US20220266407A1

US20220266407A1 - Device for processing the borders of flat workpieces

Info

Publication number: US20220266407A1
Application number: US17/628,421
Authority: US
Inventors: Johannes ZEHETHOFER; Christoph LUEGER; Franz HASELMAYR
Original assignee: Lisec Austria GmbH
Current assignee: Lisec Austria GmbH
Priority date: 2019-07-22
Filing date: 2020-07-20
Publication date: 2022-08-25
Also published as: AT17015U1; EP4003644A1; CN114080298A; WO2021013779A1

Abstract

In the case of a device for trimming plate-like workpieces, such as glass panels, a grinding ring that is rotated around a shaft by a drive is used. The grinding surfaces that act by ablation on the edges of the side of the workpiece are designed to move in the axial direction, so that during trimming, they can follow the edges of the workpiece. The grinding surfaces are automatically positioned on the edges that are to be trimmed of the workpiece, even if the edges do not lie in the prescribed target position. The grinding ring is mounted to float on its carrier via a hydrostatic bearing or a gas bearing.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is the U.S. national phase of International Application No. PCT/EP2020/070409 filed Jul. 20, 2020 which designated the U.S. and claims priority to Austrian Patent Application No. A 261/2019 filed Jul. 22, 2019, the entire contents of each of which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

Field of the Invention

The invention relates to a device for machining the sides of flat workpieces, such as glass panels.
For erosion-treating the edges on the sides of flat workpieces, such as glass panels, the device according to the invention comprises grinding surfaces that act on the edges of the sides of the flat workpiece by ablation. The device according to the invention can also be configured and equipped for polishing the sides of workpieces.

Description of the Related Art

Devices for machining the sides of flat workpieces, in particular glass panels, are known in various embodiments. There are thus devices with grinding disks that are grooved, in which connection reference can be made to WO 2015/055671 A1, EP 1 607 177 B1, and EP 1 488 886 B1.
For erosion-treating flat workpieces, in particular glass panels, in order to trim their edges, belt grinders are also known, as is known from, for example, EP 1 344 604 B1 or DE 44 19 963 C1.
It has also been proposed to allow pot-shaped grinding disks to act on the edges of the sides of glass panels, wherein a grinding disk acts on one edge, and the other grinding disk acts on the other edge. This is known from, for example, U.S. Pat. No. 9,555,516 B2.
Trimming devices with grinding belts (so-called “belt grinders”), in particular with grinding belts arranged in the shape of a cross, have the advantage that the grinding belts are positioned against the glass edges in a flexible manner, so that the precision with which the glass panel is fed to the tool is not crucial. Thus, lateral faces that produce rough spots and are oriented not at a right angle to the plane of the glass panel but rather obliquely, or else shapes that deviate slightly from the shape can be produced by blank-cut tolerances, and discarded (rough) workpieces can be easily trimmed. Deviations of the flat object, such as the glass panel, from the prescribed shape and size can be compensated for by the flexibility of the grinding belts.
Trimming devices that use grinding disks, wherein the grinding disks in general have a V-profile and can be used for various glass thicknesses, are in general rigid, so that inaccuracies of the format and the size of the flat workpiece (glass panel) that is to be machined as well as deformations of the workpiece (the workpiece is then discarded, i.e., is no longer flat) have to be compensated for by the machine. It is therefore necessary to take steps to track the edges that are to be machined, as is known from, for example, EP 2 512 732 B1. The known trim panels (grinding disks with a V-profile) often cause the problem that rough spots cannot be machined uniformly as desired.
U.S. Pat. No. 2,733,553 A shows and describes a tool for grinding knives or the like. The tool has two grinding disks, which are fixed on two sleeves using screw nuts. The sleeves are arranged on a shaft that is rotated by a motor and are held by springs in a central position, in which they are adjacent.
During grinding, the grinding disks can be moved against the force of the springs, so that the edges on both sides of a knife or the like can be machined (column 1, lines 18 to 25, and column 2, lines 50 to 59).
When flat workpieces, in particular glass panels, are being cut, deviations from the desired size and shape, rough spots, and a deviating geometry can occur (e.g., instead of a rectangle, a diamond with oblique edges is cut). When such edges that deviate from the prescribed position and size are being trimmed, a problem arises, since it is not readily possible to achieve an exact trim without fairly expensive mechanical work being done on the plate-like workpiece (glass panel).

