Patent Publication Number: US-2022226195-A1

Title: Mass measurement apparatus for automatic processing machines and mass measurement method

Description:
The present invention relates to systems and apparatuses for measuring the weight of articles in automatic processing and packaging machines. In particular, the invention relates to a mass measurement apparatus associated with an automatic filling machine or an automatic compressing machine for measuring the mass of processed articles, such as capsules, opercula or tablets, lozenges or the like, in particular for pharmaceutical or food use. The invention also relates to a method for measuring the mass of processed articles such as capsules, opercula, or tablets, lozenges, or the like in an automatic processing machine. Systems for measuring the weight or mass of processed and/or packaged articles are widely used in the processing and packaging machinery sector. Generally, although reference is made to the weight of the articles, what is actually provided at the end of the measurement is their mass (expressed in kg), since the weight (or weight force) is a force (expressed in N), given by the product of the mass of the article and the gravitational acceleration (expressed in Nm/s 2 ). Indeed, the weighing systems normally used in the manufacturing and packaging processes of capsules, tablets, and the like comprise electronic scales that measure the weight force of an article and then calculate its mass by dividing the measured weight force by the gravitational acceleration considered constant (although in fact it is variable with the latitude and altitude of the place where the measurement is carried out). In general, in the industrial field, weight is referred to as mass (so-called kilogram weight Kg p  equal to 9.81 N). 
     In the processes of filling capsules or opercula, typically in hard gelatin, with liquid, powder, granules, time-release products, tablets, etc., the use of measurement apparatuses located downstream of the filling machine or filling station of the latter to measure the mass of the product dosed in the capsules is known. 
     Similarly, apparatuses are known and used to measure the mass of tablets, lozenges made in a compressing machine, by compressing products in powder or granules. 
     Mass or weight control is necessary to discard non-compliant articles, capsules or tablets from production, because they contain a quantity of product outside the allowed tolerance range and to correct any excesses or defects in the product dosage, acting in feedback on the filling machine. 
     In fact, especially in the pharmaceutical sector it is very important to verify that the quantity of product present in the articles, capsules or tablets, is exactly that which is required, with very narrow tolerance ranges. 
     In the filling processes generally the mass (or weight) of the capsules is only measured once at the end of the dosing, since the mass of the empty capsules is known and contained within a defined tolerance range, indicated and guaranteed by the suppliers/producers of the capsules. In this way, from the measurement of the mass or weight of the filled capsule (gross weight), by subtracting the known weight of the empty capsule (tare) it is possible to calculate the weight of the dosed product (net weight) with a certain degree of precision. 
     In filling processes in which the quantity of product to be dosed in the capsules is very small, for example a few milligrams (so-called “micro-doses”), and the tolerance range required for the dosage of the product is limited, for example ±10%, it is necessary to first weigh the empty capsule as well and calculate the weight of the dosed product using the difference. In these cases, since the weight of the empty capsules is comparable to that of the dosed product, the normal weight variations of the empty capsules can be larger than the tolerance range of the allowed dosage. 
     Solutions are therefore known which provide a first weighing station, upstream of the filling machine or of the filling station, which measures the weight of the empty capsules (tare), and a second weighing station, downstream of the filling machine or of the filling station, which measures the weight of the filled capsules (gross weight). The difference between the two measured weights allows precisely calculating the net weight of the dosed product. 
     The weighing apparatuses that perform this type of direct measurement comprise electronic scales typically equipped with a plurality of measurement cells, or load cells, each of which is equipped with a respective support (plate) on which the capsule must be positioned for the time necessary for the correct measurement. 
     The weight control can be of the total type, i.e. performed on all the capsules filled with the product (so-called 100% weight control) or a partial, statistical type control carried out on a sample of filled capsules, randomly selected. 
     In certain types of pharmaceutical production, however, the control of all the filled capsules is required and in general this solution is widely preferred by pharmaceutical companies in order to guarantee a better quality of the processed articles. 
     It is known that to perform an accurate and precise weighing using electronic scales, an adequate measurement time is necessary. In particular, between the deposition of the article on the plate of the scale and the measurement of its weight, a minimum interval of time must elapse, necessary to allow the scale to stabilize, i.e. to allow the damping of the vibrations that are generated by resting the article on the plate and to proceed with the weight detection. 
     Consequently, in order to ensure this adequate measurement time, the operating or production speed of the filling machine must be considerably reduced. 
     Systems for the indirect measurement of the weight of the capsules or tablets comprising microwave sensors, capacitive sensors, sensors based on magnetic resonance imaging technology are also known. These indirect measurement systems require reduced measurement times and therefore do not require a reduction in the speed of the filling machine, but in addition to being very expensive and rather laborious and complex to adjust and use, they have the disadvantage of not guaranteeing the measurement reliability and certainty of the direct measurement systems. 
     An object of the present invention is to improve the known mass measurement or weighing apparatuses associated with automatic processing machines, in particular capsule filling machines or compressing machines, for measuring the weight of processed articles, e.g. capsules, opercula or tablets, lozenges or the like. 
     Another object is to provide a mass measurement apparatus capable of measuring the mass of the articles processed by the machine with high accuracy, precision and resolution and with very short measurement times. 
     A further object is to realize a mass measurement apparatus associated with an automatic processing machine that allows to perform a total weight control, i.e., to measure the mass of all processed articles, even at high operating speeds of the machine. 
     These and others objects are achieved by a compressing machine according to claim  1 . 
    
