Apparatus and Method for Surface Treatment

Multi Orbital Systems GmbH Heinrich-Hertz-Platz 1, D-92275 Eschenfelden

The present invention relates to an apparatus and a method for treating surfaces. Further, the invention relates to the use of a corresponding apparatus for treating surfaces, in particular surfaces of certain materials.

Apparatuses and methods for treating surfaces are known in the prior art.

In a polishing process for example, as one type of surface technology, a hard material such as metal, glass, varnish, precious stones or the like is made smooth and optionally made to shine. Very fine polishing agents are used, for example rouge cake, polishing slate, prepared chalk, tin ash, ceroxide and emery powder, which are applied for example to a cloth, felt, rubber, pitch or leather wheel and rubbed against the surface to be treated. This can take place manually or also with the use of machines, for example with polishing wheels.

Such electrically driven machines are equipped for example with a rotary polishing wheel made of felt or leather and are passed over the surface to be treated by means of a corresponding apparatus or by hand.

A disadvantage however is that the use of automatic means is only possible when the surfaces are substantially continuous or a flat surface structure is present. Problems occur when the surface comprises small projections or recesses, grooves or the like because the use of large polishing wheels is not possible. They cannot enter or only partially enter into such irregularities in the structure. For this reason, it is then necessary to rework these regions in an extensive manual work stage or to completely treat the surface manually in order to achieve the desired surface quality.

One possibility of countering this problem is to polish the surface electrolytically, although this procedure can only be used for electrically conducting materials. Preferably stainless steels or aluminum alloys are cleaned, deburred and made shiny by immersing the metal in a chemical bath and applying a direct current.

Apart from the limitation to electrically conducting materials, the surface structure can be changed, i.e. smoothed, only to a limited degree and additionally, the use of electrolytic baths is time and cost consuming.

In addition, methods and apparatuses for grinding surfaces are known in the prior art, which, as with the method and means for polishing, make use of machines to smooth rough surfaces, for example by oscillating, eccentric or band grinding machines. The disadvantage here is also that such machines can only substantially handle continuous surfaces and preferably ones without abrupt change in structure or macroscopic surface structures, for example ones having a texture, knobs, grooves, rills or the like.

Therefore, the need exists to be able to machine-work surfaces, also discontinuous or uneven surfaces or those having a desired macroscopic surface structure, for example knobs, grooves or the like, to achieve a surface quality, for example in producing imprint stamps, embossing cylinders, moulds or injection moulds, blowing moulds and the like, which does not require or at least reduces the requirement of subsequent manual reworking of the surface.

In view of the prior art, an object of the present invention is to provide an apparatus and a method for treating surfaces, which at least partially overcomes the known disadvantages of the prior art.

This object is achieved through the apparatus according to claim 1 and the method according to claim 16. Preferred embodiments of the invention make up the subject matter of the dependent claims.

The apparatus according to the invention comprises at least one first and second retaining device, the base surfaces of which are preferably substantially parallel to one another. The first retaining device holds a first body, preferably a treatment tool and the second retaining device holds a second body, preferably the workpiece to be treated, or at least one body to be treated.

The first retaining device can be subjected to a predetermined force in a first direction, in particular a compressive force, where this takes place for example by means of a hydraulic cylinder or similar means. The retaining device is movably mounted in a second movement direction or movement plane, which is substantially perpendicular to the direction in which force is applied.

The second receiving device is also movably mounted in a third movement direction or movement plane, which is substantially perpendicular to the direction in which force is applied to the first retaining device.

The invention is characterized in that the first and/or second retaining device is each driven by at least one generator and preferably by two generators. The motion in the two and/or three movement directions or planes is thereby produced. In particular, the generators of the two retaining devices are controlled, such that they oscillate or rotate with respect to one another in predetermined phases and the receiving devices are therefore set in relative motion to one another. The movement of the retaining devices takes place in particular such that the resulting movement of the two receiving devices is counter directional to one another and preferably also variable.

The relative movement between the first and second retaining devices produces a superimposed oscillation or vibration, which depending on the basic oscillations (i.e. the movement of the first and second retaining devices in the first and second movement directions) can be varied in type and/or direction and/or intensity and used for treating the workpiece.

