IMPROVED MIXING DEVICE FIELD OF APPLICATION

The present invention relates to a device for mixing agricultural compounds, meaning a device that can mix two or more products in such a way as to obtain an agricultural compound.

PRIOR ART

The compounds mixed by the device according to the present invention may be, by way of example, fertilizers, plant protection products or the like. A similar device to that of the present invention may also be used to mix food products, pharmaceuticals, detergents or the like.

There are devices of the prior art for mixing agricultural products. Such devices comprise a tank in which the substances to be mixed are deposited, for example, water and a powdered plant protection product. A mixer is placed in the tank, so as to exert a mixing action that makes the mixture uniform. A dispensing conduit is connected in fluid communication with the tank. A hydraulic pump is placed in communication with the tank and with the conduit, so as to maintain a pre-established pressure within such conduit to promote the dispensing of the mixed compound, for example, on a cultivated field.

Disadvantageously, the need to mix the product within the tank constitutes a strong limitation to the use of devices of the prior art. It is, in fact, necessary to estimate the total quantity of product to be dispensed before mixing. Usually this quantity is a function of the dimensions of the field, the type of product, the mixing percentage and the type of crop. It is usual for such a quantity to be estimated in excess, therefore some mixed product remains in the tank after the spraying of the field. The remaining product must be stored according to special procedures, which prevent the dispersion of the product into the environment. In this context, the technical task underpinning the present invention is to provide a device for mixing agricultural compounds which obviates the drawbacks of the prior art as cited above. In particular, the object of the present invention is to provide a device for mixing agricultural compounds which can mix a suitable but not excessive quantity of compound for the user requirements.

EP2908929 B1 describes a device for mixing agricultural compounds, comprising a mixing member having a discoidal shape, comprising a plurality of mixing chambers consisting of through holes, and having an axis of rotation parallel to the longitudinal axis of the hopper. The known mixing member is locked in a horizontal position between two clamp discs which allow its rotation about an axis of rotation, although in contact with the clamp discs. The clamp discs are fixed and are in turn supported by a frame.

The mixing member described in EP2908929 B1 is made of ceramic materials, through the use of relevant moulds and at least one pressing step. In figure 1 , not pertaining to the present invention, there is a view from above of the mixing member described in EP2908929 B1 , wherein the through openings 400 are visible on the peripheral zone of the discoidal surface, which form part of the mixing chambers and are filled with a dose of product to be mixed.

A further object of the present invention is to propose an alternative device for mixing agricultural products to the device described in EP2908929 B1 .

SUMMARY OF THE INVENTION

The set technical task and specified aims are substantially attained by a device for mixing agricultural compounds comprising the technical characteristics set out in one or more of the appended claims.

The invention describes a device for mixing agricultural products, comprising an inlet conduit for a first product;

an outlet conduit for a mixed product in fluid communication with said inlet conduit;

a mixing chamber that is coupleable with said inlet and outlet conduits, said mixing chamber being switchable at least between:

a collection position in which it is filled with a predetermined dose of a second product, and

a mixing position in which it is in fluid communication with said inlet and outlet conduits so as to mix said first and second products; movement means for moving said mixing chamber at least between said collection and mixing positions with a frequency; the device comprises a mixing member having an axis of rotation and a lateral surface on which said mixing chamber is afforded, the mixing member being rotatable about said axis of rotation so as to switch said mixing chamber between said collection position and said mixing position.

Preferably, the device comprises a stator suitable for rotatably housing the mixing member internally, the stator and the mixing member being coaxially coupled.

Preferably, the mixing member comprises a rotor having a cylindrical or conical shape.

Preferably, the stator comprises a plurality of through openings arranged on a lateral surface thereof.

Preferably, the device comprises three through openings arranged on the lateral surface of the stator, circumferentially spaced from each other by 90°.

Preferably, when the mixing device is in use, the collection opening for collecting the predetermined dose of the second product is arranged above the stator and the discharge opening for discharging the unmixed first product is arranged at a lower level with respect to the upper collection opening.

Preferably the movement means comprises a motor connected to said mixing member to make it rotate at a determined rotational speed.

Preferably, the device comprises a plurality of mixing chambers.

Preferably, the mixing chambers are cavities afforded on the rotor.

Preferably, the mixing chambers are circumferentially aligned with respect to the axis of rotation.

