Patent Publication Number: US-2023136750-A1

Title: Eccentric mass vibrating system

Description:
This application claims priority to Italian Patent Application No. 102021000027659 filed on Oct. 28, 2021, the disclosure of which is incorporated herein by reference. 
     DESCRIPTION 
     The present invention refers to an eccentric mass vibrating system and a method for the control of an eccentric mass vibrating system. 
     TECHNICAL FIELD 
     The presence of residual tensions in structures made of electrowelded composite fabrication work is well-known in the metal working sector. 
     BACKGROUND 
     These tensions facilitate deformation of the structure during the various work phases and the formation of cracks when the structure is fatigue stressed. The many methods and processes useful for reducing residual tensions include heat treatment, ageing and vibrations. 
     In the use of vibrations, the stressed part is made to vibrate at different frequencies by means of a vibrator fixed to the part, and the acceleration pattern of the part is analysed as the frequencies induced by the vibrator vary. 
     The amplitude of the vibration depends on the vibration frequency and the energy transmitted by the vibrator. Namely, at given frequencies and energy transmitted, the vibration amplitude increases or decreases. The frequencies at which these increasing variations are noted are called resonance peaks. The part is therefore made to vibrate at different frequencies chosen from among those identified, for a variable time, until it has been stress-relieved. 
     Normally, rotating vibrators with shaft provided with eccentric mass are used, with the possibility of varying the energy delivered by the rotating eccentric mass. This unbalance can currently be manually mechanically adjusted, by varying the eccentric mass. 
     The unbalance of the vibrator must be chosen so as to be sufficient to bring to resonance the part undergoing the work process at the maximum energy it can absorb. Different treatment frequencies may require different amounts of energy. 
     This means that vibrators with different dimensions have to be adapted to specific individual cases in relation to the energy required by the application. 
     In other situations, the rotation frequency of the rotor driving the eccentric mass is reduced or increased, but variation only of the frequency may not solve the problem or may even be detrimental to the application. 
     Sizing of the eccentric mass, and therefore the energy that can be delivered by the vibrator, is also difficult and therefore vibrators that are oversized or undersized with respect to the actual requirements of the application tend to be used. Furthermore all the frequencies detected are treated with the same phase shift angle between the eccentric masses of the vibrator, and therefore with the same energy contribution even though, for the majority of the frequencies, the component being treated could absorb greater energy than that set by the operator for reasons of treatment feasibility. 
     If the operator has fixed a range of revolution numbers below the minimum established by the treatment cycle for reasons of feasibility, some of the component frequencies may not be detected during the analysis phase, due to incorrect choice of the vibrator or incorrect adjustment of the vibrator masses and number of revolutions by the operator. 
     Finding the optimal adjustment of the above parameters according to the components to be treated can be very complex since many variables have to be taken into account such as, for example, the noise level of the process; in fact a resonance frequency stimulated at an excessive energy level can propagate in the environment, through vibration of the component, deafening noise which is unbearable for the local operators. Noise is a polluting element for the environment and must therefore be brought within the permitted safety limits, but sound insulation of the intervention area is not always possible. This means that the operator has to reduce the vibration energy contribution to the component and therefore the phase shift value of the eccentric mass, reducing the effectiveness of the treatment. 
     Another variable is the current absorption of the motor. In the case of strong acceleration of the component at given frequencies, the vibrator absorption can increase exponentially, inducing overheating of the motor with possible stoppage of the work cycle. 
     Another variable is the movement of the component. Excessive vibration of the component can create instability in the component, causing it to shift from the work position. 
     All these factors make the initial adjustment by the operator very complex and entail long system set-up times. 
     The use of electric vibrators is not limited to eliminating residual tensions in metal, they are also used extensively in the sector of movement of loose materials, for example in hoppers, storage silos, load cells, etc. 
     For these types of applications where the mechanical vibrational energy is used to facilitate the extraction of stored materials, the same silo may contain materials with variable flow characteristics, possibly conditioned by external factors such as humidity, temperature, pressure, product type, etc. 
     One single vibrator with finite dimensions can provide a solution in the case of stoppage of the flow of a certain material in given conditions passing through the silo, but can worsen the situation if the conditions of the material vary, or if the materials passing through the silo have different characteristics from one another. 
     In these cases, the vibrations, not appropriately calibrated in terms of frequency and mass, can make the compaction levels worse or not guarantee regular flow of the material, compromising the extraction thereof. 
     Vibrations are also used in the screening sector, to select different granulometric dimensions of the screened materials, in conveyors to convey the material from one point to another, in vibrating extractors and in many other applications. 
     Also in these cases the same considerations apply as those made above: the material flows can vary and require frequencies and energies that can immediately adapt to the current work requirements. 