    
     
       The invention can be better understood and implemented with reference to the attached drawings which illustrate some exemplifying and non-limiting embodiments thereof, wherein: 
         FIGS. 1 to 4  are schematic and partially sectional side views of the mass measurement apparatus of the invention associated with an automatic processing machine arranged to fill articles consisting of capsules with a product, in respective different steps of a mass measurement process of the capsules; 
         FIG. 5  is a schematic plan view of the mass measurement apparatus and the machine of  FIGS. 1-4 ; 
         FIG. 6  is a schematic plan view of a variant of the automatic processing machine of  FIG. 5 ; 
         FIG. 7  is a schematic and partially sectional side view of the mass measurement apparatus of the invention associated with an automatic processing machine adapted to realize articles consisting of tablets, in a step of the mass measurement process of the tablets; 
         FIGS. 8 to 11  are schematic and partially sectional side views of a variant of the mass measurement apparatus of the invention associated with the automatic processing machine of  FIG. 5  adapted to fill articles consisting of capsules, in respective different steps of a measurement process; 
         FIG. 12  is a schematic and partially sectional side view of the variant of the mass measurement apparatus of  FIGS. 8-11  associated with an automatic processing machine adapted to realize articles consisting of tablets, in a step of the mass measurement process of the tablets. 
     
    
    
     With reference to  FIGS. 1 to 5 , the mass measurement apparatus  1  of the invention associated with an automatic processing machine  50  for measuring the mass m a  of articles  100  or parts  101  thereof is schematically illustrated, the articles  100  being processed by the machine  50  that comprises at least one movement device  30  provided with seats  33 ,  34  adapted to house and move the articles  100 . 
     In the illustrated embodiment, the automatic processing machine is a filling machine  50  arranged to fill with a liquid, powder, granules, time-release, tablets, etc. product P, in particular a pharmaceutical product, articles  100  in the form of capsules. Each capsule  100 , of a known type and made of hard gelatin, comprises a lower part or bottom  101  and an upper part or cover  102  which can be temporarily decoupled and separated to dose the product P into the bottom  101 . 
     The filling machine  50 , schematically illustrated in  FIG. 5  comprises, for example, a plurality of operating stations  51 - 57  arranged to perform operations on the capsules  100  moved in sequence with intermittent motion through the operating stations  51 - 57  by the movement device  30 . The filling machine  50  comprises a filling station  51  arranged to dispense doses of product P into the bottoms  101  of the capsules  100  and the mass measurement apparatus  1  is, for example, positioned downstream of said filling station  51  so as to measure the mass of the bottoms  101  containing a respective dose of product P. The movement device  30 , of a known type, comprises a carousel or table, rotatable with intermittent motion about a vertical rotation axis X and provided with a plurality of supports  35 , arranged angularly spaced along the periphery or a circumferential edge of the aforementioned table. Each support  35  is formed by a first supporting element  31 , having a plurality of first seats  33 , intended to house the bottoms  100   a  of the capsules  100  and a second supporting element  32 , having a plurality of further seats  34  intended to house the covers  102  of the capsules  100 . The supporting elements  31 ,  32  have an elongated shape and are movable with respect to one another between an overlapping position in which the respective seats  33 ,  34  are aligned and overlapped for the insertion or removal of the whole capsules  100  (i.e. with the covers  102  applied to the respective bottoms  101 ) and an offset position in which the seats  33  containing the bottoms  102  are accessible to allow the dosing of the product. 
     The seats  33 ,  34  of the supports  35  comprise respective through cavities, i.e. open at the opposite ends, and having a converging shape and/or suitably shaped to receive and hold by force or interference coupling the bottoms  101  and the covers  102  of the capsules  100 . The mass measurement apparatus  1  comprises transferring and gripping means  2  arranged to remove an article  100 , in particular a part  101  thereof, in particular a lower part or bottom  101  containing a respective dose of product P, from a respective seat  33  of the movement device  30 , hold the bottom  101  in a measuring position A and then reinsert the bottom  101  into the respective seat  33 . The transferring and gripping means  2  comprise at least one gripping element  3  adapted to hold a respective bottom  101  in the measuring position A. 
     The mass measurement apparatus  1  further comprises actuator means  13 , operating with a vibration actuating signal, e.g., a harmonic type signal, on the gripping element  3  so as to make the latter oscillate or vibrate at a specific resonance frequency f 0  or natural frequency, and sensor means  4  adapted to measure a vibration response signal of the gripping element  3  vibrating and in particular supporting the bottom  101  in the measuring position A. 
     The mass measurement apparatus  1  further comprises a processing unit  15  connected to the sensor means  4  for receiving the vibration response signal and controlling the actuator means  13  in order to, alternatively:
         modify the actuating signal of the actuator means  13  so as to make the gripping element  3  supporting the bottom  101  oscillate or vibrate at an operating resonance frequency f m  (i.e. the natural frequency of the system formed by the gripping element-bottom-product dose) and then calculate a mass m a  of the bottom  101 , in particular containing a respective dose of product P, by comparing the aforementioned operating resonance frequency f m  with the specific resonance frequency f 0  of the gripping element  3  (i.e. not supporting the bottom  101 , i.e. free); or   maintaining the actuating signal of the actuator means  13  to force the gripping element  3  supporting the bottom  101  to oscillate or vibrate at the specific resonance frequency f 0  and then calculate a mass m a  of the bottom  101 , in particular containing a respective dose of product P, by measuring a delay or operating phase difference Δϕ m  between the actuating signal generated by the actuator means  13  and the response signal detected by the sensor means  4 .       

