HK1178846B - Sonotrode - Google Patents

Description

Ultrasonic generator

Technical Field

The present invention relates to an ultrasonic generator.

Background

Many pourable food products, such as fruit juice, pasteurized or UHT (ultra high temperature treated) milk, wine, tomato sauce, etc., are sold in packages made of sterilized packaging material.

A typical example of this type of packaging is the parallelepiped-shaped packaging for liquid or pourable food products, known as "tetra brik aseptic" (registered trademark), which is made by folding and sealing laminated strip packaging material.

The packaging material has a multilayer structure essentially comprising a substrate layer providing rigidity and strength, which layer may comprise a layer of fibrous material such as paper or a layer of mineral-filled polypropylene material; and a multi-layer heat-seal plastic, such as polyethylene film, covering both sides of the base layer.

In the case of aseptic packages for long-storage products, such as UHT milk, the packaging material also comprises a layer of gas-and light-barrier material, for example aluminium foil or ethyl vinyl alcohol (EVOH), which is superimposed on a layer of heat-seal plastic material, and is in turn covered with another layer of heat-seal plastic material, forming the inner face of the package eventually contacting the food product.

As is known, such packages are produced on fully automated packaging machines, on which a continuous tube is formed from a web-fed packaging material; the web of packaging material is sterilized on the packaging machine itself, for example by applying a chemical sterilizing agent, such as a hydrogen peroxide solution, which is removed from the surface of the packaging material after sterilization, for example by evaporation by heating; and the web of packaging material thus sterilized is kept in a closed, sterile environment and is folded and sealed longitudinally to form a vertical tube.

The tube is filled with sterilized or sterile-processed food product from the top and is clamped by two pairs of clamps at equally spaced cross sections (cross). More specifically, two pairs of jaws cyclically and continuously act on the tube to seal the packaging material of the tube and form a continuous strip of pillow packs connected to each other by respective transverse sealing bands.

The pillow packs are separated by cutting the relative sealing bands and are then conveyed to a final folding station, where they are folded mechanically into the final parallelepiped shape.

In a first alternative, the packaging machine comprises two forming assemblies movable along respective guides and interacting cyclically with the tube to heat seal the packaging material of the tube. Each forming assembly comprises: a sliding member movable back and forth along the corresponding guide; and two jaws hinged at the bottom to the respective slides and moving between a closed position, in which they cooperate with the tube to seal it, and an open position, in which they are separated from the tube.

In a second alternative, the packaging machine comprises two chain conveyors defining respective endless paths and equipped with a respective number of grippers. The two paths have respective branches substantially facing and parallel to each other, and the tube of packaging material is fed between the branches, so that the grippers on one conveyor cooperate with the corresponding grippers on the other conveyor along the branches of the respective paths, so as to grip the tube and seal and cut the packages at a plurality of successive crossing portions.

In the case of aseptic packages having an aluminium layer as a barrier material, the cross section of the tube is typically sealed by inducing a leakage current in the aluminium layer to locally melt the heat seal plastic.

More specifically, one of each pair of clamps comprises a body made of electrically non-conductive material and an inductor housed in a face seat (face) on the body; while the other clamp has a pressure pad made of a flexible material such as rubber.

When the associated pair of clamps grip the tube, the inductor is energized to seal the traversing portion of the tube by heat sealing the plastic cover material.

In the case of packages without an aluminum layer or other layer of conductive material, the transverse portion of the tube is typically sealed using a hot plate for locally heating the packaging material inwardly.

More specifically, one of the clamps is equipped with a hot plate, while the other one usually has one or more pressure pads of flexible material. This process, commonly referred to as "hot plate" sealing, requires relatively permanent contact between the hot plate and the packaging material.

In order to accelerate the local melting of the packaging material and thus increase the packaging production speed, ultrasonic sealing devices are increasingly used, which basically comprise a mechanical vibration generator or sonotrode and an anvil, for example known from EP-B-615907 in the name of the same applicant, which is fitted to a respective jaw of each pair of jaws and cooperates with each other to heat the packaging material by means of ultrasonic vibrations.

More precisely, the sonotrode disclosed in EP-B-615907 basically comprises a head and a single drive unit consisting of a stack of alternating piezoelectric ceramic plates and conductive metal sheets.

