Field of invention

The present invention relates to a changing station (grit changer) for changing a surface treatment media (e.g. a sheet member such as sandpaper) from a robot mounted surface treatment tool. The present invention also relates to a method for changing a surface treatment media from a robot mounted surface treatment tool.

Prior art

There has recently been an increasing use of robot-assisted machining of surfaces. Grinding machines such as orbital grinding machines are typically employed in industries. In orbital grinding machines a rota- tional movement around an axis of rotation is superimposed over an oscillation movement. Grinding machines are typically applied for the final processing of surfaces when high demands are placed on the quali- ty of the finished surface.

In many situations, robot-supported grinding apparatuses comprise a grinding tool such as an orbital grinding machine guided by an industrial robot. Grinding machines such as orbital grinding machines operate with sheet-formed, flexible and removable grinding discs (e.g. sandpa- per) that are attached to a pad portion of a head of the grinding ma- chine pad. There exist various types of grinding disc made of suitable materials such as paper or a fiber-reinforced material with a grained abrasive coating. The grinding discs are configured to be attached to the backing pad of the head of the grinding machine e.g. by means of a hook and loop fastener.

In robot-supported grinding devices, the grinding discs are often changed manually. There, however, exist various robot-supported changing stations for changing grinding discs. These solutions are, how- ever, complex, require a great deal of effort to be realized and are therefore costly.

Thus, there is a need for an improved way of removing grinding discs from a grinding machine and mounting grinding discs onto a grinding machine.

Accordingly, it is an objective of the present invention to provide an im- proved method for removing grinding discs from a grinding machine and mounting grinding discs onto a grinding machine.

It is also an object to provide an improved robot-supported changing station for changing grinding discs.

Summary of the invention

The object of the present invention can be achieved by a method as defined in claim 1 and by a changing station as defined in claim 9. Pre- ferred embodiments are defined in the dependent subclaims, explained in the following description and illustrated in the accompanying draw- ings.

The method according to the invention Is a method for automatically attaching a surface treatment media to a surface treatment tool mounted on a robot arm of a robot having an articulated robot arm, wherein the surface treatment tool comprises a head configured to re- ceive the surface treatment media, wherein the method comprises the step of placing the head on a surface and applying a predefined force to press the head towards the surface when no surface treatment media has been attached to the head, wherein the method comprises the following steps: measuring the distance between the head and the surface by means of one or more positioning sensors of the robot arm or the surface treatment tool; attaching a surface treatment media to the head and placing the head on the surface when the surface treatment media is attached to the head and measuring the distance between the head and the surface by means of the one or more positioning sensors of the robot arm or the surface treatment tool when the surface treatment media is at- tached to the head.

Hereby, it is possible to provide an improved method for removing grinding discs from a grinding machine and mounting grinding discs on- to a grinding machine. The method makes it possible to verify if a sur- face treatment media is attached to the head or not in a simple, reliable and fast manner.

The surface treatment tool may be a grinding machine such as an or- bital grinding machine configured to be mounted on the robot arm. The grinding machine may be mounted on the robot arm by using a tool changer.

The surface treatment tool comprises a head configured to receive the surface treatment media. The head may comprise a pad.

The method comprises the step of placing the head on a surface and applying a predefined force to press the head towards the surface when no surface treatment media has been attached to the head. Since a predefined force is applied a corresponding deformation of the head is experienced.

The method comprises the step of measuring the distance between the head and the surface by means of one or more positioning sensors of the robot arm or the surface treatment tool. Hereby, it is possible to take advantage of the functions that the robot arm or the surface treatment tool provides. Accordingly, no additional functionality has to be added to the robot arm or to the surface treatment tool.

The method comprises the step of attaching a surface treatment media to the head and placing the head on the surface when the surface treatment media is attached to the head.

The method comprises the step of measuring the distance between the head and the surface by means of the one or more positioning sensors of the robot arm or the surface treatment tool when the surface treat- ment media is attached to the head. Hereby, it is possible to verify if a surface treatment media is attached to the head or not in a simple, reli- able and fast manner.

