 6, the at least one fluid line 22 is releasably interconnected to a fluid source 24 such that the at least one fluid line 22 and thereto interconnected fluid outlets 23 are flushable for cleaning. The grinding head cover 1 5 is essentially bell shaped and comprises a suction port 1 6 which is designed for the removal of grinding dust.

Figures 7 to 9 show that for the removal of the grinding dust and/or the fluid from within the inside of the grinding head cover 1 5, the grinding head cover comprises a suction port 1 6. For a high suction effect, the suction port merges into a suction channel 17 which is arranged at least partially circumferential with respect to the first main direction x within the grinding head cover 1 5. To locally focus the suction effect of the suction unit, the shown grinding head cover 1 5 comprises a sickleshaped guide plate 21 . The shown suction channel 17 is defined by a leading edge 1 9 and a trailing edge 20 whereby the trailing edge is the outer wall of the grinding head cover and the leading edge of the suction channel is the sickle-shaped guide plate 21 . The sickle-shaped guiding plate 21 is interconnected to the grinding head cover 1 5 by mechanical connection means like rivets or screws. In the shown variation the suction channel 1 7 has an essentially rectangular diameter. The grinding dust and/or fluid is typically carry away from the center 6 of the housing 4 by the rotation of the arms 5 towards the wall and/or sealing element 35 of the grinding 5 disk 1 5. The grinding dust and/or fluid is transported out of the grinding head cover 1 5 through the suction channel 17 and the thereto interconnected suction port 1 6. The shown suction port 1 6 is funnel-shaped and merges into tubular suction channels 18. To direct and concentrate the air flow a V-shaped guiding plate 36 is arranged within the suction port 1 6 such that the suction effect is enhanced. In the0 shown variation the suction port 1 6 merges into two essentially tubular suction channels 18 which merge into the suction channel 1 7, whereby the diameter of the tubular suction channels 18 rejuvenates from a proximal end adjacent to the suction port 16 to a distal end which merges into the suction channel 1 7.

LIST OF DESIGNATIONS

1 Floor grinding machine 17 Suction channel

2 Electric motor 25 18 Tubular suction channel

3 Grinding unit 19 Leading edge

4 Housing 20 Trailing edge

5 Arm (Housing) 21 Guide plate (sickle

6 Center (Housing) shaped)

7 Transmission 30 22 Fluid line

8 Input shaft 23 Fluid outlets

9 Output shaft 24 Fluid source

10 Gearing 25 Chassis

1 1 Planetary transmission 26 Grinding assembly

1 2 First transmission level 35 27 Connector

(Upper) 28 Cover plate (Housing)

1 21 Sun gear 29 Bearing cover

1 22 Planetary gear 30 Feather key

1 3 Second transmission level 31 Tapered end

(Lower) 40 32 Opening

1 31 Sun gear 33 Outer contour

1 32 Planetary gear 34 Widened end

14 Gear output shaft 35 Sealing element

1 5 Grinding head cover 36 Guide plate (V-shaped)

1 6 Suction port Housing (Grinding assem- 39 Sealing element (Housing) bly) 5 Mount