Method for monitoring a transmission driven by an electric motor

Abstract

The invention relates to a method for monitoring a transmission driven by an electric motor with a motor controller, wherein zero-crossing load changes of the motor torque in the transmission are monitored, wherein at least one operating parameter of the electric motor and / or the motor controller is measured and evaluated to monitor the load changes.

Description

Technical Field

[0001] The invention relates to a method for monitoring a transmission driven by an electric motor having a motor controller. Background Art

[0002] Electric motors with this type of transmission are particularly widely used in industrial environments. This combination of electric motor, transmission and motor controller is referred to below as a drive. Such drives often perform tasks that are critical to the respective industrial process in which they are integrated. This means that if a drive fails, not only are costs incurred for repairing and / or replacing the drive itself, but further, more serious injuries may occur to the operator of the drive. This is especially true if production is interrupted due to a drive failure.

[0003] Therefore, methods have been developed in the past for designing corresponding drives in order to ensure that premature drive failure does not occur, ie in particular failure of the drive before its intended service life.

[0004] Furthermore, there are methods according to which operating parameters of such drives are monitored in order to warn sufficiently early of possible increased wear in the respective application and any resulting premature failure of the drive. The monitored operating parameters may be, for example, speed, torque and / or operating time.

[0005] However, premature drive failures can still occur in practice. Summary of the invention

[0006] It is therefore an object of the present invention to provide a method for monitoring a transmission driven by an electric motor with a motor controller which reduces the risk of premature failure of the drive and / or enables a gentler operating mode for the transmission.

[0007] The invention is achieved by a method having the features of claim 1. The features of the dependent claims relate to advantageous embodiments.

[0008] According to the invention, the method provides for monitoring load changes as the torque passes through zero. Here, at least one operating parameter of the electric motor and / or the motor controller is measured and / or evaluated to monitor the load changes.

[0009] The method is based on the recognition that zero-crossing load changes, ie load changes when the torque applied by the drive to the transmission changes direction, lead to wear of the transmission to a certain extent. The transmission can in particular be a toothed transmission.

[0010] This particularly concerns situations when the transmission has so-called play. This refers in particular to the gear tooth backlash that occurs when the torque applied by the engine to the transmission changes direction, which causes the tooth flanks in the transmission to briefly lose contact with each other during the load change. Only when the tooth flanks re-engage with each other does the transmission transfer the torque back to the device driven by the transmission. This results in the motor having to handle much lower loads at the moment of the load change than during the operating period before and after the load change, for which the motor's regulation or control is usually designed. During this brief moment, the motor only has to move a portion of itself. This causes the tooth flanks to build up a certain relative speed to each other when they are out of mesh, so that when they re-engage with each other, they hit each other with a certain force. This leads to wear on the tooth flanks and, in turn, to a further increase in the gear play or backlash.

[0011] However, this increased wear during load changes can also occur in gear sets without backlash, such as preloaded gear sets, especially preloaded planetary gear sets. In such gear sets, the tooth flanks cannot disengage. However, during load changes with zero torque of the electric machine, increased stresses on the transmission occur. In these cases, the load changes lead to increased pressure between the surfaces of the tooth flanks, which also leads to increased wear and thus premature aging of the gear set.

[0012] The method can provide for monitoring of load changes for detecting and in particular signaling critical operating states. This makes it possible, for example, to detect during a test run whether a gear set will be subjected to greater stresses than the gear set design permits due to load changes in subsequent operation. For example, an optical and / or acoustic signal can be output when a critical operating condition occurs. In this case, a more gear-protective operating mode can be achieved, for example, by changing control parameters, in particular control parameters of the engine control system. However, critical operating states can be signaled not only during the test run, but also during subsequent operation. This is particularly useful in applications in which the movements performed by the drive during operation vary greatly. This is the case, for example, with manually controlled drives. In this case, the signaling of a critical operating state warns the operator so that they can influence the operating mode of the drive in order to protect the gear set in the event of load changes.

[0013] Alternatively and / or additionally, the monitoring of load changes can be used to record the load and / or wear of the transmission. This can be achieved in particular by storing data obtained during the measurement of at least one operating parameter of the electric motor and its evaluation. Conclusions can be drawn from these data about the type and / or extent of the load and / or wear of the gear set. In this way, retrospective fault analyses can be carried out. In particular, the data can be stored in a so-called electronic logbook. The data obtained in this way can also be evaluated for the design of the drive. These data can also support maintenance and / or repair work, for example, by responding in time to increased wear before the drive fails during operation as part of a planned maintenance interval.

