WO1994020984A1

WO1994020984A1 - Non-adhesive ecologically-pure electroadhesion method of clamping and fixing materials

Info

Publication number: WO1994020984A1
Application number: PCT/NZ1994/000016
Authority: WO
Inventors: Vagiz Nurgalievitch Abrarov
Original assignee: WHITEHEAD JOHN ANTHONY BAILIE
Current assignee: WHITEHEAD JOHN ANTHONY BAILIE
Priority date: 1993-03-08
Filing date: 1994-03-08
Publication date: 1994-09-15
Anticipated expiration: 1995-09-08
Also published as: IL108893A0; CN1105740A; NO953558L; ZA941587B; CA2157875A1; FI954226L; NO953558D0; FI954226A7; FI941079A0; FI954226A0; AU6158094A

Abstract

Apparatus for non-adhesive and ecologically safe electroadhesion method of clamping and fixing materials, the apparatus including one or more electrodes (14, 16) coated with a polymer capable of being polarised and presenting a conformable (for example, flat) surface to the article or articles to be adhered, the polymer having a predetermined plasticity for accommodating any irregularities in the surface of the article or articles to be adhered for minimum presence of gaseous media between the surface of the polymer and the surface of the article/s, and a source of electrical current for charging the elecrode/s and inducing an electrical field on the article/s.

Description

TITLE: NON-ADHESIVE ECOLOGICALLY-PURE ELECTROADHESION METHOD OF CLAMPING AND FIXING MATERIALS FIELD OF THE INVENTION

This invention relates to a non-adhesive ecologically-pure electroadhesion method of clamping and fixing materials, and apparatus therefor.

BACKGROUND OF THE INVENTION

Electroadhesion of materials has, in the past, been limited because of several factors. The most important factor was the presence of gaseous media in the space between the surface of the electrode and the surface of the material required to be clamped or adhered due to irregularities in the surface or surfaces. The increase in the voltage applied to the electrode did not overcome this problem.

The application of a dielectric coating to the electrode increased the field strength but this force could not be increased by the increase of the voltage above a certain value.

It is an object of the present invention to provide a method and apparatus for achieving a far greater adhesion between materials than hitherto achieved and thereby extending the applications and materials.

THE INVENTION

According to the invention apparatus for electroadhesion includes one or more electrodes coated with a polymer capable of being polarised and presenting a conformable (for example, flat) surface to the article or articles to be adhered, the polymer having a predetermined plasticity for accommodating any irregularities in the surface of the article or articles to be adhered for minimum presence of gaseous media between the surface of the polymer and the surface of the article/s, and a source of electrical current for charging the electrode/s and inducing an electrical field on the article/s.

In a preferred form of the invention the surface of the apparatus, including the electrode/s is prepared to substantial optical precision. This ensures that the space between the surfaces of the apparatus and the article/s is minimal so that gaseous media are virtually excluded therebetween.

Although many polymers are useful, it will be appreciated that some polymers have a greater dielectric permittivity than others and, more importantly, some have a greater degree of polarisation and it is an important aspect of the invention that the polymer provides sufficient polarisation, to present a concentrated charged surface. Polyvinyl chloride has proved itself to be ideal for the purpose not only for the reason that it is capable of being dipolarised but it can also be provided in a mechanically strong form and which, at the same time, is able to be plasticised to a predetermined plasticity.

The preferred plasticisers are di-octyl phthalate, or di-octyl adipate and any other known plasticisers. The amount of plasticiser may be between about 15 to about 50 percent by mass.

The plasticised polymer sheet may be orientated in both directions and may be stretched over the surface of the apparatus to exclude gaseous media and then anchored in position in any suitable manner.

It will be appreciated that the force of adhesion is the sum of the mechanic force of the electrical force, the force due to the polarisation of the polymer and the force of molecular attraction (due to the creation of a double electrical layer in zones of close contact). The total attraction can, if as much gaseous media as possible is excluded be as much as from 0,0001 to 100 MPa. At about 2 MPa the apparatus can be used as a manipulator for.heavy objects and it will be appreciated that the apparatus can be designed for any particular purpose.

