Technical Field

[0001] The invention relates to an industrial robot for removal of dross and scum from a molten metal plating bath in a hot-dip galvanizing process line. Furthermore, the invention relates to a tool changer system that is used to change the tools connected to the robot, and a method thereof.

Background Art [0002] Hot-dip galvanizing after fabrication of steel and iron products is frequently carried out to make products more resistant against corrosion and improve the durability, longevity, versatility, stability, or even the aesthetics. A ‘clean’ pre-heated product, such as a sheet, strip or plate, is placed in or passed through a molten metal plating bath comprising zinc, a zinc alloy, or any other suitable metal or metal alloy, to provide the iron or steel with a plating layer. [0003] Consequent to a reaction between the iron or steel and molten metal or metal alloy, dross, slag and scum, hereafter referred to as dross, are formed on the liquid surface of the plating bath. These impurities can seriously affect the surface quality of the galvanized products, and therefore need to be removed from the plating bath. Often this is done manually by an operator, under extremely heavy and high risk conditions. [0004] The task of dross removal may also be carried out by industrial robots having a dross removal tool extending from the robot arm. Some robots use one tool only for the dross removal, but this leads to a relatively low efficiency. Therefore robots have been developed with changer devices that allow the automatic change of the tool that is attached to the robot arm.

[0005] Patent application CN 109423588 A (Wei et al.) describes an example of a robot able to automatically select a dross or slag removal tool. A tool changer system for connecting and holding various tools is attached to the robot arm and pneumatically driven under the control of a solenoid valve. This robot has the disadvantage that a pneumatic circuit is required to perform the clamping action, which leads to a relatively complex design and reduced robustness in use. Systems are also known where a bayonet type engagement is made by aligning a chuck axially with the shaft of a tool and performing an axial and torsional movement to engage the chuck and tool together. Such connections are however sensitive to accuracy of alignment and to the presence of any debris on the end of the tool shaft.

[0006] It would be desirable to provide a tool changer system for a dross removal robot that has a less complex design and is more robust. In particular, it should be operable under the conditions typically prevailing in such an environment where dross, slag and other types of dirt may become encrusted on the tools, making automatic engagement complicated.

Summary of Invention

[0007] Therefore, according to a first aspect of the invention, there is provided an industrial robot for removal of dross and scum, from a molten metal plating bath in a hot-dip galvanizing process line. The robot comprises a robot body, a robot arm having a shoulder end connected to the robot body and a free wrist end, and a tool clamp connected to the wrist end. The term ‘tool clamp’ refers herein to a non-actuated, passive mechanism. The tool clamp is configured to pick up, mount, and put down a dross removal tool, the dross removal tool having a tool shaft and a plurality of connecting elements extending outwardly from and spaced along the tool shaft. According to an embodiment, the tool clamp has a first jaw to engage a first connecting element and a second jaw to engage a second connecting element, whereby one of the jaws can be displaced with respect to the other jaw to engage and disengage the connecting elements by movement of the robot arm, the displacement taking place by the robot arm exerting a sequence of forces on the tool shaft of the tool against a reaction force provided by the tool holder.

[0008] The displacement of one of the jaws with respect to the other jaw opens and closes the tool clamp. An advantage of the tool clamp is that the relative displacement of the jaws and the switch between tools can be fully driven and controlled by the robot itself. This allows the clamp to be very robust and little maintenance is required on the tool clamp. In the heavy working environment of the robot, parts of an external actuator or the connection between the robot and the external actuator may easily be damaged. The tool clamp according to the invention requires no extra medium, wires or other elements for control of the pick-up, clamping and release of a tool. The tool clamp is also relatively cheap to manufacture and has low maintenance costs.

[0009] The use of connecting elements spaced along the tool shaft allows the tool clamp to resist large axial and rotational forces. In this context, reference to a rotational force is intended to denote rotation about an axis perpendicular to the tool shaft i.e. leading to a bending moment in the shaft. Reference to a rotational force coinciding with the axis of the shaft will be referred to as a torsional force.

[0010] Moreover, the use of connecting elements extending outwardly from the shaft, makes the system rather insensitive to debris. Parts of dross or other dirt on the tool shaft do not hinder the connection, since the connection is established through the connecting elements and not directly onto a surface of the tool shaft itself. It will of course be understood that debris can also attach itself to the connecting elements. The connecting elements may however be generally smaller in their relevant dimension than the shaft. Any dirt that attaches itself to the connecting elements will more easily be displaced by interaction with the jaws of the clamp. In particular, larger pressures will be encountered on the surface of a smaller connecting element than would be encountered on a larger diameter shaft, for the same connecting force exerted by the robot wrist end and tool clamp when making a connection.

