EP3288712B1 - Device for machining surfaces - Google Patents

Description

TECHNICAL FIELD

The invention relates to a device for the automated machining or smoothing of surfaces of workpieces, for example for grinding workpiece surfaces.

BACKGROUND

The final processing of surfaces in small series production is still carried out by hand in most cases. This takes a lot of time and must be carried out by an experienced skilled worker. The higher quality the final surface has to be, the more complex this step is. The surface of a car hood can be cited as an example, where the requirements for the quality of the surface are relatively high. To produce such a surface quality, there is no adequate solution for small series other than manual work with a (hand) grinding machine. The grinding results of known automatic grinders are often inadequate or require long setting times or lead-in and run-out areas in order to avoid irregularities in the grinding pattern being visible on the final surface. These irregularities arise due to vibrations in the grinding belt or too sluggish control of the contact force. The contact force is the force with which the sanding belt acts on the workpiece surface. In the publication JP S63-089263 A device is described that regulates the contact force through suitable storage. However, due to the high inertia of the grinding machine, the above-mentioned phenomena inevitably occur due to the inertia. Out of DE 198 25 698 A1 A belt sander is known which has a contact disk and several deflection rollers around which a sanding belt is guided. The contact disk is rotatably mounted on a holder, which can be moved by means of a linear drive, and can tension the belt in such a way that grinding is prevented Workpiece is possible at different angles. JP 2009 016759 A discloses an apparatus for grinding a semiconductor wafer, having three fixed deflection rollers around which a belt 31 is guided, and two tension rollers which can be displaced by a guide part in order to contact and tension the belt. JP 2002 301659 A and EP 0 477 737 A1 each disclose a belt grinding machine, whereby the entire machine moves when a workpiece is processed. DE 100 13 340 A1 , on which the preamble of claims 1 and 11 is based, discloses a belt grinding machine with an arrangement of at least one mounted drive roller or deflection roller, an adjustable tension roller with a force element loading the tension roller, a contact element that can be moved in at least one direction with a contact element in in this direction relative to a pressure element loading the workpiece and a sanding belt guided around the contact element, the drive roller or deflection roller and the tension roller. The contact element and the force element of the tension roller are functionally coupled to one another in such a way that the force element changes the position of the tension roller depending on the respective changes in position of the contact element that serve as a guide variable in such a way that a predeterminable pressure force between the contact element and the workpiece changes independently of the respective changes in position of the contact element sets.

The object on which the invention is based is therefore to provide a device which enables complex grinding or polishing tasks to be carried out partially or fully automatically with improved quality.

SUMMARY

The stated object can be achieved, for example, by a device according to claim 1 or by a method according to claim 8 and by a system according to claim 11. Different embodiments and further developments are the subject of the dependent claims.

A device for processing a surface of a workpiece is described below. According to an exemplary embodiment, the device comprises a frame and a roller carrier on which a first roller is rotatably mounted and which is mounted on the frame so as to be displaceable along a first direction. The device comprises at least a second roller, which is mounted on the frame, and a belt which is guided at least around the two rollers, and due to the tension of which a resulting belt force acts on the roller carrier, the first roller only serving as a deflection roller. The device further comprises a tension roller for adjusting a pretensioning force in the band. The device further includes an actuator mechanically coupled to the frame and the roller carrier such that an adjustable actuator force acts between the frame and the first roller along the first direction. The band is guided with the help of the second roller - or with the help of the second roller and further rollers - in such a way that the resulting band force acting on the roller carrier acts approximately in a second direction, which is orthogonal to the first direction, when the actuator is deflected to a desired extent is. The actuator works purely force-controlled.

Furthermore, a method for surface processing of a workpiece is described. According to an exemplary embodiment of the method, a device is used for this purpose which has a frame, a roller carrier on which a first roller is rotatably mounted and which is mounted on the frame so as to be displaceable along a first direction, an actuator which is mechanically connected to the frame and the roller carrier is coupled, a second roller which is mounted on the frame, and a belt which is guided around the first and the second roller and which exerts a resulting belt force on the roller carrier, the first roller serving only as a deflection roller. The device further comprises a tension roller for adjusting a pretensioning force in the band. The method includes positioning the workpiece on the first roller, measuring a contact force between the first roller and the workpiece, and adjusting a contact force between the first roller and the workpiece by adjusting a force acting between the frame and the actuator. When positioning the workpiece, it is positioned relative to the device in such a way that the deflection of the actuator corresponds to its target deflection. At the target deflection, the resulting belt force acting on the roller carrier acts approximately in one second direction that is orthogonal to the first direction. The reaction of the belt force on the actuator can therefore theoretically be reduced to zero. The actuator works purely force-controlled.