SUMMARY OF THE INVENTION

The object of the invention is to make available a device with which flat workpieces, such as glass panels, can be machined (trimmed/polished) successfully and to the desired extent even if the shape of the edges and the position of the edges deviate from the target shape or the target position, wherein an advantageous mounting of the grinding disk on its carrier is provided.
This object is achieved according to the invention with a device as disclosed and claimed.
Advantageous and preferred configurations of the device according to the invention are also disclosed and claimed.
The device according to the invention, which is designed essentially similar to a grinding disk, has a grinding ring with an outward-facing groove with grinding surfaces. The grinding ring with the grinding surfaces can be adjusted in the direction of the shaft around which the device is rotated by its drive. Thus, in the invention, the grinding surfaces can follow the edges of the sides of the workpiece (glass panel) even if the side deviates from the target position in the direction of the shaft. This can occur if the workpiece is discarded. In the invention, the grinding ring with the grinding surfaces automatically follows the side of the workpiece. Movements of the carrier (shaft), on which the grinding ring sits, with which movements the device according to the invention tracks the path and position of the sides of the workpiece, are no longer necessary. This is because according to the invention, the grinding ring is not rigidly connected to the carrier of the device in the direction of the axis (of rotation).
It is advantageous that the grinding ring is mounted to float on the carrier (the inside diameter of the grinding ring is larger than the outside diameter of the carrier), so that relative to its carrier, the grinding ring can move freely in the direction of the axis (of rotation).
In this case, the floating mount of the grinding ring on the carrier is designed as a hydrostatic bearing or as a gas (air) bearing.
The design according to the invention of the device with a hydrostatic bearing or gas bearing has the advantage that the coupling of the grinding ring to its carrier, with which the torque is transferred from the carrier to the grinding ring, can be configured in such a way that it does not disadvantageously influence the floating mount of the grinding ring.
Within the framework of the invention, it can be provided that the grinding surfaces are loaded in an elastically springy manner, so that when the device is used, these surfaces preferably rest with elastic prestress on the edges of the sides of the workpiece.
If springs are provided, the latter cause, in one possible embodiment of the invention, the grinding ring with its grinding surfaces to be moved back again into the starting position of the grinding surfaces after the device is used.
In addition, (elastic) grinding surfaces, independently from one another, have the ability to follow the edges of the workpiece even if the distance between the side of the workpiece and the shaft around which the device is rotated varies (is larger or smaller), i.e., does not remain in the target position. This is possible, for example, if the grinding ring is divided into two grinding ring parts.
In the exemplary embodiment with elastic grinding surfaces, the device according to the invention combines the advantages of belt grinders with those of grinding disks, since the grinding surfaces in this embodiment are designed to be elastically flexible, i.e., rest on the edges of the sides of the workpiece under elastic (springy) prestress.
Within the framework of the invention, the adjustability of the grinding surfaces of the device according to the invention can be achieved in various ways.
In one embodiment of the invention, it is provided that the pin is accommodated in the hole or recess with a slide guide, wherein it is preferred that the grinding surfaces are elastically springy in the direction of the shaft.
The configuration, possible in one embodiment of the invention, of the coupling between the grinding disk and its carrier in the form of at least one pin, which is fastened to the carrier and engages in a hole or recess in the grinding disk, makes it possible for the floating mount of the grinding disk to be configured in the form of a hydrostatic bearing or a gas bearing without being affected by the coupling between the grinding disk and its carrier, so that a good mounting of the grinding disk is provided.
In one embodiment of the invention, a grooved grinding ring with grinding surfaces is mounted in an adjustable manner, e.g., floating, on the carrier, which serves as a shaft for the rotary drive. In this embodiment, the grinding ring is movable in the direction of the axis (of rotation), without the grinding ring being spring-loaded into its starting position. The grinding surfaces can thus follow the edges to be trimmed on the sides of the workpiece (the glass panel), if edges, for example because of distortions of the workpiece (the glass panel), deviate in one direction or the other from the target position in the direction of the axis (of rotation).
In another embodiment of the invention, the grinding surfaces are provided on a grinding ring, which is supported on the carrier, for example in an elastic manner.
In another embodiment of the invention, the grinding surfaces are provided on two grinding ring parts, which are arranged to move relative to one another and on the carrier in the direction of the axis (of rotation) and are to be spring-loaded toward one another.
In another embodiment, the object of the invention can be achieved in that a grooved grinding ring that forms grinding surfaces with its groove walls is arranged to move in the direction of the axis (of rotation) of the carrier against spring force. This can be achieved, for example, in that the grinding ring is mounted movably on its carrier in the direction of the axis of rotation of a carrier against the force of springs, which act on both sides of the grinding ring.
A grinding ring, which optionally comprises two grinding ring parts, is in general provided on the carrier of the device according to the invention. Within the framework of the invention, however, consideration is also given to embodiments in which more than one grinding ring and/or more than one pair of grinding ring parts are provided on a carrier. Although two or more than two grinding rings and/or pairs of grinding ring parts are provided on one carrier, one-part grinding rings and grinding rings that are divided into grinding ring parts can be combined. In addition, within the framework of the invention, consideration is given to arranging grinding rings with various grooves (trapezoidal, V-shaped, etc.) and/or differently-shaped grinding surfaces on a carrier.
The grinding rings that are provided within the framework of the invention can be configured for erosion-treating (e.g., trimming) and also for polishing the sides of workpieces.
The term “spring” that is used heretofore encompasses any type of elastic means that act on a grinding ring or grinding ring parts. Examples are metal springs (coil springs), gas springs (pneumatic springs), and liquid springs.
In the embodiments, the invention offers one or more of the advantages that are mentioned below:

- The quality of the trim remains constant when the shape/size of the object that is to be machined deviates from the prescribed shape/size,
- The trim quality in the case of rough spots is clearly better than with conventional grinding disks,
- The quality of the trim can be maintained in a process-safe manner,
- If the grinding surfaces are provided on a grinding ring or on grinding ring parts, which are supported in an elastically springy manner on, for example, the carrier of the device, the change is simple and economical, since only grinding rings/grinding ring parts have to be exchanged,
- The device according to the invention can be used in all machines, and conventional grinding disks in existing machines can be replaced by the device according to the invention,
- The carrier that serves as, for example, a rotary drive for the grinding ring/the grinding ring parts does not need to track the side of the workpiece.

BRIEF DESCRIPTION OF THE DRAWINGS

Additional details and features as well as advantages of the invention follow from the description below of the embodiments that are partially diagrammatically depicted in the drawings. Here:

FIGS. 1 to 4 show, in axial section, an embodiment in various operating positions when glass panels are being trimmed,

FIGS. 5 to 9 show another embodiment in various operating positions as well as details,

FIGS. 10 and 11 show another embodiment in various operating positions, and

FIG. 12 shows an embodiment with a grinding ring that is mounted to float.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The embodiment of a device 1 that is shown in FIGS. 1 to 4, which device is designed like a grinding disk, comprises a carrier 12 that serves as a (drive) shaft and a grinding ring 25 that consists of two grinding ring parts 6. The grinding ring parts 6 are arranged to move in the direction of the shaft 2 of the carrier 12 on the carrier 12 that is designed as a spindle, as is indicated in FIGS. 3 and 4 by the arrows 13.
A line 14 for feeding liquid (feeding water) is provided in the carrier 12, so that the grinding ring parts 6 of the grinding ring 25 are mounted (to float) on the carrier 12 via a hydrostatic bearing. Instead of hydrostatic bearings for the grinding ring 25 or the grinding ring parts 6, gas (air) bearings can also be provided. In the case of gas bearings, a gas (e.g., air) is fed via the line 14.
It is also possible that fed liquid (water) exits via the gap 15 between the grinding ring parts 6 in the direction toward the workpiece 8 (the glass panel that is to be machined), so that the workpiece 8, e.g., a glass panel, is cooled with the liquid during the machining in order to trim edges 9 on its side 10.
The grinding ring parts 6 have grinding surfaces 7, which are curved in a conical or concave manner and act by ablation on the workpiece 8 (glass panel) that is to be machined when the device 1 is being used for trimming the edges 9 of a side 10.
The grinding ring parts 6 of the embodiment shown in FIGS. 1 to 4 are to be loaded on one another in terms of a movement by springs 16, coil springs in the example, that are arranged between the grinding ring parts 6 and the shoulders 17 of the carrier 12.
Since the grinding ring parts 6 are supported on the carrier 12 by springs 16, the grinding ring parts 6 can follow the path of the side 10 of the workpiece 8 (glass panel) that is to be machined, without special guide measures being necessary. The reason for this is that the grinding surfaces 7 of the grinding ring parts 6 are flexible in an elastically springy manner and are positioned under springy prestress on the edges 9 that are to be trimmed of the workpiece 8, such as a glass panel, even if the workpiece 8 deviates from the desired size, position, and/or shape.
In order to couple the grinding ring parts 6 to the carrier 12 for rotation, pins 18 that serve as driving pins and/or guide pins are provided for torque transfer, which pins are arranged on a flange 19 of the carrier 12 and grip with the slide guide through holes 20 in the gripping ring parts 6.
Shown in FIG. 1 is the ideal case, in which the workpiece 8 that is to be machined (the glass panel that is to be machined) is oriented precisely (symmetrically) to the plane of symmetry (plane perpendicular to the shaft 2, which is in the center between the grinding ring parts 6) of the device 1.
FIG. 2 shows a misalignment of a workpiece 8, as frequently occurs in practice, wherein the grinding surfaces 7 of the grinding ring parts 6 act on edges 9 of the side 10 of the workpiece 8 uniformly (centered) and in this case are offset relative to the position shown in FIG. 1.