The head defines a sealing surface extending in a first direction, and the drive unit is fitted to the head on an opposite side of the sealing surface.

The drive unit is coupled to the alternator. In this way, the piezoelectric ceramic plate converts the supply voltage into a mechanical strain which causes the oscillation of the head and therefore the sealing of the transverse sealing band.

In particular, the sonotrode constitutes a half-wave resonator, i.e. the entire length of the sonotrode in a second direction perpendicular to the first direction is half the wavelength of the oscillation of the head.

Ultrasonic sealing devices of the type described in EP-B-615907 have the following disadvantages.

When longer transverse sealing bands are required, for example for transverse sealing particularly tall packages, a plurality of the above-mentioned ultrasound generators are interconnected for additional length.

However, inevitable errors during interconnection of the sonotrodes may produce uneven vibrations between such sonotrodes. Thus, the resulting transverse sealing band may be uneven.

To overcome this drawback, WO-A-2007/020208 in the name of the same applicant discloses A one-piece sonotrode housing three drive units powered by A single generator. In more detail, the drive units are fixed into respective recesses of the sonotrode and have a respective plurality of piezoelectric elements.

Further, the sonotrode disclosed in WO-A-2007/020208 comprises A pair of slots arranged between respective pairs of drive units adjacent to each other.

Finally, the sonotrode comprises a plurality (in particular three pairs) of S-shaped hooks for fixing the sonotrode to the frame of the clamp. Each pair of S-shaped hooks is disposed on opposite lateral side surfaces of the sonotrode and may be welded or integrally formed to the sonotrode. Thereby preventing the sonotrode from oscillating at the S-shaped clevis. In other words, the S-shaped hooks define respective nodal points of the sonotrode and lie on the "so-called" nodal plane of such sonotrode.

More precisely, the slot extends perpendicular to the sealing surface of the sonotrode and between the subsequent two pairs of S-shaped hooks. Specifically, the slot extends both above and below the S-shaped hook. Thus, the slot passes through the nodal plane of the sonotrode.

The applicant has found that the vibrations of the sonotrode disclosed in WO-A-2007/020208 become unstable due to certain additional spurious frequencies.

Accordingly, the resulting transverse sealing band may still not be completely uniform and continuous. Furthermore, these additional parasitic frequencies cause additional fatigue stresses on the sonotrode, with the result that its fatigue residual life is reduced.

The need is felt in the art to obtain an ultrasonic generator capable of producing a sealing band of considerable length and whose vibrations are affected as little as possible by the above-mentioned additional frequencies.

The need is also felt in the art to reduce as far as possible the power losses due to the stagnation of water inside the sonotrode, so as to limit the consequent reduction of the effective sealing time and therefore the risk of the sealing band remaining locally unsealed.

Finally, a need is felt in the art to isolate the spurious frequencies of the sonotrode as far as possible.

EP- ｃA-1241099 discloses an ultrasonic sealing device comprising ｃA housing fixed to one of the clamps and three different ultrasonic generators arranged side by side and housed in the housing.

The sealing device also comprises two beam-like intermediate supports, each located between the heads of two sonotrodes adjacent to each other.

In particular, each sonotrode does not have any slot in its head.

Disclosure of Invention

The object of the present invention is to provide an ultrasound generator designed to meet at least one of the above-mentioned needs.

According to the present invention, there is provided an ultrasonic generator as claimed in claim 1.

Drawings

Preferred non-limiting embodiments of the present invention will be described by way of example with reference to the accompanying drawings, in which:

FIG. 1 is an exploded perspective view of an ultrasonic generator according to the present invention with parts removed for clarity;

FIG. 2 is a perspective view of the sonotrode of FIG. 1 after assembly;

figures 3 and 4 are front and rear perspective views, respectively, of the head of the sonotrode of figures 1 and 2, with some parts removed for clarity;

FIG. 5 is a cross-sectional view taken along line V-V of FIG. 3;

FIG. 6 is a perspective view of the head of the sonotrode of FIGS. 3 and 4, with a plurality of piezoelectric elements mounted thereon;

figure 7 is a schematic view of the sonotrode of figures 1 to 4 during a sealing phase of the tube of packaging material;

fig. 8 shows the sonotrode and clamp of fig. 1-7 attached to a clamp;

FIG. 9 is an enlarged perspective view of a cross section of some of the details of FIG. 2;

FIG. 10 shows a plot of the modulus and phase of the impedance of a known sonotrode as a function of the vibration frequency and with a constant sealing force; and

fig. 11 shows a graph of the modulus and phase of the mechanical impedance of the sonotrode according to the invention as a function of the vibration frequency and with a constant sealing force.