Preferably, the mixing chamber can be switched into a discharge position in which, by means of the opening in the stator, it is in fluid communication with a vent conduit, so as to be emptied before passing into the collection position.

Preferably, the device comprises a sensor that is associated with the inlet conduit and configured to detect a signal representing a flow rate of a first product in said inlet conduit; a processing unit that is associated with the sensor and with the movement means. The processing unit comprises a reading module that is configured to acquire a value of said signal, a control module that is configured to obtain a target value of the frequency as a function of the value of said signal, an operating module that is configured to activate the movement means and vary the frequency as a function of the target value.

Preferably, the flow of first product is input so as to pass through the mixing opening and directly hit the dose of second product contained in the mixing chamber.

Preferably, in proximity to the mixing opening, a portion of the inlet conduit is arranged internally and coaxially to a portion of the outlet conduit.

BRIEF DESCRIPTION OF THE DRAWINGS

Further characteristics and advantages of the present invention will become clearer from the indicative, and therefore non-limiting, description of a preferred but not exclusive embodiment of a device for mixing agricultural compounds, as illustrated in the attached drawings, in which:

- figure 1 , which does not pertain to the present invention, illustrates a view from above of the discoidal mixing member described in EP2908929 B1 ;

- figure 2 is an overall lateral view of a device for mixing agricultural compounds according to the present invention;

- figure 3 is a front sectional view of the device of figure 2;

- figure 4 is a lateral sectional view of the mixing device of figure 2;

- figure 5 shows a detail of a conical rotor the mixer of figure 2;

- figure 6 shows a detail of a stator of the mixer of figure 2, which can be coupled to the rotor of figure 5;

- figure 7 shows a front view of the conical rotor of figure 5 coupled to the stator of figure 6;

- figure 8 shows a rear view of the conical rotor of figure 5 coupled to the stator of figure 6;

- figure 9 shows in detail the lower discharge holes in the stator of the mixing device of figure 2; - figure 10 is a cylindrical stator-rotor detail of the mixing device of figure 2;

- figure 1 1 is a block diagram representative of the operation of the device of figures 2 to 10;

- figure 12 shows three devices for mixing agricultural compounds connected to each other.

DETAILED DESCRIPTION

With reference to the attached figures, 1 indicates a device for mixing agricultural compounds according to the present invention. By way of example, the device 1 according to the present invention is able to mix a first and a second product so as to obtain a mixed agricultural compound. In particular, the first and the second product may be fluids (in the liquid or gaseous state), semi-fluids (for example a paste or a gel) or incoherent solids (for example powder or granules). Furthermore, the first and the second product may not be uniform, but in turn be a pre-established mixture of further products.

Finally, it should be noted that the device 1 according to the present invention may mix any number of products, if the type of specific application requires it.

The device 1 comprises an inlet conduit 2 for the mentioned first product which may be, by way of example, water or another solvent in liquid form. Preferably, the first product is a pressurized liquid (e.g. pressurized water). Furthermore, the device 1 comprises an outlet conduit 3 for the mixed compound. Such outlet conduit 3 is placed in fluid communication with the inlet conduit 2.

Dispensing means may be connected to the outlet conduit 3, so as to directly use the mixed compound. Such dispensing means are not illustrated, since they are not part of the present invention.

In particular, the device 1 comprises at least one mixing chamber 18 associated with the inlet 2 and outlet 3 conduits. In particular, the mixing chamber 4 is switchable at least between a collection position and a mixing position.

In detail, in the collection position the mixing chamber 4 is filled with a predetermined dose of the second product to be mixed with the mentioned first product. In other words, the mixing chamber 4 is placed in fluid communication with a source 5 of second product. Such second product may be, by way of example, a powdered fertilizer or a plant protection product for agricultural use, also in liquid form.

In the mentioned mixing position, the mixing chamber 4 is placed in fluid communication with the inlet 2 and outlet 3 conduits, so as to effectively operate the mixing of the first and the second product, and obtain a mixed agricultural compound. In other words, the first product enters the mixing chamber 4 previously filled with the second product, becoming mixed with it and producing the mixed agricultural product. Such agricultural compound therefore flows through the already mentioned outlet conduit 3. The device 1 further comprises movement means 6 of the mixing chamber 7, which can move it at least between the collection and mixing positions with a frequency "f". Note that, given a flow rate of the first product that crosses the inlet conduit 2, the concentration of the second product in the mixed compound will be directly proportional to the frequency "f" with which the mixing chamber 4 alternates between the collection and mixing positions.