According to a preferred embodiment, the treatment tool has a surface shape, which is substantially complementary to the surface shape of the body to be treated or corresponds to a matrix plate. The treatment tool is configured such that when pressed to the surface of the workpiece, at least a partial region of the surface or the entire region of the surface is covered. According to a further preferred embodiment, the matrix plate is formed, so that small undercuts of the body can be at least partially treated.

This can be achieved for example in that the matrix plates, when the tool is joined with the workpiece, is introduced into the undercut region of the workpiece and subsequently altered in its extension, so that the undercut can be treated. This can for example take place in that the tool is spread in transverse direction.

In a preferred embodiment, the treatment tool is placed in direct contact with the surface of the workpiece for treating the surface. In a particularly preferred embodiment, an agent, for example a polishing or grinding material, is placed between the tool and the workpiece.

Such grinding or abrading material preferably comprises a carrier, in which the material, for example corundum, silicate or the like with a predetermined grain size distribution is present. Particularly preferred abrading materials comprise a carrier comprising paste-like, gel-like or other preferably high viscous or plastic materials. Such agents are known in the prior art and are selected, in particular, depending on the workpiece to be treated and the surface quality to be achieved.

When using such an agent, the surfaces of the tool and the workpiece remain slightly spaced from one another, where the distance results, among other things, from the amount and the selected grain size distribution of the agent.

In a particularly preferred embodiment, the introduction of the agent takes place continuously or discontinuously. The dosing of the agent can take place by means of at least one opening, preferably through the tool. For this purpose, feed devices, such

as for example piston pump, screw extruders, monopumps or the like can be used, which are dimensioned to the pressure conditions and/or the type of agent to be dosed, in particular its viscosity. This results in the particular advantage, that the polishing or abrading process need not be interrupted to introduce the agent and therefore an improved working procedure is provided.

If no additional agent is employed, the surface of the tool can comprise a correspondingly rough structure. This can be achieved for example in that the surface of the tool is made up of a synthetic material, in which a predetermined grinding or abrading agent, such as corundum, silicate or the like is imbedded. With this, the surface of the tool can directly polish or grind the workpiece surface. The scope of the present invention also encompasses methods with additional agents, for example as known in wet grinding. This can include water-based liquids, as well as those without water, for example oils or emulsions.

The first and/or second retaining device in a preferred embodiment is mechanically decoupled in the second or third movement direction from the direction in which compression force is generated, so that the movement in these directions is substantially independent from the transmission of force applied in the direction toward the work- piece.

This decoupling, according to a preferred embodiment, is provided through a tensile connection, which is arranged between the hydraulic cylinder for generating the compression force and the suspension of the retaining device. The tensile connection, which for example comprises a cable connection or any other pivotal connection subjected to tensile forces between the components, enables the transmission of the compression force. However, the mounting of the pressing device is decoupled from the mounting of the retaining device for the oscillating movement to an extent that the cylinder of the pressing device remains substantially free of oscillation, even when the retaining device moves.

According to a preferred embodiment, eccentric shafts are employed as generators for oscillation. These are preferably arranged with one end on the suspension of the retaining device or directly arranged on the retaining device via bearings. The respective other ends of the eccentric shafts are connected to the stationary housing or a counterweight, on which the drive for the eccentric shaft is arranged.

According to a particularly preferred embodiment, each retaining device has a plurality of generators with at least one eccentric shaft associated therewith, which are synchronized with one another. A predetermined phase difference is provided, when desired, between the generators of the first and second retaining devices.

It will be understood that it is within the scope of the present invention, instead of eccentric shafts, to use other oscillation generators, for example as known in the prior art.

The aim is that oscillations of the retaining devices are preferably circle-like (orbital movement). The frequency as well as the rotation direction of the orbital movement of the two retaining devices can be independently adjusted from one another. Depending on the phase relation, oscillation frequency and rotation direction of the two retaining devices, a linear, elliptic or circular movement results between the tool and the workpiece, whose amplitude and frequency is adjustable in a wide range. Such movements are also known as orbital or circular oscillations.