[0014] Alternatively and / or in addition, the monitoring can be used to trigger an automatic operating intervention. The automatic operating intervention can be an emergency stop. Such an emergency stop can in particular ultimately prevent the occurrence of consequential damage. It is also possible that the automatic operating intervention first provides an adaptation of the operating mode, for example by actuating the drive at a lower speed or torque gradient when the load changes. In other words, this means that a type of "saving operation" is triggered based on the monitoring of the load change.

[0015] The operating parameters of the motor or motor control unit that are measured can be torque, motor position, speed, voltage, current and / or power. The measurement of operating parameters in the field of motors and / or motor controls has the following advantages: In the field of motor controls and / or motors - in contrast to the field of transmissions - a specific metering infrastructure is already available. Usually, at least one suitable voltage source and / or cable is available. Usually, the motor and / or motor controller also already has the sensor technology required to measure the operating parameters, since this can be used, for example, for control purposes.

[0016] In particular, the time course of the above-mentioned operating parameters can be evaluated with respect to gear play. For example, when monitoring the motor position, the position error can be determined, i.e. the deviation of the actual motor position from the ideal (i.e. ideally rigid and without any backlash) motor position generated by the drive section. If the direction of rotation of the motor changes and there is gear play in the gear set, this leads to characteristic jumps in the position error course.

[0017] Alternatively and / or additionally, for example, the time course of the torque and the motor position can be measured and evaluated as a function of one another. Immediately after a reversal of the motor's direction of rotation during a load change, the torque will initially be low due to the gear backlash and will rise sharply at the moment when the tooth surfaces mesh with one another. Conclusions about the gear backlash can also be drawn from the angle through which the motor has rotated before the sharp torque rise.

[0018] In particular, the number of load cycles can be monitored. The number of load cycles can serve as a measure of the mechanical load on the transmission. This can be an advantageous embodiment of the method, in particular if the load changes differ from one another only to a small extent with respect to the mechanical load on the transmission caused by them. In particular, exceeding a predetermined number of load cycles can be detected as a critical operating state. The detected critical operating state can be signaled.

[0019] The frequency of the load changes can be monitored. The frequency of the load changes can be the instantaneous frequency of the load changes, which can be calculated, for example, from the time interval to the corresponding subsequent load change. Alternatively and / or additionally, the frequency averaged over a certain period of time can be taken into account. For example, the average frequency can also be determined by recording the number of load changes over a certain period of time and monitoring it with the frequency of the load changes. A higher frequency of load changes correspondingly leads to a higher mechanical load on the transmission. Exceeding a specified frequency can be detected and signaled as a critical operating condition.

[0020] Furthermore, gear backlash can be monitored. Gear backlash can be seen as a measure of existing wear on the engine. Exceeding a predetermined gear backlash can therefore be detected and signaled as a critical operating condition.

[0021] In this case, it is particularly advantageous to monitor the gear backlash as described above by monitoring the time-dependent characteristic of the motor torque as a function of the time-dependent characteristic of the motor position. Likewise, the time-dependent torque gradient can be monitored at the zero torque crossing. If a predetermined torque gradient is exceeded, this can be detected and signaled as a critical operating state.

[0022] For example, the motor position can be determined by means of a rotary encoder. This is particularly advantageous if the motor is anyway equipped with a rotary encoder (which is usually the case). The torque can advantageously be obtained from the electrical operating parameters of the motor—in particular the voltage and / or the current. In this way, operating parameters for monitoring load changes can be determined in a relatively simple manner.

[0023] Furthermore, a characteristic value of the load and / or the wear of the transmission can be determined based on the monitoring results of the number of load changes, the frequency of load changes, the gear play and / or the torque gradient. Such a characteristic value can take into account different factors of transmission wear, thereby obtaining a more accurate measurement of transmission wear overall than if only one of the above-mentioned wear-related factors were monitored. Exceeding a specified value of the characteristic value can be detected and signaled as a critical operating condition.

[0024] When determining characteristic values ​​of load and / or transmission wear, an energy balance can be used. Thus, for a "shock" that occurs in the transmission during a load change, the difference in kinetic energy in the system before and after the shock can be calculated. This difference can be used as a measure of the energy dissipated by the deformation of the plastic material during the shock, at least as a good approximation.

[0025] The electric motor can be controlled by an inverter. Operating parameters such as voltage and / or current can then be measured at the converter. Modern converters for controlling electric motors also have corresponding control and / or regulating electronics, which can thus be integrated into the implementation of the process.