     As better explained in the following description, the gripping element  3  acts, substantially, as a mechanical resonant or resonator element, capable of entering into resonance, i.e., becoming the seat of oscillations having a certain resonance frequency, when urged by a vibration actuating signal, i.e., by a periodic actuating force, for example of a harmonic type, variable with the same frequency. As well known, in a mechanical system the resonance frequency or natural frequency is the frequency at which the amplitude of the vibration is maximum. The resonance frequency of a resonator element is determined by the shape and geometry of the latter, by the physical characteristics of the material (density, elastic constant, damping factor, etc.) with which it is made, as well as by the type of constraint or mechanical fixation of the resonator element to a base or support. 
     In the embodiment illustrated in  FIGS. 1 to 4 , the transferring and gripping means  2  comprises one or more gripping elements  3  each of which movable along an extraction direction F and arranged to remove a bottom  101  from the respective seat  33 , hold it in the measuring position A and then reinsert it in the seat  33  at the end of the measurement. More precisely, the transferring and gripping means  2  comprise a plurality of gripping elements  3  arranged side by side and in a number equal to that of the seats  33  of each support  35  so as to simultaneously extract all the bottoms  101  housed in the seats  33 . The extraction direction F is almost vertical and parallel to the rotation axis X of the movement device  30 . 
     The gripping element  3  has an elongated shape and is shaped to be inserted, when moved along the extraction direction F, inside and through a respective seat  33  of the movement device  30  and has an operative end  3   a  shaped and adapted to abut and support a bottom  101 . The gripping element  3  has, for example, a cylindrical shape with smaller transverse dimensions than those of the seat  33  so as to be inserted with transverse play in the latter in order to avoid possible contact with the inner walls of the seat  33  also during the oscillation phase induced by the actuator means  13 . 
     Fastening means  11 ,  12  are associated with the gripping element  3  and arranged to fix the bottom  101  extracted from the respective seat  33  of the movement device  30  to the operative end  3   a  of the gripping element  3  so that the bottom  101  does not fall or move during the movement of the gripping element  3  in the measuring position A and, above all, when the gripping element  3  is oscillated by the actuator means  13 . 
     The fastening means  11 ,  12  comprises, for example, a suction duct  11  carried out inside the gripping element  3  and leading to the operating end  3   a  and connected to an air suction unit  12 . The gripping element  3  has in this case an elongated cylindrical tubular shape. The mass measurement apparatus  1  further comprises a supporting element  6  which rigidly supports the gripping element  3  and is movable along the extraction direction F to move said gripping element  3  between an inactive position B in which the gripping element  3  is spaced from the seat  33  and the measuring position A in which the gripping element  3  passes through the seat  33  and supports and holds the bottom  101 . In the illustrated embodiment, the supporting element  6  supports the plurality of gripping elements  3 . 
     The actuator means comprise at least one vibrating actuator  13  or oscillator, e.g., a piezoelectric actuator, operating on the respective gripping element  3  to make the latter vibrate at the respective resonance frequency by applying a periodic force, e.g., sinusoidal, with adequate frequency and amplitude. The vibrating actuator  13  is connected to, for example wirelessly, and controlled by the processing unit  15  and is preferably fixed to a lower end  3   b  of the gripping element  3 , at the supporting element  6 . 
     It is also provided that instead of comprising a vibrating actuator  13  for each gripping element  3 , the actuator means comprises a single vibrating actuator fixed to the supporting element  6  and configured to vibrate all the gripping elements  3 . 
     In a variant of the mass measurement apparatus  1  of the invention not illustrated, the actuator means comprises the same supporting element  6 , which is oscillated by external vibrations generated by the automatic processing machine  50  in the operation thereof and which, since rigidly connected to the gripping elements  3 , oscillates the latter with oscillations having the resonance frequency. 
     The sensor means  4  comprises a plurality of vibration sensors, e.g. MEMS accelerometers, fixed directly to the respective gripping elements  3 , in particular at their operating end  3   a . Alternatively, the sensor means  4  may comprise a plurality of optical sensors, for example laser measurement sensors, each of which is pointed at the respective gripping element  3 , in particular at its operative end  3   a . The sensor means  4  are wirelessly connected to the processing unit  15 . 
     Still alternatively, the sensor means  4  may comprise one or more among deformation sensors, bending sensors, torsion sensors, in particular piezoelectric or piezoresistive type sensors, for example strain-gauge sensors or PVDF elements, each of which suitably fixed to the respective gripping element  3 . 
     The operation of the mass measurement apparatus  1  of the invention is based on known technology that provides for the use of systems with resonant mechanical elements or resonators to determine or measure the mass of samples or elements made integral with the aforementioned resonators. In such systems the variations in the characteristics of the resonator vibration are in fact directly linked to the variations in the mass of the resonator and more precisely of the sample or article to be measured made integral thereto. 
     At first approximation, neglecting the resonator damping coefficient, the resonance frequency or natural frequency f 0  of the latter may be expressed by the following formula: 
     
       
         
           
             
               
                 
                   
                     f 
                     0 
                   
                   ≈ 
                   
                     
                       k 
                       m 
                     
                   
                 
               
               
                 
                   eq 
                   . 
                   
                       
                   
                   ⁢ 
                   1 
                 
               
             
           
         
       
     
     wherein
 
k is the effective elastic coefficient of the resonator;
 
m is the effective mass of the resonator.
 