[0011] It will be understood that the transmission of rotational forces from the clamp to the tool during connection and in use, will depend on the critical dimension between the clamping surfaces. For a clamp according to the invention having jaws, which engage with connecting elements, this will largely be determined by the distance between the connecting elements. This should be at least greater than a width or diameter of the tool shaft. In an embodiment, the first and second connecting elements are spaced over a distance of at least three times a width of the tool shaft, preferably about five times or more a width of the tool shaft. The spacing of the connecting elements along the tool shaft leads to a connection that can withstand sufficiently large rotational forces.

[0012] In an embodiment, the tool shaft also has what will be referred to as retaining elements spaced along the tool shaft. The retaining elements are arranged to be engaged by the tool holder, allowing the tool holder to withstand axial and rotational forces exerted by the tool clamp. The connection of the tool shaft at multiple positions along the tool shaft allows the tool holder to resist the axial and rotational forces that are exerted by the tool clamp, while keeping the tool shaft at a fixed position. Preferably, also the retaining elements are spaced along the tool shaft over a distance corresponding to the distance applicable to the connecting elements. It will be understood that the forces applied to the connecting elements will correspond largely to the forces that the retaining elements need to resist.

[0013] In an embodiment, the connecting elements and the retaining elements may coincide. In other words, the same element or part of the same element may be used for engaging the respective jaw of the clamp and also for engaging with the tool holder. Alternatively, the retaining elements and the connecting elements may be distinct and may be located at different positions along the tool shaft. The skilled person will be acquainted with various structures that may be used as connecting and retaining elements, including plates, pins, flanges, hooks, barbs and the like.

[0014] In one preferred embodiment, pins are used, which extend a sufficient distance from the shaft to allow engagement by the jaws without the jaws contacting directly with the shaft. Round pins are preferred, having a diameter that is less than a width or transverse dimension of the shaft. The pins may be less than half the width of the shaft or even less than one third a width of the shaft. The jaws are preferably provided with recesses corresponding in shape to that of the connecting elements. In the case of pins, the jaws may have slots of a similar diameter to the pins into which the pins can fall.

[0015] The first and second connecting elements may be provided by a pair of upper pins, and a pair of middle pins, and the retaining elements may be provided by the pair of middle pin and a pair of lower pins. The middle pins or parts thereof, are thus used both as a connecting element for connecting the tool to the tool clamp, as well as a retaining element for connecting the tool to the tool holder. This allows for a compact design of the tool holder, wherein the distance along the tool shaft that is used for connecting the tool to the tool clamp and tool holder is used optimally. Preferably, the distance between the upper pin and middle pin is the same as the distance between the middle pin and the lower pin. The compactness allows for the selection of tools that have a relatively short tool shaft.

[0016] In such a situation, it may be desirable for the jaws of the tool clamp to be arranged to engage the pins at a width that is greater than the width at which the tool holder engages. The tool holder may be arranged to engage the pins at a spacing that is slightly wider than the width of the shaft. The jaws of the clamp may be arranged to engage the pins at a spacing that is slightly wider than the width of tool holder. In this manner, the clamp may fit around the tool holder during picking up and putting down of the tool. It will be understood that the reverse may also be possible with the tool holder fitting around the clamp.

[0017] In an embodiment, the jaws of the tool clamp are biased towards each other through a spring element, wherein the first jaw is arranged to engage the first connecting element when the spring is unloaded and wherein the spring element is configured to allow the jaws to open when a force is exerted on the tool shaft, providing space for the second jaw to engage the second connecting element. The term “spring element” is herein used to refer to any type of spring or resilient element that biases the jaws in a direction towards each other. Only when a sufficiently large force is exerted on the spring element can the jaws be opened. The jaws and spring element contribute to a connection between the tool clamp and the tool that is rigid, and without slack.

[0018] In an embodiment, the tool clamp further comprises a blocking element that is movable between a first position wherein the blocking element prevents disengagement of the tool clamp and a second position, wherein the blocking element does not hinder disengagement of the tool clamp. The blocking element thus prevents accidental disengagement of the tool. Preferably, the blocking element prevents the jaws from opening, thus avoiding that only the spring element is acting to keep the jaws closed. The blocking element may prevent the second connecting element from exiting the second jaw e.g. by preventing axial movement of the second connecting element, which could cause a force to be exerted against the spring element.

