WO2024088511A1

WO2024088511A1 - Device and method for joining component layers of a component assembly

Info

Publication number: WO2024088511A1
Application number: PCT/EP2022/079668
Authority: WO
Inventors: Christian DENKERT; Altan BUELBUEL
Original assignee: Ejot Se & Co. Kg; Fraunhofer-Gesellschaft Zur Foerderung Der Angewandten Forschung E. V.
Priority date: 2022-10-24
Filing date: 2022-10-24
Publication date: 2024-05-02

Abstract

The invention relates to a device (10) for automatically joining components (110, 120) of a component assembly (130). At least one uppermost component layer (120) has a pilot hole (140) with a pilot hole diameter (DV) at a joint location, and the device (10) comprises a joining unit (20), a positioning unit, and a control unit. A joint axis (AS) is defined by the joining unit (20), and a connection element (150) can be connected to the component assembly (130) in a joining direction (FR) along the joint axis (AS), wherein the positioning unit (40) comprises a probe (42) which has a self-centering design on a hole edge (142). The positioning unit (40) additionally comprises a probe guiding element (44) which is connected to the probe (42), wherein the probe guiding element (44) defines a probe guiding element axis (AF), and the probe (42) defines a probe axis (AT). The probe (42) can be moved orthogonally to the probe guiding element axis (AF) relative to the probe guiding element (44), and the positioning unit (40) additionally comprises a measuring device (46), by means of which a positional deviation (V) between the probe guiding element axis (AF) and the probe axis (AT) can be ascertained. An axial force generating element is arranged on the positioning unit, said axial force generating element being used to move the probe guiding element (44) along the probe guiding element axis (AF) as part of an axial movement such that the probe (42) penetrates the pilot hole (140) as a result of the axial movement, and a radial compensation movement of the probe (42) relative to the probe guiding element (44) is carried out until the probe (42) is centered in the pilot hole (140).

Description

Device and method for joining component layers of a component assembly

The invention relates to a device for automatically joining component layers of a component assembly, in which at least one uppermost component layer has a pre-hole at the joining point, and to a method for joining component layers of a component assembly using the device.

Devices for automatically joining component layers of a component assembly, in which at least one uppermost component layer has a pre-hole through which the joining connection is to be made, have the problem that the supposedly known position of the pre-hole can be approached relatively precisely with a joining unit of the device, but in practice there are positional deviations between the theoretical position of the pre-hole and the actual position of the pre-hole.

In order to compensate for this deviation and still achieve a high process speed, the pilot holes are tolerated relatively generously in relation to the shaft diameter of the connecting elements through which the component assembly is joined.

Disadvantages in the properties of the component connection are accepted.

It is the object of the invention to carry out a rapid and exact determination of the center of a pre-hole in an uppermost component layer that is subject to a position deviation, so that a subsequent joining process, in particular a screwing process, can be carried out reliably even in pre-holes with tight tolerances.

The object is achieved for the device by the features of claim 1. The subclaims form advantageous developments of the invention.

In a known manner, a device for automatically joining components of a component assembly, in which at least one uppermost component layer has a pre-hole at the joining point, comprises a control unit and a joining unit, wherein a joining axis is defined by the joining unit, wherein a connecting element can be connected to the component assembly in a joining direction along the joining axis. The joining unit is designed to be movable relative to the component assembly. For this purpose, it can in particular have an articulated arm, for example an articulated arm robot, a traverse system or the like.

According to the invention, the device comprises a positioning unit which has a probe head and a probe head guide element connected to the probe head, wherein the probe head guide element defines a probe head guide element axis and the probe head defines a probe head axis. The probe head is mounted on the probe head guide element so as to be movable relative to the probe head guide element orthogonally to the probe head guide element axis.

Furthermore, the positioning unit comprises a measuring device by means of which a positional deviation between the probe guide element axis and the probe axis can be determined.

It is conceivable that the positioning unit comprises a traverse system, an articulated arm robot or the like, so that the positioning unit can carry out a relative movement with respect to the component assembly. It is possible, for example, for the joining unit to be arranged on the arm of the articulated arm robot of the positioning unit. Alternatively, the joining unit and the positioning unit can each have an arm.

In addition, the positioning unit has an axial force generator by means of which the probe guide element can be moved along the probe guide element axis.

