FRICKER, Daniel (Scheidgasse 21, Steffisburg, CH-3612, CH)
GURTNER, Christoph (Oberdorfstrasse 15, Steffisburg, CH-3612, CH)
DANNER, Markus (Alpenstrasse 32, Kaufdorf, CH-3126, CH)
FRICKER, Daniel (Scheidgasse 21, Steffisburg, CH-3612, CH)
GURTNER, Christoph (Oberdorfstrasse 15, Steffisburg, CH-3612, CH)
| Claims 1. Device (20) for holding a columnar workpiece (3) for the purpose of cutting the workpiece in the longitudinal direction by means of cutting means (12, 14; 60), characterised in that two essentially opposed retaining heads (22, 24) are provided and the retaining heads each comprise at least two clamping elements (28) in order to be able to place at least one cutting means for a cut in the longitudinal direction of the workpiece between the clamping elements. 2. Device (20) according to claim 1, characterised in that at least four clamping elements (28) are provided in order to be able to place two of the cutting means (12, 14) between the clamping elements which cross each other approximately centrally with respect to the workpiece and to allow quartering the workpiece in the longitudinal direction in one pass of the cutting means (12, 14; 60) . 3. Device (20) according to one of claims 1 to 2, characterised in that the clamping elements (28) are adjustable in length in order to be able to lift them off from the workpiece and to pass a dividing element (12, 14; 60) between the workpiece and the lifted clamping elements. 4. Device (20) according to any one of claims 1 to 3, characterised in that the bearing surface (48) of the clamping elements (28) that is intended to contact the workpiece (3) is covered with a natural or artificial rubber (50) in order to avoid damages of the workpiece surface and to ensure a higher friction coefficient between the bearing surface and the workpiece. 5. Device (20) according to any one of claims 1 to 4, characterised in that the pressure head (36) of the clamping elements (28) that is intended to contact the workpiece (3) comprises a support (38) and a pressure member (42) that is pivotably mounted thereon, the pressure member having a bearing surface (48) that is designed for contacting the workpiece in order to ensure a planar contact of the bearing surface on the workpiece. 6. Device (20) according to claim 5, characterised in that the pivoting ability of the pressure member (42) from one extreme position to the opposite one is at most 10°. 7. Device (20) according to any one of claims 1 to 6, characterised in that the clamping elements (28) of the retaining heads (22, 24) are arranged rotatably about a common axis in order to be able to rotate a workpiece (3) being held in the device about its longitudinal axis. 8. Use of the device according to any one of claims 1 to 7 for cutting an essentially columnar workpiece (3) into at least two portions (65, 66; 5) in its longitudinal direction, characterised in that - the workpiece (3) is clamped m the device, - the clamping elements (28) are applied to the workpiece, - at least one dividing element (12; 60) is inserted between at least two of the clamping elements of one of the retaining heads (22), - the cutting means is operated and driven through the workpiece in the longitudinal direction until it exits at the opposite end of the workpiece after cutting the latter apart in the longitudinal direction. 9. Use according to claim 8, characterised in that at least two dividing elements (12) are used which are aligned essentially perpendicularly to each other and so as to cross each other essentially at the centre of the cross-section of the workpiece (3) such that the workpiece is divided into at least four portions in the longitudinal direction. 10. Use of the device (20) according to any one of claims 3 to 7 for dividing a columnar workpiece (3), more particularly a silicon ingot, into at least two portions (65, 66; 5), each retaining head (22, 24) comprising at least two clamping elements (28) , and the following steps being performed: a) A workpiece is clamped in the device by applying the clamping elements (28) to the workpiece; b) at least one clamping element of one of the retaining heads (22) is retracted; c) a dividing element (60) is inserted between the retracted clamping element and the workpiece; d) the clamping element is again pressed against the workpiece; e) the workpiece is divided into two portions (65, 66) in the longitudinal direction by means of the dividing element, whereupon the dividing element extends between the clamping elements of the other retaining head (24). 