The present invention relates to an automatic robot tool changer that enables a robot arm to be coupled to a tool or decoupled from a tool solely by means of the movement of the robot arm .

Prior art

Small robots that are configured to handle objects or for performing simple operations, typically comprise a robot arm and a tool such as a gripping device.

The robot arm is controlled by a computer equipped with a control program, by which it is possible to rotate the joints of the robot arm in order to make the robot arm perform a desired movement or maintain a particular configuration (position). The robot arm together with the associated control program typically constitutes a standard device suited for many different types of tasks. A tool configured to perform a single specific task, is arranged on the end portion of the robot arm . Since the tool is adapted to perform a single task, it is necessary to change the tool in case the robot is intended to perform another type of task.

If it is required to change the tool, the tool can be unscrewed. Alternatively, it is possible to attach the tool to the robot arm by means of a tool changer. By using the tool changer, an operator can detach a tool from the robot arm and attach another tool without using any additional worktools. Often, however, pneumatic and electrical connections between the robot arm and the tools must be replaced manually by the operator when changing a tool. Some advanced manual tool changers, however, comprise special connectors allowing for automatic connection of electrical and pneumatic connections upon replacement or change of a tool.

When different tools are being detached and attached from a robot arm, it is important that the replaced tool is arranged exactly in the same position during attachment. Otherwise, the robot will lose its accuracy and needs to be reprogrammed in order to use the tool again. Accordingly, manual tool changers are typically formed as flange couplings that are very accurate and configured to be assembled by using a rotatable catch or a union nut.

Larger robots that need to change between different tools typically comprise an automatic tool changer. In these tool changers, the flanges are typically tightened by means of pneumatic means, hydraulic means or an electric motor integrated in the coupling.

E.g. US 8,500,132 B2 describes a coupling for attachment of a tool on a robot arm. The coupling comprises two halves, wherein a kinematic coupling having three contact elements arranged on a contact surface to form a triangle, constitutes the contact surface between the robot arm and the tool. It is desirable to provide a simpler alternative to this solution. Thus, it is an object of the present invention to provide an alternative automatic tool changer that is simpler.

The automatic tool changer according to the invention utilises the motion of the robot arm to couple and decouple a tool. The automatic tool changer according to the invention comprises a lock mechanism that is driven by the movement of the robot arm .

Summary of the invention

The object of the present invention can be achieved by an automatic tool changer as defined in claim 1. Preferred embodiments are defined in the dependent subclaims, explained in the following description and illustrated in the accompanying drawings.

The tool changer according to the invention is a tool changer for attaching a tool to a robot arm, said tool changing comprising a first part having a contact surface and a second part having a contact surface, wherein three contact elements are arranged on the contact surfaces of the first part and the second part, wherein the three contact elements are arranged in a triangular configuration and constitute a kinematic coupling, wherein the robot arm by carrying out a number of movements can connect and disconnect the tool, wherein the kinematic coupling comprises a Kelvin coupling, wherein the three contact elements comprise:

a) a first contact element comprising a sphere arranged at the contact surface of the first part, wherein said sphere is arranged and configured to be brought into contact with three spheres arranged at the contact surface of the second part,

b) a second contact element comprising a sphere arranged at the contact surface of the first part, wherein said sphere is arranged and configured to be brought into contact with two spheres arranged at the contact surface of the second part,

c) a third contact element comprising a sphere arranged at the contact surface of the first part, wherein said sphere is arranged and configured to be brought into contact with another sphere arranged at the contact surface of the second part.

Hereby, it is possible to provide an alternative automatic tool changer that is simpler than the ones known from the prior art. In one embodiment, the three spheres arranged on the contact surface of the second part are arranged in a configuration, in which the line extending between the center of one of the spheres and the center of the sphere extends perpendicular to the line extending between the center of the another of the spheres. Hereby, it is possible to provide a contact point that allows the two parts to be freely moved (e.g. rotated) in several dimensions in order to allow the remaining spheres to be brought into contact hereby connecting the first part and the second part to each other in a manner in which the first part and the second part are arranged in a predefined position relative to each other. In one embodiment, the two spheres arranged on the contact surface of the second part are arranged in a configuration, in which the line extending between the center of one of the two spheres and the center of the sphere extends perpendicular to the line extending between the center of the another one of the two spheres. Hereby, it is possible to provide a contact point that allows the two parts to be freely moved (e.g. rotated) in several dimensions in order to allow the remaining spheres to be brought into contact hereby connecting the first part and the second part to each other in a manner in which the first part and the second part are arranged in a predefined position relative to each other.