The probe has a geometry that self-centers in a hole.

If the probe guide element is now moved along its probe guide element axis, which is essentially coaxial with an assumed pre-hole axis, this leads to the probe moving orthogonally to the probe axis in a radial compensating movement due to the pressure of the hole edge. The displacement under axial force continues until the probe head is centered on the edge of the pre-hole and is in an end position. The position deviation results from the difference to the initial position of the probe head, whereby the position in the end position can be detected by the measuring device. This displacement then corresponds to the position deviation between the assumed and the actual position of the pre-hole axis. The position of the assumed pre-hole axis can preferably be stored on a memory unit of the device, in particular the control unit, and can be read out by this.

The position of the joining process can then be corrected by the determined position deviation and take place precisely at the actual hole center or pre-hole axis.

This allows the diameters of the pilot holes to be designed with tighter tolerances in relation to the joining elements to be arranged there, thereby improving the properties of the component assembly, for example with regard to load-bearing capacity and tightness.

Because no complex measurement of the pre-hole or a surface of the top component layer is required, but rather the geometric properties of the probe allow the probe to self-center, the actual position of the hole center can be determined quickly, reliably and yet very precisely.

This makes it possible to increase the process time for the joining process to an acceptable extent.

The probe head is preferably connected to the probe head guide element via a bearing, whereby the probe head overcomes a bearing reaction force for the radial compensation movement, which acts transversely to the axial movement of the probe head. The bearing is used for the defined relative movement of the probe head with respect to the probe head guide element. The bearing allows the probe head to move orthogonally to the probe head guide element axis. The bearing reaction force, in particular an adhesive force of the bearing in the displacement direction, acts transversely to the joining direction and is of a small magnitude. Due to an axial pressure of the axial force generator on the probe head, the probe head can overcome the small bearing reaction force due to its design and interaction with the hole edge and move transversely to the joining direction in the radial direction. Preferably, the bearing enables a nearly friction-free movement of the probe head transverse to the joining direction, particularly in the radial direction. The bearing can be designed, for example, as a fluid bearing, hydrostatic bearing or the like. Such bearings use a thin film of fluid or gas to support the load. Since there is no direct contact between the bearing surfaces, the coefficient of friction is very low. It is also conceivable that the bearing is designed as a two-axis linear bearing.

Preferably, the bearing is designed in particular such that the bearing reaction force is lower than a transverse force acting on the probe head at the edge of the pilot hole, which is generated by an axial force acting on the probe head.

For example, the probe head can be positioned at the edge of the pilot hole at the start of the axial movement through which it penetrates the pilot hole. The axial force then acting on the probe head causes a transverse force acting on the probe head at the edge of the pilot hole, which means that the probe head can also move orthogonally to the axial movement. The bearing reaction force acting in the transverse direction must be lower than the transverse force acting on the edge of the pilot hole.

According to a preferred embodiment, the axial force is measured with an axial force detection device. When the probe head is positioned in the center of the pilot hole, it is moved in the joining direction and a positive connection between the probe head and the edge of the hole results in a stop that can be detected by the axial force detection device through an increase in force.

Preferably, a search force is set in the form of a maximum axial force up to which the probe head is subjected to axial force. The search force is so high that the bearing reaction force is overcome before the search force is reached in a final position of the probe head or in contact with the edge of the hole.

Preferably, during the process in the joining direction, when the search force is reached, it is assumed that the probe is positioned coaxially in the pilot hole. When the axial force reaches the preset search force, the probe has found the pilot hole through the radial compensating movement and is centered in it.

The search force is preferably set to less than 600N. According to an advantageous embodiment, the probe head has a truncated cone-like contour that tapers in the joining direction. This makes the probe head easy to manufacture and allows centering on the hole edge by moving the probe head in the axial direction.

The probe head preferably has a truncated cone which has a maximum cone diameter D, a minimum cone diameter d and a height L and a cone ratio of C = (D-d) / L, which is preferably greater than 1. The half cone angle, alpha, is selected such that the bearing reaction force < search force x tan alpha. In order to overcome a slope of the truncated cone-shaped probe head at the edge of the pilot hole caused by the half cone angle alpha, a transverse force acting orthogonal to the joining direction is necessary. This is generated by the axial force and can be derived from the product of the axial force and the tangent of the half cone angle alpha. The search force acting in the joining direction is the maximum set axial force with which the probe head is acted upon and therefore causes the maximum transverse force that can act on the probe head. In order to be able to move the probe head at the edge of the pilot hole, the transverse force must exceed the bearing reaction force. This means that the half cone angle must be selected in such a way that the bearing reaction force is lower than the maximum transverse force, which is determined by the search force. The aim is to achieve the largest possible cone angle, as this also allows small sheet thicknesses to be sensed.

