Method for analyzing the status of an electromechanical joining system and electromechanical joining system for carrying out the method

Abstract

An electromechanical joining system that uses an output force or output torque for performing a joining method and includes an electrical drive connected for driving a screw drive and is configured for generating actual values of force or torque that are provided as input variables to a monitoring device. The system includes a sensor configured for measuring the course of the forces or torques over time during the joining method and for detecting additional measurement values that are supplied to the monitoring device as input variables. Wherein the monitoring device links the supplied actual values with the supplied additional measurement values to detect upcoming wear of a wear-prone component of the electromechanical joining system. A method for analyzing the status of the electromechanical joining system is also disclosed.

Claims

1. A method for analyzing the status of an electromechanical joining system wherein an output force or output torque for a joining method carried out by the electromechanical joining system is generated by an electrical drive by means of a screw drive, the method comprising the steps of: supplying actual values of the electrical drive as input variables to a monitoring device that uses an algorithm; using a sensor to determine additional measurement values from the course of forces or torques over time during the joining method; supplying the monitoring device is supplied with the additional measurement values as input variable; wherein the monitoring device uses the algorithm to generate a linkage between the actual values with and the additional measurement values; and wherein the monitoring device uses this linkage to detect upcoming wear of a wear-prone component of the electromechanical joining system.

2. The method according to claim 1, wherein the algorithm uses the actual values and the additional measurement values only during part of the time period taken to perform the joining method.

3. The method according to claim 1, wherein the algorithm uses the actual values and the additional measurement values during an additional operation outside of the joining method.

4. The method according to, claim 1, wherein the actual values and additional measurement values from which a linkage is generated by the algorithm are the actual values and additional measurement values that are transmitted to the monitoring device at the same time.

5. The method according to claim 1, wherein the algorithm calculates an efficiency from the ratio of the actual values and the additional measurement values.

6. The method according to, claim 1, wherein the algorithm uses actual values and additional measurement values during a constant rotational angular speed of the electrical drive.

7. The method according to, claim 1, wherein the algorithm uses amounts of a rotary movement of a drive shaft of the electrical drive acting on the screw drive as the actual values or the algorithm uses amounts of the power consumption of a servo drive of the electrical drive as the actual values.

8. The method according to, claim 1, wherein the monitoring device calculates a time course of the linkage of the actual values and the additional measurement values.

9. The method according to claim 8, wherein the monitoring device extrapolates the time course of the linkage of the actual values and the additional measurement values into the future.

10. The method according to claim 8, wherein the monitoring device determines an amount of time remaining until the at least one wear-prone component of the electromechanical joining system must be replaced or a service life of the electromechanical joining system, respectively.

11. The method according to, claim 8, wherein the results of the linkage of linking the actual values with the additional measurement values are stored in a storage medium of the electromechanical joining system.

12. An electromechanical joining system comprising: an electrical drive that acts by means of a screw drive on a rotatable or linearly movable output element for performing a joining method, a first means of detecting actual values of the electrical drive; a sensor for detecting additional measurement values by for measuring the course of forces or torques over time during the joining method, and a monitoring device configured for receiving the actual values and the additional measurement values, wherein the monitoring device includes an algorithm configured to generate a linkage between the actual values and the additional measurement values according to a method as defined in claim 1.

13. The electromechanical joining system according to claim 12, further comprising a control device; wherein the electrical drive includes a servo motor connected to the control device; and wherein the control device is configured to control the electrical drive.

14. The electromechanical joining system according to claim 12, further comprising a storage medium connected to the monitoring device and configured for storing the linkage of the actual values with the additional measurement values that is generated by the monitoring device.

15. The electromechanical joining system according to, claim 12, wherein the monitoring device is arranged in the electrical drive.

16. The method according to claim 2, wherein the actual values are at least nearly constant during that part of the time period.

17. The method according to claim 1, wherein the algorithm uses the actual values and the additional measurement values during an additional operation outside of the joining method, in which additional operation no force or torque acts on the electromechanical joining system.

