Abrading – Machine – Rotary tool
Reexamination Certificate
2000-09-20
2002-01-08
Banks, Derris H. (Department: 3723)
Abrading
Machine
Rotary tool
C451S550000
Reexamination Certificate
active
06336849
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field of the Invention
The invention concerns a grinding spindle, comprising a spindle housing and two coaxial shafts which are driven by a drive motor. A concentric grinding disk is fixed to each of said shafts. The shafts can be moved in an axial direction in relation to each other with a lifting or lowering movement in order to engage one grinding disk or the other.
2. Description of the Prior Art
When the surfaces of flat work pieces are worked, which may, for example, comprise wood, metal, stone, ceramic or also semiconductor material, and for which high requirements must be fulfilled in respect of the surface quality, grinding technology, especially surface grinders, can be used advantageously. To that end, a rotating, multicut cutting tool is used, for example, a grinding disk mounted on a rotating grinding spindle, which is fitted with an abrasive layer comprising bonded grains, for example, a cup grinding wheel with ring-shaped contact surface. An axial feed movement of the rotating grinding tool, generally of the total grinding spindle, brings the grains of the abrasive layer to bear on the surface of the work piece, which results in a removal of material. The use of a fully sintered grinding wheel is also possible. An additional linear or circular feed of the work piece ensures the even working of the total surface of the work piece.
To attain a high work piece surface quality, generally a multi-step, frequently two-step, machining process is applied, where first a coarse-grained grinding disk with a high cutting performance (coarse or rough grinding disk) removes the bulk of the material. The still relatively coarse surface obtained is postprocessed in a subsequent, further work step using a fine-grained grinding disk (fine or finishing grinding disk), which although it only removes a small amount of material achieves a good surface. If both work steps are carried out using the same grinding spindle, it is appropriate to use a grinding spindle which is provided with two grinding disks, each with a different grain size, which can engage selectively with the surface of the work piece. This allows the disadvantages to be avoided which otherwise prevail when grinding tools are changed, such as the time required to reset and the necessary new profiling of the grinding disk owing to the non excludable imprecise fitting, which requires time and leads to a high consumption of abrasive materials. From the state-of-the-art, a grinding spindle of the generic concept is known, for example, (DE-PS 846 663), which has two concentric cup grinding disks carried on two shafts disposed coaxially in a single spindle. The outer shaft is rotated by a motor, while the inner shaft is also moved by means of a carrier device. Thereby, the inner cup grinding disk is disposed in the grinding spindle so as to be moveable axially. Thus selectively the inner or the outer cup grinding disk can be brought to engage, without needing additional resetting or profiling time. A further grinding spindle of the class mentioned at the beginning (DE-PS 42 08 615) uses two cup grinding disks whose abrasive layers comprise uninterrupted ring segments with the same diameter, which engage with one another so that they essentially form one ring and can selectively engage the work piece surface. With this arrangement, both grinding disks function on an identical working radius, which is especially advantageous for the rotary grinding technique, where the feed function of the work piece comprises rotation about an axis extending essentially parallel to the grinding spindle and through the grinding disk abrasive layer. Therefore, different working radiuses of the two grinding disks mean disadvantageously that for the coarse and fine working of identical parts of the work pieces surface a repositioning of the work piece between the two work steps is necessary.
With precision work, for example, the grinding and polishing of silicon wafers, whose breaking strength is determined by their surface quality, sufficient rigidity of the used spindle in the radial direction is of decisive importance, because with a lack of rigidity axial loads upon the spindle can trigger radial oscillations, which can impair the resulting surface quality of the wafer and possibly form grooves, which may provide a predetermined breaking point for the single crystal. To increase the radial rigidity, in the state-of-the-art, the diameter of the spindle is increased, which, however, is only possible in a limited scope. Especially in the case of spindles with an integrated electric motor, where the stator is mounted in the spindle housing and the moved rotor is attached with the outer side to the outer shaft, the diameter of the inner and outer shaft is limited by the space available inside the electric motor. Especially in the case of small grinding spindles, therefore, the necessary radial rigidity cannot be achieved needed for precision work.
SUMMARY OF THE INVENTION
Against this background, it is the object of this invention to create a grinding spindle which can engage two different grinding disks selectively with the work piece and which even when compact in design provides sufficient radial rigidity to fulfil all existing requirements during precision working, such as, for instance, those required when grinding silicon wafers.
In accordance with the invention this task is solved therein that the inner shaft is connected to the drive motor as the main shaft, while the outer shaft is coupled to the main shaft by a carrier device. In addition, a bush is coaxially semimounted on the spindle housing, the outer shaft is pivotably mounted on the bush with a pivot bearing and the bush is provided with an actuator which executes the lifting or lowering movement.
The underlying idea of the present invention is to connect the inner shaft to the drive motor as the main shaft, and to fix the outer shaft which is coupled to the main shaft by means of a suitable carrier device, for example, a carrier pin, so that it rotates together with the main shaft, to the outer side of the spindle housing. To that end, a bush is coaxially semimounted on the spindle housing, the outer shaft is pivotably mounted on the bush with a pivot bearing. For the selective engagement of the grinding disks mounted on the inner and the outer shaft with the work piece, the bush is provided with an actuator which executes the necessary axial lifting or lowering movement Thereby, the grinding disk of the outer shaft can be moved, by means of a lowering movement, below the level of the grinding disk of the inner positioned main shaft and can thus engage with the work piece surface. The lifting movement in the opposite direction of the outer shaft allows the grinding disk of the main shaft to again appear below its counterpart so that it can engage the work piece surface. The advantage of this design of a grinding spindle lies especially in the significant increase in the diameter of the outer shaft and the resulting substantially higher radial rigidity.
Simultaneously, space is acquired inside the grinding spindle for an increase in the diameter of the inside shaft, which also acquires further radial rigidity. Overall, therefore, a grinding spindle is obtained, which enables the successive working of the work piece surface with two different grinding disks, for example, a coarse and fine grinding disk and which at the same time, even when of compact design, owing to the large diameter of the shafts carrying the grinding disks, is stable against radial oscillations and so advantageously can be used especially for precision work.
The drive of the inventive grinding spindle can be realized, for example, by means of a belt pulley fixed coaxially to the main shaft, which drives the drive motor via a suitable belt.
In a preferred inventive embodiment, to drive the grinding spindle, however, an electric motor is used which is integrated in the spindle housing and which penetrates the main shaft. Thereby, for example, the rotating rotor of the elec
Banks Derris H.
Schindler Edwin D.
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