Method and device for automatically determining the value of a state variable of a drive train for moving a load

Abstract

The invention relates to a method for automatically determining the value of a state variable of a drive train (2) for moving a load (3), wherein the drive train (2) comprises a drive (4) and a drive element (6) which is driven by the drive (4) and moved with the load (3), and a fixed support element (7), on which the drive element (6) is supported, in order to move the load (3) relative to the support element (7). The method comprises the following method steps: a) accelerating the load (3) by means of the drive (4) by specifying a driving profile (13) with acceleration reversal; b) during the acceleration of the load (3), detecting the ACTUAL acceleration of the drive (4) and detecting the ACTUAL acceleration of the load (3); and c) determining a value of the state variable of the drive train (2) by evaluating the detected ACTUAL accelerations of the drive (4) and the load (3).

Description

[0001] Method and device for automatically determining the value of a state variable of a drive train for moving a load

[0002] The invention relates to a method and a device for the automated determination of the value of a state variable of a drive train for moving a load, in particular a translationally guided load, wherein the drive train has a drive and a drive element driven by the drive, which is moved along with the load, as well as a fixed support element on which the drive element is supported in order to move the load relative to the support element.

[0003] For example, known 2D laser cutting machines use a rack and pinion drivetrain to move a translationally guided guide carriage. The drivetrain includes a motor and a pinion driven by the motor via a gearbox, all of which are attached to the guide carriage and thus move together with the guide carriage. A fixed rack meshes with the pinion to move the guide carriage relative to the rack.

[0004] Due to manufacturing tolerances and to protect all components involved from wear, rack and pinion drives typically have backlash. Backlash describes the distance between one tooth flank of the pinion and the next tooth flank of the rack when the opposing tooth flanks are in contact.

[0005] The amount of backlash must be checked regularly to ensure the machine is functioning properly. Since rack and pinion drives often do not have a direct measuring system installed, additional measuring equipment must be installed to measure the backlash and the value must be measured manually, for example during service calls. Until now, a dial indicator or a measuring probe has been attached so that the relative displacement of the guide carriage, to which the gear and pinion are attached, to the guide rail on which the guide carriage moves can be measured. The guide carriage is then moved manually along the guide rail and the distance covered without the application of great force is read from the measuring probe or the dial indicator. This value corresponds to the backlash.

[0006] In contrast, the present invention is based on the object of specifying a method and a device with which a state variable of the drive train, such as a backlash, can be measured automatically.

[0007] This object is achieved according to the invention by a method for the automated determination of the value of a state variable of a drive train for moving a load, in particular a translationally guided load, wherein the drive train has a drive and a drive element driven by the drive, which is moved along with the load, as well as a fixed support element on which the drive element is supported in order to move the load relative to the support element, with the following method steps: a) accelerating the load by means of the drive by specifying a travel profile with acceleration reversal; b) during the acceleration of the load, detecting the actual acceleration of the drive and detecting the actual acceleration of the load; and c) determining a value of the state variable of the drive train by evaluating the detected actual accelerations of the drive and the load.

[0008] According to the invention, the load is moved by means of a drive control system in accordance with the travel profile and accelerated in such a way that an acceleration reversal, i.e. a zero crossing of the acceleration, occurs. During this movement, the drive-side acceleration (actual acceleration of the drive) and the output-side acceleration (actual acceleration of the load) are recorded. By comparing these two recorded acceleration signals, the value of the state variable can be calculated using suitable algorithms. During ongoing machine operation (whenever the load transitions from acceleration to braking), the state variable can be automatically monitored. The actual acceleration of the drive can, for example, correspond to the target acceleration of the load specified by the drive control system. As part of a condition diagnosis, the method according to the invention can provide information about the condition of the machine and, if necessary, support in fault diagnosis.

[0009] Preferably, the state variable is backlash in the drive train, which is inevitably present, for example, in a rack and pinion drive or a helical gear (e.g., ball screw drive). Backlash is particularly effective when the load undergoes a reversal of acceleration. At this point, the tooth flanks of the pinion and rack separate, and the load continues to move until the backlash has been traversed once and the tooth flanks on the opposite side abut each other. In this way, the backlash can be automatically monitored during ongoing machine operation. Alternatively, the state variable can also be, for example, elasticity or a degree of contamination in the drive train.