[0026] The method can provide that at least one operating parameter is evaluated taking into account the area of ​​the transmission element that is affected by the respective load change. This is particularly useful when load changes occur with statistical accumulation, whenever the elements of the transmission are in a certain position relative to each other. The elements of the transmission, such as gears, are then statistically concentrated in certain areas that engage with each other. These areas are then subject to greater wear than other areas of the transmission that are affected.

[0027] It may therefore be useful to detect the angular position of the individual gear elements and / or the motor. At least one operating parameter can then be evaluated based on this position or these recorded positions. This makes it possible to identify areas of the individual transmission elements that are affected by increased wear due to load changes.

[0028] The transmission element may be a gear. Ideally, the individual teeth affected by the respective load change can then be identified. For this purpose, in particular the angular position of the motor shaft and / or the angular position of the shaft of the transmission can be detected. At least one operating parameter can then be evaluated based on the respective affected tooth. This can particularly allow a better evaluation of the service life of the transmission if the transmission involves repetitive movement patterns that perform frequent load changes.

[0029] The latter is the case in particular if the gear set is part of an industrial robot. In industrial robotics applications, the drives rarely complete a full rotation. Instead, they usually only rotate through an unlimited angular range. This also applies to the field of automation technology. Here too, there are a large number of drive tasks in which the drives repeatedly perform the same movement and perform a large number of load changes relative to the total distance covered.

[0030] In all these applications, if the same teeth of the transmission are repeatedly subjected to load variations, they will wear much faster than if the stresses on the teeth due to load variations in the transmission are randomly distributed and therefore evenly distributed over all teeth. Therefore, an evaluation taking into account the area of ​​the gear element that is subjected to the corresponding load variations is particularly advantageous in such applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Further practical embodiments and advantages of the present invention are described below in conjunction with the accompanying drawings. It is shown in the drawings:

[0032] Figure 1 shows the gear backlash as a function of the number of load cycles;

[0033] Figure 2 shows an example of motor position and position error caused by gear backlash;

[0034] Figure 3 An example of load position during braking is shown;

[0035] Figure 4 Examples of motor position, load position, and motor torque during two load changes are shown. DETAILED DESCRIPTION

[0036] Figure 1 An example of the variation of the gear backlash 10 as a function of the number of load changes is shown. The variation of the gear backlash 10 generally exhibits - at least substantially - an exponential behavior. The gear backlash 10 remains substantially constant during most of the useful life of the transmission. However, towards the end of the useful life of the transmission, the transmission backlash 10 increases dramatically. This is because as the transmission backlash 10 increases, the load on the transmission due to the load changes also increases, leading to damage to the transmission. This result is a self-reinforcing process that ultimately leads to damage to the gear set.

[0037] Therefore, in practice it is useful to know the point in time at which the gear backlash 10 increases relatively sharply and at which the transmission is increasingly damaged. Since in practice it is better not to let the gear set damage point be reached, but to schedule regular maintenance or regular replacement of the gear set at an earlier point in time, this provides the possibility of defining the end of the service life 14 of the gear set as the exceeding of a certain, maximum permissible gear set backlash 10.

[0038] In a particularly advantageous manner, the knowledge obtained by the method according to the invention about the dependence of the service life of the transmission on the load changes can be used for the design of future drives. Software solutions can be used in particular for this purpose. The data obtained by the method according to the invention, in particular about the influence of load changes on the service life of the transmission, can thus be used to improve the planning of future drives.

[0039] Figure 2 It is shown how the motor position 16 and the position error 20 caused by the gear backlash 10 change over time. In the example shown, the temporal characteristic of the motor position 16 has three reversal points 18 of the direction of motor movement. These are represented by maxima in the motor position 16 course.

[0040] The course of the position error 20 as a function of time shows regular jump points 22 at the reversal points 18. These are caused by the gear backlash 10, when the tooth surfaces briefly disengage at the moment when the motor torque is zero and then collide with each other again. The "height" of these jump points 22 represents the gear backlash 10.

[0041] Without changing the direction of rotation of the motor, a further load change with a zero crossing of the motor torque occurs at the transition 24 between the drive and braking operation of the motor. At the transition 24 shown as an example, a brief "intermediate braking" occurs by the motor. As a result, the tooth flanks are briefly disengaged due to the inertia of the gear set until the braking action of the motor begins. In the example shown, the brief braking is followed by another load change, during which a transition 26 occurs from the braking mode to the drive mode of the motor operation. As a result, a peak 28 of the position error 20 is formed between the transitions 24 and 26.