[0019] In a further embodiment, the blocking element is biased towards the first position. This allows the blocking element to passively lock the tool, since in its neutral position, without an external force being applied, the blocking element prevents a tool mounted in the tool clamp from disengaging. The blocking element contributes to a connection between the tool clamp and the tool that is rigid, and with a minimum slack. Preferably, the blocking element is arranged to be moved to the second position by engagement against a portion of the tool holder. This movement may be part of the movement initiated by the robot arm, causing the blocking element to be pressed against the tool holder with a force sufficient to overcome a bias of the blocking element. [0020] In an embodiment, the robot uses rotational and translational movements of the wrist end to control picking-up and putting down a tool. The rotational and translational movements are also required for successful dross removal. In preferred embodiments, no additional degrees of freedom of the wrist end are required at the wrist end, other than the degrees of freedom that are already required for the dross removal. This makes the tool clamp flexible for use in combination with already existing robots. In an embodiment, the rotational and translational movements take place in a single plane. By rotating the tool clamp onto the tool shaft, a sliding movement of the tool clamp along the surface of the tool shaft is not required. In a dirty environment, sliding of surfaces may become difficult once surfaces have become contaminated with debris.

[0021] In an embodiment, the first jaw is a pivotable upper jaw that can be displaced with respect to the second jaw, which is a fixed lower jaw, by pressing the tool downwards into the tool holder. This is convenient as pressure can easily be applied by the robot to a top surface of the tool shaft or to an upper surface of the connecting elements extending from the tool shaft. [0022] In an embodiment, the tool clamp comprises one or more centering members, contacting the tool shaft around a contact surface. The centering members are arranged to provide lateral stability to the tool during the dross removal actions. In preferred embodiments, the centering members contact the tool shaft over a circumference of at least 50% of a circumferential surface of the tool shaft, and over a distance of less than 10% of the distance between the first pair of connecting elements along the tool shaft. The limited contact surface between the tool clamp and the tool shaft prevents problems with connecting the tool once the contact surface becomes dirty in the working environment.

[0023] According to another aspect of the invention and in accordance with the advantages and effects described hereinabove, there is provided a tool clamp for use with an industrial dross removal robot. In preferred embodiments, the tool clamp comprises a conventional connector for attaching the tool clamp to an industrial robot’s wrist end.

[0024] According to yet another aspect of the invention and in accordance with the advantages and effects described hereinabove, there is provided a tool holder for use with an industrial robot and tool clamp as described above. The tool holder is configured to withstand the forces exerted by the industrial robot and tool clamp on engaging and disengaging the tool.

[0025] According to yet another aspect of the invention and in accordance with the advantages and effects described hereinabove, there is provided a dross tool for use with a robot, tool clamp, and tool holder as described above. The dross tool has a tool shaft that is configured to engage with the tool clamp and tool holder and further has an attribute aiding the process of dross removal. In embodiments, the tool may have different attributes, such as a sieve, basket, rake or net. Moreover the tools may have a different size or shaft length. The skilled person will understand when to use which tool.

[0026] According to a further aspect of the invention, there is provided a tool changer system, comprising a tool clamp, configured to be connected to a wrist end of an industrial robot; a tool for removal of dross and scum from a molten metal plating bath in a hot-dip galvanizing process line, the tool having a tool shaft and a plurality of connecting elements extending outwardly from and being spaced along the tool shaft by a distance that is greater than a width of the tool shaft; and a tool holder, configured to be mounted in a tool docking station. The tool clamp has a first jaw configured to engage a first connecting element and a second jaw configured to engage a second connecting element, whereby at least one of the jaws can be displaced with respect to the other jaw to open and close the clamp to engage and disengage the connecting elements by movement of the tool clamp to exert forces on the tool shaft against a reaction force provided by the tool holder.

[0027] The tool changer system can be used in combination with conventional industrial robots. The tool clamp is easily attached to an industrial robot’s wrist end, and the tool change mechanism relies solely on actuation by the robot itself and the interaction between the tool clamp, tool, and tool holder. No external actuation is required, which makes the tool changer system easy and flexible to use also in combination with already operational robots. In particular, although the present invention has been described in the context of dross removal robots, the tool changer may also be implemented for changing similar tools, in particular those used in challenging environments where build-up of debris on the shaft of the tool can make tool changing difficult.

