Method for monitoring a gearbox driven by an electric motor

Abstract

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

Claims

1. A method for monitoring a transmission driven by an electric motor with a motor control, comprising: monitoring load changes with zero crossing of motor torque in the transmission by measuring and evaluating at least one operating parameter of the electric motor and/or of a controller of the electric motor, wherein a number of load cycles exceeding a predetermined number of load cycles is detected as a critical operating state.

2. The method according to claim 1, further comprising: signaling critical operating states to log a load and/or a wear of the transmission and/or to trigger an automated operating intervention.

3. The method according to claim 2, wherein the automated operating intervention is an emergency shutdown.

4. The method according to claim 3, wherein the at least one operating parameter is one or more of: torque, motor position, speed, voltage, current, or power.

5. The method according to claim 1, wherein a number of load cycles is monitored.

6. The method according to claim 5, wherein a characteristic value for a load and/or wear of the transmission is determined based on monitoring the number of load cycles, a load cycle frequency, transmission backlash and/or a torque gradient and wherein the characteristic value exceeding a predetermined value is signaled as a critical operating state.

7. The method according to claim 1, wherein gear backlash is monitored and exceeding a predetermined gear backlash is detected and signaled as a critical operating state.

8. The method according to claim 1, further comprising: monitoring transmission backlash as a function of a time-dependent characteristic of the motor torque which is evaluated as a function of a time-dependent characteristic of a motor position.

9. The method according to claim 1, further comprising: monitoring a time dependent torque gradient at a time of zero crossing; and signaling a critical operating state in response to detecting the time dependent torque gradient exceeding of a predetermined torque gradient.

10. The method according to claim 1, wherein at least one operating parameter is evaluated taking into account an area of a transmission element affected by a respective load change.

11. The method according to claim 10, wherein the at least one operating parameter corresponds to a tooth of a gear of the transmission affected by a respective load change.

12. The method according to claim 1, wherein a test operation is initially carried out within a scope of commissioning and, if critical operating states occur during the test operation, parameters of an open-loop and/or closed-loop control of the electric motor are adjusted.

13. Method A method for monitoring a transmission driven by an electric motor with a motor control, comprising: monitoring load changes with zero crossing of the motor torque in the transmission by measuring and evaluating at least one operating parameter of the electric motor and/or of a controller of the electric motor, wherein a frequency of load changes is monitored and exceeding a predetermined frequency is detected and signaled as a critical operating state.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Further practical embodiments and advantages of the system described herein are described below in connection with the drawings. It is shown in:

(2) FIG. 1 shows the gear backlash as a function of the number of load cycles;

(3) FIG. 2 shows an example of the motor position and the position error resulting from the gear backlash;

(4) FIG. 3 shows an example of the load position during a braking process; and

(5) FIG. 4 shows an example of the motor position, load position and motor torque during two load changes.

DESCRIPTION OF VARIOUS EMBODIMENTS

(6) FIG. 1 shows an example of the development of the gear backlash 10 as a function of the number of load changes. The development of the gear backlash 10 typically shows anat least essentiallyexponential behavior. The gear backlash 10 remains largely constant over most of the service life of a gearbox. Towards the end of the service life of a gearbox, however, there is a steep increase in gearbox backlash 10. This is because as gearbox backlash 10 increases, so does the load on the gearbox due to load changes, and hence the resulting damage to the gearbox. The result is a self-reinforcing process that ultimately leads to the destruction of the gear unit.

(7) In practice, therefore, it makes sense to know the point in time at which the comparatively steep increase in gear backlash 10 and thus the increasingly rapid destruction of the gearbox begins. Since it is advantageous in practice not to let it get to the point of destruction of the gear unit, but rather to arrange for scheduled maintenance or scheduled replacement of the gear unit at an earlier point in time, this offers the possibility of defining the exceeding of a certain, maximum permissible gear unit backlash 10 as the end of the service life 14 of the gear unit.

(8) In a particularly advantageous way, the knowledge gained with the method according to the system described herein about the dependence of the service life of the transmission on the load changes can be used to design future drives. Software solutions in particular can be used for this purpose. Data obtained with the method according to the system described herein, in particular on the influence of the load changes on the service life of the transmission, can thus be used to improve the planning of future drives.

(9) FIG. 2 shows how the motor position 16 and the position error 20 resulting from the gear backlash 10 behave as a function of time. In the example shown, the time characteristic of the motor position 16 has three reversal points 18 of the direction of movement of the motor. The reversal points 18 are represented by maxima in the course of the motor position 16.

(10) The course of the position error 20 as a function of time shows regular jump points 22 at the reversal points 18. The jump points 22 result from the gear backlash 10 when the tooth flanks briefly disengage at the moment of zero passage of the torque of the electric motor and then strike against each other again. The height of the jump points 22 represents the gear backlash 10.

(11) Further load changes with zero crossing of the motor torque occur at transitions 24 between driving and braking operation of the motor without changing the direction of rotation of the motor. At the transition 24 shown as an example, a short intermediate braking takes place via the motor. As a result, the tooth flanks are disengaged for a short time due to the inertia of the gear unit until the braking effect of the motor sets in. In the example shown, the short braking is immediately followed by another load change, during which a transition 26 takes place from the braking mode of operation of the motor to a driving mode. As a result, a peak 28 of the position error 20 is formed between the transitions 24 and 26.