In one embodiment, the surface treatment media is a sheet member. The surface treatment media may be formed as a coated abrasive. In one embodiment, the surface treatment media is an abrasive grain bonded to a flexible substrate using adhesives. In one embodiment, the surface treatment media is sandpaper.

It may be advantageous that the method comprises the following steps:

- detaching the surface treatment media from the head;

- placing the head on the surface when the surface treatment media has been removed;

- applying the predefined force to press the head towards the surface and

- measuring the distance between the head and the surface by means of the one or more positioning sensors of the robot arm or the sur- face treatment tool. Hereby, it is possible to verify that the surface treatment media has been removed. If it has been verified that the surface treatment media has been removed a new piece of surface treatment media can be at- tached. If, however, it is not verified that the surface treatment media has been removed, the step of removing the surface treatment media from the head can be repeated.

It may be an advantage that the method comprises the step of detect- ing the orientation of the head by bringing the head into engagement with engagement structures.

Hereby, it is possible to make sure that the orientation of the surface treatment media being attached to the head is correct and corresponds to the desired orientation (in which the holes in the surface treatment media are aligned with holes in the head).

It may be beneficial that the head comprises several holes and the en- gagement structures comprise one or more detection pins arranged with a predefined mutual distance from each other or a predefined mu- tual distance from another structure that is arranged to be brought into engagement with a predefined structure of the head, wherein the one or more detection pins are configured to be brought into engagement with one or more holes of the head. Hereby, it is possible to arrange the head of a surface treatment tool in such a manner that the head of a surface treatment tool has a pre-defined and desired orientation.

In one embodiment, the head comprises several holes and the engage- ment structures comprise two detection pins arranged with a predefined mutual distance from each other, wherein the two detection pins are configured to be brought into engagement with the holes of the head.

In one embodiment, the head comprises several holes and the engage- ment structures comprise at least three detection pins arranged with a predefined mutual distance from each other, wherein the at least three detection pins are configured to be brought into engagement with the holes of the head.

It may be advantageous that the method comprises the step of applying a changing station that comprises a detachment portion configured to detach a surface treatment media from the head and an attachment portion designed and configured to attach a surface treatment media to the head.

In one embodiment, two guide pins are provided in an attachment por- tion and two detection pins are protruding from the surface of the de- tachment portion. Hereby, it is possible to provide a practical solution that makes it possible to arrange the head of a surface treatment tool in such a manner that the head of a surface treatment tool has a pre- defined and desired orientation.

In one embodiment, the method comprises the step of removing the surface treatment media from the head by moving the head along the surface of the detachment portion, wherein the detachment portion comprises a plate formed as a separation blade that is provided at a distance from the adjacent edge of the surface, wherein the plate is provided in a slightly higher level than the surface.

Hereby, a gap will be provided between the plate and the support member. It is essential that this gap is large enough to receive an edge portion of the surface treatment media.

In one embodiment, the step of removing the surface treatment media from the head can be accomplished by bringing the surface treatment media in a position, in which an edge portion of the surface treatment media enters the gap between the plate and the support member and moving the robot mounted surface treatment tool in a direction along the surface of the support member towards the plate.

In one embodiment, the orientation of the head is detected by moving (rotating) the head until two holes in the head have been received by the two detection pins.

It may be an advantage that the method comprises the step of remov- ing the lowermost surface treatment media by bringing at least the most distal portion of the head into contact with a media holder and moving the head along the length of the media holder.

It may be an advantage that, in case it has been detected that more than one surface treatment media have been attached to the head, the method comprises the step of removing the lowermost surface treat- ment media by bringing at least the most distal portion of the head into contact with a removal structure and moving the head along the length of the removal structure.

In one embodiment, the media holder Is formed as a pin that comprises alternating portions of protruding structures and groove structures.

In one embodiment, the depth of the groove structure relative to the protruding structure is in the range 0.01-5 mm.

In one embodiment, the depth of the groove structure relative to the protruding structure is in the range 0.04-4 mm.

In one embodiment, the depth of the groove structure relative to the protruding structure is in the range 0.08-3 mm. In one embodiment, the depth of the groove structure relative to the protruding structure is in the range 1.0-2.0 mm.