[0028] In an embodiment, the tool holder comprises a pair of lateral walls. The tool shaft is supported between the lateral walls with at least 1 mm of space between an exterior surface of the tool shaft and the lateral walls. Preferably, the space between the exterior surface of the tool shaft and the lateral walls is between 1 mm and 3 mm. This space provides some slack in the position of the tool shaft with respect to the tool holder, which allows the system to cope with the accumulation of debris, such as dross, slag, zinc splatter, dust or other types of dirt. Even with debris encrusted on the tool and/or the tool holder, the tool clamp may still place the tool in the tool holder. In particular, due to an accumulation of debris on one side of the shaft, the tool may be displaced away from a central position. As will be understood by the skilled person, the herein described lateral engagement of the clamp with the tool is operable even when the tool shaft is not centered in the holder.

[0029] The space between the tool shaft and the lateral walls further allows the tool holder to hold tools having different tool shaft diameters. Also the tool clamp can be configured to receive tools with different tool shaft dimension. In particular, to the extent that the connecting elements are still located at the same respective locations, the tool clamp can engage them, irrespective of the size or position of the shaft.

[0030] According to a further aspect of the invention, and in accordance with the advantages and effects described herein above, there is provided a method for picking up a dross removal tool with an industrial robot from a tool holder in a tool docking station. The industrial robot has a tool clamp attached to a wrist end of a robot arm, and the tool has a tool shaft with a plurality of connecting elements extending outwardly from and spaced along the tool shaft. The method comprises the steps of: engaging a first jaw of the tool clamp with a first connecting element of the tool; exerting a sequence of forces on the tool shaft through the connection between the first jaw and the first connecting element to open the tool clamp by increasing a distance between the first jaw and a second jaw of the tool clamp, wherein the tool holder is configured to provide resistance against the sequence of forces; controlling the robot wrist end to engage the second jaw of the tool clamp with a second connecting element; and controlling the robot wrist end to withdraw the tool from the tool holder and lock the tool in the tool clamp.

[0031] A particular characteristic of the invention is that it allows for changing of a tool using primarily lateral movement of the tool clamp towards the shaft of a tool in order to engage the shaft. This is significantly different from arrangements where a chuck or gripper is moved axially onto the shaft. According to an embodiment there is thus provided a tool changer system, comprising: a passive tool clamp, configured to be connected to a wrist end of an industrial robot; a tool having a tool shaft and a plurality of connecting elements extending outwardly from and being spaced along the tool shaft by a distance that is greater than a width of the tool shaft; and a tool holder, wherein the tool clamp is arranged to pick up and put down the tool from the tool holder by action of the robot arm to move the tool clamp in a predominantly lateral direction with respect to the tool shaft. Forces in the axial direction on the connecting elements may be applied to open and close the clamp. Such lateral engagement avoids the need for the clamp to be aligned and moved axially over an end of the shaft, requiring much greater precision and being more susceptible to the presence of debris on the shaft.

[0032] Advantageously, the robot can pick up a tool using only movement of the robot itself, in interaction with the tool and tool holder. The tool clamp itself is a passive device. Once the tool is mounted in the tool clamp, a rigid connection with little slack is provided, sufficiently strong to perform dross removal actions without accidentally disengaging the tool.

Brief Description of Drawings

[0033] Embodiments will now be described, by way of example only, with reference to the accompanying schematic drawings in which corresponding reference symbols indicate corresponding parts. In the drawings, like numerals designate like elements. Multiple instances of an element may each include separate letters appended to the reference number. For example, two instances of a particular element “20” may be labeled as “20a” and “20b”. The reference number may be used without an appended letter (e.g. “20”) to generally refer to an unspecified instance or to all instances of that element, while the reference number will include an appended letter (e.g. “20a”) to refer to a specific instance of the element.

[0034] Figure 1 schematically shows a perspective view of an embodiment of an industrial robot removing dross from a zinc bath.

[0035] Figure 2 schematically shows a front view of an embodiment of a dross removal tool. [0036] Figure 3A shows a perspective view of an embodiment of a tool clamp.

[0037] Figure 3B shows a partially sectioned perspective view of the tool clamp of Fig. 3A

[0038] Figure 3C shows a front view of the tool clamp of Fig 3A.

[0039] Figure 4 presents a tool docking station for use in combination with the tool clamp of

Figure 3.

[0040] Figures 5A-5F illustrate stages of a method for picking up a tool using the tool clamp of Fig 3.

[0041] Figures 6A-6E illustrate stages of a method for putting down a tool using the tool clamp of Fig 3.

[0042] The figures are meant for illustrative purposes only, and do not serve as a restriction of the scope or the protection as laid down by the claims.