According to a particularly advantageous embodiment, the probe head is matched to the pilot hole diameter in such a way that the minimum cone diameter is smaller than 0.7 x the pilot hole diameter and the maximum cone diameter is larger than 1.5 x the pilot hole diameter, whereby the pilot hole diameter can be stored in a memory of the control unit. This design of the probe head ensures that, within the scope of the position deviation, the probe head lies with its tapered end within the pilot hole and, accordingly, when an axial force is applied, centers itself along its conical surface in the pilot hole. The maximum diameter of the probe head is larger than the diameter of the pilot hole, thus ensuring that a stop is also guaranteed after centering, since the largest possible cone angle is possible even with low sheet thicknesses. The design of the probe head is preferably selected such that the minimum diameter of a front end of the probe head is so small that it lies completely within the area of the pre-hole within the permissible position deviation, for example 20%, when approaching the assumed pre-hole position. According to a particularly advantageous embodiment, the axial force generator comprises a spring which applies the axial force to the probe head and/or the probe head guide element in the axial direction. Alternatively, the axial force generator can also be a part, in particular a drive means, of an articulated arm robot or a traverse system of the positioning unit.

The positioning unit preferably comprises a reset unit with which the displaced probe is reset to an initial starting position, so that in particular the probe axis and the probe guide element axis are coaxial with each other. The probe is brought into the starting position so that the process of determining the hole center can begin again with a subsequent pre-hole.

The reset unit preferably comprises an element by means of which the probe head can be moved orthogonally to the probe head axis. The element can be designed, for example, as an electromagnet, at least one spring element or the like. An electromagnet, for example, represents a switchable reset element which releases the probe head as soon as it has been brought into the starting position so that only the bearing reaction forces influence the displacement of the probe head. This can be switched on again after the position detection has been completed in order to move the probe head back.

According to a preferred embodiment, the bearing specifies a maximum travel path of the truncated cone via its radial dimension. The maximum travel path, like the hole size, is in the millimeter range.

The truncated cone preferably has a hardness of more than 320 HV or a tensile strength of more than 1000 MPa. Because the truncated cone is pushed over the edge of the pilot hole on its slope, wear may be caused by loss of material on its surface. This wear can be counteracted by the appropriate hardness.

According to a further aspect of the invention, it relates to a method for joining components of a component assembly, using a device as described above.

The probe guide element with its probe guide element axis, to which the probe axis is coaxially aligned in a first position, is coaxial with the assumed Pre-hole axis positioned. Preferably, a memory of the control unit has the coordinates of the assumed theoretical center, ie the assumed pre-hole axis, of the pre-holes.

The position of the probe axis is known due to the coaxial alignment of the probe axis with the probe guide element axis or is recorded in the first position or starting position. Preferably, the probe axis is coaxial with the probe guide element axis before the measurement.

After positioning the probe guide element, it is moved in the joining direction. The probe is subjected to an axial force that leads to a movement in the joining direction and generates a transverse force acting on the probe at the edge of the hole, which causes the probe to perform a radial compensating movement until the probe is centered in the pre-hole. This results in a stop due to the positive connection in the joining direction between the probe and the edge of the hole. The reaching of the stop can be recognized, for example, due to an increase in force.

Preferably, the centering in the pilot hole is assessed as completed when the applied axial force has reached a maximum preset search force. Alternatively, the gradient of the force increase can be evaluated. When the search force is reached, it is assumed that the probe is positioned coaxially in the pilot hole. When the maximum specified axial force application or search force is reached, the probe has found the pilot hole through the radial compensation movement and is centered in it, with the probe axis coming to rest in a second position or end position that corresponds to the real pilot hole center point.

An offset or position deviation between the starting position of the probe axis and the end position of the task pot axis is determined.

Taking the determined offset into account, an adjusted joining position can be determined.