11. Use according to claim 10, characterised in that the workpiece (3) is divided into at least four portions, the retaining heads (22, 24) comprising at least four clamping elements (28) each and two adjacent clamping elements being moved in steps b) and d) , and the following steps being performed after carrying out the longitudinal cut: f)Two diametrally opposed clamping elements (69, 70) of the other retaining head (24) are retracted while the portions (65, 66) of the workpiece are maintained in their positions by the other, non-retracted clamping elements (71, 72); g) the clamping elements of the retaining heads are rotated about a common axis relative to the dividing element (60), the dividing element passing between the retracted clamping elements and the workpiece in order to assume a new cutting direction in the workpiece that is rotated with respect to the existing cuts; h) the retracted clamping elements (69, 70) are again applied to the workpiece; i)by simultaneously or successively retracting further clamping elements and a relative movement of the dividing element through the gaps formed between respective retracted clamping elements and the workpiece surface toward the edge of the workpiece, the dividing element is moved out of the area defined by the clamping elements; in order to be able to carry out a longitudinal cut that is rotated with respect to the preceding cuts in the longitudinal axis of the workpiece. 12. Use according to claim 11, characterised in that exactly one 90° rotation according to step g) is performed in order to divide the workpiece into four columnar portions (5) . |
The present invention relates to a device for holding a columnar workpiece according to the preamble of claim 1. The invention further relates to a use of the device.
A known form of semiconductor ingots, e.g. of monocrystalline silicon for photovoltaic applications, are columns having a length of usually about 80 cm up to 2.5 m and, on due to the manufacturing technique, a circular cross-section. Further processing first consists of sawing such a column into a square column, the so-called squaring operation. The cross-section of the thus obtained columns, the bricks, is square with an edge length of 156 mm. In this step, relatively voluminous strips having a circle segment- shaped cross-section are cut off peripherally. For the sawing operation, the workpiece (the ingot) is glued between two supports. In this context, the adhesive itself is a problem too. It soils the corresponding surface and has to be removed, and the surface has to be cleaned. Residues are unavoidable, however, which impair the quality of the material when it is recycled.
A new production process for ingots yields columns of monocrystalline silicon having an essentially square cross- section that is also larger than that of the conventional columns. In a known embodiment, the cross-sectional area is more than four times larger than that of the conventional ingots, i.e. the edge length is more than twice 156 mm. Therefore, basically, these more recent raw ingots could be divided into four bricks of 156 mm edge length. However, for such a division in the longitudinal direction, which moreover has to be carried out in two cutting directions that are perpendicular to one another, the earlier gluing technique suffers from serious drawbacks or is not applicable at all. In particular, the required precision would hardly be achieved.
It is therefore an object of the present invention to provide a device for holding a columnar workpiece for its division in the longitudinal direction without gluing.
This is accomplished by a device as defined m claim 1. The following claims indicate preferred embodiments and applications of the device.
In the present description as well as in the appended claims, the following definitions shall apply:
- Columnar workpiece: A workpiece having an extension in a spatial direction, the longitudinal direction, and a cross-section perpendicularly to its longitudinal axis. Additional indications determining the shape such as square, circular, polygonal, define the cross-section of such a workpiece.
- Dividing element: A sawing or cutting means for dividing a workpiece, e.g. a saw band or a saw wire.
According to the invention, the known gluing of the workpiece, more particularly of a semiconductor ingot, is replaced by clamping it between two retaining heads. To this end, the heads comprise clamping elements whose front side is pressed against the workpiece. Using a predetermined contact pressure, a sufficient connection between the clamping elements and the workpiece is achieved (preferably a frictional connection, but other connection types may also be contemplated) for the workpiece to be safely held during the cutting operation also in the preferred horizontal position, i.e. with the longitudinal axis in the horizontal direction.
For the cut essentially centrally through the workpiece, the cutting means may be inserted between the retaining head and the workpiece since the clamping elements ensure a gap for the cutting means between the retaining head and the workpiece .