With reference in particular to figure 4, the device 1 comprises a mixing member 7 which has an axis of rotation "A". Preferably, the axis of rotation "A" is substantially perpendicular to the central axis "B" of the source of the second product 5. Preferably, the axis of rotation "A" is substantially perpendicular to the gravitational acceleration vector g, i.e. it is substantially horizontal. In particular, the mixing member 7 is rotatable about the axis of rotation "A", and has a lateral surface 7a.

The mixing chamber 4 is in particular afforded on the lateral surface 7a of the mixing member. In this way, the rotation of the mixing member 7 about the axis of rotation "A" performs the switching of the mixing chamber 4 between the mentioned collection and mixing positions. Note that on lateral surface 7a of the mixing member 7 a number of mixing chambers 4 can be afforded, preferably angularly equally spaced with respect to the axis of rotation "A".

The movement means 6 comprises a motor 8 connected to the mixing member 7 so as to make it rotate with a rotational speed Vr about the axis of rotation "A". In particular, the motor 8 is of the hydraulic type and, preferably, is regulated by a hydraulic circuit valve (neither shown in the attached figures). The opening of such valve corresponds to a proportional increase in the rotational speed Vr. In an alternative embodiment of the invention, the motor 8 is an electric motor, e.g. a direct current brushless motor.

With particular reference to figures 3, 4 and 6, the mixing member 7 is comprised of a rotor 7 having a cylindrical or conical (truncated cone) shape, and the axis of rotation "A" passes, respectively, through the axis of the cylinder or of the cone.

The lateral surface 7a of the rotor will be cylindrical or conical, respectively.

Note that the mixing member or rotor 7 is arranged inside a stator 1 1 suitable for rotatably housing the member 7 internally. The stator 1 1 and the mixing member 7 are coaxially coupled. Preferably, the rotor 7 is completely arranged inside the stator 1 1 . In particular, the stator 1 1 comprises an internal surface conjugated to the outer lateral surface of the rotor 7.

Preferably, between the outer lateral surface of the rotor 7 and the inner surface of the stator there are 1 to 5 μιη; advantageously, about 2.5 μιη. It is also to be noted that beyond 5 μιη, leaks of the first product may occur. The rotor 7 is kept inside the stator 1 1 through constant pressure (e.g. through a spring) when it has a conical shape. For the cylindrical shaped rotor it is not necessary to supply any pressure to keep it inside the stator

1 1 . As shown, for example, in figure 4, the rotor 7 and the stator 1 1 are arranged horizontally, one housed inside the other and, in particular, they are arranged coaxially to each other.

Note that the stator 1 1 , with the rotor 7 housed internally, is arranged between a spacer element 10 and a clamping element 12. The spacer element 10 is placed to the rear of the stator 1 1 , on the side of the movement means, while the clamping element 12 is arranged to the front of the stator 1 1 . The function of the spacer element 10 is to centre the motor shaft with the mixer unit comprised of the rotor stator coupling. The clamping element 12 has the function of diverting by 90° the first product at the inlet and the mixed product at the outlet from the rotor 7 stator 1 1 coupling, both for conical and cylindrical rotors.

In the presence of a conical stator, the clamping element 12 also performs the function of a presser unit to keep the cylindrical stator in position inside the stator.

The movement means 6 comprises a shaft 15, arranged parallel to the axis of rotation "A". More particularly, the shaft 15 rotates about the axis of rotation "A". The mixing member 7 is fitted onto such shaft 15, so as to be set in rotation by the motor 8 through the shaft 15.

The stator 1 1 , the spacer element 10 and the clamping element 12 are not fitted onto the shaft 15 and, consequently, the mixing member 7 rotates with respect thereto, inside the stator 1 1 .

Preferably, a mechanical reducer 13 is interposed between the motor 8 and the stator 1 1 .

In further detail, the device 1 comprises a support frame inside which the mentioned inlet 2 and outlet 3 conduits are afforded.

Preferably, the mixing member 7 comprises a plurality of mixing chambers 4.

In particular, the mixing chambers 4 are cavities afforded on the lateral surface 7a of the rotor 7.

