MACHINE MONITORING

Description

[0001] The present invention relates to a method for monitoring a machine in which a motor drives a mechanism.

[0002] In such machines, where a motor drives a mechanical component, control parameters are defined, particularly during the machine's setup, within a motor control system. These parameters specify the mechanical characteristics of the machine or the mechanical component. Typically, the underlying values ​​are estimated and / or determined based on experience.

[0003] A disadvantage is that such machine settings, or rather the adjustment of the control parameters for the drive train, are not always precise. Furthermore, the behavior of the mechanics can change during operation, for example due to wear or significantly varying loads.

[0004] The originally set values ​​of the control parameters may then no longer be valid, which can lead to malfunctions or overloads.

[0005] DE 10 2011 121 839 A1 discloses a method in which an applied torque is measured and a moment of inertia is calculated from it, which in turn is used to control a drive. DE 41 11 530 A1 discloses the calculation of parameters of a spring-mass system. WO 2013 / 158849 A1 discloses a method for determining the moment of inertia and friction of a mechanism, wherein the moment of inertia and friction are determined by means of a test run and integral calculation over the test run. EP 0 031 906 A2 describes a method for monitoring friction in an electric motor.

[0006] The object underlying the invention is to provide a method by which changes to the mechanics can be reliably detected.

[0007] This problem is solved by a method according to claim 1.

[0008] The invention is based on the understanding that, by determining the torque delivered by the motor to the mechanical components and the angular acceleration of the motor, the moment of inertia and friction of the mechanical components can be calculated. This calculation can be performed within a motor control unit. Methods for this calculation are explained below.

[0009] According to the invention, the torque delivered by the motor to the mechanics is measured directly. The angular acceleration of the motor can be measured directly or calculated from another measured quantity, according to the invention. In either case, the determined angular acceleration of the motor is preferably based on a measured quantity.

[0010] To determine the angular acceleration of the motor, for example, a linear acceleration of the mechanics can be measured, from which the angular acceleration of the motor can then be calculated.

[0011] The calculated moment of inertia of the mechanics and the friction of the mechanics are thus each based on measured values, which means that the adjustment of the motor control no longer has to be based on estimated values, but can be based on measured values ​​and thus on the actual mechanical properties of the mechanics.

[0012] Furthermore, it is advantageous that the method according to the invention can be carried out at any time during the entire life cycle of the machine. Moreover, the method is independent of the current rotational speed, angular acceleration, or power of the motor, meaning that "normal" operation of the machine does not need to be interrupted to carry out the method.

[0013] The inventive method allows the initial parameters to be determined during machine setup. This enables the motor dimensions to be adjusted, if necessary, to ensure the use of a motor better suited to the mechanics. The parameters can also be repeatedly checked (e.g., at fixed intervals) and, if necessary, changed during regular operation. Furthermore, a warning signal is issued if there is a significant change in the parameters, namely the moment of inertia of the mechanics or the friction of the machine—that is, if the change exceeds a predetermined threshold—which can then be used to initiate preventative maintenance of the machine.

[0014] The method according to the invention makes it possible to achieve a higher accuracy in the continuous determination and adjustment of the mechanical parameters of a machine in a simple manner compared to methods according to the prior art.

[0015] Advantageous embodiments of the invention can be found in the description, the drawings and the dependent claims.

[0016] According to the invention, the moment of inertia of the mechanics and / or the friction of the mechanics are calculated using the formula M = J * α + M mech calculated. As already explained, M denotes the torque delivered by the motor to the mechanics, J the moment of inertia of the mechanics, α the angular acceleration of the motor and M mech the friction of the mechanics.

[0017] The aforementioned formula (1) is a linear equation of a straight line with an y-intercept, which is usually in the form y = m * x + t The slope (m) corresponds to the moment of inertia (J) in mechanics and the y-intercept (t) to the friction (M mech) in mechanics.

[0018] To determine both the slope and the axial section, the torque delivered by the motor to the mechanics and the respective angular acceleration of the motor are determined according to the invention in at least two different operating states of the machine. The operating states can be chosen arbitrarily. By determining the torque delivered by the motor to the mechanics and the angular acceleration of the motor at least twice, a system of equations with two equations and two unknowns can be formulated and solved. The unknown quantities are the moment of inertia (J) of the mechanics and the friction (Mmech) of the mechanics.

[0019] Preferably, the torque delivered by the motor to the mechanics and the angular acceleration of the motor are determined in such a way that the determined angular acceleration and the determined torque are correlated, i.e., determined at the same time and / or originate from the same operating state. An operating state can be understood, in particular, as an operating point of the machine, i.e., a specific combination of, for example, a rotational frequency of the motor, an angular acceleration of the motor, and / or a power input of the motor.

[0020] According to the invention, the moment of inertia and / or the friction of the mechanics are determined by means of a regression analysis, wherein, in particular, the respective torque delivered by the motor to the mechanics and the respective angular acceleration of the motor are determined in a multitude of different operating states. By means of the multitude of measurements in different operating states, a "cloud" of data points can be generated in a coordinate system, in which the angular acceleration of the motor is plotted on the abscissa and the torque delivered by the motor to the mechanics on the ordinate. Using the regression analysis, a straight line is preferably drawn through the point cloud, and the equation of this line is then determined. With the equation of this line, the moment of inertia (J) and the friction (Mmech) of the mechanics are then known, as explained above.

[0021] To measure the current drawn by the motor, the current of an inverter coupled to the motor can be determined or measured.

[0022] When measuring the power consumed by the motor, the current drawn by the motor can be deduced from a known voltage across the motor. It is understood that the gear ratio is only used if the motor has a gearbox, particularly one directly connected to it.

[0023] By measuring the current consumed by the motor, the motor is not only used to drive the mechanics, but also serves as a measuring device to determine characteristics of the mechanics.

[0024] Alternatively or additionally, the torque delivered by the motor to the mechanics can also be measured directly, for example with a torque sensor, using strain gauges or optical encoders that detect the torsion of a shaft.

[0025] According to a further advantageous embodiment, the angular acceleration of the motor is calculated based on the acceleration (a) of a translational or linear motion of the mechanism, in particular by multiplying the acceleration (a) by 2π and subsequently dividing by a feed constant (KV). Thus, the angular acceleration of the motor is given by: α = 2 π ∗ a / K V

[0026] Determining the angular acceleration from a translational or linear motion can be advantageous when the mechanism includes a motor-driven component that performs such a motion. For example, the velocity or acceleration of the translational or linear motion can be determined using incremental encoders.

[0027] According to an advantageous embodiment, the friction (Mmech) of the mechanism comprises static friction (Mzusatz). The static friction is essentially independent of the instantaneous rotational frequency or angular acceleration of the motor. In particular, the friction of the mechanism comprises only static friction, or, to determine the friction of the mechanism, it is assumed that the friction of the mechanism is exclusively static friction.

[0028] According to a further advantageous embodiment, the friction of the mechanics includes viscous friction (Mvisk) which depends on the rotational speed (ω) of the motor. This means that the calculation of the friction of the mechanics can be based on either static friction (Mzusatz) or viscous friction (Mvisk). The mechanical friction can therefore be calculated according to the formula... M mech = M visk * ω + M zusatz Calculate. The rotational speed (ω) of the motor can also be referred to as the angular velocity of the motor.

[0029] Substituting this into the formula (1) above yields the formula M = J * α + M visk * ω + M zusatz

[0030] If the above formula (6) is used as a starting point, in addition to the torque (M) delivered by the motor to the mechanics and the angular acceleration (α) of the motor, the rotational speed (ω) of the motor must also be determined.

[0031] For example, three sets of torque (M), angular acceleration (α), and rotational speed (ω) can be determined for three different operating conditions. From these values, the moment of inertia (J), static friction (Madditional), and viscous friction (Mvisc) can then be calculated. This can be done, for instance, by setting up a system of three equations with three unknowns. This system of equations can then be solved using the three sets of determined values.

[0032] Alternatively or additionally, a multitude of measurements can be performed, determining the torque delivered by the motor to the mechanism, the angular acceleration of the motor, and the rotational frequency of the motor as corresponding (measured) values. These values ​​can then be plotted in a three-dimensional coordinate system (α, ω, M-coordinate system). Using regression analysis, a plane can be fitted into the resulting point cloud of values, with the moment of inertia (J) of the mechanism, the static friction (Madditional), and the viscous friction (Mvisc) being known from the equation of the plane.

[0033] According to a further advantageous embodiment, the moment of inertia of the mechanism and / or the friction of the mechanism are repeatedly re-evaluated.

[0034] Based on the determined moment of inertia and / or friction of the mechanism, the motor control is preferably adjusted. For example, the maximum permissible current of the motor can be increased or decreased to adapt to the specific characteristics of the mechanism. Parameters of a control loop for the motor can also be modified. The moment of inertia and / or friction of the mechanism can be determined cyclically.

[0035] According to an advantageous embodiment, the moment of inertia of the mechanism and / or the friction of the mechanism are recalculated at least every 10 seconds, preferably at least every second. In particular, each calculation can take only a few milliseconds. The calculation can be performed especially when an operating state of the motor is changed, for example, by driving up a ramp (or any other format).

[0036] According to an advantageous embodiment, the motor control is adapted to the calculated moment of inertia and / or friction of the mechanism, in particular (as already explained) by adjusting control parameters. The calculated values ​​can therefore be used to achieve improved or more suitable motor control.

[0037] A warning signal is generated based on the calculated moment of inertia of the mechanics and / or the calculated friction of the mechanics, which announces the imminent needing maintenance of the mechanics.

[0038] A threshold value is defined for the friction of the mechanics (including static and / or viscous friction). As soon as this threshold is exceeded, a warning signal is triggered to initiate predictive maintenance or inspection of the mechanics. The advantage here is that the warning signal allows for the early detection of machine or mechanical faults, thus preventing motor overload, for example, caused by excessive current.

[0039] The invention further relates to a machine according to claim 8. In particular, the machine comprises a control unit that controls the motor and calculates the moment of inertia and friction of the mechanics. According to an advantageous embodiment of the machine, the motor is an electric motor, and in particular a servo motor with a gearbox and a rotary encoder. The rotary encoder can be used to measure both the rotational speed (ω) and the angular acceleration (α) of the motor. Both a torque constant (KM) of the motor and a gear ratio (i) of the gearbox may be known for this purpose. In particular, the torque constant (KM) of the motor and / or the gear ratio (i) are constant.

[0040] According to a further advantageous embodiment, the machine comprises a measuring device which directly measures a torque (M) delivered by the motor to the mechanics and / or determines a current (I) absorbed by the motor and / or a power of the motor and / or a rotational speed (ω) of the motor and / or an angular acceleration (α) of the motor.

[0041] Preferably, the machine includes a measuring device that determines the acceleration of the mechanics. The acceleration of the mechanics can, in particular, be an acceleration of a translational or linear motion. This translational motion can be converted into an angular acceleration of the motor using a feed constant (KV).

[0042] The feed constant (KV) indicates in particular the magnitude of the translational or linear movement of the mechanics that occurs per revolution of the motor.

[0043] According to another advantageous embodiment, the mechanism is a conveyor belt. The conveyor belt can perform a translational movement and, for example, transport objects in a manufacturing process within an industrial plant. If, for instance, the transported objects rub against an edge of the conveyor belt, the friction of the mechanism increases, which can be detected. Knowing about the increased friction, the cause of the increased friction can then be eliminated.

[0044] The statements made regarding the method according to the invention apply accordingly to the machine according to the invention, in particular with regard to advantages and preferred embodiments.

[0045] In principle, mechanics can refer to any parts driven or moved by a motor. For example, mechanics can include a robot arm, a gripper, the aforementioned conveyor belt, and / or a vehicle's drive wheel, and the like.

[0046] The invention is described below by way of example only, with reference to the drawings. The drawings show: Fig. 1 shows the schematic structure of a machine; Fig. 2 shows a regression analysis in a two-dimensional coordinate system; and Fig. 3 shows a regression analysis in a three-dimensional coordinate system.

[0047] Fig. 1Figure 10 shows a machine comprising a motor controller 12 and a servomotor 14 electrically connected to the motor controller 12. The servomotor 14 drives a mechanism, in the form of a conveyor belt 20 (here chosen as an example), via a gearbox 16 and a rotatable shaft 18. The conveyor belt 20 can move a load 22.

[0048] A motion sensor 24 is attached to the conveyor belt 20 and is connected to the motor control unit 12. The motion sensor 24 determines the speed and acceleration of the conveyor belt 20 and transmits these values ​​to the motor control unit 12.

[0049] The motor control unit 12 calculates an angular acceleration α of the servomotor 14 from the acceleration of the conveyor belt 20 using a feed constant KV. Furthermore, the motor control unit 12 determines a torque M delivered by the servomotor 14 to the mechanism from the current drawn by the servomotor 14 and a torque constant KM of the motor. The delivered torque M is transmitted to the conveyor belt 20 via the shaft 18.

[0050] The motor control unit 12 determines the output torque M and the angular acceleration α in various operating situations (i.e., operating states) of the machine 10 and plots the torque M against the corresponding angular acceleration α as first measured values ​​26 in a two-dimensional coordinate system, as shown in Fig. 2 is shown. In the two-dimensional coordinate system of Fig. 2 The angular acceleration α is plotted on the abscissa and the torque M is plotted on the ordinate.

[0051] The first measured values ​​26 form a first point cloud 28, into which a straight line 30 is placed by the motor control 12 using a regression analysis. A first slope 31 and an intercept 32 are determined for the straight line 30. The first slope 31 is represented as a slope triangle, where the first slope 31 corresponds to the moment of inertia J of the mechanics, that is, the moment of inertia J of the conveyor belt 20. The intercept 32 corresponds to an additional static friction M of the mechanics.

[0052] Based on the determined moment of inertia J of the mechanism and the friction M mech of the mechanism, the motor control 12 can adjust the control parameters for the servomotor 14 accordingly. If the friction of the mechanism exceeds a predetermined threshold, a warning signal can be issued, which may lead to maintenance of the conveyor belt 20.

[0053] To also take into account the viscous friction of the conveyor belt 20, as in Fig. 3 As shown, the rotational speed ω of the motor must also be taken into account. The rotational speed ω of the motor can be determined from the speed v of the conveyor belt 20 using the feed constant KV. The rotational speed ω corresponds to the speed v multiplied by 2π divided by the feed constant KV.

[0054] Corresponding measured values ​​of rotational speed ω of the servomotor 14, angular acceleration α of the servomotor 14 and torque M delivered by the servomotor 14 to the conveyor belt 20 can then be plotted in a three-dimensional Cartesian coordinate system ( Fig. 3 ) are entered, in which the axes perpendicular to each other represent the angular acceleration α, the rotational speed ω and the delivered torque M.

[0055] The measured values ​​can each be entered as second measured values ​​34 in the three-dimensional coordinate system and form a second point cloud 36. The second point cloud 36 can be subjected to a regression analysis by the motor control 12 to inscribe a plane 38 into the second point cloud 36. The first slope 31 in the direction of the angular acceleration α can then be determined using the plane 38. The first slope 31 corresponds to the moment of inertia J of the conveyor belt 20. A second slope 39 in the direction of the rotational speed ω corresponds to the viscous friction Mvisk of the conveyor belt 20. The distance of the intersection point of the plane 38 with the axis representing the torque M from the origin of the three-dimensional coordinate system (which corresponds to the axis intercept 32) indicates the static friction Mzusatz of the conveyor belt 20.

[0056] During operation of machine 10, the motor control unit 12 can generate the first and / or second measured values ​​26, 34 and evaluate them in the manner described. The values ​​determined during the evaluation for the moment of inertia J of the mechanism, for the static friction Madditional, and the viscous friction Mvisc can then be used to adjust the control of the servo motor 14 and / or to indicate abnormalities or wear in the conveyor belt 20 by means of a warning signal. Reference symbol list

[0057] 10 Machine 12 Motor control 14 Servo motor 16 Gearbox 18 Shaft 20 Conveyor belt 22 Load 24 Motion sensor 26 First measured values ​​28 First point cloud 30 Straight line 31 First slope 32 Intercept 34 Second measured values ​​36 Second point cloud 38 Plane 39 Second slope α Angular acceleration ω Rotational speed M Torque

Claims

1. A method for monitoring a machine (10) in which a motor (14) drives a mechanism (20), wherein - a torque (M) delivered by the motor (14) to the mechanism (20) is measured directly, and - an angular acceleration (α) of the motor (14) is determined, wherein, in at least two different operating states, - the torque (M) which is in each case delivered by the motor (14) to the mechanism (20) is measured directly, - the respective angular acceleration (α) of the motor (14) is determined, and - a moment of inertia J of the mechanism (20) and a friction Mmech of the mechanism (20) are calculated based on the directly measured torque M and the determined angular acceleration α using the formula M = J * α + M mech , wherein, in the event of a change in the moment of inertia J of the mechanism (20) or in the friction Mmech, which exceeds a predetermined threshold value, a warning signal is output, and the moment of inertia (J) of the mechanism (20) and / or the friction (Mmech) of the mechanism (20) is / are determined using a regression analysis.

2. A method according to claim 1, characterized in that, in a plurality of arbitrary different operating states, the torque (M) which is in each case delivered by the motor (14) to the mechanism (20) is measured directly and the respective angular acceleration (α) of the motor (14) is determined.

3. A method according to at least one of the preceding claims, characterized in that the angular acceleration (α) of the motor (14) is calculated based on an acceleration (a) of a translatory movement of the mechanism (20), in particular by a multiplication of the acceleration (a) by 2*π and a subsequent division by a feed constant (KV).

4. A method according to at least one of the preceding claims, characterized in that the friction (Mmech) of the mechanism comprises a static friction (Madd).

5. A method according to at least one of the preceding claims, characterized in that the friction (Mmech) of the mechanism (20) comprises a viscous friction (Mvisc) which depends on a rotational speed (ω) of the motor (14).

6. A method according to at least one of the preceding claims, characterized in that the moment of inertia (J) of the mechanism (20) and / or the friction (Mmech) of the mechanism (20) is / are repeatedly redetermined and a control of the motor (14) is adapted based on the determined moment of inertia (J) of the mechanism (20) and / or the friction (Mmech) of the mechanism (20).

7. A method according to claim 6, characterized in that the moment of inertia (J) of the mechanism (20) and / or the friction (Mmech) of the mechanism is / are redetermined at least every 10 seconds, preferably every second.

8. A machine (10) comprising a motor (14) and a mechanism (20) driven by the motor (14), wherein the machine (10) is configured - to directly measure a torque (M) delivered by the motor (14) to the mechanism (20) and - to determine an angular acceleration (α) of the motor, wherein the machine (10) is further configured, in at least two different operating states, - to directly measure the torque (M) which is in each case delivered by the motor (14) to the mechanism (20) and - to determine the respective angular acceleration (α) of the motor (14), wherein the machine (10) is configured to calculate a moment of inertia J of the mechanism (20) and a friction Mmech of the mechanism (20) based on the directly measured torque M and the determined angular acceleration α using the formula M = J*α + Mmech, wherein the machine (10) is configured, in the event of a change in the moment of inertia J of the mechanism (20) or in the friction Mmech, which exceeds a predetermined threshold value, to output a warning signal, wherein the machine (10) is configured to determine the moment of inertia (J) of the mechanism (20) and / or the friction (Mmech) of the mechanism (20) using a regression analysis.

9. A machine (10) according to claim 8, characterized in that the motor is an electric motor and in particular a servomotor (14) comprising a gear (16) and a rotary encoder.

10. A machine (10) according to claim 8 or 9, characterized by measurement devices (12, 24) which directly measure a torque (M) delivered by the motor (14) to the mechanism (20) and / or determine a current (I) consumed by the motor (14) and / or a power of the motor (14) and / or a rotational speed (ω) of the motor (14) and / or an angular acceleration (α) of the motor (14).

11. A machine (10) according to any one of the claims 8 to 10, characterized by a measurement device (24) which determines an acceleration (a) of the mechanism (20).

12. A machine (10) according to any one of the claims 8 to 11, characterized in that the mechanism is a conveyor belt (20).