In FIGS. 2, 3, and 4, for the sake of clarity, in each case a workpiece 8 that is not more greatly offset is shown above the machined workpiece 8, which is more greatly offset.
In FIG. 3, the case is shown in which the workpiece 8 is laterally offset relative to the target position and thus is larger than that corresponding to the target measurement (blank cut with excess).
Also, in this case, the grinding surfaces 7 of the device 1 follow the edges 9 of the side 10 of the workpiece 8, wherein the grinding ring parts 6 move in the direction of the shaft 2 from their basic position (FIG. 1). Since the workpiece 8 that is to be machined has an excess, i.e., is larger than that corresponding to the target size, the grinding ring parts 6 are moved apart against the force of the springs 16, and the grinding surfaces 7 are automatically oriented into the correct position.
In FIG. 4, the case is shown in which the workpiece 8 (the glass panel) is oriented correctly, i.e., is not offset laterally but has an excess, i.e., is larger than the target measurement, wherein even in this case, the grinding surfaces 7 of the grinding ring parts 6 are correctly oriented to the edges 9 and act adjoining the edges 9 in an elastic manner.
Because of the springs 16 that act as reset elements, which springs act on the grinding ring parts 6 and elastically load the latter into their basic position shown in FIG. 1, the grinding surfaces 7 of the grinding ring parts 6 of the grinding ring 25 are designed to be elastically flexible in the embodiment shown in FIGS. 1 to 4. The grinding surfaces 7 are automatically oriented relative to the edges 9 to be machined of the flat workpiece 8 (glass panel), since they adjoin the workpiece 8 (glass panel) under elastic prestress.
In FIGS. 5 to 9, an embodiment of the device 1 according to the invention, modified relative to the embodiment of FIGS. 1 to 4, which device is designed essentially as a grinding disk, is shown. The grinding ring 25 comprises two grinding ring parts 6 with conical grinding surfaces 7, which are arranged to move on a carrier 12 that serves as a base element in the direction of the shaft 2 of the device 1.
The spring forces that move the grinding ring parts 6 into their action position and in addition press in an elastically springy manner on the edges 9 that are to be trimmed of the side 10 of the flat workpiece 8 (glass panel) are applied, in the embodiment shown in FIGS. 5 to 9, by the pressure at which liquid or gas is fed for the bearing. To this end, an annular space 21, into which liquid or gas is introduced, is provided to each grinding ring part 6. The annular space 21 is bounded by the carrier 12, the grinding ring parts 6, and a sleeve-like element 22 (tube-like part) that is provided on the grinding ring parts 6. Thus, hydraulic springs or gas springs that act by pressure in the axial direction are formed, which springs load the grinding ring parts 6, and thus their grinding surfaces 7, in an elastically springy manner in terms of a movement toward one another. By changing the pressure of the liquid/gas, the pressing of the grinding surfaces 7 of the grinding ring parts 6—and thus the extent of the erosion-treating—can be varied in order to produce optionally smaller or larger bevels (see FIGS. 5 and 6).
Because of the liquid springs or the gas springs (the spaces 21 to which liquid or gas (air) is supplied), the embodiment that is shown in FIGS. 5 to 9 has the advantage that the grinding ring parts 6 of the grinding ring 25 and thus their grinding surfaces 7 can be moved by the workpiece 8 (the glass panel) in the axial direction, without changing the pressing force (in the case of unchanged pressure of the medium or gas). This makes it possible that the grinding ring parts 6 with the grinding surfaces 7 can adapt to deviating geometries of the workpiece 8 that is to be machined, in particular the glass panel (diagonal breaks, blank-cut tolerances, glass distortion).
In the embodiment, shown in FIGS. 5 to 9, of the device 1 that is designed essentially as a grinding disk, it is provided that the sleeve-like elements 22 (tube-like parts) that are provided on the grinding ring parts 6 have openings 23 (holes). Normally (cf. FIGS. 5 and 6), the openings 23 are arranged outside of the annular spaces 21, to which is fed liquid or gas for the liquid springs or the gas springs. Only when the position according to FIGS. 7 to 9 is reached are the openings 23 arranged in the sleeve-like (annular) elements 22, so that liquid or gas can exit through the openings 23 that act as leakage holes and decreases the pressure, whereupon the grinding ring parts 6 again occupy their starting position (position according to FIGS. 5 and 6).