Preferably, the mixing chambers or cavities 4 are circumferentially aligned with respect to the axis of rotation "A". The presence of a plurality of circumferentially aligned cavities 4 allows the first product to be mixed with the second product in continuous flow without any interruption.

In further detail, the stator 1 1 comprises a plurality of through openings 17,18,19 arranged on a lateral surface 1 1 a thereof.

Such through openings are arranged so that, with the rotation of the mixing member 7 with respect to the rotor 1 1 , the mixing chamber 4 transits at such openings 17, 18, 19 and is in fluid communication therewith. Preferably, the stator 1 1 comprises at least two through openings 17, 18 arranged on the lateral surface 1 1 a thereof, .e.g. circumferentially distanced by 90° from each other.

In particular, a first collection opening 17 of the predetermined dose of second product is arranged above the stator 1 1 when in use, at the source of second product 5.

A second mixing opening 18 is placed about 90° from the first opening 17. As illustrated in figure 3, the mixing opening 18 is placed on the side of the mixing member 7, when in use, at the inlet 2 and outlet 3 conduits (substantially parallel direction to the axis of rotation A-A).

Preferably, one or more discharge openings 19 of the unmixed first product, are arranged at a lower level with respect to the upper collection opening 17, i.e. substantially diametrically opposite.

Consequently, with the rotation of the mixing member 7, the mixing chamber 4 transits at the upper opening 17, in particular when it is in the collection position. In fact, the second product is inserted into the mixing chamber 4 through the first opening 17, in particular through a hopper 16 placed at the opening 17. The second product to be mixed passes from the hopper 16 to the mixing chamber 4 by gravity, in particular until the complete filling of the mixing chamber 4.

The stator 1 1 has a further through opening 18, also placed substantially at the same distance from the axis of rotation "A" of the mixing chamber 4, but at a different angular position with respect to the upper opening 17. In particular, the mixing chamber transits at the further opening 18 and enters into fluid communication therewith when it is in the mixing position.

In fact, the inlet conduit 2 is oriented in the direction of the further opening 18, so as to direct a flow of first product towards it, in particular through a nozzle 33. When the mixing chamber 4 transits at the further opening 18, the flow of first product is dispensed directly towards the mixing chamber 4 and is mixed with the second product. The resulting compound then passes out of the nozzle 33, and then flows into the outlet conduit 3. As illustrated in figure 3, the nozzle 33 of the inlet conduit 2 is arranged internally and coaxially to the outlet conduit 3, in proximity to the mixing opening 18. Such arrangement allows the first product to be mixed with the second product in a continuous flow without any interruptions.

Preferably, the flow of first product is input under pressure so as to pass through the mixing opening 18 and hit the dose of second product contained in the cavity 4 of the rotor 7.

Preferably, the diameter of the inlet conduit 2 is less than or equal to the diameter of the outlet conduit 3.

In a particular embodiment, the flow of first pressurized product contributes to giving a thrust to the rotor 7, provided by the impact of pressurized fluid against the outer lateral surface of the rotor 7 and the cavity 4. In particular, the kinetic energy of the first product, hitting the cavity and the rotor, provides rotational power.

The particular rotor stator arrangement also allows a drastic reduction of the friction in play between the parts, with respect to known mixers for example. Such an advantageous arrangement of the rotor and the stator further allows the exploitation of the thrust of the flow of first pressurized product at the inlet from the conduit 2.

The two previous characteristics of the invention allow a drastic reduction in the power required for moving the rotor through the movement means. The rotor stator seal is completely tight, both against the first and the second product, without the need to exert significant pressure forces as happens in the prior art.

Preferably, the diameter of the second mixing opening 18 and the arrangement of the mixing chambers 4 are such as to direct the flow of first product simultaneously onto at least two mixing chambers 4, as illustrated in figure 3.

It is to be noted that, following the passage at the mixing opening 18, the mixing chamber 4 may contain possible residues of first product at the inlet from the nozzle 33.

Preferably, the nozzle 33 inserts a much higher volume of first product than the quantity of second product to be mixed contained in the mixing chamber 4.

In this way, per volume, once the second product has been collected and mixed, the mixing chamber 4 is cleaned from any mixed product residues, potentially harmful to the environment, and could be filled with first product residues for discharging subsequently.