Description of Embodiments

[0043] The following is a description of certain embodiments of the invention, given by way of example only and with reference to the figures.

[0044] Figure 1 schematically shows a perspective view of an industrial robot 1 for removal of dross 5 from a zinc bath 9 in a continuous hot-dip galvanizing process line. Steel plates (not shown) are guided through the zinc bath 9, which leads to the formation of dross 5 on the surface of the zinc bath 9. The robot 1 is positioned on a side of the zinc bath 9 to remove the dross 5 from the surface. Other apparatus that are part of the hot-dip galvanizing process line may be positioned on the same side of the zinc bath 9, or any other side. Multiple dross removal robots 1 may be arranged around the same zinc bath 9 should that be required.

[0045] The robot 1 has a robot body 11 that is fixed to a base plate 3, and a robot arm 12 that extends from a shoulder 15 of the robot body 11 . The robot arm 12 has an upper arm 13 and a lower arm 14, and ends in wrist end 16. At the wrist end 16 a dross removal tool 4a is connected through a tool clamp 2. The robot 1 can control movement of the dross removal tool 4a. Dross 5 may be removed by immersing the tool 4a in the zinc bath 9 and making a scooping movement just below the liquid surface. Subsequently, the robot 1 may lift up the dross removal tool 4a, and turn sideways to deposit the scooped up material in a container 6.

[0046] Various tools 4a, 4b, 4c can be used for the removal of dross 5. The robot 1 has a first tool 4a mounted, but can automatically interchange the first tool 4a for another appropriate tool 4b, 4c that is stored in a tool docking station 7. The tools 4 are held in tool holders 71 in the docking station 7. To put down a first dross removal tool 4a and pick up a second dross removal tool 4b, 4c, the robot 1 turns around its own vertical axis, such that the wrist end 16 of the robot 1 is facing the docking station 7. Subsequently, the robot 1 makes precise movements to put down the first tool 4a in an empty holder in the docking station 7, and select a second tool 4b from another holder 71 in the docking station 7.

[0047] To enable all these movements, the robot wrist end 16 is provided with at least five degrees of freedom. The first three degrees of freedom allow the wrist end 16 to make translation movements in three-dimensional space. A fourth degree of freedom is used to make the rotational movement around the robot’s own normal axis z, for instance to face the tool docking station 7 instead of the zinc bath 9. The fifth degree of freedom is a pitch movement around a transverse axis Y perpendicular to the normal axis z. In this embodiment, the pitch movement is required to pick up or put down a tool 4 from the docking station 7. It will be understood that the robot 1 may be provided with additional degrees of freedom and that in specific embodiments not all degrees of freedom may be necessary.

[0048] Figure 2 schematically shows an embodiment of a dross removal tool 4 that can be connected to the robot 1 . The dross removal tool 4 has a cylindrical tool shaft 41 with a diameter of approximately 3 cm and a length of 1 m. In other embodiments the tool shaft may also have another diameter, for instance 4 cm or a diameter between approximately 2 and 5 cm. From one end of the tool shaft 41 , a dross removal attribute 45 extends. Alternative embodiments may have other attributes 45, for example a rake, scraper, sieve, basket, or net. Preferably the tool has both a surface that can carry removed dross and openings in this surface to release excess liquids back to the bath 9. The skilled person will understand the type of tool appropriate for the process of dross removal. It will further be understood that not all tools are meant to scoop or sieve the liquid, but for instance may be used also to stir the liquid. In addition, different embodiments of the tool 4 may not only have a different attribute 45, they may also have a different length of the tool shaft 41 .

[0049] A number of connecting elements protrude from the tool shaft 41 and are arranged to connect the tool shaft 41 to the tool clamp 2 of the robot 1 . These connecting elements can be subdivided into upper pins 43 and middle pins 42. In addition, a number of retaining elements protrude from the tool shaft 41 , which are arranged to connect the tool shaft 41 to a tool holder 71 in the docking station 7. The retaining elements can be subdivided into lower pins 44 and middle pins 42.

[0050] The upper pins 43 are arranged close to a top end of the tool shaft 41 . The middle pins 42 are spaced from the upper pins 43 over a distance of approximately 6 times the diameter of the tool shaft 41 . The middle pins 42 are spaced from the lower pins 44 over the same distance of approximately 6 times the diameter of the tool shaft 41 .

[0051] Figure 3 shows an embodiment of the tool clamp 2. Figure 3A-B show a perspective view, and Figure 3C shows a front view. In Figure 3B a number of parts on one of two symmetric sides of the tool clamp 2 have been omitted for the purpose of clarity.