     The elastic coefficient and mass are defined as effective because they include a plurality of additional physical characteristics of the resonator. For example, the effective mass is defined not only by the vibrating mass of the resonator but also by the type of mechanical attachment or constraint of the resonator to a base or support. Likewise, the elastic coefficient of the resonator comprises the elastic constant of the resonator material, but also its density, damping factor, geometric conformation, dimensions, etc. 
     By varying the mass of the resonator to which the sample or article to be measured is constrained, i.e. in the specific case by varying the mass of the gripping element  3  that collects and holds a respective bottom  101  containing a dose of product P, the resonance frequency of the resonator/sample system (gripping element/bottom  101  system) also varies correlatively. More precisely, the operating resonance frequency f m  of the gripping element  3  supporting the vibrating bottom  101  is expressed by the formula: 
     
       
         
           
             
               
                 
                   
                     f 
                     m 
                   
                   ≈ 
                   
                     
                       k 
                       
                         m 
                         + 
                         
                           δ 
                           ⁢ 
                           m 
                         
                       
                     
                   
                 
               
               
                 
                   eq 
                   . 
                   
                       
                   
                   ⁢ 
                   2 
                 
               
             
           
         
       
     
     wherein
 
m is the effective mass of the gripping element  3 ;
 
δm is the variation in mass of the resonator/sample system, i.e. the mass m a  of the bottom  101  of the capsule or article  100  processed by the machine containing a dose of product. Assuming that the elastic properties of the resonator remain unchanged and that the mass variation is small, equation 2 can be differentiated in the first order with respect to the mass, obtaining the linear proportionality ratio between the variation of resonance frequencies and the mass variation:
 
         f   m   −f   0   ∝δm   eq. 3
 
     By comparing the operating resonance frequency f m  of the resonator/sample system with the specific resonance frequency f 0  of the resonator alone, i.e. of the free gripping element  3 , it is therefore possible for the processing unit  15  to calculate the mass variation δm of the system, i.e. the mass m a  of the bottom  101  containing the product P. 
     In particular, it has been verified by the applicant that by means of the measurement apparatus  1  of the invention a mass variation of about 0.15-0.7 mg of the resonator/sample system (gripping element/bottom) corresponds to a nominal variation of about 1 Hz of the resonance frequency. Since the sensor means  4  and the processing unit  15  are capable of detecting and measuring variations around one hundredth Hz, the measurement apparatus  1  of the invention is capable of measuring the mass of the bottoms  101  at a very high resolution, e.g., between 0.0015 and 0.007 mg. 
     Alternatively, the mass measurement apparatus  1  of the invention allows to accurately calculate the mass m a  of the bottoms  101  by measuring a delay or operating phase difference Δϕ m  between the actuating signal applied by the resonant element  13 —which forces the resonator/sample system (i.e. the gripping element  3  supporting the bottoms  101  with the dose of product P) to vibrate at the specific resonance frequency f 0 —and the vibration response signal detected by the sensor means  4 . More precisely, the operating phase difference Δϕ m  between the actuating signal, with the specific resonance frequency f 0 , and the resonator/sample system response signal, can be calculated by the formula: 
     
       
         
           
             
               
                 
                   
                     tan 
                     ⁢ 
                     
                       ϕ 
                       m 
                     
                   
                   ∝ 
                   
                     - 
                     
                       
                         f 
                         0 
                       
                       
                         
                           f 
                           0 
                           2 
                         
                         - 
                         
                           f 
                           m 
                           2 
                         
                       
                     
                   
                 
               
               
                 
                   eq 
                   . 
                   
                       
                   
                   ⁢ 
                   4 
                 
               
             
           
         
       
     
     ϕ is the phase angle,
 
f 0  is the vibration resonance frequency of the gripping element  3 ;
 
f m =f 0 +Δf is the operating resonance frequency of the gripping element  3  supporting the bottom  100 , wherein Δf is the change in resonance frequency induced on the gripping element  3  by the added mass of the bottom  101  and the relative dose of product P.
 
     In other words, by varying the mass of the gripping element  3  (resonator) to which the sample or article to be measured is constrained, i.e. in the specific case by varying the mass of the gripping element  3  that collects and holds a respective bottom  101  containing a dose of product P, the phase difference Δϕ m  between the actuating signal and the response signal also varies correlatively. 
     More precisely, by forcing the gripping element  3  to vibrate at its resonance frequency f 0 , a mass change δm (mass of the bottom  101  with the dose of product P) thereon results in a change in the operating phase delay i.e. an operating phase difference Δϕ m , which in the first approximate order is expressed by the relationship: 
       Δϕ m   ∝δm   eq. 5
 