In one embodiment, the line extending between the centers of the two spheres arranged at the contact surface of the second part extends perpendicular to the line extending between the common center of the three spheres and the center of the two spheres. Hereby, it is possible to provide a contact point that allows the two parts to be freely moved (e.g. rotated) in several dimensions in order to allow the remaining spheres to be brought into contact hereby connecting the first part and the second part to each other in a manner in which the first part and the second part are arranged in a predefined position relative to each other.

It may be an advantage that the line extending between the center of the sphere arranged on the contact surface of the first part and the center of the sphere arranged on the contact surface of the second part extends perpendicular to the contact surface of the first part and/or the contact surface of the second part. In one embodiment, the first part or the second part comprises a hook and the other part comprises a corresponding structure configured to engage with the hook, wherein the hook is arranged to pull the two parts together and hereby make the two parts become attached to each other. Hereby, the hook can be used to maintain the parts together. This is an advantage if the various parts are influenced by external forces that tend to pull the various parts away from each other. In one embodiment, the hook is attached to a rotatably mounted crank, wherein the crank is arranged and configured to be released from the corresponding structure upon rotation of the crank in a rotational direction, wherein the crank is arranged and configured to pull the first part and the second part together upon rotation of the crank in an opposite rotational direction.

Hereby, it is possible to release the first part and the second part from each other as well as to pull the first part and the second part towards each other, simply by rotating the crank.

In one embodiment, the tool changer comprises a string of spheres (a plurality of spheres pairwisely arranged next to each other) and a canal extending around the crank, wherein the string of spheres is arranged and configured to be inserted into a first portion of the canal, followed by rotating the crank in a first rotational direction. Hereby, the string of spheres can be used to drive the crank.

In one embodiment, the crank comprises a wing or a pin arranged to engage with the spheres of the string of spheres, wherein said wing or a pin is arranged and configured to rotate the crank in the opposite rotational direction by pressing the string of spheres into another portion (e.g. the opposite side) of the canal while the wing or a pin simultaneously pushes the spheres in the opposite direction. Hereby, it is possible to provide a simple way of driving the crank.

In one embodiment, the tool changer comprises two strings of spheres arranged in two canals or tubes extending around the crank, wherein the two canals or tubes that discharge into a track that surrounds that part, at which the crank is attached, wherein the track is configured to maintain the spheres of the string of spheres by means of a rotatable annular structure provided with two end stops, wherein the end stops are arranged to restrict the motion of the spheres of the string of spheres in such a manner that rotation of the annular structure will force the spheres of the string of spheres forward through either of the canals depending on the direction at which the annular structure is rotated, wherein the distal portion (towards the end stop) of the spheres of the string of spheres may be replaced by a helix or a bendable rod or pipe. Hereby, it is possible to drive the crank and thus the hook by using an annular structure accessible from the outside of the tool changer.

In one embodiment the hook comprises a pin protruding from the hook arranged to engage with a guiding track extending along a portion of the hook, wherein the guiding track has a geometry and is arranged in such a manner:

- that the distal portion of the hook is moved away from the point of engagement when the crank is rotated into a position, in which the hook is brought out of engagement with the corresponding structure (e.g. a pin or a rod member arranged and configured to engage with the hook) and

- that the distal portion of the hook is moved towards the point of engagement when the crank is rotated into a position, in which the hook is brought into engagement with the corresponding structure. Herby, the movement path of the hook can be controlled in a simple and reliable manner.