[0010] Preferably, the moving drive element meshes with the stationary support element to move the load relative to the support element. For example, the moving drive element is a pinion and the stationary support element is a rack (or vice versa), both meshing with each other.

[0011] The drive is preferably moved together with the load, but alternatively it could also not be moved with the load, i.e. it could be arranged in a fixed position just like the support element.

[0012] It is particularly advantageous to determine the actual acceleration of the drive from the detected speed of a drive configured as a rotary motor. The speed of the rotary motor can be measured, for example, by a motor measurement system that is usually already present on the rotary motor. Preferably, the actual acceleration of the load is measured using an acceleration sensor attached to the load itself or to an element moving with the load. The use of such an acceleration sensor is a very cost-effective solution, especially since so-called MEMS acceleration sensors are already available inexpensively and in sufficiently good quality.

[0013] The actual accelerations of the drive and the load are preferably recorded synchronously during the acceleration of the load, but can alternatively also be synchronized with each other subsequently, i.e. after the recording processes.

[0014] Preferably, the specified travel profile includes a forward and backward movement of the load. The axis of the load to be tested is moved forward and backward by a few millimeters, for example, via the motor control system once or several times using a step-like (jerk-limited) trajectory in order to achieve a reversal of acceleration through this reversal of movement. Alternatively, a travel profile with only a forward movement of the load or only a backward movement of the load is also possible, as long as a reversal of acceleration occurs.

[0015] The recorded actual accelerations of the drive and the load can be evaluated using various methods to determine the value of the state variable of the drive train.

[0016] In a first evaluation variant, the relationship between the state variable and changes in the acceleration curves of the actual accelerations of the drive and the load is determined experimentally and stored for different values ​​of the state variable. When the tooth flanks collide after the acceleration reversal, the moving load mass is abruptly decelerated or the drive is triggered. The larger the state variable, the stronger these sudden changes in the acceleration curves are. This relationship can be determined experimentally and stored on the machine. Based on the stored

[0017] The value of the state variable can be determined from the recorded actual accelerations of the drive and the load.

[0018] In a second evaluation variant, the relationship between the state variable and the time period within which the drive and support elements separate from each other and then come into contact again during an acceleration reversal is determined experimentally for different values ​​of the state variable and stored. The larger the state variable, the longer the time period between the tooth flanks separating and colliding again. The time of separation occurs when the drive undergoes an acceleration reversal, e.g., when the drive transitions from acceleration to braking. The time of collision occurs when the mass acceleration abruptly decreases or the drive acceleration abruptly increases. The relationship between this time period and the state variable can be determined experimentally and stored on the machine.Based on the stored relationship, the value of the state variable can be determined from the recorded actual accelerations of the drive and the load.

[0019] In a third evaluation variant, the recorded actual accelerations of the drive and the load are used to analytically calculate the times at which the drive and support elements separate from each other and reconnect during an acceleration reversal, the distance traveled during this process, and the resulting value of the state variable. If the acceleration measurement signals are of sufficiently good quality (resolution, noise), the distance traveled and thus the state variable can be analytically calculated from the time of separation of the tooth flanks and the time of collision of the tooth flanks.

[0020] The invention also relates to a device for automatically determining the value of a state variable of a drive train for moving a load, in particular a translationally guided load, in particular for carrying out the method according to the invention, comprising:

[0021] - a drive train with a drive and with a drive element driven by the drive, which moves with the load, as well as with a fixed support element on which the drive element is supported in order to move the load relative to the support element,

[0022] - a first device for detecting an actual acceleration of the drive,

[0023] - a second device for detecting the actual acceleration of the load, and

[0024] - an evaluation device which is programmed or configured to determine the value of a state variable of the drive train from the recorded actual accelerations of the drive and the load.

[0025] Preferably, the drive element meshes with the fixed support element and the drive also moves with the load.

[0026] The drive can be, for example, an electric rotary or linear motor or a hydraulic motor. In the case of an electric rotary motor, the first device is preferably formed by an already existing motor measuring system of the rotary motor for determining the motor speed.

[0027] In advantageous embodiments, the drive train has a gear (e.g. planetary gear) acting between the drive and the drive element, which moves with the load.

[0028] The second device is preferably formed by an acceleration sensor which is attached to the load itself or to an element which moves with the load.

[0029] Preferably, the drive train is provided by a pinion / rack drive train, in particular with a pinion as the drive element and with a rack as the support element, or by a helical gear, in particular a

[0030] Ball screw drive. Further advantages and advantageous embodiments of the subject matter of the invention will become apparent from the description, the claims, and the drawings. Likewise, the above-mentioned and further listed features can be used individually or in combination. The embodiments shown and described are not to be understood as an exhaustive list, but rather as examples for describing the invention. They show:

[0031] Fig. 1 schematically shows a device according to the invention for the automated determination of backlash in a pinion / rack drive train;

[0032] Fig. 2a shows a backlash in the pinion / rack drive train when accelerating the pinion on the rack counterclockwise;

[0033] Fig. 2b shows a backlash in the pinion / rack drive train when accelerating the pinion on the rack in a clockwise direction;

[0034] Fig. 3 shows an exemplary travel profile (target trajectory) of a guide carriage shown in Fig. 1 and moved by the drive train when carrying out the method according to the invention for the automated determination of the backlash; and

[0035] Fig. 4 shows the time-synchronized actual accelerations of the drive and the load recorded when carrying out the method according to the invention.

[0036] The device 1 shown in Fig. 1 serves for the automated determination of the value of a state variable, here a backlash S (Figures 2a, 2b), in a drive train 2 for moving a load, which is formed here by way of example by a translationally guided guide carriage 3.

[0037] The drive train 2 comprises a drive, designed here as a (rotary) motor 4, and a drive element, designed here as a pinion 6, driven by the motor 4 via an optional gear 5. The motor 4, the gear 5, and the pinion 6 are attached to the guide carriage 3 and are thus moved along with the guide carriage 3. The drive train 2 further has a fixed support element, designed here as a rack 7, with which the pinion 6 meshes in order to move the guide carriage 3 together with the motor 4, gear 5, and pinion 6 relative to the rack 7 in its longitudinal direction A. The rotary movement of the motor 4, the gear 5, and the pinion 6, here counterclockwise, is illustrated by arrows 19, 20, and 21.

[0038] As shown in Figures 2a, 2b, for functional reasons, the tooth thickness of the teeth of the pinion 6 is smaller by the (reverse) play S than the gap width between two teeth of the rack 7. If the pinion 6 is driven counterclockwise, as shown in Fig. 2a, the pinion 6 moves to the left (rotational movement 21, direction of arrow A) rolling on the rack 7, in particular shown here with acceleration b1 of the pinion 6 to the left, whereby the guide carriage 3 together with the motor 4 and gear 5 are moved to the left. The pinion 6 engages with a tooth 8 in a tooth gap 9 of the rack 7, with the right tooth flank 8a of the tooth 8 being supported on the right tooth flank 9a of the tooth gap 9. If an acceleration reversal takes place on the guide carriage 3 and thus also on the pinion 6, the two bearings are released, as shown in Fig.2b, the right tooth flanks 8a, 9a move away from each other until, after passing through the reversal play S, the left tooth flank 8b of tooth 8 is supported on the left tooth flank 9b of the tooth gap 9. The pinion 6, rolling on the rack 7, continues to move to the left (rotational movement 21, direction of arrow A), but with acceleration b2 directed to the right, whereby the guide carriage 3 together with the motor 4 and gear 5 are accelerated to the right. The speed of the motor 4 is recorded by means of a first device, here in the form of a motor measuring system 10. The actual acceleration of the motor 4 can then be determined from the recorded speed. Alternatively, the actual acceleration of the motor 4 can also be determined by means of an additional acceleration sensor, which is attached to the pinion 6, for example.

[0039] The actual acceleration of the guide carriage 3 is determined by means of an acceleration sensor 11, which is attached to the guide carriage 3 itself or to one of the elements 4-6 moving with the guide carriage 3, for example here on the housing of the gear 5.

[0040] From the recorded actual accelerations of the drive 4 and the guide carriage 3, the value of the backlash S of the drive train 2 can be determined in an evaluation device 12.

[0041] The following procedural steps are carried out to automatically determine the value of the backlash S.

[0042] The guide carriage 3 is accelerated by the motor 4 by specifying a travel profile with acceleration reversal. The travel profile is stored, for example, in a motor control system. Fig. 3 shows such a travel profile 13 in a distance (s) / time (t) diagram in the form of a jerk-limited, step-like target trajectory 14 of the guide carriage 3. In the travel profile 13 shown, the guide carriage 3 is moved forward by 3 mm in a step-like manner at time t = approximately 1 s and retracted by 3 mm in a step-like manner at time t = approximately 2.2 s.

[0043] During this movement of the guide carriage 3, both the actual acceleration of the motor 4 is recorded by the motor measuring system 10 and the actual acceleration of the guide carriage 3 is recorded by the acceleration sensor 11. More precisely, the motor acceleration can be determined from the recorded motor speed by differentiation and optional smoothing. In the evaluation device 12, the synchronously recorded or subsequently synchronized actual accelerations of the motor 4 and the guide carriage 3 are evaluated using various methods to determine the value of the backlash S of the drive train 2.

[0044] Fig. 4 shows the accelerations of motor 4 (solid line a) and guide carriage 3 (dashed line b) recorded during travel profile 13 around time t = approximately 1 s in an acceleration(a) / time(t) diagram. During the transition from acceleration to deceleration, i.e., during the acceleration reversal (zero crossing) at time t = approximately 1.1 s, a time offset Δt occurs between the two curves a and b, which results from the backlash S. From this time offset Δt, the backlash S can be determined using various methods.

[0045] In a first evaluation variant, the relationship between changes in the acceleration curves of the actual accelerations of the motor 4 and the guide carriage 3 is determined experimentally and stored for different values ​​of the backlash S. When the tooth flanks collide after the acceleration reversal, the moving guide carriage 3 is abruptly braked or the motor 4 is kicked. The greater the backlash S, the more pronounced these sudden changes in the acceleration curves are. This relationship can be determined experimentally and stored in the evaluation device 12. Based on the stored relationship, the value of the backlash S can be determined from the recorded actual accelerations of the motor 4 and the guide carriage 3.

[0046] In a second evaluation variant, the relationship between the time period within which pinion 6 and rack 7 separate from each other and then come into contact again during an acceleration reversal is experimentally determined and stored for different values ​​of the reversal backlash S. The greater the reversal backlash S, the longer the time period between the release and the renewed collision of the tooth flanks of pinion 6 and rack 7. The time of release is when an acceleration reversal occurs in motor 4, for example when changing from acceleration to braking. The time of collision is when the mass acceleration decreases abruptly or the motor acceleration increases abruptly. The relationship between this time period and the reversal backlash S can be experimentally determined and stored in the evaluation device 12.Based on the stored relationship, the value of the backlash S can be determined from the recorded actual accelerations of the motor 4 and the guide carriage 3.

[0047] In a third evaluation variant, the recorded actual accelerations of the motor 4 and the guide carriage 3 are used to analytically calculate the times at which the pinion 6 and rack 7 separate from each other and reconnect during an acceleration reversal, the distance traveled during this reversal, and the resulting value of the backlash S. If the acceleration measurement signals are available with sufficiently good quality (resolution, noise), the distance traveled and thus the backlash S can be analytically calculated from the time of the tooth flanks separating and the time of the tooth flanks colliding.

Claims

Patent claims 1. A method for the automated determination of the value of a state variable of a drive train (2) for moving a load (3), wherein the drive train (2) has a drive (4) and a drive element (6) driven by the drive (4) and moved along with the load (3), as well as a fixed support element (7) on which the drive element (6) is supported in order to move the load (3) relative to the support element (7), comprising the following method steps: a) accelerating the load (3) by means of the drive (4) by specifying a travel profile (13) with acceleration reversal; b) during the acceleration of the load (3), detecting the actual acceleration of the drive (4) and detecting the actual acceleration of the load (3); and c) determining a value of the state variable of the drive train (2) by evaluating the detected actual accelerations of the drive (4) and the load (3).

2. Method according to claim 1, characterized in that the state variable is a backlash (S) of the drive train (2).

3. Method according to claim 1 or 2, characterized in that the drive element (6) meshes with the fixed support element (7) in order to move the load (3) relative to the support element (7).

4. Method according to one of the preceding claims, characterized in that the drive (4) is also moved along with the load (3).

5. Method according to one of the preceding claims, characterized in that the speed of a drive designed as a rotary motor (4) and the actual acceleration of the drive (4) is determined from the detected speed.

6. Method according to claim 5, characterized in that the rotational speed of the rotary motor is detected by a motor measuring system (10) of the rotary motor.

7. Method according to one of the preceding claims, characterized in that the actual acceleration of the load (3) is detected by means of an acceleration sensor (11) which is attached to the load (3) itself or to an element (4-6) which moves along with the load (3).

8. Method according to one of the preceding claims, characterized in that the actual accelerations of the drive (4) and the load (3) are recorded synchronously during the acceleration of the load (3) or are subsequently synchronized with one another after the recording processes.

9. Method according to one of the preceding claims, characterized in that the predetermined travel profile (13) comprises a forward and backward movement of the load (3), exclusively a forward movement of the load (3) or exclusively a backward movement of the load (3).

10. Method according to one of the preceding claims, characterized in that the relationship between the state variable and changes in the acceleration curves of the actual accelerations of the drive (4) and the load (3) is determined experimentally and stored for different values ​​of the state variable and that the value of the state variable is determined from the recorded actual accelerations of the drive (4) and the load (3) on the basis of the stored relationship. 11 . Method according to one of claims 1 to 9, characterized in that the relationship between the state variable and the period within which the drive and Support elements (6, 7) detach from one another and then come into contact with one another again, for different values ​​of the state variable is determined experimentally and stored, and that the value of the state variable is determined from the recorded actual accelerations of the drive (4) and the load (3) on the basis of the stored relationship.

12. Method according to one of claims 1 to 9, characterized in that from the detected actual accelerations of the drive (4) and the load (3), the times at which, in the event of an acceleration reversal, the drive and support elements (6, 7) separate from one another and contact one another again, the distance traveled and, therefrom, the value of the state variable are analytically calculated.

13. Device for the automated determination of the value of a state variable of a drive train (2) for moving a load (3), comprising: a drive train (2) with a drive (4) and with a drive element (6) driven by the drive (4) and which moves with the load (3), and with a fixed support element (7) on which the drive element (6) is supported in order to move the load relative to the support element (7), a first device (10) for detecting an actual acceleration of the drive (4), a second device (11) for detecting the actual acceleration of the load (3), and an evaluation device (12) which is programmed to determine the value of a state variable of the drive train (2) from the detected actual accelerations of the drive (4) and the load (3).

14. Device according to claim 13, characterized in that the drive element (6) meshes with the fixed support element (7).

15. Device according to claim 13 or 14, characterized in that the drive (4) is also moved along with the load (3).

16. Device according to one of claims 13 to 15, characterized in that the drive (4) is an electric rotary or linear motor or a hydraulic motor.

17. Device according to one of claims 13 to 16, characterized in that the drive (4) is an electric rotary motor and the first device is formed by a motor measuring system (10) of the rotary motor for determining the motor speed.

18. Device according to one of claims 13 to 17, characterized in that the drive train (2) has a gear (5) acting between the drive (4) and the drive element (6) which is moved along with the load (3).

19. Device according to one of claims 13 to 18, characterized in that the second device is formed by an acceleration sensor (11) which is attached to the load (3) itself or to an element (4-6) moving with the load (3).

20. Device according to one of claims 13 to 19, characterized in that the drive train (2) is formed by a pinion / rack drive train or by a screw gear.

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