COUPLING MECHANISM FOR ROBOT TOOL CHANGER WITH INCREASED TORSIONAL STIFFNESS AND ASSOCIATED METHOD

Abstract

Robot tool changer (10) comprising: a tool arrangement (14) comprising: a running ring (38); and a plurality of circumferentially spaced, shell-shaped recesses (40; 40A-40F) formed in the running ring (38), each recess (40; 40A-40F) having a depression (40V) and opposing inclined surfaces (40S); and a master arrangement (12) comprising: an arrangement of bores (28), each bore (28) being configured to receive a roller element (30; 30A-30F); and a cam (32) which is configured to force the rolling elements (30; 30A-30F) into the recesses (40; 40A-40F) to couple the master assembly (12) and the tool assembly (14), and to allow the rolling elements (30; 30A-30F) to retract in order to decouple the master assembly (12) and the tool assembly (14); wherein a plurality of the bores (28) and the rolling elements (30; 30A-30F) located therein are opposite selected recesses (40;40A-40F); and wherein, when the master arrangement (12) and the tool arrangement (14) are coupled, the plurality of bores (28) and the selected recesses (40) are configured to reduce the tendency of the tool arrangement (14) to rotate with respect to the master arrangement (12) by causing the plurality of rolling elements (30) to assume offset positions in the recesses (40; 40A-40F) and to contact opposing inclined surfaces (40S) of the recesses (40; 40A-40F).

Description

RELATED REGISTRATION

[0001] This application claims priority over US patent application No. 17 / 027,931, filed on September 22, 2020, entitled “Robotic Tool Changer Coupling Mechanism with Increased Torsional Stiffness”, the disclosure of which is incorporated herein by reference in full. AREA OF INVENTION

[0002] The present invention relates generally to robot tool changers and in particular to a robot tool changer with a coupling mechanism that achieves increased torsional stiffness and reduced backlash. BACKGROUND

[0003] Industrial robots have become an indispensable part of modern manufacturing. Whether transferring semiconductor wafers from one process chamber to another in a cleanroom or cutting and welding steel on the floor of an automotive plant, robots perform many manufacturing tasks tirelessly, in hostile environments, and with high precision and repeatability.

[0004] In many robotic manufacturing applications, the significant cost of an industrial robot is amortized across a wide range of tasks by providing various tools or end effectors that can be coupled to a general-purpose robot arm. For example, in automotive manufacturing, a robot might be used in one production run to cut, grind, or otherwise shape metal parts, while in another it performs various spot welding operations. Furthermore, a robot can utilize different tools even while performing a single task. For instance, welding tools with different geometries can be advantageously paired with a particular robot to perform welding tasks at different locations or in different orientations.

[0005] In these applications, a robot tool changer is used to couple different tools to the robot. One half of the tool changer, called the master assembly, is permanently attached to a robot arm. The other half, called the tool assembly, is attached to each tool that the robot can use. When a robot controller aligns the master assembly at the end of the robot arm with a tool assembly attached to the desired tool, it causes the master assembly to mechanically couple with the tool assembly, thus attaching the tool to the robot. Robot tool changers also facilitate the supply of utilities to the tool, such as electricity, compressed air, hydraulic fluid, cooling water, etc., as well as the transmission of data from some tools back to a robot controller.

[0006] A ball-lock configuration is commonly used as a coupling mechanism in robot tool changers. In such a configuration, a variety of rolling elements, such as steel balls, are contained within a projection of the master assembly, which is positioned in a chamber of a tool assembly. The balls are driven radially, for example by an advancing piston, and move forward to engage a raceway in the tool assembly, thus mechanically coupling the master and tool assemblies. To uncouple, the piston is retracted, and the balls retract into the projection as the master assembly separates from the tool assembly. Various configurations, drive mechanisms, and operational aspects of such ball-lock configurations are described in U.S. patents 8,005,570; 8,132,816; 8,209,840; 8,500,132; 8,533,930; and 8,601,667. 8,794,418; 9,151,343; 9,724,830; and 10,335.957. All of these patents have been assigned to the successor in title of the present application, and the disclosures of all of these patents are incorporated herein by reference in their entirety.