In a preferred embodiment, the clamping elements are retractable and extensible individually. It ^is thus possible to insert the cutting element laterally between the retracted clamping element and the workpiece in order to position it above the cutting line.
The preferred embodiment further allows an automated succession of longitudinal cuts in different orientations relative to one another. After a cut, the cutting means cannot be withdrawn from the area between the workpiece front side and the retaining head since the clamping heads which are holding a cut portion of the workpiece would have to be retracted for this purpose. By extending diametrally opposed clamping elements, it is possible, however, to continue holding the already separated portions of the workpiece while simultaneously performing a rotation of the workpiece about its longitudinal axis. In this manner, the cutting means is rotated relative to the just performed cut and it is possible by retracting other clamping elements to maintain the clamping action and simultaneously to withdraw the cutting means from the work area. Subsequently, the latter may be returned to the starting position and, by releasing clamping elements at the other end, relocated in the new cutting position in order to perform the following cut.
The invention is further explained by means of a preferred exemplary embodiment that demonstrates further advantageous features and advantages and with reference to figures.
The latter show:
Fig. 1 View of the front side of a silicon ingot with cutting lines indicated by dotted lines;
Fig. 2 View of an ingot provided with a saw wire web;
Figs. 3 - 4 View of an ingot that has been separated once;
Fig. 5 Lateral view of a device according to the invention;
Fig. 6 as Fig. 5, device partly sectioned;
Fig. 7 Enlarged lateral view of a clamping element of the device;
Fig. 8 Section through a clamping element according to Fig. 7; and
Figs. 9 - 13 In a view similar to Fig. 5, a sequence of states of the device according to the invention. Fig. 1 shows a view on the front surface 1 of an ingot 3 of silicon produced according to a more recent production process. Ingot 3 has a nearly sguare cross-section. Its edge length is more than twice that of the brick width of 156 mm that is usual for the manufacture e.g. of solar cells, the dotted lines in Fig. 1 indicate the cuts that are required in order to cut ingot 3 into four such 156 mm bricks 5 for further processing. In this operation, the peripheral portions 7, the so-called slabs, are cut off and recycled since they are contaminated.
Basically, it is conceivable to perform at least the quartering cuts, i.e. horizontal cut 9 and vertical cut 10, in a stationary clamping position of an ingot by means of two sawing wires 12 that are simultaneously guided through the ingot one after another. The removal of slabs 7 by means of peripherally guided saw wires 12 may take place parallelly or with a time delay. Also conceivable is a temporally consecutive mode of operation in which wires 12 and 14 are identical and a single wire pair is displaced in a corresponding manner. Fig. 2 shows a wire web of wires 12 and 14 for dividing an ingot into four bricks 5 and simultaneously cutting off slabs 7, the wires that are symbolized by dotted lines running in front of the wires shown in solid lines. This arrangement merely represents a preferred example, however, and different arrangements in the longitudinal direction of ingot 3 are also possible.
Fig. 5 shows a lateral view of a device 20 according to the invention for holding an ingot 3. It comprises a left-hand retaining head 22 and a right-hand retaining head 24 as well as a support 26. Support 26 receives the slab cut off on the respective lower side but may also serve for referencing ingot 3 between retaining heads 22 and 24, i.e. bringing it to the predefined working position. Retaining devices for the slabs cut off on the sides and a gripping device for the slab cut off on the upper side are realized in a conventional manner and are therefore not shown. In the yet to be described second embodiment, however, retaining heads 22, 24 are arranged so as to rotate ingot 3 about its longitudinal axis such that the respective lower slab can be cut off in consecutive steps and lateral and upper slab receivers may thus be omitted.