The track moreover allows the pin to have a large freedom of movement at the last part of the motion of the crank, in which the hook is in engagement with the corresponding structure and in which the motion of the hook accordingly is controlled by the contact at the engagement point and the motion of the crank.

In one embodiment, the corresponding structure is a conical rod member arranged in a conical hole, wherein the longitudinal axis of the rod member is angled relative to the surface of the first part and/or the surface of the second part.

It may be preferred that the surface which the hook abuts has a plane extending parallel to the contact surface of the first part and/or the second part.

At the same time, it may be advantageous that the rod member is restricted from moving along its longitudinal axis by means of an adjustable stop arranged at either one or each end of the rod member.

In one embodiment, the tool changer comprises a) a switch configured to be activated when the first part and the second part are connected, and b) a number of switches configured to be activated by the motion of the hook or the rotation of the crank. Hereby, it can be detected electrically when the first part and the second part are in connection with each other.

It may be an advantage that the switches are arranged in a circuit comprising a number of resistors arranged to constitute a voltage divider, in which an output voltage measurement point is provided . Hereby, one can carry out a voltage measurement.

In one embodiment the switches are arranged in a circuit comprising a plurality of resistors arranged in such a manner that the output voltage from the voltage divider has a predefined value that. This can, thus, be used to identify a tool attached to the tool changer.

It may be beneficial to have a system comprising a) a tool changer according to the invention having track structure, and b) a holding device comprising a plate provided with an opening and a recess having a geometry that allows the plate to be inserted into the track structure.

It may be advantageous that the plate is suspended in one or more resilient members (e.g. springs) in such a manner that the plate can be moved, which will allow the tool changer to be more easily attached to the plate.

Description of the Drawings

The invention will become more fully understood from the detailed description given herein below. The accompanying drawings are intended for illustration purposes only, and thus, they are not limitative of the present invention in any way. In the accompanying drawings: Fig. 1 shows a tool changer according to the invention in an open configuration;

Fig. 2A shows the tool changer shown in Fig. 1 seen from a slightly different view;

Fig. 2B shows the engagement between a sphere of the first part brought into engagement with two of the three spheres of the second part that constitute a second engagement point;

Fig. 2C shows a triangle, from which the distance between adjacent spheres constituting the second engagement point can be determined;

Fig. 2D shows the configuration of the spheres of the first part constituting the first engagement point and the second engagement point;

Fig. 3 shows a cross-sectional view of a tool changer according to the invention;

Fig. 4 shows the tool changer shown in Fig. 3 in a locked configuration;

Fig. 5 shows a cross-sectional view of a tool changer according to the invention;

Fig. 6 shows another cross-sectional view of the tool changer shown in Fig. 5;

Fig. 7 shows a string of spheres used in one embodiment of the invention;

Fig. 8 show a side view of the tool changer shown in Fig. 7;

Fig. 9 shows a tool changer according to the invention;

Fig. 10 shows a tool changer according to the being arranged in a holding device,

shows the tool changer shown in Fig. 10 arranged in the holding device;

shows a tool changer according to the invention in a configuration in which the first coupling part is arranged in a holding device, whereas the second coupling part is arranged under the holding device;

shows a diagram for a circuit of a tool changer according to the invention;

shows a top view of a tool changer according to the invention;

shows the engagement between a sphere from the first part brought into engagement with two of the three spheres of the second part that constitute a second engagement point and

shows engagement of two single spheres attached to the first part and the second part, respectively.

Detailed description of the invention

Referring now in detail to the drawings for the purpose of illustrating preferred embodiments of the present invention, a tool changer according to the present invention is illustrated in Fig. 1.

Fig. 1 illustrates a tool changer 1 according to the invention. The tool changer 1 comprises a first part 2. The first part 2 and the second part 3 are configured to be connected, however, in Fig. 1, the first part 2 and the second part 3 are disconnected. The first part 2 is configured to be attached to a robot arm (not shown). The second part 3 is configured to be attached to a tool (e.g. a gripping device or a cutting device) to be handled by the robot arm .