Detailed Description

Reference numeral 1 in fig. 1 denotes an ultrasonic generator according to the invention as a whole.

Sonotrode 1 may be incorporated in a packaging machine (not shown) for producing sealed packages of pourable food products, such as pasteurized or UHT milk, fruit juice, wine, etc., from a tube 2 of packaging material fed along a vertical path Q (fig. 7) by known means (not shown).

The tube 2 is formed in a known manner by longitudinally folding and sealing a web of heat-seal sheet material and is filled continuously from the top with the sterilized or sterile-processed food product.

The packaging machine comprises, in a known manner, at least one pair of forming assemblies 3 (only one shown in fig. 8) which interact cyclically and continuously with the tube 2 of packaging material to grip, ultrasonically seal and cut the tube 2 along equally spaced cross portions. More specifically, forming assembly 3 interacts with tube 2 to first transform the tube into vertical strips 4 of packages connected to each other by respective transverse sealing bands 5, and then to cut tube 2 along transverse sealing bands 5.

Each forming assembly 3, described here only as required for a clearer understanding of the invention, substantially comprises a clamp 6 (fig. 8) and a counter-clamp, located on opposite sides of tube 2, which respectively support a mechanical vibration generator or sonotrode 1 and an anvil 9, and are movable in a direction crosswise to path P between an open configuration and a closed configuration in which they grip and seal tube 2 at the relative crosswise portions to form relative sealing bands 5 of packaging strip 4.

In a first alternative of the packaging machine, the forming assemblies 3 move along respective guides and interact cyclically with the tube 2 to heat seal the packaging material of the tube 2. Each forming assembly 3 comprises a slide movable back and forth along a respective guide; and a clamp 6 and a counter-clamp hinged at the bottom to the respective slide and moving between a closed position, in which they cooperate with the tube 2 to seal the tube 2, and an open position, in which they are separated from the tube 2.

In a second alternative, the packaging machine comprises two chain conveyors defining respective endless paths and equipped with a respective number of grippers 6 and corresponding counter-grippers. The two paths have respective branches substantially facing and parallel to each other, and the tube 2 of packaging material is fed between the branches, so that the grippers 6 on one conveyor cooperate with the corresponding counter-grippers on the other conveyor along said branches of the respective paths, so as to grip the tube and seal and cut the packages at a plurality of successive crossing portions.

The sonotrode 1 substantially comprises (fig. 1 to 6 and 9):

a one-piece head 15 defining a sealing surface 14 extending along direction a;

a plurality (three in the embodiment shown) of drive units 12 connected to the head 15 and each comprising a plurality of stacked piezoelectric elements 13 (fig. 6); and

a housing 30 which houses the head 15.

The packaging machine also comprises a single alternator (not shown) which is electrically connected, in use, to all the drive units 12.

In more detail, the head 15 is delimited by a pair of walls 16, 17 opposite each other and by a pair of walls 18, 19 opposite each other and interposed between the walls 16, 17.

The wall 16 defines the sealing surface 14.

The sonotrode 1 constitutes a half-wave resonator, i.e. the entire length of the sonotrode 1 in the direction B is half the wavelength of the oscillation of the head 15.

In particular, the height H of the head 15, measured in a direction B perpendicular to the sealing surface 14, is equal to half the wavelength of the wave oscillating in the direction B in use (fig. 5).

As a result, the extension of the piezoelectric element 13 in the direction B is contained within the extension of the head 15 in the direction B.

Thus, as shown in fig. 5, the maximum amplitude of oscillation of the head 15 is reached at the sealing surface 14.

The head 15 comprises a continuous edge 20, the edge 20 being shaped as a closed line and defining an oscillating nodal line of the head 15.

In other words, when the piezoelectric element 13 of the drive unit 12 causes the rest of the head 15 to oscillate, the point of the edge 20 does not substantially oscillate.

Furthermore, the points of the edge 20 define a so-called nodal plane, in particular a so-called nodal plane P, perpendicular to the direction B.