     wherein the coefficient of proportionality depends on the specific resonance frequency f 0  and the effective mass of the gripping element  3 . 
     With this measurement methodology it is possible to take advantage of a higher speed of response signal acquisition and processing management, as it is not necessary to use automatic tracking techniques of the operating resonance frequency f m  (e.g. a phase-locked loop PLL based system) of the resonator/sample system. 
     In particular, it has been experimentally verified by the applicant that with the measurement apparatus  1  of the invention a mass variation of about 2 mg of the resonator/sample system (gripping element  3 /bottom  101 /dose of product P) corresponds to a variation of about 1 degree of the operating phase variation Δϕ m . Since the sensor means  4  and the processing unit  15  are capable of detecting and measuring variations around one hundredth of a degree, in this configuration the measurement apparatus  1  of the invention is capable of measuring the mass of the bottoms  101 , for example at a resolution of about 0.02 mg. 
     With reference to  FIGS. 1 to 4 , the operation of the mass measurement apparatus  1  of the invention associated with the automatic processing machine  50  arranged to fill capsules  100  with doses of product P, provides for the following operational steps. 
     During the operation of the machine  50 , at each step of stopping the intermittent motion of the movement device  30 , a seat  33  of the latter containing a bottom  101  with a relative dose of product P to be measured is arranged at a respective gripping element  3  of the measurement apparatus  1 . The gripping element  3  is then moved along the extraction direction F from the inactive position B to the measuring position A so as to extract the bottom  101  from the seat  33 . The latter is held and firmly constrained to the operating end  3   a  of the gripping element  3  by vacuum, by virtue of the suction of air through the suction duct  11  connected to the suction unit  12 . 
     In the measuring position A, the gripping element  3 , which crosses the seat  33  without touching the internal walls, is vibrated by the actuator means  13  with a suitable actuating signal so as to enter into resonance (i.e. so as to vibrate at the operating resonance frequency of the gripping element  3 /bottom  101 /dose of product P system) for a defined measurement interval or time, between 10 and 20 ms. In this measurement range, the sensor means  4  measures the vibration response signal and send it to the processing unit  15  which is configured to determine the above-mentioned operating resonance frequency f m  and calculate the mass m a  of the bottom  101  by comparing the above-mentioned operating resonance frequency f m  with the known specific resonance frequency f 0  of the gripping element  3  alone or free, i.e. not supporting the bottom  101 . 
     The specific resonance frequency f 0  of the gripping element  3  alone is, for example, preliminarily determined by the processing unit  15  by measuring with the sensor means  4  the response signal of the gripping element  3  vibrated by the actuator means  13  before being moved along the direction F and having extracted the bottom  101  from the seat  33 . Alternatively, in the measuring position A, the gripping element  3 , which crosses the seat  33  without touching its internal walls, is forced to vibrate by the actuator means  13  at the specific resonance frequency f 0  of the gripping element  3  for a defined measurement interval or time, between 10 and 20 ms. In this time interval, the sensor means  4  detects the response signal of the gripping element  3  supporting the bottom  101  so that the processing unit  15  is able to calculate the mass m a  of the bottom  101  by measuring an operating phase difference Δϕ m  between the actuating signal generated by the actuator means  13  and the response signal detected by the sensor means  4 . 
     At the end of the measurement, i.e. at the end of the defined time interval, the gripping element  3  is moved from the measuring position A to the inactive position B so as to reposition the bottom  101  inside the respective seat  33 . 
     After the stopping step, the movement device  30  is moved so as to position a subsequent seat  33  with the respective bottom  101  at the mass measurement apparatus  1 . 
     Thanks to the mass measurement apparatus  1  of the invention associated with an automatic processing machine  50 , in particular a filling machine for capsules, opercula or the like, it is therefore possible to measure with high accuracy, precision and resolution the mass of the articles or capsules  100  processed by the machine, and more precisely the mass m a  of the bottoms  101  of the capsules  100  filled with the product P. In particular, the mass measurement apparatus  1  allows a resolution on the measured mass between, for example, 0.0015 and 0.007 mg. 
     Furthermore, since the measurement carried out by the apparatus of the invention is very rapid, with a measurement time or interval between 10 and 20 ms, i.e. much less than the stopping time of the intermittent movement of the machine, it is possible to perform a total weight control, i.e. to measure the mass of all the processed capsules  100 , even with high machine operating speeds, i.e. with reduced values of the aforementioned stopping interval. With particular reference to  FIG. 5 , the filling machine  50  is illustrated, which comprises a feeding and opening station  52  of the capsules  100  by means of which the latter are introduced into the filling machine  1 , the covers  102  removed and separated from the relative bottoms  101  which can thus receive the product P in the subsequent filling station  51 . The bottoms  101  and the covers  102  are inserted and housed respectively in the seats  33  and in the further seats  34  of the supports  13  of the movement device  30 . A capsule closing station  54  is provided for coupling the covers  102  to the respective bottoms  101  and thus closing the capsules  100  after filling and weighing. 
     The mass measurement apparatus  1  is associated with a weighing station  53  positioned downstream of the filling station  51 , with reference to the direction of movement G of the capsules  100  in the filling machine  50 , so as to measure the mass m a  of the bottoms  100  containing doses of product P. 
     The plurality of operating stations  51 - 57  of the filling machine  50  further includes an exit station  56  in which the capsules  100  filled with the product and compliant are extracted from the movement device  30  and conveyed out of the filling machine  50  and a waste station  57  located downstream of the exit station  56  to remove the non-compliant capsules from the movement device  30 . 
     An optional initial weighing station  55  provided with a respective mass measurement apparatus  1  of the invention and positionable between the feeding and opening station  52  and the filling station  51  for measuring the mass of the empty bottoms  101  is shown in  FIG. 5  with dotted line. In this embodiment of the filling machine  50 , the actual mass of the product dosed in the capsules  100  is calculated as the difference of the masses of the capsules  100  measured before and after the filling station  51 . 
       FIG. 6  illustrates a variant of the filling machine  50  that differs from the embodiment above-described and referred to in  FIG. 5 , in that it does not comprise weighing stations since the mass measurement apparatus  1  is directly associated with the filling station  51  so as to measure the mass m a  of only the doses of product P dosed in the bottoms  101 . In this variant of the machine, the mass measurement apparatus  1  with the methods described above calculates the mass m a  of the dose of product P by comparing the specific resonance frequency f 0 ′ of the gripping element  3  supporting the empty bottom  101  vibrated by the actuator means  13  with the operating resonance frequency f m ′ of the gripping element  3  supporting the bottom  101  with the dose of product P, vibrated by the actuator means  13 . Alternatively, the mass measurement apparatus  1  is able to calculate the mass m a  of the dose of product P by measuring a delay or operating phase difference Δϕ m  between the vibration actuating signal generated by the actuator means  13  to make the gripping element  3  supporting the bottom  101  with the dose of product P vibrate at the specific resonance frequency f 0 ′ of the gripping element  3  supporting the empty bottom  101  and the vibration response signal of the gripping element  3  supporting the bottom  101  with the dose of product P detected by the sensor means  4 . 