It is important to emphasise that the groove depth can be set based on the thickness of the surface treatment media.

The changing station according to the invention is a changing station for automatically attaching a surface treatment media to a surface treat- ment tool mounted on a robot arm of a robot having an articulated ro- bot arm, wherein the surface treatment tool comprises a head con- figured to receive the surface treatment media, wherein the changing station comprises a detachment portion and an attachment portion, wherein the detachment portion comprises a support member config- ured to receive the head, wherein the detachment portion comprises two detection pins protruding from the support member and being ar- ranged with a predefined mutual distance.

Hereby, it is possible to arrange the head of a surface treatment tool in such a manner that the head of a surface treatment tool has a prede- fined and desired orientation.

The head may comprise a pad made in a compressible material. Here- by, it is possible to allow the head to at least partly adapt to the shape of the object that is to be treated by the surface treatment media.

In one embodiment, the detachment portion and the attachment por- tion are integrated into a one-piece body.

In one embodiment, the changing station comprises a frame that sur- rounds at least a portion of the detachment portion and at least a por- tion of the attachment portion. In one embodiment, the support member is basically planar.

In one embodiment, the support member comprises a semi-circular portion.

It may be an advantage that the attachment portion comprises a base portion, wherein two guide pins protrude from the base portion, where- in the two guide pins are arranged with the same mutual distance as the two detection pins.

In one embodiment, the guide pins are detachably attached to the base portion. Hereby, it is possible to replace the guide pins with longer or shorter ones.

In one embodiment, the base portion is configured to receive a pair of detachably attached guide pins in various positions so that the position of the guide pins can be changed.

It may be advantageous that the attachment portion comprises a base portion configured to receive a stack of surface treatment media and that the attachment portion comprises a plurality of media holders shaped as pin-formed stop members that are arranged in a configura- tion, in which the media holders surround the base portion.

In one embodiment, the media holders extend parallel to the guide pins and protrude from a frame surrounding the base portion.

In one embodiment, the media holders are formed and arranged to keep the correct surface treatment media orientation when a plurality of surface treatment media pieces are stacked in the attachment portion.

In one embodiment, the media holders have a cylindrical portion. In one embodiment, the media holders have a proximal cylindrical por- tion and a distal rounded portion.

In one embodiment, several of the media holders comprise alternating portions of protruding structures and groove structures.

In one embodiment, at least a plurality of the media holders comprise alternating portions of protruding structures and groove structures.

It may be an advantage that the detachment portion comprises a sepa- ration blade that is provided at a distance from an adjacent edge of the support member, wherein the separation blade is provided in a higher level than the support member.

The robot system according to the invention is a robot system compris- ing:

- a changing station according to the invention;

- a robot comprising a robot arm and

- a surface treatment tool attached to the robot arm, wherein the robot system is configured to automatically attaching a sur- face treatment media to the surface treatment tool, wherein the surface treatment tool comprises a head configured to receive the surface treatment media, wherein the robot system is configured to place the head on a surface and apply a predefined force to press the head to- wards the surface when no surface treatment media has been attached to the head.

It may be an advantage that the robot system comprises:

- a measuring unit configured to measure the distance between the head and the support member by means of one or more positioning sensors of the robot arm or the surface treatment tool;

- an attachment unit configured to attach a surface treatment media to the head and placing the head on the support member when the sur- face treatment media is attached to the head, wherein the measuring unit is configured to measure the distance be- tween the head and the support member when the surface treatment media is attached to the head and the head is placed on the support member,

In one embodiment, a predefined force is applied to press the head against the support member when measuring the distance between the head and the support member.

In one embodiment, the plate and the separation blade are attached to each other. In one embodiment, the plate and the separation blade are integrated to constitute a one-piece body.

In one embodiment, the separation blade Is movably arranged with re- spect to the support member. Hereby, the magnitude of the gap can be changed by moving the separation blade. Attachment of the separation blade may be carried out by means of screws or other attachment members.