A combination of different types of oscillation is also within the scope of the present invention, where an overlapping effect is achieved for the polishing and/or grinding movement of the tool and the workpiece by superimposing the different movements between the first and second retaining devices.

It is also within the scope of the present invention, that the amplitude, frequency or phase difference is not always held constant, but can be varied during operation, where this can also be limited to certain angular segments of the rotary movement.

According to a further preferred embodiment, the oscillation of the generators is selected such that the oscillation direction, in particular for orbital or circular oscillations, is in opposing directions (counter directional) with respect to the first and second retaining devices. Counter directional is understood here as an oscillation of the two retaining devices, whose movement direction at a certain point, preferably a contact point, is in different directions. This has the particular advantage that the direction of the resulting oscillation between the tool and workpiece, and also the type of oscillation (linear or circular) and its amplitude can be determined through the frequency, amplitude and phase relation between the two overlapping oscillations of the retaining devices.

A linear oscillation results when the oscillations have the same phase, i.e. a phase difference of 0 or an integer multiple of π. Depending on the phase relation and elongation, a circular oscillation results by using other phase differences of the oscillation generators through the resulting overlap of oscillations. Thus, the direction of the polishing or grinding movement as well as the type of grinding movement and its amplitude and position can be determined by the selection of the phase angle difference between the generator oscillations of the first and second retaining devices.

According to a further preferred embodiment, the angular speed or frequency of the oscillations is not constant, but varies at least in predetermined angular segments. This means that the retaining device or retaining devices are driven with variable angular speed, so that grinding movements can also be generated, whose end points can also reach tight angle regions.

The present invention therefore allows the generation of various types of oscillations through the alteration of the phase relation and/or oscillation frequency, which makes different treatments of workpiece surfaces possible, depending on their surface composition. The resulting superimposed oscillation has the particular advantage, that different movement patterns can be carried out depending on the workpiece to be treated, in particular to make sufficient account for the surface structure, for example with knobs or grooves.

For example with a groove, the movement direction of the two oscillations can be selected such that the resulting superimposed oscillation runs along the groove, and the surface is substantially completely worked. In addition, deeper lying edges and corners can also be handled with the polishing and/or grinding process.

According to a further preferred embodiment, the phases and/or the amplitudes and/or the frequencies of the two oscillations are varied during treatment of the surface and adapted to the surface composition of the workpiece during the course of the polishing and/or grinding process by means of a controller, so that an optimal treatment is achieved by specific adaptation of the resulting movement for every surface structure. It will be understood that the application pressure can also be varied in the course of the treatment process.

To further improve the surface quality of the workpiece to be treated, not only the polishing agent, but also the process parameters, especially the frequency, phase difference and amplitude of the polishing and/or grinding path can be varied according to a further preferred embodiment. The polishing and/or grinding path, depending on the surface quality to be achieved, lies between 0 mm and 3 mm, preferably between 0 mm and 1.5 mm, particularly preferred between 0 mm and 0.75 mm and in particular is less than 0.75 mm. The polishing and/or grinding path can be larger than 3 mm according to the present invention, where this especially occurs for relatively continuous surfaces or large workpieces to be treated.

The object of the present invention is also achieved by a method, by which an approximate form-fit connection is established between at least one treatment tool and one body to be treated. The form-fit can either be directly between the surfaces or, as described above, through the use of agents.

The treatment of the workpiece occurs according to the invention through the super- imposition of at least two oscillations, where oscillations are present at the tool or the workpiece and are preferably orbital oscillations. The oscillations according to the

present invention are present in predetermined phases, which lie preferably between 0° and 180°.

By changing the oscillation path, in particular by changing the oscillation at the tool or workpiece, the oscillation path can be varied depending on the surface form or structure to be treated, specifically by altering the amplitude, frequency and/or phase angle difference. Specific grinding paths can be determined, where discontinuous changes in the surface can be accounted for to achieve the desired surface quality.

According to a further preferred embodiment of the method, an apparatus is employed for carrying out the polishing and/or grinding process, as described above.

The apparatus and method of the present invention are preferably employed for the treatment of surfaces, for example wood, glass, varnish, synthetic materials, metal, combinations thereof and the like. According to the present method, three dimensional surface structures can also be treated, which have steps, projections, knobs, rills, grooves and the like, apart from continuous flat surfaces.