The edge 20 substantially comprises two sections 25 parallel to the direction a and two sections 26 perpendicular to the sections 25 and rounded to the sections 25 at their opposite ends.

Furthermore, the plane P divides the head 15 into a first portion 21 and a second portion 22.

Head 15 also includes shoulders 70 and 71 (fig. 9). The rim 20 is interposed between the shoulders 70,71 in the direction B and projects therefrom.

The drive unit 12 has respective ends lying on a plane P (fig. 1).

The portions 21,22 comprise walls 16, 17, respectively.

The thickness of portion 21 begins to be constant and then gradually increases from surface 14 towards edge 20.

The portions 21,22 also comprise respective pairs of slots 23, 27 elongated in direction B and passing through the head 15 from wall 18 to wall 19.

Advantageously, slot 23 extends entirely within portion 21, slot 27 extends entirely within portion 22, and slots 23, 27 extend at a distance from plane P. In other words, the slots 23, 27 are separated from each other and do not intersect the plane P.

In other words, the slots 23, 27 terminate at a distance from the plane P. In particular, the slot 23 extends the entire length thereof between the edge 20 and the sealing surface 14.

The slots 27 extend on the opposite side of the edge 20 with respect to the slots 23 and are arranged on the extension of the respective slot 23 along the direction B.

The portion 22 defines a plurality of seats 24, three in the illustrated embodiment, for respective drive units 12.

Head 15 is connected to housing 30 along edge 20.

The casing 30 comprises (fig. 1 and 2):

a box-shaped element 31 housing the portion 22 of the head 15;

a plate 32 cooperating with the side of the element 31 facing away from the sealing surface 14;

a plate 33 cooperating with a portion of the side of plate 32 facing away from element 31 by the interposition of a sealing ring 41;

a connector 35 for connecting the piezoelectric element 13 to the generator and cooperating with a further portion of the side of the plate 33 facing away from the plate 32.

The element 31 comprises an end edge 36 on the opposite side to the plate 32.

The edge 36 is rectangular and comprises two long sides 37a, 37b parallel to the direction a and two short sides 38a, 38b perpendicular to the sides 37a, 37b and interposed between them.

As shown in fig. 9, element 31 also includes notch 34 and shoulder 72 rounded to notch 34. More precisely, the recess 34 extends between the shoulder 72 and the inner profile of the edge 36.

The sealing ring 40 is interposed in the direction B between the rim 20 and the shoulder 72 of the element 31 and is mounted between the shoulder 70 and a portion of the recess 34 adjacent to the shoulder 72.

Likewise, the seal ring 42 is mounted between the shoulder 71 and the end portion 73 of the recess 34.

The housing 30 further includes:

an element 45 defining a plate 46, a crossbar 47, and a plurality of spacers 48 (four in the illustrated embodiment), the crossbar 47 being elongated parallel to direction a and projecting downwards from the plate 46, the spacers 48 being spaced along direction a and projecting from the plate 46 on opposite sides of the crossbar 47;

a plate 49 fitted to the element 45 by means of a plurality of screws;

a crossbar 50.

The sealing ring 42 is interposed in the direction B between the edge 20 and the crossbar 50.

The element 45, the plate 49 and the crossbar 50 define a hollow compartment housing the portion 21 of the head 15.

Crossbar 47 is connected to side 37a of terminal edge 36 by a plurality of screws 51, and crossbar 50 is connected to side 37b of terminal edge 36 by a plurality of screws 52.

Thus, screws 51, 52 connect member 45 and crossbar 50 to member 31 along sides 37a, 37b of terminal edge 36, respectively.

The housing 30 is connected to the clamp 6 by a plurality (four in the illustrated embodiment) of screws 60a, 60b, 60c, 60 d.

More precisely, screws 60a, 60b pass through a first hole defined by the opposite end of crossbar 50 and a second hole defined by the opposite end of side 37a of terminal edge 36, and are screwed to clamp 6.

Screws 60c, 60d pass through a third hole defined by the opposite end of crossbar 47 and a fourth hole defined by the opposite end of side 37b of terminal edge 36, and are screwed to clamp 6.

Thus, screws 60a, 60b, 60c, 60d connect housing 30 to clamp 6 at opposite ends of sides 38a, 38 b.