[0052] The tool clamp 2 has a connection plate 21 for connecting the tool clamp 2 to the robot’s wrist end 16 (schematically indicated in Fig. 3A). The connection plate 21 is connected to a frame 22 that extends along a central axis C, which is defined as the axis along which the tool shaft 41 extends when mounted in the tool clamp 2.

[0053] A plurality of centering members 23a, 23b are connected to the frame 22 and spaced at different positions along the central axis C. The centering members 23 guide the tool shaft 41 and prevent any movement of the tool shaft 41 in a direction other than along the central axis C, or a radially outward unmounting movement through an opening 26 between two side walls that are extending from the frame 22 on opposite sides of the central axis C. The centering members 23 thereby also prevent any rotation of the tool 4 other than rotation about the central axis C. In embodiments, the centering members 23 may be configured to provide guidance to the respective tool shafts of a plurality of tools that each have a different tool shaft diameter.

[0054] The side walls have an upper side wall portion 48 and a lower side wall portion 24. The lower side wall portion 24 comprises lower support seats 25, which are configured to receive the middle pins 42 extending from the tool shaft 41 . When a tool 4 is mounted in the tool clamp 2, the middle pins 42 are supported by the lower support seat 25.

[0055] The upper side wall portions 48 are protected by a housing 27. The opening 26 between the side walls extends between two parts of the housing 27. The opening 26 extends along a direction parallel to the central axis C and is sufficiently wide to allow lateral entrance of the tool shaft 41 through the opening 26.

[0056] Figure 3B shows that the tool clamp 2 further has an upper support structure 29. The upper support structure 29 has two lateral bars 31 on opposite sides of the central axis C, and a hinge 28, which is rotatably connected to the upper side wall portion 48 . Each of the lateral bars 31 has a upper support seat 30 on its lower edge. These upper support seats 30 are arranged to receive the upper pins 43 that extend from the tool shaft 41 .

[0057] Two extension springs 32 (of which one is shown) are positioned at opposite sides of the central axis C. The extension springs 32 are arranged to bias the upper support structure 29 to rotate about the hinge 28. A first end (not shown) of each extension spring 32 is connected to the lower side wall portion 24. The second end 34 of each extension spring 32 is connected to the upper support structure 29. The upper support structure 29 can thus act as one jaw of the tool clamp 2. The second jaw of the tool clamp is provided by the lower side wall portion 24.

[0058] The tool clamp 2 further comprises two cams 35 that guide the actions of picking up and putting down a tool 4. Moreover, the cams 35 provide a blocking mechanism when a tool 4 is mounted. Each of the cams 35 has a tip 36 and a blocking part 37. The cams 35 are connected to each other to rotate together about a transverse axis y and biased through a torsion spring 38.

The torsion spring 38 is connected to the frame 22, and biases the cams 35 towards a neutral position. In the depicted view, the cams 35 are in the neutral position, wherein the blocking part 37 is positioned above the exit path of a middle pin 42. As such, the blocking parts 37 blocks the disengagement of the middle pins 42 from the lower support seats 25.

[0059] Figure 3C shows a front view of the tool clamp 2 with a tool shaft 41 of a tool mounted therein. The cams 35 are thin and each cam 35 is located in a narrow space between the tool shaft 41 and the lower side wall portions 24. The middle pins 42 have a larger diameter close to the tool shaft 41 , and a smaller diameter towards the end. Where the diameter is smallest, the middle pins 42 engage with the lower support seat 25 in the lower side wall portion 24. This leaves a space between the tool shaft 41 and the side walls portions 24,48 for part of the tool holder 71 to engage with the middle pins 42. This part of the tool holder 71 is also aligned with the cams 35.

[0060] The tool clamp 2 is shown in Figs. 3A-C in a position wherein the tool 4 is mounted in the frame 22. The connection of the tool 4 to the tool clamp 2 is rigid. A clamping mechanism is provided by the lower support seats 25, upper support structure 29, and extension springs 32. In the unloaded position of the extension springs 32, displacement of the tool shaft 41 along the central axis C is prevented. Only upon extension of the spring 32, the clamp is opened. Also displacements in directions perpendicular to the tool shaft 41 are partially prevented by the clamp. [0061] In addition, the blocking part 37 of the cam 35 prevents the middle pins 42 from disengaging from the lower support seat 25, and the centering members 23 prevent movement of the tool shaft 41 in lateral directions. Since the tool clamp 2 supports the tool 4 at different positions spaced along the tool shaft 41 , also rotation is prevented.