Such structures include for example casting or blowing moulds, which are used to produce bottles and the like. The moulds are preferably of metal, and in the past were normally polished by hand, because the fine structure was not worked by machine. Also this problem of the prior art can be overcome by the present invention.

The invention will be explained in the following in conjunction with the preferred embodiment, without limiting the invention, in particular the possible applications of the invention. For example, it is also within the scope of the invention to use the apparatus and method for other treatment processes apart from surface treatment.

Fig. 1 shows a schematic and perspective view of the first and second retaining devices.

Fig. 2 shows a schematic diagram of the principle of the apparatus according to the invention.

Fig. 3 shows a preferred embodiment of the apparatus of the present invention.

Fig. 4 a) to 4 f) show the resulting superimposed oscillations between tool and work- piece with the same phase and different amplitudes.

Fig. 5 a) to 5 h) show the resulting superimposed oscillations between tool and work- piece.

A perspective illustration of the retaining devices according to a preferred embodiment of the present invention is shown in Fig. 1, where the tool 4 is mounted by a plain flange 6 to the oscillator plate 1 of the first retaining device 10. The connection makes possible the transmission of inertial, gravitational and shearing forces, which act substantially vertical to the guide path of the plain flange. In a preferred embodiment, a wrap-around ledge can be provided to prevent lifting of the carriage. Further, the sides can be guided by adjustable wedge-shaped ledges, with little play.

A swallowtail coupling can be provided as an alternative to the plain flange, which prevents lifting of the carriage, among other things, by the inclinations of the side surfaces. An advantage here is the small height dimension, as well as the good damping behavior. The side guidance can also be configured with adjustable wedge-shaped ledges, with little play.

It will be understood that other mounting means may be used, for example a prisma guide or a cylinder guide, as known in the prior art. A further advantage of such guide means is that both the tool 4 and also the workpiece 5 can be relatively simply and rapidly exchanged.

The workpiece mount 3 according to the embodiment of Fig. 1 is a holding means encompassing the workpiece at least partially on five sides. The workpiece can be sim-

ply inserted and fixed. In the illustrated example, a cylindrical half-shell is shown, where a grinding agent 12 in the form of a paste is placed between the tool 4 and the workpiece 5. When closing the apparatus, the corresponding compressive force distributes the paste throughout the gap between the tool and the workpiece and therefore provides a uniform distribution of polishing or grinding material over the surface.

The workpiece mount 3 is connected to a oscillator plate 2 and together they form the second retaining device 11. In the closed condition, a compressive force acts between the tool 4 and the workpiece 5, which is preferably substantially perpendicular to the oscillator plates. This force is illustrated in Fig. 1 by the arrows Fw and F _F .

As can be taken from Fig. 1, the surface of the tool corresponds substantially to the form of the workpiece surface. The arrows 7 and 8 indicate schematically the preferred oscillation movement in the form of an orbital movement of the oscillator plates 1 and 2, which results for example in a linear or circular movement in the contact region between the tool and the workpiece. The oscillator plate 1, as seen from above, moves in counterclockwise direction and the oscillator plate 2 in clockwise direction, so that the movement in the contact region is counterdirectional.

Fig. 2 shows a schematic drawing of the principles of the treatment apparatus, where the tool 4 as a first body is arranged in the upper portion and the workpiece 5 as a second body is arranged in the lower portion of the apparatus.

The first oscillator plate 1 of the first retaining device 10 is connected to a drive plate 21 through a frame 20, which may be equipped with struts. The drive plate 21 is connected to an end 23 of the eccentric shaft 22 by corresponding bearings. In the present embodiment, the drive plate 21 comprises a plurality of eccentric shafts, which are moved by corresponding drives 24. The drives 24 are arranged with the respective eccentric shafts 22 on a base plate 29, so that the drive plate 21 is caused to oscillate through rotation of the eccentric shafts.

In addition, the eccentric shafts 22 can be provided with balancing weights to compensate for imbalance caused by the non-symmetrical weight distribution of the moved masses. The bearings as well as the mechanical connections and possibly the drive units are then subjected to reduced transverse and/or shear forces. On the whole, a smooth movement of the drive plates or drive means is guaranteed and the danger of damage is at least reduced.