[0007] Alignment between the master and tool assemblies is necessary for the proper mechanical coupling of the ball locking mechanism with the tool assembly's bearing ring and for coupling the modules attached to the master and tool assemblies for the passage of operating materials. This alignment is typically achieved by one or more alignment pins on the master assembly that interact with corresponding alignment bushings in the tool assembly. Furthermore, these alignment pins and bushings also provide torsional stiffness to the coupled tool when the robot is in operation. To prevent jamming, a small diametrical clearance between an alignment pin and its associated alignment bushing is required.This minute amount of play is the primary cause of rotational backlash in the tool changer, negatively impacting positional repeatability and torsional stiffness. This effect is amplified with large tools at the end of the arm and can lead to undesirable deviations or positional errors at the operating point of each end effector. Backlash also causes problems with electrical signal modules attached to tool changers, as the contact pins on the master and tool sides can move relative to each other, potentially resulting in intermittent signal loss. Furthermore, this back-and-forth movement can cause excessive wear, leading to premature failure.

[0008] To reduce torsional play, it is known to incorporate spherical or cylindrical recesses—referred to here as "shells" or "scallops"—into the tool bearing ring of the tool assembly at the corresponding position of the respective roller element. These features reduce the play but do not eliminate it. A disadvantage of known designs is that the shell features must inherently have larger radii than the corresponding roller elements to prevent jamming. This diametrical play provides the roller elements with a tiny amount of play to wobble back and forth within their respective shells under reverse torsional loads.For coupling purposes, each roller element has a three-point contact, with one contact point being the bottom of the bore in the master assembly's projection, a second contact point being the bottom of the shell in the tool's running ring, and a third point located on the conical piston cam. These three contact points lie in the same plane and are spaced approximately 120 degrees apart, although the contact point on the piston or any other mechanism that moves the roller elements forward does not carry any significant torsional coupling load. This three-point contact arrangement, combined with even the slightest clearance, is sufficient to generate detrimental torsional play in the tool changer.

[0009] The background section of this document serves to place embodiments of the present invention in a technological and operational context in order to help those skilled in the art to understand their scope and benefits. Unless expressly identified as such, none of the statements contained herein shall be deemed prior art merely by virtue of their inclusion in the background section. SUMMARY

[0010] The following is a simplified summary of the disclosure to provide the person skilled in the art with a basic understanding. This summary is not a comprehensive overview of the disclosure and is not intended to identify important / critical elements of embodiments of the invention or to define the scope of the invention. The sole purpose of this summary is to present some concepts disclosed herein in simplified form as a prelude to the more detailed description that follows.

[0011] According to the invention, a robot tool changer according to independent claim 1 or independent claim 10 and a method for coupling a master assembly and a tool assembly of a robot tool changer according to independent claim 7 are provided. The dependent claims define preferred and / or advantageous embodiments of the invention. The disclosed tool-changing robot is designed to reduce or minimize torsional play and increase torsional stiffness. As already mentioned, when the master and tool assembly of a robot tool changer are coupled, the torsional stiffness is often weak, resulting in play about the z-axis of the tool changer. To improve torsional stiffness, the running ring of the tool assembly is provided with a plurality of circumferentially spaced, shell-like ("scalloped") recesses or depressions.Each recess has a depression and opposing inclined surfaces, i.e., inclined surfaces on each side of the depression. In one embodiment, the master and tool assemblies are coupled by forcing a plurality of roller elements into contact with opposing inclined surfaces of the recesses. That is, some roller elements contact one of the inclined surfaces of a set of recesses, while other roller elements contact the opposing inclined surfaces of other recesses. The resulting contacts between the roller elements and the inclined surfaces prevent or minimize relative rotation between the master and tool assemblies.

[0012] In one embodiment, the shell-shaped recesses are evenly distributed around the raceway. Misalignment between the rollers and the recesses is achieved by modifying the roller-bore pattern in the master assembly. Unlike the recesses, the bores in the master assembly are not all equidistant. Two pairs of aligned bores are slightly offset relative to the position of the intended recesses. This causes the rollers of the two pairs of bores to contact opposing inclined surfaces of several recesses.