Description of the Drawings

The invention will become more fully understood from the detailed de- scription given herein below. The accompanying drawings are given by way of illustration only, and thus, they are not limitative of the present invention. In the accompanying drawings:

Fig. 1 shows a perspective view of a changing station according to the invention;

Fig. 2 shows a schematic side view of a changing station accord- ing to the invention arranged next to a robot;

Fig. 3A shows a changing station according to the invention;

Fig. 3B shows another view of the changing station shown in Fig, 3A;

Fig. 4A shows another view of the changing station shown in Fig. 3A and Fig. 3B;

Fig. 4B shows another view of the changing station shown in Fig. 3A and Fig. 3B;

Fig. 5 shows another view of the changing station shown in Fig.

4B;

Fig. 6A shows a cross-sectional view of a detachment portion of a changing station according to the invention;

Fig. 6B shows another cross-sectional view of the detachment por- tion shown in Fig. 6A;

Fig. 6C shows another cross-sectional view of the detachment por- tion shown in Fig. 6B;

Fig. 6D shows another cross-sectional view of the detachment por- tion shown in Fig. 6C;

Fig. 7A shows a cross-sectional view of an attachment portion ac- cording to the invention;

Fig. 7B shows another cross-sectional view of a portion of the at- tachment portion shown in Fig. 7A;

Fig. 7B shows a cross-sectional view of a portion of the attachment portion shown in Fig. 7A;

Fig. 7C shows another cross-sectional view of the portion of the attachment portion shown in Fig. 7B;

Fig. 7D shows another cross-sectional view of a portion of the at- tachment portion shown in Fig. 7C and

Fig. 7E shows another cross-sectional view of a portion of the at- tachment portion shown in Fig. 7D.

Detailed description of the invention

Referring now in detail to the drawings for the purpose of illustrating preferred embodiments of the present invention, a changing station 2 of the present invention is illustrated in Fig. 1. Fig. 1 is a perspective view of a changing station 2 according to the in- vention. The changing station 2 comprises a frame 50 provided with a detachment portion 4 and an attachment portion 6.

The detachment portion 4 comprises a plate-shaped support member 8 configured to receive a surface treatment media (e.g. a sheet member such as sandpaper shown in Fig. 2) 24 attached to the distal end of a robot mounted surface treatment tool (e.g. a grinding machine shown in Fig. 2). The support member 8 is provided at a lower level than the frame 50 that is surrounding a large portion of the support member 8. The support member 8 is configured to receive a circular surface treat- ment media and to allow the circular surface treatment media to be moved along the support member 8 in order to remove the surface treatment media from the support member 8. Three axes X, Y, Z of the detachment portion 4 are indicated.

The detachment portion 4 comprises a plate 12 formed as a separation blade that is provided at a short distance from the adjacent edge of the support member 8. The plate 12 is provided in a slightly higher level than the support member 8. Hereby, a gap (see Fig. 2) is provided be- tween the plate 12 and the support member 8. This gap is large enough to receive an edge portion of the surface treatment media.

Removal of the surface treatment media from a head of a surface treatment tool like the one shown in Fig. 2 can be accomplished by bringing the surface treatment media in a position, in which an edge portion of the surface treatment media enters the gap between the plate 12 and the support member 8 and moving the robot mounted sur- face treatment tool in a direction along the surface of the support member 8 towards the plate 12 (along the X axis).

The detachment portion 4 comprises two detection pins 14, 14' ar- ranged with a predefined distance in order to use the detection pins 14, 14' for detecting corresponding holes in a head of a surface treatment tool configured to receive the surface treatment media. Hereby, it is possible to arrange the head of a surface treatment tool in such a man- ner that the head of a surface treatment tool has a predefined and de- sired orientation.

The attachment portion 6 comprises a circular base portion (configured to receive the media) 22. Two mounting structures 18, 18 are provided at base portion 22. The mounting structures 18, 18' are shaped to re- ceive detachably mounted guide pins 34, 34'. When mounted, the guide pins 34, 34' protrude from the base portion 22 along the Z axis.

A plurality of media holders 20 shaped as pin-formed stop members 20 surround the base portion 22. The media holders 20 extend parallel to the mounting structures 18, 18' and the guide pins 34, 34' and protrude from the frame 50 surrounding the base portion 22. Each of the mount- ing structures 18, 18' is provided with a distal female receiving struc- ture configured to receive a matching male potion of the proximal por- tion of the corresponding guide pin 34, 34'.