As it will be explained with reference to the subsequent figures, an exact positioning of the first part 2 relative to the second part 3 during attachment of the first part 2 to the second part 3 is achieved by using a kinematic coupling (also known as a "Kelvin coupling") comprising fixtures that are designed to exactly constrain the first part 2 relative to the second part 3 and vice versa. The kinematic coupling comprises a number of contact points, sufficient to constrain all six (three translational and three rotational) degrees of freedom of the first parts 2 and the second part 3. The two parts 2, 3 of the tool changer 1 engage in three points that constitute a triangle indicated by dotted lines. A first triangle is indicated at the first part 2 and a second triangle is indicated at the second part 3. When the two parts 2, 3 are attached to each other, the first triangle and the second triangle coincide.

Fig. 2A illustrates the tool changer 1 shown in Fig. 1 seen from a slightly different view. The tool changer 1 comprises a first part 2 and a second part 3 that are disconnected from each other. The second part 3 comprises a contact surface 42 provided with three associated spheres 4, 4', 4" constituting a first coupling structure configured to engage (and thus bear against and abut) a corresponding second coupling structure 5 formed as a single sphere 5 provided at a contact surface 40 provided at first part 2. The first coupling structure formed by the spheres 4, 4', 4" and the second coupling structure formed by the sphere 5 constitute a first engagement point. The spheres 4, 4', 4" are fixed to the second part 3, whereas the sphere 5 is fixed to the first part 2. The parts 2, 3 comprise a contact surface extending along a plane spanned by a first longitudinal axis X and a lateral axis Y extending perpendicular thereto. A third normal axis Z extends perpendicular to the axis X and the axis Y.

In the first engagement point, three degrees of freedom are restricted by fixing the second coupling structure (formed by the single sphere 5) in the corresponding first coupling structure (formed by the three spheres 4, 4', 4"). This is done by pressing the single sphere 5 into engagement with the three spheres 4, 4', 4". The three spheres 4, 4', 4" are symmetrically arranged so that the distances between adjacent spheres 4, 4', 4" are the same.

The three spheres 4, 4', 4" are arranged in a configuration, in which the lines extending between the centers of the engaging spheres 5, 4, 4', 4' extend perpendicular to each other (see Fig. 2B and Fig. 2C).

Fig. 2B illustrates the engagement between a sphere 5 from the first part 2 and two spheres 4, 4' of the three spheres 4, 4', 4" of the second part 3 constituting a second engagement point. The first sphere 4 has a center C and a radius r and is arranged on the contact surface 42 of the contact surface of the second part 3. Likewise, the second sphere 4' has a center C and a radius r.

The line U extending between the center C of the sphere 4 and the center of the sphere 5 is indicated. It can be seen that the line U goes through the contact point Pi between the sphere 4 and the sphere 5.

The line L ₂ extending between the center C of the sphere 4' and the center of the sphere 5 is indicated. The line L ₂ goes through the contact point P ₂ between the sphere 4' and the sphere 5.

Moreover, it can be seen that the line U and the line L ₂ extend perpendicular to each other. Accordingly, the angle a between horizontal and the line U is 45°. Furthermore, the angle a between vertical and the line U is 45°.

Fig. 2C illustrates the triangle, from which the distance d between adjacent spheres 4, 4', constituting the second engagement point, can be determined. According to the law of cosines, the following relationship exists:

Accordingly, one can derive that

In Fig. 2A one can see that, in the second engagement point, a single sphere 7 attached to the first part 2 is brought into engagement with two spheres 6, 6'. The sphere 7 is inserted into the gap provided between the two spheres 6, 6'. The distance between the two spheres 6, 6' is selected in such a manner that the equation (2) is fulfilled.

The two spheres 6, 6' are arranged in a configuration, in which the lines extending between the centers of the engaging spheres 7, 6, 6' (when the first part 2 and the second part 3 are connected to each other) extend perpendicular to each other.

Fig. 2D illustrates (a top view of) the configuration of the spheres 4, 4', 4" and the spheres 6, 6' of the first part 2 constituting the first engagement point and constituting the second engagement point, respectively. In Fig. 2D it is illustrated that the line L ₃ extending between the centers of the two spheres 6, 6' and the line L ₄ extending between the common center of the three spheres 4, 4', 4" and the center of the two spheres 6, 6' in the second engagement point, extend perpendicular to each other.