[0042] The peak 28 resulting from the brief "intermediate deceleration" is - strictly speaking - two subsequent jump points 22, since they also occur at the reversal point 18. Since the present case involves a very short intermediate deceleration, followed by a driving phase, the two jump points 22 show the shape of the peak 28. If the deceleration phase between the transitions 24 and 26 lasted longer, the two jump points 22 would form in the course of the position error 20 instead of the peak 28.

[0043] The situation is different if the motor's movement only undergoes an acceleration 30 in the direction of the motor's movement. In this case, the torque increases sharply, but the torque curve does not cross zero, i.e. there is no load change. Therefore, there is no jump point 22 in the course of the position error 20.

[0044] Figure 3 An example of how the load position changes due to existing gear backlash is shown. Gear backlash 32 corresponds to the difference between a maximum position 34 and a minimum position 36. The load moved by the drive can be in a position between the maximum position 34 specified by the motor position and the minimum position 36 also specified by the motor position. In the case of the maximum position 34 and the minimum position, the tooth surfaces of the transmission are in contact with each other.

[0045] As in Figure 3 The motion sequence shown in the example in shows a load change in the form of a deceleration of a load driven by a motor, which initially moves at a constant initial speed. Therefore, the load position 38 at time 0 is equal to the minimum position 36. This means that the tooth surfaces are adjacent to each other so that the force driving the load in the positive direction of motion can be transmitted to the load, but not to the deceleration end.

[0046] The deceleration results in a flatter curve for the maximum position 34 specified by the motor position and the minimum position 36 specified by the motor, compared to the steeper curve for the load position 38 due to the initial speed of the initially still unbraked load. The tooth flanks initially disengage until the load position 38 reaches the maximum position 34. At this impact point 40, the tooth flanks collide with each other.

[0047] Due to the elastic component of this impact, the direction of movement of the load is reversed until the load position 38 at the impact point 41 again corresponds to the minimum position 36. The tooth flanks collide again and the direction of movement of the load is reversed again.

[0048] During the further movement, the load position 38 reaches the maximum position 34 again. Since the kinetic energy has been partially dissipated by the previous impact, the contact of the tooth flanks during the further movement enables the braking force to be transmitted to the load via the tooth flanks. The load position 38 then corresponds to the maximum position 34. Further braking of the load can now take place without further impacts.

[0049] Figure 4 Exemplary graphs of a motor speed 42 of the motor and a load speed 44 of the driven load are shown. Figure 4 The second diagram in shows the corresponding curve of the motor torque 46. The time axis of both diagrams is the same.

[0050] In the example shown, a first load change 48 occurs when the engine accelerates from a stationary position. Here, the motor torque 46 initially increases only slightly when the motor speed 42 begins to rise. In the example shown, the tooth surfaces initially do not contact each other, so the load speed 44 initially remains at 0. Only when the tooth surfaces contact each other does the load speed 44 of the load begin to increase suddenly. The torque also increases sharply.

[0051] The impact of the tooth flanks on each other and their elastic component accelerate the load to such an extent that the tooth flanks initially disengage again. The load speed 44 "overtakes" the motor speed 42 for a short time until the tooth flanks collide during further impact. This initially reduces the load speed 44 and thus brakes the load, causing the motor torque 46 to change suddenly and even assume negative values ​​for the moment of impact of the tooth flanks.

[0052] However, due to further acceleration of the motor and increase in motor speed 42, the tooth flanks soon engage each other again, this time causing the load to accelerate and the load speed 44 to start increasing again. The motor torque 46 accordingly rises suddenly again. As the process continues, the motor speed 42 and the load speed 44 converge.

[0053] In the further course, a further load change 50 occurs, during which a deceleration of the load is initiated by the motor. As a result, a slightly negative motor torque 46 is initially generated, which causes the motor speed 42 to decrease. Due to inertia, even in the case of a load change 50, the load speed 44 initially remains constant until the tooth flanks engage with each other. Initially, the tooth flanks engage with each other in such a way that they can transfer the load braking force from the motor to the load. As a result, the load speed 44 starts to decrease rapidly and the amplitude of the motor torque 46 increases towards more negative values, forming a negative torque peak.

[0054] Due to the elastic component of the tooth flanks impacting each other, the load is initially suddenly decelerated to such an extent that the load speed 44 is below the value of the motor speed 42. At this point, the tooth flanks again first disengage from each other and then collide with each other in a direction, wherein the motor speed 42 is now higher than the load speed 44, and the motor again exerts an accelerating effect on the load. Therefore, there is a positive torque peak of the motor torque 46, and due to the elastic component of this impact, the load speed 44 initially assumes a value slightly higher than the motor speed 42 again.

