Apparatus for carrying and transporting a product

The invention relates to an apparatus for carrying and transporting a product, comprising a conveyor having a surface, which during use is directed towards the product and is provided with inlet openings and outlet openings for a me- dium providing the product with traction.

Such an apparatus for carrying and transporting a product is known from the European patent application EP-A 0 962 409 and also from the American patent US-A 5 634 636. Such an apparatus is also known from the article "Motion Control of Planar Objects using Large-Area arrays of Mems-like Distributed Manipulators" by Andrew Berlin, et al. of June 2000, presented at Micromechatronics 2000.

The subject of the above-mentioned publications con- cerns the transport of flexible products, and in particular the transport of sheets of paper using air as the medium that provides the product with traction.

The apparatus referred to in the preamble is also known from the article "Air Film System for Handling Semicon- ductor Wafers" by J.A. Paivanas and J.K. Hassan, published in IBM Journal of Research and Development, vol. 23, nr. 4, July 1979, pp 361-375.

Although the field of apparatuses for carrying and transporting products using air as transport means is exten- sively documented, as yet there has been no suitable proposal for an embodiment of such an apparatus that would allow simple and reliable transport of thin, fragile products, and with which loss of such products resulting from damage during transport is avoided as much as possible. The products con- cerned include wafers, glass substrates, silicon solar cells, glass plates, displays and printing plates, whose dimensions and whose thickness may vary widely (an indication of possible dimensions : for example approximately 100 x 100 mm with a thickness of approximately 1 mm) . In general, the known apparatus for carrying and transporting a product applies a relatively strong air stream of a turbulent nature. This air stream is usually so strong

that, without taking countermeasures, the product to be transported levitates too much, making the apparatus less precise and, without such countermeasures, even useless. In order to avoid this problem, use is often made of a conveyor surface provided at each side of the product to be transported, wherein each surface is provided with inlet openings for a gas, see for example the European patent application EP-A 0 962 409 and the American patent US-A 5 634 636 but also the Dutch patent application NL-A-8402410, mentioned below. The added surface thus provides a counterpressure for positioning the product accurately between both surfaces.

From the Dutch patent application NL-A-8 402 410 an apparatus for carrying and transporting a product is known, comprising a conveyor having a surface, which during use is directed towards a product, comprising inlet openings and outlet openings for a medium that provides the product with traction, which surface is at least provided with cells delimited by walls separating the cells from each other and whose upper sides form the surface, and which cells are uniform and in the transport direction of the product, evenly distributed in the surface such that during use several cells operate simultaneously to carry the product and provide it with traction, and wherein each cell is provided with at least one inlet opening for the medium. In the prior art according to the Dutch patent application NL-A-8 402 410, the walls of the cells are provided with openings so as to create a flow path from the inlet openings to the outlet openings for the medium. This creates a flow from cell to cell so as to provide the product with trac- tion. A disadvantage of the known apparatus for carrying and transporting a product is that the configuration, and in particular the direction and the measure of traction of this known apparatus for carrying and transporting a product, is predetermined by the design and cannot be varied during opera- tion. Another drawback relates to the relative depths of the cells reported in the Dutch patent application NL-A-8 402 410, wherein a small pressure difference can create a relatively strong air flow without producing any significant traction.

The object of the invention is to simplify the known apparatus for carrying and transporting a product and to make

it more useful for the traction of thin, fragile products such as the above-mentioned wafers and glass substrates .

To this end the apparatus for carrying and transporting a product according to the invention is characterized by one or several of the appended claims. This apparatus for carrying and transporting a product makes it possible to handle many different types of products without, in principle, imposing any limits on their dimensions. The product to be handled must, at the side directed towards the conveyor, merely be im- permeable to the medium.

In a first aspect of the invention, the apparatus for carrying and transporting a product is characterized in that each cell is also provided with at least one outlet opening for the medium, and in that the walls are impermeable to the medium. This medium may be a gas or a liquid. In this way it is shown to be possible to operate the inlet opening at a slight overpressure and the outlet opening at a slight underpressure, whereby sufficient levitation of the product is obtained while at the same time, the product is provided with sufficient traction without resorting to high flow rates of the medium, as in the case of the prior art. The traction provided by the apparatus for carrying and transporting a product according to the invention therefore, is not based on momentum transfer from the outflowing medium, but is based on the transmission of energy in the boundary layer formed between the medium flowing into each cell and the product located near the cell. The cells may be embodied relatively shallow so as to optimize the relation between the amount of medium to be used and the traction obtained. It is worth mentioning that it is not necessary for all the cells to be such (adjustable) traction cells. So- called overpressure cells (for carrying the product, and being provided with at least one inlet opening and no outlet opening) and so-called underpressure cells (for pretensioning the product, and being provided with at least one outlet opening and no inlet opening) may also be added.

If it is desired to optimally control the position and speed of the product to be transported, it is preferred for each of the cells to be provided with two inlet openings and two outlet openings that are individually adjustable to

control the amount of medium to be supplied and discharged. By pairing each inlet opening with an outlet opening, and by arranging these pairs of inlet openings and outlet openings in an orthogonal configuration in relation to one another it is possible, by suitably regulating the amount of medium to be supplied or discharged per inlet opening and outlet opening, to provide the product to be transported with a precise traction in a desired direction.