In Fig. 2A it can be seen that in the third engagement point, a single sphere 9 from the first part 2 is arranged and configured to be brought into engagement with a corresponding sphere 8 of the second part 1. The "contact plane" between the spheres 8, 9 extends parallel to the plane (spanned by the axes X, Y and) for coupling of the two parts 2, 3. This can be seen in Fig. 14, in which this plane is indicated by a square.

This principal of coupling the first part 2 and the second part 3 corresponds to a kinematic coupling (Kelvin coupling), in which holes, V-shaped grooves and plane engagement structures have been replaced by three spheres, two spheres and one spheres, respectively.

The kinematic coupling (Kelvin coupling) is known to provide a very high repetition accuracy. Accordingly, the kinematic coupling (Kelvin coupling) is often used in optical devices.

In Fig. 2A it can be seen that the two parts 2, 3 are configured to be maintained attached to each other by means of a hook 10 provided in the second part and a rod member 11 provided in the first part, wherein the hook 10 is configured to be lockingly attached to the rod member 11.

The hook 10 is arranged centrally at the first part. Accordingly, the hook 10 is arranged approximately between the three engagement points. The position at which the hook engages the rod member 11 is selected in such a manner that there is the distance from the point of engagement to any of the three sides of the three "fictive" sides og the triangle that the contact elements of the kinematic coupling constitute. The distance between the engagement point of the hook and the line between corners of the triangle influence the level of the torque, at which the tool changer can be exerted in this direction. In order to enable the tool changer to resist equal torque in each direction, the engagement of the hook is selected in such a manner that there is equal distance to any of the three axes at which the tool changer can rotate with respect to.

The hook is arranged and configured to pull the two parts 2, 3 together. The hook 10 is arranged on a crank 12, in such a manner that the crank 12 can be rotated over the top point when the tool changer 1 is assembled (the first part 2 and the second part 3 are connected).

The crank 12 is arranged so as to be rotated and slightly pass the top point to bear against a stop member and hereby be brought into a locked position. The two parts 2, 3 comprise corresponding protruding structures 25 and receiving structures 26 arranged to make sure that the tool changer 1 can be assembled when the structures 25 and receiving structures 26 are positioned correctly with respect to each other.

The first part 2 is provided with a track structure 19 and a first contact member 27. The contact member 27 may be configured to establish electrical connections between the first part 2 and the second part 3. The second part 3 comprises an annular structure 18 and a second contact member 28 configured to be connected to the first contact member 27.

Fig. 3 illustrates a cross-sectional view of a tool changer 1 according to the invention. The tool changer 1 is disassembled and arranged in a configuration, in which the hook 10 is out of engagement with the rod member 11. It can be seen that the sphere 5, attached to the first part 2, is arranged at a distance from the three spheres 4, 4', 4" attached to the second part 3. Likewise, the sphere 9, attached to the first part 2, is arranged in a distance from the corresponding sphere 8' attached to the second part 3. It can be seen that the hook 10 can rotate with respect to the crank 12.

Fig. 4 illustrates a cross-sectional view of the tool changer 1 shown in Fig. 3 in a locked configuration, in which the hook 10 engages the rod member 11 and hereby is fixed to it. The rod member 11 has a conical shape arranged in a corresponding conically shaped hole 13 provided in the first part 2. The conically shaped hole 13 has a geometry so that the part of the rod member 11 that the hook 10 is in contact with and pulls, extends parallel with the X-Y-plane (spanned by the X axis and the Y axis) of the tool changer 1.

Fig. 5 illustrates a cross-sectional view of a tool changer 1 according to the invention and Fig. 6 illustrates another cross-sectional view of the tool changer shown in Fig. 5 arranged in a locked configuration. In Fig. 6 it can be seen that the hook 10 engages the conical rod member 11 and thus is attached thereto. The hook 10 is mounted on the crank 12 which is suspended in ball bearings.