[0013] Further features and advantages of the present invention will become clear and obvious from studying the following description and the accompanying drawings, which serve only to illustrate the invention. List of characters

[0014] The present invention is described in more detail below with reference to the accompanying drawings, which illustrate embodiments of the invention. However, the present invention is not to be understood as being limited to the embodiments shown herein. Rather, these embodiments are provided to ensure that this disclosure is thorough and complete and fully conveys the scope of the invention to those skilled in the art. Reference numerals refer throughout to the same elements. Fig. Figure 1 is a perspective view of a robot tool changer. Fig. Figure 2 is a cross-sectional view of the robot tool changer in a coupled state. Fig. 3A is a perspective view showing the circular approach of the master arrangement and the running ring of the tool arrangement. Fig. 3B is an enlarged view of one of the shell-like recesses in the running ring. Fig. 3C is a perspective view showing the circular projection and the running ring, and furthermore showing the rolling elements that are accommodated in the bores formed in the annular running ring and touch the inclined surfaces of the recesses in the running ring. Fig. Figure 4 is a schematic representation showing a series of rolling elements in contact with opposing inclined surfaces of various recesses in the running ring. Fig. Figure 5 is a cross-sectional view showing the contact points between a multitude of roller elements and the inclined surfaces of various recesses, as well as the resulting force vectors. Fig. 5A shows the contact of a rolling element with the right inclined surface of a recess. Fig. Figure 5B illustrates the contact of a rolling element with the left inclined surface of a recess. Fig. Figure 6 is a schematic view illustrating the offset of selected holes in the master arrangement to cause a misalignment of selected holes with different recesses in the bearing ring. Fig. Figure 7 shows an alternative embodiment and is a schematic view illustrating the offset of selected recesses in the tool arrangement to cause a misalignment of selected bores and the rolling elements located therein with different recesses in the running ring of the tool arrangement. DETAILED DESCRIPTION

[0015] For the sake of simplicity and illustration, the present invention is described primarily with reference to an exemplary embodiment. Numerous specific details are set forth in the following description to provide a comprehensive understanding of the present invention. However, it is readily apparent to a person skilled in the art that the present invention can also be carried out without being limited to these specific details. Known methods and structures have not been described in detail in this description in order to avoid unnecessarily obscuring the present invention.

[0016] Fig. Figure 1 shows a robot tool changer 10 that uses a ball-lock coupling mechanism. One half of the robot tool changer 10, called the master assembly 12, is permanently attached to a robot arm (not shown). The other half, called the tool assembly 14, is attached to each tool (not shown) that the robot can use. In a specific application, these attachments may be reversed. Accordingly, the terms "master" and "tool" are used here as reference terms. As described in Figure 1, the tool assembly 14 is attached to each tool (not shown) that the robot can use. Fig. As can be seen in Figure 1, alignment pins 16 on the master assembly 12 fit into alignment sockets 18 on the tool assembly 14 to ensure correct alignment of the master and tool assemblies 12, 14 when the assemblies are coupled together.

[0017] The master assembly 12 has a housing 20 and a circular projection 22 that extends from it and beyond the plane of the surface of the housing 20. The tool assembly 14 has a housing 24 and a circular chamber 26 formed therein. A bearing ring 38 is located in the chamber 26. The bearing ring 38 has a series of circumferentially spaced, shell-like recesses or depressions 40 (see Fig. 3A, Fig. 3B). As it is in Fig. As shown in Figure 2, the approach 22 is located in the chamber 26 when the master and tool arrangements 12, 14 are coupled, and is spaced inwards from the running ring 38.

[0018] The projection 22 has several bores 28 extending through it. The bores 28 are spaced circumferentially around the projection 22. The bores 28 may taper and have a slightly larger diameter on the inner surface of the projection 22 than on the outer surface. Each bore 28 contains a rolling element 30, e.g., a spherical ball. Each rolling element 30 is held within the projection by a tapered bore 28, which has a diameter on the outer surface of the projection 22 that is slightly smaller than the diameter of the corresponding rolling element 30.Accordingly, the rolling element 30 moves between a retracted position, in which the outermost surface of the rolling element is flush with or within the outer surface of the projection 22, and an extended position, in which each rolling element 30 extends beyond the outer surface of the projection 22 by an amount that is typically slightly smaller than the radius of the rolling element 30.

[0019] In this embodiment, a cam 32, attached to the end of a pneumatic piston, is arranged within the interior space defined by the projection 22. The cam 32 has at least one conical surface 34 which contacts the roller elements 30 when the master and tool assemblies are coupled. The conical surface 34 is oriented such that it engages with the roller elements 30 and displaces them radially outward through the bores 28 as the cam moves toward the tool assembly 14 to couple the master and tool assemblies 12, 14. To uncouple, the cam 32 retracts into the master assembly 12, thus creating a space that allows the roller elements 30 to retract into the projection 28.In other embodiments, the rolling elements 30 can be extended and retracted by a mechanism other than a cam attached to a pneumatic piston, as described in the above-mentioned patents US 8,132,816 and US 8,209,840.