     With reference to  FIG. 7 , the mass measurement apparatus  1  of the invention can also be associated with an automatic processing machine  60 , in particular a compressing machine, arranged to realize articles  200  in the form of tablets or lozenges by compressing a product. The compressing machine  60 , of known type and not illustrated and described in detail, comprises a movement device  130  adapted to transfer the tablets  200  to the mass measurement apparatus  1 . The movement device  130  comprises, for example, a table rotatable about a vertical rotation axis and peripherally provided with a plurality of seats  133  adapted to house the tablets  200  produced in a previous product compression station. 
     The mass measurement apparatus  1  is identical to that previously described for the filling machine  50 , the gripping elements  3  of the transferring and gripping means  2  in this case being arranged to remove from the seats  133  respective tablets  200  held on the shaped ends  3   a  of the aforementioned gripping elements  3  by the fastening means  11 ,  12 . 
     The mass of the tablets  200  is calculated by the processing unit  15  by comparing the operating resonance frequency f m  of the resonator/sample system (gripping element  3 /tablet  200 ) and the specific resonance frequency f 0  of the resonator (gripping element  3 ) or, alternatively, by calculating the delay or operating phase difference Δϕ m  between the resonator actuating signal (gripping element  3 ) and the response signal, detected by the sensor means  4  of the resonator/sample system (gripping element  3 /tablet  200 ) both vibrated by the actuator means  13  to the specific resonance frequency f 0  of the resonator. 
     Referring to  FIGS. 8 to 11 , a variant of the mass measurement apparatus  1  of the invention is illustrated that differs from the embodiment described above and illustrated in  FIGS. 1 to 4  for the transferring and gripping means  2  comprising at least one transferring element  5  movable along an extraction direction F and for removing an article  100 ;  200  or a part  101  thereof from a respective seat  33  of the movement device  30  and transferring it to a respective gripping element  7  of said transferring and gripping means  2 , said gripping element  7  being provided with a housing  17  adapted to receive and hold the article  100  or a part  101  thereof. 
     Also in this variant, the mass measurement apparatus  1  is associated, by way of example and not of limitation, with a filling machine  50  arranged to fill with a product P articles  100  in the form of capsules  100 , consisting of a lower part or bottom  101  and an upper part or cover  102 . 
     The filling machine  50  is for example that illustrated in  FIG. 5  and comprises the operating stations  51 - 57  arranged to perform operations on the capsules  100  moved in sequence with intermittent motion through the operating stations  51 - 57  by the movement device  30 . 
     The transferring element  5  of the transferring and gripping means  2  in the filling machine  50  is then arranged to remove the lower part or bottom  101  (containing a dose of product P) of the capsule  100  from the respective seat  33  of the movement device  30  and transfer said bottom  101  to the corresponding gripping element  7 . In particular, the transferring and gripping means  2  comprise a plurality of transferring elements  5  arranged side by side and in a number equal to that of the seats  33  of each support  35  so as to simultaneously extract all the bottoms  101  housed in the seats  33  and transfer them into a plurality of respective gripping elements  7 . 
     The transferring and gripping means  2  also comprise at least one further transferring element  9  also movable along the extraction direction F and arranged to remove the bottom  101  from the respective gripping element  7  and insert it into the seat  33  of the movement device  30 , after vibrating the gripping element  7  and measuring its operating resonance frequency f m . In particular, the measurement apparatus  1  comprises a plurality of further transferring elements  9  arranged side by side and in a number equal to that of the transferring elements  5  and the gripping elements  3 . 
     The transferring elements  5 ,  9  are movable along the extraction direction F, in particular almost vertical, between a first operative position D 1 , in which said transferring elements  5 ,  9  are disengaged and spaced from the bottom  101 , housed in the respective seat  33  of the movement device  30  so as not to interfere with the movement of the latter, a second operative position D 2 , in which the transferring element  5  has extracted the bottom  101  from the seat  33  and inserted it into the respective gripping element  7 , a third operative position D 3  or measuring position, in which the transferring elements  5 ,  9  are disengaged and spaced from the bottom  101  housed and held in the housing  17  of the gripping element  7  so as to allow the latter to vibrate freely, and a fourth operative position D 4 , in which the further transferring element  9  has completely extracted the bottom  101  from the housing  17  and inserted it into the respective seat  33  of the movement device  30 . 
     Each transferring element  5  has an elongated shape and is arranged to insert, when moved along the extraction direction F, inside a respective seat  33  of the movement device  30  to abut a lower portion of the bottom  101  and push the latter out of the seat  33  and inside the housing  17 . 
     Each further transferring element  9  also has an elongated shape and has a shaped end  9   a  adapted to abut an upper portion of the bottom  101  so as to push the latter out of the housing  17  and inside the seat  33 . 
     The mass measurement apparatus  1  comprises a supporting element  6  that supports the transferring elements  5 ,  9  and is movable along the extraction direction F, in particular to arrange the transferring elements  2 ,  9  in the different operative positions D 1 -D 4 . 
     The mass measurement apparatus  1  further comprises a further supporting element  8  adapted to rigidly support the gripping element  7  above the movement device  30  and aligned to the respective seat  33 . The further supporting element  8  supports, in particular, the plurality of gripping elements  7  and is arranged above the movement device  30 . 
     The housing  17  of each gripping element  7  has a lower opening that allows the insertion or disconnection of the bottom  101  into/from the housing  17  and for this purpose has a bevelled or rounded edge to facilitate the insertion of the bottom  101 . 
     The housing  17  extends longitudinally, in particular parallel to the extraction direction F, and has an extension such as to contain the bottom  101  or the whole capsule  100 . In the illustrated embodiment, the housing  17  is further converged or tapered starting from the lower opening towards the additional supporting element  8  above, its inner transverse section (almost orthogonal to the extraction direction F) progressively decreasing from the lower opening to a smaller dimension than an outer transverse dimension of the bottom  100   a  or the capsule  100 , so that, upon complete insertion, the bottom  101  is held by force or interference coupling (by virtue of the elasticity of the material of which the bottom  101  is made and its hollow shape). 
     Alternatively, mechanical or pneumatic fastening means may be associated with the gripping element  7  to constrain the bottom  101  within the housing  17 . 
     Each gripping element  7  also has one or more side, through and parallel openings to the extraction direction F, which allow the insertion and sliding of the terminal end  9   a  of the transferring element  9  inside the housing  17  and along the extraction direction F. 
     The actuator means include a vibrating actuator  13  or oscillator, for example a piezoelectric actuator, acting on the respective gripping element  7  with an actuating signal for oscillating or vibrating the latter, in particular at the respective resonance frequency, in particular the vibration actuating signal comprising a periodic force, for example sinusoidal, of adequate frequency and amplitude. The vibrating actuator  13  is connected, for example wirelessly, and controlled by the processing unit  15  and is fixed, for example, to an upper portion  7   a  of the gripping element  7  at the further supporting element  8 . 
     It is also provided that instead of comprising a vibrating actuator  13  for each gripping element  7 , the actuator means comprise a single vibrating actuator fixed to the further supporting element  8  and configured to vibrate all the gripping elements  7 . 