18. The electromechanical joining system according to claim 12, wherein the monitoring device is positioned outside the electrical drive.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Other advantages, features and details of the invention are given in the following description of preferred exemplary embodiments referring to the figures in which

(2) FIG. 1 shows a perspective view of a portion of an embodiment of an electrical drive of an electromechanical joining system for joining two components according to the prior art;

(3) FIG. 2 shows a schematic representation of a first embodiment of an electromechanical joining system for joining two components comprising an electrical drive according to FIG. 1 that is additionally configured with a monitoring device for implementing the method according to the invention integrated in an electrical drive;

(4) FIG. 3 shows a schematic representation of a second embodiment of an electromechanical joining system for joining two components comprising an electrical drive according to FIG. 1 that is additionally configured with an external control device for implementing the method according to the invention; and

(5) FIG. 4 and FIG. 5 each show representations of a time course of the efficiency or the service life of the electromechanical joining system according to FIG. 2 or 3 as a result of a status analysis carried out by the monitoring device by using an algorithm.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

(6) In the figures, the same elements or elements having identical functions are designated by the same reference numbers.

(7) Each of FIG. 2 and FIG. 3 provides a schematic representation of a different presently preferred exemplary embodiment of an electromechanical joining system 100 for joining two components 1, 2. FIG. 1 shows a perspective view of a portion of an embodiment of an electrical drive 10 as known in the prior art for an electromechanical joining system 100 for joining two components. Advantageously, the electrical drive 10 comprises a servo motor 12 and a brake 4. The main function of the brake 4 is to hold a ram of the screw drive 20 in a particular position with high precision when the servo motor 12 is in the non-powered mode. Another function of the brake 4 is to decelerate the servo motor 12. Servo motor 12 rotatably drives a drive shaft 18 by means of a gear 5 and a belt drive 6. Drive shaft 18 is rotatably supported by at least one bearing 7. Servo motor 12 rotates the drive shaft 18 in a clockwise or counterclockwise direction with a rotational speed n. An absolute value encoder 11 detects the rotational speed n of the drive shaft 18. Preferably, the absolute value encoder 11 is arranged in close proximity to the brake 4 or the servo motor 12. The absolute value transmitter 11 is not shown in detail in FIG. 1. In light of the present invention it is also possible, however, that the servo motor 12 drives the drive shaft 18 in a gearless or beltless manner.

(8) The electrical drive 10 comprises a screw drive 20. Screw drive 20 comprises a threaded spindle having a spindle nut, an anti-rotation device 8 and a guide 9. The spindle nut is fitted onto the threaded spindle. The threaded spindle comprises an external thread, the spindle nut comprises an internal thread, and the external and the internal thread are made to fit to one another. One end of the drive shaft 18 is non-rotatably connected to the threaded spindle and rotates the threaded spindle. A rotary movement of the threaded spindle results in a linear movement of the threaded nut. Guide 9 guides the threaded nut during linear movement. One end of the threaded nut opposite of the drive shaft 18 comprises a ram. The ram is used for holding the tool; such a tool is not shown in detail in FIG. 1. The anti-rotation device 8 secures the ram against rotation.

(9) FIGS. 2 and 3 are schematic representations of two embodiments of an electromechanical joining system 100 for joining two components 1, 2 in a greatly simplified manner. As an example, the electromechanical joining system 100 is to be used for pressing a first component 1 in the direction of the arrow 3 into an opening of a second component 2 up to a specific position.

(10) The electromechanical joining system 100 comprises an electrical drive 10 as shown in FIG. 1. The electrical drive 10 is controlled by a control device 13. Advantageously, the electrical drive 10 is a servo drive comprising a servo motor 12 and the control device 13 is a servo amplifier. The control device 13 is a computer. A double arrow in FIGS. 2 and 3 indicates that the servo motor 12 is controlled by the control device 13. A rectangular box in dashed line outline in FIGS. 2 and 3 schematically indicates the housing of the electrical drive 10. The housing accommodates the servo motor 12, control device 13, drive shaft 18 and absolute value encoder 11.

(11) In the context of the present invention, wear-prone means that the efficiency of the electromechanical joining system 100 is reduced over the service life of the electromechanical joining system 100, for example, due to abrasion or increasing tolerances between components of the electromechanical joining system 100. This means that for achieving the same result with an output element 22 that is operatively connected to the screw drive 20 and performing the actual joining process, it becomes necessary to increase the input of electrical energy at the electrical drive 10. The output element 22 mentioned above can be a tool that is operatively connected to the first component 1 to be pressed into component 2.