     SUMMARY The object of the present invention is to provide an eccentric mass vibrating system which is more versatile than those of the known art. 
     A further object is to provide an eccentric mass vibrating system which is simple to produce. 
     In accordance with the present invention, said objects and others are achieved by an eccentric mass vibrating system comprising: a first motor having a first shaft; a first eccentric mass connected to said first shaft; a second motor having a second shaft; a second eccentric mass connected to said second shaft; said first motor and said second motor are adapted to be associated with an object to be vibrated; said first motor and said second motor being electrically adjustable so as to arrange said first eccentric mass and said second eccentric mass at a predefined angle therebetween; said first motor and said second motor being adapted to be placed on an object to be vibrated; characterised in that it comprises: at least one sensor associated with said object to be vibrated; a control computer of said system adapted to modify said predefined angle if the value measured by said sensor exceeds a predefined value. 
     Said objects and others are also achieved by a method for the control of an eccentric mass vibrating system having a first motor with a first eccentric mass and a second motor with a second eccentric mass; 
     comprising the steps of: positioning said system on the object to be vibrated; associating at least one sensor with the object to be vibrated; positioning said first eccentric mass and said second eccentric mass phase shift from each other by a first predefined angle; varying the speed of said first motor and said second motor between a first number of revolutions and a second number of revolutions; checking the value measured by said at least one sensor; varying said first predefined angle if the value measured by said at least one sensor exceeds a predefined value. Further characteristics of the invention are described in the dependent claims. 
     This solution has several advantages compared to the solutions of the known art. 
     Thanks to the present invention an eccentric mass vibrating system is obtained with the possibility of varying the energy delivered by two eccentric masses rotated by electric motors by modifying the deviation angle therebetween. 
     The automatically controlled eccentric mass vibrating system allows us to limit the vibrator range, optimise performance with a lower electrical energy consumption, facilitate sizing, minimise production stoppages, remote-control the work parameters semiautomatically or automatically, minimise the fatigue stress discharged onto the structures thereby reducing the risk of structural failure, etc. 
     Since variation of the vibrating mass by manual mechanical intervention is no longer necessary, risks to the safety of the personnel responsible for said intervention are minimised. Said interventions often have to be carried out in awkward positions and in sub-optimal environmental conditions. 
     The present system therefore offers significant advantages. It is possible to eliminate the manual intervention of the operator for correct set-up and balancing of the system to carry out the treatment in an optimal manner. 
     It is possible to avoid having to treat all the frequencies with the same phase shift angle between the eccentric masses of the motor and therefore with the same energy contribution even though, for the majority of the frequencies, the component can absorb higher energy levels. 
     It is possible to reduce the application positions of the vibrator and the number of treatments necessary for complete stress relief of the structure. 
     It is possible to avoid the spread of noise pollution in the environment. 
     It is therefore possible to carry out the stress-relieving treatment always at the optimal condition for the component. It allows us to increase the effectiveness level of each individual treatment and reduce the number of treatments necessary to achieve complete stress relief. 
     To do this, the system involves the use of an automatically variable mass vibrator which, dialoguing with systems located in the field (sensors) and with a central control unit, automatically adapts the phase shift angle between the two masses to the specific working needs of each individual frequency of each specific component detected during the search cycle. 
     This means that the scanning phase can always search for the frequencies of the component throughout the standard frequency range. Each individual frequency identified is treated at the maximum level of energy that can be absorbed by the component being treated. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The characteristics and the advantages of the present invention will be evident from the following detailed description of a practical embodiment thereof, illustrated by way of non-limiting example in the attached drawings, in which: 
         FIG.  1    shows schematically a block diagram of an eccentric mass vibrating system, in accordance with the present invention; 
         FIG.  2    shows schematically two motors with relative eccentric weights of an eccentric mass vibrating system, in accordance with the present invention; 
         FIG.  3    shows schematically the eccentric weights of an eccentric mass vibrating system, in accordance with the present invention; 
         FIG.  4    shows schematically the eccentric weights in the position of maximum eccentricity, of an eccentric mass vibrating system, in accordance with the present invention; 
         FIG.  5    shows schematically the eccentric weights in a neutral position, of an eccentric mass vibrating system, in accordance with the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to the attached figures, an eccentric mass vibrating system  10 , in accordance with the present invention, comprises a vibrator  11 , a first drive circuit  12  of the vibrator  11 , a second drive circuit  13  of the vibrator  11  and a control computer  14  of the eccentric mass vibrating system  10 . 
     The vibrator  11  comprises a first electric motor  21  and a second electric motor  22 , preferably stepper motors or brushless motors that allow precise quick movements with compact overall dimensions and great versatility. 