     In a variant of the mass measurement apparatus  10  of the invention not illustrated, the actuator means comprise the same further supporting element  8 , which is oscillated by external vibrations generated by the automatic processing machine  50  in the operation thereof and which oscillates the gripping elements  7  (rigidly supporting them) with oscillations having the resonance frequency. 
     The sensor means  4  comprise a plurality of vibration sensors, e.g. MEMS-type accelerometers, fixed directly to the respective gripping elements  7 , in particular at their one of the lower portions  7   b  thereof. 
     Alternatively, the sensor means  4  may comprise a plurality of optical sensors, for example laser measurement sensors, each of which is pointed at the respective gripping element  7 , in particular at one lower portion  7   b  thereof. The sensor means  4  are wirelessly connected to the processing unit  15 . 
     Still alternatively, the sensor means  4  may comprise one or more piezoelectric and/or piezoresistive vibration sensors, e.g. strain-gauge sensors or PVDF elements, each of which are suitably fixed to the respective gripping element  7 , in particular at a lower portion  7   b  thereof. 
     The operation of this variant of the mass measurement apparatus  1  of the invention is identical to that described above. However, the gripping element  7  can be suitably made with shapes and dimensions, in addition to the material (for example made of titanium alloy) which allow to significantly increase the resolution of the measurement apparatus  1 . More specifically, it has been verified by the applicant that with a adapted configuration of said gripping element  7  in the measurement process of the measurement apparatus  1  of the invention at a mass variation of about 0.015-0.2 mg of the resonator/sample system (gripping element  3 /bottom  101 ) corresponds to a variation of about 1 Hz of the resonance frequency. Since the sensor means  4  and the processing unit  15  are capable of detecting and measuring variations in hundredths of Hz, this variant of the measurement apparatus  1  of the invention is capable of measuring the mass of the bottoms  101  at a high resolution ranging from, for example, 0.00015 to 0.002 mg. 
     The measurement interval or time in which the sensor means  4  are able to measure the operating resonance frequency f m  of the gripping element  7  supporting the bottom  101  and send the relative signal to the processing unit  15  is between 10 and 20 ms. 
     It is also possible to accurately calculate the mass m a  of the bottoms  101  based on an operating phase difference Δϕ m  between the actuating signal generated by the vibrating actuator  13  and the response signal detected by the sensor means  4 , suitably connected to the corresponding gripping elements  7 , and processed by the processing unit  15 . 
     With reference to  FIGS. 7 to 10 , the operation of the mass measurement apparatus  1  of the invention associated with the automatic processing machine  50  arranged to fill capsules  100  with doses of product P, provides for the following operational steps. 
     During the operation of the machine, at each step of stopping the intermittent motion of the movement device  30 , a seat  33  of the latter containing a bottom  101  with a relative dose of product P to be measured is arranged at a respective transferring element  5  of the transferring and gripping means  2  of the measurement apparatus  1 . The transferring element  5 , together with the corresponding further transferring element  9 , is then moved along the extraction direction F from the first operative position D 1  ( FIG. 8 ) to the second operative position D 2  ( FIG. 9 ) so as to extract the bottom  101  from the respective seat  33  and insert it into the housing  17  of the gripping element  7  where it is held for example by interference coupling. The transferring elements  5 ,  9  are then moved to the third operative position D 3  ( FIG. 10 ) in which they are disengaged and spaced from the bottom  101  housed and held in the housing  17  of the gripping element  7 . The latter is then vibrated by the actuator means  13  so as to resonate for the defined measurement interval or time, between 10 and 20 ms during which the sensor means  4  are able to measure the operating resonance frequency f m  of the gripping element  7  housing the bottom  101  with the dose of product P and send the relative signal to the processing unit  15 . The latter is thus able to calculate the mass m a  of the bottom  101  by comparing the operating resonance frequency f m  with the known specific resonance frequency f 0  of the gripping element  7  not supporting the bottom  101 . 
     Alternatively, the gripping element  7 , which holds the bottom  101  with the dose of product P, is forced to vibrate by the actuator means  13  at the specific resonance frequency f 0  of the gripping element  7  alone, for the defined measurement interval or time, between 10 and 20 ms. In this time interval, the sensor means  4  measure the vibration response signal of the gripping element  7  with the bottom  101  and the dose of product P and the processing unit  15  calculates the mass m a  of the bottom  101  by measuring the operating phase difference Δϕ m  between the vibration actuating signal generated by the actuator means  13  and the vibration response signal measured by the sensor means. 
     At the end of the measurement, i.e. at the end of the measurement time, the further transferring element  9 , together with the transferring element  5 , is moved to the fourth operative position D 4  ( FIG. 10 ) so as to remove the bottom  101  from the housing  17  of the gripping element  7  and insert it into the respective seat  33  of the movement device  30 . After the stopping step, the movement device  30  is moved so as to position a subsequent seat  33  with the respective bottom  101  at the mass measurement apparatus  1 . 
     Referring to  FIG. 12 , the variant of the mass measurement apparatus  1  of the invention described above can also be associated with a compressing machine  60 , arranged to realize articles  200  in the form of tablets or lozenges by compressing a product. 
     The mass measurement apparatus  1  is identical to that previously described for the filling machine  50 , the transferring elements  5  in this case being arranged to remove the respective tablets  200  from the seats  133  and insert them into the housings  17  of the respective gripping elements  7  and the further transferring elements  9  being arranged to remove the tablets  200  from the housings  17  and insert them into the respective seats  33  of the movement device  30 . 
     The mass of the tablets  200  is calculated by the processing unit  15  by comparing the operating resonance frequency f m  and the specific resonance frequency f 0  of the gripping elements  7  with or without the tablets  200  and oscillated or vibrated by the actuator means  13 . Alternatively, the mass of the tablets  200  may be calculated based on the delay or operating phase difference Δϕ m  between the actuating signal of the gripping element  7  and the response signal, detected by the sensor means  4  of the gripping element  7 /tablet  200  system both vibrated by the actuator means  13  at the specific resonance frequency f 0  of the gripping element  7 . 
     The method of the invention for measuring the mass m a  of articles  100 ;  200  or parts  101  thereof processed in an automatic processing machine  50 ,  60 , which includes at least one movement device  30 ;  130  provided with seats  33 ,  34 ;  133  for housing and moving the aforementioned articles  100 ;  200 , comprising the following steps of:
         removing an article  100 ;  200  or a part  101  thereof from a respective seat  33 ;  133  of the movement device  30 ;  130 , holding the article  100 ;  200  or a part  101  thereof in a measuring position A; D 3  and then reinserting the article  100 ;  200  or a part  101  thereof into the respective seat  33 ;  133  by means of transferring and gripping means  2  comprising at least one gripping element  3 ;  7  adapted to hold the article  100 ;  200  or a part  101  thereof in the measuring position A; D 3 ;   applying, via an actuating signal, in particular a vibration or mechanical oscillation, a mechanical action to actuator means  13 ;  6  on the gripping element  3 ;  7  supporting the article  100 ;  200  or a part  101  thereof in the measuring position A; D 3  to make the gripping element  3 ;  7  vibrate;   measuring by sensors means  4  a response signal of the gripping element  3 ;  7  supporting the article  100 ;  200  or a part  101  thereof and vibrated;
 