(12) The electromechanical joining system 100 comprises a plurality of wear-prone components 21 such as the brake 4, gear 5, belt drive 6, bearing 7, guide 8, anti-rotation device 9, and the like shown in FIG. 1.

(13) Thus, the way the brake 4 is installed in the housing may be different from that specified in the instruction manual and it may drag during operation leading to increased abrasion of the friction pad. However, brake 4 may also be electrically contacted with the control device 13 in a manner different from that specified in the instruction manual causing excessive braking forces which also result in increased abrasion of the friction pad.

(14) Gearbox 5 contains oil that may age prematurely due to improperly high operating temperatures.

(15) Furthermore, the belt drive 6 shown in FIG. 1 is also subject to wear. Belt drive 6 comprises a belt and belt wheels, which belt wheels are supported by bearings. The belt may be improperly fitted on the belt pulleys leading to increased abrasion of the belt material. The belt pulleys may rotate out of center resulting in premature wear on the bearings.

(16) This may similarly apply to the bearing 7 of the drive shaft 18 shown in FIG. 1. Due to overload or damage, bearing 7 may be subject to premature wear.

(17) Moreover, the guide 8 shown in FIG. 1 may be soiled during operation leading to an increase in frictional resistance on guide surfaces of the guide 8 and resulting in premature wear of guide surfaces.

(18) Finally, the anti-rotation device 9 shown in FIG. 1 is also exposed to high forces during operation and may be subject to premature wear due to overload or damage.

(19) The output element 22 is further operatively connected to a sensor 24 as schematically shown in FIG. 2 and FIG. 3. The sensor 24 is used to determine a force or torque (depending on the type of joining process) that is applied by the output element 22 during the process of joining component 1 to component 2. Sensor 24 may be a strain gauge or a piezoelectric sensor. Sensor 24 may be integrated in the ram or attached to the ram. The amount of force or torque determined by the sensor 24 represents an additional measurement value ZMW and is transmitted as an input variable to a monitoring device 30 by the sensor 24 via the control device 13 as schematically shown in the embodiment depicted in FIG. 2. Alternatively, as schematically shown in FIG. 3, an additional measurement value ZMW is transmitted as an input variable to a monitoring device 30 by the sensor 24 via a monitoring device 14. However, those skilled in the art and being aware of the present invention may also use a sensor that determines a pressure applied by the output element 22.

(20) Another input variable that is supplied from the control device 13 of the servo motor 12 is at least one actual value IW, IW′ of the electrical drive 10. One example of an actual value IW is a rotational speed n of the drive shaft 18, and another example of an actual value IW′ is a current intensity I required by the servo motor 12.

(21) The actual values IW, IW′ of the electrical drive 10 as well as the additional measurement values ZMW of the sensor 24 are determined at the same point of time in the joining process and transmitted to the monitoring device 14.

(22) A monitoring device 14 is provided according to the invention. As shown in FIG. 2, the monitoring device 14 is arranged in the electrical drive 10. Preferably, the monitoring device 14 is an integral part of the control device 13. As shown in FIG. 3, the monitoring device 14 is designed as an external computer located outside the electrical drive 10. The monitoring device 14 comprises an algorithm 16 designed to link actual values IW, IW′ of the electrical drive 10 with additional measurement values ZMW of the sensor 24. The result of this linkage is used for performing a status analysis of the electromechanical joining system 100 whereby upcoming wear and therefore imminent failure or required replacement of a wear-prone component 21 is detected at an early time. Preferably, the linkage of the actual values IW, IW′ of the electrical drive 10 with the additional measurement values IMW of the sensor 24 is carried out in real time. For the purposes of the present invention, real-time is defined to mean that a result of the linkage is available in the monitoring device 14 in less time than it takes to supply the actual values IW, IW′ of the electrical drive 10 and the additional measurement values ZMW of the sensor 24.