Furthermore, a system for robot-assisted surface processing of workpieces is described. According to one exemplary embodiment, the system comprises a processing device and a manipulator for positioning the workpiece relative to the processing device. This has a frame and a roller carrier on which a first roller is rotatably mounted and which is mounted on the frame so as to be displaceable along a first direction. The processing device comprises at least a second roller, which is mounted on the frame, and a belt which is guided at least around the two rollers, and due to the tension of which a resulting belt force acts on the roller carrier, the first roller only serving as a deflection roller. The system further includes a tension roller for adjusting a pre-tension force in the belt. The processing device further comprises an actuator that is mechanically coupled to the frame and the roller carrier such that an adjustable actuator force acts between the frame and the first roller along the first direction. The band is guided with the help of the second roller - or with the help of the second roller and further rollers - in such a way that the resulting band force acting on the roller carrier acts approximately in a second direction, which is orthogonal to the first direction, when the actuator is deflected to a desired extent is. The actuator works purely in a force-controlled manner and a position of the workpiece relative to the processing device is only determined by the manipulator.

BRIEF DESCRIPTION OF THE ILLUSTRATIONS

• Figur 1 zeigt eine Bandschleifvorrichtung gemäß einem nicht durch die Ansprüche abgedeckten Beispiel, bei der die Kontaktkraft zwischen Werkstück und Schleifband mit Hilfe eines Manipulators erzeugt wird.
• Figur 2 zeigt eine Bandschleifvorrichtung gemäß einem nicht durch die Ansprüche abgedeckten Beispiel mit nachgiebiger Lagerung einer ersten Rolle der Bandschleifvorrichtung.
• Figur 3 zeigt eine Bandschleifvorrichtung gemäß einem Ausführungsbeispiel der Erfindung, bei dem die erste Rolle um einen Rollensatz ergänzt worden ist.
• Figur 4 zeigt ein Detail der Vorrichtung aus Fig. 3 zur besseren Darstellung der auf die Rollen wirkenden Kräfte im Arbeitspunkt (Fig. 4a und 4c) und außerhalb des Arbeitspunktes (Fig. 4b).
• Figur 5 zeigt ein weiteres Ausführungsbeispiel, bei dem die resultierende Zugkraft im Schleifband und die Kontaktkraft zwischen Werkstück und Schleifvorrichtung annähernd orthogonal zueinander sind.
• Figur 6a zeigt ein Detail der Vorrichtung aus Fig. 5 zur besseren Darstellung der auf die Rollen wirkenden Kräfte und Figur 6b zeigt eine Alternative zu Fig. 6a.
• Figur 7 zeigt ein weiteres Beispiel, das nicht durch die Ansprüche abgedeckt ist, als Alternative zum Beispiel aus Fig. 3.
• Figur 8 zeigt eine Variante, bei der nicht das Werkstück, sondern die Schleifvorrichtung von einem Manipulator geführt sind.
• Figur 9 zeigt ein alternatives Beispiel, das nicht durch die Ansprüche abgedeckt ist, zur Entkopplung von Bandkräften und Aktorkraft.
• Figur 10 zeigt ein Blockschaltbild betreffend die Regelung der Kontaktkraft in einer Vorrichtung gemäß den dargestellten Ausführungsbeispielen.

The invention is explained in more detail below using the examples shown in the figures. The illustrations are not necessarily to scale and the invention is not limited only to the aspects shown. Rather, emphasis is placed on presenting the principles underlying the invention. Shown in the pictures:

• Figure 1 shows a belt grinding device according to an example not covered by the claims, in which the contact force between the workpiece and the grinding belt is generated with the aid of a manipulator.
• Figure 2 shows a belt grinding device according to an example not covered by the claims with flexible mounting of a first roller of the belt grinding device.
• Figure 3 shows a belt grinding device according to an embodiment of the invention, in which the first roller has been supplemented by a set of rollers.
• Figure 4 shows a detail of the device Fig. 3 for a better representation of the forces acting on the rollers at the working point ( Figs. 4a and 4c ) and outside the operating point ( Fig. 4b ).
• Figure 5 shows a further exemplary embodiment in which the resulting tensile force in the grinding belt and the contact force between the workpiece and the grinding device are approximately orthogonal to one another.
• Figure 6a shows a detail of the device Fig. 5 for a better representation of the forces acting on the rollers and Figure 6b shows an alternative to Fig. 6a .
• Figure 7 shows another example, not covered by the claims, as an alternative to the example Fig. 3 .
• Figure 8 shows a variant in which not the workpiece but the grinding device is guided by a manipulator.
• Figure 9 shows an alternative example, not covered by the claims, for decoupling band forces and actuator force.
• Figure 10 shows a block diagram relating to the control of the contact force in a device according to the exemplary embodiments shown.

In the figures, the same reference numbers designate the same or similar components, each with the same or similar meaning.