By displacing the conical rod member 11 backwards and forwards in the conical hole, the position of the contact surface at which the hook 10 engages can be varied. This option to vary the distance between the crank 12 and the rod member 11 can be applied to adjust the tension of the hook 10 and to compensate for variations originating from the manufacturing of the first part 2 and the second part 3. The motion of the hook 10 is controlled by a pin 14 protruding from the hook 10 (see Fig. 5). This pin 14 is configured to be moved in a track 15 provided in the plate structure of the first part 2. The motion of the crank 12 and the engagement between the pin 14 and the track 15 makes the distal portion of the hook 10 to move in a path, in which the hook 10 is rotated away from the rod member 11 when first part 2 and the second part 3 of the tool changer is disconnected from each other.

In a similar manner, the hook 10 is rotated into a position above the rod member 11, when the crank 12 starts to finish/close the motion. Hereafter, the distal portion of the hook 10 is pulled forward against the rod member 11. Just before the crank 12 reaches its top position, the hook 10 is fee to move between the crank 12 and the rod member 11. In Fig. 5 it can be seen that the hook 10 with the pin is guided along and by the track 15.

Fig. 7 illustrates a string 16 made of spheres used in one embodiment of the invention and Fig. 8 illustrates a side view of the tool changer lshown in Fig. 7. It can be seen that the crank 12 is driven by the string 16 that is pressed into a "wing pump" at the end of the crank 12. By pressing the spheres into the first or second side of the canal that surrounds the crank 12, the wing 17 will rotate the crank 12. Fig. 7 illustrates an end view of the crank 12 with the hook 10. Accordingly, one can see the ring-shaped canal with the wing 17 that constitutes a permanent part of the crank 12. A string 16 of spheres has been pressed into each side of the canal. Accordingly, the string 16 can drive the crank 12 round and thus make the crank 12 rotate. When the spheres are pressed into one side of the canal, the spheres in the other side will be automatically moved in the same rotational direction. If the spheres of the string 16 are inserted in to the left side canal and the crank 12 is rotated in the clockwise, the spheres in the right side of the canal will also be moved clockwise. In Fig. 8 one can se the components shown in Fig. 7, however, seen from the opposite side. The crank 12 and the hook 10 with the pin 14 are visible in Fig. 8. The spheres are introduced into a tubular canal from two pipe structures provided in the coupling plate of the tool changer.

Fig. 9 illustrates a first part 2 of a tool changer according to the invention. It can be seen that the first part 2 comprises an annular structure 18 arranged and configured to be rotated with respect to the coupling plate. Hereby, the spheres of the string 16 will be pressed into the first or second canal and thus be brought into engagement with the wing pump of the crank 12. Fig. 9 thus illustrates the mechanism of the crank 12 together with the spheres of the string 16 and the annular structure 18.

Fig. 10 illustrates a perspective view of a tool changer 1 according to the invention. Fig. 11 illustrates the tool changer 1 shown in Fig. 10 arranged in the holding device 21. The first part 2 of the tool changer 1 that is configured to be attached to a tool (e.g. a gripping device or a cutting device) is provided with a track structure 19 extending along an outer periphery of the tool changer 1. The geometry of this track structure 19 corresponds to the geometry of a recess 20 in a holding device 21, in which the tool can be placed when the tool is not being used.

An opening 23 is provided in a parking plate 22 into the position, into which the tool is being parked. This opening 23 is, however, slightly smaller than the diameter in the parking position. A couple of recesses provided in the bottom portion of the coupling plate of the tool changer 1 allow the tool changer 1 to enter the recess 20 in the parking plate 2.

When the tool changer 1 is arranged in the parking position, the tool changer is being rotated so that the tool changer cannot be retracted from the holding device. The annular structure 18 of the tool changer 1 comprises a protruding portion 24. The protruding portion 24 has a width that fits into the parking plate 22. When the tool changer 1 enters the parking plate 22, the protruding portion 24 is brought into engagement with a corresponding structure. Hereby, the protruding portion 24 is brought into a locked position.