Retaining heads 22, 24 each comprise four clamping elements 28 in a square disposition. The clamping elements are thus so arranged that each of their front surfaces 30 is applied approximately centrally to a respective front surface of a future brick 5. Clamping elements 28 are adjustable in length. Preferentially, they are guided pneumatic cylinders. Characteristic features of such pneumatic cylinders are the lateral guide rods 32 and the central piston 34 actuated by air pressure (see Fig. 6) . Pneumatic cylinders of this kind are known in the art per se.
For their contact with the workpiece, i.e. ingot 3, clamping elements 28 each comprise a pressure head 36 that is shown on an enlarged scale in Figs. 7 and 8. A support plate 38 is provided with a spherical recess 40. The latter holds a pressure member 42 whose rear side has a cambered portion 43 that is complementary to recess 40. Pressure member 42 is retained in recess 40 by a screw 44 that is screwed into support plate 38. However, screw 44 is fastened in support member 40 and pressure member 42 designed in such a manner that there is a certain amount of play around screw 44 in pressure member 42. Pressure member 42 is therefore movable to a small extent and thus capable of adjusting to minor irregularities of an ingot 3 by pivoting in recess 40. In this manner it is ensured that bearing surface 48 may contact the surface of an ingot 3 in a planar manner.
Bearing surface 48 is provided with a hard rubber coating 50 in order to ensure a superior frictional connection. At the same time, coating 50 prevents a direct contact between pressure member 42 of steel and the silicon of ingot 3.
The rubber coating may consist of a natural or synthetic rubber. Suitable materials are known in the art per se.
Pressure head 36 is mounted on a mounting plate 52.
With the described arrangement it is possible to position an ingot 3 between retaining heads 22, 24 by means of support 26 and subsequently clamp it by extending clamping elements 28. Now, to cut off slabs 7, dividing elements can be driven through ingot 3 peripherally in the longitudinal direction. Furthermore, dividing elements can be introduced between clamping elements 28 in order to carry out the central cuts 9, 10, thereby quartering ingot 3. In particular, it is conceivable to build up a wire web of saw wires 14, 12 (see Fig. 2) between ingot 3 and e.g. left-hand retaining head 22 and to guide it through ingot 3 in a single pass to obtain a set of 4 separate bricks 5 directly. It is obvious that each brick 5 is still retained by a respective pair of opposed clamping elements 28. By seizing a brick and releasing a corresponding pair of clamping elements, the bricks can be withdrawn individually. In a preferred embodiment, however, clamping elements 28 are jointly supported in heads 22, 24, respectively, in a rotatable manner. In this manner, clamped ingot 3 can be rotated about its longitudinal axis. Thus, within the scope of the preceding description, the following is possible:
1) Only the slab located on the lower side is cut off so that it comes to lie on support 26 and can be separated from the ingot by retracting the support (arrow 54) .
2) One or alternatively both lower bricks are deposited on support 26 and lowered according to 1) like the slabs. After rotating the clamping elements by 180°, the upper bricks reach the lower position and may in turn be received by support 26 and withdrawn from the holding device. It is also possible to perform a 90° rotation at a time and to withdraw a single brick 5 only.
Alternatively, it may be contemplated to withdraw bricks 5 from the top by means of a gripping device.
However, this foregoing embodiment and application of the device still require the manual threading of saw wire between clamping elements 28 in order to carry out the central cuts 9, 10. Furthermore, the highest possible precision of the cuts is desired, for which purpose band saws are more suitable. Thus, for example, a deviation of the edge length over the entire length of +/- 0.2 mm should not be exceeded. The same tolerance is expected with regard to the parallelism of the cuts, and the roughness Ra of the cut surfaces should be no more than 0.0009 mm. As maximum values for each of the indicated tolerances, 0.5 mm may be admitted, and 0.002 mm for the surface roughness Ra. In addition, minimum cut losses are an important issue, and as a maximum value therefor, 2 mm may be admitted while usual values range between 0.7 and 0.9 mm. With the foregoing device including the possibility of rotating ingot 3 and of individually extending clamping elements 28, a fully automatic sawing and subdivision of an ingot 3 into bricks 5 is also possible by means of a band saw, as described hereinafter.