Once the actual pre-hole axis has been determined in this way, the connecting element is joined at the adjusted joining position. The rapid hole location due to the self-centering probe geometry means that the pre-hole center can be found quickly and easily, so that the positioning process can be carried out before the joining process. According to a further preferred embodiment, the probe is returned from the end position to the starting position.

Further preferably, the positioning unit is moved away from the area of the pre-hole and the joining unit is moved to the adjusted joining position.

Further advantages, features and possible applications of the present invention will become apparent from the following description in conjunction with the embodiments shown in the drawings.

In the drawing:

Fig. 1 schematic representation of a device for connecting two component layers of a component composite;

Fig. 2a schematic representation of hole center determination, wherein the probe guide element axis is aligned with an assumed hole axis;

Fig. 2b schematic representation of hole center determination, with the probe axis aligned with the actual pre-hole axis;

Fig. 3a Placing a screw in the corrected position; and

Fig. 3b the component assembly joined with the screw.

Fig. 1 shows a schematic representation of a device 10 for automatically joining component layers 110, 120 of a component assembly 130, in which at least one uppermost component layer 120 has a pre-hole 140 with a pre-hole diameter Dv at a joining point. The pre-hole 140 was already made in the uppermost component 120 before the joining process, in particular before the component layers 110, 120 were arranged one above the other.

The device 10 according to the invention comprises a joining unit 20 and a positioning unit 40. The joining unit 20 defines a joining axis As, wherein the joining unit 20 has a connecting element 150 in a joining direction FR along the joining axis As with the component assembly 130, as shown in Fig. 3a, Fig. 3b.

The positioning unit 40 comprises a probe head 42 which has a design by which the probe head 42 centers itself on a hole edge 142 of the pre-hole 140.

The positioning unit 40 further comprises a probe guide element 44 connected to the probe head 42, wherein the probe guide element 44 defines a probe guide element axis AF and the probe head 42 defines a probe axis AT. The probe axis AT is preferably located centrally to the probe head 42. The probe head 42 is movable relative to the probe guide element 44 orthogonally to the probe guide element axis AF and thus in particular also orthogonally to the probe axis AT.

Furthermore, the positioning unit 40 comprises a measuring device 46, by means of which a positional deviation or an offset V between the probe guide element axis AF and the probe axis AT can be determined. In Fig. 1, the probe guide element axis AF and the probe axis AT are coaxial to one another in a first position, i.e. a starting position.

The positioning unit 40 comprises an axial force generator, which in Fig. 1 is designed in the form of a robot arm 48, by means of which the probe guide element 44 can be moved along the probe guide element axis AF in an axial movement, so that the axial movement of the probe 42 penetrates into the pre-hole 140 and a radial compensating movement of the probe 42 to the task pot guide element 44 occurs until the probe 42 is arranged centered in the pre-hole 140. The positioning unit 40 also has a memory in which position data of the assumed pre-hole position are stored, whereby this position can be approached by the robot arm 48.

The function of determining the position of the pilot hole 140 is described in more detail in Fig. 2a and Fig. 2b.

Fig. 2a and Fig. 2b show a basic schematic representation of a positioning unit 40 according to the invention. The positioning unit 40 comprises a probe guide element 44 in which a probe 42 is accommodated in a bearing 50 so as to be transversely displaceable to the probe guide element 44. The probe guide element 44 is moved with its probe guide element axis AF to the position at which the assumed pre-hole axis Av is located according to the values stored in the memory of the positioning unit. 40 stored data should be located. As shown in Fig. 2a, the positions, namely the position of the actual pre-hole axis Av, deviate from the assumed position, which is identical to the guide element axis AF, by an offset V.

To determine the offset V, the probe head 42 is moved according to the invention by an axial movement in the joining direction FR. In the present example, an axial force generator in the form of a spring 52 is provided for this purpose, which moves the entire probe head guide element 44 together with the probe head 42 in the joining direction FR. Due to the conical design of the probe head 42 at the hole edge 142, the axial force F, which can be detected by a force detection device 54, exerts a transverse force on the probe head 42, which is located eccentrically in the pre-hole 140, so that it is displaced transversely relative to the probe head guide element 44. The probe head guide element axis AF and the pre-hole axis Av are aligned in particular parallel or approximately parallel to one another.