The grinding ring parts 6 of the embodiment shown in FIGS. 5 to 9 are coupled to the carrier 12 for rotation. For example, for torque transfer, pins 18, similar to the pins 18 of the embodiment that is shown in FIGS. 1 to 4, are provided.
In the embodiment shown in FIGS. 10 and 11, the device 1 has an undivided grinding ring 25 with a trapezoidal groove 5, wherein the lateral (conical) groove surfaces are designed as grinding surfaces 7. The grinding ring 25 is coupled for rotation to the carrier 12 by the pins 18, which are fastened on the flange 19 of the carrier 12 and engage in a sliding manner in recesses, e.g., holes 20, of the grinding ring 25, so that torque transfer is provided.
Also, in the embodiment shown in FIGS. 10 and 11, springs 16, e.g., coil springs, are provided as elastically springy reset elements, which orient the grinding ring 25 in its starting position (standby position), which is shown in FIG. 10.
In the embodiment shown in FIGS. 10 and 11, a line 14 for feeding a liquid or gaseous medium for a hydrostatic bearing or a gas bearing of the grinding ring 25 (floating mount), which makes possible its movement relative to the carrier 12 in the axial direction, is provided.
The grinding ring 25 of FIGS. 10 and 11 is coupled for rotation by pins 18 to the carrier 12.
FIG. 11 shows the case in which the workpiece 8 (the glass panel that is to be machined) deviates from the target position (indicated above in FIG. 10), e.g., because of a discarded workpiece. The grinding ring 25 that can be moved against spring force on the carrier 12 and thus its grinding surfaces 7 are automatically oriented with respect to the edges 9 by the grinding ring 25 moving on the carrier 12 in the direction of the shaft 2. Thus, in the embodiment shown in FIGS. 10 and 11, the grinding surfaces 7 are also elastically springy, follow the edges 9, and under elastic prestress are uniformly positioned on the edges 9 that are to be trimmed of the workpiece 8.
Within the framework of the invention, consideration is also given to an embodiment in which the grinding disk 25 with its grinding surfaces 7 is mounted to float on the carrier 12, without springs 16 or the liquid springs/gas springs provided in the embodiment of FIGS. 6 to 10 being provided.
Such an embodiment is shown by way of example in FIG. 12.
The device 1, shown in FIG. 12, for trimming the edges 9 of the sides 10 of a flat workpiece 8, such as, for example, a glass panel, is designed essentially in the form of a grinding disk and essentially corresponds to the embodiment shown in FIGS. 10 and 11, wherein, however, the springs 16 are not provided.
An arrangement of the grinding ring 25 that can be moved in the direction of the axis (of rotation) 2 is produced by the floating mount of the grinding ring 25 on the carrier 12, so that the latter can automatically follow the side 10 of the workpiece 8, even if the latter deviates from the target position, as is shown by the arrows in FIG. 12. This is the case in particular when deviations of the side 8 occur in the direction of the shaft 2, around which the device 1 with its grinding ring 25 is rotated, since the workpiece 8 (the glass panel) is discarded, i.e., is rough.
The groove 5 of the grinding ring 25 can also be V-shaped—instead of trapezoidal as shown.
Grinding rings 25 with a trapezoidal groove 5 can be used for trimming the edges 9 and for machining (grinding and/or polishing) the lateral faces of the workpiece 8 that are oriented crosswise to the plane of the workpiece 8. In this case, the base of the groove 5 acts on the lateral face of the workpiece 8 in a machining manner, for example polishing.
Grinding rings 25 with a V-shaped groove 5 are used, for example, if only the edges 9 are to be erosion-treated (trimmed) on sides 10 of workpieces 8.
In summary, an embodiment of the invention can be described as follows:
In the case of a device 1 for trimming plate-like workpieces 8, such as glass panels, a grinding ring 25 that is rotated around a shaft 2 by a drive is used. The grinding surfaces 7 that act by ablation on the edges 9 of the side 10 of the workpiece 8 are designed to move in the axial direction, so that during trimming, they can follow the edges 9 of the workpiece 8. The grinding surfaces 7 are automatically positioned on the edges 9 that are to be trimmed of the workpiece 8, even if the edges 9 do not lie in the prescribed target position.