DETAILED DESCRIPTION

The examples of the invention described here are described in connection with a belt grinding device 100. Other applications of the invention, for example for surface coating or polishing surfaces, are also possible.

The final processing of technically and optically high-quality surfaces requires very high precision in production. Compliance with the required accuracy is made more difficult by the fact that the condition of the workpiece surface 200a changes over the processing period. That's why the finishing of the surfaces in many areas, especially in small series, is predominantly done by hand. An example of a grinding device 100 known per se is shown in Figure 1 shown. The grinding device 100 is stationary and has a rotating grinding belt 102, which is guided over at least two rollers 101, 103. In this example it is assumed that the belt rotates clockwise. The sanding belt 102 is tensioned by a tensioning element 105 (tensioning roller), which is mounted in a linearly displaceable manner by a suitable bearing 130 (for example by means of a plain bearing). The components (rollers 101 and 103, clamping element 105) are connected to a frame 160 (eg a machine bed or a housing part) using one or more supports 401, 402, 403.

For processing, the surface 200a of a workpiece 200 to be processed is pressed against the sanding belt 102 in the area of the first roller 101 while the sanding belt 102 is running. The contact force F _K (grinding force) required for this can be set, for example, manually or with the help of a manipulator 150, which holds the workpiece. The manipulator 150 can be, for example, a standard industrial robot (with six degrees of freedom). Alternatively, however, another manually or mechanically operated clamping and/or pressing device can also be used as a manipulator. The contact force F _K creates friction between the workpiece surface 200a and the Grinding belt 102 and material removal occurs. The main influencing factors for the machining result are the contact force F _K per surface (support surface on which the sanding belt 102 and the surface of the workpiece 200a touch), hereinafter also referred to as contact pressure, and the rotational speed of the sanding belt 102. Since the contact surface is between the workpiece and grinding belt 102 generally does not change significantly during a grinding process, contact pressure and contact force F _K are de facto proportional. In the area of corners and edges, the contact force (ie its target value) can be reduced accordingly due to the smaller contact surface.

For a uniform grinding result, a correct setting (ie regulation) of the contact force F _K is desirable throughout the entire machining process. Force control by the generally "rigid" manipulator proves to be difficult in known automated grinding devices, especially when placing the workpiece 200 on the grinding belt. In general, transient disturbances (force peaks) in the contact force F _K are very difficult to compensate for through control using conventional means. This is usually a result of the inertia of the moving parts of the manipulator 150 and limitations in the actuators (minimum dead time, maximum force or torque, etc.). Insufficient force control results in inhomogeneous micrographs with chatter marks. Chatter marks are surface irregularities caused by inadequate control of the contact force F _K. In areas in which a (temporarily) higher contact force F _K acts, depressions are created in the workpiece surface 200a due to the higher material removal. At the points where there is temporarily a lower contact force F _K , less material is removed and increases remain. An experienced skilled worker can correct these inaccuracies when sanding by hand. When the workpiece surface 200a is automatically pressed against the grinding belt 102, especially with the help of a manipulator 150, these inaccuracies cannot be easily compensated for. Due to the high inertia of the manipulator 150, the rapid adaptation to the prevailing grinding situation is associated with large time delays. In addition, the manipulator can 150 oscillate to varying degrees around its predefined target position, which can lead to an uneven grinding pattern.

Instead of moving the workpiece 200 with the help of a manipulator, it is also possible to clamp the workpiece 200 and mount the grinding machine in a movable manner. In this case, the actuator that controls the grinding force would be coupled to the grinder so that the grinder presses against the (stationary) workpiece. In this case, too, there is the problem that the mass of the grinding machine and therefore its inertia is relatively large and consequently the same problem exists as with the variant described above.

In the in Fig. 2 In the example shown, which is not covered by the claims, the workpiece 200 is held and positioned by a manipulator 150. However, the manipulator 150 only requires a simple position control; the contact force control is implemented in the grinding machine 100 - as described below. Relatively inexpensive manipulators (e.g. industrial robots) can therefore be used that can hold the workpiece at a desired position and move it along a desired trajectory. In particular, no expensive force or torque sensors are necessary in the joints of the manipulator. In the present example, the actuator 302 used for force control can be a simple linear actuator, for example an actuator with low static friction and passive compliance. Possible examples include pneumatic cylinders, air muscles, bellows cylinders, and electric direct drives (without gearboxes). In the present example, a pneumatic cylinder is used as actuator 302.

The actuator 302 does not act on the grinding machine 100 as a whole, but only on that roller of the grinding machine 100 that presses against the workpiece during operation (ie on the roller 101). The roller 101 is mounted on the frame 160 in a linearly displaceable manner (linear guide 140) (via the roller carrier 401). The actuator 302 acts between the roller carrier 401 and the frame 160. In the present example, the actuator is mounted on the roller carrier 401 and on a further carrier 404, which is rigidly connected to the frame 160. According to the control of the actuator 302, the Roller 101 exerts an actuator force F _A , which acts along the direction of movement (x-direction) of the linear guide 140. Due to the comparatively low mass of the first roller 101 (and the roller carrier 401), only small inertia forces occur on the actuator 302.