In this way, after the first product has been dispensed from the nozzle 33 and mixed in the opening 18, the nozzle continues to insert quantities of first product under pressure and the rotor 7 to turn. At this point, the mixing chamber 4 is filled with first product, which must be discharged before passing again to the initial collection step from the source of second product 5. Therefore, the through opening 19 present in the lower part of the stator 1 1 is used for discharging residual quantities of first product by gravity and repeating the collection cycle again from the upper opening 17. It is to be noted that the quantities of product at the outlet from the opening 19 can be discharged to the ground as they exclusively contain first product residues and should they contain any second product residues they would be so diluted in the first product as to comply with legislation on disposal on the ground.

To dispose of the first product residues, the mixing chamber 4 is switchable to a discharge position, in which it is in fluid communication with an outlet conduit and with the vent or through opening 19.

Preferably, discharge tanks 20 and 21 afforded below the lower through openings 19 are placed in fluid communication with the outlet conduit 9. Therefore, when the mixing chamber 4 passes into the discharge position it enters into fluid communication with the lower through opening 19 and with the discharge conduit 9. The mixing chamber 4 therefore pours its contents into the discharge tanks 20, 21 and the discharge conduit 9, and is therefore emptied before passing into the collection position.

Preferably, there may be a plurality of discharge through openings 19 on the stator 1 1 , so as to allow quicker discharging of the excess first product. Note that, during the operating cycle of the device 1 , a presser member keeps the rotor 7 internally in close contact with the stator 1 1 , so as to prevent any leakages between them. Purely by way of example, such presser member may be a spring, arranged coaxially with respect to the shaft 15. Additionally or alternatively to such spring, the presser member may comprise a plurality of vices (not illustrated).

The cavities 4 may, by way of example, be circle, ellipse, truncated cone or polygon shaped, with a depth that is preferably variable from 1 mm to 50 mm.

The rotor 7 and the stator 1 1 are made using stainless steels appropriately treated with special coatings to increase the surface hardness. Optionally, the rotor 7 and the stator 1 1 are made of ceramic materials, through the use of relevant moulds and at least one pressing step.

The seal for preventing leakage of the first and/or second product is by friction. The mechanical seal is guaranteed through a uniform thrust on the axis of rotation "A" performed by springs or any other preloaded or fixed system.

As illustrated in figure 12, it is possible to connect various mixing devices 1 together in series.

Advantageously, in the embodiments with a conical or cylindrical rotor, the source of second product 5 is removably fixed to the clamping element 12 through a closing pin 28.

In the embodiment with a conical rotor 7, centrally to the clamping element 12 there is a preloading cylindrical pin 29 that is used to preload the spring acting on the conical rotor 7 or on the preloading system on the conical system.

Furthermore, in such embodiment, the seal is made by interference and there is no need to press on the rotor, which is free to rotate inside the jacket.

Advantageously, the inclination of the truncated cone shaped stator is comprised between 8° and 15° (sexagesimal degrees). Preferably, the inclination is comprised between 9° and 1 1 °.

Advantageously, the stator may be cylinder shaped, with the consequent lower construction costs, greater construction simplicity and without the need for the presence of a preloading system such as in the conical rotor. The invention achieves a plurality of technical effects:

• modularity of the mixing device, as it is possible to connect numerous devices, without being obliged to place them all in line and at the same level but being able to position them however and wherever necessary;

• possibility to mix any formulation directly in water or another product effectively distributed, avoiding pre-mixing in a tank, implying advantages in terms of safety for the operator and for the environment;

• direct mixing allows the elimination of numerous components, including the stirring system, with the consequent possibility to use pumps with lower flow rates in favour of containing the absorbed power;

• reduced risk of contamination;

· reduced possibility of dosing errors;

• reduced absorbed power, as there is less friction and the particular stator/rotor arrangement allows the thrust of the flow of first pressurized product to be exploited;

• 30%-40% more compact device with respect to known ones;

· possibility to create devices of any size and at reduced costs, never having to use ceramic materials and pressing systems as in known devices;

• construction simplicity with respect to known devices, having to use two elements (rotor and stator) instead of three elements (ceramic discoidal mixing member between two clamping discs);

• lower first product inlet pressure, with up to 80% reductions with respect to known devices, as there is a substantial reduction in friction between the parts and due to the particular arrangement of the mixing chambers;

· lower pressure of the presser member to keep the rotor inside the stator;

• less wear on the components, as there is less friction and lower pressure of the presser member;

• lower manufacturing costs of the mixing member.