The- layer of polymer may be between about 4 to 1000 mem for many applications and may have a tensile strength v/hen in position of between about 0,0001 and 0,5 MPa.

The electrode or electrodes should be as thin as possible and -may be applied to the surface of the apparatus by any known method, but preferably by vacuum deposition and may be etched. The thickness may be between about 0,05 and 5 mem. The source of electrical voltage may be alternating or direct and will be chosen according to the desired application. An important application of the invention is for the grinding, polishing and super-finishing processing of semi-conductor (e.g. silicon) discs for the electronic industry. This was previously carried out by using an adhesive for the discs to be stuck to a surface. After the necessary grinding, the very thin discs are removed and then the adhesive layer has to be removed. This limited the degree of grinding and the desired precise parameters of the discs which could be attained. With the present invention, the avoidance of the adhesive makes it possible to machine these discs to precise parameters necessary for sub-micron technology, and to a fraction of the thickness achieved hitherto. The apparatus in such a case may be small and may be powered by a small dry cell or any other independent power source, or any other source. The electrodes may be annular and may alternate in polarity. EMBODIMENT OF THE INVENTION

An embodiment of the invention is described below with reference to the accompanying drawings in which:

Figure 1 is a plan view of the surface of an apparatus according to the invention;

and

Figure 2 is a side view thereof. In the drawing the apparatus includes a shell 10 which houses the electrical circuit. This may comprise a dry cell and an oscillator

(not visible) or any other power source. The surface 12 is machined to optical precision and includes annular electrodes 14,15 which have alternate polarities. The electrodes and surface are covered with a sheet of plasticised and orientated polyvinyl chloride (not visible) held in a ring 20.

Apparatus according to the invention for other applications will be designed specifically. The applications are extensive and include temporary fixing, transportation, assembly and machining, the invention avoiding the use of mechanical, electromechanical, suction, adhesive and other labour consuming and otherwise inconvenient methods. This results in the avoidance of multiple heating, cooling, sticking off, pollution, clearing of adhesives, use of solvents for adhesives, for vacuum equipment, toxicity, explosive production and other inconveniences.

Among the advantages of the invention include the speed regimes of machining, increasing accuracy parameters, increased quality decreasing reject ratios and the saving of expenses of manufacturing, power, staff and the like. The apparatus may be used in outer space, under water, in corrosive media and in remote control circumstances. Other uses include instrumentation, electronic, radio, optical, medial, machine building, mechanical machining of dielectric and current conductive parts, packing systems, hatches, covers, thermal vacuum chambers, robotic equipment and in aviation, rocket and cosmic technology at various temperatures, in rarified media and under radiation effects.

It may also be used in submicron technology to automate processes and considerably increase efficiency in operations such as thermal impurity diffusion, alloying by ion implantation, epitaxy, covering formation, metallization, photolighography, assembly and hermetic sealing of mircocircuits. Complex uses include electronic indication, check and control systems, with operation sensing devices which permits the use of automated lines and production sections.

An advantage of the invention is that the polymeric material is easily stripped and replaced when damaged - merely by removing the ring, replacing the polymeric material and replacing the ring.

Referring now to Figures 3 to 8 the values of the widths of the electrodes and the distances therebetween are shown to be critical.

For the purpose of defining the present invention it is necessary to assign specific references to the pertinent dimensions and regard to be had to Figure 3 which is a cross-sectional view on the line 3-3 of Figure 2.

In Figure 4, the pertinent dimensions are indicated as d, L and λ. d being half of the distance apart of the electrodes 12, 15, L being the thickness of the polymer layer and being the distance equal to 2d plus the width of an electrode.

These dimensions are shown in detail in Figure 4 in which X and Y axes are shown for the graphs which follow as Figures 5 to 8.

It has been found that the following equations must be observed in order to obtain optimal results

L/λ < 0,4

d/λ ≤ 0,25

The results of numerous experiments with varying values of the dimensions are expressed in the graphs of Figures 5 to 8.