[0020] Fig. Figure 2 is a sectional view of the robot tool changer 10, showing the coupled master and tool assemblies 12, 14. The cam 32 is designed to move between a retracted and an extended position. The term "designed to" used here and in the claims means "constructed to". Fig. 2. The cam 32 assumes the extended position. The movement of the cam 32 is controlled by a robot controller (not shown). When the cam 32 moves from the retracted to the extended position, it engages with the roller elements 30 and pushes them outwards through the bores 28.

[0021] In the fully extended position, the cam 32 moves the rolling elements 30 into contact with the shell-like recesses 40 formed in the running ring 38 of the tool assembly 14. How the rolling elements 30 come into contact with sections of the recesses 40 is explained in more detail below. In any case, it shows Fig. 2 the coupled master and tool arrangement 12, 14. The Z-axis of the robot tool changer 10 is in Fig. Figure 2 shows that when the robot tool changer is coupled, the Z-axis passes through the centers of the projection 22 and the bearing ring 38. As explained below, the projection 22, the bores 28, the roller elements 30, and the recesses 40 are designed to prevent or minimize relative rotation about the Z-axis.

[0022] Fig. Figure 3A shows sections of the master and tool arrangement 12, 14. In this embodiment, the projection 22 has six bores 28 and six roller elements 30. The number of bores and roller elements can vary. The bores 28 are spaced circumferentially around the projection 22 and arranged such that pairs of bores are aligned with each other. Consequently, pairs of roller elements 30 are also aligned. As is also shown in Fig. As shown in Figure 3A, the shell-shaped recesses 40 are arranged circumferentially around the running ring 38 of the tool assembly 14. Pairs of the shell-shaped recesses 40 are also aligned. When the cam 32 is fully extended, the rolling elements 30 therefore project outwards from the projection 22 and contact sections of the shell-shaped recesses or indentations 40. As explained below, at least some of the rolling elements 30 are not located exactly in the center of the shell-shaped recesses 40. That is, some of the rolling elements 30 are slightly misaligned with the shell-shaped recesses 40.

[0023] Each shell-shaped recess 40 has a depression 40V and opposing inclined surfaces 40S extending from the depression. See Fig. 3A and Fig. 3B. The recess 40V is located in the center of the shell-shaped indentation 40. The inclined surfaces 40S are located on both sides of the recess 40V. If one of the indentations 40 is considered a reference point, one of the inclined surfaces is referred to as the left inclined surface and the other as the right inclined surface. The term "opposite inclined surface" or "opposite inclined surfaces" refers to the left and right inclined surfaces of a recess 40. In the illustrated embodiments, the inclined surfaces 40S are bent or curved. The radius of curvature can vary. It must be dimensioned such that the rolling element 30 contacts one of the inclined surfaces 40S and is simultaneously at least slightly offset from the center of the indentation.As will be discussed further below, the robot tool changer 10 is designed such that at least some of the roller elements 30 engage with and touch the inclined surfaces 40S – not the recess 40V – when the master and tool arrangements 12, 14 are coupled. See . Fig. 5A and Fig. 5B.

[0024] In one embodiment, two roller elements touch the right inclined surface of opposing recesses, while two other roller elements touch the left inclined surface of other opposing recesses. See Fig. 4 and Fig. 5. To provide this contact pattern, some of the bores 28 and their roller elements 30 are misaligned with respect to their intended recesses, where an intended recess is a recess that is the target of a roller element 30 during coupling. When seated on one of these inclined surfaces 40S of a recess 40, the roller element 30 is slightly offset relative to the depression 40V of the recess. Since the left and right inclined surfaces of a plurality of recesses 40 are contacted by multiple roller elements 30, relative rotation between the master and tool assembly 12, 14 is prevented or minimized. This contributes to the torsional stiffness of the robot tool changer 10.