Claims

1. Device for erosion-treating the edges on sides of flat workpieces with at least one grinding ring, which has grinding surfaces, wherein a carrier that can be driven in rotation around a shaft is provided for the grinding ring and wherein the grinding ring is coupled for rotation to the carrier, the grinding ring is arranged to move on the carrier in the direction of the shaft, wherein the grinding ring is mounted to float on the carrier and wherein the grinding ring is mounted to float on the carrier via a hydrostatic bearing or gas bearing.

2. The device according to claim 1, wherein the coupling has at least one pin as a driving pin and/or guide, which is fastened to the carrier and engages in a hole or recess in the grinding ring.

3. The device according to claim 2, wherein the pin is accommodated in the hole or recess with a slide guide.

4. The device according to claim 1, wherein the grinding surfaces are elastically springy in the direction of the shaft.

5. The device according to claim 1, wherein the grinding ring is loaded in an elastically springy manner in its starting position.

6. The device according to claim 1, wherein the grinding ring comprises two grinding ring parts and wherein the grinding surfaces are provided on the grinding ring parts.

7. The device according to claim 1, wherein the grinding surfaces are designed to be conical or concave.

8. The device according to claim 6, wherein the grinding ring parts are to be loaded on one another by springs.

9. The device according to claim 7, wherein the grinding ring parts are loaded by pneumatic or hydraulic springs.

10. The device according to claim 6, wherein the grinding ring parts are arranged to move on the carrier for the grinding ring in the direction of the shaft.

11. The device according to claim 6, wherein the grinding ring parts are to be loaded on one another on the carrier by springs in terms of a movement.

12. The device according to claim 1, wherein at least one line for feeding a liquid or gaseous medium is provided in the carrier and wherein line branches branch off from the line, which branches flow between the inside surface of the grinding ring and the outside surface of the carrier.

13. The device according to claim 1, wherein the grinding ring is coupled for rotation to the carrier.

14. The device according to claim 13, wherein the coupling comprises at least one pin that engages in a hole or recess in the grinding ring or the grinding ring parts, which pin is fastened to the carrier for the grinding ring.

15. The device according to claim 14, wherein the pin is accommodated in the grinding ring or the grinding ring parts with a slide guide.

16. The device according to claim 1, wherein springs that elastically load the grinding ring or the grinding ring parts into its/their starting position are provided on the carrier.

17. The device according to claim 1, wherein at least one annular space is provided, which space is bounded in places by a grinding ring part, and wherein the line for feeding the liquid or gaseous medium empties into the annular space.

18. The device according to claim 17, wherein a sleeve-like element that encompasses the carrier and that bounds the annular space is provided on at least one grinding ring part and wherein at least one opening is provided in the sleeve-like element, which opening is in the area of the annular space, when the grinding ring part is in the grinding ring part's starting position.

19. The device according to claim 1, wherein the grinding ring has a groove that has grinding surfaces and that is outward-facing.

20. The device according to claim 19, wherein the groove is trapezoidal or V-shaped.