In Figures 5 to 7 it is clear that the optimum results are obtained at λ = 0,33

λ = 0,25

λ = 0,167 In Figure 8 it is clear that the optimum ratio d/Λ,must be less than or equal to 0,25

It is also to be noted that the width of the space 2d is limited by

L≤λ. the inter-electrode arcing distance, which means that L≤ d and

Δ

The minimum possible width 2d is limited by the electrical field strength of the space. If it is required to to increase the average field density for a chosen space 2d, the distance λ should be increased, the maximum increase being limited by the size or sizes of the object or objects to be attached.

The degree of fixing of an article on the surface of the apparatus is dependent to a large extent on the width of the electrodes but this dimension is limited by the drop in the intensity of the electrical forces over a wide electrode.

It is clear that if the article to be fixed to the surface is an electrically conducting material, the forces of adhesion are due to the oppositely polarised charges. Thus, if one considers Figures 3 and 4, the opposite charges are on the surface of electrode, the under surface of the dielectric (via the gap d₁) the top surface of the dielectric and the underside of the artice (via the gap d₂).

If the article to be fixed is a dielectric, the adhesion is due to a non-uniform field over the surface of the device with a high gradient of normal electrical intensity. The dielectric article tends to move to the area of maximum electrical intensity to fasten on the surface of the device.

Thus, the mechanism of interaction of oppositely polarised charges which are involved in the fixing of electrical conducting materials, and the residual polarisation of the dielectric, as well as the adhesion component of the adhesive force, due to intermolecular interaction caused by the plasticity of the dielectric, contribute significantly to the efficency of the fixing.

As far as a dielectric article is concerned, it is the migration and dipole polarisation in the polymer film material, which contribute to the fixing force.

The roughness of the surface of the article and of the device results in randomly arranged series of microcavities which are referred to hereunder as R_a, and R_z, in which R_a is the arithmetic means of the deviation of the surface of the article from a reference line within the limits of the basic length; and R_z is the average height of the microcavities.

Thus, assuming that the term 2R_a is approximately equal to d₁ and R_z/2 for d₂, then the following relationships exist. At R_a = I,25mcm;

d₂ = 2 R_a article +2 R_a dielectric; d_I = 2 R_a dielectric + 2 R_a base; or d₂ = R_z article/2 + R_z diel./2;

d_I = R_a diel./2 = R_z base/2.

At R_a = I,25 mem;

d₂ = R_z article/2 + R_z diel./2; d₁ = R_z diel./2 = R_z base/2.

Claims

WHAT WE CLAIM IS:

1.

Apparatus for electroadhesion includes one or more electrodes (14,16) coated with a polymer characterised in that it is capable of being polarised and presenting a conformable (for example, flat) surface to the article or articles to be adhered, the polymer having a predetermined plasticity for accommodating any irregularities in the surface of the article or articles to be adhered for minimum presence of gaseous media between the surface of the polymer and the surface of the article/s, and a source of electrical current for charging the electrode/s and inducing an electrical field on the article/s.

2.

The. .apparatus of claim 1 in which the surface of the apparatus, including the electrode/s is characterised in that it is prepared to substantial optical precision.

3.

The apparatus of either of the above claims characterised in that the polymer is polyvinyl chloride.

4.

The apparatus of claim 3 characterised in that the polyvinyl chloride is plasticised.

5.

The apparatus of claim 4 characterised in that the plasticiser is chosen from di-octyl adipate.

6.

The apparatus of any of the above claims characterised in that the polymer is orientated in both directions.

7.

The apparatus of any of the above claims characterised in that

L/a < 0,4

d/a ≤ 0,25

in which d is half the distance apart of the electrodes, L is the thickness of the polymer layer and is the distance equal to 2d plus the width of an electrode.

8.

The apparatus of claim 7 in which λ is between 0,167 and 0,33 and the ratio d/ λ is less than or equal to 0,25.

9.

Apparatus for electroadhesion substantially as herein described with reference to the accompanying drawings.

10.

A method of processing semi-conductors including the step of locating the workpieces on apparatus according to any one of the above claims and then carrying out the finishing operation.