Otherwise, the grinding device is in accordance with Fig. 2 constructed in the same way as the grinding device in the previous example Fig. 1 . The second role 103 is mounted immovably on the frame 160 via the (roller) carrier 403. In this context, immovable does not mean that the position of the roller 103 cannot be changed, for example to set a suitable tension in the sanding belt. However, the position of the roller 103 does not change during operation of the device (for example, during a grinding process). The roller 103 is driven (motor 104), whereas the roller 101 only serves as a deflection roller. The sanding belt 102 is guided around both rollers 101 and 103. As in the example Fig. 1 A tensioning device can be provided for adjusting a pretension of the sanding belt. The tensioning device can, for example, have one or more tension rollers 105 which rest on the belt 102 and which can be moved approximately at right angles to the grinding belt 102 in order to tension the grinding belt 102. In the present example, the tension rollers 105 are mounted on the roller carrier 402 with the aid of a linear guide 130, which in turn is rigidly connected to the frame 160. The pretension can be generated, for example, with the help of a spring which acts between the roller carrier 402 and the tension roller (or tension rollers) 105.

Das bedeutet, dass die resultierende Bandkraft F_{B, x} bei der Regelung der Kontaktkraft F_K berücksichtigt werden muss. Die Bandkraft F_{B, x} muss dazu bekannt sein. Diese kann dazu entweder gemessen werden (z.B. mittels eines Kraftsensors in der Spannvorrichtung und des Antriebsmoments des Motors) oder mit Hilfe eines mathematischen Modells abgeschätzt werden. Durch geeignete Umlenkung des Schleifbandes kann jedoch der Einfluss der Bandkräfte F_B1, F_B2 auf die Kontaktkraft F_K reduziert (im Idealfall eliminiert) werden. In anderen Worten, Aktorkraft F_A und die resultierende Bandkraft F_B,x in Wirkrichtung (x-Richtung) des Aktors 302 werden entkoppelt. Ein Beispiel für eine geeignete Umlenkung des Schleifbandes 102 ist in Fig. 3 dargestellt.The forces acting in the sanding belt 102 are in Fig. 2 shown as band forces F _B1 (force in the upper part 102a of the band 102) and F _B2 (force in the lower part 102b of the band 102), whereby both forces F _B1 and F _B2 each have a force component in the x direction (F _B1,x or . F _B2,x ) and have a force component in the y direction (F _B1,y or F _B1,y ). The resulting belt force F _B,y acting on the roller 101 in the y direction (ie F _B,y = F _B1,y +F _B2,y ) is absorbed by the linear guide 140 and the tensioning device. However, the resulting belt force F _B,x acting on the roller 101 in the x direction (ie F _B,x =F _B1,x +F _B2,x ) also acts on the actuator 302 and thus against the actuator force F _A. The contact force F _K applies in the stationary case $${\mathrm{F}}_{\mathrm{K}}={\mathrm{F}}_{\mathrm{A}}+{\mathrm{F}}_{\mathrm{b}\mathrm{,x}}.$$

This means that the resulting belt force F _{B, x} must be taken into account when controlling the contact force F _K. The band force F _{B, x} must be known. This can either be measured (e.g. using a force sensor in the clamping device and the drive torque of the motor) or estimated using a mathematical model. However, by appropriately redirecting the grinding belt, the influence of the belt forces F _B1 , F _B2 on the contact force F _K can be reduced (ideally eliminated). In other words, actuator force F _A and the resulting belt force F _B,x in the effective direction (x direction) of actuator 302 are decoupled. An example of a suitable deflection of the sanding belt 102 is shown in Fig. 3 shown.

This in Fig. 3 The example shown essentially corresponds to the previous example Fig. 2 , whereby two further deflection rollers 101a and 101b are arranged on the roller carrier 401 in addition to the deflection roller 101. Furthermore, two further deflection rollers 121a, 121b are provided, which are mounted immovably on the frame 160. As in the previous example, the roller carrier 401 with the rollers 101, 101a and 101b is mounted on the frame 160 by means of the linear guide 140, the linear guide enabling the roller carrier 401 to be displaced in the horizontal direction (x direction) and blocking other degrees of freedom. The deflection rollers 101a and 101b as well as the deflection rollers 121a and 121b are arranged so that - at a nominal deflection x ₀ (target deflection) of the actuator 302 - the resulting belt force F _B 'acting on the roller carrier 401 is the actuator force F _A (at least approximately) is at a right angle. In other words, the x component F _B,x 'of the resulting belt force F _B' is approximately zero, with the linear guide 140 allowing force transmission from the actuator 302 to the roller carrier 401 only in the x direction. As in the previous example, the resulting band force F _B ' is equal to the sum of the band force F _B1 ' in the upper part 102a of the band 102 and the band force F _B2 ' in the lower part 102b of the band 102 (F _B ' = F _B1 ' + F _B2 '). If the deflection x of the actuator 302 corresponds to the nominal deflection x ₀ , this is referred to as the operating point x=x ₀ .