The pin-formed media holders 20 are formed and arranged to keep the correct surface treatment media orientation when a plurality of surface treatment media pieces are stacked in the attachment portion 6.

The changing station 2 is provided with holes for being mounted to a mounting surface (e.g. a table or another working station).

During normal use, the changing station 2 is orientated in such a man- ner that the Z axis extends vertically.

Fig. 2 illustrates a schematic side view of a changing station 2 according to the invention arranged next to a robot 30. The robot 30 comprises an articulated robot arm 28. A surface treatment tool 26 is mounted to the robot arm 28. In the embodiment shown in Fig. 2, the surface treatment tool 26 is a grinding machine 26 comprising a head 40 formed as a pad configured to receive a sheet formed surface treatment media 24 such as sandpaper.

A sensor 48 configured to detect force and/or torque is attached to the robot arm 28 or alternatively integrated in the robot arm 28 or the sur- face treatment tool 26.

The surface treatment tool 26 is arranged above an object 36 that needs a surface treatment.

A changing station 2 according to the invention is arranged next to the robot 30. The changing station 2 corresponds to the one shown and ex- plained with reference to Fig. 1. It can be seen that a plurality of sur- face treatment medias 24 are stacked in the attachment portion 6 of the changing station 2.

Fig. 3A illustrates a changing station 2 according to the invention In a configuration, in which a stack of surface treatment media 24 has been received by the attachment portion 6 of the changing station 2. The surface treatment medias 24 are maintained within a receiving area of the attachment portion 6 of the changing station 2, wherein the receiv- ing area is surrounded by media holders 20 provided as rod-shaped stop members 20.

It can be seen that each surface treatment media 24 comprises holes 38 and that the attachment portion 6 comprises a guide pin 34 that ex- tends through one of the holes in the surface treatment medias 24. A head 40 of a surface treatment tool (not shown) rests on the support member of the detachment portion 4 of the changing station 2. A num- ber of holes 42 are provided in the head 40. The holes 38 in the surface treatment medias 24 are placed in such a manner that they can be aligned with the holes 42 provided In the head 40. Hereby, dust can be removed from a surface treatment media 24 through these holes 38, 42 during use of the surface treatment media 24.

The detachment portion 4 comprises two detection pins 14 (however, only one is visible in Fig. 3A) arranged with a predefined distance in or- der to use the detection pins 14 to detect corresponding holes 42 in a head 40 (see Fig. 2) and allow the detection pins 14 to be received in the holes 42. Hereby, it is possible to arrange the head 40 in a prede- fined and desired orientation.

Fig. 3B illustrates another view of the changing station 2 shown in Fig. 3A in a configuration, in which the holes 42 in the head 40 are being detected on the basis of force F and/or torque T data measured by a sensor corresponding to the one shown and explained with reference to Fig. 2. In practice, the robot arm rotates the surface treatment tool un- til the detection pins 14 have been received by holes 42 in the head 40 and the expected force F and/or torque T data have been measured by the sensor.

Fig. 4A illustrates another view of the changing station 2 shown in Fig. 3A and Fig. 3B in a configuration, in which the detection pins 14 have been received by and thus aligned with the holes in the head 40. A pre- defined force F ₁ is applied to press the head 40 downwards (along the axis Z). By using one or more positioning sensors of the robot arm, to which the surface treatment tool (see Fig. 2) is attached, it is possible to detect the vertical position of the head 40. Based on this vertical po- sition measurement, a reference level (the position in which the z value is zero) is established.

Fig. 4B illustrates another view of the changing station 2 shown in Fig. 3A and Fig. 3B. In this configuration, the head 40 is placed on the top of a stack of surface treatment media 24 arranged in the receiving area of the attachment portion 6 of the changing station 2. It can be seen that the receiving area is surrounded by rod-shaped media holders 20.

A downwardly directed (along the axis Z) force F is applied to the head 40. Accordingly, the head 40 presses against the stack of surface treatment media 24 and one piece of surface treatment media 24 is at- tached to the head 40. In one embodiment, the applied force is within the range 5-100 N.