(12) Peak 28, which results from a short intermediate deceleration, is-strictly speaking-two jump points 22 immediately following one another, as they also occur at the reversal points 18. Since the present case involves a very short intermediate deceleration which is immediately followed by a drive phase again, the two jump points 22 show the shape of the peak 28. If the deceleration phase between the transitions 24 and 26 were to continue for a longer time, two jump points 22 would be formed in the course of the position error 20 instead of the peak 28.

(13) The scenario is different if the movement of the motor only experiences an acceleration 30 in the direction of movement of the motor. In this case, there is a sharp increase in torque, but the torque curve does not undergo a zero crossing, i.e. there is no load change. Accordingly, there is also no jump point 22 in the course of the position error 20.

(14) FIG. 3 shows an example of how the position of the load behaves due to an existing gear backlash. The gear backlash 32 corresponds to the difference between a maximum position 34 and a minimum position 36. The load moved by the drive can assume a position between the maximum position 34 specified by the motor position and the minimum position 36 also specified by the motor position. Both in the case of the maximum position 34 and in the case of the minimum position, tooth flanks of the gearbox are in contact with each other.

(15) The motion sequence shown as an example in FIG. 3 shows a load change in the form of the deceleration of a load, which initially moves at a constant initial speed, by the motor. Accordingly, the load position 38 at time zero is equal to the minimum position 36. This means that the tooth flanks are adjacent to each other in such a way that a force driving the load in the positive direction of movement could be transmitted to the load, but not a deceleration end.

(16) Deceleration results in a flatter curve of the maximum position 34 specified by the motor position and the minimum position 36 specified by the motor compared to the curve of the load position 38, which is steeper 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 a point of impact 40, the tooth flanks collide with each other.

(17) Due to the elastic component of the 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.

(18) In the further course of the movement, the load position 38 again reaches the maximum position 34. Due to the kinetic energy already partially dissipated by the previous impacts, the tooth flanks come into contact in the further course of the movement in such a way that a braking force can be transmitted to the load via the tooth flanks. The load position 38 then corresponds to the maximum position 34. The further braking of the load can now take place without further impacts.

(19) FIG. 4 shows an exemplary curve of the motor speed 42 of a motor and the load speed 44 of a driven load. The second diagram in FIG. 4 shows the corresponding curve of the motor torque 46. The time axes of both diagrams are identical.

(20) In the example shown, a first load change 48 takes place when the engine is accelerated from a rest position. Here, the motor torque 46 initially increases only slightly when the motor speed 42 begins to rise. In the example shown, tooth flanks are not initially in contact with each other, so the load speed 44 initially remains at zero. Only when the tooth flanks come into contact with each other does the load speed 44 of the load begin to increase abruptly. The torque also increases abruptly.

(21) The impact of the tooth flanks against each other and a corresponding elastic component accelerates 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 moment until the tooth flanks collide in a further impact. This initially lowers the load speed 44 and consequently brakes the load, causing the motor torque 46 to change abruptly and even assume negative values for the moment of impact of the tooth flanks.

(22) Due to the further acceleration of the motor and the increase in motor speed 42, however, the tooth flanks come into engagement with each other again shortly afterwards, this time in such a way that the load is accelerated and the load speed 44 begins to increase again. The motor torque 46 rises abruptly again accordingly. As the process continues, the motor speed 42 and the load speed 44 converge.

(23) In the further course, a further load change 50 takes place, during which a deceleration of the load is initiated by the motor. Accordingly, a slight negative motor torque 46 is initially generated, which leads to a decrease in motor speed 42. Due to the inertia, even in the case of the 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 transmit a load braking force from the motor to the load. Accordingly, the load speed 44 begins to decrease rapidly, and the motor torque 46 increases in magnitude toward higher negative values, forming a negative torque peak.

(24) Due to the elastic component of the impact of the tooth flanks against each other, the load is initially decelerated abruptly to such an extent that the load speed 44 falls 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 an orientation in which the motor, which at this moment has a higher motor speed 42 than the load speed 44, again exerts an accelerating effect on the load. Accordingly, there is a positive torque peak of the motor torque 46, and the load speed 44 initially again assumes a slightly higher value than the motor speed 42 due to the elastic component of the impact.

(25) The tooth flanks separate from each other again due to the elastic component of the impact, and then engage with each other with reversed orientation, i.e. so that the motor can exert a decelerating effect on the load. Accordingly, a further negative torque peak is initially formed. In this example, however, so much kinetic energy has already been dissipated by the previous impacts that there is no renewed torque reversal, i.e. no renewed meshing of the tooth flanks in reverse orientation. Rather, the load speed 44 equalizes to the motor speed 42 in the course of the further course of movement. The torque peaks, which can be clearly seen in the course of the motor torque 46 in FIG. 4, are well suited for identifying and evaluating critical load changes when evaluating the course of the motor torque 46.

(26) The features of the system described herein disclosed in the present description, in the drawings as well as in the claims may be essential, both individually and in any combination, for the realization of the system described herein in its various embodiments. The invention is not limited to the embodiments described. It may be varied within the scope of the claims and with due regard to the knowledge of the person skilled in the art.