[0055] Due to the elastic component of the impact, the tooth flanks separate from each other again and then mesh with each other in the opposite direction, i.e., the motor applies a deceleration effect to the load. Therefore, a further negative torque peak is initially formed. However, in this example, the previous impact has dissipated so much kinetic energy that there is no renewed torque reversal, i.e., there is no renewed meshing of the tooth flanks in the "reverse direction". Instead, during the further movement, the load speed 44 is equal to the motor speed 42. Figure 4 The torque peaks that can be clearly seen in the course of the motor torque 46 are very suitable for identifying and evaluating critical load changes when evaluating the course of the motor torque 46.

[0056] The features of the invention disclosed in the present specification, drawings and claims are essential for the realization of the invention in its various embodiments, both individually and in any combination. The invention is not limited to the embodiments described above. Changes may be made within the scope of the claims and taking into account the knowledge of the relevant person skilled in the art.

[0057] Reference numerals list

[0058] 10 Gear backlash

[0059] 12 Maximum permissible gear backlash

[0060] 14 End of life

[0061] 16 Motor position

[0062] 18 Reverse Point

[0063] 20 Position error

[0064] 22 Jump Point

[0065] 24 Drive-Brake Transition

[0066] 26 Brake-Drive Transition

[0067] 28 Peak

[0068] 30 Acceleration

[0069] 32 Gear Backlash

[0070] 34 Maximum position

[0071] 36 Minimum position

[0072] 38 Load position

[0073] 40 Impact Point

[0074] 41 Impact Point

[0075] 42 Motor speed

[0076] 44 Load speed

[0077] 46 Motor torque

[0078] 48 Load Change

[0079] 50 Load Change

Claims

1. A method for monitoring a transmission driven by an electric motor with a motor controller, wherein a load change (48, 50) with a zero motor torque in the transmission is monitored, at least one operating parameter of the electric motor and / or the motor controller is measured and evaluated in order to monitor the load change (48, 50), characterized in that Exceeding a predetermined number of load changes (48, 50) is detected as a critical operating state.

2. The method according to claim 1, characterized in that The monitoring of load changes (48, 50) is used to signal critical operating states, to record load and / or transmission wear and / or to trigger automatic operating interventions.

3. The method according to claim 1 or 2, characterized in that: The operating parameters are torque, motor position (16), speed, voltage, current and / or power.

4. The method according to claim 1, characterized in that: The number of load changes (48, 50) is monitored.

5. The method according to claim 1, characterized in that Exceeding a predetermined number of load changes (48, 50) is detected as a critical operating state and signaled.

6. The method according to claim 1, characterized in that The frequency of load changes (48, 50) is monitored.

7. The method according to claim 6, characterized in that Exceeding a predetermined frequency is detected and signaled as a critical operating state.

8. The method according to claim 1, characterized in that The gear backlash (10) is monitored.

9. The method according to claim 8, characterized in that Exceeding a predetermined gear backlash (10) is detected and signaled as a critical operating state.

10. The method according to claim 8, characterized in that To monitor the transmission backlash (10), a time-dependent characteristic of the motor torque is evaluated as a function of a time-dependent characteristic of the motor position (16).

11. The method according to claim 1, characterized in that: The time-dependent torque gradient is monitored at the zero crossing.

12. The method according to claim 11, characterized in that The exceeding of a predefined torque gradient is detected and signaled as a critical operating state.

13. The method according to any one of claims 4 to 12, characterized in that According to the monitoring results of the number of load changes, the load change frequency, the gear clearance (10) of the transmission and / or the torque gradient, the characteristic value of the load and / or the wear of the transmission are determined.

14. The method according to any one of claims 4 to 12, characterized in that The characteristic value of the load and / or the wear of the transmission is determined in that the characteristic value exceeds a predetermined value and is detected and signaled as a critical operating state.

15. The method according to claim 1, characterized in that The at least one operating parameter is evaluated taking into account the region of the transmission element that is affected by the respective load change (48, 50).

16. The method according to claim 1, characterized in that The at least one operating parameter is evaluated taking into account teeth of a gearwheel of the transmission that are affected by a corresponding load change (48, 50).

17. The method according to claim 1, characterized in that The method is used within the scope of a test run, wherein first a test operation is carried out within the scope of the test run and if a critical operating state occurs during the test operation, parameters of an open-loop and / or closed-loop control of the electric motor are adjusted.

Images