When the tool changer 1 is rotated while being arranged in the parking position/configuration, the protruding portion 24 will maintain the annular structure 18 so that the annular structure 18 rotates with respect to the tool change 1.

Parking of a tool is done by letting the robot arm move the tool changer 1 into the parking plate 22 and rotate the tool changer 1 around, whereby, the annular structure 18 rotates with respect to the parking plate 22 with the crank 12. The annular structure 18 moves the spheres of the string (see Fig. 7-9) through the canals and into the wing pump of the crank 12.

The crank 12 is rotated and the hook 10 is released from the rod member 11. Hereafter the robot arm can pull the first part 2 of the tool changer out of the second part 3, herby disassembling the tool changer 1.

The parked tool changer 1 is illustrated in Fig. 12. When a tool is being attached to the robot arm, the holding device 21 may be used. In Fig. 12, the second part 3 is arranged in the holding device 21 and the first part 2 of the tool changer 1 is arranged under the holding device 21.

The tool changer 1 is provided with protruding side portions that constitute a conical structure extending towards the kinematic coupling . Corresponding conical surfaces are provided at the coupling plate. The se conical surfaces facilitate that the robot arm can enter the tool changer 1. The conical structures comprise protruding structures 26 and receiving structures 26 that restrict the first part 2 and the second part 3 of the tool changer to be only assembled when the first part 2 and the second part 3 are positioned in a predefined position relative to each other.

The parking plate 22 with a tool is suspended in a flexible manner that allows the robot arm to make minor movements if the robot arm does not enter accurately or if it is moved too much. When the first part and the second part are brought so close to each other that the spheres of the kinematic coupling are brought into contact, the spheres will cause the first part 2 and the second part 3 to rotate relative to each other, hereby bring the first part 2 and the second part 3 into the predefined relative position, in which the first part 2 and the second part 3 can be attached to each other.

When the kinematic coupling is established, there will be no contact between the conical structure of the first part 2 and the second part 3. In this situation, the protruding portion 24 on the annular structure 18 will be placed in the entering structure of the parking plate. When the robot arm is rotating the tool changer 1, the parking plate 22 will restrict the annular structure 18 from moving and the annular structure 18 will push the spheres of the string to move along the canals, whereby the crank 12 and thus the hook 10 will be driven/moved. Eventually, the rotational motion of the crank 12 will cause the crank 12 to pass the top point and the hook 10 will maintain the first part 2 fixed to the second part 3. Now, the robot arm can move the arm with the assembled and locked tool changer out of the holding device 21. In between the spheres of the kinematic coupling, a set of electrical contact members 27, 28 (see Fig. 2) are arranged. These electrical contact members 27, 28 are configured to transfer electrical power and control signals between a robot arm and tool attached to the robot arm by mean of the tool changer 1. Corresponding pneumatic contact members 29, 30 (see Fig. 2) are provided at the first part 2 and the second part 3.

The electrical contact members 27, 28 in the first part 2 and the second part 3 are formed as individual structures that may be replaced or omitted. In the same manner, the pneumatic coupling by means of the pneumatic contact members 29, 30 may be replaced or omitted .

Fig. 13 illustrates a diagram for a circuit of a tool changer according to the invention. The tool changer comprises three integrated electrical switches that are configured to be activated upon coupling of the first part and the second part of the tool changer.

The first switch SI is arranged and configured to be activated by a pin arranged between the spheres of the kinematic coupling. When a sphere in the opposite part of the first engagement structure (comprising three spheres arranged or engage with a single sphere), the first switch SI is activated. The two other switches S2 and S3 are activated by the hook when the hook is released from the rod member and when the crank has passed the top point (and the hook is in the locked configuration), respectively.

The three switches SI, S2, S3 are accompanied by a number of electrical resistors Rl, R2, R3, R4, RID and RTOOL. By using this circuit, it is possible to impose a supply voltage (Power as well as ground, GN D) . A voltage drop will be provided across each of the electrical resistors Rl, R2, R3, R4, RID, RTOOL.