Fig. 5 illustrates another view of the changing station 2 shown in Fig. 4B, In this configuration, the head 40 is moved back to the original po- sition to check if the surface treatment media 24 has been successfully attached to the head 40. By applying a force Fi corresponding to the force explained and shown with reference to Fig. 4A and using one or more positioning sensors of the robot arm, to which the surface treat- ment tool (see Fig. 2) is attached, it is possible to detect the vertical position of the head 40 and thus determine the distance between the support member 8 of the detachment portion 4 of the changing station 2. If the distance between the support member 8 of the detachment portion 4 of the changing station 2 corresponds to the expected value, it is concluded that a single surface treatment media 24 has been suc- cessfully attached to the head 40. If two layers of surface treatment media 24 have been attached to the head 40, the detected distance would be larger than the expected distance. Accordingly, the test pro- cedure will reveal if more than a single surface treatment media 24 is attached to the head 40. In one embodiment, the surface treatment media 24 is a piece of sand- paper having a thickness of 0.5 mm. In this case, the expected value would be 0.5 mm.

In one embodiment, the surface treatment media 24 is a piece of sand- paper having a thickness of 1.0 mm. In this case, the expected value would be 1.0 mm,

In one embodiment, the surface treatment media 24 is a piece of sand- paper having a thickness of 1.5 mm. In this case, the expected value would be 1.5 mm.

Fig. 6A illustrates a cross-sectional view of a detachment portion 4 of a changing station 2 according to the Invention. A single piece of a sur- face treatment media 24 is attached to the head 40 of a surface treat- ment tool (not shown). The head 40 with the surface treatment media 24 rests on the support member 8 of the detachment portion 4 of the changing station 2.

The detachment portion 4 comprises a plate 12 having a distal portion formed as a separation blade 32. The separation blade 32 is provided in a short distance from the adjacent edge of the support member 8. The top portion of the plate 12 and the separation blade 32 are provided in a slightly higher level than the support member 8. Hereby, a gap 10 Is provided between the separation blade 32 and the support member 8. This gap 10 is large enough to receive an edge portion of the surface treatment media 24.

In one embodiment, the plate 12 and the separation blade 32 is at- tached to each other. In one embodiment, the plate 12 and the separa- tion blade 32 are integrated to constitute a one-piece body. In one embodiment, the separation blade 32 is movably arranged with respect to the support member 8. Hereby, the magnitude of the gap 10 can be changed by moving the separation blade 32. Attachment of the separation blade 32 may be carried out by means of screws or other attachment members.

The distance between the head 40 and the support member 8 is meas- ured by means of one or more positioning sensors of the robot arm, to which the surface treatment tool (see Fig. 2) is attached. Hereby, it is possible to detect the vertical position of the head 40.

Fig. 6B illustrates another cross-sectional view of the detachment por- tion 4 shown in Fig. 6A. It can be seen that the head 40 of a surface treatment tool (not shown) is moved to the left along the X axis. The movement of the head 40 is indicated by an arrow.

Fig. 6C illustrates another cross-sectional view of the detachment por- tion 4 shown in Fig. 6B. It can be seen that the surface treatment me- dia 24 has entered the gap 10 between the separation blade 32 and the support member 8. Accordingly, the surface treatment media 24 is be- ing detached from the head 40.

Fig. 6D illustrates another cross-sectional view of the detachment por- tion shown in Fig. 6C. In this configuration, the head 40 is placed in the same position as shown in Fig. 6A and the vertical position of the head 40 (or the distance between the head 40 and the support member 8) is detected by means of one or more positioning sensors of the robot arm, to which the surface treatment tool is attached (see Fig. 2). Hereby, it is possible to detect the vertical position of the head 40.

If the distance between the head 40 and the support member 8 is de- creased as expected (so that the distance between the head 40 and the support member 8 corresponds to the value referred to when describing Fig. 6A), it is concluded that the surface treatment media 24 has been successfully removed.