(23) FIG. 4 shows a diagram representing the efficiency η over time t for a longer operation period of the electromechanical joining system 100. For this purpose, the individual time points where the corresponding actual values IW, IW′ of the electrical drive 10 and additional measurement values ZMW of the sensor 24 were transmitted to the monitoring device 14 were connected to a curve 34 are schematically represented by the solid black circles. A ratio of the actual values IW, IW′ from the electrical drive 10 and the additional measurement values ZMW from the sensor 24 at the respective time points has been calculated by the algorithm 16 and represents the efficiency η of the electrical joining system 100. Moreover, an extrapolation into the future may be seen from the point where the time course of the curve 34 is shown as a dashed line.

(24) In particular, it may be seen that the level of the efficiency η decreases with increasing time t. A threshold value GW identifies a threshold at which it would be advantageous from an economic point of view, for example, to replace a worn component of the electromechanical joining system 100 due to decreasing efficiency η or incipient wear of a wear-prone component 21 before wear and tear would lead to an undesired interruption in operation of the electromechanical joining system 100. The time t.sub.1 when the threshold value GW is reached may be extrapolated by the algorithm 16. The time t.sub.1 is referred to as the service life of the wear-prone component 21.

(25) For comparison, FIG. 5 shows a curve 36 representing the expected remaining service life LD of the electromechanical joining system 100 over time t. In this case, the algorithm 16 used the actual values IW, IW′ of the electrical drive 10 and the additional measurement values ZMW of the sensor 24 in a service life equation, wherein said service life equation may optionally include further factors or values which may have to be determined using further measurement values or information, respectively.

(26) For example, using the actual values IW of the rotational speed n of the drive shaft 18 measured by the absolute value encoder 11 and additional measurement values ZMW of forces F measured by the sensor 24, a service life LD may be determined according to the following service life equation:

(27) $\mathrm{LD}~B^{-\frac{1}{3}}=\frac{\underset{i}{\overset{m}{.Math.}}{q}_i}{\underset{i}{\overset{m}{.Math.}}{q}_i{n}_i{F}_i^3}$

(28) Accordingly, the service life LD is inversely proportional to the third power of an average load B during a number m of uses wherein i is the index of the individual use in operation. A length of time of an operation period is denoted by q.sub.i. And n.sub.i represents an average rotational speed measured during an operation period. Finally, F.sub.i is an average force measured during an operation period.

(29) Those skilled in the art and being aware of the present invention may use a different service life equation. Thus, a service life LD.sub.10 achieved when 90% of the wear-prone components have been used. Also in this case is:

(30) ${\mathrm{LD}}_{10}=K_{10}{B}^{-\frac{1}{3}}$

(31) Alternatively, a service life LD.sub.5 achieved by 95% of the wear-prone components may be used. Wherein K.sub.10 and K.sub.5 are experimentally determined proportionality factors.

(32) Also in this case shown in FIG. 5, the algorithm 16 may calculate in advance a critical threshold value GW and a time t.sub.2 when the threshold value GW will be reached. The time t.sub.2 is referred to as the service life of the electromechanical joining system 100.

(33) The curves 34, 36 shown in FIGS. 4 and 5 may be for example displayed on a display device 30, in particular a screen, connected to the monitoring device 16 schematically shown in FIG. 2 and FIG. 3. Furthermore, it is possible to store the shape of the curves 34, 36 or the numerical values given by the shape of the curves 34, 36 as well as the corresponding actual values of the electrical drive 10 or additional measurement values of the sensor 24 by means of a storage medium 32 schematically shown in FIG. 2 and FIG. 3. Preferably, the storage medium 32 is a transducer electronic data sheet (TEDS) in accordance with standard IEEE 1451.4.

(34) The method described above may be altered or modified in a number of ways without departing from the spirit of the invention.

LIST OF REFERENCE NUMERALS

(35) 1 component 2 component 3 arrow 4 brake 5 gear 6 belt drive 7 bearing 8 anti-rotation device 9 guide 10 electrical drive 11 absolute value encoder 12 servo motor 13 control device 14 monitoring device 16 algorithm 18 drive shaft 20 screw drive 21 wear-prone component 22 output element 24 sensor 30 display device 32 storage medium 34 curve shape 36 curve shape 100 electromechanical joining system LD service life GW threshold value t time t.sub.1 calculated service life of wear-prone component t.sub.2 calculated service life of electromechanical joining system or screw drive IW actual value of rotational speed of drive shaft IW′ actual value of current intensity of servo drive ZMW additional measurement value η efficiency