Figure 4 shows the on a roll carrier 401 (e.g. from Fig. 3 ) acting forces in detail. Fig. 4a shows a deflection x=x ₀ of the actuator at an operating point. Fig. 4c is a variant of Fig. 4a , in which the actuator force F _A attacks exactly in the center of the roller carrier 401, so that all forces cancel out at the operating point and no torque acts on the roller carrier 4. With a deflection x≠x ₀ of the actuator, the x component F _B,x ' of the belt force F _B ' is no longer zero, but is F _B,x ' = F _B '·sin(ϕ), where ϕ is the angular deviation of the force vector F _B 'from the y-direction. This means that with an angular deviation of 3 degrees, around 5% of the resulting belt force F _B ' would act in the x direction and thus on the actuator 302 as a disturbing force. When designing the grinding machine, it can be constructed in such a way that the angular deviation ϕ remains so small during operation that this disruptive force remains negligible. In this context, it should be noted that (only) the force F _A exerted by the actuator 302 (and thus the contact force F _K ) is regulated. The actual deflection x of the actuator 302 depends on the position of the workpiece 200 during grinding operation, which in turn is set by the manipulator 150. However, the manipulator is position-controlled and can position the workpiece so that the actuator deflection x corresponds to the desired working point x ₀ , at which the angular deviation ϕ is zero.

In Fig. 4a and Fig. 4b the relevant forces on the rollers 101, 101a, 101b mounted on the roller carrier 401 are shown again in detail. For the sake of clarity, only the rollers 101, 101a and 101b, which are mounted displaceably in the x direction, as well as the sanding belt 102 and the workpiece 200 are shown. The position of the axes of rotation of the rollers 101, 101a and 101b relative to one another is fixed and does not change during operation. The actuator force F _A and the contact force F _K act on the rollers in the x direction (actuator and contact forces in other directions would be absorbed by the linear guide 140). In Fig. 4a the actuator deflection x corresponds to the operating point x ₀ and consequently the belt forces F _B1 ' and F _B2 ' acting on the rollers 101a and 101b are oriented in the vertical direction and have no component in the horizontal direction (x direction). Consequently, the actuator force F _A and the resulting belt force F _B '=F _B1 '+F _B2 ' are decoupled. This means that the band forces F _B1 ' and F _B2 ' do not act back on the actuator 302. In Fig. 4b a situation is shown in which the Workpiece is shifted out of the working point, that is, the actuator deflection is not equal to x ₀ and consequently the belt forces F _B1 'and F _B2 ' acting on the rollers 101a and 101b are no longer (exclusively) oriented in the vertical direction, but at an angle ϕ tilted relative to the y direction. As already mentioned, this has the consequence that the resulting band force F _B ' has a component in the x direction, ie F _B,x ' = |F _B '|·sin(ϕ). This force component F _B,x 'acts back on the actuator and is either compensated for by the force control or a control error occurs in the amount of the belt force component F _B,x '. If the workpiece is guided and positioned by a manipulator 150, it can be ensured that the workpiece is always at the working point and consequently the actuator force F _A and the belt forces F _B1 ', F _B2 ' acting on the roller 101 are decoupled. At this point it should be mentioned again that the actuator 302 only acts on the roller carrier 401, which carries the deflection rollers 101, 101a, 101b, and not on the entire grinding device. In the variant in Fig. 4c , the actuator force acts exactly at the center point C, so that the clamping forces F _B1 ', F _B2 ' and the friction force F _R cancel each other out. In the same way, contact force F _K and actuator force F _A cancel each other out. Because the "lever" between the point of application of the respective force F _B1 ', F _B2 ' and F _R and the center C is always the same, no torques act (the sum of all moments is zero). There is then no - possibly disturbing - torque load on the actuator.

Fig. 5 shows an alternative embodiment of the grinding device 100, which is also suitable for decoupling the actuator force F _A and the belt forces F _B1 , F _B2 . Essentially, the grinding device 100 is constructed in the same way as that in the previous example Fig. 4 . However, the linear guide 140 of the roller carrier 401 and the actuator 302 are compared to the example Fig. 4 rotated by 90 degrees. For this purpose, the frame 160 includes an arm 402 on which the roller carrier 401 is mounted (with the help of the linear guide 140). The actuator 302 acts in the vertical direction (x direction) between the arm 402 of the frame 160 and the roller carrier 401. The coordinate system is also rotated by 90 degrees compared to the previous example, so that the effective direction of the actuator 302 is the x- direction is. Additional deflection rollers are not essential in this exemplary embodiment necessary. The sanding belt 102 is only guided around the deflection roller 101 and the roller 103 (driven by the motor 104). As in the previous examples, a tensioning device with a tension roller 105 ensures the necessary pretension of the sanding belt 102.