A measurement voltage (M) from the voltage will depend on the resistors Rl, R2, R3, R4, RID, RTOOL and on the configuration of the three switches SI, S2, S3.

A diagram of the circuit is shown in Fig. 13. By detecting the measurement voltage, one can distinguish between three modes of the tool changer. The tool changer can be arranged in a configuration, in which the hook is in an open configuration without any tool mounted so that the tool changer is ready to be attached to a tool.

The measurement voltage can also indicate that the link is in an intermediate position where the hook is activated, and a link of coupling is in progress. In the third mode, the measurement voltage indicates that the robot arm coupling is connected to a tool and that the hook is in the locked position. The measurement voltage can alternatively indicate that the tool changer is in a configuration, in which the hook is activated and an attachment of the first part and the second part of the tool changer is initiated. In the third configuration, the measurement voltage indicates that the robot arm is connected to the tool changer and that the hook is in a locked configuration hereby preventing the first part and the second part of the tool changer to be disassembled. If an electrical coupling unit is mounted in the coupling plate of the tool changer and this electrical coupling unit comprises an appropriate resistor R _ID , this resistor will also be coupled to the voltage divider.

In Fig. 13, the connection to the that part of the tool changer that has to be attached to a tool is illustrated as an electrical coupling comprising Pogo pins. If a resistor RID from the that part of the tool changer that has to be attached to a tool is connected to the circuit, it will result in a voltage at the output M of the voltage divider, which depends on the resistance of this resistor RID. By detecting the measuring voltage in this situation, it is possible not only to detect that the tool changer is closed and locked, but it is also possible to identify the tool from the level of the voltage.

If there is no resistance in the tool's electrical coupling unit, one will only measure a voltage indicating that the tool changer is closed and locked. An identification of the tool will not be available.

The voltage divider comprises an additional resistor R3. The purpose of the additional resistor R3 is to restrict/limit the current if an error condition occurs when multiple contacts are activated simultaneously. A rectifier Dl is arranged in the input portion configured to be electrically connected to a connection being electrically connected to the resistor RID. This rectifier Dl prevents the current from running in a wrong direction through the circuit e.g . during the coupling of the spring- loaded contact pins Pogo Pin .

Fig. 14 illustrates a top view of a portion of a tool changer according to the invention basically corresponding to the one shown in Fig . 2A. A first plane 32 extending parallel to the contact surface 40 of the first part 2 is indicated at the sphere 8. A first plane 34 and a second plane 34 extending perpendicular to the first plane 34 is indicated at the spheres 6, 6'. Three planes 36 extending perpendicular to each other are indicated at area between the spheres 4, 4', 4". Fig. 15 illustrates the engagement between a sphere 7 from the first part brought into engagement with the two corresponding equal sized spheres 6, 6' of the second part 3 that constitute a second engagement point. It can be seen that the first sphere 6 has a center C" and a radius r and is arranged on the contact surface 42 of the contact surface of the second part 3. Likewise, the second sphere 6' has a center C" and a radius r.

The line L ₅ extending between the center C" of the sphere 6 and the center of the sphere 7 is indicated . It can be seen that the line L ₅ goes through the contact point P ₃ between the sphere 6 and the sphere 7.

The line extending between the center of the sphere 6' and the

center of the sphere 7 is indicated . The line L ₆ goes through the contact point between the sphere 6' and the sphere 7.

Additionally, it can be seen that the line and the line extend perpendicular to each other. Accordingly, the angle between

horizontal and the line is 45°. Furthermore, the angle β between vertical and the line L5 is 45°. Like explained with reference to Fig. 2B, one can calculate the distale d' between the spheres 6, 6' in terms of the radius r.

Fig. 16 illustrates engagement of two single equal sized spheres 8, 9 attached to the first part 2 and the second part 3, respectively. It can be seen that the line L ₇ extending between the center E' of the sphere 9 arranged on the contact surface 40 of the first part 2 and the center E of the sphere 8 arranged on the contact surface 42 of the second part 3 extends perpendicular to the contact surface 40 of the first part 2 and the contact surface 42 of the second part 3.