The drive plate 21 is mounted to the eccentric shaft 22 substantially for orbital movement, where the connection between the eccentric shaft 22 and the drive plate 21 is configured so that the drive plate can be displaced by a predetermined amount in a direction perpendicular to the orbital movement. This freedom of movement is necessary both for closing the gap between the tool 4 and the workpiece 5 and also for transmitting compressive force.

The compressive force in the present embodiment is provided by a pressure cylinder 25. It does not act directly on the drive plate 21, but is connected to the drive plate 21 through the suspension 26 and the plunger 27. The drive plate 21 and the pressure cylinder 25 are at least substantially decoupled by the suspension 26 in respect of the forces directed perpendicularly, so that the pressure cylinder or the plunger are subject to substantially no shear and/or transverse forces. To achieve a uniform distribution of the pressing force over the drive plate 21 , the plate is configured to be symmetrical in a preferred embodiment and has an opening 28 in its central region, through which the pressure cylinder 25 and the plunger 27 are operable.

It will be understood that it is also in the scope of the present invention to provide a plurality of pressure cylinders, to achieve a uniform force distribution on the plunger 27.

The workpiece 5 is connected to a second oscillator plate 2 of the retaining device 11 via the workpiece mount 3, where the second oscillator plate 2 is set to oscillate, just as the first oscillator plate 1, by the generators 29, which in the present embodiment are provided as driven eccentric shafts 22. In contrast to the suspension of the tool 4,

the workpiece 5 is only caused to oscillate by the generators 29 and in particular, is not adjustable in height during operation. However, it is also within the scope of the present invention, that the retaining device of the workpiece 5 be movably arranged with respect to the tool 4, so that the closure movement takes place through both retaining devices or only through the retaining device 11.

The treatment process takes place according to the invention through the superposi- tioning of oscillations, which are produced by the generators 24 of the first retaining device 10 and the generators 29 of the second retaining device 11. Such superposi- tioning generates a resulting relative movement between the tool and the workpiece, which according to the invention is employed for the treatment by grinding and/or polishing the surfaces.

Fig. 3 shows a schematic view of a preferred embodiment of the present apparatus which also comprises two retaining devices 10 and 11, as in Fig. 2, which have corresponding drives 24 and 29, with the corresponding eccentric shafts 22. These cause the drive plates 1 and 2 to rotate or oscillate. The drive plate 1 is connected to the drive plate 21 by a frame 20, where the two drive plates 1 and 21 comprise bearings 35 to receive the eccentric shafts in order to transmit the movement of the eccentric shafts 22 or the eccenter 32 to the plates. The plate 21 in the illustrated embodiment includes a mounting 30, for receiving a rod or a cable 31, which together with the bearing forms the suspension 26. The force Fw applied by the pressure cylinder 25 to the plate 21 is transmitted through this suspension by the frame member 34 to the drive plates 21 and 1. Further, the frame 20 with the two drive plates and the frame member 34 is movable along the force path, so that the tool and the workpiece come into contact with one another or are moved toward one another to a predetermined spacing. The frame member 34 has openings 37 in the region of the frame 20, which allow the horizontal oscillation of the drive plates 1 and 21 and the suspension 26. In addition, the frame 20 has an opening 28, through which the hydraulic cylinder 25 is passed. The opening is selected to be in a region, so that contact between the hydraulic cylinder and the drive plate 21 is avoided.

The workpiece 5 at the lower side of the apparatus, according to the present embodiment, is arranged on the drive plate 2, which is caused to oscillate via the bearings and the corresponding driven eccentric shaft 22. The lower drive plate 42 is connected with the frame member 40 via a corresponding suspension 51, to accommodate the pressing force, which in operation, is transferred from the hydraulic cylinder 25 and the tool 4 to the workpiece 5 and the corresponding drive plate 2. The frame 40 itself is fixed to the housing 50 of the apparatus and provides the corresponding counterforce Fp in operation. The frame 40 comprises openings 47 both for the frame and also for the suspension 51 to allow oscillating movement of the drive plate 2. The eccentric shaft 22 is supported to the frame 40 via the bearing 46, so that the relative movement between the frame 40 and the drive plate 2 or drive plate 42 is provided.