As shown, for example, in figure 1 1 , the device 1 comprises a sensor 22 associated with the inlet conduit 2. Such sensor 22 is configured to detect a signal "S1 " representative of a first product flow rate in the inlet conduit 2. In particular, the sensor 22 is a flow meter. For example, the sensor 22 may be of the turbine, vane, nutating disc or electromagnetic type.

In greater detail, the device 1 comprises a processing unit 23 associated with the sensor 22 and with said movement means 6 of the mixing chamber 4.

In general, it should be noted that in the present context and in the subsequent claims, the processing unit 23 is presented as being split into distinct functional modules (storage modules or operating modules) for the sole purpose of describing its functionalities clearly and completely.

In actual fact, this processing unit 23 can comprise a single electronic device, appropriately programmed to perform the functionalities described, and the different modules can correspond to hardware entities and/or routine software that are part of the programmed device.

Alternatively or additionally, such functions may be performed by a plurality of electronic devices over which the aforesaid functional modules can be distributed.

The processing unit 23 can also make use of one or more processors for executing the instructions contained in the storage modules.

The aforementioned functional modules can also be distributed on different local or remote computers, depending on the architecture of the network in which they reside.

The processing unit 23 comprises a reading module 24 configured to acquire a value "Q" of the mentioned signal "S1 ". In detail, the reading module 24 acquires such value "Q" in digital form. In an alternative embodiment, the value "Q" may be kept in analog form.

The processing unit 23 further comprises a control module 25 configured to obtain a target value "fO" of the switching frequency "f" of the mixing chamber 4 as a function of the mentioned value "Q". In other words, the control module 25 is able, as a function of the value "Q" detected of the flow rate of first product within the inlet conduit 2, to calculate the corresponding frequency value "f" (i.e. the number of steps of the mixing chamber 4 in the unit of time) necessary in order for the mixing percentage between the first and the second product to be kept constant. In particular, the control module 25 is configured to obtain the target value "fO" of frequency "f" in a directly proportional way to the value "Q". In yet further detail, the calculation module 25 is configured in order to calculate the target value "fO" by multiplying the value "Q" of the signal "S1 " by a pre- established gain "G".

The processing unit 23 further comprises an operating module 26, configured to activate the movement means 6 and therefore to vary the frequency "f" as a function of the target value "fO". In particular, the operating module 26 is associated with the motor 8, and is able to increase and/or decrease the revolutions of the motor 8 as a function of the target value "fO" of frequency "f". In other words, the operating module 26 is configured to vary the rotational speed "Vr" of the motor 8 as a function of the target value "fO" of frequency "f".

In particular, the operating module 26 is configured to increase the frequency "f", in particular the revolutions of the motor 8, in the event that such frequency "f" is less than the target value "fO". Likewise, the operating module 26 is configured to reduce the frequency "f" in the event that the frequency "f" is higher than the target value "fO". In other words, the operating module 26 is configured to pursue the target value "fO".

In further detail, the operating module 26 is configured to send a control signal "U" to the motor 8. Such control signal "U" is representative of a target rotational speed "VO" of the motor 8. It is to be noted that the target rotational speed "VO" is directly proportional to the target frequency "fO". The processing unit 23 is further configured to calculate the mentioned gain "G" as a function of a pre-established parameter "c" to be inserted by a user. Such a parameter "c" is in particular representative of a mixing ratio between the first and the second product. Even more in particular, the processing unit 23 comprises an interface module "27" configured to enable a user to enter such a parameter "c". Merely by way of example, such interface module 27 may comprise a monitor or a keyboard, a knob or equivalent devices.

The present invention reaches the proposed object. Since the mixing is performed at the same time as the dispensing of the product mixed by the outlet conduit, only the amount of compound effectively needed is produced, avoiding the problems connected with excess mix.

The present invention also provides important advantages. In fact, the processing unit is able to guarantee a suitable mix for varying the incoming amount of first product, guaranteeing the effectiveness of the mixing device in a wide interval of values of such flow rate.

The user further has the possibility to select the mixing ratio and, once it has been selected, the device can keep it constant.