alternatively:
   generating an actuating signal of the actuator means  13 ;  6  for applying a mechanical action adapted to vibrate the gripping element  3 ;  7  supporting the article  100 ;  200  or a part  101  thereof at an operating resonance frequency f m , and then calculating a mass m a  of the article  100 ;  200  or a part  101  thereof by comparing the operating resonance frequency f m  with a specific resonance frequency f 0  of the gripping element  3 ;  7  when vibrated alone by the actuator means  13 ;  6 ; or   generating an actuating signal of the actuator means  13 ;  6  capable of applying a mechanical action adapted to vibrate the gripping element  3 ;  7  supporting the article  100 ;  200  or a part  101  thereof at a specific resonance frequency f 0  of the gripping element  3 ;  7  when vibrated alone and then calculating a mass m a  of the article  100 ;  200  or a part  101  thereof by measuring an operating phase difference Δϕ m  between the actuating signal of the actuator means  13 ;  6  and the response signal detected by the sensor means ( 4 ).       

     The method further provides that the specific resonance frequency f 0  of the gripping element  3 ;  7  is preliminarily determined by the processing unit  15  by measuring by means of the sensor means  4  the response signal of the gripping element  3 ;  7  vibrated alone by the actuator means  13  before holding the article  100 ;  200  or a part  101  thereof, in particular before moving the transferring and gripping means  2  to remove the article  100 ;  200  or a part  101  thereof from a respective seat  33 ;  133  of the movement device  30 ;  130 .