The probe head 42 is designed as a truncated cone and has a half truncated cone angle alpha, which results in an oblique contact of the outer surface of the probe head 42 on the hole edge 142. The applied axial force F causes the probe head at the edge of the pre-hole to be moved into the center of the hole by the transverse force caused by the axial force F. The transverse force must exceed a bearing reaction force of the bearing 44 acting in the transverse direction. The required transverse force can be derived from the product of the axial force F and the tangent of the half cone angle alpha.

The transverse displacement of the probe head 42 continues until the probe head 42 is completely centered and thus rests positively on the hole edge 142 of the pre-hole 140, as shown in Fig. 2b.

Fig. 2b shows the centered probe 42, which now rests positively on the hole edge 142 in the joining direction, so that the probe axis AT is coaxial with the actual pre-hole axis Av. The probe guide element axis AF, on the other hand, is still coaxial with the assumed pre-hole axis.

The probe guide element 44 carries a measuring device 46 which can determine the offset V of the probe axis AT to the probe guide element axis AF. This offset V then corresponds to the deviation of the actual position of the pre-hole axis Av from the assumed position. Thus, taking the offset V into account, the subsequent joining process, which is shown as a screwing process in Fig. 3a and Fig. 3b by way of example, can be carried out by the setting device 20 at a position corrected by the offset V.

Fig. 2b shows the final position of the positioning unit 40, in which the probe axis AT is aligned parallel to the actual pre-hole axis Av, and also the design of the probe 42. This is preferably selected such that the minimum diameter d of a front end of the probe 42 is so small that it lies completely within the area of the pre-hole 140 within the permissible position deviation, for example 20%, when approaching the assumed pre-hole position. The maximum diameter D is of course larger than the maximum permissible pre-hole diameter Dv, so that a reliable stop is provided on the hole edge 142. The height L of the probe 42 is dimensioned such that the front end does not touch the lower component 110 before an upper end rests on the hole edge 142.

Fig. 3a shows the beginning of the joining process for a connecting element 150, which in the present case is designed as a screw, wherein the stored position information for the joining position has been corrected by the offset V, so that a very precise positioning of the screw with the shaft outer diameter Ds in the middle of the pilot hole 140 can take place, so that the screwing process can also be carried out in a pilot hole 140 with close tolerances.

Due to the geometrically determined self-centering of the probe head 42, the offset can be determined so quickly and precisely that, as part of the automatic joining, a position correction can be sensibly carried out before the joining process.

Fig. 3b shows the finished component connection 130.

In Fig. 3a and Fig. 3b, the joining unit 20 is designed with an actuator 56 or the like, via which the connecting element 150 can be moved in the joining direction FR in order to position it in the pilot hole 140 and to connect it to the component layers 110, 120. In the present case, the movement of the connecting element 150 is thus caused by the joining unit 20.

It is also conceivable, for example, that the positioning unit 20 and the joining unit 40 each comprise an articulated arm 48, 58, wherein the respective articulated arms 48, 58 are responsible for the movement of the probe head 42 and the connecting element 150. Alternatively, it is also possible, for example, that the joining unit 20 and the positioning unit 40 have a common articulated arm, ie the movement of the probe head 42 and the connecting element 150 in the joining direction is carried out only by an articulated arm.