Clamping elements 28 of retaining device 20 are retracted. A workpiece, i.e. a silicon ingot 3, is referenced between retaining heads 22, 24 by means of support 26, i.e. manoeuvred to the working position (see arrows 54) . Clamping elements 28 are extended and saw band 60 is moved to the home position for cutting off the lower slab, after which the configuration according to Fig. 5 results.
By repeating the following steps four times, the slab each time located on the respective lower side is removed. For this purpose, saw band 60 is moved to the right in Fig. 5. The slab which has been cut-off is lowered by means of support 26, ingot 3 is rotated 90° about its longitudinal axis, saw band 60 is returned to its left-hand home position, and after removing the cut-off slab, support 26 is again raised to pick up the next slab.
After removing the fourth slab and returning saw band 60 to its home position near left-hand retaining head 22, the two lower clamping elements 62 of left-hand head 22 are retracted and through the thus created gap, saw band 60 is moved to the position of central horizontal cutting line 9 (Fig. 9) . Ingot 3 is being held by upper clamping elements 63 of left-hand head. The lower clamping elements 62 are again extended (Fig. 10) and cut 9 is performed, which results in the cut ingot 3 according to Fig. 3. It is now divided into an upper half 65 and a lower half 66 by a longitudinal cut 9. Now, obviously, it is no longer possible to move saw band 60 out of retaining device 20 upwardly or downwardly as this would require an upper or lower pair of clamping elements 28 to be released, in which case one of the two halves 65, 66 would no longer be retained.
Now, of right-hand retaining head 24, forward upper clamping element 69 and rearward lower clamping element 70, which are diametrally opposed, are retracted (Fig. 11) . In this manner, upper half 65 is still being held by rearward upper clamping element 71 of right-hand head 24 while the two opposed upper clamping elements 62 of the left-hand head prevent a rotation. Correspondingly, lower half 66 is safely held by forward lower clamping element 72 of right-hand head 24 in conjunction with the lower clamping elements 62 of left-hand head 22.
Ingot 3 is now rotated according to arrow 74 while the retracted retaining elements 69, 71 are moved past the rear of saw band 60. As shown in Fig. 4, cutting. line 9 is thus oriented vertically. The saw band is now basically in the position for carrying out the pending other central cut 10, which is now horizontal. As shown in Fig. 12, after extending retracted clamping element 70, the lower clamping elements, i.e. the former forward clamping element 69 and lower forward clamping element 72 (hidden behind clamping element 69) , may now be released and saw band 60 moved out downwardly. The saw band is moved to left-hand retaining head 22 and the lower clamping elements 62 thereof (prior to - l i ¬
the rotation: the forward clamping elements of the upper and lower clamping element pair, respectively) are retracted (Fig. 13) . The saw band can now be moved to the home position for the now horizontally extending second central cut 10. After having carried out this cut, the two lower bricks 5 can successively or simultaneously be received by support 26 and withdrawn. Saw band 60 is thus free and can be moved out of the device, whereupon the two upper bricks can also be received by support 26 after a rotation about the longitudinal axis.
From the foregoing description of exemplary embodiments, numerous modifications and supplementations are accessible to one skilled in the art without departing from the scope of protection of the invention which is defined by the appended claims. In particular, it may be contemplated:
- To perform the sawing operation with ingot 3 in a vertical or other orientation;
- to perform the relative movement particularly between the cutting means and the retaining device in another way than
" by moving the cutting means, e.g. by moving the holding device;
- to use a drive other than pneumatic for the clamping elements, e.g. a hydraulic or electric one;
- to realise the clamping elements by an array of pressure members; - to use different positions or a different number of cuts, possibly with a correspondingly adapted different number and arrangement of clamping elements.
- It may be contemplated to position the grid according to Fig. 2 between the clamping elements before the ingot is clamped, thereby avoiding the introduction of the saw wires between the clamping elements.