[0025] Fig. Figure 4 illustrates these principles schematically. Here, four roller elements (30A, 30B, 30C, and 30D) are shown contacting the inclined surfaces of four recesses (40A, 40B, 40C, and 40D). It should be noted that the center lines of the opposing roller elements 30 are slightly offset from the center or recess 40V of the intended recesses. Roller elements 30A and 30B contact the right inclined surfaces of the recesses 40A and 40B. This prevents or minimizes the counterclockwise rotation of the recesses, and thus of the tool assembly 14, relative to the master assembly 12. Similarly, roller elements 30C and 30D contact the left inclined surfaces of the recesses 40C and 40D. This prevents or minimizes the clockwise rotation of the recesses, and thus of the tool assembly 14, relative to the master assembly 12.Thus, if there is any relative rotation at all, it is very small between the master and the tool arrangement 12, 14, which leads to an increase in the torsional stiffness of the tool changer 10.

[0026] Fig. Figure 5 is a horizontal sectional view of the tool changer 10. It is similar in some respects to the Fig. Figure 4 is more detailed in that it shows all the rolling elements that are in contact with the respective recesses. Also shown are the contact points C of rolling elements 30A, 30B, 30C, and 30D, and the resulting force vectors. In addition to these four rolling elements, two further rolling elements, 30E and 30F, are shown, which are located in the recesses 40E and 40F. Unlike the other rolling elements, rolling elements 30E and 30F are located directly in the opposite recesses 40E and 40F. This effectively reinforces the connection between the master and tool arrangements 12, 14. The contact points C along the reference lines 50, 52 should be noted. Reference lines 50, 52 pass through the contact points C and form an "X". Fig. Figure 5 shows the resulting force vectors arising from the contact of a rolling element with the inclined surfaces 40S of the respective recesses 40. On each side of the tool changer 10, the resulting force vectors are generally opposite, and this prevents or at least minimizes the relative rotation between the master and tool arrangements 12, 14.

[0027] There are several ways in which the bores 28 and the roller elements 30 located therein may be misaligned with the intended recesses 40. One approach is to vary the angular distance of the bores 28 or the recesses 40 so that, when the master and tool arrangements 12, 14 are coupled, selected bores are not precisely aligned with the corresponding recesses 40. For practical reasons, it may be advantageous to make this adjustment with respect to the bores 28 so that the master arrangement 12 fits appropriately with existing tool arrangements 14 on site. Fig. Figure 6 is a schematic representation illustrating the spacing of the holes that leads to this misalignment or offset. The reference lines 100 (the long dashed lines) show the circular projection 22, which is divided into six equal quadrants, each quadrant being a 60° quadrant. In this example, the reference lines 100 are aligned with the center of the shell-shaped recesses 40 when the master and tool arrangements 12, 14 are coupled. The reference lines 102 show the centerlines of selected holes 28, which are slightly offset relative to the reference lines 100. This means, of course, that the rolling elements 30 in these four holes are misaligned with respect to the nominal recesses 40 when the master and tool arrangements 12, 14 are coupled. The degree of angular deviation between the reference lines 100 and 102 can vary. In this example, the difference is approximately 2°.

[0028] The same effect can be achieved by slightly shifting the roller element bore planes. That is, the roller element bore planes are slightly offset so that selected roller elements 30 touch opposite inclined surfaces 40S of the recesses 40.

[0029] Fig. Figure 7 illustrates an alternative embodiment in which selected recesses 40A, 40B, 40C, and 40D are arranged slightly offset from the corresponding rolling elements 30A, 30B, 30C, and 30D, resulting in a misalignment of the selected recesses relative to the corresponding rolling elements. This embodiment is similar to the one shown in Fig. 5 shown embodiment, with the difference that in the embodiment of Fig. 7. The bores and roller elements are all equally spaced, while four of the recesses 40A, 40B, 40C, and 40D are slightly offset with respect to the four roller elements 30A, 30B, 30C, and 30D. This offset is in Fig. 7 illustrated by the angle β, where the angle α represents the equal distance between the holes and the rolling elements 30A - 30F. As in the Fig. 5 and Fig. In the embodiment shown in Figure 6, this relationship between the respective recesses and rolling elements leads to force vectors that arise from the contact of a rolling element with inclined surfaces 40S of the respective recess 40. The resulting force vectors are generally opposite, thereby preventing or at least minimizing a relative rotation between the master and the tool arrangement 12, 14.