[0062] Figure 4 shows an embodiment of a docking station 7 that is compatible for use with the tool clamp 2 of Figs. 3A-C. The docking station 7 has three tool holders 71 for receiving a tool 4. Each tool holder 71 is symmetrically shaped, and has lateral walls 73 on each side of a central axis C. Here the central axis C is again defined as the axis along the direction of the tool shaft 41 of a tool 4 when mounted in the tool holder 71.

[0063] Each of the lateral walls 73 has a top wing 75 with a top seat 72 and a lower wing 76 with a lower seat 74. The top seat 72 is configured to receive the middle pin 42 of a tool 4, and the lower seats 74 are arranged to receive the lower pins 44 of the tool 4.

[0064] The lateral walls 73 and wings 75, 76 are thin and arranged with just a slight spacing from the tool shaft 41 . Preferably, the space between the exterior surface of the tool shaft 41 and the lateral walls 73 is between 5% and 10% of the diameter of the tool shaft 41 . This spacing allows the system to cope with some debris accumulation on the tool 4 and tool holder 71 without preventing or hindering a tool 4 to be placed in the tool holder 71. In this embodiment, the space between the tool shaft 41 and the tool holder lateral walls 73 is approximately 2 to 2.5 mm.

[0065] The spacing is sufficiently small to allow the tool clamp 2 to be placed over the top wings 75 of the tool holder 71 , meaning that the tool clamp 2 receives the top wings 75 in the interior of the housing 27, in the space between the lower side wall portions 24 o and the tool shaft 41 as described in relation to Figure 3c above. In a double mounted position, i.e. , wherein the tool 4 is mounted in both the tool clamp 2 and tool holder 71 simultaneously, the top wing 75 is thus positioned in between the tool shaft 41 , and the lower side wall portions 24 of the tool clamp 2. In such a double mounted position, the thicker parts of the middle pins 42 are supported by the top seat 72 of the top wing 75, and the thinner parts of middle pins 42 are supported by the lower support seat 25 of the tool clamp 2. The tool clamp 2 and tool holder 71 are further aligned to allow the cam tip 36 to contact the edge 77 of the lateral wall 73 when picking up or putting down a tool.

[0066] Figures 5A-F show a method for picking up a tool 4 from a tool holder 71 in a docking station 7. The different steps are illustrated in a side-view of the tool clamp 2 and tool holder 71. For the sake of clarity, continuous lines are used also for most of the components that are not visible in the side-view.

[0067] Fig. 5A illustrates a starting position of the tool clamp 2 for picking up a tool 4. The central axis C of the tool clamp 2 is tilted with respect to a main axis of the tool shaft 41. The robot 1 controls the movement of the tool clamp 2 to approach the tool holder 71 laterally, in a slightly tilted condition. The robot wrist end 16 moves the tool clamp 2 through an X-Z plane, without rotating it, until the upper supporting bar 29 makes contact with the tool shaft 41. A sliding motion through the x-z plane continues until the upper pins 43 engage in the upper support seat 30.

[0068] Figure 5B illustrates the position. The connection that is made allows the upper support structure 29 to pivot around the upper pins 43. After this connection has been made, the robot wrist end 16 is rotated around the transverse axis Y, in the X-Z plane, while pressing the tool 4 downwards into the tool holder 71. Rotation of the tool 4 in the X-Z plane is prevented by the support of the tool shaft 41 in the top seats 72 and lower seats 74 of the tool holder 71 . The resistance provided by the tool holder 71 allows the spring 32 to be extended. Rotation is continued until the cam tip 36 contacts an edge 77 of the lateral walls 73 of the tool holder 71 (Fig. 5C).

[0069] The rotation is then continued further while the cam tips 36 keep in contact with the edge 77 of the lateral walls 73. The resistance provided by the edge 77 pushes the cams 35 inward while the robot 1 continues forcing the rotation. This resistance is sufficient to counteract the bias of the torsion spring 38 that is connected to the cams 35. The cams 35 are rotated and the blocking part 37 is moved away to free up a path for engaging the middle pins 42 in the lower support seats 25. Meanwhile, the rotation continues and the top wings 75 including the top seats 72 are received in between the frame side walls 24 of the tool clamp 2, and the tool shaft 41. [0070] Once the central axis C of the tool clamp 2 is aligned with the main axis of the tool shaft 41 , the rotation is automatically stopped. The lower support seat 25 of the frame 22 has now been moved to a position below the middle pins 42 (Fig. 5D).