One of the distinguishing aspects of the apparatus for carrying and transporting a product according to the invention as opposed to that of the prior art is that the surface directed towards the product adequately provides the product with traction, and that a further traction-providing organ placed opposite this surface may be dispensed with. The cells of the apparatus for carrying and transporting a product are preferably formed like rectangular chambers with the inlet openings and outlet openings being provided in the corners of the chambers. The upper sides of the walls separating the cells from each other thus form the sur- face of the conveyor.

The simplicity of construction of the apparatus for carrying and transporting a product according to the invention and its control is served by an even distribution of the cells in the surface. It is further preferable for the pressure of the medium in each cell to be individually adjustable.

In order to fully develop the advantages of the invention, the apparatus for carrying and transporting a product is provided with one or several position detectors for deter- mining the position of a product, as well as a regulator connected with the position detectors for adjusting, per individual cell or group of cells, the amount of medium to be supplied and/or discharged so as to provide the product with a predetermined, desirable degree of traction in a predetermined direction.

To optimally facilitate matters, the apparatus is embodied such that the regulator is connected to and controls adjustable resistances in the pipes for the medium to and from the inlet openings or the outlet openings, respectively, of each cell. The advantage is that this provides a constant po-

sition regarding the distance of the product in relation to the conveyor.

Hereinafter the invention will be further elucidated by way of a schematic representation of an exemplary embodi- ment of the apparatus according to the invention, which does not limit the appended claims, and with reference to the drawing.

The drawing shows in

Fig. 1, a schematic illustration of an apparatus for carrying and transporting a product according to the invention, carrying a product and,

Fig. 2, a detail of the apparatus for carrying and transporting a product as shown in Fig . 1.

Identical reference numerals used in the Figures re- fer to similar components.

In Fig. 1, reference numeral 1 generally indicates the apparatus for carrying and transporting a product according to the invention.

Said apparatus 1 for carrying and transporting a product comprises a conveyor 2 having a surface 4, which during use is directed towards a product 3, comprising inlet openings and outlet openings for a medium, for example, a gas to provide the product 3 with traction, as will be explained below. Fig. 1 shows that the surface 4 of the conveyor 2 is at least provided with cells 5, also referred to as traction cells.

Fig. 1 also clearly shows that theβe cells 5 are evenly distributed in the surface 4. In Fig. 2, four such cells 5 are shown in juxtaposition. Fig. 2 clearly shows that the cells 5 form rectangular chambers delimited by walls 6 separating the chambers 5 from each other, and whose upper sides form the surface 4 of the conveyor. It should be mentioned that the inlet openings 7 and outlet openings 8 are provided in the corners of the cells that form the chambers.

Each cell 5 must have at least one inlet opening 7 and one outlet opening 8 for the medium (gas or liquid) that provides the traction. Preferably, however, each cell 5 is

which are, moreover, individually adjustable to regulate the amount of medium to be supplied and to be discharged.

In addition to the (traction) cells 5 mentioned above, different kinds of cells such as overpressure cells (comprising only one or more inlet openings) and underpressure cells (comprising only one or more outlet openings) may also be provided. This is not shown in the figures but is quite obvious to those skilled in the art. As already mentioned, the surface 4 of the conveyor 2 directed towards the product 3 provides the product 3 with adequate traction so that a further traction-providing organ placed opposite this surface 4 may be dispensed with all together.

With further reference to Fig. 1, it is shown that a regulator 9 is provided, which is coupled with a plurality of position detectors for determining the position of a product. Said position detectors carry reference numeral 10 in Fig. 2 and are shown at the corner points of each cell 5. The signal from the position detectors 10 is transmitted to the regulator 9 via signal lines 11, shown in Fig. 1. The regulator 9 is also coupled with provisions for, per individual cell 5 or group of cells 5, adjusting the amount of medium to be supplied and/or discharged, so as to provide the product 3 with a predetermined, desired degree of traction in a predetermined direction. To this end signal lines 12 and 13 are provided via which actuators may be controlled for the regulation of the gas flow through each cell. The above description of an exemplary embodiment of an apparatus for carrying and transporting a product according to the invention serves merely to elucidate the appended claims, without limiting these claims to this specific exemplary embodiment .

The protective scope due the claims is determined exclusively by that which those skilled in the art perceive as essential contribution to the prior art, as embodied in the appended claims .

In accordance with the above many variations are feasible, all of which fall within the scope of the invention and, without claiming completeness, these may include:

- The apparatus will work not only in a horizontal but also in a sloping position and, in an adapted embodiment, even in a vertical and upside-down position.

- The apparatus is not only suitable for transporting but also for positioning a product in a desired position. In combination with a suitable sensor and control system both translation and rotation are possible.

- The cells are not necessarily identical in shape. Different requirements (for example, desired precision or preferential directions) at different positions of the apparatus may call for the selection of differently shaped cells, such as squares, rectangles, hexagons or triangles.

- It should be mentioned that it is not necessary for all the cells to be (adjustable) traction cells. So-called overpressure cells (for carrying the product, and provided with at least one inlet opening and no outlet opening) and so- called underpressure cells (for pretensioning the product, and provided with at least one outlet opening and no inlet opening) may also be added.