[0030] Embodiments of the present invention offer numerous advantages over the prior art. In the embodiment of the Fig. For example, opposing contact forces are applied to two roller elements on each side of the tool changer. See the four in Fig.The force vectors shown in Figure 5 prevent the respective roller elements 30 from moving from one side to the other. By having some roller elements 30 touch the left inclined surfaces of some recesses 40 and other roller elements touch the right inclined surfaces of other recesses, these contact points practically eliminate the torsional play in the robot tool changer 10.

[0031] The present invention can, of course, also be implemented in ways other than those specifically set forth herein without deviating from the essential features of the invention. The present embodiments are to be regarded in every respect as illustrative and non-limiting, and all modifications that fall within the scope and equivalence of the appended claims are intended to be included therein. QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] US 17 / 027931

[0001] US 8132816

[0019] US 8209840

[0019]

Claims

[1] Robot tool changer (10) comprising: a tool arrangement (14) comprising: a bearing ring (38); and a plurality of circumferentially spaced, shell-like recesses (40; 40A-40F) formed in the running ring (38), each recess (40; 40A-40F) having a depression (40V) and opposing inclined surfaces (40S); and a master arrangement (12) comprising: an arrangement of bores (28), each bore (28) being configured to accommodate a rolling element (30; 30A-30F); and a drive mechanism (32) which is designed to force the roller elements (30; 30A-30F) into the recesses (40; 40A-40F) to couple the master arrangement (12) and the tool arrangement (14), and to allow the roller elements (30; 30A-30F) to retract in order to decouple the master arrangement (12) and the tool arrangement (14); wherein a large number of the bores (28) and the rolling elements (30; 30A-30F) located therein are incorrectly aligned with selected recesses (40; 40A-40F); and wherein, when the master arrangement (12) and the tool arrangement (12) are coupled, the plurality of bores (38) and the selected recesses (40) are designed such that they reduce the tendency of the tool arrangement (12) to rotate with respect to the master arrangement (12) by causing the plurality of rolling elements (30) to assume offset positions in the recesses (40; 40A-40F) and to contact opposing inclined surfaces (40S) of the recesses (40; 40A-40F). [2] Robot tool changer (10) according to claim 1, wherein the recesses (40V) of the cutouts (40; 40A-40F) have a center point, and wherein, when the master arrangement (14) and the tool arrangement (12) are coupled, the plurality of roller elements (30; 30A-30F) do not contact the center point of the recesses (40V). [3] Robot tool changer (10) according to claim 1 or claim 2, wherein: the plurality of bores (28) has a first pair of aligned bores (28) and a second pair of aligned bores (28); wherein the first pair of aligned holes (28) has a first pair of aligned roller elements (30A, 30B), each of the first pair of roller elements (30A, 30B) contacting a right inclined surface of a first pair of opposing recesses (40A, 40B); and wherein the second pair of aligned holes (28) has a second pair of aligned rolling elements (30C, 30D), wherein each of the second pair of rolling elements (30C, 30D) contacts a left inclined surface of a second pair of the opposite recesses (40C, 40D). [4] Robot tool changer (10) according to claim 3, wherein contact points (C) between the roller elements (30A-30D) and inclined surfaces of the recesses (40A-40D) together with connected reference lines (50, 52) form a general “X” shape. [5] Robot tool changer (10) according to claim 3 or claim 4, wherein a central axis of the first pair of aligned holes (28) is generally aligned with a 10 and a 4 o'clock position on the tool changer (10); and wherein a central axis of the second pair of aligned holes (28) is generally aligned with an 8 and a 2 o'clock position on the tool changer (10). [6] Robot tool changer (10) according to one of the preceding claims, wherein the plurality of recesses (40; 40A-40F) are spaced evenly around the running ring (38); wherein the plurality of bores (28) are formed in a circular projection (22) which forms part of the master arrangement (12); and wherein all of the plurality of bores (28) are not spaced evenly around the circular projection (22), since some of the bores (28) are offset relative to the opposite recesses (40; 40A-40F) in the running ring (38), resulting in a misalignment of a plurality of the roller elements (30; 30A-30F) and the opposite recesses (40; 40A-40F). [7] Method for coupling a master arrangement (12) and a tool arrangement (14) of a robot tool changer (10), comprising: Moving a plurality of roller elements (30; 