The resulting superimposed oscillation, as already discussed, results out of the oscillation of the two drive plates 1 and 2, which according to the present invention are caused to oscillate by one or a plurality of generators. The oscillations can be in the same direction or counterdirectional, where apart from the direction, the frequency, the amplitude and the phase difference of each oscillation is variable.

In a preferred embodiment, the oscillations are both in the same direction, so that the resulting superimposed oscillation is linear or circular, depending on the phase difference, as long as the frequency of the two oscillations is constant. The elongation allows determination of the path or the area, which can be worked by the resulting movement.

Fig. 4 illustrates a number of possible resulting oscillations as a coordinate diagram which can be generated by superimposing two orbital movements, when the two movements are in the same phase and in opposing directions. This results in linear oscillations between the tool and the workpiece, whose direction is determined by the relationship of the amplitudes of the two orbital movements.

For example, the result of overlapping two circular oscillations is shown in Fig. 4a, where the first oscillation has an amplitude of E _x =O and the second oscillation in am-

plitude of E _y =1. One obtains an oscillation, which is directed along the y-axis. If one then varies the magnitude of the amplitudes with respect to one another, one obtains a result rotated by a certain angle (oscillation vector) depending on the respective amplitude relationship. If the two amplitudes are the same (E _x = E _y = 1 ) as shown in Fig. 4c, one obtains an oscillation rotated by 45°. As can readily be taken from the illustration, the oscillation vector can be arbitrarily determined with respect to the zero point, depending on the selected relationship of the amplitudes. Apart from altering the direction, the invention also encompasses a variation of the amplitudes of the resulting oscillation.

In the following Table 1 , the amplitudes E _x and E _y for the superimposed oscillations illustrated in Fig. 4 are given, where 1 indicates a maximal amplitude and 0 indicates a minimal amplitude.

Table 1

If the superimposed oscillations do not have the same phase, the resulting oscillation vector of the superimposed oscillation moves for example on a circular path. By changing the phase shift and the difference of the angular speed between the two basic oscillations, the vector can be caused to follow various movements in the xy-plane, so that the resulting path is in the form of circles or ellipses.

Fig. 5a and 5e show a particular case, in which the phase angle difference is 0 or an integer multiple of π, so that a straight line is generated. If the basic oscillations have a phase angle difference of 90° or an arbitrary multiple of ττ/2, the movement of the oscillation vector follows a circular path. The curves of the paths given in the figures result from the determination of the elongations at the various time points and the connection of the resulting end points. Such figures are also known as Lissajous figures and arise by altering the angular speed, the phase difference and the elongation.

When overlapping the two basic oscillations, these variations lead to the resulting path, which can be a linear movement (Fig. 4, in different directions) as well as an elliptic movement (Figs. 5b, 5d, 5f, 5h) or a circular movement (Fig. 5c, 5g). In addition, the rotary direction of the resulting oscillation vector can be altered by the direction of the phase shift, where for example in Fig. 5c a right hand circular oscillation and in Fig. 5g a left hand circular oscillation results.

In the following Table 2, the phase angle ωt and the magnitude of the amplitudes E _x and Ey are given for the superimposed oscillations illustrated in Fig. 5. The results derive from overlapping of x and y oscillations with the same amplitude, but also of different relative phases. The components E _x and E _y are both given in real and complex form.

Table 2

The resulting vectors are indicated in Table 2 in the x and y direction using complex numbers (i) in order to simplify the data on the phase angle difference, where a distinction is to be made between the real and imaginary components of the complex oscillation vector.

This illustration also makes it clear that a plurality of oscillations can be generated by selection of the phase angle difference, which allows variation in the type of oscillation, the orientation and also in the rotary direction.

Considering this capability of varying the resulting oscillation, it becomes clear that a movement pattern of the apparatus is provided for the treatment of surfaces, which can be adjusted to the surface composition or also the intensity of the treatment to be performed. It will be understood that it also possible to determine or to vary the parameters, substantially continuously, by means of a controller, so that changes in the process operation, i.e. in the movement pattern, can be made during the process.