The belt forces acting on the displaceably mounted deflection roller are designated F _B1 (force in the upper belt part) and F _B2 (force in the lower belt part). The force components F _B1,x and F _B2,x in the x direction at least partially compensate each other (F _B1,x >0 and F _B2,x <0), so that the resulting force component in the x direction F _B1,x +F _B2,x is negligibly small. With a suitable design of the grinding device, the resulting force F _B1,x +F _B2,x is equal to zero and there is no reaction of the belt forces F _B1 and F _B2 on the actuator 302. Fig. 6a corresponds to the situation in Fig. 5 , in which the grinding belt (relative to the y-axis) runs at an angle ϕ ₂ to and at an angle ϕ ₁ from the deflection roller 101 (clockwise direction). The force component in the x direction of the upper band force F _B1 is therefore |F _B1 |·sin(ϕ ₁ ), and the force component in the x direction of the lower band force F _B2 is equal to -|F _B2 |·sin(ϕ ₂ ). With a suitable design of the grinding device, the resulting belt force disappears in the x-direction |F _B1 |·sin(ϕ ₁ )-|F _B2 |·sin(ϕ ₂ ) and there is no reaction on the actuator 302 (for example because ϕ ₁ =ϕ ₂ and |F _B1 |=|F _B2 |). In the modified example Fig. 6b Two deflection rollers 121a and 121b, which are firmly mounted on the frame 160, ensure that the angles ϕ ₁ and ϕ ₂ are equal to zero, so that the belt runs horizontally back and forth to the roller 101. Consequently, in this case, the resulting belt forces in the x direction are zero, provided that the factory return and thus the actuator 302 are at the operating point (x=x ₀ ). However, as with reference to the previous example ( Fig. 3 ) explained - set with the help of the manipulator 150.

The Figures 7a and 7b show devices which are not covered by the claims. In the example in Fig. 7a Two rollers 101a and 101b are arranged on the roller carrier 401, on which the actuator 302 also acts. The belt 102 runs over the two rollers 101a, 101b essentially at right angles to the direction of action of the actuator 302. The workpiece 200 can be processed (eg ground or polished) between the rollers 101a, 101b; the tape can follow the contour of the workpiece 200 adjust. Otherwise the example is as follows Fig. 7a constructed in the same way as the example Fig. 3 . In order to avoid repetitions, we will therefore refer to the explanations Fig. 3 referred. The alternative Fig. 7b essentially corresponds to the previous example Fig. 7a with the only difference that no rollers are arranged on the carrier 401 '. The carrier 401' (sliding carriage) instead has a sliding surface 101c along which the belt can slide essentially at right angles to the effective direction of the actuator 302. In both examples, the band 102 runs essentially perpendicular to the effective direction of the actuator 302 at the operating point. The actuator force F _A and the contact force (reaction force) F _K (F _K =-F _A ) are therefore dependent on the band forces F _B1 ', F _B2 '. decoupled in that there is no reaction of the band forces F _B1 ', F _B2 ' on the actuator 302.

Unlike the previous exemplary embodiments, the example according to Fig. 8 It is not the workpiece that is guided by the manipulator 150, but rather the grinding machine. The frame 160 (see e.g Fig. 3 ) is therefore part of the manipulator 150 or rigidly connected to it (its tool center point TCP). The workpiece 200 can be arranged on a fixed support (not shown). Similar to the example Fig. 3 Two further deflection rollers 101a and 101b are arranged on a roller carrier 401 in addition to the deflection roller 101. Furthermore, two further deflection rollers 105 and 103 are provided, which are mounted on the manipulator 150 (a, frame 160) by means of the roller carriers 402 and 403, respectively. As in the example Fig. 3 The roller 4 can be driven with the help of a motor. The motor (not explicitly shown) can also be mounted on the carrier 402. The roller 105 on the roller carrier 402 is designed as a tension roller.

The roller carrier 401 with the rollers 101, 101a and 101b is similar to the example according to Fig. 3 slidably mounted on the manipulator, allowing the roller carrier 401 to be displaced in the x direction and blocking other degrees of freedom. The carrier 404 is also mounted on the manipulator 150. The actuator 302, which acts on the roller carrier 401, is arranged on the carrier 404. Unlike the previous examples, according to Fig. 8 no sanding belt used, but a simple belt. The tool with the frontmost roller 101 is a grinding wheel 101 '(or a other rotating tool). As in the previous examples, at a working point of the actuator (actuator deflection x=x ₀ ), the belt runs essentially at right angles to the direction of action of the actuator, so that the belt forces F _B1 ', F _B2 ' are decoupled from the actuator force and there is no reaction from the belt forces F _B1 '. ', F _B2 ' takes place on the actuator 302.