With reference to fig. 7, in the illustrated embodiment, the anvil 9 is of the type described and illustrated in patent EP-B-615907 and is substantially defined by two separate top portions 61 and bottom portions 62, the top portions 61 and bottom portions 62 defining between them a seat 64 for housing a knife 65. In short, knife 65 is housed in sliding manner inside seat 64 of anvil 9 and is controlled by known actuating means (not shown) to cut tube 2 at transverse sealing band 5 and thus separate from strip 4 the packages produced by forming assembly 3 and to be folded into the final shape.

The operation of the sonotrode 1 will be described below in connection with only one pair of clamps 6 and counter-clamps, starting from a configuration in which the clamps 6 and counter-clamps are in a closed configuration and clamp the tube 2 at a cross-over portion.

In such a configuration, the sonotrode 1 cooperates with the anvil 9 and clamps the cross portion of the tube 2 therebetween.

At this stage, the generator feeds the drive unit 12 with an alternating current of given value, causing an ultrasonic vibration of the piezoelectric element 13 and therefore of the sonotrode 1.

The ultrasonic vibration of the sonotrode 1 causes the sealing of the tube 2 and the formation of the sealing band 5.

In particular, the continuous closed edge 20 does not oscillate when the sonotrode 1 vibrates.

In fact, the edge 20 is arranged against the terminal edge 36 of the element 31 of the casing 30;

element 31 of casing 30 is connected to element 45 and to crossbar 50 along sides 37a, 37b of terminal edge 36; and is

The end edge 36 of the housing 30 is connected to the clamp 6.

In other words, the edge 20 forms a continuous closed nodal line of the sonotrode 1.

Once the drive unit 12 is deactivated and before the jaws 6 and counter-jaws are opened to start the next forming cycle, the knife 65 is activated and ejected from the seat 64 in the anvil 9 so as to cut the packaging material along the relative sealing band 5 and thus separate the relative pillow packs, which are subsequently folded into the final shape, from the tube 2.

The advantages of the sonotrode 1 according to the invention will be apparent from the above description.

In particular, slots 23, 27 extend completely within respective portions 21,22 and at a distance from plane P defined by edge 20.

The applicant has found that, since the slots 23, 27 do not pass through the plane P defined by the continuous nodal line of the head 15, the vibrations of the sonotrode 1 are substantially free of the additional spurious frequencies affecting the sonotrode disclosed in the introductory part of this description. More precisely, the applicant has found that, as shown in figure 10, for an ultrasonic generator similar to that disclosed in WO-A-2007/020208, A plot G, Z of the modulus and phase of the impedance as A function of frequency and with A constant sealing force has A respective low frequency inflection point I, J near the resonant frequency and A succession of very close maximA and minimA.

The presence of inflection point I, J with very close maxima and minima is primarily due to additional modes excited by additional spurious frequencies.

In contrast, as shown in fig. 11, the plot K, L of modulus and phase of impedance with the sonotrode 1 varying with frequency and the sealing force being a constant value has no low frequency inflection point and a succession of very close maxima and minima.

This is because the vibration of the ultrasonic generator 1 does not have the above-mentioned additional frequency.

Therefore, even when they are particularly long, the transverse sealing bands 5 formed by the sonotrode 1 are particularly uniform. This is because the same head 15 accommodates a plurality of piezoelectric elements 13 and because the plane P does not intersect the slots 23, 27.

Furthermore, since the slots 23 extend only within the portion 21, water stagnation is limited to only the portion 21 and is substantially prevented in the portion 22. Accordingly, the power loss caused by water stagnation is greatly reduced, thereby increasing the possibility of the transverse sealing band 5 being completely sealed.

The sealing rings 40,42 effectively reduce the transmission of vibrations from the head 15 to the elements 31, 45 and the crossbar 50.

Finally, the applicant has found that, thanks to its odd number of drive units 12, the sonotrode 1 exhibits spurious frequencies at a greater distance from one another than known sonotrodes with an even number of drive units.

It is clear that modifications can be made to the sonotrode 1 described herein without, however, departing from the scope of the present invention.

In particular, instead of the edge 20, the head 15 may comprise a plurality of impact elements (atteclements) connected to the clamp 6.

In this case, the impact elements define respective nodes of head 15 and lie on plane P, while slots 23, 27 are separated from plane P.