30A-30F) arranged in bores (28) in the master arrangement (12) in the direction of a plurality of shell-like recesses (40; 40A-40F) formed in a running ring (38) of the tool arrangement (14), wherein each shell-like recess (40; 40A-40F) has a depression (40V) and opposing inclined surfaces (40S); Placing the majority of the roller elements (30; 30A-30F) onto opposing inclined surfaces (40S) of the recesses (40; 40A-40F) by misaligning the roller elements (30; 30A-30F) with the recesses (40; 40A-40F) and contacting the inclined surfaces (40S) with the roller elements (30; 30A-30F), so that the roller elements (30; 30A-30F) are offset with respect to the recesses (40V) of the recesses (40; 40A-40F); and wherein some of the rolling elements (30; 30A-30F) contact an inclined surface (40S) of some recesses (40; 40A-40F) and other rolling elements (30; 30A-30F) contact the opposite inclined surface (40S) of other recesses (40; 40A-40F), thereby generating counterforces which prevent or minimize a relative rotation between the master arrangement (12) and the tool arrangement (14). [8] Method according to claim 7, wherein the rolling elements comprise a first pair of aligned rolling elements (30A, 30B) and a second pair of aligned rolling elements (30C, 30D); and wherein the inclined surfaces (40S) which are contacted by the first pair of aligned rolling elements (30A, 30B) are opposite the inclined surfaces (40S) which are contacted by the second pair of aligned rolling elements (30C, 30D). [9] Method according to claim 8, wherein the first pair of aligned rolling elements (30A, 30B) and the second pair of aligned rolling elements (30C, 30D) and their respective contact points (C) with the inclined surfaces (40S) form a general “X” configuration. [10] Robot tool changer (10) comprising: a tool arrangement (14) comprising: a bearing ring (38); and a plurality of recesses (40; 40A-40F) formed in the bearing ring (38), wherein the recesses (40; 40A-40F) are spaced apart circumferentially around the bearing ring (38) and each recess (40; 40A-40F) has a depression (40V) and opposing inclined surfaces (40S); and a master arrangement (12) comprising: a circular approach (22); an arrangement of bores (28) formed in the projection (22), each bore (28) being designed to accommodate a rolling element (30; 30A-30F); and a drive mechanism (32) which is designed to force the roller elements (30; 30A-30F) into the recesses (40; 40A-40F) to couple the master arrangement (12) and the tool arrangement (14), and to allow the roller elements (30; 30A-30F) to retract in order to decouple the master arrangement (12) and the tool arrangement (14); wherein the arrangement of bores (28) comprises a first pair of generally oriented bores (28) which are formed in the projection (22) and a first pair of rolling elements (30A, 30B) and a second pair of generally oriented bores (28) which are formed in the circular projection (22) and which have a second pair of rolling elements (30C, 30D); where, if the master arrangement (12) and the tool arrangement (14) are coupled: the first and second pair of holes (28) and the first and second pair of roller elements (30A-30D) therein are misaligned with respect to the respective recesses (40A-40D); wherein the respective roller elements are offset in relation to the recesses (40V) in the designated cutouts (40A-40D) and contact inclined surfaces (40S) of the respective designated cutouts (40A-40D); wherein the rolling elements (30A, 30B) of the first pair of bores (28) contact inclined surfaces (40S) of two predetermined recesses (40A, 40B), which are opposite the inclined surfaces (40S) that are contacted by the rolling elements (30C, 30D) of the second pair of holes (28); and the torsional stiffness of the tool changer (10) is increased, since respective contact points (C) between the rolling elements (30; 30A-30D) and the inclined surfaces (40S) prevent or minimize rotation of the tool arrangement (14) relative to the master arrangement (12). [11] Robot tool changer (10) according to claim 10, wherein the first pair of bores (28) and the second pair of bores (28) and the rolling elements (30A-30D) located therein are designed such that they assume a general “X” configuration in the tool changer (10). [12] Robot tool changer (10) according to claim 11, wherein the first pair of roller elements (30A, 30B) is configured to contact the inclined surfaces (40S) of the two recesses (40A, 40B) and prevents or minimizes the tool arrangement (14) from rotating in one direction relative to the master arrangement (12); and wherein the second pair of roller elements (30C, 30D) is configured to contact the inclined surfaces (40S) of two other recesses (40C, 40D) and prevents or minimizes the tool arrangement (14) from rotating in the opposite direction relative to the master arrangement (12).

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