Methods for damping disturbance vibrations and balancing machine

Abstract

Method for damping disturbance vibrations with a balancing machine (1) comprising a rotary drive (7) and a bearing component (4) mounted on a fixed machine part (6) to allow vibration for supporting a rotor (2) to be balanced, wherein at least one vibration sensor (8) is provided in the method, the vibration measuring element of which comprises a first end (10) supported on the bearing component (4) and a second end electrically connected to an evaluation unit (13) and designed as a coil (11) to be movable in a magnetic stator (9), wherein the vibration sensor (8) is electrically short-circuited by an electrical switching element (14) by bridging the electrical connection (12) between the evaluation unit (13) and the vibration sensor (8) and thereby damping disturbance vibrations emanating from the bearing component (4).

Description

[0001] The invention relates to a method for damping parasitic vibrations that arise in a balancing machine and interfere with the measurement of the imbalance of a rotor. The method comprises at least one vibration sensor whose vibration measuring element comprises a first end supported on the bearing component and a second end electrically connected to an evaluation unit and configured as a coil movable in a magnetic stator. Furthermore, the invention relates to a balancing machine with a rotary drive connectable to the rotor for driving the rotor, a bearing component supported on a fixed machine part in a manner capable of oscillating, for rotatably supporting the rotor, and at least one vibration sensor electrically connected to an evaluation unit.

[0002] To determine an imbalance, an unbalanced rotor is mounted in a bearing component of a balancing machine, which is supported in a way that allows it to vibrate against a stationary machine part, e.g., the foundation of the balancing machine or the machine bed. The rotor is set in rotation, and the vibrations of the bearing component relative to the machine part can be recorded using a sensor and used to determine the imbalance. The bearing component can be designed as a balancing frame.

[0003] To detect the vibrations of the bearing bridge generated by the driven rotor, moving coils can be used as vibration sensors, whose output signals are then further processed. During an unbalance measurement, the bearing bridge of the balancing machine is set into vibration in accordance with the rotor unbalance, causing the moving coil to move in the magnetic field, thus inducing a voltage in the coil, which is then amplified accordingly in a downstream voltage amplifier.

[0004] From DE 11 27 599 A, a balancing machine with two plunger coils acting as vibration sensors is known, whereby disturbing vibrations can be eliminated by the disclosed structure.

[0005] US 2015 / 0 035 544 A1 deals with the adaptation of sensors, such as acceleration sensors, speed sensors, and displacement sensors, and particularly relates to devices for such sensors with configurable damping and associated methods. Damping is used to protect the sensors during transport, for example.

[0006] DE 12 37 807 B describes a balancing machine with a bearing base fixed to the foundation and a bearing component supported against it in a way that can vibrate, e.g., a bearing bridge that carries the rotor to be balanced. The sensor can be attached to the rigid bearing base in such a way that the sensor does not move in the direction of vibration, while the actuating rod is supported by the vibrating bearing bridge. For this purpose, the actuating rod is guided outward through the permanent magnet and, in the installed position, is supported on the rigid bearing base via a lever transmission.

[0007] However, it is problematic that the natural vibrations of the bearing component cause disturbing vibrations to be included in the measurement of the rotor unbalance.

[0008] DE 10 2012 107 590 B4 describes a method for determining the influences of the machine's environment on the measurement accuracy of a balancing machine that measures vibrations. A measurement signal from at least one vibration sensor of the balancing machine, recorded when the drive of the balancing machine is at a standstill, is combined with a predetermined speed signal. An unbalance comparison value describing the environmental influence is calculated from the combined signals using the balancing machine's signal evaluation method.

[0009] US 3,164,995 A discloses a method for reducing interference, in which an additional sensor is provided on the device for determining unbalance, with which the absolute vibrations of the frame are recorded. The two sensors, designed as moving-coil sensors, are arranged coaxially one behind the other and fastened to one another. The first sensor has a sensor element in the form of a moving-coil rod, which is connected to the vibrating bearing component for the rotor, the balancing bridge. The second sensor has a sensor mass that is matched to the structure of the device and the rotor to be tested. The measurement signal emitted by the second sensor is proportional to the vibrations of the frame and thus to the interference vibrations of the sensor housing, and is superimposed on the signal emitted by the first sensor.

[0010] US Pat. No. 5,209,116 A discloses a method for reducing interference during unbalance measurement. This method involves placing a simulation mass, which has the same weight as the rotor under test, adjacent to the oscillating bearing component for the rotor. The vibrations of the bearing component are recorded by a first pair of sensors arranged between the bearing component and the frame, while the vibrations of the simulation mass are recorded by a second pair of sensors arranged between the bearing component and the frame. The first pair of sensors records unbalance-induced and spurious vibration-induced vibrations, while the second pair of sensors records spurious vibrations between the simulation mass, which is stationary due to its inertial mass, and the frame. The signals from both pairs of sensors are superimposed and evaluated.

[0011] A problem with existing balancing machines, especially soft balancing machines and processes, is that the bearing component typically reaches its critical speed during startup, causing strong spurious vibrations. Either you have to wait until these vibrations have subsided, or the bearing component is locked during startup. The disadvantage of this, however, is that spurious vibrations arise again when the locking mechanism is released.

[0012] The invention is based on the object of providing a method and a device by which the influence of the disturbing vibrations on the calculation of the unbalance is minimized.

[0013] The object is achieved by the features of claim 1 and those of claim 5. Preferred embodiments are described in the dependent claims.

[0014] The object is achieved according to the invention in that a method for damping disturbing vibrations is provided, with a balancing machine comprising a rotary drive and a bearing component supported on a fixed machine part in a vibration-capable manner for supporting a rotor to be balanced, wherein the method comprises at least one vibration sensor, the vibration measuring element of which comprises a first end supported on the bearing component and a second end electrically connected to an evaluation unit and designed as a coil movable in a magnetic stator, in which the vibration sensor is electrically short-circuited by an electrical switching element, in that the switching element bridges the electrical connection between the evaluation unit and the vibration sensor and thereby dampens parasitic vibrations emanating from the bearing component. It has been shown that the method according to the invention effectively dampens parasitic vibrations emanating from the bearing component and thus are not included, or at least in a weakened form, in the calculation of the imbalance of the rotor to be balanced. The method according to the invention achieves mechanical damping so that essentially no vibration measurement is possible during the short circuit and thus parasitic vibrations are not taken into account. By actuating the switching element again, the electrical short circuit is canceled so that vibrations of the bearing component are recorded virtually undamped by the vibration sensor and measured by the evaluation unit.The magnetic stator of the vibration sensor can be part of a housing attached to the machine part.

[0015] It can be provided that the coil comprises two poles that can be electrically connected to the evaluation unit, and the switching element electrically short-circuits the electrical connections between the poles and the evaluation unit, so that the voltage between the poles drops to a value close to zero. The coil, i.e. the vibration sensor, advantageously remains in contact with the evaluation unit even when the switching element is actuated. However, actuating the switching element short-circuits, in particular, the electrical connections between the coil and the evaluation unit, so that essentially no voltage can be measured by the evaluation unit. This dampens any parasitic vibrations of the bearing component.

[0016] The switching element can be actuated at various times during the unbalance measurement. It can preferably be that the vibration sensor is electrically short-circuited before the bearing component is loaded with the rotor and connected to the rotary drive. Experience has shown that disruptive vibrations can already occur due to the loading of the bearing component, so it can be advantageous to actuate the electrical switching element before loading and to trigger an electrical short circuit in the vibration sensor. Furthermore, it can be advantageous if the vibration sensor is electrically short-circuited before the rotary drive is started up and / or during start-up. Depending on requirements, it can also be provided that the vibration sensor is short-circuited before loading and remains short-circuited during start-up until the desired measuring speed or measuring speed range is reached.

[0017] Furthermore, the invention relates to a balancing machine for determining the imbalance of a rotor, comprising a rotary drive connectable to the rotor for driving the rotor, a bearing component supported in an oscillating manner on a fixed machine part for rotatably supporting the rotor, and at least one vibration sensor electrically connected to an evaluation unit, the vibration measuring element of which comprises a first end supported on the bearing component and a second end electrically connected to the evaluation unit and designed as a coil movable in a magnetic stator, wherein an electrical switching element is present at the electrical connection between the evaluation unit and the vibration measuring element and can be brought into operative engagement with the connection in such a way that the vibration sensor can be electrically short-circuited and spurious vibrations emanating from the bearing component can be damped.The previously described advantages and preferred embodiments of the method apply analogously to the device. The balancing machine is used in particular to carry out the method.

[0018] In one embodiment, the vibration sensor can be designed as a moving coil. The first end of the vibration measuring element of the vibration sensor, in particular the moving coil, can be designed as an actuating rod made of aluminum.

[0019] The magnetic stator of the vibration sensor can comprise a ring-shaped permanent magnet or a permanent magnet array. Depending on the application, the stator can also be a non-closed ring arrangement or form an array of multiple permanent magnets. As an alternative to a permanent magnet or a permanent magnet array, the magnetic stator can also be designed as an electromagnet.

[0020] The invention is explained in more detail below using an embodiment of the invention which is shown in the drawing.

[0021] Fig. 1 shows an embodiment of a preferred balancing machine 1, with which the imbalance of a rotor 2 can be determined. The rotor 2 is rotatably mounted in bearings 3 in a bearing component 4. The bearings 3 can be conventional plain, roller, air or fluid bearings. The bearing component 4 can, for example, be designed as a balancing frame and supported in an oscillating manner against a stationary machine part. In the exemplary embodiment, the bearing component 4 is supported via a spring system 5 on a stationary machine part, such as the foundation 6 of the balancing machine 1. The spring system 5 can, for example, comprise flat springs or several round bar springs. The rotor 2 is driven by a Fig. 1 schematically indicated rotary drive 7.

[0022] A schematically illustrated vibration sensor 8 is arranged at a distance from the bearing component 4 and is at least partially connected to a fixed machine part, for example, the foundation 6. Further sensors can be provided in the respective bearing plane; the sensors can be designed, for example, as displacement, speed, or acceleration sensors. Furthermore, a sensor can be provided that senses the rotational behavior of the rotor 2 via a rotor marking.

[0023] The vibration sensor 8 has a magnetic stator 9, which can be designed, for example, as a permanent magnet arrangement enclosed by a housing and, in particular, as a cylindrical one. The housing and the stator 9 can be attached to a stationary machine part, such as, for example, the foundation. Furthermore, the vibration sensor 8 comprises a vibration measuring element, which has a first end supported on the bearing component 4 and designed as an actuating rod 10 and a second end designed as a coil 11. The vibration measuring element can be reversibly or irreversibly attached to the movable bearing component 4 via the actuating rod 10. The coil 11 can, for example,The coil 11 can be designed with or without a coil core and a copper wire winding. Various designs and possibilities for optimizing the coil, the magnetic stator, or the actuating rod 10 are known to those skilled in the art, so that the invention is not limited to one design. The stator 9 forms a channel or air gap in which the coil 11 is movably guided. This can vary depending on the application and can be configured, for example, vertically, obliquely, or horizontally.

[0024] The actuating rod 10, which can consist, for example, of an aluminum sleeve with a cast-in metal rod, is supported on the bearing element 4.

[0025] The coil 11 comprises two electrical connecting lines 12 extending from its poles, which are electrically connected to an evaluation unit 13. The evaluation unit 13 can typically comprise an analog-to-digital converter and an amplifier for amplifying the measurement signal and can be designed as a measuring device.

[0026] An electrical switching element 14 is present on the connecting lines 12, which, as an electrical assembly, can establish or break an electrically conductive connection by means of two electrically conductive materials or a semiconductor component. Fig. In the preferred embodiment shown in Figure 1, the switching element 14 can be brought into operative engagement with the two connecting lines 12 leading from the poles of the coil 11. The electrical switching element 14 can also be referred to as a short-circuit switch within the meaning of the invention.

[0027] The control of the balancing machine 1, and in particular the control of the electrical switching element 14, the rotary drive 7, and the vibration measurement, is handled by a control and monitoring device 15, which is in contact with the components of the balancing machine 1 to be controlled and can, for example, be in the form of a computer. The control and monitoring device 15 can comprise an electronic computer programmed for signal evaluation and a data storage device, and can be connected to an input device. Via the input device, rotor-specific data, such as dimension and shape data, machine-specific data, such as resonant mass and stiffness of the bearing pedestals, and position-specific data, such as the distances and position of the bearing and balancing planes, can be specified to the control and monitoring device 15 and stored for calculations.The control and monitoring device 15 calculates the magnitude and direction of one or more unbalance values ​​to be corrected from the measurement signals received from the vibration sensor 4 and specified data. The results of the control and monitoring device 15 can be displayed on a screen connected to the computer.

[0028] During operation, the bearing component 4 is loaded with the rotor 2, and the rotor 2 is accelerated by the rotary drive 7 to the measuring speed or measuring speed range. The vibration sensor 8 then detects any vibrations of the bearing component 4 resulting from an imbalance in the rotor 2 at the desired speed or within the speed range. The vibrations cause a movement, for example a horizontal movement of the actuating rod 10 and consequently of the coil 11 in the magnetic stator 9. This creates an electrical voltage between the poles of the coil 11, which is transmitted via the connecting lines 12 to the evaluation unit 13 and can be measured by the latter and converted into an imbalance. However, since the vibrations also include parasitic vibrations, which can result, for example, from the loading of the bearing component or from the bearing component 4 passing through the critical speed, the vibration sensor 8 can be short-circuited by the electrical switching element 14 if necessary.The electrical short circuit, i.e., the creation of an electrical connection between the connecting lines 12 by the electrical switching element 14, creates a virtually resistance-free connection between the two poles of the electrical voltage source, namely the coil 11, so that the voltage between the poles of the coil 11 drops to a value close to zero. This essentially creates mechanical damping, so that parasitic vibrations do not occur at all or are mechanically dampened, particularly as long as the short circuit exists. The parasitic vibrations are therefore not taken into account in the calculation of the imbalance, or have a significantly weaker influence, since they are dampened during the short circuit before the measurement. Nevertheless, the vibration sensor 8 remains connected to the evaluation unit 13.

[0029] By reactivating the electrical switching element 14, the electrical short circuit is eliminated, and vibrations can essentially be detected again by measuring a voltage. The electrical switching element 14 can be activated, for example, before loading the rotor 2 and / or after loading but before starting up the rotary drive 7. These are only examples, as the time of activation of the switching element 14 or its deactivation can depend on the type of unbalance measurement or the application and is therefore flexible in its use. The switching element 14 can be controlled by the control and monitoring device 15.

[0030] A significant advantage of the invention is that a controlled short circuit of the vibration sensor 8 can be achieved in a simple manner by means of the electrical switching element 14, so that disturbing vibrations emanating from the bearing component 4 are damped, which in turn considerably improves the quality of the unbalance measurement.

[0031] An exemplary embodiment is mathematically modeled below. The moving-coil sensor is modeled with discrete linear elements, which can be justified for small vibrations and constant ambient conditions. An equation for the electrical potential of the vibration sensor 8, for example, a moving coil, is (Equation (2)): Ri+Ldidt+Kdxdt={u(measurement)0(short circuit)

[0032] R is the resistance of the coil (Ω) and i is the electric current (A). The physical movement is measured by the displacement x(m), and its time derivative is the velocity that induces electrical voltage in the coil.

[0033] K can be interpreted as the sensor constant when the sensor is used as a device for indirect velocity measurement by voltage measurement. Its unit can then be V / (ms) It can also be interpreted as the electromotive constant that connects force and current, expressed in units of N / A.

[0034] L is the inductance (H), which induces a voltage proportional to the change in electric current. In normal operation, the meter is "inline" and measures the voltage u on the right side. The meter itself has a high internal resistance, and the circuit is essentially open. When the short-circuit switch is applied, the potential at both ends of the coil is at the same level, and the three terms on the left side are in balance.

[0035] R, L, and K are physical parameters of the vibration sensor design itself and are independent of the surrounding system to which the sensor is attached. The electrical potential equation is coupled to the motion of the balancing machine by the following equation (3): Md2xdt2+Cx=Ki

[0036] M is the total mass (kg) of the oscillating parts above the spring system, which includes the rotor, the support frame, and sometimes the drive itself. C is the total stiffness (N / m), which is usually a combination of springs.

[0037] The equations imply the free motion of the oscillating system without external excitation, such as drive or unbalance forces, which would be required to describe the unbalance measurement system. Of interest are the free oscillations that are excited when the rotor passes the critical speed of the spring-mass system or when a locking device is suddenly released. However, the forced oscillations are not included in this formulation.

[0038] The combination of both equations leads to a linear differential equation with constant third-order coefficients. The temporal evolution can be investigated by applying initial conditions, e.g., a displacement x = x0, at a time t = 0, by integration.

[0039] The comparison of the first two terms in the voltage equation shows that for a practical system the ratio between the self-induced voltage compared to the voltage drop in the resistor is negligible, equation (4) ωL / R<<(≈1 / 100) and the short circuit system can be simplified to equation (5) Ri+Kdxdt=0

[0040] This can be applied directly to the equation of motion (3), which leads to an equation of the damped free oscillations for the displacement x (equation (6): Md2xdt2+K2Rdxdt+Cx=0

[0041] K 2 / R denotes the part of the damping parameter that is often explained by the viscous damping constant of a vibration damper.

[0042] As already mentioned, the equation depends on physical dimensions, e.g., the parameters M, C, K, R, time t, and displacement x. To investigate the effect of damping, a free form is more suitable. This can be achieved, for example, by defining the damping factor D (equation (7)): D=K2 / R2Mω

[0043] Using this parameter, a weakly damped system has small values ​​of D << 1, while the non-oscillatory case of high damping has D > 1. D = 1 is the aperiodic case, which is preferred for the given application. Damping levels much smaller than D = 1 / 10 may be insufficient.

Claims

[1] Method for damping disturbing vibrations with a balancing machine (1) comprising a rotary drive (7) and a bearing component (4) supported on a fixed machine part (6) in an oscillating manner for supporting a rotor (2) to be balanced, wherein in the method at least one vibration sensor (8) is provided, the vibration measuring element of which comprises a first end (10) supported on the bearing component (4) and a second end which is electrically connected to an evaluation unit (13) and designed as a coil (11) to be movable in a magnetic stator (9), in which the vibration sensor (8) is electrically short-circuited by an electrical switching element (14) in that the switching element (14) bridges the electrical connection (12) between the evaluation unit (13) and the vibration sensor (8) and thereby dampens disturbing vibrations emanating from the bearing component (4). [2] Method according to claim 1, characterized bythat the vibration sensor (8) is electrically short-circuited before the bearing component (4) is loaded with the rotor (2) and the rotor (2) is connected to the rotary drive (7). [3] Method according to claim 1, characterized by that the vibration sensor (8) is electrically short-circuited before starting up the rotary drive (7) and / or during start-up. [4] Method according to one of the preceding claims, characterized by that the coil (11) comprises two poles electrically connectable to the evaluation unit (13) and the switching element (14) electrically short-circuits the electrical connections (12) between the poles and the evaluation unit (13) so that the voltage between the poles drops to a value close to zero. [5] Balancing machine (1) for determining the imbalance of a rotor (2), comprising a rotary drive (7) connectable to the rotor (2) for driving the rotor (2), a bearing component (4) supported on a fixed machine part (6) in an oscillating manner for rotatably supporting the rotor (2), and at least one vibration sensor (8) electrically connected to an evaluation unit (13), the vibration measuring element of which comprises a first end (10) supported on the bearing component (4) and a second end electrically connected to the evaluation unit (13) and designed as a coil (11) movable in a magnetic stator (9), wherein an electrical switching element (14) is provided at the electrical connection (12) between the evaluation unit (13) and the vibration measuring element and can be brought into operative engagement with the connection (12) in such a way that the vibration sensor (8) can be electrically short-circuited and Disturbing vibrations can be damped. [6] Balancing machine (1) according to claim 5, characterized by that the vibration sensor (8) is designed as a moving coil. [7] Balancing machine (1) according to claim 5 or 6, characterized by that the first end (10) of the vibration measuring element is designed as an actuating rod made of aluminum. [8] Balancing machine (1) according to one of claims 5 to 7, characterized by that the magnetic stator (9) comprises an annular permanent magnet or a permanent magnet arrangement. [9] Balancing machine (1) according to one of claims 5 to 7, characterized by that the magnetic stator (9) is an electromagnet.

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