Claims (13)

1. An ultrasonic generator (1) comprising:

-a head (15), said head (15) defining a sealing surface (14) elongated in a first direction (a); and

-at least one first and one second driving unit (12), said at least one first and one second driving unit (12) being different from each other and each comprising at least one piezoelectric element (13);

wherein the first and second drive units (12) are electrically connectable in use to a single generator so as to cause oscillation of the head (15) in a second direction (B) transverse to the sealing surface (14) in use, the oscillation having a wave of a given wavelength;

-the height (H) of the head (15) measured along the second direction (B) is substantially equal to half the wavelength of the oscillation in the direction of the second direction (B);

the ultrasonic generator (1) further comprises:

-at least one first slot (23), said at least one first slot (23) extending through said head (15) transversely to said first and second directions (a, B);

-at least a limited number of nodes (20), at which, in use, the amplitude of the oscillation of the head (15) is substantially equal to zero at the at least limited number of nodes (20); and

-a plane (P) on which at least some of said nodes (20) lie and which divides said head (15) into a first portion (21) and a second portion (22);

characterized in that said at least one first slot (23) extends completely only within one (21) of said first and second portions (21,22) and at a distance from said plane (P).

2. The sonotrode of claim 1, characterized in that said first portion (21) defines said sealing surface (14) and said first slot (23) extends within said first portion (21) for the entire length of said first slot (23).

3. The sonotrode of claim 1 or 2, characterized in that said driving unit (12) is connected to said second portion (22) and in that it comprises at least one second slot (27), said at least one second slot (27) extending the entire length of said at least one second slot (27) within said second portion (22).

4. -the sonotrode of claim 3, characterized in that said at least one second slot (27) extends on the opposite side of plane (P) with respect to said at least one first slot (23) and on the extension of said at least one first slot (23) along said second direction (B).

5. -the sonotrode of claim 1, characterized in that said head (15) comprises a continuous first edge (20), said first edge (20) defining an infinite number of said nodes (20) and lying on said plane (P); the at least one first slot (23) extends between the sealing surface (14) and the first edge (20).

6. The sonotrode of claim 5, characterized by comprising a casing (30), said casing (30) housing said head (15) and being connectable, in use, to a packaging machine, and said head (15) being connected to said casing (30) along said first edge (20).

7. The sonotrode of claim 1, characterized by comprising an odd number of said driving units (12).

8. The sonotrode of claim 6, characterized in that said casing (30) comprises:

-a box-shaped element (31), said box-shaped element (31) housing one (21) of said first and second portions (21, 22);

-at least one additional element (45,49,50), said at least one additional element (45,49,50) defining a compartment which in turn houses the other (22) of said first and second portions (21, 22);

the box-shaped element (31) comprises a second edge (36), the first edge (20) being arranged against the second edge (36);

the second edge (36) of the box-shaped element (31) is connected to said at least one of the additional elements (45,49,50) so as to maintain the first edge (20) in a given position.

9. The sonotrode of claim 8, characterized by comprising:

-a first sealing ring (40), said first sealing ring (40) being interposed between said first edge (20) and said box-shaped element (31) along said second direction (B); and

-a second sealing ring (42), said second sealing ring (42) being opposite to said first sealing ring (40) with respect to said first edge (20) and being interposed between said first edge (20) and said at least one additional element (45,49,50) along said second direction (B).

10. The sonotrode of claim 9, characterized in that said first and second sealing rings (40,42) are interposed, transversely to said first and second directions (a, B), between respective shoulders (70,71) of said head (15) and recesses (34) of said box-shaped element (31).

11. A packaging machine for producing sealed packages, comprising sealing means (1,9) for sealing packaging material;

the sealing device (1) comprises an anvil (9) and an ultrasonic generator (1);

characterized in that the sonotrode (1) is a sonotrode (1) according to any one of the preceding claims.

12. The packaging machine according to claim 11, characterized by comprising a single generator electrically connected to the first and second drive units (12) of the sonotrode (1).

13. The packaging machine according to claim 11 or 12, characterized in that the anvil and the sonotrode (1) are carried by a first and a second clamp (6), respectively; -said second clamp (6) is fixed to a second edge (36) of the box-shaped element (31);

said packages are produced, in use, from a tube (2) of packaging material fed along a vertical path (Q), said tube (2) being continuously filled with food products and gripped at equally spaced cross portions.