[0071] After that, the robot 1 pulls up the tool clamp 2 in a straight upward direction along the central axis (Fig. 5E). The extension springs 32 unload, and the middle pins 42 are automatically received in the lower support seats 25. The tool 4 is now locked in the tool clamp 2 between a clamp formed by the extension spring 32, the lower support seats 25 and upper support structure 29.

[0072] The robot 1 may then move the tool clamp 2 away from the tool holder 71. When removing the tool clamp 2, the torsion spring 38 forces the cams 35 to automatically move back to their neutral position, wherein the blocking part 37 of the cams 35 are positioned above the lower support seats 25 (Fig. 5F). The path to disengage the middle pins 42 is now blocked.

[0073] The entire process of picking up and mounting a tool is driven by robot own movements, and requires no external forces, energy or media to establish the locking, other than reaction forces due to the interaction between the robot 1 and docking station 7. This has several benefits. For example, it makes the tool clamp 2 robust, and relatively cheap. No external actuator apart from the robot itself is required to pick-up a tool.

[0074] The connection takes place through rotation, wherein the tool clamp and tool holder contact each other only at a limited number of contact areas. It is beneficial that the engagement of the tool does not require a surface of the tool clamp and a surface of the tool to slide over each other. In the heavy working environment where a dross removal robot is operating, surfaces easily get dirty or damaged, which may create problems for smooth sliding of two parallel surfaces. The tool clamp according to the invention does not have this problem.

[0075] The method for pick-up is thus robust, and the required accuracy for picking-up a tool is relatively low. Despite the possible inaccuracy of the position of the tool shaft in the tool holder, the tool clamp can still pick up the tool from the tool holder. The robot can operate the tool clamp with a very high accuracy of approximately a few tens of a millimeter. Once the first jaw has engaged the first connecting element, forces are exerted on the tool shaft of the tool against a reaction force provided by the tool holder. These forces dictate the position of the tool shaft in the tool holder that is required for the engagement of the connecting elements by the tool clamp.

[0076] Figures 6A-6E illustrate a method for putting down a tool 4 in a tool holder 71 of a docking station. Fig. 6A illustrates a starting position of the tool clamp 2 for putting away a tool 4. The central axis C of the tool clamp 2 is parallel to the central axis of the tool holder 71. The robot 1 controls the movement of the tool clamp 2 to approach the tool holder 71 without rotating it. [0077] Fig. 6B shows that the tool clamp 2 first contacts the tool holder 71 with the cam tips 36.

The middle pins 42 and lower pins 44 are at a vertical level higher than the top seats 72 and lower seats 74 of the tool holder 71 , respectively. The cam tips 36 need to be aligned with the edges 77 of the lateral walls 73.

[0078] After the first contact between the tool clamp 2 and tool holder 71 has been made, the movement is continued and the cam 35 is pushed inward into the housing 27 of the tool clamp 2, between the upper wall portion 48 and the tool shaft 41. This motion is continued until the lower support seat 25 and middle pins 42 are aligned with the central axis of the tool holder 71. The cam 35 is now fully retracted, and the blocking part 37 has been moved away from the lower support seats 25. [0079] After that, the tool clamp 2 is moved downward, so that the middle pins 42 are received in the top seats 72 of the tool holder 71 , and the lower pins 44 are positioned in the lower seats 74 of the tool holder 71.

[0080] Fig. 6C shows the tool 4 in this double-mounted position. To disengage the tool clamp 2, the robot 1 rotates the wrist end 16, while pushing the tool shaft 41 downward in the top seats 72 and lower seats 74 of the tool holder 71 . The resistance provided by the tool holder 71 results in an extension of the extension spring 32, opening the clamp that is formed by the lower support seat 25 and upper support structure 29. Once the spring has been extended enough, the tool clamp 2 can be removed from the tool holder 71 (Fig. 6D).

[0081] While moving the tool clamp 2 away from the tool holder 71 , the torsion spring 38 forces the cams 35 back into their neutral position. The robot 1 with tool clamp 2 is then ready to pick-up another tool 4 (Fig. 6E).

[0082] The present invention may be embodied in other specific forms without departing from its spirit or essential characteristics. The described embodiments are to be considered in all respects only as illustrative and not restrictive. The scope of the invention is, therefore, indicated by the appended claims rather than by the foregoing description. It will be apparent to the person skilled in the art that alternative and equivalent embodiments of the invention can be conceived and reduced to practice. All changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope.