Balancing with VibroMatrix

Transcription

1 Balancing with VibroMatrix IDS Innomic Gesellschaft für Computer- und Messtechnik mbh

2 Balancing with VibroMatrix Version , 03/30/2007 Author Dipl.-Ing. Thomas Olschewski IDS Innomic Gesellschaft für Computer- und Messtechnik mbh Zum Buchhorst 25 D Salzwedel Germany All rights reserved. Reproduction (also in extracts) only with permission of IDS Innomic GmbH. VibroMatrix InnoBeamer InnoMaster InnoStreamMachine InnoMeter InnoLogger InnoPlotter InnoAnalyzer InnoScope InnoBalancer are registered trademarks of IDS Innomic GmbH Windows is registered trademark of Microsoft Corporation Despite accurate work we cannot exclude errors in this manual. We hereby disclaim all warranties and conditions related to this information regarding fitness for a particular purpose and non-infringement. In no event shall IDS Innomic GmbH and/or its respective suppliers be liable for any special, indirect or consequential damages or any damages whatsoever resulting from loss of use, data or profits, whether in an action of contract, negligence or other tortuous action arising out of or in connection with the use of information available in this manual.

3 Contents 1.Introduction Some basics...5 Unbalance so what?... 5 Unbalance and vibrations how are they related?...5 Now, what is unbalance?... 5 Types of unbalance Balancing with VibroMatrix Measurement hardware The balancing software Measuring arrangement for balancing Measurement process Compensating an unbalance Useful hints for balancing Balancing propellers Preparations Mounting the sensors Laying sensor cables In the cockpit Initial unbalance run Calibration run Correction Control run... 19

4 1.Introduction 1. Introduction We are pleased to welcome you as a new VibroMatrix user. You have purchased a powerful, expandable and economical solution for balancing. The precision hardware allows balancing different rotors from cent-sized engines to generators weighing several tons. The balancing software InnoBalancer runs on your notebook, guides you through the measurement process and clearly presents the measurement results numerically and graphically. This manual shows you how to efficiently apply VibroMatrix for balancing your rotors. First, some basics explain unbalance characteristics and measurement methods. Afterwards you learn how VibroMatrix with its InnoBalancer software supports you when measuring and correcting unbalances. Practical examples for balancing of different rotors provide you with useful hints for the everyday use. As a start, balancing propellers is described. The newest version of this manual can be found on We are at your disposal for increments, complaints and wishes. We are sure you will use VibroMatrix successfully. Salzwedel, 03/30/ VibroMatrix Development Team Introduction

5 2.Some basics 2. Some basics Unbalance so what? Why is unbalance a topic of interest? Because an unbalance leads to vibrations on a rotating body. These vibrations are mostly disturbing and they are to be remedied. Seldom are they wanted, for instance with vibratory plates. With unbalance determination, both goals can be achieved its reduction or adjustment to a certain level. Unbalance and vibrations how are they related? Let us have a look on a discoidal rotor. It is to be a thin, rigid, homogeneously built up, ideally round and centrically mounted disc. It it is put into rotation, centrifugal forces occur everyone knows that from a carousel. Still, there are no forces in radial direction to the spindle. The reason: With our rotor, the centrifugal forces of all mass particles cancel out each other. Now we add mass on the outer of the disc. If the rotor is put into rotation, an additional centrifugal force in radial direction (i.e. on the spindle) occurs now. It is situated in a bearing and the rotating centrifugal force stresses the bearing periodically. Vibrations occur. One characteristic of vibrations caused by unbalances is a vibration frequency which corresponds to the rotation speed of the rotating object. F Now, what is unbalance? So unbalance and mass are closely related to each other. However, not only the amount of the mass influences the centrifugal force, but also it distance from the rotating axis (radius). The same mass mounted more closely to the rotating axis causes less centrifugal forces. The amount of an unbalance is consequently calculated as follow: mass radius. The unit often is gmm (gram millimeter). So simply comparing the masses in order to compare unbalances is only possible if the same radius is used. r m U = r m Example r/2 r m Some basics The exemplary unbalances have the same amount, although the mass in right picture has the double amount of the left mass. The reason: The mass is on a radius which is only half as long as the radius in the left picture. 2 m 5

6 2.Some basics For balancing, not only the amount of the unbalance must be known, but also its position. 180 Since rotation is a circular movement, the balancing plane is presented as a circular area as well. The unbalance position is speci0 fied with an angle from The distance from the rotating axis (radius) indicates the amount of the unbalance. This form of representation can be found in the InnoBalancer as well and is called polar chart. Purpose of balancing During balancing, the mass allocation of a rotor is checked and afterwards improved so that the forces and vibrations caused by unbalance are within acceptable limits. By balancing, a low-vibration running is achieved which has several positive effects within the machine, for instance: Improvement of product quality Extension of machine life Reduction of noise emission When is a rotor balanced? Theoretically, it is balanced when the unbalance is zero, i.e. when the center of gravity is within the rotation axis again and all centrifugal forces cancel out each other. Practically, this cannot be achieved. That is why tolerances have to be defined. If the unbalance value is below these limits, the rotor is considered as balanced. There are different ways of defining a tolerance. If you are not responsible for defining the tolerance, you will have to act in accordance with the specifications. 1. As tolerance, a maximum unbalance can be defined. You can check it directly with the InnoBalancer then. In its polar chart, it fades in a green tolerance circle. An unbalance outside this circle exceeds the tolerance. Within the circle, the tolerance is adhered. 2. As tolerance, a maximum mass can be defined which is related to a given radius. This tolerance can be checked with the InnoBalancer as well, because it can display unbalance or mass. 3. With rotating machines, the effects of unbalance, i.e. the caused vibration, is often regarded as success criterion. For instance, many manufacturers define maximum vibration severities for their machines acc. to DIN ISO In this standard, vibration velocity as r.m.s. value in a frequency range from Hz is defined. This value can be measured easily with the VibroMatrix instrument InnoMeter. 6 Some basics

7 2.Some basics When using the last method, you should keep in mind that an unbalance at the rotor can be one reason for vibrations, but not the only one. For instance, bearing damages can cause vibrations as well. Now, how do now whether the vibrations of the examined rotor are caused by unbalance or not? Every vibration signal can be decomposed into different frequency parts. Such a decomposition is displayed by the InnoAnalyzer. The following pictures show an example: An engine runs with /min. By means of a gear, a propeller with 1:3.3 is stepped down, which means it runs with /min. The graphics show the situation before and after balancing. The time signal is displayed by the InnoScope, the frequency analysis is carried out by the InnoAnalyzer. The InnoMeter measures vibration velocity in the frequency range of Hz ( /min). In the upper picture, the unbalance of the propeller is dominant and the biggest part of the mm/s vibration severity. The lower picture shows the vibrations after balancing. The vibration caused by the propeller could be reduced to under 1 mm/s. But since the vibrations before the gear are not changed by balancing the propeller, they cause the remaining vibration severity now. So balancing the propeller cannot make a contribution to a further improvement of the total vibration situation any longer now. Some basics 7

8 2.Some basics Types of unbalance Two basic types of unbalance are distinguished. The first one has already been explained with the disc rotor example. 1. If an unbalance is added at the radial plane located US in the center of gravity of an absolutely balanced rotor then the unbalance is named static unbalance. Such unbalances have been known for millennia, e.g. at water wheels on mills. They could be corrected by oscillation on cutting edges or rollers or by empiric attachment of masses. A static unbalance can be measured in one plane by one vibration sensor. 2. In these days, couple unbalance was unknown. It UM was discovered when the first fast-running machines appeared. Two unbalances equal in magnitude at both bearings, but 180 opposite in direction are not obvious in neutral state or at slow rotation UM speeds. But they create an overturning moment at higher rotation speeds. The measurement in two balancing planes (with two vibration sensors) is necessary to correct a couple unbalance. Most common are combinations of both types, which are called dynamic unbalances. The part of couple unbalance can be neglected in most cases of discoidal rotors. SinglePlane-Balancing is sufficient here. For all other rotors, Two-Plane-Balancing is recommended. InnoBalancer can correct static unbalances as well as combinations of static and couple unbalances dynamic unbalances.1 1 In the aircraft industry the term Dynamic Balancing has become wide spread to name balancing of driven rotating parts. This term is used to distinguish from passive oscillation of rotors which is a historic method for balancing. The measurement of a static unbalance is called dynamic balancing as well in this sector, if measurement is performed on active rotating objects. 8 Some basics

9 3.Balancing with VibroMatrix 3. Balancing with VibroMatrix The measurement system VibroMatrix consists of matched electronic and software components for measuring, analyzing and reducing vibrations. The latter is carried out by balancing Measurement hardware The kit for balancing includes all required components. For different industrial branches it is available in different variants. The following exemplary picture shows the equipment for balancing propellers. USB cable for connection with the PC InnoBeamer Digital DAQ device Pocket scale with 0.1 gramme resolution Calibration weights for pocket scale Photoelectric reflex switch with 2 m cable Relection foil, selfadhesive Piezoelectric precision vibration transducer with 5m cable 3.2. The balancing software VibroMatrix is a modular system for vibration measurement. Like a building set it includes components which work stand-alone but which can also be combined for more complex measuring tasks. For balancing, the InnoBalancer was designed. Additional measurements, for instance frequency analysis, are carried out by other instruments from the VibroMatrix system. All instruments can work simultaneously and display the measured data immediately (called on-line or real-time measurement). The balancing software 9

10 3.Balancing with VibroMatrix Some instruments from the VibroMatrix system InnoAnalyzer for frequency analysis InnoMeter InnoBalancer for balancing InnoPlotter for long-term measurements The operation of all instruments is explained detailed in the VibroMatrix manual. You can find the InnoBalancer there as well Measuring arrangement for balancing Unbalance cannot be measured directly. The measured parameters are the effects of unbalance. Either the centrifugal forces or the vibrations caused by rotating centrifugal forces are measured. In order to determine the amount of the unbalance, accelerometers are applied with VibroMatrix. Position information is acquired contactlessly by means of a photoelectric reflex switch Vibration sensor balancing plane A 2 Vibration sensor balancing plane B (for Two-Plane-Balancing) 3 Photoelectric reflex switch 4 Reflection foil 5 InnoBeamer connects sensors and PC 6 To the PC via InnoBeamer Preferably bearing cases or other locations close to the bearings are used for sensor mounting the vibration sensors because vibrations can be measured best here. One accelerometer is sufficient for Single-Plane-Balancing, two for Two-Plane-Balancing. The photoelectric reflex switch can be positioned advantageously for example by means of a suitable stand. A reflecting label is stuck on the rotor. Before the measuring run is carried out, the correct registration of the label can be checked by means of a flashing LED on the reflex switch. All sensors are directly connected to the InnoBeamer and supplied by this device. 10 Measuring arrangement for balancing

11 3.Balancing with VibroMatrix 3.4. Measurement process Effects of the unbalance are measured with two measuring runs: 1. Initial unbalance run: First, the vibration signals of the rotor in the present state are recorded. 2. Calibration run: Then, a known unbalance is generated at the rotor by adding a mass with known amount and mounting angle. The altered vibration signals are recorded now.2 By comparing the signals from the initial unbalance and calibration run, the InnoBalancer calculates the originally existing unbalance. After compensation, a test run is recommended. With clear instructions, the InnoBalancer guides the user through the measurement process Compensating an unbalance After having measured an unbalance, it is compensated. This procedure is called correction. The objective is to achieve a mass allocation in a way that no centrifugal forces occur any longer. There are two general ways for mass allocation: Removing mass at the unbalance position. Adding mass on the opposite of the unbalance position. For both ways, several technical methods exists. They are all supported by the InnoBalancer. The software calculates the respective parameters for each method and indicates the compensation information directly in the polar chart. In the InnoBalancer, methods for removing mass are labeled with and methods for adding mass with ++. Methods for removing mass at the unbalance position Removing mass in general This correction method indicates how much mass is to be removed at the unbalance position in general. As a parameter, the maximum mass can be specified in case of having a technological limit. 2 During Two-Plane-Balancing, two calibration runs are carried out, one for each plane. Compensating an unbalance 11

12 3.Balancing with VibroMatrix Drilling in radial direction From the given maximum number of drill holes, maximum drill hole depth, drill diameter and drill bit angle, the actual drilling depth required for the unbalance correction is calculated. The rotor density is important as well. It is specified in the rotor characteristics and it also influences the unbalance correction by milling. Milling From the given maximum milling depth and the milling cutter diameter, the actual milling depth required for the unbalance correction is calculated. Set screws Set screws are moved in radial direction. Before balancing, they are put into a neutral position, i.e. they are put on the outer edge of the rotor. Parameters to be entered into the software are screw mass and maximum screw depth. The InnoBalancer calculates the actual screw depth for each screw. Since this screws can be found at fixed angle positions only, fixed positions are to be defined in the rotor characteristics. Methods for adding mass on the opposite of the unbalance position Adding mass in general This correction method indicates how much mass is to be added on the opposite of the unbalance position in general. As a parameter, the maximum mass can be specified in case of having a technological limit. Mounting the mass, for instance by screws, adherence or welding, must ensure a secure hold at all rotation speeds occurring during operation. Counterweight list It is often more efficient to combine prefabricated counterweights in a way that altogether, they achieve the the mass to be added. The InnoBalancer is able to determine the optimum combination very fast, so that there is no extensive trying. Entering a counterweight list has to be done only once. More information can be found in the VibroMatrix manual. 12 Compensating an unbalance

13 3.Balancing with VibroMatrix Balancing rings When using this correction method, two similar weights on fixed radius can change their angle position and be arrested in this position. In machine construction, a version as swivels has developed, slide blocks are applied with many generators. Before balancing, the balancing rings are brought into a neutral position by placing them with their unbalance 180 opposite to each other. The ring unbalance is entered in the InnoBalancer, which calculates the angles which lead to an unbalance correction Useful hints for balancing Accelerometers should be mounted as close as possible to the bearings. All balancing runs must be performed at the same rotary speed. Do not change the measuring setup (sensors, reflecting label) during the balancing process. With VibroMatrix, all angles refer to the position of the calibration mass. If the position of the calibration mass is defined as 0, all other measurements and correction measures can be referred to this point. The angle positions of InnoBalancer are always measured against the rotary direction of the rotor. The calibration mass is to be removed after the calibration run. After compensation, a test run is recommended. A step-by-step procedure with repeated calibration can be necessary. InnoAnalyzer and InnoMeter can be used to check whether the total vibration behavior is influenced by an unbalance or other sources. Useful hints for balancing 13

14 4.Balancing propellers 4. Balancing propellers The balancing of aircraft propellers ensures an operation without too heavy vibrations. The life of machine parts and instruments is extended, the noise level is reduced, the flight comfort is increased. With a little routine, the whole procedure does not take more than 30 minutes Preparations Balancing is carried out on ground. Since the engine is started and the propeller put into rotation, the machine must be locked sufficiently. Balancing can be carried our by on person alone. He or she must have the ability and permission to start the engine on ground. An environment with only little wind enhances the measurement accuracy considerably with regard to fine balancing. If such an environment does not exist, the wind should cross the propeller sideways. The occurring vibrations are caused by the unbalanced propeller. In order be able to well measure the vibrations caused by the unbalance, the measurement is carried out near the propeller. It is often advantageous to mount the sensors on the engine respectively the gear. The cowling is to be removed Mounting the sensors The vibration sensor (1) is mounted in radial direction to the propeller axis. A reflecting label is stuck to the baseplate of the spinner and the reflex switch (2) is oriented towards it. You do not need to use the complete (50 cm²) reflection foil. A small part suffices. However, the length of its edges should be at least 2 cm. Both sensors are to be mounted securely, that means in a way they cannot loosen or detach themselves during propeller rotation. Vibration sensor and reflex switch can be mounted by screwing. The vibration sensor provides an M5 thread in base. The reflex switch provides drill-holes and inside threads for M4 screws. By simple adapters, both sensors can be mounted on different engines. Due to the variety of engines, adapters are not normally included in delivery. 14 Mounting the sensors

15 4.Balancing propellers 4.3. Laying sensor cables The small USB box InnoBeamer is preferably positioned in the cockpit. Sensor cables transfer the signals for digitization. Cables should not be in contact with hot parts and they should be fixed at suitable places (for instance with cable ties) to ensure that they do not flutter during propeller rotation In the cockpit The notebook can be placed on the seat of the copilot, the InnoBeamer plus connected cables can be stored on the ground of the cockpit. The vibration sensor is connected with the input ACh1, the reflex switch is connected with the DCh input. When the notebook is switched on, the InnoBeamer and connected sensors are supplied as well. Now you check the reflex switch once again. If it detects the reflecting label, a yellow LED in the reflex switch flashes. The control center InnoMaster RT can be started on the notebook now. If now workspace for propeller balancing has been configured yet, some settings are to be made. For the following steps, take a look into the VibroMatrix manual. 1. The purchased sensor should be entered to the sensor database. 2. The vibration sensor is assigned to measuring channel 1 of the active InnoBeamer. 3. The balancing software InnoBalancer is started. Two settings are to made in the InnoBalancer. Basically, this can be done at any time, also after measurement. The InnoBalancer simply recalculates all results then. But since we want to see valid results immediately after the measurement, it is a good opportunity to enter the data now. In the cockpit 15

16 4.Balancing propellers 1. As unbalance quantity, we want to use a mass in gram referring to a fixed rotor radius. An unbalance is often defined as mass x radius. But if the radius remains the same like in our example, the mass alone can be regarded as well. When balancing propellers, the unit gram is suitable. 2. The radius of the rotor is to be entered. As radius, the distance from the rotating axis to the circumference where the calibration/correction masses are attached. For instance, this could be the baseplate of the spinner (also compare chapter 4.6 page 17) Initial unbalance run The first measuring run is called initial unbalance run. The propeller is measured in its original state with a still unknown unbalance. Therefore, a constant rotation speed is set, possibly similar to the one during machine operation. If you are sure not to endanger nearby persons or objects, the engine can be started. We recommend to warm up the engine one or two minutes before first-time measurement. This process does not require full throttle. Then the gear is to be set to the constant rotation speed. With a click on the Start button in the InnoBalancer, the rotation speed recognition is started. The rotation speed is indicated in the user guide. It should be plausible. When estimating roughly, a possible gear transmission ratio is to be taken into account. Now simply keep a constant rotation speed. The InnoBalancer continuously monitors the rotation speed stability and only carries out the measurement at constant rotation speed. During the measurement, the rotation speed is monitored as well. If the rotation speed varies too much during the measurement, the measurement automatically starts anew. A certain number of revolutions is read. The standard number is 100. If the InnoBalancer has read all revolutions, the user guide informs you to stop the engine now. The initial unbalance run is finished then Calibration run The second measuring run is for calibration. At a defined position, a known mass is mounted. Now some considerations with regard to mounting the calibration respectively correction masses are necessary. 16 Calibration run

17 4.Balancing propellers Mounting calibration/correction masses on the propeller The correction of an unbalance is preferably achieved by adding masses opposite to the unbalance. They are mounted if existing on the baseplate of the spinner. If not, other places must be found where masses (for instance washers) can be mounted without interfering with the propeller operation. The closer you come to the rotation axis, the heavier the correction masses. Except the InnoBalancer Light, all versions are able to handle fixed positions. If there are mounting places for masses on the propeller, which are evenly allotted on the circumference, the InnoBalancer can take them into consideration. Then it will calculate a mass allocation for these fixed positions only, which also corrects an unbalance between the fixed positions. Examples for fixed positions Therefore, the number of fixed positions is entered into the rotor properties, The angle of the first fixed position should remain zero, then the first fixed position will be at 0. The minimum number of fixed positions is 3. If you enter a value below 3, the calculation with fixed positions will be deactivated. Correction masses have to be mounted at the angles indicated by the software. In this case, selfadhesive mass pieces like in the automotive industry can be applied. For long-time adherence, the respective point is to prepared accordingly, i.e. it must be free of fat and dirt. An additional assurance by means of epoxy glue is recommended. For an exact correction, the mass of the additional adhesive must be included in the total mass. Preparations for the calibration run After having decided whether to use fixed positions or not, the calibration mass is mounted. A value of approx gmm is recommended after tests on ultralights. For example, this means: At a radius of approx. 100 mm, 10 gram apply and respectively 20 gram at a radius of 50 mm. But this value should be considered as approximate value only. The calibration mass is entered into the calibration control panel of the InnoBalancer software. The angle position is to be entered as well. The angle of 0 is not given by the reflecting label. The angle can be chosen completely freely, for example the angle of 0 can have the position of the calibration mass. But with all following tests, you have to refer to this position as 0. Angles are always counted from the defined zero angle against the rotary direction. Calibration run 17

18 4.Balancing propellers Carrying our the calibration run If you had to remove the spinner for mounting the calibration mass, you must mount it again now. All measuring runs have to be carried out with the same superstructural parts. When mounting the spinner, take care to mount it in the same way like before and not turned by 180. A small label on the spinner /baseplate is useful. The measurement is carried out in the same way like the initial unbalance run. The propeller is put into rotation with a constant rotation speed, in fact the rotation speed of the initial unbalance run. The InnoBalancer recognizes the constant rotation speed, carries out the measurement and asks you to stop the propeller. With these both run, amount and angle position of the unbalance have determined. They are displayed in the InnoBalancer now Correction Now the known unbalance should be corrected. Therefore the correction control panel has to be activated in the InnoBalancer. Different correction methods are available. For our example, we use the correction by adding mass (Weight ++) on the opposite of the unbalance. In case of having a technological limit, enter the maximum mass. When balancing with fixed positions, the InnoBalancer allocates the total mass to different fixed positions, so that the maximum mass is exceeded at no position. The polar chart displays position and amount of the mass to added, provided the unbalance exceeds the entered tolerance. If the unbalance is within the tolerance circle, no correction method is indicated. The tolerance can be adjusted in the rotor characteristics. When balancing propellers, 5 gram on the baseplate of the spinner (radius approx. 100 mm) can be considered as a realistic result. In case of having good measurement conditions, results of below 1 gram can be achieved. When mounting the counterweight, the calibration mass is to be removed. The position for the counterweight is to be counted from the zero angle against the rotary direction. 18 Correction

19 4.Balancing propellers 10 gram calibration mass are still mounted The calibration mass was removed, the correction mass was mounted in the indicated angle against the rotary direction Control run After correction, the unbalance is to be measured again. The procedure is the same again. The propeller is put into rotation with a constant rotation speed, in fact the rotation speed of the initial unbalance run. The InnoBalancer recognizes the constant rotation speed, carries out the measurement and asks you to stop the propeller. The indicated unbalance should be considerably reduced now. By means of further corrections, a further correction of the unbalance can be achieved step by step. To make sure that the measurement conditions allow a further unbalance correction, a control run can be carried out two or three times without adding correction masses. If the indicated unbalance has a similar amount and position in all measuring runs, a further correction is possible. If the result varies, no improvements can be expected from a further correction. Control run 19