Figure 9 shows an example not covered by the claims, in which two rollers 101, 101a are arranged on an elongated roller carrier 401 at opposite ends of the roller carrier 401. The roller carrier is on the frame 160 (cf. Fig. 3 , in Fig. 9 not shown) stored slidably. Two further rollers 103 and 105 are also mounted on the frame (carriers 403 and 402), whereby the roller 105 can be driven by a motor (cf. Fig. 3 , in Fig. 9 not shown) and the other roller 103 can be part of a tensioning unit to tension the rotating belt 102. Alternatively, the tensioning unit can also be integrated in the drive (roller 105). The movable roller carrier 401 (slide) is arranged between the rollers 103 and 105; The belt running around the rollers 101, 103, 101a, 105 approximately forms a convex square in the cross-sectional view. The illustration makes it clear that the belt forces acting on the roller carrier 401 cancel each other out in the direction of action of the actuator 302, and no belt forces act back on the actuator 302, which acts on the roller carrier 401. The actuator presses the roller carrier 401 with a force F _A and thus the roller 101 onto the workpiece. The contact force F _K (reaction force) corresponds to the actuator force F _A (F _K = -F _A ).

According to Figure 9 the workpiece is guided by a manipulator 150 and positioned so that the deflection x of the actuator 302 lies at a defined working point x ₀ . The actuator 302 works purely in a force-controlled manner; the position is determined by the (position-controlled) manipulator 150. Small deviations from the operating point (e.g. due to shape and positional tolerances of the workpiece or due to limited positioning accuracy of the manipulator 150) do not lead to any significant change in the geometry of the device and the belt forces, so that the grinding force can always be specified by the force-controlled actuator 302.

Fig. 10 shows an example of a control loop for regulating the contact force F _K between the workpiece 200 and the grinding belt 102 on the deflection roller 101. With complete decoupling between the actuator force F _A and the resulting belt force F _B,x in the effective direction of the actuator (x direction), the actuator force F _A and contact force F _K are equal in magnitude but oppositely oriented, ie -F _K =F _A . If part of the resulting band force F _B acts back on the actuator 302, the amount of the contact force is the sum of the actuator force F _A and the resulting band force in the effective direction of the actuator F _B,x , ie -F _K = F _A +F _B,x .

The force measurement (force measuring unit 303) can take place directly via a force sensor integrated in the actuator 302 or coupled to it. In the case of a pneumatic actuator, however, the force measurement can also take place indirectly via the pressure p in the pneumatic actuator, taking into account the deflection x of the actuator 302. This means that the actuator force F _A (p, x) is a function of the pressure p in the actuator (e.g. in the pneumatic piston) and the deflection x of the actuator. The desired measured value F _K,m for the contact force can be determined from the measured actuator force F _A. If there is a decoupling between the resulting belt force F _B and the actuator force F _A , F _K,m =-F _A (p, x). If there is no complete decoupling between the actuator force F _A and the resulting belt force F _B,x in the effective direction of the actuator 320, an estimate or a separate measurement of the resulting belt force can be taken into account when measuring the contact force. In this case, the following applies to the measured value F _K,m : F _K,m =-F _A (p, x)-F _B,x . A control error F _E can be calculated from the measured value F _K,m for the contact force and a corresponding setpoint value F _K,s (F _E =F _K,s -F _K,m ), which is supplied to the controller 301 on the input side. The controller 301 can be, for example, a P controller, a PI controller, or a PID controller. However, other types of controllers can also be used.

Claims (12)

1. A device (100) for machining a surface of a workpiece (200a), having:

   a frame (160);

   a roller support (401) on which a first roller (101) is rotatably mounted and which is slidably mounted on the frame (160) along a first direction (x);

   a second roller (103) which is mounted on the frame (160);

   a belt (102) which is guided around the two rollers (101, 103) and due to the tension of which a resulting belt force (F_B, F_B') acts on the roller support, wherein the first roller (101) only serves as a deflection roller; and

   an idler (105) for adjusting a biasing force in the belt (102) ;

   characterized by

   an actuator (302) which is mechanically coupled to the frame (160) and the roller support (401) such that an adjustable actuator force (F_A) acts between the frame (160) and the first roller (101) along the first direction (x);

   wherein the belt is guided by means of the second roller (103) or by means of the second roller (103) and further rollers such that the resultant belt force (F_B, F_B') acting on the roller support (401) at a target deflection of the actuator (302) acts approximately in a second direction (y) which is orthogonal to the first direction (x), wherein the actuator (302) operates in a purely force-controlled manner.
2. The device according to claim 1, further having:

   a force measuring device for direct or indirect measurement of a contact force (F_K) between the first roller (101) and a workpiece (200), or between a rotating tool (101') connected to the first roller (101) and the workpiece (200), and

   a control unit which is adapted to adjust the actuator force (F_A) such that the contact force (F_K) corresponds to a predefinable setpoint value (F_K,S).
3. The device according to claim 2,

   wherein the actuator (302) is a pneumatic linear actuator, and

   wherein the force measuring device has a pressure sensor which is adapted to measure the air pressure (p) in the pneumatic linear actuator.
4. The device according to any one of claims 1 to 3,
   in which the first roller (101) is rotatably mounted on the roller support (401) about an axis of rotation, and the roller support (401) is displaceable along the first direction (x) relative to the frame (160) by means of a linear guide (140).
5. The device according to any one of claims 1 to 4,
   wherein-at a target deflection of the actuator (302)-the belt (102) runs towards the roller support (401) and away from the roller support (401) approximately at a right angle to the first direction.
6. The device according to any one of claims 1 to 5, in which

   the first roller (101) is mounted on a first end of the roller support (401) and a further roller (101a) is mounted on a second end of the roller support (401) opposite the first end, and

   the belt (102) is guided symmetrically around the first roller (101) and further roller at a nominal deflection (x₀) of the actuator (302) such that the resulting belt force on the roller support (401) in the first direction is zero or negligibly small.
7. The device according to any one of claims 1 to 6,

   in which the frame support has deflection rollers (101a, 101b) for deflecting the belt (102).

   wherein the deflection rollers (101a, 101b) are arranged such that, at a nominal deflection (x₀) of the actuator (302), the belt runs towards the roller support (401) and away from the roller support (401) in a second direction (y) which is orthogonal to the first direction.
8. A method for machining surfaces of a workpiece (200) by means of a device (100), having:

   a frame (160),

   a roller support (401) on which a first roller (101) is rotatably mounted and which is slidably mounted on the frame (160) along a first direction (x),

   a second roller (103) which is mounted on the frame (160),

   an actuator (302) which is mechanically coupled to the frame (160) and the roller support (401),

   a belt (102) which is guided at least around the two rollers (101, 103) and which exerts a resulting belt force (F_B, F_B') on the roller support (401), wherein the first roller (101) only serves as a deflection roller, and

   an idler (105) for adjusting a biasing force in the belt (102),

   wherein the method comprises:

   positioning the workpiece (200) on the first roller (101),

   measuring a contact force (F_K) between the first roller (191) and the workpiece (200);

   adjusting a contact force (F_K) between the first roller (101) and the workpiece (200) by adjusting a force acting between the frame (160) and the actuator (302), wherein the positioning of the workpiece (200) positions the same relative to the device (100) such that the deflection of the actuator (302) corresponds to its target deflection, at which the resulting belt force (F_B, F_B') acting on the roller support (401) acts approximately in a second direction (y) which is orthogonal to the first direction (x), wherein the actuator (302) operates in a purely force-controlled manner.
9. The method according to claim 8, in which the retroactive effect of the resulting belt force (F_B, F_B') on the actuator at the target deflection is approximately zero.
10. The method according to claim 8 or 9, in which the actuator is a pneumatic linear actuator, and the measuring of a contact force (F_K) comprises measuring the pressure (p) in the pneumatic linear actuator.
11. A system for robotic surface machining of workpieces, having:

    a machining device (100), and

    a manipulator (150) for positioning the workpiece relative to the machining device (100),

    wherein the machining device (100) has:

    a frame (160);

    a roller support (401) on which a first roller (101) is rotatably mounted and which is slidably mounted on the frame (160) along a first direction (x);

    at least one second roller (103) which is mounted on the frame (160);

    a belt (102) which is guided at least around the two rollers (101, 103) and due to the tension of which a resulting belt force (F_B, F_B') acts on the roller support, wherein the first roller (101) only serves as a deflection roller; and

    an idler (105) for adjusting a biasing force in the belt (102),

    characterized by

    an actuator (302) which is mechanically coupled to the frame (160) and the roller support (401) such that an adjustable actuator force (F_A) acts between the frame (160) and the first roller (101) along the first direction (x);

    wherein the belt is guided by means of the second roller (103) or by means of the second roller (103) and further rollers such that the resultant belt force (F_B, F_B') acting on the roller support (401) at a target deflection of the actuator (302) acts approximately in a second direction (y) which is orthogonal to the first direction (x), wherein the actuator (302) operates in a purely force-controlled manner, and a position of the workpiece relative to the machining device (100) is only determined by the manipulator (150).
12. The system according to claim 11,
    in which the manipulator (150) positions the workpiece relative to the machining device (100) such that the deflection of the actuator (302) corresponds to its target deflection.

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