     The first electric motor  21  and the second electric motor  22  are fixed on a common base  23 , which will be fixed to the object to be vibrated. The motors  21  and  22  are preferably positioned with the respective shafts  24 ,  25  opposite each other (but separate from each other) and preferably supported by two bearings  26  fixed on two structures  27  fixed perpendicularly on the common base  23 , and joined to each other at the top to give the base  23  greater solidity. 
     Preferably, as shown in the figures, the shafts  24  and  25  are positioned on the same axis. But they can be opposite each other, adjacent or in different positions. 
     The motors  21  and  22  could be fixed to the base  23  also opposite each other with the respective shafts  24  and  25  facing outwards. The component to be vibrated, normally made of electrowelded composite fabrication work, can act as a base for direct fixing of the motors  21  and  22 , without the use of the base  23 . 
     On each shaft  24  and  25 , a respective bar  28  and  29  is positioned to form the eccentric mass. 
     The two bars  28  and  29  can have enlargements or expansions to reach the desired weight, and are equal in terms of dimension, form and weight. 
     The first drive circuit  12  drives the first electric motor  21 , and the second drive circuit  13  drives the second electric motor  22 , and the control computer  14  controls the drive circuits  12  and  13  and the whole of the eccentric mass vibrating system  10  which comprises various sensors for control of the vibrator  10 , for example current sensors (ammeter) to detect the value of the current absorbed by the motors  21  and  22  and vibration sensors (accelerometers) which will be positioned on the object to be vibrated and will provide the feedback of the excitation applied, for example, by observing the amplitude of the vibrations as well as acoustic sensors (microphones) to be positioned in the vicinity of the object to be vibrated to monitor the value of the noise generated by the object to be vibrated, and frequency meters or spectrum analyzer. 
     The motors  21  and  22  are preferably stepper motors or brushless motors, with which it is possible to adjust, by means of the control computer  14 , the phase of each of them, namely position the shaft  24  and  25 , and consequently the bars  28  and  29 , in the required position. 
     In this way it is possible to position, independently of each other, the bars  28  and  29  in every position from 0° to 360°. Consequently it is possible to position the bars  28  and  29  with an angle a as required, as shown in  FIG.  3   . 
     It is therefore possible to choose an angle a between the two bars  28  and  29  from 0°, in the position of maximum eccentricity, as in  FIG.  4   , to an angle a between the two bars  28  and  29  at 180°, in position, as in  FIG.  5   . 
     Both the motors  21  and  22  can be adjustable, but to simplify the electronics, the phase of only one of the two motors is adjusted. In this case one motor is of the stepper or brushless type, therefore having adjustable phase, while the other can be an electric motor of any type. 
     Thanks to the present invention it is therefore possible to choose the amount of eccentricity, namely the unbalance, of the vibrator  10  automatically. 
     The procedure is carried out as follows. The object to be vibrated is positioned on elastic load bearings, to isolate the object from the ground and vibrate it more easily. 
     The vibrator is positioned, oriented and locked securely on the object to be vibrated. 
     The vibration sensor is positioned on the part to be vibrated and/or the other sensors in the most appropriate positions. 
     The unbalance of the vibrator is adjusted, by adjusting the phase of at least one of the two motors  21  and  22 , then the bars  28  and  29  are positioned with a predefined angle a between them. Initially the phase shift is maximum and equal to 180°. 
     The speed of the two motors  21  and  22  is varied within a predefined speed range, for example between 1500 and 6000 revolutions per minute, corresponding to vibrations of the part to be vibrated at different frequencies, at the maximum energy transmittable, maintaining fixed the predefined angle a between the bars  28  and  29 . 
     The resonance or the resonances of the part to be vibrated are found. 
     In the case of a resonance in which the vibrations and/or the noise and/or the motor absorption is excessive and exceeds predefined preference values, the phase shift between the bars  28  and  29  is reduced, by means of the control computer  14 , and in such a way as to reduce the excesses of the detected value to acceptable levels and the scan is repeated. 
     As soon as possible the phase shift between the bars  28  and  29  is increased again to avoid losing any resonance values. 
     At the end of the scan, the various resonance frequencies of the object to be vibrated have been obtained, corresponding to particular values of the motor revolutions, and the relative maximum phase shift angles between the bars  28  and  29  which allow treatment without excessive vibration, noise and absorption values. 
     The treatment cycle of the object to be vibrated is then started, in automatic mode, applying to the bars  28  and  29  the maximum phase shift values possible for each frequency to be treated. 
     The eccentric mass vibrating system with adjustment of the unbalance of the eccentric masses thus conceived is subject to numerous modifications and variations, all falling within the scope of the inventive concept; furthermore, all the details can be replaced by technically equivalent elements.