Fig. 7A illustrates a cross-sectional view of an attachment portion 6 of a changing station according to the invention. A head 40 of a surface treatment tool (not shown) rests on a stack of surface treatment medi- as 24 placed on the support member of the attachment portion 6. The stack is surrounded by media holders 20 provided as rod-shaped stop members 20. The media holders 20 comprise a surface structure adapted for separating adjacent pieces of surface treatment medias 24 that are attached to each other. The surface structure of the media holders 20 comprises alternating portions of protruding structures 44 and groove structures 46, respectively. In Fig. 7A, the magnitude of the protruding structures 44 and the groove structures 46 have been exag- gerated for illustrative purposes.

In order to attach a surface treatment media 24 to the head 40, a force F is applied from the head 40 towards the stack of surface treatment medias 24.

Fig. 7B illustrates another cross-sectional view of the left-side portion of the attachment portion 6 shown in Fig. 7A. The head 40 and the surface treatment medias 24 attached thereto are moved slightly to the right by using a predefined force level.

Fig. 7C illustrates another cross-sectional view of the portion of the at- tachment portion 6 shown in Fig. 7B in a configuration, in which the head 40 and the surface treatment medias 24 attached thereto are raised from the remaining surface treatment medias 24 of the stack. Accordingly, the head 40 and the surface treatment medias 24 attached thereto are moved upwards. It can be seen that the two surface treat- ment medias 24 are attached to the head 40.

Fig. 7D illustrates another cross-sectional view of a portion of the at- tachment portion 6 shown in Fig. 7C. In order to remove the lowermost surface treatment media 24 from the surface treatment media 24 that is in contact with and attached to the head 40, the head 40 is moved towards the adjacent media holder 20.

Fig. 7E illustrates another cross-sectional view of a portion of the at- tachment portion 6 shown in Fig. 7D. In order to remove the lowermost surface treatment media 24 from the surface treatment media 24 that is in contact with and attached to the head 40, the head 40 is moved up in a direction away from the support member of the attachment portion 4 while the head 40 is pressed towards the adjacent media holder 20 in order to keep the head 40 and the surface treatment media 24 in con- tact with the adjacent media holder 20. Accordingly, a protruding struc- ture 44 will detach the lowermost surface treatment media 24 from the uppermost surface treatment media 24 and the head 40 has been re- ceived by the groove structure 46 and the lowermost surface treatment media 24 has not. Basically, the (sticking) uppermost surface treatment media gets into the groove structure 46 and hereby gets separated from the lowermost surface treatment media 24, In Fig. 7E it can be seen that the distance D between adjacent protruding structures 44 is large enough to allow the groove structure 46 to receive the uppermost surface treatment media 24 and the head 40, The thickness H of the uppermost surface treatment media 24 and the head 40 is indicated. Since the uppermost portion of the head 40 tapers, it is not required that D is larger than H. Moreover, the head 40 may be made in a com- pressible material. If the head 40 is made in a compressible material, it is possible to detach the lowermost surface treatment media 24 even if H is slightly larger than D because the lowermost portion of the head 40 may be received by the groove structure 46 hereby enabling the low- ermost portion of the head 40 and the uppermost surface treatment media 24 to be received by the groove structure 46.

If the lowermost surface treatment media 24 protrudes to the upper- most surface treatment media 24 and the head 40, it is possible to re- move the lowermost surface treatment media 24 by placing a part of it in a groove structure 46 and move the uppermost surface treatment media 24 and the head 40 along the length of the adjacent media hold- er 20.

List of reference numerals

2 Changing station (grit changer)

4 Detachment portion

6 Attachment portion

8 Support member

10 Gap

12 Plate

14, 14' Pin

18, 18' Mounting structure

20 Media holder (stop member)

22 Base portion (for the media)

24 Surface treatment media (e.g. a sheet member such as sandpaper)

26 Robot mounted surface treatment tool (e.g. a grinding machine)

28 Robot arm

30 Robot

32 Separation blade

34, 34' Guide pin

36 Object

38 Hole

40 Head (e.g. formed as a pad)

42 Hole

44 Surface structure (protruding structure)

46 Surface structure (groove structure)

48 Sensor

50 Frame

F, F ₁ Force

T Torque

D Distance

H Thickness