Claims

Patent claims Device (10) for automatically joining components (110, 120) of a component assembly (130), in which at least one uppermost component layer (120) has a pre-hole (140) with a pre-hole diameter (Dv) at a joining point, wherein the device (10) comprises a joining unit (20), a positioning unit and a control unit, wherein a joining axis (As) is defined by the joining unit (20) and a connecting element (150) can be connected to the component assembly (130) in a joining direction (FR) along the joining axis (As), wherein the positioning unit (40) comprises a probe head (42) which has a self-centering design at a hole edge (142), wherein the positioning unit (40) further comprises a probe head guide element (44) connected to the probe head (42), wherein the probe head guide element (44) define a probe guide element axis (AF) and the probe (42) define a probe axis (AT), wherein the probe (42) is movable relative to the probe guide element (44) orthogonally to the probe guide element axis (AF), and furthermore the positioning unit (40) comprises a measuring device (46) by means of which a positional deviation (V) between the probe guide element axis (AF) and the probe axis (AT) can be determined, wherein the positioning unit has an axial force generator by means of which the probe guide element (44) is movable along the probe guide element axis (AF) within the scope of an axial movement, so that the axial movement causes the probe (42) to penetrate into the pre-hole (140) and a radial compensating movement of the probe (42) relative to the probe guide element (44) occurs until the probe (42) is centered in the Pre-hole (140) is arranged. Device according to claim 1, characterized in that the probe head (42) is connected to the probe head guide element (44) via a bearing (50), wherein the probe head (42) overcomes a bearing reaction force for the radial compensating movement, which acts transversely to the axial movement of the probe head (42). Device according to claim 2, characterized in that the bearing (50) enables a nearly friction-free movement of the probe head (42) transversely to the joining direction (FR), in particular in the radial direction. Device according to one of the preceding claims 2 or 3, characterized in that the bearing reaction force is less than a transverse force acting on the probe head (42) at the hole edge (142) of the pilot hole (140), which is generated by means of an axial force (F) acting on the probe head (42). Device according to claim 4, characterized in that the axial force (F) is measured with an axial force detection device (54). Device according to one of the preceding claims 4 or 5, characterized in that a search force is set up to which the probe head (42) is subjected to axial force (F); the search force is so high that the bearing reaction force is overcome before the search force is reached in the stop or in a final position. Device according to claim 6, characterized in that when the search force is reached, it is assumed that the probe head (42) is positioned coaxially in the pilot hole (140). Device according to one of the preceding claims 6 or 7, characterized in that the search force is less than 600N. Device according to one of the preceding claims 1 to 8, characterized in that the probe head (42) has a truncated cone-like contour that tapers in the joining direction (FR). Device according to one of the preceding claims 1 to 9, characterized in that the probe head (42) has a truncated cone that has a maximum cone diameter (D), a minimum cone diameter (d) and a height (L), and corresponds to a cone ratio of C = (Dd) / L > 1, in particular the half cone angle (alpha) is selected such that the bearing reaction force < search force x tan alpha. 11. Device according to claim 10, characterized in that the minimum cone diameter (d) is < 0.7 x the pre-hole diameter (Dv) and the maximum cone diameter (D) is > 1.5 x the pre-hole diameter (Dv).

12. Device according to one of the preceding claims 1 to 11, characterized in that the positioning unit (40) comprises a reset unit with which the displaced probe head (42) is reset to an initial position, so that in particular the probe head axis (AT) and the probe head guide element axis (AF) are coaxial with one another.

13. Device according to claim 12, characterized in that the reset unit comprises an element by which the probe head (42) is movable.

14. Device according to one of the preceding claims 10 to 13, characterized in that the truncated cone has a hardness of more than 320 HV.

15. Device according to one of the preceding claims 1 to 14, characterized in that the axial force generator is a spring (52) and/or a drive means of a machine moving the probe head guide element (44), in particular an articulated arm robot (48) or a traverse system, wherein the drive means applies the axial force to the probe head and optionally also to the probe head guide element in the axial direction.

16. Method for joining components (110, 120) of a component assembly (130) with a device (10) according to one of the preceding claims, characterized in that:

(a) the probe guide element (44) with its probe guide element axis (AF), with which the probe axis (AT) is coaxially aligned in a first position and can be brought into a second position in which the probe axis (AT) is arranged offset with respect to the probe guide element axis (AF), wherein the probe guide element axis is positioned coaxially with the assumed pre-hole axis (Av);

(b) the probe guide element (44) is moved in the joining direction (FR) until the probe (42) is centered on the pilot hole (140);

(c) for positioning the probe head (42) in the pre-hole (140), the probe head (42) is subjected to an axial force (F); (d) when centering in the pilot hole is complete and the probe axis (AT) is in a second position with an offset (V) relative to the probe guide element axis (AF), an adjusted joining position is determined taking into account the determined offset (V); (e) joining the connecting element (150) at the adjusted joining position. Method for joining components (110, 120) of a component assembly (130), according to claim 16, characterized in that the probe (42) is returned from the second position to the first position. Method for joining components (110, 120) of a component assembly (130), according to claim 16 or 17, characterized in that the positioning unit (40) is moved away from the region of the pilot hole (140) and the joining unit (20) is moved to the adjusted joining position.